Newsletter 20

Tel-Tek, dept. POSTEC / Telemark University CollegeKjoelnes ring, 3918 Porsgrunn, Norway. Tlf: 35 57 40 00 Fax: 35 57 40 10 www.tel-tek.no - [email protected]

No. 20 November 2001

A programme of research in POwder Science and TEChnology

Powder TechnologyContributing to a Greener Environment

Tel-TekTelemark Technological Research and

Development CentreDepartment of POwder Science and

TEChnology (POSTEC)Teknologisentret,Kjoelnes Ring

3918 Porsgrunn,NorwayTelephone:

+47 35 57 40 00Fax:

+47 35 57 40 10

Prof. Sunil R. de SilvaEksath R. de Silva

Eksath R. de Silva

Managing Director:Yngve Stentun

Dept. Manager (POSTEC):Gisle G. Enstad

Advertisements:Eksath R. de Silva

Printed by:Wergeland Grafisk

What is Tel-Tek?he Telemark Technological Research and Development Centre was founded in 1986 by Telemark County and local business interests to promote the transfer of competence, technology and

research results from the then Telemark Institute of Technology to local industries, as well as to promote the formation of new enterprises. Its various departments are headed by professors at what is now the Faculty of Technology of Telemark University College, and its personnel are allowed full access to the Faculty’s facilities. In addition to Powder Technology, groups have been established in Simulation of Industrial Flow Processes, Chemometrics, Polymeric Membranes, Process Equipment, Combustion and Environment and Water and Waste Water Treatment.

This POSTEC Newsletter - - is a report on the research activities in Powder Technology carried out at

the Telemark Technological Research and Development Centre and Telemark University College.

POSTEC Newsletters are published annually and distributed free of charge to anyone who indicates an interest in receiving them. Please fill in the appro-

priate form on the last page of this issue if you want your own copy.

We will publish articles from our part-ners and friends from other parts of

the world, if we consider such articles to be topical and of interest to our

readers. Such articles are to be sub-mitted to the editor by June. The editor, however, neither guarantees publica-tion nor the return of any material so

sent.

In order to support the costs of pub-lication and distribution, we welcome advertising. 3000 copies of the News-letter are distributed around the world. Advertising copy must also be sent to

the editor by June.

...and POSTEC?OSTEC is the Department of Powder Science and Technology at Tel-Tek. The name originates from the time that a multi-client programme was set up to support the research activities in Powder

Technology at Chr. Michelsen Institute, Bergen, in 1983. The programme continues to this day, and members receive concessional hourly rates, discounts on services, and access to the results of all general research projects. It is one of the longest surviving multi-client programmes of its kind in the world.

Silo Design Gisle Enstad [email protected] Flow & Pressures Mladen Jecmenica [email protected] Are Dyrøy [email protected] Powder Properties Sivert Ose [email protected] & Mixing Ali Ghaderi [email protected] Conveying Biplab Datta [email protected] Classification Franz O. von Hafenbrädl [email protected] Slides Thoralf Sannes [email protected] Sivert Ose [email protected] of Flow Proc. Vidar Mathiesen [email protected] Equipment Morten Melaaen [email protected]&Environment Dag Bjerketvedt [email protected] Separation Magnar Ottøy [email protected]@hit.noWater & Waste Water Treatm. Rune Bakke [email protected]

Cover PictureParticulate emissions to the atmosphere are every bit as undesirable as gaseous emissions. As the article on page 12 demonstrates, Powder Technology can make a significant contribution to keeping these under control.

Contact Persons

Editors

Publisher

Administration

Design and Lay-out

In This IssueEditorial

POSTEC Fighting for a Greener Environment in a Global World .............................................................. 4More Changes in Norwegian Education and Research - New Challenges for the State Colleges.... 5News Items ................................................................. 6Upcoming Events ....................................................... 7One Summer in Norway............................................ 8From Poland to Norway ............................................ 8Mythical Place Called Powder Hall........................... 9

Current ActivitiesA Study of Pressure Gradients in Vertical and Horizontal Pneumatic Transport Lines ................. 10Effects of Segregation on the Environment and Yield in Aluminium Production ........................... 12Using Noise to Predict Particle Size and Segregation Online .................................................. 16Uniaxial Tester as a Tool for Predicting Tabletting Performance of Powder Mixtures........................... 17Predictions of Loads on Walls and Insert in a Gravity Flow Silo using ABAQUS™........................ 18Use of an FE-Method for Calculating Stresses in Silo Structures.......................................................... 21

Other ActivitiesCFD Modelling of a Lab-Scale Fluidised Bed ........ 23Computational & Experimental Studies of a Vane Separator .................................................................. 24Comminution and Air Classification ..................... 28

ServicesPublications and Reports ........................................ 30Standard Services at Affordable Prices! ................. 32Enquiry Form........................................................... 33POSTEC-members List ........................................... 35POSTEC-programme benefits ................................ 36

3

Marie Curie FellowshipsTel-Tek is a foundation which carries out industrially oriented R&D in coopera-tion with Telemark University College. Its Department for Powder Science and Tech-nology is one of the leading groups in this field in the Nordic countries.

We invite applications for• 1 post-doc position (1 year)• 3 post-graduate positions (1-2 years)

from those with prior experience of the behaviour of particulate materials (pow-ders). The post-graduates must be regis-tered for doctorates at their home univer-sities and be citizens of an EU country.

The Fellowships will be awarded under the EU Marie Curie programme, at the follow-ing rates (less Norwegian taxes)

• Post-doc Euro 4.702 / month• Post-graduate Euro 3.411 / month

Contact:Sunil de Silva at

[email protected].: +47 3557 5120

Ønsker du å være Høgskole- eller Sivilingeniør

uten å si opp din stilling?

Vi kan tilrettelegge et deltidstudium

i samarbeid med deg og din arbeidsgiver!

Ta kontakt med:Ragnar Moland

Tel: 3557 5106 Fax: 3557 7547E-post: [email protected] for teknologiske fag

Kjølnes Ring 56, 3918 Porsgrunn

www.hit.no

The POSTEC Newsletter No. 20

CONTENTS

4 The POSTEC Newsletter No. 20

POSTEC Fighting for a Greener Environment in a Gisle G. Enstad

It is now more than one year since Sunil de Silva handed over the leadership of POSTEC to the new leader group,

which also included him. Recently he has seldom come to the meetings of the leader group, claiming he has not got time. He is getting more and more involved in the affairs of the Telemark University College, and only now and then gives us some strong advice on what to do. We are, however, grateful that he still is handling most of the applications for public funds, which still makes him a key person of the leader group.

This type of leadership may seem an experiment in itself, so now we are doing research not only on Powder Technology, but also on research management. There have been some hints that the leadership is a bit too soft, not giving clear signals about what should be done and what should not be done, and when people should be allowed to relax. On the other hand it seems that what has to be done, is being done. We are in fact better off than we were one year ago. The members of the leader group are still good friends, we are getting new projects, and we are able to carry out most of the work on time. Since we do not have Sunil to take the responsibility for us anymore, we have to share it, and take more personal responsibility, at the same time as this also gives a feeling of more freedom. Maybe this also improves our creativity?

The work that Are Dyrøy currently is heading from our side, together with Morten Karlsen from Hydro Aluminium, is now paying off. The anti segregation system that has been described before, as well as other innovations, have resulted in better environment, both internally and externally at the aluminium plants, at the same time as the stability of the production has been considerably improved, which leads to higher yields as well. This is the result of a long-term co-operation (started in 1985!) between POSTEC and Hydro Aluminium, which has led to increased competence of the employees of Hydro Aluminium, who also have made their own inventions, sometimes in co-operation with us, but also sometimes independently of us.

Thanks to the long-term co-operation, and to the enthusiastic people who have been involved, where Are Dyrøy and Morten Karlsen are the key persons, we now see results that are very pleasing both for Hydro Aluminium and POSTEC.

Unfortunately we have never had any similar long-term co-operation with any other branches of Norsk Hydro, or any other companies, since we have never had any other client as visionary and stub-born as Morten Kalrsen, and we therefore have not been able to achieve similar improvements with other partners. One sad example is Hydro Magnesium Porsgrunn, right on our doorstep. Over the years we have been called in to solve some small problems, but we have never been able to get into a long-term co-operation, which could bring any significant breaks-through like the ones we have had with Hydro Aluminium, although we could see there was a lot we could have done. Now it is too late. Although Hydro Magnesium in Porsgrunn is one of the cleanest and most efficient magnesium producers in the world, it has been decided that it is going to be closed down in the spring of the year 2002. Some wise, but shortsighted, economists have decided it is not possible to compete with the cheap magnesium pro-duced in China, where there is cheap labour and much less environmental restrictions.

This is a result of the free market forces, and the globalisation that is going on. It is a tragedy for those who have lost their jobs in Porsgrunn. Maybe it feels like a victory for the Chinese, who now can take over a bigger share of the world market, but if it is at the expense of the environment, it may be only a short term victory. In the long run the environment is more important than any market shares, and it has to be taken seriously on a global basis, not only in our part of the world. China will have to implement the same environmental restrictions as we have, if they are entering into the industrial era. Hopefully their wages will gradually increase, and China will start to use magnesium, perhaps at a higher rate than it can produce. Then China will become a growing market for magnesium, and it will be a pity that Norsk Hydro closed down its magnesium plant early in 2002.

A more long-term approach would have been to improve the efficiency sufficiently to make the production of magnesium in Norway able to compete with the produc-tion in China. Especially in those parts of the world that are so densely populated, protection of the environment is of vital importance, and has to be implemented. It is also seen over and over again that proper protection of the environment makes production more profitable. Pollution is nearly always raw materials in the wrong place, and it will pay off to collect these raw materials instead of just letting them disappear into the air, or into the water.

After the cold war ended, the free market forces really have come into play, and we must be careful and watch in what direction they are taking us. We see the multinational concerns are moving production from the industrialised countries in the West to developing countries in the East, where there is cheap labour, and where there are less environmental restrictions. One positive effect of this is that industry and development is being brought to new parts of the world, but other effects are that industry becomes less environmentally friendly, and that people in the industrial-ised world are losing jobs, often replaced by people in the East, who are being exploited nearly as slaves by the multinational con-cerns, perhaps indirectly via local compa-nies. Leaving everything to the free market forces, we will end up with unemployment and decreasing wages in the West, as people will have to compete for jobs, and damaged environment in addition to continued low wages in the East, where dictatorship and oppression prevent people from demand-ing their human rights. We may end up with a few extremely rich people, and the rest of us extremely poor. Somehow the market forces have to be controlled to avoid such a development.

In the global world where we are living now, the big gap between rich and poor has to be reduced to avoid a growing conflict, with oppression and violence. Recently the development has been in the other direction. We can see a growing pressure where people from the poor countries or oppressive regimes are trying to escape to the rich countries, who are closing their borders, using warships to enforce the

5The POSTEC Newsletter No. 20

Sunil R. de Silva

After the revolutionary document “Research at a Paradigm Shift” (see Newsletter No. 18) the outgoing

Norwegian Government has come up with another revolutionary White Paper - this time entitled “Do Your Duty, Demand Your Rights” (Gjør din plikt - Krev din rett). The White Paper was approved by the Norwegian Parliament and is currently being transformed into law. I have previ-ously complained about the tendency of Norwegian authorities to ostensibly give autonomy while retaining the right to overrule or change decisions made by the supposedly autonomous institutions (see Newsletter No. 16). The new law which is being proposed will change this situation significantly. Financing of education and research at universities and the state col-leges will no longer be based on a decision by the Ministry of Education and Research on how many students a university or college is supposed to have, but more and more on what they actually produce - both in terms of credits and in terms of research. There will still be a basic grant, based on historical data, but this will only be 50-70% of the total. As far as Telemark University College is concerned, the basic grant will be 60.4%. The remaining 40% will be based on the production of credits (25%) and research activity (15%). This creates

major challenges since the Government simultaneously wishes to open the doors to higher education to all and sundry, a considerable portion of whom will not have the necessary competence to complete a higher degree. Nor does it appear to have considered the high risk of institutions lowering their standards to achieve a higher pass rate! To try to counter this risk, it is creating a body for accreditation, with the power to examine the quality of education provided, and a right to cancel previous accreditations given to courses considered not to be upto standard. With 26 state colleges, 4 wide-rangeing and 6 specialist universities in Norway, which together have something like 150,000 students, this is going to be no easy task!

The Ministry of Education’s suggestion as to how the 15% for research is to be allocated is even more surprising. Both the universities and state colleges will receive 40% of this 15% based on senior positions (assistant-, associate- and full professors) and not on publications by the institutions concerned. This at a time when the Ministry insists on better reporting of publications. Then comes the difference. Universities will receive 30% of the 15% for doctorates produced, 10% for Masters degrees and 20% for funds obtained from the EU and the Research Council (no mention of other income sources, i.e. the industrial relevance of their research is not

important). The state colleges will have to rely on credits produced for 40% of the 15% and must in fact count all external income for the remaining 20%. It is not easy to understand why there is such a dif-ference at the same time as instructions are given to state colleges to increase ‘depth’ at the cost of ‘breadth’. Such a large emphasis on credits produced will lead to exactly the opposite result! Nor is the proposed basis of allocations consistent with the main objective of the reform - the develop-ment of knowledge of high quality and relevance! The number of senior positions doesn’t necessarily reflect high quality. It is what they produce that does. Thus publications, doctorates and master degrees ought to receive a much greater weighting than that proposed. Relevance must be judged by a) student numbers - one part of our market and b) external income - the other part of the market. Both types of institutions should have the same criteria - total external income.

There is, however, a bright spot for the state colleges. This is the allocation of 15 MNOK for strategic programmes. Previ-ously state colleges were denied the right to apply for strategic university programmes - much to their frustration! This is a step in the right direction, and one hopes that in a few years time the amounts available for strategic research at both types of institutions will be identical.

More Changes in Norwegian Education and Research - New Challenges for the State Colleges

departure of the ones who did not drown on their way in their miserable vessels. Should not free and borderless markets also apply to people?

Perhaps the terrible act of terror on the World Trade Center on September 11 this year was also part of this growing global conflict between rich and poor? Osama bin Laden, who has been pointed out to be mainly responsible for this terror, is hardly fighting for the rights of the poor. He seems to be closely connected to the Taliban regime, a regime known for its oppression of women and people opposing them, with little concern for the poverty of

its people. He is probably seeking power by using terror. What is his goal is hard for us to understand, but somehow it probably has something to do with the gap between rich and poor, and if we want to avoid such atrocities in the future, we have to do something to reduce this gap.

At POSTEC we are grateful we are not responsible for solving the tremendous problems our politicians have to face as a result of the globalisation of the world. Our job is to help industry in the Nordic countries to develop in such a way that they can compete on a global market, at the same time as all the environmental

requirements are met. Very often Powder Technology is an important component of this work, and we are here to help. If you are willing to invest in a long-term co-operation, we may end up with successes like we have had with Hydro Aluminium. In any case we can help making sure industry in our part of the world can compete, without being harmful to the environ-ment. In that way we will help a develop-ment towards a greener, more just, global world.

Remember, what the future is going to be, is a result of the combined efforts of all of us.

Telemark University College: www.hit.no


Thoralf becomes a FatherThoralf Sannes (or Speedy as he is affec-tionately known) got married last year and hasn’t wasted much time in ensuring a line of succession! His wife Mette gave birth to a daughter, Mia, on June 19th. With the added responsibility Thoralf will find it necessary to be a little slower in his more adventurous endeavours!

Roger gets his Craftsmans CertificateRoger Lid, who has spent his last two years as an apprentice automatician at Telemark University College and POSTEC, was awarded his craftsmans certificate at the end of his training period at the end of March.

He has been supervised and trained by personnel from both Telemark University College (Morten Pedersen) and POSTEC personnel (Svein Thorstensen and Jens Atle Møller Johansen), who all had a share in looking after him and guiding him on his way towards getting his certificate.The final examination was at the end of March, and Roger passed well with good results.

After he had finished his exam, we applied for funds to have him with us for a period of 2-3 months to help us in completing the wiring of the large silo battery, on which he did an excellent job. The funds were made available by Leif Åge Eilertsen, who is responsible for promoting cooperations between Telemark University College and SME’s (small to medium sized enterprises), to whom we extend our thanks. Roger’s work has already permitted us to accept an external contract, which we otherwise would have been unable to commence on time.

Roger is now doing his military service, and will - hopefully - decide to carry on with his education at Telemark University College! We wish him all the best for the future.

Sivert is Awarded a Ph.D.After nine years of hard work possibly trying to explain the inexplicable (bipolar electrostatic charging of powders), Sivert Ose was awarded a Ph.D. by the Univer-

News Itemssity of Southampton in May based on a thesis with the title “Characterisation of the Bipolar Electrostatic Charg-ing of Powders”. In his thesis, he shows that physical prop-erties of the particles (particle size etc.) do not influence the polarity of the electro-static charge. The charge is mainly a func-tion of the process in which the powder is charged. The distribution of charges is very similar between various powders that are bipolarly charged, evn though the magnitude varies so that electrically insulating materials have a higher charge.The external examiner was Brian Makin from the University of Dundee and the internal examiner from the University of Southampton Alun Vaughan. He was supervised at Southampton by Prof. Adrian Bailey and in Norway by Sunil de Silva.

Franz gets MarriedFranz Otto von Haf-enbrädl (who by the way doesn’t speak any German in spite of his very German name) got married to his Heidi in Sep-tember. He has been even quicker than Thoralf in ensuring his line of succes-sion.

A Dr.Ing degree for Qianpu Wang…Qianpu Wang, who has con-tributed articles to previous versions of this Newsletter, defended his Dr.Ing. thesis entitled “An Experimental and Computational Study of Gas/Particle Multiphase Flow in Process Equipment” in August. Qianpu (or Sham-poo as he was inevitably called), simulated three pieces of process equipment ( a cross flow air classifier, the acceleration tube in an erosion tester and a de-duster) using the CFD code FLUENT™ and then compared his results with measurements carried out using LDA. His work revealed both the potential and weaknesses of CFD simula-tions and will provide a useful platform for further work in modelling process equipment.

The examination committee consisted of Dr. Michael Bradley of the University of Greenwich, Prof II Stein Tore Johansen of

SINTEF/NUST and Prof II Gisle Enstad. Qianpu was supervised by Prof. Morten Melaaen, with Sunil de Silva as co-super-visor. Qianpu has been awarded a post-doc fellowship at NUST (Norwegian University of Science and Technology) and intends to stay in Norway for a while before returning to China.

…and for Jun HuangJun Huang, who came to us at the same time as Qianpu in 1997 from Zejian Uni-versity of China, also defended his Dr.Ing. thesis entitled “Developments in Applied Chemometrics: AMT, Acoustic Chemo-metrics and N-way Image Analysis” in May.

Jun’s thesis contained a new unified Angle Measure Technique (AMT) for characterizing and discriminating between components of images based on multivari-ate data modelling, which will be marketed by a leading software company, and a contribution to acoustic chemometrics which involved acoustic monitoring of particle attrition in pneumatic conveying (see article on page 16).

The examination committee consisted of Prof. Paul Gelardi of the University of Umeå, Prof II Harald Martens of the Norwegian University of Science and Technology and Dr. Kristian Helland of Borealis AS. Jun was supervised by Prof. Kim Esbensen.

Heading for New PasturesKim Esbensen, who was our professor of Kimometrics (Chemometrics), decided to return to his homeland, Denmark, in July and has been appointed Research Profes-sor in Chemometrics at the University of Aalborg at Esbjerg, where he joins our former colleague Bjørn Hjertager. Logically enough, his partner May-Britt Hägg, who was one of the pillars of the faculty of Technology, decided to head in the other direction, and has accepted a position as Professor of Separation Processes at the Norwegian University of Science and Technology in Trondheim! When free, they will rendezvous on the island Løvøya - a few kilometres from Porsgrunn, so we still expect to see them quite often.

Cooperations with both are expected to continue via participation in joint research programmes, but we will miss their enthusiasm and engagement. We wish them the best of luck in their new habitats!

The 4th International Conference for Conveying and Handling of Particulate SolidsBudapest, Hungary, 27-30 May, 2003

The Conference will take place in Hungary, in the very heart of Budapest, at Hotel Inter-Continental, between 27-30 May, 2003. Its objective is to bring together researchers, engineers and industrialists from all over the world, who are active in the areas of conveying and handling of particulate solids, to report on the recent developments in the field and to exchange experiences and insights. The Conference will consist of plenary and keynote lectures on emerging technologies, as well as con-tributed papers, to be presented in oral or poster sessions. Satellite workshops and meetings are also envisaged. The scope of this event covers all the important topics of particle technology, such as production and processing of particulate solids (e.g. crystallization and precipitation, drying and coating of particulate materials; size reduction & enlargement, production & handling of nanoparticles, etc.); storage of bulk solids; pneumatic, hydraulic & capsule conveying; freight transportation; mechanical conveyors & feeders; separation & classification; environmental aspects; measurements, control & on-line monitor-ing; particle characterization, segregation & mixing; modeling and fundamentals; and other relevant topics.

More and updated information, First Announcement and Call-for-Papers, Forms for Preliminary Indication of Interest and Abstract Submission can be obtained from Prof. J. Gyenis, Conference Chair, or can be downloaded from the official web-site of the Conference at www.partconf2003.hu.

The deadline for Abstracts submission is August 15, 2002.

10th European Symposium on ComminutionHeidelberg, Germany, 2-5 Sept., 2002

The Symposium will take place in Heidel-berg, one of the most famous and pleasant cities in Germany about 100 km south of Frankfurt am Main and at the rim of the Black Forest. The objectives of the Symposium are to provide a forum for the presentation and discussion of recent developments in science and technology relating to Comminution and Classifica-

tion. It will offer the opportunity to meet researchers, engineers and industrialists active in these fields, not only from Europe but from all over the world. The program will consist of plenary lectures and oral presentations held in three parallel sessions. Comminution and classification of all kind sof materials will be considered (i.e. miner-als, metal, coal, chemicals, pigments, fillers, biological materials, pharmaceuticals, food, agricultural products, ceramics, waste and recycling materials, etc.). Areas being covered will be fundamentals (micro-processes including fracture physics, par-ticle breakage, material characteristics related to comminution, particle motion and stressing in mills, multi-phase fluid dynamics, local energy density distri-butions, residence time distributions, etc.), mechanical activation, mechano-chemical reactions and mechanical alloy-ing, modelling and simulation, machines and apparatus (design, operation, wear) and comminution/classification systems (operation, control and instrumentation, mill-classifier-circuits).

More and updated information, addres-ses for first contact and forms for indica-tion of interest can be downloaded from the official web-site of the Symposium at www.comminution2002.de.

For more information contact the chair-man of the Organizing Committee: Dr.-Ing. Detmar Redeker, Wolff Walsrode AG, Stormstraße 19, D-29664 Walsrode, Germany, phone: +49 (05161)-912772, fax: +49 (05161)-912769, e-mail: [email protected].

4th World Congress on Particle TechnologySydney, Australia, 22-26 July, 2002

The technical program will run for four full days from Monday July 22 to Thursday July 26. The program consists of plenary lec-tures, research oral presentations, research poster presentations, and tutorial sessions on “Getting Started in Particle Technol-ogy”.

Both oral and poster presentation ses-sions will be organised to maximise discus-sion and debate. The Sydney Convention and Exhibition Centre provides wonderful facilities for all presentations.

The conference covers all aspects of Particle Technology. We have divided the conference into four main themes, particle

Upcoming Eventsand bulk solids characterisation, particle design and new technologies, powder handling and multiphase flow and solid-fluid separation. Each theme is further divided into a number of topic areas.

We expect between 400 and 500 research presentations at the conference running in four parrallel streams each day.

“Getting Started in Particle Technology” will be a series of invited overviews of different aspects of Particle Technology by international experts in the field. These tutorials are designed for practitioners that are new to the field or wish brush up on their knowledge in a particular area. They will provide a quick and easy way to get up to speed in an area of interest.

For more information and forms for indication of interest please check out our website at www.wcpt4.com.

Reliable Flow of Particulate Solids IVColombo, Sri Lanka, January 2004

Planning has begun for the fourth Sympo-sium on the Reliable Flow of Particulate Solids. Since it will be the last of these symposia for which Sunil de Silva will be responsible, we hope (conditions permit-ting) to hold it in Sri Lanka! Sri Lanka is a beautiful island just south of India of which it has been said “every prospect pleases and only man is vile”! The weather in January is barmy, and the ocean very inviting. Its long history, which stretches back some 2500 years, has left it with many interesting sights to see, including the giant artificial reservoirs built by ancient kings and a palace built on the top a sheer 300 m high rock by a patricidal king who wished to escape the wrath of his brother in the 5th century AD.

We hope the symposium will bring together scientists, suppliers of equipment and engineers from industry in much the same proportions as the first three symposia did. We expect much greater participation from Asian countries and especially invite our colleagues in these countries to submit papers. There will be eight invited plenary lectures and, hope-fully, upto 60 papers in parallel sessions. The deadline for submissions of abstracts is December 31st, 2002. Full manuscripts will be required by July 31st, 2003. Contact [email protected] for details.



Stephanie Tappe, Exchange Student Technical University of Cottbus

After having spent almost 6 months working at POSTEC, I have to say that I enjoyed my time here very

much. Before I came here I could not imagine

how it would be to live that far away from home and working for the first time in my life. But it went better than expected. The nice and friendly atmosphere at POSTEC made it easy feeling comfortable, and soon I got used to my all day life. I was living in one of the quiet students houses where it is rather easy to get in contact with other students. Thus, it did not take a long time till I met some nice people with whom I spent my time after work. Also the first parties at the weekend started, and let me forget my distance from home. When in spring the weather was cold and rainy I went often to the swimming hall nearby, but finally the clouds disappeared in the

One Summer in Norwaybeginning of May and the sun came out so that I could use my bicycle I brought

with me from home. Although Norway is supposed to be very mountainous, the area around Porsgrunn is ideal for cycling. More hills than mountains are covering the landscape and a lot of well signed bicycle routes lead through the nature. Soon I explored a very nice forest lake near Skotfoss that became my favourite bathing place.

The project I was working on was inves-tigations of pressure drops in horizontal and vertical pneumatic conveying. It was really impressive listening to the noise created by the plugs moving through the pipeline and I found out that working could even be enjoyable. Especially at the end of my stay time seemed to run so fast that the end was coming faster than expected. Thus, unfortunately my time is over now, I have to go back home, but I will remember POSTEC and Norway as being an enjoyable time in my life. Thanks a lot.

Michal Wójcik, Marie Curie Post-Graduate Fellow

ilo problems have always appealed to me. Therefore I particularly welcomed the chance to come to Norway. How-

ever, I must admit I wasn’t keen on going to a “cold country” at first, after hearing about it from my Polish supervisor, Prof. Jacek Tejchman. He was the one who encour-aged me to collect materials for my Ph.D thesis and to get some experience here at POSTEC. And as I had already searched for quite a long time in Poland, I found the idea to carry on my work in a foreign country a very good one. But Norway? Scandinavia was always said to be rather “cold”, in more than one sense.Finally, I plucked up courage, took warm clothes and arrived in Porsgrunn...and so far I’ve never used those clothes. Summer this year was even hotter than the one in my home town - Gdansk. And even if it happened to be a bit colder here, the atmosphere makes me feel really comfort-able. I enjoy meeting, at work as well as elsewhere, nice and helpful people, both Norwegian and from all over the

world. And what’s most important, the working process on my Ph.D project is being improved productively here. I deal with a numerical simulation of silo flow and structures and take advantage of great possibilities to carry out the calculations

From to Norwayand compare them with research work.What more could I expect? Working condi-tions enable me to work efficiently and to not come home too late. Then I can spend nice evenings with my wife and weekends surrounded by beautiful nature. Now I’m sure - it was a good decision!!

Marie Curie Fellowships

We invite our colleagues in the EU to consider sending their Ph.D. students to spend a year with us. As the advertisement on page 3 indicates - the pay is good, and as the stories here indicate, those visiting us enrich both themselves and us! Candidates must be citizens of an EU country and be working on the reliable flow of particulate materials. We also have a 12 month Fellowship for a post-doc. Any takers?


It is with the deepest regret that we learnt of the premature and untimely death of our colleague and friend

Predrag Marjanovic in September. He was playing golf at Troon, near Ayr in a University tournament, when he suddenly collapsed and died instantly. He had no prior history of illness and was only 50 years old.

Predrag was born on 1 May 1951 in Belgrade, Yugoslavia, where he lived until November 1992. He then moved with his wife Mara and daughter Nevena to Glasgow, Scotland, where he continued to reside throughout his time in the UK.

Predrag obtained a 1st class Honours degree in Mechanical Engineering in 1974 from the University of Belgrade. He then joined the Fluid Mechanics Department of the University of Belgrade as a teaching assistant - where he was employed for 18

Saverio Tani, Exchange Student, University of Rome

About six months have past since I’ve left Norway and my memories are still fresh and lovely.

I was in Porsgrunn to carry out a project under the EU’s Leonardo da Vinci pro-gramme for my degree in Environmental Engineering of Rome University. My thesis focused on gas cyclones, and my task was to verify through experimental data, and check how accurate the predictions were of the mathematical models that are used to describe a cyclone’s flow in terms of separation efficiency and pressure drop.

After having given an overview on lots of powder technology’s fields and applica-tions, I started going in detail into my project. Initially I spent most of my time collecting information by reading and studying books, reports and articles. This was an inevitable and fundamental phase of learning, and thanks to all of the docu-ments and references that have been col-lected through the years at POSTEC on cyclones, I managed to put together several models and analyse the evolution of these throughout the years.

My conclusions were that no current analytical model is able to take correctly

into account all of the parameters that influence the separation process and there-fore only by combining different models, which follow different approaches, is it possible to represent the separation proc-ess. A possible design tool may come in

the next years with software development on CFD, but currently the approximations that are necessary to represent a highly turbulent two-phase flow, as the one inside a cyclone, are still too many.

The experimental phase of my thesis

was carried out in the mythical POWDER HALL, a place where practicality and innovation, geniality and experience are continuously combined by everyone. I have to admit that during this phase I collected several failures, but at the same time I learnt much more from these than I did from most of my successes. Mainly because I was allowed to make my own mistakes and it was up to me to find the correct solutions to my problems. It was also very nice that everyone found some time to talk about my project with me, that allowed me to get a broader view and different perspective of my work.

Conversations often then carried on following all sorts of pathways and I found it highly fascinating getting to know people coming from such different countries and cultures from mine.

These are just some of the reasons that made me spend an unforgettable winter in Norge, on both the human and profes-sional sides. I do regret not having learnt more Norwegian and I still have to visit the north and the west coast of the country. This means that I definitely will be coming back, maybe for work or maybe on holiday but I’m sure to see you all soon, tusen takk for everything.

Mythical Place Called Powder Hall

Obituary - Predrag Marjanovicyears rising to the position of Associate Professor. During this time he obtained an MSc with distinction in Process Engineer-ing and a PhD for a thesis entitled ‘An Investigation of the Behaviour of Gas-Solids Mixture Flow Properties for Verti-cal Pneumatic Conveying in Pipelines’. The experimental work for the PhD was undertaken at Thames Polytechnic (now the University of Greenwich) and Predrag was awarded a PhD in 1984.

I first met Predrag and his wife Mara in Stratford-on-Avon in 1982 when he was doing his research for a PhD at the then Thames Polytechnic, and had kept in sporadic touch ever since. After his return to the UK (to Glasgow Caledonian University) in 1990 our contacts were more regular, and we were very pleased to have him here in Norway for RELPOWFLO III in August 1999. The last time I saw him

was in Israel last year, and at all such meetings Predrag’s intrin-sic friendliness was always de-m o n s t r a t e d . After his eleva-tion to a Chair in 1999, I had hoped that we could increase our coopera-tions, but time has now run out. Predrag will be sadly missed by all of us in the powder technology community. The whole team at POSTEC, and I, extend our deepest sympathies to Mara and their daughter Nevena on their great loss.

- Sunil de Silva


A Study of Pressure Gradients in Vertical & Horizontal Pneumatic Transport LinesDr. Biplab K. Datta, Senior Scientist Stephanie Tappe, Exchange Student

In the next three years Tel-Tek hopes to ‘re-visit’ the scale-up of pneumatic convey-ing systems. In the last issue, Chandana Ratnayake reported on our preliminary findings regarding scale-up with respect to pipe diameter. Here Biplab Datta and Stephanie Tappe look at pressure drops in vertical and horizontal sections.

The major challenge now facing the designers of pneumatic transporta-tion systems is to scale-up reliably

based on the results from pilot scale test facilities. Whatever might be the scaling technique used, it is of utmost importance to be able to predict the total pressure drop of the system. A large number of articles [1- 6] can be found in the literature dealing with calculation techniques for pressure drops in pneumatic conveying systems. Many of these techniques depend on conveying trials in a pilot scale test facility. The results obtained are then processed using empirical tools to predict the expected pressure drop of a full-scale plant. While calculating the total pressure drop of the system, people often differenti-ate between steady state pressure drop and acceleration pressure drop. Also the steady state pressure drop rate in vertical and horizontal conveying is generally recognised to be different because of the additional gravitational force in the vertical pipeline. Naturally, the question arises ‘Is there any relationship between these two pressure drops?’ If there existed such a reliable relationship then it would be an extremely useful tool for designers, because then they could undertake experiments using only horizontal test loops and predict the pressure drop for the vertical pipes as well. This would eliminate the need for an elaborate test loop.

Unfortunately very little published work could be found in the literature in this respect. The only literature found was that of Marjanovic [7,8] and that of Hettiaratchi et al [9]. Marjanovic carried out a large number of tests and concluded that the

ratio of the pressure gradient in the vertical pipe section to that in the horizontal pipe section varied between 1.2 and 2.1, and that the ratio was also dependent on the material being conveyed. Hettiaratchi et al. undertook a study using polyethylene pellets and wheat flour and concluded that the pressure gradient ratio was in the range of 1.3 to 2.0 for polyethylene pellets and in the range of 2.0 to 9.5 for wheat flour.

2 m 3 m 2 m

2 m

2 m

1 m

1 m

9 8 7 6

5

4

3

2

1

Figure 1. Schematic layout of the test section showing location of the pressure transducers.

The complete experimental test rig (not shown here) consisted of a 140 m long test loop of 3” bore pipeline. In order to study the variation of pressure drop along a vertical pipe section and a horizontal pipe section under near identical conditions with respect to gas velocity and volumetric concentrations, a section of the transport loop was chosen as the test section as shown in Figure 1. The vertical pipe was followed by a bend (R/D = 5) and a horizontal stretch of pipeline of about 10 m length. The transducers used for this experiment had an accuracy of +/-1 mbar and it was expected that in spite of the inherent fluctuation of pressure during pneumatic transportation, we would be able to get a trend of variation of pressure with a reasonable degree of accuracy. The pres-sure data was recorded using LabVIEW™ software and analysed. The test material was alumina used in aluminium produc-tion.

The size distribution of the alumina was monitored at regular intervals during the experimentation. The tests were conducted at different start pressures at the blow tank, and an attempt was made to cover a wide range of solids loading ratios during the

tests in order to achieve a wide range of pressure drops. The start pressures used at the blow tank for this study were 2.5 bar, 3.0 bar, 3.5 bar, 4.0 bar, 4.5 bar.

The variation of solids flow rate with change in air flow rate at the different start pressures used at the blow tank are presented in the Figure 2. The variation of the solids loading ratio with change in inlet air velocity is presented in the Figure 3 for all the blow tank start pressures used during the experimentation.

0

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acit

y [

t/h

]

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m

m is mass loading ratio

Figure 2. Variation of solids flow rate with change in airflow rate.

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Figure 3. Variation of mass loading ratio with change in airflow rate.

During the experimentation, all the pres-sure values at the different pressure trans-ducers were recorded and were plotted for different start pressure conditions. In Figures 4 to 8 the first five points represent the pressure readings in the vertical pipe section and the subsequent four points represent the pressure readings in the horizontal section. For the zone showing steady pressure drop rates, trend lines were drawn for both the vertical and the horizontal sections. Consequently, the ratio of the gradients of these trend lines for the vertical and horizontal sections would give us the ratio of the pressure


y = -27,276x + 1666,9

y = -13,672x + 1531,5

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Figure 4. Variation of pressure along the vertical and horizontal section. Start pressure 2.5 bar, loading ratio 46.11.

y = -21,362x + 1954,5

y = -33,662x + 2083,1

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drop rate in the vertical section to that of the horizontal section. In the figures the first pressure transducer is mounted at a distance of 1 m from the line leading into the test section.

Having thus obtained the pressure drop results, the gradients of the trend lines were recorded and used for calculating the pressure drop gradient ratio between the vertical and the horizontal lines. Although tests were conducted at different set pres-sures at the blow tank, the pressures at transducer no 1 on the vertical pipe were different for different solids loading ratios even for a given start pressure at the blow tank. Naturally it was expected that the

pressure gradient ratio would be dependent on the Froude number at transducer no 1. Hence for comparing the pressure gradient ratios it was thought best to use the Froude number at transducer no 1. Further, since it was expected that the pressure drop rate would be dependent on the volumetric concentration of solids, we plotted the pressure gradient ratio with change in the product of the Froude number and the volumetric concentration on the basis of the velocity and the pressure at transducer no 1 and the results are presented in Figure 9.

It could be seen that the pressure gradi-ent ratio varied from about 0.1 to 1.9

y = -37,765x + 2781,1

y = -30,817x + 2725,5

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ssu

re g

rad

ien

t ra

tio

4.5 bar2.5 bar3,0 bar3,5 bar4,0 bartrendy

Figure 9. Variation of pressure gradient ratio with product of volume concentration and Froude number.

and there existed a trend that the ratio increased with increase in the product of volume concentration and Froude number. It could be seen that at 2.5 bar pressure all the pressure gradient ratio values were less than 1. As the pressure was increased, more numbers of points could be found above 1. At 4.5 bar pressure all the data points were above 1. Although no clear relationship could be established, it was evident that the system pressure had an influence on the pressure gradient ratio.

From the above study it could be con-cluded that the pressure gradient ratio could vary between 0.1 to 1.9 for alumina, under the test conditions used in this study.


Effects of Segregation on the Environment and Yield in

Production

It also showed that the pressure gradient ratio depends on the product of the Froude number and volumetric concentration. The system pressure also has a significant effect on the pressure gradient ratio. The results indicate that there is a need to further investigate the nature of variation of the pressure gradient ratio.

The authors gratefully acknowledge the support of the Norwegian Research Council and members of the POSTEC programme for providing funds for this research work, and the EU’s Leonardo da Vinci programme for a grant to Ms Tappe to do her project at Tel-Tek.

References1. Chambers, A.J.: Scaling pneumatic

conveying characteristics for pipeline

pressure - a revisit. Powder and Bulk Solids Conference, Chicago, USA, May 1995.

2. Pan, R., Wypych, P.W.: Scale-up proce-dures for pneumatic conveying design. Powder Handling & Processing, Vol 4, No 2, June 1992.

3. Williams, O.A.: Pneumatic and hydrau-lic conveying of solids. Marcel Dekker, New York, 1983.

4. Klinzing, G.E., Marcus, R.D., Rizk, F, Leung, L.S.: Pneumatic conveying of solids - a theoretical and practical approach. Chapman & Hall, UK, 1997.

5. Muschelknautz, E.: Theoretische und experimentelle Untersuchungen über die Druckverluste pneumatischer Förderleitungen unter besonderer Berücksichtigung des Einflusses von

Gutreibung und Gutgewicht. VDI-Forschungsheft 476; 1959.

6. Bohnet, M.: Experimentelle und theo-retische Untersuchungen über das Absetzen, das Aufwirbeln und den Transport feiner Staubteilchen in pneu-matischer Förderleitungen. VDI-For-schungsheft 507, 1965.

7. Marjanovic, P.: A comparative study of the performance characteristics for horizontal and vertical pneumatic conveying in pipelines. Pneumatech 1, UK, 1982.

8. Marjanovic, P.: An investigation of the behaviour of gas-solid mixture flow properties for vertical pneumatic conveying in pipelines. Ph.D. thesis, Thames Polytechnic, London, UK, 1983.

Are Dyrøy, Research Scientist Morten Karlsen, Senior Engineer, Hydro Aluminium, Årdal Research Centre

For several years, Tel-Tek’s POSTEC Department and the Technology Centre at Hydro Aluminium’s Årdal Plant have been cooperating in identifying and counteracting the effects of segregation in aluminium production. In this article, the effects of segregation are investigated further, and it is concluded that any further efficiencies in production and any improvements as regards environmental pollution will, to a large extent, depend on paying more attention to the handling of alumina.

The raw material for alumin-ium production is alumina, which is a particulate solid.

As for most processes, constant conditions are essential for obtain-ing optimal results, also in alumin-ium production. Constant process conditions depend on constant quality of the raw materials, but since alumina is a particulate solid, segregation will easily cause quality variations, which can make it nearly impossible to maintain continuous

optimal process conditions. By collecting and analysing a large number of samples of alumina from plants in normal operation, and comparing the results with essential process variables, it has been possible to

quantify the direct effects of segregation as well as improvements achieved after installation of anti segregation equipment, which have been described in previous issues of this Newsletter.

Production of aluminium from alumina involves large amounts of alumina (2 kg alumina gives approximately 1 kg of aluminium) and, as described earlier, alumina is a particulate solid that can easily segregate. Aluminium is obtained from alumina by electrolytic reduction - a chemical term meaning the removal

of oxygen atoms from aluminium oxide. The calcined alumina is reduced to aluminium metal in electrolytic cells, or “pots”, con-nected in parallel to a direct cur-rent power source. The cells are rectangular steel pots lined with refractory bricks and carbon blocks acting as the cathode.

The pot contains a molten elec-trolyte, called “bath” in which alu-mina is dissolved. The electrolyte is a mixture of cryolite (Na

3AlF

6),

and certain additives to give it the appropriate density, conductivity and viscosity. The principal addi-tive is aluminium fluoride (AlF

3),

which must be replaced from time to time due to losses through evaporation and a chemical reaction converting it into cryolite. The emitted fluorides are collected, treated in the dry scrubber section of the fume treatment plant, and recycled to the

A

B

C

D

E

F

G

Main storage typicalcapacity of 20-60 kton

Conveyor from mainstorage to day silo

Buffer siloprimary alumina

Buffer silosecondaryalumina

Alumina shiped by boat

Pot-rooms sampling fomselected pots

Fume treatment

Figure 10. Typical layout of one line in an aluminium plant, showing sampling points.

Claudius Peters

BMH Claudius Peters GmbHSchanzenstraße 40D-21614 BuxtehudePhone: +49 4161 706 0Fax: +49 4161 706 270Email: [email protected]: www.bmhcludiuspeters.com

BMH Technologies Materials processing technologies and engineered systems

Brandnames of BMH

BMH Claudius Peters Alumina silo with Anti -Segregation System

What the experts call anti-segregationi.e. maintaining the distribution of grainsin mixtures unchanged is reached byBMH Claudius Peters silos by specificarrangement of aerated aeroslides andsimultaneously air locking of the inner silo area.

Characteristic data:

• Storage capacity up to 100,000 t• Diameter up to 75 m• Discharge Capacity up to 2000 t/h• Feeding Capacity up to 1500 t/h• Residual Discharge > 99%• No drives inside the silo

Facts at a glance:

• Reduced anode effects• Decreased CO2 emission• Increased efficiency of gas cleaning systems• Reduced dust formation• Clearly improved working conditions


pots, in the form of secondary alumina. Suspended in the electrolyte are a

number of anodes (positive electrodes), which act as electrical conductors for a high intensity direct current. Electrical current passing from the anode through the electrolyte to the cathode reduces the dissolved alumina into aluminium and oxygen at a temperature of approximately 950°C. This process is called electrolysis. The oxygen is released at the carbon anode, where it combines with the carbon to form carbon monoxide and carbon dioxide (CO and CO

2). The aluminium, having a higher

density than the bath, settles to the bottom of the pot. Considerable electrical energy, between 13 and 17 kWh per kilogram of aluminium, is consumed in the process.

Each pot is tightly closed to achieve greater energy efficiency and to capture the pollutants emitted, and gas treatment cen-tres provide a very effective environmental protection. At regular intervals, the molten aluminium is tapped from the bottom of the pot into a crucible and transferred to holding furnaces for casting.

In order to quantify the effects of seg-regation, several sampling points were configured as shown in Figure 10. The intention was that all transitions and handling operations were to be covered. As a general approach the sampling campaigns were carried out in such a manner that the day to day operations did not have to be affected in any way, since the main objective was to find the status of the plant in question in normal operation. The campaigns had a duration of usually 40 days, this number being chosen based on the process cycles in the plant in order to avoid and identify process systematic variations. Usually one took one sample at every point, and in the pot room one sample from several pots, also in some cases several samples every day. Typically such a campaign delivered between 1200 to 2000 samples to be analysed for size distributions and sometimes for chemical composition of samples after fume treatment.

Data generated from a campaign were compared and checked against logged data from the electrolysis process, levels in silos and other logged material. All these data are then pre-analysed by the use of multivariate tools, and then the individual relationships were picked out and studied closer.

Effects on the Working EnvironmentDuring one of our sampling campaigns [1] continuous monitoring of dust was carried

out using a NEO DM4 in one of the prebake pot rooms. The alumina was sampled from 22 pots with one sample from a point feeder each day over a period of 41 days. The average of the daily 22 samples is used in the comparison. The dust and fines content values are centred and normalized in order to compare them with each other. The centring and normalizing was done using Equation 1:

1n

n1iii

s

xxy

-

-=-=

(1)

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i - normalized and centred value

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xi =1-n

- mean value of all samples (1 to n) s

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series

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Figure 11. Centred and normalized data for sub 42 µm content and dust concentration in pot room.

As can be seen from the plot in Figure 11, the dust concentration in the pot room air follows the content of fines in the alumina fed to the pots. This plot illustrates not only the variation in the working environment for the operators, but also the total dust emission from the pot room. Keeping a strict control of the alumina when handled can reduce this variation. However, the co-variation also indicates a possibility of using dust monitoring to indicate the alumina quality. Also this co-variation shows that when buying a cargo of alumina having a high content of fines, one should reroute this alumina to the sections of the factory having both sufficient “hooding” and gas collection efficiency.

Effects on the ProcessWhen producing aluminium, as explained earlier, one adds alumina to the electrolytic

bath. Nowadays one uses mostly volumetric point feeders to add the alumina. Volumet-ric measuring of a bulk solid has its very weakness in the fact that the particle size distributions influence the bulk density. Also the same distribution influences the flowability of the bulk solid. In the electrolysis cells one may encounter a phenomenon called an Anode Effect (AE). When a so called anode effect occurs in the reduction cell, the cell voltage increases and as a consequence the process yield drops due to solubility properties of the alumina in the molten bath. Other process side effects are that instead of producing aluminium, one uses energy to pollute the environment. The form of pollution is emissions of CF

4 and C

2F

6 having an

approximate CO2 equivalent of 8000, and

these gases are mainly produced by AE in the primary aluminium production process. Anode effects are countered by the use of different feeding programs for the alumina to the pot. The variations in the fine fraction, below 42 µm, found from the sampling campaign are compared with the anode effects. In order to do this, one has to compare an integer value (number of AE’s) with a real number (% below 42 µm), so the values were normalized using the same normalization procedure as given before.

-4,0

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Figure 12. Centred and normalized sub 42 µm content and number of anode effects (AE) pro day at the same pots as alumina is sampled.

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Figure 13. Historical data comparing the CO2 equivalent with frequency of anode effects (AE’s).


Are you interested in

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As can be seen from the curves [1] (Figure 12) the co-variation is not random and, especially when the content of fines rises rapidly, the regulating system cannot respond quickly enough and results in AE. Later comparisons show also the same level of co-variation.

Looking further at the next figure (Figure 13) one sees the correlation between the CO

2 equivalent of the emissions, and AE’s.

Of course, in a complex process as in the production of aluminium, variations of fines due to segregation are not the sole reason for AE’s. However, a co-variation has been found. Co-variations show that the variations from segregation, undoubt-edly contribute to both the production yields and environmental impacts of the aluminium production.

CounteractionIn an attempt to reduce the variations described in the foregoing sections, systems to counter segregation and reducing the effects of the segregation in the aluminium industry have been developed. To directly counter segregation one would need to put the effort into the filling procedures for, or the configurations of, the storage systems. A system for filling a silo via several tubes has been installed in two 6000 t silos.

To measure the effect, the standard deviation of the content of fines in the in-going material is divided by the standard deviation of the content of fines in the material discharged. If this value, called the

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Figure 15. Comparing variations in fines with pot section using ADS (C3) and section filled using overhead cranes (D3).

homogenisation factor, is equal to 1, there is no segregation or homogenisation. If the value is below 1 one has segregation, and if larger than 1 one has a homogenisation effect. The new system gives a H

fact of 1.7

compared to the old storage having 0.7 (as shown in Figure 14), indicating that the old storage increases the variations because of segregation, while the new system not only prevents segregation but also reduces the variations (homogenising).

Figure 14. Homogenising factors from old A-frame storage compared with homogenis-ing factors for new silos using AS-System (A99/C99 = A-frame and A00/C00 = new silos).

As shown, the reduction of variation is possible by using the AS-System©, however one needs to do this throughout the whole of the process line in order to preserve the homogeneity gained. For further distribu-tion of the alumina to the pots, there are available several distribution systems using

different methods of conveying. If one runs such systems in the right way, one will both preserve the homogeneity achieved earlier in the upstream handling processes, and ensure that different pots gets the same quality of raw material. This gives one the opportunity to run several pots as one unit instead of several individuals. A system developed by Hydro Aluminium uses high capacity air-slides for distribution of alumina in small amounts rapidly to the different pots. This method of running the distribution system, results in what can be seen when looking at Figure 15. The section filled by the distribution system called Aerated Distribution System (ADS) to the right in Figure 15 marked C3, gives less variation than the section filled using overhead cranes (Figure 15 to the left marked D3).

By the use of AS-system© and ADS©, the variations of the alumina to the pots may be reduced to a negligible level. Considering the co-variations described earlier, one can improve the yield by stabilising the process, the stability will further also have a positive effect on the working environment and the overall emissions from the process.

References1. Dyrøy, A: Segregation and attrition

when conveying from main storage in Øvre Årdal to electrolysis pot in sections ÅIIC and ÅIII (Norwegian restricted report). Tel-Tek report no. 410089-3, March 2000.


Using Noise to Predict Particle Size and Segregation Online Sivert Ose, Scientist Jun Huang, CAMO as

Different sounds and noises surround us, and we all know the familiar feeling of “What

has happened now” when a familiar sound suddenly disappears. From the factory floor, we know the mechanic that can hear a ball bearing running warm or the operator that can hear when a process does not run as expected. In many ways, this is what acoustic chemometrics does in a more automated way. For a number of years, POSTEC has maintained close relationships with the chemometrics group (ACRG) at Tel-Tek and HiT.

As an add-on part to another project on the abrasion of particles, we investigated the relationship between noise and particle size distribution. This was done using an accelerometer mounted on the conveying pipeline. For information about our earlier use of accelerometers on pneumatic pipelines, see POSTEC Newsletters nos 15 & 16. The accelerometer will pick up both general “noise” as well as vibrations from the pipeline. Our hope (and assumption) was that this “noise” would be related to the particle size distribution and thus the dust content in the powder. We knew from earlier experience that repeated runs in a pneumatic pipeline would crush particles. The powders used in the test were 6 different alumina powders, from different manufactur-ers and with various production histories, making them both strong and weak. These tests were originally commissioned to search for attrition patterns in various aluminas. As an add-on to the attrition testing, we investigated whether we could find a correlation between noise and particle size.

We did the attrition testing in our industrial scale pneumatic conveying rig with a transport length of 140 m in each run. In each run, the powder was

transported in two loops of 70 metres each. The rig is fully instrumented with pressure transducers, load cells etc, and also with acoustic measure-ment equipment. Physical samples of the powders were taken during transport with two samplers placed in the rig. The particle size distributions of the samples were then determined using our laser diffraction instrument: Sympatec Helos.

Using a LabVIEW™ application developed by ACRG, we sampled the acoustic signals and then correlated them with results from particle size analysis data. For the correlation, the dust content, i.e. percentage smaller than 21 and 42 µm was used. The content of particles below 21 and 42 µm serves as important quality parameters in the aluminium indus-try, which is why they were chosen for initial correlation.

A typical trend in the particle size distribution is shown in Figure 16. The different alumina types had dif-ferent breakage characteristics, which will report on later, if permitted.

Chemometric analysis is an ad-vanced mathematical tool to search for patterns within a large quantity of data. The correlation coefficient shows how well we could model the correlation between particle size and sound, and the results are shown in Table 1. In general we had a correla-tion coefficient of 0.8-0.9, something that is considered reasonably good. A correlation coefficient = 1 is ideal. It is however to be noted that the slope of the model was somewhat lower than hoped for.

We find the results of this investiga-tion promising. We were able to find a model that can find a correlation between the noise and dust content in the pipe. This is something that surely can be of help, especially in determining whether severe segrega-tion occurs. We hope to develop this method further, so that it can be implemented for use by industry.

Table 1. Correlation coefficients between particle size and noise.

Type of Alumina Sampler/Dust Fraction Corr.Coeff Sampler A: <21 µm 0.72 Sampler A: <42 µm 0.71 Sampler B: <21 µm 0.80

AL-A

Sampler B: <42 µm 0.73 Sampler A: <21 µm 0.94 Sampler A: <42 µm 0.95 Sampler B: <21 µm 0.95

AL-B


AL-C


AL-D


AL-E


AL-F

Sampler B: <42 µm 0.87

0

5

10

15

20

25

Transport cycles

% b

elo

w 2

1 o

r 42

µm

Sampler A-21 µm

Sampler A-42µm

Sampler B-21µm

Sampler B-42µm

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Figure 16. Increase in fines content as the powder is transported through the pneumatic conveying line (no of rounds).

Figure 17. Acoustic sensors are small and quite robust.

www.tel-tek.no


Uniaxial Tester as a Tool for Predicting Tabletting Performance of Powder MixturesGisle G. Enstad, Prof. II, Chief Scientist

The uniaxial tester developed by POSTEC, has been described in a number of previous issues of this

Newsletter [1], but as a reminder, the main principles are repeated in Figure 18. The consolidation stage is shown in Figure 18a, where the powder in the cylindrical die is consolidated axially by means of the piston moving in the downward direction. An elastic membrane between the powder and the die wall, and with lubrication on the interface with the die wall, reduces the friction along the die wall to a minimum, giving a homogeneous consolidation of the powder sample. Having consolidated the sample to the prescribed consolidation stress σ

1u, the sample is unloaded by a

small upward movement of the piston, before the die is pulled upwards, leaving the consolidated sample as an unconfined powder plug, as shown in Figure 18b. In this position the strength is measured by moving the piston downwards until the axial stress passes a peak value, which is the strength f

c for that particular consolidation

stress σ1u

.

Piston

Die

Flexiblemembrane

Sample

Bottom plate

σ1u

ε1u

fc

α = 45˚+ ϕ/2

Figure 18. The main principles of the uniaxial tester is a) consolidation and b) strength measurement.

In 1999 a major investigation was carried out for Pharmacia AB by means of the uniaxial tester in order to see if the tester could be used to predict the behaviour of powders in a tabletting machine. Figure

19 shows a picture of the tester developed by POSTEC, in use during this investigation, where 4 points of the uniaxial flow function were determined, using the consolidation stresses 5, 10, 20 and 40 kPa. Most of the mixtures that were tested had very low strength, and in a few cases where no cohesive plug was obtained even at 40 kPa, consolidation stresses of 80 kPa were also used. A number of other parameters were tested as well, including particle size distribu-tions, moisture contents, and other flow property measurements, and a detailed description of the results is now being published elsewhere [2]. Only some important details will be summarised here.

Figure 19. The investigations of the mixtures from Pharmacia AB were carried out by Anne Berdal, using the latest version of the uniaxial tester.

The normal type of flow function as illus-trated in Figure 20 was obtained for many of the powder mixtures that were tested, but more typical of the mixtures was a flow function crossing the abscissa, as also indicated in Figure 20.

fc

σ1u

Normal flow function

Flow function typical of mostmixtures from this investigation

Figure 20. Illustration of flow functions obtained during the investigation for Phar-macia [2].

Flow functions crossing the abscissa some-times appear, often when the powder is a mixture which might contain agglomer-ates, which may start to disintegrate, contributing more to the strength at high stresses, but not at low stresses.

The mixtures consisted of 19.0% of the active ingredient, 77.5% of a filler, 2.2% of a binder/disintegrant, 0.5% of a glidant and 0.8% of a lubricant. The ingredients were tested individually, except the glidant and the binder/lubricant, showing that the active ingredient was considerably more cohesive than all the mixtures. The filler was somewhat more cohesive than the most cohesive mixtures, whereas the lubricant was like the less cohesive mixtures, except at the low stress levels, where it always formed a coherent plug. It was interesting to see that the mixtures mostly were less cohesive than the individual ingredients. This shows that the minor ingredients, like the glidant and the lubricant, are acting as flow aids, as is the intention.

Mixtures included in the investigation were used for pressing tablets in a tablet-ting machine using forced feeding. The performance of the various mixtures in the tabletting machine was noted, and can be compared with the results from the uniaxial tester, as has been done in Table 1, where the results from the uniaxial tester are represented by lkon, the lowest consolidation stress giving a coherent plug, and konso40, which is the strength of the

Table 2. Tabletting performance of powder mixtures in relation to the results from the uniaxial tester.

Batch Tablettingmachine speed

(tablets per hour)

Tablettingperformance

lkon[kPa]

konso40[kPa]

802 Poor - 5 6.384803 Poor - 5 7.028804 Medium 110 000 20 4.984805 Good 130 000 10 3.283812 Medium 77 000 20 3.381813 Good 130 000 40 1.841814 Good 130 000 40 2.380815 Good 130 000 40 2.989821 Poor - 5 5.922823 Poor - 5 5.985824 - - 10 5.453

Continues on page 27...


Predictions of Loads on Walls and Insert in a Gravity Flow Silo using ABAQUS™Songxiong Ding, Stipendiate Mladen Jecmenica, Assoc. Prof. Telemark University College

This article describes the first attempts to use the finite element package ABAQUS™ to predict the load on the walls of silos. Next year the large silo battery at Telemark University College will be used to test these predictions.

In the case of the structural design of silos, considerable uncertainty still exists because of the complexity of

the pressures which a silo is subjected to. Until now, there has been no international agreement on a standard for silo design, even though many such attempts are cur-rently being made [1, 2]. Instead, one has still to rely on a formula developed by Janssen in 1895, and its modifications [3, 4, 5, 6]. Janssen’s simple model, and its modified versions have been proven to be acceptable for the analysis of simple geo-metrical shapes and granular materials at rest conditions, but, because of their basic assumptions for mathematical simplifica-tion, they are inadequate for more complex situations created by silo geometry, the interactions between the granular material and the silo wall, and various handling processes.

The assumptions made by Janssen, and others who have followed him, have been necessary to obtain analytical solutions to the equations governing the loads on the walls of a silo; otherwise such attempts will be extremely difficult. In order to extend current knowledge, however, other methods are required to gain a better understanding in more complex situa-tions. To date computational models and numerical approaches present the possibili-ties and opportunities for such progress. Eliminating a number of assumptions, the numerical models, which are still at an early stage of development, can theoretically provide a description of problems in as great a detail as required to resolve all types of problem. With the provision of various software packages in the market, such work has become easier. In fact, much research

has been dedicated to such an approach. As a result, significant progress has been achieved so far [7, 8]. In some aspects, the results produced are quite realistic.

It is well known that a ‘smooth’ hopper surface is one of the requirements for mass flow to occur. Deterioration of the surface during operation could cause the flow pattern to change from mass flow to funnel flow and even lead to stoppages. Interaction between the material and silo wall can be quite complex. It depends on both wall material and granular material properties, wall roughness etc [9], so modelling the mechanical interaction is still a great challenge, and is essential [10]. Since the research to be carried out here is assumed to be in a mass flow silo, a ‘smooth’ wall surface is a precondition, and therefore a constant friction coefficient between the granular material and possible inserts was assumed.

There were two kinds of geometry under investigation. In the first case, the silo is made of steel. The cylindrical section was 6 m in height and 2.5 m in diameter, and its wall thickness was 6 mm. The hopper in the first case was 3.94 m high, with a 15° hopper angle and a 0.41 m in diameter outlet. In the second case, the height of hopper was shortened to 1.5 m with a 35° hopper angle; the other geometries remained unchanged; but a double-cone insert was installed. Since the installation of a double-cone insert would make the geometry complex, the silo itself was kept axi-symmetrical for the sake of simplicity; for the same reason, the double-cone insert was designed axi-symmetrically and put into the silo axi-symmetrically too. The material was filled to a height 2 m below the top of the silo, from which a conical surcharge with a 25° repose angle η starts to form.

For the steel silo wall, the Young’s modu-lus E

w and Poisson’s ratio ν

w was set as

2 × 1011 Pa and 0.25 respectively. The setting of material parameters relates to the material model. In this investigation, the measurable parameters were based on the Mohr-Coulomb model for a granular material. They are: the bulk density ρ =

1000 kg/m3, the material internal friction angle ϕ = 30°, and its friction angle with the wall φ = 18°. Young’s modulus E

p was

assumed as 10 MPa, while its Poisson ratio ν

p is given by [11] as:

ϕ-

ϕ-=ν

sin2

sin1p

(1)

q

d

β

σm = (σ1 - σ3) / 2

σ1 σ1 σ3 σ3

c

(σ, τ)

σ

τ

S = (σ1 - σ3) / 2ϕ

p

Figure 21. Mohr-Coulomb (upper) and linear Drucker-Prager model (lower).

The material plastic parameters were adjusted during the analysis for the sake of convergence, but are usually set as 1 thousandth of its Young’s modulus at the beginning of failure.

However, these data cannot directly used; they need to be converted into for the parameters of a linear Drucker-Prager model offered in ABAQUS™. In a non-associated flow case, the converted relation-ships are [12]:

ϕ=β sin3tan (2)

ϕ= cos3c

d

(3)

where β, ϕ, c and d are parameters in the Mohr-Coulomb failure model and the Linear Drucker-Prager model for granular material as shown in Figure 21.

As known, the flow patterns and magni-tudes of pressures in silos are related; the pressure cannot itself be predicted without the flow pattern being known. If the flow pattern is mass flow, the silo pressures can


be predicted reasonably well. However, at present, the flow pattern itself is still dif-ficult to predict. Even with such difficulties, mass flow in a silo with a steep hopper can be secured for most materials. This was confirmed for the first case [13].

A Lagrangian-Eulerian approach was therefore used to simulate the material movement in the silo. Based on the silo geometry, axi-symmetrical shell (SAX1) elements and structural continuum ele-ments (SAX4) were designed for the wall and granular material. A rigid element was used to represent the insert. In order to get a better mesh domain, partition was used in the material region. Examples of meshes used are shown in Figure 22. In the material region, an adaptive mesh was defined. In this adaptive mesh region, a zero movement of adaptive mesh constraint and an Eulerian surface region type were applied to the boundary of the outlet. By doing so, the meshes at the outlet were fixed, but the material can still flow through across these meshes. Whereas at other boundaries, a Lagrangian region type was applied to ensure that the edges of the meshes follow the movement of material.

Two simulation steps were carried out. In the first step, by applying the silo’s active state stress i.e. 0.0 Pa at the material on the top, but 35,000 Pa at that on the outlet as an initial condition (see Figure 25), an equilibrium state was adopted to simulate the material storage state stress. This stress is needed to trigger material motion. In the second step, a free discharge process was simulated. With the pre-knowledge

Ref. Pt

l

Ref. Pt

(a) (b) (c) (d)Figure 22. Examples of meshes in use. (a) Steep silo mesh (b) Steep silo’s hopper mesh (c) Flatter silo mesh(with insert) (d)After smoothing corner, flatter hopper mesh with insert.

that a mass flow pattern will occur in our cases, the work of predicting the loads generated by the granular material on the walls of the silo and the surface of insert was carried out. In such a flow, there is a moment at the beginning of dis-charge when the stress state changes from the so-called active to a pas-sive state in the hopper sec-tion. This change leads to a dramatic increase of pressure on the wall at the transition between the hopper and cyl-inder. This is usually the cause of damage to most silos, so the analysis was carried out in order to cover the change occurring during this period.

This part of work was car-ried out using ABAQUS™/Standard,where more flexible element designs are available. In the mesh design, partition was always used in the material region where a CAX8R (8-node axi-symmetric quadrilateral, reduced) element was adopted. A SAX2 (3-node quadratic axi-symmetric thin shell) was used for the wall, and a rigid analytical surface was defined for the

insert. With such a mesh design, gravity load-

ing was applied and the outlet was kept open. Under such conditions, the material will undergo a deformation. Divergences were met, but overcome by adjusting the material parameters, namely the materials plastic yield parameter. Converging results were achieved with this parameter set at between 50,000-280,000 Pa.

Very high pressure peaks were obtained at the transition when this was modelled as a sharp corner. So finite element smoothing technology was used to avoid any sharp corners. In both silo cases, the transition was assigned radii of 0.5 m and 1 m, and a 0.1 m radius was assigned to the corner of the insert. After such geometry modifications, the mesh was redesigned as shown and given in Figure 22d. By doing

so, convergence was much easier to achieve, and some results for the contact pressures are shown in Figures 23, and 24 for the silos walls and the surface of the insert respectively. There are theories to predict silo wall pressures induced by stored material [4, 5, 14, 15]. The results shown in Figures 23 and 24 were compared with results using theories in these references. In order to make such comparisons easier, a Fortran and a Matlab program were created respectively based on these formulae. They were run independently and comparisons of the calculations gave the same results. Comparisons were then car-ried out using these two programs by importing the data in Figures 23 and 24. The results are shown in Figures 25 and 26. In the figures, it can be seen that the Janssen’s active state was extended to the hopper section based on Roberts’ suggestion [16]. The result at the top from Janssen’s and the result at the outlet from Roberts’ suggestion were used as an initial condition.

0

1

2

3

4

5

6

0 10000 20000 30000 40000 50000 60000

Pressure [Pa]

Hei

gh

t [m

]

arc35_10

arc35_5

(a) Steep silo

0

1

2

3

4

5

6

7

8

9

0 20000 40000 60000 80000 100000Pressure [Pa]

Hei

gh

t [m

]

arc15_10

arc15_5

(b) Flatter hopper with insertFigure 23. Abaqus predictions of pressure along the wall (arc15_5/10 means hopper angle 15°, filleted radius 0.5 m/1.0 m).

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 20000 40000 60000 80000 100000 120000 140000 160000 180000Pressure Pa

Hei

gh

t o

f in

sert

m

arc35_10arc35_5

Figure 24. Abaqus predictions of pressure on the insert.


Overall, as seen in Figures 25 and 26, the ABAQUS™ predictions agree quite well with those from theoreti-cal predictions in the silo’s cylinder section in both cases, but differences exist in the hopper section. The differences become greater as the hopper becomes flatter. In such flat hoppers, there is a doubt whether the theoretical formulae can still be applied. But in any case, the results from ABAQUS™ for the two radii used at the transition fit reasonably well through the whole silo.

The fact that the ABAQUS™ pre-diction results drop to zero before reaching its peak is apparently wrong. That is because when the material deforms, there exist separations in that area (Figure 27). With no con-tact, the pressure in this area then becomes zero.

Below the separation, there are contact pressure peaks. These peaks could be very high (8 × 105 Pa for the flatter hopper and 5 × 105 Pa for the steep hopper) due to point (line) contact between the material and wall when there was no fillet at the transi-tion. These line contacts were modi-fied into surface contacts by filleting the corner. After such modifications, the peaks dropped close to and even lower than the theoretically predicted peaks.

It was also interesting to observe the effect the insert had on the pressures on the wall. Referring to the results as shown in Figure 24, one found that the insert takes a significant part of the load. Comparing the maximum contact pressure in the steep hopper with those in the flat hopper (Figure 28) shows that the insert decreases the pressure peak at the transition greatly, even though there is no significant change in other places. The insert does have some effects on the peak of contact pressure. However this decrease gets less obvious when the fillet radius becomes larger.

AcknowledgementThe authors acknowledge their grati-tude to the Norwegian Research Council and members at the POSTEC programme for financial support.

References1. Roberts, A.W.: Loads on Bulk Solids Containers. Draft Austra- lian Standard for Comment,

0 1 2 3 4 5 6 7 8 9 10

x 104

0

1

2

3

4

5

6

7

8

Pressure Pa

Silo

hei

gh

t m

Abaqus, arc 0.5 m Walker modified, activeEnstad, passive Walker, passive Abaqus, arc 1.0 m

Janssen, active

Roberts’ suggestion: Stress at theoutlet used as an initial condition

Figure 25. Comparisons between ABAQUS predictions and theoretical results in a steep hopper silo.

0 1 2 3 4 5 6 7 8

x 104

0

1

2

3

4

5

6

Pressure Pa

Silo

hei

gh

t m

Abaqus, arc 0.5 mWalker modified, activeEnstad, passive Walker, passive Abaqus, arc 1.0 mJanssen, active

Figure 26. Comparisons between ABAQUS predictions and theoretical results in a flat hopper silo with a double-cone insert.

Separation and linecontact betweenmaterial and wall at the transition

Figure 27. When material deforms, it drops down a bit and separates from the wall at the transition; it leads to line contact which is responsible for the very high pressure peak.

0

0,5

1

1,5

2

2,5

3

3,5

4

0 20000 40000 60000 80000 100000Pressure [Pa]

Ste

ep s

ilo's

ho

pp

er h

eig

ht

[m]

0

0,3

0,6

0,9

1,2

1,5

arc15_10

arc15_5

arc35_5

arc35_10

Fla

t si

lo's

ho

pp

er h

eig

ht

[m]

Figure 28. Insert significantly decreases the pressure peak at the transition

1989.2. Rotter, J.M.: Flow and Pressure in Silo

Structural Integrity Assessment. Sym-posium on Reliable Flow of Particulate Solids (RELPOWFLO III), Porsgrunn, August 1999.

3. Walker, D.M.: An Approximate Theory for Pressures and Arching in Hoppers. Chemical Engineering Science, 1966.

4. Walters, J.K.: A Theoretical Analysis of Stress in Silos with Vertical Walls. Chemical Engineering Science, 1966.

5. Enstad, G.G.: A Novel Theory on the Arching and Doming in Mass Flow Hopper. Ph.D. Thesis, Norwegian Insti-tute of Technology, Bergen, 1981.

6. Jenike, W.: Storage and Flow of Solids. Bulletin 123, Utah Engineering Exper-iment Station, University of Utah, 1964.

7. U. Häß, Eibl, J.: Numerical Investigation of Discharging Silos. Journal of Engineering Mechanics, Vol. 110, 1984.

8. Tuzun, U., Heyes, D.M.: Distinct Ele-ment Simulations and Dynamic Micro-structural Imaging of Slow Granular Flows. Mechanics of Mechanics and Porous Material (Eds. Fleck, N.A. and Cocks, A.C.F.), Kluwer Academic, London.

9. Ooms, M., Roberts, A.W.: Significant Influence on Wall Friction in the Gra-vity Flow of Bulk Solids. Bulk Solids Handling, December 1985.

10. Ooi, J.Y., Rotter, J.M.: Wall Pressure in Squat Silos from Simple Finite Element Analysis. Computers & Structures, Vol. 37, 1990.

11. Qu, Q., Negi, S.C., Jofriet, J.C.: Storage of Cohesive material in Silos - Part 2: Parametric Study. Powder Handling Processing, January/March, 2001.

12. Hibbitt, Karlsson & Sorensen, INC ABAQUS: Theory Manual, 2001.

13. Ding, S., Enstad, G.G., Jecmenica, M., de Silva, S.R.: Simulation of a Double-Cone’s Effects on the Granular Material Flow in Silos. 7th Interna-tional Conference on Bulk Materials Storage, Handling and Transportation, Newcastle, Australia, 2001.

14. Nedderman, R.M.: Static and Kinema-tics of Granular Materials. Cambridge University Press, 1992.

15. Drescher, A.: Analytical Methods in Bin-Load Analysis. Elsevier Science Publishers B.V., 1991.

16. Roberts, A.W.: Storage, Flow and Han-dling of Bulk Solids. Department of Mechanical Engineering, University of Newcastle, N.S.W. Australia, 1987.


Mladen Jecmenica, Assoc. Prof. Telemark University College Michal Wójcik, Marie Curie Post-Graduate Fellow, Tel-Tek

FEM is a very useful means for calculating stresses and deformations in the silo structure, since it can take into account complex silo geometries and wall pres-sures. In this paper, some numerical results for large axisymmetric silo at Telemark University College are presented. The calculations were carried out with the com-mercial software ABAQUS™. A symmetric and non-symmetric load according to Jans-sen [1] and a load from an FE-simulation was considered. In the calculations, the stiffening rings and ribs along the silo mantle were taken into account.

Finite Element ImplementationThe silo is made of steel and consists of a cylindrical part and a conical hopper. The height of the cylinder is about 8 m and the diameter 2.5 m. The height of the hopper is 4 m. Its inclination to the vertical is 15°. The wall thickness of the silo is 6 mm. Along the bin, there are 5 stiffening rings and 52 stiffening ribs (Figure 29a).

2.51

11.8

9

15.0˚

support

level

5.15

6.73

7.94

3.95

a)

b)Figure 29. Axisymmetric large silo at Telemark University College showing actual dimensions (a) and the FE grid used (b).

Figure 30. FE-mesh with stiffening ribs.

The FE-calculations were performed with 16000 shell elements (4-node elements with 6 degrees of freedom). The symmetry of the silo was taken into account (Figure 29b). The following elastic data were assumed for the silo wall: modulus of

elasticity E = 2.0⋅1011 Pa and Poisson’s ratio v = 0.3. In reality, the cylindrical part of the silo is connected with the hopper along the perimeter with the aid of bolts. In the calculations, a fixed connection between the cylinder and the hopper was assumed. Each rib of a trapezoid shape was fixed on 3 edges (Figure 30).

The following material properties of the bulk solid were assumed to calculate horizontal loads on the wall: bulk specific weight γ = 10.5 kN/m3, coefficient of the wall friction µ = 0.3 and angle of internal friction φ = 35°. The analysis was carried out with 3 different horizontal loads for the case of flow: a symmetrical and a non-symmetrical load distribution of the normal based on Janssen equations and Australian Standards [1] and a load obtained from a FE-simulation of the silo flow [2]. A non-symmetric load was created by allowing the height of the solid on one side of the silo to be lower than on the other side.

Numerical ResultsFigures 31 and 32 (see nest page) present the calculated circumferential normal stresses and displacements in the silo wall using the equations proposed by Janssen [1]. The positive values of stresses indicate a tensile region.

The maximum tensile stresses are at the transition point between the cylindrical section and the hopper. They are about 12-13 MPa (Figure 31). They are insignifi-cant as compared to the strength of the shell (250 MPa). The stresses during non-symmetric loading are higher by 10%. A non-symmetric load influences the wall displacements strongly (Figure 32). The maximum wall displacement occurs at the top and is about 0.2 mm.

The results of Figure 33 presents the circumferential normal stresses in the silo wall produced by symmetric horizontal loads from the FE-simulation of the silo flow [2]. The maximum tensile normal stresses take place below the transition level and the local compression at the silo support.

ConclusionsThe presented results show that a FE-method is a useful tool to calculate stresses

Use of an FE-Method for Calculating Stresses in Silo Structures


in the silo wall. It is particularly useful when the geometry of the silo is complex and the distribution of wall pressures caused by the bulk solid is non-uniform.

In the next calculation step, wall shear stresses will be taken into account which are of importance for the stability of steel silos.

The authors are grateful to the Nor-wegian Research Council which largely financed the construction of the large silos at Telemark University College and to the EU’s Marie Curie programme for the post-graduate Fellowship to Michal Wójcik.

References1. Roberts, A.W.: Bin wall loads. Course of

Bulk Solids Handling. The University of Newcastle, January 1997.

2. Ding, S., Wojcik, M., Jecmenica. M.: Finite element predictions of loads on walls and insert in a gravity flow silo. In preparation.

a) b)Figure 31. Calculated circumferential stresses in the silo wall for a symmetric (a) and a non-symmetric (b) horizontal load.

a) b) Figure 32. Calculated magnitude of displacements of the silo wall for (a) a symmetric and (b) a non-symmetric horizontal load.

Figure 33. Calculated circumferential normal stresses of the silo wall for a symmetric horizontal load [2].

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CFD Modelling of a Lab-Scale Fluidised BedBritt Halvorsen, Senior Engineer Vidar Mathiesen, Assoc. Prof. Telemark University College http://www-pors.hit.no/tf/forskning/gisp/

Computational fluid dynamics (CFD) of multiphase flow processes provides a new tool for design and optimisation of multiphase gas/solids flow systems. In order to be able to calculate complex industrial fluidised bed reactors, the bed expansion and bubble formation have to be correctly calculated. The flow behaviour of a lab-scale fluidised bed with a central jet has been simulated. The study has been performed using FLOTRACS-MP-3D [1]. The CFD model is based on a multi-fluid Eulerian description of the phases, where the kinetic theory for granular flow forms the basis for turbulence modelling of the solids phases. The simulations are performed with one and three solids phases, with two dif-ferent drag models and with different values of the coefficient of restitution. A reasonable flow pattern, including bubble formations, is calculated. This paper discusses different factors that should be considered when modelling bubbling fluidised beds. This paper is a summary of reference [2].

A two-dimensional bed has been constructed in order to study the bed expansion and bubble forma-

tion in gas/solid flow. The purpose of the experimental study was to verify the predictive capability of the CFD model. The fluidised bed is constructed with a cross-sectional area of 19.5 x 2.5 cm and a height of 63 cm. Spherical glass particles with a particle density of 2485 kg/m3 and a settled bulk density of 1500 kg/m3 were used in the experiments. The volume aver-age mean particle diameter is measured to be 550 mm. The experimental set-up is shown in Figure 34, and the experimental conditions are given in Table 3.

The bed is fluidised by introducing compressed air with a velocity of 0.29 m/s through a distributor plate. Jet air is injected at a velocity of 4.9 m/s. A digital video camera is applied to measure bubble formation and velocity. A movie sequence of the experimental results is shown in Figure 35.

Table 3. Experimental conditions.

Height of experimental set-up 63.0 cm

Conditions

Width of experimental set-up 19.5 cm

Depth of experimental set-up 2.50 cm

Mean particle size 550 µm

Freeboard pressure 101325.0 Pa

Initial bed height 28.0 cm

Fluidisation velocity 0.29 m/s

Jet velocity 4.9 m/s

Solid density 2485 kg/m

Bulk density 1500 kg/m

19,5 cm

63 cm

28 cm

Figure 34. Experimental set-up.

t=0.120 s t=0.320 s t=0.440 s

t=0.740 s t=0.800 sFigure 35. A movie sequence of experi-mental results.

In the simulations 39 and 63 control vol-umes are used in the horizontal and verti-cal direction respectively. Computational set-up is given in Table 4. Simulations have been run with both one and three solid phases in order to discuss possible improvement of several solid phases.

The results of the simulations with one and three particle phases are given in Figures 36 and 37 respectively.

Figure 36. Volume fraction of solids, simulation with one particle phase

Figure 37. Volume fraction of solids, simulation with three particle phases.

Table 4. Computational set-up.

Height of computational set-up 63.0 cmWidth of computational set-up 19.5 cmInitial bed height 28.0 cm

One phase Particle mean diameter 550 µm

Three phases Particle mean diameters 630 µm (18%)

500 µm (50%) 400 µm (32%)

Horizontal grid size 5.0 mmVertical grid size 10.0 mm Gas phase shear viscosity 1.8⋅10-5 Pa s Initial void fraction 0.50Max. volume fraction of solids 0.64356 Jet velocity 4.9 m/s Fluidisation velocity 0.29 m/s Freeboard pressure 101325.0 PaSolid density 2485 kg/m3

Bulk density 1500 kg/m3

Computations

The comparison between simulations with one and three solid phases shows that three solid phases give continuous bubble formations, whereas simulation with one solid phase give formation, rise and erup-tion of only one bubble. Simulations with one particle phase give a smaller bubble.

Figures 38 and 39 show the results from the simulations with two different drag models, Ergun/Wen and Yu drag model


Fan

Nozzle

Liquid Drain

Mist eliminator

Channel, 1 m

Vane Separator

Air

P

F F

Water

P

F

Airflow meter

Figure 42. Principal sketch over the experimental model.

and Gibilaro et al. drag model, respectively. Three particle phases are included in both simulations. A comparison of the two drag models shows that Erguns drag model gives the largest bubbles, the highest bed and the lowest concentration of particles. The performed measurements confirm that the Ergun model calculates a more reasonable

Figure 38. Volume fractions of solids, simula-tions results by using Erguns drag model.

Figure 39. Volume fractions of solids, simula-tions results by using Gibilaros drag model.

bubble formation and bed height for these flow conditions.

Figure 40. Volume fraction of solids, simulations with various values of the coefficient of restitution at time t=0.180 s.

Figure 41. Volume fraction of solids, simulations with various values of the coefficient of restitution at time t=0.580 s.

Figures 40 and 41 show the results from the simulations with various coefficients of restitution at time 0.180 s and 0.580 s, respectively. The numerical results indicate that the bubble velocity and the shape of the first bubble seem to be almost independent of the coefficient of restitu-tion. However, it seems that the coefficient of restitution influences the bubble size and local concentration of solids. The maximum concentration of solids increases significantly when the coefficient of restitu-tion is decreased from 1 to 0.95. After the first bubble has erupted (Figure 41), and by using unity coefficient of restitution, no further bubbles are formed.

References1. Mathiesen, V, Solberg, T, Hjertager,

B.H.: Prediction of Gas/Particle Flow Including a Realistic Particle Size Dis-tribution. Powder Technology, 112 (2000), p.34-45.

2. Halvorsen B., Mathiesen V.: CFD Mod-elling and Simulation of a Lab-scale Fluidised Bed. 42nd Conference on Simulation and Modelling. October 2001, Porsgrunn, Norway.

Computational & Experimental Studies of a Vane SeparatorAage I. Jøsang, Stipendiate Telemark University College Morten Chr. Melaaen, Professor Telemark University College

The separation of droplets from a gas stream is a matter of necessity in many processes. The equipment used for this separation is widely spread from various types of cyclones, vane-type separators, packed bed separators, scrubbers, and wire/fibre separators. In this work a vane-type separator is studied.

The model of the vane separator unit is designed to give a good basis for the measurements (Figure 42).

The fluid flow in the experimental model is studied by laser Doppler anemometry (LDA). Detailed velocity profiles appear and mean velocities and turbulence proper-ties are calculated. The centre distance between the vanes is 2.5 cm. More details about these measurements are given in Jøsang and Melaaen (1).

The positions measured can be identi-fied in Figure 43. In addition, an inlet profile is measured 50 mm upstream of the vanes, i.e. at x = -50 mm. In this posi-tion a fully developed flow is measured. The comparison between simulations and measurements are carried out the same positions as shown in Figure 43 (not at x = 0.0 mm).

X = 00 mm

X = 50 mm

X = 68.75 mmX = 87.5 mm

X =112.5 mmX =137.5 mm

X =165 mm

Figure 43. The different positions of the measured profiles in the vane separator.

The Computational Fluid Dynamics (CFD) simulations cover various turbulence models (k-ε and RSM turbulence models), near wall treatments (“Law-of-the-wall” and “ Two-layer zonal model”), numerical schemes and structured grid as well as un-structured grid simulations. Earlier simula-


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SIVILINGENIØR?På Høgskolen i Telemarks avdeling for teknologiske fag i Porsgrunn finner du et av Norges fremste forsknings- og utdanningsmiljøer innen prosess-, automatisering- og miljørelaterte fagområder. Her kan du også få en av landets mest fleksible ingeniørutdanninger. Du kan bli Høgskoleingeniør på tre år, eller Silvilingeniør på fem. Men du trenger ikke å bestemme deg med én gang. Begynner du f.eks. på det 5-årige sivilingeniørstudiet, kan du hoppe av etter 3 år og likevel få med deg tittelen Høgskoleingeniør. På samme måte kan du først ta 3-årig ingeniørutdanning, fortsette i 2 år og bli Sivilingeniør. Og ønsker du å strekke deg enda lenger, kan du fortsette helt til du har en doktorgrad. Det forventes flere nye tilbud fra høsten 2002. Besøk oss på internettet. Vil du vite mer? Ring oss og spør etter Ragnar Moland eller Unni Solvi.

Høgskolen i TelemarkFellesadm., Porsgrunn: 35 57 50 00Opptakskontoret: 35 57 53 00http://www.hit.noE-post: [email protected]


tions show that a proper matching between the grid and the near wall treatment is important. However, most important is the effect of the two different numerical schemes together with the turbulence models. The selected numerical schemes are two different first order schemes (the power law scheme for Fluent v4.5 and the first order upwind scheme for Fluent v5.3) and the higher order QUICK scheme.

The Law-of-the-wall grid is coarse by the wall. The number of control volumes is considerably higher for the simulations of the Two-layer zonal model compared to the Law-of-the-wall since a fine grid is needed by the wall. For the structured simulations (Fluent v4.5) the grid size was 875 x 32 (28000) cells for the Law-of-the-wall case, and 1440 x 52 (74880) cells for the Two-layer zonal model. For the un-structured simulations (Fluent v5.3) the Law-of-the-wall grid consisted of 30202 cells, and for the Two-layer zonal model the un-structured grid consisted of 52528 cells. For the un-structured cases, only triangle cells are used.

The analysed case has an inlet velocity equal to 3.54 m/s, and the turbulence intensity is set equal to 5%. The simulation started 1 m upstream of the vane, and the velocity profile is close to fully developed when the flow reaches the vane. The inlet boundary conditions for the turbulence are therefore not important for the simulations of the vane. The flow properties of air at 20°C are used.

Pressure DropBefore presenting any comparisons between measured and predicted velocities, the pressure drops are studied (Table 5). The measured pressure drop is equal to 40.0 Pa. The calculated pressure drops have a large variation, from 35.0 Pa to 61.5 Pa. The results from the structured grid have less variation compared to the un-structured grid. The two different wall treatments give different pressure drops, but no clear trends are seen. The pressure drops calculated by the k-ε turbulence model have a variation from -12.5% to 10.8%, and the higher order scheme does not produce better results than the first order scheme. The RSM model overpre-dicts the pressure drop compared to both measurements and the k-ε turbulence model, and the un-structured result is worst, especially when the un-structured grid is used together with the higher order scheme. The most likely reason for the increased predicted pressure drop for the RSM cases, compared to the other cases,

is the overprediction of the recirculation zones and overprediction of the maximum velocities within the separator (seen from later figures).

Mean Velocities The measured velocities at x = 87.5 mm show a strong recirculation zone, extending almost 5 mm from the wall, with backflow velocities about 2 m/s (Figure 44). The structured cases are shown to the left, and the un-structured cases to the right. The profiles of the RSM model are closest to the experimental values. The recirculation zone is however not predicted well enough.

Structured x = 87.5 mm

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Figure 44. x-velocity profiles at x= 87.5mm.

The transition from negative to positive

x-velocity is well predicted, even though the magnitude of the negative velocities is not correctly predicted. The k-ε model predicts a somewhat linear velocity profile, ending in a negative velocity close to the wall. For the un-structured cases the deviations are similar the structured cases, but for the RSM model the first and higher order schemes produce different results.

Structured x = 137.5 mm

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k-e, Law of the wall, 1. order

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k-e, Two-layer zonal model, 1. order

k-e, Two-layer zonal model, Higher order

RSM, Law of the wall, 1. order

RSM, Law of the wall, Higher order

Experimental

Figure 45. x-velocity profiles at x = 137.5 mm.

Table 5. Pressure drops over the vane separator.

Case DP [Pa]First order scheme

Higher orderscheme

Experimental 40.0 Structured, k-ε, Law-of-the-wall 43.1 35.0

Structured, k-ε, Two-layer zonal model 38.0 36.4Structured, RSM, Law-of-the-wall 48.7 45.2Un-structured, k-ε, Law-of-the-wall 44.3 42.8

Un-structured, k-ε, Two-layer zonal model 43.9 36.9Un-structured, RSM, Law-of-the-wall 50.7 61.5


For the profiles at x = 137.5 mm a recir-culation zone is present at the upper wall. Figure 45 shows the structured and un-structured results for this position. The predicted values at position x = 137.5 mm coincide well with measurements for most of the k-ε cases except in the recirculation zone. The RSM case overpredicts the posi-tive velocity, and misses the magnitude of the backflow. The shape of the profile in the backflow area is better for the RSM model. The k-ε cases are somewhat steeper towards the upper wall. In an earlier work by Jøsang and Melaaen (2) the rms veloci-ties are shown.

For a full discussion of the results readers are referred to reference 2. In the compari-son between the simulations and measure-ments, the pressure drop, the mean veloci-ties and the fluctuation velocities (rms velocities) are analysed. The predicted pressure drop is closely related to the prediction of the recirculation zones within the separator. The different combination of models produce some different results, and it is not easy to arrive at a final conclusion. The differences between the structured and un-structured simulations are usually small. Normally, the highest order scheme is believed to produce the most accurate results, but in the present work the combi-nation of the best turbulence model (RSM) and QUICK on the unstructured grid gave the worst result. The pressure drop was overpredicted by 50%. The pressure drops are predicted with an accuracy of ±13% for the k-ε turbulence model. The k-ε turbulence model combinations gave satisfactory predictions for the flow fields, although some deviations exist for the prediction of the recirculation zones. To differentiate between the k-ε and the RSM models is not straightforward, since the quality of the predictions varies from position to position in the separator, and depends on which variable is analysed (pressure drop, mean velocity or rms veloc-ity). For this vane separator a first order scheme together with the k-ε turbulence model seems best.

References1. Jøsang, Aa.I., Melaaen, M.C. (2000):

Detailed Measurements and Simula-tions of a Vane Separator. International Conference on Applied Computational Fluid Dynamics, October 17-20, Bei-jing, China, 2000.

2. Jøsang, Aa.I., Melaaen, M.C. (2001): Fluid Flow Simulations of a Vane Sepa-rator. 42nd SIMS Conference, October 8-9, Porsgrunn, 2001.

plug at a consolidation stress of 40 kPa.The performance of the tabletting

machine is based on the variation of tablet weight and machine speed during com-mercial tablet production. For the “good” mixtures tablets within specification were produced at top speed, for medium ones the speed had to be reduced, but for the poor ones tablets within specification were not produced even when the speed was reduced. Using the lkon value it is seen that one can clearly distinguish batches of poor performance from batches of medium and good performance, as all batches of poor performance have lkon = 5 kPa, and medium and good batches have higher lkons. However, whereas both batches of medium performance have lkon = 20 kPa, 3 of the good ones have lkon = 40 kPa, whereas no. 805 has lkon = 10 kPa, which is an outlier.

On the other hand, looking at konso40, it is seen that konso40 < 3.3 kPa applies to all batches of good performance, 3.3 kPa < konso40 < 5.9 kPa applies to batches of medium performance, and all batches of poor performance have konso40 > 5,9 kPa. The only inconsistency here seems to be that judging by the speed, konso40 of batch 804 should have been less than that of batch 812, and not the other way around. However, as the forced feeding may have caused higher stresses in the powder than 40 kPa during tabletting, the agreement might have been better if measurements had been carried out also at a higher stress level. That may also be the reason why the agreement is better for konso40 than for lkon.

The number of batches included in Table 1 is probably too low for any statistical proof of the performance of the uniaxial tester, but this example is an indication that the uniaxial tester can be used for predict-ing the behavior of a powder mixture in a tabletting machine, or any other similar equipment.

References1. Enstad, G.G.: Uniaxial Tester Devel-

oped by POSTEC is Further Perfected. POSTEC-Newsletter No. 18, 1999.

2. Lindberg, N.-O., Berdal, A., Enstad, G.G., Seifert, E., Lundstedt, T.: Investi-gation of Flow Properties of Powders by Means of a Uniaxial Tester, in Relation to Direct Tablet Compression. Drug Development and Industrial Pharmacy, 28(1), p.15-27 (2002).

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...Continued from page 17


Jacek Kolacz, Senior Scientist Stein Tore Johansen, Chief Scient., Prof. II SINTEF Materials Technology, Trondheim

During processing of minerals, combined comminution and classification is an inte-grated process. These two process steps interact closely and need to be optimized simultaneously. Due to the complexity of these systems experienced engineers have historically performed such optimization. However, numerical simulation techniques have been developed substantially during the last decade and can now offer significant support to the optimization process.

SINTEF has for more then 20 years worked with development of mul-tiphase flow modelling techniques.

There has also been a close cooperation with POSTEC in this area [4]. These tech-niques have many applications in powder technology and are continuously under development. SINTEF is now working with a strategic institute program called CARPET [5]. In this program multiphase flow methods will be further developed. In particular methods to deal with collision dominated flows are in focus. Applications can be mills, classifiers and segregation phenomena in powder handling.

At the same time SINTEF has come up with industrially successful concepts for comminution and air classification. A challenge is now to bridge theoretical and process knowledge in order to supply industry with better equipment.

Hicom MillHicom mills are new and versatile high intensity grinding mills. Their unique design delivers high power intensity to the grinding process and introduces new pos-sibilities in comminution practice [2]. They can operate autogenously or with a charge of steel balls or other media. Depending on the application, steel, ceramic or sand media may be used. Feed sizes up to 60 mm can be accepted. Thus the mills are extremely versatile, and can be used for a wide range of mineral processing and industrial grinding duties, wet or dry, in open and closed circuit, as well as in batch mode. Hicom mills are particularly well suited to energy-efficient fine grinding down to 10 microns and below. Grinding tests in Hicom mills have shown that both hard and soft ores can be reduced efficiently

to fine sizes ranging from 80% passing 20 µm down to 2 µm and below. Available power drives on Hicom mill ranges from 15 to 110 kW. Larger units up to 1000 kW are planned to be manufactured.

The grinding process in Hicom mills is achieved through a unique combination of the grinding chamber geometry and a high-speed nutating motion (Figure 46). The charge in the grinding chamber tumbles rapidly in a mechanically induced acceleration field many times stronger than gravity. This creates very high power input per unit mill volume and exceptionally fast particle breakage rates, typically 50 to 100 times greater than conventional tumbling mills. In fact, the motion of the Hicom mill chamber is similar to that of a centrifugal or planetary mill, except that the diameter and acceleration intensity vary down the length of the mill. The result is high productivity from a compact, efficient and cost-effective machine.

Figure 46. Cut-away view showing feed material flow path: Hicom 110/30 mill, with 110 kW motor and 30 litre grinding chamber.

The SINTEF ClassifierThe SINTEF air classifier was developed in Trondheim [12] and compares favourably with other air classifiers. The classifier design results in increased classification efficiency [10] and especially reduced specific energy requirements [11]. Com-mercially available models (licensed to Carpco-Inprosys in USA) range in clas-sification capacity from 1 to 100 t/h.

A schematic diagram of the classifier is shown in Figure 47. As can be seen, the feed material enters the classifier suspended in air through a vertical pipe positioned at the bottom of the classifier. Initial classification

takes place in the classifying chamber. After passing the feed dispersion cone, the coarse material is discharged from the classifier by gravity through the coarse fraction outlet. Remaining material rises with the air stream to the top of the classifier.

A rotor accelerates the material to its peripheral speed thus creating a centrifugal force in the particle to act against the air drag forces. As particle velocity increases, the centrifugal force rises and coarser particles can be rejected outside the rotor, while finer particles pass through the rotor and are discharged from the classifier fines outlet.

A secondary air inlet, supplying the classifier with an additional air stream, is used to clean the coarse fraction from the very fine particles agglomerated on the surface of the coarser grains. This results in an improvement of the classification efficiency.

Figure 47. Schematic drawing of the SINTEF air classifier.

Pilot Plant Tests Continuous closed-circuit grinding, which is normally more efficient than batch grinding, has been tried with the Hicom mill and the SINTEF air classifier [13]. A series of tests under different conditions have been performed to demonstrate the effectiveness of this equipment combina-tion for the production of many different fine powders. As an example a closed circuit grinding of calcium carbonate to a range of product sizes from 98% passing 26 down to 6.4 microns is shown, to determine the specific energy requirements for grinding of this material. A feed sample of the

Comminution and Air Classification


limestone powder had a size of nominally 98% passing 94. The full particle size dis-tribution curves for the product curves for these three runs are displayed in Figure 48.

Comparison of Grinding ResultsThe specific energies required for the milling of this material to the products shown earlier are given below as Figure 49. The energies for the production of the same sized material based on d

80’s for an

optimised ball mill are also given. These figures were estimated on the basis of pilot scale ball mill grinding carried out by SINTEF. The results were compared with optimised industrial scale ball milling circuits, where similar energy consumption levels were recorded. All of the ball milling reference values are based on grinding in the closed circuit with the same type of the SINTEF air classifier. This gives confidence in the accuracy of the estimates, where two different grinding machines are compared employing the same type of classifier.

This graph clearly illustrates the reduction in energy required to mill this calcium carbonate to fine sizes in the Hicom mill dry pilot plant over what would be expected for a typical ball milling circuit. For the material sizes produced during this test the milling energy requirements were between 31 and 70% lower than would be expected for a conventional ball milling circuit.

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Figure 48. Particle size distribution of the feed and three products.

Numerical Modelling EffortsNumerical modelling of air classifiers started in the late 80’s [6]. However, the techniques were not able to deal with high particle fractions and inter-particle colli-

sions. This defect was removed later by the introduction of granu-lar flow models [7]. The numerical models have been applied to a large number of industrial processes [8], but so far only to a smaller degree to milling and development of classification equipment. By introduction of Discrete Element Particle methods ([5-9]) SINTEF plans to study particle-particle interaction on a detailed level. Such techniques will make it pos-sible to analyze various sorts of mills and classification equip-

ment. In order to understand phenomena in

such complex devises, new and improved techniques for diagnoses and verification of models will be of crucial importance. This is also one important issue in the CARPET Program [5].

ConclusionsThe efficient separation of product and recycle material in the IAC 200 classifier as well as the high intensity milling environ-ment of the Hicom 25 mill combine to result in a substantial reduction in milling energy requirements for the production of fine sized material. For the material sizes produced during this test the milling energy requirements were between 31 and 70% lower than would be expected for a

ball milling circuit.The milling energy requirements

of the Hicom mill/SINTEF classi-fier combination is significantly less than that of an ordinary ball milling circuit, and operating costs are therefore likely to be substan-tially lower. Further increases in the milling efficiency of this plant are likely with additional optimization work on the classifier operating parameters. Existing numerical simulation techniques can be a valuable support in this

optimization.By a further development of the under-

standing of the flow phenomena in these devices it may be possible to push the technology even further in the direction of higher energy efficiency and finer cut-sizes. The numerical simulation techniques are expected to be an important tool for such optimization in the years to come.

References1. Brown, M.R., Kolacz, J., Hoyer, D.: Fine

Dry Comminution of Calcium Carbon-ate in the Hicom Mill and an Inprosys Air Classifier. Minerals Engineering Conference, 21-23 March, Brisbane, Australia.

2. Hoyer, D.I., Boyes, J.M.: High-Inten-sity Fine and Ultrafine Grinding in the Hicom Mill. XVth CMMI Con-gress. Johannesburg, SAIMM, 1994, 2, p.435-441.

3. Hicom Internet address: www.hicom-mill.com.

4. Johansen, S.T., de Silva, S.R.: Some Considerations Regarding Optimum Flow Fields for Centrifugal Air Clas-sification. Int. J. Miner. Process, 44-45 (1996), p.703-721.

5. CARPET internet address: www.carpet. ntnu.no.

6. Johansen, S.T., Anderson, N.M., de Silva, S.R.: A Two-Phase Model for Particle Local Equilibrium Applied to Air Classification of Powders. Powder Technology, 63 (1990), p.121-132.

7. Laux, H.: Modelling of dilute and dense dispersed fluid-particle flow. Dr.Ing Thesis, The Norwegian University of Science and Technology, 1997.

8. Johansen, S.T.: Application of Compu-tational Fluid Dynamics in Optimiza-tion and Design of Metallurgical Proc-esses. Modelling, Identification and Control, 19 (1997), p.101-122.

9. Johansen, S.T., Laux, H.: Simulations of Granular Materials Flows. Proceedings of the Int. Symp. on the Reliable Flow of Particulate Solids (RELPOWFLO III), 11-13 August 1999, Telemark College, Porsgrunn, Norway.

10. Kolacz, J.: Improving the Air Classifica-tion Process by Optimal Operating Parameters. XXI International Mineral Processing Congress, 23-27 July, 2000, Rome, Italy.

11. Kolacz, J.: Optimal Air Classification. Proceedings, the 3rd Processing for Profit - International Industrial Miner-als Conference, 26-28 April, 1999, Antwerp, Belgium.

12. Kolacz J.: Apparatus for classification of particulate material. Norwegian Patent No. 300257, May 1997, Norway.

13. Kolacz, J.: Benefits from Optimized Dry Ball Mill Circuit Grinding - Economical and Technical Aspects during Equip-ment Selection. Proceedings, the 2nd Processing for Profit - International Industrial Minerals Processing Confer-ence, 20-22 April, 1997, New Orleans, USA.

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Figure 49. Specific energy for grinding 94 micron calcium carbonate to different sizes.


Publications and ReportsBelow is a list of the reports written after November 1998. Reports with classification K2 (strictly confidential) not included. Reports marked K1 are confidential, but references open. Those marked P are available only to members of POSTEC. Those marked A are freely available. Contact your library. Please use order form on next page.

Berdal, A.: Investigation of the flow properties of some lactose mixtures using the uniaxialtester. Tel-Tek-report no. 430031-1, 2001 March 3. P.43. K1.

Datta, B.K.: Assessment of stickiness of densified microsilica. Tel-Tek-report no. 420011-1, 2001 Sept. P.12. K1.

Datta, B.K., Sannes, T., Davidsen, F.: Pneumatic Transport of a Dry Chemi-cal Powder for Fire Fighting on Ships. PARTEC 2001, International Congress for Particle Technology, Nürnberg, Germany. Report no. 01-1000-1, 2001 March 27-29. P.6. A.

Datta, B.K., Tappe, S., de Silva, S.R.: An Experimental Study of Pressure Gradients in Vertical and Horizontal Pneumatic Transport. 7th International Conf. on Bulk Material, Storage Han-dling and Transportation, Newcastle, Australia. Report no. 01-1000-8, 2001 June. P.8. A.

Ding, S., Enstad, G.G., Jecmenica, M., de Silva, S.R.: Simulations of a Double-Cone’s Effects on Granular Material Flow in Silos. 7th Int. Conference on Bulk Materials Storage, Handling and Transportation, Newcastle, Australia. Report no. 01-1000-3, 2001 P.11. A.

Ding, S., Hafenbrädl, F.O.v., Enstad, G.G., Jecmenica, M., de Silva, S.R.: Observations on the Change from Funnel to Mass Flow in Silos by means of a Double-Cone. 7th Int. Conference on Bulk Materials Storage, Handling and Transportation, Newcastle, Aus-tralia. Report no. 01-1000-2, 2001 October. P.10. A.

Ding, S., Jecmenica, M., Wójcik, M.: Finite Element Predictions of Loads and Walls and Insert in a Gravity Flow Silo. ABAQUS Scandinavian Users Confer-ence, Sweden. Report no. 01-1000-5, 2001 September. P.11. A.

Dodd, A.: CFD Modeling of Air Current Segregation. Loughborough University-report 410031-2, 2001 July. P.75. A.

Dyrøy, A.: Anti segregation solution F02, for A-frame at ASU. Tel-Tek-report no. 410080-7, 2000 Dec 22. P.10. K1.

Dyrøy, A.: Effekt av AS-System i sam-menligning med vanlig fylling av silo - Tester i liten skala. Tel-Tek-report no. 410059-3, 2001 Mai. P.9. A.

Dyrøy, A., Karlsen, M.: An argument for the use of AS-System© compared to alternative solutions. Tel-Tek-report no. 410080-4, 2000 October 12. P.9. A.

Dyrøy, A., Karlsen, M.: A guide of how to design an ADS based on information given in a tender document. Tel-Tek-report no. 410081-2, 2001 April 3. P.32. K1.

Dyrøy, A., Karlsen, M.: Process Response of Segregation - Environment and Yield in Aluminium Production. 7th Interna-tional Conf. on Bulk Material, Storage Handling and Transportation, Newcas-tle, Australia. Report no. 01-1000-7, 2001 September. P.10. A.

Dyrøy, A., Ose, S., Hafenbrädl, F.O.v., Berdal, A.: Aluminium Fluoride - Capa-city testing and material properties. Tel-Tel-report no. 410081-6, 2001 June 18. P.13. K1.

Enstad, G.G.: Homogeniseringsforsøk med 1 - 10 mm FSM. Tel-Tek-report no. 410041-1, 2001 July 23. P.17. K1.

Enstad, G.G.: Segregation of Particulate Solids and its Mitigation based on Understanding its Causes. Report no. 01-1000-4, 2001 P.40. A.

Enstad, G.G., Ding, S.: Måling av vegg-friksjon av hvetemel. halvsiktet hvete-mel og grovt rugmel, på 4 stålplater med forskjellig overflatebehandling. Tel-Tek-report no. 410071-6, 2001 October. P.18. K1.

Enstad, G.G., Hua, L.: Kritiske silopara-metere for nytt fettholdig fiskemel. Tel-Tek-report no. 410070-12, 2000 October 18. P.16. K1.

Enstad, G.G., Hua, L.: Kritiske silopara-metere for massestrømning av anhydritt og modifikasjon av eksisterende silo ved hjelp av innmat. Tel-Tek-report no. 410070-9, 2000 November 6. P.20. K1.

Enstad, G.G., Hua. L.: Critical silo para-meters for mass flow of an animal feed flour. Tel-Tek-report no. 410070-10, 2000 December. P.14. K1.

Enstad, G.G., Hua, L.: Design of silos for dolomite and anhydrite. Tel-Tek-report no. 410070-11, 2000 December 19. P.35. K1.

Enstad, G.G., Hua, L.: Silolagring av va-nillin FP. Tel-Tek-report no. 410070-13, 2000 December 18. P.17. K1.

Enstad, G.G., Hua, L.: Silolagring av E-PVC - Løsning av utmatingsproble-mer. Tel-Tek-report no. 410070-14, 2000 December 19. P.18. K1.

Enstad, G.G., Hua, L.: Kritiske silopara-metere for massestrømning av hyllekalk - Design av innmat. Tel-Tek-report no. 410070-3, 2000 June 23. P.17. K1.

Enstad, G.G., Hua, L.: Kritiske silopara-metere for massestrømning av jernpul-ver - Vurdering av eksisterende siloer. Tel-Tek-report no. 410071-2, 2001 September. P.17. K1.

Enstad, G.G., Hua, L.: Kritiske silopara-metere for massestrømning av jernpul-ver - Utforming av egalisator med innmat. Tel-Tek-report no. 410071-3, 2001 September. P.15. K1.

Enstad, G.G., Sjølyst, K.N.: Uniaxial Testing of Flow Properties of Powders Sample Preparations by Means of Vibration. 7th Int. Conference on Bulk Materials Storage, Handling and Transportation, Newcastle, Australia. Report no. 01-1000-9, 2001 P.7. A.

Enstad, G.G., Hafenbrädl, F.O.v.: Pre-liminary investigations of the segrega-tion of a cemented carbide powder.


To order reports......please tick off the appropriate for the reports (P & A)

you want and return the sheet(s) to:

Tel-Tek, Dept. POSTEC, Attn.: Eksath de Silva, Kjølnes Ring, N-3914 Porsgrunn, Norway, Fax: (+47) 35 57 40 10

Reports marked P available only to members of the POSTEC programme. Those marked A are freely available.

Charge of NOK 2 per page will be invoiced together with POSTEC invoice at the beginning of each year for members.

Tel-Tek-report no. 410071-1, 2001 June 26. P.12. K1.

Hafenbrädl, F.O.v.: Partikkelstørrelses-målinger av karbonprøver. Tel-Tek-report no. 430011-2, 2001 May 4. P.48. K1.

Hafenbrädl, F.O.v.: Uttesting av avstøver. Tel-Tek-report no. 430011-4, 2001 July 7. P.14. K1.

Hafenbrädl, F.O.v.: Partikkeltetthet-smålinger av FMC prøver. Tel-Tek-report no. 430011-1, 2001 September 9. P.3. K1.

Hafenbrädl, F.O.v.: Avstøvning av kop-peroksid. Tel-Tek-report no. 430011-3, 2001 September 8. P.5. K1.

Huang, Jun: Developments in Applied Chemometrics: AMT, Acoustic Chemo-metrics and N-way Image Analysis. Dr.Ing. thesis. HiT/NTNU-report o. sit0103, 2001 August. A.

Nilsen, A.J.: Luftstrømtørking av par-tikulære ferroforbindelser. Høgskolen i Telemark-report no. sit0101, 2001 Mai. P.77. A.

Ose, S.: Charactersation of the Bipolar Electrostatic Charging of Powders. Ph.D.-thesis, University of Southhamp-ton-report no. R0065, 2001 August. P.171. A.

Ose, S., Berdal, Anne: Breakage of alu-mina during pneumatic conveying. Tel-Tek-report no. 410111-1, 2001 June 28. P.20. K1.

Tani, S.: Investigations, Development and Experimental Verifications of Mathematical Models of Gas Cyclones. University of Roma-report no. R0063, 2001 March. P.92. A.

Tappe, S.: An Experimental Study on Pressure Drops in Vertical and Horizon-tal Pneumatic Conveying. University of Cottbus-report no. R0064, 2001 August. P.75. A.

Wang, Q., Melaaen, M.C., de Silva, S.R.: A Computational and Experimental Study of Fluid Flow in a De-Duster. SIMS 2001. Report no. 01-1000-6, 2001 October. P.10. A.

Wang, Q.: An Experimental and Com-putational Study of Gas/Particle Mul-tiphase Flow in Process Equipment. Dr.Ing. thesis. HiT/NTNU-report no. sit0102, 2001 August. A.

STOP PRESS: Into Round Two!Earlier this year the Norwegian Research Council invited applications to pre-qualify for submitting an application to become a Centre of Excellence in Research (Senter for fremragende forskning - SFF). It is anticipated that ten such centres will be set up in 2002, which will be guaranteed funding of 10 MNOK per year for four years and, depending on performance, similar amounts for another six! 129 applications were received and 40 have been invited to submit full applications. One of the latter is the application submitted jointly by Tel-Tek, Telemark University College, Borealis, Norcem and Norsk Hydro. We hope that SINTEF’s Division of Materials Technology will join us in the next round, and invite any Norwegian industry which wishes to see further development of competence in Powder Technology in Norway - On a long term basis to contact [email protected]. Information on the initiative is to be found at www.forskningsradet.no.

Particle and Powder Properties(Contact: Sivert Ose or Franz Otto von Hafenbrädl)

The first price is for the first powder sample. Prices in paranthesis are for further samples of the same or similar material, using the same measurement conditions. Results are normally given as print-outs or test-sheets, in addition to a letter with a short summary of results. For a full scientific report with comparisons, discussions of results and comprehensive documentation, we charge NOK 2.200 extra. Results will normally be ready within 10 working days from receipt of powder. Contact us in advance for special prices on large numbers of samples or for “next day” measurement results.

Particle Size Analysis

HELOS diffraction pattern analyser ............ NOK 2.200 (800) (Range 0.6-1750 µm) Measurement using the well known diffraction principle (0.1 litre powder)RODOS/GRADIS ...........................................NOK 2.200 (800) (Range 0.6-1750 µm) The RODOS and GRADIS dry dispersion units allow the analysis of dry powders using the HELOS (1 litre powder)Coulter Counter TA II ................................... NOK 2.200 (800)(Range 0.6-215 µm) Determines the size distribution of particles suspended in a conductive liquid (0.1 litre powder)Sedigraph 5100 ............................................... NOK 2.200 (800)(Range 0.1-300 µm) Determines the size distribution using incremental sedimenta-tion and measuring the concentration of particles at a known depth at a known time using an x-ray beam (0.1 litre powder)

Sieving

Machine Dry Sieving ..................................... NOK 2.200 (800) Consisting of max. 7 sieves with measuring range from 90 to 11200 µm (0.5 litre powder)Machine Wet Sieving...................................... NOK 2.200 (800)Same machine and sieves as for dry sieving but with water washing (0.5 litre powder)Ultrasonic Wet Sieving .................................. NOK 2.200 (800)The micro-sieves are placed in an ultra-sonic bath. The measuring range is from 5 to 25 µm (0.5 litre powder)Air Jet Sieving (per sieve) .............................. NOK 2.200 (800)Analysis down to 20 µm (0,5 litre powder)

Density

Bulk densities ................................................. NOK 1.650 (600) Loosely packed bulk density, and tapped bulk density, based on Geldart’s procedure (1 litre of powder)Particle density............................................... NOK 1.650 (600)(Range 0.1-9.9 g/cm3) True density measured using a helium pycnometer (0.5 litre powder)

Specific Surface Areas

Specific surface area using gas adsorption .................................................NOK 2.200 (1000/600) Adsorption of a helium/nitrogen mixture on the powder (Micromeritics Flowsorb II 2300) (Range 0.01-1000 m2/g) (0.1 litre powder)Specific surface area using permeametry ..................................................NOK 1.650 (600)Blaine apparatus which uses permeametry (Range 0-12.200 cm2/cm3) (0.1 litre powder)

Fluidization(Contact: Wenche Bergland Fougner)

Fluidization of powders ................................ NOK 7.500Minimum fluidization/bubbling velocity, expansion and de-aeration characteristics, and tendency to dusting and attrition (20 litres of powder)

MicroscopesWe have two microscopes in our laboratory. A stereomicroscope (Carl Zeiss Jena Technical 2), and a plane microscope (Olympus BHS). A video printer is connected to the microscopes through a video camera, which makes it possible to print photos on paper.

Erosivity(Contact: Franz Otto von Hafenbrädl)

Erosivity apparatus........................................ NOK 7.500The abrasivity of powders on a metal plateat angles from 20° to 90° or, alternatively, ability of materials to withstand erosion. Theprice is for the first combination of velocity,loading and impact angle. Additional combi-nations NOK 2.600 (20 litres of powder)

Standard Services at Affordable Prices!(POSTEC members receive a 10% discount on the listed prices)

Please note: Samples for characterization must be representative! (In terms of size, humidity etc.) Contact us for advice on proper sampling when in doubt. Additional costs for sample splitting of very large samples is NOK 1.000.


Enquiry FormPlease send me following information (tick off):

Tel-Tek’s strategic institute programme for 2002-2006 List of lectures available for in-house courses POSTEC contract documents (Nordic countries only) Information on Telemark University College List of chapters in the forthcoming book “Innføring i Pulverteknologi: Del 1 -

Karakterisering, Lagring og Transport av Pulvere” (in Norwegian) Put me on your database for receipt of your Newsletter and other information Details of Tel-Tek’s incubator programme

www.tel-tek.no

Flow Properties for Silo Design(For more details, contact Gisle G. Enstad)

Jenike flow function....................................... NOK 11.000Four tests are necessary to determine a yield locus. Four yield loci are required for a flow function (5 litres of powder required)Biaxial flow function ..................................... NOK 11.000Four tests are required for a flow function (10 litres of powder)Jenike wall yield locus.................................... NOK 2.000The kinematic angle of friction between the solid and the wall material (5 litres of powder)Jenike time flow function .............................. NOK 7.000A six cell consolidating bench is used in conjunction with the shear tester (5 litres of powder) Angle of repose ............................................... NOK 2.500Dynamic and static angles of repose (5 litres of powder)Uniaxial test .................................................... NOK 7.000Consolidation curve, elastic properties, relaxation curve and strength properties (5 litres of powder)Uniaxial time flow function .......................... NOK 7.000Four cell consolidating bench is used in conjunction with the uniaxial tester (5 litres of powder)Design of reliable silos based on above tests..................................................................NOK 10.000Critical silo parameters, and a report with silo design suggestionPrice example 1 .............................................. NOK 27.500Silo design based on critical silo parame-ters, including measurement of the Jenike

flow function, time flow function, moisturecontent and one wall yield locus of a cohe-sive powder (10 litres of powder)Price example 2 .............................................. NOK 12.000Silo design based on critical silo parame-ters, including one wall yield locus, mois-ture content and the angle of repose of afree flowing powder (5 litres of powder)

Electrostatic Measurements(For more details, contact Sivert Ose)

Specific resistance .......................................... NOK 1.500One powder with repeated tests (0.2 litre powder)Electrostatic charging, field test ................... NOK 7.000Measurement of charge with Faraday cup, & field meter. Prices per day (+travel costs)Charge decay characteristics......................... NOK 3.000One powder with repeated tests(0.2 litre powder)Distribution of electrostatic charges ........... Price on requestCharging during pneumatic transportSmall scale transport rig ............................... Price on request

Production of Fine Powders(For more details, contact Franz Otto von Hafenbrädl)Samples for market analyses, or product testing, can be produced using a range of equipment available at various Nordic laborato-ries. Prices will be provided on request. We can produce fine powders with top sizes of less than 3 microns by classification. An opposed jet fluid energy mill is also available for the production of any required size distribution below 50 micron.

Our partner institutes at Trondheim (ball mill, Alpine fluid bed mill, high pressure roller mill), Luleå (stirred ball mills, annular ball mills, SAM mill), and Helsinki (hydrocyclones, SAM mill), can supplement our own services.

Segregation(For more details, contact Are Dyrøy)

Segregation tendencies .................................. NOK 9.000One powder with repeated tests (40 litres of powder) Tests using our segregation tes-ter. The test will determine which segrega-tion mechanisms dominate and enable the identification of counter measures. Pricesfor the standard tests incl. particlesize ana-lysis of tests taken with the tester (10 litres)

Pneumatic Transport(For more details, contact Biplab K. Datta)

The transport rig with a 3 m3 blow tank and 140 m each of 1 1/2”, 2”, 3” and 70 m each of 4” and 5” piping allows flexibility when it comes to defining projects to find solutions to problems. Of special interest may be stepping of pipelines to save energy and reduce product degradation. The accuracy when scaling laboratory data to actual plant conditions is much improved using the new rig. Design and commissioning data for pneumatic conveying systems can thereby be improved. The systems can be run with both positive and negative pressures. The equipment we have should now be able to satisfy most needs, so please take contact if you have problems we might help you to solve. Price on request.

Homogenization and Mixing(For more details, contact Ali Ghaderi)

We have both Forberg and Ide-Con batch mixers, as well as an Ide-Con continuous mixer and a homogenising silo. For demonstrations and/or production of small batches for market or loan of the units, contact Ali Ghaderi.

Large Silo Battery(For more details, contact Sunil de Silva)

The large silo battery is functional at last! This installation consisting of a 50 m3 axisymmetric silo and a 50 m3 plane symmetric silo will be instrumented in 2002 to measure normal and shear stresses at the walls, and is probably the largest experimental silo facility in the world. As the articles on pages 18 and 21 show, we are well on the way to developing simulation tools for the prediction of flow and stresses in silos. Much more can be done. We can look at the effects of discharge aids, loads on discharge equipment and test instrumentation for level monitoring etc. Contact us if you want to discuss a joint project.

Other Services

We can also offer standard services on the transportability of powder in air-slides. Prices on request.

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Areas of interest. Please tick:

Particle Characterisation ComminutionClassification DryingMixing Gas/Solids SeparationSize Enlargment StorageNumerical Simulation TransportHomogenisation

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______________________________________________Signature, place and date

Eksath de SilvaTel-TekKjølnes Ring, 3918 PorsgrunnNORWAY

Fax: +47 35 57 40 10

Check us out at:

www.tel-tek.noor contact us at:

[email protected]

POSTEC-members as of November 2001

1. Alstom Power Norway AS Oslo (Geir Wedde/Odd Strand) 2. Astra Draco AB Lund, Sweden (Kyrre Thalberg) 3. Astra Zeneca, Liquid Production AB Södertälje, Sweden (Johan Drakenberg) 4. Bjølvefossen AS, Ålvik Tore Førland 5. Dyno Industrier ASA, Forsvarsprodukter Sætre i Hurum (Øyvind Hammer Johansen) 6. Elkem Aluminium ANS, Lista Verk Farsund (Karl G. Forslund) 7. Elkem Aluminium ANS, Mosjøen Verk Mosjøen (Gaute Nyland) 8. Elkem ASA, Carbon Kristiansand (Thorbjørn Aanes) 9. Glasma AB Emmaboda, Sweden (Arne Fransson) 10. Hydro Agri, Porsgrunn Porsgrunn (Olav Skyllingstad) 11. Hydro Aluminium A/S, Karmøy Fabrikker Håvik (Knut Arne Paulsen) 12. Hydro Aluminium A/S, Sunndal Verk Sunndalsøra (Ola Jakobsen) 13. Hydro Aluminium A/S, Teknologisenteret Årdal Øvre Årdal (Morten Karlsen) 14. Höganäs AB, Iron Powder Division Höganäs, Sweden (Johann Arvidsson) 15. Ide-Con A/S Porsgrunn (Geir Nordahl) 16. Larvik Pigment (Norway) Larvik (Ludvig Levinsen) 17. MinFo Stockholm, Sweden (Marianne Thomaeus) 18. Norcem AS, Brevik Brevik (Erik Stoltenberg-Hansson) 19. Norconsult AS Årdal (Robert Sandvik) 20. Norsk Hydro ASA, -PF, Forskningssenteret Porsgrunn (Eirik Manger) 21. Norsk Hydro ASA, -PF, PVC Division Porsgrunn (Stephen Hanson) 22. Norton A/S Lillesand (Lars Petter Maltby/Jostein Mosby) 23. Pharmacia & Upjohn AB, Pharmaceutical R&D Helsingborg, Sweden (Nils-Olof Lindberg) 24. T. Skretting A/S Stavanger (Odd Geir Oddsen)

a programme of research inPOwder Science and TEChnology

in cooperation with industry

Objectives To provide wider access to research results To maintain a centre of excellence in powder technology in Scandinavia To enhance the technical competence of Scandinavian industry To provide industry with quick and effective advice To promote contact between people with similar problems To ensure relevance of research to industrial need To create a cluster of users and suppliers of powder handling and

processing equipment

Who can join?Any company who has a registered place of business in one of theNordic countries*

What does it cost?Contributions in multiples of NOK 30.000 per year depending on need, interest and size of company (NOK 15.000 for equipment manufacturers with an annual turnover of less than NOK 20.000.000)

What are the benefits? Access to the results of all general research programmes Advice at the end of a telephone Ability to influence the direction of research Rapid access to specialist advice in the field Services such as systems design, literature reviews, and equipment

selection at low cost Product development/improvement to meet special customer

requirements Product demonstrations/evaluations In-house and public courses in key areas of the subject Lower hourly rates Discounts of 10% on standard services

* The Telemark Research and Development Centre reserves the right to deny

membership in the programme to any company whatever without giving reason.

Newsletter 20

Documents

Transcript of Newsletter 20