Impact of Refractory Lining Design on Its

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Abstract--- Reliable and Predictable performance ofrefractory lining system of a boiler is an indispensablecondition for smooth functioning of a thermal power plant.This is much more applicable for a power plant boilerworking on CFBC technology. In India the availability of coalof prime quality is limited and interior quality coal isavailable in abundance. Under this situation the CFBC based

power plants are gaining popularity due to its flexibility ofusing coal of interior quality and many other combustibles as

fuel. This was unthinkable in case of P.C. fired boilers.

However, there is one drawback, specific to CFBC boiler,being faced by the power plant operators. The processtechnology of a CFBC boiler generates conditions of severeerosion and corrosion on the path of flue gases. Application ofrefractory lining becomes essential for protection of the boilerstructure and its pressure parts. The present design ofrefractory lining system has proved inadequate to withstandthe destructive forces working on the lining. These results in

failure of the lining in highly stressed areas forcing power plant operators to take unplanned shut downs for repairs atthe cost of uninterrupted functioning of the power plant.

This paper deals with the causes of refractory lining failures due to design deficiencies and some possibleimprovement for a trouble free operation of the thermal power

plant.

I. PERFORMANCE OF A R EFRACTORY LINING SYSTEMDEPENDS LARGELY ON THE FOLLOWING THREE

FACTORS

Lining Design Quality of Installation and initial Heat-up Consistent OperationFor a reliable, predictable, and consistent performance all

the above factors must be given due importance. (Fig.1).This paper deals with the issue of Lining design work and itsimpact on the overall performance of a Refractory liningsystem. The causes of lining failure due to designdeficiencies and possible remedial measures have also beendiscussed in detail.

D.K. Singh, Refractories Dynamics, Pune. Ashok Kumar, Refractories Dynamics, Pune. E-mail:

[email protected] Lata Singh, Refractories Dynamics, Pune. E-mail:

[email protected]

Fig. 1The ultimate aim of a designer is to provide a lining

system which remain Stable during its entire campaign life,i.e. at the beginning of the campaign period when the lining isnew and also at the end of the campaign when the gets wornout. Stability is an important property of any liningconstruction. The statement that No lining fails because ofwear itself but because of instability is no exaggeration(Fig2).

Fig. 2Any lining work has a campaign life. Depending upon the

duty conditions to which the lining is exposed, the designedcampaign life may vary from few weeks to many years. At theend of the campaign the lining needs overhauling, partially orcompletely, to begin the new campaign. The lining wearwhich takes place during the campaign must be uniform or

balanced so that the lining stability is maintained throughout.To achieve a balanced lining wear the lining design indifferent parts of any refractory lined unit has to be different

based on the prevailing service condition in that part. (Fig. 3)

Fig. 3

Impact of Refractory Lining Design on itsPerformance

D.K. Singh, Ashok Kumar and Prem Lata Singh

National Seminar on Thermal Power Plant Performance Management - NSTPPPM 131

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To design a lining system which wears out uniformly andmaintain its Stability it is important to understand the factorswhich cause the lining wear. Such factors are the Stresses ofdifferent nature and dimensions working individually or invarious combinations on the lining and cause their destruction.

Fig. 4

In Fig.4 the different types of stresses working on thelining in service are given. Such stresses or the Destructiveforces cause wear and tear of the lining. The lining must bedesigned in a way so that it can withstand such stresses andallow a balanced or uniform wear pattern. Non uniform wear

will always give an unstable lining configuration resulting in premature failures. Fig. 5-8 gives in detail the causes of suchstresses and the properties required in the refractory materialwhich can resist them.

The first step in the design work is to obtain completeinformation and knowledge about the service conditions whichwill be encountered by the refractory lining during service.Refractory materials are then chosen which will be compatiblewith the thermal, thermo mechanical and thermo chemicalrequirements of the process. Once this is done the engineering

part of the design work follows. This is the most crucial stepin the entire process of design activity. Due to multiplechoices available, such as shaped, unshaped, or precast formof refractory material, the designer is confronted with thedilemma of selecting the best option. The choice between ashaped refractory material and an unshaped one is one such


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dilemma. Both have got their advantages and disadvantages.Fig 9-12 gives the advantages and disadvantages of using ashaped or an unshaped refractory material for any application.While selecting any of them it remains uppermost in the mindof the designer that any selection must result in a stable liningconstruction.

At this point of time it is worthwhile to discuss brieflyabout the lining geometries which are followed in refractorylining construction work in any refractory lined unit. There isclose relationship between lining stability and the lininggeometry. All lining designs can be classified into five majorgeometries:

Flat Walls Arches Cones Spherical Domes CylindersOut of the five geometrical forms the Flat wall

construction is the weakest from stability point of viewwhereas, the cylindrical constructions provide maximumstability. Therefore, a flat construction, either shaped orunshaped, require external support system to attain stability.These supports, which, in majority of the cases are metallic

parts, are non-refractory materials. Unless they are designedand installed with great precision, can do more harm than helpthe lining integrity and stability. A lining which does notrequire external support for its stability will perform bettercompared to a lining requiring a support system such asmetallic anchors, holders, shelf plates etc.

In any lining system which is exposed to high temperature,the working face and the cold face behave differently. The hotface will remain in compression while the cold face will beunder tension. For stability and rigidity of refractory structure

it is important that the lining is maintained under compressionduring service. This is especially important where liquid metalis to be contained or hot gases flow past the lining under

positive pressure. It is also necessary that the thermal gradientthrough the lining is maintained in a way that the outside shelltemperature does not exceed its safe limit. If the shell expandstoo much at service temperature, the linings will becomeloose. In other words compression of the lining will be lostwhich may give rise to problems such as liquid metal

penetration, gas leakages, loss of lining stability, and in worstcase collapse of the lining itself. Therefore, a lining which isunder compression, that is fully contained (or restrained) willresult in a successful lining and will give a reliable,

predictable and consistent performance. Example of a fullycontained lining is a cylindrical lining. At the design stage one

must take care to provide correct expansion allowances so thatat the operating temperature the lining does not get crusheddue to lack of space for expansion or does not become loosedue to more than required expansion allowance.

The above issues must be addressed adequately at thedesign stage. The following few points, if kept in mind, willgo a long way in designing a stable lining system.

Can a lining geometry be followed which gives themaximum stability?

Can a lining be designed which is self-sustaining anddoes not require any or minimal external supportsystem for its stability?

Can a refractory be used, such as a brick or a precastshape, which does not require any treatment at site toachieve the desired properties unlike a monolithicwhose performance entirely depends upon the mannerin which it has been prepared at site and installed?

If a monolithic lining is to be installed, can all therequirements of a technically correct lining installation

be met at site? Is proper storage facility available at site especially for

materials which are hydroscopic in nature and has alimited shelf life?

If we critically analyze the above requirements it may beconcluded that a lining made preferably of a shaped refractorymaterial is likely to perform better under specified conditions.However, one must not forget its limitations and take adequatemeasures and safeguards at the design stage to nullify or atleast minimize the risks involved. Provision of expansionallowances and design of joints needs special attention.

In the light of what have been mentioned above we wouldexamine the refractory lining system generally adopted in aCFBC boiler. The working lining consists of both shaped and

unshaped refractory materials. Unshaped product (mostlycastable) contributes almost 80% of the total working lining.The service condition for refractory of the boiler duringoperation is shown in Fig.3. The entire boiler is an assemblageof many sub units having complicated geometry joinedtogether. The service conditions vary widely and hence thelining is subjected to varying degree of stresses duringoperation. Under such stresses the refractory lining failuremostly takes place in the areas mentioned in Fig. 13. Theseareas have been further shown in Figs. 14-17.

Bull-Nose of cyclone (Fig.14) Seal Pot/Loop Seal (Fig.15) Cyclone Inlet and Target area (Fig.16) Return Legs (Fig.17)


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Fig. 17The failures do take place in other areas also but they areless frequent. Examination and failure analysis of the aboveareas reveal few critical observations and possible causes offailure, which are listed below:

The profile/geometry of failure prone areas is verycomplex and the lining is subjected to extremethermo-chemical stresses.

Due to complicated geometry the refractory lining isdone with unshaped refractories, mostly castables,which entirely depend on the reliability of anchoragesystem for their stability. It has been found that mostof the failure takes place due to the failure ofanchorage system. The metallic anchors fail either dueto quality reasons anchor design and its orientation orthe anchor weld fails under the prevailing stress.

The other cause of failure may be attributed to poorquality of lining installation. Quality suffers due to thefact that the job of monolithic installation in such

complicated geometrical contour requires supervisionand skill of highest order. Invariably, the laid down

procedures are not followed which result is poorinstallation work and ultimately result in its failure.

We have been able to find out few reliable solutions toarrest such failures. Our approach to solve the problem is by:

Design modification, without altering the originallining profile, with use of shaped refractoryrefractories (Bricks or Precast) in place of castables.

In case of lining with shaped refractories, suitable self-locking arrangements have been provided and the useof non-refractory supports has been minimized.

The above design philosophy was followed for modifyingthe refractory lining system for one our clients having acaptive power plant with CFBC boiler (Fig.18-21). Aftermodifications the refractory lining failure and breakdownshave become nonexistent.


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Refractories Dynamics

It is further working on development of integrated liningdesign for the refractory ling of failure prone areas of CFBC

boiler mostly with shaped materials (bricks/pre casts) andhope that the modified design will eliminate most of the

problems associated with lining failures (Fig.-22).

Fig. 22

II. CONCLUSIONProponents of maximizing the use of monolithic for

refractory lining work may not agree to some of the pointsmentioned in this paper. This is due the fact that today muchsophisticated high performance monolithic is available whichcan perform better than shaped refractories. We appreciatetheir feelings any may agree to the fact that such materials areavailable. But, the moot point is, can a technically correctinstallation be guaranteed with these materials all the time?

The answer is No. Therefore, when the performance of alining system ultimately depends upon technically correctinstallation, one has to move cautiously. RefractoriesDynamics, in its lining design work keeps a balance betweenthe use of shaped and unshaped refractory materials to developa most stable lining which gives a reliable, consistent, and

predictable performance.

R EFERENCES [1] Refractories Lining Design and Installation Charles A. Schacht,

Pittsburgh, U.S.A.Michael Maupin, Michigan, U.S.A.[2] Refractories for Copper North American Refractories- TUCSON-1997[3] Refractories Engineering: Material-Design-Construction, VULKAN-

VERLAG-ESSEN

ABOUT THE AUTHOR Mr.D.K. Singh is Graduated in Ceramic Engineeringfrom BHU, Varanasi,in the year 1970. Joined TataSteel, Jamshedpur, India in the year 1970 as GraduateTrainee and worked till 1992, during which he occupiedvarious senior positions in the company. Lead therefractories team in PhaseI & II expansion &modernization projects of TATA STEEL as Chief ofRefractories and received special recognition from

Bharat Ratna late J. R. D. Tata for excellent performance with respect totimely execution of refractories work in the largest and most modern blastfurnace of the company. He worked as Divisional Manager of RefractoriesDevelopment and Control Department of Tata Steel till 1992.

Joined Tata Refractories Limited, India in 1993 and worked till 2005.Occupied senior management positions in the company like General Manager(Scientific Services), General Manager (Operations), Director (Operations),Vice President (Operations) & Head of Camp, Executive Vice President(Marketing & Technology), Executive Vice President (Strategy Management).

Joined Global Steel Holding Company in 2005 and worked for one yearas their Advisor (Refractories) for overseas operations. Appointed as ChiefExecutive Officer of Magnohrome Refractories, Serbia, a company acquired

by Global Steel Holding Company Limited and served there for a brief period.

Started own Company, Refractories Dynamics in the year, 2007. Thiscompany was later incorporated as partnership firm with its Head Office atPune and Branch Office at Jamshedpur. At present working as ManagingDirector & Chief Executive Officer of the company.

The Indian Ceramic Society honored him with RefractoryTechnologistof the year award in 2008. Indian Refractory MakersAssociation awarded him as Refractory Technologistof the year in 2009 forcontribution in the field of refractories technology


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Mr. Ashok Kumar is a refractories and industrialengineer served TATA STEEL for nearly 38 years inarea of refractories lining design, application andmaintenance activities. Attended 1.5 months training

programs on stee l plant refractories practices in BritishSteel- U.K. and Thyssel Germany in connection withthe modernization program of TATA STEEL Phase I& phase II. Developed refractories lining design forvarious refractory lined units of TATA STEEL its

modernization programs.

He visited many countries of Europe, Australia, Africa and Asia inconnection with refractories, design and application of Refractory liningsystems for ferrous and nonferrous industries. He presented technical paperson refractories lining design development and application in national andinternational seminars.

He served TATA REFRACTORIES LTD., INDIA for 4 years (1999-2003). Established and headed Refractories Solutions Department, a new

business unit to meet the emerging demand of customers. Presently he is Jt.MD & COO of Refractories Dynamics

Mrs. Prem Lata Singh did her diploma in Ceramicengineering from Government Polytechnic, Gulzarbag,Patna in the year 2000 securing a Gold Medal for heracademic excellence. She joined Refractories Dynamicsas an officer in the year 2008. Presently she is workingas Asst. General Manager (Tech. & Adm.) in the sameorganization.

She obtained training from the Govt. recognized professional institute in the area of CAD, Administration and companyfinance.

During her instinct with RD, she had developed refractory lining designfor various units such as steel ladles, Incinerators, CFBC Boilers etc. Designsdeveloped by her are successfully performing.


ISBN 978-93-83459-12-4 2014 Bonfring

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