Presented at ENTREE ’97, Environmental Training in Engineering Education, November 12-14, 1997, Sophia-Antipolis, France.

Biomass as a sustainable energy source, a multi-disciplinary approach

P.P.A.J. van Schijndel, J.M.N. van Kasteren and F.J.J.G. JanssenEindhoven University of Technology (TUE), The Netherlands Faculty of Chemistry and Chemical EngineeringCentre for Environmental Technology (CMT)

SummaryThis paper reports the results of a ‘Biomass for energy’ study within the framework of a multi-disciplinary course called ‘Sustainable development’ at the Eindhoven University of Technology. The main goals of this course are to learn and apply project management and to solve problems in a project team. Since it’s introduction in 1994 students of different disciplines within the engineering education work together to find solutions for an issue or technical problem put forward by industry or (governmental) institutions.

The task of the group was the technical feasibility, logistics and conceptual design of a small scale integrated biomass gasification combined cycle plant. This plant has to supply part of the city of Eindhoven both with electricity and heat from biomass waste produced in the city. One of the results was the design of a 8 MWelectric plant which uses biomass waste produced in the Eindhoven region, produces heat for city heating or for industry and fulfils the Dutch statutory requirements for burning waste.

The outcome of the ‘Biomass for Energy’ study is that small biomass waste powerplants are technically and economically feasible in The Netherlands. A combined cycle technology for biomass waste is most suitable because of its high efficiency for electricity production.Most important outcome of these projects are the positive learning experience of the students like improvement of interdisciplinary thinking and skills, improvement of knowledge, improvement in practical skills like groupworking and the use of know-how in an application.

1. IntroductionAt the University of Technology Eindhoven the course on Sustainable Development has been given each year since 1994. This course is organised by TDO, Technology for Sustainable Development, a department of the University.A group of 6-8 students from different disciplines study a problem in the field of sustainable development. Main goals of this course are to obtain project-oriented experience for the students and gaining of knowledge in the area of sustainable development.This paper summarises the general set-up of the course in chapter 2 and focuses on the outcome of the study ‘Biomass as a sustainable energy source’ in chapter 3.

2. Multi-disciplinary Course on ‘Sustainable Development’The set-up of this course has already been described in two articles [1,2]. Therefore, only some historical facts, a short overview of the course, the current developments and the students evaluation of the biomass study are highlighted.

HistorySince 1994 the multi-disciplinary courses have been held at this University. Focused on sustainable energy techniques it was organised by Studium Generale in the first year. The project showed to be a success and was picked up by the TDO-centre. Table 1 shows the number of students participating the course. It shows that its popularity is increasing [3].

Table 1. Number of students participating the multidisciplinary course TDOYear Groups Number of students

1994/1995 6 401995/1996 5 321996/1997 11 79

Overview of the courseThe group consists of 6 to 8 students from at least three different disciplines. The projects involves some 160 hours per student and it is performed within 7 months. The group is supervised by a tutor and there is also an external principal.The group has to manage their own work and write it down in a special syllabus which acts as a sort of project guide. They have to write a workplan with the main goals and specific research questions, contact with the principal to focus the research, write an interim report, follow a presentation practice, hold an interim presentation with the principal, write the final report and present the final results. The tutor and principal act as references and control for their activities.

Current developments Tutors: Because there had been problems finding enough tutors to support the groups, 2nd phase researchers (PhD students) were called in for this years projects. This has been a real success and TDO will go on with it. All the tutors get a tutor training programme so they know their task in this project. During the project there are several possibilities for the tutors for an evaluation of the project. The PhD students were very positive of being a tutor and they think to have learned a lot about groupprocesses and working together with people from other disciplines.

Course length:It has been the experience that the project has to be carried out in two trimesters (20 weeks, two half days a week). Performing the project in a shorter time period is not desirable, because students find it very difficult to combine it with other exams. In this case also all the literature has to be available at the start of the project.

Changes in the course:Since the start the project has been changed to increase it’s quality. The extended start-up program in the first year has been skipped for a very large extend. The groups can now have a quicker start which is better for the group process. More emphasis however, will be put on project management and on teambuilding. High commitment of the principal will also be emphasised next year. Another problem experienced is finding suitable projects, thus, also more emphasis on the preparation before project start should be made.Because the multi-disciplinary courses have been a success, most faculties of the TUE are planning to make this kind of courses compulsory to their curriculum. In this way all students will experience interdisciplinary teaching thus improving their communication and working skills. It is not yet known how this will influence the group process. A way to deal with this could be by evaluating the input of every students on the project in stead of only evaluating the outcome of the group as a whole.

Students evaluation of the ‘Biomass’ projectThe students liked to work as a groupmember although it was not always easy to work together with people from different disciplines. For the group it has been an interesting and stimulating course in which they have learned many things. A very important learning goal was to write the aim of research out of the problem description. The students also found it important to learn how to work together with a group on a specific problem. They especially liked the interdisciplinary character of the problem. Not only the gathering of knowledge from the own discipline was important for the students but also the clear transfer of this knowledge to the other group members. There have been few problems within the group and they could be solved quickly. The role of the tutor to steer the groupprocess was widely appreciated. The students also think the principal should take decisions to direct the students, if necessary, to focus their study.

3. Project ‘Biomass gasification as a sustainable source for electricity and heat’In this project (1996/1997) 7 students were involved: two Physics students, three Chemistry and Chemical Engineering students and two students in Society and Technology1.

BackgroundAt this time most electricity in the Netherlands is generated by non-sustainable energy sources. These sources, fossil fuels and nuclear energy, will become exhausted in the future because of their depletion. Use of fossil fuel also increases the concentration in atmospheric CO2, the notorious greenhouse gas. A sustainable source for energy in the future will be biomass because it can be renewed in a relative short time and because the CO2 produced by burning the biomass will be taken up by growth of new biomass. Therefore, biomass is an important renewable energy source.In two preliminary studies of 1995 and 1996 [7,8] the emphasis was put on the availability of biomass and the feasibility of energy crops in the Netherlands. By literature search it was found that the possibilities in growing biomass for energy in the Netherlands are small because of the small area available. Best options for biomass energy crops are miscanthus, cane or willow. Problems expected are the economics concerned with demand and availability of biomass. This problem was recognised in this project and because of economical and availability reasons it was chosen only to use biomass waste generated in the own region.

AimsAim of this study was the technical feasibility, logistics and conceptual design of a medium scale (15 - 30 MW) biomass gasification plant. It should be a ‘best known’ technology plant which can provide a new part of Eindhoven city with electricity and if possible heat. The task of the group was to find out what biomass source is available, what kind of logistics are necessary and what the type of technology and economic figures are. With this knowledge they should be able to design the plant. One of the aims was also to check if it is possible to produce electricity using a fuel-cell. Main target of the research should be the economical and technical feasibility of the system. Also social and environmental issues had to be looked upon.

After a first discussion with the principal and some talks with experts of ECN (Dutch centre for energy research) in the field of fuel cells and biomass gasification reactors the title of the study was decided to be: ‘What is the feasibility of a biomass gasification plant coupled with a fuel cell for the production of electricity and heat to supply the new city part ‘Meerhoven’ in Eindhoven using biomass waste streams available in the region’.

Technique of gasification:

1 Biomass 1996/1997 TDO group consisted of: Mascha Cleven, Jan Cloin, Ingrid Dimmers, Dianne Huibers, Jaco Huisman, Yuri van de Vijver and Dennis Wouters; students from Eindhoven University of Technology.

The technique of coal gasification for energy production is being used in the Netherlands at Buggenum. In the gasification process the fuel is heated to high temperatures (1500 °C) in air. The different stages of gasification are: fuel drying, water evaporation, different decomposition reactions and oxidation reactions. Finally the fuel is converted into CO en H2 via endothermic reactions like:

C(s) + H2O ◊ CO + H2

C(s) + CO2 ◊ 2 COCO + H2O ◊ CO2 + H2

Energy necessary for these endothermic reactions is supplied by exothermic reactions like:

C(s) + ½ O2 ◊ COC(s) + O2 ◊ CO2

C(s) + 2 H2 ◊ CH4

Before burning the hot gasses have to be cleaned in order to remove components like tar, dust, acid gasses and heavy metals. After the gasturbine no end-of-pipe treatment will be necessary because stack gasses fulfil the Dutch statutory requirements for energy production or waste incineration. See figure 1 for a schematical outline of such a biomass powerplant.

Summarising the advantages of biomass gasification over biomass burning:• Amount of flue gas for cleaning is much less;• During gasification, polluting substances are formed in a easy to treat way;• High efficiency possible by use of combined cycle (gasturbine and steamturbine).

Results of the project, technical outcome of the study[4]:With the results from the study on available biomass waste streams in the region, quantities and caloric values, the maximum available energy could be calculated (see table 2.). Using all available biomass the calculated electrical plant output would be about 8 - 10 MWe [5].

Table 2. Energy of biomass waste streams in Eindhoven areaType of biomass waste Quantity of bio

waste (ton/yr)Energetical

contents (MW)GFT-waste (biowaste) 85.650 11,4Waste paper (non recyclable) 38.300 17,5Wood (waste from municipality) 9.000 2,7Sludge 7.300 2,5

Totals 140.250 34,1

The next step was to determine the necessary logistics and pre-processing techniques of biomass. The logistics data were used for the cost analysis. In one year 140 kton of waste is necessary for gasification for a 10 MWe power plant, which means about 380 tons a day. Because there is no

input during the weekends and the installation will work continuously a storage room for about 1500 ton of biomass is necessary.All the different streams have to be pre-treated before feeding into the gasification reactor. The biomass is dried in a rotary drum drier using excess heat out of the process and particle size is decreased to 15 mm by chopping and crushing using a roll crusher.

Different gasification reactors may be used for biomass gasification like current and countercurrent flow reactors, fixed bed reactors, circulating fluidized bed reactors and entrained flow reactors. Out of different reactor possibilities a circulating fluidized bed reactor was chosen. Criteria for this selection were: the designed power output of 20 MW, amount of by-products like tar and the availability of the technology.

After gasification bed material and dust are separated from the biogas by means of two cyclones. Before the wet gas treatment the hot gas is cooled down generating steam for industry or the biomass drying step. In this treatment SO2, HCl and heavy metals are removed. Gas composition is about 18 mole % H2, 20 mole % CO, 14 mole % CO2, 44 mole % N2 and 4 mole % hydrocarbons.

Next step in the plant is electricity production out of the chemical energy contents of the cleaned gas. From the point of view of available technology and economics the fuel cell technique is still not feasible. From the different fuel cell technologies for this specific task the Molten Carbonate Fuel Cell (MFC) is probably the best choice because of working temperature range (650°C) and because of the internal reforming CO and CO2 are permitted. However, the system is not yet commercial available on the scale of 10 MWe, so another system had to be chosen.

Figure 1. Schematical outline of a biomass power plant [5,6]

The second choice for electricity generation after fuel cells is the so called combined cycle technology (see figure 2). In this system the gas is first combusted in a gasturbine which generates electricity. The excess heat of the flue gas is then used to generate steam, which generates electricity in a steam generator. These systems are technically and economically feasible. Although the gasses from the gasifier have a low calorific value (6 MJ/m3 compared to 40 MJ/m3 for methane), retrofitted gasturbines are now available which can operate under these conditions. Compared to other systems, combined cycle technology will have a relative high fuel efficiency of about 24-30%. Without the drying step which consumes about 10 MW, however, efficiency will be in the order of 40% which is acceptable. This is due to the chosen combined cycle technology and the selling of some excess heat (10% or 1.2 MW) to the industry. For larger gasification units an efficiency of about 43% is possible, which is much larger then the 20% efficiency for municipal waste incinerators [6]. In the near future high temperature gas cleaning can also enhance performance because a cooling step is not necessary with this system.

Pre treatment And

Storage

Biomass

Waste

Gasification GasCooling

Gas- and Steamturbine (Combined Cycle)

Electricity

GasCleaning

Heat

Heat

Heat

Figure 2. Outline of the Combined Cycle, with heat recovery steam generator (HRSG) [9].

In order to determine the economical feasibility of the plant, calculation of costs and benefits of the plant have been carried out. The costs per kWh in this system are only slightly higher than the price for conventional electricity production using fossil fuels. Price of ‘bio’-electricity is 0,04 Ecu per kWh against 0,018-0,041 Ecu per kWh for conventional electricity production.

Besides the economical feasibility, also the environmental and juridical feasibility of the plant was determined. The result of this study showed no difficulties concerning the feasibility on these aspects in The Netherlands.

4. Conclusions1. An important outcome from these projects are the positive learning experience of the students like

improvement of interdisciplinary thinking and skills, improvement of knowledge, improvement in practical skills like groupworking and the use of know-how in an application.

2. The outcome of the ‘Biomass for Energy’ study is that a 10 MWelectric biomass waste powerplants are technically and economically feasible in The Netherlands.

3. Best proven method for electricity production from biomass waste will be combined cycle technology because it has a very high efficiency compared to other technologies.

4. Costs for producing energy using biomass waste for small capacity plants will be marginally higher then conventional fossil fuel plants.

Literature1. Kasteren, J.M.N. van, Interdisciplinary Teaching within Engineering Education, Eur. J. Eng.

Ed., 21(4), 1996, p.387-392.2. Kasteren, J.M.N. van, Technology for Sustainable Development: Co-operation between

Research and Education, ENTREE ’95 Proceedings, p.49-56.3. Kirkels, A., TDO course evaluation 1996/1997, TDO internal memo, Eindhoven University of

Technology, August 1997 (in Dutch).4. TDO Biomass report by Mascha Cleven, Jan Cloin, Ingrid Dimmers, Dianne Huibers, Jaco

Huisman, Yuri van de Vijver and Dennis Wouters, Energy Production with the System

GasturbineFuel

Air

HRSG

Stack

Pump

~

Condensor

Steamturbine

Hot gasses

Steam

Water

Biomass gasification and Fuel Cell, Eindhoven University of Technology, June 1997 (in Dutch).

5. Ree R. van, Biomass gasification: a ‘new’ technology to produce renewable power, An inventory of technologies, ECN report, 1994.

6. Crok, M. (Faaij, A.), Biomassa: Brandstof of afvalstof?, Chemisch Magazine, p.327, september 1997 (in Dutch).

7. SG report on Biomass 1995, Biomassa als energiebron in Nederland, Eindhoven University of Technology, 1995 (in Dutch).

8. TDO report on Biomass 1996, Biomassavergassing in Noord-Brabant; een haalbaarheidsstudie naar een 30 MWe biomassvergassingsinstallatie, Eindhoven University of Technology, 1996 (in Dutch).

9. Bathie, W., Fundamentals of gas turbines, Iowa state University of Science and Technology, John Wiley & Sons, 1984.

Background notes about:the author;Patrick van Schijndel studied chemical engineering at the Eindhoven University of Technology and graduated in 1994. He got his teaching degree in chemistry at Eindhoven University in 1995. During his studies from 1991 and until 1996 he worked as consultant of the so called ‘Chemistry shop’, a university section doing ‘duty-free’ environmental research for local groups. Since 1996 he is doing his PhD on cleaner production at CMT, and combines this with setting up a MSc. course in environmental technology for the University of Dar es Salaam in Tanzania.

the co-authors;J.M.N. van Kasteren studied chemical engineering at the Eindhoven University of Technology and in 1990 he received his PhD degree. In 1990 he worked at the Inter-University Environmental Institute Brabant (IMB). From 1991 he works as appointed lecturer at the TUE, in the field of environmental technology. In 1995 he was appointed director at TDO. In 1996 he was appointed director of PRI at the TUE. At PRI economic and technical feasibility studies of the recycling of wastes are carried out.

F.J.J.G. Janssen is head of the department responsible for gasification, combustion of fossil fuels and chemical processes at KEMA in Arnhem, The Netherlands. At KEMA he is working in the field of research and development of gas cleanup systems for gasification of coal, heavy oils and biomass, pyrolysis of waste and biomass, energy saving technologies and water purification. At the TUE he is director of the Centre for Environmental Technology of the Faculty of Chemical Engineering. CMT focuses on environmental education and environmental research.

Eindhoven University of TechnologyFaculty of Chemistry and Chemical EngineeringCentre for Environmental TechnologyP.O. Box 513 5600 MB Eindhoven, The Netherlandstel.: +31 40247 4934 / 3197Fax: +31 40245 3762email: TGTIPS@CHEM.TUE.NLhttp://www.chem.tue.nl/cmt