Final Report Summary - GREEN-FUEL-CELL (SOFC Fuel cell fueled by biomass gasification gas)
The main objective of the GREEN-FUEL-CELL project was to produce a gas that can meet the requirements for fuel to feed solid oxide fuel cells (SOFCs) through reliable, up-scalable and cost-effective staged gasification of biomass. The overall technical objective of the project was therefore to develop a tar decomposition and gas cleaning system that can be integrated with biomass gasifiers in order to make them able to produces a gas suitable for SOFC fuel cell application.
To achieve this goal, the general research objectives of GREEN-FUEL-CELL were directed towards understanding of the deterministic mechanisms of tar reduction with char and behaviour of volatile in-organics (metals and salts) with respect to cooler fouling. Research of low and high temperature gas filtering also took place as this project adopted techniques that are commercially available and well developed for coal gasification and perform the necessary modifications.
Innovative sustainable technologies with high 'fuel to electricity' efficiency are required to supply the increasing electricity demand and at the same time to fulfil the objectives of reducing the emission of green house gases. SOFC is one promising technology to obtain a high efficiency in electricity production, which would be sustainable so long as the feeding fuel is produced from renewable energy sources. The hydrogen-rich gas produced by gasification of biomass could be such a sustainable fuel for SOFC. For biomass gasification- SOFC conversion systems the most cost-effective size is expected to be plants from 1 to 30 MWe, with a total electric efficiency expected to be well above 50 %. However, the gases produced by most of the current gasification technologies are still too dirty to be directly fed into SOFC without extensive and expensive gas cleaning systems.
The resulting specific scientific objectives in support of the technological development were to:
- determine relations between char properties (e.g. extent of devolatilisation, ash content, and composition) and catalytic effect for tar reduction;
- develop of a model for in-process char gasification (partial oxidation) by the oxidised pyrolysis gas and in relation to air or oxygen concentration;
- obtain understanding of hydrodynamics of char-beds, both with and without bed material;
- understand the fate of volatile metals and salts in the gasification process and upon cooling in the gas cooler.
The main work packages, excluding the management efforts, have been the following:
WP 2: Char bed without bed material
This work package had the focus on one of the two gasification systems. The specific technical objective for this gasification system was to prepare a basic-design for a full-scale (1-50 MWth) innovative gasifier system. Based on the conducted calculations and experiments the following main conclusions have been stated:
- The principle of a fixed bed placed in a conical reactor has been proven cold and hot as a gasification reactor. Furthermore shows the calculations that the principle are up scalable.
- An updraft gasifier has been developed for gasification of residual char from a gasifier and operation conditions have been established.
- A concept for gasification of wood pellets has been developed, constructed and tested semihot at pilot scale with success. The final pilot scale plant was not tested successfully as there still are some problems to be solved with pyrolysis unit.
WP 3: Char bed with bed material
The objectives of WP3 were:
- to produce a product gas suitable as feed gas for an SOFC with respect to the presence of organic compounds;
- to prove that the TREC-technology is suitable as filter for particles (and S and / or Cl).
The TREC reactor has proven to be a valuable first cleaning reactor for the removal of mainly organic components that need to be removed for the use in an SOFC. It, however, does need additional gas cleaning equipment to meet the stringent specifications of an SOFC. These additional reactors have been developed within the project and the complete system has been tested successfully during two 100 h test runs.
Furthermore, the TREC reactor has proven to be a versatile cleaner. By changing bed material size and material, additional functionalities could be added, including the partial removal of organic sulphur species. WP3 therefore has fully reached its targets.
WP 4: Char bed with bed material
This WP aimed at evaluating TKE's and ECN's process designs with respect to the objectives of the project such as: low tar concentration, high carbon conversion.
A monitoring procedure for reviewing and comparing the two gasification processes was developed and presented early in the project. Due to the cancellation of measurements, evaluation of the two core processes ended up being performed at a conceptual level, and the results are thus more speculative than anticipated at time of project proposal formulation.
WP 5: Tar investigation
The objectives of this WP were:
- to bring experimental results and scientific interpretation to minimise global tar formation during biomass pyrolysis at a relevant scale for further industrial up scaling;
- to perform pyrolysis experiments on various biomass compositions and various operating conditions to study tar composition;
- to perform tar destruction experiments on high temperature reactors using a representative pyrolysis gas as input;
- to develop a tar dew point model and a measurement system for the on-line detection of the tar dew point in product gas.
WP 6: Inorganic modelling
The objectives of WP were:
- to evaluate the inorganic content of the biosyngas, the interactions of inorganic species with a SOFC;
- to investigate the hot cleaning of a gas coming from biomass gasification, in particular the removal of sulphur, chloride and alkali impurities;
- to design and build a gas cleaning facility that will provide a clean gas to the SOFC.
The three gas cleaner prototypes at CEA, ECN and TKE were designed and built. Moreover, the efficiency and the limitations of the sorbents proposed by ICT were evaluated, both through calculations and tests. The objectives of this task are then fully fulfilled.
Unfortunately, only the ECN gas cleaning train was in the end used in realistic conditions in WP8, as TKE gasifier was not operable and as the CEA gasifier and tar cracker were not coupled in due time.
WP 7: Technical economical and environmental assessment
This WP aimed at performing a techno-economic assessment covering process specific data with regards to technical, economical and environmental data. The aim was to evaluate the process in order to determine the technical potential, the market opportunities and environmental impact.
WP 8: Fuel cell specification and operation
The objectives of this WP were:
- investigation of the performance of a SOFC in relation to the presence (both concentration and type) of organic compounds and inorganic impurities in the feed gas;
- determination of the maximum allowable concentrations for different types of organic compounds and inorganic impurities in the SOFC feed gas;
- prove-the-principle by 2 long-duration (100 hours) SOFC stack test with cleaned product gas from 2 selected integrated gasification system.
For the proof of principle test, a SOFC stack with 30 cells was connected to a gasifier fuelled with beech-wood. For the cleaning of the gas a gas cleaning section was developed which meets the requirements of the SOFC. The operating temperature of the gas cleaning unit was minimal 400 degrees Celsius, which limits the number of heat exchangers between the gasifier and the SOFC stack.
The whole system of gasifier, gas cleaning section and the SOFC stack has run for 2 periods of 100 hours continuously without any degradation. This proof-of-principle test has showed that a SOFC stack can be fuelled with gas from a gasifier.
The project has already generated spin-offs for use internally in TKE. Experiments concerning the up-draft gasifier included in the project will be used in combination with TKE's existing gasification technology of small scale plant (0.3-2 MWe). The long term perspectives for the reactor being designed and tested in this project does not only include high efficiency CHP based on woody biomass it also includes specialised energy crops and a number of attractive waste fraction.
The TREC-reactor is a concept where at high temperature, solids are filtered from the gas, creating solid residence time and gas/solid contact time to convert solids and / or have catalytic effects of solids act upon the gas phase. The TREC-concept has mentioned functionalities without increasing pressure drop significantly. ECN is the sole owner of the idea. A NL patent has been granted. One industrial party has shown interest for the idea, and negotiations as to how to proceed are ongoing.
The exploitable result is the specification of the allowable concentration for single cell SOFC for organic compounds, as for instance present in the gas of a gasifier fuelled on woody biomass. The exploitable product or measure is the experience on the coupling of a SOFC stack on a gasifier including a gas cleaning step, such as performance and degradation.
The project has resulted in a gas cleaning train that has proven to be good for the coupling of biomass gasifier and SOFC. This probably then is also applicable for any other high demanding application such as catalytic processes for the synthesis of e.g. biofuels. The gas train consists of different units that work together and are a balanced set. The knowledge may be applied in similar systems by ECN in their work on the development and realisation of demonstration plants for biofuel production.
The tar dew points analyser has proven to be a very valuable measurement device for on-line monitoring of the performance of tar reducing reactors. It therefore is an exploitable product. Some industries already showed interest.
To achieve this goal, the general research objectives of GREEN-FUEL-CELL were directed towards understanding of the deterministic mechanisms of tar reduction with char and behaviour of volatile in-organics (metals and salts) with respect to cooler fouling. Research of low and high temperature gas filtering also took place as this project adopted techniques that are commercially available and well developed for coal gasification and perform the necessary modifications.
Innovative sustainable technologies with high 'fuel to electricity' efficiency are required to supply the increasing electricity demand and at the same time to fulfil the objectives of reducing the emission of green house gases. SOFC is one promising technology to obtain a high efficiency in electricity production, which would be sustainable so long as the feeding fuel is produced from renewable energy sources. The hydrogen-rich gas produced by gasification of biomass could be such a sustainable fuel for SOFC. For biomass gasification- SOFC conversion systems the most cost-effective size is expected to be plants from 1 to 30 MWe, with a total electric efficiency expected to be well above 50 %. However, the gases produced by most of the current gasification technologies are still too dirty to be directly fed into SOFC without extensive and expensive gas cleaning systems.
The resulting specific scientific objectives in support of the technological development were to:
- determine relations between char properties (e.g. extent of devolatilisation, ash content, and composition) and catalytic effect for tar reduction;
- develop of a model for in-process char gasification (partial oxidation) by the oxidised pyrolysis gas and in relation to air or oxygen concentration;
- obtain understanding of hydrodynamics of char-beds, both with and without bed material;
- understand the fate of volatile metals and salts in the gasification process and upon cooling in the gas cooler.
The main work packages, excluding the management efforts, have been the following:
WP 2: Char bed without bed material
This work package had the focus on one of the two gasification systems. The specific technical objective for this gasification system was to prepare a basic-design for a full-scale (1-50 MWth) innovative gasifier system. Based on the conducted calculations and experiments the following main conclusions have been stated:
- The principle of a fixed bed placed in a conical reactor has been proven cold and hot as a gasification reactor. Furthermore shows the calculations that the principle are up scalable.
- An updraft gasifier has been developed for gasification of residual char from a gasifier and operation conditions have been established.
- A concept for gasification of wood pellets has been developed, constructed and tested semihot at pilot scale with success. The final pilot scale plant was not tested successfully as there still are some problems to be solved with pyrolysis unit.
WP 3: Char bed with bed material
The objectives of WP3 were:
- to produce a product gas suitable as feed gas for an SOFC with respect to the presence of organic compounds;
- to prove that the TREC-technology is suitable as filter for particles (and S and / or Cl).
The TREC reactor has proven to be a valuable first cleaning reactor for the removal of mainly organic components that need to be removed for the use in an SOFC. It, however, does need additional gas cleaning equipment to meet the stringent specifications of an SOFC. These additional reactors have been developed within the project and the complete system has been tested successfully during two 100 h test runs.
Furthermore, the TREC reactor has proven to be a versatile cleaner. By changing bed material size and material, additional functionalities could be added, including the partial removal of organic sulphur species. WP3 therefore has fully reached its targets.
WP 4: Char bed with bed material
This WP aimed at evaluating TKE's and ECN's process designs with respect to the objectives of the project such as: low tar concentration, high carbon conversion.
A monitoring procedure for reviewing and comparing the two gasification processes was developed and presented early in the project. Due to the cancellation of measurements, evaluation of the two core processes ended up being performed at a conceptual level, and the results are thus more speculative than anticipated at time of project proposal formulation.
WP 5: Tar investigation
The objectives of this WP were:
- to bring experimental results and scientific interpretation to minimise global tar formation during biomass pyrolysis at a relevant scale for further industrial up scaling;
- to perform pyrolysis experiments on various biomass compositions and various operating conditions to study tar composition;
- to perform tar destruction experiments on high temperature reactors using a representative pyrolysis gas as input;
- to develop a tar dew point model and a measurement system for the on-line detection of the tar dew point in product gas.
WP 6: Inorganic modelling
The objectives of WP were:
- to evaluate the inorganic content of the biosyngas, the interactions of inorganic species with a SOFC;
- to investigate the hot cleaning of a gas coming from biomass gasification, in particular the removal of sulphur, chloride and alkali impurities;
- to design and build a gas cleaning facility that will provide a clean gas to the SOFC.
The three gas cleaner prototypes at CEA, ECN and TKE were designed and built. Moreover, the efficiency and the limitations of the sorbents proposed by ICT were evaluated, both through calculations and tests. The objectives of this task are then fully fulfilled.
Unfortunately, only the ECN gas cleaning train was in the end used in realistic conditions in WP8, as TKE gasifier was not operable and as the CEA gasifier and tar cracker were not coupled in due time.
WP 7: Technical economical and environmental assessment
This WP aimed at performing a techno-economic assessment covering process specific data with regards to technical, economical and environmental data. The aim was to evaluate the process in order to determine the technical potential, the market opportunities and environmental impact.
WP 8: Fuel cell specification and operation
The objectives of this WP were:
- investigation of the performance of a SOFC in relation to the presence (both concentration and type) of organic compounds and inorganic impurities in the feed gas;
- determination of the maximum allowable concentrations for different types of organic compounds and inorganic impurities in the SOFC feed gas;
- prove-the-principle by 2 long-duration (100 hours) SOFC stack test with cleaned product gas from 2 selected integrated gasification system.
For the proof of principle test, a SOFC stack with 30 cells was connected to a gasifier fuelled with beech-wood. For the cleaning of the gas a gas cleaning section was developed which meets the requirements of the SOFC. The operating temperature of the gas cleaning unit was minimal 400 degrees Celsius, which limits the number of heat exchangers between the gasifier and the SOFC stack.
The whole system of gasifier, gas cleaning section and the SOFC stack has run for 2 periods of 100 hours continuously without any degradation. This proof-of-principle test has showed that a SOFC stack can be fuelled with gas from a gasifier.
The project has already generated spin-offs for use internally in TKE. Experiments concerning the up-draft gasifier included in the project will be used in combination with TKE's existing gasification technology of small scale plant (0.3-2 MWe). The long term perspectives for the reactor being designed and tested in this project does not only include high efficiency CHP based on woody biomass it also includes specialised energy crops and a number of attractive waste fraction.
The TREC-reactor is a concept where at high temperature, solids are filtered from the gas, creating solid residence time and gas/solid contact time to convert solids and / or have catalytic effects of solids act upon the gas phase. The TREC-concept has mentioned functionalities without increasing pressure drop significantly. ECN is the sole owner of the idea. A NL patent has been granted. One industrial party has shown interest for the idea, and negotiations as to how to proceed are ongoing.
The exploitable result is the specification of the allowable concentration for single cell SOFC for organic compounds, as for instance present in the gas of a gasifier fuelled on woody biomass. The exploitable product or measure is the experience on the coupling of a SOFC stack on a gasifier including a gas cleaning step, such as performance and degradation.
The project has resulted in a gas cleaning train that has proven to be good for the coupling of biomass gasifier and SOFC. This probably then is also applicable for any other high demanding application such as catalytic processes for the synthesis of e.g. biofuels. The gas train consists of different units that work together and are a balanced set. The knowledge may be applied in similar systems by ECN in their work on the development and realisation of demonstration plants for biofuel production.
The tar dew points analyser has proven to be a very valuable measurement device for on-line monitoring of the performance of tar reducing reactors. It therefore is an exploitable product. Some industries already showed interest.
