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Development of a new and highly efficient micro-scale CHP system based on fuel-flexible gasification and a SOFC

Periodic Reporting for period 3 - FlexiFuel-SOFC (Development of a new and highly efficient micro-scale CHP system based on fuel-flexible gasification and a SOFC)

Reporting period: 2017-11-01 to 2019-06-30

The FlexiFuel-SOFC project aimed at the development of an innovative, highly efficient and fuel-flexible micro-scale biomass CHP technology consisting of a small-scale fixed-bed updraft gasifier, a gas cleaning unit and a solid oxide fuel cell (SOFC). The technology should be developed for a capacity range of 25 to 150 kW (fuel power) and thus be applicable for micro-scale CHP applications.
To reach this overall goal the project focussed on several specific objectives. An existing small-scale fixed-bed updraft gasifier technology should be further developed towards enhanced fuel flexibility (from woodchips and pellets towards the utilisation of SRC and selected agricultural fuels) and integration into a SOFC based CHP system. Moreover, a compact gas cleaning concept covering particle precipitation, HCl and H2S removal as well as tar cracking should be developed. The aim was to provide a product gas with no PM, H2S contents <1 ppm and HCl contents <5 ppm as well as to upgrade the tar rich product gas by cracking specific tar compounds which cannot be converted by reforming in the fuel cell system. Last but not least, a SOFC technology enabling an operation at nearly atmospheric pressure, a defined temperature range of the product gas (750 to 850°C), a high power density as well as cost efficiency of the SOFC stacks and a high electric efficiency (stack efficiency of about 40% with product gas from the updraft gasifier) should be developed. Two testing plants, a basic and an advanced one should be developed and manufactured. The performance and evaluation of test runs with different biomass fuels should form the basis to finally achieve an optimised system design at project end. Accompanying risk assessments, safety analyses, techno-economic and environmental impact assessments as well as market studies should be performed in order to assure that the new technology resulting from the project is also market competitive.
During the first project period, work focused on the development of the single plant components and the design, manufacturing and assembly of a first testing plant. The operating conditions for the single units and their interfaces have been defined and a detailed plant concept has been worked out. With this system design, the SOFC is operated with a side stream of the product gas from the gasifier while the remaining product gas is combusted in a burner directly coupled with a boiler. This provides the advantage that the SOFC can be operated at nominal load while the amount of the product gas directly utilised for heat production is variable and can be adapted to the heat demand of the consumer. Therefore, high load flexibility in a heat controlled system is provided while maintaining a maximum of full load operating hours of the SOFC unit.
Regarding the gasifier, a product gas heating and extraction system which also provides a thermal tar reforming stage was developed. Moreover, the gasifier was further developed towards the utilisation of biomass fuels with comparably low ash melting temperatures (such as agro-pellets) thus achieving a significantly enhanced fuel flexibility. Therefore, experimental studies and comprehensive CFD (computational fluid dynamics) simulations have been performed. With respect to the gas cleaning unit (GCU), experimental work, process modelling and chemical equilibrium calculations were employed in order to develop the different reactors needed and to select appropriate sorbents for Cl and S-removal as well as catalysts for tar reforming. Based on this, a first generation GCU has been designed and constructed. Furthermore, a SOFC system tailored to the gas composition of the product gas downstream the GCU has been developed. The stack module has been modified with respect to the product gas properties and the balance of plant components have been newly developed for integration into the whole plant concept.
At the end of the first project period, the assembly of the first generation FlexiFuel-SOFC testing plant took place. The second project period started with cold and warm start-up tests. Then, test runs for the evaluation of the GCU have been performed and several adaptations have been made in order to gain continuous operation and to meet the gas quality requirements of the SOFC. Subsequently, testing campaigns with the whole CHP system followed. At the end of the second project period the new technology has for the first time been operated in CHP mode at the targeted electricity production of 6 kW.
Subsequently, during the third project period, the gasifier, the GCU and the SOFC system as well as the whole CHP system have been further developed based on the evaluation of the test run results and the experiences made during plant operation. A second generation testing plant has been assembled and comprehensive test runs have been performed. The purification targets set for the GCU could be reached and again, an electrical load above 6 kW and flexible thermal output could be achieved. Moreover, the fuel flexibility of the gasifier could be proven during test runs with wood chips, willow, poplar and Miscanthus pellets. In total more than 250 hours of CHP operation have been reached and TRL 5 could be achieved. Based on these promising results, a final system design has been worked out, which shall form the first step for later industrialisation.
Economic and environmental assessments as well as market analyses accompanied the technical development work throughout the whole project resulting in a comprehensive market study regarding the market potentials and future trends for micro-scale biomass CHP systems in Europe, a long-term roadmap for the successful deployment of the FlexiFuel-SOFC technology on the market, techno-economic analyses and environmental and overall impact assessment reports. These studies show considerable market opportunities for the FlexiFuel-SOFC technology as well as hi
Reaching TRL 5 with the FlexiFuel-SOFC technology represents a significant step beyond the present state-of-the-art. For the first time a micro-CHP technology with close to zero emissions, high electric (more than 40% efficiency regarding the conversion of the product gas heating value into electricity) and overall efficiency (90% according to the final system design) was realised. The wide range of solid biomass fuels applicable shall result in a positive impact regarding energy security in the EU.
According to the results of the impact assessment performed, the new technology promises considerably lower air pollutant emission intensities than state-of-the-art biomass-based technologies, since almost zero CO, OGC and PM emissions as well as comparably low NOx emissions were achieved. Thus a large emission reduction potential is given if broad market diffusion rates can be achieved in the future. Furthermore, the technology can lead to negative cumulated greenhouse gas emissions due to the substitution of the existing electricity production with electricity produced from (GHG-neutral) biomass fuels.
Assuming that the expected market potential will be reached, the FlexiFuel-SOFC technology is expected to create in future, in addition to the positive environmental effects, also large turnover and additional job creation potentials (high socio-economic impact), especially for small and medium-sized enterprises.
FlexiFuel-SOFC second generation testing plant (2)
FlexiFuel-SOFC second generation testing plant (1)