Development of a multi fuel SOFC platform for CHP and CCHP applications

摘要

AVLs development towards universally applicable and highly fuel flexible SOFC CHP systems led to an extension of fuel capability to the utilization of multiple renewable fuels such as biogas, product gas from biomass gasification and synthetic diesel as well as the coupling of an SOFC system with an absorption chiller to create an SOFC CCHP system. Based on AVLs natural gas operated platform with the power range of 5 - 10 kW_(EL) and an electrical efficiency of >55 % using the Plansee/IKTS stack technology, two different systems have been developed and tested. This paper shows the coupling of a stationary 6 kWEL SOFC CHP system developed by AVL using an IKTS stack module with a 5 kWCOLD absorption chiller developed by TU Graz, Institute of Thermal Engineering. The absorption chiller utilizes the thermal energy of the SOFC systems exhaust gas with a temperature of > 200 °C to create cooling power. Optimization of the ratio between electrical power of the SOFC system and cooling power of the absorption chiller was a main target to maximize the CCHP’s overall efficiency. Evaluation of different cold and cooling water temperatures of potential applications showed that high efficiencies can be reached in applications such as office buildings and hospitals with a ratio of the electrical and cooling power between 4 and 6. This platform was also developed towards the operation of renewable fuels such as biogas and synthetic diesel. As these renewable fuels may lead to lower electrical efficiencies of the SOFC system compared to natural gas, more heating power in the SOFC system’s off gas could be utilized in the absorption chiller. Depending on the chosen fuel the off-gas mass flow and its temperature differs, which has a large influence on the dimensioning of both sub systems in relation to each other. Furthermore, AVL’s SOFC platform was coupled with a functional biomass updraft gasifier which is able to be operated with a variety of gasified biomasses. System heat up and power generation with gasified wood chips has been performed successfully. The biomass SOFC plant was equipped with a hot gas cleaning unit for Cl, S and particulate removal. Tar was converted by thermal cracking and steam reforming. The process will allow electrical efficiencies of up to 40 % from solid biomass. This paper provides an overview of the development of both systems and recent system testing results.