The Bio-HyPP system is a hybrid power plant system – a combination of solid oxide fuel cells (SOFC) and a micro gas turbine (MGT). This hybrid power plant concept is a highly-efficient as well as highly load- and fuel-flexible CHP system with lowest emissions.
The main objective of this project is to develop and realise a full-scale technology demonstrator of a Hybrid Power Plant in a lab environment suitable for gaseous sustainable biomass feedstock derived from fermentation processes. Realising this system will validate the great potential of the hybrid plant concept as an efficient and energy-sustainable source of heat and electrical power.
The potential of the SOFC/MGT Hybrid Power Plant concept is based on the interconnection of a high-temperature SOFC with a MGT. (Figure 1). Using the compressor (1), the process air is compressed. The compressed air or part of it is used to purge the remaining air volume of the SOFC pressure vessel (13) to control the temperature of the auxiliary units and to ensure fuel-free conditions in case of leakages. Afterwards it is pre-heated in the recuperator (6) up to approximately 700°C-730°C. The pressurised and pre-heated air is used for the required thermal management and for the air supply of the SOFC (10). The fuel for the SOFC has to be conditioned and pre-reformed in a reformer (9) before entering the SOFC (10). To ensure high electric efficiency fuel cells are operated at a fuel utilisation rate between 60 and 90%. Thus, the exhaust gas of the fuel cell still contains hydrogen and carbon monoxide, which are oxidized in a controlled manner in a fuel-flexible combustion chamber (7), combining the functionality of an SOFC off gas burner and conventional gas turbine combustor using at least two stages.
Block diagram of the top-performance layout concept for the Hybrid Power Plant including main subcomponents
In order to maximize efficiency, the individual components as well as the matching of both subsystems must be adjusted and optimised to minimize additional supply of fuel to the combustion system. The exhaust gases are expanded to ambient pressure in the turbine (2). A generator (3) mounted on the same shaft (4) produces electrical power alongside the power production of the fuel cell. The exhaust gases pass the recuperator to heat up the compressed fresh air. The remaining heat can be used for domestic heating purposes (12).
The Hybrid Power Plant represents a power plant concept with the highest prospective electric efficiency possible (Figure 2) with achievable electric efficiencies of 60% for small power levels in the range of 30 kW and up to 70% for large scale power plants. Furthermore, total efficiencies of above 100% can be achieved in combined heat and power operation. Moreover, the pressurised SOFC/MGT Hybrid Power Plant cuts the investment costs per kWe installed thanks to the reduced number of stacks for the same power output.
Electrical efficiency of the SOFC/MGT Hybrid Power plant concept compared to other power plant concepts depending on installed power output
Considering the advantages of high efficiency, high flexibility and low emissions, the Hybrid Power Plant system can be perfectly utilised in the field of combined heat and electrical power production using all varieties of biogas. Hybrid Power Plants can be installed at the location of biogas production or within a local biogas grid as a satellite CHP system.
Installed at the location of biogas production, Hybrid Power Plants can, because of the high power-to-heat ratio, significantly reduce the waste heat. Currently, more than 30% of the produced heat is heat loss and cannot be used by the fermentation process itself or externally.
The operation flexibility of Hybrid Power Plants also increases the profitability of the system in optimising the sale revenues or increasing the self-consumption of power generated on site.
Since an important aspect on hybrid systems is related to cost reduction, a top-economic layout is also planned to be analysed with an adapted emulator rig (i.e.: a real system including all components except for the SOFC stack).
In this top-economic layout (Figure 4) the core-engine of the MGT is substituted with a turbocharger.
Block diagram of the planned cycle concept for a top-economic layout