Study Of Heat Exchanger Coupled Catalytic Combustion Technology For Compact SOFC

Solid oxide fuel cells(SOFC)have the advantages of high fuel adaptability,simple and pollution-free systems and low noise levels.However,SOFC reactors operate at high temperatures and require the treatment of anode exhaust gas during stable operation,for which a thermal management system has to be matched.The burner and heat exchanger are important components in the SOFC thermal management system,however,an overly complex and bulky thermal management system is also not conducive to the need for SOFC compactness.Therefore,this study couples the burner and heat exchanger into a combustion heat exchange coupler(CHE),thus reducing the space required for the thermal management system,making the SOFC system more compact and increasing the heat exchange efficiency as much as possible,providing sufficient heat for the system during the SOFC start-up phase and treating the anode exhaust gas during the stabilisation phase,with certain applicability and promise.In this dissertation,the heating power of the SOFC system is calculated with reference to the basic parameters of the reactor during the start-up process and the internal structure is designed by considering the start-up and stable operation conditions.The comparison was carried out to lay the foundation for the subsequent application of CHE.The main work and conclusions are as follows:(1)CHE successfully couples the heat exchanger and the burner in the SOFC system.Experiments have proven that the CHE achieves a heat transfer efficiency of 86.97%,which is 30%higher than when only heat transfer is carried out,and that the cold-side outlet air temperature is higher than when only heat transfer is carried out.At a hot-side inlet mixture temperature of 770 K,the CHE reached its maximum catalytic conversion efficiency in less than five minutes,which also met the system start-up requirements.However,the test specimen did not reach the output heating power of the standard operating design and further structural optimisation is required.(2)The optimum overall performance of the sloping finned CHE with an additional through-hole(0.8 mm diameter)has been determined by structural optimisation and is capable of delivering 8.95 kW of heating power under standard design conditions,far exceeding the 6.35 kW required to heat up the reactor,and the cold side outlet air temperature can reach 1146 K,also exceeding the 1070 K required for the reactor.It also provides a part of the heat surplus for the system to be used by other thermal components or to be exported in the form of heat.In practice CHE can effectively improve the start-up time of the system or have a higher energy utilisation for the same start-up time.(3)The optimised CHE burns very well,with a fuel conversion rate close to 100%and all emission concentrations close to zero over the range of common fuel concentrations and hotside inlet mixture temperatures,indicating that it is a clean burner that meets the needs of current developments.At the same time its maximum internal wall temperature is further reduced,but this does not affect its combustion performance,but rather reduces the risk during the operation of the CHE and extends its service life.In addition,the exhaust gas temperature of the CHE is much lower than the exhaust gas temperature of conventional ignition burners,allowing for a significant reduction in the heat load on downstream components,which is expected to reduce material requirements and further cut costs.(4)The optimised CHE was applied to the system in the stable operation phase and the results showed that it was able to completely burn the anode exhaust gas within the range of SOFC fuel utilisation involved in the system,while its heat transfer efficiency was even as high as 94.59%at a stack fuel utilisation of 0.8,verifying that the CHE is suitable for all phases of the SOFC system and can be well matched to the compact SOFC system.