| Solid Oxide Fuel Cell(SOFC)uses methanol as a substitute for hydrogen,overcoming the difficulty of storing and transporting hydrogen and offering great potential for application.However,the development of methanol SOFCs is hampered by the problem of carbon buildup.In order to solve this problem,this thesis proposes a combined chemical looping hydrogen generation(CLHG)/SOFC system,and makes full use of the waste heat of each equipment in the system,not only to achieve the normal operation of the system,but also to use the excess heat to generate electricity,thus improving the efficiency of the system.The main research of this thesis is as follows:(1)The principle of the methanol CLHG/SOFC combined cycle system is first described,then the effects of hydrogen utilisation,methanol flow rate,SOFC operating temperature and SOFC cathode air flow rate on the methanol CLHG and SOFC combined cycle system are analysed.As the hydrogen utilisation rate increases,SOFC power increases,turbine(GT)power decreases and total system power increases.As the hydrogen utilisation rate increases from 0.6 to 0.8,the electrical efficiency of the system increases by 4.02% and the electrical efficiency of the system reaches 48.66%.The effect of cathode air flow on the SOFC output power and efficiency is negligible,however the air compressor power consumption increases dramatically.The cathode air flow rate increases from 2.03 mol/s to 3.55 mol/s and the power consumption of the air compressor increases from 14.5 k W to 24.02 k W,resulting in a decrease in the electrical efficiency of the system from 47.91% to 41.84%.(2)The analysis of the methanol CLHG/ SOFC combined cycle system in Chapter 3reveals that the exhaust gas temperature from the system is above 200℃(medium temperature heat source).If this heat is not recovered,it will result in a significant waste of energy.The Organic Rankine Cycle(ORC)has been found to be superior in recovering and utilising medium and low temperature heat sources.This thesis further utilises ORC to recover waste heat from a methanol CLHG/SOFC combined cycle system to generate electricity.Compared to the methanol CLHG/SOFC combined cycle system(System 1),the methanol CLHG/SOFC combined cycle ORC waste heat recovery system(System 2)has a 2.55 %improvement in power generation efficiency.The output power of System 1 and System 2increases and then remains the same as the methanol flow rate increases,with the turning point occurring when the methanol flow rate is 0.11125 mol/s,when the corresponding output power of System 1 and System 2 are 33.38 k W and 35.19 k W respectively.The largest loss in the system was found to be SOFC,followed by CLHG,and the percentage of the loss in SOFC and CLHG is 34.75% and 21.96%,respectively.(3)A methanol CLHG/SOFC/cathode tail gas recirculation utilization system is constructed,and the effects of cathode tail gas recirculation ratio on SOFC voltage,current density,system electrical efficiency,and system efficiency are analyzed.It is found that the system reaches a maximum power of 35.43 k W when the cathode tail gas recirculation R(CA)=0.35.The ORC cycle is then added to the methanol CLHG/SOFC cathode tail gas recirculation system to recover waste heat for power generation and domestic hot water supply.Compared to methanol CLHG/SOFC combined cycle ORC waste heat recovery system(System 2),the methanol CLHG/SOFC/ORC and cathode tail gas recirculation system(System 3)has a 10.09 % increase in system electrical efficiency,a 15.78 % increase in total system efficiency and a 13.78 % increase in system house efficiency,reflecting the importance of cathode tail gas recirculation.The results of this study may provide a new way of thinking for future SOFC combined cycle systems and provide theoretical guidance for the practical establishment of distributed energy systems. |
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