Study On Carbon Capture And Cold Energy Utilization In Hybrid Power System Of Natural Gas Fuel Cell

In this paper,the triple hybrid power system with natural gas as fuel is modeled and simulated,and the thermodynamic model of the combined cycle power generation system of fuel cell,gas turbine and steam turbine is constructed.The thermodynamic performance of the system is analyzed from the aspects of compressor pressure ratio,steam carbon ratio,fuel utilization,fuel cell operating temperature and gas recirculation.After considering various limiting factors,the thermodynamic performance of the triple hybrid system is optimized,and the system achieves high exergy efficiency under the new operating parameters.Then,the triple hybrid system is coupled with the carbon capture subsystem and the LNG cold energy cascade utilization system to capture a large amount of carbon dioxide emitted by natural gas combustion and recover waste heat.According to the characteristics of the hybrid system,it is decided to use a more practical post combustion carbon capture scheme which is conducive to the stable operation of the system.Based on this,two new low-carbon power generation systems including hybrid power system,carbon capture and cascade utilization of LNG cold energy are designed,and the influence of important operating parameters on carbon capture subsystem is studied.The adsorbents used in the two carbon capture subsystems are MDEA and CaO,and their capture processes are very different.In the carbon capture subsystem of MDEA method,flash tower and shunt process are added to reduce energy consumption.In the carbon capture process of calcium circulation method,carbon dioxide reflux process is adopted to adjust the temperature in the calciner,and secondary waste heat boiler is set to use a large amount of waste heat of carbon dioxide waste gas and clean flue gas respectively.Finally,in order to further improve the energy utilization efficiency,a method of cascade utilization of liquefied natural gas cold energy for the recovery of waste heat in the system is proposed,which increases the power generation of the whole system,provides fuel for the two fuel cell systems,and outputs available natural gas.The calculation results show that the electrical efficiency of the optimized triple hybrid combined cycle system is 73.08%.After coupling the carbon capture subsystem,the exergy efficiency of the system decreases,and the energy efficiency loss under this mode is greater than that of the traditional coal-fired power plant.In terms of thermodynamic performance,the electrical efficiency of MDEA capture process and calcium circulation capture process are 62.13% and 60.32% respectively.In addition,the cascade utilization of LNG cold energy compensates the energy loss caused by the coupled carbon capture subsystem,providing 410.86 k W and 382.64 k W electric energy and natural gas with appropriate temperature and pressure for the two systems respectively.In this paper,the coupling modes of combined cycle power generation,carbon capture and LNG cold energy utilization are deeply studied and analyzed.The research results can provide a valuable reference for the design of low-carbon and efficient power generation system based on fuel cell.