Integrated Process of Natural Gas Decarbonization to Produce Zero-Carbon Fuel by Double Chemical Looping Coupling

A novel integrated process of natural gas decarburization to produce zero-carbon fuels of H2 and NH3 is proposed to capture its carbon emission, which includes chemical looping hydrogen generation, chemical looping ammonia generation, solar methane cracking , calcium looping, and a waste heat utilization unit. In the cycle, chemical-looping-based hydrogen generation is effectively integrated with chemical-looping-based ammonia generation to avoid the additional energy consumption caused by the preparation of N2 in the carbothermal reduction reaction. Thermodynamic models of components are established, and both the energy and exergy analysis methods are constructed. The design performances of this integrated process are simulated, and the impacts of key parameters such as reactor temperature, solar energy input, fuel input mass rate, and solar fuel contribution rate on the yield of NH3 and H2 are analyzed and discussed. The results show that its energy and exergy efficiencies are, respectively, 63.15% and 71.3% under the design condition. At the same time, it will produce 37.307 MW of electric energy. As the CH4 flow rate of the solar MC subsystem changes from 200 to 800 kmol/h, the energy and exergy efficiency increase by 2.41% and 3.87%, respectively. Besides, the contribution of solar energy to fuel is discussed; the contribution of solar energy to H2 and NH3 increased by 31.67 MW and 8.39 MW, respectively, with the increase of CH4 flow rate, but the solar H2 contribution rate decreased by 6.92% due to the significant increase of output power.