Thermodynamic assessment of SNG and power polygeneration with the goal of zero CO2 emission

The current coal-to-SNG (synthetic natural gas) projects are facing two main issues, addressing on insufficient energy utilization and large amount of carbon emissions. For this reason, we proposed a coal-based SNG and power cogeneration process, at the ability to achieve high-efficiency and achieve zero-energy-penalty separation of CO2, by incorporation with chemical looping combustion (CLC). The main objective of this paper is to estimate thermodynamic performances under the effects of key parameters in order to pre-examine whether the proposed process is thermodynamically viable. At optimal condition (oxygen to carbon ratio (O/C) = 0.4, steam to carbon ratio (S/C) = 0.8 and recycling ratio of unreacted gas (Ru) = 3), the overall plant energy efficiency, exergy efficiency and energy saving ratio are 58.84%, 56.59% and 10.82%, respectively. The proposed process is compared with several traditional systems that aims to further demonstrate the superiority of such process design in terms of thermodynamic and preliminarily economic assessment. A sensitivity analysis is also included to examine the effects of different coal feedstocks and oxygen carriers of CLC on system performances.