Research On Coal-based SNG Power Co-production System Based On Chemical Chain Combustion

Coal,as a primary energy source,is irreplaceable for the coming decades.Coal-to-SNG(synthetic natural gas)technology is regarded as one of the most important and clean coal technologies based on the fact of the limited sources of natural gas and oil and abundant reserve of coal in China.Furthermore,with the increasing demand and price of natural gas in recent years,coal-to-SNG plan has received considerable attentions by Chinese policy-maker.There are several advantages associated with coal-to-SNG technology,i.e.ensuring energy security,reducing natural gas imports,stabilizing fuel prices and diversifying energy options.However,high energy consumption,high carbon emissions and low energy efficiency of the system are mainly obstacles to the rapid development of the coal-to-SNG industry.It is an important issue to coordinate the energy utilization and environment protection.To solve the energy utilization problem in the traditional coal-to-SNG system and to explore the low energy penalty and low cost for CO2 capture.This essay proposed a coal-based SNG and power cogeneration process,integrating chemical looping combustion(CLC)into coal-to-SNG and power polygeneration system might be very attractive for the goal of zero-energy-penalty carbon capture by burning the unreacted gas from methanation unit.This is the aim of this paper which examines the potential benefits and technical feasibility of such process from both energy-efficient and environmental-sound views.And it is of great significance to guarantee the security of China’s energy supply and achieve a healthy socio-economic development.CLC is regarded as the most promising technology for CO2 capture to mitigate greenhouse gas effect.In this work,a technical and economic performance of CH4-feed CLC power plant by means of utilizing promising nickel-,copper-,and ilmenite-based oxygen carriers is studied.Nickel-based CLC power plant has the highest net power efficiency of 50.14%,followed by 48.02%for ilmenite-based case and 45.59%for copper-based case.By contrast nickel-based case has a specific CO2 emission of 1.44 kg/MW h,which is dramatically lower than the referenced NGCC with CCS system(40.10 kg/MW h).The economic analyses reveal nickel-based case is most economic-benefits due to the lowest cost of electricity(COE)of 71.66€MW h,approximately 0.32 €MW h and 13.06€/MW h COE reduction benefits have been increased in comparison with ilmenite-based and copper-based case,respectively.The natural gas price has an important influence on COE,as approximately 49.73%,48.60%and 56.30%of COE enhancement is expected with the natural gas price ranging in 4-8 €/GJ for nickel-based,copper-based,and ilmenite-based case,respectively.Finally a comparison between NGCC and CLC-related power system in terms of economic performance further demonstrates the feasibility of the latter system.The current coal-to-SNG 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 CLC.Moreover,the sensitivity analysis and optimization of key parameters are performed.In addition,the thermal performance,energy-saving mechanism as well as the economic feasibility of the polygeneration system are explored.The results show that oxygen to carbon ratio(O/C)has a great influence on the yield of syngas,while high steam to carbon ratio(S/C)and recycling ratio of unreacted gas(Ru)will lead to a reduction in the amount of steam used to drive the turbines to generate electricity,which is not conducive to the improvement of system performance.At optimal condition(O/C =0.4,S/C =0.8 and Ru =3),the overall plant energy efficiency,exergy efficiency and energy saving ratio are 58.84%,56.59%and 10.82%,respectively.For comparison,conventional coal-to-SNG and power polygeneration system and other standalone systems have been presented.Compared with conventional polygeneration system,the energy efficiency is improved by 2.83%in this proposed process.As with single product systems(SNG+CC,IGCC and IGCC+CC)the energy efficiency has been turned out to be increased by 2.5%,15%and 26%,respectively.Moreover,a preliminary economic analysis is involved and the financial feasibility of this novel polygeneration system is further demonstrated.In addition,a sensitivity analysis is also included to examine the effects of different coal feedstocks and oxygen carriers of CLC on system performances.Attention should be paid to excessive CO content in the captured CO2 stream,probably with the potential solution by downstream oxygen polish.