Numericalanalysis Of Biomass Co-Gasification With Coaland Coupled Combustion Of Syngas With Coal

Co-gasification of biomass and coal to produce syngas can effectively solve the unstable problem of biomass gasification,the power generation of syngas co-firing in a coal-fired boiler can effectively improve the combustion performance of the boiler.In this paper,A 660MW coal-fired boiler with syngas co-firing system,which is a super-critical unit.And an atmospheric pressure fluidized bed gasifier was taken as the research object for the process of syngas production and its co-firing.Moreover,the whole system of gasification and co-firing was analyzed from the perspective of exergy.The key found are as follows:1 Using bagasse and bituminous coal as raw materials,the processes of pure bagasse gasification and the co-gasification of bagasse mixed with coal to produce syngas were studied.Co-gasification can improve gasification efficiency and increase the calorific value of gas.With the increase of gasification temperature,the ratio of steam-to-fuel bagasse to xuzhou bituminous coal and the blending ratio of bagasse,the gasification efficiency increased at the initial stage and then decreased.The influence of gasification temperature on the co-gasification of bagasse mixed with xuzhou bituminous coal was studied,it was found that the co-gasification effect was better when the temperature was around 900℃;When the steam was used as the gasifying agent,the gasification effect was the best when the steam-to-fuel ratio is 0.6;Finally,the effect of Bagasse to xuzhou bituminous coal ratio on gasification performance was studied,Gasification performance was the best when bagasse blending ratio was of 30%.The best values above of gasification effect were all based on gasification efficiency.2 The effects of different proportion of syngas on combustion temperature and pollutant emissions were studied.With the blending ratio of syngas increasing,the combustion temperature decreased gradually,and nitrogen oxides and sulfides also decreased.The effects of coal types,such as fushun bituminous coal,kailuan washing medium coal and yuanbaoshan lignite on combustion temperature and pollutant emission were studied under different excess air coefficients with a mixing ratio of 10%syngas.It was found that the combustion temperature increased firstly and then decreased with the increase of excess air coefficient,and the nitrogen oxides increased gradually while the sulfides decreased gradually.3 The energy efficiency was analyzed by exergy analysis methods.Firstly,cogasification is studied,With the increasing of gasification temperature,the exergy values of H₂ and CO increased,but the exergy values of CH₄ and CO₂ decreased;With the increase of steam-to-fuel ratio,the exergy values of H₂ and CO increased firstly and then decreased,the exergy value of CH₄ reduced gradually,the exergy values of CO₂ rised slowly;With the increase of bagasse blending ratio,the exergy value of H₂ rised at the beginning stage and then decreased gradually,the exergy values of CO and CH₄ decreased gradually,the exergy values of CO₂rised gradually.The exergy efficiency increased firstly and then decreased.The exergy efficiency and exergy loss of the whole system were researched,the study showed that the boiler exergy efficiency was lower than that of the gasifier for more exergy loss in boiler.Some effective measures should be applied to improve energy efficiency of the boiler equipment.