Research On CH₄ Formation During Yining Coal Gasification In Fixed Bed Gasifier

Natural gas is one kind of the clean energy source and resource,but there is a serious shortage of natural gas in China.However,synthetic natural gas?SNG?can make up for the disadvantage of natural gas shortage.Compared with other coal gasification technologies,the most obvious advantage of fixed bed gasification technology in SNG is the high content of CH₄.In fixed bed gasifier,the gas and coal move counter-currently forms dry zone,dry distillation zone,methane zone,gasification zone and combustion zone,and CH₄ is derived from the dry distillationzone and methane zone.The formation of CH₄ is complicated since the CH₄ formation in the two zones is affected by the upstream gas from the next zone.There is currently a lack of clear understanding of CH₄ formation in fixed bed gasifier.In this work,the composition of gasification gas and the experimental conditions of dry distillation zone and the gasification zone were simulated.The CH₄ formation during Yining coal gasification in fixed bed gasifier was investigated under 0.1 MPa and 2.0 MPa.Experimental research showed that:?1?In different single atmospheres,H₂ is most beneficial for CH₄ formation,followed by H₂O,especially at 2.0 MPa.In dry distillation zone,CO₂ promotes CH₄ formation,which can be weaked at 2.0 MPa.In methane zone,CO₂ inhibits CH₄ formation,which can be enchanced at 2.0 MPa.The CO atmosphere has little effect on CH₄ formation,but slightly promotes CH₄ formation at 2.0 MPa.?2?Different gases are added to H₂ atmosphere that has the most influence on CH₄ formation,and the addition of H₂O promotes CH₄ formation,especially at 2.0 MPa.The addition of CO₂ inhibits CH₄ formation,which is more pronounced at 2.0 MPa.The addition of CO has no significant effect on CH₄formation,but slightly promotes CH₄ formation at 2.0 MPa.?3?CO and CO₂ gas are separately added to H₂O+H₂ atmosphere which is most favorable for CH₄ formation,and it is found that CO₂ addition is beneficial to CH₄ formation in dry distillationzone and hinders CH₄ formation in methane zone,while the effect of CO₂ on CH₄ formation in the two zones is weakened at2.0 MPa.The addition of CO is favorable for CH₄ formation in dry distillationzone,but inhibits CH₄ formation in dry distillationzone at 2.0 MPa.The addition of CO has no significant effect on CH₄ formation in methane zone,while is favorable for CH₄ formation in methane zone.?4?In fixed bed gasifier,the upstream gasification gas significantly promotes CH₄ formation in dry distillationzone and methane zone,especially at 2.0 MPa.The H·provided by gasification gas can stabilize CH_x·produced by coal dry distillation in dry distillationzone,and the heterogeneous methanation reaction occurs in methane zone,which is the source of CH₄ formation during Yining coal gasification.The former is the main source of CH₄ at 0.1 MPa,while the latter is the main source of CH₄ at 2.0 MPa.In addition,there is no obvious homogeneous methanation reaction between CO₂ or CO and H₂ from gasification gas in dry distillationzone or methane zone,but the water gas shift reaction apparently occurres.