Simultaneous Tar Reforming And Syngas Methanation Of Biogenous Syngas

With the increasing awareness of environmental protection,the utilization of renewable environmentally friendly energy such as biomass and reduction the utilization of fossil energy are becoming more and more important.Converting biomass to synthetic natural gas?SNG?via gasification is very attractive.Based on the main obstacles of acquiring clean SNG through gasification such as the tar removal and suitable methanation process,methanation coupled with tar reforming reaction in a gas-solid countercurrent moving bed reactor was proposed.Firstly,a bifunctional NiO/hematite catalyst for tar reforming and methanation was prepared and tested in a fixed bed reactor.The tests of methanation on the effects of carrier calcination temperature,nickel loading,catalyst calcination temperature,reduction temperature and reaction temperature showed that the Ni-Fe alloy enhanced the resistance to carbon deposition ability of the catalyst.Under the conditions of reaction temperature 400^oC,H₂/CO₂ molar ratio 6.0 and catalyst reduction temperature of 400^oC,the CO₂ conversion and CH₄ selectivity could reach 94.2%and 97.7%respectively.The tests of toluene?tar model compound?steam reforming showed that 35⁵0%toluene was reformed to small molecules gas such as CO,CO₂ and CH₄ at the reaction temperature 600°C.This indicated that the NiO/hematite catalyst could catalyze tar steam reforming effectively.In addition,the TG curve of the NiO/hematite after the reaction showed that the catalyst had a better resistance to carbon deposition.Biomass gasification coupled with tar steam reforming and methanation was performed in a free fall reactor with a gas-solid countercurrent moving bed reactor.It was found that the tar yield decreased 95.8%with NiO/hematite used,and the content of CH₄ in product gas increased 47.5%.The results indicated that the NiO/hematite was effective for tar steam reforming and methanation.Meanwhile,the NiO and Fe₂O₃ in the bed material were reduced to the metal Ni and Fe₃O₄/FeO/Fe by the CO.At the same time,the CO,hydrocarbon?HC?and H₂ in the syngas are oxidized to CO₂ and H₂O.This process resulted in CO content in production gas decreasing and the CO₂ content increasing.The mixture of hematite,NiO/quartz sand and calcined limestone were used as the bed materials to clarify the effect of different component of bed materials?hematite,NiO and calcined limestone?on the production gas and tar reforming of different compositions.The data suggested hematite,NiO/quartz sand and calcined limestone could adjust the gas compositions and promote the catalytic tar steam reforming.With the addition of absorption enhanced reforming into coupled reaction,more than 95%CO₂ was adsorbed and tar reforming was strengthened.At temperature gradient of the moving bed of 500-600°C,S/B 0.4,and bed materials composed of 20%NiO/hematite 60%calcined limestone 20%quartz sand,the tar,CO₂ and CO in the syngas was deeply removed and a high concentration fuel gas of H₂ and CH₄??97%?was obtained.