Research On Catalytic Steam Gasification Of Biomass Char For Hydrogen-rich Syngas

Hydrogen,as a clean and efficient energy carrier,has the potential to replace fossil fuels,and biomass steam gasification is one of the most promising hydrogen production technologies.However,the main problem of biomass gasification for hydrogen production is the lower hydrogen content in the syngas,followed by the high tar content during the process.Biomass carbonization technology can reduce effectively the volatile components of raw materials.Thus,char gasification can avoid effectively the influence of tar on the gasification process.In addition,the carbonized material has high water absorption,and it can absorb catalyst solution to achieve the purpose of loading catalysts,so as to enhance the gasification rate.In this paper,using biomass char:sawdust char,woodchip char,corncob char and so on as raw materials,biomass char catalytic steam gasification for hydrogen-rich syngas in a fixed bed updraft gasifier was investigated.The main research contents and achievements are as follows:1.Biomass char steam gasification for hydrogen-rich syngas was studied.The effects of reaction temperature?750-950??,water vapor flow?0.2-1.0 g/min?,different chars and particle sizes on gasification characteristic were investigated.First of all,the syngas with high hydrogen content?>60%?can be obtained by biomass steam gasification.The H₂/CO ratio in the syngas can reach about 3.Moreover,under the same gasification conditions,the maximum hydrogen yield can be obtained by woodchip char gasification,to 222.8 g/kg.The effects of particle size on the gasification results were explored using woodchip char and corncob char as feedstock.The results showed that the particle size had little effect on the gas components,but the char conversion rate increased obviously with the increase of the particle size.Big particle size can effectively avoid the process entrainment loss.The effect of reaction temperature and steam flow rate on sawdust char gasification was studied.Increasing reaction temperature and steam flow rate was in favor of char conversion.The char conversion rate,gas production rate and hydrogen yield increased with the increase of temperature and steam flow rate.However,the high temperature is unfavorable to the content of H₂.With the increase of temperature to950?,the content of H₂ decreased from 65.8%to 61.2%,and the content of CO increased obviously and the content of CO₂ decreased,while the content of H₂/CO decreased to 3.35.Although the increase of steam flow rate can promote the hydrogen content,too much water vapor has little influence on the gasification result,and the most suitable steam flow rate is0.4-0.6 g/min.2.Using corncob char absorbed in impregnating solution to support catalysts,the effects of different catalysts?KOH,NaOH,K₂CO₃ and Na₂CO₃?,mass fraction of catalyst solution,reaction temperature and steam flow rate on corncob char steam gasification were studied.Char conversion rate can be greatly increased after absorbing in catalyst solutions.Introducing catalysts were less influence on gas composition,but the char conversion rate,gas production rate and hydrogen yield increased obviously.Maximum hydrogen yield can be obtained when KOH was used as catalyst.Catalytic capacity of four catalysts is:KOH and NaOH slightly larger than K₂CO₃ and Na₂CO₃.Increasing the mass fraction of catalytic solution?KOH?can increase the loading of catalyst,which is more conducive to char gasification.The content of CO₂ decreased and the content of CO increased,meanwhile the content of H₂ decreasing slightly.Hydrogen yield increased firstly and then decreased with increasing impregnation mass fraction.The maximum hydrogen production rate was 197.8 g/kg,which was obtained when the solution mass fraction was 6%.The effect of temperature and steam flow rate on char gasification is similar to that without adding catalysts,but for obtaining the same char conversion rate,the reaction time can reduce half with the catalyst and water consumption can be significantly reduced.3.The effects of different catalysts?KOH,K₂CO₃,CH₃COOK and KCl?,catalyst solution mass fraction,reaction temperature and gasification agent on woodchip char gasification were explored by the same catalyst loading method.The catalytic ability of KOH and K₂CO₃ on the gasification was similar.The CO mass fraction was obviously improved and the contents of H₂and CO₂ decreased,and the carbon conversion rate and hydrogen production rate also increased obviously.CH₃COOK's catalytic capacity is lower than that of KOH and K₂CO₃,the changing degree of each component was not as good as when KOH and K₂CO₃ were used as catalyst,and the char conversion rate and hydrogen yield were also low.The effect of KCl on the gasification of woodchip char is not significant.The catalytic activity of the four catalysts is in order:KOH?K₂CO₃>CH₃COOK>KCl.The effect of impregnating solution mass fraction?KOH?on the woodchip char gasification was similar to that of corncob char,with the content of H₂ and CO₂ decreasing and the content of CO increasing.The maximum hydrogen yield was197.2 g/kg with the mass fraction of impregnating solution of 6%.The effect of temperature and steam flow rate on the char gasification was always consistent with that without adding catalyst.The addition of oxygen increased the conversion of char and can adjust the H₂/CO ratio.However,the increase of ER was unfavorable to hydrogen production.The content of H₂and hydrogen yield decreased with the increase of ER,while the content of CO increased first and then decreased.The CO₂ content kept rising,so the ER value should not be too large,and the more appropriate ER value is between 0.2-0.3.In this study,biomass char catalytic steam gasification to obtain hydrogen-rich syngas was studied.Char absorbing in catalyst solution is an effective method,and gasification rate can improve significantly.Furthermore,hydrogen content is higher than 60%and without tar is produced in production gas.The H₂/CO ratio can vary between 1.0 to 4.0,which can meet a wide range of applications.