Biomass Catalytic Gasification In A Decoupled Dual Loop Gasification System

Steam gasification of pine sawdust over hematite was carried out in a decoupled dual loop gasification system.The system is composed of three parts,i.e.a fluidized bed gasifier,a moving bed reformer and a fluidized bed riser combustor.Two parallel loops based on the above three parts were set up followed by a particles grading cyclone.The bed material in gasification loop was fine quartz sand while that in the reforming loop was the mixture of coarse hematite and quartz sand.The circulation rate of hematite,reforming temperature,steam to carbon mass ratio?S/C?and the effect of NiO/Hematite were investigated.The results show that the above factors play crucial roles in biomass steam gasification.Higher reforming temperature promotes tar removal and water conversion,higher S/C increases H₂/CO ratio and dry gas yield while the addition of NiO/Hematite promotes carbon conversion and dry gas yield.At gasification temperature 750^oC and reforming temperature 700^oC,the tar yield of 4.2g/Nm³ and 29.6g/Nm³have been obtained with hematite and quartz sand as bed material,respectively.Heat balance of gasifier/reformer and riser combustor is also given when quartz sand was used as bed material.Results show gasifier and reformer were operated under a similar condition as the autothermal reactor while for riser combustor,heat of combustion is insufficient and additional biomass is needed to add into the combustor to use as fuel.Toluene as a tar model compound,catalytic steam reforming experiments were carried out in a fixed bed reactor.The effects of reaction temperature,S/C,liquid hourly space velocity?LHSV?of toluene and NiO/Hematite were investigated.Results show that hematite has good self-reduction property and good tar cracking capacity.At the condition of reaction temperature was 850^oC,toluene feeding rate was 6ml/h,S/C was 1,carbon conversion over hematite reached19.3%,compared to that of only 7.5%over quartz sand.The increase of S/C and LHSV will lead to the reduction of carbon conversion rate.The high S/C is favorable for the directed conversion of gas to H₂.The loading of Ni promotes the cracking of tar and greatly increases the yield of H₂.Tar composition from the gasification process in DDLG were analyzed by GC-MS and then classified and organized.They were divided into four categories mainly according to their number of rings.Results show with the increase of circulation rate of hematite,the composition of gasification tar is gradually heavy;with the increase of reforming temperature,the composition of gasification tar is gradually lighter;NiO/Hematite catalyst can make the composition of gasification tar lighter and at the same time,the sulfur content in the tar is significantly reduced.