Kinetics Study Of Two Hydrogen Producing Reactions:Biomass Char Catalytic Gasification And Water Gas Shift Reaction(WGS)

Biomass char catalytic gasification with steam and WGS,which are two important reaction processes for hydrogen production from biomass energy,and the latter is also an important reaction process for hydrogen production from fossil energy.This thesis is purposed to the kinetics of two reactions processes.The main research contents include two aspects as follows.A comparative kinetics study of K2CO3-catalysed steam gasification of biomass char has been conducted in a vertical blown reactor(VBR)and a horizontal boat reactor(HBR).A characteristic difference of VBR from HBR was that the steam stream passed through the sample grain bed with a high flow velocity in the former reactor,resulting in an accelerated external mass transfer.It was found that the mean gasification rate obtained in VBR is 2.0-2.8 times as high as that from HBR at a comparable condition.The activation energies obtained in VBR decreased with increasing carbon conversion,while those obtained in HBR showed an increase trend.These results are attributed to the different effects of external diffusion limitations in two types of reactors.A modified random pore model(MRPM)was found to be fit to the profiles of rate versus carbon conversion obtained from both reactors,but with distinct differences in the kinetic parameters.The physico-chemical properties and catalytic activities of two sulfur-tolerant WGS catalysts,RM and TD,have been studied.Furthermore,a kinetic model of RM has been established.It was found that the BET surface area of TD was larger than that of RM.However,the mechanical strength of TD was inferior relative to that of the other one.The results of activity test showed that the catalytic activity of RM and TD increase with the increasing temperature,pressure or space velocity,but when it came to the molar ratio of steam/gas(S/G),the activity of both catalysts showed an increase trend with the increasing S/G at early stage and reached a maximum at S/G=1,then declined thereafter.In all above experiments,the activity of TD was superior to that of RM.A kinetic model was established for RM under the condition that the concentration of CO2 was 15%and the concentration of H2 was 15%:rco =4.28 × 10-23e-62.6/RTPCP2.77PH2O5.08(1-β).The results of mathematical analysis proved the kinetic model to be highly significant and reliable.