External Circulating Countercurrent Moving Bed Biomass Gasification For Hydrogen

In this thesis,a novel process of catalytic gasification of biomass with solid heat carrier is proposed,which is called External Circulating Countercurrent Moving-Bed(ECCMBⅢ) gasification system.It was used to reduce tar content and improve hydrogen yield in product gas,and keep the energy balance.The ECCMBⅢsystem is composed of three reactors,a gas-solid countercurrent moving-bed gasifier,a pyrolyzer and a riser-type combustor,and the gases are completed separated in the three reactors.A circulation loop of bed material is achieved through the three reactors.The circulating bed material acts as not only solid heat carrier from the combustor to the gasifier,which supplies the required energy of gasification reactions of biomass,but also catalyst in tar reduction.Rapid pyrolysis of biomass in the pyrolyzer,catalytic reforming of tar in the gasifier continuously occurs.A dry gas with low tar content and high hydrogen content should be obtained in the process.In the combustor, reheating of solid heat carrier and regenerated catalyst are made by burning off the residual char and coke on catalyst.At the same time,the highest yield of hydrogen can be obtained from biomass.During the process,fast pyrolysis of biomass,reforming of tar,heating of solid carrier and catalyst regeneration occur simultaneously and continuously.Based on supplying energy by burning off the residual char and coke on catalyst,it is possible to transform the hydrogen in biomass into hydrogen gas.In this paper,using the legume straw,mass balances and thermodynamic equilibrium calculations of ECCMBⅢsystem were calculated,the composition and yield of product gas and information of heat utilization initially obtained,as well as the operation parameters of controlling the balance.It was feasible to keep heat balance of ECCMBⅢby controlling the carbon conversion efficiency,and for the system,a wide range of feedstock can be gasify in a stable state of mass and energy balance.A lab-scale facility of external circulating countercurrent moving-bed(ECCMBⅢ) biomass gasification for hydrogen was designed and established based on the balance calculation and the existing experimental device.Structure rationality and operation performances of this system were investigated by a series of cold tests.Feed rate of different biomass,heat carrier circulation volume,pressure drop of riser reactor(combustor),residence time of heat carrier in riser reactor and the wear of heat carrier were determinate。In these experiments,pressure drop of riser reactor varies proportional to the air volume,and in inverse proportion to the heat carrier circulation volume, wear of heat carrier was proportional to the heat carrier circulation volume,when the circulation time was extended to 120min,it tended to a stable number.By in a series of preliminary hot tests,temperature stability of the ECCMBⅢsystem balance of pressure and regeneration of heat carrier were investigated to study the performance parameters.In experiments,temperature of ECCMBⅢsystem can reach their desired value and keep stable in 120min after beginning of experiment,using heat carrier as material sealing prevent the gas flow from combustor to pyrolyzer and gasifier,char and semi-coke can be combusted completely after combustor,regeneration effect of heat carrier is good.