Experimental Research And Establishment Of A Mathematic Model For Biomass Gasification In A Dual Fluidized Bed

Bio-energy is renewable and with less pollution, and is an importantform of the new energy which is under great attention in the21stcentury.Fluidized bed gasification, especially dual fluidized bed gasification applyto relatively larger-scale gasification programs, are the key technical supportfor the spreading of biomass gasification power generation which is one ofthe common techniques for bio-energy utilization. This thesis presents anovel dual fluidized bed gasification system for a biomass gasificationpower generation project by the experimental study in a fluidized bed forbiomass steam gasification and the establishment of a mathematic model fordual fluidized bed gasification.At first, a fluidized bed gasifier system was built. The gasificationperformance in different conditions was investigated. Medium calorificsyngas with34vol%H2content and no more than20g/Nm3tar content couldbe obtained under800℃with S/B（Steam/Biomass） ratio at0.9andolivine as the bed material. The results indicate that under experimentalconditions, syngas quality (including H2content, gasification efficiency,reduction of tar, and so on) is in positive correlation with temperature andS/B, the optimum S/B was suggested at0.9~1.0; Syngas quality is innegative correlation with fluidized number, no more than1.4was suggestedfor fluidization number; Olivine is more suitable for fluidized bed comparedwith quartz sand and dolomite because it’s catalytic and also of resistance toabrasion.Using the thermochemical equilibrium principle, a primary model fordual fluidized bed gasification was established by introducing presetting the amount of residual char and Newton–Raphson method. The simulationresults agree with that from the model built in Aspen Plus by otherresearchers, however, don’t agree with most experimental research dates,which means that the model needs a modification.Based on mass balance, chemical equilibrium and the experimentaldates, a modified model for single fluidized bed gasifier was built by usingthe fitting formula between temperature and efficiency of carbon conversion,and innovatively introducing correction coefficients λ1, λ2of the equilibriumconstants and correction coefficients λ3, λ4of the carbon balance andhydrogen balance. The results from this model are in good agreement withthe current experimental results.The primary model was modified by using the above-mentionedmodifying mode to get a modified model for dual fluidized bed gasificationwhich is able to predict the working condition for a special dual fluidizedbed gasification system. A design scheme for a dual fluidized bed gasifier ina6MW biomass gasification power generation system was obtained basedon the experimental results and the modified model for dual fluidized bedgasifier: temperature=818℃, S/B=0.9, steam inlet temperature=500℃,steam velocity in the gasifier=0.74m/s, recirculation of bed material=25.4.In this working condition, syngas with11.7MJ/Nm3and38.5vol%H2content could be obtained, and the gasification efficiency is higher than50%.On the basis of this, a novel dual fluidized bed gasification system for theproject was designed, and three new techniques including dolomite catalyticlayer, local region with high-temperature, tri-bed structure were proposed.