Study On The Gasification Of Biomass-molded Fuel In Fluidized Bed And The Synergistic Effect Of Co-combustion Of Coke And Coal

The biomass agricultural and forestry wastes produced in China each year occupy the first place in the world.Coal-fired coupled biomass gasification power generation sends syngas generated by biomass gasification to a coal-fired boiler for auxiliary combustion.It is a technology that can deal with biomass on a large scale and has higher power generation efficiency compared with biomass direct combustion power generation.This kind of indirect mixed combustion power generation technology has been listed as a new industry encouraged by the state.At present,there are some engineering cases.Molding technology will improve the quality of biomass energy,but will change its components.At present,there are few reports on the gasification and slagging characteristics of briquetted biomass-molded fuel in fluidized bed.A large amount of coke will be produced in the gasification process,and the research on its large-scale utilization is insufficient.If the gasification of biomass-molded fuel can be efficiently utilized and the gasification coke can be treated on a large scale,the utilization prospect of coal-fired coupling biomass gasification technology will be widened.In this paper,formed eucalyptus bark and formed corn straw were used,and rice husk and sawdust were selected for comparison.Fluidization and gasification test in pilot scale fluidized bed.Using pressure sensor,temperature sensor and gas analyzer to monitor furnace working condition and gasification characteristics.Analysis of slagging characteristics by XRD,XRF,EPMA and other instruments.The characteristics and yield of gasified coke were analyzed.The results show that the crushing is beneficial to the feeding of the auger in the gasification test,but the crushing after forming will make the particle size distribution uneven and the fluidization unstable.The forming process has little influence on the gasification effect,and the ash content and water content are the main factors affecting the gasification.The best Er value of formed eucalyptus bark,rice husk and sawdust is 0.2,the calorific value of syngas is 5.5 MJ/m~3,5.5 MJ/m~3and 6 MJ/m~3 respectively,and the gasification efficiency is 60%,45%and 52%respectively.Due to the high ash content and low calorific value,the molding corn straw needs more air,the best Er value is 0.24,the calorific value of syngas is4 MJ/m~3,and the gasification efficiency is 35%.The increase of temperature promotes the gasification reaction,and the increase of primary air temperature has no obvious effect on the furnace,but it will greatly increase the furnace bottom temperature and affect the equipment safety.biomass-molded fuel is easier to produce slagging in gasification,because it contains more ash,alkali metal and alkaline earth metal.The main reason of slagging is that K and Mg are concentrated in the bed material to form low melting point molten salt and to bond the quartz sand bed material.High density and ash content make coke yield and energy yield higher.The gasified semi coke is called EBC,CSC,RHC and SC respectively.The chemical composition,pore structure and surface morphology were studied by XRF,bet and SEM,and the combustion characteristics and reaction kinetics were studied by TGA.The results show that the forming and compression process will not obviously destroy the carbon skeleton structure of gasified coke,but will mix more impurities in the pores.The pore volume and comparative area of the four kinds of gasified coke are significantly smaller than that of the same kind of pyrolysis coke,which is not suitable for use as adsorbent.With the increase of ash content,the combustion peak of gasified coke gradually moves to the high temperature region.SC and EBC are dominated by volatile combustion,while RHC and CSC are dominated by coke combustion.The comprehensive combustion characteristic index of SC is 40 times that of RHC and CSC,and its combustion characteristic is the best,followed by EBC.Ash content has a significant effect on the reaction kinetics and combustion mechanism of gasified coke.With the increase of ash content,the combustion mechanism changed from the first-order chemical reaction model to the third-order diffusion reaction model,and the activation energy gradually increased,in the order of CSC>RHC>EBC>SC.The combustion characteristics and reaction mechanism of the mixture of gasified coke and pulverized coal were studied by TGA.Qualitative and quantitative methods were used to evaluate the synergism,and the mechanism of catalysis and non catalysis in synergism was differentiated quantitatively.The results show that the mixture of EBC and SC can improve the combustion characteristics of the pulverized coal,while the mixture of CSC and RHC is opposite.The catalytic mechanism of minerals and the non catalytic mechanism of volatile matter play an important role in promoting the positive synergistic effect,while the ash plays an inhibitory role.When the blending ratio of EBC is more than 15%,the contribution of catalysis to synergism will not increase any more.With the increase of the blending ratio,the activation energy of the mixture decreases.The third-order diffusion model is the most effective reaction mechanism between the end coal and RHC,EBC,CSC in various mixing ratios.When SC is mixed,the first-order chemical reaction is dominant in high proportion,and the second-order chemical reaction is dominant in 50%and below.