Research On Biomass Staged Gasification Characteristics In A Dual Circulated Fluidized Bed

China is a big country that consumes a large quantity of energy,in addition a substantial proportion of the energy is the fossil energy in the energy structure,so our country faces the huge pressure of CO2 emission reduction.Biomass energy is a kind of carbon-neutral energy that comes from solar energy,and has the advantages of renewable property and low-carbon environmental protection.China produces a large number of agricultural and forestry wastes every year,however most of which are abandoned or directly burned in the open air,thereby wasting resources and energies.It also causes environmental pollution and endangers people's health.In order to solve this problem,Zhejiang University developed the biomass dual fluidized bed gasification technology,the main features of this process is that combustion furnace combust gasification char to provide the heat of gasification,gasification furnace uses synthesis gas as the fluidizing medium,calcium oxide is used to reduce the tar in gasification furnace.Therefore,the key parameters of this technology were studied in terms of simulation and experiment,in order to provide guidance for future engineering practice.The biomass dual fluidized bed gasification model was established by using Aspen Plus software.Under the condition that the combustion furnace temperature is 930? and the air excess coefficient is 1.1,three operating conditions at the gasification temperature of 750,800,850? were simulated.And the energy balance of each condition was analyzed.And the effects of gasification temperature and biomass moisture on the syngas composition and yield were also analyzed.The simulation results show that in order to increase the gasification temperature,more char should be transferred into combusition furnace.With the increase of gasification temperature,the yield of syngas decreases,the sensible heat of syngas increases,the chemical heat of syngas decreases,and the concentration of H2 and CO2 in the syngas increases,the concentration of CO and CH4 decreased.With the increase of biomass moisture,the yield of syngas and the conversion rate of water decreased.Cassava straw high-temperature pyrolysis experiments with different amount(0,5%,10%,20%)of calcium oxide were carried out in a experimental fluidized bed,under the temperature range from 700 ? to 850 ?.And using GC—MS to analyze the components of tar,using FTIR to analyze the functional groups of char.The results show that,calcium oxide can fix a few oxygen-containing functional groups in the char,thus the yield of char is increased;At the same time,the yield of tar is decreased with the addition of calcium oxide,calcium oxide can reduce the amount of oxygen-containing functional groups in the tar,it also promotes the condensation polymerization reaction.The addition of calcium oxide can apparently raise the yield of H2,reduce the yield of CO2 and CO,and improve the quality of pyrolysis gas.The gasification experiment of cassava stalk in the syngas atmosphere was also carried out in a experimental fluidized bed gasification at temperature range of 700 ?to 850 ?.The experimental results were compared with the nitrogen atmosphere.The results showed that the syngas atmosphere promoted the formation of tar and water compared with the nitrogen atmosphere.The syngas atmosphere promoted the formation of H2 and CO and inhibited the production of CH4 and CO2.In the syngas atmosphere,the effect of calcium oxide on the pyrolysis product characteristic is the same as that in the nitrogen atmosphere.