Simulation Of Corn Straw Internal Circulating Fluidized Bed Gasification Based On CPFD Method

With the increasing demand for energy,biomass energy as a renewable energy has attracted more and more attention.As a large agricultural country,China has abundant corn straw production.Improving its utilization efficiency is very important to increase the market competitiveness of corn straw.It is an efficient and clean way to use corn straw for fluidized bed gasification.In this paper,based on the computational particle fluid dynamics（Computational Particle Fluid Dynamics）method,the Barracuda simulation software was used to simulate the flow and the gasification characteristics of corn straw in a laboratory-scale internal circulating fluidized bed.The generation of gas products was discussed,and the effects of different conditions on the gasification characteristics of corn straw in the internal circulating fluidized bed were studied.This topic can provide theoretical guidance for the study of corn straw gasification in the internal circulating fluidized bed.Firstly,a full-scale mathematical model is established for a laboratory-scale internal circulating fluidized bed.The Euler-Lagrangian method is used to study the gas-solid flow characteristics of the internal circulating fluidized bed.On the basis of completing the grid independence verification,the material layer resistance characteristics,particle velocity distribution,particle volume fraction distribution and particle size distribution of the internal circulating fluidized bed are studied,and the internal circulation mechanism of the internal circulating fluidized bed is mastered.Secondly,based on the study of gas-solid flow characteristics of internal circulating fluidized bed,the gasification process of corn straw was simulated by adding relevant chemical reaction models.The accuracy of the model is verified by comparing the simulated data with the measured data.The simulation results are analyzed,and the distribution characteristics of the temperature in the internal circulating fluidized bed furnace and the distribution characteristics of each gas component are obtained.The results show that the gas temperature decreases slightly with the increase of the furnace height,and near the feed port,due to the occurrence of combustion reaction,the gas temperature has a peak value.The maximum molar fraction of CO₂in the syngas appears in the dense phase zone at the lower part of the furnace.The maximum molar fraction of CO,CH₄ and H₂ in the syngas appears near the middle and upper part of the furnace.Finally,the formation of gas products under different conditions and the influence of different conditions on various gasification indexes were studied with air-water vapor as gasification agent.The results show that increasing the gasification temperature will increase the content of hydrogen and carbon monoxide in the syngas,and increase the low calorific value LHV,cold gas efficiency and carbon conversion rate of the syngas.The increase of corn stalk particle size is not conducive to the gasification reaction.The molar fraction of combustible gas in the syngas decreases,and the LHV,cold gas efficiency and carbon conversion rate of the syngas also decrease.Increasing the content of water vapor in the gasification agent will increase the molar fraction of hydrogen in the syngas,slightly reduce the LHV of the syngas,and increase the cold gas efficiency and carbon conversion rate.However,the introduction of excessive water vapor will reduce the temperature in the furnace and adversely affect the gasification reaction.When the air equivalence ratio ER increases appropriately,the combustible gas composition in the syngas increases,and the LHV and cold gas efficiency of the syngas reach the maximum value.When the air equivalence ratio continues to increase,the LHV and cold gas efficiency of the syngas begin to decrease,indicating that there is an optimal value of the air equivalence ratio.When the air equivalence ratio continues to increase,the reaction in the furnace tends to burn.