Numerical Simulation Of Flow Field And Gasification Process Of Biomass Gasifier

Biomass is a renewable resource with abundant resources and wide distribution.Biomass pyrolysis gasification technology can utilize biomass resources flexibly and efficiently,the development of biomass pyrolysis gasification technology is of great significance to solve the energy crisis,environmental pollution and other issues,as the core component of the pyrolysis gasification system,the research on the flow field and the gasification performance index is of great significance.With the rapid development of computational fluid dynamics,numerical simulation has been widely used in the research of biomass gasification.In this paper a kind of biomass gasifier is used as the research object,and the cold gas phase flow field is simulated by using FLUENT software,the distribution of pressure field and velocity field is obtained,and the reliability of the model is verified by multi-point pressure measurement.The influence of the internal structure of the gasifier on the flow field is analyzed by using the different opening rate of the grid plate and the angle of the swirl plate.The result shows that the airflow in the gasifier mainly presents a spiral upward movement,which has three directions of speed:tangential velocity,axial velocity,radial velocity.Tangential velocity occupies the dominant position,the pressure loss and velocity increase with the increase of flow rate,the tangential velocity in the lower part of the gasifier(Z1= 0.5m)presents a distinct distribution "hump",and the upper part(Z2=0.86m,Z3=1.29m),it is "double" distribution;the axial velocity is "M" shape;grid plate opening rate mainly affects the gasifier pressure,axial velocity and turbulence intensity,and the swirl plate angle mainly affects the distribution of tangential velocity and turbulence intensity.A simplified model of biomass gasifier is built,the effects of steam/biomass mass ratio(S/B),air equivalence ratio(ER),biomass particle size and the inner cylinder depth on the main gasification performance indexes such as gasifier outlet gas components,effective gas(CO+H2),gas calorific value and carbon conversion rate are studied.The result shows that with the increase of steam/biomass mass ratio(S/B),air equivalence ratio(ER),and biomass particle size,the effective gas composition(CO+H2),the calorific value of gas and the carbon conversion rate of the gasifier are decreased.The inner cylinder depth of gasifier has a great influence on the gasification performance,increasing the depth of the inner cylinder gasifier is favorable to the gasification reaction,when the inner cylinder depth of the gasifier is increased from 632mm to 1032mm,the gasifier effective gas mole fraction increases from 33.9%to 47.3%,the gas calorific value increases from 4.14 MJ·Nm-3 to 5.73 MJ·Nm-3,and the carbon conversion rate increases from 62%to 93%.