Study On Thermal Conversion Model Of Biomass Particles

It is of great significance for reducing environmental pollution and carbon emissions to use biomass energy rational.In this paper,the numerical calculation of the pyrolysis process of herbaceous biomass particles and the gasification process of semi-coke particles were carried out,and the criterion number of semi-coke gasification were analyzed.The main conclusions are as follows:?1?When the pyrolysis starts for 0.5s,the maximum concentration of volatiles in the particles is 4.5%at 0.85r_p;At the beginning of pyrolysis for 0.9s,the maximum concentration of volatiles in the particles was 9%at 0.65 r_p.In the early stage of pyrolysis of biomass particles,with the passage of time,the concentration of volatiles in the particles gradually increased,and the reaction position gradually deepened.And as the particle size decreases and the final temperature increases,the heating rate and pyrolysis reaction rate increase.?2?In the pyrolysis process of biomass particles,the effect of mass transfer coefficient is smaller than the effective diffusion coefficient.Therefore,during the transfer of volatiles to the particles,the reaction rate is mainly controlled by the diffusion process of volatiles in the ash layer.?3?During the gasification of biomass semi-coke particles,the closer to the center of the particle,the longer the gasification reaction rate is controlled by the CO₂ diffusion process;And as the particle size decreases and the gas phase ambient temperature increases,the semi-coke gasification reaction time becomes shorter.?4?At a gasification temperature of 1123K,when the radius is between 0.1mm and2mm,the internal diffusion resistance of the biomass semi-coke particles is greater than that of the outside.When the particle radius is less than 0.26mm,the reaction speed of the semi-coke gasification process is mainly controlled by the chemical reaction process;When the particle radius is in the range of 0.26mm-1.45mm,the reaction speed of the semi-coke gasification process is jointly controlled by the chemical reaction process and the CO₂ diffusion process;When the particle radius is greater than 1.45mm,the reaction rate of the semi-coke gasification is mainly controlled by the CO₂ diffusion process.?5?For biomass semi-coke particles with a radius of 1mm,when the gasification temperature is between 973K-1223K,with the increase of temperature,the influence of CO₂ diffusion process on the reaction rate gradually increases,And the internal diffusion resistance is greater than the external one;When the temperature exceeds 1223K,the CO₂ diffusion process becomes the main controlling factor of the semi-coke gasification reaction rate.