Regulation Of Heat And Mass Transfer During The Organic Solid Waste Pyrolysis Process

Gasification is currently one of the most important technologies for the utilization of organic solid waste raw materials.However,the low energy density,high water content and high volatile content of organic solid waste leads to high tar content in the gas produced by gasification and there are many problems with the subsequent use of gas produced by gasification.Pyrolysis is the initial stage of organic solid waste gasification and the main stage of volatile release.Therefore,the release of volatile during the pyrolysis of organic solid waste is investigated in order to achieve effective suppression of volatile release during the reaction process and to reduce the tar content in the gas produced by gasification.This paper models the pyrolysis process of pine sawdust particles,in the model,the secondary pyrolysis reaction of tar and mass and momentum transfer process of volatiles in particle pores are considered,and the flow phenomenon of volatiles in the particle pores is simulated.The internal temperature,pressure and composition of the pyrolysis product of the particles were obtained with time and temperature.The mechanisms of endothermic reaction during particle pyrolysis and convective heat transfer as volatiles escape on particle temperature are obtained,and the effects of particle size and pyrolysis temperature on particle pyrolysis are investigated.However,due to the wide range of sources of organic solid waste and the large variation in physical properties and chemical composition of the materials,the model was further modified to improve its applicability.The modified model was used to study the heat/mass transfer laws of pine sawdust,corn stover and furfural residue during the pyrolysis.The main findings and conclusions are as follows:(1)The relationship between thermal cleavage and heat transfer of raw material macromolecules during the pyrolysis of pine sawdust particles is divided into three main intervals.Below 500 K,the absorption of heat from cracking is superimposed on the heat transfer hindrance of the particles and the reaction rate is linearly and positively correlated with temperature.In the 500 ～ 750 K,the temperature inside and outside the particle is essentially the same,the reaction rate and the amount of product are only related to the amount of reaction material,and the reaction rate remains constant.After greater than 750 K,the volatile escape ends,the degree of condensation reaction of the particles increases significantly,and the gas and cracking liquid show a clear reciprocal relationship in yield,with an increase in the amount of gas product and a decrease in the amount of liquid product.The control of the pyrolysis process by heat transfer and reaction kinetics also takes a reciprocal form in the particle radial direction.(2)The time required for complete precipitation of volatile decreases with increasing instantaneous heat flux from the particle surface,with a significant negative linear correlation between the two.Therefore,in order to increase the raw material carbon conversion rate and ensure sufficient product volume,the pyrolysis temperature can be appropriately increased when the conditions permit,increasing the temperature difference between the surface of the particles and the environment when the low energy density material is pyrolyzed.Or add internal components with high thermal conductivity to the fixed bed reactor to increase the instantaneous heat flux on the particle surface and achieve enhanced reactions through the enhancement of heat transfer on the particle surface.(3)The modified model has a wide applicability to simulate the pyrolysis of raw materials such as pine sawdust particles,corn straw and furfural residues using multi-step kinetics through the elemental and chemical composition of the raw materials.