Simulation of fast pyrolysis process of tar-rich coal based on secondary reaction supplementation

YANG Panxi; GUO Wei; YU Zunyi; WANG Jing; LI Hongqiang; YANG Bolun; WU Zhiqiang

doi:10.13225/j.cnki.jccs.2024.0802

Abstract：Tar-rich coal has the resource attribute of high tar production potential,which matches with the process charac-teristic of high tar yield in fast pyrolysis of pulverized coal.The use of oil-rich coal as the raw material for fast pyrolysis can achieve high tar yield,but still faces the challenge of too much heavy component in tar.The secondary reactions between volatile components is an important factor affecting the quality of fast pyrolysis tar,and an in-depth understand-ing of the mechanism and characteristics of the pyrolysis secondary reaction is a prerequisite and foundation for solving the problem of low tar quality.However,there is a lack of effective kinetic models describing the secondary reactions between gas-phase volatiles within the high-temperature environment as well as application cases coupling them in the simulation of pyrolysis processes in real reactors.Starting from CPD(Chemical Percolation Devolatilization)model,a secondary reaction system was further constructed based on the simplification of the coal molecular structure and the primary reaction network.The secondary reaction involved the interconversion of the internal components of tar and light gas,and the disproportionation of tar to generate gas-solid products.Using a two-dimensional fixed-bed reactor model as a framework,the product evolution in the fast pyrolysis process considering the secondary reaction modification was calcu-lated based on OpenFOAM open source software.The effects of pyrolysis carrier gas temperature,particle size and volat-ile residence time on the pyrolysis product distribution of the tar-rich coal were investigated.The results showed that the pyrolysis kinetic model with secondary reaction modification was able to describe the trend of increasing and then de-creasing tar yield with increasing temperature,and the tar yield reached the highest value of 10.1％at a carrier gas temper-ature of 873 K.The particle size mainly affected the rate of pyrolysis and the residence time of volatiles,which indirectly affected the tar yield and quality.When the particle size was reduced to 48 μm(300 mesh),the tar yield could be further increased to 12.4％.As the residence time was shortened,the degree of secondary reaction decreased,and the total yield and quality of tar was also improved.The tar yield increased by nearly 20.1％,and the proportion of light components in tar increased from 0.621 to 0.677.This results are expected to provide theoretical guidance for the quality control of the tar products from the rapid pyrolysis of tar-rich coal.