Effect of char powder on gaseous tar reaction during low-rank coal pyrolysis

The char powder entrained in gaseous tar influences the reaction of gaseous tar that exists in the transportation pipeline or dust removal equipment, which further affects the distribution and composition of pyrolysis products. This study investigated the effect of char powder on the reaction of gaseous tar during Naomaohu long-flame coal pyrolysis from 400 to 500 ℃ in a two-stage fluidized bed reactor. Results indicated that in addition to its thermal cracking and polycondensation reactions, catalytic cracking reaction of gaseous tar also occurred when char powder was added, resulting in the decrease of tar yield and pitch content, and the increase of pyrolysis gases and coke yield at different reaction temperatures. The thermal cracking and polycondensation reactions of gaseous tar intensified with increasing reaction temperature, which stabilized the gaseous tar and made it difficult to be catalyzed by char powder. Therefore, with the increase of reaction temperature, the influences of char powder on tar yield, tar pitch content and pyrolysis gases yield were reduced. The polycondensation reaction of free radicals from catalytic cracking of gaseous tar was prone to occur with increasing reaction temperature, which enhanced the effect of char powder on coke yield. Also, the catalytic cracking action of char powder reduced the content of heterocyclic compounds in tar at different reaction temperatures, and the reaction between gaseous tar and water was promoted by char powder, resulting in the decrease of aliphatics and aromatics contents in tar, and the increase of phenols and oxygenated compounds contents in tar at different reaction temperatures.