Effect of filter media on gaseous tar reaction during low-rank coal pyrolysis

When a granular bed filter is used for the dust removal of hot gas containing tar from low-rank coal pyrolysis, the filter media will affect the reaction behavior of gaseous tar to a certain extent. Four granular bed filter media including ceramic ball (CB), expanded perlite (EP), activated carbon (AC) and γ-Al₂O₃, were selected to investigate their influence on the gaseous tar reaction during Naomaohu long-flame coal pyrolysis in a downer-bed pyrolysis reactor. The results indicate that the distribution and compositions of pyrolysis products and the coke deposition behavior are significantly affected by the filter media. The inert CB and EP increase the residence time of gaseous tar, which intensifies the cracking and polycondensation reactions of gaseous tar, resulting in a reduction in the tar yield and an increase in the gas, water and coke yield. In the meantime, the pitch content in tar is increased due to the polycondensation reactions of gaseous tar, while the chemical composition of tar and the amount of coke in tar have less change. The AC and γ-Al₂O₃, which have a strong catalytic cracking action, reduce the pitch content and the amount of coke in tar. Also, partial gaseous tar is transformed into gas, water and coke, resulting in an obvious reduction in the tar yield. Also, AC and γ-Al₂O₃ can crack some oxygen-containing compounds and nitrogen-containing or sulfur-containing heterocycles in the gaseous tar into aromatics.