Performance of expanded perlite as granular bed filtration media: Effect on coal pyrolytic products

Granular bed filtration is considered one of the most promising engineering solutions to the dust removal from high temperature coal pyrolytic vapors. Expanded perlite as filtration media was studied in a lab-scale fixed bed reactor to understand its effect on pyrolysis products. Factors including filtration temperature, filtration time, dust accumulation and regeneration effect were investigated. The results show that there is around 12.9 % reduction in tar yield even under an optimized temperature of 550 °C after filtration bed. Dust accumulation would further promote tar cracking reactions. Coke deposition on the perlite increases with filtration time, which causes further reduction in tar yield. The redox cycle between filtration and regeneration significantly alters the properties of perlite. It is found that carbon deposition on perlite is alleviated in the initial cycles due to the formation of potassium carbonate. And the extent of tar cracking becomes weak. With the cycle numbers further increasing, the situation is inversed. Characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) were applied to explore the mechanisms behind the findings. Potassium and transition metals such as iron contained in perlite may make significant contributions.