Research on coal tar catalytic cracking over hot in-situ chars

A comparison of coal tar catalytic cracking over hot char from in-situ coal pyrolysis and cooling char was investigated. The results show that the in-situ char has a higher capability of removing tar than the cooling char under the same reaction conditions. The tar content in the product gas is reduced to as low as 100 mg/m³ when the temperature of the in-situ char bed and the gas residence time in the bed are 1 100 ℃ and 1.2 s, respectively. BET analysis shows that the in-situ char has larger specific surface area and more micro pores than the cooling char, while the uniformity of the carbon crystallite structure in the cooling char increases, causing the decrease of the char's catalytic activity for tar removal. With the increase of gas residence time in the char bed or of cracking temperature, the tar content in the product gas decreases greatly, while the difference of catalytic activity for tar cracking between in-situ char and cooling char also decreases. The activity of the spent char is decreased significantly. However, the activity of the spent char can be basically recovered when it is partially gasified with steam.