Behavior of coal chlorine in cokemaking process

The behavior of coal chlorine in metallurgical cokemaking process was investigated. Various coals were carbonized (heat-treated) in a nitrogen atmosphere and the ratio of the chlorine in the heat-treated sample to that in the coal was defined as the chlorine residue ratio. The release of chlorine from coal during carbonization is a slow process and the chlorine residue ratio decreased with increasing the heat-treatment temperature, increasing the soaking time, and decreasing the heating rate. It increased with increasing the Ca content in coal and with an addition of CaO. This is because chlorine in coal is released as HCl, which is trapped in coke again in the form of CaCl2. The chlorine residue ratio of coke produced in an actual coke oven was higher than that of coke produced in a laboratory scale tube furnace. This is because released gas from coal has more chances to contact with calcium in the actual coke oven than in the tube furnace. Moreover, the removal of chlorine from NaCl was promoted by the co-carbonization of NaCl with coal, which implies that H2O derived from coal decomposition may help chlorine to be released.

Research highlights
► The release of chlorine from coal during carbonization is a slow process.
► The chlorine residue ratio decreased with increasing the heat treatment temperature.
► It increased with increasing the Ca content in coal and with an addition of CaO.