The fate of fluorine and chlorine during thermal treatment of coals.

Release behaviors of fluorine and chlorine during thermal treatments of two Chinese coals, DT and JC, were studied in a quartz tube reactor. The thermal treatments included temperature programmed decomposition (TPD, 300-1000 degrees C) in N2 and gasification (800-1100 degrees C) under a H2O or CO2 atmosphere. The TPD results show that F and Cl in the two coals can be classified into three forms of occurrence, evolving in three temperature ranges, 150350 degrees C, 350-750 dgrees C, and >870 degrees C. Fluorine in the coals is significantly more stable than Cl during the TPD process. Both elements in DT coal are more volatile than that in JC coal, which may be attributed to coexisting F or Cl salts with minerals in JC coal. Gasification under a H2O or CO2 atmosphere may promote the release of F and CI. The promotion effect is more significant in a H2O steam, which is due possibly to reactions of H2O with F and Cl salts in the coals. For both coals, the release ratios are close to 94% for F and 98% for Cl at 1000 degrees C in a H2O steam. Under these conditions, the difference in release ability of F and Cl from the two coals diminishes. No clear correlation can be found between the release ratio of F or Cl with the corresponding volatile yield of the coals.