Chlorine Release during Fixed-Bed Gasification of Coal Chars with Carbon Dioxide

CO2 gasification of two kinds of coal chars has been carried out using a fixed-bed quartz reactor mainly at 0.1 MPa and 1000 degrees C to investigate the behavior of chlorine release during char gasification. For this purpose, an Indonesian subbituminous coal or an American bituminous coal is first pyrolyzed at 400 degrees C/min up to 1000 degrees C, and the resulting char is gasified in situ at 1000 degrees C with 50 vol % CO2. The Cl contents of the sub-bituminous and bituminous coal chars are 310 and 1300 mu g/g-dry, respectively. Conversion of the Cl to gas species increases with increasing char conversion, and there is an almost 1:1 linear relationship between the two. Chlorine distribution depends strongly on char conversion: yield of water-soluble Cl species increases significantly with increasing conversion up to approximately 50 mass %-daf and then levels off, whereas that of water-insoluble Cl increases more remarkably at the latter stage of the gasification. No measurable amounts of Cl-2 are detectable, irrespective of the extent of char conversion, but HCl can be detected significantly. The temperature-programmed desorption run of an activated carbon sorbent recovered after gasification also shows that most of the water-insoluble Cl is thermally stable even at a high temperature of 1000 degrees C. The formation of water-insoluble Cl-functional groups is discussed mainly on the basis of the results of some model experiments and subsequent Cl 2p XPS measurements.