A literature review of formation and release of PCDD/Fs from gas manufacturing: A previously unidentified source?

The requirements commonly accepted as requisite for PCDD/F formation in thermal processes of coal and coke (presence of carbon, chlorine, metal catalysts, and adequate temperature) were also found to exist in several places within the gas manufacturing process. The coal and coke used in gas manufacturing typically contained up to about 95% carbon and 0.1% chlorine, which, at the operating temperatures seen in most older, carburetted water gas units, were sufficient for chlorination reactions to occur. Reactor conditions also suggest that PCDD/Fs could be formed during the gas generating process as well as in the waste streams. The gas generating unit has a welt-defined temperature profile with maximum temperatures of 1000°C occurring within the bottom of the charge. PCDD/F formation could occur in the upper cooler zone (possibly associated with fly ash) near the gas exit. In addition, PCDD/F formation could occur where residence times are longer such as the fly ash outlet and bottom ash outlets.