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Pyrolysis of 29 coals with carbon contents of 71-92 mass% on a dry, ash-free basis (daf) has been performed mainly in a temperature-programmed mode at 10ºC/min up to 800ºC with a flow-type fixed bed quartz reactor, and some factors controlling HCl formation have been examined. The rate profiles of HCl formation exhibit at least three distinct peaks at around 260-360, 470-510 and 580-630ºC, and the lowest temperature peak is present for 8 coals alone, whereas the middle and highest temperature peaks are common with almost all of the coals. The HCl profile is also affected by the size of coal particles and the height of coal particles in the fixed bed. Yields of HCl and char-Cl at 800ºC for 28 coals except an American bituminous coal are 44-95 and 4-54%, respectively, and tar-Cl is as low as ≤ 7% in all cases. The chlorine distribution is almost independent of the heating rate in the range of 2.5-400ºC/min and has no distinct relationship with carbon or chlorine content in coal, but HCl tends to increase with increasing amount of (Na + 2Ca) in coal with a corresponding decrease in char-Cl. When an Indonesian sub-bituminous coal is injected into an O2-blown entrained bed gasifier under pressure, there is an almost 1:1 relationship between carbon and nitrogen conversions, whereas the sulfur and chlorine are enriched in the remaining char, and the degree of the enrichment is higher with chlorine. The method of evaluating coal-Cl forms quantitatively using model chlorine compounds is proposed.

Temperature-programmed pyrolysis of low-rank coals physically mixed with goethite-rich limonite ore has been studied with a fixed-bed quartz reactor for the purpose of developing a novel coprocessing method for the removal of coal-bound nitrogen and the reduction of goethite. Limonite at loadings of 5–40 mass % promotes the formation of N2 from brown coal at 650–1000 °C and the consequent nitrogen removal, although the effect levels off beyond 20 mass % and thus seems to be limited. X-ray diffraction (XRD) measurements after pyrolysis showed that goethite can readily be reduced to metallic iron (α-Fe), irrespective of the limonite loading and the type of coexisting coal, and that part of the α-Fe reacts with a small amount of carbon to form cementite, a solid solution of iron and carbon. This method might have potential for the simultaneous production of low-nitrogen chars and reduced iron materials by utilizing low-value coals and limonite ores.

The chemical forms of the carbon and chlorine present in dust samples obtained from windboxes of the iron are sintering machine have been studied with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The chlorine in the dust samples is present as KCl with the average crystalline size of 40-50 nm and covalent C-Cl bonds in condensed aromatic structures of unburned carbon surface. The proportion of chlorinated aromatic structures increases almost linearly with increasing that of surface oxygen complexes on unburned carbon, strongly suggesting that active surface sites of the carbon formed in the sintering process work as reaction sites with HCl and Cl2. Model experiments using a coke show that HCl reacts with it at 500°C to form several types of Cl-functional forms, from which the HCl desorption takes place at the wide range of 500-900°C upon reheating. Such a profile for HCl formation is almost unchanged after washing of the HCl-treated coke by water. These observations indicate the formation of organic chlorides. It is therefore likely that HCl and Cl2 evolved in the combustion process react with active sites of unburned carbon surface to form organic chlorine compounds.