Ash Sintering Research Articles

The behaviour of chlorine in Kentucky and Illinois coals during combustion and its effects on ash deposits

Ash deposition tests were performed in a laboratory-scale, pulverized coal combustor with four different coals. These four coals, Kentucky No. 9, Kentucky No. 11, Illinois No. 5 and Illinois No. 6 had chlorine contents of 0.18, 0.10, 0.42 and 0.36 wt%, respectively. Five repetitive, 1 h firings were performed for each coal at a coal feed rate of 11 kg h −1. Ash samples were obtained from simulated waterwall and superheater probes, from an exhaust cyclone, and from a water-quenched char sample probe. Chlorine was found to release quickly from the coal to the gas phase. The amount of gas phase chlorine that concentrated on the ash collection surfaces was inversely dependent upon the temperature of the collection surface. The chlorine conversion rate from the char was equal to the carbon conversion rate for levels above 65%. Ash fusion temperature, ash sintering temperature, emittance, thermal conductivity, shear strength and compressive strength measurements, which were performed on samples from the waterwall and superheater probes showed no observable differences among the four coals tested. Obvious corrosion of the stainless steel test surfaces was observed during the combustion tests with the Illinois coals. The l h firings were too short for many of the physical properties of the ash deposits to reflect the influence of metal corrosion. Emittance, ash sintering temperature, compressive strength and shear strength of ash deposits were dependent on sample location.

石炭チャー燃焼時における粒子内温度と，石炭灰のガラス化，焼結に伴う灰中の鉱物質の挙動

石炭チャー燃焼時における粒子内温度と，石炭灰のガラス化，焼結に伴う灰中の鉱物質の挙動

Studies of sintering of coal ash relevant to pulverized coal utility boilers: 1. Examination of the Raask shrinkage—electrical resistance method

The Raask shrinkage and electrical resistance method for determining the onset of sintering of fly ash has been tested on a soda lime glass, coal ASTM ashes, fly ashes and pulverized synthetic mineral mixtures. Results with the glass confirmed those of Raask and showed that particle size distribution and bulk density affected the resistance values: the sinter point was indicated by a change in the characteristic temperature coefficient of resistance. The shrinkage and electrical sinter points were usually the same, but a high Na content lignite gave 850°C for shrinkage but 600°C for characteristic resistance change. Sinter points were 200°C less for fly ash than for ASTM ash. The fly ashes had a slight enrichment of alkalies and a decrease in Fe content compared to the total ash. Holding a compact at a temperature above the sinter point gave increased strength and shrinkage, but no decrease in electrical resistance, indicating that the decrease in resistance as temperature increased was due to the establishment of contact points between particles, with little effect of the continued growth of a contact neck. Addition of pulverized sodium silicate or iron silicate glasses to a synthetic ash also reduced the sinter points, as did alkali additions, whereas addition of pyrite did not. It was concluded that the method was a valuable tool, but sources of variability had to be determined and controlled.

Some recent developments in the lime-fly ash process for alumina and cement

Recent developments from research of the limestone-fly ash sinter process for the extraction of alumina from coal fly ash and use of the residue in the manufacture of portland cement may result in substantial reductions in processing costs. It has been found that cement kiln dust can be used in place of limestone, and that the addition of coal refuse to the sinter mixture will increase alumina recovery and reduce kiln temperatures. The soluble compound formed in the sintering reactions has been identified through use of XRD methods as calcium sulfoaluminate (C 4A 3S). Compound formation conditions have been determined for a range of sinter compositions. In other work, a systematic investigation of minor additives to sinter compositions has resulted in the determination of a group of ions which, when present in sintered material, will prevent the auto-disintegration (dusting) upon cooling of the clinker formed. Several ions, even at very low concentrations, can enter the lattice of the minor sinter compound, calcium orthosilicate (C 2S), and inhibit the phase transformation of beta-C 2S to gamma-C 2S and the accompanying lattice expansion that causes clinker disintegration.

Western Coals—Laboratory Characterization and Field Evaluations of Cleaning Requirements

Many discussions have pointed out the differences in the characteristics of eastern and western coals. Low rank western coals have higher moistures, lower calorific values, and the ash constituents are more basic. Slagging and fouling indexes based on the ash chemistry of eastern bituminous coals are not applicable for low rank western coals. These differences led to dissimilarities in the behavior of eastern and western coals, so we have directed our efforts toward a study of the behavior of low rank western coals and how they differ from eastern coals. Three nonroutine laboratory tests: (1) burning profiles, (2) coal ash sintering strengths, and (3) viscosity temperature relationship of coal ash were used to distinquish the difference in the behavior of these coals. Three generating stations were selected to compare slagging and fouling predictions with soot blower performance. The coals burned at these stations were: (1) a North Dakota lignite, (2) a Montana subbituminous coal, and (3) an Illinois bituminous coal. Excellent results were noted as the observed soot blower performance and the performance predicted by our evaluation of the slagging and fouling characteristics of the coals were in agreement.