Changdong Sheng

Comparison of sulphur retention by coal ash in different types of combustors

During coal combustion, a part of the total sulphur in coal will be retained as solid compounds in ash. In the present paper, the retention of sulphur by ash of typical Chinese coal used for electric power generation was correlated with the contents of alkaline elements relative to sulphur in the parent coal. Comparison was performed among the capabilities of sulphur retention by coal ashes in laboratory ashing procedure, pulverised coal-fired combustor and fluidised bed combustor (FBC). It was shown that calcium plays a dominant role in sulphur retention of laboratory-prepared ash and the sulphur retention percentage increases with the increase of Ca/S molar ratio of the parent coal, while the contributions of other elements are limited. The sulphur retention behaviour in pulverised coal-fired combustor is significantly different from that in laboratory ashing procedure. The contribution of calcium is reduced markedly, while the roles of the other alkaline elements are obviously enhanced. Using the literature data from foreign coals, it was found that the sulphur retention in FBC is comparable with that in laboratory ashing procedure. It was suggested from the results obtained in this study that the sulphur retention of laboratory-prepared ash can be applied to fluidised bed combustion because the behaviour of calcium is similar to that of lime in FBC.

Characterization of coals utilized in power stations of China

Abstract The petrographic composition of 21 types of typical Chinese coals obtained directly from the power stations was analyzed. The vitrinite reflectograms of them were measured and shows an obvious difference from that of single rank coals, which suggests that the coals utilized in the power stations have the characterization of a blended coal in terms of coal rank. The index S M has been developed to describe the occurrence of mineral in the coals and the results show quite a difference in the occurrence of the mineral for the coals studied. The petrographic constituents of different size fractions were analyzed for three coals and showed little systematic change with the particle size, but revealed the trend that the large particles contained much more of the higher rank coal and the small particles contained much more of the low rank coal.

Derivation of Low-temperature Coal Oxidation Kinetics from Non-steady Heat Generation Rate Measured by Isothermal Calorimetry

The present work aimed at developing isothermal calorimetric technique for kinetics analysis of low-temperature coal oxidation, based on non-steady heat generation rate measured by using sealed vessels in the calorimeter. Isothermal calorimetric analyses on the oxidation of two coals were conducted at five incremental temperatures of 30–70 °C. The measured heat generation rates versus time were interpreted by fitting with simple kinetic models. The results showed the first-order kinetics fairly well representing the heat evolution after early hours (~12 h) of the reaction while Elovich equation roughly following the heat evolution at the early stage. Empirical expressions, considering the overall oxidation as two reaction pathways, chemisorption and first-order direct burn-off reaction, can describe the heat evolution over entire process. While fitting with empirical expressions provides little kinetic information, fitting the measured heat generation rate after early hours with the first-order kinetics yields the apparent kinetic parameters and the heat of reaction of low-temperature coal oxidation. The parameters are valuable for using simple kinetic model to evaluate or numerically simulate the self-heating of coals in terms of engineering applications.