The influence of coal–associated trace elements on sintering and agglomeration of a model coal mineral mixture
A series of experiments was conducted to investigate the potential influence of selected inorganic compounds on sintering and agglomeration of a model mineral mixture. The minerals and inorganic compounds were chosen based on the constituents found in coal. The study simulated ash formation processes in the temperature range of 500 °C to 1000 DC. The mineral mixture consisted of kaolinite, quartz, pyrite, siderite, calcite, Ti02 and magnesite in a fIxed ratio. The mixture was doped with 4% (by weight) of each trace or minor element species. Different analytical methods were employed to investigate the extent of sintering and agglomeration and to identify the possible interactions between the species. Compressive strength measurements, TG/DTA, SEMIEDS and XRD analysis were used to evaluate the interactions in oxidizing and inert atmospheres. The influence of the compounds on the reducing-atmosphere ash fusion temperatures of the mineral mixture was also investigated. The results indicated that NaCl, Na2C03, Ge02, Mn20 3, NbS2, srCo3 and PbS increased sintering in the mineral mixture in the oxidizing atmosphere. Sintering was increased by enhancing sulfation of limestone, and/or by affecting the characteristics of the aluminosilicate phases. Na2C03, Ge02 and Mn2O3 increased sintering of the mineral mixture in the inert atmosphere by affecting the characteristics of the alurninosilicate phases. MOS2 and PbMo04 decreased sintering of the mineral mixture in the oxidizing atmosphere, while CU2S, CuS, PbS and NaCI decreased sintering in the inert atmosphere. The results obtained in oxidizing and inert atmospheres indicated that the oxidation numbers of the cations and the anions associated with the different compounds affected the potential of the additives to influence sintering and agglomeration of the mineral mixture. The influence of the inorganic compounds on the mineral mixture at different ashing temperatures was investigated with the ash fusion temperature test. The results indicated that the ash fusion temperatures were decreased by the addition of GeS and PbC03 at an ashing temperature of 500°C, decreased by SrC03 at an ashing temperature of 815°C, and increased by cr03 at an ashing temperature of 500°C. The results confirm that the addition of trace element compounds can result in the formation of species with lower melting points, and that the ashing temperature has an influence on the ash fusion temperatures.