A Study On Different Pretreatment Methods For Preventing Coal Slagging

Studies have shown that ash-related issues can be handled either by pre-treatment or by addition of certain additives to the coal. Researchers lately believe that minerals in coal play a major role in the ash fusion characteristics. Mineralogy investigators observe that coal shows higher AFT and low slagging propensities with the existence of mullite in ash deposition,.This paper reports changes and reactions in mineral species in ash, and presents different ways of pre-treatments in generating more mullite and preventing slagging. Experiments compare blending coals, washed coals and coals with additives to explore effective methods to weaken slagging propensities.14 coals from different geological areas of China are selected as samples. The additives are coal gangue (rich in kaolinite), kaolinite, bauxite, y-Al2O3. Ash samples are heated in the muffle furnace under closely controlled conditions in the range of 900-1400℃. Samples are examined by quantitive X-ray diffraction to determine the content of mullite, other minerals and amorphous phases. SEM observes the morphology of slag. This paper regards AFT as criterion to estimate slagging propensities. Results show as bellow:By blending coals in accordance with systematic investigation of ash constituents, the performance of slagging of blended coal could be superior to low-rank coals.Washed coals show the best performance among all methods, it removes impurities and surface ash and makes ash fusion temperature (AFT) and mullite both increased obviously.Ash+y-Al2O3 samples show the highest contents of mullite, raised AFT and the lowest amorphous content; ash+kaolinte samples show high contents of mullite, but some amorphous phases; ash+bauxite samples show little mullite increasing but much corundum and high AFT. Mullite is also included as an additive to gauge the results of the above methods, but AFT decreased and much glass generated. There are no such cases in coal mixtures with bauxite, kaolin and diaspore. The reason is, the inherent amorphous SiO2 involved in the generation of mullite, the decrease of input material reduces eutectic melting. Present experimental observations are of practical significance to power utilities.