Experimental Research On Utilization Of Coal Gangue,Tailings As Clay Mixed With Low-grade Limestone For Cement Clinker Calcinations

China is the largest cement producers in the word. It needs a lot of clay and limestone to manufacture cement. However, the environment has been influenced because clay and limestone have been exploited. A large number of tailings and coal gangue had been accumulated in the field, which not only took up our land, but also threatened our ecological environment. Facing to discover some new raw materials for cement production, and sponsored by the National Key Technologies R&D Program of China in11th-five-year ("key technology research on resource utilization for coal gangue"), this paper has carried out detailed experimental research and theory analysis on utilization of coal gangue, tailings as clay and mixed with low-grade limestone.Experimental research, theory analysis and industrial test are carried out according to the theory of cement clinker calcinations in new dry-process rotary kiln. The experimental research includes:(1) grinding experiment to coal gangue and limestone;(2) physical&chemical characters and thermal decomposition research for coal gangue, limestone and tailings;(3) experimental research of influential factors for cement clinker calcinations;(4) the hydration properties analysis to cement clinker. Theory analysis includes:(1) the model of closed packing and predicting fractal dimension for the distribution of particle sizes;(2) kinetics of thermal decomposition for coal gangue, limestone and tailings;(3) strength prediction models for cement clinker;(4) the formation mechanism on utilization of coal gangue and tailings as clay mixed with low-grade limestone for cement clinker calcinations. At last, some industrial test and efficiency analysis are carried out in the new dry-process rotary kiln on2500tons per day (t/d) and5OOOt/d.The grinding experiment found that the grindability of coal gangue is less than sandstone. The raw meal which is mixed with low-grade limestone has a lower grindability compared to that mixed with high-grade limestone in the initial stage, but has a similar grindability in the last stage. The theory analysis on the modeling of closed packing and predicting fractal dimension to particle sizes also verified the experimental conclusion.The analysis results of physical&chemical characters for coal gangue, limestone and tailings show that coal gangue and tailings are belong to the clay. The heavy metal components of coal gangue is prior to the third class standard of soil and the standard of pollution control on fly ash for agricultural use. The result of their thermal decompensate kinetics found that their activate energy are increased during their thermal decomposition, and activate energy of high-grade limestone is higher than that of low-grade limestone.Experimental research of influential factors for cement clinker calcinations showed that temperature is one of the main factors to the quality of clinker. The temperature of clinker sintering is below the temperature of actual production. Coal gangue contains certain calorie capacity which can improve clinker sintering. Tailings contain certain geological potentiality, and it can accelerate burning process. The chemical composition and lattice structure of low-grade limestone are different from that of high-grade limestone. The low-grade limestone can decrease the raw material’s decomposition temperature. The material mixed with tailings, coal gangue and low-grade limestone is easy to happen solid state reaction.The result of hydration properties analysis found that hydration products increased with the time past, and it became cement paste structure finally. The predicted model of improved Error Back Propagation (BP) and Radial-Basis Function (RBF) were set up based on neural networks for cement clinker.9parameters as input datas for predicted model. The expected output datas came from cement paste for28days strength, and the datas of sample were obtained at last. The result showed that it is feasible for three prediction models on cement strength, and the network model of RBF is better to improved model of BP.The formation mechanism on utilization of coal gangue, tailings as clay and mixed with low-grade limestone was discussed. Potentials of coal gangue and tailings during their thermal-activation were analyzed. The functions of heat excitation were founded in coal gangue, tailings and low-grade limestone. The kinetic model was put forward to them. The kinetic parameters such as the conversion rate for calcium oxide and apparent activation energy. Experimental results showed that they can reduce energy consumption during cement clinker calcinations.Industrial tests were carried out in the new dry-process rotary kiln of2500t/d and5OOOt/d. The results showed that the two production lines can increase cement output56381tons (t) and280503t in every year. They can save3601t and8132t of the clinker standard coal consumption. The two powers can save1488245kw.h and11351274kw.h. Coal gangue can be used up to290OOOt in each year.The research in this paper provides a technical and theoretical basis for coal gangue, tailings, and low-grade limestone for cement clinker calcinations.