The Study Of Physicochemical Process Simulation And Optimum Design For Cement Precalciner

Precalciner is an important facility in the cement production process. The application of the precalciner can make raw material decomposing, reduce the heat capacity of rotary kiln and the releasing of pollutant gases. Up to now, the design of precalciner is carried on cold, hot tests and pilot-scale tests, and then enlarged by industrial application. But the in-line precalciner enlarged by industrial application can not meet the requirements of design in fact because of the inner complex physical-chemical processes. The studies of precalciner in the world tend to using sophisticated numerical-theory technology combining with researches of experiments. The methods of theoretical studies are mostly simplified by one-dimensional and two-dimensional ones, but the results of simulation are half-qualitative. At the mean time, the simulations in three-dimension mostly focus on solid-gas two-phase flow, combustion and decomposition individually, and the results of these previous works are qualitative, but the results can not disclose the physical-chemical process of precalciner in quantity. Under the requirements of sufficient simulation and disclosing the information of flow, combustion, decomposition and coupling relationship among them, the theoretical simulation in full-scale and optimum design for precalciner become the emphasis in the world chemical engineering field.In this dissertation, the full-scale theoretical simulation models of physical-chemical process and methods of optimum design are presented, and the corresponding numerical technologies and schemes of optimum design are established. The following investigations are made in this dissertation:The pole-zero problem is presented while simulating the flow field under the circular cylindrical coordinates, and the new method of transportation equations for pole-zero is deduced. The RNG k-εturbulent model combined with resolution of transportation equations for pole-zero as boundary condition is used to simulate the flow field of DD-precalciner (dual combustion and denitrator process precalciner), the results of simulation are agreed well with the measurements. The method of shape formation for swirl-spray precalciner is presented here and used to predict the flow field in swirl-spray precalciner.Based on the description of solid-gas two-phase transportation equations, the stack phenomemon of particle trajectories occurs under the structure grid of cartesian coordinate, and the new means for particle-wall collision boundary condition is deduced. In this dissertation, the"four-mixture-fraction"model for coal combustion, raw meal decomposition and the coupling relationship is presented innovatively, and the homogeneous and heterogeneous reactions of char are coupled into the simple chemical reaction process. By using these models mentioned above, the numerical simulation technology is carried on the in-line DD-precalciner and in-line swirl-spray precalciner in full-scale. The model results illustrate the distributions of gas species, temperature and particle phase, and the theoretical models are validated by comparing simulation results with experimental results.The generation and transformation of NO are modeled based on analyzing the mechanics of nitrogen oxide. The simulation results are appropriate by comparing with measurements and the simulating models are carried on the in-line 2500t/d DD-precalciner. The effect on the formation of NO at stage combustion is analyzed and the theory references are presented for reducing the releasing of NO at the exit of the in-line precalciner.An optimum design method for precalciner system is presented in this dissertation, and the formation of precalciner virtual, the orthogonal design arranging test scheme, the nerve net analyzing the nonlinear relationship between the input and output, the variance analysis tool deducing the effect significance of structural parameter on results and the genetic algorithm anti-deducing the optimum structural parameter are introduced carefully. By combining the mathematical tools, useful methods, theoretical models and operating experiences, this dissertation establishes a set optimum method and obtains the optimum structural parameter of precalciner. The results of this dissertation have been used in the real industrial process, and also have been applicated as an important method in the National High Technology Research and Development 863 Program of the People's Republic of China -"The study of low-NOx control technology in the cement kiln system"...