The Numerical Simulation Of Flow Field In Reinforced Suspension Precalciner

Dry-process precalciner kiln technology is the most advanced technology in cement manufacture at present, and precalciner is one of the hard core and key technology equipment in it. The performance of precalciner has great effect on energy consumption, pollutants discharge and producing efficiency of the system. The flow field in precalciner system is very complex as well as the reactions of fuel combustion and raw materials decomposing, which are influenced by each other, are taken place in suspension of the air flow. For these reasons, it is difficult to research and develop the precalciner system. In the past years, design of the precalciner system depends mainly on experimental data and empirical formula.The numerical simulation based on the Computational Fluid Dynamics (CFD) is applied widely in the engineering field due to its accurate numerical prediction for the flow, heat exchange, chemistry reaction and multiphase flow. So numerical simulation on the turbulence flow is adopted to investigate the flow character in the precalciner to optimize system structure and improve system performance. This method can save the R&D cost and time so that it is significant in the engineering application.In this dissertation, CFD numerical simulations of three-dimensional turbulent flow in 2500t/d Reinforced Suspension Precalciner were studied. The integrity and authenticity of geometry structure of the precalciner is ensured at model establishing process. Mixed gridding technology is applied at gridding drawing process, and the gridding of small structure is minished. All of this measure ensures the reality of the results. The gas phase is expressed with renormalization group (RNG) k-ε two-equation model. This model is more reasonable to strong eddy flow in precalciner. Movement of raw material and coal particle is simulated by the particle stochastic trajectory model. This model is capable in simulating particle with complicated experience. It also enables to simulate coupling interaction between gas phase and particle phase, turbulence diffusion of particle is also regarded in this model. Non-premixed combustion model is adopted in simulating coal combustion;volatilescombustion is expressed with the probability density function model;char combustion is expressed with the surface reaction model;released rate of the volatiles is expressed with the two competing rates model;radiation of the combustion is expressed with the P-l radiation model. At calculating process, Control Volume Method (CVM) is applied in discretizing the gas phase control equation. The difference format applied is second order upwind difference. Coupling between pressure and velocity is solved by the SIMPLE arithmetic. Tri-Diagonal Matrix Algorithm (TDMA) method and low relaxing factor are also applied in solving the control equation.The simulating result predicts the flow field, the particle movement and the coal combustion, which is coincident with the flow tendency. The result provides useful information for analyzing the kinetics regulation and reaction in precalciner, and also gives important theoretical basis for structure optimizing and practical operation parameter selecting of the precalciner.