The Numerical Simulation Study Of The Flow Field In A Precalciner For Low-quality Coal Combustion

As the key equipments of the new type dry-process cement production system, precalciner are actually a reactor in which intricate physics and chemical reaction thermal processes, such as multiphase flow, combustion, raw materials decomposing etc, take place. Furthermore the processes interact and couple with each other. As a result, the traditional cold or thermal model test is inevitably restricted by test instruments, which results in some not being measured "blind zones";on the other hand, thermal test not only has the restriction of test instrument, but also often needs large quantity of research funds. Therefore it is rather difficult to carry out the study of precalciner system, even impossible to thoroughly research the inner flow field structure of the system.Since CFD(Computational Fluid Dynamics) Technology was invented, it has been attached great importance as a new technique and has been greatly developed. Due to being proved true by the high precise numerical forecasts of flow, heat transference, combustion, chemical reaction, multiphase flow in many engineering practices in high technology industry such as aviation spaceflight etc, the numerical simulation increasingly becomes popularized and adopted in many other engineering industries.In this paper combined with the characteristic of low-quality coal combustion, the CFD commercial software, Fluent, was adopted to simulate the gas-solid two-phase flow and coal combustion in the 2500t/d precalciner for using low-quality coal, and the main results are as follows:(1) Based on the CFD basic theoretics and algorithms, combined with the characteristic of the flow field in the precalciner, a suit of methods have been ascertained to simulate the flow field of the precalciner system, including: the choice of turbulent flow models, the tactics of numerically solving the turbulent flow movement difference equations and so on.(2) The three-dimension turbulence flow in the precalciner cold model was simulated by the Realizable k-ε model and SIMPLE methods, By the method of numerical simulation to study the flow field in the cold model and comparing the simulation result with that of cold model test, the rationality of that numerical simulation methods is testified, and the adaptability of the precalciner to low-quality coal was preliminary testified.(3) The three-dimension turbulence flow and combustion in the precalcinerwas simulated, The gas phase flow is expressed with Realizable ^ ￡ model, The movement of raw material and coal particle is simulated by the particle stochastic trajectory model, The gas combustion is expressed with the Mixture-Fraction/PDF model, char combustion is expressed with the kinetics/diffusion —limited rate model, released rate of the volatiles is expressed with the constant rates model, radiation of the combustion is expressed with the P-l radiation model, by analysis of the simulation result, the adaptability of the precalciner to low-quality coal was testified.(4) By analysis of the two-phase flow field structure of the precalciner, and studying advantage and disadvantage of the precalciner structure and technics, some further improvement and optimization have been put forward.