Application Of CFD Technology To Combustion And Decomposition In Precalciners

It has been publicly acknowledged that the Technology of Precalcination is the most advanced cement manufacturing method. Precalciner, the most important machine in the System of Precalcination, is a combustion furnace and a chemical reaction equipment. Multi-phase flow, combustion of fuel, heat transfer and decomposition of carbonate co-exist in it. The main chemical reactions in a precalciner, namely the combustion of pulverized coal and the decomposition of carbonate, occur in a suspending state and interact with each other, which makes the researching jobs extremely tough. The researching methods always decide the level of researching jobs on precalciners. Native researchers have struggled a lot to study precalciners numerically, but they still have a long way to go to put their achievements into factual use.Since CFD (Computational Fluid Dynamics) Technology was invented, it has been attached great importance as a new technique and has been greatly developed. By now, it can be used to solve some problems involved in a precalciner, such as multi-phase flow, heat transfer and combustion of pulverized coal, etc. But precalciner is characterized by its own traits, for example, pulverized coal combusts without flame because of the existence of raw meal, which is a particular phenomenon that could not be found in other industries. As a result of this, the existing CFD softwares could not been directly adopted in the numeric simulation for a precalciner. In order to resolve the problem, a new method was put forward by combining a piece of routine compiled in the dissertation with the existing CFD softwares. The routine is designed to deal with the combustion of pulverized coal and the decomposition of carbonate.A long and thin cubic pipe geometrically is built to debug the routine. Parameters in the debugging are set according to those of a typical precalciner. Results of the debugging showed that the temperature in the pipe was equally distributed and the temperature on the outlet was almost equal to that of a normal precalciner. In addition, the mass fractions reasonably varied alone the pipe. Carbonate almost decomposedcompletely. All of the above means that the routine designed in the dissertation is able to describe the process of combustion and decomposition.In the particular numeric simulation for a certain precalciner, it is very important to properly set the kinetic parameters of char and carbonate, because improper parameters always lead to useless results. In order that correct parameters were given in the simulation, kinetic experiments were carried out on a high-temperature furnace and corresponding parameters were got.With the routine and parameters, we carried out a numeric simulation by taking the ejecting-revolving pipe precalciner designed by NCDRI (Nanjing Cement Design and Research Institute) as a geometric model. Parameters such as flow field, particles' tracks, pressure field, temperature field, decomposition proportion of raw meal and combustion proportion of pulverized coal, etc. are got. The result inosculated with the reports from NCDRI, which means the routine is capable of forecasting the properties of a newly designed precalciner and is capable of providing information to improve its structure and operation.