| Circulating Fluidized Bed (CFB) boiler is widely used in the world, because of the characteristics of fuel flexibility, high combustion efficiency and low pollution emissions. CFB combustion is a new technology of coal cleaning combustion and will inevitably have a great development in all over the world due to its many merits.At present, CFB is heading for the large-scale. There are many aspects such as design technology, the operation characteristics known for large CFB, which need to know and master the flow, combustion, temperature and so on in the boiler. But only finite data can be got through the measurement of traditional experiment, which becomes a barrier to develop CFB capability, these days, with the fast development of computer and the theory of pulverized coal's combustion, numerical experiment, which can make up for the shortcoming of the traditional means, becomes another crucial method to study the above cases. Numerical simulation is a very powerful method assisting the test method in research of gas-solid multiphase flow, This paper focuses on the burning process of the DG440/13.7-Ⅱ2 CFB boiler, and several conditions are simulated, which hope to provide instructive guidance for the optimum design and operation of the boiler.The combustion process in the boiler including turbulent flow and chemical reaction is very complex, which is concerned with three-dimensional turbulent flow, multiphase and multi-component flows; Heat transfer includes convection, radiation and conduction; while chemical reaction includes gas combustion, char combustion and so on. The paper adopted non-premixed combustion model, The equations for the mixture fraction are used to simulate volatile's turbulent combustion, and the simulation of gas turbulent transport employs theκ-εturbulent model, then for the radiation P-1 model is used to simulate radiation heat transfer, Besides, it selects the SIMPLE difference methods of non-interleaving gridding for the gas flow field (solving the N-S equations), and accordingly the resolution of the turbulent diffusion about solid particle chooses the stochastic tracking model. The simulation emphases of the particle reaction are the separateness of the volatile and the oxidation of the char, the first one uses Kobayashi model, and the other one takes the kinetic/diffusion surface reaction rate model, NOx, including thermal NOx and fuel NOx, are post-processed from combustion.FLUENT6.2 is employed in total simulation. Last, the paper shows the results of numerical simulation and analyzes it qualitatively. The results showed pay special attention to the following points: the boiler furnace flow; temperature distributions; oxygen species concentrations, carbon monoxide concentrations, carbon dioxide species concentrations; particles track; how the particles diameter of feed carbon affect the combustion and distribution; NOX (NO) emission and controlling the NOX (NO) emission by controlling the speed of air and adding reductive materials. The trend of the numerical simulation'results are correct and pretty reasonable to the mechanism analysis, The conclusions have a certain significance of guide and value to the mechanism analysis of combustion process, design and operation of the circulating fluidized bed.
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