Study On Solids Diffusion And Combustion In The Dense-phase Zone Of A CFB Boiler

Supercritical circulating fluidized-bed (CFB) boiler combines the advantages of CFB combustion technology and supercritical pressure steam cycle. Its superiority in achievement of clean coal combustion and improvement of power efficiency has been fully demonstrated, so developing large-scale supercritical CFB boiler can meet the requirements on efficient and clean utilization of coal in China. As CFB boiler is developed in the direction of large capacity and high parameters, the boiler furnace sizes are enlarged step by step leading growing inhomogeneity diffusion problems of coal feeding. Supportted by the"11th Five-Year Plan"national science and technology support program—"Study on the coal distribution uniformity of supercritical CFB boiler", the coal distribution characteristics in the large-scale CFB boiler were studied in order to realize uniform feeding, and also explore a feasible experiment method understanding fuel distribution characteristics in CFB boiler conveniently and quickly.The thermal tracer particles and colored tracer particles were used to simulate the diffusion and mixing process of the real coal granules in furnace with a 0.9m×0.47m×6m of cold-state CFB experimental plant. With sampling and image analysis to determine granule concentration in multipoints place, the law between temperature and heat tracer particles concentration was established. The experiment results indicated that the transverse diffusion coefficient increased with coal feeding height, fluidized wind speed, static bed height increased.Based on the experimental data, two-dimensional transverse particle diffusion model of the dense-phase area is established, which includes granular diffusion model, energy model and thermocouple response model. The simulated temperature and granule concentration are in good agreement with the experimental data, and the ratio of simulation concentration to temperature is also presented, which explain the delay between the concentration diffusion and the heat spread and lead to the dimensionless equation of diffusion coefficients.Based on the two-dimensional flow model, coal combustion model in dense phase area is established, and the model considers the releasing of volatile matter, burning and char burning submodels. The coal burning situation in dense phase area of 600MW supercritical CFB prototype boiler was simulated, and the influence of the fluidized velocity, static bed height were analyzed. The measures improving diffusion uniform are put forward at last.