| Yong, Yumei (Engineering Thermophysics) Directed by Professor Lu, QinggangScale-up is a symbol that Circulating Fluidized Bed (CFB) is commercialized and CFB's technology is established so there is important theoretic and practice worth to research scale-up CFB boilers. The thesis adopted numerical simulation to study what the influence of coal on the performance of CFB boiler combustion systems is and how parameters in CFB furnaces change with the scale-up of CFB capacity, and how to build a three-dimensional model.First, a set of mathematical models of a CFB boiler is built and the models systematically integrated with the update theories and results of existing studies on the partial aspects or component behavior of CFB boilers. The main processes, such as hydrodynamics of gas and solid, devolatilization of coal, char and volatile combustion, formation and reduction of harmful substances of SOz and NOx, attrition and burst of solid particles, separation characteristics and post-combustion in a cyclone, models of external heat exchanger (EHE) and cooling dreg, are all considered in detail so the model can simulate combustion characteristics of different CFB boiler capacities with different coals.In order to investigate the influences of different coal types on performance of CFB boilers, a burst model of coal is added into the integrated model, and the combustion model is combined constant-density shrinking core model with constant-diameter shrinking core model so a diffusion reaction rate of ash layer resistance is added. A general theory of coal type for coal combustion is added into kinetic reaction rate. The integrated model can be for combustion of different coal types in CFB boilers. Modified integrated model is verified by experimental data of five typical coal types and numerical results agree well with the experimental results. According to these computational results, characteristics of burning rates, comminution characterization of coal particles, heat release fraction distribution and emission characteristics of SO2 and NOx in the same CFB boiler for different coal types are analyzed.CFB boilers with capacities 130t/h, 440t/h and 670t/h were simulated to get characteristics of hydrodynamics, mixing process of gas and solids and patterns of heat and mass transfer. The computational results of 130t/h and 440t/h CFB boilers agree well with experimental results. The thesis predicts characteristics of the combustion system of a 440t/h CFB boiler for different distribution of coal particles, fraction of the primary air, location of the secondary air and different elements andparticles distribution of limestone. Based on the design of a 670t/h CFB boiler made by Institute of Engineering Thermophysics, the influence of three components: the cyclone, the EHE and the cooling dreg on CFB's combustion system with and without EHE are predicted. Some rules are got about changes of configuration, flow and heat transfer with the enlargement of CFB's capabilities from these computational results. Local influence of feed ports, outlet and corner on a CFB is more important to a larger CFB so it is necessary to build a three-dimensional model. A three-dimensional model is built not only to follow the structure and the code of the program and mathematical model of established annular-core model, but also to reflect three-dimensional characteristics. The three-dimensional mathematical model can be fully developed with refined cells.
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