The Development Of Baffle Downer Dryer For Lignite Dewater With High Temperature Flue Gas And The Research Of The Key Technologies

With the reference of the vibrating bed lignite drier with low-temperature fluegas technology, the baffle downer dryer for lignite particles dewater with hightemperature flue gas and its drying process combining with circulating fluidized bedflue gas generator was suggested, which is characterized by high-temperature flue gas.The whole drying system was designed for the coal quality improvementdemonstration project of200t/h which has been established based on this technology.And this unit has been commissioned preliminary and successfully. Afterwhile someretrofitting designs were provided for the debugs and improvement.In the field test, the coal property was analyzed to judge the unit performance.And the operation parameters were gained. During the commissioning operation, thedebugs were achieved. Through the calculation of the process parameters, the debugswere investigated. And the solution methods was suggested and carried out by theuser. The measurement of the coal shown that the moisture decreased from33.3%inthe raw coal to12.75%in the product coal particle when the gas temperature at theinlet of the drier was500℃with the exhaust gas temperature of100℃ant the drieroutlet. And the heat value increased5257kJ/kg to19271kJ/kg. In the same time, thecombustible gas was not found in the lazy gas by the online monitors. Thecommissioning operation confirmed the suggested dewater technology.Base on the theoretical investigation, a comprehensive model for baffle downerdryer for lignite particles dewater with flue gas was suggested. This model consists ofsingle lignite particle drying sub model and bed surface drying sub model. In thesingle lignite particle drying sub model, the finite volume method was adopted tosimulate the dry region and wet region model where evaporation interface moves inone-dimensional spherical coordinate system. And Crank-Nicolson scheme was usedto solute the equations. For the bed surface drying sub mode, considering themovement of the particles due to the vibration, the evaporation interface was locatedat the bed surface. And the drying process was divide it into two stages based on the critical water content, one is constant-rate periods and the other is falling-rate periods.In constant-rate periods, it is convection mass transfer mechanism, while it is waterdiffusion mechanism in falling-rate periods.With the model, some predictions were carried out. And it was found that thepredictions agreed well with the experimental data, which verifies the reliability andrationality of the model to simulate the drying process. Further, the performance waspredicted with the model for different flue gas temperature, gas velocity, initial watercontent in the coal, the ratio of gas to coal, and the average inlet particle diameter oflignite in the drier, and their effects on the drying process was achieved.