| As the grain of industry, coal provides energy for electric, steel and cement industry. China has a huge coal consumption, but the coal reserve per capita is extremely low. Under such a contradictory background, the efficient utilization of coal seem very significant. For coal-fired power plant, current practice is to grand coal into powder to improve the efficiency of combustion. Pulverizing consume large amounts of energy, so to grasp characteristics of pulverizing equipment and to select the appropriate granule size of pulverized coal to balance the combustion efficiency and grand power consumption is very important. Especially when the power plant use coal different from coal the power plant was designed on, to find a new balance point can improve the utilization efficiency of coal. For HP mill, a kind of mill applied commonly, problems like the intensifying of wear, undercapacity, the lack of reference of coal fineness and unknown of coal fineness appear when coal changing. This thesis built a mathematical model of HP mill, and corrected it with test data from a power plant in Zhengjiang (hereinafter referred as testing power plant). A mathematical model which showed the steady characteristics of HP mill was obtained and it was used for simulation of HP mill to provide reference for the adjustment of HP mill during production when operating parameters and coal changed.This thesis took HP1163/Dyn coal mill as research object, and built the mathematical model based on crushing theory, gas-solid flow theory, heat and mass transfer theory and mass balance in mill. A field test was conducted at the coal pulverizing system of 14# boiler at testing power plant and the test data was used to correct the mathematical model based on least square method. The corrected model fit well with test data. The pulverized coal size distribution at different place in mill, the influence of operating parameters including flow and temperature of primary air, coal feed rate and rotational speed of classifier to indicators including pulverized coal fineness, specific power consumption of mill and outlet air temperature was simulated with corrected model.Adaptability of HP mill when coal changing was researched with corrected model. Through a method of changing a single coal quality parameter a time, the maximum capacity of HP mill was simulated and the reason the limit the capacity of mill was analyzed. For coal with high ash, low grindability and low volatile matter, the maximum capacity can be improved through increase the preload pressure of rollers. When ash content increases 10%, mill capacity decreases 2.4t/h, and it can be overcame by the increasing of preload pressure by 8.4%. When Hardgrove grinding index(HGI) decreases 10, mill capacity decreases 8t/h, and it can be overcame by the increasing of preload pressure by 33.3%. When volatile matter decreases 10%, mill capacity decreases 7.5t/h, and it can be overcame by the increasing of preload pressure by 26.8%. For high moisture coal, the capacity can be improved by increasing the temperature of inlet primary air.Based on the corrected model, the relationship between specific power consumption of mill Em and coal fineness R90 was researched. And based on the principle of minimum of total sum of combustion loss, loss caused by wear, and power consumption of mill, a corrected calculation method ofeconomic granule size of pulverized coal R90 opt was proposed as below: R90 opt decreases by 0.02% as HGI increase by 1; R90 opt decreases by 0.173% as lower heating value of coal increase by 1 MJ/kg;R90 opt decreases by 0.89% as price of coal increase by 100 RMB per ton. R90 opt for coals used by testing power plant are as follows:25.7% for lignite, 17.4% for Shenghua mixed coal 2,17.4% for Shenghua mixed coal 3,18.0% for Zhong coal, 25.9% for Indonesia coal and 18.4% for Guo4 coal. |
PDF Full Text Request