The Study Of Combustion Operation Problems In Large Low-volatile Coals Boiler

With the constant growth of the energy demand, we are facing the enormous challenge on the technology of utilization of energy. Following the further exploitation of the resource of the low-volatile coals,there will be constant growth of burning low-volatile coals in power generation plant.Large power plants have been developed widely all over the world with high efficiency, cleanliness and fewer spaces required. These lager power plants using low-volatile coals as main fuels have two major combustion modes, which are tangential fire mode and W-shape flame mode.Burning the low-volatile coals has been very difficult for many pulverized coal fired furnaces in power generation plants, such as low combustion efficiency, temperature deviation, high temperature corrosion and so on. Low combustion efficiency is the most obvious problem in W-shape flame furnace. This dissertation focuses on W-shape flame furnace combustion characteristic and tangential fire furnace high temperature corrosion. Experimental and theoretical analyses have been performed on a 300MW W-shape flame furnace of manufactured by FW Company:(1)According as characteristics of W shape flame boiler , test of airflow field at room temperature was carried out, the flow-field performance was analyzed, that the momentum ratio of arched air and wall air is the key to control the flow-field is demonstrated. (2)Further researches on the combustion process in W-shape flame furnace have been done based on gas analysis and particle synthetically tests. (3)Cross-section temperature fields in furnace have been measured and measurement results have been studied carefully. The results show the cross-section temperature field's distribution and the characteristic of temperature distribution along the height of furnace which the combustion processes of W-shape flame furnace have been represented based on the temperature distribution.Economical operation method has been found through our research and had confirmed the best operation position of burning system through burning adjusting experiment for the furnace of manufactured by FW Company. Hot test of W-shape flame furnace of manufactured by B&W Company are carried out. In the hot test,the impacts of internal-air-allocated vane angle, oxygen quantities, air-allocated panel position and mill systems on boiler efficiency on boiler efficiency are studied, the results of the studies explain the reason of low efficiency is exit gas temperature and combustible matter quantity in ash higher than normal. The impact elements on combustible material quantity in ash and exit gas temperature are also studied .Through reduce the airproofed wind quantity, improving the pulverized coal fineness, the exit temperature of mills and optimize the operation mode, the boiler efficiency can excess the designed value.Numerical simulation has been used in this dissertation to simulation the flow, heat transfer and combustion in two type W-shape flame furnaces (the furnaces were made by B&W Companies and FW Companies). Simulation results of temperature, oxygen concentration and flow fields were compared. The comparison shows good agreement between simulation results and experimental results.The simulation results also proved that the numerical method used in this dissertation can be used as the aid design tools to provide optimized operation condition for the furnace in power generation plants. New combustion method has been applied by fixing the burned out air located on the throat of furnace and 5-10% primary air has been injected into the furnace center from same place. The benefits of this method applied to W-shape flame furnace have been proved that the furnace temperature would be lower a little after add the burned out air based on the numerical simulation calculation, the oxygen concentration at the center of the furnace increased 1-2%, the burning off rate will improved 1-2%.Grey systematic theory was utilized in this dissertation to investigate the high temperature corrosion. The results show the major factors coursed high temperature corrosion include S content in the coal, CO content near the water-cold wall, diameter of circle contact and wall temperature. We can use this method to predict the water wall corrosion of 300MW units boiler which would belongs to the medium corrosion. This prediction matches with the actual conditions of existing furnace. This dissertation also used PIV to study the flow fields of dual channel burner in 300MW units boiler. Based on the PIV measurement results, optimized parameters were obtained and applied to develop the wedge body transforms technology. The application of this technology had been used in existing pulverized coal fired furnace and proved to be useful on improving the combustion stability and combustion efficiency.Finally, we summarized the research contents and research conclusions, cleared the direction of further research.