Modeling And Simulation Of Typical Auxiliary Equipment In A Coal-fired Power Plant

Coal-fired power plants take three quarters of the electric power industry in China. As the typical fire power station auxiliary equipment, rotary air preheater and the coal mill have a great influence on the safe operation and production efficiency of the thermal power plant. The main concern of this paper is the temperature field and air leakage rate of the rotary air preheater, mass flow rate of the coal into the boiler and load scheduling of the coal mill.Sulfuric acid is likely to condensate at the cold end of rotary air preheater during operation, which causes corrosion. Therefore, understanding heat transfer mechanism of air preheater and obtaining its interior temperature field is necessary for monitoring rotary air preheater. This paper presents a self-tuning numerical model for rotary air preheater. The model divides air preheater into several infinitesimals, and then equations of energy conservation and mass conservation for each infinitesimals are established. Finally temperature distribution is obtained through iteration. Air leakage rate is another factor which needs to be monitored as it affects the air preheater efficiency and fan power consumption. The algorithm presented in this paper is different from the traditional oxygen based air leakage rate calculation method. The instantaneous air leakage amount is obtained using conservation of energy in the process of flue gas leakage. In order to reduce the influence of errors of measuring points, this paper uses differential pressure method to get the instantaneous air leakage area, and then utilizes historical data to get fixed air leakage area. Finally, total air leakage and the leakage rate are obtained. Without oxygen measuring points or on the condition of imprecise temperature measuring points, this method is still effective.The fact that mass flow rate of the coal into the boiler cannot be measured online has become the bottleneck of the minute-level combustion optimizing control. Because there is a variety of coal mills and their control logics are not identical, it is not possible to apply a universal algorithm to all coal mills. This paper builds models for medium speed roller ring mill and ball mill,respectively. The former uses the mechanism modeling, while the latter is based on dynamic air coal ratio. Since each coal mill in the pulverizing system has different performance, in order to reduce energy consumption, an optimized load scheduling of coal mills can be applied while they are running in parallel. Firstly, this paper sets different work modes based on total number of working coal mills. Then optimal start-stop combination under each work mode is established. Finally, work mode is determined according to coal supply instruction and load scheduling of coal mills is optimized. When the work mode is changed, buffer zone can be used to avoid frequent start-stop. The simulation results show that this coal mill load optimization algorithm has potential to reduce energy consumption and avoid frequent start-stops.