Operation Optimization And Practice Of Cold End Of Direct Air Cooling Unit

As some coal-rich regions in the north part of China area so seriously short of fresh water. The construction of air cooling system of power station in these areas will alleviate the contradiction between large-scale construction of pithead power plants and local water shortage in an effective way. But so far there is no proved or unified design procedure applied to the design process of making air cooling power plant localized in China. So making a summary of experiences of operating direct air cooling units in recent years can be helpful to optimize the selection of main design parameters and the operation mode of the unit. It is of great significance to improve operational efficiency and safety of the direct air cooling unit.Through analyzing the advantages and disadvantages of existing methods for determining the designed temperature, this thesis proposes a more reasonable method which utilizes weighted average number of hours to determine the initial temperature. In contrast with the calculation results of four power plants in the north part of China present certain gradient distribution, it proves the rationality of this method. On the basis of the thermo dynamic model of direct air cooling system, taking the minimum annual fee as the objective function of optimization and the initial temperature difference and face velocity as optimization parameters, as the optimal wind speed is obtained, the optimal value of initial temperature difference and the minimum annual fee are obtained. It is concluded that, with the increase of coal price, the optimal initial value of temperature difference is becoming smaller and smaller, which means reducing the annual average operational back pressure of the air-cooling condenser by lowering the initial temperature difference value of the air cooling system can effectively reduce the operation cost of the air-cooling power plant. It provides theoretical reference for the reconstruction of operation units and the selection of parameters of new-built units in north part of China. Based on the mathematical model at variable conditions of the cold side system of the direct air cooling unit, it is confirmed that the law of face velocity, ambient temperature and the variation of exhaust stream flow of unit have influence on back pressure, which forms the basis of determining the reasonable operation mode of the air cooling condenser at variable working conditions. Under the guidance of theoretical analysis and combined with domestic and international operational experience of direct air cooling unit, a series of operational optimizations and transformations were conducted on the 300 MW and 600 MW direct air cooling units of Zhangshan Power Plant. Practice has proved that a good effect has been achieved when the units were dealing with summer heat, strong ambient wind and hot air recirculation, anti-freezing in winter and other aspects.