Study On The Adjustment Of Windshield Area Of Cooling Tower And Its Influence On Coal Consumption Of Units

The thermal performance of natural draft counter flow wet cooling tower is directly related to the safety and economy of the whole unit. The thermal performance of cooling tower is greatly influenced by ambient conditions. When the ambient temperature is relatively low, the heat transfer between water and air is great, water freezing phenomenon occurs at some areas in cooling tower. The installation of the windshield boards at the air inlet of the cooling tower is an effective measure to avoid water freezing.However, during the actual operation of power plants, it often appears the situation that the number of windshield boards is over large in order to avoid water freezing in cooling tower, which decreases the economics of unit. Therefore, it is of great significance to study the effects of the installing area of windshield boards on water temperature in tower and unit coal consumption and find the installing area of windshield boards which just can avoid water freezing at different ambient temperatures and wind speed, which can not only reduces the cost of power generation, but also provides a theoretical basis for the reasonable installation of windshield boards to avoid water freezing at different ambient temperatures and wind speed.A numerical model of a cooling tower for a 600 MW unit with windshield boards installed is established. The velocity and temperature field in cooling tower are simulated.The influence of the installing area of windshield boards on water temperature in tower and coal consumption is further analysed. The corresponding optimal installing area of windshield boards at different ambient temperatures and wind speed is found. The research results indicate that: water freezing phenomenon in different degrees occurs without anti freezing measures at the ambient temperature of 266.15 K, 261.15 K and255.15 K respectively. In order to avoid water freezing, the installing area of windshield boards will increase too much with adding a layer of windshield boards, which leads to the cooling performance of cooling tower decrease sharply. The installing area of windshield boards can be found by using windshield boards partially suspended plan,under which condition the cooling tower can just avoid freezing. The installing area of windshield boards described above is 323.41m~2, 1739.88m~2 and 2236.99m~2 respectively,which is smaller than the corresponding installing area of windshield boards according to the optimal layers of windshield boards(970.23m~2, 1973.48m~2 and 2485.55m~2respectively). This is more favorable to the unit energy saving. Through the study of the suspension plan of windshield boards, a new suspension plan of windshield boards is proposed to avoid water freezing in tower, namely uniformly spaced longitudinal installation. The optimal installing area of windshield boards which can just avoid waterfreezing with windshield boards installed at a regular longitudinal spacing is as follows:when the wind speed is 1.5m/s and the ambient temperatures are 261.15 K, 258.15 K and255.15 K respectively, the optimal installing area of windshield boards is 1578.79m~2,1864.16m~2 and 2071.29m~2respectively; when the wind speed is 4m/s and the ambient temperatures are 258.15 K and 255.15 K respectively, the optimal installing area of windshield boards is 727.65m~2 and 1242.77m~2 respectively; when the wind speed is6.5m/s and the ambient temperatures are 261.15 K, 258.15 K and 255.15 K respectively,the optimal installing area of windshield boards is 1657.03m~2,1988.44m~2 and 2174.85m~2 respectively. The standard coal rate is remarkably influenced by installing area of windshield boards. When the ambient temperature is 264.15 K, the standard coal consumption rate at the installing area of 1739.88m~2 increase by 0.384g/(k W·h)compared with that at the installing area of 848.96m~2; when the ambient temperature is261.15 K, the standard coal consumption rate at the installing area of 2154.14m~2 increase by 0.493g/(k W·h) compared with that at the installing area of 1578.79m~2; when the ambient temperature is 258.15 K, the standard coal consumption rate at the installing area of 2347.46m~2 increase by 0.579g/(k W·h) compared with that at the installing area of1864.16m~2.