自然通风冷却塔变工况下防冻的数值优化设计

Numerical Optimization Design on Natural Draft Cooling Tower Anti- icing at Off- design Operating Conditions

为了找到我国北方冬季冷却塔变工况运行时防止塔内结冰的最佳挡风板悬挂层数,论文建立了600 MW机组自然通风逆流湿式冷却塔的传热传质模型,利用FLUENT软件模拟并分析了在循环水量不同的工况下,未加装挡风板以及加装不同层数挡风板时塔内最低水滴温度的变化规律。结果表明:(1)随着挡风板层数的增加,塔内不同特征面上最低水滴温度均升高,填料层下平面空气温度梯度逐渐变小,降低了塔内结冰的可能性;(2)在环境温度为253.15 K,7 m/s的横向风速下,当循环水质量流量分别为9 011、11 830、13 863和17 329 kg/s时,防止塔内结冰的最佳挡风板层数分别为5层、3层、3层和1层,这不仅对火电机组的节能降耗具有一定的实际意义,也为挡风板的优化设计提供了理论依据。

In order to find the optimal layers of windshield boards at off- design operating conditions of cooling tower in winter in the north of China. A heat and mass transfer model of a natural draft counter- flow wet cooling tower for a 600 MW thermal power unit is established. By using the FLUENT software,the changing regularity of the minimum water droplets temperatures in the cooling tower with no windshield boards installed and with different layers of windshield boards installed under different circulating water mass flow rate conditions is simulated. The results indicate that：（ 1） with the increasing layer of windshield boards,the lowest water droplets temperatures at different characteristic planes will all increase and the air temperature gradient at the bottom surface of fill zone becomes little,thus reducing the icing probability.（ 2） when the circulating water mass flow rates are 9 011 kg /s,11 830 kg / s,13 863 kg /s and 17 329 kg /s respectively at the ambient temperature of 253. 15 K and the crosswind velocity of 7 m /s,the optimal layers of windshield boards to avoid water freezing in the tower are 5 layers,3 layers,3 layers and 1 layer,which has some practical significance to the energy saving of thermal power units and provides theoretical evidence for optimum design of windshield boards.