自然通风冷却塔预热式防冻系统控制研究

Research on Control for Preheating Antifreeze System of a Natural Draft Cooling Tower

提出一种预热式防冻系统,利用凝汽器出口高温循环水加热冷空气,建立了流动与传热数学模型,并且针对某1 000 MW机组,在防冻约束下建立运行控制模型并验证防冻效果,给出最优控制参数。研究结果表明:采用防冻系统既可以提高进风温度避免结冰,又可以冷却循环水;当环境温度或机组负荷降低时,优先增大调节阀开度以增加预热器的循环水量,保证进风温度高于防冻阈值,但是达到循环水量调节上限后,需要减小百叶窗开度以降低进风量。优化控制后,出塔水温可维持在3~12℃,机组热耗平均降低60.70 kJ/(kW·h),经济效益显著。

A preheating antifreeze system was proposed by adopting the high-temperature circulating water at the outlet of the condenser to heat the cold air, and a mathematic model was established for flow and heat transfer. Meanwhile, for a 1 000 MW unit, a model with the antifreeze constraint was established for operation control, and the antifreeze effect was verified. After which, the optimal control parameters were given. Research results show that, by using the antifreeze system, the inlet air temperature can be increased for avoiding freeze, while the circulating water can be cooled. When the ambient temperature or the unit load decreases, the regulating valve opening should be increased in priority to ensure that the inlet air temperature is higher than the antifreeze threshold by increasing circulating water flow, but after reaching the upper regulating limit of the circulating water flow, the control shutter opening should be decreased to reduce the ventilation flow. Through the optimization control, the outlet water temperature of the cooling tower can be maintained at 3-12 ℃, and the heat consumption of the unit can be reduced by 60.70 kJ/(kW·h) on average. This presents a significant economy.