大型火电机组母管制空冷系统特性

Characteristics of Piping-main Air-cooled System for Large Thermal Power Unit

为提高大型火电直接空冷机组对气象条件和发电负荷变化的适应能力,提出了一种联建式直接空冷机组母管制冷却系统。建立数学物理模型,对其空气侧流场进行数值模拟,并以此为外部边界条件,开发汽轮机排汽在冷却系统内流动阻力损失和蒸汽流量计算程序。综合考虑外部冷却空气流场和内部蒸汽流动凝结过程,获得夏季和冬季不同环境温度、不同冷却单元投运数量下,各空冷单元的凝结蒸汽流量及汽轮机背压。结果表明,采用母管制冷却系统,在夏季高温环境下冷却一台机组乏汽时,可以显著降低汽轮机背压,提高机组热经济性;冬季环境温度低至??25℃,冷却两台机组乏汽仍可保证汽轮机背压高于阻塞背压,翅片管不发生冻结。

In order to improve the adaptability of the large-scale direct air-cooled power generating units to the variations both of meteorological conditions and power loads, a piping-main scheme of the air-cooled system was proposed for the co-established power generating units. The physicomathematical model of such piping-main air-cooled system was established for the 2×600 MW power generating units,with which the air-side flow characteristics of cooling system were obtained through computational fluid dynamics(CFD)simulation. Taking this as the external boundary condition, the calculating programs both for exhaust steam flow resistance loss and flow distributions inside air-cooled condenser(ACC)cells were developed. Taking the external cooling air flow field and the internal steam flow condensation process into account,the condensate flow rate in ACC cells, as well as the back pressure of turbine can be acquired under different environmental temperatures of summer and winter and different operating ACC cells. The results indicate that the present proposed piping-main scheme of direct air-cooled system for co-established power generating units can reduce the back pressure of the steam turbine significantly and improve the thermal economy of the unit while cooling the exhaust steam of one steam turbine by the whole piping-main cooling system under the summer high ambient temperature. It also can ensure the back pressure higher than block back pressure and the finned tubes do not freeze with the ambient temperature as low as -25℃ while cooling the exhaust steam of two steam turbines by part ACC cells of the piping-main cooling system during the winter.