Abstract: Generally, the design and type selection of natural draft cooling towers in large wet cooling generating units are made according to the average annual weather conditions, which leads to surplus cooling capacity in winter and insufficient cooling capacity in summer, especially in the areas where the monthly temperatures change substantially in a year. Therefore, two hybrid cooling schemes adopting both natural draft cooling towers and mechanical ventilation cooling towers are proposed for a power plant with two 660-MW coal-fired units. Comparisons between the two hybrid cooling schemes and the natural draft cooling tower are conducted. The result shows that the hybrid cooling schemes are more adaptable to load variation and need less initial investment and running cost. Moreover, in the two hybrid cooling schemes, the one with fewer mechanical ventilation cooling towers is more economical than the other one. Finally, issues in adopting the hybrid cooling schemes are put forward and analyzed.

Key words: circulating cooling system, hybrid cooling style, natural draft cooling tower, mechanical ventilation cooling tower, large generating unit