Abstract:

 The fan speed of direct air-cooling unit related with exhaust pressure directly affects unit’s operation economy. Therefore, it is important to determine the optimal fan speed for energy saving, considering the influences of environmental temperature, wind velocity, wind direction and so forth. Taking a 600 MW direct air-cooling unit as example, the objective function of fan speed optimization was developed. The value of objective function was obtained through the relationship of fan’s working point, speed and exhaust steam pressure, as well as the back pressure characteristics of turbine, and then the optimal fan speed was determined through appropriate optimization algorithm. The results show that exhaust pressure increases with the increase of environmental temperature, wind speed or unit load, which will make the optimal fan speed increase； the contrary decreases. When environment temperature is higher than 20 ℃, its impact on fan speed is more significant. Wind direction also has an influence on the optimal fan speed, whose maximum value appears in the x wind direction, and minimum value appears in dominant wind direction.

Key words: direct air-cooling unit, optimal fan speed, environmental factors, exhaust pressure