Optimization of an air-cooling system and its application to grid stability

Because of the energy shortage, fluctuation of grid load and preparing for large-scale new energy power plants connected to the grid, it is important to ensure high efficiency of coal-fired power plants and improve the adjustment range of unit loads in China. In this research, based on the characteristics of direct air-cooling systems, calculation of the heat transfer coefficient and exhaust steam enthalpy in a variation condition is put forward, and a cold-end adjustment system using the frequency conversion adjustment of axial-flow fans is proposed to improve the efficiency of power plants and the capability of thermal power plants to execute rapid load changes. A case study on the cold-end adjustment system shows that the adjustment range of a direct air-cooling unit is affected greatly by ambient temperature; therefore, to overcome the shortcomings of a direct air-cooling system, the authors combine a cold-end adjustment system with a condensate throttling system, and thus rapid and broad-load-range adjustment of coal-fired power plants is achieved. •We give the calculation of heat transfer coefficient in variation conditions.•The determination of turbine backpressure in a steady state is given.•A new method for unit efficiency improving and load regulating is proposed.•The disadvantages of two given adjusting methods are studied.•We give a combined mode to realize the depth and rapid load adjusting.