Energy efficient strategies for anti-freezing of air-cooled heat exchanger

摘要

In cold winter, the air-cooled heat exchanger of natural draft dry cooling system in thermal power plants is easy to freeze, so the turbine back pressure is generally lifted to avoid freezing at the cost of reduced energy efficiency of power generating unit in practical engineering. In this paper, the energy-efficient strategies for the anti-freezing of air-cooled heat exchanger are proposed with matching the water and air side heat capabilities. By applying the macro heat exchanger model to air-cooled heat exchanger, the thermo-flow behaviors of circulating water, cooling air and exhaust steam in a representative 600 MW power generating unit are synchronously modeled and resolved. The results show that, at a low temperature, the air cooing capability should be fully utilized firstly by adjusting the water flow rate alone. But the air-side cooling capacity becomes conspicuously large as the ambient temperature decreases further, and the louvers of cooling deltas should be turned down in priority so as to match the maximum water-side heat load. Moreover, from -5 degrees C to -10 degrees C of ambient temperature, the anti-freezing turbine back pressure drops at all wind speeds, while it keeps at the chocking back pressure if the ambient temperature further decreases, so that the optimal energy efficiency of cold end system can be achieved.