Thermal Economic Analyses Of A Power Unit Using Indirect Dry Cooling System With Evaporative Cooler

Indirect dry cooling system has been applied in the water shortage regions in northern China widely because of its water saving performance,but the high temperatures and windy weather will affect the cooling performance of dry-cooling tower,increase the steam turbine back pressure.Take an indirect-air cooling unit of a 600 MW as an example,established the mathematical model of indirect-air cooling system,analyzes the influence of the humidity,circulating water flow and air temperature and wind speed on the back pressure.The results showed that when the ambient air temperature rise from 15? to 31?,the back pressure of unit increased from 11.6 kPa to 25 kPa with the wind speed of 1.7 m/s;when the wind speed increased from 1.7 m/s to 2 m/s,the unit pressure is reduced from 25 kPa to 22.9 kPa with 31? of the ambient temperature.As a new cooling technology,evaporative cooler take the advantage of the latent heat of water evaporation to improve the heat transfer efficiency combined with the air convection heat transfer,is a kind of efficient energy-saving heat exchanger equipment.A heat transfer calculation model of evaporative cooler is established,and this paper analyses the influence of environmental air humidity,air flow,spray water flow and heat load on evaporative cooler,coming to the conclusions that when the humidity increases,the cooled-water temperature at exit increases too,but the water consumption decreased;when the air flow rate increased,the water consumption of evaporative cooler is increased with the outlet water temperature decreased;when spray water flow changes,change of export water temperature and water consumption is very small;when water temperature at entrance increase,water temperature drops slightly in the evaporative cooler,but the drop of water temperature will become smaller and smaller with the water flow increasing.Indirect dry cooling systems are widely used in coal-fired power plants.However,high environmental temperatures affect the heat dissipation performance of the dry cooling tower,thus,the back pressure of steam turbine increases.In this work,the evaporative cooler operating with the dry cooling tower to reduce the temperature of circulating water and the exhaust steam pressure,thus,the thermal efficiency of the power unit can be improved.A mathematical model is established for a 600 MW indirect dry-cooled power unit with evaporative cooler,the characteristic of the heat load distribution between the evaporative cooler and the dry cooling tower is analyzed.The exhaust steam pressures,water consumption and the pump power consumption are analyzed for various heat loads.The results show that the ratio of the water flow rate for the evaporative cooler to the total circulating water flow rate is between 0.21 and 0.31,the temperature of cooling water at the entrance of the condenser drops from 54.4 ? to 46.5 ?,the back pressure of the unit reduces from 25 kPa to 17.3 kPa,the generation standard coal consumption rate decreases about 7.4 g/(kW · h).