On-Line Optimization Calculation For Cold-End System Of Direct Air-Cooled Unit

The proportion of thermal power in China's power industry is about 60% to 70%.Most thermal power generating units are direct air-cooled units,due to the scarcity of water resources in northern China.The air is directly used as the cooling medium to cool the turbine exhaust,and the water saving rate can reach 65% to 70%.The widespread use of direct air-cooled generator sets in China has broken through the limitations of the development of large-scale thermal power units in the "rich coal-poor water" regions and minimized the consumption of thermal power generation for water resource.The advantages of air-cooled technology are obvious but there are also many drawbacks.The back pressure of direct air-cooled units is generally 5~10 kPa higher than that of wet-cooled units of the same capacity,and the coal consumption is 12~17 g/kWh.The relevant experimental research shows that the back pressure of air-cooled units can be reduced by 3~5kPa through optimization of the cold end,which has great potential for energy saving.This project aims at a 600 MW direct air-cooled unit and establishes a mathematical model for the cold-end system under variable conditions.It analyzes the influence of various factors on condenser vacuum and unit back pressure.Through the performance monitoring of the air island cooling state,the condensate depression of each air-cooling unit,the condenser cleaning factor and the tube wall temperature were monitored on-line to fully analyze the running performance of the unit cold end system.A cold-end optimization objective function was established,and based on the equivalent thermal drop method,the best real-time back pressure of the unit was determined on-line.At the same time,basing on the monitoring results of the air-cooled unit operating conditions.It can achieve the optimal adjustment of the air-cooled fan by the fine tuning of the aircooling fan frequency.A cold-end optimization calculation program was compiled,and the real-time operation data of the power plant database was retrieved through the interface function,and the optimization calculation results of the cold end of the air-cooled unit were given in real time.The direct air-cooled unit cold-end monitoring system and operation optimization procedures proposed in this thesis have been applied in the 600 MW direct air-cooled unit of Guodian Datong Power Generation Co.,Ltd.,and have achieved good operational results and economic benefits.