Study On The Characteristics Of A Piping-main Scheme Air-cooled System For Large Thermal Power Unit

Owing to its good water-saving performance,the air-cooled system has been widely used in the dry areas of northern China.At present,there is an excess capacity of air-cooled power plants in China,and most of the units are operated in low-load condition,which cause the low operation efficiency.With the development of new power generation technology,the thermal power plants will burden more and more peaking duties.The frequent variable load operation puts forward new requirements for the original air-cooled system.It is greatly influenced by the environment,and ambient wind speed,direction and temperature can take great influence on the performance of air-cooled system.So,it is particularly important to design air-cooled system which can adapt to the complex environment.In order to improve the adaptability of the large thermal power direct air-cooled units to the meteorological conditions and the variation of power load,a co-built direct air-cooled system is designed.The corresponding mathematical physical model is established for numerical simulation of external flow field.As an external boundary condition,the flow resistance loss calculation program and steam flow calculation program are developed for steam turbine exhaust steam.Comprehensive consideration of external cooling air flow field and internal flow steam condensation process,access to the different environment,different operating strategy,the air-cooled unit head on wind speed distribution,the condensed steam flow and the steam turbine back pressure.The results show that this co-built direct air-cooled system,without considering the wind environment,under the environment of high temperature in summer,can significantly reduce the steam turbine back pressure,and improve the thermal efficiency;In the winter environmental temperature as low as-25℃,cooling exhaust steam for two units.It can still ensure that the back pressure of the steam turbine is higher than the minimum back pressure,and the fin tube does not freeze.In the case of environmental wind influence,in summer,the co-built direct air-cooled system can effectively solve the problem of the unequal distribution of air cooling units in the air-cooled island under the influence of environment wind.It can reduce the back pressure of the steam turbine and improve the thermal economy of the air-cooled unit.At the same time,in extreme high wind weather,the air-cooled system can be adjusted to protect the safety of air-cooled plants.