Transient Analysis for Effect of TDFWP on the Operation of Main Equipments in Direct Air-Cooled Thermal Power Generating Unit

For the air-cooled thermal power generating unit, specific climatic conditions exert fast and great impact on the condenser pressure. When equipping turbine driven feed water pumps (TDFWP), as the exhaust steam leaving the boiler feed pump turbine (BFPT) is directly discharged into the air-cooled system, the change of environmental conditions such as air temperature and wind speed will result in the distinct change of BFPT back-pressure both in scope and magnitude. For once-through boilers, such changes will cause disturbance to feed water, and further lead to the change of fuel and air feeding. The back-pressure of main steam turbine is much higher in summer climatic condition. In order to maintain rated or certain power load, steam supplied into the main steam turbine has to be increased. Meanwhile, it is necessary to increase the steam flux in the driving turbine to maintain the needed power for feed water pumps, so there is a conflict that the driving turbine for feed water pumps will compete for steam with the main steam turbine. A dynamical mathematical model of a 600MW direct air-cooled thermal power generating unit is built in this paper. The focus is on the transient analysis of the effect of TDFWP on main equipments when the back-pressure changes in the manners of slope and step mutations. Simulation results show that when the disturbance is smaller, the unit can be quickly adjusted to the operational status at given steam and feed water flow rates. The greater the magnate of back-pressure mutation, the greater the changing range of the parameters, and the longer time is needed for adjusting. Under the condition of the same change magnitude of back-pressure, when the back-pressure rise time is longer, the parameters fluctuation is smaller. When the disturbance is larger, the steam flow of TDFWP is gradually increased to its maximum value. With further increase in the back-pressure, the steam flux in the turbine of TDFWP is gradually decreased, so it is difficult to ensure the feed water flow in this case. The results in this study provide important theoretical significance and engineering reference for the implementation of utilizing direct cooling steam feed pump technology in the actual unit.