At the initial starting period of the unit, the steam is required for the shaft seal heater, and water is also required for cooling the shaft seal heater, therefore the recirculation line of the condensation water shall be provided in front of the shaft seal heater. If it is provided in the rear of the shaft seal heater, the water through the shaft seal heater will be less, the cooling effect of the shaft seal heater will be poor, the shaft seal heater is easily burnt, thus the economical efficiency is reduced.