| 摘要 |
PROBLEM TO BE SOLVED: To prevent a dew formation at a surface of piping of a heater and prevent a low temperature corrosion without increasing cost of equipment constituting the plant or its power. SOLUTION: There is provided a heat exchanger 28 over an inlet line 25 and an outlet line 26 of a preheater 23. There is provided a control device 34 in which opening or closing of a flow rate control valve 30 is controlled in response to detected information of a temperature sensor 31, to keep a temperature of water at an inlet side for the preheater 23 more than a dew forming temperature and a flowing amount of hot water at the outlet line 26 to the heat exchanger 28. A temperature of water fed from the inlet line 25 is increased by the heat exchanger 28 to keep it more than a dew forming temperature. At the same time when the heat exchanging operation is not required, a pressure loss at the outlet line 26 is decreased, the dew formation at the surface of the pipe in the preheater 23 is prevented, and a low temperature corrosion is prohibited.
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