| 摘要 |
PROBLEM TO BE SOLVED: To provide a vertical natural circulation type exhaust heat recovery boiler so designed that a cavity part may not be produced in the upper part of an economizer during the shutdown of operation of the boiler. SOLUTION: A natural circulation type exhaust heat recovery boiler 2 comprises the tube bank of an economizer 3, the tube bank of an evaporator 4, an economizer inlet header 5, an economizer outlet header 6, an evaporator inlet header 7, an evaporator outlet header 8, a steam separating drum 9, a boiler feed pump 11, a water supply pipe 12, an economizer outlet connecting pipe 13, a water supply control valve 14, a downcast pipe 15, a riser pipe 16, a steam pipe 17, an air vent piping 18, an air vent opening/closing valve 19, etc. A circulation connecting pipe 20 and a circulation connecting valve 21, which either connect the downcast pipe 15 with the economizer outlet header 6, or connect the downcast pipe 15 with the lowest part of the economizer outlet connecting pipe 13, are added. During the shutdown of operation such as a night time, the valve 19 of the piping 18 is left open, and the valve 21 of the circulation connecting pipe 20 is left open at the same time, so that there is no possibility of a cavity produced in the economizer 3 due to the backup of the large quantities of water in the steam separating drum 9 even in the case of a slight fall-off in volume. Therefore, there is no need for the operation of venting air bubbles even in the case of the start-up of the next boiler.
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