JPH07332601A - Exhaust heat recovery boiler operating method - Google Patents

Abstract

(57) [Abstract] [Purpose] By forcibly circulating the water in the evaporator 3 of the exhaust heat recovery boiler 1 by the circulation pump 8, the heat transfer coefficient in the evaporator heat transfer tube is increased and the startup time is shortened and thermal stress is increased. Prevent damage to the evaporator heat transfer tubes. [Structure] An evaporator branch line 7 for branching and rejoining the circulating water to an evaporator downcomer 6 of an evaporator 3 is provided, and a valve b10 is provided between the branch and the confluence of the evaporator downcomer 6. A method for operating an exhaust heat recovery boiler having a circulation pump 8 and a valve a9 in the evaporator branch line 7. [Effect] By forcibly circulating the water in the evaporator 3 of the exhaust heat recovery boiler 1 by the circulation pump 8, the heat transfer coefficient in the evaporator heat transfer tube is increased, the start-up time is shortened and the evaporator transfer due to thermal stress is increased. It becomes possible to prevent damage to the heat tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust heat recovery boiler and a method of operating the same, and particularly to an exhaust heat recovery boiler suitable for shortening the startup time of the exhaust heat recovery boiler and reducing the thermal stress of the evaporator heat transfer tube during startup. And its driving method.

[0002]

2. Description of the Related Art In a conventional exhaust heat recovery boiler, a vapor drum is installed above an evaporator and an evaporator downcomer as a means for circulating hot water in the evaporator and evaporator downcomer, and a heated evaporator is installed. The natural circulation force generated by the difference in the specific gravity of the hot water inside and the specific gravity of the hot water inside the evaporator downcomer was used.

[0003]

In the above prior art, the time from when the exhaust heat recovery boiler starts to introduce high-temperature exhaust gas to when it generates steam under a predetermined condition is that the hot water in the steam drum has a predetermined temperature. The temperature rise time of the hot water in the steam drum depends on the circulating power of the hot water between the evaporator and the downcomer of the evaporator. Therefore, the starting time of the exhaust heat recovery boiler largely depends on the circulating force of the hot water.

Therefore, in order to shorten the start-up time of the exhaust heat recovery boiler, it is important to increase the hot water circulating force between the evaporator and the evaporator downcomer, and for that purpose, it is supplied to the exhaust heat recovery boiler. It is necessary to increase the exhaust gas flow rate or increase the exhaust gas temperature. However, it is difficult to supply a large amount of high-temperature gas at the time of startup because the exhaust gas supply equipment is also operating with a low load. Even if this is possible, at the time of startup, the hot water in the evaporator and the evaporator downfall pipe Since the difference in specific gravity of the hot water is small and the circulation force is small, the evaporator heat transfer tube is locally overheated and there is a problem of damage to the heat transfer tube due to thermal stress.

[0005]

The above object can be achieved by installing a branch line in the evaporator downcomer and installing a circulation pump in the branch line to forcibly circulate the water in the evaporator.

[0006]

By forcibly circulating the water in the evaporator with the circulation pump, the heat transfer coefficient in the evaporator heat transfer tube is increased and the heating efficiency is increased, so that the start-up time can be shortened. In addition, since the heat transfer coefficient in the evaporator heat transfer tube is increased, local overheating of the evaporator heat transfer tube is reduced and damage to the heat transfer tube due to thermal stress can be prevented.

[0007]

FIG. 1 shows an embodiment of the present invention.

First, the steam generation process of the exhaust heat recovery boiler 1 will be described. Water supply 1 supplied to the exhaust heat recovery boiler 1
1 is heated by a economizer 4 and is supplied to a steam drum 5. The steam drum 5 transfers hot water in the drum between an evaporator downcomer 6 and an evaporator 3 in order to generate saturated steam having a predetermined pressure. Circulate. The steam generated from the steam drum 5 is supplied to the superheater 2 and superheated to a predetermined temperature.

[0009] Here, at the time of start-up, in order to forcibly circulate the hot water in the evaporator 3, an evaporator branch line 7 for branching the circulating water from the evaporator downcomer 6 and joining them again, and on the evaporator branch line 7 A circulation pump 8 is installed in the valve, and valves a9 and b10 are installed on the evaporator downcomer 6 and the evaporator branch line 7 downstream of the branch.

When the exhaust heat recovery boiler 1 is started, the valve b10 is closed, the valve a9 is opened, and hot water is circulated by the circulation pump 8.
By forcibly circulating the water in the evaporator 3 with the circulation pump, the heat transfer coefficient in the evaporator heat transfer tube is increased and the heating efficiency is increased, so that the start-up time can be shortened. In addition, since the heat transfer coefficient in the evaporator heat transfer tube is increased, local overheating of the evaporator heat transfer tube is reduced and damage to the heat transfer tube due to thermal stress can be prevented.

When the temperature and pressure inside the steam drum 5 reach predetermined values, the circulation pump 8 is stopped, the valve b10 is opened, and the valve a is opened.
The auxiliary machine power is reduced by closing 9 and switching to natural circulation. Although the valve a9 is installed on the inlet side of the circulation pump 8 in FIG. 1, the same effect can be obtained by installing it on the outlet side.

[0012]

According to the present invention, the start-up time of the exhaust heat recovery boiler 1 can be shortened, local overheating of the evaporator heat transfer tube can be reduced, and damage to the heat transfer tube can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

1 ... Exhaust heat recovery boiler, 2 ... Superheater, 3 ... Evaporator, 4 ... Economizer, 5 ... Steam drum, 6 ... Evaporator downcomer, 7 ... Evaporator branch line, 8 ... Circulation pump, 9 ... Valve a, 10 ... valve b,
11 ... Water supply.

Claims (1)

[Claims] 1. An evaporator for heating feed water, a steam drum installed above the evaporator for evaporating hot water supplied from the evaporator, and a precipitation line for circulating the hot water in the steam drum to the evaporator. In the waste heat recovery boiler, a branch line for branching the circulating water to the evaporator precipitation line and joining the precipitation line again is provided, and a circulation pump and a shut-off valve are provided on the branch line for the evaporator precipitation line. A method for operating an exhaust heat recovery boiler, comprising a shutoff valve between the branch section and the confluent section, and forcibly circulating hot water in the evaporator with a circulation pump when the exhaust heat recovery boiler is started.