JPH09112807A - Deaerator protection device for exhaust gas reburn system - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To provide an emergency avoidance means when a protection system of a deaerator becomes abnormal. In the exhaust gas re-combustion system, a degasser 21 is provided with a bypass pipe 26 that bypasses a low pressure water supply system.
Avoid excessive rise of inlet water temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device suitable for protecting a deaerator when the feed water temperature at the deaerator inlet rises abnormally in an exhaust gas reburn system.

[0002]

2. Description of the Related Art An exhaust gas reburning system that uses the exhaust gas of a gas turbine as combustion air for a fuel for a boiler has been in the limelight in recent years because it can improve plant efficiency by 3 to 7% as compared with a conventional system. Various configurations have been proposed and put into practical use.

A typical system configuration is shown in FIG.
After lowering the temperature of the exhaust gas 3 of the gas turbine 1 through the gas turbine exhaust gas cooler 4 in parallel with the combustion air system in which the pressure of the atmosphere is raised by the forced draft fan 5, the temperature is raised by the air preheater 6 and then sent to the boiler 7, It is composed of a combustion air system that is sent to the No. 7.

A part of the exhaust gas 9 discharged from the boiler 7 is discharged to the chimney 13 through the air preheater 6, while the remaining exhaust gas is steam turbine by the gas high pressure feed water heater 10 and the gas low pressure feed water heater 11. After performing cycle water supply and heat exchange, it is discharged to the chimney 13.

Regarding the low pressure feed water heater system, the condensate pump 18 to the ground condenser 19 and the low pressure feed water heater 2
A low-pressure feed water heater 11 for heating the feed water by the boiler exhaust gas 9 is installed in parallel with the low-pressure feed water heater system connected to the deaerator 21 through 0.

As one of the features of the exhaust gas reburn system, the load of the boiler / steam turbine system and the gas turbine 1
The loads can be arbitrarily combined within a specific range. Above all, the plant efficiency can be increased by operating the gas turbine 1 as high as possible.

Therefore, when the load on the plant is reduced, it is highly efficient to reduce the load on the boiler / steam turbine system as much as possible. However, in such an operating state, the load of the boiler / steam turbine system is low, that is, the load of the gas turbine 1 is high although the amount of water supply is small. Therefore, there is an unbalanced state in which the heat exchange amount of the low pressure gas feed water heater 11 does not decrease so much.

As a result, the temperature of the feed water heated by the low pressure feed water heater 20 and the gas low pressure feed water heater 11 becomes higher than that of the conventional system.

On the other hand, in the deaerator 21 into which the feed water is introduced, the internal pressure of the deaerator 21 decreases almost proportionally as the load of the boiler / steam turbine system decreases. Due to the structure of the deaerator 21, there is a risk of causing a water hammer if the introduced water is flushed during the process, and in the worst case, the equipment may be damaged. Therefore, the inlet feed water temperature of the deaerator 21 is the same as that of the deaerator 21. A certain margin (10 to 10) for the saturation temperature corresponding to the internal pressure
The upper limit temperature is set in consideration of 20 ° C).

In the exhaust gas re-combustion system, there are cases where this limitation is imposed at the time of partial load, and in that case, a condensate blow system 24 is installed to flow a part of the outlet feed water of the gas low pressure feed water heater 11 to the condenser 17. However, an excessive rise in the inlet temperature of the deaerator 21 is prevented by flowing the feed water commensurate with the heat quantity into the gas low-pressure feed water heater 11 having a large heat exchange amount.

In the figure, 2 is gas turbine fuel, 8 is boiler fuel, 12 is an induced draft fan, 14 is a high pressure steam turbine, and 1
5 is an intermediate pressure steam turbine, 16 is a low pressure steam turbine, 22
Is a feed water pump, 23 is a high-pressure feed water heater, and 25 is a condensate blow adjustment valve.

[0012]

The prior art described above considers only the protection of the deaerator 21 during normal operation. For example, the stick of the condensate blow adjusting valve 25, the condensate blow adjusting valve 25 due to control abnormality, and the like. There is a problem that there is no avoidance means for cases such as closing.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide an emergency avoiding means when the protection system of the deaerator 21 during normal operation becomes abnormal.

[0014]

In order to achieve the above object, the present invention provides a system for bypassing the low pressure feed water system in the exhaust gas reburning system so that an excessive rise in the deaerator inlet feed water temperature can be urgently avoided. It is characterized by that.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is configured as described above, and when the deaerator inlet feed water temperature exceeds a limit value, a valve installed in the low pressure feed water heater bypass pipe opens, and the low pressure feed water heater. The low-temperature feed water (30 to 50 ° C.) at the inlet flows into the deaerator inlet to prevent the deaerator inlet feed water temperature from rising excessively.

A specific example of the present invention is shown below in FIG. The feed water boosted by the condensate pump 18 is divided by the low pressure feed water distribution valve 28 into a low pressure feed water heater system and a gas low pressure heater system, that is, a low pressure feed water heater 20 and a gas low pressure feed water heater 11, respectively. After the heat exchanger (heat absorption), they merge and enter the deaerator 21.

The inlet feed water temperature of the deaerator 21 is controlled to be equal to or lower than the upper limit value which is set in consideration of a certain margin in the saturation temperature corresponding to the internal pressure of the deaerator 21.

However, when the inlet feed water temperature of the deaerator 21 rises and exceeds the upper limit value due to malfunction of the condensate blow adjusting valve 25 and control, the outlet of the condensate pump 18 and the inlet of the deaerator 21 are connected. The low-pressure feed water heater bypass valve 27 installed in the low-pressure feed water heater bypass pipe 26 is opened promptly, and the feed water temperature at the inlet of the deaerator 21 is rapidly lowered by the low temperature feed water at the outlet of the condensate pump 18.

[0019]

EFFECTS OF THE INVENTION By using the deaerator protection device described above, the present invention can safely stop the plant without damaging the deaerator even when the deaerator inlet feed water temperature control becomes unsuccessful. It becomes possible to treat such as.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a specific example of a low pressure water supply system of an exhaust gas reburn system according to the present invention.

FIG. 2 is an overall system diagram of an exhaust gas reburn system according to a conventional technique.

[Explanation of symbols]

 1 Gas Turbine 3 Gas Turbine Exhaust Gas 7 Boiler 11 Gas Low Pressure Water Heater 20 Low Pressure Water Heater 21 Deaerator 26 Bypass Pipe 27 Bypass Valve 28 Low Pressure Water Distribution Valve

Claims (1)

[Claims] 1. An exhaust gas re-combustion type boiler that introduces the exhaust gas of a gas turbine into a boiler and uses it as combustion air for fuel used in the boiler, in order to recover the heat of the boiler exhaust gas by low-pressure feed water of a steam turbine cycle. Gas low-pressure feed water heater is configured in parallel with the low-pressure feed water heater of the steam turbine cycle, and the low-pressure feed water bypass bypasses the low-pressure feed water heater system from the condensate pump outlet to the deaerator inlet. A deaerator protection device for an exhaust gas reburn system, which is provided with a pipe.