JPH09209715A - Low-temperature corrosion preventing device for exhaust gas re-combustion type combined plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent low-temperature corrosion by utilizing the exhaust gas of a gas turbine as boiler combustion air, and providing a heat exchanger utilizing the fluid circulated between a low-pressure gas heater inlet condensate system and a boiler water feed system to transfer heat to the low-pressure gas heater inlet condensate system. SOLUTION: This exhaust gas re-combustion type combined plant is provided with a high-pressure steam turbine 9 driven by the steam from a boiler 5, an intermediate- pressure steam turbine 10 driven by the steam obtained when the exhaust steam is reheated by the boiler 5, and a low-pressure steam turbine 11 driven by the exhaust steam of the intermediate-pressure steam turbine 10. A power generator 12 is driven by these steam turbines 9-11. The combined plant is also provided with a heat exchanger 29 heating condensate on the inlet side of a low-pressure gas heater 7 and a heat exchanger 30 heating feed water at the inlet of a high-pressure gas heater 6. The heat exchangers 29, 30 are connected by a pipe, a heat medium is circulated to increase the inlet condensate temperature of the low-pressure gas heater 7, and the low-temperature corrosion on the heat transfer surface of the low-pressure gas heater 7 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recombustion type combined plant, and more particularly to a low temperature corrosion prevention device.

[0002]

2. Description of the Related Art FIG. 1 is a system diagram of a conventional exhaust gas re-combustion combined plant.

In the combustion air supply system to the boiler, a gas turbine (compressor 1, combustor 2,
Turbine 3), forced draft fan 20, and air preheater 21
Is provided.

The boiler exhaust gas system is equipped with a high pressure gas heater 6, a low pressure gas heater 7, a draft fan 22, and a chimney 8. Since the air preheater 21 is a boiler heat exchanger for intake / exhaust air, it is also an exhaust gas system device.

The steam turbine side cycle is composed of the following: First, as a steam portion, a boiler 5 for converting feed water into steam, a high-pressure steam turbine 9 driven by steam generated in the boiler 5, and an exhaust steam of the high-pressure steam turbine 9 driven by steam reheated in the boiler 5 A low pressure steam turbine 11 driven by the exhaust steam of the pressure steam turbine 10 and the intermediate pressure steam turbine 10. The generator 12 is driven by these steam turbines. Next, in the condensate / water supply system, a condenser 13 for condensing the exhaust steam of the low-pressure steam turbine 11, a condensate pump 14 for boosting the condensate of the condenser 13 and discharging it to the condensate system, a condensate A low-pressure feed water heater 15 that heats the condensate supplied from the pump 14 by the extracted steam of the low-pressure steam turbine 11, a low-pressure gas heater 7 that exchanges heat with the boiler exhaust installed in parallel with the low-pressure feed water heater 15, a low-pressure gas heater In order to control the outlet condensate temperature of No. 7 lower than the internal temperature of the deaerator 16, the low pressure gas heater condensate flow rate distribution control valve 25 for controlling the passing condensate flow rate ratio of the low pressure gas heater 7 to the low pressure feed water heater 15 side. If the outlet condensate temperature of the low pressure gas heater 7 cannot be suppressed even if the low pressure gas heater condensate flow distribution control valve 25 is fully opened, the low pressure gas heater 7
Condensate dump system 19 for dumping condensate from the outlet to the condenser 13, condensate dump flow rate control valve 26 for adjusting the condensate dump flow rate, low pressure gas heater outlet Condensate is recirculated to the inlet side, and low pressure gas heater inlet The low-pressure gas heater recirculation system 23 that raises the condensate temperature, the low-pressure feed water heater 15, and the low-pressure gas heater 7 supply the condensate to the medium-pressure steam turbine 1.
A deaerator 16 that deaerates with 0 extraction steam, a water supply pump 17 that pressurizes condensate deaerated by the deaerator 16 and discharges it to a water supply system, and a water supply supplied from the water supply pump 17 to a high-pressure steam turbine. The high-pressure feed water heater 18 that is heated by the extracted steam of 9 and the high-pressure gas heater 6 that exchanges heat with the boiler exhaust gas that is installed in parallel with the high-pressure feed water heater 18.

The flow of the intake / exhaust system of the boiler 5 in the exhaust gas reburn type combined plant of the prior art will be described below.

Exhaust gas from the gas turbine 3 and forced air from the forced draft fan 20 are supplied to the boiler 5 as combustion air. Since the gas turbine exhaust gas is a high temperature gas of 500 ° C. or higher, it is combined with the boiler suction air of 200 ° C. or higher at the outlet of the air preheater 21 and supplied to the boiler 5. On the other hand, since the exhaust gas temperature of the exhaust gas of the boiler 5 is relatively high at about 350 ° C., the air preheater 21 is used to recover heat to the boiler intake air, the high pressure gas heater 6 is used to recover heat to the feed water, and the high pressure gas heater 6 is also used. The low-pressure gas heater 7 recovers heat from the exhaust gas from the condensate.

FIG. 2 shows a temperature gradient diagram of feed water / condensate and boiler exhaust gas in an exhaust gas re-combustion combined plant. In FIG. 2, a to e are boiler exhaust temperature change curves from the boiler outlet to the low pressure gas heater outlet, and A to F are condensate / feed water temperature change curves from before the low pressure gas heater recirculation system integrated flow at the low pressure gas heater inlet to the boiler inlet. Indicates. In the boiler exhaust temperature change curves a to e, the boiler exhaust flows from a to e. a is a boiler outlet, b is a high pressure gas heater inlet, c is a high pressure gas heater outlet, d is a low pressure gas heater inlet, and e is a boiler exhaust gas temperature at a low pressure gas heater outlet. Condensate / Water Supply Temperature Change Curves A to F
Flows from F to F. A is the low pressure gas heater recirculation system integrated flow, B is the low pressure gas heater inlet, C is the low pressure gas heater outlet, D is the high pressure gas heater inlet, E is the high pressure gas heater outlet, and F is the boiler inlet feed water temperature. here,
The condensate temperature rise from A to B occurs at the low pressure gas heater inlet.
The increase in the condensate temperature due to recirculation of the condensate at the outlet of the low-pressure gas heater is shown.

This is to maintain the temperature of the outer surface of the heat transfer tube of the low-pressure gas heater above the acid dew point temperature of the sulfur component and prevent corrosion due to the sulfur component in the exhaust gas adhering as condensed water to the inlet of the low-pressure gas heater. Although it raises the condensate temperature, in the conventional exhaust gas reburn type combined plant, the condensate is taken out from the low pressure gas heater outlet, the low pressure gas heater recirculation pump is operated, and the low pressure gas heater recirculation flow rate control valve Circulating flow rates are being adjusted.

As related to the exhaust gas re-combustion type combined plant, JP-A-4-209904 and JP-A-4-209904
There is 234506 publication.

[0011]

In the exhaust gas re-combustion type combined plant of the prior art, as a means for raising the low pressure gas heater inlet condensate temperature and preventing low temperature corrosion in the low pressure gas heater 7, the low pressure gas heater 7 is cooled by the recirculation pump 27. The temperature was controlled by recirculating the condensate, but there are the following problems to raise the condensate temperature of the low-pressure gas heater inlet to prevent low temperature corrosion only by this control means.

(A) It is necessary to take a large amount of water distribution control between the high-pressure gas heater and the high-pressure feed water heater, the pressure fluctuation range of the water supply system for the same steam turbine load becomes large, and the boiler feed water flow rate control system becomes complicated. To do.

(B) A large amount of condensate distribution control is required between the low-pressure gas heater and the low-pressure feed water heater, and the pressure fluctuation range of the condensate system with respect to the same steam turbine load becomes large. Becomes complicated.

(C) When the low pressure gas heater condensate recirculation flow rate control is performed, the pressure fluctuation width of the condensate system with respect to the same steam turbine load becomes large, and the condensate distribution control between the low pressure gas heater and the low pressure feed water heater and the dewatering control are performed. The air level control system becomes complicated.

(D) If the feed water / condensate flow rate ratio on the high pressure feed water heater and the low pressure feed water heater side using the extracted steam from the steam turbine as a heating source becomes too small, the extraction steam installed in the extracted steam system. Since the chattering phenomenon occurs in the check valve, the feed water distribution control and condensate distribution control ranges are limited.

An object of the present invention is an exhaust gas re-combustion type combined plant that uses the exhaust gas of a gas turbine as boiler combustion air, and either a low pressure gas heater inlet condensate system, a boiler feed water system, or a low pressure gas heater outlet condensate system, or A combination of the two systems is equipped with a heat exchanger that transfers heat between the systems using a fluid that circulates in a closed cycle, exchanges heat with the low pressure gas heater inlet condensate system, and changes the condensate temperature of the low pressure gas heater inlet with the sulfur content of acid. An object of the present invention is to provide a low-temperature corrosion prevention device for an exhaust gas re-combustion combined plant, which prevents low-temperature corrosion in a low-pressure gas heater by raising the dew-point temperature or higher.

[0017]

According to the present invention, a heat exchanger is provided in any one of a low pressure gas heater inlet condensate system and a boiler feed water system, a low pressure gas heater outlet condensate system or between two heat exchangers. The low pressure gas heater inlet condensate temperature is raised and low temperature corrosion is prevented by circulating a fluid that serves as a heat transfer medium in a closed cycle, but the low pressure gas heater inlet condensate temperature is raised to prevent low temperature corrosion. Various problems pointed out when only the condensate recirculation flow rate of the low pressure gas heater 7 is controlled by the recirculation pump 27 as means are overcome.

The structure and means of the present invention created from the above are as follows.

(A) As a low temperature corrosion prevention device for an exhaust gas reburn type combined plant, a heat exchanger is provided in either the low pressure gas heater inlet condensate system, the boiler feed water system, the low pressure gas heater outlet condensate system, or in two systems.

(B) A fluid serving as a heat transfer medium is circulated by connecting the installed exchangers in a closed cycle.

(C) The set heat exchange amount of the heat exchanger is controlled by changing the flow rate of the fluid circulating between the heat exchangers.

In the conventional exhaust gas re-combustion combined plant, the condensate temperature of the low pressure gas heater is set to be equal to or higher than the acid dew point temperature by increasing the condensate temperature of the low pressure gas heater and recirculating the condensate of the low pressure gas heater 7 as a means for preventing low temperature corrosion. However, in the present invention, a low-temperature corrosion prevention device for raising the low-pressure gas heater inlet condensate temperature is provided by providing a heat exchanger in each system and circulating a fluid serving as a heat transfer medium by connecting the heat exchangers in a closed cycle. Set up. That is, since the heat exchange is performed by the fluid in the independent closed cycle, the recovered heat quantity ratio in each heater and the gas heater can be varied, and the controllability is improved.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a configuration diagram in which an exhaust gas reburning type combined plant according to an embodiment of the present invention is provided with a low temperature corrosion prevention device.

In the combustion air supply system to the boiler, a gas turbine (compressor 1, combustor 2,
Turbine 3), forced draft fan 20, and air preheater 21
Is provided.

The boiler exhaust gas system is provided with a high pressure gas heater 6, a low pressure gas heater 7, an induced draft fan 22, and a chimney 8. Since the air preheater 21 is a boiler heat exchanger for intake / exhaust air, it is also an exhaust gas system device.

The cycle on the steam turbine side is composed of the following. First, as a steam portion, a boiler 5 for converting feed water into steam, a high-pressure steam turbine 9 driven by steam generated in the boiler 5, and an exhaust steam of the high-pressure steam turbine 9 driven by steam reheated in the boiler 5 A low pressure steam turbine 11 driven by the exhaust steam of the pressure steam turbine 10 and the intermediate pressure steam turbine 10. The generator 12 is driven by these steam turbines. Next, in the condensate / water supply system, a condenser 13 for condensing the exhaust steam of the low-pressure steam turbine 11, a condensate pump 14 for boosting the condensate of the condenser 13 and discharging it to the condensate system, a condensate Low-pressure feed water heater 15 that heats the condensate supplied from the pump 14 by the extracted steam of the low-pressure steam turbine 11, low-pressure gas heater 7 that performs heat exchange with the boiler exhaust installed in parallel with the low-pressure feed water heater 15, steam turbine From the condensate dump system 19 for securing the condensate flow rate of the low-pressure gas heater 7 under partial load, the heat exchanger 29 for heating the condensate at the inlet side of the low-pressure gas heater 7, the low-pressure feed water heater 15, and the low-pressure gas heater 7. A deaerator 1 for deaerating the supplied condensate with the extracted steam of the medium-pressure steam turbine 10.
6, a feed water pump 17 that pressurizes the condensate deaerated by the deaerator 16 and discharges it to the water supply system, and a high-pressure feed water heater that heats the feed water supplied from the feed water pump 17 by the extraction steam of the high-pressure steam turbine 9. 18, and a high-pressure gas heater 6 installed in parallel with the high-pressure feed water heater 18 for exchanging heat with the boiler exhaust gas 6, and a heat exchanger 30 for heating the feed water at the inlet of the high-pressure gas heater 6.

The low-temperature corrosion prevention device according to this embodiment is composed of: A heat exchanger 29 that heats the condensate at the inlet side of the low-pressure gas heater 7, a heat exchanger 30 that takes in the heat quantity of the feed water into the closed cycle at the inlet side of the high-pressure gas heater 6, each heat exchanger 2
A pipe line for circulating the liquid of the heat medium that connects 9, 30 and 30, a circulation pump 31, a flow rate control valve 32, and a circulation pump minimum flow system 33.

The relationship between the feed water / condensed water and the boiler exhaust gas temperature in the exhaust gas re-combustion combined plant of this embodiment is shown in the temperature gradient diagram of FIG.

In FIGS. 4A to 4E, a to e are boiler exhaust temperature change curves from the inlet of the high pressure gas heater 6 to the outlet of the low pressure gas heater 7, and A to G are heat exchangers according to the present invention installed at the condensate inlet of the low pressure gas heater 7. The condensate / feed water temperature change curve from the 29 inlet to the high pressure gas heater 6 outlet is shown. In the boiler exhaust temperature change curves a to e, the boiler exhaust flows from a to e. a is an outlet of the boiler 5, b to c are high-pressure gas heaters 6,
d to e show changes in boiler exhaust gas temperature in the low-pressure gas heater 7. Condensation / supply water temperature change curves A to G
To G. A to B are heat exchangers 29 installed at the condensate inlet of the low pressure gas heater, B to C are low pressure gas heaters 7, a temperature rise between C to D is a deaerator 16, and a water supply pump 17, and D to E are high pressure gas heaters. The heat exchangers 30 and E to F installed at the 6 feed water inlet indicate changes in the boiler exhaust gas temperature in the high-pressure gas heater 6.

Among the respective temperatures shown in FIG. 4, the following items are listed as items that need temperature limitation for stable operation of the power generation plant and for ensuring performance. First, as a temperature limit item for stable operation of the plant, a boiler economizer inlet feed water temperature (that is, high-pressure gas heater 6 outlet feed water temperature F) for avoiding the steaming phenomenon in the economizer inside the boiler 5,
Degasifier inlet condensate temperature (that is, low pressure gas heater 7 outlet condensate temperature C) for ensuring degassing performance in the deaerator 16, and low temperature corrosion prevention temperature (that is, low pressure) of the heat transfer tube surface portion of the low pressure gas heater 7. Gas heater 7 inlet condensate temperature B). In normal plant rated load operation, F point is about 250-280 ° C or less,
The point C is about 10 to 20 ° C. lower than the saturation temperature in the deaerator, and the point B is about 60 ° C. in the case of a plant using gas fuel, although it depends on the fuel type of the plant. Next, there is a chimney inlet boiler exhaust gas temperature (that is, the low-pressure gas heater 7 outlet gas temperature e) as a temperature item that is limited to ensure plant performance. However, in normal plant rated load operation, the point e is about 100 to 110 ° C. is there.

In the present embodiment, among these temperature restrictions, the low temperature corrosion prevention control of the heat transfer tube surface of the low pressure gas heater 7 is not performed by the recirculation control of the condensate in the low pressure gas heater 7, but the heat exchangers 30, 29 are used. The method is controlled by the heat transfer of the fluid sealed in between. That is, the heat exchanger 30 takes in a part of the heat supply amount of the inlet water of the high-pressure gas heater 6, and the heat exchanger 29 radiates the heat to the inlet water of the low-pressure gas heater. Even though heat is transferred from such water supply to the low pressure gas heater 7 inlet condensate, since heat is transferred by an independent system, the flow rate distribution in the high pressure gas heater 6 and the low pressure gas heater 7 in the water supply / condensation system is performed. It does not become a control disturbance factor.

In addition to the embodiment of FIG. 3, there are FIGS. 5 and 6 as a structure in which the low temperature corrosion prevention device is provided in the exhaust gas re-combustion combined plant according to the embodiment of the present invention.

In the embodiment shown in FIG. 5, the heat exchanger 34,
It is a method of controlling by heat transfer of the fluid sealed in 29. That is, the heat exchanger 34 takes in a part of the heat of condensate at the outlet of the low-pressure gas heater 7, and the heat exchanger 29 radiates heat to the condensate at the inlet of the low-pressure gas heater. In this way, the low-pressure gas heater 7
Although the heat is transferred from the outlet condensate to the inlet condensate of the low-pressure gas heater 7, it is a heat transfer by an independent system, so it does not become a disturbance factor of the flow rate distribution control in the low-pressure gas heater 7 in the condensate system. .

In the embodiment of FIG. 6, the heat exchangers 34, 30,
And 29, the method is controlled by the heat transfer of the fluid. That is, the heat exchanger 34 takes in a part of the low pressure gas heater 7 outlet condensate heat amount, while the heat exchanger 30 takes in a part of the high pressure gas heater 6 inlet feed water heat amount and the heat exchanger 29 takes it to the low pressure gas heater inlet condensate water. Dissipate heat. Although heat is transferred from the low pressure gas heater 7 outlet condensate water and the high pressure gas heater inlet condensate water to the low pressure gas heater 7 inlet condensate in this way, since heat is transferred by an independent system, the high pressure in the water supply / condensation system is high. It does not become a disturbance factor of the flow rate distribution control in the gas heater 6 and the low pressure gas heater 7.

[0036]

By providing the low temperature corrosion preventive device according to the present invention in the exhaust gas reburn type combined plant, heat transfer to the low pressure gas heater inlet condensate system is made possible by heat transfer in the closed cycle, and therefore low pressure gas heater inlet condensate. By raising the temperature, it is possible to prevent low temperature corrosion on the heat transfer surface of the low pressure gas heater. Further, in the conventional method using the low pressure gas heater condensate recirculation system, the pressure fluctuation in the condensate system is large due to the amount of recirculation, which is a major disturbance factor to the low pressure gas heater condensate distribution control. According to the invention, the low pressure gas heater condensate recirculation itself can be omitted,
The flow control of the condensate system can be stabilized.

[Brief description of drawings]

FIG. 1 is a system diagram of a conventional exhaust gas reburn type combined plant.

FIG. 2 is a temperature gradient diagram of water supply / condensate and exhaust gas in a conventional exhaust gas re-combustion combined plant.

FIG. 3 is a system diagram showing an embodiment of an exhaust gas reburn type combined plant according to the present invention.

FIG. 4 is a temperature gradient diagram of water supply / condensate and exhaust gas in an exhaust gas re-combustion combined plant according to an embodiment of the present invention.

FIG. 5 is a system diagram showing an embodiment of an exhaust gas reburn type combined plant according to the present invention.

FIG. 6 is a system diagram showing an embodiment of an exhaust gas re-combustion combined plant according to the present invention.

[Explanation of symbols]

1 ... Compressor, 2 ... Combustor, 3 ... Gas turbine, 4, 12
... Generator, 5 ... Boiler, 6 ... High pressure gas heater, 7 ... Low pressure gas heater, 8 ... Chimney, 9 ... High pressure steam turbine, 10 ...
Medium-pressure steam turbine, 11 ... Low-pressure steam turbine, 13 ... Condenser, 14 ... Condensate pump, 15 ... Low-pressure feed water heater, 16
… Deaerator, 17… Water pump, 18… High-pressure water heater,
19 ... Condensate dump system, 21 ... Air preheater, 22 ... Induction draft fan, 24 ... High pressure gas heater feed water flow distribution control valve, 2
5 ... Low pressure gas heater condensate flow distribution control valve, 26 ... Condensate dump flow rate control valve, 29 ... Low pressure gas heater condensate heater on the inlet side, 30 ... High pressure gas heater feed water cooler on the inlet side, 31 ... Circulation pump , 32 ... flow control valve, 33 ... recirculation pump minimum flow system.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tetsuzo Kuribayashi 3-2-1, Saiwaicho, Hitachi, Ibaraki Hitachi Engineering Co., Ltd. (72) Inventor Katsumi Ura 3-1-1, Saiwaicho, Hitachi, Ibaraki No. 1 Stock company Hitachi Ltd. Hitachi factory

Claims (3)

[Claims] 1. A low-pressure gas heater inlet condensate by a fluid that circulates in a closed cycle between a low-pressure gas heater inlet condensate system and a boiler feed water system in an exhaust gas re-combustion combined plant that uses the exhaust gas of a gas turbine as boiler combustion air. A low-temperature corrosion prevention device for an exhaust gas re-combustion combined plant, which is provided with a heat exchanger for transferring heat to a system and increases an inlet condensate temperature of the low-pressure gas heater. 2. In an exhaust gas recombustion type combined plant which uses the exhaust gas of a gas turbine as boiler combustion air, the low pressure gas heater is circulated in a closed cycle between a low pressure gas heater inlet condensate system and a low pressure gas heater outlet condensate system. A low-temperature corrosion prevention device for an exhaust gas re-combustion combined plant, comprising a heat exchanger for transferring heat to an inlet condensate system to raise an inlet condensate temperature of the low-pressure gas heater. 3. A fluid which circulates in a closed cycle between a low pressure gas heater inlet condensate system and a boiler feed water system and a low pressure gas heater outlet condensate system in an exhaust gas re-combustion combined plant which uses the exhaust gas of a gas turbine as boiler combustion air. A low-temperature corrosion prevention device for an exhaust gas re-combustion combined plant, wherein a heat exchanger for transferring heat to the low pressure gas heater inlet condensate system is provided to raise the inlet condensate temperature of the low pressure gas heater.