JPH0510501A - Waste heat recovery boiler - Google Patents

Abstract

PURPOSE:To reduce the differential pressure across a water feed valve and prevent steam generation in an economizer. CONSTITUTION:An inlet control valve 38 is mounted on a water feed pipe 23 economizer 11 or an outlet control valve 42 is mounted can a drum water feed pipe 24. As steaming occurs in the economizer 11 with a decrease in load of a gas turbine, the differential pressure across a drum water feed valve 28 is shared by the inlet control valve 38 and the water feed valve 28 or by the water feed valve 28 and the outlet control valve 42 in order to keep the economizer 11 at the saturation pressure or higher.

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 device, and more particularly to a mixed pressure type exhaust heat recovery boiler for a combined gas turbine plant.

[0002]

2. Description of the Related Art A large-capacity thermal power plant is constructed to meet a rapidly increasing power demand, but these boilers are required to perform a transformer operation in order to obtain a high power generation efficiency even at a partial load. ing. This is a feature of recent electric power demand, and the difference between the maximum and minimum loads increases along with the growth of nuclear power generation, and thermal power generation tends to shift from base load use to load adjustment use. In other words, when operating thermal power generation for load adjustment, few boiler loads are always operated at full load, with 75% load and 50% load.
Load, 25% load increase, decrease load to operate or stop operation, so-called daily start / stop (Da
ily Start Stop (hereinafter simply referred to as DSS)
By carrying out an operation or the like to carry an intermediate load, the DSS operation allows operation only in the daytime when power demand is high, and stops operation at night to improve power generation efficiency. For example, a combined gas turbine plant has recently attracted attention as a part of high-efficiency power generation. In this combined gas turbine plant, power is first generated by the gas turbine, and the exhaust heat in the exhaust gas discharged from the gas turbine is recovered by the exhaust heat recovery boiler, and the steam generated in the exhaust heat recovery boiler is used. Then, the steam turbine is operated to generate electricity. In this way, the combined gas turbine plant has high power generation efficiency due to simultaneous power generation by the gas turbine and power generation by the steam turbine, and is also excellent in load responsiveness, which is a characteristic of the gas turbine. , It can cope with the descent well and has excellent load following ability, which is convenient for performing the DSS operation.

FIG. 4 is a schematic system diagram of a combined gas turbine plant. In FIG. 4, combustion air A from the air supply pipe 1 and fuel F from the fuel supply pipe 2 are supplied to the combustor 3
Are mixed and burned, and the combustion gas is used to rotate the gas turbine 4 to generate electricity. The exhaust gas G that has rotated the gas turbine 4 is introduced into the exhaust gas passage 6 of the exhaust heat recovery boiler 5. In the exhaust gas passage 6, from the downstream side to the upstream side, a low pressure boiler 10 including a low pressure economizer 7, a low pressure evaporator 8 and a low pressure drum 9, a high pressure economizer 11, a high pressure evaporator 12, a high pressure drum 13 and a superheater 14 are provided. A high-pressure boiler 15 composed of is arranged.

On the other hand, the feed water W _F, which is the fluid to be heated, is supplied from the feed pump 16 to the low-pressure economizer 7 via the feed pipe 17, is preheated to a predetermined temperature, and then passes through the low-pressure drum feed pipe 18 to low pressure. It is supplied to the drum 9. The water supply W _F supplied to the low-pressure drum 9 is supplied to the low-pressure down pipe 19 of the low-pressure drum 9.
After that, the low pressure evaporator 8 and the low pressure drum 9 are naturally circulated or forcedly circulated in that order, and then heated and separated into water and steam in the low pressure drum 9, and then the water is again reduced in pressure to the low pressure downcomer 19 and the low pressure evaporator. 8 and the low pressure drum 9, but the steam is supplied to the steam turbine 21 through the low pressure main steam pipe 20.

On the other hand, part of the high temperature water W _R split at the outlet of the low pressure economizer 7 is supplied from the boiler transfer pump 22 to the high pressure economizer 11 via the high pressure water supply pipe 23 and preheated to a predetermined temperature. Then, the water is supplied to the high-pressure drum 13 through the high-pressure drum water supply pipe 24. The high-temperature water W _R supplied to the high-pressure drum 13 is circulated in the order of the high-pressure evaporator 12 and the high-pressure drum 13 via the high-pressure downcomer pipe 25 of the high-pressure drum 13 similarly to the low-pressure boiler 10, and is separated in the high-pressure drum 13. The steam is sent to the superheater 14 via the drum steam outlet pipe 26, where the temperature is further raised, and then the steam turbine 21 is supplied from the high pressure main steam pipe 27.
Is supplied to the steam turbine 21 to generate electric power.

The water separated by the high pressure drum 13 is
It is recirculated to the high-pressure downcomer 25, the high-pressure evaporator 12, and the high-pressure drum 13. The water supply levels of the high-pressure drum 13 and the low-pressure drum 9 are controlled by operating the high-pressure drum water supply valve 28 and the low-pressure drum water supply valve 29, respectively.

On the other hand, the steam turbine 21 uses the steam turbine 21.
The steam obtained by rotating 1 becomes water in the condenser 30, and is supplied to the exhaust heat recovery boiler 5 again from the water supply pump 16. Since the water supply W _F of the water supply pipe 17 is as low as about 30 ° C., when the water is supplied to the low pressure economizer 7 at the same water supply temperature, low temperature corrosion occurs in the low pressure economizer 7, so the low pressure boiler 10 It is necessary to mix the hot water W _R in the high-pressure boiler 15 to raise the feed water temperature to a predetermined temperature at which low-temperature corrosion does not occur, and then feed the low-pressure economizer 7. That is, the high pressure water supply pipe 2
A part of the high temperature water W _R of No. 3 is supplied from the outlet of the boiler transfer pump 22 to the water supply pipe 17 through the recirculation flow path 33 having the recirculation flow rate adjusting valve 32 to prevent low temperature corrosion of the low pressure economizer 7. ing.

Reference numeral 31 is a generator, and 34 is between the high-pressure evaporator 12 and the high-pressure economizer 11 or the high-pressure evaporator 12 in order to remove nitrogen oxides in the exhaust gas G of the gas turbine 4.
Denitration device placed in the middle of the, 35 is a superheated steam communication pipe,
36 is a superheated steam stop valve, and 37 is a pressure regulating valve.

While the above description has explained the general flow of exhaust gas, water supply, steam, etc. in a combined gas turbine plant, the low pressure drum water supply pipes 18 of the low pressure economizer 7 and the high pressure economizer 11 will be described below. The reason why the high-pressure drum water supply valve 28 and the low-pressure drum water supply valve 29 are arranged in the high-pressure drum water supply pipe 24 will be described.

The exhaust gas characteristics of the gas turbine 4 are shown in FIG. 5. The exhaust gas amount hardly changes even when the load of the gas turbine is low as shown by the curve B in FIG. 5, but the exhaust gas temperature shows the curve in FIG. As indicated by C, the lower the gas turbine load, the lower the load. Therefore, when the load is low, the evaporation amount decreases and the water supply amount decreases as the exhaust gas temperature decreases, but since the exhaust gas amount hardly changes, a phenomenon occurs in which steam is generated in the economizers 7, 11. In this case, the attached equipment may be damaged due to the generation of a water hammer or the like.
By utilizing the characteristic that the discharge pressure increases as the flow rate of 2 decreases, the high pressure drum water supply valve 2 is connected to the low pressure drum water supply pipe 18 and the high pressure drum water supply pipe 24 located at the outlets of the economizers 7 and 11.
8, the low-pressure drum water supply valve 29 is installed, the economizer 7, 11
Was boosted at low load to prevent steam generation. In the conventional plant, the operating pressure is about 60 kg / cm in the high pressure system.
² g, a low pressure system of about 10 kg / cm ² g at a relatively low pressure.
8. The differential pressure of the low-pressure drum water supply valve 29 is also about 5 to 100 kg.
As small as / cm ² , there was no problem.

[0011]

However, with the recent increase in the combustion temperature of the gas turbine, the steam pressure of the exhaust heat recovery boiler is also increased, and high efficiency is aimed at. In this case, the pressure is about 100 to 150 kg / cm ² g in the high pressure system.
Also, the differential pressure between the high-pressure drum water feed valve 28 and the low-pressure drum water feed valve 29 becomes a very high differential pressure of about 5 to 200 kg / cm ^2, and therefore, the erosion of the high-pressure drum water feed valve 28 and the low-pressure drum water feed valve 29, etc. The problem arises. The present invention is intended to solve the drawbacks of the prior art, and an object thereof is to provide an exhaust heat recovery boiler capable of reducing the differential pressure of the water supply valve and preventing steam generation in the economizer. To do.

[0012]

In order to achieve the above-mentioned object, the present invention provides a control valve for adjusting the pressure of the economizer in at least one of the water supply pipe and the drum water supply pipe.

[0013]

[Function] Since the pressure of the economizer is shared by the drum water supply valve and the control valve, the differential pressure of the water supply valve can be reduced, and erosion of the water supply valve and steaming of the economizer can be prevented.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a system diagram of a main part of an exhaust heat recovery boiler according to an embodiment of the present invention, FIG. 2 is a characteristic curve diagram showing pressure and feed water temperature on the vertical axis, and gas turbine load on the horizontal axis, and FIG. It is a principal part system diagram which showed other Examples. 1 and 3,
Reference numerals 11 to 28 are the same as conventional ones. 38 is an inlet control valve provided in the high pressure water supply pipe 23, 39 is a pressure detector, 40 is a feed water temperature detector, 41 is a pressure controller, and 42 is an outlet control valve provided in the high pressure drum water supply pipe 24. Curve D in FIG. 2 is the pressure at the outlet of the high-pressure feed pump (boiler transfer pump), curve E is the operating pressure of the high-pressure drum 13, curve H is the saturation pressure equivalent to the outlet feed water temperature of the high-pressure economizer 11, and curve I. Represents the operating pressure of the high-pressure economizer 11, and curve J represents the outlet water temperature of the high-pressure economizer 11.

When one high-pressure drum water feed valve 28 is installed only at the outlet of the high-pressure coal economizer 11 as in the prior art, as shown in FIG. 2 under a low load, a very large differential pressure K is applied to the high-pressure drum water feed valve. However, there is a problem that the life of the high-pressure drum water supply valve 28 is shortened and noise is increased due to the generation of erosion of the high-pressure drum water supply valve 28. On the other hand, in the embodiment of the present invention, as shown in FIG. 1, the inlet control valve 38 is also installed in the high pressure water supply pipe 23 of the high pressure economizer 11, and the feedwater temperature at the outlet of the high pressure economizer 11 is detected. By controlling the operating pressure of the high-pressure economizer 11 (curve I in FIG. 2) detected by the vessel 40 to be equal to or higher than the saturation pressure (curve H in FIG. 2) at which steam is not generated in the high-pressure economizer 11, As shown in FIG. 2, the high pressure drum water supply valve 28 and the inlet control valve 38 share and reduce the differential pressure L of the drum water supply valve 28.
This eliminates the problems of erosion and noise.

FIG. 3 shows another embodiment of FIG. 1. In FIG. 1, the high pressure water supply pipe 23 is provided with an inlet control valve 38, but in FIG. 3, it is a high pressure drum water supply pipe. 24 is provided with an outlet control valve 42 so that the differential pressures L and M in FIG. 2 are shared by the high-pressure drum water feed valve 28 and the outlet control valve 42, and other explanations are the same as those in FIG. ..
The effect of the embodiment shown in FIG. 3 is that it is not necessary to control the outlet feed water temperature of the high-pressure economizer 11, and the high-pressure economizer 11 does not generate steam at a saturated high pressure (curve H or higher in FIG. 2).
It can be maintained at.

[0017]

According to the present invention, the generation of steam in the economizer can be prevented, the differential pressure of the valve can be reduced, and erosion and noise can be prevented.

[Brief description of drawings]

FIG. 1 is a system diagram of essential parts of an exhaust heat recovery boiler according to an embodiment of the present invention.

FIG. 2 is a characteristic curve diagram showing pressure and feed water temperature on the vertical axis and gas turbine load on the horizontal axis.

FIG. 3 is a system diagram of main parts of an exhaust heat recovery boiler showing another embodiment.

FIG. 4 is a schematic system diagram of a combined gas turbine plant.

FIG. 5 is a characteristic curve diagram in which the vertical axis represents exhaust gas amount and exhaust gas temperature, and the horizontal axis represents gas turbine load.

[Explanation of symbols]

 7 Low pressure economizer 9 Low pressure drum 11 High pressure economizer 13 High pressure drum 17 Water supply pipe 18 Low pressure drum water supply pipe 23 High pressure water supply pipe 24 High pressure drum water supply pipe 28 High pressure drum water supply valve 29 Low pressure drum water supply valve 38 Inlet control valve 42 Outlet adjustment valve

Claims (1)

Claims: 1. A water supply pipe is connected to the inlet of the economizer, the outlet of the economizer is connected to the drum by a drum water pipe, and the drum water valve of the drum water pipe is used for the economizer. An exhaust heat recovery boiler, wherein at least one of the water supply pipe and the drum water supply pipe is provided with a control valve for adjusting the pressure of the economizer.