JP2949287B2 - Auxiliary steam extraction method for waste heat recovery boiler - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust heat recovery boiler in a combined cycle power plant, and more particularly to a method of extracting air from an exhaust heat recovery boiler that supplies generated steam to an auxiliary steam system. .

[Conventional technology]

As part of high-efficiency power generation, construction of a combined cycle power plant has recently been promoted. This plant generates electricity using a gas turbine, collects the heat of the exhaust gas discharged from the gas turbine with an exhaust heat recovery boiler, and drives a steam turbine with the steam generated by the exhaust heat recovery boiler to generate power. Has become.

In addition to the high-efficiency power generation described above, this plant has the features of gas turbines, such as easy start-up and high load responsiveness, making it suitable for intermediate load operation in accordance with recent power demand patterns. Power plant. In addition, this power plant has a power output of about 120,000 kw in combination of a gas turbine, an exhaust heat recovery boiler, and a steam turbine. Therefore, a high output power plant is configured by combining a plurality of these devices.

 FIG. 10 is a schematic system diagram of this combined plant.

The exhaust gas G from the gas turbine 4 is supplied to an exhaust heat recovery boiler 5
Into the exhaust gas passage 6. In this exhaust gas passage 6,
A superheater 12, a high-pressure drum 8, a high-pressure evaporator 10, and a high-pressure economizer 7 are arranged.

On the other hand, water W _F is a heated fluid is supplied to the high pressure economizer 7 through the water supply pipe 18 from the condensate pump 17, after being preheated up to a predetermined temperature, is supplied to the high pressure drum 8.

A part of the water supplied to the high-pressure drum 8 passes through the high-pressure downcomer 9 of the high-pressure drum 8 and becomes a part of steam in the high-pressure evaporator 10, and the rest returns to the high-pressure drum 8 by water supply. The steam separated in the high-pressure drum 8 is sent to a superheater 12 via a drum steam outlet pipe 11, where the temperature is further increased, and then supplied to a steam turbine 14 from a high-pressure main steam pipe 13, and the steam turbine 14 By generator
Drive 15 to generate electricity.

Also, as shown in FIG. 11, when starting or stopping the plant, steam for the gland seal of the steam turbine 14 is required, so that the steam is supplied from the auxiliary steam header 21 to the auxiliary steam pipe.
The steam is supplied to the steam turbine 14 via the 20 and the gland seal steam pipe 22. The auxiliary boiler 23 is usually used as a steam supply source to the auxiliary steam header 21, but in the case of a combined cycle power plant, a plurality of exhaust heat recovery boilers 5 are installed. The steam from the main steam pipe 13 is also supplied via the high-pressure main steam extraction pipe 19.

On the other hand, nitrogen oxides (hereinafter referred to as NO
In general, a denitration device 31 is provided in the exhaust heat recovery boiler 5 to remove the high pressure evaporator 10 as shown in FIG.
It is installed on the downstream side or between the high-pressure evaporators 10.

[Problems to be solved by the invention]

As described above, when the steam generated from the exhaust heat recovery boiler 5 is used as the auxiliary steam, when the steam is extracted, the pressure of the high-pressure drum 8 decreases, and the amount of evaporation increases. The following problems arise. (1) When the pressure of the high-pressure drum 8 decreases, the amount of evaporation increases, the separation performance of the steam separator installed inside the drum decreases, water droplets in the steam increase, and the turbine blades of the steam turbine Damage. Further, if the number of steam-water separators is increased in response to the decrease in the separation performance of the steam-water separator, the drum becomes unnecessarily large, which is very uneconomical.

(2) Since the amount of evaporation increases, the high-pressure evaporator outlet connection pipe 24
And the steam flow rate in the drum steam outlet pipe 11 increases, and vibration occurs. In addition, it is very uneconomical to increase the diameter of the tube in response to an increase in the amount of evaporation.

(3) When the pressure of the high-pressure drum 8 decreases, the amount of evaporation increases, the fluid temperature in the high-pressure evaporator decreases, and the heat retained by the exhaust gas of the gas turbine that exchanges heat with it is taken away more than necessary. The gas temperature decreases, the reaction rate of the denitration reaction decreases, and the exhausted NOx increases.

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art,
An object of the present invention is to provide a method for extracting steam generated from an exhaust heat recovery boiler for auxiliary steam without lowering the operation performance.

[Means for solving the problem]

The above object has a plurality of exhaust heat recovery boilers provided with a system for generating steam by performing denitration and heat recovery from exhaust gas and supplying the generated steam to a steam turbine and an auxiliary steam system. The auxiliary steam extraction method of the exhaust heat recovery boiler detects the drum pressure of any one of the exhaust heat recovery boilers and selects the exhaust heat recovery boiler that supplies steam to the auxiliary steam system according to the signal. You.

Instead of the drum pressure signal, a signal of steam or feed water flow rate in the pipe or flow rate in the pipe, a signal of the denitration apparatus inlet gas temperature, and a signal of the steam turbine inlet pressure are detected and used. Is also good.

[Action]

The present invention relates to a signal of a drum pressure, a flow rate of steam or feed water in a pipe or a flow rate in a pipe, a signal of an inlet gas temperature of a denitration apparatus, and a signal of a steam turbine inlet pressure of any one of a plurality of exhaust heat recovery boilers. The above-mentioned drawbacks of the prior art are eliminated by operating the steam generated from the exhaust heat recovery boiler for auxiliary steam by selecting the exhaust heat recovery boiler that supplies steam to the auxiliary steam system according to the detected signal. Bleed can be performed without deteriorating performance.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic system diagram of a combined cycle power plant according to a first embodiment of the present invention. The reference numerals 1A to 24 in the figure are the same as those of the related art. Prior to the description of FIG. 1, the characteristics of the pressure of the high-pressure drum 8, the amount of evaporation, and the temperature of the gas entering the denitration apparatus when the steam generated from the exhaust heat recovery boiler 5 is extracted will be described.

FIG. 2 shows that even when the gas turbine 4 has the same load, the pressure of the high-pressure drum 8 decreases as the steam extraction amount increases, the evaporation amount increases accordingly, and the inlet gas temperature of the denitration device 31 decreases. Is shown.

FIG. 3 shows the relationship between the amount of extracted steam, the pressure of the high-pressure drum 8 and the amount of steam that can be processed by the steam-water separator. The separation performance is reduced, and there is a lower limit of the high pressure drum 8 pressure. That is, the vapor pressure drum 8 pressure, so that it is bled to decrease the pressure P ₀ in the case of no bleed until the pressure P ₁ (permissible pressure). Further, when the auxiliary steam more than the bleedable amount is required, it is necessary to cope by increasing the number of cans of the exhaust heat recovery boiler 5 to be bleed or operating the auxiliary boiler 23. Accordingly, the present invention is a high pressure drum 8 pressure as shown in FIG. 1 is detected by the pressure detector 27, until a pressure P _1, No.1 by the control valve 26A opens the exhaust heat recovery boiler 5 If steam is extracted from, and more steam is required, increase the number of exhaust heat recovery boilers that extract in No.2, No.3, or operate the auxiliary boiler 23. is there. Here, whether to bleed air from the exhaust heat recovery boiler 5 or to operate the auxiliary boiler 23 is programmed in advance in the controller 25 such that the operating exhaust heat recovery boiler 5 is given priority over the auxiliary boiler 23. It should be decided in. Also, depending on the load of the gas turbine 4, the allowable pressure
P ₁ can also be left in partnership with different since, programmed into the controller 25 seeking allowable pressure P ₁ of the relationship between the load of the gas turbine 4. The fact that a program is formed based on the gas turbine load also applies to the following second to fourth embodiments.

FIG. 4 is a diagram for explaining a second embodiment of the present invention.

This embodiment differs from the first embodiment in that the first embodiment detects the pressure of the high-pressure drum 8 to control the amount of extracted steam, whereas the second embodiment employs a high-pressure drum. The flow rate (flow rate) in the evaporator outlet communication pipe 24 is measured by the flow meter 28, and thereby the amount of extracted steam is controlled.

Figure 5 is a steam flow rate of extracted steam flow rate and the high-pressure evaporator outlet connection pipe 24, shows the relationship between the flow rate, is that possible extraction until the vapor flow rate W ₁ as a Seime flow velocity V _1. Here, instead of the flow rate in the high-pressure evaporator outlet connection pipe 24, it is also possible to control the flow rate in the drum steam outlet pipe 11, the high-pressure main steam pipe 13, and the water supply pipe 18.

FIG. 6 is a diagram for explaining a third embodiment of the present invention. This embodiment differs from the first and second embodiments in that, in the first and second embodiments, the amount of extracted steam is controlled by the pressure of the high-pressure drum 8 and the flow rate in the high-pressure evaporator outlet communication pipe 24. On the other hand, in the third embodiment, the amount of extracted steam is controlled by the gas temperature at the inlet of the denitration device 31.

Figure 7 is shows the relationship between the extracted steam amount and the denitrification device 31 inlet gas temperature, is that the bleed until acceptable gas temperature Tg ₁ to satisfy the NOx emission regulation value.

FIG. 8 is a view for explaining a fourth embodiment of the present invention. FIG. 8 shows a low-pressure evaporator 33 and a low-pressure evaporator 33 of a relatively low pressure system on the gas downstream side of the high-pressure economizer 7 of the exhaust heat recovery boiler 5 as compared with the first, second and third embodiments. Economizer
30 is provided. Water w _F from condensate pump 17 is supplied to the low-pressure economizer 30, where it is preheated to a predetermined temperature, it is supplied to the low pressure drum 37. The water supplied to the low-pressure drum 37 is supplied to the low-pressure
The refrigerant circulates through a low-pressure evaporator 33 and a low-pressure drum 37 in this order via 32.
The steam separated in the low-pressure drum 37 is sent to the steam turbine 14 via the low-pressure main steam pipe 35. Low pressure economizer for high pressure system
Part of the 30 outlet water supply is branched and passes through the high pressure water supply pump 34,
It is supplied to the high-pressure economizer 7. After that, it is as described above.

In the first, second and third embodiments, the exhaust heat recovery boiler 5 having only the high pressure system has been described. Of course, the same applies to the exhaust heat recovery boiler 5 having the high pressure system and the low pressure system. .

The fourth embodiment differs from the first embodiment in that the amount of extracted steam is controlled by the pressure of the high-pressure drum 8 in the first embodiment, whereas the steam turbine of the low-pressure main steam pipe 35 is different from that of the first embodiment. The amount of extracted steam is controlled by the inlet pressure 36. Of course, it is also possible to control with the low pressure drum 37 pressure instead of the steam turbine inlet pressure 36.

FIG. 9 shows the relationship between the amount of extracted steam and the pressure of the steam turbine inlet 36 of the low-pressure main steam pipe 35 and the pressure of the low-pressure drum 37.
Until the minimum pressure P ₁ to maintain the steam turbine inlet pressure 36 higher than the atmospheric pressure is that bleed possible. The reason why the pressure higher than the atmospheric pressure is ensured here is that when the pressure becomes a negative pressure, air enters and a problem such as corrosion occurs. Of course, it is also possible to control with the low pressure drum 37 pressure instead of the steam turbine inlet pressure 36.

〔The invention's effect〕

According to the present invention, when the steam generated by the exhaust heat recovery boiler is extracted and used as auxiliary steam, excessive extraction can be prevented, so that there is an effect that the normal operation of the exhaust heat recovery boiler is always possible.

[Brief description of the drawings]

FIG. 1 is a schematic system diagram of a combined cycle power plant according to a first embodiment of the present invention, and FIG. 2 is a table showing a relationship among a steam extraction amount, a high-pressure drum pressure, an evaporation amount, and a gas temperature at an inlet of a denitration apparatus.
FIG. 3 is a chart showing the relationship between the amount of steam extracted, the high-pressure drum pressure, and the amount of steam that can be processed by the steam separator. FIG. 4 is a schematic system diagram of a combined cycle power plant according to a second embodiment of the present invention.
Fig. 6 is a table showing the relationship between the amount of steam bleed, steam flow rate, and flow velocity. Fig. 6 is a schematic system diagram of the combined cycle power plant according to the third embodiment of the present invention. FIG. 8 is a schematic diagram of a combined cycle power plant according to a fourth embodiment of the present invention, and FIG. 9 is a diagram showing the relationship between the amount of steam bleed, the inlet pressure of the steam turbine of the low-pressure main steam pipe, and the low-pressure drum pressure. FIG. 10 is a schematic diagram of a conventional combined cycle power plant, and FIG. 11 is a diagram of a conventional auxiliary steam system. 4… Gas turbine, 5… Waste heat recovery boiler, 8… High pressure drum, 14… Steam turbine, 21… Auxiliary steam header, 23…
Auxiliary boiler, 24… High pressure evaporator outlet connection pipe, 27… Pressure detector, 28… Flow meter, 31… Denitration equipment, 36 …… Steam turbine inlet pressure, G…

Claims (4)

(57) [Claims] 1. A plurality of exhaust heat recovery boilers having a system for generating steam by performing denitration and heat recovery from exhaust gas and supplying the steam to a steam turbine and an auxiliary steam system. An auxiliary heat recovery boiler, wherein a drum pressure of any one of the exhaust heat recovery boilers of the boiler is detected and an exhaust heat recovery boiler for supplying steam to the auxiliary steam system is selected based on the detected signal. Steam extraction method. 2. The auxiliary steam extraction method for an exhaust heat recovery boiler according to claim 1, wherein the signal of the steam pressure or the flow rate of the steam or feed water in the pipe is used instead of the signal of the drum pressure. 3. The auxiliary steam extraction method for an exhaust heat recovery boiler according to claim 1, wherein the signal of the gas temperature at the denitration device is used instead of the signal of the drum pressure. 4. The method according to claim 1, wherein a signal of a steam turbine inlet pressure is used instead of the drum pressure signal.