JP2001003711A - Exhaust heat recovery boiler and operating method for exhaust heat recovery boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heat a NOx removal system in a short time even in the cold start operation to lower NOx concentration by providing a high temperature water supply means for supplying external high temperature water to a high pressure drum and a steam supply means for supplying external steam to a high pressure evaporator. SOLUTION: This exhaust heat recovery boiler is provided with a high temperature water supply pipe 27 for supplying high temperature water to a high pressure drum 22. Further, the boiler is provided with a steam pipe 31 for supplying some of steam to the high temperature water supply pipe 27 and the remaining to a high pressure evaporator 23. When the internal pressure of the high pressure drum 22 and the high pressure evaporator 23 becomes predetermined pressure, the exhaust heat recovery boiler closes a communicating valve 29 so that the high temperature water is supplied to the high pressure drum 22 and the high pressure evaporator 23 to raise the temperature of the periphery of a high pressure superheater 21 and the NOx removal system 24. Subsequently, purge operation is performed, and at that time, the purge air takes heat from the high pressure superheater 21 and the high pressure evaporator 23 to become high temperature, and the temperature of the NOx removal system 24 is further elevated. Thus, during warming-up and purge operation, the temperature of the NOx removal system 24 is elevated so that from the start, NOx concentration is suppressed.

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 for operating the exhaust heat recovery boiler, in which the concentration of nitrogen oxides contained in exhaust gas is kept low.

[0002]

2. Description of the Related Art In recent years, in view of high plant thermal efficiency, high frequency of use, and a small adverse effect on the environment, a number of combined cycle power plants combining a gas turbine plant and a steam turbine plant have been used in thermal power plants as actual machines. Has been applied.

[0003] This combined cycle power plant uses natural gas, which generates little sulfur oxide, as a fuel, and uses nitrogen oxide (NO) when producing combustion gas.
The environmental pollution is reduced by using a gas turbine combustor that keeps the concentration of x) low.

Further, this combined cycle power plant is provided with an exhaust heat recovery boiler for generating steam by using exhaust gas discharged to a gas turbine plant as a heat source, thereby increasing the thermal efficiency of the plant by effectively utilizing heat while increasing the gas thermal efficiency. N contained in exhaust gas from turbine plant
A denitration device for keeping the Ox concentration low is accommodated in an exhaust heat recovery boiler, so that it can sufficiently comply with the pollution control value set by law.

As described above, the heat of the exhaust gas is effectively used,
An exhaust heat recovery boiler incorporated in a combined cycle power plant that suppresses NOx concentration is a long tubular body 2 extending in the flow direction of exhaust gas 1 as shown in FIG.
A reheater 3, a high-pressure superheater 4, a high-pressure evaporator 6 having a high-pressure drum 5, a denitration device 7,
High pressure first economizer 8, medium pressure superheater 9, medium pressure evaporator 11 having medium pressure drum 10, low pressure superheater 12, medium pressure economizer 1
3, a low-pressure evaporator 16 having a high-pressure second economizer 14, a low-pressure drum 15, a low-pressure economizer 17, and a high-pressure third economizer 18 are accommodated.

In the exhaust heat recovery boiler, a damper 18a is provided outside the cylinder 2, when the operation is stopped, the damper 18a is closed, the exhaust gas 1 is confined in the cylinder 2, the reheater 3, the high-pressure superheater 4, so-called hot banking operation for keeping the temperature of the steam remaining in the heat exchanger high. The exhaust heat recovery boiler shown in FIG. 5 has a high-pressure drum 5 having a pressure of 130 kg / cm ² class,
Pressure is 40 kg / cm ^2nd class medium pressure drum 10, pressure is 8
kg / cm ² with a low pressure drum 15 of the ^second class,
Although it is of the drum type, the steam drum may be of a double pressure type with a high and low pressure depending on the temperature of the exhaust gas discharged from the gas turbine plant.

As described above, the conventional exhaust heat recovery boiler uses the exhaust gas 1 from the gas turbine plant as a heat source, and sequentially flows to the reheater 3 as a high-pressure heat exchanger, the high-pressure superheater 4, and the high-pressure evaporator 6. The steam is raised to a high pressure and high temperature, and the high pressure and high temperature steam is supplied to a steam turbine plant, and the NOx concentration contained in the exhaust gas 1 is reduced by the denitration device 7.
Further, the steam flowing sequentially through the high-pressure first coal economizer 8, the medium-pressure superheater 9, etc. as a high-medium-low-pressure heat exchanger is pressurized and heated to bring the temperature of the exhaust gas 1 to about 100 ° C.
a, It is released to the atmosphere via a chimney.

[0008]

By the way, in the denitration device 7 housed in the exhaust heat recovery boiler, its denitration performance largely depends on the temperature of the catalyst itself. As shown in FIG. 6, the relationship between the temperature of the catalyst itself and the denitration efficiency is such that the denitration efficiency increases proportionally up to about 200 ° C., and when the temperature exceeds 200 ° C., a state of saturation occurs.

According to this diagram, the exhaust gas temperature is 200 ° C.
If the temperature falls below the limit, the denitration efficiency will be low, so even if the exhaust heat recovery boiler can keep the NOx concentration low during rated operation, the plant will not be able to operate for a long period of time due to planned or forced shutdown of cold start, periodic inspection, etc. When restarting after shutdown, exhaust gas 1 is reheated 3
When passing through heat exchangers such as the high-pressure superheater 4, the high-pressure evaporator 6, ..., etc., heat is taken away and the temperature of the exhaust gas 1 itself decreases,
There was a problem that it was not possible to maintain a low NOx concentration as designed.

In recent years, due to environmental considerations, there are plants in which environmental regulation values such as NOx emission concentration / total emission amount are set not only during the rated operation but also during the start-up operation of the exhaust heat recovery boiler. NOx during cold start
Measures are needed.

As a specific countermeasure against such a problem, for example, Japanese Patent Laid-Open Publication No. Sho 61-76803 is disclosed.

In this technique, while circulating the water in the drum and the water in the evaporator, steam supplied from another heating source is added to heat and pressurize the water, and the exhaust gas flowing through the denitration device is discharged. It raises the temperature.

However, at the time of cold start, the water in the drum and the like has dropped to near the atmospheric temperature, and the pressure thereof has also approached the atmospheric pressure, so that the steam having relatively low specific heat has a specific heat (heat capacity).
It takes a long time to raise the temperature of the drum water or the water in the evaporator, which has a large size. Therefore, there is a problem or inconvenience that it takes a long time to raise the temperature of the denitration apparatus and to increase the denitration efficiency.

The present invention has been made in view of such circumstances, and even in a cold start-up operation, an exhaust heat recovery boiler in which a NOx concentration is kept low by heating a denitration apparatus in a short time and an operation of the exhaust heat recovery boiler. The aim is to provide a method.

[0015]

In order to achieve the above object, the exhaust heat recovery boiler according to the present invention is housed in a cylindrical body, and re-circulated along the flow of exhaust gas. A high-temperature evaporator provided with a heater, a high-pressure superheater, a high-pressure drum, and a high-temperature water supply means for supplying high-temperature water from an external heat source to the high-pressure drum; First steam supply means for supplying steam from an external heat source to the vessel.

Further, in order to achieve the above object, an exhaust heat recovery boiler according to the present invention has the following features.
The reheater is housed in the cylinder and follows the flow of the exhaust gas,
A high-pressure superheater, a high-pressure evaporator having a high-pressure drum, a high-temperature water supply means for supplying high-temperature water from an external heat source section to the high-pressure drum, and an external heat source provided to the evaporator. A first steam supply unit for supplying steam from the unit and a second steam supply unit for supplying steam from an external heat source unit to the reheater.

Further, in order to achieve the above object, the exhaust heat recovery boiler according to the present invention has the following features.
The high-temperature water supply means is a high-temperature water supply pipe that connects the external heat source and the high-pressure drum.

Further, in order to achieve the above object, the exhaust heat recovery boiler according to the present invention has the following features.
The first steam supply means is a high-pressure evaporator warming pipe for connecting the external heat source section and the high-pressure evaporator.

In order to achieve the above object, an exhaust heat recovery boiler according to the present invention has the following features.
The second steam supply means is a reheater warming pipe for connecting the external heat source and the reheater.

In order to achieve the above object, the method for operating a waste heat recovery boiler according to the present invention supplies high-temperature water to a high-pressure drum before fuel ignition of a gas turbine. At the same time, a warming operation of the high-pressure drum and the high-pressure evaporator is performed by supplying steam to the high-pressure evaporator, and then a purge operation of guiding the exhaust gas remaining in the gas turbine to the high-pressure evaporator is performed. This is a method of heating the denitration apparatus with air deprived of heat from the high-pressure evaporator heated by the operation and the purge operation.

According to a seventh aspect of the present invention, in order to achieve the above object, high-temperature water is supplied to the high-pressure drum before the fuel of the gas turbine is ignited. Along with supplying steam to each of the high-pressure evaporator and the reheater, the high-pressure drum, the high-pressure evaporator and the reheater are warmed, and then the exhaust gas remaining in the gas turbine is discharged to the reheater and This is a method in which a purging operation guided to a high-pressure evaporator is performed, and the denitration apparatus is heated with air that has been deprived of heat from the reheater and the high-pressure evaporator heated in the warming operation and the purging operation.

In order to achieve the above object, the operating method of the exhaust heat recovery boiler according to the present invention discharges exhaust gas remaining in the gas turbine before the fuel of the gas turbine ignites. When performing the purge operation for guiding to the heat recovery boiler, the damper provided on the downstream side of the exhaust heat recovery boiler is opened, and the exhaust gas of the gas turbine is forcibly flowed, guided to the denitration device, and heated. It is a way to make it.

[0023]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a waste heat recovery boiler and a steam operating method according to the present invention.

FIG. 1 is a partially cutaway schematic system diagram illustrating a first embodiment of an exhaust heat recovery boiler and an operation method of the exhaust heat recovery boiler according to the present invention.

The exhaust heat recovery boiler according to this embodiment has a high-pressure evaporator provided with a reheater 20, a high-pressure heater 21, and a high-pressure drum 22 in a long cylindrical body 19 in order along the flow of the exhaust gas EG. 23, a denitration device 24, and a heat exchanger such as a high-pressure first economizer 25 are accommodated.

Further, the waste heat recovery boiler supplies high temperature water from a high pressure economizer or a medium pressure economizer of an adjacent exhaust heat recovery boiler to the high pressure drum 22 through the connecting pipe 26. A tube 27 is provided. The connecting pipe 26 is connected to a high-pressure first economizer 25 provided with a drum water supply valve 28, and supplies high-temperature water generated in the high-pressure first economizer 25 to the high-pressure drum 22.

The exhaust heat recovery boiler supplies, for example, a part of the steam supplied from the high pressure drum of the adjacent exhaust heat recovery boiler to the high temperature water supply pipe 27 through the communication valve 29 and the other part. A steam pipe 31 is provided to supply the high-pressure evaporator 23 via a high-pressure evaporator warming pipe 30 having a warming valve 30a. The high pressure drum 22 has a drum water blow system 32, the high pressure evaporator 23 has an evaporator blow valve 33, the high pressure drum 22 has a vent valve 34, and the high pressure superheater 21 has a high pressure superheater drain valve 35. Each is provided.

Next, an operation method of the exhaust heat recovery boiler based on the above configuration will be described.

At the time of cold start, the internal pressure of the high-pressure drum 22 is substantially close to the atmospheric pressure, and the drum water is in a state close to the atmospheric temperature. In such a state, when performing the start-up operation, the exhaust heat recovery boiler first blows the drum water out of the system through the drum water blowing system 32, opens the evaporator blow valve 33, and discharges the water inside the device. Even after blowing out of the system,
The steam supplied from the steam pipe 31 is supplied to the high-pressure drum 22 through the communication valve 29, the high-temperature water supply pipe 27, and the communication pipe 26, and the high-pressure drum 22 and the high-pressure evaporator 23 are warmed (warmed up). Let At that time, the high-pressure superheater outlet valve 36 is closed, and the high-pressure superheater drain valve 35 is interposed.
The high-pressure superheater 21 is also caused to perform the warming operation.

After the warming operation, the exhaust heat recovery boiler closes the evaporator blow valve 33, the vent valve 34, and the high pressure superheater drain valve 35, closes the drum water blow system 32, and connects the steam pipe 31 to the communication valve 29. , High-temperature water supply pipe 27, connecting pipe 2
The internal pressure of the high-pressure drum 22 and the high-pressure evaporator 23 is increased by, for example, steam of 350 ° C. and 7 ata supplied through 6.

When the internal pressure of the high-pressure drum 22 and the high-pressure evaporator 23 reaches a predetermined pressure, the exhaust heat recovery boiler closes the communication valve 29, and the boiler recovers approximately 250 mm from the high-temperature water supply pipe 27.
The high-temperature water of ° C. is supplied to the high-pressure drum 22 and the high-pressure evaporator 23, and the surroundings of the high-pressure superheater 21 and the denitration device 24 housed therein are heated.

When the temperature around the high-pressure superheater 21 and the denitration device 24 becomes high, the gas turbine plant performs a purge operation during rotation of the gas turbine at an increased speed, for example, at 30% of the rated rotation speed in consideration of preventing explosion due to residual gas. Then, the residual air in the gas turbine is purged and supplied to the exhaust heat recovery boiler. At this time, the purge air takes heat from the high-pressure superheater 21 and the high-pressure evaporator 23 to raise the temperature, and further raises the temperature of the denitration device 24. The high-pressure evaporator 23 whose heat has been removed by the purge air may open the warming valve 30a and supply the steam supplied from the steam pipe 31 through the high-pressure evaporator warming pipe 30. When the steam in the high-pressure superheater 21 whose heat has been removed by the purge air is drained, the high-pressure superheater drain valve 35 may be appropriately opened to blow the drain out of the system.

As described above, in this embodiment, the NOx concentration can be kept low from the initial stage of the start-up operation because the temperature of the denitration device 24 is raised in advance during the warming operation and the purge operation.

FIG. 4 is a NOx concentration diagram at the time of starting operation of the gas turbine, in which the present embodiment is compared with the conventional one. In FIG. 4, r is a rotation speed distribution line of the gas turbine,
e ₁ is a conventional denitration efficiency distribution line, e ₂ is a denitration efficiency distribution line according to the present embodiment, g is a NOx concentration distribution line contained in exhaust gas supplied to an exhaust heat recovery boiler, and g ₁ is a conventional denitration device 24. by suppressing the NOx concentration NOx concentration suppression distribution line, _{g 2} inhibits NOx concentration NOx concentration suppression distribution line by denitration apparatus according to the present embodiment, _{T 1} is the fuel ignition time of the gas turbine, _{T 2} is the gas turbine exhaust Times indicating peak values of the NOx concentration supplied to the heat recovery boiler are shown.

[0035] Conventionally, heat recovery steam generator, because it was allowed to heat the denitrator 24 combustion gas generated in the fuel ignition time T ₁ of the gas turbine as a heat source, NOx concentration in the exhaust gas supplied from the gas turbine There also is a peak value time T ₂ low denitration efficiency e ₁ of the denitration apparatus 24, N
It could not suppress the Ox concentration value g _1.

On the other hand, in the present embodiment, the denitration device 2
4 because the are heated during warming operation and the purge operation, the denitration efficiency e ₂ of the denitration apparatus 24 by the fuel ignition time T ₁ of the gas turbine has high, NOx concentration value g
₂ can be kept low from the start of the start-up operation.

Therefore, according to the present embodiment, since the NOx concentration is kept low from the beginning of the starting operation of the gas turbine, the N.sub.
Ox concentration can be kept sufficiently within the legally regulated values,
Environmental pollution can be reliably prevented.

FIG. 2 is a partially cutaway schematic system diagram illustrating a second embodiment of the exhaust heat recovery boiler and the method of operating the exhaust heat recovery boiler according to the present invention. The same parts as those of the first embodiment are denoted by the same reference numerals.

The exhaust heat recovery boiler and the operation method of the exhaust heat recovery boiler according to the present embodiment are described as follows.
A reheater warming pipe 37 provided with a warming valve 37a for supplying steam for warming to the reheater 20 is provided, and a reheater drain valve 38 for blowing the drain having warmed the reheater 20 out of the system is provided. The reheater 20 is always maintained at a high temperature.

The exhaust heat recovery boiler and the operation method of the exhaust heat recovery boiler according to the present embodiment are characterized in that the air for heating the denitration device 24 removes heat in the reheater 20 during the warming operation and the purge operation. The steam pipe 3
A reheater warming pipe 37 branching from 1 and connected to the reheater 20 is provided, and steam is always supplied to the reheater 20 to keep the reheater 20 in a high temperature state.

As described above, in the present embodiment, since the reheater 20 is always maintained at a high temperature, the temperature of the air flowing through the reheater is increased more quickly, and the denitration device 24 is heated in a relatively short time. The NOx concentration can be kept low under high denitration efficiency even during the start-up operation.

FIG. 3 is a partially cutaway schematic system diagram for explaining a third embodiment of the method for operating the heat recovery steam generator according to the present invention. The same parts as those of the first embodiment are denoted by the same reference numerals.

The operation method of the exhaust heat recovery boiler according to the present embodiment is the same as that of the low pressure evaporator 4 having the low pressure drum 39 which is accommodated on the downstream side of the cylindrical body 19 and is arranged along the flow of the exhaust gas EG.
0, a low-pressure economizer 41 and a high-pressure third economizer 42 were installed.
The damper 43 provided outside the high-pressure third economizer 42 is opened during the purge operation, and the air in the cylinder is forcibly flown by using the tunnel effect to heat the denitration device 24. According to actual measurement, the rotation speed of the gas turbine is 100 rpm
When the damper 43 was opened even at m, it was recognized that the air in the cylinder 19 flowed by the tunnel effect.

As described above, in the present embodiment, during the purge operation, the damper 43 is opened, and the air in the cylinder 19 is forcibly flowed to heat the denitration device 24. , NOx concentration can be kept low.

[0045]

As described above, according to the exhaust heat recovery boiler and the operation method of the exhaust heat recovery boiler according to the present invention, the air is heated by the heat taken from the heat exchanger heated in the warming operation and the purge operation. And the heated air is used to heat the denitration device.
Ox concentration can be kept low.

[Brief description of the drawings]

FIG. 1 is a partially cutaway schematic system diagram illustrating a first embodiment of an exhaust heat recovery boiler and an operation method of the exhaust heat recovery boiler according to the present invention.

FIG. 2 is a partially cutaway schematic system diagram illustrating a second embodiment of an exhaust heat recovery boiler and an operation method of the exhaust heat recovery boiler according to the present invention.

FIG. 3 shows a third method of operating the waste heat recovery boiler according to the present invention.
1 is a partially cutaway schematic diagram illustrating an embodiment.

FIG. 4 is a NOx concentration diagram at the time of a gas turbine start-up operation in which an exhaust heat recovery boiler according to the present invention and an operation method of the exhaust heat recovery boiler are compared with a conventional method.

FIG. 5 is a schematic system diagram showing a conventional exhaust heat recovery boiler.

FIG. 6 is a denitration efficiency distribution diagram showing the denitration efficiency with respect to the temperature of the denitration apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust gas 2 Cylindrical body 3 Reheater 4 High-pressure superheater 5 High-pressure drum 6 High-pressure evaporator 7 Denitration device 8 High-pressure first-coal saving device 9 Medium-pressure superheater 10 Medium-pressure drum 11 Medium-pressure evaporator 12 Low-pressure superheater 13 Medium Pressure-saving economizer 14 High-pressure second economizer 15 Low-pressure drum 16 Low-pressure evaporator 17 Low-pressure economizer 18 High-pressure third ecosystem 18a Damper 19 Cylindrical body 20 Reheater 21 High-pressure superheater 22 High-pressure drum 23 High-pressure evaporator Reference Signs List 24 denitration device 25 high-pressure first economizer 26 communication pipe 27 high-temperature water supply pipe 28 drum water supply valve 29 communication valve 30 high-pressure evaporator warming pipe 30a warming valve 31 evaporator pipe 32 drum water blow system 33 evaporator blow valve 34 Vent valve 35 High pressure superheater drain valve 36 High pressure superheater outlet valve 37 Reheater warming pipe 37a Warming valve 38 Reheater drain valve 39 Low pressure drum 0 low pressure evaporator 41 low-pressure economizer 42 high third economizer 43 damper

Claims (8)

[Claims] 1. A waste heat recovery boiler that is housed in a cylindrical body and sequentially arranged along a flow of exhaust gas, a reheater, a high pressure superheater, a high pressure evaporator having a high pressure drum, and a waste heat recovery boiler having a denitration device. An exhaust heat recovery boiler comprising: a high-temperature water supply unit that supplies high-temperature water from an external heat source unit; and a first steam supply unit that supplies steam from the external heat source unit to the high-pressure evaporator. 2. A waste heat recovery boiler, which is housed in a cylindrical body and sequentially arranged along a flow of exhaust gas, a reheater, a high-pressure superheater, a high-pressure evaporator having a high-pressure drum, and a waste heat recovery boiler having a denitration device. High-temperature water supply means for supplying high-temperature water from an external heat source, first steam supply means for supplying steam from the external heat source to the evaporator, and supply of steam from the external heat source to the reheater Waste heat recovery boiler, comprising: 3. The exhaust heat recovery boiler according to claim 1, wherein the high-temperature water supply means is a high-temperature water supply pipe connecting the external heat source and the high-pressure drum. 4. The exhaust heat recovery boiler according to claim 1, wherein the first steam supply means is a high pressure evaporator warming pipe connecting the external heat source and the high pressure evaporator. 5. The exhaust heat recovery boiler according to claim 2, wherein the second steam supply means is a reheater warming pipe connecting the external heat source and the reheater. 6. A high-temperature water is supplied to a high-pressure drum and steam is supplied to a high-pressure evaporator to perform a warming operation of the high-pressure drum and the high-pressure evaporator before fuel ignition of the gas turbine. A purging operation for guiding exhaust gas remaining in the high-pressure evaporator to the high-pressure evaporator, and heating the denitration apparatus with air deprived of heat from the high-pressure evaporator heated in the warming operation and the purge operation. How to operate the heat recovery boiler. 7. A high-pressure drum is supplied with high-temperature water and steam is supplied to each of a high-pressure evaporator and a reheater before fuel ignition of the gas turbine. Performing a purge operation for guiding the exhaust gas remaining in the gas turbine to the reheater and the high-pressure evaporator. The reheater and the high-pressure evaporator heated in the warming operation and the purge operation are performed. A method for operating a waste heat recovery boiler, comprising heating a denitration apparatus with air from which heat has been removed. 8. When a purge operation for guiding exhaust gas remaining in the gas turbine to an exhaust heat recovery boiler is performed before fuel ignition of the gas turbine, a damper provided on a downstream side of the exhaust heat recovery boiler is opened. A method for operating an exhaust heat recovery boiler, comprising forcibly flowing exhaust gas from a turbine, guiding the exhaust gas to a denitration device, and heating the denitration device.