EP2612008A1

EP2612008A1 - Flushing the exhaust gas recirculation lines of a gas turbine

Info

Publication number: EP2612008A1
Application number: EP11743518.0A
Authority: EP
Inventors: Floris Van Straaten; Jürgen Hoffmann
Original assignee: Alstom Technology AG
Current assignee: Ansaldo Energia Switzerland AG
Priority date: 2010-09-02
Filing date: 2011-08-09
Publication date: 2013-07-10
Also published as: KR101577611B1; JP2013538969A; US8955302B2; CA2809394C; US20130174535A1; KR20130102055A; RU2013114470A; US20150107257A1; CN103097695B; JP5943920B2; WO2012028430A1; CH703770A1; CA2809394A1; RU2537327C2; CN103097695A

Abstract

The invention relates to a method for reliably flushing the exhaust gas recirculation line (8) of a gas turbine (14) having exhaust gas recirculation, without using additional blow-out fans, and to a gas turbine (14) for carrying out the method. In order achieve the aim, the invention relates to a method, in which a blow-off flow of the compressor (2) is used for flushing the exhaust gas recirculation line (8). The invention further relates to a gas turbine (14) having at least one flushing line (20) connecting a compressor blowoff point to the exhaust recirculation line (8).

Description

DESCRIPTION

RINSING THE EXHAUST RECIRCULATION CIRCUITS OF A GAS TURBINE

TECHNICAL AREA

The present invention relates to purging an exhaust gas recirculation line of a gas turbine with exhaust gas recirculation. It relates to a method for purging the exhaust gas recirculation line and a gas turbine for carrying out the method.

PRIOR ART In order to reduce the power losses and efficiency losses of gas turbines and combined cycle power plants with carbon dioxide deposition, various possibilities have been proposed in the literature to increase the carbon dioxide partial pressure before deposition. Exhaust gas recirculation is a technology that can be used for various purposes in gas turbines. For example, it can be used to control NOx emissions by providing an intake gas with reduced reactivity, that is usually used with respect to fresh air reduced oxygen content, or for the reduction of the exhaust gas volume for carbon dioxide deposition. In the exhaust gas recirculation in a gas turbine, a substantial proportion of the exhaust gas from the entire

Branch exhaust stream and is, typically after cooling and if necessary after cleaning, the Ansaugmassenstrom the turbine respectively the compressor of the gas turbine fed again. This is the recirculated

Exhaust gas stream mixed with fresh air and then fed this mixture to the compressor. A corresponding power plant with a gas turbine and exhaust gas recirculation is known for example from WO2010 / 072710.

In a HRSG (heat recovery steam generator or waste heat boiler) and exhaust pipes downstream of the gas turbine, fuel residues can accumulate when the system is switched off. These fuel residues are removed by a so-called boiler flushing before restarting the system from the volumes concerned. This safety measure aims to free the exhaust pipes and the HRSG of residual fuels and explosive gas mixtures and to avoid possible explosions during start-up. Boiler purging is accomplished by driving the shaft train through a launching device at a low speed and low mass flow thereby

Residual fuels are driven out of the system via the chimney.

In gas turbines with exhaust gas recirculation also fuel residues in the exhaust gas recirculation lines and can when switching off the system

Auxiliary equipment, such as recooler, water separator, etc. of

Collect exhaust gas recirculation system. Before restarting, or before these lines and auxiliary equipment are accessible for inspection or repair, they too, e.g. be flushed with fresh air. Preferably, the exhaust gas recirculation lines are opposite to

Flushed flow direction of normal operation. Thus, the scavenging air can be discharged through the normal fireplace. In addition, it is ensured that evtl. existing fuel residues not from the boiler in the

Exhaust gas recirculation lines get and the flushing time must be extended again or even creates a cycle. EP2060772 discloses a system and method for purging

Exhaust gas recirculation lines proposed. Here, additional flaps and, for example, an additional fan are proposed for exhaust gas recirculation, which allow to flush the exhaust gas recirculation line. The variety of

Flaps the additional fan lead to additional costs and increased

Energy demand during the rinsing process, which may affect the competitiveness of such plants with CO2 capture.

PRESENTATION OF THE INVENTION

It is therefore an object of the invention to provide a method that allows a reliable flushing of the exhaust gas recirculation lines without the use of additional blow-off blowers. Further, specify a gas turbine capable of reliably rinsing the exhaust gas recirculation piping without the use of additional blowers. In addition, the number of additional flaps, valves and piping should be minimized.

The object is solved by the entirety of the features of claims 1 and 15. The inventive method is characterized in that a blow-off of the compressor is used for purging the exhaust gas recirculation line.

When operating a compressor with speeds that are well below the

Nominal speed are (standstill to about 20% below the rated speed), for example, at start, at shutdown and boiler flushing, a part of the sucked air from the compressor must be blown off. For it is partially compressed air over Plena discharged from the compressor and, for example blown directly into the environment or routed through lines in the exhaust pipe of the gas turbine and blown off over the fireplace. Typically, a gas turbine is operated for boiler purging at speeds well below the rated speed. This means that the gas turbines are operated in a speed range in which air is blown out of the compressor. These are, for example, a range of 20% to 50% of the rated speed, wherein in large gas turbines, the rated speed is equal to the mains frequency. For boiler purging, the generator is typically operated by means of a frequency converter, typically a so-called SFC (static frequency converter), as a motor that drives the gas turbine.

Depending on the compressor design and speed, a large part of the compressor intake flow is blown off via the blow off valves during boiler rinsing. The

Blowing rate can be up to 60%, in special cases even more, of

Compressor Ansaugstrom. The bleed off mass flow is

typically proportional to the compressor pressure ratio of the compressor at full load and the compressor intake flow proportional to the speed at which blowoff occurs. As the pressure in the plena of the compressor above the

Ambient pressure is, this mass flow can be used in whole or in part for purging the exhaust gas recirculation lines. For this purpose, at least one connecting line is provided with a control element from a compressor plenum to the exhaust gas recirculation line.

In a preferred embodiment, the blow-off air is introduced into an end region of the exhaust gas recirculation line and at another end of the

Exhaust gas recirculation line discharged. For practical reasons, it may be difficult to introduce the blow-off air directly into the end of the exhaust gas recirculation line. An initiation in the end region, ie, is typically in a portion of at most 10 to 20% of the one end of the line is removed preferred to avoid larger dead spaces at the end of a line and to ensure a well-defined flow direction.

In one embodiment, the blow-off air at a second end of the

Exhaust gas recirculation line, which opens into the intake line of the compressor of the gas turbine, initiated. From there, the blow-off air flows counter to the direction of the recirculation flow in the normal operation of the gas turbine through the exhaust gas recirculation line and is at a first end of the

Exhaust gas recirculation line discharged. The first end of the

Exhaust gas recirculation line is the end at which the exhaust gas recirculation line is connected to an exhaust line of the gas turbine. This connection is

For example, combined with a control element, such as a control flap.

When rinsing is after flowing through the Abgasrezirkulationsleitung the

Blow-off air is directed from the first end of the exhaust gas recirculation line directly or indirectly into the chimney.

The flow of blow-off air from the recirculation line into the

Compressor intake flow of the compressor is controlled by a control element disposed between the location where the blow-off air is disposed in the exhaust gas recirculation passage and a second end of the exhaust gas recirculation passage. This control element is typically a flap or a valve.

This control element also permits the ratio of the blow-off air flowing to the second end of the exhaust gas recirculation line and the blow-off air flowing to the first end of the exhaust gas recirculation line. For example, blowing air is blown through the second end of the air for a short time

Rinsed exhaust gas recirculation line in the compressor inlet line and then rinsed the exhaust gas recirculation line in the direction of the first end. As a short time, this is a period of a few seconds to a few minutes to understand. Typically about one tenth to one fifth of the kettle flushing time. In a further embodiment, a first part of the blow-off air is introduced into the exhaust gas recirculation line for purging, and a second part of the blow-off air is fed via a blow-off line to the exhaust pipes and typically to the HRSG.

In yet another embodiment blow-off air from a first blow-off point of the compressor is introduced into the exhaust gas recirculation line for purging and blow-off air from a second blow-off point of the compressor is supplied via a blow-off line to the exhaust pipes and thus typically to the HRSG.

In addition to the method, a gas turbine with recirculation, which allows flushing of the exhaust gas recirculation line by Verdichterabblasluft, the subject of the invention. A gas turbine according to the invention with an exhaust gas recirculation line, which connects an exhaust line of the gas turbine to the compressor intake line for the recirculation of exhaust gases into the compressor intake flow, has at least one purge line which connects a compressor exhaust point to the exhaust gas recirculation line.

Typically, in this purge line, a purge valve for controlling the

Spülmassenstromes provided. This allows the blow-off flow, with which the exhaust gas recirculation line is purged by blow-off air to regulate. This purge valve may be arranged in series with conventional relief valves or replace them and their function, that is to take over the closing of the blow in normal operation of the gas turbine and the opening for starting and stopping the gas turbine.

Furthermore, a blow-off line can connect the compressor blow-off point, to which the flushing line is connected, to the exhaust gas line of the gas turbine. This allows one part of the blow-off air to be used for backflushing the exhaust gas recirculation line and the other part through the blow-off line into the exhaust line to lead. Further, it can be prevented at a shutdown of the gas turbine or at a quick shutdown (trip) that gases pass under high pressure and temperature from the compressor into the Abgasrezirkulationsleitungen. In this case, the purge valve remains closed and the blow-off valve is opened at shutdown as in a conventional gas turbine. Even during the start, it may be advantageous to close the flush valve after flushing and blow off the blow-off during startup only via the blow-off. In order to regulate the blow-off separately, in one embodiment a blow-off valve is arranged in the blow-off line.

In a further embodiment, at least one second blow-off line is provided by a second compressor blow-off point, which connects it to the exhaust gas line of the gas turbine. Typically, in the exhaust gas recirculation line of a gas turbine with

Exhaust gas recirculation provided a recirculation fan, which supports the recirculation of the exhaust gases in the compressor intake. During the flushing process, the flow direction is opposite to that of normal operation and the recirculation fan leads to an increased pressure gradient. To avoid this additional pressure gradient, the recirculation fan is in a

Embodiment connected via a coupling with its drive. This coupling makes it possible to disengage the recirculation fan during the flushing process, so that it can run freely contrary to its normal direction of rotation and thus its pressure loss is reduced.

In a further embodiment, the recirculation fan is designed with adjustable guide and / or moving blades. These can be opened to reduce the flow resistance. Alternatively, they can be switched so that the recirculation fan operates counter to its normal flow direction and assists flushing. Typically, large recirculation fans are driven by a variable motor. In a further alternative embodiment, the control allows the motor to be driven counter to its normal direction of rotation so that the recirculation fan is reduced during flushing

Provides flow resistance or rinse assist.

A further embodiment of the invention is characterized in that the flushing process is performed by the recirculation fan. For flushing the exhaust gas recirculation line, the adjustable guide and / or moving blades will be switched so that the recirculation blower operates counter to its normal flow direction and thus the exhaust gas recirculation lines against the normal flow direction with air coming from the suction line of

Discharged compressor rinses. Alternatively, the engine of the

Recirculation blower are driven controlled against its normal direction of rotation, so that the exhaust gas recirculation lines is flushed against the normal flow direction with air, which is branched off from the suction line of the compressor. For these embodiments can be dispensed with the purge line and blow-off from the compressor in the exhaust gas recirculation line.

BRIEF EXPLANATION OF THE FIGURES

The invention will be described below with reference to embodiments in the

Connection with schematic drawings will be explained in more detail. Show it

1 shows a gas turbine with HRSG and exhaust gas recirculation, discharge line into the exhaust gas recirculation line for purging the exhaust gas recirculation lines,

2 shows a gas turbine with HRSG and exhaust gas recirculation, discharge line into the exhaust gas recirculation line for purging the exhaust gas recirculation lines and a blow-off line to the HRSG.

WAYS FOR CARRYING OUT THE INVENTION

A gas turbine with HRSG and exhaust gas recirculation is shown schematically in FIG. Further, the lines and actuators for blowing off compressor air into the exhaust gas recirculation line for flushing this line are shown.

The gas turbine comprises a compressor 2 (compressor), a combustion chamber 3 and a turbine 4. The combustion air compressed in the compressor 2 is fed to the combustion chamber 3 there and then the hot combustion gases in the turbine 4 are expanded. The useful energy generated in the turbine is converted into electrical energy, for example, by means of a generator 5 arranged on the same shaft. The exhaust gases exiting the turbine 4 are used to make optimum use of the energy still contained therein in a HRSG 23 (heat recovery steam generator) or heat recovery steam generator, steam for one

Steam turbine or other plants to produce.

A compressor intake stream 1 for the compressor 2 is typically supplied via an inflow channel. Fresh intake air is initially passed through an air filter arranged at the inlet. Downstream of this air filter can

Muffler be arranged in the guide channel of the compressor intake 1. The air supply with filter and muffler is referred to simplifying as compressor intake manifold.

A portion of the exhaust gases is introduced at such a system behind the HRSG 23 in a flow divider 1 1, which may be regulated, in a first end 16 of an exhaust gas recirculation line 8 and is about this

Exhaust gas recirculation line 8 recirculated into the compressor intake stream 1. For the recirculated exhaust gases flow from a second end 17 of the

Exhaust gas recirculation line 8 in the compressor intake stream 1, are mixed with the fresh intake air and are thus returned to the suction side of the compressor 2. The non-diverted portion of the exhaust gases is typically led to a carbon dioxide separation unit or discharged to the environment via a chimney 12.

The recirculated exhaust gas flow is in an exhaust gas recooler 13 or

Heat exchanger, which may be equipped with a condenser, cooled to slightly above ambient temperature. Downstream of this exhaust gas recooler 13, a recirculation fan 9 may be arranged, which is driven for example via a coupling 24 by a drive 25. The drive is typically an electric motor.

In normal operation, the intake air is mixed with recirculated exhaust gases before the compressor 2. Here are the first blow-off valve 6 and in normal operation Flushing valve 7 closed. Further, a control element 10, with which the outlet of the exhaust gas recirculation line 8 can be closed in the compressor suction, opened. To allow purging of the exhaust gas recirculation line 8 is a

Purge line 20 from a Abblasstelle of the compressor 2 to the second end 17 of the exhaust gas recirculation line 8 is provided. It does not lead directly to the second end of the exhaust gas recirculation line 8 but is replaced by the

Control element 10 separated from the compressor intake. For controlling the purge flow itself, a purge valve 7 is provided. A blow in the

Exhaust pipe 21 of the gas turbine 14 is possible through a first discharge line 18. To control the blow-off in the exhaust pipe 21, a first blow-off valve 6 is provided. For rinsing, the gas turbine 14 is brought to rinsing speed. For this purpose, it is typically driven by the motor 5 operated as a generator. For flushing the exhaust gas recirculation line 8, the flush valve 7 is opened. About the purge valve 7, the blow-off air from the compressor 2 through the

Exhaust gas recirculation line 8 is blown into the chimney 12 and thus the

Flue gas recirculation lines 8 rinsed. The control element 10 is closed for at least part of the purging duration to ensure that the blow-off air can not flow into the compressor intake flow.

The first blow-off valve 6 allows dividing the blow-off flow into a part with which the exhaust gas recirculation line is purged and into a part which is supplied to the exhaust pipe 21. Further, the first blow-off valve 6 allows e.g. to blow off large amounts of hot air during a trip of the plant. If one

Blowdown is provided via the exhaust gas recirculation line 8, this must be designed for correspondingly hot air.

Depending on the volume of the exhaust gas recirculation line 8 and the Abblasluftmengen only a portion of the blow-off air for flushing the exhaust gas recirculation line 8 is required. For example, the air from a first plenum, for example after the low pressure part of a compressor 2, is used for purging the exhaust gas recirculation line 8. The air from a second plenum, for example, after the medium-pressure part of a compressor 2, however, via a second blow-off valve 15 and a second blow-off 19 directly to the exhaust pipe 21 of the gas turbine 14th

recycled. A corresponding system is shown schematically in FIG.

All explained advantages can be used not only in the respectively specified combinations, but also in other combinations or alone, without departing from the scope of the invention. For example, instead of the

Use of blow-off air from a blow-off point, as shown in FIGS. 1 and 2, the blow-off air from several blow-off points of the compressor 2 are combined and used for purging the exhaust gas recirculation line 8. For simplicity, the control of valves or flaps is described. This regulation is representative of a regulation or a control. the

A person skilled in the art will continue to be familiar with the various suitable control elements, such as flaps or valves. A blow-off point of the compressor is typically a location at which cooling air for the turbines and / or combustion chamber cooling is also removed from the compressor. The purge line 20 does not have to go directly from the compressor but may be from a conventional exhaust line or

Be diverted cooling air line. The examples show a gas turbine 14 with a simple combustion chamber. The invention is correspondingly applicable to gas turbines with sequential combustion, as known for example from EP0718470. LIST OF REFERENCE NUMBERS

1 compressor intake flow

2 compressors

3 combustion chamber

4 turbine

5 generator

6 first blow-off valve

7 flushing valve

8 exhaust gas recirculation line

9 recirculation fan

10 control element

1 1 flow divider

12 Fireplace / pipe for CO2 capture

13 exhaust gas recooler

14 gas turbine

15 second blow-off valve

16 first end

17 second end

18 first blow-off line

19 second blow-off line

20 flushing line

21, 22 exhaust pipe

23 HRSG

24 clutch

25 drive

Claims

1 . A method for purging an exhaust gas recirculation line (8) of a

Gas turbine (14), characterized in that the gas turbine (14) is operated at a flushing speed, from the compressor (2) blow-off air is discharged and this air is introduced into the exhaust gas recirculation line (8) for flushing.

2. The method according to claim 1, characterized in that the

Blow-down air is introduced into one end of the exhaust gas recirculation line (8) and discharged at another end of the exhaust gas recirculation line (8).

3. The method according to claim 1 or 2, characterized in that the

Blowdown air at a second end (17) of the exhaust gas recirculation line (8), which opens into the intake line of the compressor of the gas turbine, is introduced through the exhaust gas recirculation line (8) counter to the direction of

Recirculation flow in normal operation of the gas turbine flows and is discharged from a first end (16) of the exhaust gas recirculation line (8).

4. The method according to claim 3, characterized in that the

Blow-off air after passing through the exhaust gas recirculation line (8) from the first end (16) of the exhaust gas recirculation line (8) is passed directly or indirectly into the chimney.

5. The method according to any one of claims 1 to 4, characterized in that the blow-off air is introduced into the exhaust gas recirculation line (8), a partial flow in the direction of the second end (17) of the exhaust gas recirculation line (8) is passed and a second partial flow in the direction of first end (16) of the exhaust gas recirculation line (8) is passed.

6. The method according to claim 5, characterized in that the

Ratio of the blow-off air leading to the second end (17) of

Exhaust gas recirculation line (8) flows and the blow-off air, which flows to the first end (16) of the exhaust gas recirculation line (8) is controlled by a control element (10).

7. The method according to any one of claims 1 to 6, characterized in that a first part of the blow-off air for purging in the exhaust gas recirculation line (8) is introduced and a second part of the blow-off air via a second blow-off line (19) is supplied to the HRSG (23) ,

8. gas turbine (14) with an exhaust gas recirculation line (8) having a

Exhaust pipe (21, 22) of the gas turbine with the compressor intake to

Recirculation of exhaust gases in the compressor intake flow (1) connects, characterized in that at least one purge line (20) of a

Compressor blow-off in the exhaust gas recirculation line (8) leads.

9. Gas turbine (14) according to claim 8, characterized in that a flushing valve (7) for controlling the Spülmassenstromes, with the

Exhaust gas recirculation line (8) is purged by blow-off, is arranged in the purge line (20).

10. Gas turbine (14) according to any one of claims 8 or 9, characterized

characterized in that in the exhaust gas recirculation line (8) a control element (10) between the mouth of the purge line (20) in the exhaust gas recirculation line (8) and the mouth of the exhaust gas recirculation line (8) in the

Compressor suction, is arranged to regulate a back purging of the blow-off air into the compressor inlet or to prevent.

1 1. Gas turbine (14) according to one of claims 8 to 10, characterized

characterized in that a first discharge line (18) the Verdichterabblasstelle, to the purge line (20) is connected to the exhaust pipe (21, 22) of the gas turbine (14) connects.

12. Gas turbine (14) according to any one of claims 8 to 1 1, characterized

in that a first blow-off valve (6) is arranged in the first blow-off line (18).

13. Gas turbine (14) according to any one of claims 8 to 12, characterized

in that a second discharge line (19) has a second discharge line (19)

Verdichterabblasstelle with the exhaust pipe (21, 22) of the gas turbine (14) connects.

14. Gas turbine (14) according to any one of claims 8 to 13, characterized

characterized in that in the exhaust gas recirculation line (8) a

Rezirkulationsgeblase (9) is provided by its drive (25)

is arranged decoupled, so that during the blow-off the

Rezirkulationsgeblase (9) against its normal direction of rotation can run freely.

15. Gas turbine (14) according to any one of claims 8 to 13, characterized in that in the exhaust gas recirculation line (8) a recirculation blast (9) is arranged with adjustable guide and / or blades, or a

Rezirkulationsgeblase (9) with a drive (25) is connected

Direction of rotation is reversible, so that the recirculation blower (9) during the blow-off offers a reduced flow resistance or supports the rinse.