METHOD FOR COUNTERACTING DRAFT THROUGH AN ARRANGEMENT INCLUDING A GAS TURBINE DURING A STOP

Abstract

The method for counteracting draft through an arrangement including a gas turbine during a stop, including stopping the gas turbine and then equalizing the pressure at least through the gas turbine.

Description

TECHNICAL FIELD

The present invention relates to a method for counteracting draft through an arrangement including a gas turbine during a stop. The gas turbine is preferably part of a power plant for electric power generation. In addition, preferably the arrangement also comprises a heat recovery steam generator, i.e. a steam generator in which heat from the exhaust gas discharged from the gas turbine is recovered to generate steam that is e.g. used in a steam cycle. Naturally the gas turbine and possibly heat recovery steam generator can also be used in applications different from power plants, e.g. mechanical-drive units (e.g. for application in the oil & gas field to move compressors/pumps); other applications are further possible.

BACKGROUND

Power plants with gas turbines and possibly heat recovery steam generators supplying a steam cycle are connected to electric grids that are also connected to power plants using renewable energy sources. For this reasons the power plants with gas turbines and possibly heat recovery steam generators must allow a flexible operation, with possibility to stop the gas turbines and then when required restart the gas turbines to provide electric power to the electric grid.

When the gas turbines e.g. with a heat recovery steam generator are stopped, due to natural convection caused by the hot gas contained in the gas turbine and/or heat recovery steam generator and/or in the flue gas stack and/or due to the pressure differences caused by the wind speed and/or direction, cold air is constantly dragged through the gas turbine and the heat recovery steam generator.

This cold air causes cooling of the gas turbine and heat recovery steam generator.

Cooling of the gas turbine and heat recovery steam generator prevents a quick restart.

In fact, when the gas turbine and heat recovery steam generator have to be restarted, their loading has to comply with the constrains imposed by the gas turbine and heat recovery steam generator temperature.

In addition, the lower temperature can cause the pressure of the steam/water within the heat recovery steam generator to drop below the atmospheric pressure; this can result in deformation of the walls of some components of the water/steam path of the heat recovery steam generator. In order to prevent such deformation it could be needed introduction of ambient air into the steam/water of the heat recovery steam generator, with the consequent need of purging before the gas turbine and heat recovery steam generator are restarted. In case the gas turbines and heat recovery steam generators are stopped for long time (e.g. months in case of “conservation”), air could circulate through the gas turbine and heat recovery steam generator because of different pressure (e.g. caused by wind intensity and/or direction) between the inlet of the gas turbine filter and the stack. In case air contains humidity, corrosion can occur.

Therefore, in order to allow restarting of the gas turbine and heat recovery steam generator as quickly as possible and/or to prevent corrosion, the draft through the gas turbine and heat recovery steam generator must be counteracted.

Traditionally, in order to counteract the draft, the variable inlet guide vanes of the gas turbine compressor (i.e. the vanes provided at the inlet of the compressor to control the air flow through the gas turbine) are closed and/or shutters (provided e.g. in the filter upstream of the compressor) and/or dampers (provided e.g. at the stack) are closed.

By way of these measures the natural draft through the gas turbine and possibly the heat recovery steam generator is reduced, but because of leakages there can still be a substantial amount of natural draft.

SUMMARY

An aspect of the invention includes providing a method and an arrangement that permit to efficiently counteract the natural draft through the gas turbine.

Preferably, the method and arrangement permit to counteract natural draft through both the gas turbine and the heat recovery steam generator of the arrangement, when the gas turbine is stopped.

These and further aspects are attained by providing a method and an arrangement in accordance with the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages will be more apparent from the description of a preferred but non-exclusive embodiment of the method and arrangement, illustrated by way of non-limiting example in the accompanying drawings, in which:

FIGS. 1 through 3 show different examples of the arrangement;

FIG. 4 shows the internal pressure within the arrangement with reference to an embodiment of the arrangement;

FIGS. 5 through 9 show the internal pressure within the arrangement with reference to different schematic embodiments of the arrangement;

FIGS. 10 and 11 show the draft interceptors such as stack damper in different configurations.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following the arrangement is described first.

The arrangement 1 includes a gas turbine 2 and possibly (but this is not mandatory) a heat recovery steam generator 3.

The gas turbine 2 comprises a compressor 5, a combustion chamber 6 and a turbine 7; the turbine can be connected to an electric generator 8 that is in turn electrically connected to an electric grid; in other applications the gas turbine can be connected to other machines according to the need and design.

Upstream of the compressor 5 the gas turbine 2 has a filter 9 for the air coming from the environment to be supplied to the compressor 5; the filter 9 usually has a higher elevation than the inlet of the compressor 5, e.g. the filter can have an elevation about 8 meter higher than the inlet of the compressor 5. In addition, the compressor 5 is typically provided with variable inlet guide vanes 10 to control the amount of air that is supplied to the compressor 5.

Downstream of the turbine 7 typically a discharge duct 11 is provided. The discharge duct 11 can be connected to a stack like for example the embodiments shown in FIGS. 2 and 3 or the discharge duct 11 can be connected to the heat recovery steam generator 3, like for example the embodiment shown in FIG. 1. In the heat recovery steam generator 3 steam is generated by cooling the exhaust gas from the discharge duct 11. Downstream of the heat recovery steam generator 3 (with reference to exhaust gas flow during normal operation) the stack 12 is provided; usually the stack 12 is provided at the top of the heat recovery steam generator 3.

The arrangement 1 comprises one or more than one draft interceptors.

The draft interceptors are components that are provided in the arrangement in order to counteract the draft of cold air when the gas turbine is not operating, i.e. it is stopped.

The draft interceptors can be components specifically provided for counteracting the draft or they can be components with another main function but that are also used as draft interceptors; for example the variable inlet guide vanes are mainly provided for the regulation of the air mass flow through the gas turbine, but they can also be used as draft interceptors, because when the gas turbine is stopped they can be set to a closed configuration or to a configuration with a minimum opening.

The draft interceptors are generally associated to the arrangement 1, i.e. they can be provided at the gas turbine 2 and/or at the heat recovery steam generator 3 (when this is provided).

The draft interceptors can include one or more among:

• • a shutter 15 at the filter 9 (e.g. the shutter can be located in the filter house); this solution has the advantage that the suction speed in low and thus the risk of sucking shutter parts in the gas turbine is low;
  • the variable inlet guide vanes 10; in this case the variable inlet guide vanes 10 can be set to closed position;
  • a shutter 17 between the gas turbine 2 and the heat recovery steam generator 3; this solution allows to counteract the draft through the gas turbine caused by the natural convection in the heat recovery steam generator;
  • a flap 18 between the gas turbine 2 and the heat recovery steam generator 3, to divert the exhaust gas between an auxiliary stack 12a (to allow operation in single mode) and the heat recovery steam generator 3 (to allow operation in combined cycle). When the gas turbine 2 is stopped, the flap 18 can be used to either stop the draft in the heat recovery steam generator 3 or to close the auxiliary stack 12a;
  • a flap 19 at the heat recovery steam generator 3 (e.g. at a position at the lower part of the heat recovery steam generator 3 (preferably this flap 19 has the same altitude as the air intake 20;
  • a damper 21 at the stack 12.

These draft interceptors counteract the cooling of the gas turbine 2 and possibly of the heat recovery steam generator 3, but because of e.g. leakages or their configuration, they cannot completely prevent it.

The arrangement 1 further comprises a sucker 25 connected to the arrangement 1, for sucking gas from the arrangement 1, for equalizing the pressure through at least the gas turbine 2 when the gas 2 turbine is stopped. In case the arrangement 1 also has a heat recovery steam generator 3, the pressure through the heat recovery steam generator 3 can be equalized with the pressure within the gas turbine 2 as well (but this is not mandatory).

Preferably, the sucker 25 is connected to a first zone 26 adjacent a draft interceptor 15, 10, 17, 18, 19, 21. The zone 26 is within the arrangement 1, such that gas is sucked from the inside of the arrangement 1.

In different embodiments, the sucker 25 can discharge outside of the arrangement 1 the gas sucked from the first zone 26; alternatively, the sucker 25 can discharge the gas sucked from the first zone 26 to a second zone 27 also within the arrangement 1. In this case the sucker 25 is connected between the first zone 26, with and a second zone 27, with the first zone 26 facing a first side of the draft interceptor 15, 10, 17, 18, 19, 21, and the second zone 27 facing a second side of the draft interceptor 15, 10, 17, 18, 19, 21.

The sucker 25 is preferably a fan or a blower or a compressor and more preferably it is a reversible sucker (i.e. a reversible fan or blower or compressor, i.e. a fan or blower or compressor able to exchange inlet with the outlet or provided with or connected to piping and possibly valves that allow to suck gas from the second zone 27 and feed gas to the first zone 26.

Preferably the first zone 26 is located downstream of the draft interceptor 15, 10, 17, 18, 19, 21, with reference to a flow through the gas turbine during operation.

When the sucker 25 is provided at the draft interceptor 21 at the stack (FIGS. 10, 11), in order to reduce the leakages, the draft interceptor 21 such as damper can be made with a hollow structure and the sucker 25 can be used to increase the pressure within the hollow structure of the draft interceptor 21. This allows to reduce the leakages of gas from the heat recovery steam generator 3.

The operation of the arrangement is apparent from that described and illustrated and is substantially the following.

In the following reference to FIG. 4 is made, that shows the pressure within the arrangement in one embodiment (namely the pressure shown is the pressure through the filter 9 and over the axis 29 through the gas turbine 2 and heat recovery steam generator 3). In this case the draft interceptor is defined by the variable inlet guide vane 10 and the sucker 25 is connected between a first zone 26 and a second zone 27 adjacent the variable inlet guide vane 10.

The pressure at the air intake 20 and filter 9 is the ambient pressure Pa. The pressure Pc at the inlet of the compressor 5 is higher than the pressure at the inlet 20 of the filter, because of the higher altitude of the filter 9 than the inlet of the compressor 5.

The pressure at the heat recovery steam generator 3 (at the lower part thereof, i.e. at the part of the heat recovery steam generator 3 facing the gas turbine 2) is P1, with

P1<Pa

because of the wind and/or heat condition of the gas turbine and/or heat condition of the heat recovery steam generator and because of the height of the heat recovery steam generator. The pressure at the top of the stack 12 is Ps, with

Ps<P1.

In addition, since typically the stack has a much higher elevation than the air intake 20, typically it is also

Pa>Ps.

When the gas turbine 2 and the heat recovery steam generator 3 are stopped the variable inlet guide vanes 10 are closed; at the same time the sucker 25 (e.g. a fan) sucks gas from downstream the variable inlet guide vanes 10 and pumps this gas upstream of the variable inlet guide vanes 10; this causes a pressure difference through the variable inlet guide vanes 10 such that the pressure downstream of the variable inlet guide vanes 10 (i.e. at the first zone 26) is substantially the same as the pressure P1. Since the pressure through the gas turbine 2 and heat recovery steam generator 3 is equalized or substantially equalized, there is no draft or a limited draft through the gas turbine 2 and heat recovery steam generator 3.

In the following some examples of the pressure course through the gas turbine and possibly heat recovery steam generator are described with reference to FIGS. 5 through 9; in these figures Pa indicates the ambient pressure at the inlet of the filter 9, Pc the pressure at the inlet of the compressor 5, Ps the pressure at the outlet of the stack, P1 the pressure at the lower part of the heat recovery steam generator 3, P2 the pressure at the discharge duct 11; the pressure is measured within the filter 9 or, for the gas turbine 2 and heat recovery steam generator 3, over the axis 29.

FIG. 5 schematically shows the internal pressure within the arrangement in an embodiment with sucker 25 connected at the variable inlet guide vanes 10 (i.e. like in FIG. 4; the pressure through the filter 9 is not shown). From this figure it is apparent that the pressure through the gas turbine 2 and the heat recovery steam generator 3 is uniform (i.e. the pressure is equalized) such that no draft through the gas turbine 2 and heat recovery steam generator 3 occurs.

FIG. 6 schematically shows the internal pressure within the arrangement 1 in an embodiment with sucker 25 connected to the filter 9. Also in this case the pressure through the gas turbine 2 and the heat recovery steam generator 3 is uniform and no draft through the gas turbine 2 and heat recovery steam generator 3 occurs.

FIG. 7 schematically shows the internal pressure within the arrangement in an embodiment with sucker 25 connected downstream of the gas turbine (e.g. the sucker 25 can be connected in correspondence of the shutter 17). Also in this case the pressure through the gas turbine 2 is uniform (but it is different from the pressure at the heat recovery steam generator 3. Therefore no draft through the gas turbine 2 occurs.

FIG. 8 schematically shows the internal pressure within the arrangement in an embodiment with sucker 25 connected at the stack 12. Also in this case the pressure through the gas turbine 2 and the heat recovery steam generator 3 is uniform and no draft through the gas turbine 2 and heat recovery steam generator 3 occurs.

FIG. 9 schematically shows the internal pressure within the arrangement in an embodiment with gas turbine 2 and suckers 25 connected at the filter 9, at the variable inlet guide vanes 10 and at the stack 12, but without the heat recovery steam generator 3 (this arrangement is for example shown in FIG. 3). Also in this case the pressure through the gas turbine 2 is uniform, even if this is made in different steps; thus also in this case no draft through the gas turbine 2 occurs (naturally pressure steps are also possible in case the heat recovery steam generator 3 is provided downstream of the gas turbine 2).

The present invention also refers to a method for counteracting draft through an arrangement including a gas turbine during a stop.

The method comprises stopping the gas turbine and then equalizing the pressure at least through the gas turbine 2.

Equalizing the pressure comprises sucking gas; preferably the gas is sucked from a first zone 26 adjacent the at least one draft interceptor 15, 10, 17, 18, 19, 21. At least a part of the sucked gas can be fed to a second zone 27 facing a second side of the draft interceptor 15, 10, 17, 18, 19, 21.

Advantageously the method can comprise alternate feeding or sucking gas from a same first and/or second zone 26, 27 according to the environmental conditions. In fact according to the environmental conditions the pressure outside the arrangement 1 can be higher or lower than the pressure inside, therefore the possibility to alternatively suck gas from or feed gas into the same first and/or second zone 26, 27 allows to adapt the operation to the external environmental conditions.

Preferably, sucking gas occurs from a first zone 26 located downstream of the at least one draft interceptor with reference to a flow through the gas turbine during operation.

In different embodiments the draft interceptors can be upstream of the compressor 5 and/or downstream of the turbine 7 and/or at the heat recovery steam generator 3 and/or downstream of the heat recovery steam generator 3.

Advantageously, according to the arrangement and method, even if there are fuel leakages within the combustion chamber 6 during the gas turbine stop, these fuel leakages cannot reach the heat recovery steam generator, because there is no draft within the gas turbine 2.

Naturally the features described may be independently provided from one another.

REFERENCE NUMBERS

• 1 arrangement
• 2 gas turbine
• 3 heat recovery steam generator
• 5 compressor
• 7 combustion chamber
• 7 turbine
• 8 electric generator
• 9 filter
• 10 variable inlet guide vanes
• 11 discharge duct
• 12 stack
• 12 a auxiliary stack
• 15 draft interceptor/shutter
• 18 draft interceptor/flap
• 19 draft interceptor/flap
• 20 air intake
• 21 draft interceptor/damper
• 25 sucker
• 26 first zone
• 27 second zone
• Pa ambient pressure at the inlet of the filter 9
• Pc pressure at the inlet of the compressor 5
• Ps pressure at the outlet of the stack
• P1 pressure at the lower part of the heat recovery steam
• generator 3
• P2 pressure at the discharge duct 11

Claims

1. A method for counteracting draft through an arrangement including a gas turbine during a stop, the method comprising: stopping the gas turbine; andthen equalizing the pressure at least through the gas turbine (2).

2. The method of claim 1, wherein equalizing the pressure comprises: sucking gas.

3. The method of claim 2, wherein the gas turbine comprises includes a compressor, a combustion chamber, and a turbine, and the arrangement includes at least one draft interceptor, wherein the gas method comprises: gas sucking from a first zone adjacent the at least one draft interceptor.

4. The method of claim 3, wherein the first zone faces a first side of the draft interceptor, the method being further comprising: feeding at least a part of the sucked gas to a second zone facing a second side of the draft interceptor.

5. The method of claim 4, comprising: alternatively feeding or sucking gas from a same first and/or second zone according to the environmental conditions.

6. The method of claim 3, comprising: sucking gas from a first zone located downstream of the at least one draft interceptor with reference to a flow through the gas turbine during operation.

7. The method of claim 1, wherein the arrangement includes a heat recovery steam generator downstream of the gas turbine.

8. The method of claim 3, wherein the at least a draft interceptor is upstream of the compressor and/or downstream of the turbine and/or at the heat recovery steam generator and/or downstream of the heat recovery steam generator.

9. An arrangement comprising: a gas turbine, characterized by further comprising: anda sucker connected to the arrangement for sucking gas from the arrangement, for equalizing the pressure through at least the gas turbine when the gas turbine is stopped.

10. The arrangement of claim 9, wherein the gas turbine comprises: a compressor, a combustion chamber, and a turbine, and wherein the arrangement comprises:at least one draft interceptor, wherein the sucker is connected to a first zone adjacent the at least one draft interceptor.

11. The arrangement of claim 9, wherein the sucker is connected between the first zone (26) and a second zone, wherein the first zone faces a first side of the draft interceptor, the second zone faces a second side of the draft interceptor.

12. The arrangement of claim 9, wherein the sucker is a fan or a blower or a compressor.

13. The arrangement of claim 9, wherein the sucker is a reversible sucker.

14. The arrangement of claim 10, wherein the first zone is located downstream of the at least one draft interceptor with reference to a flow through the gas turbine during operation.

15. The arrangement of claim 9, characterized by further comprising: a heat recovery steam generator downstream of the gas turbine.