Process for retrofitting an industrial gas turbine engine for increased power and efficiency

Abstract

A process for retrofitting an industrial gas turbine engine of a power plant where an old industrial engine with a high spool has a new low spool with a low pressure turbine that drives a low pressure compressor using exhaust gas from the high pressure turbine, and where the new low pressure compressor delivers compressed air through a new compressed air line to the high pressure compressor through a new inlet added to the high pressure compressor. The old electric generator is replaced with a new generator having around twice the electrical power production. One or more stages of vanes and blades are removed from the high pressure compressor to optimally match a pressure ratio split. Closed loop cooling of one or more new stages of vanes and blades in the high pressure turbine is added and the spent cooling air is discharged into the combustor.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit to U.S. Provisional Application 62/299,248 filed on Feb. 24, 2016 and entitled PROCESS FOR RETROFITTING AN INDUSTRIAL GAS TURBINE ENGINE FOR INCREASED POWER AND EFFICIENCY.

GOVERNMENT LICENSE RIGHTS

This invention was made with Government support under contract number DE-FE0023975 awarded by Department of Energy. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to a power plant with an industrial gas turbine engine, and more specifically to a process for retrofitting an industrial gas turbine engine for increased power and efficiency.

Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98

Single shaft gas turbine engines are limited in power and efficiency when pressure ratios and firing temperatures are raised to the point where the last turbine stage is loaded to where Mach numbers reach the maximum aerodynamic capability. In these cases, the engine has limited capability to be upgraded for either power or efficiency. In some cases, the two shaft engine configuration is coupled to a larger free spinning turbine with the generator on the low speed shaft to create an upgrade in power. This also has limitations in total flow and is limited in the maximum pressure ratio that the unit could sustain.

BRIEF SUMMARY OF THE INVENTION

In the present invention, existing single shaft turbine engines are retrofitted with a low speed turbine coupled to a low speed compressor that is aerodynamically coupled in front of the existing compressor, now deemed the high compressor, where the existing turbine (now deemed the high pressure turbine) is coupled to the low speed turbine. Further enhancements to the cooling systems enhance the ability to increase the firing temperature of the existing section of the gas turbine and elevate the overall power rating and efficiency.

A process for retrofitting an industrial gas turbine engine in which a new independently operated low spool shaft with a power turbine and a low pressure compressor is installed with the low pressure compressed air being directed into an inlet of the high pressure compressor. A variable area turbine vane assembly is added to the power turbine and a variable inlet guide vane to the low pressure compressor. In another embodiment, a power turbine that drives an electric generator is retrofitted by using the power turbine to drive a low pressure compressor that feeds low pressure air to an inlet of the high pressure compressor, and relocates the electric generator to the high speed shaft on a cold end of the compressor. Regenerative or closed loop cooling can also be used to increase efficiency by bleeding off air from the compressor, cooling the air and then pressurizing the air further in order to pass through stator vanes for cooling, where the spent cooling air is then discharged into the combustor upstream of the flame. Air for cooling can be bled off from a middle stage of the compressor or from the exit end of the compressor. Or, ambient air from atmosphere can be used with an external compressor to further compress the air to P3 level followed by intercooling prior to cooling of the stator vanes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a single shaft industrial gas turbine engine that drives an electric generator of the prior art.

FIG. 2 shows a retrofitted industrial gas turbine engine with a low speed low pressure turbine and low pressure compressor of the present invention.

FIG. 3 shows a turbine exhaust system for a retrofitted engine of the present invention.

FIG. 4 shows a single shaft retrofitted industrial gas turbine engine with at least one of the high pressure compressor stage removed.

FIG. 5 shows a prior art two shaft industrial gas turbine engine with a low speed power turbine driving an electric generator.

FIG. 6 shows a retrofitted two shaft industrial gas turbine engine with an electric generator and an optional gearbox on the high speed shaft of the present invention.

FIG. 7 shows a low spool retrofitted with a high pressure turbine having regenerative cooling of the present invention.

FIG. 8 shows a single shaft industrial gas turbine engine comprising a turbine vane cooling system retrofit with bleed air from the compressor intercooled and then further compressed with regenerative cooling before discharge into the combustor of the present invention.

FIG. 9 shows an industrial gas turbine engine comprising a turbine vane cooling system retrofit with ambient air compressed and then cooled to provide cooling for a row of stator vanes in the turbine before discharge into the combustor of the present invention.

FIG. 10 shows an industrial gas turbine engine comprising a turbine vane cooling system retrofit with bleed air intercooled and then further compressed for use in turbine vane cooling and then discharged into the combustor of the present invention.

FIG. 11 shows an industrial gas turbine engine comprising a turbine vane cooling system retrofit with bleed air compressed and then intercooled for use in turbine vane cooling and then discharged into the combustor of the present invention.

FIG. 12 shows an industrial gas turbine engine comprising a turbine vane cooling system retrofit with compressed air further compressed and then intercooled for use in turbine vane cooling and then discharged into the combustor of the present invention.

FIG. 13 shows an industrial gas turbine engine comprising a turbine vane cooling system retrofit with bleed air compressed and then intercooled for use in turbine vane cooling and then discharged into the combustor of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a process for retrofitting an industrial gas turbine engine of a power plant for increased power and efficiency.

In the present invention, existing single shaft turbine engines 10 like that shown in FIG. 1 are retrofitted with a low speed turbine (LST) coupled to a low speed compressor (LSC) that is aerodynamically coupled in front of the existing compressor, now deemed the high pressure compressor (HPC), where the existing turbine (now deemed the high pressure turbine or HPT), is coupled aerodynamically to the low speed turbine (LST). The existing single shaft industrial gas turbine engine includes a compressor 11 driven by a turbine 13 with a combustor 12, and an electric generator 14 driven by the rotor on the cold side which is in front of the compressor 11. Bearings 15 support the rotor of the engine.

Further enhancements to the cooling systems enhance the ability to increase the firing temperature of the existing section of the gas turbine and elevate the overall power rating and efficiency. The retrofit-able upgrade consists of several optional elements. Most or all of the cooling air used to cool turbine airfoils is discharged into the combustor upstream of the flame instead of into the hot gas path of the turbine in order to improve the efficiency of the engine. In one embodiment, some of the turbine airfoil cooling air can be discharged through trailing edge exit holes and into the hot gas stream with most of the spent cooling air being discharged into the combustor. Passing cooling air through the turbine airfoil for cooling and then discharging most or all of the spent cooling air is referred to as a closed loop cooling where the cooling circuit in the turbine airfoil is a closed loop instead of an open loop in which all of the cooling air is discharged out from the airfoil and into the hot gas stream through film holes or exit holes in the airfoil.

The first upgrade element is to introduce a low speed turbine (LST) 21 directly driving a low speed compressor (LSC) 22 is coupled aerodynamically to the existing single shaft industrial gas turbine engine (IGTE) 10. The existing industrial gas turbine exhaust system is removed and replaced with a close coupled turbine section featuring a variable area low pressure turbine stator vane (turbine 21 with variable turbine inlet guide vanes 25). This variable turbine stator vane 25 is used in conjunction with the low compressor variable geometry, Inlet guide vane and variable geometry Stator guide vanes part of compressor 22, to control the low shaft speed and to simultaneously match the low speed and the high speed compressor for aerodynamic performance (FIG. 2).

The discharge of the low pressure compressor 22 is connected aerodynamically to the inlet of the existing compressor 11 through a compressed air line 23, now the high pressure compressor 11, boosting the overall pressure ratio of the engine. The generator connected to the original gas turbine is now defined as being on the high speed shaft, as the new turbine 21 and compressor 22 make the low speed shaft.

The existing gas turbine has the exhaust diffuser removed and is close coupled to the new low pressure gas turbine 21 with the variable area turbine stator vane 25. The flow discharging the existing gas turbine 13 now enters the low pressure gas turbine 21 which passes through the variable area turbine stator vane 25 and passes across the low speed turbine and out the new exhaust system (FIG. 3). A turbine exhaust duct 26 is installed to pass the high pressure turbine exhaust into the low pressure turbine and variable inlet guide vanes 25.

The retrofit in this configuration can increase the existing industrial engines overall pressure ratio significantly, a range from 1.1 to even over 7×, thus greatly enhancing the engines mass flow and power output. The upgrade including the new low pressure gas turbine 21 may entail removing one or more of the front high pressure compressor blading stages 11A to optimally match the pressure ratio split between the low pressure and high pressure compressors 11A and 22 (FIG. 4). A new inlet 24 to the high pressure compressor 11A is also added to receive the compressed air from the low pressure compressor 22. To get the maximum power out of the upgraded engine and higher efficiency at low power modes, variable inlet guide vane assemblies are used in the high pressure compressor and the low pressure compressor and the low pressure turbine in order to control flows.

An alternate embodiment of this invention is to retrofit a two shaft gas turbine, where the high speed shaft has a compressor 11 and turbine 13 on one shaft, and a low speed turbine (Power turbine) 15 driving a generator 14 or mechanically driven equipment (Pump, process compressor etc.) as shown in the FIG. 5 embodiment. In the FIG. 6 embodiment, the power turbine 21 is used to drive a low speed compressor 22 that is connected aerodynamically to the existing compressor 11 (Now deemed the high pressure compressor) through compressed air line 23. The generator 14 is moved to the high speed shaft connected on the cold end of the high pressure compressor 11. In the FIG. 6 embodiment, one or more stages of the front of the high pressure compressor 11A would be removed in order to match a pressure ratio split between the LP compressor 22 and the HP compressor 11A.

In the process for retrofitting the prior art IGT engines in FIGS. 1 and 5, the old electric generator would require replacement since the retrofitted IGT engine would then produce around twice the power as the old engine and thus require a new electric generator. For example, if a prior art IGT single spool engine of FIG. 1 which is capable of producing 300 MW of power is retrofitted, the new IGT engine would be capable of producing twice that power or 600 MW. Thus, the old 300 MW electric generator would need to be replaced with a 600 MW electric generator. The old 300 MW electric generator could be reused, but a second 300 MW generator would have to be added in which both generators would be driven by the same output shaft. This modification would probably be more costly than replacing the old 300 MW generator with a new modern 600 MW generator. In limited upgrade cases, the old electric generator can still be used with a slightly more powerful industrial engine upgrade. The electric generator is chosen that has the capability of producing more electrical energy than the IGT engine operating at a standard operating temperature so that when a cold day occurs and the engine can produce more power, the electric generator can produce more power. Thus, if an IGT engine upgrade does not produce more power than the electric generator is capable of producing, then the old electric generator can still be used in the upgraded IGT engine.

The second upgrade elements are cooling system retrofits and are also available to be created alone, or in combination with the low speed spool retrofit. This use of regenerative (closed loop) cooling for the first several rows of cooled turbine vanes in the now high speed turbine 13 are implemented where the existing turbine stator vanes with cooling flow discharges into the gas path (such as through film cooling holes or exit holes) are replaced by stator vanes that collect the post cooling coolant and return it into the combustor 12 upstream of the flame. The use of the regenerative or closed loop cooling increases the thermal efficiency of the engine, and further enhances the overall power and efficiency coupled with the low speed compressor 22 and turbine shaft (FIG. 7). Cooling air line 27 passes the spent turbine vane cooling air into the combustor 12.

The cooling system if upgraded alone, would source cooling air from one of several places. This first option would be from ambient air such as that in FIG. 9 with the external cooling air compressor 33 driven by a motor 32 would raise the cooling air pressure to the required level.

In the FIG. 8 embodiment, the cooling air compression could be partially compressed (bled off from a stage of the HPC 11), intercooled with an intercooler 31, and further compressed for reduced compressor work and increased compressor efficiency, and then to reduce the cooling air compressor to the desired coolant temperature. Cooling air is bled off from a stage of the compressor 11, passed through an intercooler 31, and then boosted in pressure by compressor 33 so that enough pressure remains in the cooling air after passing through the stator vanes in order to discharge the spent cooling air into the combustor 12. Cooling air passage 34 from the compressor 11 can come from the compressor exit or from an earlier stage which is at a lower pressure than the exit discharge pressure.

A second approach is shown in FIG. 9 where this ambient sourced air is compressed and then cooled in an intercooler to the desired cooling air temperature. In this second case the cooling air work of compression is higher than in the FIG. 8 embodiment, however the configuration could be made simpler. In the third and fourth case the cooling air is bled from one of the existing compressor bleed ports where the flow is both intercooled and recompressed in the third case, or compressed and after-cooled being the fourth case, FIGS. 10 and 11.

A fifth case the fully compressed air from the main compressor is extracted and cooled and then further compressed, FIG. 12. A sixth option is extracting the cooling air from the compressor exit and further compressing followed by post cooling to the desired cooling air temperature for vane cooling, FIG. 13.

In each of these cases the externally compressed cooling air is created at a pressure significantly over the main compressor 11 discharge pressure, commonly designated P3. This intercooled and over pressurized coolant provides optimized low temperature high pressure coolant to the turbine stator vanes to provide cooling of the vanes to the desired level while the captured cooling flow exiting the vane exists with positive pressure margin to pass it into the combustor shell to mix with the existing compressor discharge air.

This configuration of closed loop air cooing (meaning most or all of the airfoil cooling air is discharged into the combustor instead of the hot gas stream through the turbine) optimized thermal efficiency and augments power by increasing the overall flow through the combustor while preventing coolant form diluting the main hot gas stream. By closed loop cooling of the turbine airfoil, the present invention means that most or all of the spent cooling air passing through the turbine airfoils is discharged into the combustor instead of being discharged into the hot gas stream.

In the cases where the regenerative turbine vane cooling implemented on the HPT is coupled with the low spool turbine and compressor, the cooling air source could be from the LPC discharge, or from an intermediate LPC bleed, HPC bleed or the HPC compressor discharge.

Claims

1. A process for retrofitting an industrial gas turbine engine of a power plant, the industrial gas turbine engine having a main compressor driven by a main turbine and an electric generator either driven by the main compressor or by a power turbine driven by the main turbine, the process comprising the steps of:

adding a new inlet to the main compressor capable of receiving a greater air flow;

adding a low spool with a low pressure turbine driving an low pressure compressor to the main turbine such that the low pressure turbine is driven by exhaust from the main turbine;

adding a variable inlet guide vane assembly to an inlet side of the low pressure turbine;

adding a compressed air line connecting the low pressure compressor to the new inlet of the main compressor such that compressed air from the low pressure compressor flows into the main compressor; and, replacing the electric generator with a new electric generator that has around twice the electrical power production.

2. The process for retrofitting an industrial gas turbine engine of a power plant of claim 1, and further comprising the steps of:

removing at least one stage of rotor blades and stator vanes from the main compressor to optimally match a pressure ratio split between the low pressure compressor and the main compressor.

3. The process for retrofitting an industrial gas turbine engine of a power plant of claim 1, and further comprising the steps of:

removing the old electric generator from the power turbine;

adding a low pressure compressor to be driven by the power turbine;

adding a variable inlet guide vane assembly to an inlet side of the power turbine;

adding a compressed air line connecting the low pressure compressor to the new inlet of the main compressor such that compressed air from the low pressure compressor flows into the main compressor; and,

adding a new electric generator having around twice the electrical power production of the old generator to be driven by the high pressure compressor shaft.

4. The process for retrofitting an industrial gas turbine engine of a power plant of claim 3, and further comprising the steps of:

removing at least one stage of rotor blades and stator vanes from the main compressor to optimally match a pressure ratio split between the low pressure compressor and the main compressor.

5. The process for retrofitting an industrial gas turbine engine of a power plant of claim 3, and further comprising the steps of:

adding a gear box between the new electric generator and the high pressure compressor shaft.

6. The process for retrofitting an industrial gas turbine engine of a power plant of claim 1, and further comprising the steps of:

removing at least one stage of the stator vanes form the high pressure turbine;

installing new at least one stage of stator vanes in the high pressure turbine in which the new stator vanes have a closed loop cooling circuit;

providing a source of compressed air for cooling of the new stage of turbine stator vanes; and,

discharging spent cooling air from the new stage of turbine stator vanes into the combustor that produces the hot gas stream for the high pressure turbine.

7. The process for retrofitting an industrial gas turbine engine of a power plant of claim 6, and further comprising the steps of:

bleeding off cooling air from the high pressure compressor;

intercooling the cooling air;

increasing the pressure of the cooling air to a pressure slightly higher than an outlet pressure of the high pressure compressor; and,

passing the higher pressure cooling air through the closed loop cooling circuit in the new stage of turbine stator vanes.

8. The process for retrofitting an industrial gas turbine engine of a power plant of claim 6, and further comprising the steps of:

compressing ambient air with an external compressor to a pressure slightly higher than an outlet pressure of the high pressure compressor;

intercooling the cooling air; and,

passing the higher pressure cooling air through the closed loop cooling circuit in the new stage or stages of turbine stator vanes.

9. The process for retrofitting an industrial gas turbine engine of a power plant of claim 6, and further comprising the steps of:

bleeding off compressed cooling air from an outlet of the high pressure compressor;

intercooling the compressed cooling air;

increasing the pressure of the compressed cooling air to a pressure slightly higher than an outlet pressure of the high pressure compressor; and,

passing the higher pressure cooling air through the closed loop cooling circuit in the new stage of turbine stator vanes.

10. The process for retrofitting an industrial gas turbine engine of a power plant of claim 6, and further comprising the steps of:

bleeding off compressed cooling air from an outlet of the high pressure compressor;

increasing the pressure of the compressed cooling air to a pressure slightly higher than an outlet pressure of the high pressure compressor;

intercooling the compressed cooling air; and,

passing the higher pressure cooling air through the closed loop cooling circuit in the new stage or stages of turbine stator vanes.

11. The process for retrofitting an industrial gas turbine engine of a power plant of claim 6, and further comprising the steps of:

bleeding off some of the compressed air from the compressed air line between the low pressure compressor and the high pressure compressor for use as the cooling air for the new stage of turbine stator vanes; and,

cooling and compressing the cooling air to a pressure slightly higher than an outlet pressure of the high pressure compressor.

12. The process for retrofitting an industrial gas turbine engine of a power plant of claim 1, and further comprising the steps of:

adding a variable inlet guide vane assembly to both the main compressor and the low pressure compressor.

13. A power plant with a retrofitted industrial gas turbine engine capable of producing greater power and at high efficiency, the power plant comprising:

an old main compressor driven by a high pressure turbine with a combustor;

a new inlet for the old main compressor capable of greater compressed air flow;

re-using the old electric generator;

a low spool with a new low pressure turbine or an old power turbine driven by exhaust gas from the high pressure turbine;

a new low pressure compressor driven by the low pressure turbine;

a new compressed air line connecting the new low pressure compressor to the new inlet of the high pressure compressor; and,

a new variable inlet guide vane assembly for the new low pressure turbine or the old power turbine.

14. The power plant of claim 13, and further comprising:

the old main compressor is without at least one stage of stator vanes and rotor blades such that a pressure ratio is optimally matched between the main compressor and the new low pressure compressor.

15. The power plant of claim 13, and further comprising:

the high pressure turbine has at least one stage of new stator vanes with a closed loop cooling circuit;

a source of compressed cooling air;

a compressed air cooling circuit to deliver compressed cooling air to the closed loop cooling circuit of the stator vanes and discharge spent cooling air into the combustor.

16. The power plant of claim 15, and further comprising:

a new boost compressor between the source of compressed cooling air and the stage of stator vanes to increase the pressure of the cooling air; and,

a new intercooler between the source of compressed cooling air and the stage of stator vanes to cool the compressed cooling air.

17. The power plant of claim 13, and further comprising:

Replacing the old electric generator with a new electric generator driven by the old main compressor with the new electric generator having a greater electrical power production than the old electric generator.