Industrial gas turbine engine with turbine airfoil cooling

Abstract

A process for retrofitting an electric power plant that uses two 60 Hertz large frame heavy duty industrial gas turbine engines to drive electric generators and produce electricity, where each of the two industrial engines can produce up to 350 MW of output power. The process replaces the two 350 MW industrial engines with one twin spool industrial gas turbine engine that is capable of producing at least 700 MW of output power. Thus, two prior art industrial engines can be replaced with one industrial engine that can produce power equal to the two prior art industrial engines.

Claims

1: An industrial gas turbine engine to produce electrical power comprising: a main engine with a high pressure compressor driven by a high pressure turbine and a combustor to produce a hot gas stream; a direct drive electric generator connected to the main engine; a turbocharger having a low pressure turbine driving a low pressure compressor; the low pressure turbine driven by exhaust from the high pressure turbine; a compressed air bypass line connecting the low pressure compressor to the high pressure compressor; a first row of variable inlet guide vanes in the high pressure compressor; a second row of variable inlet guide vanes in the low pressure turbine; a third row of variable inlet guide vanes in the low pressure compressor; a stage of turbine stator vanes with a cooling circuit in the high pressure turbine; a source of air cooling located upstream from the cooling circuit of the stage of turbine stator vanes to provide cooling air; an intercooler and a boost compressor located downstream from the cooling circuit of the stage of turbine stator vanes and connected to the combustor; and, cooling air from the source of cooling air passing through the cooling circuit of the stage of turbine stator vanes to provide cooling to the stage of turbine stator vanes, and then flows through the intercooler to be cooled, and then is boosted in pressure by the boost compressor to a high enough pressure to be discharged into the combustor.

2: The industrial gas turbine engine to produce electrical power of claim 1, and further comprising: the source of cooling air is a cooling air line connected to the compressed air bypass line; and, a second intercooler and a second boost compressor is located in the cooling air line upstream of the cooling circuit of the stage of turbine stator vanes.

3: The industrial gas turbine engine to produce electrical power of claim 1, and further comprising: the source of cooling air is the high pressure compressor.

4: The industrial gas turbine engine to produce electrical power of claim 1, and further comprising: the industrial gas turbine engine is a 60 hertz engine capable of producing greater than 700 MW of power.

5: The industrial gas turbine engine to produce electrical power of claim 1, and further comprising: the industrial gas turbine engine is a 50 hertz engine capable of producing greater than 1,000 MW of power.

6: The industrial gas turbine engine to produce electrical power of claim 1, and further comprising: the turbocharger is capable of rotating independently from the main engine.

7: The industrial gas turbine engine to produce electrical power of claim 1, and further comprising: the electric generator and the main engine operate equal to a synchronization speed of a local electrical power grid.

8: An industrial gas turbine engine to produce electrical power comprising: a compressor capable of discharging compressed air at a compressor discharge pressure; a turbine connected to drive the compressor; an electric generator connected to the industrial gas turbine engine to produce electrical power; a row of turbine stator vanes with an internal cooling circuit; a combustor to produce a hot gas stream for the turbine from compressed air discharged from the compressor; a turbine stator vane cooling circuit having an inlet connected to a source of compressed air and an outlet connected to the combustor; the turbine stator vanes cooling circuit connected to the turbine stator vane internal cooling circuit to supply and return cooling air to the turbine stator vanes cooling circuit; an intercooler connected to the turbine stator vane cooling circuit to cool the cooling air; and, a boost compressor connected to the turbine stator vane cooling circuit to increase a pressure of the cooling air to a pressure greater than the compressor discharge pressure; wherein, cooling air from the source of compressed air passes through the turbine stator vane cooling circuit and then into the combustor at a pressure greater than the compressor discharge pressure.

9: The industrial gas turbine engine to produce electrical power of claim 8, and further comprising: the source of compressed air is the compressor.

10: The industrial gas turbine engine to produce electrical power of claim 8, and further comprising: the intercooler is located downstream from the turbine stator vane cooling circuit; and, the boost compressor is located downstream from the intercooler.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0020] FIG. 1 shows a prior art single shaft spool IGT engine with a direct drive electric generator on the compressor end.

[0021] FIG. 2 shows a prior art dual shaft IGT engine with a high spool shaft and a separate power turbine that directly drive an electric generator.

[0022] FIG. 3 shows a prior art dual shaft aero gas turbine engine with concentric spools in which a high spool rotates around the low spool, and where a separate low pressure shaft that directly drives an electric generator.

[0023] FIG. 4 shows a prior art three-shaft IGT engine with a low pressure spool rotating within a high pressure spool, and a separate power turbine that directly drives an electric generator.

[0024] FIG. 5 shows a cross section view of a prior art twin spool aero gas turbine engine with a high spool concentric with and rotatable around the low spool.

[0025] FIG. 6 shows a cross section view of a mechanically uncoupled twin spool turbo charged industrial gas turbine engine of the present invention.

[0026] FIG. 7 shows a diagram of a gas turbine engine with a fourth embodiment of a mechanically uncoupled turbo charged twin spool industrial gas turbine engine of the present invention.

[0027] FIG. 8 shows an embodiment of the twin spool turbo charged industrial gas turbine engine of the present invention in which cooling air for the turbine airfoils is cooled and then boosted in pressure prior to discharge into the combustor.

[0028] FIG. 9 shows an embodiment of the twin spool turbo charged industrial gas turbine engine of the present invention similar to the FIG. 24 embodiment except that the cooling air is supplied from bleed air off from the high pressure compressor.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention is a turbo charged twin spool industrial gas turbine engine that drives and electric generator to produce electrical power. The turbocharged IGT engine is associated with a HRSG (Heat Recovery Steam Generator) that drives another electric generator in what is referred to as a combined cycle power plant.

[0030] FIG. 6 shows a basic concept of the twin spool turbocharged industrial gas turbine engine of the present invention which includes a high spool 11 with a high pressure compressor driven by a high pressure turbine and a combustor 15, and a low spool 12 with a power turbine that drives a low pressure compressor. Turbine exhaust from the high pressure turbine flows into the power turbine of the low spool 11, where the power turbine drives the low pressure compressor. Variable guide vanes 14 are used in the inlet to the power turbine as well as the high pressure compressor and the low pressure compressor. The low spool 12 is rotatable independent of the high spool 11. Compressed air from the low pressure compressor is delivered to an inlet of the high pressure compressor of the high spool 11. The high spool 11 is connected directly to an electric generator 13. The low spool 12 does not rotate within the high spool 11 as in the prior art industrial engine of FIGS. 3 and 4 or the aero engine of FIG. 5. In the twin spool turbocharged IGT engine of the present invention, the low spool 12 can be referred to as a turbocharger for the main engine or high spool 11.

[0031] FIG. 7 shows the twin spool turbocharged industrial gas turbine engine of the present invention with the high spool 11 having a high pressure compressor 21 and a high pressure turbine 22 and a low spool 12 having a low pressure compressor 32 and a low pressure turbine 31. The high spool 11 directly drives an electric generator 13. Exhaust from the HPT 22 flows into the LPT or power turbine 31 and then out the exhaust duct and into a HRSG, the power turbine 31 drives the LPC 32 to supply low pressure compressed air through line 16 to an inlet of the HPC 21 of the high spool 11. The low spool 12 with the LPT 31 and the LPC 32 is referred to as the turbocharger for the high spool 11 or main engine.

[0032] The low pressure compressor 32 of the low spool 12 includes an inlet guide vane and variable stator vanes that allow for modulating the compressed air flow. Similarly, the high pressure compressor 21 of the high spool 11 can also include variable stator vanes that allow for flow matching and speed control. Thus, the low pressure spool 12 can be shut down and not be operated while the main engine or high speed spool 11 operates to drive the electric generator 13. The low pressure compressor 32 of the low spool 12 is connected by a line 16 to an inlet of the high pressure compressor 21 of the high spool 11. An intercooler can be used in compressed air line 16 between the outlet of the low pressure compressor and the inlet of the high pressure compressor to cool the compressed air. A valve can also be used in the compressed air line 16 for the compressed air from the low pressure compressor 32 to the high pressure compressor 21.

[0033] Major advantages of the twin spool turbo-charged industrial gas turbine engine of the present invention are described here. A large frame heavy duty industrial gas turbine engine of the prior art uses only a single spool with the rotor shaft directly connected to an electric generator 3 (see FIG. 1). The FIG. 1 design permits a large amount of power transfer to the generator 3 without the need for a gearbox. In large frame heavy duty industrial engine, a gear box cannot be used because the power output of the engine is far greater than a gear box can be exposed to. Due to these factors, the gas turbine must operate with a very specific rotor speed equal to the synchronization speed of the local electrical power grid. By separating the components of the gas turbine into modular systems according to the present invention, each can then be individually optimized to provide maximum performance within an integrated system. Also, substantial power output and operability improvements can be realized over the prior art industrial engines. For example, the largest 60 hertz IGT engine of the prior art can produce at most 350 MW while the 60 Hertz version of the twin spool turbo-charged industrial engine of the present invention can produce over 700 MW. The largest 50 hertz IGT engine of the prior art can produce at most 500 MW while the 50 Hertz version of the twin spool turbo-charged IGT engine of the present invention can produce over 1,000 MW of power. In both the 50 hertz and 60 hertz versions, the turbine exhaust temperature would be substantially the same as the turbine exhaust temperature of the older IGT engines being replaced such that no substantially modifications or structural changes would be required to the HRSG. Only the duct work channeling the turbine exhaust to the HRSG would need to be modified. In a combined cycle power plant that uses very old engines such as those with 180 MW of power, a single new engine of 360 MW of power could be used to replace these two older IGT engines but the turbine exhaust temperature of the new engine would be significantly higher than the two older engines being replaced such that significant modification or changes would be required of the HRSG to accommodate the higher turbine exhaust temperature. With the twin spool turbo-charged IGT engine of the present invention, one twin spool turbo-charged IGT engine of the present invention could be used to replace the two older 180 MW engines without significant change to the HRSG required.

[0034] The efficiency of the gas turbine is known to be largely a function of the overall pressure ratio. While existing IGTs limit the maximum compressor pressure ratio that can be achieved because optimum efficiency cannot be achieved simultaneously in the low and high pressure regions of the compressor while both are operating at the same (synchronous) speed, an arrangement that allows the low pressure compressor 32 and high pressure compressor 21 to each operate at their own optimum rotor speeds will permit the current overall pressure ratio barrier to be broken. In addition, segregating the low pressure and high pressure systems is enabling for improved component efficiency and performance matching. For example, the clearance between rotating blade tips and outer static shrouds or ring segments of existing IGTs must be relatively large because of the size of the components in the low pressure system. In the present invention, the clearances in the high pressure system could be reduced to increase efficiency and performance.

[0035] The twin spool turbocharged IGT of the present invention enables a more operable system such that the engine can deliver higher efficiency at turn-down, or part power, and responsiveness of the engine can be improved. Further, this design allows for a greater level of turndown than is otherwise available from the prior art IGTs.

[0036] In yet another example, the power output and mass flow of prior art IGT engines is limited by the feasible size of the last stage turbine blade. The length of the last stage turbine blade is stress-limited by the product of its swept area (A) and the square of the rotor speed (N). This is commonly referred to as the turbine AN.sup.2. For a given rotor speed, the turbine flow rate will be limited by the swept area of the blade. If the rotor speed could be reduced, the annulus area could be increased, and the turbine can then be designed to pass more flow and produce more power. This is the essence of why industrial gas turbines designed for the 50 Hz electricity market, which turn at 3,000 rpm, can be designed with a maximum power output capability which is about 44% greater than an equivalent industrial gas turbine designed for the 60 Hz market (which turns at 3,600 rpm). If the industrial gas turbine engine could be designed with modular components as in the present invention, a separate low pressure system comprising a low pressure compressor 32 and turbine 31 could be designed to operate at lower speeds to permit significantly larger quantities of air to be delivered to the high pressure (core) of the gas turbine.

[0037] In prior art IGT engines, size and speed, AN.sup.2, and limits on the past stage turbine blade eventually lead to efficiency drop-off as pressure ratio and turbine inlet temperatures are increased. In addition, as pressure ratio increases, compressor efficiency begins to fall off due to reduction in size of the back end of the compressor which leads to higher losses. At higher pressure ratios, very small airfoil heights relative to the radius from the engine centerline are required. This leads to high airfoil tip clearance and secondary flow leakage losses. The twin spool turbocharged IGT engine of the present invention solves these prior art IGT engine issues by increasing the flow size of a prior art large IGT engine up to a factor of 2. Normally, this flow size increase would be impossible due to turbine AN.sup.2 limits. The solution of the present invention is to switch from single spool to independently operable double spool (high spool 11 and low spool 12) which allows for the last stage turbine blade to be designed at a lower RPM which keeps the turbine within typical limits. A conventional design of a dual spool engine would place the electric generator on the low spool, fixing the speed of the electric generator, and have a higher RPM high spool engine. With the twin spool turbocharged IGT engine of the present invention, the electric generator 13 is located on the high spool 11, and has a variable speed low spool 12. This design provides numerous advantages. Since the low spool 12 is untied from the grid frequency, a lower RPM than synchronous can be selected allowing the LPT 31 to operate within AN.sup.2 limits. Another major advantage is that the low spool 12 RPM can be lowered significantly during operation which allows for a much greater reduction of engine air flow and power output than can be realized on a machine with a fixed low spool speed. The twin spool turbocharged IGT of the present invention maintains a higher combustion discharge temperature at 12% load than the prior art single spool IGT operating at 40% load. In the twin spool turbocharged IGT engine of the present invention, power was reduced by closing the inlet guide vanes on the high pressure compressor 21. Low and high pressure compressor aerodynamic matching was accomplished using a variable LPT vane which reduces flow area into the LPT, thus reducing the RPM of the low spool 12.

[0038] A prior art single spool IGT is capable of achieving a low power setting of approximately 40-50% of max power. The twin spool turbocharged IGT engine of the present invention is capable of achieving a low power setting of around 12% of max power. This enhanced turndown capability provides a major competitive advantage given the requirements of flexibility being imposed on the electrical grid from variable power generation sources.

[0039] During periods of high electrical power demand, the main engine with the high spool 11 is operated to drive the electric generator 13 with the gas turbine exhaust going into the power turbine 31 of the low spool 12 to drive the low pressure compressor 32. The exhaust from the power turbine 31 of the low spool 12 then flows into the HRSG to produce steam to drive a steam turbine that drives a second electric generator. The low pressure compressed air from the low spool 12 flows into the inlet of the high pressure compressor 21 of the high spool 11.

[0040] During periods of low electrical power demand, the low pressure compressor 32 of the low spool 12 is operated at low speed and the exhaust from the high pressure turbine 22 of the high spool 11 flows into the HRSG through the low pressure turbine 31 of the low spool 12 to produce steam for the steam turbine that drive the second electric generator and thus keep the parts of the HRSG hot for easy restart when the engine operates at higher loads. Flow into the high pressure compressor 21 of the high spool 11 is reduced to 25% of the maximum flow. Thus, the high spool 11 can go into a very low power mode. The prior art power plants have a low power mode of 40% to 50% (with inlet guide vanes in the compressor) of peak load. The Turbocharged IGT engine of the present invention can go down to 25% of peak load while keeping the steam temperature temporarily high of the power plant hot (by passing the hot gas flow through) for easy restart when higher power output is required. An intercooler can also include water injection to cool the low pressure compressed air.

[0041] At part power conditions between full power and the lowest power demand, it may be necessary to operate the low pressure compressor 32 of the low spool 12 and low pressure turbine 31 at an intermediate rotor speed. A means for controlling the engine is necessary in order to reduce low spool 12 rotor speed without shutting off completely, while ensuring stable operation of the low pressure compressor 32 and high pressure compressor 21. Without a safe control strategy, part power aerodynamic mismatching of the compressors can lead to compressor stall and/or surge, which is to be avoided for safety and durability concerns. A convenient way to control the low spool 12 speed while correctly matching the compressors aerodynamically is by means of a variable low pressure turbine vane. Closing the variable low pressure turbine vane at part power conditions reduces the flow area and flow capacity of the low pressure turbine 31, which subsequently results in a reduction of low pressure spool 12 rotational speed. This reduction in rotor speed reduces the air flow through the low pressure compressor 32 which provides a better aerodynamic match with the high pressure compressor 21 at part power.

[0042] While the evolution of the current state-of-the-art industrial gas turbine engine has found broad utility in the electricity generation market, the efficiency of these machines is limited because of the engineering tradeoffs that have been accepted without that evolution. Interestingly, the evolution of gas turbine engines for aircraft propulsion has taken a decidedly different direction. There, weight, performance/efficiency, and operability are the design drivers that are paramount to the successful evolution of turbomachinery for that application. To improve efficiency, aircraft (aero) engines have been designed to operate at higher pressure ratios than industrial (IGT) engines. Further, the vast majority of aircraft (aero) gas turbine systems have multiple shafts whereby the low pressure components (i.e., low pressure compressor, low pressure turbine) reside on what is called a low spool. High pressure components such as the high pressure compressor and the high pressure turbine reside on the high spool. The two spools operate at different speeds to optimize the efficiency of each spool. The use of multiple shafts in a gas turbine engine yields benefits that increase component and overall efficiency, increase power output, improve performance matching, and improve operability. The latter is manifested in both responsiveness of the engine and in part-power performance.

[0043] The twin spool turbocharged industrial gas turbine engine of the present invention offers many advantages relative to the current state-of-the-art engines. By separating the components of the gas turbine into modular systems, each can then be individually optimized to provide maximum performance within an integrated system. In addition, substantial power output and operability improvements can be obtained.

[0044] In one example, the efficiency of the gas turbine can be increased using modular components. The efficiency of the gas turbine is known to be largely a function of the overall pressure ratio. While existing IGTs limit the maximum compressor pressure ratio that can be achieved because optimum efficiency cannot be achieved simultaneously in the low and high pressure regions of the compressor while both are operating at the same (synchronous) speed, an arrangement that allows the low and high pressure compressors to each operate at their own optimum rotor speeds will permit the current overall pressure ratio barrier to be surpassed. In addition, segregating the low and high pressure systems is enabling for improving component efficiency and performance matching. For example, the clearances between the rotating and non-rotating hardware such as in clearances between rotating blade tips and stationary outer shrouds or ring segments of existing IGTs must be relatively large because of the size of the components in the low pressure system. In the configuration of the present invention, the clearances in the high pressure system could be reduced to increase efficiency and performance.

[0045] In another example, the component technology of the turbocharged IGT engine of the present invention enables a more operable system such that an engine can deliver higher efficiency at turn-down or part power, and responsiveness of the engine can be improved. Further, this modular arrangement allows for a greater level of turndown than is otherwise available from the prior art large frame heavy duty IGTs of the prior art. This is important when considering the requirements imposed on the electrical grid when intermittent sources of power such as solar and wind become an increasing percentage of the overall capacity.

[0046] In yet another example, the power output and mass flow of prior art large frame heavy duty IGTs is limited by the feasible size of the last stage turbine rotor blade. The length of the last stage turbine rotor blade is stress-limited by the product of its swept area (A) and the square of the rotor speed (N). This is referred to in the art as the turbine AN.sup.2. For a given rotor speed (N), the turbine flow rate will be limited by the swept area of the last stage blade. If the rotor speed (N) could be reduced, the annulus area could be increased, and the turbine can then be designed to pass more flow and produce more power. This is the essence of why gas turbines designed for the 50 Hertz (3,000 rpm) electricity market can be designed with a maximum power output capability which is about 44% greater than an equivalent gas turbine designed for the 60 Hertz (3,600 rpm) market. If the gas turbine engine could be designed with modular components, a separate low pressure system comprising a low pressure compressor and turbine could be designed to operate at lower speeds to permit significantly larger quantities of airflow to be delivered to the high pressure (core) of the gas turbine engine.

[0047] Limitations exist in the prior art gas turbine engine design. Size and speed, AN.sup.2, limits on the last stage turbine rotor blade eventually lead to efficiency drop-off as pressure ratio and turbine inlet temperature (TIT) are increased. In addition, as pressure ratio increases, compressor efficiency begins to fall off due to reduction in size of the back end of the compressor which leads to higher losses. The root cause of that efficient aerodynamic work per stage improves with higher airfoil rotational speed. This means that the aerodynamic engineer tries to keep a relatively high radius placement. At high pressure ratios, this leads to very small airfoil heights relative to radius from the engine centerline. This leads to high airfoil tip clearance and high secondary flow leakage losses.

[0048] Higher engine efficiency is obtained with higher pressure ratio and higher turbine inlet temperature. The first obstacle is reduction of component efficiencies due to size effects because of the higher pressure ratio. The IGT engine of the present invention solves this issue by increasing the flow size of a typical large frame IGT by a factor of 2. Normally, this flow size increase would be impossible due to the turbine AN.sup.2 limits. The IGT engine of the present invention solution is to switch from a single spool engine to a dual spool engine with the two spools capable of operating independently where the low spool does not rotate within the high spool. This allows for the last stage blade to be designed at a lower RPM which keeps the turbine within limits. Prior art design of a dual spool engine would place the electric generator on the low spool, fixing its speed, and have a higher RPM high spool engine. The IGT engine of the present invention goes against this convention and places the electric generator on the high spool, and has a variable speed low spool. This arrangement provides for numerous advantages. Since the low spool is untied from the grid frequency, a lower PRM than synchronous can be selected allowing for the LPT to operate within AN.sup.2 limits. Another major advantage is that the low spool RPM can be lowered significantly during operation which allows for a much greater reduction of engine air flow, and power can be realized on a machine with a fixed low speed spool. The IGT engine of the present invention can maintain a higher combustion discharge temperature at 12% load than the prior art single spool IGT engines operating at a 40% load.

[0049] FIG. 8 shows the twin spool turbocharged industrial gas turbine engine of the present invention in which cooling air for the high pressure turbine airfoils is boosted in pressure by a boost pump downstream from the airfoils in order to be discharged into the combustor at about the same pressure as the compressor discharge pressure. Compressed air from the low pressure compressor 32 is bled off from the main bypass flow 16 and passed through an intercooler 41 where the temperature of the compressed air is lowered. The lower temperature compressed air is then boosted in pressure by a first cooling air compressor 42 driven by a motor 43 to a pressure suitable for cooling the turbine airfoils such as the stator vanes 23 in the high temperature turbine 22. The spent cooling air is then passed through a second intercooler 44 and then a second cooling air compressor 45 driven by a second motor 46 to boost the pressure so that the compressed air used to cool the stator vane 23 will be at a pressure substantially matching the outlet pressure of the high pressure compressor 21 for discharge into the combustor 15. With the embodiment in FIG. 8, the compressed air pressure passing through the air cooled airfoils 23 does not have to be high enough to both cool the airfoils and be high enough for discharge into the combustor 15. This would require higher pressure seals. With the FIG. 8 embodiment, the extra pressure is added to the cooling air after passing through the air cooled airfoils so that lower pressure seals can be used. The HPC 21 includes variable inlet guide vanes 24, the LPT 33 includes variable inlet guide vanes 33, and the LPC 32 includes variable inlet guide vanes 34 in order to allow for the higher power output of the twin spool turbocharged IGT engine of the present invention as well as the low turn-down speed.

[0050] FIG. 9 shows another embodiment of the turbocharged industrial gas turbine engine similar to the FIG. 8 embodiment except that the cooling air for the turbine airfoil 23 is bled off from the high pressure compressor 21 (instead of the low pressure compressor 32), then passed through cooling passage and the turbine airfoil such as the row of stator vanes 23 to provide cooling. The spent cooling air in line 48 is passed through an intercooler 44 to further cool the spent cooling air and is then increased in pressure by the boost compressor 45 driven by the motor 46 to a high enough pressure that it can be discharged into the combustor 15 at substantially the same pressure as the high pressure compressor 21 discharge.

[0051] In both embodiments of FIGS. 8 and 9 of the twin spool turbocharged IGT engine of the present invention, high pressure is produced in the cooling air of the turbine airfoils so that the cooling air can be discharged into the combustor 15 without requiring higher pressure seals in the cooling air flow paths through the turbine and airfoils.