HYBRID COMBUSTION TURBINE POWER PLANT

Abstract

Some embodiments are directed to a hybrid combustion turbine power generation system, which includes a gas turbine integrated with an ACAES via fluid connection(s) between the compressor and turbine , to allow air to be extracted from, and injected into, the gas turbine, the ACAES including a direct TES and compressed air store , a top-up compressor being disposed between the fluid connection(s) and the direct TES and fluidly connected so that its inlet receives air extracted from the gas turbine in an extraction mode and its outlet sends air at a higher temperature and pressure towards the downstream direct TES , thereby optimising the temperature at which returning air is injected into the gas turbine in an injection mode. This may extend the operational power range of the gas turbine and address changes in the gas turbine operating conditions between injection and bleed modes.

Claims

1. A hybrid combustion turbine power generation system (CTPGS), comprising: a combustion turbine (GT) system including a first compressor, a combustor and a turbine fluidly connected downstream of each other, wherein the turbine and compressor are coupled on a drive shaft and operatively associated with a generator or motor/generator, and an adiabatic compressed air energy storage system (ACAES) integrated therewith via one or more fluid connections disposed between the compressor and turbine, so as to allow air to be extracted from, and injected into, the GT system; wherein the ACAES includes a flow passageway network and associated valve structure leading from the one or more fluid connections to a compressed air store via a first direct thermal energy store (TES); and, wherein a top-up compressor is disposed in the flow passageway network between the one or more fluid connections and the direct TES, and is so fluidly connected that its inlet receives air extracted from the GT system and its outlet sends air at a higher temperature and pressure towards the downstream direct TES.

2. The hybrid CTPGS according to claim 1, wherein the ACAES further includes a charging compressor, having an associated air inlet, that is fluidly connected upstream of the top-up compressor, such that an outlet of the charging compressor sends compressed air towards an inlet of the top-up compressor for charging the compressed air store.

3. The hybrid CTPGS according to claim 1, wherein the charging compressor is operable over a similar pressure ratio to that of the first compressor.

4. The hybrid CTPGS according to claim 1, wherein the flow passageway network includes an alternative flow pathway that allows flow to bypass the top-up compressor.

5. The hybrid CTPGS according to claim 1, wherein second stage power machinery is provided in the flow passageway network between the direct TES and the compressed air store, and wherein the second stage power machinery comprises a compressor and a pressure reducing device disposed in alternative respective flow pathways between the at least one direct TES and the compressed air store.

6. (canceled).

7. The hybrid CTPGS according to claim 1, wherein, in an injection mode, returning air follows a flow pathway that bypasses the top-up compressor.

8. The hybrid CTPGS according to claim 1, wherein in the ACAES, in a bleed mode, extracted air is compressed in the top-up compressor and in the second and any subsequent stage power machinery disposed between the direct TES and the compressed air store, but, in an injection mode, returning air is only expanded in the ACAES in power machinery disposed between the compressed air store and the direct TES.

9. The hybrid CTPGS according to claim 1, wherein, during a bleed mode, the top-up compressor raises the air pressure in the direct TES to a selected pressure and, in an injection mode, the second and any subsequent stage power machinery disposed between the direct TES and the compressed air store expand the air so that it returns to the direct TES at substantially the same selected pressure.

10. The hybrid CTPGS according to claim 1, wherein the pressure ratio of the top-up compressor in a bleed mode is selected such that heat is stored in the direct TES at a temperature within 40 C. or less, or 30 C. or less, or 20 C. or less of the first compressor air outlet temperature in the injection mode.

11. The hybrid CTPGS according to claim 1, wherein the pressure ratio of the top-up compressor in a bleed mode is selected such that heat is stored in the direct TES at a temperature of 50 C. or more, or even 80 C. or more, of the first compressor air outlet temperature in the injection mode.

12. The hybrid CTPGS according to claim 1, wherein the second and any subsequent stage power machinery disposed between the direct TES and the compressed air store operates with a greater overall pressure ratio upon expansion in an injection mode than their overall pressure ratio upon compression in a bleed mode, such that the direct TES operates at a lower operating pressure during the injection mode than in the bleed mode.

13. The hybrid CTPGS according to claim 1, wherein the at least one direct TES includes a direct thermal transfer, sensible heat store comprising a gas permeable, solid thermal storage medium disposed in respective, downstream, individually access controlled layers.

14. The hybrid CTPGS according to claim 1, wherein the compressed air store includes a constant pressure, compressed air store.

15. (canceled).

16. (canceled).

17. The hybrid CTPGS according to claim 1, wherein, in a bleed mode, the inlet guide vanes are at least partly open.

18. The hybrid CTPGS according to claim 1, wherein, in a bleed mode, the bleed mass flow rate is at least two times the maximum injection mass flow rate that is achievable in the hybrid CTPGS.

19. A hybrid CTPGS according to claim 1, wherein the apparatus is configured so that, when the hybrid CTPGS is operating in a bleed mode, the total output power of all the power machinery in the hybrid CTPGS, and any steam turbine plant that is coupled downstream to it, is either zero or negative.

20. (canceled).

21. The hybrid CTPGS according to claim 19, wherein, in a bleed mode, the bleed mass flow rate is selected such that the mass flow rate through the gas turbine downstream of the one or more fluid connections is lower than that achievable when the inlet guide vanes are closed and no bleed or injection is occurring in the gas turbine.

22. The hybrid CTPGS according to claim 19, wherein, in a bleed mode, the pressure ratio across the first compressor is at least 10% lower than the normal minimum pressure ratio that is achievable across it when the inlet guide vanes are closed and no bleed or injection is occurring.

23. (canceled).

24. (canceled).

25. A method of operating a hybrid combustion turbine power generation system (CTPGS), wherein the hybrid CTPGS comprises: a combustion turbine (GT) system including a first compressor, a combustor and a turbine fluidly connected downstream of each other, wherein the turbine and compressor are coupled on a drive shaft and operatively associated with a generator or motor/generator, and an adiabatic compressed air energy storage system (ACAES) integrated therewith via one or more fluid connections disposed between the compressor and turbine, so as to allow air to be extracted from, and injected into, the GT system; wherein the ACAES includes a flow passageway network and associated valve structure leading from the one or more fluid connections to a compressed air store via a first direct thermal energy store (TES); and, wherein a top-up compressor is disposed in the flow passageway network between the one or more fluid connections and the direct TES, and is so fluidly connected that its inlet receives air extracted from the GT system and its outlet sends air at a higher temperature and pressure towards the downstream direct TES; the method comprising: (i) operating the system in a bleed mode comprising extracting some air via the one or more fluid connections from air passing respectively downstream through the compressor, combustor and turbine of the GT system and supplying the extracted air to the compressed air store of the ACAES system via the direct TES; and, (ii) operating the system in an injection mode comprising supplementing air passing respectively downstream through the compressor, combustor and turbine of the GT system by injecting, at the one or more fluid connections, pressurised air that is returning from the compressed air store of the ACAES system via the direct TES.

26. The method according to claim 25, wherein, during the bleed mode, the first compressor air outlet temperature is at least 30 C. lower than it is during the

27. (canceled).

28. (canceled).

29. (canceled).

30. (canceled).

31. (canceled).

32. (canceled).

33. (canceled).

34. (cancelled).

35. (canceled).

36. (canceled).

37. (canceled).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0133] Some embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

[0134] FIG. 1 is a schematic diagram of a conventional combined cycle gas turbine (CCGT) system of the related art;

[0135] FIG. 2a shows a first embodiment operating in an air bleed (or charge) mode;

[0136] FIG. 2b shows the first embodiment operating in an air injection (or discharge) mode;

[0137] FIG. 3a shows a second embodiment operating in an air bleed mode;

[0138] FIG. 3b shows the second embodiment operating in an air injection mode;

[0139] FIG. 4 shows a third embodiment operating in an air bleed mode with operating conditions indicated for a zero power bleed mode; and,

[0140] FIG. 5 shows a fourth embodiment operating in an air bleed mode with operating conditions indicated for a negative power bleed mode;

[0141] FIG. 6 shows a fifth embodiment with reversible second stage power machinery;

[0142] FIG. 7a shows a sixth embodiment that does not have a second TES;

[0143] FIG. 7b is a graph showing intercooler compressor power against time over a recharge period; and,

[0144] FIGS. 8a to 8c respectively show a seventh embodiment, including a charging compressor upstream of the top-up compressor, operating in various respective modes.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0145] FIG. 1

[0146] FIG. 1 shows a typical layout of a related art combined cycle gas turbine (CCGT) 1 used for peaking power generation, with an upstream compressor 11 directly coupled to a downstream turbine (expander) 14 and driving a generator 15 (e.g. connected to a transformer/grid). Between compressor 11 and turbine 14 is a combustion chamber 12 supplied with natural gas 13. In a normal configuration the compressor, turbine and generator are all directly coupled on the same shaft by drive couplings (not shown). Filtered air enters the compressor at ambient conditions (e.g. 30 C., 1 bar) and is compressed up to a higher pressure and temperature (e.g. 400 C., 16 bar). The hot high pressure air enters the combustion chamber where it is mixed with natural gas and caused to combust, heating the gas to a much higher temperature (e.g. 1400 C., 16 bar). This air is then expanded back to atmospheric pressure in the turbine, which produces more power than the compressor absorbs, hence there is a net generation of power that can drive the generator 15.

[0147] In the case of an open cycle gas turbine (OCGT), the cooled air is exhausted from the turbine well above ambient temperature (e.g. 450 C., 1 bar). However, in the case of a CCGT, the turbine operates with an exhaust temperature that is slightly hotter, either by operating at a lower pressure ratio or by combusting to a higher turbine inlet temperature. After the exhaust from the turbine 14, the hot high temperature exhaust gas (e.g. at 550 C., 1 bar) enters a heat exchanger 16, where it is cooled while heating a counter-flow of water that is at high pressure. The water normally becomes superheated during the heat exchange process and is then expanded through steam turbine 17 to a lower pressure. This steam is then condensed in condenser 20 before being pumped back to a high pressure by water pump 19 to return to the heat exchanger 16. The condenser 20 is normally supplied with a cooling water flow from a river or the sea. Steam turbine 17 is normally directly coupled to water pump 19 by generator 18 and the expansion of the steam in the steam turbine 17 produces more power than the water pump 19 absorbs, resulting in a supplementary net production of power. Due to the large thermal mass of different components, a CCGT needs to avoid switching on and off wherever possible, and hence, any features conferring variable turn-up &down capability are of particular value to such plants.

[0148] The remaining figures show some embodiments. All embodiments relate to a conventional combustion turbine arrangement in which the compressor, combustor and turbine are permanently fluidly connected downstream of each other, so that whenever the gas turbine is operating at least some air flow passes successively downstream through all those components in turn, regardless of whether or not a portion of the flow is being extracted or augmented at the one or more fluid connections, and in that the turbine is non-detachably coupled to the compressor so that both operate together when power is being generated by the turbine.

[0149] Further, all embodiments are shown as part of a combined cycle gas turbine system (CCGT), but they could be any other suitable derivative combustion turbine plant, or could be merely a simple cycle gas turbine (OCGT) system.

[0150] According to some embodiments, an additional compressor is provided upstream of the direct thermal energy store (TES) so that air extracted from the gas turbine in a bleed mode is subjected to a top-up (adiabatic or near adiabatic) compression stage prior to entering the direct TES, thus entering it at a higher temperature and pressure.

[0151] In the case of a hybrid combustion turbine power generation system with an integrated ACAES system and a non-decouplable gas turbine, air bleed and air injection usually takes place at or near minimum load and maximum load, respectively, when generating power.

[0152] To explain, gas turbines are often used in only two generating modes. The first is full power, where the price of electricity in the wholesale market is above the marginal cost of production, and hence the operator of the plant wants to maximise the sale of electricity at that point. The second is minimum load, which is where the cost of electricity is below the marginal cost of production, but where the losses may be less than the cost associated with stopping and restarting the gas turbine. The minimum load is normally determined by a requirement that CO emissions do not go above a certain level (associated with a low combustion temperature) and, for most gas power plant the minimum load is around 40-50% of the maximum load. Minimum load is normally achieved with the Inlet Guide Vanes (IGV's) closed. Maximum power is normally achieved with the IGV's open. Ambient temperature also has a significant impact on the maximum power that can be achieved and, on a warm day, this is likely to be well below the maximum power rating of the power plant. The maximum power rating is normally only achieved on very cold days.

[0153] A problem for a hybrid CTPGS with integrated ACAES including a direct TES downstream of the GT is that the GT compressor (first compressor) exit conditions (pressure and temperature) are likely to vary between air bleed (e.g. charge to further reduce minimum load) and air injection (e.g. discharge to increase peak power). During normal maximum power operation, the compressor exit conditions might be 450 C. and 18 Ba r. During maximum bleed operation, however, the pressure and temperature can drop much lower to e.g. 380 C. and 12 bar. If inlet guide vanes are used (closed) in conjunction with an air bleed, the temperatures and pressures can drop even further. There are two problems associated with bleeding at this temperature and pressure.

[0154] The first is that the direct TES (thermal store) is then not being charged at the ideal correct temperature for feeding back into the gas turbine (e.g. 450 C.). During discharge, thermal mixing would occur (irreversible mixing) between the gas flow from the store (e.g. 380 C.) and the gas flow from the GT compressor (e.g. 450 C.). More fue I would then be required to achieve the same turbine inlet temperature (reducing GT efficiency), changing the air fuel ratio (possibly resulting in a sub-optimal air/fuel ratio and an increase in GT emissions). If more fuel is required per kg of air, the efficiency of the gas turbine will reduce resulting in an increase in the GT heat rate. Some of the benefits are therefore lost from storing the compressed air, resulting in a reduction in the round trip efficiency of the compressed air storage system.

[0155] The second is that the compression ratio in the second stage compressor (after the direct TES) will be higher resulting in a high temperature post compression. During the discharge process this expansion ratio is likely to be lower than the charging compression ratio, because on discharge the GT is operating at a higher pressure ratio. Consequently there will be an associated increased temperature after the expansion in the second stage turbine that needs to be rejected as waste heat to ambient via heat exchangers i.e. some heat cannot be usefully converted back into power resulting in a lower efficiency. This will result in the work of compression of the second stage compressor being significantly higher than the work recovered (for the same mass flow) from the second stage turbine.

[0156] According to some embodiments, it is possible at least partially to alleviate these issues by the provision of a top-up compressor upstream of the direct TES. In this way, the temperature and pressure conditions at the thermal store can be controlled to be optimal for injection back into the GT combustor. The thermal store exit temperature and pressure can then, for instance, be selected closely to match that of the GT compressor exit during injection mode, resulting in minimal thermal mixing and optimum injection flow. The thermal store can also run at a constant pressure, if desired, rather than seeing a different pressure on charge versus discharge. These are exemplified in the embodiments of FIGS. 2a and 2b below.

[0157] Additionally, the power required from the top-up compressor can significantly increase the turn-down (reduction in output power) during storage/air bleeding. This increases the flexibility of the GT plant (power range over which the GT plant can operate). An alternative way of viewing this benefit is that, for the same bleed rate (kg/s), the GT output power can be reduced further than would originally have been possible with compressors after the direct TES. The reason for this increased power requirement is that the energy required to compress a kg of gas over a fixed pressure ratio increases if the starting temperature is higher. As an example, to compress 1 kg/s of air from 12 bar 380 C. to 20 bar 500 C. will require 122 kW of shaft power for a centrifugal compressor. To compress the same quantity of air from 12 bar 15 C. to 20 bar would only require 54 kW of shaft power.

[0158] A further benefit is that use of the top-up compressor means that the second stage compressor is compressing air that starts at a higher initial pressure (but usually cooled back to ambient). Hence, for a selected peak pressure ratio in the second stage machinery a higher final pressure will be achieved in the compressed air store (leading to improved storage density and the possibility of using a smaller volume compressed air store) and the efficiency of the storage process will be higher as the power per unit mass flow required to compress on charge and expand on discharge will be closer i.e. there will be lower losses.

[0159] It is also possible to charge the thermal store at a higher temperature (and pressure) than say 450 C. (and 18 bar) in bleed mode. This is exem plified in the embodiments of FIGS. 3a and 3b below. This will not only increase the turn-down capability further (power required for additional pre-store compressor increases by a factor of three if the first stage thermal store is at 615 C.), but the GT efficiency will increase slightly upon discharge (the amount of fuel required to heat the air to a certain turbine inlet temperature is reduced). It will raise the peak pressure that can be reached for a given pressure ratio in the second stage compressor. Power output during air injection may also be enhanced if, as exemplified in those figures, the overall expansion ratio of the second and any subsequent stage power machinery is selectively increased (beyond the charging compression ratio of that machinery stage) to expand the air back down to a pressure below the store pressure in the bleed mode, i.e. closer to the (lower) operating pressure in the gas turbine in the injection mode.

[0160] FIGS. 2a and 2b

[0161] Referring now to FIGS. 2a and 2b, these show a first embodiment.

[0162] Hybrid combustion turbine power generation system (CTPGS) 330 includes a conventional GT arrangement with an upstream compressor 11 directly (and non-detachably) coupled to a downstream turbine (expander) 14, which drives a generator or motor/generator 15 connected for example to a transformer/grid. Between compressor 11 and turbine 14 is a combustion chamber/combustor 12 with a fuel inlet 13.

[0163] The CTPGS 330 may be coupled downstream to an optional (shown as dotted lines) steam turbine plant 21 to form part of a combined cycle gas turbine system (CCGT).

[0164] An adiabatic compressed air energy storage system (ACAES) is integrated with the GT, usually as a retrofit process. The ACAES is integrated via one or more fluid connections 32 disposed downstream of the compressor and upstream of the turbine, for example, at the compressor outlet, at the turbine inlet or in between those, for example, in the combustor casing. Note it may also be possible for the extraction point to be close to the compressor exit but located in one or more of the later stages of the compressora compressor might have 18 stages for example. These allow a fraction of the airflow to be extracted (bled) from, and/or some pressurised air to be injected into the GT system upstream of the turbine, when it is active (with an airflow passing successively down through the compressor, combustor and turbine). The one or more fluid connections 32 may be a single fluid connection or multiple connections, for example, for respective extraction and injection. For example, for a gas turbine with multiple can combustors, they may include individual ports into each combustor casing with a manifold connecting them all to the pressurised air supply.

[0165] The ACAES includes a flow passageway network 33 and associated respective downstream valve structure 31a-31d configured to allow selective operation in various modes. Successively downstream of the fluid connection 32, the flow passageway network 33 includes a top-up compressor 333 in a (charge) pathway and an alternative (discharge) bypass pathway 33, these being arranged in parallel between respective selector valves 31a and 31b, at least one direct TES store 40, preferably a heat exchanger 48 (e.g. allowing heat rejection to ambient), second stage (higher pressure) power machinery including a second stage compressor 370 (e.g. axial flow compressor, reciprocating, centrifugal or turbo-compressor to name a few examples) disposed in a charging flow pathway, and a second stage expander 372 (e.g. centrifugal, turbo or axial flow turbine to name a few examples) disposed in an alternative discharging flow pathway, these being arranged in parallel between respective selector valves 31c and 31d, followed by an optional second (direct or indirect) TES 72, and optional heat exchanger 54 (e.g. again allowing heat rejection to ambient), and finally, the compressed air store 60.

[0166] The high pressure compressed air storage 60 may be a manufactured pressure vessel such as high pressure pipe or a welded steel vessel or a larger containment means such as an underground gas cavern. In the examples below, the compressed air storage 60 is a constant pressure, compressed air store. This can be achieved by means of using a 1000m column of water to maintain the pressure.

[0167] The compressed air store may however be a variable pressure store, in which case the second and any subsequent stage power machinery 370, 372 should be suitable for operation over the varying pressure ratio associated with the operational pressure range of the compressed air store.

[0168] The second stage power machinery may instead include one or more single reversible compressor/expander, which may be a positive displacement device, such as a reciprocating piston compressor/expander that is able to vary between compressing and expanding gas by changing of valve timing and it may again be operable over a variable pressure ratio.

[0169] The direct TES system may include one or more thermal stores 40 based on direct heat transfer to the thermal storage media. The thermal store 40 may be a direct TES with solid, gas permeable thermal storage media 46 such as crushed rock, concrete or other suitable particulate material, or, more structured gas permeable material such as formed ceramic blocks, held within a thermally insulated vessel 44. The media may thus have a monolithic or packed bed structure and be a layered or unlayered design. In particular, thermal media 46 may include a packed bed of suitable thermal media such as high temperature concrete, ceramic components, refractory materials, natural minerals (crushed rock) or other suitable material.

[0170] Thermally insulated vessel 44 must be designed so that the high pressure flow can pass through the vessel transferring heat directly to/from the thermal media 46 at the required charging or discharging rates. As there is direct heat transfer of heat to the media from the compressed gas, the thermally insulated vessel 44 will normally be an internally insulated pressure vessel. Whilst a direct TES does need to be built to withstand the gas pressure, it has the capability to store and return heat very efficiently, particularly if it is a layered store arrangement, and (unlike heat exchangers which require pre-conditioning) it can be switched from a storage (dormant) mode to a charging or discharging mode within seconds, which is important for a quick response hybrid GT system.

[0171] Referring to FIG. 2a, the gas turbine 11/12/14 is shown in operation generating power in a bleed (charging) mode, while in FIG. 2b, the gas turbine 11/12/14 is in operation generating power in an injection (discharging) mode.

[0172] In this example the thermal store pressure conveniently remains the same between charge and discharge, namely it is controlled to be at about 20 bar during charge and discharge, which is a suitable pressure for discharging back into the GT combustor.

[0173] During bleed mode (charge), the IGV's are at least partly open. Compressed air is selectively bled from the one or more fluid connections 32 at 12 bar and passed down passageway 33 such that the remaining mass flow rate through the GT is chosen to be about the same mass flow rate as at normal minimum load (IGV's fully closed). Selector Valves 31a and 31b are set to allow the air to pass through top-up compressor 333 where it is then compressed up to 20 bar. This increases the temperature of the store inlet air close to 500 C. so that heat that is close to this peak temperature can be stored in the direct TES as the air passes through the gas permeable storage media 46 with direct heat transfer thereto. Waste heat is then discarded to ambient as the air passes through heat exchanger 48 so that the air cools to about 35 C. (actual figure dependent upon ambient temperature and type of heat exchanger).

[0174] Second stage compressor 370 (e.g. axial flow or turbo-compressor) is then used to compress the air at a 1:5 compression ratio to the maximum allowable temperature for the indirect TES 72, for example, 250 C. and 100 bar, before waste heat is again discarded through heat exchanger 54, resulting in the air being stored in the compressed air store 60 at a constant pressure of about 100 bar is used.(A low cost liquid thermal store using a mineral oil can easily be achieved at 250 C.. If the temperature is higher it is normally necessary to use more expensive synthetic thermal oils, which may also require higher pressure tanks. At 250 C. it is normally possible to use an oil with a very low vapour pressure, which means that the storage tank is unpressurised.)

[0175] During the injection mode, the IGV's are fully open. The air returns through the same components to the direct TES 40, except that it passes through turbo-expander 372. This is sized so that it can deliver the correct mass flow to the gas turbine. There is normally a limit on the amount of air that can be injected into a gas turbine before the compressor stalls (surge). (This injection limit is normally much lower than the amount of air that can be bled from the GT.) Turbo-expander 372 is in a parallel pathway, accessed via switching of the settings of selector valves 31c and 31d, and expands the air back across the same ratio (5:1) to the same thermal store pressure of 20 bar, resulting in an air temperature of 84 C. at the entry to the heat exchanger 48 (e.g. when compressed air store is at peak pressure of 100 bar). This increase in temperature is the result of irreversible processes in the turbo-expander. As a result some heat then needs to be rejected via the heat exchanger 48 to reduce the store entry temperature of the air down to 35 C.

[0176] The air then passes back in reverse through direct TES 40 before selector valves 31b and 31a direct it along a bypass pathway 335 so that it circumvents the top-up compressor 333. The air is then returned to the one or more fluid connections 32 at about 20 bar, 500 C. and enters the combustor to mix with the 19.5 bar, 450 C. air from the GT compressor 11. In this case it is assumed that there is a 0.5 bar pressure drop between the TES 40 and the gas turbine. With careful design of ducting, corners, junctions and valves it should be possible to minimise this pressure difference. Thus, use of the top-up compressor in the bleed mode has allowed the air to be returned to the GT at a selected temperature and pressure suited (i.e. matched) to the gas turbine operating conditions.

[0177] It should be understood that there is likely to be a slight temperature difference (not described in these examples) between the air entering the direct TES on charge and the air exiting the direct TES on discharge. With careful design this temperature difference can be very low. For an indirect TES this temperature difference is likely to be greater as there are a number of losses occurring in the heat transfer process.

[0178] In the FIG. 2a embodiment, it was possible to obtain a turn-down (reduction in output power) during storage/air bleeding down to 20% of base load power (i.e. the maximum power with IGV's open and no bleed or injection) with the top-up compressor. By contrast, in apparatus that did not include the top-up compressor, a turn-down during storage/air bleeding could only be achieved to 26% of base load power. Hence, turn-down has been extended by 6%.

[0179] In FIGS. 2a and 2b and FIGS. 3a and 3b below, it is possible that all power machinery is directly coupled to a single main shaft operatively coupled to a generator or motor/generator. However, power machinery in the ACAES may be individually coupled to alternative drive shafts and have their own respective motor/generators or all compressors are connected on a single shaft via a clutch to a motor/generator and all turbines/expanders are connected on a single shaft via a clutch to the same motor/generator.

[0180] FIGS. 3a and 3b

[0181] FIGS. 3a and 3b show a second embodiment. In this embodiment, the operating pressure in the direct TES changes between the bleed and injection modes and the second stage power machinery operates over different pressure ratios between the two modes.

[0182] FIGS. 3a and 3b depict the hybrid CTPGS running in a power generation bleed (charge) mode and power generation injection (discharge) mode, respectively. Once again, the CTPGS 330 may be coupled downstream to an optional (shown as dotted lines) steam turbine plant 21 to form a CCGT.

[0183] The only difference in system components between FIGS. 3a and 3b and FIGS. 2a and 2b is that in FIGS. 3a and 3b the second stage expander 373 is a larger power machine than the second stage compressor 370 reflecting the fact that it expands the air over a greater pressure ratio. Otherwise, the differences materialise in how the system is operated.

[0184] During bleed mode (charge), the IGV's are again at least partly open and the bleed rate is again selected such that the remaining mass flow rate through the GT is chosen to be about the same mass flow rate as at normal minimum load (IGV's fully closed).

[0185] In this example, in the bleed mode, the top-up compressor 333 uses a higher ratio such that the air enters the direct TES 40 at 615 C. and 30 bar. This increases the power consumed during the bleed mode and will increase the turn-down capability of the GT. In the FIG. 3a embodiment, it was thus possible to obtain a turn-down (reduction in output power) during storage/air bleeding to 15% of base load power with the top-up compressor.

[0186] Once again, the air is cooled to 35 C. in the heat exchanger 48 after leaving the store 40, and is again subjected to a 1:5 compression ratio in the second stage compressor 370. But in this case, that ratio results in air being stored in the air store at an even higher pressure of 150 bar; this may reduce the store cost in that the same mass of air may be stored in a smaller volume.

[0187] In the injection mode, the IGV's are fully open. The air returns through the larger second stage expander 373, which operates over a 7.5:1 expansion ratio, expanding the gas down to 20 bar, which is suitable for returning the hot air to the combustor. This increases the power output from expander 373 as compared with previous expander 372, thereby increasing the GT turn-up capability in the injection mode. In this mode, the direct TES store operating pressure is at 20 bar.

[0188] Irreversibility from the compression stages during charge and the second stage expansion during discharge at expander 373 results in excess heat within the system that in the FIG. 2a/b embodiment is partially rejected by heat exchanger 48 (air is at 84 C.). By increasing the expansion ratio of expander 373, there is a better thermal match between the exit temperature of expander 373 and the entry temperature at the bottom of the TES 40, in that the expander outlet temperature in this example is only 50 C. (when air store at peak pressure of 150 bar). Hence, less waste heat is being rejected in this embodiment than the previous one.

[0189] More heat is retained in the system and is then fed back into the gas turbine combustor. When within the gas turbine, this extra heat can be usefully used to increase the temperature of the working fluid, thus requiring less fuel to reach optimum turbine inlet temperature. This results in an improvement in GT efficiency and a reduction in heat rate.

[0190] Possible benefits of this embodiment may be summarised as: [0191] i. Improved GT efficiency from injecting air that is hotter than GT compressor exit temperatures. [0192] ii. Less rejection of waste heat due to compression/expansion process irreversibility. [0193] iii. Higher round-trip efficiency. [0194] iv. Increased turn-down as the power required to drive the top-up compressor is increased. [0195] v. Increased turn-up as the power from the second stage expander is increased. [0196] vi. Increased compressed air store pressure for a given second stage compression ratio, so less volume is required to store the same mass of air. This might reduce the cost of the compressed air store in some circumstances.

[0197] Although not shown in this embodiment, the temperature and pressure of the direct TES 40 could be increased further resulting in an exact thermal match between expander 373 exit and the TES inlet temperature. This would result in no heat rejection at heat exchanger 48 on discharge. This would, however, require compressors and a thermal store that would work over these temperature ranges. Note that it is difficult to design compressors that can operate much above 600 C. and pressure vessels become very expensive a s the pressure requirement increases.

[0198] FIGS. 4 and 5

[0199] These Figures depict a further embodiment including a hybrid CTPGS of the same arrangement as that of FIGS. 2a-2b, namely, with a steam turbine 21 located downstream of the gas turbine 11/12/14, and at least motor/generator 15 operatively coupled thereto.

[0200] FIGS. 4 and 5 respectively illustrate how, in the bleed mode, a hybrid CTPGS with a top-up compressor 333 may be operated in the bleed mode so as further to lower the power output (as compared with FIG. 2a) so as to achieve zero power, or, indeed, to achieve a negative power so as to draw power from the grid, respectively, taking into consideration the summed (total) power figures for (1) the Gas Turbine including gas turbine compressor 11 and gas turbine expander 14, (2) the Steam Turbine including ST plant 21, and (3) the ACAES system including top-up compressor 333 and second stage compressor 370.

[0201] In the earlier examples of FIG. 2a,b and FIG. 3a,b, the fluid connections diverted a selected mass flow to storage such that the mass flow rate of the remaining flow through the GT (after the fluid connections) was maintained at roughly the usual minimum load (IGV's closed) mass flow rate.

[0202] In FIGS. 4 and 5, in bleed mode the IGV's are again part open. However, in these embodiments, the bleed rate is selected so that the remaining GT mass flow rate is dropped to below the minimum base load flow rate through the GT. As a result, the operating pressure in the GT upstream of the combustor is lower (10 bar) than the lowest operating pressure that can be achieved at minimum load conditions (e.g. usually about 12 bar in this example) in FIG. 2. Because more of the mass flow has been diverted to storage, the respective compressor powers in the ACAES are higher, consuming more power than in FIG. 2. The gas turbine should have a combustor that is designed or adapted for operation at these low flow rates. There is no problem of CO emissions as the combustion temperature can be maintained at a suitable level. However, the lower mass flow rate through the turbine means that for the same turbine inlet temperature that would be used at normal minimum load, the pressure ratio will fall to a level well below that which can be achieved at normal minimum load operating conditions. As has been explained in this example, it might be 9 or 10 bar versus a normal minimum load pressure of 12 bar (25% lower),or it could be as low as 6 bar or less, i.e. a 50% lowering of the normal minimum pressure ratio. This low operating pressure ratio cannot be achieved without some form of bleed as there is only a limited variation in mass flow through the main compressor that can be achieved with IGV's. This variation is fixed between these two conditions. The bleeding of additional air reduces the mass flow through the turbine to below the level which can be achieved with IGV's fully closed.

[0203] The lower mass flow rate and lower pressure through the turbine also results in a much lower power output from the turbine section and the steam turbine section. In addition the lower pressure ratio of the main GT also increases the work of the top-up compressor 333 for a target pressure ratio i.e. it is increased per kg of air that is bled from the system. As has been previously explained, the reason for this increased work is that a lower pressure ratio at the gas turbine means that the top-up compressor must operate over a larger pressure ratio (for a target pressure in the first TES), resulting in more work being carried out per kg of air compressed in the top-up section. The air that simply passes through the combustor/turbine section of the GT is not subjected to this additional compression work.

[0204] Comparing FIGS. 4 and 5, as mentioned above, both use partly open IGV's. The IGV's are more open in FIG. 5 than FIG. 4 (mass flow rate increases from 572 to 624 kg/s), and the extra air admitted is all diverted down to storage (224 kg/s as opposed to 172 kg/s), thereby raising the top-up and 2nd stage compressor powers in bleed mode, as well as the gas turbine compressor 11 power. Thus, while FIG. 4 achieves zero power, a condition where all the combined gas turbine, steam turbine and ACAES power machinery outputs are equally balanced, in FIG. 5 the power output in the bleed mode actually becomes negative (44 MW) such that the overall system needs to draw power from the grid to operate the three respective sub-systems. This can have the economic advantage that part of the power plant fuel is now being supplemented in the form of cheap electricity. As the wholesale cost of electricity is likely to be below the marginal cost of production (or there would be no reason to turn down) this should lead to a slight reduction in the cost of the fuel required to operate the power plant as the cheap electricity is being blended with the gas fuel input. However, in certain markets it may be simpler to operate in the zero power mode as it avoids the complication of having to purchase wholesale electricity.

[0205] In FIGS. 4 and 5, it is possible that all the power machinery in the system is directly coupled to a single main shaft operatively coupled to a generator or motor/generator. However, power machinery in the ACAES may be individually coupled to alternative drive shafts and have their own respective motors or generators or motor/generators.

[0206] It should be understood that the use of clutches and synchronous motor/generators means that electrical equipment used for driving compressors during bleeding can also be used to generate electricity from turbine/expanders during injection by clutching and de-clutching suitable machinery.

TABLE-US-00001 TABLE 1 Power Output Mode IGV's Embodiment +ve 115% High - Injection Fully Hybrid CTPGS: FIGS. but uses open 2b&3b less fuel +ve 115% High Injection Fully Comparative Example: open Hybrid CTPGS without top-up compressor +ve 100% Base None Fully Normal Gas Turbine Load open +ve ~40% Mini- None Closed Normal Gas Turbine mum Load +ve 26% Low Bleed Partly Comparative Example: Open Hybrid CTPGS without top-up compressor +ve 20% Low Bleed Partly Hybrid CTPGS: FIG. 2a Open +ve 15% Low Bleed Partly Hybrid CTPGS: FIG. 3a Open Zero 0% 0 Bleed Partly Hybrid CTPGS: FIG. 4 power Open ve 10% ve Bleed Partly Hybrid CTPGS: FIG. 5 Open

[0207] Table 1 above summarises, by way of example only, likely power figures for various operating modes of a normal gas turbine, a hybrid CTPGS, and a hybrid CTPGS with a top-up compressor as proposed in accordance with some embodiments. Thus, while a hybrid CTPGS may extend the turn-up and turn-down capability of a normal gas turbine beyond its normal power range of 40-100% (wrt Base load), the present examples show that capability may be further extended in the case of a hybrid CTPGS with a top-up compressor, when the system is suitably configured in the bleed mode, for example, so that the IGV's are selected to provide a suitable GT inlet mass flow rate, a suitable bleed mass flow rate is selected (e.g. using variable valves), suitable pressure ratio's are selected for the respective (appropriately sized) power machinery and any TES and compressed air stores are designed to meet the selected pressure and temperature conditions.

[0208] In the injection mode, the turn-up capability of the gas turbine may be extended (e.g. at least 5%, or at least 10%) beyond the base load 100% power figure (eg ISO conditions) that is attainable under the same ambient conditions during a normal power generation mode in which air passes respectively downstream through the compressor, combustor and turbine of the GT system to generate power without any power augmentation step, including any air injection.

[0209] In the bleed mode, the turn-down capability of the gas turbine may be extended (e.g. at least 20%, or at least 30%) beyond the minimum load % power figure that is attainable under the same ambient conditions during a normal power generation mode in which air passes respectively downstream through the compressor, combustor and turbine of the GT system to generate power without any bleed of air flow.

[0210] In the above examples, mass flow rates, including bleed and injection mass flow rates, pressure ratio's and TES and compressed air store conditions are given merely by way of example only. It will be appreciated that in any system those parameters need to be selected having regard to the operating limits of the power machinery and stores concerned. For example, in the zero and negative power examples given the inlet guide vanes are partly open, but in some GT systems this may be possible with fully open inlet guide vanes. Moreover, the capacities of the respective direct TES's, any indirect TES's and the compressed air store usually need to be relatively evenly matched relative to one another.

FIG. 6

[0211] This figure shows an embodiment 350 similar to that of FIG. 2a operating in bleed mode, except that there is a reversible second stage compressor/expander 370 upstream of the second TES 72. In a normal injection mode (not shown), air from the compressed air store 60 will be raised in temperature as it passes through the second TES 72 before expanding (and cooling) in the expander 370.

[0212] However, for use in a boost injection mode where rapid power is required, a throttle valve 504 is provided in an alternative (e.g. parallel) pathway; although the energy of re-expansion is lost in such apparatus, this may be acceptable for a short period of boost running. The throttle valve 504 is located in connection structure that extends directly between the direct TES 40 (including its heat exchanger) and the compressed air store 60 to allow air to pass out from the compressed air store directly to the throttle valve for re-expansion before entering the direct TES 40. Such a valve re-expands the air without significantly changing its temperature and hence such a flow pathway can bypass the second TES 72.

FIGS. 7a and 7b

[0213] FIG. 7a shows a simpler, lower cost system embodiment 360 that does not include a second TES and where the second stage power machinery only includes a compressor 508. In this embodiment, air is shown passing in the bleed mode through an intercooled compressor 508, a shut-off valve 510 (to protect the power machinery from the compressed air store), and an aftercooler 506, before entering the compressed air store 60. In the injection mode (not shown), air passes back from the compressed air store 60 but is expanded by a throttle valve 504 located in an alternative pathway that bypasses the compressor. The system has a lower efficiency due to the heat of compression being discarded, but is a significantly lower cost system that may provide a rapid response, boost injection mode.

[0214] The pressure in the compressed air store 60 (e.g. steel pipes) is variable and therefore the intercooler compressor 508 power increases with the time during the Recharge mode. By way of example, a Recharge mode may last for 6 hours, and in that time the maximum compressor power may rise to within the region of 15 MW. FIG. 7b is a graph showing the profile of the power consumption at the intercooler compressor during that Recharge period.

[0215] By way of example only, cycle parameters during a recharge mode and boost mode for the FIG. 7a embodiment (modelling based on a GE 9FA turbine) are shown in Table 2 below at respective successive downstream locations A to F, as identified on FIG. 7a.

TABLE-US-00002 TABLE 2 Parameter Unit Recharge Mode Boost Mode A Ambient Pressure bar 1.01325 Ambient Temperature C. 15 Relative Humidity % 60 Inlet mass flow kg/s 400 641.78 B Pressure bar 8 or 23.5 23.45 Temperature C. 286.6 522.7 Bleed Mass flow kg/s 50.00 50.00 C Pressure bar 23.5 23.45 Temperature C. 528.0 522.7 D Pressure bar 23.45 23.50 Temperature C. 35.00 15.00 E Pressure bar 255.10 245.00 Temperature C. 129.46 15.00 F Pressure bar 250.00 250.00 Temperature C. 35.00 15.00 Compressor Capacity kW 14,926

[0216] The performance of the gas turbine and the complete cycle (including the power consumption of the intercooler compressor) for the FIG. 7a embodiment are shown in Table 3 below in the respective bleed and injection modes and for minimum load and 100% load.

TABLE-US-00003 TABLE 3 CCGT 100% load Bleed Mode Injection Mode CCGT part load (No bleed, (50 kg/s) (50 kg/s) (40% GT load) No injection) Standard GT Gross Output kW 89,238 291,597 102,624 252,665 Turndown GT Gross Heat Rate kJ/kWh 14,450 8,831 13,738 9,697 ST Gross Output kW 89,971 133,486 100,289 130,288 CCGT Net Output kW 147,743 415,394 195,475 373,704 Output as percentage % 39.5% 111.2% 52.3% 100% of rated (CCGT) CCGT Net Heat Rate kJ/kWh 8,690 6,139 7,213 6,556 Weighted Average kJ/kWh 6,808 6,780 CCGT Heat Rate

FIGS. 8a to 8c

[0217] These figures show an embodiment 401 similar in principle to FIG. 2a, except that in addition there is a charging compressor 402 that acts (at least) as an alternative first stage compressor feeding the top-up compressor 333 to charge the compressed air store. The presence of charging compressor 402 means that charging of the high pressure compressed air store can occur while the gas turbine is inactive, or, indeed, while it is active but without needing to extract air from the gas turbine.

[0218] Charging compressor 402 is disposed in a flow pathway that connects to the main flow passageway network upstream of the top-up compressor 333, and it has its own upstream, external air (e.g. filtered atmospheric air) inlet and a valve 404 downstream of its outlet that acts as an on/off valve.

[0219] In FIG. 8a, the gas turbine is shown inactive in a charge mode and all first stage compression is undertaken by the charging compressor 402. Valve 31a is closed and valve 31b is open such that it directs flow towards TES 40. Charging compressor 402 is preferably configured to compress external air over the same pressure ratio as the first compressor (e.g. at low load), but may be a smaller, lower power/cost machine since it need only be sized to match, for example, the maximum (bleed) mass flow rate seen by the top-up compressor 333 and the pressure ratio of the first compressor at low load.

[0220] In FIG. 8b, the gas turbine is shown active in a charge mode where bleeding is taking place such that air is supplied from both charging compressor 402 and the first compressor 11, with valves 31a and 31b both open so as to allow downstream flow towards TES 40; for example, the charging compressor may be needed to expedite charging. If a combined feed mode is required, the top-up compressor 333 must also be sized for the maximum combined mass flow rate. Alternatively, a plurality of smaller top-up compressors may be provided in parallel and selectively used in combination to address the different respective mass flow rates.

[0221] Thus, multiple charging modes are potentially available which include charging from charging compressor 402, a combination of charging compressor 402 and bleed air from the gas turbine compressor 11, or just bleed air from the latter.

[0222] The combination of the charging compressor 402 in series with the downstream top-up compressor 333 means that the system can also provide an alternative source of heated, compressed air for injection into the gas turbine for power augmentation if, for example, the storage system was in an uncharged state. This is possible because the power drawn from the grid to operate both of those compressors is roughly the order of half the power boost obtained in the gas turbine.

[0223] One mode of operation is shown in FIG. 8c, where heated, pressurised air compressed successively by the charging compressor 402 and top-up compressor 333 is selectively diverted by the three-way valve 31b along the (usual discharge) bypass pathway 335 in the usual discharge direction before being selectively directed by three-way valve 31a back towards the fluid connections 32, before being injected into the gas turbine to boost mass flow and power.

[0224] It will be appreciated that other related modes of operation are possible to meet operating requirements. For example, (i) a combined storage/power augmentation mode might be where some of the above-mentioned heated, pressurised air (generated by the charging compressor and top-up compressor) may be split by valve 31b such that a proportion is sent to storage and the remainder is used to boost gas turbine power, or (ii) valve 31b may direct all the above-mentioned heated, pressurised air along the bypass pathway 335 via directed by three-way valve 31a back towards the fluid connections 32 and gas turbine, but valve 31b may also permit heated, pressurised air returning from storage to supplement that air.

[0225] While some embodiments have been described in detail, other embodiments are possible. Therefore, the scope of the appended claims should not be limited to the description of the preferred embodiments contained herein. For example, the CTPGS may be a simple cycle SCGT/open cycle OCGT plant, with only one power cycle and no provision for waste heat recovery, or it may be any known or suitable future variant or derivative thereof which could still benefit from integration of a top-up compressor in the ACAES sub-system, such as a combined cycle gas turbine CCGT (i.e. with a steam turbine bottoming cycle in addition to the topping cycle), or a variant thereof, for example, a CTPGS with intercooling, reheat, recuperation, or with steam injection. Some embodiments further provide any novel combination of the above-mentioned features which the person of ordinary skill would understand as being capable of being combined.