GAS TURBINE WITH DILUTED LIQUID FUEL

Abstract

 The invention refers to a gas turbine (1) with a compressor (3), a turbine (5), and a combustor (8) comprising a burner (9) for admitting a liquid fuel (10) into a combustor inlet gas during operation and a fuel distribution system (27) for supplying liquid fuel to the burner (9).
The fuel distribution system comprises a liquid fuel line (25) and a CO2 line (24) connected to the liquid fuel line (25) for admixing CO2 into the liquid fuel before injection into the burner (9).
The disclosure further refers to method for operating a gas turbine (1) with such a combustor (8) and fuel distribution system (27).

Description

Technical field

[0001] The disclosure refers a gas turbine with liquid fuel and CO2 dilution of the liquid fuel. The invention additionally refers to a method for operating such a gas turbine.

Background of the disclosure

[0002] This invention relates generally to gas turbine engines, and more specifically to methods and apparatus for operating a gas turbine with liquid fuel.

[0003] Gas turbines are used to drive generators for power generation and among other to drive compressors and to power oil and gas production facilities. For many facilities only liquid fuel such as fuel oil is available to power the gas turbines. NOx water is typically used for emission control during fuel oil operation. This requires a separate NOx water system. In particular on off shore installations space and support infrastructure for such a NOx water system are limited and expensive. At the same time, emission limit values and overall emission permits are becoming more stringent also for off shore installations.

[0004] State-of-the-art combustion systems are designed to operate with water injection to reduce NOx emissions. However, the purity requirements on NOx water are very high and it is difficult and costly to provide NOx water treatment systems in remote areas where water is rare or offshore installations. In addition water injection reduces the efficiency of gas turbine plants.

[0005] Besides low emissions the efficiency of gas turbines powering the production facilities should be improved.

Summary of the disclosure

[0006] The object of the present disclosure is to provide a gas turbine and a method for operating a gas turbine, which enables stable, safe, efficient, and clean operation with liquid fuel without the need of water injection to mitigate NOx emissions.

[0007] A gas turbine according to an embodiment of the disclosure has a compressor, a turbine, and a combustor. The combustor typically comprises a burner for admitting a liquid fuel into the compressed air leaving the compressor and which enter the combustor as combustor inlet gas during operation. Further such a gas turbine has a fuel distribution system for supplying liquid fuel to the burner. The fuel distribution system comprises a liquid fuel line and a CO2 line which is connected to the liquid fuel line for admixing CO2 into the liquid fuel before the mixture is injected into the burner.

[0008] Such a gas turbine allows admixing of CO2 for dilution of the liquid fuel and the injection of a CO2 liquid fuel mixture into the combustor. The viscosity of the diluted liquid fuel is reduced thereby facilitating the creation of a fine spay during injection. In addition the presence of the CO2 delays the combustion reaction. Both effects reduce local peak temperatures and thereby reduce the production of thermal NOx.

[0009] The ratio of CO2 mass flow to fuel mass flow can for example be in the range of 0.1 to 2.5, or in the range of 0.2 to 1.5.

[0010] To facilitate rapid mixing of CO2 with fuel static mixers or vortex generators, like for example swirlers or lobed profiles can be arranged in the fuel line.

[0011] According to a further embodiment a liquid fuel control valve is arranged in the liquid fuel line and the CO2 line for admixing CO2 to the liquid fuel is connected to the liquid fuel line upstream of the liquid fuel control valve. Such an arrangement allows the control of the total mass flow of the liquid fuel CO2 mixture. In addition the liquid control valve typically creates flow inhomogeneities which facilitate mixing of the CO2 with the liquid fuel.

[0012] According to an alternative embodiment a liquid fuel control valve is arranged in the liquid fuel line and the CO2 line is connected to the liquid fuel line downstream of the liquid fuel control valve. Such an arrangement allows the use of a smaller liquid fuel control valve. In addition a lower supply pressure of the CO2 is required as the pressure downstream of the liquid fuel control valve is lower than upstream.

[0013] In any case a separate control means such as a control valve can be provided to control the CO2 mass flow, respectively the CO2 volume flow.

[0014] Different connections of the CO2 line to the liquid fuel line are conceivable. The CO2 line can for example be joined to the liquid fuel line with a T-connection. To reduce pressure losses a y-shaped joint can be advantageous. Further, for example an annular arrangement in which CO2 is feed in a center pipe surrounded by a liquid fuel flow can be used. Alternatively an annular arrangement with liquid fuel feeding in a center pipe surrounded by a CO2 flow can be used.

[0015] According to a further embodiment a liquid fuel pump pressurizing the liquid fuel is provided in the liquid fuel line and a fuel preheater is arranged upstream of the liquid fuel pump. The CO2 line is connected to the liquid fuel line downstream of the liquid fuel pump. The liquid fuel pump pressurizes the liquid fuel to an injection pressure which is typically above the critical pressure of CO2. The pressure in the fuel distribution system downstream of the CO2 admixing can be kept above the critical pressure of CO2 thus reducing the volume flow of CO2. The reduced volume flow reduces the required size of the piping. The temperature of the CO2 can be either below or above the critical temperature of CO2 or at the critical temperature of CO2.

[0016] Advantageously, the CO2 has a pressure higher than the critical pressure. In the liquid phase or supercritical CO2 can be mixed to liquid fuel, such as oil, much easier than in the gas phase. The liquid or supercritical phase of CO2 facilitates the mixing and dilution of the liquid fuel. A larger CO2 to oil ratio can easily be achieved than by admixing gaseous CO2.

[0017] By keeping the temperature of both the liquid fuel and CO2 below the critical temperature of CO2 both flows and their mixture remain in the liquid phase which minimizes the volume flows and facilitates mixing.

[0018] In a further embodiment the fuel distribution system additionally comprises a NOx water line connected to the fuel line for admixing NOx water to the liquid fuel. The NOx water system allows alternative or combined use of CO2 or NOx water depending on the availability of water, respectively CO2.

[0019] Besides the gas turbine a method for operation such a gas turbine is an object of this disclosure.

[0020] According to a first embodiment of the method for operating a gas turbine with a compressor, a turbine, and a combustor comprising a burner, and a fuel distribution system for supplying liquid fuel to the burner comprises the steps of admixing CO2 to the liquid fuel, forming a mixture of the liquid fuel and the CO2 and of injecting the mixture into the burner.

[0021] According to a further embodiment of the method the CO2 is admixed to the liquid fuel upstream of a liquid fuel control valve.

[0022] According to an alternative method the CO2 is admixed to the liquid fuel downstream of a liquid fuel control valve.

[0023] CO2 admixing can also be done at fuel injection lines just upstream of individual burners. In a gas turbine with more than one fuel oil control valve for like for example in a gas turbine with sequential combustion the CO2 can also be feed into the liquid fuel supply system downstream of each fuel control valve.

[0024] According to a further embodiment of the method the CO2 is admixed to the liquid fuel in one of a T-connection, a Y-connection, a concentric pipe connection, and a venturi nozzle.

[0025] According to yet a further embodiment of the method the liquid fuel is preheated in a fuel preheater, then pressurized by a liquid fuel pump for pressurizing the liquid fuel, and then pressurized CO2 is admixed to the pressurized liquid fuel for dilution.

[0026] The liquid fuel can for example be pressurized to a pressure between the critical pressure of CO2 and 200 bars.

[0027] Preheating reduces the viscosity of the liquid fuel. For example when using heavy fuel oils or even crude oils a preheating is required before the fuel can be pressurized in a pump. The preheated pressurized oil can be diluted by admixing of CO2 and then injected as a fine spray for example via swirl nozzles or any conventional liquid fuel nozzle. Fuel can also be preheated using low grade heat or waste heat to improve the efficiency of the gas turbine or a combined cycle plant with such a gas turbine.

[0028] Mixing of the liquid fuel with the CO2 can take place at temperatures below the critical temperature of CO2 or above critical temperature. It can also take place with one flow, e.g. the liquid fuel, above and one flow, e.g. the CO2, below the critical temperature of CO2.

[0029] The CO2 can be supplied with a temperature below the critical temperature to reduce volume flow of CO2. Admixing cool liquid CO2 can lead to mixing temperature below the critical temperature thus keeping the total volume flow of the mixture low.

[0030] The temperature of the mixture can also be increased above the critical temperature of CO2 upon admixing leading to an increase in volume flow during admixing. This increase can for example be used to in a venturi type admixer to boost the liquid fuel pressure.

[0031] The temperature of liquid fuel and CO2 can also be above critical temperature for both flows before mixing.

[0032] According to a further embodiment of the method NOx water is admixed to the liquid fuel in addition to CO2 or during periods when no CO2 is available. NOx water can be admixed for reduction of the NOx emissions as well as for power augmentation.

[0033] According to yet another embodiment of the method the mixture of liquid fuel and CO2 is injected into the combustor with a pressure higher than or equal to the critical pressure of CO2 wherein the combustion pressure inside the combustor is lower than the critical pressure of CO2. The pressure drop leads to a strong increase of the CO2 volume flow which enhances the creation of small droplets during injection. As an example, the pressure of the CO2 can be higher than the CO2 critical pressure (about 73.9 bar) and can be for example in the range 73.9-90 bar or preferably 73.9-80 bar and more preferably 73.9-77 bar; the combustion pressure (i.e. the pressure within the burner into which the mixture of fuel and CO2 is injected) can be in the range 15-60 bar, preferably 20-40 bar and more preferably 25-35 bar.

[0034] According to a further embodiment of the method the mixture of liquid fuel and CO2 is injected into the combustor with pressure higher than the critical pressure and a temperature below the critical temperature of CO2, and wherein the combustion pressure is lower than the critical pressure of CO2. The injection leads to flash evaporization of the CO2 during injection into the combustor. Due to the flash evaporisation the mixture of liquid fuel and CO2 is burst into very small droplets. As a result a fine spray of liquid fuel in a CO2 enriched gas is created which allows good mixing with the compressed gas supplied to the combustion chamber by the compressor. The CO2 further delays the ignition time so that peak temperatures are reduced and thermal NOx emissions are minimized.

[0035] Typically, the droplets can be about one order of magnitude smaller than droplets obtained by injection of the liquid fuel without flashing CO2. For example the droplet size can be reduced from an order of 20 µm to 2 µm.

[0036] According to another embodiment of the method the CO2 is expended from a pressure higher than the critical pressure of CO2 to a pressure below the critical pressure of CO2 during admixing into the liquid fuel for boosting the pressure of the liquid fuel. This can for example be done in a venturi nozzle.

[0037] Different burner types can be used. For the first combustor so called EV burner as known for example from the EP 0 321 809 or AEV burners as known for example from the DE195 47 913 can for example be used. Also a BEV burner comprising a swirl chamber as described in the European Patent application EP12189388.7, which is incorporated by reference, can be used. In a can architecture a single or a multiple burner arrangement per can combustor can be used. Further, a flamesheet combustor as described in US6935116 B2 or US7237384 B2, which are incorporated by reference, can be used as first combustor.

[0038] The disclosure relates to gas turbine with one combustor as well as for gas turbines with sequential combustion. In a gas turbine with more than one fuel oil control valve for like for example in a gas turbine with sequential combustion the CO2 can also be feed into the liquid fuel supply system downstream of each fuel control valve.

Brief description of the drawings

[0039] The disclosure, its nature as well as its advantages, shall be described in more detail below with the aid of the accompanying schematic drawings.

[0040] Referring to the drawings:

Fig.1 shows a gas turbine with liquid fuel distribution system for supplying a mixture of liquid fuel and CO2 to a combustor;

Fig.2 shows a gas turbine with a liquid fuel distribution system for supplying a mixture of liquid fuel and CO2 to a combustor with a busted liquid fuel pressure;

Fig.3 shows a gas turbine with a liquid fuel distribution system for supplying a mixture of preheated liquid fuel and preheated CO2 to a combustor.

Figs. 4a, 4b, and 4c show different connecting types for connecting a CO2 line to a liquid fuel line.

Embodiments of the disclosure

[0041] Fig. 1 shows in a schematic representation the essential elements of a gas turbine power plant according to the invention. The gas turbine 1 comprises a compressor 3 in which intake air 2 is compressed to form compressed air 11 for combustion. This is fed to a combustor. A mixture of liquid fuel and CO2 (carbon dioxide) is injected into the compressed air 11 in a burner 9 and the mixture of fuel, CO2 and air is combusted in the combustion chamber 4. The hot combustion gases 13 are then expanded in a turbine 5. The useful energy which is generated in the turbine 5 is then transmitted to a consumer by the shaft 6. The consumer can be a generator 12 which converts the mechanical energy into electric energy.

[0042] The hot exhaust gases 7 which issue from the turbine 5, for optimum utilization of the energy still contained therein, are typically used in a heat recovery steam generator (HRSG) for generating steam for a water-steam cycle (not shown).

[0043] The gas turbine 1 can further comprise a cooling system for the turbine 5 and combustor 8, which is also not shown as it is not subject of the invention.

[0044] The fuel is supplied to the burner 9 by fuel distribution system 27. The fuel distribution system comprises a liquid fuel line 25 with a liquid fuel control valve, a CO2 line 24 with a CO2 control valve 21, and an optional NOx water line 26 with an optional NOx water control valve 23.

[0045] The liquid fuel line 25, the CO2 line 24, and the optional NOx water line 26 are connected to each other downstream of the respective control valves to a diluted fuel line 28 which is connected to the burners 9 of the gas turbine 1. The CO2 line 24 is also connected to a source of CO2 having a pressure higher than the critical pressure.

[0046] For connection to the burners 9 the diluted fuel line 28 can comprise a ring shaped section encircling an arrangement of combustors 8 from which lines branch to each burner 9.

[0047] The embodiment of Fig. 2 is based on Fig. 1. It differs from the example of Fig. 1 in that the CO2 line 24 is connected to the liquid fuel line 25 upstream of the liquid fuel control valve 22. The CO2 is admixed to the liquid fuel with the help of a venturi nozzle 32 which is arranged in the liquid fuel line 25 upstream of the liquid fuel control valve 22. The CO2 line is connected to the inlet of the venturi nozzle 32 for the driving fluid. Thus, the CO2 can be used to boost the liquid fuel pressure.

[0048] The optional NOx water line 26 is connected to the diluted fuel line 28 which connects the liquid fuel control valve 22 to burners 9.

[0049] In addition, the example of Fig. 2 shows a gas turbine 1 used as a mechanical drive which is connected to an industrial compressor 16, such as for example a pipeline compressor.

[0050] The embodiment of Fig. 3 is also based on Fig. 1. It differs from example of Fig. 1 in that the optimal NOx water line is not shown. In this example a liquid fuel preheater 30 and a liquid fuel pump 31 are arranged along the liquid fuel line 25 upstream of the liquid fuel control valve 22. Further, a CO2 compressor 14 followed by a CO2 heater 15 is arranged in the CO2 line 24 upstream of the CO2 control valve 21.

[0051] Figs. 4a to 4c show different connecting types for connecting the CO2 line 24 to the liquid fuel line 25.

[0052] The Fig 4a shows an example in which the CO2 line 24 is connected to the liquid fuel line 25 in a T-arrangement.

[0053] The Fig 4b shows an example in which the CO2 line 24 and the liquid fuel line 25 join in a y arrangement where the diluted fuel line 28 is the foot of the y. In this arrangement the pressure drop is reduced. For better mixing of liquid fuel with the CO2 a static mixer 29 is arranged in the diluted fuel line 28.

[0054] The Fig 4b shows an example in which the CO2 line 24 and the liquid fuel line 25 are arranged concentrically to minimize the pressure drop of the liquid fuel. The CO2 line 24 penetrates the liquid fuel line 25 from a side wall and turns in a right angle into the flow direction of the liquid fuel.

[0055] For all shown arrangements can or annular architectures or any combination of the two is possible. Flame Sheet, EV, AEV or BEV burners can be used for can as well as for annular architectures.

[0056] All the explained advantages are not limited to the specified combinations but can also be used in other combinations or alone without departing from the scope of the disclosure.

List of designations

[0057] 

1

Gas turbine

2

Intake air

3

Compressor

4

Combustion chamber (annular combustion chamber/ cans)

5

Turbine

6

Shaft

7

Exhaust gas

8

Combustor

9

Burner

11

Compressed air

12

Generator

13

Hot gases

14

CO2 compressor

15

CO2 heater

16

Industrial compressor

21

Liquid fuel control valve

22

CO2 (liquid or supercritical) control valve

23

NOx water control valve}

24

Liquid fuel line

25

CO2 line

26

NOx water line

27

Fuel distribution system

28

Diluted fuel line

29

Static mixer

30

Liquid fuel preheater

31

Liquid fuel pump

32

Venturi nozzle

Claims

1. A gas turbine (1) with a compressor (3), a turbine (5), and a combustor (8) comprising a burner (9) for admitting a liquid fuel (10) into a combustor inlet during operation and a fuel distribution system (27) for supplying liquid fuel to the burner (9),
characterized in that the fuel distribution system comprises a liquid fuel line (25) and a CO2 line (24) connected to a source of CO2 having a pressure higher than the critical pressure of CO2 and to the liquid fuel line (25), for admixing CO2 into the liquid fuel for injection of a diluted liquid fuel into the burner (9), wherein the combustion pressure in the burner is lower than the critical pressure of CO2.

2. A gas turbine (1) of claim 1, characterized in that a liquid fuel control valve (22) is arranged in the liquid fuel line (25) and in that the CO2 line (24) is connected to the liquid fuel line (25) upstream of the liquid fuel control valve (22).

3. A gas turbine (1) of claim 1, characterized in that a liquid fuel control valve (22) is arranged in the liquid fuel line (25) and in that the CO2 line (24) is connected to the liquid fuel line (25) downstream of the liquid fuel control valve (22).

4. A gas turbine (1) of any of claims 1 to 3, characterized in that the CO2 line (24) and the liquid fuel line (25) are joined forming one of a T-connection, a Y-connection, a concentric pipe connection, and a venturi nozzle (32).

5. A gas turbine (1) of any of claims 1 to 4, characterized in that a fuel preheater (30) is arranged in the liquid fuel line (25) upstream of a liquid fuel pump (30) for pressurizing the liquid fuel and in that the CO2 line (24) is connected to the liquid fuel line (25) downstream of the liquid fuel pump (30).

6. A gas turbine (1) of any of claims 1 to 5, characterized in that it comprises a NOx water line (26) connected to the fuel line (25) for admixing NOx water to the liquid fuel.

7. Method for operating a gas turbine (1) with a compressor (3), a turbine (5), and a combustor (8) comprising a burner (9), and a fuel distribution system (27) for supplying liquid fuel to the burner (9), characterized in that CO2 having a pressure higher than the critical pressure of CO2 is admixed to the liquid fuel forming a mixture of liquid fuel and CO2 and in that the mixture is injected into the burner (9), and wherein the combustion pressure is lower than the critical pressure of CO2.

8. Method for operating a gas turbine (1) according to claim 7, characterized in that the CO2 is admixed to the liquid fuel upstream of a liquid fuel control valve (22).

9. Method for operating a gas turbine (1) according to claim 7, characterized in that the CO2 is admixed to the liquid fuel downstream of a liquid fuel control valve (22).

10. Method for operating a gas turbine (1) according to one of the claims 7 to 9, characterized in that the CO2 is admixed to the liquid fuel in one of a T-connection, a Y-connection, a concentric pipe connection, and a venturi nozzle (32).

11. Method for operating a gas turbine (1) according to one of the claims 7 to 10, characterized in that the liquid fuel is preheated in a fuel preheater (30), then pressurized by a liquid fuel pump (30) for pressurizing the liquid fuel and then pressurized CO2 is admixed to the pressurized liquid fuel for dilution.

12. Method for operating a gas turbine (1) according to one of the claims 7 to 11, characterized in that in addition to CO2 or during periods when no CO2 is available NOx water is admixed to the liquid fuel.

13. Method for operating a gas turbine (1) according to claim 7, characterized in that the mixture of liquid fuel and liquid CO2 is injected into the combustor (8) with a temperature lower than the critical temperature of CO2.

14. Method for operating a gas turbine (1) according to one of the claims 7 to 12, characterized in that the CO2 is expended from a pressure higher than the critical pressure of CO2 to a pressure below the critical pressure of CO2 during admixing into the liquid fuel for boosting the pressure of the liquid fuel.

Drawing