A system for purging fuels containing reactive gases.

Abstract

The system for purging a hydrogen-containing fuel includes a gas turbine having at least one combustion chamber (20) with at least one injector (52) of fuel, an exhaust section, and a hot gas circuit extending from the combustion chamber (20) to the exhaust section. The system includes at least one injection point (A, A') of air and / or an inert gas disposed in the hot gas circuit.

Description

Technical Field

[0001] The present invention relates in particular to a system for purging fuel based on a reactive gas such as hydrogen (more precisely molecular hydrogen) used for the supply to a gas turbine.

Background Art

[0002] The present invention belongs to the field of combustion systems, particularly to gas turbines including a combustion chamber and a hot air passage for combustion gases.

[0003] A gas turbine generally consists mainly of a compression section including one or more compression stages.

[0004] Most of the compressed air is mixed with gaseous or liquid fuel injected through an injector into at least one combustion chamber to be burned. Generally, the combustion system is of the annular type, i.e., of the type including several combustion chambers in communication with the air generated by the compressor.

[0005] The flow of hot gases generated by combustion then passes through a hot gas cavity to an expansion turbine including one or more expansion stages before being discharged to an exhaust section or a recovery boiler. The passage within the turbine section causes rotation, thus enabling the recovery of mechanical energy by the rotor. A part of the rotational energy is used to rotate the rotor sections of the compressor and the alternator. Due to the extreme temperature, the velocity of the hot gases, and the speed of the rotor, it is necessary to reduce the thermal stress by internal cooling of the blades.

[0006] The expansion turbine consists of at least one row or stage of blades fixedly attached to the rotor. Since the blades are hollow, the cavities of these blades enable the provision of an internal cooling circuit that allows the compressed air generated by the compressor to be sent to the fixed blades. Each of these blades includes an aerodynamic profile having a side receiving the pressure of the flow and a suction side connected by a trailing edge.

[0007] Patent Document 1 describes a combustion chamber that includes an injector for a fuel oil / air mixture, enabling a reduction in the emission of nitrogen oxides or carbon monoxide, for low-load combustion mode (diffusion mode) or full-load combustion mode (premixed mode).

[0008] Patent Document 2 also describes a combustion chamber that includes several combustion stages, a primary combustion section or primary division, and a secondary combustion section or secondary division arranged axially in the direction of the combustion gas flow downstream of the primary division. The secondary division includes an additional inlet for the air / fuel oil mixture.

[0009] Patent Document 3 describes a compressor section and a turbine section for a gas turbine, which include rows of movable blades that are spaced apart and separated by fixed blades attached to a stator and attached to the rotor of a turbine, and all of these blades are capable of being cooled.

[0010] Furthermore, the use of mixtures of gaseous fuels such as natural gas, which may contain reactive gas fractions such as hydrogen, offers several advantages, particularly in reducing the amount of concentrated mixtures and carbon dioxide emissions. For example, a fuel mixture containing 30% hydrogen can reduce carbon dioxide emissions by 10%.

[0011] In particular, during turbine startup after a malfunction, fuels or fuel mixtures containing hydrogen or other reactive gas fractions, which may contain hydrogen at a percentage of up to 100%, require purging of the fuel supply pipe and the turbine cavity to discharge unburned fuel. This is because the hydrogen fraction in the fuel forms an air / fuel mixture that has a lower minimum ignition energy than natural gas and is easier to ignite.

[0012] Thus, in cases of misstarting, there is a high risk of accumulation and explosion in the combustion system and the stagnant air / fuel mixture passing downstream. Deflagration can damage equipment located downstream of the expansion section, such as the exhaust pipe, and in the case of a combined cycle, even the recovery boiler.

[0013] In particular, when hydrogen is at atmospheric pressure and ambient temperature, its ignition range in air is between 4% and 75%, and its minimum ignition energy varies depending on the concentrations of hydrogen and oxygen and the stoichiometry of the mixture (half the amount of oxygen for each hydrogen molecule). On the other hand, spontaneous ignition of hydrogen occurs at approximately 585°C / 858K, which is therefore higher than most other flammable gases.

[0014] Ignition of a reactive gas cloud can produce a sudden release of energy that results in the propagation of a flame front and blast waves. The theoretical conditions for the explosion of hydrogen in air essentially depend on its concentration in the fuel, for example, in the range of 4% to 8%, while deflagration can be achieved from 8%, and in some cases detonation can occur from 11%.

[0015] However, the use of hydrogen fractions presents a significant challenge in the design of equipment adaptation. This is particularly true when the high diffusion capacity in air, especially when forced by compressed air from the compression sector, can trap the gas mixture in the turbine cavity downstream of combustion.

[0016] Thus, when using hydrogen in the fuel mixture to start a gas turbine, the following points should be considered. - Limit the energy accumulated in the gas mass downstream of combustion, especially at the exhaust port. - The lower heating value (LHV) and higher heating value (HHV) of the mixture will be corrected. - Remove from the flammable area. - Increases the auto-ignition temperature. - Enhances equipment's resistance to explosions.

[0017] Several approaches have been proposed to mitigate the risks associated with the presence of explosive gas masses in turbine cavities. Specifically, - When designing equipment, consider the energy released during possible deflagrations. - Dilution of hydrogen downstream of combustion by air, an inert gas, or a combustion suppression gas. - Decreased fuel quantity during startup. - Ignition of the flame at a rate that allows purging of the gas by increasing the air flow and in the cleaning of the turbine cavity.

[0018] The simplest and most economical approach consists of diluting the hydrogen mixture with air or an inert gas to modify the LHV and HHV of the mixture. However, this solution requires means for injecting an inert gas into the high-temperature gas cavity and the downstream passage of the combustion.

Prior Art Documents

Patent Documents

[0019]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0020] The object of the invention is to modify the LHV and HHV of the mixture and purge the reactive fuel that may be present in the high-temperature gas circuit of the gas turbine, for example, to allow dilution of a reactive fuel mixture containing a hydrogen fraction, without the need to provide a passage for an additional flow of air or an inert gas, especially in the case of misstarting.

Means for Solving the Problems

[0021] With this as the goal, the present invention provides a system including a gas turbine for purging a reactive fuel containing hydrogen. The gas turbine includes at least one combustion chamber having at least one fuel injector, an exhaust section, and a high-temperature gas circuit extending from the combustion chamber through an expansion turbine to the exhaust section. It is worth noting that the high-temperature gas circuit includes at least one injection point for air and / or an inert gas and / or a combustion inhibitor.

[0022] Thus, the provided solution makes it possible to add a purge system using an additional flow of air and / or an inert gas and / or a combustion inhibitor to the combustion chamber and the cavities downstream thereof. In particular, the present invention attempts to provide a flow of air and / or an inert gas and / or a combustion inhibitor under optimal conditions in order to at least dilute the reactive gas fraction such as hydrogen in the air-fuel mixture. This dilution can be achieved by the distribution and / or installation of injection points in the high-temperature gas circuit.

[0023] At least two sections for the injection of air and / or an inert gas and / or a combustion inhibitor can be considered, namely injection downstream of the flame to avoid interruption of combustion and injection at the inlet of the exhaust section at the outlet of the expansion turbine. Preferably, in order to enhance the effectiveness of dilution, the two types of injection should be carried out in opposite flows.

[0024] Thus, in a specific embodiment, at least one injection point is installed downstream of at least one fuel injector, preferably an injection downstream of the flame section.

[0025] In this specific embodiment, at least one injection point can be installed at the inlet of the exhaust section.

[0026] In another specific embodiment where the expansion turbine additionally includes a cooling circuit having fixed blades installed in the high-temperature gas circuit, at least one injection point is installed in this cooling circuit.

[0027] In another specific embodiment, the purge system additionally includes a distribution ring mounted inside the exhaust port downstream of the exhaust section, with at least one injection point located on the distribution ring.

[0028] In all of these specific embodiments, at least one injection point of the purge system may be connected to an external supply source.

[0029] The inert gas used in the purge system is nitrogen, carbon dioxide, or vapor.

[0030] The combustion suppression gases used by the purge system may be bromomethane, tetrachloromethane, or halogen hydrocarbons, or in practice, hydrofluorocarbons.

[0031] In another embodiment, at least one injection point may contain a mixture of air, an inert gas, and a combustion suppression gas.

[0032] Diluting a combustible mixture with air, or with an inert gas such as carbon dioxide, nitrogen, or vapor, allows for the modification or reduction of the low explosion level (LEL), minimization of the volume of inert gas used, and improvement of process economics.

[0033] On the other hand, when it is desirable to address the problem of detonation (as uneven dilution may create a risk of accumulation), it is preferable to combine the use of air and an inert gas to use an inert gas to suppress the detonation properties of the combustible mixture, while the use of a combustion inhibitor allows for the cessation of the propagation of possible deflagration and detonation.

[0034] This system may include several injection points located at different points in the high-temperature gas circuit.

[0035] Other aspects and advantages of the invention will become apparent from the following detailed description of specific embodiments, which are listed as examples and are not limiting in any way, with reference to the accompanying drawings. [Brief explanation of the drawing]

[0036] [Figure 1] This graph shows curves representing the detonation and flammability of a combustible mixture of air and hydrogen according to the percentage of added inert gas in a specific embodiment of the purge system according to the invention, where the added inert gas is nitrogen. [Figure 2] This graph shows curves representing the detonation and flammability of a combustible mixture of air and hydrogen according to the percentage of added inert gas in a specific embodiment of the purge system according to the invention, where the added inert gas is carbon dioxide. [Figure 3] This is a longitudinal cross-sectional diagram of a conventional gas turbine, including its main components and high-temperature gas circuit. [Figure 4] This is a detailed diagram of the high-temperature gas passage in an expansion turbine. [Figure 5] This is a diagram illustrating a first embodiment of the invention. [Figure 6] This is a diagram illustrating a second embodiment of the invention. [Figure 7] This is a diagram illustrating a third embodiment of the invention. [Modes for carrying out the invention]

[0037] In the graph in Figure 1, the horizontal axis represents the volume percentage of nitrogen added to the combustible mixture of air and hydrogen, while the volume percentage of hydrogen is shown on the vertical axis.

[0038] The continuous curves represent the limits of the flammable zone, while the dashed curves represent the limits of the detonation zone.

[0039] At point D, the combustible mixture contains 30% hydrogen by volume and 70% air by volume. At point C, it is possible to escape the detonation compartment when the hydrogen concentration drops to 13% by volume and 58% nitrogen by volume is added, in which case the mixture contains 29% air by volume.

[0040] In the graph in Figure 2, the horizontal axis represents the volume percentage of carbon dioxide added to the combustible mixture of air and hydrogen, while the volume percentage of hydrogen is shown on the vertical axis.

[0041] The continuous curved lines represent the limits of the flammable zone, while the dashed curved lines represent the limits of the detonation zone.

[0042] At point D, the combustible mixture contains 30 vol% hydrogen and 70 vol% air. At point C, it is possible to escape the detonation compartment when the hydrogen concentration drops to 13 vol% by adding 30 vol% carbon dioxide, in which case the mixture contains 57 vol% air.

[0043] Figure 3 shows a linear diagram of the longitudinal section of a conventional gas turbine 10. The main components of the gas turbine 10 are as follows: Compression section 12 including a compressor 16, an air inlet 14 and a compressed air outlet 38; Combustion system section 18 from which a combustion gas stream 40, known as hot gas, is released; Expansion section or turbine 22 including fixed blades and movable blades attached to a rotor 26 on a rotating shaft 28. The rotor 26 connects the compression section 12, the expansion turbine 22 and one or more combustion chambers 20, and the flow of hot gas 40 crosses the stages of the expansion turbine 24 (of the expansion section 22) to the inlet of the exhaust section 30.

[0044] Figure 4 shows a detailed depiction of the upper part of the expansion turbine 24 through which the high-temperature gas 40 passes. The stages of blades 32A, 32B, and 32C are fixed to the stator, while the movable blades 34A, 34B, and 34C are fixed to the rotor 26 shown in Figure 3. Thus, the passage and cavity for the high-temperature gas exiting the combustion chamber 20 shown in Figure 3 are formed upstream of the exhaust section 30 shown in Figure 3.

[0045] Figure 5 illustrates a first embodiment of the invention in which the purge system includes injection points "A and A'" of air and / or inert gas and / or combustion inhibitor into the combustion system, preferably downstream of the flame or combustion compartment of the combustion chamber.

[0046] We will consider fuels that contain a predetermined proportion of hydrogen.

[0047] The purge system according to the present invention includes a gas turbine of the type of gas turbine 10 described above with reference to Figure 3. In particular, the gas turbine 10 includes at least one combustion chamber 20 having at least one fuel injector 52 as described above. The gas turbine 10 also includes an exhaust section 30 (see Figure 3) and a high-temperature gas circuit 40 extending from the combustion chamber 20 to the exhaust section 30.

[0048] The combustion chamber 20 shown in Figure 5 is generally limited on the one hand by a cover 51 at the inlet where an inlet connection for a fuel injector 52 is visible, and on the other hand by a tailpipe 53 at the outlet that extends to the stage of the expansion turbine 24 (not shown in Figure 5 but visible in Figure 3).

[0049] Inside the combustion chamber 20, the liner 56 allows compressed air 57 from the compressor 16 (shown in Figure 3) to pass through to the intake port of the fuel injector 52. Inside the combustion chamber 20, a combustion section 54 and a dilution section 55 may be formed during operation.

[0050] Reference numerals A and A' indicate, in this first embodiment, at least one injection point for air and / or inert gas and / or combustion inhibitor. This injection point is located in the high-temperature gas circuit immediately downstream of the compartment where the flame is presumed to be present, in the case of ignition. Thus, injection points A and A' are located downstream of the fuel injector 52.

[0051] In a specific embodiment shown in Figure 5, injection points A and A' are located in the combustion compartment 54. Thus, since the gas turbine is equipped with a controller (not shown), the controller enables the opening of valves to control the reactive gas flow and enable the combustion system to start. Simultaneously with this start, the controller also activates the purge system either before or simultaneously for the injection of air and / or inert gas to create a flow F that mixes with the hydrogen-based fuel in the turbine's combustion chamber 20 and high-temperature gas circuit.

[0052] Figure 6 illustrates a second embodiment of the invention in which a gas turbine includes a cooling circuit having fixed blades. In this second embodiment, the injection of air and / or inert gas can be carried out through the cooling circuit. Thus, it is sufficient to make at least one injection point of air and / or inert gas in the cooling circuit 50 available.

[0053] The cooling circuit 50 includes several fixed blades, including those indicated by reference numerals S1N and S2N in Figure 6. These blades are fixed to the stator in the hot gas passage and cavity 40. Furthermore, the source to which the cooling circuit is injected may be air supplied from the compressor 16, or an external supply source 60 of air and / or inert gas and / or combustion inhibitor.

[0054] Figure 7 illustrates a third embodiment of the invention, in which the gas turbine includes a distribution ring 75 mounted inside an exhaust section 74 located immediately downstream of the expansion turbine 24. In this third embodiment, the injection of air and / or inert gas and / or combustion inhibitor can be carried out through the distribution ring 75. To this end, it is sufficient to make at least one injection point of the distribution ring 75 available. Furthermore, the source of injection into the distribution ring 75 may be an external supply source 77 for air and / or inert gas and / or combustion inhibitor.

[0055] In all of the embodiments described above as non-limiting examples, the inert gas used for purging may be nitrogen, carbon dioxide, or vapor.

[0056] Needless to say, in all the embodiments described above, the volume and flow rate of the air and / or inert gas and / or combustion inhibitor selected to be injected also depend on the hydrogen fraction of the fuel, the volume of fuel injected for misstarting, and the volume of the turbine's hot gas circuit.

[0057] Furthermore, the three embodiments described may be combined to provide an effective solution that enables the mixing of a hydrogen fraction fuel with air and / or an inert gas. [Explanation of symbols]

[0058] 10 Gas Turbines 12 Compression Classification 14 Air Inlet 16 Compressors 18 Combustion System Classification 20 Combustion chamber 22 Expansion Category / Turbine 24 Expansion Turbine 26 rotors 28 rotational axes 30 Exhaust Classification 32A, B, C blades 34A, B, C Movable Blades 38 Compressed air outlet 40 High-temperature gas circuit 50 Cooling circuit 51 Cover 52 Injector 53 Tailpiece 54 Combustion Sections 55 Dilution section 56 Raina 57 Compressed air 60 External sources 74 exhaust ports 75 distribution ring 77 External sources A,A' injection point F flow S1N, S2N Fixed Blade

Claims

1. A purge system for purging a hydrogen-containing fuel, comprising a gas turbine (10), wherein the gas turbine (10) comprises at least one combustion chamber (20) having at least one fuel injector (52), an exhaust section (30), and a high-temperature gas circuit (40) extending from the combustion chamber (20) to the exhaust section (30), and comprises at least one injection point (A, A') of air and / or inert gas and / or combustion inhibitor and / or vapor disposed in the high-temperature gas circuit. The combustion system of the gas turbine (10) includes the combustion chamber (20), The purging system further includes a controller that activates the injection of air and / or inert gas and / or combustion inhibitor and / or steam at at least one injection point (A, A') before starting the combustion system of the gas turbine (10), At least one injection point (A, A') is located in the combustion chamber (20), At least one injection point (A, A') of the combustion chamber (20) is dedicated to purging the fuel. A purge system in which the at least one injection point (A, A') of the combustion chamber (20) is located downstream of the combustion section of the at least one fuel injector (52).

2. The purge system according to claim 1, further comprising a cooling circuit having fixed blades (S1N, S2N) installed in the high-temperature gas circuit (40), wherein at least one injection point (A, A') is installed in the cooling circuit (50).

3. The purge system according to claim 1, further comprising a distribution ring (75) installed inside an exhaust port (74) downstream of the exhaust section (30), wherein at least one injection point is installed on the distribution ring (75).

4. The purge system according to claim 2, wherein at least one of the injection points is connected to an external supply source (60; 77).

5. The purge system according to any one of claims 1 to 4, wherein the inert gas is nitrogen.

6. The purge system according to any one of claims 1 to 4, wherein the inert gas is carbon dioxide.

7. The purge system according to any one of claims 1 to 4, wherein the controller is configured to control a valve for controlling the reactive gas flow, which is the fuel, to enable the starting of the combustion system.

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