Purge system and method for a gas turbine Technical field of the invention

The present invention relates to the field of gas turbines, in particular to a purge system and method for a gas fuel supply pipeline of a gas fuel system of gas turbines.

Background of the invention

Gas turbines are used in many fields to drive generators or working machines. The principal components of a gas turbine are a compressor, a combustion chamber, a burner and a turbine. Air is drawn from the external environment into the compressor, where it is compressed to a high degree to form combustible air; fuel and air are then channeled into the combustion chamber. The combustible air is burned together with the fuel by the gas turbine burner in the combustion chamber to form hot gas, which then drives the operation of the gas turbine.

A gas turbine engine burns a mixture of compressed air and fuel to produce combustion gas; some gas turbines comprise a dual fuel system, using gas fuel and liquid fuel for example. The dual fuel system allows switching from one fuel system to the other. In the case where it is necessary to switch from the gas fuel system to the liquid fuel system, the burner and gas fuel supply pipeline of the gas turbine is still full of gas fuel, such as natural gas or coal gas, after the gas sup ^¬ ply valve has been closed; therefore, direct switching to the liquid fuel system for continued operation will result in autoignition and deflagration of the gas fuel in the gas fuel supply pipeline and burner. This will cause damage to compo ^¬ nents such as the gas fuel supply pipeline and burner of the gas turbine. Moreover, some fuel turbines use multi-stage gas burners, and under certain working conditions one or more burner stages must be closed, in which case fuel remaining in the gas supply pipeline and burner of the gas system in the closed part may cause autoignition or deflagration. In response to the above problem, the following technical so ^¬ lution has already been proposed: an inert gas, steam, nitro ^¬ gen or carbon dioxide gas is used to purge the gas supply pipeline, burner or other relevant components of the gas fuel system, filled with gas fuel such as natural gas, of the gas turbine. The inert gas etc. is used to blow the gas fuel in ^¬ side the gas supply pipeline, burner or other relevant compo ^¬ nents of the gas fuel system into the combustion chamber, thereby avoiding problems such as autoignition or deflagra ^¬ tion. However, the above technical solution requires an addi- tional system, hardware components, and an inert medium as well as associated maintenance and service, etc., making the structure relatively complicated and the cost relatively high. For example, Fig. 1 shows an existing gas turbine sys ^¬ tem, comprising a gas fuel supply system, a compressor, a burner, a combustion chamber and a turbine. It can be seen from the figure that in order to solve the above problem, a nitrogen purge system connected to the gas fuel supply system is provided. The nitrogen purge system comprises a nitrogen storage tank a, nitrogen supply pipelines b, and valves pro- vided correspondingly in the nitrogen supply pipelines, for example control valves c. This gas turbine system is afflict ^¬ ed by the problems of complex structure and high cost men ^¬ tioned above. US patent publication no. US2013/0118178A1 has disclosed a gas turbine system, comprising a multi-fuel gas turbine, a liquid fuel system and a gas fuel system, wherein the multi- fuel gas turbine comprises a compressor, a burner and a tur ^¬ bine. The system also comprises a gas fuel purge system, con- figured to purge a gas fuel pipeline of the gas fuel system during liquid fuel operation of the gas turbine, wherein the gas fuel purge system is configured to sequentially purge the gas fuel system using air and steam. Such a system can also eliminate the problems of autoignition and deflagration af ^¬ flicting gas turbines having dual fuel systems, but it still has flaws similar to those of the system shown in Fig. 1. It similarly requiresan additional purge gas supply system, with complex structure and high costs.

Thus, there is currently a demand for a purge system for a gas turbine with a simple structure and a reduced cost. Summary of the invention

To achieve the above objective, the present invention pro ^¬ vides a purge system for a gas turbine, the gas turbine com ^¬ prising a compressor, a combustion chamber, at least one burner and a gas fuel system, characterized in that the purge system comprises: a cooler having an inlet end and an outlet end, a first pipeline connecting the compressor to the cooler inlet end, and at least one second pipeline connecting the cooler outlet end to a gas fuel supply pipeline of the gas fuel system, so that when the gas fuel system is at least partially closed, air from the compressor can purge the gas fuel supply pipeline and burner in the closed part of the gas fuel system after being cooled in the cooler. In this solution of the present invention, when the gas fuel system is partially or completely closed, the compressor is used to draw air from the external environment into the cooler, so that the temperature of the air falls to a suitable degree in the cooler; the cooled air is then passed through the gas fuel supply pipeline and burner in the closed part at a cer- tain speed and pressure, so that gas fuel in the gas fuel supply pipeline and in the burner in fluid communication therewith in the closed part can be blown into the combustion chamber. During purging, low-temperature air from the cooler will cool both the gas fuel supply pipeline and the burner, lowering the temperature thereof to less than the

autoignition point of the gas fuel, so as to avoid the phe ^¬ nomena of autoignition and deflagration. With regard to the purge system for a gas turbine described above, air from the compressor can be blown into the gas fuel supply pipeline continuously at a certain pressure and flow speed after being cooled, thereby preventing back-flow of combustible gas remaining in the combustion chamber into the burner, and hence serving to seal the burner or a particular stage of a multi-stage burner. Furthermore, when the gas tur ^¬ bine is out of operation for a longperiod of time, moisture condensation may occur in the gas fuel supply pipeline; be- fore reoperation is initiated, gas can be supplied in by means of the compressor, to remove condense present in the gas fuel supply pipeline.

According to one solution of the present invention, the at least one burner is a multi-stage burner, the gas fuel system has multiple gas fuel supply pipelines in communication with each stage of the multi-stage burner, respectively, the num ^¬ ber of said second pipelines is equal to the number of said gas fuel supply pipelines, the outlet end is in communication with the gas fuel supply pipelines via the corresponding se ^¬ cond pipelines, respectively, and cooled air can purge the closed gas fuel supply pipelines and the stages of the burn ^¬ er. For example, the burner may be a two-stage burner, in which case the gas fuel system is provided with two gas fuel supply pipelines in communication with the first stage and second stage of the burner, respectively. When the first stage burner is closed, cooled air can be blown into the gas fuel supply pipeline in communication with that stage as well as the first stage burner.

To deliver air from the compressor to the gas fuel supply pipelines, and then to the burner, in a controllable way, a throttle control mechanism can be provided between the com ^¬ pressor and the gas fuel supply pipeline, for controlling the supply of purging air from the compressor to the gas fuel supply pipeline. In one solution of the present invention, the throttle control mechanism is a control valve arranged in each second pipeline, the control valve being used for cut- ting off or connecting the supply of gas fuel to the burner and for controlling the pressure and flow speed of the air ^¬ flow from the cooler. Alternatively, the throttle control mechanism comprises an orificeplate regulating flowing volume of the airflow and a shutoff valve arranged in the second pipeline, wherein the shutoff valve is used for cutting off or connecting the supply of gas fuel to the burner; the ori ^¬ fice plate is used for controlling the pressure and flow speed of the airflow from the cooler. The control valve, shutoff valve and orifice plate mentioned here are all known in the art, so are not described superfluously herein.

It is advantageous if the throttle control mechanism is so configured that, when the gas fuel system is partially or completely closed, air from the compressor can purge the gas fuel supply pipeline and burner in the closed part of the gas fuel system after being cooled in the cooler.

Preferably, the throttle control mechanism is so configured that air from the compressor can purge the gas fuel supply pipeline and the burner continuously, so as to avoid back- flow of combustion gas from the combustion chamber into the burner . In a preferred solution of the present invention, each gas fuel supply pipeline is provided with a control valve for regulating the gas fuel supply to the burner when the gas fuel system is at least partially closed. The at least one second pipeline is downstream of a control valve in the gas fuel supply pipeline and in a position close to the control valve. Here, "downstream" is specified by the direction of flow of gas fuel from the gas fuel source to the burner. Such a configuration enables substantially all of the gas fuel and air in the section of gas fuel supply pipeline between the gas supply and the burner to be purged.

According to one solution of the present invention, the cooler is configured to be able to lower the temperature of air from the compressor to a level sufficient to lower the tem ^¬ perature of the gas fuel supply pipeline and burner through which it passes to less than the autoignition temperature of the gas fuel (e.g. less than 200 degrees Celsius) . In the present invention the cooler may be any suitable cooler, for instance, a water cooler, oil cooler or air cooler, which work with different media, or a recuperative cooler, plate cooler, jacket cooler or coil cooler, etc, which have different structures.

According to another solution of the present invention, a gas turbine system is also provided, comprising a gas turbine and the purge system for a gas turbine described above. Not only can such a gas turbine system eliminate phenomena such as autoignition, deflagration, back-flow and moisture condensation, it also has the advantages of a simple, compact struc ^¬ ture, and a relatively low cost.

Furthermore, one solution of the present invention also pro- vides a method for purging a gas fuel system of a gas tur ^¬ bine, the gas turbine comprising a compressor, a combustion chamber and at least one burner and a gas fuel system, and the method comprising the following steps: feeding air from the compressor into the cooler to be cooled to a predeter- mined temperature; when the gas fuel system is at least par ^¬ tially closed, using cooled air to purge a gas fuel supply pipeline and burner of the gas fuel system.

It is advantageous if, to prevent the occurrence of phenomena like autoignition and deflagration in the gas fuel supply pipeline and burner when the gas fuel system is partially or completely closed, the purging step is performed on the gas fuel supply pipeline of one or more stages in which the gas fuel is cut off. In the purging step, gas fuel remaining in the gas fuel supply pipeline and burner is blown into the combustion chamber to take part in combustion, while the supply pipeline, burner or other components passed through by the air can be cooled at the same time. In addition, to prevent back-flow of combustion gas from the combustion chamber into the burner when the gas turbine is running and the gas fuel is completely or partially cut off, the purging step is performed continuously, thereby prevent ^¬ ing back-flow of combustion gas from the combustion chamber into the burner.

Some of the other features and merits of the present inven- tion should be obvious to those skilled in the art after reading this application, while some are described in con ^¬ junction with the accompanying drawings in the particular embodiments which follow. Description of the accompanying drawings

Embodiments of the present invention are explained in detail below in conjunction with the accompanying drawings, wherein: Fig. 1 is a structural schematic diagram of a nitrogen purge system for a gas turbine in the prior art;

Fig. 2 shows a structural schematic diagram of the purge sys ^¬ tem for a gas turbine according to the present invention.

In the present invention, identical labels in the accompany ^¬ ing drawings are used to indicate identical or similar fea ^¬ tures . Detailed description of the invention

Illustrative solutions for the device disclosed in the pre ^¬ sent invention are now explained in detail with reference to the accompanying drawings. Although provided to present cer- tain embodiments of the present invention, the drawings need not be drawn according to the dimensions of a specific embod ^¬ iment; moreover, certain features may be magnified, removed or partly cut away in order to better show and explain the content disclosed in the present invention. The phrase "in the accompanying drawings" or similar wording appearing herein need not refer to all of the accompanying drawings or ex ^¬ amples .

Certain terms relating to direction which are used below to describe the accompanying drawings, such as "top", "bottom", "left", "right", "upwards", "downwards", "upstream" and

"downstream" amongst others, shall be understood as having their normal meanings, indicating the directions involved when the accompanying drawings are viewed in the normal way. This should not be interpreted as a specific restriction on the technical solutions in the attached claims. The terms "about" and "approximately" as used herein should be understood by those skilled in the art, and shall vary within a certain range depending on the context in which they are used. Fig. 2 shows an embodiment of a purge system for a gas tur ^¬ bine according to the present invention. It can be seen from Fig. 2 that the gas turbine comprises a compressor 1, a com ^¬ bustion chamber 2, multiple burners 3, a turbine 4 and a gas fuel system. In this embodiment, multiple burners 3 are ar- ranged around the annular combustion chamber 2. For the sake of clarity, only two burners are shown, but the content shown in the figures should not constitute a restriction of the present invention. When the gas turbine is in operation, the compressor 1 draws air in from the external environment and subjects it to stepwise compression so that it becomes pres ^¬ surized; at the same time, the temperature of the air rises correspondingly. The compressed air is delivered under pres ^¬ sure to the combustion chamber 2 where it is mixed with fuel injected by the burners 3, burning to produce gas at high temperature and pressure. The gas then enters the turbine where it expands to drive the turbine to work. In this embod ^¬ iment, the positional relationship between the combustion chamber 2 and the burners 3 is known in the art, and will not be explained here superfluously.

Purely as an example, the burners 3 shown in Fig. 2 are two- stage burners, and the gas fuel system correspondingly com ^¬ prises two gas fuel supply pipelines 5 and 6 to supply gas fuel to the burners 3. The gas fuel supply pipeline 5 is a manifold, comprising multiple branch pipes 5a in fluid commu ^¬ nication with the first stage of each burner 3respectively, And the gas fuel supply pipeline 6 is also a manifold, com ^¬ prising multiple branch pipes 6a in fluid communication with the second stage of each burner 3respectively, to Control valves 7 and 8 are provided in the gas fuel supply pipelines 5 and 6, respectively, for cutting off or connecting the sup- ply of fuel from a gas fuel source 12 to the burners 3, and controlling the flow rate of gas fuel. The control valves used in this invention are known in the art, so their specif ^¬ ic structure and method of control will not be described in detail .

Furthermore, the present invention may be used with many types of existing burners, including single-stage and multi ^¬ stage burners, or liquid fuel and gas fuel burners, or burn ^¬ ers capable of switching between liquid fuel and gas fuel.

It is advantageous if a purge system is provided in the gas turbine described above. This purge system comprises a cooler 9 having an inlet end 9a and an outlet end 9b, the inlet end 9a being in fluid communication with the compressor 1 via a first pipeline 13, and the outlet end 9b being in fluid com ^¬ munication with the gas supply pipelines 5 and 6 via two se ^¬ cond pipelines 14, respectively. It can be seen from the fig ^¬ ure that the second pipelines 14 are preferably connected with the gas fuel supply pipelines downstream of the control valves 7 and 8, in a position close to said control valves.

In order to control the flow rate of air from the compressor 1, a throttle control device is provided in each second pipe- line 14, for cutting off or connecting the supply of cool air, which comes from the compressor 1 and has been cooled in the cooler 9, to the gas fuel supply pipelines 5 and 6, and for controlling the pressure and flow speed of the cool air. In this embodiment, the throttle control device comprises a flow rate orifice plate 11 and a shutoff valve 10 disposed in the second pipeline, the flow rate orifice plate 15 being used for controlling the pressure and flow speed of cool air from the cooler 9, and the shutoff valve 10 being used for controlling the cutting off or connecting of cool air from the cooler. In this embodiment, the structure and configura ^¬ tion of the flow rate orifice plate 11 and shutoff valve are both known in the art, and will not be described in detail again here.

In other embodiments, as an alternative, the throttle control device may comprise a flow rate orifice plate 11 and control valve disposed in the second pipeline, or just a control valve may be disposed for cutting off or connecting the sup- ply of cool air for purging to the gas fuel supply pipeline, and controlling the pressure and flow speed of the cool air.

In the present invention, the cooler 9 is configured to be able to lower the temperature of air from the compressor 1 to less than the autoignition temperature of the gas fuel. In general, the temperature of air exiting the compressor 1 is for example higher than 400 degrees Celsius, but after cooled in the cooler, the temperature thereof may be reduced to less than 200 degrees Celsius, for example between 200 and 170 de- grees Celsius. Furthermore, the flow speed and pressure of the cool air in the process of purge depend on the specific configuration of the gas fuel system of the gas turbine; they need only be selected so as to be able to completely blow away the gas fuel present in the gas fuel supply pipelines and burners downstream of the control valves 7 and 8 within a given time. In the present invention, the cooler may be any suitable cooler, for instance, a water cooler or an oil cool ^¬ er, which work with different media, or a recuperative cool- er, jacket cooler or coil cooler, etc, which have different structures .

In the case of the purge system for a gas turbine described above, functions such as purging, cooling and sealing can be realized with no need for an additional air source to be pro ^¬ vided. To be specific, when the gas fuel system is partially or completely closed, cool air from the compressor 1, having undergone cooling in the cooler 9, is conveyed at a certain pressure and flow speed along the second pipelines 14 into the gas fuel supply pipelines 7 and 8 by means of the throt ^¬ tle control device, and purges the gas fuel supply pipelines and the burners 3 in communication therewith, thereby blowing the gas fuel inside the gas fuel supply pipelines and burners into combustion chamber 2 to take part in combustion, avoiding the phenomena of autoignition and deflagration in the gas fuel supply pipelines and burners when part of the gas fuel system stops running, while also being able to cool compo ^¬ nents such as the burners and the parts of the gas fuel sup- ply pipelines through which the cool air passes.

Furthermore, cooled air from the compressor 1 may also be used to purge the gas fuel supply pipelines and burners con ^¬ tinuously at a lower pressure and flow speed, so as to pre- vent back-flow of combustion gas from the combustion chamber into the burners 3, or series flow between burners, thereby serving to seal the burners. Here, the flow speed and pres ^¬ sure of cool air may be selected according to specific re ^¬ quirements .

In other embodiments of the present invention, the burner 3 may be a single-stage or multi-stage burner, for instance with three stages, four stages, five stages or more. Corre ^¬ spondingly, three, four or more gas fuel supply pipelines would have to be provided, with three, four or more second pipelines 14 for supplying air from the compressor for purging, cooling and sealing also being correspondingly provided. It should be understood that although the description herein is based on various embodiments, it is by no means the case that each embodiment contains just one independent technical solution. This mode of presentation is adopted purely for the sake of clarity. Those skilled in the art should consider the description as a whole; the technical solutions in the vari ^¬ ous embodiments could also be suitably combined to form other embodiments capable of being understood by those skilled in the art .

The embodiments above are merely specific illustrative embod ^¬ iments of the present invention, which are not intended to define the scope thereof. Any equivalent changes, amendments or combinations made by those skilled in the art without de ^¬ viating from the concept and principles of the present inven ^¬ tion should fall within the scope of protection thereof.