Description

TECHNICAL FIELD

[0001] The present disclosure concerns a gas turbine fuel treatment circuit for starting up a gas turbine, and an operating method thereof, which allows to speed up the startup of a gas turbine, reducing the consumption of the fuel gas dispersed in the environment.

BACKGROUND ART

[0002] Gas turbines are well-known plants used for transforming chemical energy into mechanical energy. More specifically, a gas turbine is a combustion engine that can convert fuel gas to mechanical energy. This energy can drive a generator that produces electrical energy by rotating one or more shafts. The generated energy is then introduced into the power lines to supply homes and businesses. Alternatively, the mechanical energy of the gas turbine can be used to operate a machine, such as a pump, a compressor, or the like.

[0003] Usually, to start up a gas turbine it is required a specific procedure. Among the several phases for starting up a gas turbine, it is required that the gas is warmed up in advance, before introducing it into the gas turbine to be burned and starting the same gas turbine. To this end, any gas turbine is equipped with a heater, connected upstream to the gas turbine inlet and, more specifically, interposed between the fuel gas manifold, whereby the fuel gas is supplied, and the fuel inlet of the gas turbine. While the heater heats up the fuel gas taken from the fuel gas manifold, the fuel gas that is not at the required temperature for starting the operation of the gas turbine is dispersed into the environment.

[0004] This approach causes the dispersion of the fuel gas into the environment, which is detrimental to the pollution and the conservation of the environment itself. In particular, this approach turns out to have an impact on greenhouse gas emissions, not reducing the hydrocarbon gas in the atmosphere. Among other things, it is also known that energy plants in some countries are subject to strict regulations, which require in particular the fulfillment of several technical requirements about the pollution.

[0005] In addition, the gas treatment method according to the prior art implies that a certain amount of time is required for starting up the operation of the gas turbine, mainly due to the time required for warming up the gas to start the operation of the gas turbine.

[0006] Accordingly, an improved system for treating the gas taken from the fuel gas manifold before it is used to supply the gas turbine would be welcomed in the field.

SUMMARY

[0007] The above problems are solved by recirculating the fuel gas with a new system, recompressing back gas in the line upstream the heater. Such a solution avoids the continuous release of hydrocarbon gas to the atmosphere up to reach the right fuel gas temperature for starting up the gas turbine.

[0008] In one aspect, the subject matter disclosed herein is directed to a fuel gas treatment circuit connected between a fuel gas source, whereby the fuel gas is supplied, and a gas turbine, to be fed by the fuel gas from the fuel gas source. The fuel gas treatment circuit comprises a heater, to heat the gas taken from the fuel gas source, up to a temperature suitable for starting up the gas turbine, and a temperature sensor, to measure the fuel gas temperature downstream the heater before it enters the gas turbine. The fuel gas treatment circuit comprises also a recirculator, to feedback the fuel gas mass flow from the heater to the fuel gas source, if the temperature sensor detects a temperature below a threshold so that the heater can heat a partially heated fuel gas mass flow, to accelerate the start-up step of the gas turbine. A recirculation shut-off valve connected in series to the recirculator is then controlled and closes, allowing the warmed gas to feed the gas turbine, when the fuel gas reaches the temperature for staring up the gas turbine.

[0009] In another aspect, the subject matter disclosed herein concerns a recirculation valve, connected in series with the recirculator, and an external shut-off valve is connected or coupled in series to the heater. The recirculation valve is provided with a vent to the atmosphere for venting at least part of the gas mass flow contained between the external shut-off valve and the gas turbine shut-off member, into the atmosphere, when the external shut-off valve is closed and the gas turbine shut-off member is closed and before the start-up of the gas turbine, reduce the pressure of the fuel gas contained between the external shut-off valve and the gas turbine shut-off member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 illustrates a scheme of the gas turbine fuel treatment circuit according to a first embodiment;

Fig. 2 illustrates a scheme of the gas turbine fuel treatment circuit according to a second embodiment;

Fig. 3 illustrates a scheme of the gas turbine fuel treatment circuit according to a third embodiment;

Fig. 4 illustrates an embodiment of a schematic of a control logic unit; and

Fig. 5 illustrates flow charts of methods for treating the fuel gas for starting up a gas turbine according to the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0011] The gas turbines are complicated systems, designed to burn a fuel gas, to transform the chemical energy in mechanical energy. The gas turbine requires that the fuel gas has a certain temperature, to operate and to start-up. When starting-up a gas turbine is required, the fuel gas is heated by a heater, namely a device designed to increase the temperature of the fuel gas. However, to reach the right temperature, the fuel gas that has not reached the required temperature is dispersed in the ambient. To avoid or significantly reduce the dispersion of the fuel gas, a feedback line is provided, to the feedback part or the whole fuel gas to the heater, so that the latter can heat up the fuel gas quicker and without dispersing the same.

[0012] Referring now to the drawings, Fig. 1 shows a scheme of the gas turbine fuel treatment circuit according to a first embodiment, wholly indicated with the reference number 1. [0013] The fuel gas treatment circuit 1 is interposed between a fuel gas manifold 2, and a gas turbine 3.

[0014] The fuel gas manifold 2 is a line, whereby the fuel gas is supplied, in order to feed the gas turbine 3 during its operation. The gas manifold 2 can be a gas line or it can be connected to a gas tank (not shown in Fig. 1).

[0015] The gas turbine 3, to be supplied with the gas fed through the gas manifold 2, can be of several types. Just for example, the gas turbine 3 can be heavy-duty and/or aeroderivative type. The gas turbine 3 is a turbomachine capable of transforming the chemical energy of the gas fuel into mechanical energy. It is provided with a compressor combustion chamber and an expansion wheel.

[0016] To operate, the gas turbines 3 need that the gas is supplied according to some requirements (purity, Wobbe index. . .). Also, to start-up the gas turbine 3 and to allow it to operate, the fuel gas has to be above e threshold temperature.

[0017] The gas turbine 3 can be of several types. For example, it can be of heavy-duty or airfoil type. The gas turbines 3, in general, are controlled by a computer-based control system, which can be installed close to the gas turbine 3 itself or remote with respect to it. In general, each gas turbine 3 has a gas inlet 31, connected to the burners of the gas turbine 3, and a shut-off member 32, usually an electronically controlled valve, capable of opening or closing to allow the fuel gas to feed the gas turbine 3 or not.

[0018] As said, the gas treatment circuit 1 is connected to the fuel gas manifold 2, to take the fuel gas flowing therethrough, and the gas turbine 3, to which the gas treatment circuit 1 provides the fuel gas, for it to operate.

[0019] The gas treatment circuit 1 comprises a main line 11, which connects the fuel gas manifold 2 to the gas turbine 3, and a feedback line 12, which connects the main line 11 to the fuel gas manifold 2.

[0020] The main line 11 comprises a heater 13, having an inlet 131, connected to the fuel gas manifold 2, and an outlet 132. The heater 13 is capable of heating the fuel gas passing through it. [0021] The main line 11 also comprises an external shut-off valve 14, connected in series with the heater 13. In particular, the external shut-off valve 14 is connected to the outlet 132 of the heater 13 and the shut-off member 32 of the gas turbine 3.

[0022] The gas treatment circuit 1 comprises also a temperature sensor 15, adapted to detect the temperature of the fuel gas before it enters the gas turbine 3 to be burned. In the embodiment shown, the temperature sensor 15 is connected close to the shut-off member 32 of the gas turbine 3.

[0023] The main line 31 also comprises a fuel gas vent valve 16, which, in the embodiment shown, is connected between the external shut-off valve 14 and the shut-off member 32 of the gas turbine 3. The fuel gas vent valve 16 is configured to vent at least a part of the gas mass flow into the atmosphere when the temperature of the fuel gas passing through the main line 11, as detected by the temperature sensor 15, is below a certain threshold, as better specified below.

[0024] Also, the fuel gas vent valve 16 vents at least a part of the fuel gas contained between the external shut-off valve 14 and the gas turbine shut-off member 32 to the ambient, after gas turbine 3 shuts down. More specifically, the fuel gas vent valve 16 opens at each gas turbine 3 shut down, to depressurize the section between the external shut-off valve 14 and the gas turbine shut-off member 32. This also prevents the gas turbine enclosure (not shown in the figure), where the valves of the plant are contained from filling up with fuel gas in case of leakage of the shut-off member 32 or any conduit of the gas turbine 3, so that the gas vents into the ambient or is burned by a torch.

[0025] In this way, the fuel gas not warmed enough to feed the temperature is dispersed in the ambient, preventing an increase of the pressure within the main line 11.

[0026] The threshold temperature depends on the specific fuel gas and the gas turbine 3 types. Usually, it ranges between room temperature and 149 °C. Also, it can change according to the ambient conditions, such as the humidity.

[0027] The feedback line 12 comprises a recirculator 17, having an inlet 171 and an outlet 172. The outlet 172 of the recirculator 17 is connected to the fuel gas manifold 2, in a point placed upstream the point of the fuel gas manifold 2 in which the inlet 131 of the heater 13 is connected. In some embodiments, the recirculator 17 is a reciprocating compressor.

[0028] The feedback line 12 also comprises a recirculation valve 18, connected to the main line 11, and in series with the recirculator 17. The recirculation valve 18 has a vent 181 The recirculation valve 18 can assume a first state, in which the vent 181 is opened, to disperse the fuel gas flowing in the recirculation valve 18, and a second state, in which the vent 181 is closed so that the fuel gas can pass through the recirculation valve 18, to reach the recirculator 17.

[0029] The feedback line 12 also comprises a recirculation shut-off valve 19, connected between the recirculation valve 18 and the inlet 171 of the recirculator 17, in series with the recirculator 17. The function of the recirculation shut-off valve 19 will be better explained below.

[0030] The fuel gas treatment circuit 1 also comprises a control logic unit U, operatively connected to the temperature sensor 15, the external shut-off valve 14, the fuel gas vent valve 16, the recirculation valve 18, and the recirculation shut-off valve 19. The control logic unit U can be also operatively connected to the shut-off member 32, or it can be connected to the control unit of the gas turbine 3 (not shown in the figure), to allow the (indirect) control of the shut-off member 32.

[0031] The control logic unit U can be a computer, a server, a cloud-based computer, or any other computer system, capable of executing a computer program, to coordinate the operation of the external shut-off valve 14, the fuel gas vent valve 16, the recirculation valve 18, and the recirculation shut-off valve 19, as a function of the temperature measured by the temperature sensor 15.

[0032] The fuel gas treatment circuit 1 of Fig. 1 can operate as follows.

[0033] For starting up the gas turbine 3, the external shut-off valve 14 is opened, the fuel gas vent valve 16 is opened, the shut-off member 32 is closed, so that the fuel gas cannot enter the inlet 31 of the gas turbine 3, the recirculation valve 18 is in the first state, and the recirculation shut-off valve 19 is opened. Then the fuel gas from the fuel gas manifold 2 enters the heater 13 through the relevant inlet 131, to be heated up by the same. [0034] The temperature of the fuel gas, once warmed by the heater 13, is measured by the temperature sensor 15. If the temperature sensor 15 detects a temperature below the set beforehand threshold, namely the fuel gas within the main line 11 is not at a temperature suitable to start-up the gas turbine 3, the fuel gas can reach the recirculator 17, since the recirculation valve 18 is in the first state and the recirculation shut-off valve 19 is opened, to allow the fuel gas to pass through them.

[0035] The recirculator 17 reintroduces the partially warmed fuel gas into the fuel gas manifold 2, in an upstream position, then the point the inlet 131 of the heater is connected to the fuel gas manifold 2. In this way, the above-mentioned partially warmed fuel gas enters again the heater 13, to be further heated. The heater 13 then heats up a fuel gas at a temperature greater than the previous one, thanks to the effect of the feedback line 12. Also, the above-mentioned fuel gas vent valve 16 is opened, so that the fuel gas of the pressure of the main line 11 is kept under a certain threshold. In some embodiments, the pressure is kept below the nominal operating pressure.

[0036] When the temperature sensor 15 detects a temperature of the fuel gas of the main line 11, and in particular at the shut-off member 32 of the gas turbine 3, is above the above-mentioned temperature threshold, suitable for starting-up the gas turbine 3, the control logic unit U operates so as to close the recirculation shut-off valve 19, allowing the fuel gas to pass through the gas inlet 31 of the gas turbine 3.

[0037] Also, the vent 181 assumes the open position to for venting at least part of the gas mass flow contained between the external shut-off valve 14 and the gas turbine shut-off member 32 into the atmosphere, when the external shut-off valve 14 is closed and the gas turbine shut-off member 32 is closed, before the start-up of the gas turbine 3. This allows reducing the pressure of the fuel gas contained between the external shut-off valve 14 and the gas turbine shut-off member 32.

[0038] Referring now to Fig. 2, a second embodiment of the gas treatment circuit 1, which differs from the first embodiment shown in Fig. 1, only in that the recirculation shut-off valve 19 is connected between the outlet 172 of the heater 17, and the fuel gas manifold 2.

[0039] The gas treatment circuit 1 according to Fig. 1 operates likewise the first embodiment and it is just a variant of the embodiment illustrated in Fig. 1. [0040] Referring now to Fig. 3, a third embodiment of the gas treatment circuit 1, which differs from the first embodiment shown in Fig. 1 in that the recirculation shutoff valve 19 is directly connected between the inlet 171 of the heater 17, and the main line 11. Also, instead of the recirculation valve 18, a conventional vent valve 18’ is connected to the feedback line 12.

[0041] According to the present disclosure, when the fuel gas reaches the threshold temperature to start up the gas turbine 3, as detected by the temperature sensor 15, like the first embodiment disclosed in Fig. 1 the vent valve 18’ is open to vent the feedback line 12.

[0042] The method disclosed in Fig. 1 can be implemented by the control logic unit U, executing a computer program. The control logic unit U coordinates the opening and the closing of the valves and the venting by the recirculation valve 18.

[0043] In some embodiments, and particularly referring to Fig. 4, the central control unit U may comprise a processor 41, a bus 42, to which the processor 41 is connected to, a database 43, connected to the bus 42, so as to be accessed and controlled by the processor 41, a computer-readable memory 44, also connected to the bus 42, so as to be accessed and controlled by the processor 51, a receiving-transmitting module 45, connected to the bus 42, configured to receive the signal from the temperature sensor 15, and transmit the control signals to external shut-off valve 14, the fuel gas vent valve 16, the recirculation valve 18, the recirculation shut-off valve 19, and the shutoff member 32 of the gas turbine 3.

[0044] In some embodiment the central control unit U may be realized or implemented as a cloud computing system, a computer network or other installations capable of processing data by running appropriate computer programs based on a maintenance optimization method or algorithm.

[0045] Fig. 5 shows a flowchart summarizing operating method 5 of the fuel gas treatment circuit 1 disclosed herein for starting up a gas turbine 3 and carried out by the control logic unit U.

[0046] The method 5 comprises a heating step 51, where the fuel gas from the fuel gas manifold 2 by the heater 2, which enters through the heater inlet 131. [0047] The method further comprises a measuring step 52, for measuring the fuel gas temperature of the fuel gas before the same enters into the gas turbine 3. As mentioned above, if the temperature of the fuel gas into the main line 11 is below the threshold temperature, then the fuel gas heated in the heating step 51, is circulated by the recirculator 17, thus carry out a recirculating step 53 of the gas flow. In the recirculating step 53, the heated fuel gas is reintroduced in the gas source 2, namely in the fuel gas manifold 2.

[0048] Instead, if the temperature measured in the measuring step 52 by the temperature sensor 15 reaches the threshold temperature, namely the temperature of the fuel gas in the main line 11 is greater or equal the threshold temperature, then, the recirculation of the fuel gas is interrupted in step 54 and the shut-off member 32 of the gas turbine 3 is opened. In this way, the gas turbine 3 is fed with a fuel gas at the temperature suitable for starting up and operate the gas turbine 3.

[0049] While the invention has been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing from the spirit and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

[0050] Reference has been made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to "one embodiment" or "an embodiment" or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase "in one embodiment" or "in an embodiment" or "in some embodiments" in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. [0051] When elements of various embodiments are introduced, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.