Gas turbine having fuel monitoring

Abstract

The invention relates to a method for detecting a fuel leakage in the fuel distribution system between a fuel control valve and at least one burner of a gas turbine during the operation of the gas turbine. In order to detect a fuel leakage, the fuel consumption is approximated in accordance with the mechanical power of the gas turbine, the fuel amount fed to the fuel distribution system is determined, and the leakage flow is determined from the difference between the fed fuel amount and the fuel consumption. The invention further relates to a gas turbine for performing such a method.

Claims

1. A method for detecting a fuel leakage during operation of a gas turbine, the gas turbine being controlled by a governor configured to compute an amount of a leakage flow of fuel in a fuel distribution system between a fuel control valve and at least one burner of the gas turbine, the method comprising: in the governor: approximating a fuel consumption of the gas turbine as a function of a mechanical power output of the gas turbine; defining an amount of fuel supplied to the fuel distribution system; computing the amount of the leakage flow from a difference between the defined amount of fuel supplied and the approximated fuel consumption; and closing a trip valve in a fuel feed line of the fuel distribution system via a signal generated based on the computed amount of the leakage flow.

2. The method for detecting a fuel leakage as claimed in claim 1, wherein approximating the fuel consumption of the gas turbine as a function of the mechanical power output of the gas turbine further comprises accounting for both an efficiency of the gas turbine and a heating value of the fuel.

3. The method for detecting a fuel leakage as claimed in claim 1, wherein approximating the fuel consumption of the gas turbine as a function of the mechanical power output of the gas turbine comprises calculating a sum of a fuel mass flow in idling mode and a fuel mass flow in power output mode, wherein the fuel mass flow in power output mode is determined based on mechanical power output of the gas turbine, power output efficiency of the gas turbine, and a heating value of the fuel.

4. The method for detecting a fuel leakage as claimed in claim 1, comprising: approximating the mechanical power output of the gas turbine during steady-state load operation via a generator power output.

5. The method for detecting a fuel leakage as claimed in claim 1, comprising: measuring, during start-up of the gas turbine and during changes of a network frequency, acceleration of a shaft train of the gas turbine; and approximating the mechanical power output of the gas turbine from a sum of generator power output and power for accelerating the shaft train.

6. The method for detecting a fuel leakage as claimed in claim 1, wherein computing the amount of the leakage flow from the difference between the defined amount of fuel supplied and the approximated fuel consumption comprises calculating a time increment of the leakage flow; and judging detection of fuel leakage when the calculated time increment exceeds a threshold value.

7. The method for detecting a fuel leakage as claimed in claim 6, wherein the time increment of the leakage flow is calculated according to the equation: $m_{\mathrm{leak}\_\mathrm{inc}}=m_{\mathrm{leak}}\left(1-\frac{1}{}{e}^{-\frac{t}{}}dt\right)=m_{\mathrm{leak}}{e}^{-\frac{t}{}},$ wherein is an integration duration over time t of the time increment calculation.

8. The method for detecting a fuel leakage as claimed in claim 1, comprising: judging detection of fuel leakage when the computed amount of the leakage flow exceeds a threshold value.

9. The method for detecting a fuel leakage as claimed in claim 1, wherein defining the amount of fuel supplied involves calculating the amount of fuel supplied as a function of at least a position of a fuel control valve and fuel pressure at the fuel control valve.

10. The method for detecting a fuel leakage as claimed in claim 1, wherein defining the amount of fuel supplied involves setting a set point amount of fuel by the governor.

11. The method for detecting a fuel leakage as claimed in claim 1, comprising: deactivating detection of the fuel leakage when a change of operating conditions of the gas turbine occurs at a rate which exceeds a threshold.

12. The method for detecting a fuel leakage as claimed in claim 11, wherein the operating conditions include a load shedding or an operating mode for frequency support.

13. The method for detecting a fuel leakage as claimed in claim 11, wherein deactivating detection of the fuel leakage includes deactivating a threshold of the computed amount of the leakage flow, which occurs during operating conditions, wherein the operating conditions include a load shedding or an operating mode for frequency support.

14. A power plant comprising: a gas turbine; a governor configured to control the gas turbine; a fuel distribution system between a fuel control valve and at least one burner of the gas turbine; and a generator which is arranged to be driven by the gas turbine; wherein the governor is further configured to: detect a fuel leakage during operation of the gas turbine by: (i) approximating a fuel consumption of the gas turbine as a function of a mechanical power output of the gas turbine, (ii) defining an amount of fuel supplied to the gas turbine, and (iii) computing an amount of a leakage flow of fuel in the fuel distribution system between the fuel control valve and the at least one burner from a difference between the defined amount of fuel supplied and the approximated fuel consumption; and close a trip valve in a fuel feed line of the fuel distribution system via a signal generated based on the computed amount of the leakage flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is to be explained below in more detail for exemplary embodiments with reference to the drawing. In the drawing

(2) FIG. 1 shows a greatly simplified schematic diagram of a power plant with a gas turbine, a governor and a fuel distribution system;

(3) FIG. 2 shows a greatly simplified detail from the fuel distribution system between the fuel control valve and the burners of a gas turbine;

(4) FIG. 3 shows a flow diagram of the increment calculation.

DETAILED DESCRIPTION

(5) 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 2 in which intake air 6 is compressed to form combustion air.

(6) This is fed to a combustion chamber 3 and combusted there with the supplied fuel m.sub.comb. The hot combustion gases are then expanded in a turbine 4. The useful energy which is generated in the turbine 4 is then converted into electric energy, for example, by means of a first generator 5 which is arranged on the same shaft.

(7) The hot exhaust gases 7 which issue from the turbine 4, 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).

(8) The operation of the gas turbine 1 is controlled by a governor 10. In particular, the amount of fuel m.sub.fuel supplied is controlled by means of a control valve 9, to which is transmitted a set point amount of fuel m.sub.CMD (command) via a signal line 11. The fuel is fed to the combustion chamber 3 via a fuel distribution system which in the depicted example comprises a fuel line 20, a fuel ring main 21 and individual lines 23 to the burners. The sum of the amount of fuel which is introduced through the individual lines 23 into the combustion chamber 3 is equal to the fuel consumption m.sub.comb of the gas turbine. During steady-state, leakage-free operation, the fuel consumption m.sub.comb is equal to the amount of fuel m.sub.fuel which is supplied by means of the control valve 9. Additional measurement lines and additional signal lines to the governor 10, such as for the transmission of the actual position of the fuel control valve 9, are not shown.

(9) FIG. 2 shows a greatly simplified detail from the fuel distribution system between the fuel control valve 9 and the burners 12 of a gas turbine 1. The burners 12 open into the combustion chamber 3 which in the example is shown as an annular combustion chamber. The burners 12 are supplied with fuel by the fuel control valve 9 via a fuel distribution system, comprising a fuel line 20, a fuel ring main 21 and individual lines 23. In the process, some of the amount of fuel supplied m.sub.fuel is lost as fuel leakage m.sub.leak so that the actual fuel consumption m.sub.comb of the combustion chamber 3 is less than the amount of fuel supplied m.sub.fuel.

(10) FIG. 3 shows an exemplary flow diagram of the increment calculation, wherein the increment of the fuel leakage m.sub.leak.sub._.sub.inc is established from the difference of the determined fuel leakage m.sub.leak and the value of a first-order low-pass filter 22 of the fuel leakage.

(11) The fuel consumption m.sub.comb of the gas turbine 1 is the quotient of heat input Q as a result of combustion and the lower heating value (LHV) of the fuel:
m.sub.comb=Q/LHV(2),
wherein the heat input Q is equal to the quotient of the entire generated power output and efficiency of the gas turbine. With the generated power output as the sum of generator power output P.sub.geno (the generator efficiency is set as being equal to one for simplification) and acceleration power of the gas turbine, the following results:
Q=(P.sub.geno+J{dot over ()})/(3),
wherein the acceleration power of the gas turbine is the product of the inertia moment J, the angular speed and the angular acceleration {dot over ()}.

(12) For steady-state operation, the angular acceleration is equal to zero and therefore the following applies:
Q=P.sub.geno/ (4),
wherein the efficiency for different operating states is known and can be determined as a function of the most important operating parameters, such as load, compressor inlet temperature, position of the compressor guide vanes, inlet pressure, etc., or can be stored in tables.

(13) In practice, it has been shown that the heat input Q can be split into a heat input for idling mode Q.sub.idle plus a heat input for power generation mode Q.sub.load:
Q=Q.sub.idle+Q.sub.load(5)
wherein the heat input for load Q.sub.load is determined from the generator power output and a load efficiency .sub.load:
Q.sub.load=P.sub.geno/.sub.load(6).

(14) Since the heat which is released during the complete combustion is the product of the lower heating value and the fuel mass flow, the following results from 5 and 6:
m.sub.comb=P.sub.geno/(.sub.load*LHV)+m.sub.idle (7),
wherein m.sub.idle is the fuel mass flow which is required for releasing the heat input during idling mode Q.sub.idle. The division into idling and power proportions allows the fuel mass flow m.sub.comb to be approximated with the aid of a constant mass flow in idling mode m.sub.idle and a constant power output efficiency .sub.load.

(15) The fuel leakage m.sub.leak in the fuel distribution system is equal to the difference of the supplied fuel mass flow and the exhausted fuel mass flow, i.e. of the amount of fuel supplied m.sub.fuel and the fuel consumption m.sub.comb in the combustion chamber 3:
m.sub.leak=m.sub.fuelm.sub.comb (8).

(16) With the equations 7, 8 and an approximation of the amount of fuel supplied m.sub.fuel by means of the set point fuel mass flow m.sub.cmd, the simple equation for the leakage flow m.sub.leak results:

(17) $\begin{array}{cc}{m}_{\mathrm{leak}}=m_{\mathrm{cmd}}-\left(\frac{P_{\mathrm{geno}}}{{}_{\mathrm{load}}\mathrm{LHV}}+m_{\mathrm{idle}}\right).& \left(9\right)\end{array}$

(18) Since all the values during steady-state operation of a gas turbine which are required for calculating the leakage flow m.sub.leak according to equation 9 are known, the leakage flow m.sub.leak can therefore be calculated in a governor 10.

(19) The possible embodiments of the invention are not limited to the examples which are represented here. Based on the examples, a large number of possibilities, equivalent circuits and methods open themselves up to the person skilled in the art for implementation.

(20) Also to be taken into consideration during operation with gas as fuel is the volume of the fuel distribution system. The fuel distribution system can act as a fuel gas accumulator and lead to a considerable delay. A pressure build-up or pressure decay in the system is to be taken into consideration for an accurate leakage calculation. By the change of pressure of the fuel gas in the fuel distribution system, the volume of the fuel distribution system and the temperature of the fuel gas in the fuel distribution system, the difference can be calculated from the fuel consumption m.sub.comb in the combustion chamber 3 and the amount of fuel m.sub.fuel supplied to the fuel distribution system, which is to be attributed to the accumulating effect of the fuel distribution system. An effective leakage flow is the differencereduced by the accumulating effectof the fuel consumption m.sub.comb in the combustion chamber 3 and the amount of fuel supplied m.sub.fuel.

(21) Furthermore, the use is not limited to gas turbines with a single combustion chamber, as is shown in FIG. 1, but can also be used without limitation for gas turbines with sequential combustion, as are known from EP0718470, for example.