EP3788246A1

EP3788246A1 - Method for operating a gas turbine plant with gaseous fuel

Info

Publication number: EP3788246A1
Application number: EP19727869.0A
Authority: EP
Inventors: Björn Beckmann; Niklas Nauber; Maarten Over
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2018-07-10
Filing date: 2019-05-16
Publication date: 2021-03-10
Also published as: KR20210019113A; JP2021524555A; JP6999858B2; WO2020011426A1; CN112513442A; KR102346323B1; CN112513442B; EP3594475A1; US11242807B2; US20210246839A1

Abstract

The invention relates to a method for operating a gas turbine plant with gaseous fuel, which is conveyed to the gas turbine plant through a gas line (6), burnt in a combustion chamber (4) and then supplied to a gas turbine. At least one valve (12a, 12b) for controlling the flow of the fuel to the combustion chamber (4) is installed in the gas line (6), a critical opening position (S_krit) being defined for the valve (12a, 12b). According to the invention, to provide an improved method for operating a gas turbine plant in which the power (P) of the gas turbine plant is kept at a maximum for as long as possible in the event of insufficient pressure in the gas line (6), a temperature (TB) of the fuel in the gas line (6) is reduced when the valve (12a, 12b) is about to exceed the critical opening position (S_krit).

Description

Method for operating a gas turbine system with gaseous fuel

The invention relates to a method for operating a gas turbine system with gaseous fuel, which is transported through a gas line to the gas turbine system, burned in a combustion chamber and then fed to a gas turbine. The invention further relates to a Steuerervor device for performing the method and a gas turbine with such a control device.

Gas turbine plants are usually supplied with natural gas as fuel via a gas line. The optimal operation of the gas turbine system depends on the quality of the fuel, the right pressure and the right temperature. A minimum required pressure, which is defined as a prerequisite for the operation of the gas turbine system and must be guaranteed, also depends on various operating and environmental conditions, e.g. Turbine load, ambient temperature, ambient pressure, gas composition, gas temperature, etc. Due to various situations, the pressure in the gas line may not be sufficient, e.g. due to pressure fluctuations in the local gas network, failures in the lines to and in the gas turbine system, failure of the gas compressor, if one is present, fluctuations in the gas quality, pressure losses along the gas line system, increase in the fire output, etc. In the event that the gas turbine combustion depends on the exact distribution of the mass flow of fuel on two or more stages (e.g. main burner and pilot burner), the combustion stability in the above-mentioned situations can no longer be guaranteed.

From EP 1 730 444 B1 it is known to reduce the fuel temperature in order to ensure a higher supply pressure in a gas line than the pressure in the combustion chamber. However, this is always done in combination with others Measures to reduce the performance increase of the gas turbine, which is a higher priority than the reduction of

Have fuel temperature. The motivation here is to avoid flame setbacks by stabilizing the fuel supply pressure, by which the operational safety of the entire fuel supply is endangered and the gas turbine system can fail for a considerable period of time. The measures for reducing the power and possibly the gas temperature are initiated depending on the defined pressure curves or pressure characteristics. The pressure characteristics must be based on design calculations and / or empirical values from other machines. If the combustion chamber pressure, which is dependent on the output, is taken into account, the gas pressure is an approximate measure of the maximum adjustable fuel volume flow. Due to calculation inaccuracies and natural

Fluctuations from machine to machine (e.g. due to manufacturing tolerances) and time-varying pressure loss coefficients via the gas system and the burner (wear or pollution), the maximum fuel volume flow that can be set for a specific gas pressure is subject to a certain spread.

The invention is therefore based on the object to overcome the disadvantages of the prior art and to propose an improved method for operating a gas turbine system, in which, in the event of insufficient pressure in the gas line, the power of the gas turbine system is kept as high as possible for as long as possible.

The object is achieved by a method of a gas turbine system with gaseous fuel, which is transported through a gas line to the gas turbine system, burned in a combustion chamber and then fed to a gas turbine, wherein at least one fitting for flow control of the fuel to the combustion chamber is built in the gas line , whereby a critical opening position is defined for the valve and if the valve is there the critical see exceeding the opening position, a temperature of the fuel in the gas line is reduced.

The object is further achieved according to the invention by a control device comprising means for carrying out such a method.

The object is finally achieved according to the invention by egg gas turbine system with such a control device.

The parts and preferred embodiments listed below with respect to the method can be applied analogously to the control device and the gas turbine system.

Any device for controlling or regulating the mass flow in the gas line is referred to here as a valve. The valve is particularly in a position to completely shut off the gas line so that the gas flow is interrupted. The fitting is preferably designed as a control or regulating valve, but it can also be designed in the manner of a flap, a slide or a tap.

The invention is based on the finding that a particularly reliable controllability of the gas turbine storage unit is sufficient, as a criterion when a lowering of the fuel temperature is required, the position of the

Flow armature is used. The position of the armature is a direct measure of the pressure actually required in front of the combustion chamber or of how far the fuel mass flow can still be raised in response to an insufficient pressure in the gas line. The measures only intervene if this is really necessary, so the set target power of the gas turbine remains unchanged for as long as possible. In contrast to the prior art, the method is characterized in particular by the fact that it is independent of the load, ie the position of the valve in correlation brought with the critical opening position is a fixed criterion and is independent of the operating point.

The current position of the valve is always known because the mass flow in the gas line, a part of which the valve is, is known. In particular, the position of the valve is set depending on the mass flow. This is measured directly or determined indirectly using various parameters. If the valve is in the critical opening position, but the pressure in the gas line is not sufficient, especially since the pressure requirements increase or the pressure in the line decreases, the lowering of the gas temperature must be initiated as a first measure so that the target output is maintained preserved. The temperature of the fuel has a significant effect on the pressure in the gas line. By reducing the gas temperature, the density of the gas increases, which leads to lower pressure losses in the fuel system.

The critical opening position of the valve is preferably in the range above 70% of the maximum opening position. The maximum opening position is the position at which the mass flow in the gas line is greatest. The decisive, critical opening position of the valve is therefore not necessarily the maximum open position of the valve (however, the critical opening position can also be defined by the maximum opening position), but a position with a slightly minimized flow. The advantage here is that quick, short-term changes to the operating parameters, such as Fluctuations in the quality of the fuel can be responded to by opening the valve again. The critical opening position can also be subsequently adjusted to the operating conditions by changing it during operation.

The temperature of the fuel can be reduced via active cooling measures. However, the gas turbine system preferably has a preheating system for the fuel and the temperature of the fuel in the gas line is reduced by reducing the heat supplied to the fuel in the pre-heating system. This is a particularly simple and efficient procedure for lowering the temperature, which requires no additional hardware and is not associated with any energy expenditure.

According to a preferred embodiment, a threshold value for the minimum temperature of the fuel is determined taking into account an operating parameter of the gas turbine system and the reduction in the temperature of the fuel in the gas line is stopped when the threshold value is reached. There may be potential restrictions in the gas turbine system give so that compliance with a minimum gas temperature may be necessary. At low gas temperatures e.g. Problems with combustion stability and / or emissions occur. Such an operating parameter is e.g. the NOx value in the exhaust gas, which represents an additional criterion by which it is decided whether the method according to the invention is started or continued. Egg ne monitoring of a fixed minimum value of the temperature of the fuel can be provided for gases with increased proportions of higher hydrocarbons, since there is a risk of condensate formation at low gas temperature. In very cold locations there is also the risk of icing at low gas temperatures, a fixed minimum value of 5 ° C has proven to be advantageous. If the reduction in the temperature of the fuel continues, an interruption of the process, if this has already been initiated, is referred to as standard. Alternatively, the fuel cooling should not be active when the

Threshold for emissions has already been reached, gas cooling is dispensed with as long as the emission value corresponds to the threshold value.

Appropriately, several fittings are installed in the gas line and the position of each of the fittings is used. In the case of multi-stage burners, the lines to individual stages, for example to the main burner and pilot burner, usually each have a fitting for flow control. If at least one of the fittings is in the critical opening position and can no longer react to growing mass flow requirements, the temperature of the fuel in the gas line is reduced, as already explained.

In those cases where fluctuations in the gas quality are the cause of the insufficient pressure in the gas line, the lowering of the fuel temperature will generally be sufficient. However, should the reduction in fuel temperature not be able to meet the pressure requirement, a turbine power is preferably additionally reduced. Only when the pressure requirements cannot be met when the valve reaches the critical opening position despite a reduction in temperature, is the turbine output reduced in a controlled manner, in particular by specifying a reduced power setpoint. In emergencies, a gas turbine shutdown can even take place. Both measures, the lowering of the gas temperature and the reduction in output, should be combined with one another in such a way that the output remains unchanged or as high as possible for as long as possible, whereby it must always be ensured that the valve does not exceed the critical opening position. It is important to prioritize both measures, i.e. they may be initiated at the same time, but the turbine output will be increased again as soon as possible. A reduction in the turbine output is initiated, in particular, as a rapid reaction to a particularly large pressure gradient if the reduction in the fuel temperature alone is not sufficient to counteract the pressure gradient.

An embodiment of the invention is based on a

Drawing explained in more detail. Show here:

1 schematically and greatly simplified a burner

material system of a gas turbine plant, and 2 shows a diagram of the time course of various parameters of the gas turbine system.

The same reference numerals have the same meaning in the figures.

In Figure 1, the structure of a fuel system 2 is shown schematically, which is part of a gas turbine plant, not shown, in which natural gas is used as fuel. The gas turbine system generally comprises a compressor, a combustion chamber 4 and a gas turbine, on which e.g. a generator is coupled to generate electricity.

The fuel system 2 comprises a gas line 6, via which gaseous fuel is fed to the combustion chamber 4. In the combustion chamber 4, in particular several burners are angeord net, which in the exemplary embodiment shown are formed in several stages and which are symbolically represented by a in the figure

Main burner 8 and a pilot burner 10 are shown. A branch line 6a, 6b is branched off to each of the burner stages 8, 10, in each of which a control valve 12a, 12b is installed. The gas line 6 also includes an emergency valve 14. Upstream of the emergency valve 14, a heat exchanger 16 is also arranged on the gas line 6, which is part of a Vorwärmsys system, which serves to preheat the fuel in the gas line 6.

The gas turbine system further comprises a control or regulating device 18 which, among other things, regulates the position of the regulating valves 12a, 12b. In the control device 18, a critical opening position for the control valves 12a, 12b is stored, which is, for example, 80% of a maximum opening position of the control valves 12a, 12b. The critical opening position can, for example, also be 70%, 75%, 85%, 90%, 95% of the maximum opening position of the control valves 12a, 12b or correspond to the maximum opening position. The course of the method according to the invention can be seen from FIG. 2. In general, the position of the respective control valve 12a, 12b is always set via a control circuit in the control or regulating device 18 in such a way that the gas turbine runs at a predetermined power or combustion temperature. It thus automatically reacts indirectly to fluctuations in the following sizes: natural gas supply pressure, natural gas temperature, natural gas quality, ambient conditions,

Pressure loss across the natural gas supply system and the burner (contamination / wear) and / or efficiency of the gas turbine (wear). All of these parameters represent possible interference factors, on the basis of which the position of the control valves 12a, 12b is regulated, in order to thereby set a turbine power P in particular.

In FIG. 2, a decreasing fuel supply pressure BD, here natural gas supply pressure, is considered as the disturbance variable. Instead of a decreasing natural gas pressure, a deteriorating gas quality, a falling ambient temperature, a rising ambient air humidity, a rising ambient pressure, contamination of the burner or natural gas system components, a reduced gas turbine efficiency, etc. could alternatively be used.

According to FIG. 2, the fuel supply pressure BD is constant from the point in time to to the point in time ti, a control valve position RV is below a critical opening position S _crit .

The fuel temperature T _B and the turbine power P remain stable at their target value (P _s for the turbine power).

The fuel supply pressure BD in the gas line 6 drops from ti to t ₂ . In order to keep the turbine power P (or the fuel mass flow) constant, the corresponding control valve or both control valves 12a, 12b is opened further until a critical opening position S _{crit is} reached.

In the period from t ₂ to t ₃ , the fuel supply pressure BD drops further. The control valves 12a, 12b have their Defined critical opening position S _{crit is} reached, therefore they are not opened further from t ₃ , but remain in S _crit · In order to keep the power P (or the fuel mass flow) constant, the gas temperature T _{B is} reduced.

From t ₃ the fuel supply pressure BD continues to decrease with an even steeper gradient. The gradient is too large to be compensated for by the sluggish change in the fuel temperature T _B. The fuel temperature T _B continues to drop with its maximum gradient, in addition, the Gastur is binenleistung P slightly reduced, so that the control valves 12a, 12b are further th _crit supported in the critical opening position S.

Between t ₄ and ts, the fuel supply pressure BD stabilizes at a lower level than the original one. The control valves 12a, 12b are still in the critical opening position S _crit . The turbine power P has been below the power setpoint P _s since t ₃ , but in parallel with the progressive reduction in the fuel temperature T _B, the gas turbine power P slowly returns to the setpoint P _s raised. It should be ensured that the fuel temperature T _B remains above a _minimum threshold value T _min , the threshold value T _min correlating, for example, with the NOx emissions or another operating parameter of the gas turbine system.

From 1 ₅ , stable operation is achieved again. The gas turbine power P has reached its setpoint P _s again and the gas turbine continues to be operated at a reduced fuel temperature T _B. Only when the control valves 12a, 12b assume a position RV below the critical opening position S _crit will the fuel temperature T _B be raised again (the case is not shown).

Claims

claims

1. A method for operating a gas turbine system with gaseous fuel, which is transported through a gas line (6) to the gas turbine system, burned in a combustion chamber (4) and then fed to a gas turbine,

characterized in that at least one fitting (12a, 12b) for flow control of the fuel to the combustion chamber (4) is installed in the gas line (6), a critical opening position (Skrit) being defined for the fitting (12a, 12b) and if the valve (12a,

12b) in the process of exceeding the critical opening position (Skrit), a temperature (T _B ) of the fuel in the gas line (6) is reduced.

2. The method according to claim 1,

characterized in that the critical opening position (Skrit) of the valve (12a, 12b) is above 70% of a maximum opening position.

3. The method according to any one of the preceding claims,

characterized in that the gas turbine system has a preheating system for the fuel and the temperature (T _B ) of the fuel in the gas line (6) is reduced by reducing the heat supplied to the fuel in the preheating system.

4. The method according to any one of the preceding claims,

characterized in that a threshold value (T _min ) for the minimum temperature (T _B ) of the fuel is determined taking into account a current value for an operating parameter of the gas turbine system and the reduction in the temperature (T _B ) of the fuel in the gas line (6 ) is stopped when the threshold is reached.

5. The method according to any one of the preceding claims, characterized in that several fittings (12a, 12b) are installed in the gas line (6) and the position of each of the fittings (12a, 12b) is used.

6. The method according to any one of the preceding claims,

characterized in that a turbine power (P) is additionally reduced.

7. Control device (18) comprising means for performing the method according to one of the preceding claims.

Gas turbine plant with a control device (18) according to claim 7.