Gas turbine operation at reduced load and MEL.

Abstract

Gas turbine operation at reduced load and MEL. A method for operating a gas turbine (GT), the compressor for which has variable guide vanes (IGV) at the inlet of the compressor, the compressed air by the compressor is mixed with fuel and this mixture is burned in a combustor, with a predetermined value by the addition of fuel, the gas turbine (GT) is controlled from a high load to a predetermined house load (HL), in a first step the variable guide vanes (IGV) are continuously closed and the fuel rate is likewise reduced in a particularly constant manner, and in a second and final step, at a turning point, the variable guide vanes (IGV) are not closed any more but the fuel consumption is further reduced until the predetermined house load (HL) is reached and a predetermined exhaust flow rate is maintained.

Description

[Technical field]

[0001] The present invention relates to a method of operating a gas turbine to meet emission standards even at low loads on the gas turbine.

[0002] Typically, a Gas Turbine (GT) is controlled from Base Load (BL) through Part Load (PL) to MEL (Minimum Emission Compliant Load) by constantly closing the IGVs (Variable Guide Vanes) and constantly reducing the fuel or fuel flow rate to the GT's combustion system. This reduces the Turbine Inlet Temperature (TIT). This curve is approximately linear because the IGVs are always closed and the Turbine Inlet Temperature (TIT) decreases as the fuel is reduced. This is a common method for reducing the speed of gas turbines (GTs) to comply with emission regulations.

[0003] This has the advantage that the combustion is very stable up to meeting the emission standards for a single GT or a combined cycle (CC) GT. Downstream from this point, the GT or plant is not compliant with discharge standards until domestic use (HL).

[0004] Emissions are primarily determined by the following factors: (i) GT: Emissions and load characteristics of GT, e.g., NOx, CO, etc. (ii) Optional catalytic section (SCR): The SCR reduces the emissions of the GT according to the selected design by using ammonia slip, which is guaranteed in many countries.

[0005] SCR failures occur especially at very low gas turbine loads. Therefore, it is not only the exhaust gas characteristics of the GT that limit the guaranteed emissions at the tailpipe exit, including NOx, CO, ammonia slip, etc., but also the SCR exhaust gas flow distribution at the SCR inlet. Furthermore, there is very limited experience at ultra-low loads (<50% CC load) across all OEMs.

[0006] So even the GT can achieve a lower MEL, but the optional SCR flow distribution requires a higher MEL to ensure emissions assurance. The MEL is becoming increasingly important for power plants. Power plants that can operate at very low MEL have the following advantages:

[0007] (i) It avoids shutting down the plant (impact on lifespan) (ii) Power producers can respond quickly to the grid and do not need to worry about slow start-up times. (iii) Supporting the grid will allow us to realize benefits faster

[0008] However, due to the environmental commitments of authorities and operators, it is important to comply with increasingly stringent emission requirements from national authorities. The object of the present invention is to overcome the above mentioned problems. This problem is solved by the method according to claim 1.

[0009] The dependent claims recite further advantages which may be combined in any desired manner to yield further advantages. The present invention improves MEL points while maintaining compliance with emissions standards.

[0010] GTs in all power ranges in single mode, especially those in the power range from 150 MW to over 600 MW or below, and other GTs in plants in smaller power ranges, are suitable for this approach. In particular, a certain exhaust flow rate is required in front of the SCR to ensure uniform flow distribution and good functionality of the SCR to avoid malfunction of the optional SCR, especially at very low GT loads and exhaust flow rates. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a diagram showing the load of a gas turbine GT (unit: %) relative to the exhaust flow rate f (unit: kg / s) of the gas turbine GT. [Diagram 2] FIG. 2 shows the dependence of load [%] on turbine inlet temperature (TIT).

[0012] 1 and 2 show the invention in the context of the state of the art. A gas turbine GT can operate alone or as part of a combined cycle CC, in which at least one heat recovery system (HRSG) and at least one steam turbine are combined and used in conjunction with at least one GT.

[0013] The gas turbine GT has an exhaust gas path and may be equipped with, among other things, a catalytic section SCR. The outside air is compressed by a compressor equipped with an openable and closable variable guide vane (IGV) at the inlet.

[0014] The compressed air is mixed with fuel and this fuel / air mixture is burned in a combustor to produce hot gases. Fuel is supplied at a constant fuel rate at steady state. The hot gases expand in the hot gas path and then the exhaust gases pass through the exhaust gas path.

[0015] The present invention relates to a method of operating a gas turbine GT to meet emission standards even at low gas turbine loads, especially in a catalyst or bypass stack downstream of a heat recovery steam generator (HRSG) in a combined cycle or simple cycle power plant. The gas turbine GT consists of a compressor equipped with variable guide vanes (IGV), and it is also possible to control the gas turbine output by opening and closing these guide vanes, controlling the amount of fuel supplied to the combustion system, and the combustion temperature inside the turbine.

[0016] When the gas turbine is operating between the MEL (load at which emissions standards are met) and baseload, the guide vanes are closed and the fuel flow or fuel rate is adjusted to reduce the load and power of the gas turbine GT and combined cycle to the load point at which emissions standards are met.

[0017] FIG. 1 is a diagram showing the load of a gas turbine GT (unit: %) relative to the exhaust flow rate f (unit: kg / s) of the gas turbine GT. The gas turbine GT is operated at base load (BL), during which the IGV is fully or nearly open.

[0018] First, as a first step, in order to decelerate the gas turbine GT from the base load (BL), the IGV is preferably always closed, the load of the gas turbine GT is reduced, and the exhaust flow rate f is also reduced.

[0019] The fuel rate is also preferably constantly reduced, in particular linearly reduced, as is known from the state of the art. Throttling of the gas turbine (GT) can occur even from loads lower than the base load BL.

[0020] However, in the second step, at a certain turning point (turning point TP), our invention stops the IGV closure before it is completely closed, specifically, at least 10% of the angle opening range is still open, but the fuel rate is further reduced until the domestic load HL is reached.

[0021] This is shown by the line from TP to HL, which is parallel to the y-axis (load [%]). The dashed line after TP is an extension of the line from BL to TP, and shows the latest state.

[0022] In figure 2 the dependence of the load [%] on the turbine inlet temperature (TIT) is shown. The dashed line again shows the state of the art.

[0023] At the turning point TP, the IGV is no longer closed, but the fuel flow rate is further reduced (HFR), resulting in a further reduction in TIT.

[0024] The reduction in fuel consumption rate in the first step (up to TP) has a first reduction rate (reduction in fuel consumption rate per hour), and the reduction rate in the second step (after TP) can have in particular a second reduction rate, which is at least 10% higher than the first reduction rate (not shown).

[0025] The turning point (TP) is defined as the percentage of the GT or CC's prescribed household load (HL) plus a difference D of at least 5% to 20%. For example, the prescribed household load is 36%BL, and if the household load (HL) is 44%, the IGV will not be closed. For example, D=8%.

[0026] For CC in GT, the MEL is predicted. If the emissions are e.g.: - 2mg / Nm 3 Ammonia slip over the entire operating range (MEL to BL) - NOx 10mg / Nm 3 - CO 10mg / Nm 3 As a benchmark for emission requirements, the MEL at 50% CC load and the required exhaust flow rate at SCR are achieved.

[0027] However, by applying the above operating method, it is possible to reduce the CC MEL while maintaining the same emissions.

[0028] Considering that 1MW costs 350 euros, every 1% improvement in MEL translates into an advantage in terms of operating costs.

Claims

1. A method for operating a gas turbine (GT), comprising: A gas turbine (GT), especially in a combined cycle (CC), a compressor for the gas turbine (GT) having variable guide vanes (IGV) at an inlet of the compressor; The compressed air from the compressor is mixed with fuel and the mixture is combusted in a combustor; and adding fuel to the gas turbine to provide a predetermined fuel rate at steady state; The gas turbine (GT) is controlled from a high load, in particular from a full load or base load (BL) to a predetermined domestic load (HL), In a first step, the variable guide vanes (IGVs) are closed continuously or in particular at all times, and the fuel rate is reduced accordingly, in particular at all times; And in a second and final step, starting from a turning point (TP), the variable guide vanes (IGV) are not closed any more, but the fuel rate is further decreased such that a predetermined exhaust flow rate is maintained, particularly at all times, until the predetermined domestic load (HL) is reached. method.

2. The gas turbine (GT) operates in a single mode. The method of claim 1.

3. The gas turbine (GT) operates in a combined cycle (CC). The method of claim 1.

4. The turning point (TP) is a predetermined load (L), This is the percentage [%] of the predetermined household load (HL) plus the [%] of the difference (D), The difference (D) is at least 5% to 20% in absolute value; The method according to any one of claims 1 to 3.

5. The gas turbine (GT) has an exhaust gas path, and the exhaust gas path has a catalyst (SCR). The method according to any one of claims 1 to 3.

6. The turning point (TP) is defined by a critical SCR exhaust gas distribution, especially when death corners and improper distribution occur, and an emissions compliant load is maintained. The method according to claim 5.

7. The fuel rate decreases linearly with time. The method according to any one of claims 1 to 3.

8. At the turning point (TP), the variable guide vane (IGV) is in a state where it is open at least 10 percent of the angle opening range of the variable guide vane (IGV). The method according to any one of claims 1 to 3.

9. the reduction in the fuel rate in the first step comprises a first rate of reduction in the fuel rate; The rate of decrease in the second step after the turning point (TP) has a second rate of decrease that is at least 10 percent higher than the first rate of decrease. The method according to any one of claims 1 to 3.

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