WO2014033220A1

WO2014033220A1 - Cooling method for operating a gas turbine

Info

Publication number: WO2014033220A1
Application number: PCT/EP2013/067918
Authority: WO
Inventors: Michael Wagner
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-08-31
Filing date: 2013-08-29
Publication date: 2014-03-06

Abstract

The invention relates to a method for operating a gas turbine (100) having a combustion chamber (106) and a secondary air system (145), wherein air is withdrawn in at least two areas under different pressures that lie before the combustion chamber (106) on the flow medium side and is at least partially introduced into an area lying after the combustion chamber (106) on the flow medium side. According to the invention the method should enable especially flexible modes of operation without limitation of the service life. For this purpose, the amount, pressure, and temperature of the introduced air are controlled by controlling the amount of air withdrawn at the particular drawing areas, wherein coolant is injected into the withdrawn air by means of an injection system (163) and the amount of injected coolant is controlled.

Description

description

The invention relates to a method for operating a gas turbine with a combustion chamber and a secondary air system, in which air is taken off in at least two regions subjected to different pressures and located upstream of the combustion chamber and into a flow medium side downstream of the combustion chamber At least partially introduced.

A gas turbine is an internal combustion engine, consisting of the gas turbine in the strict sense with an upstream compressor and an intermediate combustion chamber. The principle of operation is based on the Joule cycle: it compresses air via the blading of one or more compressor stages, then mixes them in the combustion chamber with a gaseous or liquid fuel, ignites and burns. The result is a hot gas (mixture of combustion gas and air), which relaxes in the subsequent turbine part, with thermal converts into mechanical energy and first drives the compressor. The remaining portion is used in the shaft engine for driving a generator, a propeller, a rotor, a compressor or a pump. In the jet engine, on the other hand, the thermal energy accelerates the hot gas flow, which generates the thrust. A stationary gas turbine basically consists of an inlet, a compressor, a combustion chamber, a turbine and an output shaft for shaft engines. The term "turbine" is not used quite clearly, because strictly speaking, only one component of the gas turbine is actually a turbine, but on the other hand, the entire unit is colloquially referred to as a "gas turbine". Except for the inlet, all other moving components are coupled via one or more shafts. Both the compressor and the turbine usually have several blades mounted on the shaft. Blades mounted in a plane each form a paddle wheel or impeller. The blades are slightly curved profiled, similar to an aircraft wing. Before each impeller is usually a stator. These guide vanes protrude from the housing into the flowing medium and place it in a swirl, which serves to optimally flow the impeller. The stator and the impeller together are called stages. Usually, several such stages are connected in series. Since the stator is stationary, its vanes can be mounted both on the inside of the housing and on the outside of the housing, and thus provide a bearing for the shaft of the impeller.

For cooling the blading of the turbine, a gas turbine usually has a secondary air system. This removes at one or more points air in the compressor, which is guided past the combustion chamber and is introduced into the turbine, usually through corresponding cooling air openings. The cooling air openings can also be arranged in the guide vanes, so that forms a protective air film here.

Normally, the turbine blade is for a nominal operating point respect. Lifespan, costs and cooling air consumption are optimized, which leads to a reduction in service life in unfavorable operating conditions such as overfiring. This becomes particularly important in part-load operation, in which to achieve increased machine flexibility in the future is increasingly over-fired. On the other hand, it is interested in a low base load combustion temperature to save cooling air, otherwise there is to be reckoned with an unnecessary overcooling of the components and thus a corresponding loss of efficiency. In addition, very unfavorable operating conditions, such as too low supply pressures in the case of unfavorable compressor prevent characteristic regardless of the combustion temperature.

Up to now, a corresponding adaptation of the secondary air system via adjustable flaps in the outer extraction lines has been attempted; in addition, there are concepts for switching / cascading the cooling air supply to higher pressure levels from corresponding areas of the compressor. A disadvantage of these concepts is the respectively very specific use case, since different

Objectives are present.

The invention is therefore based on the object of specifying a method for operating a gas turbine and a secondary air system for a gas turbine, which allow particularly flexible modes of operation without limiting the life.

This object is achieved with respect to the method according to the invention by the amount, pressure and temperature of the introduced air are controlled by the amount of air removed at the respective removal areas is controlled and wherein coolant is injected by means of an injection system in the extracted air and the amount of injected Coolant is controlled.

The invention is based on the consideration that an increased flexibility with respect to future requirements of the gas turbine mode of operation would be achievable if a free and continuous control of the amount, pressure and temperature of the cooling air would be possible. The requirements are namely characterized by an increased operating range between low part load and peak load with very high turbine inlet temperatures. The different operating ranges have very different requirements for cooling air pressure and cooling air temperature of the turbine blades, so that the fulfillment of all requirements is only very limited: generally cooling air is to be saved to maximize efficiency, ie low temperatures and pressures are desirable. At the same time, however, CO emissions are to be reduced, especially at partial load, which is possible due to high combustion temperatures. However, these require a high cooling air consumption, ie high pressures with the lowest possible temperatures ren. The same applies to other unfavorable operating conditions such. B. overfiring. Finally, a sufficient supply pressure under unfavorable operating conditions such. B. partial load and low ambient temperatures.

The adaptation to these operating states is possible by coupling a cooling air cascading with a corresponding regulation. However, the removal of air in a high pressure compressor area also causes a correspondingly high cooling air temperature. This cooling air temperature increase when switching to higher pressure levels in the cooling air cascading severely limits the flexibility. However, this is solvable by additionally providing a coolant injection, in particular with water in the cooling air. If the amount of injected water is also regulated, this results in a largely independent of the pressure control of the temperature control of the cooling air.

Advantageously, when the injection system fails, the amount of air introduced is increased. This allows the

Operating state are kept identical, but at the expense of additional cooling air. An increase to a higher pressure level with a corresponding loss of efficiency due to the compressor work, however, is usually not yet necessary because sufficient pressure reserves are available by opening the flow control valves.

In a further advantageous embodiment, the pressure and / or the amount of introduced air is increased when the combustion temperature is increased. This avoids excessive

Shovel life reduced. In order to allow overfiring with simultaneous failure of the water system should be advantageously switched to the pressure higher overhead removal, at the expense of cooling air consumption.

Advantageously, as the combustion temperature is increased, the amount of coolant injected is increased, or the flow control valves are opened so as not to reduce the blade life. If at relatively high overfeed the supply pressure of the existing

Removal is not sufficient to ensure the life of the blade is advantageously switched to a higher extraction with sufficient supply pressure at moderate additional cooling air consumption. In the event of failure of the water system, sufficient pressure should be provided for the higher-level removal.

In a further advantageous embodiment of the method, when the base load combustion temperature is lowered, the pressure and / or the amount of introduced air is reduced. This reduces the cooling air consumption and thus increases the efficiency.

In an additional or alternative advantageous embodiment of the method is switched at extreme partial load operation at low ambient temperatures of the gas turbine to a higher pressure level, ie increases the proportion of the removed in the area acted upon with the higher pressure air. Due to the physically given compressor characteristic, considerably lower removal pressures are to be expected in part-load operation. For this reason, the backflow margin, ie the difference in pressure between the cooling air pressure and the hot gas pressure at the point of introduction, should be switched over independently of the thermal load to the higher extraction, in particular when it is not reached. This has the advantage that in comparison to the usual procedure when selecting the compressor discharge point comparatively less security are kept, as can be switched to higher pressure. This reduces the required compressor capacity and thus increases the gas turbine performance for all operating points.

If over-firing at partial load for CO reduction, advantageously the supply pressure should be increased significantly under water injection in order not to reduce the life of the blade. Furthermore, the cooling air consumption is simultaneously increased at maximum water injection and maximum supply pressure, which considerably increases the potential for CO reduction.

With regard to the secondary air system for a gas turbine having a combustion chamber, the object is achieved by the secondary air system comprising at least two air extraction devices connected to different areas of the gas turbine, located on the output side and having a flow medium side associated with each of the air extraction devices is a flow control valve and wherein the secondary air system comprises an injection system for coolant, which is associated with a flow control valve. A gas turbine advantageously comprises such a secondary air system and / or is advantageously operated with the described method.

Advantageously, a power plant includes such a gas turbine.

The advantages achieved by the invention are in particular that the combination of a Kühlluftkaskadie- tion or switching to higher pressure level with controllable control valves and a Wassereindüsung for lowering the temperature in the supply line a flexible and infinitely adjustable combination of cooling air pressure and temperature can be achieved in order to optimize the operating conditions for all operating conditions. murti for lifetime and cooling air consumption.

At the same time, this concept enables extreme operating conditions such as low partial load operation and overfiring to be intercepted.

The invention will be explained in more detail with reference to a drawing. Show:

1 shows a longitudinal partial section through a gas turbine,

2 shows a schematic representation of a secondary air system with regulation of pressure, quantity and temperature of the cooling air, FIG. 3 shows a diagram of the temperature against the pressure of the cooling air in a secondary air system with an air extraction device without regulation,

4 shows a diagram of the temperature against the pressure of the cooling air in a secondary air system with an air extraction device with control,

5 shows a diagram of the temperature against the pressure of the cooling air in a secondary air system with an air extraction device with injection system,

6 shows a diagram of the temperature against the pressure of the cooling air in a secondary air system with an air extraction device with control and injection system,

7 shows a diagram of the temperature against the pressure of the cooling air in a secondary air system with two air sampling devices with control, FIG. 8 shows a diagram of the temperature against the pressure of the cooling air in a secondary air system with two air sampling devices with control and injection system, FIG. 9 shows the diagram from FIG. 8 with a representation of the directions of change in the case of specific control actions, FIG.

10 is a graph of the temperature against the pressure and the

Representation of the mass flow at base load of the gas turbine, and

11 shows a diagram of the temperature against the pressure and the

Representation of the mass flow at part load of the gas turbine.

Identical parts are provided with the same reference numerals in all figures. 1 shows a gas turbine 100 in a longitudinal partial section of the upper half. The gas turbine 100 has inside a rotatably mounted around a rotation axis 102 (axial direction) rotor 103, which is also referred to as a turbine runner. Along the rotor 103 successively follow an intake housing 104, a compressor 105, a toroidal combustion chamber 110, with a plurality of coaxially arranged burners 107, a turbine 108 and the exhaust housing 109th

The combustion chamber 106 communicates with an annular hot gas channel 111. There, for example, four turbine stages 112 connected in series form the turbine 108. Each turbine stage 112 is formed from two blade rings. As seen in the direction of flow of a working medium 113, in the hot gas channel 111 of a row of guide vanes 115, a blade row 125 formed from guide disk 120 follows.

The vanes 130 are attached to the stator 143, whereas the blades 120 of a row 125 are mounted on the rotor 103 by means of a turbine disk 133. The rotor blades 120 thus form components of the rotor or rotor 103. Coupled to the rotor 103 is a generator or a working machine (not shown). During operation of the gas turbine 100, air 105 is sucked in and compressed by the compressor 105 through the intake housing 104. The compressed air provided at the turbine-side end of the compressor 105 is fed to the burners 107 where it is mixed with a fuel. The mixture is then burned to form the working fluid 113 in the combustion chamber 110. From there, the working medium 113 flows along the hot gas channel 111 past the guide vanes 130 and the rotor blades 120. The working medium 113 expands on the rotor blades 120 in a pulse-transmitting manner, so that the rotor blades 120 drive the rotor 103 and drive the machine connected to it ,

The components exposed to the hot working medium 113 are subject to thermal loads during operation of the gas turbine 100. The guide vanes 130 and rotor blades 120 of the first turbine stage 112, viewed in the direction of flow of the working medium 113, are subjected to the highest thermal load in addition to the heat shield stones lining the combustion chamber 106. In order to withstand the temperatures prevailing there, they are cooled by means of a coolant. Likewise, the blades 120, 130 can have coatings against corrosion (MCrAlX, M = Fe, Co, Ni, rare earths) and heat (thermal barrier coating, for example ZrO 2, Y 2 O 4 -ZrO 2).

Furthermore, the guide vanes 130 are supplied with cooling air via a secondary air system 145. The cooling air is guided there into the guide vanes 120 and emerges from the surface thereof in a plurality of cooling air openings in the manner of a film cooling in the hot gas channel 111.

The gas turbine 100 is part of a power plant, not shown. 2 shows schematically the components of the secondary air system 145. It has two air extraction devices 147, 149, of which the first air extraction device 147 is connected to a central region of the compressor 105, the second air extraction device 149 connected to an end portion of the compressor 105. In the end region, there is a higher pressure than in the middle region. The air sampling device 147 is a line 151 downstream of a flow control valve 153. Similarly, the air extraction device 149 is a line 155 connected downstream of a flow control valve 157. The lines 151, 155 open into a common line 159, which leads to an air introduction device 161, the cooling air in the turbine 108, in particular in the guide vanes 130th

In line 159, an injection system 163 is provided for water, which also includes a not shown in detail flow control valve. Thus, pressure, quantity and

Temperature of the cooling air at the air inlet 161 regulated.

The secondary air system 145 may also include a plurality of parallel arrangements according to FIG. 2, which lead into different areas of the turbine 108 and remove air in different areas of the compressor 105.

FIGS. 3 to 9 each show a diagram of the cooling air temperature plotted against the cooling air pressure, the illustrations being only schematic, and therefore no numerical values are shown on the axes. In FIGS. 3 to 7, a schematic representation of the associated configuration of the secondary air system 145 is arranged in the right-hand edge of the diagram.

FIG. 3 shows an uncontrolled cooling air line 151 from the air extraction device 147 in the compressor 105 to the air introduction device 161 in the turbine 108. The pressure and temperature of the air can not be influenced and are determined by the conditions in the compressor 105, shown as point 165. FIG. 4 shows a regulated cooling air line 151 with a flow control valve 153 from the air extraction device 147 in the compressor 105 to the air introduction device 161 in the turbine 108. The temperature of the air can not be influenced and is determined by the conditions in the compressor 105 Flow control valve 153 vary, shown as line 167. The maximum is represented by the point 165. 5 shows an uncontrolled cooling air line 151 with an injection system 163 for water from the air extraction device 147 in the compressor 105 to the air introduction device 161 in the turbine 108. The pressure of the air can not be influenced and is determined by the conditions in the compressor 105. However, the temperature can be due to injection system 163, shown as line 167. The maximum is represented by point 165.

6 shows a regulated cooling air line 151 with a flow control valve 153 and an injection system 163 for water from the air extraction device 147 in the compressor 105 to the air introduction device 161 in the turbine 108. Pressure and temperature of the cooling air can be compared to the conditions in the compressor 105 by appropriate control of the flow control valve 153 and injection system 163, shown as area 169. The uncontrolled operating point is represented by point 165.

7 shows a first regulated cooling air line 151 with a flow control valve 153 and a second regulated one

Cooling air line 155 with a flow control valve 157, which open into a common line 159. The first cooling air line 151 is connected on the input side to the air extraction device 147 in the compressor 105, the second cooling air line 155 to the air extraction device 149 in a region of the compressor 105 subjected to higher pressure. The common line 159 leads to the air introduction device 161 in the turbine 108. Alternatively, now Cooling air from the air extraction Means 147 or be removed from the air sampling device 149, wherein the withdrawal via the flow valves 153 and 157 can be regulated. The pressure can thus be varied in each case, represented by the lines 167 and 171, respectively. The uncontrolled operating point is represented by the points 165 and 173, respectively. Due to the physical conditions in the compressor 105, the temperature level of the air from the air extraction device 147 is lower than that from the air extraction device 149.

FIGS. 8 and 9 show corresponding diagrams of the configuration from FIG. 2, which is not additionally shown here. The combination of the injection system 163 with the configuration of FIG. 7 in FIG. 8 results in infinite controllability of pressure and temperature, represented by the area 175 with the maximum represented by the point 173 and the partially underlying area 169.

FIG. 9 shows all the features of FIG. 8, wherein here also the point 165, which represents the maximum with respect to the surface 169, is also shown. From the point 165, which roughly represents the operating state in a simple, uncontrolled system of FIG. 3, the operating state can now be optimally optimized with regard to pressure and temperature, depending on the desired driving style, represented by arrows 177, 179, 181, 183 : Arrows 177 show an increase in the pressure z. For example, at partial load with adaptation of the temperature to expand the CO emissions-compliant operating range of the gas turbine 100. Arrow 179 shows the maximum of cooling air consumption by maximum reduction of the temperature at maximum

Cooling air pressure. Arrows 181 show the possibility of lowering the cooling air temperature without increasing the pressure, z. B. to expand the operating range or to allow the use of less high quality materials. Finally, arrows 183 show the minimization of cooling air temperature and pressure for maximum cooling air savings and optimization of efficiency and reduction of NOx emissions. FIGS. 10 and 11 show the cooling air temperature plotted against the relative supply pressure (pressure of the cooling air divided by pressure of the hot gas) of the respective guide blade 130 in the compressor 105, in each case for the configuration from FIG. 2. Depicted is the mass flow of the cooling air corresponding to the respective point represented in legend 184.

FIG. 10 describes the control concept on a real gas turbine 100 during base-load operation: Box 185 describes the possible operating range of a pressure-controlled compressor removal with water injection, and box 187 describes the pressure-controlled, higher-level compressor removal or the compressor end space with water injection. The lower limit of the supply pressure is always the back flow margin, represented by line 189, which must not be exceeded, irrespective of the operating regime. This is particularly important in film-cooled blades of importance.

The design of the blade is carried out under nominal conditions with optimization of costs, service life and cooling air consumption. The associated operating point is represented by point 191. Starting from this point 191, it is possible to vary supply pressure and temperature (curve 193) so that the blade temperature and temperature gradient are identical under nominal conditions and thus no limitation for the service life is to be expected. If the injection system 163 fails, the thermal load on the blade can be kept identical by opening the flow control valve 153, but at the expense of additional cooling air consumption, see point 195. Switchover to the higher removal, ie. H. the air extraction device 149 is not yet required.

At higher combustion temperatures (normal overfiring, see point 197), the supply pressure must be increased under water injection at the same supply temperatures so as not to significantly reduce the service life of the blade. In order to enable a normal overfiring with simultaneous failure of the injection system 163, it may be necessary to switch to the higher-level removal, see point 201, at the expense of the cooling air consumption.

If, in the event of heavy overfeeding, the supply pressure of the existing extraction is insufficient to ensure the life of the blade, the system allows a switchover to the higher extraction, see point 199, with water injection and sufficient supply pressure with moderate additional cooling air consumption. If the injection system 163 fails, sufficient pressure must be available for the higher extraction, see item 203. In the case of under-firing, the supply pressure can be reduced so that a cooling-air saving can be achieved to increase the efficiency, see point 205. The technical limits of the blade ( BFM line 189). If the injection system 163 fails, the cooling air pressure can also be increased here, see point 205.

11 shows the diagram analogous to FIG. 10 for the case of a low partial load. Due to the physically given compressor characteristics, considerably lower removal pressures are to be expected, characterized by a displacement of the boxes 185 and 187 to smaller supply pressures. If the BFM line 189 is not reached, the system switches over to the higher extraction, regardless of the thermal load, see item 209.

If the CO reduction is over-fired at partial load, the supply pressure is considerably increased under injection of water, see arrow 211, so as not to reduce the service life of the bucket. Furthermore, the cooling air consumption is increased simultaneously with maximum water injection and maximum supply pressure (see point 213), which considerably increases the potential for CO reduction.

Claims

claims

Anspruch [en] A method for operating a gas turbine (100) having a combustion chamber (106) and a secondary air system (145), in which air is taken in at least two regions subjected to different pressures and located upstream of the combustion chamber (106)

Flow rate on the combustion chamber (106) lying area is at least partially introduced, wherein amount, pressure and temperature of the introduced air are controlled by the amount of air taken at the respective removal areas is controlled and wherein coolant by means of an injection system (163) in the withdrawn Air is injected and the amount of injected coolant is controlled.

2. The method according to claim 1,

in which in case of failure of the injection system (163), the amount of introduced air is increased.

3. The method according to any one of the preceding claims, wherein the increase in the combustion temperature of the pressure and / or the amount of introduced air is increased.

4. The method according to any one of the preceding claims, wherein the increase in the combustion temperature, the amount of the injected coolant is increased.

5. The method according to any one of the preceding claims, wherein in a lowering of the combustion temperature of

Pressure and / or the amount of introduced air is lowered (cooling air saving).

6. The method according to any one of the preceding claims, wherein in a power reduction of the gas turbine (100), the proportion of the air taken in the area subjected to the higher pressure area is increased.

7. secondary air system for a gas turbine (100) having a combustion chamber (106), comprising at least two, each with different pressures acted on the stream side of the combustion chamber (106) lying areas of the gas turbine associated air extraction devices (147, 149), the output side are connected to an air introduction device (161) connected to a region of the gas turbine (100) lying downstream of the combustion chamber, wherein each of the air extraction devices (147, 149) is assigned a flow control valve (153, 157) and wherein the secondary air system ( 145) comprises an injection system (163) for coolant, to which a flow control valve is assigned.

8. Gas turbine (100) with a secondary air system (145) according to claim 7.

9. Gas turbine (100), operated by the method according to one of claims 1 to 6.

10. Power plant with a gas turbine (100) according to claim 8 or 9.