EP2592241A1 - Method for operating a gas and steam turbine facility for frequency support - Google Patents

Abstract

The method involves increasing injectivity of a steam turbine and lowering pressure in a waste heat steam generator to utilize storage reserves in the waste heat steam generator to increase steam generation such that heat energy is quickly supplied to the waste heat steam generator. A power characteristic of a gas and steam turbine system due to increasing of the injectivity of the steam turbine and decreasing of the pressure in the waste heat steam generator is made greater or equal to existing or present power of a stationary operation.

Description

The invention relates to the frequency support operation of a gas and steam turbine plant.

The energy market is increasingly demanding highly flexible power plants that can cover not only fast startup and shutdown times but also a large power range and are well prepared for frequency support operations.

This includes u.a. also the ability to release additional power at high power consumption (so-called peak load operation). In the future, it is expected that power plants operating at their nominal point will also participate in peak load coverage and frequency support.

Today's solutions rely on the use of power reserves within the components or are based on technologies that can provide only a very low power reserve. For both frequency support and peak load coverage, the gas turbine may overfill, the compressor vanes may be opened beyond the base load range, or water may be injected into the intake air duct. Requirements relating only to peak load coverage can be met by steam injection into the gas turbine combustor, by cooling the gas turbine intake air, for example with evaporative coolers or chillers, or by providing the heat recovery steam generator (AHDE) with auxiliary firing to raise the steam turbine power. For frequency support, the live steam or the steam from the reheat (modified Gleitdruckfahrweise) can be accumulated and the turbine control valves are then opened quickly.

The EP 1 164 254 B1 describes a gas and steam turbine plant with steam diversion for the peak load coverage, ie for additional power at full load. In this case, a portion of the steam generated in the heat recovery steam generator bypass ducts past the turbine inlets downstream of these turbine inlets arranged further inputs the turbine parts, whereby the pressure in the heat recovery steam generator can be kept substantially constant and the absorption capacity of the steam turbine and thus the output power are increased ,

The object of the invention is to provide a method for the frequency support operation of a gas and steam turbine plant, which provides an improved power reserve available.

The invention solves this problem by providing that in the operation of a gas and steam turbine plant with a gas turbine, a steam turbine and a heat recovery steam generator, in the heat exchange with exhaust gas from the gas turbine steam for the steam turbine can be generated for frequency support in the power grid from a stationary operation out the absorption capacity of the steam turbine increased and the pressure in the heat recovery steam generator can be lowered to use storage reserves in the heat recovery steam generator for increased steam generation, and that the heat recovery steam generator so quickly heat energy is supplied that a performance curve of the gas and steam turbine plant as a result of the increase Damping ability of the steam turbine and the pressure reduction in the heat recovery steam generator is greater than or equal to an immediately prior existing power of stationary operation.

The invention is therefore based on the idea to use storage reserves in the heat recovery steam generator to generate additional steam at sudden opening of the valves. The pressure drop in the heat recovery steam generator additionally generates steam and a sufficiently large and rapid supply of heat energy is the usual dent in the performance curve prevent. This method can provide control power at partial and full load.

The inventive method, the flexibility and efficiency of the power plant can be significantly increased, since high power requirements additional energy is available, which leads to increased revenue especially at high electricity revenues in electricity markets and the operation of the system designed more economical (peak load capacity). This applies to the frequency support operation, in particular for secondary and tertiary support. Thus, it is not necessary for the primary frequency support or the peak load operation to design the high-pressure or the reheat part higher in the pressure than for the nominal operation. In addition, it is not necessary to run the system in the so-called modified sliding pressure operation, which produces power and efficiency losses in the standby mode of the plant by throttling the steam turbine control valves. With the inventive method, the load range of the power plant can be extended, since even the low load operation can be set more flexible.

Advantageously, to increase the absorption capacity of the steam turbine, at least one valve in a bypass channel for bypassing a steam turbine stage or a steam turbine module is opened.

It is expedient if steam is passed via the bypass channel downstream of a high-pressure inlet into the steam turbine.

It is particularly advantageous if steam is fed alternatively or additionally via the bypass channel downstream of a medium-pressure inlet into the steam turbine.

Alternatively or additionally, it may be advantageous if at least one to increase the absorption capacity of the steam turbine

Valve of a control wheel on a high-pressure turbine and / or a medium-pressure turbine is opened.

Preferably, the heat energy is supplied by an additional power of the gas turbine and thus an increased exhaust gas flow.

Furthermore, it may be advantageous if the heat energy is supplied via an additional firing. However, this must be dimensioned accordingly.

In order to further increase the Ausspeichervermögen, it is advantageous if a steam drum pressure is accumulated in stationary operation by a valve which is opened for frequency support.

Figur 1

ein vereinfachtes Schaltschema einer Gas- und Dampfturbinenanlage mit Hoch- und MitteldruckÜberlasteinleitung sowie Regelrädern in der Dampfturbine und einer Zusatzfeuerung im Abhitzedampferzeuger,

Figur 2

Dampfturbinen-Leistungsverlauf bei Überlasteinleitung in die Hochdruckturbine für verschiedene Frischdampfdruck zu Einleitdruck-Verhältnisse und

Figur 3

Dampfturbinen-Leistungsverlauf bei Überlasteinleitung in die Mitteldruckturbine für verschiedene Frischdampfdruck zu Einleitdruck-Verhältnisse.

The invention will be explained in more detail by way of example with reference to the drawings. Shown schematically and not to scale:

FIG. 1

a simplified circuit diagram of a gas and steam turbine plant with high and medium pressure overload discharge and control wheels in the steam turbine and an additional firing in the heat recovery steam generator,

FIG. 2

Steam turbine power curve with overload introduction into the high-pressure turbine for various live steam pressure to inlet pressure ratios and

FIG. 3

Steam turbine power curve with overload introduction into the medium-pressure turbine for various live steam pressure to inlet pressure conditions.

FIG. 1 shows a gas and steam turbine plant 1, which includes a gas turbine 2 and a steam turbine 3. About a shaft 4, a rotor of the gas turbine, a rotor of a generator 5 and a rotor of the steam turbine 3 are coupled together, the rotor of the steam turbine 3 and the Rotor of the generator 4 via a clutch 6 rotatably separable from each other and can be coupled. The rotor of the generator 5 and the gas turbine 2 are rigidly connected to each other via the shaft 4. A flue gas outlet of the gas turbine 2 is connected via an exhaust pipe 7 with a heat recovery steam generator 8, which is provided for generating the operating steam of the steam turbine 3 from waste heat of the gas turbine.

During operation of the gas and steam turbine 1, a compressor 9 is driven by the rotating rotor of the gas turbine 2 via the shaft 4, which sucks combustion air from the environment and a combustion chamber 10 supplies. There, the combustion air is mixed with fuel supplied by a fuel supply 11 and burned and the hot, pressurized exhaust gases are supplied to the gas turbine 12 and there relaxed under the power of work. The still about 500 to 600 ° C hot exhaust gases are then fed through the exhaust pipe 7 to the heat recovery steam generator 8 and flow through this until they pass through a chimney 13 into the environment. On their way through the heat recovery steam generator 8, they pass their heat to a high pressure superheater 14, then a high pressure reheater 15, a high pressure evaporator 16, a high pressure preheater 17, then a medium pressure superheater 18, a medium pressure evaporator 19, a medium pressure preheater 20, then a low pressure superheater 21 Low-pressure evaporator 22 and finally a condensate preheater 23rd

In the high pressure superheater 14 superheated steam is supplied through a steam discharge line 24 of a high pressure stage 25 of the steam turbine 3 and there relaxed under the power of work. With the work - analogous to the work done in the gas turbine - the shaft 4 and thus the generator 5 is moved to generate electrical energy. The partially relaxed in the high-pressure stage 25 hot steam is then fed to the high-pressure reheater 15, where it is reheated and fed via a derivative 26 a medium-pressure stage 27 of the steam turbine 3 and there relaxed under the power of mechanical work. The there partially relaxed steam is via an overflow 28 of a low pressure stage 29th fed to the steam turbine 3 and further relaxed there with the release of mechanical energy.

The expanded steam is condensed in the condenser 30 of the steam turbine 3, and the resulting condensate is a condensate pump 31 directly to a low pressure stage 32 of the heat recovery steam generator 8 or via a feed 33 - and provided by the corresponding pressure - a medium-pressure stage 34 or a high-pressure stage 35th the heat recovery steam generator 8 supplies, where the condensate is evaporated. After steam generation and overheating, the steam is supplied via the corresponding outlets 24, 26, 36 of the heat recovery steam generator 8 back to the steam turbine 3 for relaxation and performance mechanical work.

In the steam outlets 24 and 26 shut-off valves 37 and 38 are arranged. From the high pressure stage 25 of the steam turbine 3 leading steam discharge line 24 branches off a bypass channel 39 with a shut-off valve 40 for bypassing the high-pressure stage 25 from. Similarly, a bypass channel 41 branches off with a shut-off valve 42 for bypassing the intermediate-pressure stage 27.

In the flow direction in front of the high-pressure part 25, a first control wheel 43 is attached to the rotor of the steam turbine 3. Analogously, in the flow direction in front of the medium-pressure part 27, a second control wheel 44 is attached to the rotor of the steam turbine 3. A control wheel comprises valves controlled via valves, which can be acted upon by segments of a turbine. Depending on how many of the valves are opened, a more or less large amount of additional steam flows through the nozzles into the turbine.

Further shows FIG. 1 an additional firing 45 at the entrance of the heat recovery steam generator 8, in which the gas turbine exhaust gas, which still contains much oxygen, fuel is added and the mixture is burned. Thus, the live steam over the temperature of the gas turbine exhaust gas can be overheated or for generating process steam when the steam generation is to be decoupled from the power generation of the gas turbine 2. In particular, supplemental firing 45 may be of interest to increase the output of electrical power during peak demand periods.

The inventive method provides that the steam mass flow is increased by the steam turbine in the short term by opening an overload valve 40, 42 and a turbine bypass 39, 41 and connected to the power of the steam turbine 3 increases rapidly (seconds range).

According to the invention, the overload introduction can be utilized both on the high-pressure turbine 25 for raising the live steam mass flow and on the medium-pressure turbine 27 for increasing the reheat steam mass flow as well as before each further turbine stage (for example low-pressure turbine 29).

Alternatively, the intake capacity of the steam turbine can be increased via a control wheel 43, 44 on the high-pressure turbine 25 and / or the medium-pressure turbine 27 by opening associated valves.

Storage reserves can be released from all pressure stages 32, 34, 35 of the heat recovery steam generator 8 (for example also medium and low pressure systems, if present). By accumulating the drum pressure, e.g. by a pressure control valve 46 in the medium-pressure steam system 34, while the Ausspeichervermögen can be increased. This increase in steam mass flow rate is due to an increase in the absorption capacity of the steam turbine and an associated pressure drop in the system.

This pressure drop leads to a depletion of thermal reserves (hot water, steel masses in the heat recovery steam generator) and thus to a short-term increase in output of the steam turbine, as the FIGS. 2 and 3 for the performance curve for overload introduction for different size ratios of live steam pressure to inlet pressure in high and medium pressure turbine demonstrate. The horizontal line shows the value for steady state operation.

Since the thermal storage reserves are limited, according to the invention the decreasing storage effect either by a self-igniting supplementary firing 45 in the heat recovery steam generator 8, operated in continuous minimum load additional firing 45 or by existing power reserves in the gas turbine 2 (turning up the compressor vanes, over-firing, steam injection or water injection in the compressor. 9 or combustion chamber 10) compensated or further increased.

Claims (8)

Method for operating a gas and steam turbine plant (1) with a gas turbine (2), a steam turbine (3) and a heat recovery steam generator (8), in which in heat exchange with exhaust gas from the gas turbine (2) steam for the steam turbine (3) can be generated is characterized in that for frequency support in the power grid from a stationary operation, the capacity of the steam turbine (3) increases and the pressure in the heat recovery steam generator (8) are lowered to use storage reserves in the heat recovery steam generator (8) to increased steam generation, and the heat recovery steam generator (8) heat energy is supplied so quickly that a performance curve of the gas and steam turbine plant (1) as a result of increasing the absorption capacity of the steam turbine (3) and the pressure reduction in the heat recovery steam generator (8) greater than immediately prior existing power of the stationary Operation is. The method of claim 1, wherein to increase the absorption capacity of the steam turbine (3) at least one valve (40, 42) in a bypass channel (39, 41) for bypassing a steam turbine stage (25, 27, 29) or a steam turbine module is opened. Method according to one of the preceding claims, wherein steam is passed via the bypass channel (39) downstream of a high-pressure inlet into the steam turbine (3). Method according to one of the preceding claims, wherein steam is passed via the bypass channel (41) downstream of a medium-pressure inlet into the steam turbine (3). Method according to one of the preceding claims, wherein to increase the absorption capacity of the steam turbine (3) at least one valve of a control wheel (43, 44) on a high-pressure turbine (25) and / or a medium-pressure turbine (27) is opened. Method according to one of the preceding claims, wherein the heat energy is supplied by an additional power of the gas turbine (2) and thus an increased exhaust gas flow. Method according to one of the preceding claims, wherein the heat energy via an additional firing (45) is supplied. Method according to one of the preceding claims, wherein a steam drum pressure in stationary operation by a valve (46) is accumulated, which is opened for frequency support.

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