Gas-and-Steam Combined-Cycle Power Plant

Abstract

The present disclosure relates to power plants. Various embodiments thereof may include a method for operating a gas-and-steam combined-cycle power plant. For example, some embodiments may include a method for operating a gas-and-steam combined-cycle power plant including: providing exhaust gas from a gas turbine to a steam generator; generating steam by means of the exhaust gas; driving a generator with the steam via a turbine installation to provide an electric current; removing the exhaust gas from the steam generator; and using at least a portion of heat contained in the exhaust gas downstream from the steam generator to affect an endothermic chemical reaction.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2016/072847 filed Sep. 26, 2016, which designates the United States of America, and claims priority to DE Application No. 10 2015 219 403.5 filed Oct. 7, 2015, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to power plants. Various embodiments thereof may include a method for operating a gas-and-steam combined-cycle power plant.

BACKGROUND

Gas-and-steam combined-cycle power plants may be known as COGAS power plants. The gas-and-steam power plant is also referred to as a combined-cycle power plant, and typically comprises at least one turbine installation, at least one generator that can be driven by the turbine installation, for providing electric current, and at least one gas turbine. When the generator is driven by the turbine installation, the generator can convert mechanical energy into electrical energy, or electric current, and provide this electrical energy, or the electric current. The electric current can then be fed, for example, into an electricity grid.

The gas turbine provides exhaust gas, by means of which hot steam may be generated. For example, a fuel, such as a gaseous fuel for example, natural gas, is supplied to the gas turbine, the fuel then burned by means of the gas turbine. In particular, in addition to the fuel, oxygen or air is supplied to the gas turbine, such that a fuel-air mixture is produced from the air and the fuel. This fuel-air mixture is burned, resulting in exhaust gas of the gas turbine. By means of the exhaust gas, a fluid, e.g. water, is heated and thereby evaporated, resulting in hot steam. This means that the hot steam is generated by means of the exhaust gas of the gas turbine in such a manner that a fluid such as, for example, water, is evaporated by means of the hot exhaust gas of the gas turbine.

The steam is then supplied to the turbine installation, such that the turbine installation is driven by means of the steam. As already described, the generator is driven via the turbine installation, or by means of the turbine installation. The gas-and-steam combined-cycle power plant is a power plant in which the principles of a gas-turbine power plant and a steam power plant are combined. The gas turbine, or its exhaust gas, serves in this case as a heat source for a downstream steam generator, by means of which the steam for the turbine installation, for driving the turbine installation, is generated. The turbine installation is thus realized as a steam turbine.

This means that the gas turbine provides its exhaust gas, which is supplied to the steam generator. Thus, by means of the exhaust gas supplied to the steam generator, and by means of the steam generator, hot steam is generated, by means of which the turbine installation is driven and, via the turbine installation, the generator is driven, for the purpose of providing electric current. In addition, the exhaust gas supplied to the steam generator is removed again, at least in part.

It has been found that such a gas-and-steam combined-cycle power plant (COGAS power plant) must be switched off in response to the electricity demand, such that the generator does not provide an electric current and, for example, is not driven, and such that no current is fed into the electricity grid by means of the COGAS power plant. Owing to the switch-off, the gas-and-steam combined-cycle power plant can cool down, whereupon a renewed start-up, or ramping-up, of the gas-and-steam combined-cycle power plant requires a particularly long time and a particularly high energy demand.

For this reason, the gas-and-steam combined-cycle power plant is usually kept warm during the period in which the gas-and-steam combined-cycle power plant is switched off. In this case, the gas-and-steam combined-cycle power plant is kept warm by means of steam. This steam for retaining warmth is usually generated by means of a boiler, e.g. a gas boiler. The boiler evaporates a fluid such as, for example, water. The steam generated by means of the boiler is routed at least through a part of the gas-and-steam combined-cycle power plant, to keep the latter warm, or heat it. The gas-and-steam combined-cycle power plant, after having been switched off, can then be started in a warm-start operation, since the gas-and-steam combined-cycle power plant then already has a sufficiently high temperature at which it can be started. Nevertheless, as the time during which the gas-and-steam combined-cycle power plant is switched off increases, an increasing quantity of steam is required to keep the gas-and-steam combined-cycle power plant warm, or to heat it, since it cools down gradually.

SUMMARY

The teachings of the present disclosure may be embodied in methods that offer particularly efficient operation. For example, a method for operating a gas-and-steam combined-cycle power plant (10) in which exhaust gas is provided by a gas turbine (12) and is supplied to a steam generator (20), wherein hot steam is generated by means of the exhaust gas supplied to the steam generator (20) and by means of the steam generator (20), which steam is used to drive at least one generator (30), via at least one turbine installation (22), for the purpose of providing electric current, and wherein the exhaust gas supplied to the steam generator (20) is removed from the steam generator (20), may include at least a portion of heat contained in the exhaust gas downstream from the steam generator (20) is used to effect an endothermic chemical reaction.

In some embodiments, at least the portion of the heat contained in the exhaust gas downstream from the steam generator (20) is transferred, via a heat exchanger (38), to educts of the endothermic chemical reaction.

Some embodiments include branching-off at least a portion of the steam generated by means of the steam generator (20) and storing the branched-off steam in a steam accumulator (34); removing at least a portion of the steam, stored in the steam accumulator (34), from the steam accumulator (34); heating the steam removed from the steam accumulator (34) by means of heat that is released in an exothermic chemical reaction; and routing the heated steam to the turbine installation (22), which is driven by means of the supplied heated steam.

In some embodiments, products of the endothermic chemical reaction are used as educts of the exothermic chemical reaction.

In some embodiments, the heated steam for driving the turbine installation (22) is supplied to the turbine installation (22), in order to ramp up the gas-and-steam combined-cycle power plant (10) from a first load range into a second load range that is higher than the first load range.

In some embodiments, the endothermic chemical reaction is effected in the second load range.

Some embodiments may include a gas-and-steam combined-cycle power plant (10) that executes a method as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features, and details are disclosed by the following description of an exemplary embodiment and with reference to the drawing. The features and feature combinations mentioned in the description and the features and feature combinations mentioned in the following description of the FIGURE and/or shown alone in the single FIGURE can applied, not only in the respectively specified combination, but also in other combinations or singly, without departure from the scope of the invention.

The drawing, in the single FIGURE, shows a schematic representation of a gas-and-steam combined-cycle power plant, in which a thermochemical heat accumulator is used to realize a particularly high efficiency according to the teachings of the present disclosure.

DETAILED DESCRIPTION

Particularly efficient operation can be realized in embodiments wherein at least a portion of heat contained in the exhaust gas of the gas turbine downstream from the steam generator is used to effect an endothermic chemical reaction, i.e. a reaction that absorbs chemical heat. This means that the exhaust gas, for example flowing out of the steam generator—in the direction of flow of the exhaust gas of the gas turbine—has a temperature downstream from the steam generator, such that, in the exhaust gas of the gas turbine downstream from the steam generator, i.e. after generation of the steam, there is heat contained in the exhaust gas of the gas turbine. This heat that is contained in the exhaust gas downstream from the steam generator, or after the steam generator, is used to affect the endothermic chemical reaction. For this purpose, the heat contained in the exhaust gas is supplied to the endothermic chemical reaction, or to educts of the endothermic chemical reaction.

As a result, at least a portion of the heat supplied to the endothermic chemical reaction is stored in products of the endothermic chemical reaction, such that a thermochemical accumulator, in particular a thermochemical heat accumulator, can be created. The heat contained in the exhaust gas of the gas turbine downstream from the steam generator can be stored, at least partly, in the products of the endothermic chemical reaction, wherein the heat stored in the products can be used, for example, at a subsequent point in time and/or for other purposes. Some embodiments use heat contained in the exhaust gas of the gas turbine after the steam generator, which is usually lost without being used, for the purpose of storing at least a portion of the heat contained in the exhaust gas downstream from the steam generator.

In particular, the heat may be stored for district heating purposes. For example, an exothermic chemical reaction, i.e. a reaction giving off chemical heat, can be affected, wherein the products of the endothermic chemical reaction are educts of the exothermic chemical reaction, or are used as educts of the exothermic reaction. In the course of the exothermic chemical reaction, heat is released, by means of which a medium, in particular water, can be heated efficiently. Products of the exothermic chemical reaction may be used, for example, as the educts of the endothermic reaction.

The thermochemical heat accumulator can be used to realize particularly high flexibility in respect of the realization of district heating. In particular, it is possible to store heat, or energy, in the thermochemical heat accumulator, such that, in particular in the case of high demands for heat, a medium, in particular water, can be heated effectively by means of the heat stored in the thermochemical heat accumulator. Since energy contained in the exhaust gas downstream from the steam generator is used for this purpose, a particularly high efficiency can be realized. The heat that is stored in the products of the endothermic reaction, and released in the exothermic reaction, is transferred, for example, to heat the medium. The medium can then be used for heating purposes, in particular to realize district heating.

In some embodiments, at least a portion of the heat contained in the exhaust gas downstream from the steam generator is transferred, via a heat exchanger, to educts of the endothermic chemical reaction.

In some embodiments, at least a portion of the steam generated by means of the steam generator is branched-off and stored in a steam accumulator. In addition, at least a portion of the steam stored in the steam accumulator is removed from the steam accumulator. The steam removed from the steam accumulator is heated by means of heat that is released in the exothermic chemical reaction. In addition, the heated steam is routed to the turbine installation, which is driven, in particular accelerated, by means of the supplied heated steam.

In some embodiments, products of the endothermic chemical reaction are used as educts of the exothermic chemical reaction.

In some embodiments, the heated steam for driving the turbine installation is supplied to the turbine installation, to ramp up the gas-and-steam combined-cycle power plant from a first load range into a second load range that is higher than the first load range. In some embodiments, the endothermic chemical reaction is affected in the second load range.

Some embodiments may include a gas-and-steam combined-cycle power plant executing a method a described above. Advantageous designs of the method are to be regarded as advantageous designs of the gas-and-steam combined-cycle power plant, and vice versa.

The single FIGURE, in a schematic representation, shows a gas-and-steam combined-cycle power plant 10, also referred to as a COGAS power plant or—to improve readability—as a power plant. The power plant 10 comprises at least one gas turbine 12, to which fuel is supplied, for example in the course of a process for operating the power plant 10. This supply of fuel to the gas turbine 12 is indicated in the FIGURE by a direction arrow 14. The fuel may include a gaseous fuel such as, for example, natural gas. In addition, air is supplied to the gas turbine 12, this being indicated in the FIGURE by a direction arrow 16. The fuel is burned by means of the gas turbine 12, resulting in exhaust gas of the gas turbine 12. The gas turbine 12 thus provides the exhaust gas, as indicated in the FIGURE by a direction arrow 18. A mixture of the fuel and the air, for example, is formed in the gas turbine 12, this mixture being burned. This results in the exhaust gas of the gas turbine 12.

It can be seen from the direction arrow 18 that the exhaust gas is supplied to a steam generator 20 of the power plant 10. The steam generator 20 may be referred to as a boiler or evaporator. In addition, a fluid, e.g. water, is supplied to the steam generator 20. A transfer of heat is affected from the exhaust gas of the gas turbine 12 to the water, as a result of which the water is heated and evaporated. As a result, steam is generated from the water. This means that, by means of the exhaust gas of the gas turbine 12 and by means of the steam generator 20, steam is generated from the water (fluid) supplied to the steam generator 20. As a result of this transfer of heat from the exhaust gas to the water, the exhaust gas is cooled, such that it is removed from the steam generator 20, for example, at a first temperature T1. The first temperature T1 is, for example, at least substantially 90° C. (degrees Celsius).

The power plant 10 additionally comprises a turbine installation 22, which in the present case comprises a first turbine 24 and a second turbine 26. The turbine 24 may comprise a high-pressure turbine and turbine 26 may comprise a medium-pressure and low-pressure turbine. The steam generated by means of the exhaust gas of the gas turbine 12 and by means of the steam generator 20 is supplied to the turbine installation 22, such that the turbine installation 22, in particular the turbines 24 and 26, are driven by means of the generated hot steam. By means of the turbine installation 22, energy contained in the hot steam is converted to mechanical energy, the mechanical energy being provided via a shaft 28. The turbine installation 22 comprises, for example, turbine wheels, not represented in detail in the FIGURE, to which the steam is supplied. As a result, the turbine wheels are driven by means of the steam. The turbine wheels are connected, for example, in a rotationally fixed manner to the shaft 28, such that the shaft 28 is driven by the turbine wheels when the turbine wheels are driven by means of the steam.

The power plant 10 additionally comprises at least one generator 30, which can be driven, or is driven, by the turbine installation 22, via the shaft 28. The mechanical energy provided via the shaft 28 is thus supplied to the generator 30, at least a portion of the supplied mechanical energy being converted to electrical energy, or electric current, by means of the generator 30. The generator 30 can provide this electric current, which, for example, can be fed into an electricity grid.

The steam is removed from the turbine installation 22 and supplied to a heat exchanger 32, which may comprise a condenser. By means of the heat exchanger 32, the steam is cooled, as a result of which the steam condenses. As a result of this, the steam again becomes the aforementioned water, which can be supplied back to the steam generator 20. To cool the steam by means of the heat exchanger 32, a cooling medium, in particular a cooling fluid, may be supplied to the heat exchanger 32. A transfer of heat can then be affected from the steam to the cooling fluid, as a result of which the steam is cooled and subsequently condenses.

The power plant 10 has a plurality of lines, not represented in greater detail in the FIGURE, flowing through which there are respective flows of the steam generated by means of the exhaust gas of the gas turbine 12. These flows may have differing temperatures. Represented in the FIGURE are differing temperatures T2, T3, and T4 of the steam generated by means of the exhaust gas of the gas turbine 12, for example the temperature T2 being 595° C., the temperature T3 360° C., and the temperature T4 240° C. The water leaves the condenser, for example, at a temperature T5, which is, for example, 40° C.

Depending on the demand for electricity, the power plant 10 is activated, i.e. switched on, and/or deactivated, i.e. switched off. For example, the power plant 10 is switched off if there is only low demand for electricity. If the demand for electricity increases, then the power plant 10, after having been switched off, is switched on again. This switching-on subsequent to switching-off may be a warm start, to enable the power plant 10 to be switched on in a rapid and energy-efficient manner. To realize this warm start, in particular to realize a particularly energy-efficient warm start, the power plant 10, after having been switched off and during a period in which the power plant is switched off, is kept warm, or heated, in order to avoid excessive cooling off, or cooling down, of the power plant 10.

The gas turbine 12 provides its exhaust gas to the steam generator 20. In addition, the water is supplied to the steam generator 20. By means of the exhaust gas of the gas turbine 12 supplied to the steam generator, and by means of the steam generator 20, the water is heated and evaporated, at least partly, as a result of which steam is generated. In addition, the exhaust gas of the gas turbine 12 that is supplied to the steam generator 20 is removed, at least partly, from the steam generator 20.

To realize a particularly high efficiency, or particularly efficient operation, the power plant 10 may comprise a thermochemical heat accumulator 34 comprising at least one reactor. Since the exhaust gas of the gas turbine 12—relative to a direction of flow of the exhaust gas of the gas turbine 12—downstream from the steam generator 20, i.e. after the steam generator 20, has the temperature T1, the exhaust gas of the gas turbine 12 downstream from the steam generator 20 contains heat.

At least a portion of this heat contained in the exhaust gas of the gas turbine 12 downstream from the steam generator 20—as indicated in the FIGURE by a direction arrow 36—is supplied to the thermochemical heat accumulator 34 (reactor). This heat supplied to the thermochemical heat accumulator 34 is used to affect an endothermic chemical reaction. In other words, an endothermic chemical reaction is affected by means of the heat, from the exhaust gas removed from the steam generator 20, that is supplied to the thermochemical heat accumulator 34. As a result, the heat supplied to the thermochemical heat accumulator 34, or at least a portion of the heat supplied to the thermochemical heat accumulator 34, is stored in products of the endothermic chemical reaction, the stored heat being able to be used according to demand.

At least the portion of the heat contained in the exhaust gas of the gas turbine 12 downstream from the steam generator 20 is supplied to the thermochemical heat accumulator 34, in particular to the endothermic chemical reaction, or educts of the endothermic chemical reaction, for example via at least one heat exchanger 38, through which at least a portion of the exhaust gas flows. In this case, there is a transfer of heat from the exhaust gas, via the heat exchanger 38, to educts of the endothermic chemical reaction. Relative to the direction of flow of the exhaust gas, the heat exchanger 38 is arranged downstream from the steam generator 20.

As a result of the described transfer of heat, the exhaust gas is cooled. The exhaust gas that is supplied to the heat exchanger 38—as indicated in the FIGURE by a direction arrow 40—is, for example, removed from the heat exchanger 38, and downstream from the heat exchanger 38 has, for example, a temperature T6 that is 70° C. and less than the temperature T1. In addition, the exhaust gas may have a mass flow rate of 884 kg/s and a pressure of one bar. Furthermore, at least a portion of the exhaust gas flowing out of the steam generator 20 is supplied to the heat exchanger 38, or to the thermochemical heat accumulator 34.

The endothermic chemical reaction is, for example, a forward reaction of a chemical equilibrium reaction. In the course of the forward reaction, products of the endothermic chemical reaction are produced from the educts of the endothermic chemical reaction (forward reaction). This chemical equilibrium reaction also comprises a back reaction, realized as an exothermic chemical reaction. In this case the products of the forward reaction are educts of the back reaction, and products of the back reaction are the educts of the forward reaction. The forward reaction and/or the back reaction is/are affected, for example, in the reactor, i.e. in the thermochemical heat accumulator 34.

Heat is released in the course of the back reaction. This heat that becomes free or is released in the course of the back reaction can be used for heating purposes, in particular for district heating purposes. For example, it is conceivable to use heat released in the course of the back reaction to generate steam, and/or to heat, in particular to superheat, provided steam, in order to heat, for example, at least a portion of the power plant by means of the generated, or heated, steam, or alternatively to drive, in particular to accelerate, the turbine installation 22, such that, for example, the power plant can be ramped-up from a first load range into a second load range that is higher than the first.

In the present case, however, the heat released in the back reaction is used for heating purposes, in particular district heating purposes. In some embodiments, a fluid may be heated by means of the heat released in the back reaction. The water is supplied to a further heat exchanger 42 of the thermochemical heat accumulator, as indicated in the FIGURE by a direction arrow 44. The heat released in the back reaction is supplied, via the heat exchanger 42, to the water flowing through the heat exchanger 42, as a result of which the water is heated. The heated water is removed from the heat exchanger 42, as indicated in the FIGURE by a direction arrow 46. The water has, for example, a mass flow rate of 1100 kg/s (kilograms per second). The water is provided at a temperature T7, for example, the water being supplied at the temperature T7 to the heat exchanger 42. By means of the heat exchanger 42, the water is heated to a temperature T8, for example the temperature T7 being 65° C. (degrees Celsius) and the temperature T8 being 100° C. The temperature T8 is thus greater than the temperature T7, the water having the temperature T7 upstream from the heat exchanger 42, and the temperature T8 downstream from the heat exchanger 42. It is additionally provided, for example, that the water has a pressure of 14.5 bar, the water being provided at this pressure and at the temperature T7, and supplied to the heat exchanger 42.

Since the forward reaction is affected with the exhaust gas at 90° C., the thermochemical heat accumulator is charged at 90° C. Since the water is heated, by means of the thermochemical heat accumulator 34, to 130° C., the thermochemical heat accumulator 34 is discharged at 130° C.

The use of the heat exchanger 38 makes it possible to realize a spatial separation of the educts of the forward reaction from the exhaust gas, such that the exhaust gas does not come into direct contact with the educts of the forward reaction. Alternatively, it is conceivable that the exhaust gas does come into direct contact with the educts of the forward reaction, and in this case flows onto, or around, the educts. The heat exchanger 38, for example, is then omitted. This is also transferrable to the back reaction: the use of the heat exchanger 42 makes it possible to realize a spatial separation of the educts and/or products of the back reaction from the water that is heated by means of the released heat, such that the water does not come into direct contact with the educts and/or products of the back reaction. Alternatively, it is conceivable that the water does come into direct contact with the educts and/or products of the back reaction, and in this case flows onto, or around, the educts and/or products. The heat exchanger 42, for example, is then omitted.

The water heated by means of the thermochemical heat accumulator 34 can be used, for example, to supply households with hot water, and/or for household heating. As a result, a particularly efficient process overall can be realized. In addition, it is possible to realize particularly high flexibility of the heat supply. In particular, it is conceivable for peak loads, or high demands for heat, to be covered in an energy-efficient manner by means of the thermochemical heat accumulator 34, since at least a portion of the energy contained in the exhaust gas downstream from the steam generator 20 is used, at least indirectly, to heat the water. Depending on the mass flow rate of the exhaust gas and of the water, it is conceivable to supply only a portion of the exhaust gas downstream from the steam generator 20 to the heat exchanger 38, and/or only a portion of the water to the heat exchanger 42, to ensure, in particular, an at least substantially continuous heating of the water by means of the thermochemical heat accumulator 34.

Claims

1. A method for operating a gas-and-steam combined-cycle power plant, the method comprising:

providing exhaust gas from a gas turbine to a steam generator;

generating steam by means of the exhaust gas;

driving a generator with the steam via a turbine installation to provide an electric current;

removing the exhaust gas from the steam generator; and

using

at least a portion of heat contained in the exhaust gas downstream from the steam generator to affect an endothermic chemical reaction.

2. The method as claimed in claim 1, wherein the at least a portion of the heat contained in the exhaust gas downstream from the steam generator is transferred via a heat exchanger to educts of the endothermic chemical reaction.

3. The method as claimed in claim 1, further comprising:

branching-off at least some of the steam generated by the steam generator and storing the at least some of the steam in a steam accumulator;

removing at least a portion of the steam stored in the steam accumulator from the steam accumulator;

heating the at least a portion of the steam removed from the steam accumulator with heat released in an exothermic chemical reaction; and

routing the heated steam to the turbine installation to drive the turbine installation with the heated steam.

4. The method as claimed in claim 3, further comprising using products of the endothermic chemical reaction as educts of the exothermic chemical reaction.

5. The method as claimed in claim 3, further comprising supplying the heated steam to the turbine installation to ramp up the gas-and-steam combined-cycle power plant from a first load range into a second load range that is higher than the first load range.

6. The method as claimed in claim 5, wherein the endothermic chemical reaction is affected in the second load range.

7. (canceled)