CA2618016A1

CA2618016A1 - A method for operating a gas turbine as well as a gas turbine for implementing the method

Info

Publication number: CA2618016A1
Application number: CA002618016A
Authority: CA
Inventors: Eribert Benz; Manfred Wirsum
Original assignee: Individual
Current assignee: Ansaldo Energia IP UK Ltd
Priority date: 2005-08-10
Filing date: 2006-08-07
Publication date: 2007-02-15
Anticipated expiration: 2026-08-07
Also published as: CA2618016C; JP2009504966A; DE112006001975A5; WO2007017487A1; DE112006001975B4

Abstract

The invention relates to a method for operating a gas turbine (11) in a combined cycle power plant (40), in which method air, which is used to burn a syngas that is recovered from coal, is drawn in and compressed by the gas turbine (11), the compressed air is fed into a combustor (18, 19) [text does not give specific combuster references though the list does] and such that a portion of the compressed air is separated into oxygen and nitrogen. An improved degree of efficiency is achieved by this method by virtue of the fact that a gas turbine (11) with reheating and two combustors (18, 19) [text does not give specific combuster references though the list does] and two turbines (16,17) is used. In the first combustor (18), syngas is burned using the compressed air, and the resultant hot gases are expanded in the first turbine (16). In the second combustor, syngas is burned using the gases coming from the first turbine (16) and the resultant gases are expanded in the second turbine (17) such that the nitrogen that occurs in the separation of the air is led to the gas turbine (11) to be compressed.

Description

SPECIFICATION
A METHOD FOR OPERATING A GAS TURBINE AS WELL AS A GAS TURBINE
FOR IMPLEMENTING THE METHOD
TECHNICAL FIELD

The present invention relates to the field of power plant technology. It pertains to a method for operating a (stationary) gas turbine according to the over-arching concept of Claim 1, as well as to a gas turbine for implementing the method.
PRIOR ART

A gas turbine with reheating (reheat gas turbine) is known (see, for example, the US patent application US-A-5,577,378 or "State-of-the-art gas turbines - a brief update," ABB Review 02/1997, Fig. 15, turbine type GT26), which combines flexible operation with very low flue gas emission values.

The machinery architecture of the gas turbine of Type GT26 is unique and is exceptionally well-suited to realizing a concept that is the subject matter of the present invention, because:
- even in the case of the compressor, there is a significant diversion of compressor air at intermediate compressor pressures, - the concept of sequential combustion renders an increased stability of combustion possible in conjunction with reduced levels of excess oxygen, and a secondary air system is present, which renders it possible to divert air from the compressor, to cool it down, and to use the cooled air for cooling the combustor and the turbine.
The principle of the known gas turbine with reheating is shown in Fig. 1. The gas turbine 11, which is a portion of a combined cycle power plant 10, comprises two

2 connected compressors, arranged behind one another on a commonly shared shaft 15, namely a low pressure compressor13 and a high pressure compressor14, as well as two combustors, namely a high pressure combustor 18 and a reheat combustor 19, and the pertinent turbines, namely a high pressure turbine16 and a low pressure turbine 17. The shaft 15 drives a generator 12.
The manner in which the unit works is as follows: air is drawn in from the low pressure compressor 13 via an air inlet 20, and is compressed initially to a level of intermediate pressure (ca. 20 bar). The high pressure compressor14 then further compresses the air to a level of high pressure (ca.32 bar). Cooling air is diverted at both the level of intermediate pressure and at the level of high pressure and cooled down in pertinent OTC coolers (OTC = Once Through Cooler) 23 and 24 and conducted further to the combusters 18 and 19 [text does not give specific combuster references though the list does] and turbines 16, 17 for cooling purposes. The remaining air from the high pressure compressor 14 is led to the high pressure combustor 18, and heated there by the combustion of a fuel introduced by fuel feedline 21. The resultant flue gas is then expanded in the downstream high pressure turbine 16 to an intermediate level of pressure as it performs work. After expansion, the flue gas is heated again in the reheat combustor 19 by the combustion of a fuel introduced by fuel feedline 22 before it is expanded in the downstream low pressure turbine 17, performing additional work in the process.

The cooling air, which flows through the cooling lines 25, 26, is sprayed in at suitable points of the combustors 18, 19 [text does not give specific combuster references though the list does] and turbines 16, 17 to limit the material temperatures to a reasonable degree. The flue gas coming out of the low pressure turbine 17 is sent through a heat recovery steam generator 27 (HRSG) to generate steam, which flows through a steam turbine 29 within a water-steam circuit, and performs additional work there. After flowing through the heat recovery steam generator 27, the flue gas is finally given off to the outside through a flue

3 gas line 28. The OTC coolers 23, 24 are part of the water-steam circuit;
superheated steam is generated at their outlets.

Due to the two combustions in the combustors 18 and 19, [text does not give specific combuster references though the list does] which are independent of each other and follow each other in sequence, great operational flexibility is achieved;
the temperatures in the combustors can be adjusted in such a way that the maximum degree of efficiency is achieved within the existing limits. The low flue gas levels of the sequential combustion system are the result of the inherently low emission levels that can be achieved in the case of reheating (under certain conditions, the second combustion even leads to a consumption of NOx).

On the other hand, combined cycle power plants with single stage combustion in the gas turbines are known (see, for example, the US patent application US-A-

4,785,622 or US-B2-6,513,317), in which a coal gasification unit is integrated in order to provide the requisite fuel for the gas turbine in the form of syngas, which is recovered from coal. Such combined cycle power plants are designated IGCC
(Integrated Gasification Combined Cycle) plants.

The present invention now proceeds from the recognition that due to the use of gas turbines with reheating in an IGCC plant, the advantages of this type of gas turbine can be made usable for the plant in a particular manner.
REPRESENTATION OF THE INVENTION
It is the invention's task to indicate a method for the operation of a gas turbine, especially one that works in concert with a coal gasifier, which is characterized by an improved degree of efficiency, which also exhibits, in particular, the advantages of intermediate cooling [sic-not reheating?-Trans.], as well as to create a gas turbine for implementing the method.

The task is realized by the totality of the characteristics of Claims 1 and.
8. It is essential that a gas turbine with reheating be used in a gas turbine unit that works with syngas from a coal gasifier, which comprises two combustors and two turbines, in which, in the first combustor, syngas is burned using the compressed air, and the resultant hot gases are expanded in the first turbine, and in which syngas is burned in the second combustor, using the gases that come from the first turbine, and the resultant hot gases are expanded in the second turbine and the nitrogen that occurs in the separation of the air is led to the gas turbine to be compressed again. Due to the addition of the comparatively cold nitrogen to the compressor, the compressor air is cooled, and the result is a kind of compressor-[related] intermediate cooling that is associated with all the advantages of such intermediate cooling. In addition to the advantages with respect to the thermodynamic degree of efficiency, the temperature in the compressor is reduced, which leads to a reduction of the quantity of cooling air that is required, or renders the additional cooling of the cooling air unnecessary.

One embodiment of the method according to the invention is characterized [in]
that the gas turbine comprises an first compressor for the compression of drawn in air to an first pressure stage and a second compressor for the further compression of the air from the first pressure stage to a second, higher pressure stage, that a portion of the air coming from the first compressor is separated into oxygen and nitrogen and that the nitrogen that occurs in the course of this separation is led to the second compressor to be compressed.

In the process, the nitrogen preferably undergoes pre-compression in another compressor before it is led to the second compressor.

The pre-compressed nitrogen can, in the process, be led to the inlet of the second compressor, in particular.
Another embodiment of the method according to the invention is characterized in that the gas turbine exhibits an first compressor for the compression of drawn in air to an first pressure stage and a second compressor for the further compression of the air from the first pressure stage to a second, higher pressure stage, that a portion of the air coming out of the first compressor is separated into oxygen and nitrogen, and that the nitrogen that occurs in the course of this separation is led to

5 the first compressor to be compressed.

In the process, the nitrogen can be conducted to the first compressor at an intermediate stage. Alternatively, however, it can also be conducted to the inlet of the first compressor.
An embodiment of the gas turbine according to the invention is characterized in that two compressors, one connected behind the other, are provided, that the nitrogen line is led back to the second compressor, and that an additional compressor is provided in the nitrogen line.
In particular, the nitrogen line can be led back to the inlet of the second compressor.

Another embodiment is characterized in that two compressors, one connected behind the other, are provided and that the nitrogen line is led back to the first compressor, either to the inlet of the first compressor or to an intermediate stage of the first compressor.

Preferably, the air separation unit exhibits an oxygen line on the same side of its outlet for the purpose of giving off the oxygen that occurs in the course of the separation, which is led to a unit for the purpose of generating syngas by means of coal gasification in which a syngas feed line transports the syngas that is generated from the syngas generation unit to the combustors.

6 BRIEF EXPLANATION OF THE FIGURES

In what follows, the invention is to be illustrated in greater detail by virtue of the embodiment examples in conjunction with the drawing.
Fig. 1 shows the simplified schematic of a combined cycle power plant with a gas turbine with reheating or sequential combustion in accordance with the prior art;

Fig. 2 shows the simplified schematic of an IGCC plant with a gas turbine with reheating or sequential combustion, respectively, as it lends itself to the realization of the invention;

Fig. 3 shows an first embodiment example of the return of the nitrogen recovered in the separation of the air to the compressor, in a unit of the type shown in Fig. 2; and Fig. 4 shows a second embodiment example of the return of the nitrogen recovered in the separation of the air to the compressor in a unit of the type depicted in Fig. 2, according to the invention.

WAYS OF EXECUTING THE INVENTION

In Fig. 2 in a markedly simplified schematic, an IGCC plant with a gas turbine with reheating or sequential combustion, respectively, is shown as it lends itself to the realization of the invention. The combined cycle power plant 30 comprises a gas turbine 11 with a low pressure compressor 13, a downstream high pressure compressor 14, a high pressure combustor 18 with a downstream high pressure turbine 16 and a reheat combustor 19 with a downstream low pressure turbine 17.
The compressors 13, 14 and the turbines 16, 17 sit on a commonly shared shaft 15, by means of which a generator 12 is driven. Via feedline 31, the combustors 18 and 19 [text does not give specific combuster references though the list does]

7 are supplied with syngas as fuel, which is generated by the gasification of coal (coal feeding 33) in a coal gasifier 34. The coal gasifier 34 is topped by a cooling device 35 for the syngas, a filtering device 36 and a C02 separator 37 with a outlet 38 for giving off the separated CO2.
Oxygen (02), which is recovered in an air separation unit 32, and introduced via an oxygen line 32a, is used to gasify the coal in the coal gasifier 34. The air separation unit 32 receives compressed air from the outlet of the low pressure compressor 13. The nitrogen (N2), which also occurs in the separation, is led, for example, to the low pressure combustor 19 via nitrogen line 32b.

To cool the components of the combustors 18, 19 and turbines 16, 17 [text does not give specific combuster and turbine references though the list does] that have been exposed to hot gas, compressed cooling air is tapped off at the outlets of the two compressors 13 and 14, cooled off in a topped OTC cooler 23 or 24 and then led to the points to be cooled via the corresponding cooling lines 25 and 26.

At the outlet of the low pressure turbine 17, a heat recovery steam generator 27 is provided, which, together with a steam turbine 29 that is connected, is part of a water-steam circuit. The flue gas that emerges from the heat recovery steam generator 27 is released to the outside via a flue gas line 28.

In such a plant configuration, according to Fig. 3 or 4, the use of the cool nitrogen that occurs in the separation of the air is now rearranged. In the combined cycle power plant 40 of Fig. 3, the reheat combustor 19 and the low pressure turbine are cooled now, as in the past, by compressed air that is diverted at the outlet of the low pressure compressor 13, and then cooled down in an OTC cooler 23. The same also applies to the high pressure combustor 18 and the high pressure turbine 16, with the distinction that in the latter case, the OTC cooler 24 is no longer necessary.

8 According to Fig. 3, this is achieved in the following manner: the nitrogen (N2) that occurs in the air separator 32 in conjunction with the separation of the air is fed into the high pressure compressor 14 via the nitrogen line 32b, and compressed there. In order to arrive at the requisite pressure level, an additional compressor 39, which compresses the nitrogen, is connected to the nitrogen line 32b. In Fig.
3, the nitrogen is input directly into the inlet of the high pressure compressor 14. It is also conceivable, however, for it to be introduced to the high pressure compressor 14 in an intermediate stage.

In the alternative configuration that is depicted in Fig. 4, the nitrogen coming out of the air separator 32 is fed into the low pressure compressor 13 via the nitrogen line 32b, either in an intermediate stage (continuous line in Fig. 4), or directly at the entrance of the low pressure compressor (line of dashes in Fig. 4). Pre-compression is not necessary in these cases.
To summarize, the principle of the invention can be described as follows:
At an intermediate level of pressure (ca. 11-20 bar), air is diverted at the compressor and led to an air separation unit.
The nitrogen that occurs in the separation of the air, which exhibits a comparatively low temperature, is led back to the compressor, either to the input of the compressor or o to an intermediate stage that is lower than the intermediate stage at which the air was diverted, or o to exactly the intermediate stage at which the air was also diverted.
In all three instances, the cool nitrogen cools the compressor air, thus representing a kind of "intermediate compressor cooling," with which all the known advantages of intermediate cooling are associated.

A prerequisite for the realization of this concept is that in both combustors of the gas turbine, undiluted coal gas (without the addition of N2) can be used.
Since the separation of the air provides relatively cold nitrogen, and the nitrogen is not

9 needed for dilution in the combustor (as this is shown in Fig. 2), the nitrogen can be used very effectively for the intermediate cooling. By these means, it becomes possible (see Fig. 4) to dispense with both OTC coolers (23, 24) for the cooling of the cooling air.

List of Reference Signs

10,30,40 combined cycle power plant

11 gas turbine

12 generator

13 low pressure compressor

14 high pressure compressor shaft (gas turbine) 16 high pressure turbine 17 low pressure turbine 18 high pressure combustor 19 reheat combustor air inlet 21,22 fuel feedline 23,24 OTC cooler 25,26 cooling line 27 heat recovery steam generator 28 flue gas line 29 steam turbine (steam cycle) 31 syngas feed line 32 air separation unit 32a oxygen line 32b nitrogen line 33 coal feeding 34 coal gasifier 35 cooling device 36 filtering device 37 CO2 separator 38 CO2 outlet 39 compressor

Claims

1. ~A method for the operation of a gas turbine (11), which is used, in particular, in a combined cycle power plant (30, 40), in which method air is drawn in and compressed by the gas turbine (11), the compressed air is led to a combustor (18, 19) to burn a syngas that is recovered from coal, and the hot gases that occur in conjunction with the combustion are expanded in a downstream turbine (16, 17) as they do work, such that a portion of the compressed air is separated into oxygen and nitrogen, and the oxygen is used in a coal gasifying plant (34) to generate the syngas and such that a portion of the compressed air is used to cool those parts of the gas turbine (11) that were exposed to the hot gases, characterized in that - ~a gas turbine (11) with reheating is used, which comprises two combustors (18, 19) and two turbines (16, 17) such that, in the first combustor (18), syngas is burned using the compressed air and the resultant hot gases are expanded in the first turbine (16) and such that, in the second combustor, syngas is burned using the gases coming from the first turbine (16) and the resultant hot gases are expanded in the second turbine (17), and the nitrogen that occurs in conjunction with the separation of the air is conducted to the gas turbine (11) for compression.

2. ~A method according to Claim 1, characterized in that the gas turbine (11) comprises a first compressor (13) for compressing drawn in air to an first stage of pressure and a second compressor (14) for compressing the air further from the first pressure stage to a second, higher pressure stage, that a portion of the air coming from the first compressor (13) is separated into oxygen and nitrogen, and that the nitrogen that occurs in this separation is led to the second compressor (14) to be compressed.

3. ~A method according to Claim 2, characterized in that the nitrogen undergoes first compression in another compressor (39) before it is led to the second compressor (14).

4. ~A method according to Claim 3, characterized in that the pre-compressed nitrogen is led to the inlet of the second compressor (14).

5. ~A method according to Claim 1, characterized in that the gas turbine (11) comprises an first compressor (13) for compressing drawn in air to an first pressure stage, and a second compressor (14) for compressing the air further from the first pressure stage to a second, higher pressure stage, that a portion of the air coming from the first compressor (13) is separated into oxygen and nitrogen and that the nitrogen that occurs in the course of this separation is led to the first compressor (13) to be compressed.

6. ~A method according to Claim 5, characterized in that the nitrogen is led from the first compressor (13) to an intermediate stage.

7. ~A method according to Claim 5, characterized in that the nitrogen is led to the inlet of the first compressor (13).

8. ~A gas turbine (11) for implementing the method according to Claim 1, which gas turbine (11) is designed as a gas turbine with reheating and comprises compressors (13, 14) for compressing drawn in air as well as two combustors (18, 19) and two turbines (16, 17), such that in the first combustor (18) a fuel is burned using the compressed air and the resultant hot gases are expanded in the first turbine (16) and such that, in the second combustor, the fuel is burned using the gases coming from the first turbine (16) and the resultant hot gases are expanded in the second turbine (17), characterized in that an air separation unit (32) is provided, which, on the same side as its inlet, is connected to the compressors (13, 14) and on the same side as its outlet, exhibits a nitrogen line (32b) for giving off the nitrogen that occurs in conjunction with the separation, and that the nitrogen line (32b) is led back to the compressors (13, 14).

9. ~A gas turbine according to Claim 8, characterized in that two compressors (13, 14), one connected behind the other, are provided, and that the nitrogen line (32b) is led back to the second compressor (14) and that an additional compressor (39) is provided in the nitrogen line (32b).

10. ~A gas turbine according to Claim 9, characterized in that the nitrogen line (32b) is led back to the inlet of the second compressor (14).

11. ~A gas turbine according to Claim 8, characterized in that two compressors (13, 14), one connected behind the other, are provided and that the nitrogen line (32b) is led back to the first compressor (13).

12. ~A gas turbine according to Claim 11, characterized in that the nitrogen line (32b) is led back to the inlet of the first compressor (13).

13. ~A gas turbine according to Claim 11, characterized in that the nitrogen line (32b) is led back to an intermediate stage of the first compressor (13).

14. ~A gas turbine according to one of the Claims 6 through 13, characterized in that the air separation unit (32), on the same side as its outlet, exhibits an oxygen line (32a) to give off the oxygen that occurs in the course of the separation, which is led to a unit (33,..,38) [note that these reference numbers do not refer to anything called a "unit" on the reference list] for the generation of syngas by means of gasifying coal, and that a syngas feedline (31) transports the syngas that is generated from the unit (33,..,38) [note that these reference numbers do not refer to anything called a "unit" on the reference list] for the generation of syngas to the combustors (18, 19) [text does not give specific combuster references though the list does] .