PROCEDE POUR ACTIONNER UNE TURBINE A GAZ ET TURBINE A GAZ APPROPRIEE POUR METTRE LEDIT PROCEDE EN OEUVRE

A METHOD FOR OPERATING A GAS TURBINE AS WELL AS A GAS TURBINE FOR IMPLEMENTING THE METHOD

Abrégé français

L'invention concerne un procédé permettant d'actionner une turbine à gaz (11) dans une centrale mixte (40), selon lequel la turbine à gaz (11) aspire de l'air et le comprime et l'air comprimé est cheminé jusqu'à une chambre de combustion (18, 19), pour assurer la combustion d'un gaz de synthèse extrait du charbon. Une partie de l'air comprimé est décomposée en oxygène et en azote. Un meilleur rendement est obtenu, du fait qu'il est prévu d'utiliser une turbine à gaz (11) à surchauffe intermédiaire, qui comprend deux chambres de combustion (18) et deux turbines (16, 17). Un gaz de synthèse est brûlé dans la première chambre de combustion (18), avec l'air comprimé et les gaz chauds produits sont détendus dans la première turbine (16). Du gaz de synthèse est brûlé dans la seconde chambre de combustion avec les gaz provenant de la première turbine (16) et les gaz chauds produits sont détendus dans la seconde turbine (17). L'azote dégagé lors de la séparation de l'air est utilisé pour refroidir la turbine à gaz (11).

Abrégé anglais

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.

Revendications

11
CLAIMS
1. A method for the operation of a gas turbine, wherein the gas turbine
comprises a first compressor for compressing drawn in air to a first stage of
pressure and a second compressor for further compressing air from the first
pressure stage to a second, higher pressure stage, the method comprising:
drawing in air and compressing said air with said first and second
compressors of the gas turbine;
conducting the compressed air to a combustor;
combusting said compressed air with a syngas in said combustor, said
syngas recovered from coal, to generate hot gases;
expanding the hot gases from the combustion in a downstream turbine as
said hot gases do work;
separating a portion of the compressed air from the first compressor into
oxygen and nitrogen;
using the oxygen in a coal gasifying plant to generate said syngas;
cooling portions of the gas turbine that are exposed to hot gases with a
portion of the compressed air;
wherein said gas turbine comprises a reheating gas turbine including a first
combustor, a second combustor, a first turbine, and a second turbine;
wherein combusting comprises combusting said syngas in the first
combustor with the compressed air;
wherein expanding the hot gases comprises expanding in the first turbine;
combusting syngas in the second combustor with gases from the first
turbine;
expanding hot gases from the second combustor in the second turbine; and
conducting the nitrogen from said separating to, and compressing said
nitrogen in, said gas turbine.
2. A method according to claim 1, further comprising; conducting said
nitrogen from said separating to the second compressor.

12
3. A method according to claim 2, further comprising: compressing said
nitrogen from said separating in another compressor, to generate pre-
compressed
nitrogen, before it is conducted to the second compressor.
4. A method according to claim 3, comprising: conducting said pre-
compressed nitrogen to an inlet of the second compressor.
5. A method according to claim 1, further comprising: conducting said
nitrogen from said separating back to the first compressor.
6. A method according to claim 5, wherein conducting the nitrogen
comprises conducting from the first compressor to an intermediate stage.
7. A method according to claim 5, wherein conducting the nitrogen
comprises conducting to an inlet of the first compressor.

Description

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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, 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

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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

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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 N0x).
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.
f-

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SUMMARY OF THE INVENTION
Some embodiments of the present disclosure proceed 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.
According to an aspect of the present invention, there is provided a method
for the
operation of a gas turbine, wherein the gas turbine comprises a first
compressor for
compressing drawn in air to a first stage of pressure and a second compressor
for
further compressing air from the first pressure stage to a second, higher
pressure
stage, the method comprising: drawing in air and compressing said air with
said first
and second compressors of the gas turbine; conducting the compressed air to a
combustor; combusting said compressed air with a syngas in said combustor,
said
syngas recovered from coal, to generate hot gases; expanding the hot gases
from
the combustion in a downstream turbine as said hot gases do work; separating a
portion of the compressed air from the first compressor into oxygen and
nitrogen;
using the oxygen in a coal gasifying plant to generate said syngas; cooling
portions of
the gas turbine that are exposed to hot gases with a portion of the compressed
air;
wherein said gas turbine comprises a reheating gas turbine including a first
combustor, a second combustor, a first turbine, and a second turbine; wherein
combusting comprises combusting said syngas in the first combustor with the
compressed air; wherein expanding the hot gases comprises expanding in the
first
turbine; combusting syngas in the second combustor with gases from the first
turbine;
expanding hot gases from the second combustor in the second turbine; and
conducting the nitrogen from said separating to, and compressing said nitrogen
in,
said gas turbine.
Some embodiments of the present disclosure are directed to 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

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particular, the advantages of intermediate cooling, as well as to create a gas
turbine
for implementing the method.
In one embodiment, a gas turbine with reheating is used in a gas turbine unit
that
works with syngas from a coal gasifier, which comprises two combustors and two
5 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.
In one embodiment of the method, 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, a portion of the air coming from the first compressor is
separated into
oxygen and nitrogen and the nitrogen that occurs in the course of this
separation is
led to the second compressor to be compressed.
In the process, in some embodiments, the nitrogen preferably undergoes pre-
compression in another compressor before it is led to the second compressor.
In some embodiments, the pre-compressed nitrogen can, in the process, be led
to
the inlet of the second compressor, in particular.

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5a
In another embodiment of the method, the gas turbine exhibits a 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 the first compressor to be compressed.
In the process, in some embodiments, 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.
In an embodiment of the gas turbine, two compressors, one connected behind the
other, are provided, the nitrogen line is led back to the second compressor,
and 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.
In another embodiment, two compressors, one connected behind the other, are
provided and 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.
In some embodiments, 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.

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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 an embodiment 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.
DESCRIPTION OF EMBODIMENTS
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.
= 30 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]

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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 002 separator 37 with a
CO2
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
17
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.

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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
_ 0 to the input of the compressor or
0 to an intermediate stage that is lower than the intermediate stage at
which the air was diverted, or
0 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 cornbustors
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

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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.

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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

Dessin représentatif