Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-03-30
2002-12-03
Gartenberg, Ehud (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039120, C060S806000
Reexamination Certificate
active
06487863
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains generally to gas turbines and more particularly to high temperature gas turbines that employ a cooling medium to maintain the components within the working gas flow path within acceptable temperature limits.
BACKGROUND OF THE INVENTION
In most industrial combustion turbines, ambient air is drawn into the intake of a compressor, compressed and delivered to a combustion where it is combined with a fuel, ignited and transported through a transition member to a turbine wherein the working gas is expanded to produce mechanical energy. The compressor and turbine rotor are typically coupled to a common shaft so that rotation of the turbine rotor drives the compressor. Similarly, in power plant applications, the turbine rotor is also connected to a generator rotor to drive the generator to produce electricity.
A typical combustion turbine system
10
portion of such a power plant is illustrated in FIG.
1
. Generally, the combustion turbine is made up of a compressor section
12
, a combustion section
34
and a turbine section
41
. The compressor section
12
is made up of a plurality of stationary vanes
14
supported by the outer housing and rotating blades
16
which are mounted on a common shaft
18
. Each rotating blade row followed by a stationary vane row constitutes a compressor stage.
FIG. 1
shows sixteen compressor stages. The compressor shown is also equipped with an inlet guide vane (IGV)
9
, and an outlet guide vane (OGV)
29
. The compressor is also arranged to form compressor bleed ports
22
,
24
and
26
for bleeding compressed air for cooling high temperature turbine components. Ambient air
13
is introduced through an inlet
11
and successively compressed in each compressor stage, and it flows by all the bleed ports
22
,
24
and
26
, and the rest of compressor stages
28
, and OGV
29
after which the compressed air travels through annular diffuser
30
to compressed air plenum
32
which surrounds the combustion
34
and transition member
36
. A portion of the compressed air
13
can be diverted from each of the bleed ports for cooling turbine components as discussed above. A portion of the compressed air, as shown by the arrow, reverses direction in the plenum
32
and travels between the combustion housing
38
and the combustion shell
40
where it is directed to a combustion inlet and combined with fuel introduced through the nozzle inlets
42
. The combined fuel and compressed air is burned in the combustion
34
to create a working gas which is directed through the transition member
36
to an inlet
44
to the first stage of the turbine
41
. The turbine section
41
is made up of a serial arrangement of stationary vanes
52
and rotating blades
54
. The rotating blades are supported by a common rotor system
56
and the vanes and blades are arranged in serial stages
44
,
46
,
48
and
50
, which form the first through fourth stages of the turbine section. The working gas exiting the transition member
36
then expands through the stages
44
,
46
,
48
and
50
causing rotation of the blades
54
which in turn impart mechanical, rotational power to the rotor system
56
. The turbine rotor system
56
is connected to the compressor shaft
18
so that rotation of the turbine rotor system
56
drives the compressor
12
. Normally, in power plant applications, the rotor system
56
is coupled to the rotor of a generator to drive the generator to create electricity. The working gas ultimately is exhausted at the exit to the turbine
58
and directed through an exhaust stack to the ambient atmosphere.
It is generally desirable to have the turbine work at the highest efficiency possible. It is also known that the higher the temperature of the working gas, the higher the efficiency of the turbine. However, the upper temperature that the working gas can practically function at is limited by the temperature characteristics of the materials that it interfaces with. In addition, the higher the temperature of the combustion process and working gas, the more pollutants such as NO
x
that are created. Stringent environmental restrictions require such pollutants to be kept below a minimal level. These competing interests have been addressed by leaning out the combustion mixture to reduce flame temperature while maintaining an overall higher average thermal output and cooling the various components interfacing with the working gas flow path.
A system which has been employed for cooling the various turbine components is illustrated in FIG.
1
. The cooling system shown is an open loop cooling system wherein compressed air is introduced into the various components and after traversing a cooling path within a component, is exhausted into the working gas within the turbine, providing power augmentation. To assure that the working gas does not backflow through the cooling system, the pressure of the compressed air has to be greater than that of the working gas at the point at which the cooling air is introduced into the working gas flow path. In this regard, air
60
is bled from the first bleed port
22
of the compressor and introduced at the fourth stage
50
of the turbine to cool the turbine stationery components before being introduced into the working gas flow path around the rotating blades
54
at a point where the working gas is at its lowest pressure among the turbine stages. Similarly, air
62
is bled from a second bleed port
24
of the compressor
12
and introduced at the third stage
48
of the turbine
41
; and air
64
is bled from the third bleed port
26
of the compressor
12
and introduced at the second stage
46
of the turbine. The compressed air exiting the compressor outlet
30
is used to cool the combustion shell and liner and the transition member before being introduced into the working gas path within those components. The air
66
exiting the compressor outlet
30
is also used to cool the first stage of the turbine and further diverted, as represented by reference character
68
, to cool the internal components of the rotor and the rotating blades
54
, before being introduced into the working gas flow path. In this manner, the internal components of the combustion, transition and turbine are able to accommodate higher temperatures for greater overall turbine efficiency. However, diverting compressed air from the compressor for cooling has a negative affect on the efficiency of the operation of the turbine in that there is less air available for combustion and to be introduced at the first stage of the turbine for power conversion from thermal power to mechanical power. Accordingly, it is desirable to find another means of cooling the turbine components interfacing with the working gas flow path that does not require or minimizes the diversion of air from the compressor. Accordingly, it is an object of this invention to provide a system that minimizes the use of compressed air for cooling a turbine's internal components along the working gas flow path.
SUMMARY OF THE INVENTION
The instant invention takes advantage of a nitrogen source in a power plant to supply nitrogen in lieu of compressed air to at least a portion of the cooling circuit in a combustion turbine. In a preferred arrangement, the nitrogen is supplied from an air separation unit that separates oxygen from the nitrogen in the air for use in an integrated gasification combined cycle (IGCC) plant. Upon startup of the plant, air is initially supplied to the cooling circuit of the combustion turbine until the nitrogen becomes available. In one preferred arrangement, a cooling control system monitors the availability of nitrogen and controls valves within separate legs of the combustion turbine cooling circuit to supply the nitrogen in lieu of the compressed air sequentially, one leg at a time as the nitrogen becomes available. In a preferred scheme, the cooling leg corresponding to the hottest turbine components is supplied nitrogen first along with compressed air until sufficient nitrogen is available to replace th
Chen Allen G.
Horazak Dennis A.
Gartenberg Ehud
Siemens Westinghouse Power Corporation
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