Power plants – Combustion products used as motive fluid – Plural combustion products generators in ring coaxial with...
Reexamination Certificate
1999-11-10
2001-09-04
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Plural combustion products generators in ring coaxial with...
C060S760000
Reexamination Certificate
active
06282886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a combustor of a gas turbine, and more particularly to a combustor structured such that uniformity of combustion air intake is attained so as to enhance combustion efficiency and combustor cooling ability, as well as a fitting structure of structural portions which are less durable against thermal stress, such as a combustor main swirler or a pilot cone. They are improved so as to not be influenced by high temperature, whereby overall efficiency of the gas turbine combustor is enhanced in view of recent tendencies of higher temperature combustion gas. The present invention also relates to a combustor of a gas turbine having reduced combustion vibration.
2. Description of the Prior Art
FIG. 20
shows a structural arrangement of a representative gas turbine combustor and surrounding portions thereof in the prior art. In
FIG. 20
, numeral
20
designates a combustor, which is provided in a turbine casing
50
. Numeral
21
designates main fuel nozzles provided in plural pieces in a circumferential direction the combustor and is to be supplied with a main fuel of oil or gas. Numeral
22
designates a pilot fuel nozzle, which is provided in a central portion of the plural main fuel nozzles
21
for igniting the main fuel nozzles
21
. Numeral
23
designates a combustion chamber, and numeral
24
designates a tail tube, from which a high temperature gas produced in the combustion chamber
23
is led into a gas turbine. Numeral
62
designates a compressor, numeral
63
designates an air outlet, numeral
64
designates an air separator for supplying gas turbine blades with outside air for cooling thereof, numeral
65
designates a gas turbine stationary blade and numeral
66
designates a gas turbine moving blade.
In the combustor constructed as mentioned above, air
40
coming from the compressor
62
flows into the turbine casing
50
via the air inlet
63
and further flows into the combustor
20
, for effecting combustion, from around the combustor
20
through spaces formed between stays, described later, as air shown by numerals
40
a,
40
b.
In the flow of the air
40
at this time, there arises differences in the flow rate and pressure between the air
40
a
which is near the air outlet
63
or the compressor
62
and the air
40
b
which is far from the air outlet
63
or the compressor
62
. This causes a non-uniformity in the air flow entering the combustor
20
according to the circumferential directional position thereof, with the result that a biased flow of air arises in an inner tube, described later, in the combustor
20
, causing a non-uniformity of fuel flow as well, which leads to an increase of NO
x
formation.
FIG. 21
is an enlarged schematic view of the gas turbine combustor of FIG.
20
. In
FIG. 21
, there are shown several structural portions having shortcomings to be addressed. That is, an (X-
1
) portion and an (X-
2
) portion are air intake portions into the fuel nozzles, an (X-
3
) portion is a main swirler fitting structural portion, an (X-
4
) portion is a pilot cone fitting structural portion and an (X-
5
) portion is a tail tube cooling structural portion. There are problems to be solved in the respective portions. Such problems as exist in the present situation will be sequentially described below.
The air intake portion (X-
1
) will be described first.
FIG. 22
is a cross sectional view of a top hat type fuel nozzle portion of a prior art gas turbine. In
FIG. 22
, the air
40
a,
40
b
coming from the compressor flows into the combustor
20
for effecting a combustion from around the combustor
20
through spaces formed between supports
25
provided in the combustor
20
. Between the air
40
a
which is near the compressor and the air
40
b
which is far from the compressor, there are differences in the flow passages themselves and the shapes thereof, which causes a non-uniformity in the flow rate of the air flowing into the combustion chamber
23
according to the circumferential directional position thereof so as to cause a biased flow of the air. By this biased flow of the air, fuel flow also becomes non-uniform in the combustion chamber, and NO
x
formation increases. It is needed, therefore, that the air flow into the combustor be uniform in the circumferential direction.
Also, in the combustor of
FIG. 22
which is of the top hat type, there is fitted to the turbine cylinder
50
an outer tube casing cover
51
for covering a portion where the fuel nozzles are inserted. On the other hand, in the combustor of
FIG. 20
, the air intake portion is arranged in a space formed by a cylindrical casing of the turbine casing
50
. In the example of
FIG. 22
, a portion surrounding the supports
25
as the air intake portion is covered by the cylindrical outer tube casing cover
51
. The outer tube casing cover
51
is of a hat-like shape which projects toward the outside. In this type of combustor, a central axis
61
of the outer tube casing cover
51
of the turbine casing
50
and a central axis
60
of the combustor do not coincide with each other, and the combustor is fitted to the outer tube casing cover
51
so as to incline slightly thereto. Although a detailed explanation of the reason therefor is omitted, while the combustion gas flowing through the inner tube and the tail tube is led into a gas turbine combustion gas path, the temperature distribution of the gas flow is needed to be made as uniform as possible. In order to realize an optimized temperature distribution according to the manner in which the combustor is fitted, the central axis
60
of the combustor is inclined slightly relative to axis
61
of the outer tube casing cover
51
.
In the portion surrounding the supports
25
, as the air intake portion in such combustor, there are differences along the circumferential direction in the space areas formed by the outer tube casing cover
51
and the supports
25
, and while the quantity of intake air is varied in this way, there is still a non-uniformity of the intake air. In this type of combustor, while the outer tube casing cover
51
functions as a correcting tube to some extent, so that there is obtained some correction effect of the air flow coming in the combustor, as compared with the combustor of
FIG. 20
, the air takes turns at the air intake portion surrounding the supports
25
to flow into the nozzle portion. This causes a non-uniformity of the air flow, and hence improvement so as to realize a more uniform flow of the air is desired.
Next, a problem existing in the air intake portion (X-
2
) will be described.
FIG. 23
is a side view of an inner tube portion of the combustor
20
of FIG.
20
. In
FIG. 23
, a high temperature combustion gas
161
flows through the inside of an inner tube
28
. In a circumferential surface of the inner tube
28
, which is exposed to the high temperature gas, there are provided a multiplicity of small cooling holes (not shown). Air flowing through these cooling holes cools the inner tube
28
to then flow out to be mixed into the combustion gas flowing inside the inner tube
28
. On the other hand, there remains an unburnt component of fuel in the combustion gas flowing through the inner tube
28
, increasing the NO
x
formation, and hence it is necessary to sufficiently burn the unburnt component. For this purpose, there are provided in the circumferential surface of the inner tube
28
, air holes
10
-
1
,
10
-
2
, and
10
-
3
formed in three rows, with six air holes in each of the rows. The six air holes of each row are arranged with equal intervals between them in the circumferential direction of the inner tube
28
, as shown in FIG.
23
.
In the inner tube
28
constructed as above, the combustion gas
161
produced by the main fuel nozzle
21
flows through the inner tube
28
to flow to the tail tube
24
. For combustion of the unburnt component of fuel contained in the high temperature combustion gas
161
, air
130
is led into the inner tube
28
through the first row of
Akagi Koichi
Akamatsu Shinji
Chikami Rintaro
Haruta Hideki
Kobayashi Kazuya
Artenberg Ehud G
Mitsubishi Heavy Industries Ltd.
Thorpe Timothy S.
Wenderoth , Lind & Ponack, L.L.P.
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