Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
2001-04-05
2002-10-15
Gartenberg, Ehud (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
Reexamination Certificate
active
06463742
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas turbine and, specifically, the present invention relates to a cooling system for a gas turbine combustor.
2. Description of the Related Art
In general, there are two types of cooling systems for the wall of a gas turbine combustor. One is a compound air cooling system employing both convective cooling and film air cooling using air as cooling fluid and another is steam cooling system using steam as cooling fluid. In an actual gas turbine, one of the compound air cooling system and the steam cooling system is selected according to the temperature of combustion gas at the inlet of turbine.
FIG. 1
is a sectional view showing a general construction of a gas turbine combustor employing a compound air cooling system.
In
FIG. 1
, reference numeral
1
designates a combustor of a gas turbine as a whole. The combustor
1
consists of a combustion tube
5
b
which acts as a combustion chamber for burning fuel injected from fuel nozzles
33
and a tail pipe
5
a
which directs combustion gas generated in the combustion tube to the first stage stator of the turbine. The combustor tube
5
b
and the tail pipe
5
a
are made as separate parts and joined together to form a combustor
1
.
Fuel is injected into the combustion tube
5
b
from the main nozzles
33
as a premixed air-fuel mixture. The air-fuel mixture is ignited by a pilot flame formed by a pilot nozzle
31
and generates a premixed flame in the combustion tube.
FIG. 8
is a enlarged section of the wall of the combustor tube
5
b
employing a conventional compound air cooling system. As can be seen from
FIG. 8
, in an actual gas turbine, the combustor tube
5
b
is formed by joining a plurality of cylindrical shells
55
having different diameters. The respective shells
55
are aligned in the axial direction and are joined to each other through stepped diameter portions thereof. Each of the shells
55
acts as a structural member forming the combustor tube
5
b
. A heat insulating member
155
is disposed at inside of each cylindrical shell
55
in order to protect the shell from the flame in the combustor tube and, thereby, preventing a strength degradation of the shell as a structural member.
In the conventional cooling system, fin-rings are used for the heat insulating members
155
. The fin-ring consists of a cylindrical member having numerous grooves on the outer surface thereof extending in the axial direction. Each of the fin-rings
155
is held inside of the shell by attaching one end thereof to the smaller diameter portion of the corresponding shell
55
(i.e., a fuel nozzle side end of the shell
55
), for example, by brazing.
In this system, pressurized air in the casing
7
(
FIG. 1
) is introduced from inlet openings
57
distributed around the smaller diameter portion of the shell
55
into the space between the shell
55
and the fin-ring
155
. Air introduced into the space passes through the axial grooves outside of the fin-ring
155
and cools fin-ring
155
by convective cooling. After passing through the axial grooves, air is injected from the outlet
159
at the end of the fin-ring
155
in the direction along the inner surface of the heat insulating member (in
FIG. 8
, indicated by reference numeral
155
b
) adjacent thereto. Thus, the wall surface of the combustion chamber, i.e., the inner surface of the adjacent fin-ring
155
b
is cooled by the film of the injected air.
On the other hand,
FIG. 10
is a sectional view similar to
FIG. 1
showing a gas turbine combustor employing a conventional steam convective cooling system.
Since the heat-transfer coefficient of air is relatively low, sufficient cooling can not be obtained by convective cooling and, usually, a compound air cooling system using both convective cooling and film air cooling is employed in the air cooling system. However, compound air cooling system has its inherent problem. In the compound air system, air used for film air cooling is injected into the combustion tube and mixes with combustion gas. This cause dilution of combustion gas and lowers its turbine inlet temperature and, thereby, causes deterioration in the gas turbine output and efficiency.
In order to prevent this problem, the combustor in
FIG. 10
employs steam cooling system using steam convective cooling instead of compound air cooling. Since the heat-transfer coefficient of steam is larger than that of air, the combustor is sufficiently cooled solely by convective cooling in the steam cooling system.
In
FIG. 10
, reference numerals the same as those in
FIG. 1
denotes elements similar to those in FIG.
1
.
The combustor in
FIG. 10
is a one-piece construction in which the combustion tube
5
b
and the tail pipe
5
a
are formed as an integral part. Therefore, the combustion tube
5
in the combustor
1
in
FIG. 10
has outlet
52
at one end thereof in order to supply combustion gas to the first stage stator of the turbine.
The combustion tube
5
in
FIG. 10
has a double-wall construction including an outer shell (outer wall) and an inner shell (inner wall). The space between the outer shell and inner shell acts as a passage for cooling steam. Cooling steam is supplied to the cooling steam passage between the outer and the inner shells from a steam inlet connection
507
disposed near the center of the length of the combustion tube
5
. The steam introduced into the cooling passage is divided into two streams flowing in the directions opposite to each other. Namely, a portion of the cooling steam flows through an upstream cooling passage in the wall of the combustion tube
5
from the inlet
507
in the upstream direction (i.e., towards the main nozzle
33
side) and other portion of the cooling steam flows through a downstream cooling passage in the wall of the combustion tube
5
from the inlet
507
in the downstream direction (i.e., towards the outlet
52
of the combustion tube). Cooling steam outlet pipes
509
a
and
509
b
are connected to the cooling steam passage at the upstream (main nozzle
33
side) end and the downstream (outlet
52
side) end of the combustion tube
5
, respectively, in order to collect cooling steam after it cooled the combustor walls. Since the heat-transfer coefficient of steam is-relatively large, the walls of the combustor are sufficiently cooled by convective cooling using cooling steam.
The conventional compound air cooling system and the steam cooling system as explained above include respective drawbacks.
In the first place, in the compound air cooling system using the fin-rings, consumption of cooling air is large.
FIG. 9
is a cross sectional view taken along the line IX—IX in FIG.
8
. As explained before, the fin-ring
155
is provided with grooves extending along the axial direction on the outer surface thereof. When the fin-ring
155
is attached to the shell
55
, an annular clearance
155
c
must be disposed between the shell
55
and fin-ring
155
in order to avoid contact between the shell
55
and fin-ring due to thermal expansion of the fin-ring. When the manufacturing tolerance and the tolerance in the assembling of the combustor are taken into account, the required width of the clearance
155
c
becomes almost the same as the depth of the grooves
155
b
in some cases. Therefore, in the conventional compound air cooling system, since a relatively large clearance
155
c
between the outer surface of the fin-ring
155
b
and the inner surface of the shell
55
, a large amount of cooling air passes through the clearance
155
c
in the axial direction and flows into the combustion chamber without passing through the grooves
155
b
. In other words, a large portion of the cooling air introduced from the inlet
57
flows into the combustion chamber without being used for cooling the fin-ring
155
. Consequently, in order to obtain sufficient convective cooling of the fin-ring
155
, the amount of cooling air supplied from the inlet
57
must be increased so that a sufficient amount of air passes through the grooves
155
b
Mandai Shigemi
Suenaga Kiyoshi
Tanaka Katsunori
Gartenberg Ehud
Mitsubishi Heavy Industries Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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