Power plants – Motive fluid energized by externally applied heat – Process of power production or system operation
Reexamination Certificate
1999-10-28
2001-05-29
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Process of power production or system operation
C060S657000, C415S134000, C415S135000
Reexamination Certificate
active
06237338
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a flexible inlet tube for a high and intermediate pressure steam turbine. More particularly, it relates to a flexible inlet tube for a high and intermediate pressure steam turbine, in which an inlet tube for reheat steam has a flexible construction of a double tube and is also cooled by steam to restrain the thermal effect on a casing.
FIG. 3
is a sectional view of a steam inlet portion of a high and intermediate pressure steam turbine relating to the present invention. In
FIG. 3
, reference numeral
11
denotes a casing for covering the whole turbine, and
12
denotes a rotor. Both ends of the casing
11
are sealed by a seal portion
13
. Reference numeral
14
denotes a main steam inlet tube. A tip end portion
14
a
of the main steam inlet tube
14
is installed by a weld
22
, and a base portion thereof is fixed to or formed integrally with the casing
11
. The main steam inlet tube
14
introduces main steam into the casing
11
. Reference numeral
15
denotes a reheat steam inlet tube. The reheat steam inlet tube
15
is formed integrally with the casing
11
, and introduces reheat steam into the casing
11
.
Reference numeral
16
denotes a high pressure turbine stationary portion, and
17
denotes a high pressure turbine section. Although not shown in the figure, in the high pressure turbine section
17
, rotor blades installed to the rotor
12
and stator blades fixed to the high pressure stationary portion
16
are arranged in a multi-stage mode, forming a steam passage. Reference numeral
18
denotes an intermediate turbine stationary portion, and
19
denotes an intermediate pressure turbine section. In the intermediate pressure turbine section
19
, as in the high pressure turbine section
17
, rotor blades installed to the rotor
12
and stator blades fixed to the intermediate pressure stationary portion
18
are arranged in a multi-stage mode, forming a steam passage. A seal ring
20
partitions a turbine section into the high pressure turbine section
17
and the intermediate pressure turbine section
19
by providing a seal around the rotor
12
. A thermal shield
21
prevents a base portion of the reheat steam inlet tube
15
of the casing
11
from being heated by heat from steam flowing into the steam passage in the intermediate pressure turbine section
19
. Also, the thermal shield
21
, which has an opening
24
, introduces reheat steam
31
into the steam passage. Reference numeral
23
denotes a space provided between the casing
11
and the high pressure turbine stationary portion
16
, and
25
denotes a nozzle chamber for main steam
30
introduced through the main steam inlet tube
14
.
In the high and intermediate pressure steam turbine configured as described above, the high-pressure main steam
30
, which is introduced into the casing
11
through the main steam inlet tube
14
, enters the steam passage in the high pressure turbine section
17
through nozzles of the nozzle chamber
25
, and flows to an exhaust system (not shown) after passing between the rotor blades and the stator blades, by which the rotor
12
is driven. Further, the reheat steam
31
, which is introduced into the casing
11
through the reheat steam inlet tube
15
, enters the steam passage in the intermediate pressure turbine section
19
through the opening
24
in the thermal shield
21
, and flows to the exhaust system after passing between the rotor blades and the stator blades, by which the rotor
12
is driven.
For the aforementioned reheat steam inlet tube
15
, which is constructed integrally with the casing
11
and is provided with the thermal shield
21
, a tube side wall thereof is heated by the introduced reheat steam
31
, so that the temperature of the base portion of the inlet tube
15
, that is, the temperature of the tube base is increased, and the casing
11
constructed integrally with this tube base is also heated by this increase in temperature. Therefore, a high-strength material capable of withstanding a thermal stress at high temperatures is used.
As described above, in the high and intermediate pressure steam turbine relating to the present invention, since the reheat steam inlet tube
15
is constructed integrally with the casing
11
, the reheat steam
31
directly heats the integrally constructed casing
11
through the tube base of the reheat steam inlet tube
15
. Therefore, as the temperature of the reheat steam
31
rises, the temperature of the tube base increases, by which a high thermal stress is given to the casing
11
. For this reason, as the material for the casing
11
, a 12Cr material that has a high strength and contains much chromium must be used, which results in a high cost.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to improve a construction of a reheat steam inlet tube for a high and intermediate pressure steam turbine to provide a flexible inlet tube which has a construction capable of absorbing a change caused by heat and a construction capable of performing steam cooling to restrain a temperature rise of a casing constructed integrally with the inlet tube, and can use a material equivalent to an inexpensive low alloy steel as the material for the casing.
To achieve the above object, the present invention provides the following means of (1) and (2). (1) In a flexible inlet tube for a high and intermediate pressure steam turbine, which is used for a high and intermediate pressure steam turbine in which there are provided a main steam inlet tube for introducing main steam into a high pressure turbine section in a casing and a reheat steam inlet tube for introducing reheat steam into an intermediate pressure turbine section in the casing, and a thermal shield, which has an opening for introducing the reheat steam and thermally shields a surrounding portion at the lower end of the reheat steam inlet tube from the steam in the casing, is provided at the lower end of the reheat steam inlet tube, the flexible inlet tube is characterized in that the reheat steam inlet tube is constructed as a double tube formed with an annular groove around an inner tube of the reheat steam inlet tube, and there are provided a cylindrical member one end of which slidably overlaps with the lower end portion of the inner tube of the double tube and the other end of which is fixed to the periphery of an opening of the thermal shield and a seal ring interposed between the cylindrical member and the lower end portion of the inner tube of the reheat steam inlet tube. (2) In the invention of the above means (1), steam having a temperature lower than that of the reheat steam is introduced into the annular groove of the reheat steam inlet tube and is circulated in the annular groove.
In the means (1) of the present invention, the reheat steam inlet tube is constructed as a double tube, and has the annular groove therein. Also, the lower end portion of the inner tube of the double tube overlaps with the cylindrical member fixed to the thermal shield, and the seal ring is interposed therebetween, by which a vertical sliding motion can be accomplished, and the reheat steam flowing into the inlet tube can be prevented from flowing into the annular groove. The reheat steam flowing into the inlet tube passes through the inside of the double tube construction, and the periphery is isolated by the annular groove, so that heat is prevented from being transmitted from the peripheral wall surface to the casing wall. Also, even if thermal elongation of a double tube portion is developed by heating, the double tube portion is slidable with respect to the cylindrical member via the seal ring, so that the thermal elongation can be absorbed easily. Therefore, in the flexible inlet tube of the means (1) of the present invention, a temperature rise on the casing side caused by the reheat steam is made less liable to be conveyed to the surroundings by the annular groove, and thermal elongation is absorbed. Therefore, as the material for the casing, an inexpensi
Magoshi Ryotaro
Nakano Takashi
Alston & Bird LLP
Mitsubishi Heavy Industries Ltd.
Nguyen Hoang
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