Power plants – Combustion products used as motive fluid
Reexamination Certificate
1999-02-23
2001-05-01
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Reexamination Certificate
active
06223520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a so-called gas turbine combined plant or a combined-cycle plant and a method of operating the same. The present invention further relates to a steam-cooling system for a hot section in a gas turbine in which the hot section such as a combustor in the gas turbine of the combined-cycle plant may be cooled by steam from an exhaust heat recovery boiler as an example.
2. Description of the Related Art
Hitherto, air has been utilized to cool hot sections or elements such as combustors in gas turbines. However, with a need for higher combustion temperature levels, there has been developed a method of cooling these elements by steam. Furthermore, a plan has been undertaken in which gas turbines containing the hot sections to be cooled by steam are applied to a combined-cycle plant and combined with steam turbines, thereby providing a high efficient power plant.
FIG. 2
is a schematic view showing an example of a gas turbine steam system in conventional combined-cycle plants. In
FIG. 2
, an exhaust gas from a gas turbine
1
is delivered into an exhaust heat recovery boiler
2
. The steam from a high-pressure drum
5
in the exhaust heat recovery boiler
2
is delivered into a high-pressure steam turbine
3
through a high-pressure superheater
6
and a high-pressure steam governing valve
13
. On the other hand, the steam from an intermediate-pressure drum
9
in the exhaust heat recovery boiler
2
is delivered into an intermediate-pressure steam turbine
4
through an intermediate-pressure superheater
10
, a reheater
7
, and an intermediate-pressure steam governing valve
14
in the order named.
The steam is then supplied to a hot section
8
from a cooling steam source
12
, and is used to cool the hot section
8
. Auxiliary steam of the power plant or the steam (for example, the steam at the outlet of the intermediate-pressure superheater
10
) in the exhaust heat recovery boiler
2
may be used as the cooling steam source
12
. The steam after cooling is then confluent with the steam at the outlet of the reheater
7
to be fed together to the intermediate-pressure steam turbine
4
through the intermediate-pressure steam governing valve
14
, as described above.
Such a combined-cycle plant is provided with a system having the following arrangement. During starting up the plant or at the start-up time of the gas turbine unit
1
, the steam temperature detected at a hot section outlet steam temperature detector
15
and the steam temperature detected by a reheater outlet steam temperature detector
16
are both too low to allow the steam to be effectively directed to the intermediate-pressure steam turbine
4
. Thus, an intermediate-pressure steam turbine inlet steam temperature detector
22
is provided to a pipe connected to the intermediate-pressure steam governing valve
14
, and detects the steam temperature thereof. While the intermediate-pressure steam governing valve
14
is held closed based upon this detection signal, the steam can by-pass from a turbine by-pass valve
18
to a condenser
11
. When the steam temperature rises to reach a tolerance, the intermediate-pressure steam governing valve
14
is then opened based upon the detection signal from the intermediate-pressure steam turbine inlet steam temperature detector
22
, resulting in starting up the intermediate-pressure steam turbine
4
.
However, while the temperature rises as described above, it has been found that, in a certain period, the temperature detected by the hot section outlet steam temperature detector
15
may be kept considerably higher in rising ratio than the temperature detected by the reheater outlet steam temperature detector
16
. This fact indicates that there occurs a large difference between both the outlet steam temperature levels. Accordingly, there is a fear that an undesirable thermal stress be generated at the point, or in the vicinity thereof, where the pipe extending from the reheater
7
and the pipe extending from the hot section
8
are confluent with each other.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the foregoing problem, and an object of the present invention is therefore to provide a gas turbine unit combined plant, a method of operating the same, and a steam-cooling system for a gas turbine hot section, whereby the occurrence of such an undesirable thermal stress can be utmost reduced.
In terms of the above object, a gas turbine combined plant in an aspect of the present invention comprises: a first path directing steam from an exhaust heat recovery boiler to a steam turbine unit; a second path branched from the first path, connected to a condenser through a first valve unit; and a third path directing steam after cooling a gas turbine hot section to the first path, wherein a second valve unit is disposed to the third path (assuming that a part of the third path which joins the steam to the first path be provided onto the third path), and the gas turbine combined plant further comprises a fourth path connected to the condenser through a third valve unit from the point located at the upstream side of the second valve unit disposed to the third path.
According to another aspect of the present invention, a gas turbine combined plant comprises a controller connected to the first valve unit, the second valve unit, and the third valve unit, wherein the first valve unit, the second valve unit, and the third valve unit are opened/closed under the control of the controller.
According to still another aspect of the present invention, a gas turbine combined plant further comprises a first steam temperature detector disposed to the first path for detecting the outlet temperature of the steam of the exhaust heat recovery boiler, and a second steam temperature detector disposed to the third path for detecting the outlet temperature of the steam of the gas turbine hot section, the first steam temperature detector and the second steam temperature detector both being connected to the controller.
According to still another aspect of the present invention, a gas turbine combined plant further comprises a steam turbine inlet steam temperature detector disposed to the first path at the downstream side of the point where the second path is branched from the first path, and a fourth valve unit disposed to the first path at the downstream side of the steam turbine inlet steam temperature detector, the steam turbine inlet steam temperature detector and the fourth valve unit being connected to the controller.
Preferably, a gas turbine combined plant according to still another aspect of the present invention further comprises a hot section outlet steam pressure detector for detecting the outlet steam pressure of the gas turbine hot section which occurs at the upstream side of the point where the fourth path is branched from the third path, the hot section outlet steam pressure detector being connected to the controller.
Further, in order to attain the above-noted object, the present invention provides a method of operating a gas turbine combined plant for introducing the steam after cooling a gas turbine hot section to a path directing steam from an exhaust heat recovery boiler into a steam turbine. The method comprises the steps of: detecting the temperature of the steam from the exhaust heat recovery boiler and the temperature of the steam after cooling the gas turbine hot section; and directing a part or the whole steam after cooling the gas turbine hot section to a condenser in the case where the detected temperature has a difference equal to a predetermined value or more.
According to a further aspect of the present invention, there is provided a gas turbine hot section steam-cooling system for cooling a hot section of a gas turbine by steam from an exhaust heat recovery boiler and supplying the steam after cooling to a steam turbine. The system comprises: a first temperature detector for detecting the outlet temperature of the steam of the hot section of the gas turbine, a
Mitsubishi Heavy Industries Ltd.
Rodriguez W.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Thorpe Timothy S.
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