Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-07-20
2003-04-01
Koczo, Michael (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039281
Reexamination Certificate
active
06539722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas turbine plant used in a power generation plant and to a method of controlling such a gas turbine plant.
2. Description of the Related Art
FIG. 9
shows the general structure of a conventional single-shaft combined plant (i.e., gas turbine plant).
In the shown single-shaft combined plant, reference numeral
101
indicates a compressor for absorbing and compressing the air, reference numeral
102
indicates a combustor to which combustion oil and combustion air (which has been compressed in the compressor
101
) are supplied, reference numeral
103
indicates a gas turbine which rotates when receiving a combustion gas generated by the combustor
102
, reference numeral
104
indicates a steam turbine coupled with the gas turbine
103
, and reference numeral
105
indicates a generator.
The above gas turbine
103
, compressor
101
, steam turbine
104
, and generator
105
are coupled with each other via a coupling shaft
106
.
The drive source for the steam turbine
104
is an exhaust heat recovery boiler
108
. The exhaust heat recovery boiler
108
generates steam by using heat collected from the high-temperature exhaust gas output from the gas turbine
103
, and introduces the generated steam into the steam turbine
104
. Reference numeral
107
indicates a condenser into which exhaust steam from the steam turbine
104
is introduced. The condenser
107
condenses the introduced steam and returns condensate (i.e., condensed water) to the exhaust heat recovery boiler
108
.
Reference numeral
109
indicates a fuel valve for controlling the amount of fuel supplied to the combustor
102
. This fuel valve
109
is controlled by a controller
110
.
The combustor
102
has a structure shown in FIG.
10
. In
FIG. 10
, reference numeral
112
indicates a main combustor, and reference numeral
113
indicates a tail pipe of the main combustor. Fuel is supplied to the main combustor
112
via the fuel valve
109
, and air
114
is also supplied to the main combustor
112
from the compressor
101
, thereby combusting the fuel.
Reference numeral
115
indicates a bypass valve which is controlled by the controller
110
. Depending on the degree of opening of the bypass valve
115
, the distribution of air from the compressor
101
, that is, the ratio of air supplied to the main combustor
112
to air supplied to the tail pipe
113
, is determined.
In the combined plant explained above, when the frequency of the electric power system is changed due to a load change, the frequency must be stabilized by controlling the generated power. The above controller
110
controls the fuel valve
109
so as to recover a suitable frequency, thereby controlling the output of the gas turbine
103
.
A concrete example of such a control will be explained below.
In
FIG. 11
, reference symbol S
1
indicates a governor CSO (control signal output) signal output by the controller
110
to the fuel valve
109
so as to control the output of the gas turbine
103
.
As shown by reference symbol “a”, in the normal state, the controller
110
suitably varies the governor CSO signal S
1
(corresponding to the output of the gas turbine
103
) so as to fix the frequency.
When the amount of load suddenly decreases, the relevant revolution speed suddenly increases, and thus the frequency also increases. In this case, as shown by reference symbol b
1
, the controller
110
decreases the level of the governor CSO signal S
1
so as to avoid a sudden increase of the revolution speed.
On the other hand, when the amount of load suddenly increases, the relevant revolution speed suddenly decreases, and thus the frequency also decreases. In this case, as shown by reference symbol c
1
, the controller
110
increases the level of the governor CSO signal S
1
so as to avoid a sudden decrease of the revolution speed.
However, if the governor CSO signal S
1
is suddenly increased, the temperature of the gas turbine
103
suddenly increases. It is not preferable because the gas turbine
103
should have a stress. Therefore, the controller
110
calculates, in advance, a load-limiting CSO signal S
2
shown by reference symbol S
2
. In the normal state, the load-limiting CSO signal S
2
has a level higher than that of the governor CSO signal S
1
by a predetermined tracking width TW. When the governor CSO signal S
1
suddenly increases or decreases, the load-limiting CSO signal S
2
is increased or decreased by a specific rate. The controller
110
uses the load-limiting CSO signal S
2
as an upper-limit value of the governor CSO signal S
1
.
Therefore, when the governor CSO signal S
1
suddenly decreases, the level of the load-limiting CSO signal S
2
is never less than the level of the governor CSO signal S
1
(refer to reference symbol b
1
′); however, when the governor CSO signal S
1
suddenly increases, the level of the load-limiting CSO signal S
2
may be higher than the level of the governor CSO signal S
1
(refer to reference symbol c
1
′). Therefore, the governor CSO signal S
1
is limited so as not to increase with a rate higher than the above-explained specific rate (refer to reference symbol d
1
).
If the load suddenly increases immediately after a sudden decrease of the load, then the governor CSO signal S
1
is controlled in a manner such that the signal suddenly decreases, and then suddenly increases (see FIG.
12
).
That is, when the load suddenly decreases, as shown by reference symbol b
2
, the governor CSO signal S
1
decreases without limitation, and the load-limiting CSO signal S
2
decreases by a specific rate (see reference symbol b
2
′).
After that, when the load suddenly increases, the governor CSO signal S
1
suddenly increases (see reference symbol c
2
). In this case, the load-limiting CSO signal S
2
continuously decreases until the load-limiting CSO signal S
2
obtains a level 5% higher than that of the governor CSO signal S
1
(see reference symbol b
2
′). The load-limiting CSO signal S
2
then enters an increase phase, where the increase is performed at a specific rate because of a sudden increase of the governor CSO signal S
1
(see reference symbol c
2
′). Accordingly, the governor CSO signal S
1
is limited so as not to increase with a rate higher than the specific rate (see reference symbol d
2
), that is, the load-limiting CSO signal S
2
functions as an upper-limit level of the governor CSO signal S
1
.
In the above operation as shown in
FIG. 12
, in a time period t
2
(i.e., before the increase of the governor CSO signal S
1
is limited), fuel is also suddenly increased so that the gas turbine
103
has a stress.
In addition, the combustor
102
operates according to the variation of the governor CSO signal S
1
, as follows: when the load suddenly decreases, the controller
110
limits the amount of fuel supplied to the main combustor
112
by suitably closing the fuel valve
109
, thereby suppressing the increase of the relevant revolution speed. In this process, the controller
110
opens the bypass valve
115
so as to maintain a suitable fuel-air ratio, so that the amount of air supplied from the bypass valve
115
to the tail pipe
113
of the combustor increases. Accordingly, the amount of air supplied to the main combustor
112
is decreased, and the suitable fuel-air ratio is maintained.
However, in the conventional combined plant, the opening/closing speed of the bypass valve
115
is fixed. Therefore, the operation of opening the bypass valve
115
cannot follow the sudden closing of the fuel valve
109
, so that an excessive amount of air is introduced into the main combustor
112
, and this situation causes unstable combustion or the like.
SUMMARY OF THE INVENTION
In consideration of the above circumstances, an objective of the present invention is to provide a gas turbine plant and a method of controlling a gas turbine plant, for limiting a sudden increase of the load of the gas turbine, that is, a sudden increase of the amount of fuel, and suppressing a stress
Komiyama Hiroya
Nagata Shouichi
Koczo Michael
Mitsubishi Heavy Industries Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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