Power plants – Combustion products used as motive fluid – With safety device
Reexamination Certificate
2001-08-29
2003-03-11
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
With safety device
C060S039281
Reexamination Certificate
active
06530207
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gas turbine system, which permits to monitor occurrence of flashback of combustion gas on the basis of data of NOx concentration detected from the combustion gas.
A combined cycle power generation system has characteristic properties such as an improved plant thermal efficiency, a reduced start-stop time, decreased amounts of hot drainage and the like, which have been highly rated. The combined cycle power generation system has recently become one of the leading mainstreams of the latest thermal power plants.
The combined cycle power generation system is composed of a gas turbine system, a steam turbine system and a heat recovery steam generator in a tandem or single shaft arrangement, so that utilization of exhaust gas from the gas turbine system as heat source for the heat recovery steam generator causes the boiler to generate steam, and the thus generated steam is supplied to the steam turbine system to generate power. The exhaust gas from the gas turbine system can be utilized thoroughly, leading to a remarkably high plant thermal efficiency in comparison with the gas turbine system alone or the steam turbine system alone.
There has recently been made a reassessment of a gas turbine-combustor to be incorporated into the combined cycle power generation system having a high plant thermal efficiency, in view of prevention of pollution of the environment. Such a reassessment is made with an eye to monitoring of combustion condition of combustion gas and reduction in NOx concentration.
The former technical measures, i.e., to monitor the combustion condition of the combustion gas have conventionally been proposed. One of these measures is disclosed in Japanese Laid-Open Patent Publication No. SHO 53-82909.
Such a prior art exemplifies a gas turbine system alone as shown in FIG.
6
. In the prior art, temperature of exhaust gas from an exhaust gas duct
2
of a gas turbine
1
is detected by means of a plurality of thermocouples
3
. An intermediate temperature (i.e., a median temperature) is calculated from the detected temperatures. A comparison is made between the intermediate temperature and the individual temperatures actually detected. When deviation exists between the former and the latter, or the deviation exceeds a prescribed value, a combustion monitoring device
4
judges combustion condition of the combustion gas. In case where the combustion monitoring device judges the combustion to be “improper”, it supplies an alarm signal ALM or an operation shutdown command TRP to a gas turbine control device
5
to control a fuel valve
6
so as to be opened or closed. The above-described prior art, which is based on a theory that abnormal combustion is always revealed as decrease in temperature of the exhaust gas, has been put to practical use.
Japanese Laid-Open Patent Publication No. SHO 59-134332 for example discloses the latter technical measures, i.e., to reduce the NOx concentration.
Such a prior art exemplifies a combined cycle power generation system as shown in
FIG. 7
, in which diffusion combustion is applied as a combustion system for a gas turbine-combustor
7
. In the prior art, a NOx concentration sensor
10
is provided on the downstream side of a catalyst
9
of a heat recovery steam generator
8
in the flowing direction of the exhaust gas. A NOx concentration value signal P detected by means of the NOx concentration sensor
10
is compared with a predicted NOx concentration value signal Q from a NOx concentration predictor
11
integrated into a gas turbine control device
5
, in an NH
3
-injection control system
12
to make a calculation. On the basis of the calculation result, an amount of ammonia to be supplied is calculated. Ammonia is supplied in an amount thus calculated into, for example, an exhaust gas duct
2
connecting a gas turbine
1
and the heat recovery steam generator
8
with each other. In addition, a valve opening of a fuel valve
6
is controlled to adjust the flow rate of fuel, thus maintaining a low NOx concentration.
The technical measures as shown in
FIGS. 6 and 7
concerning the monitoring of combustion condition of the combustion gas and the reduction in NOx concentration have already been put into practice, thus contributing prevention of the pollution of the environment. Especially, according to the technical measures as shown in
FIG. 7
, there is provided a high precision of prediction of the NOx concentration even with the use of calculation measures in case of a diffusion combustion, thus becoming one of the excellent measures in the field of art.
Gas turbine-combustors providing an extremely low NOx concentration have recently been demanded due to the further enhanced environmental regulation against the NOx concentration. With respect to such a demand, the diffusion combustion type gas turbine-combustors as shown in
FIGS. 6 and 7
have already reached their limits. In view of this fact, dry type premixing lean combustion type gas turbine-combustors have alternatively been put into practice as service equipment.
According to the dry type premixing lean combustion, air is previously added into fuel to provide a lean-fuel condition and burned under such the lean-fuel condition to reduce a flame temperature, thus reducing the NOx concentration so as to completely conform to legally regulated values.
However, the dry type premixing lean combustion type gas turbine-combustors, which are excellent in reduction in the NOx concentration, even have some problems. One of these problems is a phenomenon of flashback (backfire) of the combustion gas.
The problem of flashback of the combustion gas is inherent in the dry type premixing lean combustion system. With respect to the flashback, sudden ignition occurs in a lean-fuel premixing zone, causing flame temperature to increase locally. As a result, there is generated the combustion gas having a high NOx concentration.
It is conceivable to apply the technical measures for calculation as shown in
FIG. 7
to predict the NOx concentration from temperature distribution of the exhaust gas as the device for monitoring such a phenomenon.
However, flame of the flashback, which occurs in the lean-fuel premixing zone, then reaches the combustion zone to flow into flame in the combustion zone. It is difficult to judge increase in NOx concentration due to the flashback from the temperature distribution of the exhaust gas, even when the above-mentioned technical measures for calculation is applied. If the flashback is not detected, operation continues in the presence of the flashback, leading to a possible burnout accident of the gas turbine-combustor.
For these reasons, the realization has been demanded of the combustion monitoring device suitable for the dry type premixing lean combustion.
SUMMARY OF THE INVENTION
An object of the present invention, which has been made in view of the above-described problems, is therefore to provide a gas turbine system that makes it possible to surely detect a flashback of fuel gas in a gas turbine-combustor through NOx concentration of an exhaust gas measured.
This and other objects can be achieved according to the present invention by providing, in one aspect, a gas turbine system which comprises a compressor, a gas turbine-combustor, a gas turbine and a generator, which are operatively connected in series, a combustion monitoring device for detecting NOx concentration of an exhaust gas to be exhausted from the gas turbine so as to monitor combustion condition of the combustion gas in the gas turbine-combustor, and a gas turbine controller operatively connected to the combustion monitoring device and provided with a NOx value predictor,
the combustion monitoring device comprising:
an alarm signal calculation circuit for operating an alarm signal based on the NOx concentration detected from the exhaust gas at a time when flashback of the combustion gas in the gas turbine-combustor occurs to reach a premixed combustion zone;
a shutdown calculation circuit for operating a shutdown command when the
Hasegawa Akira
Oguchi Haruo
Tobo Masayuki
Yasui Hajime
Kabushiki Kaisha Toshiba
Kim Ted
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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