JPS6128704A - Operating method of combined plant - Google Patents

Abstract

PURPOSE:To improve an emission characteristic of NOX in a plant when it is started, by stopping the plant increasing the drum pressure of a waste heat boiler to a level higher than that of the pressure when the plant is stopped. CONSTITUTION:A combined plant sets a gas turbine 1, waste heat boiler 20, catalytic denitrifying device 11 and an NH3 injection nozzle 12. The plant, when it is stopped, holds the residual pressure of a drum 22 in the waste heat boiler 20, when it is restarted, to a high level by increasing the pressure of generated steam 54 while the temperature of gas in and around the denitrifying device 11 to a high level by an evaporator 23. In this way, the plant, when it is restarted, enables its emission characteristic of NOX to be improved by expending the injection timing of NH3 further enhancing the efficiency of denitrification.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a combined plant of a gas turbine and a steam turbine, and particularly to a plant operating method for improving N0w emission characteristics at the time of plant start-up.

[Background of the invention]

Figure 1 shows the overall configuration of the combined plant.

The gas turbine 1 sucks in atmospheric air 51, burns fuel 52, and drives the generator 2. The exhaust gas 53 of the gas turbine is introduced into the exhaust heat recovery boiler 20, where its heat is recovered, and the feed water 57 sent by the water feed pump 35 passes through the economizer 21, the evaporator 23, and the superheater 24, where it is converted into steam 54. Become. Wax vapor 54 is injected into steam turbine 31 and drives generator 36 . In addition, if the amount of steam generated by the exhaust heat recovery boiler 220 is greater than the flow rate of the steam 54 required by the steam turbine 31 during plant startup and shutdown, etc., the refractory steam 54 is used to absorb the surplus steam. , the steam 54 is branched and discharged to the condenser 34 through the turbine bypass pipe 56 and the turbine bypass valve 33.

Further, a catalytic denitration device 11 is installed in a part of the evaporator 23 in the exhaust heat recovery boiler 20, and NHsS&
is injected, and NOx in the exhaust gas is decomposed into harmless HzO and N3 gas by the NHs 58 and the denitrification device catalyst 11.

FIG. 2 shows a method of starting and stopping the combined plant according to the prior art and the NOx emission characteristics at that time.

The combined plant is published in Thermal and Nuclear Power Generation Magazine VOB,
3447r Higashi Niigata Thermal Power Plant No. 3 Series Plan” (
As described in 1982-7), a variable pressure operation is performed in which the pressure of the steam 54 is changed according to the plant load.

This is because, as is generally known, the gas turbine exhaust gas temperature decreases during partial load, and the pressure of the steam 54 is changed in accordance with this characteristic, thereby improving the plant thermal efficiency.

Therefore, even when the plant is stopped, there is no load drop,
The steam 54 is stopped by lowering its pressure.

On the other hand, in the exhaust heat recovery boiler 2o, an evaporator 23 is installed in front of the denitrification device 11, and the pressure of the evaporator 23 greatly influences the inlet gas temperature of the denitrification device 11. Further, the performance of the denitrification device 11 is mainly controlled by the inlet gas temperature, and as the inlet gas temperature decreases, the denitrification performance also decreases.

Therefore, in the conventional shutdown method of lowering the steam pressure when shutting down a plant, as shown in FIG. Since the pressure in the drum 22 further decreased during this time, the residual pressure in the drum at the time of restarting the plant decreased significantly.

For this reason, when the plant is restarted, the temperature of the log gas entering the denitrification equipment 110 drops, and because it takes time to raise the temperature to the required gas temperature that allows injection of NHa 58, the timing of N Hs injection is delayed, and the denitrification equipment There was a drawback that the start-up characteristics of 111 were delayed.

In addition, since NHs58 has the risk of ammonium nitrate formation at low temperatures,
The gas temperature at the inlet of the denitrification device is generally 180 to 200 C or higher, and NHs is injected through the NHs injection nozzle 12. Thereby, the denitrification action is started in the denitrification device 11.

In the prior art method shown in FIG. 2, during the plant shutdown process, the pressure of the steam 54 was kept low due to variable pressure operation, and furthermore, the curve K in FIG. The steam during the plant shutdown period shown.

Due to the pressure drop in the steam 54, the pressure of the steam 54 is only about 10 atm when the plant is started up the next morning, 8 to 10 hours after the plant was shut down. The temperature is not higher than the saturation temperature of about 180C at a pressure of 10 atmospheres of the steam 54, and therefore the timing of NH3 injection is delayed, and the denitrification efficiency of the denitrification device 11 at startup is delayed. Therefore, as shown in FIG. 2, the NOx value at the outlet of the denitrification device 11 reached a very high peak value.

[Purpose of the invention]

As mentioned above, the purpose of the present invention is to eliminate the drawbacks of the prior art,
The objective is to improve the NOx emission characteristics during gas turbine startup.

[Summary of the invention]

For the above purpose, an exhaust heat recovery boiler 20 is installed as shown in FIG.
The evaporator 23 is installed in the vicinity of the denitrification equipment 11, and the residual pressure of the evaporator greatly affects the gas temperature at the denitrification equipment inlet. The steam pressure is increased, the residual pressure in the drum 22 in the exhaust heat recovery boiler 2o is kept high at the time of restart, and the evaporator 2
3 By keeping the temperature of the denitrification equipment 11 and the gas around the denitrification equipment high, when restarting the plant,
By advancing the timing of NHs injection and further increasing the denitrification efficiency, the start-up of the denitrification characteristics of the denitrification equipment was improved.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

FIG. 3 shows the compound plant stop-start method according to the present invention and the NOx emission characteristics during start-up.

In FIG. 1, for example, before a stop command is issued, the gas turbine 1 and the steam turbine 31 are operating at a load of 501, and the exhaust gas 5 from the gas turbine 1 is
3 is introduced into the exhaust heat recovery boiler 20, where the heat is recovered, and the feed water 57 is heated and injected into the steam turbine 31 as steam 54 at about 30 atmospheres.

When a stop command is issued here, the steam turbine 31 first gradually reduces its load and stops. Next, the gas turbine 1 gradually reduces its load and stops. Here, as just one example of a stopping method, the loads on the steam turbine 31 and the gas turbine 1 are lowered at the same time.

Although the case has been shown, it is of course possible to shift the load drop start timing.

When the steam turbine 31 is about to stop, the steam turbine 3
Since the amount of steam generated in the exhaust heat recovery boiler 20 is larger than the flow rate of the steam 54 corresponding to the load of and is discharged to the condenser 34.

By utilizing the energy possessed by this turbine bypass steam 56, the pressure setting is gradually increased by the pressure regulator 37 installed upstream of the turbine bypass valve 33, and the pressure setting of the pressure regulator 37 is increased. Then, the opening degree of the turbine bypass valve 33 is adjusted to increase the steam pressure on the upstream side of the turbine bypass valve 33, that is, the pressure of the steam 54 to the rated pressure of about 60 atmospheres.

Here, 60 atm is the rated pressure, and as shown in the curve in Figure 4, it is the pressure that can ensure 30 atm when the plant is restarted even during a plant shutdown period of approximately 8 to 10 hours. The saturation temperature of the drum 22 is approximately 233C, and even considering the difference between the saturation temperature for the internal pressure of the drum 22 and the atmospheric gas temperature of the drum 22, the denitrification equipment inlet gas temperature is approximately 233C.
0 C (D) can be secured.The ultimate pressure boost at the time of plant shutdown is determined by the length of the plant shutdown period, the degree of decrease in steam pressure during plant shutdown, etc. It will be decided.

Note that the energy of the turbine bypass steam 56 is the same as that of the steam 54
It has enough energy to raise the pressure from 30 atmospheres to 60 atmospheres9, and conventionally the energy was wasted in the condenser.

With the above plant shutdown method, the pressure of the steam 54 immediately after the plant shutdown is approximately 60 atm, and the pressure of the steam 54 is approximately 60 atm.
At startup the next morning after 0 hours, the pressure of the steam 54 can be maintained at about 30 atmospheres.

Therefore, the saturation temperature of the steam 54 at a pressure of 30 atmospheres is approximately 23
As a result, the temperature of the gas in the denitrification device 11 is maintained at a high temperature of about 200 t:' or more.

This makes it possible to inject NHa58 through the NHs injection nozzle 12 at the time of restarting the plant, near the start of the gas turbine, and earlier than in the conventional technology, and the denitrification characteristics of the denitrification device 11 are significantly improved. Improved.

FIG. 3 shows the NOx emission characteristics at the time of start-up in the present invention. As shown in FIG.
Compared to the conventional method, it is possible to suppress the level to an extremely low level.

Other embodiments of the invention are as follows.

(1) Gas turbine 1 and steam turbine 31J11
If a plant stop command is issued while the plant is operating under a load of 0.000 or more, the rated pressure of the steam 54 at that time, approximately 60 atmospheres, will be maintained and the plant will be stopped.

In the above, the pressure of the steam 54 is increased by the turbine bypass valve 33 installed in the turbine bypass pipe 56 and the pressure regulator 37 installed on the upstream side of the valve. The pressure may be increased by other methods such as adjustment using the steam control valve 32 installed at the inlet of 31.

(3) When restarting the plant, other steam may be introduced into the drum 22 before starting the gas turbine to increase the pressure of the canned water in the drum.

(4) Furthermore, in the combined plant equipped with a plurality of blocks each having a gas turbine yl and a steam turbine 31, it is also possible to use the steam of the blocks during operation.

〔Effect of the invention〕

(1) The amount of NOx emissions during startup is significantly reduced.

- For example, in the conventional system shown in Fig. 2, the NOx emission amount at the outlet of the denitrification equipment during plant start-up is approximately 14 Nm"/H as an hourly average total amount, and approximately 25 Nm"/H as the maximum instantaneous value, but In the present invention shown in the figure, the hourly average total amount is about 9
Nm”/Hs instantaneous value maximum value approximately 1 ONm”
/H.

(2) It can be implemented by simply improving the control method, and the above objective can be achieved without a significant increase in cost.

[Brief explanation of the drawing]

Fig. 1 is a combined plant configuration, Fig. 2 is a characteristic diagram showing the starting and stopping method of the prior art, Fig. 3 is a characteristic diagram showing the starting and stopping method of the present invention, and Fig. 4 is a characteristic diagram showing the starting and stopping method of the present invention. It is a steam pressure characteristic. 1... Gas turbine, 20... Exhaust heat recovery boiler, 3
1... Steam turbine, 11... Denitration equipment, 22...
・Drum, 23... Evaporator, 54... Steam, 33.
...Turbine bypass valve.

Claims (1)

[Claims] 1. In a combined plant where a gas turbine, its exhaust heat recovery boiler, and a catalytic denitrification device and an NH_3 injection nozzle are installed in the exhaust gas system, when the plant is stopped, and when the drum pressure of the exhaust heat recovery boiler is stopped. A method of operating a combined plant characterized by raising the pressure to a pressure higher than the pressure of .