JPH0370805A - Controlling method of compound generating plant - Google Patents

Abstract

PURPOSE:To eliminate a gas turbine trip caused by rough burning by either reducing the steam turbine output to an output, which is lower than an ordinary output, or making run-back, when a load dump takes place. CONSTITUTION:If a load dump contact 14 of a load dump detecting circuit 17 is turned on, when a load dump takes place, a relay 26 is excited, and its auxiliary contact 26a is turned off, while another auxiliary contact 26b is turned on. Owing to this switching, automatic selection is made from governing ratio of 1/R1, 16a, to another governing ratio of 1/R2, 16b. As a result, a steam turbine control valve 13 is operated at a high governing ratio only when the load dump takes place. Therefore, the output of a steam turbine 6 is suppressed to a governing ratio which is lower than an ordinary one, and, as a result, a gas turbine 3 is continuously operated at an high output. Accordingly, stabler, low-load operation of the gas turbine 3 can be obtained, thereby increasing the possibility of continuous, isolated operation of the turbine within the plant.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a gas turbine (regardless of whether it is a -shaft type or a multi-shaft type).
and an exhaust heat recovery boiler (HR) that generates steam from the exhaust gas.
The present invention relates to a control method during load shedding of a combined power generation plant comprised of a steam turbine (referred to as 8G) and a steam turbine that generates steam power.

(Prior art) In particular, in a combined cycle power plant equipped with a gas turbine that uses fuel such as coal gas, which has poor combustion safety at low flow rates, the calorific value of gas such as coal gasified fuel is Combustion stability is very poor at low flow rates, i.e., extremely low output of the gas turbine. , combustion may become unstable and a misfire may occur, potentially causing a gas turbine trip.

Conventional gas turbine fuels have been fuels with a high calorific value such as LNG and kerosene, but in recent years coal gasified fuel or blast furnace exhaust gas has a low calorific value of 1000 Kcal/Kg, so when a load shedding occurs There are problems with continued operation of gas turbines.

For this purpose, Japanese Patent Application Laid-Open No. 58 (1982) has also attempted to achieve stable combustion and continuous operation of the gas turbine by automatically switching the fuel from coal gas fuel to liquid fuel with a high calorific value when load interruption occurs. It is published in Publication No.-119933.

An example of the system configuration of this conventional system will be explained using a combined power generation plant using coal and gas shown in FIG. 5 as an example. That is, in FIG. 5, coal fuel is gasified and refined in coal gasification equipment 1. The gas turbine fuel control valve 2 adjusts the gas fuel flow rate of this purified gas to the gas turbine 3, and the output of the gas turbine generator 4 is controlled. The exhaust gas from the gas turbine 3 enters the HR8G5 to generate steam. The steam generated by cooling the generated gas of the coal gasification equipment is also diverted to the HR8G5, and the steam produced by the HR8G5 is sent to the steam turbine 6 via the steam turbine control valve 13 to do work and generate steam. A turbine generator 8 generates electric power.

In the case of a coal gasification power plant, as mentioned above, steam generation is accompanied by cooling the coal gas, so the ratio of the output of the gas turbine 3 to the output of the steam turbine 6 is 1:1 compared to normal combined cycle power generation. 1, the steam turbine output accounts for a large proportion of the overall output. In addition, normal N
In G-fired combined power generation, the ratio of gas turbine output to steam turbine output is 2:1. Furthermore, as mentioned above, coal gasification power plants have a feature that the calorific value of coal gas, which is the fuel for the gas turbine, is very low, and the combustion stability in the gas turbine is poor at low flow rates.

Now, the steam turbine generator 8 and the gas turbine generator 4
The electric power generated in each case is boosted by a step-up transformer 11 via a circuit breaker 10.9, and connected to the power grid via a system breaker 12. In addition, the in-house electric power of this plant uses a portion of the output of each of the gas turbine and steam turbine. Generally, the amount of electricity in a station is about 10% of the total power generation output.

During operation in a system such as that shown in FIG.
When this combined cycle power generation plant is disconnected from grid 6, the power that was previously transmitted to the power grid and the in-house load grid L'
As a result, the frequency of the station system L' increases instantaneously (about 1 to 2 seconds), the governors of the gas turbine 3 and steam turbine 6 operate, and the gas turbine fuel control valve 2 and steam turbine control Valve 13 is continuously throttled. This operation continues until the sum of the gas turbine output and the steam turbine output matches the station load.

This operation supplies the load only for the in-house power demand, while
Because it continues to operate at low output, it is called in-plant isolated operation, and is an important function that most conventional thermal power plants have in the event of an accident on the power system side.

(Problem to be solved by the invention) However, during this isolated operation within the station, by simply calculating,
In the case of load interruption during 100% rated load operation, if the gas turbine:steam turbine output ratio is 1:1, the station load is approximately 10%, so both the gas turbine and the steam turbine must be operated at 5% output. By doing this, the power generated by the gas turbine balances the on-site load, the on-site frequency is also stabilized, and on-site independent operation is achieved. However, 5% gas turbine output corresponds to 10% of the gas turbine output rating, resulting in significant combustion instability and a high probability of gas turbine misfire trips. If gas turbine 3 trips, H
The steam generation of R865 is inhibited, and the steam turbine 6 subsequently trips, resulting in a serious situation where the entire station is shut down.

The purpose of the present invention is to prevent gas turbine tripping caused by unstable fuel in the gas turbine at low fuel flow rates in a combined cycle power plant that uses fuel with a low calorific value, to achieve continuous operation of the gas turbine, and to The present invention provides a method for controlling a combined power generation plant during load interruption to achieve successful islanding.

[Structure of the Invention] (Means for Solving the Problems) The method for controlling a combined cycle power plant of the present invention is a method for controlling a combined cycle power plant of the present invention, which uses a gas turbine, an exhaust heat recovery boiler, and a steam turbine that use fuel with a low calorific value such as coal gas and blast furnace exhaust gas. A combined power generation plant constructed of the following is characterized in that when a load shedding occurs, the steam turbine output is throttled or run back to an output lower than the load throttled by a normal governor.

(Function) In the present invention, when a load cutoff occurs, the governor of the steam turbine increases the restriction to increase the output reduction effect of the steam turbine, or the steam turbine is forcibly tripped.

As a result, the gas turbine output is kept high, the combustion stability of the gas turbine is improved, and the gas turbine continues to operate, thereby achieving successful isolated operation within the station.

(Example) The present invention will be described below with reference to examples shown in FIGS. 1, 2, 3, and 4. The control system of a combined cycle power plant in which the control method for a combined cycle power plant of the present invention is implemented is similar to that shown in FIG. It is something.

Therefore, the embodiment of the present invention shown in FIG.
The relationship diagram will be explained. In FIG. 1, the steam turbine controller 25 has a speed setting S. and the speed S of the steam turbine 6 are added by an adder 1-58 to obtain the deviation △f.
Calculate this deviation △f and load setting. and adder 15
The control signal S2 for the steam turbine control valve 13 is created by adding the signals at step b.

In order to carry out the new control method of the present invention, a 1/R1 adjustment rate 16a and a 1/R2 adjustment rate 16b are provided in the circuit for the deviation Δf between the adder 15a and the adder 15b, and The fixed ratios 16a and 16b are configured to be selectively switched by switching contacts 26a and 26b. In the embodiment shown in FIG. 1, two adjustment rates 16a, 1
6b is switched by the load cutoff detection circuit 17. That is, when a load shedding occurs, the contact 14 of the load shedding detection circuit 17 closes and the relay 26 operates, the contact 26a of the regulation rate switching circuit opens and the contact 26b closes, and the deviation △f becomes 1/R2 regulation rate 16b. Adder 1 via
5b.

Here, 1/R4 regulation rate 1 of the steam turbine control device 25
6a is 5% of the normal adjustment rate (R0 = 0.05), 5
It has a function of reducing the output of the steam turbine 6 to no load when a % rotation speed deviation occurs.

On the other hand, when a load interruption occurs, an even larger 1/R2 regulation ratio 16b of 2% (R2 = 0.02) is automatically selected, and the output of the steam turbine 6 is adjusted with a rotational speed deviation of 2%. The output of the steam turbine is reduced by reducing the load to no load, and as a result, the output of the gas turbine 3 is increased to ensure stable operation of the gas turbine.

Next, a method of controlling a combined cycle power plant according to the present invention will be explained using the embodiment shown in FIG. During normal operation, speed is set to S. and speed S1 are parallel to the system, the deviation △f is zero, and the load is set. The control valve 13 of the steam turbine is opened or closed by the change in the steam turbine 6, and the output of the steam turbine 6 is increased or decreased.

In this state, the normal adjustment rate 16a is selected to be 1/R.

Generally, generators connected to the power system are set to the same regulation rate, and a value of about 5% is often used. FIG. 2 illustrates the frequency (increase in rotational speed) and the movement of the steam turbine control valve 13, that is, the rate of change in the output of the steam turbine 6 in this setting.

That is, in FIG. 2, when the 1/R adjustment rate 16a is 5% at 100% load setting, the deviation Δf.

It is shown that the load is reduced to the output of the steam turbine 6 to the output Pl when a rotational speed deviation occurs. On the other hand, the auxiliary contacts 26a, 26 of the relay 26 of the load cutoff detection circuit 17
By switching b, the 1/R adjustment rate 16a is switched to the 1/R2 adjustment rate 16b.

Since this 1/R2 regulation rate 16b is a 2% regulation rate as shown in FIG. 2, the output of the steam turbine 6 can be reduced to the output P2 with the same rotation speed deviation Δf.

Therefore, in FIG. 1, when a load shedding occurs, the load shedding contact 14 of the load shedding detection circuit 17 is turned on, the relay 26 is exemplified, its auxiliary contact 26a is turned off, and its auxiliary contact 26b is turned on. Both auxiliary contacts 26a,
By switching 26b, the adjustment rate 16a of 1/R1 is changed to 1/R1.
The adjustment rate 16b of R2 is automatically selected. This regulation rate switching operates the steam turbine control valve 13 at a high regulation rate only when a load cutoff occurs, and the steam turbine control valve 13 is operated at a high regulation rate only when load interruption occurs.
The output of the gas turbine 3 is suppressed to the regulation rate (0,2), which has a lower setting value than the normal regulation rate (0,5) of 1/R1, and as a result, the output of the gas turbine 3 continues to operate at a high output. becomes possible.

As described above, according to the control method of the present invention, the steam turbine 6
Since the output reduction is large and the output of the gas turbine 3 can be increased accordingly, the fuel flow rate of the gas turbine 3 is also large.

Therefore, more stable low-load operation of the gas turbine is possible, and the possibility of continuing independent operation within the plant increases.

The embodiment shown in FIG.
6b switches between the 1/R1 adjustment rate 16a and the 1/R2 adjustment rate 16, but this circuit can also be realized by a set value switching circuit of a digital circuit. In addition, in Fig. 1, the method focuses on changing the regulation rate of the governor, but the ultimate purpose is to operate the steam turbine 6 with the output as low as possible (for example, without using a governor). Alternatively, the opening degree setting of the steam turbine control valve 13 may be run back so as to forcefully control the output to a certain minimum output.

Next, another embodiment of the present invention shown in FIG. 3 will be described. In this embodiment, the adder 1 of the steam turbine control device 25
Only a 1/R adjustment rate 16a is provided between 5a and 15b, and a low value priority circuit 23 is provided between the adder 15b and the steam turbine control valve 13, and a preset minimum output signal generator 22 signal is provided. The lowest output signal is given to the steam turbine control valve 13 to rapidly reduce the output of the steam turbine 6 by giving priority to the lowest value of the deviation Δf.

In other words, the load shedding occurrence contact of the load shedding detection circuit 17↑
4 turns on, the auxiliary contact 26a of the relay 26 turns on and inputs the signal from the lowest output signal generator 22 to the low value priority circuit 23. Therefore, the steam turbine control valve 13 is controlled by the signal from the low value priority circuit 23, and rapidly reduces the output of the steam turbine 6. Moreover, this load reduction method does not use the low value priority circuit 23 as shown in FIG. 3, but instead sets the load. This can also be handled by running back. That is, as a result, any method that can set the steam turbine control valve 13 to an opening degree lower than the opening degree of the steam turbine control valve 13 set by the governor is sufficient instead of the usual governor control.

Next, another embodiment shown in FIG. 4 will be described.

In this embodiment, when a load interruption occurs, the steam turbine 6 is forced to
shows how to trip. That is, the steam stop valve 2 is connected in series with the steam turbine control valve 13 of the steam turbine 6.
1 is provided, and this trip electromagnetic valve 18 is controlled by a load cutoff detection circuit 17 and a steam turbine trip circuit 27.

In FIG. 4, the contact 26c of the relay 26 of the load interruption detection circuit 17 is input to the steam turbine trip circuit 27. This steam turbine trip circuit 27 has another steam turbine trip causing contact 20 that excites the trip relay 19, and a load interruption generation contact 26c is inserted in parallel with these contacts.

Trip relay 19 is activated by this load cutoff generation contact 26c.
is excited, the trip electromagnetic valve 18 is excited, the oil supplied to the oil cylinder of the steam stop valve 21 is drained, the steam stop valve 21 is instantly fully closed, and the steam turbine 6 is tripped. If the steam turbine 6 trips, the entire station load will be borne by the gas turbine 3, and as a result, the gas turbine 3. When the steam turbines 6 share half the power, the output of the gas turbine 3 can be twice as much as when the gas turbine 3 is operated independently in the plant compared to the case where the gas turbine and the steam turbine coexist. greatly contributes to the stable combustion of

[Effects of the Invention] As described above, in the present invention, when a load interruption occurs, the output of the steam turbine is lowered to an output lower than the set output in normal control, or the steam turbine is forcibly tripped. As a result, by reducing the gas turbine output, which reduces the plant load,
The fuel flow rate of the gas turbine increases accordingly, and the stable combustion of the gas turbine allows the gas turbine to continue operating.As a result, by achieving successful isolated operation within the station, it is possible to prevent serious accidents that would result in a complete shutdown of the station. I can do it.

[Brief explanation of drawings]

FIG. 1 is a control system diagram showing an embodiment of a steam turbine control device for explaining the control method for a combined cycle power plant of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between the steam turbine output and deviation. 3 and 4 are control system diagrams of a steam turbine control device showing other embodiments of the present invention, respectively, and FIG. 5 is a schematic configuration diagram for explaining a composite plant. 3...Steam turbine control valve 4...Load cutoff occurrence contacts 5a, 15b...Adders 6a, 16b...Adjustment rate 7...Load cutoff detection circuit 9...Trip relay 8... Trip solenoid valve 0...Steam turbine trip cause contact 1...Steam stop valve 2...Minimum output signal generator 3...Low value priority circuit 5...Steam turbine control device 6...Relay 7...Steam turbine trip circuit 1...Coal gasification equipment 3...Gas turbine 5...Exhaust heat recovery boiler (HR3G) 6...Steam turbine (8733) Agent Patent attorney Sho Inomata ( (and 1 other person) Figure 1 Figure 3 Figure 2

Claims (1)

[Claims] In a combined power generation plant consisting of a gas turbine that uses fuel with a low calorific value such as coal gas or blast furnace exhaust gas, an exhaust heat recovery boiler, and a steam turbine, when a load shedding occurs, the steam turbine output is lower than the load that is throttled by a normal governor. A method for controlling a combined power generation plant, characterized in that the output is reduced to a low output or runback.