JPS6124523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combined plant operation control method, and more particularly to a combined plant operation control method that suppresses steam turbine rotor thermal stress, which is largely affected by changes in the load of the combined plant.

Here, a conventional method of operating a combined plant in which a gas turbine and a steam turbine are combined will be explained.

In FIG. 1, exhaust gas that has passed through a gas turbine 1 is guided to a steam generator 2 that uses the exhaust gas as a heat source to generate steam, and this generated steam drives a steam turbine 3. This is a combined plant in which steam discharged from the steam turbine 3 is condensed into condensate in a condenser 4, and is circulated to the steam generator 2 again via a condensate pump 5. In the operation control of the combined plant, the load command device 9 issues an output request signal L _D for the combined plant, and the adder 11 outputs the gas turbine output L _G from the gas turbine load 6 and the steam output from the steam turbine load 7. The total output L including the turbine output L _s is calculated, and the comparator 10 calculates the required output L _D
The deviation between the total output L _s and the total output L s is calculated as the output change signal ΔL. This output change signal ΔL is then transmitted to the fuel control device 12 that controls the fuel supplied to the combustor 13 of the gas turbine 1, where it is converted into a fuel control signal F to adjust the load L _G of the gas turbine. It's summery. However, the load adjustment of the gas turbine is controlled at a certain constant load change rate, which is set without taking into account the rotor thermal stress of the steam turbine.

The reason why the steam turbine rotor thermal stress was not considered in conventional combined plant operation control is as follows. That is, in a combined plant, as shown in Figure 2, when the load L _G of the gas turbine changes, the exhaust gas temperature T _G changes greatly, and the temperature of the steam flowing into the steam turbine changes accordingly. do. Therefore, as shown in FIG. 3, both the steam turbine load L _s and the steam temperature T _s after the first stage of the steam turbine change, making it difficult to control the rotor thermal stress of the steam turbine.

In a typical thermal power plant, the steam temperature is constant, and the steam temperature inside the turbine can be adjusted by adjusting the load on the steam turbine, so if thermal stress occurs, the thermal stress can be immediately brought within the allowable value. It is possible to suppress the

However, in a combined plant, when the output of the gas turbine changes, the steam turbine load fluctuates with a delay equal to the time constant of the steam generator.
At the same time, the steam temperature itself fluctuates, so it was completely impossible to control thermal stress using the steam turbine alone.

In other words, as shown in Fig. 4, the gas turbine load L
When _G changes by ΔL _G within Δt time, the exhaust gas temperature T _G also changes by ΔT _G , but due to the response delay of the steam generator, the steam temperature T _s and the steam turbine load L _s
There is a time delay td in the change of This was already too slow and the thermal stress of the steam turbine exceeded the limit value, which was extremely difficult to control.

In other words, even if the thermal stresses in the steam turbine were monitored, this would not protect the steam turbine. However, in recent years, emphasis has been placed on life consumption management based on rotor thermal stress of steam turbines in the transition to medium-sized thermal power generation, and it goes without saying that management of rotor thermal stress is also required for steam turbines in combined plants, so it is urgently necessary to manage rotor thermal stress. There was an urgent need to establish this type of technology.

An object of the present invention is to provide a combined plant operation control method that enables life consumption management of steam turbines in a combined plant that combines a gas turbine and a steam turbine.

A feature of the present invention is that in order to manage the rotor thermal stress, which is a control value for the life consumption of the steam turbine, an allowable load change rate of the steam turbine is defined, and thereby the load of the gas turbine is A method for controlling the operation of a combined plant that controls changes.

Next, a method for controlling the operation of a combined plant combining a gas turbine and a steam turbine, which is an embodiment of the present invention, will be described.

In FIG. 5, since the schematic system of the combined plant is the same as that shown in FIG. 1, the explanation will be omitted, and the details of the operation control will be explained. In the figure, an output request signal L _D issued from a load command device 9 is input to a comparison device 10. Output signal L _G from load 6 of gas turbine 1
and the output signal L _s from the load 7 of the steam turbine 3
is calculated by the adder 11 as the output signal L of the combined plant, and is input to the comparator 10 where it is compared with the output request L _D. The deviation signal between the two calculated by the comparison device 10, that is, the output change signal ΔL, is input to the output control device 14 to calculate the allowable load change rate ΔL/Δt, and this allowable load change rate signal ΔL/Δt is The signal is guided to the combustion control device 12 and converted into a fuel control signal to control the load on the gas turbine. In this case, the temperature and flow rate of the steam that has passed through the steam generator 2 change due to the temperature change of the exhaust gas, which causes a change in the load on the steam turbine. thermal stress occurs. Therefore, the output control device 14 is designed to reduce the lifetime consumption of the steam turbine due to this thermal stress to within a specified range.

In other words, Figure 6 shows the lamp response characteristic diagram.
A response signal B is obtained with a delay of a certain time constant with respect to the input signal A, but this corresponds to a change in the temperature of the steam generated in the steam generator or a change in the load on the steam turbine in response to a change in the load on the gas turbine. are doing. FIG. 4 specifically shows these relationships. In other words, when the gas turbine load L _G fluctuates over a certain time period _Δt ,
The exhaust gas temperature T _G becomes a temperature change ΔT _G , and after the time delay td of the steam generator, the steam temperature T _s and the steam turbine load L _s become a temperature change ΔT _s and a load change Δ, respectively.
produces L _s .

In this series of changes, the average rate of change for each is
The maximum is equivalent to the load change rate of a gas turbine,
Generally lower, it is possible to limit the thermal stresses that occur in the steam turbine rotor during plant load changes in the manner described below.

That is, in FIG. 7, the gas turbine load is L.
When the load changes ΔL _G from _G1 to L _G2 , a temperature change ΔT _G occurs in the exhaust gas temperature from T _G1 to T _G2 . As shown in FIG. 8, the load L _s of the steam turbine also changes ΔL _s with a delay of a certain time (response delay of the steam generator) td, and the steam temperature after the first stage of the steam turbine ΔT _s (a steam turbine without a regulating stage) (equivalent to the steam temperature at the turbine inlet) is also the temperature change Δ
L _s occurs. Although it is not actually a linear characteristic,
There is not much difference even if we consider typical average gradients. The rate of temperature change after the first stage of the steam turbine at this time is defined as ΔT _s /ΔL _s .

An allowable rate of temperature change is determined for this temperature change ΔT _s .

FIG. 9 shows the temperature change rate ΔT _s /Δ that is allowable for a steam turbine for a certain temperature change width ΔT _s .
Indicates t.

This figure shows the metal allowable temperature change rate-temperature change width limit characteristic that can be calculated in advance for each steam turbine, and is defined for the set life consumption rate.

In other words, at a certain set life consumption rate, the temperature change width at the thermal stress point of the steam turbine is ΔT
_s , the maximum allowable temperature change specified at this time is ΔT _s /Δt.

Based on the above conditions, the maximum allowable load change rate ΔL _s /Δt in the steam turbine is expressed by the formula shown below.

ΔL _s / Δt = ΔT _s / Δt / ΔT _s / ΔL _s = Allowable temperature change rate / Temperature change rate after first stage In other words, when the amount of steam turbine load change when the plant load changes by ΔL _p is ΔL _s , the steam The maximum allowable load change rate ΔL _s /Δt of the turbine is the change rate ΔT _s /ΔL _s after the first stage of the steam turbine, and the allowable temperature change rate ΔT _s /at a certain set life consumption rate.
This can be determined by Δt. Maximum allowable temperature change rate ΔL _s /Δt of this steam turbine
can be expressed as shown in FIG. 10 using the load change width ΔL _s of the steam turbine as a parameter.

Furthermore, Fig. 11 shows the relationship between the plant load L _p and the steam turbine load L _s , which is an almost linear relationship, and the characteristics shown in Fig. 10 can be used as is as the allowable load change rate for a combined plant. be.

In other words, it is possible to determine what the allowable load change rate should be from the amount of load change based on the above characteristics.

Therefore, by controlling the load on the gas turbine based on this allowable load change rate, it is possible to manage the life consumption of the steam turbine.

By using this operation control method, it is possible to operate a combined plant at the maximum load change rate that can be achieved at that time, and it is possible to maintain reliability and durability without sacrificing the originally required speed and flexibility. This enables much better plant operation in terms of Furthermore, according to this embodiment, operation control can be performed not only manually but also in automatic plant operation.
It goes without saying that proper and safe combined plant operation can be expected.

According to the present invention, in a combined plant that combines a gas turbine and a steam turbine, it is possible to realize load control of the combined plant that enables lifetime consumption management of the steam turbine.

[Brief explanation of the drawing]

Figure 1 is a diagram of the operation control system of a conventional combined plant, Figure 2 is a diagram of exhaust gas temperature characteristics of a gas turbine, Figure 3 is a diagram of temperature characteristics after the first stage of a steam turbine, and Figure 4 is a diagram of exhaust gas when the gas turbine load changes. ,
Steam temperature and steam turbine load response characteristic diagram, Figure 5 is an operation control system diagram of a combined plant that is an embodiment of the present invention, Figure 6 is a general ramp response characteristic diagram, and Figure 7 is a gas turbine exhaust gas diagram. Temperature characteristic diagram, Figure 8 is the temperature characteristic diagram after the first stage of the steam turbine, Figure 9 is the allowable temperature change rate characteristic diagram of the steam turbine, Figure 10 is the allowable load change rate limit characteristic diagram, Figure 1 is the temperature characteristic diagram after the first stage of the steam turbine.
Figure 1 is a diagram showing the relationship between steam turbine load and plant load. 1...Gas turbine, 2...Steam generator, 3...
... Steam turbine, 6, 7 ... Load, 9 ... Load command device, 10 ... Comparison device, 11 ... Addition device,
12...Fuel control device, 14...Output control device,
13...Combustor.

Claims (1)

[Claims] 1. A method for controlling the operation of a combined plant having a gas turbine, a steam generator using the exhaust gas of the gas turbine as a heat source, and a steam turbine driven by the steam generated from the steam generator,
Operation control of a combined plant, characterized in that an allowable load change rate of a steam turbine is calculated according to a load change between a required load and an actual load of the plant, and a gas turbine load is controlled based on this load change. Method.