JPS6239653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiler switching system for starting and stopping an exhaust gas boiler for a combined plant.

In a combined plant that aims to be a high-efficiency power generation plant, it consists of a combination of multiple gas turbines, steam generation equipment (exhaust gas boiler) that uses their exhaust gas, and one steam turbine that is driven by the generated steam. An automatic switching device that sequentially connects or disconnects the exhaust gas boilers when starting and stopping and changing the number of boilers is essential, but these devices have not been developed to date.

To minimize fuel loss, to shorten startup, shutdown, and switching times of a combined plant consisting of a plurality of gas turbines, their associated gas boilers, and one steam turbine, and to minimize fuel losses and shorten startup, shutdown, and switching times. It is necessary to start, stop, and switch while satisfying various limiting conditions. In particular, since there are multiple exhaust gas boilers, one of the key points for the success or failure of a combined plant is to be able to perform complex operations safely, reliably, and automatically. Therefore, it is an object of the present invention to provide a boiler switching system for cold startup/stop among exhaust gas boiler switching systems that achieves these objectives.

The present invention controls the pressure at the outlet of the exhaust gas boiler in accordance with the plant state in order to obtain the required pressure at the time of starting, stopping, and switching the combined plant. In order to adjust the amount of air sent from the exhaust gas boiler, the opening/closing speed of the exhaust gas boiler outlet stop valve is controlled to allow the steam sent from the exhaust gas boiler to flow into the steam turbine, and at the same time to control the opening and closing speed of the exhaust gas boiler outlet stop valve. The basic idea is to control the pressure according to the state of the plant and to control the steam turbine control valve so that the front pressure does not fall below a specified pressure, and to connect and disconnect the exhaust gas boiler.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below as illustrated in the accompanying drawings.

FIG. 1 shows a steam system that supplies air from, for example, three steam generation equipment (boilers) to one steam turbine in a combined plant, and control equipment and circuits that control them.

In the steam system, steam generated in the No. 2 exhaust gas boiler 1 is sent to the steam turbine 4 through the boiler stop valve 2 and the steam turbine control valve 3,
It becomes condensed water in the condenser 5. Similarly, the steam generated in No. 1 and No. 3 boilers (not shown) passes through boiler stop valves 6 and 7, and then is combined with steam from other boilers and sent to the steam turbine 4.

When the boiler stop valve 2 is closed, the pressure transmitter 8 detects the boiler pressure of the No. 2 boiler, the pressure controller 9 compares and controls this boiler pressure with the set pressure, and this output signal is used for common pressure control. After being compared with the control signal from the device 13 and selected by the high signal selector 10, the turbine bypass control valve 11 is controlled.
The amount of steam released to the condenser 5 is adjusted. As a result, the steam pressure of No. 2 boiler 1 is maintained at a specified value.

When the boiler stop valve 2 is open, the common pressure after merging with steam from other boilers is transmitted to the pressure transmitter 12.
The steam pressure of the three boilers is commonly controlled by the common pressure controller 13.

Pressure settings are performed as follows depending on plant conditions.

First, when the boiler stop valve 2 is closed and the boiler pressure is to be controlled individually, the pressure setting device 14 is used to arbitrarily set the pressure, and the signal switch 15 is switched to the individual setting signal side. If not, the common pressure setting device 16 sets the pressure for the three boilers in common, and the signal switch 15 is switched to the common setting side. Furthermore, when the boiler pressure is made to follow the turbine inlet pressure, the signal from the pressure transmitter 12 is smoothed by the signal smoother 17, after a bias is added by the bias adder 18, or after the signal from the smoother 17 is smoothed by the signal smoother 17. is directly applied to the common pressure setter 16 via the signal switch 19 to command the set pressure.

When the boiler stop valve 2 is open, in addition to the common pressure setting or follow-up setting described above, the turbine inlet pressure is detected by the pressure transmitter 37, and the program pressure setting device is set based on this signal (i.e., turbine load). The boiler set pressure can be programmed by 20 set pressures. That is, ultimately, the high signal among the program setting value, follow-up or common setting, and minimum pressure setting (setting by the minimum pressure setting device 21) is selected by the high signal selector 22, and then the maximum pressure setting ( (set by the maximum pressure setting device 23), and the low signal is selected by the low signal selector 24,
A set pressure is applied to the individual pressure controller 9 or the common pressure controller 13.

Boiler stop valves 2, 6 and 7 are high speed opening/closing controller 2
5 or the control signal from the low-speed switching controller 26, the signal switch 27 selects one of the control signals, and the switch is opened or closed in accordance with this signal.

As a protection at this time, the rate of change of the turbine inlet pressure (ie, the rate of change of the turbine load) is kept within a limit value. For this purpose, the turbine inlet pressure is detected by the pressure transmitter 37, the rate of change is detected by the change rate detector 28, and when the value exceeds the limit value, the signal limiter 29 is activated, and the opening/closing controller is activated. The opening/closing operations of 25 and 26 are temporarily suspended. Similarly, the pressure change rate of the boiler is monitored by a pressure transmitter 8, a change rate detector 30, and a signal limiter 31. In addition, since there is a limit to the minimum boiler pressure, the signal limiter 3
The minimum pressure is also monitored in step 2 and operated in the same manner.

The turbine inlet steam pressure is adjusted by controlling the steam turbine control valve by the pressure controller 34 so that the pressure detected by the pressure transmitter 12 becomes the pressure set by the pressure setting device 33. The pressure settings of the pressure setting device 33 include direct pressure setting, in which the pressure setting device 33 directly sets the pressure, and signal switching device 35.
The actual inlet pressure of the steam turbine control valve 3 is detected by the pressure transmitter 12, and this is passed through a signal smoother to set the set pressure, thereby making the pressure setting follow the turbine inlet pressure. There are pressure setting and ramp pressure setting in which the target pressure setter 36 is selected by the signal switch 35 to increase or decrease the target set pressure at a predetermined rate of change.

The operation of the system according to the present invention will be explained.

Examples of cold startup and shutdown curves for a combined plant are shown in FIGS. 2 and 3. The operation of the exhaust gas boiler switching system corresponding to this will be explained.
In a combined plant as well, the distinction between cold startup and shutdown and hot startup and shutdown is determined by the steam turbine rotor temperature, and in the case of cold startup, steam is slowly released to avoid thermal shock to the steam turbine rotor. Although complicated operations are required to flow the electricity, it is also necessary to quickly reach the required amount of power generation, which is the mission of a power generation plant. Furthermore, it is necessary to start the engine with as little fuel loss as possible. An example of a startup method that satisfies these requirements is shown in FIG. Even in the case of suspension,
It is desirable to have a stopping method that takes a short time and reduces fuel loss. An example is shown in FIG.

During cold start-up, the No. 1 gas turbine (abbreviated as #1G/T in the drawing) starts early to heat soak the steam turbine (abbreviated as S/T), and the No. Generate steam. In this case, the No. 1 boiler outlet stop valve 6 is already fully open, and the No. 1 turbine bypass control valve (not shown) is controlling the turbine inlet steam pressure to a specified pressure. When the load on the steam turbine increases and steam from the No. 2 exhaust gas boiler reaches a state where it can be added, the No. 2 gas turbine is started, steam is generated from the No. 2 boiler, and the conditions for mixing are met. Once the conditions are met, additional steam is sent to the steam turbine.

This method of supplying additional air is called switching during cold startup.

The switching procedure will be explained with reference to FIG.
First, the No. 2 boiler outlet pressure is changed from individual pressure control to follow-up mode using the turbine bypass control valve 11, pressure transmitter 8, and pressure controller 9, and the pressure setting is switched to follow-up mode using the signal switch 19, and the pressure setting device 16 is activated. The pressure is controlled to be the same as the turbine inlet pressure. This is to prevent the turbine inlet steam pressure from changing when steam from No. 2 boiler 1 is mixed.

At this time, the steam turbine control valve 3 is controlled by a load control device (not shown) so that the steam turbine 4 increases its load at a required load change rate. In this state, the steam needed to increase the load on the turbine 4 is
In order to supply air from the No. 2 boiler, the signal switch 27 selects the low-speed opening/closing controller 26 to gradually open the boiler stop valve 2 at the outlet of the No. 2 boiler. When the boiler stop valve 2 is fully opened, the turbine inlet steam pressure is controlled by the common pressure controller 13 for both the No. 1 boiler and the No. 2 boiler.

As the load on the turbine increases, the turbine bypass control valve 11 gradually closes. As mentioned above, during this time, the boiler pressure and the turbine inlet pressure are each monitored and controlled.

The boiler side of No. 3 also has the same turbine bypass control section and boiler outlet stop valve control section as No. 2.
In the same manner, steam is delivered to a steam turbine. When the load on the steam turbine further increases and the entire amount of steam generated in the boiler is consumed, all the bypass control valves 11 are fully closed and startup is completed.

Along with this, the turbine control valve 3 is fully opened.
When this state is reached, the turbine inlet steam pressure becomes sufficiently high, the pressure transmitter 37 and the program pressure setting device 20 operate, essentially setting the boiler pressure, and the turbine bypass control valve 12 functions as an advance safety valve. It operates to maintain the safety of the system.

Next, FIG. 3 shows an example of a stopping method that minimizes fuel loss and performs stopping for a short period of time when the purpose is to stop the engine for a long period of time. In this case as well, an example of a combined plant with three gas turbines (three exhaust gas boilers) and one steam turbine is shown. In order not to give any disturbance to the steam temperature to the steam turbine 4, the load on the three gas turbines is reduced to the point where the steam temperature of the boiler can be maintained at a specified value, thereby saving fuel. At this load, No. 1 boiler is disconnected (#1S/G disconnection),
The front pressure of the steam turbine control valve 3 at this time is different from that in the case of cold startup. Further, the pressure when disconnecting the No. 2 boiler is also different from the pressure when disconnecting the No. 1 boiler.

Therefore, it is much easier to control if the pressure setting value of the turbine bypass control valve 11 is set in accordance with the state of the plant.

The switching procedure will be explained with reference to FIG. First, the gas turbine load is lowered, and when it is time to disconnect the boiler, the signal switch 19 is activated by a switching command, and the common pressure setting device 16 is set to follow mode.
The pressure is set to +α ^K to the front pressure of the steam turbine control valve 3. The turbine bypass control valve 11 is controlled by the pressure controller 9 and the common pressure setting device 16 so that the pressure follows the turbine inlet pressure. At the same time, the signal switch 27 is operated to select the high speed opening/closing controller 25 to close the boiler stop valve 2 at high speed in accordance with the load change rate of the steam turbine. As a result, the remaining steam turbine bypass control valve 11 dumps the remaining steam to the condenser 5. When the boiler stop valve 2 is fully closed, the pressure setting device 14 is selected by the signal switch 15 to switch from common pressure control to individual pressure control. After that, when the gas turbine load further decreases and it is time to stop the No. 2 boiler, each boiler is switched in the same manner.

Boiler No. 3 will be stopped when the gas turbine is stopped, and the shutdown will be completed.

Although not particularly shown in the drawings, starting and stopping the boiler switching device described above at the required times can be performed by an operator or a computer. Furthermore, once the switching is completed, each control circuit can of course be removed as necessary.

In a combined plant where multiple gas turbines and exhaust gas boilers are combined with one steam turbine, it is necessary to start and stop the gas turbines and exhaust gas boilers in an orderly, safe and reliable manner. One of the key points for the success or failure of this combined plant is that it can be carried out more easily and safely than conventional plants, but according to the present invention, as mentioned above, it is possible to automatically operate multiple exhaust gas boilers. The cold startup and shutdown can be performed safely and in an orderly manner, that is, by coordinating the turbine bypass control system and the boiler stop valve control system, the above can be achieved.

Although the present invention has been described above in detail with reference to its preferred embodiment, the present invention is not limited to this specific embodiment and can be modified in many ways without departing from the spirit of the invention. For example, in this example, the opening and closing speed of the boiler stop valve 2 is described as high speed and low speed, but
This can be further subdivided depending on the number of boilers 1 to be operated and the required speed of the steam turbine. In addition, particularly when there is a possibility that the number of boilers 1 to be operated at the same time may be changed, sensitivity correction may be performed in order to equalize the influence on the rate of change in load of the steam turbine.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an exhaust gas boiler switching system according to the present invention, FIG. 2 is a diagram showing a cold startup curve, and FIG. 3 is a diagram showing a normal shutdown curve. 1... Boiler, 2, 6, 7... Boiler stop valve, 3
...Steam turbine control valve, 4...Steam turbine,
5... Condenser, 8, 12, 37... Pressure transmitter,
9,13,34...pressure controller, 10,22...
High signal selector, 11... Turbine bypass control valve, 14, 16, 33, 36... Pressure setting device, 1
5, 19, 27, 35...signal switch, 17...
Signal smoother, 18...Bias adder, 20...
Program pressure setter, 21...Minimum pressure setter, 23...Maximum pressure setter, 24...Low signal selector, 25...High speed switching controller, 26...Low speed switching controller, 28, 30... rate of change detector, 29,
31, 32...Signal limiter.

Claims (1)

[Claims] 1. In a complex combined plant consisting of multiple gas turbines, multiple exhaust gas boilers that generate steam using exhaust gas from the gas turbines, and one steam turbine, the steam pressure is set at the outlet of each exhaust gas boiler. A turbine bypass control valve and a boiler stop valve are provided to control the boiler outlet pressure by dumping the steam, and the steam after merging at the outlet of the boiler stop valve is supplied to the steam turbine. A plurality of individual pressure controllers that individually control the control valves and a common pressure controller that simultaneously controls all of the control valves, and the individual pressure settings are related to the pressure settings of the individual pressure controllers. The common pressure controller includes a turbine bypass control valve control device that is associated with a common pressure setting and a follow-up pressure setting, and a boiler stop valve control device that opens the boiler stop valve at a low speed and closes the boiler stop valve at a high speed,
At the time of plant startup, the first boiler stop valve is fully opened and the first exhaust gas boiler is controlled to the lowest pressure by individual pressure settings, and when the additional air supply conditions for the second exhaust gas boiler are satisfied, the set pressure is changed to the follow-up pressure. As a setting, the first and second turbine bypass control valves are controlled, and when the boiler outlet pressure and the turbine inlet pressure become the same, the second boiler stop valve is opened at low speed, and when the second stop valve is fully open, the second boiler stop valve is opened at low speed. All boiler stop valves are fully opened and all turbine bypass control valves are fully closed so that the boiler switching in step 3 is started, and when the plant is stopped, all gas turbine loads have been lowered to the specified value. One of the boiler stop valves is closed at high speed, and the boiler stop valve is closed in accordance with the load change rate of the steam turbine while controlling the boiler outlet pressure to a value slightly larger than the turbine inlet pressure using the set pressure as the follow-up pressure setting. A boiler switching system during cold startup and shutdown of a combined plant, characterized by sequential closure at high speed.