JPS6360211B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for controlling a low-pressure turbine bypass system for protecting a condenser against a reduction in the amount of cooling spray in the control of a low-pressure turbine bypass system.

[Prior art]

A conventional method for controlling a low-pressure turbine bypass system is to spray cooling water at a constant rate to the amount of low-pressure turbine bypass steam to perform cooling. Therefore, in the event that this cooling water is no longer available, the cooling water pressure switch detects this and forcibly closes the steam control valve (low-pressure turbine bypass valve) that controls the amount of bypass steam. Was. However, although this detection method could protect against cooling water cutoffs due to pump failure, it did not protect against cases where the spray amount was not actually flowing due to a stuck spray valve or a clogged spray nozzle.

[Purpose of the invention]

An object of the present invention is to provide a control method for a low-pressure turbine bypass system that can realize appropriate protection against abnormalities in the low-pressure turbine bypass system, particularly when the required amount of cooling water is actually no longer supplied.

[Summary of the invention]

In the present invention, the actual flow rate of cooling water is detected, an allowable amount of steam flowing into the low-pressure turbine bypass system is calculated from the detected value, and the actual amount of steam flowing in is controlled to match this amount of steam.

[Embodiments of the invention]

Examples will be described below with reference to the drawings. FIG. 1 shows an example of an entire plant system having a low pressure turbine bypass system. Steam generated in a heater 2 in a boiler 1 is normally sent to a high-pressure turbine 4 to perform work, and then returned to a reheater 3. However, if steam is not required due to circumstances on the turbine side such as the turbine startup conditions not being met or a failure on the turbine side, the high pressure turbine inlet valve 40 is closed and the high pressure turbine bypass valve 7 is closed.
By opening, the steam bypasses the high pressure turbine 4 and returns the steam generated by the boiler 1 to the reheater 3. This steam is reheated and sent to the intermediate pressure turbine 5 again. In this case, the amount of surplus reheated steam is controlled by adjusting the low-pressure turbine bypass valve 8 so that the amount of incoming steam on the intermediate-pressure turbine side is equal to that on the high-pressure turbine side. The bypassed steam is dumped into the condenser 10 after being cooled down. That is, the pressure detector 18 detects the reheat steam pressure when the high pressure turbine bypass valve 7 opens and the reheat steam flow rate increases.
The detected value increases from the normal operating value. This rise in pressure opens the low-pressure turbine bypass valve 8, bypasses the steam flowing into the intermediate-pressure turbine 5 and the low-pressure turbine 6, and dumps the steam to the condenser 10.
In order to suppress the temperature rise in the condenser 10, cooling spray water proportional to the amount of low-pressure bypass steam is supplied to the steam attemperature device 9 by the condensate pump 13 via the spray control valve 12. In the steam temperature reduction device 9, the bypassed reheated steam and spray water are mixed and cooled and dumped into a condenser. Inside the condenser 10, the water is further cooled by the condenser cooling water 11 and becomes condensed water. This condensate is recycled to the boiler. That is, this condensate is supplied to a low-pressure heater 14 by a pump 13, further deaerated by a deaerator 15, and then supplied to a high-pressure heater 17 by a feed water pump 16, and then supplied to the boiler 10. The low-pressure turbine bypass control device 21 opens the low-pressure turbine bypass valve (bypass steam control valve) 8 in response to an increase in the detection value of the pressure detector 18 that detects reheat steam pressure.
The amount of bypass steam flowing by opening this bypass steam control valve 8 is detected by a pressure detector 19. The spray control valve 12 is controlled by the output of this detector 19.

In the present invention, when this spray water no longer flows as required, the high temperature steam flowing through the bypass steam control valve 8 flows directly into the condenser 10 and protects the condenser from being damaged.

An example of a control circuit for this protection is shown in FIG.
In this figure, 18 is a pressure detection valve that detects the reheat steam pressure, and 19 is a pressure detector that detects the outlet pressure of the bypass steam control valve 8. 20 is a spray flow rate detector that detects the flow rate of cooling spray water. 22 is a flow rate detector that detects the amount of steam flowing into the high-pressure turbine. These 18, 19,
The installation locations of the detectors 20 and 22 are illustrated in FIG. 23-1 to 23-3 are function generators. Reference numeral 23-1 inputs the high-pressure turbine steam amount and outputs a reheat steam pressure setting value, and generates a function as shown in FIG. 3a. 23-
2 inputs the spray flow rate which is the output of the flow rate detector 20 and determines the allowable upper limit amount (weight) of bypass steam amount.
It outputs a function as shown in FIG. 3b. 23-3 outputs the amount of opening of the bypass steam control valve 8 with respect to the amount of bypass steam;
A function as shown in FIG. 3c is generated. 24-1 and 24-2 are desuperheaters. 25-1 and 25-2
is a proportional-integral controller. 26-1 is a coefficient multiplier which inputs the output of the pressure detector 19 and outputs a spray water flow rate set value. 27 is a divider,
Outputs the allowable upper limit value (volume) of bypass steam amount. In other words, 27 has a function of converting the allowable amount of bypass steam expressed in weight, which is the output of the function generator 23-2, into the allowable amount of bypass steam expressed in volume. 28 indicates a low value priority circuit;
The smaller signal between the output of 25-1 and the output of 23-3 is passed, and the bypass steam control valve 8 is controlled by that signal.

Next, the operation shown in FIG. 2 will be explained. In FIG. 2, the function generator 23-1 inputs the high-pressure turbine steam amount and outputs a reheat steam pressure setting value. This set value is given to the subtractor 24-1, and the difference from the actual reheat steam pressure (output of the pressure detector 18) is calculated. This difference signal is given to the proportional-integral controller 25-1, where a control signal is calculated. Bypass steam control valve 8 is controlled by this control signal. As a result, the reheat steam pressure is controlled to be constant. Further, the coefficient unit 26-1, which inputs the output of the pressure detector 19, outputs a spray water flow rate setting value corresponding to the amount of bypass steam, and controls the spray control valve 12. In the desuperheater 24-2, the difference between this set value and the actual spray water flow rate (output of the flow rate detector 20) is calculated, and this is calculated by the proportional-integral controller 2.
Given to 5-2. The controller 25-2 outputs a control signal to control the spray control valve 12. At this time, the function generator 23-2 inputs the actual spray water flow rate and outputs the amount of bypass steam that can be cooled with the spray water flow rate (allowable bypass steam amount). The divider 27 is the pressure detector 18
Using the output of , convert it to volumetric flow rate.
This converted allowable bypass steam amount is given to the function generator 23-3, and a valve opening control amount corresponding to the steam amount is given to the low value priority circuit 28.

Now, if enough spray water for cooling is supplied to the steam detemperature device 9 (9 in Figure 1),
Flow rate detector 20 generates a large electrical signal commensurate with the flow rate. Therefore, the function generator 23-2
, or the output of the divider 27 will output a relatively large value. Of course, the function generator 23-3 also has a large value. In this case, the low value priority circuit 28 selects the output signal from the proportional-integral controller 25-1 side, and the bypass steam amount is controlled to maintain the reheat steam pressure set value.

However, the status of the spray control valve 12,
If spray water is not sufficiently supplied due to a clogged spray nozzle or a malfunction of the pump 13, the flow rate detector 20 generates a small electrical signal commensurate with the flow rate. As a result, the allowable amount of bypass steam becomes small, and the function generator 23-3 outputs a small signal (a signal commensurate with the allowable amount of bypass steam). Therefore,
The low value priority circuit 28 selects the output signal of the function generator 23-3, and the amount of bypass steam is limited to the amount allowed by the actually supplied spray water flow rate.

This embodiment is advantageous in that it uses only functional calculations that do not include delays, and operates immediately when the spray amount becomes insufficient. The part indicated by the dashed line in FIG. 2 is the part that implements the protection function.

Next, another embodiment of the present invention will be described. Another embodiment of the invention is shown in FIG. In this figure, parts given the same reference numerals as in FIG. 2 have the same functions. 24-3 is a subtracter, 25-3 is a proportional-integral controller, and 26-2 is a coefficient unit. In this method, the amount of bypass steam is limited by a flow rate control circuit. That is, the function generator 23-2 outputs the allowable bypass steam amount according to the spray water flow rate (output of 20), and this value and the actual bypass steam amount (26-2
The subtracter 24-3 calculates the deviation from the output (output), and from this value, the proportional-integral controller 25-3 calculates and outputs a control signal. This control signal is applied to the low value priority circuit 28. Therefore, the output of 20 becomes small,
When the deviation of the subtracter 24-3 becomes small, the low value priority circuit 28 selects the output of the controller 25-3. As a result, the bypass steam control valve 8 is controlled, and the amount of bypass steam is limited to an allowable value.
Although this method accurately limits the amount of turbine bypass steam, it requires initialization by tying back the opening of the bypass valve 8 so that the controller 25-3 does not become saturated during normal operation.

In addition, in the above-mentioned example, only an example realized by an analog type is given, but a part or all of it may be realized by an analog calculation type. In this case, if a microcomputer or the like is used, an inexpensive and highly reliable system can be realized.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to provide appropriate protection against abnormalities in the low-pressure turbine bypass system.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the entire plant including the low-pressure turbine bypass system, FIG. 2 is a diagram showing one embodiment of the present invention, and FIGS. 3 a to c are function generation of the function generator in the embodiment of FIG. 2. FIG. 4 is a diagram showing another embodiment of the present invention. 4...High pressure turbine, 5...Intermediate pressure turbine, 6...Low pressure turbine, 7...High pressure turbine bypass valve, 8...
Low pressure turbine bypass valve (bypass steam control valve),
9... Steam temperature reduction device, 10... Condenser, 12... Spray control valve, 18... Pressure detector, 19... Pressure detector, 20... Flow rate detector, 21... Low pressure turbine bypass control device, 22... Flow rate detector , 23-1~2
3-3...Function generator, 24-1 to 24-3...Subtractor, 25-1 to 25-3...Proportional-integral controller, 26
-1 and 26-2... Coefficient unit, 27... Divider, 28...
Low value priority circuit.

Claims (1)

[Claims] 1. A bypass steam control valve for controlling the amount of steam that bypasses the medium and low pressure steam turbine, and a steam temperature reduction device for reducing the temperature of the bypassed steam.
A method for controlling a low pressure turbine bypass system comprising a spray control valve for controlling a cooling spray flow rate in a steam temperature reduction device, wherein the spray flow rate is detected, and the detected value is equal to or less than a spray flow rate necessary for temperature reduction. When the spray flow rate is used, an allowable amount of steam flowing into the condenser is calculated, and the steam control valve is adjusted to the allowable amount to limit the amount of steam flowing into the bypass system. Control method for turbine bypass system.