JPH08200608A - Water supply flow rate control method for thermal power plant - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to stably and rapidly increase the feed water flow rate of a boiler feed water pump that continues to operate when a boiler feed water pump stop load runback of a thermal power plant occurs. It is intended to suppress fluctuations in the flow rate of water supplied to the plant and contribute to stable operation of the thermal power plant. [Structure] In the feed water flow control circuit, when the boiler feed pump stop load runback occurs, proportional /
The preceding signal of the integrator 18 is rapidly increased at a prescribed rate of change from the water supply master command before the load runback to the maximum flow rate. [Effect] Boiler feed pump stop load When a runback occurs, the feed water flow rate of the boiler feed pump is increased rapidly and stably, contributing to stable operation of the plant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedwater flow rate control method for a thermal power plant having a load runback function, and in particular, secures a feedwater flow rate promptly when a load runback occurs due to a boiler feedwater pump stoppage, thereby stabilizing the plant. The present invention relates to a water supply / water supply control method for a thermal power plant that enables continuous operation.

[0002]

2. Description of the Related Art The feedwater flow control system for a thermal power plant is
Generally, it is composed of a plurality of boiler feed pumps and a control device for controlling these in parallel by a feed water flow rate command based on a boiler input command. Here, the operation of the conventional feed water flow rate control method in the case where two boiler feed water pumps having a capacity of 50% of the unit rated feed water flow rate are stopped while one pump is running and load runback occurs will be described.

During operation of two boiler feed water pumps with the generator output at the rated output, each boiler feed water pump shares 50% of the unit rated feed water flow rate, and each pump feed water flow rate is approximately 1%.
It is operating at 00% capacity. When one boiler feed pump stops, a load runback occurrence is detected, and the generator output that can continue operation with the boiler feed pump in operation is 50%.
The load drops rapidly until. In this case, the boiler feed water pump in operation is controlled to continue the operation at almost 100% of the pump rated capacity in order to share 50% of the unit rated feed water flow rate as before the occurrence of runback.

The runback operation in the case where one boiler feed pump is stopped during operation when the generator output is less than 100% will be described by taking the case where the generator output is 60% of the rated output as an example. When the generator output is 60% of the rated output, each boiler water supply pump shares 30% of the unit rated water supply flow rate while operating two boiler water supply pumps, and operates at 60% capacity of each pump rating. . When one boiler feed pump stops, a runback is detected and the generator output is rapidly lowered to 50%, but the boiler feed pump in operation tries to secure 50% of the unit rated feed flow rate. The water supply flow rate fluctuates greatly because the water supply flow rate is about 60% of the pump rating before the runback occurs to almost 100% of the water supply flow rate, and the water supply flow rate changes sharply only by proportional / integral control.
The operating status of the unit becomes extremely unstable.

That is, the closer the generator output is to the 50% output which is the load runback target load when the boiler feed water pump is stopped, and the state where the pump is operating with a smaller capacity than the boiler feed water pump rated capacity. The occurrence of load runback when the boiler feed pump is stopped becomes a disturbance to the stable operation of the unit.

As an example of the conventional system, there is an example shown in "Automatic control of boiler" (Ohm Co., Ltd.), pages 276 to 279, section 5.3, Control system for once-through boiler, [1] Feed water flow rate control.
Since the method is only to calculate the deviation of the total water supply flow rate and adjust the water supply flow rate of each pump, the water supply flow rate greatly fluctuated when the boiler water supply pump runback occurred due to the above reason.

[0007]

In a partial load where the generator output is less than 100% of the rated output, one or more of the boiler feedwater pumps are stopped during parallel operation with a load runback. If the above occurs, the load is rapidly lowered to the maximum unit output that can continue operation with the remaining boiler feed pumps. At this time, the boiler feed water pump that continues to operate needs to rapidly increase the feed water flow rate from the feed water flow rate before the load runback occurrence to the unit feed water flow rate corresponding to the load runback target output.

However, in the conventional technique, since the water supply increase control is performed by the proportional / integral control by decreasing the feedback water supply flow rate, there is a drawback that the water supply flow rate largely changes and the operating state of the unit becomes extremely unstable.

An object of the present invention is to solve the above-mentioned problems, and when a load runback occurs due to the boiler feed water pump being stopped at a partial load, the feed water flow rate of the boiler feed water pump that continues to operate is promptly adjusted to almost the pump feed rate. It is to provide a feedwater flow rate control method for a thermal power plant in which the flow rate is increased to 100% and then returned to normal control.

[0010]

In order to achieve the above object, the present invention individually adopts the following means.

1. When the boiler feed pump stop load runback control is performed, it has a function of rapidly increasing the preceding signal of the feedwater master command from the value before the runback occurred to the maximum operable pump flow rate, and then returning to the normal control.

2. When the boiler feed pump stop load runback occurs, it has the function of rapidly increasing the feed water master command to the maximum value of the boiler feed pump feed water flow that continues operation, and then returning to normal control.

3. When the boiler feed pump stop load runback occurs, it has a function of rapidly increasing the operation command of the boiler feed pump that continues to operate to the rated output point of the boiler feed pump in an open loop, and then returning to normal control.

[0014]

The above-mentioned solving means operates as follows.

1. In the case of the solution means 1, when the boiler feed pump stop load runback occurs, the advance signal of the feed water master command is increased to almost 100% of the pump rating at the specified change rate, so that the fluctuation of the boiler feed water flow rate is reduced.

2. In the case of the solution means 2, when the boiler feed water pump stop load runback occurs, the feed water master command is increased to almost 100% of the pump rating at the specified change rate, whereby the fluctuation of the boiler feed water flow rate is reduced.

3. In the case of the solution means 3, the fluctuation of the boiler feed water flow rate is reduced by increasing the boiler feed water pump operation command, which continues the operation when the boiler feed water pump stop load runback occurs, up to almost 100% of the pump rating at the specified change rate.

[0018]

【Example】

(Embodiment 1) FIG. 1 is a diagram showing a boiler feed pump stop load runback control system and apparatus according to an embodiment of the present invention.

FIG. 1 shows a flow rate 5 of water supplied to the boiler 1.
Is described as an example of a system that supplies 50% of the rated feed water flow rate of the unit by parallel operation of two boiler feed water pumps (A) 2 and (B) 3.

Referring to FIG. 1, a normal control operation will be described. In the figure, the portion surrounded by the dotted line is according to the present invention, and the other portions are control circuits conventionally used. In the normal state, the function generator 11 creates the feedwater flow rate command 12 based on the boiler input command 10 and the boiler 1
The deviation from the water supply flow rate 5 supplied to the water is calculated by the subtractor 13, and this control deviation is calculated by the proportional / integrator 18 for water supply master control.
And the supply master command 23 is created. Each boiler feedwater pump controls using this feedwater master command 23 as a feedwater flow rate command for the pump. In the case of the boiler feed water pump (A) 2, the deviation between the feed water master command 23 and the boiler feed pump feed water flow rate 6 is calculated by the subtractor 19, and this is calculated by the proportional / integrator 20 to create an operation command, The boiler feed water pump 2 is controlled.

When the boiler water supply pump (B) 3 is stopped and a runback is detected, proportional control for water supply master control is performed.
The integrator 18 is temporarily set to the tieback mode to hold the water supply master command 23 immediately before the runback, and
The advance signal of the water supply master command also switches the switch 16 to the X1 side and sets the change rate limiter 17 in the tracking mode to follow the water supply master command 23. During this period, the BFP automatic operation number correction 14 is changed by stopping one boiler feed water pump, and the output of the multiplier 15 is switched to the signal for operating one boiler feed water pump. After that, the proportional / integrator 18 for water supply master control is automatically controlled, the change rate limiter 17 is set to the change rate limit mode, the switch 16 is switched to the X2 side, and the preceding signal is changed from the current value to the signal for one pump. Corrected multiplier 1
The output of 5 and the pump / rate will rapidly increase at the specified rate of change to almost 100%. After the completion of the load runback, the change rate limiting device 17 is set to the tracking mode again to return to the normal control by observing the time until the change rate limiting operation ends. By this method, when the boiler feed pump stop load runback occurs, the feed water flow rate of the boiler feed pump that continues the automatic operation promptly can be increased to almost the rated flow rate.

(Embodiment 2) FIG. 2 is a diagram showing another embodiment of the present invention. The water supply pump system was the same as in Example 1.

When the boiler feed pump (B) 3 is stopped and a load runback is detected, the proportional / integrator 18 for feed water master control is set to the tieback mode, and the feed water master command 23
Switches the switch 25 to the X1 side, and limits the change rate limiter 24 from the value before load runback to the post-runback water supply master command (approximately 100% of the rating) set by the signal generator 26. It increases at the rate of change.

Since the control system of the boiler feed water pump (A) 2 on the downstream side continues automatic control, this feed water master command 23
Increase the water supply flow rate based on

After the water supply master command 23 reaches the target value, the proportional / integrator 18 for water supply master control is automatically returned to the normal control after the time for stabilizing the water supply control is observed.

This is a method of controlling the boiler feed water pump on the side of the feed water master control system in the same manner as in the first embodiment, using a control circuit different from that of the first embodiment.

(Embodiment 3) FIG. 3 is a diagram showing another embodiment of the present invention. The water supply pump system was the same as in Example 1.

When the boiler feed pump (B) 3 is stopped and the occurrence of load runback is detected, the boiler feed pump (A) 2
The proportional / integrator 20 is set to the manual / tieback mode, the switch 30 is switched to the X1 side, the change rate limiter 31 is set to the change rate limit mode, and the switch 32 is switched to the X1 side to change the rate limiter 31. The input signal of the pump is set by the signal generator 33 from the operation command before the load runback, and the pump rating is almost 1
By setting the operation command to 00%, the boiler feed pump operation command increases at the specified change rate, and the feed water flow rate increases.
During this period, the proportional / integrator 18 for water supply master control is in the tieback mode, and follows the water supply flow rate 6 of the boiler water supply pump (A) 2 in automatic operation selected by the switch 28. After the operation command of the boiler feed water pump (A) 2 reaches the value of the signal generator 33, the proportional / integrator 20 and the proportional / integrator 18 for feed water master control are automatically controlled after the time for stabilization is taken. Return to normal control.

This is an effective method in the case of a system in which the feed water flow rate control is divided into a control device for performing minor loop control of the boiler feed water pump and a control device for performing feed water master control.

[0030]

According to the present invention, when the boiler feed pump stop load runback occurs, the boiler feed pump flow rate for continuing the operation is increased stably and rapidly, so that the fluctuation of the feed water flow rate is suppressed and the main steam pressure is reduced. ， The operation of the thermal power plant can be performed more stably because the fluctuation of the main steam temperature is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a feedwater flow rate control method according to an embodiment of the present invention.

FIG. 2 is a block diagram of a feedwater flow rate control method according to another embodiment of the present invention.

FIG. 3 is a block diagram of a feedwater flow rate control method according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Boiler, 2 ... Boiler feed pump, 10 ... Boiler input command, 16 ... Switching device, 17 ... Change rate limiter, 18 ... Proportional / integrator for water supply master control, 23 ... Water supply master command.

Claims (3)

[Claims] 1. A water supply master command common to a plurality of boiler water supply pumps is created based on a water supply flow rate supplied to a boiler and a water supply flow rate command based on a boiler input command, and each boiler water supply pump is based on the water supply master command. In the feed water flow rate control method for a thermal power plant that controls the feed water flow rate of each boiler feed water pump, when the boiler feed water pump is stopped, the load is reduced to the maximum unit output that can be continuously operated by the remaining boiler feed water pumps that are not stopped. At the time of load runback control, the advance signal of the water supply master command is changed from the value before the load runback occurs to approximately 10
A method for controlling the feedwater flow rate of a thermal power plant, which is characterized by increasing to 0% and then returning to normal control. 2. The method for controlling a feedwater flow rate of a thermal power plant according to claim 1, wherein when the load runback occurs,
Water supply master Proportional integrator is set to manual, and water supply master command continues automatic operation.
A method for controlling the feedwater flow rate of a thermal power plant, which is characterized by rapidly increasing it to 0% and then returning to normal control. 3. In the feedwater flow rate control of a thermal power plant according to claim 1, when a load runback occurs, an operation command for a boiler feedwater pump that continues automatic operation is issued in an open loop to approximately 100% of the boiler feedwater pump rating. %, And then returning to normal control, which is a method for controlling the feedwater flow rate of a thermal power plant.