JPS62129606A - Drum boiler feedwater controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a drum boiler water supply control device in a drum boiler thermal power plant, and in particular, to a drum boiler water supply control device that allows drum water levels to be stably maintained at the time of plant startup. Regarding equipment.

[Technical backstory of the invention and its problems 1 Generally, water supply control for a drum boiler in a drum boiler thermal power plant is a method of stably controlling the drum water level to prevent the evaporation tubes in the furnace from drying out due to a drop in the water level. It also plays a very important role in preventing water from entering the turbine due to rising water levels.

FIG. 3 shows an example of the configuration of a typical drum boiler thermal power plant. In the figure, steam generated in a drum 1 is heated in a heater 2 and supplied to a high-pressure turbine 3. After being expanded and cooled in the high-pressure turbine 3, the temperature is raised again in a reheater 4, and then sent to a low-pressure turbine 5. It is supplied and cooled in the condenser 13 to become water. In addition, water to the drum 1 is supplied from a condenser 13 to a deaerator 7 by a condensate pump 6.
After being deaerated, the water is sent to the drum 1 by the water supply pump 8 via the water supply control valve 11. On the other hand, water circulates from the drum 1 to the evaporation tube 9 in the furnace, and steam generated by being heated by combustion in the burner 10 returns to the drum 1. Note that the main steam pipe leading from the heater 2 to the high-pressure turbine 3 is equipped with a drain valve 12 for discharging drain at the time of starting/stopping the plant.

Now, in the conventional drum boiler water supply control device in this kind of plant, the drum water level is detected by the drum water level detector 15, this is fed back and compared with the drum water level standard value, and the deviation between the two is calculated. P based on
An ID control method is adopted, and in a high load state of 40% or more of the generator output, mismatch deviation between the main steam flow rate and the feed water flow rate is further used as a preceding element in the PID control. However, when the plant is started up, especially in the operating state before the initial load is established, it is impossible to stably maintain the drum water level using the PID control for the following reasons.

(a) Main steam flow rate and feed water flow rate are 10% or less, and PID control used during normal operation is proportional.

If integral and differential constants are used as they are, excessive control will result and hunting will occur.

(b) Since the promotion operation is performed to increase the drum steam pressure from atmospheric pressure to the rated operating pressure, the system head of the water supply pump 8 fluctuates, and the flow rate relative to the opening degree of the water supply control valve 11 changes in the drum steam pressure. It cannot be controlled by linear compensation control such as lID1lJIl].

(c) When starting up the plant, temperature control is performed to prevent damage to equipment due to thermal stress caused by temperature mismatch in the boiler and turbine. Various complicated operations are performed, and the resulting changes in voids within the evaporator tube and changes in the steam flow rate act as a large disturbance on the drum water level.

[Object of the Invention] The present invention was made to solve the above problems, and its purpose is to stably control the drum water level in response to various disturbances at the time of plant startup and changes in plant characteristics. The object of the present invention is to provide a highly reliable drum boiler water supply control device that can perform the following steps.

[Summary of the invention] In order to achieve the above object, the present invention detects the drum water level of a drum boiler thermal power plant with a drum water level detector, and uses a drum water level signal from the drum water level detector and a drum water level reference signal. In a drum boiler feed water control device that controls the feed water flow by adjusting the opening degree of the feed water control valve based on the drum water level deviation signal obtained by comparison, the drum water level deviation signal and this drum water level deviation signal are differentiated. A measurement controller that receives the drum water level deviation change rate signal returned via the element as an input and derives a feed water flow rate manipulated variable signal by each means shown in (a) to (d) below, and a drum that detects the drum steam pressure. a first computing unit that computes a pressure correction signal for correcting the feed water control valve operation amount signal in accordance with the drum steam pressure signal from the steam pressure detector; and a pressure correction computed by the first computing unit. By comprising a second computing unit that corrects the feed water flow rate operation amount signal from the above-mentioned measurement controller using the signal and derives the feed water control valve operation amount signal, it is possible to prevent various disturbances at the time of plant startup. It is characterized by the ability to stably control the drum water level accordingly.

(a) The above drum water level deviation signal and drum water level deviation change rate signal are "large in the positive direction", "medium in the positive direction", "small in the positive direction", "zero", "small in the negative direction", "medium in the negative direction". ” Means for storing the concept of “greater in the negative direction” as a measure distribution function (b) A means for storing the water supply flow rate manipulated variable signal [ Dog J in the positive direction “Medium in the positive direction” “Small J in the positive direction “Zero”
Means for storing the control law of "small in the negative direction", "medium in the negative direction", and large in the negative direction and the concept of the value that the water supply flow rate manipulated variable signal should take as a measure distribution (c) Drum water level deviation signal and a drum water level deviation change rate signal, means for calculating a measure corresponding to the water level deviation and a measure corresponding to the water level deviation change rate for each control law in (b) above (d) Calculating in (c) above. The measure distribution of the water supply flow rate manipulated amount signal of the control law is cut using the smaller of the measured measures, and the measure distribution of the water supply flow rate increase amount signal of the control law corresponding to the newly given state is recalculated. , a means for determining the water supply flow rate manipulated variable signal by selecting the maximum value of the measure distribution for all control laws, superimposing it, further weighting it with the measure distribution, and calculating the average value [Embodiment of the invention] First, the present invention drum boiler water supply control system, when the plant is started, a skilled operator determines the control law for the controller based on an algorithm that manipulates the water supply flow rate according to the behavior of the drum water level, and also determines the plant status judgment criteria and operation criteria. By giving a measure distribution to the concept of , smooth water supply control operation is realized.

Hereinafter, an embodiment of the present invention based on the above concept will be described with reference to the drawings.

FIG. 1 shows an example of the configuration of a drum boiler water supply control device according to the present invention. In FIG. 1, 25 is a drum level signal detected by the drum water level detector 15 in FIG.
A subtractor 22 calculates a deviation signal 8=(L LREF) from REF, and 22 is a time change rate signal Δed of the drum water level deviation signal e.

21 is a differentiator that calculates the drum water level deviation signal e and the drum water level change rate signal Δe, and calculates the water supply flow rate manipulated variable signal Δ1 based on the logical control law described later. It is a measure controller.

On the other hand, 24 is the drum steam pressure detector 16 in FIG.
Pressure correction signal PC for inputting the drum steam pressure signal detected by PC and correcting the operation amount of the water supply control valve accordingly.
The function generator 23 inputs the water supply adjustment operation amount signal 80 from the measurement controller 21, and calculates the function generator 2.
This multiplier uses four pressure correction signals PC to calculate the water supply control valve operation signal ΔZ.

Next, the logical control law in the measure controller 21 will be described.

Control law 1: When e is 1 large in the positive direction, ΔU is made large in the negative direction.

Control law 2: When e is "human in the negative direction", ΔU is "large in the positive direction".

Control law 3: e is small in the positive direction by 1 and 80 is a positive value
In this case, ΔU is defined as "inside in the angular direction".

Control law 4: e is small in the negative direction by 1, and Δe is a negative value.
In this case, △U is set as "inside in the positive direction".

111tl law 5: e is "small in the positive direction" and Δe is "
When it is a negative value, ΔU is set to zero.

Control law 6: e is "small in the negative direction" and Δe is "positive value"
In the case of , 80 is considered "zero".

Control law 7: When e is "small in the positive direction" and Δe is "zero", ΔU is "small in the negative direction" φ.

Control law 8: When e is small in one angular direction and Δe is zero J, ΔU is made small in the positive direction.

Control law 9: When e is "zero" and 80 is "zero", ΔU is "zero".

Next, a specific calculation method of the measure controller 21 will be explained using FIG. 2.

In each graph in Fig. 2, the horizontal axis shows the drum water level deviation signal eo, the drum water level deviation change rate signal Δe, and the water supply flow rate operation amount signal Δ1 in the range of -100 to 100%, and the vertical axis shows the above "Large in the positive direction" described in the control law [Medium in the positive direction "Small in the positive direction""Zero" Large in the r angle direction "
"Medium in the negative direction""Small in the negative direction""Positive value j" The measure corresponding to the concept of "negative value" is taken in the range of O to 1, and the concept of each control law is expressed by quantifying it by the measure. .

Now, when the drum water level deviation signal 60 and the drum water level deviation change rate signal ΔeO are input, the measure controller 21 generates the measure μI(eo) corresponding to the deviation signal for each control law l and the deviation change rate signal. The corresponding measure μshi(ΔeO) is calculated, and from this value, the measure μMIN = Illil'1(μyo(eO), μ
(ΔeO)) is calculated. Then, using the measure μMIN indicating this applicability, the measure distribution of the water supply flow rate operation amount signal ΔU according to each control law was cut above μMIN, and 〇〇 was input to the m difference signal e0 and the deviation change rate signal. The measure distribution μi (ΔU) according to each control law at the time is recalculated. Furthermore, the maximum value μMAX (Δμ>=IIlaX DZI (Δ
u)), and then calculate the average value using the measure to determine 〇 for the control law.

That is, the above operation of the measure controller 21 is set to eo=80%.
, Δeo=60% is input as an example. μe(6a).

μΔe (Δeth > and μMIN are as follows for each control law, as shown in FIG. 2.

11J1111 Law 1: μ! (eo)-〇1. μ3e(
Δeo)-1,μ4,1,-01 Control Law 2:μ:(e
o)-〇, μ(Δeo)-1, μL-0 control law 3
:μ,'(eo)=0.5,μ]8(Δeo)=o,
s, μ3-=0.5IN Control law 4: μ; (eo)=o, μ3゜(Δeo
)−〇, Bow, N=.

Control law 5: μco(eo)=o, 6. μ38 (ΔeO)
-01μ5-0IN Control law e:μ;(eo)-o, μje(Δeo)
-o courtesy μ section 1N=0 control law 7: l'e (eO
)-06*l'l. (Δe) −〇 + l” ”'
00 MIN Mm law 8: µ: (eo) - 〇, µ3e (Δeo) - 〇, µ: rN - 〇 Control law 9: µx (eo) = 0. μ38
(Δeo)−o l μ; r N =0 Therefore, only control law 1 and control law 3 can be applied, and this μm
(Δu) and μ3 (ΔU) are as shown in the shaded areas A and B in FIG. And this μm (Δu), μ3 (ΔU
), the result of calculating μMAX (ΔU) is the shaded area C in FIG. Furthermore, by calculating this average value, Δuo
Determine.

Next, in the drum boiler water supply control device according to this embodiment configured as described above, the drum water level detector 15 shown in FIG.
When the drum water level signal is given by , the subtractor 25
A deviation signal e from the drum level reference signal LREF is calculated by the differentiator 22, and a deviation change rate signal Δe is calculated by the differentiator 22 and inputted to the measurement controller 21. Then, by performing the above-mentioned functional operations in the measure controller 21, the water supply flow rate manipulated variable signal that realizes the following control is determined to be O.

(a) According to control laws 1 and 2, when the deviation signal e becomes very large and approaches the region where a plant trip occurs due to high/low drum water level, the first step is to drastically reduce or increase the water supply flow rate to avoid a trip. Control with priority.

(b) According to control laws 3 and 4, if the deviation signal e and the deviation change rate signal Δe have the same sign, the deviation of the drum water level is increasing. It is controlled so that it becomes zero and becomes stable.

(c) According to Control Laws 5 and 6, if the deviation signal e and the deviation change rate signal Δe have different signs, the deviation of the drum water level is decreasing, so the current flow rate should be maintained without changing the water supply flow rate. control so that the deviation naturally decreases.

(d) According to control laws 7 and 8, the deviation change rate signal is stable at zero, but the deviation signal e is not zero (if an offset remains, the water supply flow rate may be slightly increased or decreased depending on the direction of the deviation). By doing this, the offset is controlled to be eliminated.

(e) In control law 9, since both the deviation signal e and the deviation change rate signal Δe are zero, the water supply flow rate is not changed and the current state is maintained.

Furthermore, when the drum steam pressure signal P is given by the drum steam pressure detector 16 in FIG.
By setting an appropriate monotonically increasing function in 4, a pressure correction signal PC having a large value when the drum steam capacity is high and a small value when it is low can be obtained, and this is used as the feedwater flow rate manipulated variable signal by the multiplier 23. By multiplying by Δ0, a feed water control valve operation amount signal ΔZ that corrects the influence of the feed water control valve opening degree due to a change in steam pressure can be obtained.

As described above, the drum boiler water supply control device with this configuration provides the following effects.

In other words, as mentioned above, when starting up the plant, the drum water level is stably balanced when the water supply flow rate is 10% or less.
PID control during normal operation is proportional.

Stable control cannot be achieved unless the effectiveness of the integral and differential control parameters is reduced. Also, fuel flow rate.

Because a fairly large disturbance element is often added due to drain valve operation, etc., simply reducing the effectiveness of the parameters will worsen the control response of the water supply flow rate when disturbance occurs.
High/low drum water levels can lead to plant trips.

In this respect, the drum boiler water supply control IV device with this configuration is as follows:
Unlike linear control such as the above-mentioned PID control, the measurement distribution of the water supply flow rate manipulated variable ΔU can be freely determined depending on the drum water level deviation and the deviation change rate.
When entering the trip danger area due to a large disturbance, a large change in the water supply flow rate can be applied to compensate for this, and in order to offset the normal operation area,
It is also possible to give very small changes in the water supply flow rate, making it possible to realize flexible control according to plant conditions.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without changing the gist thereof.

[Effects of the Invention] As explained above, the present invention provides an extremely reliable drum boiler that can stably control the drum water level in response to various disturbances during plant startup and changes in plant characteristics. Water supply control equipment can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a drum boiler feed water control device according to the present invention, FIG. 2 is a diagram showing the measurement distribution and operation function for each control law of the measurement controller in the same embodiment, and FIG. The figure is a configuration diagram showing an example of a typical drum boiler thermal power plant. DESCRIPTION OF SYMBOLS 1... Drum, 8... Water supply pump, 11... Water supply adjustment valve, 12... Drain valve, 15... Drum water level detector, 16... Drum steam pressure detector, 21...・Measure controller, 22... Differentiator, 23... Multiplier, 24
...Function generator, 25...Subtractor.

Claims (1)

[Claims] The drum water level of a drum boiler thermal power plant is detected by a drum water level detector, and the drum water level deviation signal obtained by comparing the drum water level signal from the drum water level detector with a drum water level reference signal. In a drum boiler feed water control device that controls the feed water flow rate by adjusting the opening degree of the feed water control valve based on the drum water level deviation signal and the drum water level deviation change rate obtained by differentiating the drum water level deviation signal through a differentiating element. With the signal as input, the following (a) to (
d) The feed water control valve manipulated variable signal is determined in accordance with the drum steam pressure signal from the measurement controller that derives the supplied water flow manipulated variable signal based on each means shown in d) and the drum steam pressure detector that detects the drum steam pressure. A first computing unit that computes a pressure correction signal for correction, and a water supply adjustment by correcting and computing the water supply flow rate operation amount signal from the measurement controller using the pressure correction signal computed by the first computing unit. A drum boiler feed water control device comprising: a second computing unit that derives a valve operation amount signal. (a) The drum water level deviation signal and the drum water deviation change rate signal are "large in the positive direction", "medium in the positive direction", and "small in the positive direction"
Means for storing the concepts of "zero,""small in the negative direction,""medium in the negative direction," and "large in the negative direction" using a measure distribution function. (b) A plant expressed by a combination of the concepts in (a) above. Depending on the state of (c) Means for storing the concept of the value that the feedwater flow rate manipulated variable signal should take in the form of a measure distribution (c) When the drum water level deviation signal and the drum water level deviation change rate signal are given, the above (b) Means for calculating a measure corresponding to the water level deviation and a measure corresponding to the water level deviation rate of change for each control law (d) Calculating the water supply flow rate for that control law using the smaller of the measures calculated in (c) above At the same time as cutting the measure distribution of the manipulated variable signal, the measure distribution of the water supply flow rate manipulated variable signal of the control law corresponding to the newly given state is taken again, and the maximum value of the measure distribution is selected for all control laws. Means for determining the water supply flow rate manipulated variable signal by superimposing the signals and calculating the average value by weighting with the measure distribution.