JPS63201404A - Boiler-drum level 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] [Purpose of the invention] (Industrial application field) The present invention relates to a drum level control device for a boiler.

(Conventional trick) In a thermal power plant, drum level control, which is the water level adjustment of the drum in which boiler drum water and generated steam are accumulated, not only ensures the performance of the power plant, but also controls the empty firing of the furnace and It is also important to prevent damage to the turbine due to moisture intrusion.

Normally, drum level control is performed by PI control of the water supply control valve that adjusts the amount of water supplied to the boiler based on the deviation between the target value set according to the operating status of the plant and the actual value. .

Additionally, the drum is equipped with a drain valve that discharges the water inside, and when the drum level suddenly rises, the drain valve is manually operated to lower the drum level.

(Problems to be Solved by the Invention) At the start of plant operation, the drum temperature before the initial load is around 80 seconds to 100 degrees, that is, the state where air swells begin to occur in the drum water for the first time.

Alternatively, under a low load condition of 40% or less of the rating, the FA/P
When performing plant operations such as A switching, pressure damping, and burner switching, the main steam flow rate, gas flow rate, and furnace outlet gas temperature may generally change significantly.

These changes result in disturbances to the drum level, causing sudden changes in the boiler level. This disturbance occurs suddenly or disappears rapidly.

・The occurrence situation differs each time it is started.

However, when trying to control a boiler level that changes suddenly by PI control of the water supply control valve as described above.

Since parameters such as gains are set to constant values, there are many cases where extreme overshoot occurs or the control response is not in time. Also.

In some cases, a boiler trip may occur due to a high or low drum level.Also, when attempting to control the drain valve using PI or PID control in the same way as the water supply control valve, the stable Cannot be controlled.

For this reason, in the past, operators monitored the drum level and manually operated the drain valve in an on-off control manner, such as fully opening the drain valve when the level rose and fully opening it when the level fell.

As described above, with conventional boiler drum level control devices, automatic control is impossible because the control device becomes unstable under low load conditions, and operators have to manually adjust the level depending on plant conditions. However, stable control could only be achieved by a skilled operator.

An object of the present invention is to provide a boiler drum level control device that can automatically and stably control the drum level even in a low load state without making the plant unstable.

[Configuration of the Invention (Means for Solving Problems)] Therefore, the present invention inputs the deviation between the target value and the measured value of the boiler level, and applies the control law used when operated by a skilled operator as is. Configure the controller.

This controller controls the opening and closing of the drain valve.

(Function) Since control similar to that previously performed by experienced operators relying on their intuition is automatically performed, the drum level is appropriately controlled and the plant can be operated stably.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of a thermal power plant to which a boiler drum and level control device according to an embodiment of the present invention is applied. In FIG. supplied to At the same time, auxiliary air is supplied from the burner 12 to the furnace through the air flow rate regulating damper 14 by the forced draft fan 13, and combustion is performed. The exhaust gas that has exchanged heat with the evaporator 15 due to the combustion of fuel in the furnace is further transferred to the first heater 16. Reheater 17.
Final heater 18. Heat exchange with the second heater 19 and by the suction ventilation fan 20.

It is released into the atmosphere from the chimney 21.

Further, the steam generated in the evaporator 15 is accumulated in the drum D, and the steam is further transferred to the first heater 16. Second heater 1
9. The temperature is further increased in the final heater 18, passes through the turbine control valve 22, and is supplied to the high pressure turbine 23. The cold steam leaving the high-pressure turbine 23 is heated by the reheater 17-17, and is heated by the intermediate-pressure turbine 24. It is supplied to the low pressure turbine 25 and becomes water in the condenser 26. The water stored in the condenser 26 is transferred to the deaerator 28 by the condensate pump 27.

Furthermore, the water is supplied to the drum D by the water supply pump 29 through the water supply flow rate control valve 30 . The drum D is provided with a drain valve B for discharging drum water.

The generator 31 is a high pressure turbine 23. Medium pressure turbine 24. It is rotated by a low pressure turbine 25 and generates electric power.

Spray is supplied to the outlet side of the first heater 16 and the outlet side of the second heater 19 through a primary spray control valve 32 and a secondary spray control valve 33 to prevent overheating and adjust the temperature, respectively. Piping is provided.

The boiler drum level control device C controls the drain valve B based on the target value of the drum level of the drum D and its actual measured value, thereby controlling the drum level.

FIG. 2 shows the block configuration of the boiler drum level control device c, in which an adder 41 is connected to a drum level target value S set by a setting device (not shown) and a drum level disposed in the drum D. The actual measured value of the drum level detected by a water level sensor (not shown) is input, and the deviation e=Ls-L between the two is calculated. The differentiator 42 calculates the time differential Δe: de/dt of the deviation e.

The controller 43 is a controller that inputs the deviation e and its time differential Δe and calculates the control output ΔU based on the following control laws 1 to 5.

When the control law 1 deviation e is large in the positive direction and the differential value Δe of the deviation is large in the negative direction, the control output ΔU is made small in the positive direction.

Control law 2: When the deviation e is large in the positive direction and the differential value Δe of the deviation is large in the negative direction, the control output ΔU is made large in the positive direction.

Control law 3: When the deviation e is close to zero, the control output ΔU is set to a value close to zero, regardless of the value of the differential value Δe of the deviation.

Control law 4: When the deviation e is large in the negative direction and the differential value Δe of the deviation is large in the negative direction, the control output ΔU is made large in the negative direction.

Control law 5: When the deviation e is large in the negative direction and the differential value Δe of the deviation is large in the positive direction, the control output ΔU is made small in the negative direction.

FIG. 3 is a diagram illustrating a specific calculation method of this controller 43. In the same figure, each graph has a deviation e on the horizontal axis,
The differential value Δe of the deviation and the control output ΔU are -100 to 10.
0%, and the vertical axis represents the concepts of ``large in the positive direction,'' ``small in the positive direction,''``zero,'' ``small in the negative direction,'' and ``large in the negative direction.'' Measure μ to which each concept belongs
is taken from 0 to 1, and each of the above control laws is expressed graphically.

That is, looking at (control law 1) in the same figure, in order to calculate the measure μe from the deviation e at this time, the deviation e is defined as large from 10% to 100% in the positive direction, and the measure μe is calculated as the deviation Pattern P in which the measure μe is set to 0 when e is 10%, increases gradually as the deviation e increases, reaches a maximum of 1 at a deviation of 70%, and then decreases again to 0 at a deviation of 100%.
es has been established. Here, the reason why the deviation is set to be the highest at 70% and the measure is decreased thereafter is that the deviation e is 7
The opinion is that the maximum deviation is around 0%, and that deviations larger than that are unlikely to occur under normal control conditions.

Next, in order to calculate the measure μΔe from the differential value Δe of the deviation, the differential value Δe of the deviation is defined as small from -10% to -100%, and the measure μΔe is.

A pattern PΔe1 is provided in which the maximum value is 1 at -60%.

Further, the control output ΔU is defined as being small in the positive direction from −20% to +70%, and a pattern PΔU1 is provided in which the measure μΔU becomes the highest 1 at +20%.

As can be seen from these patterns Per, PΔet, and PΔU1, the control law l is such that the control deviation e is large in the positive direction, but the differential value Δe of the deviation is large in the negative direction, which means that the deviation rapidly moves toward recovery. In this case, the control output ΔU should be kept small and corrective action should be taken sparingly.

This means preventing excessive control in the opposite direction.

Further, the magnitude of the control output ΔU at this time is determined depending on the magnitude of the deviation e and the differential value Δe of the deviation.

Hereinafter, similarly for control laws 2 to 5, the illustrated patterns Pe 2 to Pe s , PΔez to PΔes, PΔ
U2 to PΔU5 are provided.

The controller 43 is equipped with the above-mentioned control laws 1 to 5, and based on the input deviation e and the differential value Δe of the deviation, first calculates the measure μe obtained from each pattern of e and Δe,
μΔe is determined, the upper part of the control output ΔU pattern is cut off using the smaller μMIN, the remaining portion PBΔυ is determined for each control law, their maximum value μMAX is calculated, and the average value of the obtained pattern PμMAXΔU is sent to the controller 43. Let the output dT be

For example, to explain the case where the values of e=40% and Δe=30% are input, in control law 1, pe1=0.1. With pΔe1=0, μMI
In Nt=0 control law 2, μe 2 =o, 7, μΔoz=
0.5, μ is lN2 = 0.5, and in control law 3, μe3 = 0
．． 2. μΔe3: 1.0, μMIN3=0.2 Control law 4: pe<=0, μΔe4=0, μMIN<=0 Control law 5: μes=0.2, μΔes=0, it M
IN s =0, and only control law 2 and control law 3 are applicable. PaΔU was calculated for this control law.

These are the shaded areas PBΔU2 and PBΔU3 in FIG.

The maximum value μMAX for these PBΔU2 and PBΔU3 is calculated in the shaded area PμMAXΔU in FIG. 2, and the output dT of the controller 3 is calculated from this average value. This output dT
The opening degree of the drain valve B is controlled by this.

As described above, according to the present invention, a controller is configured in which the deviation between the target drum level value and the actual measured value and its time derivative are input, and the control law used when operated by a skilled operator is directly applied. A controller controls opening and closing of the drain valve B. In the unstable region where the temperature of the drum water is around 80' to 100°, operators had to rely on their intuition and manually operate the drum water. Similar control will now be performed automatically.

In addition, unlike when using PI control or PID control, which is generally known as S, even if a large deviation occurs, it does not cause hunting due to saturation of the differential integrator, resulting in stable and stable control.
It becomes possible to bring about rapid control operations.

[Effects of the Invention] As described above, according to the present invention, a controller is configured to which the control law used when operated by a skilled operator is directly applied, and this controller is used to control the opening and closing of the drain valve. ,
Controls similar to those performed by operators are performed automatically,
The plant can be operated stably even under low load conditions.

Further, even if there is a large deviation between the target value and the actual measured value of the drum level, it is possible to provide stable and quick control operations without causing hunting due to saturation of the differential integrator.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a thermal power plant to which a boiler drum level control device according to an embodiment of the present invention is applied;
The figure is a block diagram of the boiler drum level control device, and FIG. 5 is an explanatory diagram of the operation of the controller shown in FIG. 2. D... Drum, B... Drain valve, C... Boiler drum level control device, 1... Adder, 2... Differentiator, 3... Controller. (7317) Agent: Patent Attorney Noriyuki Chika (
8105) King Hongbun Figure 2

Claims (1)

[Claims] means for calculating the deviation between the target value of the drum level and the actual drum level; and means for differentiating the calculated deviation with respect to time;
Input the deviation and its time derivative, and for each input, specify in advance "large in the positive direction,""small in the positive direction,""zero,""small in the negative direction," and "large in the negative direction." The concept of the operator is given as a measurement parameter, and the control output can be set to ``large in the positive direction'', ``small in the positive direction'', ``zero'', ``small in the negative direction'', and ``negative'' for each combination of the above concepts. A measure parameter is also given to the operator's control law that makes the deviation larger in the direction, and when the deviation and its time derivative are input, the minimum value of the corresponding measure of the deviation and its time derivative is selected for each control law, and each The measure distribution of the control output of the control law is valid only if it is less than the minimum value, and the measure distribution is re-taken, and the resulting measure distributions of each control output are superimposed so as to select the maximum value, and then the control is averaged. A boiler drum level control device comprising a control means for determining an output, and a means for controlling opening and closing of a drain valve according to the control output.