JPS647281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a load control device for reducing the number of times a boiler automatically starts and stops as much as possible in order to reduce the heat dissipation loss of a hot water boiler or a steam boiler as much as possible.
In particular, the present invention relates to a load control device in a low load range.

Conventionally, in a boiler load control device, during normal operation, a control motor 7 (an electric actuator also called a module troll motor) is driven by receiving a signal from a pressure regulator 9, as shown in FIGS. 5 and 6. The load on the boiler is controlled by operating the oil amount control valve 14 and the combustion air damper 13, which are connected by a rod 18 and a lever 19. In other words, the oil amount adjustment valve 14 opening degree (100% load state) at the minimum control pressure of the pressure regulator 9 (for example, 6 kg/cm ² G) and the oil amount adjustment at the maximum control pressure (for example, 7 kg/cm ² G) The valve opening degree (eg, 20% load state) is set via the rod 18 and lever 19 in response to the rotation of the control motor 7.

In the above control, if the load on the user side is very small, the boiler pressure will rise quickly.
When the load of the burner becomes lower than the minimum combustion, the burner starts and stops firing frequently, and the boiler efficiency decreases as shown by the straight line 20 in FIG. 7.

Figure 7 is a diagram showing the relationship between intermittent combustion and a reduction in boiler efficiency in a fire-tube boiler, and the straight line 20 is the relationship between the ratio of boiler startup and shutdown (X) and the boiler efficiency reduction value (△Y). This shows that the longer the boiler stop time, the greater the drop in boiler efficiency (ΔY), so it is desirable to minimize the number of times the boiler is turned on and off.

The present invention solves the above-mentioned problems of the conventional technology by automatically saving the maximum burner combustion amount when the boiler load is light, or maintaining the burner maximum combustion amount at the minimum combustion amount, making it simple and inexpensive to turn on and off the burner as little as possible. This is what I am trying to do.

In this case, this is done by detecting an increase in the number of times the burner starts and stops, or a decrease in the number of times the water pump starts and stops, as shown in Figure 2. Boiler load control is normally performed by controlling the boiler pressure. In the present invention, when the boiler load is light, priority is given to the signal from the converter that detects the number of times the other burner starts and stops, or the number of times the feed pump starts and stops, and for this purpose, the signals shown in FIG.
As shown in FIG. 6, a conventional automatic continuous control circuit is provided with a converter 16 for detecting the number of times the burner starts and stops or the number of times the water pump starts and stops as described above.

Generally, a proportional control system with automatic start/stop is adopted for boiler load control. FIG. 1 shows an example of the relationship between boiler pressure and combustion amount in proportional control with automatic start/stop of a steam boiler.

In Figure 1, when the boiler is cold-started, the stroke is ignited at point A, starts low combustion, and reaches point B, which is high combustion after several tens of seconds, and the pressure begins to rise, and the pressure exceeds point _P3 . When it reaches ₁ point, it enters the proportional control range P ₂
The combustion amount is proportionally controlled until the point is reached.

Therefore, the pressure at point _P2 is at the low combustion position, but if the pressure rises beyond that, it reaches the combustion stop line _L2 at point _P4 , closes the fuel valve, and returns to point C. During the combustion stop, steam is consumed on the plant side and the boiler pressure drops to the combustion start line L _1. After passing through point D, the fuel valve opens at the low combustion position of point E, ignites and starts combustion, then P ₃ . Pressure begins to rise from the high combustion position of the point.

Since the load applied to the boiler varies depending on the steam usage status on the plant side, conventionally the proportional band △P 1 of the pressure regulator was set to high pressure with respect to the operating range △P ₂ of the pressure controller shown in Figure ₁ . Set by moving to P ₄ points on the side, or P ₃ points on the low pressure side, or setting with P _2.
By widening only the area between _{the four} P points, control suitable for the plant was performed to some extent.

However, in the conventional method described above, even when the amount of steam used on the plant side is less than the amount of steam generated by the boiler at low combustion in the combustion equipment, the pressure remains low.
When the pressure rises to point _P4 , combustion is stopped once, and the temperature reaches point C, ignition does not occur until the pressure drops below point _P3 , and then E
Even if the ignition occurs at point P3, the pressure is below point _P3 , so even though the amount of steam used by the plant is small, it reaches point B, resulting in high combustion, and the rate of pressure rise becomes faster. As a result, the boiler automatically starts and stops frequently.

In order to ensure the safety of combustion, the automatic start and stop of the boiler uses forced ventilation called pre-purge and post-purge, which forces the boiler itself to cool down, increasing heat loss and significantly reducing thermal efficiency. becomes. Therefore, reducing the number of times the boiler starts and stops as much as possible has a large energy saving effect and promotes the effective use of energy.

In view of the above-mentioned drawbacks of the conventional boiler, the present invention aims to reduce the heat dissipation loss of the boiler as much as possible, and to reduce the number of times the boiler automatically starts and stops when the amount of steam used on the plant side is small. We intend to provide the equipment, and 1 in Figures 5 and 6.
As shown in 6, a load request on the plant side corresponding to a small combustion amount or less in the combustion device in the boiler is detected, and the combustion amount of the combustion device is automatically maintained at the minimum combustion amount or the maximum combustion amount. This is a boiler load control device that can set the amount of combustion to any partial load of the rated combustion amount.

In other words, when the amount of steam used on the plant side is low, the boiler repeatedly starts and stops automatically, and the low load situation of the boiler can be detected by the number of times the combustion equipment is turned on and off within a certain period of time. I can do it. In other words, the number of automatic starts and stops of the combustion device within a certain period of time is counted by a counter, and if the number exceeds a certain limit, the fuel valve is opened at point E as shown in Figure 1 to ignite, but after ignition it remains as is. Reduce the number of times the boiler automatically starts and stops by providing a control device that maintains the low combustion position of point E or limits the high combustion position to an arbitrarily preset partial load point F instead of point B. It is possible to do so.

In addition, if the water supply method of the boiler is on-off water supply, the amount of water supplied by one operation of the water pump is approximately constant, so the water supply pump is on-off. Since the load condition of the boiler can also be detected based on the number of off times, it is also possible to construct the control circuit using this as shown in 16 in FIGS. 5 and 6.

Next, the present invention will be explained with reference to FIGS. 2, 3, and 4, which schematically represent the present invention.

The effects of the present invention can be achieved by electrically incorporating FIGS. 5 and 6 as shown in FIGS. 2, 3, and 4.

FIG. 2 shows an embodiment of the counter circuit block diagram of the present invention, in which the counter 1 is set when the set input 2 is in the conductive state and reset when the set input 2 is in the non-conductive state. Set input 2 automatically starts and stops the boiler.
That is, it is a signal that is made conductive when the combustion device automatically starts and stops ignition or stops, sets the counter 1, and is then held for a certain period of time.

Counter input 3 is a counter input that is input every time the boiler or combustion device is automatically started and stopped.

Counter output 4 is output only when counter input 3 is input a certain number of times to set input 2, which is a counter held for a certain period of time.

The signal of this counter output 4 causes relay R5 to
The control motor 7 is controlled by exciting the .

Figures 3 and 4 show control motor operating circuits, and Figure 3 shows an example of a low combustion maintenance circuit, which controls the combustion air damper 13 and oil amount control valve 14 to maintain low combustion. The electrical evaporation pressure adjustment circuit is formed by a control motor 7 in which the steam pressure of 10 is detected by a bellows and the rotation angle is determined accordingly. The control motor increases or decreases the combustion amount of the combustion device in the closing direction or opening direction.

Therefore, by configuring the circuit as shown in Fig. 3, when the low load signal from Fig. 2 is received, the control motor 7 rotates in the closing direction to forcibly hold the combustion device in the low combustion position. I can do it.

Similarly, Fig. 4 shows an example of an arbitrary partial load holding circuit.The circuit is configured as shown in Fig. 4, and variable resistors r ₁ and r ₂ are provided and set arbitrarily to make it a partial load. Therefore _, when relay R ₅ in FIG. It can be limited as point F in the diagram.

As indicated by the → mark in FIG. 1, FIG. 3 shows the movement of E→P ₂ , and FIG. 4 shows the movement of E→F→P ₂ .

As shown in Fig. 3, the combustion valve is opened at point E shown in Fig. 1 to ignite, and after ignition, the low combustion position of point E is maintained as it is, or
As shown in the figure, there is a control circuit (Fig. 4) which limits the high combustion position to point F instead of point B, thereby reducing the number of times the boiler is automatically started and stopped.

In addition, if the load on the plant side increases and the boiler pressure decreases while the above control circuit is operating, a separate detection method is used to detect the decrease in boiler steam pressure within the allowable limit of steam pressure required by the plant side. The set input 2 of FIG. 2 is detected and output by a separate conventional device (not shown).
By canceling , that is, making it non-conductive, the relay R5 is de-energized, and the conventional E→F→
It is possible to return the signal to the control circuit passing through P ₁ →P ₂ →P ₄ →C.

As described above, the present invention reduces the number of times the boiler automatically starts and stops, thereby reducing the heat dissipation loss in the boiler, and the thermal efficiency of the boiler is significantly improved compared to the conventional method, which has the advantage of greatly contributing to the energy saving of the boiler. .

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between boiler steam pressure and load in the conventional proportional control system with automatic start/stop, Fig. 2 is a schematic explanatory diagram of an embodiment showing a block diagram of the control circuit of the present invention, and Fig. 3 , and FIG. 4 show one embodiment of an electric proportional boiler steam pressure regulating device used in the present invention. Fig. 5 is a wiring diagram of the boiler automatic operation control circuit of the present invention equipped with a converter for detecting the number of times the burner starts and stops and the number of times the feed water pump starts and stops, and Fig. 6 shows the operation of the pressure regulator and control motor shown in Fig. 5. 7 are diagrams showing the relationship between the value of boiler efficiency reduction and the boiler's intermittent combustion. 1... Counter, 2... Set input, 3... Counter input, 4... Counter output, 5... Relay R, 6, 6'... Pressure regulator, 7, 7'... Control motor, 8, 8'... Potentiometer,
10... Boiler, L ₁ ... Combustion start line, L ₂ ...
... Combustion stop line, △P ₁ ... Proportional band of pressure regulator, △P ₂ ... Operating width of pressure controller, 16... Number of burner starts/stops, converter for detecting number of times of water pump starts/stops,
9...Pressure regulator, 20... Straight line showing boiler efficiency.

Claims (1)

[Claims] 1. In a boiler, load requests on the plant side corresponding to a small combustion amount or less in the combustion equipment are determined by counting the number of automatic starts and stops of the combustion equipment, and are set within a certain limit within a certain period of time by counting the number of times the combustion equipment automatically starts and stops. It can be detected by detecting the above, or if the boiler water supply method is on-off water supply, the load request on the plant side can be detected by counting the number of times the water supply pump starts and stops. It is detected that the combustion amount exceeds a certain limit within a certain period of time, and the combustion amount of the combustion device can be automatically maintained at the minimum combustion amount or the maximum combustion amount can be set to an arbitrary partial load of the rated combustion amount. A boiler load control device characterized by being able to.