JPH0259371B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application] The present invention relates to a combustion control device for a boiler, and in particular,
The present invention relates to a combustion control device that ensures proportional control of combustion by converting the valve opening range, that is, the valve opening scale, of a fuel control valve that controls the amount of fuel, depending on the magnitude of the load on a boiler.

[Prior art and its problems]

Combustion control of boilers that generate steam pressure, which is applied to heating equipment, etc., has conventionally been proportionally controlled by controlling the valve opening of a fuel control valve connected to a control motor that is operated by the output of a pressure converter that responds to steam pressure. At the same time, combustion safety control devices were used to start and stop combustion in a fail-safe manner.

With this conventional combustion control, when the size of the boiler load corresponds to the combustion capacity of the boiler, the desired steam pressure can be obtained through reliable proportional control, but it is applied to heating equipment, for example. If the load on the boiler becomes lighter than the combustion capacity range due to a rise in room temperature, etc., the valve opening of the fuel control valve mentioned above should be changed from the maximum opening position to the minimum opening position. Even if the fuel is throttled down to the maximum level, an excessive supply of fuel will result and the vapor pressure will exceed the desired pressure, and the pressure switch installed for safety will operate and stop combustion.
When the steam pressure falls below the desired pressure due to this stop, ON/OFF control is performed so that the pressure switch becomes inoperable and combustion starts again. this
Due to the frequent start and stop of combustion due to ON/OFF control, the pre-purge and other operations performed by the combustion safety control device have the disadvantage of increasing heat loss and, therefore, increasing economic loss. .

[Summary of the invention]

The present invention has been made in view of the above circumstances, and it detects the load of the boiler by signal processing,
By changing the valve opening range of the fuel control valve when the load becomes lighter than a predetermined value, a proportional control region is established under this light load condition, thereby preventing frequent starts and stops of combustion. .

〔Example〕

Hereinafter, the present invention will be explained in detail based on Examples.

FIG. 4 shows an overall configuration diagram of combustion control of a boiler to which the combustion control device according to the present invention is applied.

A boiler 1 is filled with water 2, and steam 5 generated by the heat of a flame 4 burned in a combustion chamber 3 is supplied to a load (not shown) through a pipe 6. 7 is the combustion flue. 8 is a combustion safety control device that starts and stops combustion in a fail-safe manner, and after pre-purging with a fan motor 9, drives an igniter 10 to perform ignition operation, and opens a main valve 11 to start the burner 12. Execute ignition. 13 is a flame sensor that confirms the ignition of the flame. Here, the fan motor 9 supplies air for combustion after ignition.

Reference numeral 14 denotes a pressure converter, which converts the vapor pressure of the steam 5 into, for example, a corresponding electrical resistance value through mechanical displacement, etc. Conventionally, the control motor 15 is controlled by changing this resistance value, etc. Proportional valve 1 for actuation and fuel supply via linkage 16
The opening degree of the valve 7 and the opening degree of the damper 18 for adjusting the air amount were controlled proportionally. That is, the proportional valve 17 and the damper 18 are controlled proportionally in order to achieve the desired steam pressure value set by the pressure converter 14, and the proportional valve 17 and the damper 18 are synchronized by one control motor 15. Air-fuel ratio control is achieved by controlling the

Reference numeral 19 denotes a pressure switch with hysteresis, which turns OFF when the steam pressure exceeds the pressure setting value of the pressure converter 14 and reaches a predetermined upper limit value, and notifies the combustion safety control device 8 to that effect, and controls the combustion. It instructs to stop and also turns on when the steam pressure drops to a predetermined lower limit pressure value to instruct restart of combustion. When the size of the boiler load is within the range corresponding to the combustion force of the boiler (hereinafter referred to as scale), the steam pressure is
4, the pressure switch 19 is not activated, but the pressure switch 19, which reduces the load beyond this scale, is activated.

20 is a combustion control device according to the present invention,
The operating mode of the pressure switch 19 is read through the conventional combustion safety control device 8,
By determining the size of the boiler load and selecting the valve opening scale of the valve opening scale converter 21,
The input to the control motor 15 is changed to convert the operation scale of the control motor. In other words, the valve opening scale when the load is appropriate is set to 0.
-100%, the valve opening degree scale during light load is changed to, for example, 0 to 50%, and the fuel supply during light load is halved.

Further, 22 is a release pressure switch, which is a steam pressure pressure switch for detecting that the boiler load has returned to a normal state.

FIG. 5 shows an operational diagram of conventional boiler combustion control, where the horizontal axis represents the flow of time and the vertical axis represents steam pressure. An OFF operating point, which is the upper limit value, and an ON operating point, which is the lower limit value, of the pressure switch 19 are set across the pressure setting value set in the pressure converter 14.

When the burner 12 starts combustion, the steam pressure increases over time, but when the combustion capacity of the boiler and the load appropriately correspond, the control motor 15 driven by the pressure transducer 14 controls the proportional valve 17. The opening is controlled to maintain the desired pressure setting.

On the other hand, when the load on the boiler becomes lighter than its combustion capacity, the steam pressure continues to rise even if the opening degree of the proportional valve 17 is reduced to a predetermined lower limit, and eventually the pressure switch 19 turns OFF. The point will be reached. When this OFF operation is reached, the combustion safety control device 8 detects the OFF operation of the pressure switch 19 and forcibly stops combustion.

As a result, the steam pressure is set to ON when pressure switch 19 is turned on.
When the ON operation point is reached, the combustion safety control device 8 detects the ON operation of the pressure switch 19 and restarts combustion according to a predetermined sequence. When the combustion is restarted, the combustion safety control device 8 performs a pre-purge operation, resulting in extremely large heat loss, and therefore, the prior art has the drawback of large economic loss.

Moreover, as shown in Figure 3, since it is ON/OFF control, the steam pressure value is the OFF state of the pressure switch 19.
It also had the disadvantage that it fluctuated greatly between the operating point and the ON operating point, making it difficult to achieve sufficient temperature control on the load side.

Next, the operation of the present invention, which is designed to overcome these drawbacks of the prior art, will be described in detail. FIG. 2 shows a combustion control device 2 according to the present invention.
0, and a wiring diagram of the combustion safety control device 8, which is an external device, the release pressure switch 22, the pressure transducer 14, the scale converter 21, and the control motor 15. Here, the combustion control device 20 includes a CPU 23, a ROM 24, a RAM 2
5, and the CPU 23 executes a flowchart shown in FIG. 1, which will be described later, according to a predetermined program stored in the ROM 24 in advance.

The ON/OFF mode of the pressure switch 19 is read into the combustion control device 20 via the combustion safety control device 8, and it is determined which mode the CPU 23 is in. Also, the release pressure switch 22
The ON/OFF mode is directly read into the combustion control device 20 and similarly determined by the CPU 23.

The valve opening degree scale converter 21 is configured by selecting different resistance values, for example, as shown in FIG. 2, and the combustion control device 20 selects one of the resistance values via the I/O port. This will change the valve opening scale.

Note that in this embodiment, the pressure transducer 14
Assuming that the control motor 15 is a device whose electrical resistance value changes in response to steam pressure, and assuming that the control motor 15 is a device that operates based on the balance of the bridge circuit, the valve opening scale converter 21 Although an example of resistance value selection has been illustrated, the present invention is not limited thereto, and may be configured based on the operating principles of the pressure transducer 14 and the control motor 15.

FIG. 1 shows a flowchart executed by the CPU 23. The combustion control device 20 includes a pressure switch 1
9 is constantly checking whether it has reached the OFF operating point. If the load is suitable for normal combustion,
As shown in the operational diagram of the present invention in FIG. 3, the steam pressure is proportionally controlled near the pressure setting value set by the pressure converter 14.

If a phenomenon in which the load becomes lighter occurs, combustion becomes excessive, and the steam pressure increases, eventually reaching the OFF operating point of the pressure switch 19.
The combustion safety control device 8 controls the pressure switch 19.
When the OFF operation is detected, combustion will be stopped immediately, so the steam pressure will decrease over time, and eventually the pressure switch 19 will stop.
The ON operating point will be reached.

The CPU 23 of the combustion control device 20 controls the time from the OFF operation to the ON operation of this pressure switch.
Count t ₀ . If the load is sufficiently light, the steam 5 will not be used much, so this time t ₀ will be sufficiently long. When the counting time t ₀ becomes larger than a predetermined value T ₀ , the load has become lighter, and the valve opening degree scale converter 21 is switched, and the input to the control motor 15 is changed to change the drive range of the control motor. By narrowing the valve opening scale of the proportional valve 17 from 0 to 100%, the small valve opening scale of 0
Change to ~50%.

By this switching, the fuel supply will be halved, so when the combustion safety control device 8 detects the ON operation of the pressure switch 19 and starts combustion again, the steam pressure will be proportional to the pressure setting value of the pressure converter 14. It will be controlled.

Furthermore, the present invention has a flowchart shown in FIG.
As shown in the operation diagram in the figure, when the boiler load returns to an appropriate value again, the reduction in steam pressure due to insufficient combustion caused by changing the valve opening scale of the proportional valve 17 is suppressed by turning on the release pressure switch 22. This can be handled by detecting the movement and returning the valve opening degree scale converter 21 to its original state.

As explained above, the present invention realizes constant proportional control without ON/OFF control by changing the valve opening scale of the fuel control valve in accordance with fluctuations in the boiler load. This is what makes it possible.

The invention is not limited to this example. For example, in the embodiment shown in FIG. 2, the valve opening degree scale converter 21 discloses two-stage switching, but it is not limited to two stages, but can have a multi-stage switching, and can be selected with the size of the counting time t ₀ . It may be something that does.

In addition, in the operation diagram of FIG. 3, the ON operating point of the release pressure switch 22 is set to the ON operating point of the pressure switch 19.
Although an example has been shown in which the steam pressure is set to be lower than the ON operating point, the present invention is not limited to this, and the ON operating point of the release pressure switch 22 is set to the pressure switch 1.
The vapor pressure may be set to be higher than the ON operating point of No. 9.

Furthermore, in this embodiment, only the ON operating point of the release pressure switch 22 is used to detect that the load on the boiler has been restored; however, the OFF operating point of the release pressure switch 22 is used as the
Set between the OFF operating point and the pressure set value, once t ₀
After detecting that the load has become light in the state of ≧T ₀ , when the load becomes light again and the release pressure switch 22 reaches the OFF operating point, the pressure is changed by switching the valve opening scale converter 21. switch 1
It is also possible to configure the combustion safety control device 8 so that the combustion safety control device 8 does not stop the combustion.

At this time, the release pressure switch 22 is turned on.
If the operating point is set between the ON operating point of the pressure switch 19 and the pressure set value, the pressure switch 19 will
Since combustion can be controlled before turning ON/OFF,
Favorable control can be achieved.

〔Effect of the invention〕

As explained above, according to the present invention, the boiler load condition is detected by signal processing, and when the load becomes lighter than a predetermined value, the valve opening scale of the fuel control valve for boiler combustion is changed. Since the system is configured so that the proportional system area is applied even when the load is light, wasteful fuel consumption can be suppressed and economic loss can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a flowchart executed by the CPU of the combustion control device according to the present invention, FIG. 2 is a hardware configuration diagram showing an embodiment of the combustion control device according to the present invention, and FIG. 3 is a flowchart according to the present invention. An operation explanatory diagram showing the operating state of the device, FIG. 4 is an overall configuration diagram of combustion control of a boiler to which the combustion control device according to the present invention is applied,
FIG. 5 is an operational explanatory diagram showing the operational state of combustion control in a conventional boiler. 8... Fuel safety control device, 14... Pressure transducer, 15... Control motor, 20... Combustion control device, 21... Scale converter, 22... Release pressure switch, 23... CPU, 24...
ROM, 25...RAM.

Claims (1)

[Claims] 1. A fuel supply pipe that supplies fuel to a burner provided in the combustion chamber, an air supply pipe that supplies combustion air to the combustion chamber, and a pressure transducer that responds to the steam pressure generated by being heated by the heat in the combustion chamber. , a control motor that controls a proportional valve provided in the fuel supply pipe and a damper provided in the air supply pipe according to an output value of the pressure converter supplied via a valve opening range converter; When it detects that the steam pressure has reached a predetermined upper limit due to the light load, it turns off, and the load on the boiler returns to its original value, and detects that the steam pressure has reached a predetermined lower limit.
A pressure switch that operates ON, a release pressure switch that detects a drop in the steam pressure, and a release pressure switch that detects the OFF operation of the pressure switch and stops the combustion operation, and detects the ON operation of the pressure switch and restarts the combustion operation. A combustion safety control device reads the operating mode of the pressure switch through the combustion safety control device, determines the magnitude of the load on the boiler, and selects the valve opening range of the valve opening range converter to control the control. A combustion control device for a boiler, comprising: a combustion control device that converts an operating range of a motor, detects ON operation of the release pressure switch, and restores the selected valve opening range.