JPS62406B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for controlling the amount of air supplied to a boiler.

Fig. 1 is a circuit diagram showing a conventional general boiler air flow control device. In the figure, 1 is a wind path that guides the air to be sent to the boiler (not shown), and 2 is a circuit diagram showing the air flow through this air path. A fan that supplies air to the boiler; 3 a damper provided in the air passage 1; opening and closing the damper to adjust the amount of air supplied to the boiler; 4 a damper opening control device that controls the opening of the damper; This is an air volume control signal generator that generates an air volume control signal corresponding to the optimum air volume according to the combustion state of the boiler, and its output signal is transmitted to the damper opening degree control device 4 as shown in the figure.
The damper 3 is opened and closed to control the optimum amount of air to be supplied to the boiler. Reference numeral 6 denotes an electric motor energized by a commercial power source 7 to rotate the fan 2 at a constant speed.

In the conventional device shown in FIG. 1, since the electric motor 6 that drives the fan 2 is energized by the commercial power source 7 as described above,
The fan 2 is always driven at a constant rotational speed, and a fixed amount of air is always generated from the fan 2. This fixed amount of wind is confined by the damper 3 to an optimum amount. In other words, even when only a small amount of air is supplied to the boiler, the electric motor 6 continues to rotate at a constant rate, and the fan 2 continues to generate a maximum amount of air at all times. is hardly a desirable control device.

FIG. 2 shows a device that solves the drawbacks of the device shown in FIG. 1, and 8 in the figure is a variable frequency power source such as an inverter, the output frequency of which is controlled by the output signal of the air volume control signal generator 5. It is becoming. That is, the device shown in FIG. 2 utilizes the fact that the rotational speed of the electric motor 6 is proportional to the power supply frequency, and that the rotational speed of the fan 2 and the air volume are in a proportional relationship. By controlling the fan 2, it is intended to generate an optimal air volume. According to the device shown in Fig. 2, the required amount of air is generated by the fan 2 each time, and unnecessary air volume is not wasted by the damper 3 as shown in Fig. 1. Therefore, it can be said that it is a preferable device.

However, since this device shown in FIG. 2 uses a variable frequency power source 8 as an energizing power source for the electric motor 6, there is a problem in that the power supply is unstable. This is because the variable frequency power source 8 such as an inverter may fail. However, boilers are generally not allowed to stop, so a so-called equipment redundancy strategy is used in which two variable frequency power supplies are prepared in case the variable frequency power supply 8 fails, and when one fails, the other variable frequency power supply is used. I have no choice but to take it. However, installing two expensive variable frequency power supplies in parallel poses a problem in terms of equipment costs.

The present invention has been made to solve the problems of the conventional device described above, and one embodiment thereof is shown in FIG.
In FIG. 3, 9a and 9b are switching contacts for selectively selecting either the commercial power source 7 or the variable frequency power source 8 as the auxiliary power source for the electric motor 6, and 10a and 10b are switching contacts for switching the output signal of the air volume control signal generator 5 to open the damper. A switching contact 11 that selectively supplies power to the frequency control device 4 or the variable frequency power source 8 is a failure detector that operates when the variable frequency power source 8 fails, and when activated, the switching contacts 9a, 9b, 10a, 10b It is designed to switch automatically.

That is, normally, the switching contacts 9b and 10b are closed, and the switching contacts 9b and 10b are closed.
a, 10a are open, and the circuit is operated in the circuit state shown in FIG. 2 above. In this case, the damper 3 is preferably fixed at its maximum opening in order to reduce loss. Next, if the variable frequency power supply 8 fails in this operating state, the failure detector 1
1 operates and opens switching contacts 9b and 10b, 9
A, 10a are closed and the circuit state is automatically switched to the circuit state shown in FIG. 1 above.

As described above, according to the present invention, the air volume can be controlled without energy loss by controlling the rotation speed of the motor using the variable frequency power supply, and even if the variable frequency power supply fails, the boiler can continue operating without stopping. Moreover, there is no need to worry about high equipment costs.

Although the intended purpose can be achieved according to Figure 3 above,
It is advisable to take measures to address the following problems. That is, FIG. 4 shows the changes in the damper opening degree and the motor (fan) rotational speed during the operation switching shown in FIG. 3, and the air volume error based on the deviation of these changes. That is, at time t ₁ when the variable frequency power supply 8 is operating, the required air volume of the boiler is small, and the electric motor 6 is rotating at a low speed.
Assume that the power source of is switched from the variable frequency power source 8 to the commercial power source 7. At this time, the electric motor 6 starts speeding up as shown by the solid line in Figure 4, and at time _t2 , the commercial power supply 7
However, as the rotation speed increases, the air volume increases, so the air volume control signal generator 5 sends a signal to the damper opening control device 4 to maintain the air volume at the level immediately before the failure of the variable frequency power supply 8. Give a command in the closing direction. Therefore, the damper opening degree receives a closing command from time t ₁ and attempts to operate in the closing direction, but due to a mechanical delay, closing starts after t ₀ has elapsed (see the solid line in Figure 4), and at time t ₃ The opening degree will settle down to match the required air volume of the boiler. However, since the damper 3 is confined due to mechanical operation as the speed of the electric motor 6 increases, generally t ₂ <t ₃ , and between t ₁ and t ₂ , the air volume gradually increases due to the speed increase of the electric motor 6. This amount is larger than the gradual decrease due to the confinement of the damper 3, and a large air volume error occurs with respect to the optimum air volume of the boiler (solid line in Figure 4). However, in a boiler, if the air volume increases or decreases beyond the optimum value, the boiler may be damaged or the stability of combustion cannot be maintained, exposing the boiler to the risk of explosion, etc. Therefore, it is necessary to suppress the error air volume within a certain allowable value.

FIG. 5 shows another embodiment of the present invention in which this air volume error is suppressed within an allowable value, and as is clear from the figure, a reactor 12 for suppressing speed increase is inserted in the circuit of the commercial power supply 7. did. According to FIG. 5, when the fault detector 11 is activated during operation with the variable frequency power supply 8, the switching contacts 9b and 10b are opened and the switching contacts 9a and 10a are closed, but the reactor short circuit switch 13 remains open. Therefore, even if the power source is switched to the commercial power source 7, the speed increase of the electric motor 6 is suppressed by the action of the reactor 12, and the speed increases slowly as shown by the two-dot chain line in FIG. The increase in air volume will change slowly. That is, by inserting the reactor 12, the voltage applied to the electric motor 6 is lowered by the voltage drop caused by the reactor 12. Therefore, the voltage applied to the electric motor 6 decreases. (Torque decreases in proportion to the square of the voltage.) Therefore,
The acceleration torque (the difference between the torque generated by the electric motor and the load torque) is reduced, and the speed increase of the electric motor 6 is suppressed.
Therefore, the closing operation of the damper opening for correcting this increase in air volume can sufficiently follow changes in the speed of the electric motor 6. Therefore, the gradual increase in air volume caused by increasing the speed of the electric motor 6 becomes almost equal (as shown by the two-dot chain line in FIG. 4), and the air volume error can be suppressed within the permissible value. Note that 13 in Figure 5
is a short-circuit switch for removing the reactor 12 from the circuit at time _t4 when the motor 6 reaches its rated rotational speed. Although the two-dot chain line in FIG. 4 shows the case where the reactor capacity is increased, it is also possible to make the damper opening match the solid line state by appropriately selecting the capacity.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit diagrams showing conventional equipment, and Figure 3 is a circuit diagram showing a conventional device.
FIG. 4 is a circuit diagram showing one embodiment of the invention, FIG. 4 is a diagram for explaining the operating state of the invention, and FIG. 5 is a circuit diagram showing another embodiment of the invention. In each figure, 1 is the wind duct, 2 is the fan, 3 is the damper, and 4
is a damper opening control device, 5 is an air volume control signal generator, 6 is an electric motor, 7 is a commercial power source, 8 is a variable frequency power source, 9a, 9b, 10a, 10b are switching contacts,
11 is a failure detector, 12 is a reactor, and 13 is a short circuit switch, and the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A fan that supplies wind to a boiler via a damper provided in a wind path, an electric motor that is selectively energized by a commercial power source or a variable frequency power source that drives this fan, and the boiler described above. an air volume control signal generator that generates an air volume control signal corresponding to the optimum air volume according to the combustion state of the engine, and selectively controls the opening degree of the damper or the frequency of the variable frequency power source according to the signal, and the variable frequency power source The output signal of the air volume control signal generator is switched from the frequency control of the variable frequency power supply to the damper opening control by the operation of the fault detector. A boiler air volume control device characterized in that the auxiliary power source for the electric motor is switched from a variable frequency power source to a commercial power source. 2. A fan that supplies wind to the boiler via a damper installed in the wind duct, an electric motor that is selectively energized by a commercial power source or a variable frequency power source that drives this fan, and a motor that is selectively energized by a commercial power source or a variable frequency power source that operates according to the combustion state of the boiler. An air volume control signal generator that generates an air volume control signal for the optimum air volume and selectively controls the opening degree of the damper or the frequency of the variable frequency power supply using the signal, and a failure that detects a failure of the variable frequency power supply. A detector is provided, and when the fault detector is activated, the output signal of the air volume control signal generator is switched from being used for frequency control of the variable frequency power source to being used for controlling the opening of the damper, and the auxiliary power source for the electric motor is used. A boiler air volume control device characterized in that a variable frequency power supply is switched to a commercial power supply, and a reactor is inserted into the commercial power supply circuit at the time of this switching.