JPS6089621A - Airflow control method for balanced draft type boiler - Google Patents

Abstract

PURPOSE:To provide an airflow control method which prevents the occurrence of response lag when automatic switching is made to a commercially available frequency power source when an inverter fails in operation during operation of an induction motor, which drives the ventilator of a balance draft boiler, through control of the number of revolutions by the use of the inverter. CONSTITUTION:When an inverter 13 fails in operation during control of the number of revolutions of an induction ventilator 5, an inverter primary breaker 11 and a secondary breaker 15 are brought to an OFF-state, and a commercially-available side breaker 10 is brought to an ON-state in a condition that a breaker 18 for short-circuiting a series reactor is in an OFF- state. Numeral 10 is a series reactor. Simultaneously, a diver control signal, which performs full-opening output by means of a control selector 19, is momentarily tracked, as shown by a diagram (b), to a damper control signal with the number of revolutions at a commercially- available frequency matching an output signal provided from a regulator 8 for a pressure in a furnace for control of the number of revolutions right before a trouble occurs. By means of this method, acceleration through the reduced voltage of the induction ventilator 5 is effected simultaneously with rapid throttling of the diver 4, and after the number of revolutions of the induction ventilator attains the number of revolutions at a commercially-available frequency, the breaker 18 for short-circuitng a series reaction is brought to an ON-state, and airflow control is made on the damper by means of a pressure in a furnace.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a system for automatically switching to a commercial frequency power source when the inverter fails while the induction motor that drives the ventilator of a balanced draft boiler is being operated under rotational speed control by an inverter. This is the method of controlling the air volume when doing so.

As shown in Figure 1 (a), the balanced draft boiler 3 has a strong pressure draft fan 1 and an induced draft fan 5, and the air volume of the strong pressure draft fan 1 is automatically controlled based on the theoretical air volume and excess air volume due to fuel. The air volume of the induced draft fan 5 is automatically controlled to maintain the pressure inside the boiler constant with respect to the reference. Therefore, for the purpose of power saving, it is also possible to control the air volume by changing the rotational speed of the induction motor 6 for driving the ventilation fan using an inverter. In the figure, there is a 2G motor for driving a strong pressure draft fan, 7 is a furnace pressure transmitter, 12 is an input transformer, 14 is an output transformer,
16 is a chimney.

(Prior art) Conventionally, the pressure inside the furnace was controlled by changing the rotational speed of the induction motor used to drive the induced draft fan in a balanced draft boiler using an inverter, and when the inverter failed, a method was used to directly connect the commercial frequency power supply (recommended). There is an example in which the pressure in the furnace is switched to damper control at the same time.For example, as shown in FIG. , turn off the commercial side breaker 10.

The in-furnace pressure regulator 8i for rotational speed control controls the output of the inverter I3, and the in-furnace pressure regulator 9i for damper control controls the output of the inverter I3.
By fully opening the damper 4 and changing the rotational speed of the induced draft fan 5, the air volume is controlled. Induced draft fan 5
If the inverter 13 breaks down during the rotation speed control,
Turn inverter primary breaker 11 and secondary breaker 15 to O
FF'[,,The commercial side breaker 10 was turned ON, and the induced draft fan 5 was accelerated.At the same time, the damper was controlled by the in-furnace pressure regulator 9 for damper control, which was at full output as shown in Figure 1 (b). This is a method of starting control.

(Purpose of the invention) According to the method of automatically switching to the commercial frequency power supply in the event of an inverter failure, the rotation speed of the induced draft fan reaches the rotation speed ζ at the commercial frequency as shown in Fig. 2. -The time from fully opening the damper to operating at the turn bar control opening at the rotation speed at commercial frequency is considerably shorter than the time required to operate at the turn bar control opening, so the pressure inside the boiler furnace can be kept within the permissible fluctuation value. This prevents stable combustion in the boiler. This trend is.

Particularly in the case of automatic switching from a low rotational speed, the pressure inside the furnace fluctuates significantly in the negative direction. using this method.

If automatic switching to commercial frequency power is performed due to an engine failure during rotation speed control, there is a risk that the boiler's internal pressure may exceed the permissible fluctuation value and the flame may blow out.
The boiler has no choice but to be extinguished.

Unless this operational problem can be resolved, it will not be possible to adopt rotational speed control using an inverter for the ventilation fans of power generation and ventilation boilers, even though the amount of power saved is significant.

The present invention has been made to advantageously solve this problem.

(Structure and operation of the invention) The present invention provides a method for automatically switching to a commercial frequency power source due to an inverter failure while an induced draft fan is being operated by controlling the rotation speed using an inverter ζ. The induced draft fan is accelerated using a voltage reduction method to make the rotation speed rise slowly (force), and at the same time, the time it takes to reach the rotation speed at the commercial frequency is increased. The in-furnace pressure regulator for rotation speed control instantly tracks the control signal to the damper control signal at the rotation speed at the commercial frequency corresponding to the control signal immediately before the inverter failure, speeding up the damper operation and generating induced draft. This is an air flow control method for balanced draft boilers that simultaneously accelerates the mechanical induction motor and throttles the damper to keep the boiler furnace pressure within the permissible fluctuation value.

The acceleration time t of the induction motor is determined by the difference between the torque TM of the induction motor and the load torque TL of the induced draft fan, as shown in FIG.

Here, GD2: Moment of inertia of induced draft fan and driving induction motor TM: Torque of induction motor TL: Load torque Therefore, if a series reactor is inserted and acceleration is performed using a reduced voltage method, the torque of the induction motor is TM' + Decreased.

The acceleration time can be increased by 1/+.

Regarding the damper operation, as shown in Figure 4 (a), the furnace pressure regulator for damper control is at full output when controlling the number of revolutions, but at the same time as the inverter failure occurs, ), the turn control signal is instantly tracked at the rotation speed at the commercial frequency that corresponds to the rotation speed control signal just before the failure occurred.If automatic switching is performed using this method, there is no delay in the response of the controller. ,
As soon as a failure occurs, the damper operates at a speed specific to the turnper.

(Example) The following is a detailed explanation based on the example.As shown in FIG. side breaker 10,
The series reactor short-circuit breaker 18 is turned off, the inverter output is controlled by the furnace pressure regulator 8 for controlling the rotation speed, the damper is fully opened by the furnace pressure regulator 9 for damper control, and the induced draft fan 5 is rotated. The air volume is controlled by changing the number.

While controlling the rotation speed of the induced draft fan 5, if the inverter 13 breaks down, the inverter's primary breaker 11 and secondary breaker 15i are turned OFF, and the commercial side breaker 10 is turned OFF while the breaker 18 for shorting the two series reactors remains OFF. ON and 1-
Ru. 17 is a series reactor. At the same time, the control selection device 19 changes the damper control signal, which had been fully output, to a commercial frequency corresponding to the output signal of the furnace pressure regulator 8 for speed control immediately before the failure, as shown in FIG. 5(O). The damper control signal Q at the rotation speed is instantly tracked. By this method, the induced draft fan 5 is accelerated by voltage reduction, and the damper 4 is quickly throttled down at the same time.

After the rotation speed of the induced draft fan reaches the rotation speed at the commercial frequency, the series reactor short-circuit breaker 18 is turned on, and the damper is used to control the air volume based on the furnace pressure 9.

FIG. 6 shows the output of each controller, the movement of the damper and induced draft fan, and the fluctuation of the pressure inside the furnace in the example.

(Effects of the Invention) The method of the present invention makes it possible to control the minimum rotational speed of the induced draft fan (
30%], even when automatically switching to a commercial frequency power source, the pressure inside the boiler's furnace will fluctuate by -150 to +10 m.
It is about mAq, and the fluctuation tolerance (-200 to +100m
Aq), it solves the problem of using an inverter to control the air volume of the induced draft fan in a balanced draft boiler instead of using a damper, and saves a lot of power. There is.

[Brief explanation of drawings]

Figure 1 (a) is an explanatory diagram showing an overview of the /stem in the conventional embodiment, Figure 1 (b) is a diagram showing the control of the induced draft fan and bumper in that case, and Figure 2 is the conventional implementation. Figure 3 shows the output of each controller, movement of the damper and induced draft fan, and pressure fluctuations in the furnace in the example. A diagram showing a comparison, a diagram illustrating the tracking method of FIG.
Figure 5 (a) is a diagram showing an overview of the system in the embodiment of the present invention. Figure 5 (b) is a diagram illustrating the rotation speed control and lever control at that time, and Figure 6 is a diagram showing the system outline in the embodiment of the invention. It is a diagram showing the output of each controller, the movement of the damper and the induced draft fan, and the pressure fluctuation in the furnace in the example. 1: Strong pressure draft fan, 3: Balanced draft boiler, 4: Induced draft damper, 5: Induced draft Ventilator, 7: Furnace pressure transmitter,
8: Furnace pressure regulator for rotation speed control. 9: Furnace pressure regulator for damper control, 10: Commercial side breaker, 11: Inverter primary breaker, 13: Inverter,] 5: Inverter secondary breaker. ] 7: Series reactor, 18: Series reactor short-circuit breaker, one or two control selection devices. Patent Applicant Representative Patent Attorney Tomoyuki Yafuki (and 1 other person) 3rd (/ill 〃0￭11% liability)

Claims (1)

[Claims] In a method for automatically switching a ventilator of a balanced draft boiler to a commercial frequency power source while the rotation speed is controlled by an inverter, the ventilator is operated at a reduced voltage via a series reactor built into the commercial frequency power supply circuit at the time of switching. At the same time, the damper control signal is tracked to the damper control signal at the rotation speed at the commercial frequency corresponding to the rotation speed control signal immediately before switching, and the valve is throttled. A method for controlling the air volume of a balanced draft boiler, which is characterized by simultaneously performing throttling.