JPS5963418A - Apparatus for controlling operation of forced draft fan for boiler - Google Patents

Abstract

PURPOSE:To reduce variation in the flow rate of air at the time of changing the mode of operation from variable-speed operation to operation using a commercial back-up circuit, by operating an air-flow control valve immediately in response to the output signal of a pattern generator. CONSTITUTION:On the basis of the output of a main steam flow detecting circuit 18, a pattern generator 19 produces a reference value of the valve opening for determining the flow rate of main steam, i.e., the flow rate of air based on the fuel supply rate and the reference value is applied to a means 13 for driving an air-flow control valve 12 via a contact 20b. Then, forced restriction of the opening of the air-flow control valve 12 is started. Further, when it is detected by an equality detecting circuit 20 that the reference value produced by the pattern generator 19 is equal to a feedback signal produced by an air-flow detector 16, the control mode is shifted to the normal air-flow control by controlling the opening of an air-flow control valve 6. At the time of shifting the control mode, a breaker 11a of a commercial power source back-up circuit 11 is opened and a breaker 11c is closed, thereby connecting a voltage reducing reactor 11b in the circuit. Thus, a motor 9 supplied with current from the circuit 11 can reduce the speed of rotation after shifting of the control mode by way of reduced- voltage starting.

Description

Detailed Description of the Invention (a) Description of the Technical Field The present invention relates to a control device for a forced draft fan in a boiler, which is equipped with a backup circuit powered by a commercial power source, and is capable of controlling a forced draft fan when a variable speed motor is used as the motor for driving the forced draft fan. This invention relates to a control device for a boiler forced draft fan.

(b) Description of the Prior Art Many boiler facilities are used as steam generation sources in power plants or general factories. In recent years, for the purpose of energy saving, a method has been implemented in which a forced draft fan (p, 11. Boiler equipment in general factories is the most important load, and often has a backup circuit powered by commercial power.

Figure 1 shows the concave configuration of such boiler equipment, where 1 is the combustion chamber of the boiler, 2 is a water pipe installed in the combustion chamber 1, and while water passes through this pipe, It is heated to become steam. 3 is a pipe line for supplying fuel such as heavy oil, 4 is a flow rate control valve for supplying fuel such as heavy oil, 5 is a pump for supplying fuel such as heavy oil, and 6 is for driving this pump 5. It is an electric motor for

Further, 7 is a ventilation pipe for supplying air for burning fuel such as heavy oil into the combustion chamber 1, 8 is a forced draft fan installed to be connected to the ventilation pipe 7, and is used to force air into the combustion chamber 1; 1 is an electric motor for driving the forced draft fan 8, 1 is a variable speed drive device, 11 is a backup circuit powered by a commercial power source,
12 is the wind meter adjustment vane of the forced ventilation fan, 13 is the wind μ adjustment vane drive device, and 14 is the air 1K corresponding to the fuel supply Ell.
15 is a chimney for discharging the exhaust gas burned in the combustion chamber l to the outside;
6 is an air volume detector.

2 (Figure 42 shows the variable speed drive device 1o and backup circuit 1
1, the variable speed drive device 1o is connected to an input transformer 101 provided as necessary via a power switch breaker 1.
], consists of a variable speed control device (inverter) 10c that converts commercial power supply into variable frequency variable voltage, an output transformer IQ+t provided as necessary, and a switching breaker 10e that opens and closes simultaneously with the power switching breaker 10a. , ``connected to the electric motor 9. On the other hand, the back-up circuit 11 is connected in parallel to the reactor llb for suppressing the air flow at startup via the power switch breaker 11a,
It is connected to the electric motor 9 via 1c.

Normally, the rotation speed of the electric motor 9 is controlled by a variable speed control device 10c using an output signal from a wind h1 setting circuit 13 that sets the air frame necessary to burn fuel commensurate with the load (steam amount). ■The air volume control valve 12 of the nn wire machine 8 is fixed at a setting value close to fully open.

Also, when the variable speed control device 10c is out of order, or
The total variable speed drive loss is greater than the air conditioning vane loss. In the rotation speed range, the aforementioned backup circuit 1
Power is supplied from the motor 1 to the electric motor 9. On the other hand, the wind @ control valve 12 of the forced ventilation fan 8 is controlled to open IW by the output signal of the approximately 11m setting circuit 13, and the wind tl 1iliq is adjusted.

During variable speed operation, the air reserve required to burn the lookout fuel canopy in the steam load chamber is determined by the wind star setting device 14, and compared with the feedback signal output from the air volume detector 16. And with that output signal, the variable speed drive device】O
As a result, the rotational speed of the drive motor 9 of the forced draft fan 8 is controlled. At this time, the wind Pi' control valve 12 is set to a predetermined constant value. If a failure occurs in the variable speed control device 10c, the switching breaker 10a and 10
e immediately shifts to an open state, the electric motor 9 enters a free run state, and the input changeover meter 17 is switched, and the wind h1 control valve 12 is set to the air volume setting device 1 by the wind field adjustment valve drive device 13.
Start moving to an angle that matches the output of step 4.

On the other hand, after disconnecting the variable speed drive device in from the electric motor 9, after the residual voltage of the electric motor 9 has had time to stop affecting the motor body, the forced draft fan, and the power supply system, Close 11a.

At the same time, in order to insert a decompression reactor llb to reduce the startup time of the motor in order to suppress wind (J), switch 11c is opened and pj startup is started, and after startup is completed, switch 11.c is opened. Close it to complete the cut 8e.

Figure 3 shows a time chart for the month 1 hour, (a) shows the change in air volume 11 - the angle of J joint 12, (1)
) is the change in the rotational speed of the electric motor 9, (c) is the change in the number of revolutions of the electric motor 9, and (c) is the change in the air volume control 1Yj5 valve 12 and the wind 1 due to the gauging of the electric motor 9! ``C'' represents the transformation of the body. Note that in the same figure, t and b] represent the time when the power supply is switched, and t2 represents the time when the power supply is switched.Generally, the operating time of the 12 air volume adjustment valves is very long, ranging from several seconds to hundreds of tens of seconds. Normally, when the push-in air conditioner 8 is driven at variable speed, the wind h1 control valve 12 is fixed at a point close to the full range, and from this state an increase in air volume due to an increase in the motor rotation speed is detected. Since the air volume control valve 12 is closed, a large time delay occurs.

On the other hand, after the speed decreases due to free running, the electric motor 9 performs angular acceleration by starting the reactor with the decompression reactor Ilb. It is determined by the characteristics and the rate of pressure drop of the pressure reducing reactor 11b, and the lower the load factor of the boiler device, that is, the rotation speed of the forced draft fan 8, the more the wind fluctuates, which is a disadvantage that the boiler burner may misfire. It was extremely dangerous.

(c) Purpose of the Invention The present invention has been made in view of the above circumstances, and has been developed to provide a forced ventilation system for boilers having commercial backup circuits such as a variable speed drive system in the event of a failure of the variable speed control system. Te 1 from operation to commercial backup circuit! It is an object of the present invention to provide a control device for a forced draft fan for a boiler which does not have the above-mentioned drawbacks and prevents boiler misfires and damage to the boiler hearth etc. by reducing the fluctuation in the air volume when switching from one to the other. .

((1) Summary of the Invention The present invention minimizes the 1Δ fluctuation of the wind when switching to commercial power when the variable speed drive device of the motor 9 for the boiler forced draft fan breaks down, thereby preventing misfires and damage to the hearth, etc. To prevent this, a pattern generator is installed, and the pattern generator calculates the main steam amount or the opening degree of the air volume control valve for the required ventilation.
Instead of adjusting after the air volume increases or decreases <tt L/, the air flow control valve is operated immediately using the output signal of the pattern generator in advance, eliminating the delay in the control signal of the air flow control valve, and driving the push-in air flow machine. By starting the electric motor 9 at a reduced voltage using a reactor, sudden changes in air volume are avoided.

(e) Structure and operation of the invention The present invention will be explained below with reference to the drawings. FIG. 4 shows an embodiment of the present invention, and since parts having the same reference numerals as those in FIG. 1 are the same, their explanation will be omitted.

When the variable speed control device 10c fails, the drive motor 9 of the forced draft fan 8 is switched from the variable speed drive device 10 to the commercial power backup circuit 11 as described above because the variable speed control device 10c fails. The air volume control valve 12 is switched from the constant opening degree to the air volume control based on the valve opening degree control by the switching switch 17, but the operation will be described later until the switching is completed. 18 is a main steam amount detection circuit, 19 is a pattern generator newly provided according to the present invention, N20 is a matching detection circuit between the opening degree of the control valve 12 and the setting value of the control valve opening degree, 20a,
b is a coincidence detection contact output.

General (In Nipoiler control, it is necessary to maintain the steam pressure and steam temperature of the steam exiting to the outside at predetermined values according to requests from the load side, and for this reason, the fuel supply must be changed,
The amount of air used to burn the fuel is changed to adjust the exothermic group within the combustion chamber 1 to a predetermined value 114. The ratio between the fuel supply 11 and the amount of combustion air (air-fuel ratio) needs to be kept constant. This is because if the fuel supply 14 is excessive, there will be a lack of oxygen and incomplete combustion will occur, causing black smoke to come out of the chimney, causing pollution problems and lowering efficiency. Furthermore, if the ventilation is excessive, the thermal energy generated by combustion heats the air and is discharged from the chimney, resulting in a decrease in efficiency.

As mentioned above, the boiler is the most important load, and it has a backup circuit 11 from the commercial power source, so even if the variable speed device fails, there is a system that can shorten the downtime of the boiler equipment or continue operation. It becomes necessary. On the other hand, fluctuations in air volume during operation of the boiler equipment may cause burner misfires or damage to the boiler hearth, so care must be taken.

- In the configuration described above, the output of the main steam amount detection circuit 18 is:
The pattern generator 19 outputs a valve opening setting pattern for the main steam, that is, the fuel supply 11-1, to provide a small amount of air. i Force the penalty control valve 12 to start narrowing down. Then, the -number output circuit 2o detects that the setting value from the pattern generator 19 and the feedback signal from the wind detector 16 match, and the contact 20b is opened and the contact 20a is closed. The process then shifts to air volume control by controlling the opening degree of the air flow control valve 6.

On the other hand, when the motor 9 is powered by the commercial backup circuit 11, the switching breaker 11a is turned on and the switching breaker 11c is closed, thereby inserting the pressure reducing reactor llb into the circuit and reducing the voltage. The rotation speed of the electric motor 9 after switching is made gentle by starting. Further, the decompression reactor Ilb has multiple taps, and can be selected in accordance with the load condition and damper operation time.

(f) Overall effect In this way, according to the present invention, when the variable speed control device fails, the air volume control valve is operated without any operation delay time, and the corner φ
It is possible to provide an effective boiler forced draft fan control device that narrows down the air volume and reduces air volume fluctuations.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of boiler equipment, Fig. 2 is a configuration diagram of a variable speed drive device and a backup circuit using a commercial power supply, Fig. 3 is a time chart at the time of switching the power supply, and Fig. vJ4 is an example of an implementation of the present invention. FIG. 2 is a block diagram illustrating an example. 2... Water pipe, 3... Fuel supply pipe, 4... Fuel supply valve. 5... Fuel supply pump, 6... Pump drive electric motor, 7... Air ventilation pipe, 8... Forced ventilation fan (F, D
, F), 12... Air volume control valve, 16... Air volume detector, 17... Switching device, 11b... Pressure reducing reactor, 2
0a, b...-Number of circuit output contacts. (7317) Agent Patent attorney Noriyuki Chika (and 1 other person) Figure 1, l; 43 Figure 3

Claims (1)

[Claims] In a control device for a boiler equipped with a variable speed drive device having a variable speed control device that converts commercial power supply into variable frequency and variable voltage, and a backup circuit using the commercial power supply, when switching to the commercial power supply due to a failure of the variable speed drive device, , a pattern generator is installed that operates only when the power is switched, and calculates the required ventilation (4) of the main steam flow generated from the boiler or fuel supplied to the boiler combustion chamber and operates the air leaf control valve opening to adjust the air volume. A control device for a boiler forced draft fan characterized by eliminating valve response delay and reducing air volume fluctuations.