JPS6337290B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a furnace pressure control method for an induced draft fan;
In particular, the present invention relates to a furnace pressure control method using an induced draft fan intended to prevent isoplosion in a balanced draft boiler.

If the supply of fuel to a balanced draft boiler is drastically reduced or cut off, implosion occurs, which is a phenomenon in which the inside of the furnace rapidly becomes negative pressure as the gas temperature inside the furnace rapidly decreases. As a result, accidents such as denting or damage to the boiler body are likely to occur. To avoid this, the general method is to quickly close the inlet damper of the induced draft fan, and when the degree of negative pressure is too high, the induced draft fan is stopped. but,
Merely closing the damper does not effectively prevent negative pressure. Furthermore, the number of times the induced draft fan can be started and stopped in a short period of time is limited by the temperature rise caused by the starting current of the drive motor.

That is, in the method of controlling the furnace pressure using the inlet damper of the induced draft fan, structural limitations cannot be avoided in accelerating the operation of the damper operating mechanism. Furthermore, a method has been proposed in which the rate of throttling of the amount of fuel supplied is delayed when the load is reduced to 50%, such as when one of two water pumps in operation is brought to an emergency stop. Since it acts in the direction of increasing pressure, it has the disadvantage that safe driving cannot be expected. Furthermore, when one of the two forced draft fans stops, etc., incomplete combustion occurs due to a difference in the air-fuel ratio, causing undesirable problems such as black smoke generation and misfires.

In particular, in coal-fired boilers, a large amount of fuel supply is cut off when the pulverized coal supply device is stopped, so a solution to the above problem is desired. Further, as the size of the boiler increases, the volume of the furnace increases, and the problem of implosion prevention as described above is becoming an increasingly important technical issue.

The present invention, in response to the above-mentioned demands, provides a furnace pressure control method for an induced draft fan that prevents implosion that occurs when the amount of fuel supplied is drastically reduced and also enables a sudden reduction in load. The purpose is to

In short, in the present invention, the electric motor used to drive the induced draft fan used is of a pole-number switching type to enable both high-speed and low-speed operation, and a fuel throttling signal based on a sudden decrease in the amount of fuel supplied reduces the power consumption on the high-speed side. Implantation was prevented by cutting off the flow rate and rapidly narrowing down the damper at the inlet or outlet.

Hereinafter, the present invention will be explained in detail with reference to the drawings.
FIG. 1 shows a boiler flue duct system and a furnace pressure control system in which the present invention is implemented. A wind path is constructed. That is, as shown in the figure, an air preheater 2, an air passage 3, a burner air box 4, a boiler air furnace 5, a flue 6, a dust collector 7, and an inlet damper 8 driven by a damper control drive 19 are provided. Then, the furnace pressure control system processes the furnace pressure signal P obtained from the furnace pressure transmitter 11, the set value stored in advance in the setting device 12, and the air volume signal A in the wind duct obtained from the air flow transmitter 15. Then, a control signal C is output for operating the damper control drive 19 so that the furnace pressure reaches a predetermined target value. In the illustrated embodiment, the difference calculation unit 13 compares the furnace pressure signal P and a predetermined control target value in the setting device 12, and the control signal C that eliminates the deviation between this P and the predetermined value is generated. It is calculated in the proportional integral calculator 14 so as to obtain the air volume signal A as a preceding signal.
is added by the addition calculator 16.

The control output signal thus obtained passes through a signal switch 17 which inputs the output from the damper narrowing signal generator 18 and has a control signal switching function.
The damper control drive 19 is operated to open and close the inlet damper 8 to achieve desired furnace pressure control. The schematic structure and interlock system of these control systems are shown in Figure 2. When a fuel throttling command is issued and the IDF 9 is operating at high speed, the high speed side power supply is shut off so that the inlet damper 8 is throttled at full speed. The inlet damper is narrowed down. Then, when the rotation speed of the IDF becomes low and reaches the low speed side rotation speed, the inlet damper is configured to shift to a predetermined furnace pressure automatic control at the same time as the low speed side power is turned on.
In this way, by cutting off the IDF drive power and narrowing down the damper, it is possible to narrow down the damper at high speed without causing abnormal phenomena such as implosion, which is different from the conventional method. I understand.

FIG. 3 shows the results of a simulation comparison between the case according to the present invention and the case according to the conventional method of only opening and closing the damper regarding the change in furnace pressure during fuel shedding. That is, it has been confirmed that according to the present invention, the furnace pressure can be brought significantly closer to its control target value. In this way, it is possible to reduce the range of negative fluctuations in furnace pressure due to sudden fuel reduction or cut-off to less than 50% of the conventional value, which is extremely effective in preventing implosion. Furthermore, since the IDF drive motor operates in a switching manner between high speed and low speed, there is an advantage in that there is no operational problem such as temperature rise due to starting current caused by repeated starting and stopping.

[Brief explanation of the drawing]

Figure 1 is a system diagram for boiler flue duct and furnace pressure control using the present invention, Figure 2 is a schematic diagram of the control system and interlock system, and Figure 3 shows changes in furnace pressure due to fuel shedding. It is a graph diagram. 1: Forced draft fan, 5: Boiler furnace, 8: Inlet damper, 9: Induced draft fan (IDF), 11: Furnace pressure generator, 12: Setting device, 13: Deviation calculator, 1
4: Proportional-integral calculator, 16: Addition calculator, 17:
Signal switcher, 18: Damper narrowing signal generator, 1
9: Diaper control drive.

Claims (1)

[Claims] 1. In a method of controlling furnace pressure using an induced draft fan equipped with a drive motor and a damper that can be selectively switched to high-speed or low-speed rotation, the furnace pressure signal P is detected and the deviation from a predetermined pressure value is determined by a deviation calculator. a step of calculating by a proportional-integral calculator so as to obtain a pressure control signal C such that the deviation becomes zero; A step of adding control to the control signal C, a step of rapidly narrowing down the damper according to a damper narrowing command and simultaneously cutting off the high-speed side power supply, and a step of turning on the low-speed side power supply after confirming that the rotation speed has decreased. A method for automatically controlling furnace pressure using a damper, characterized in that: