JPH08226608A - Preventing apparatus for implosion of boiler - Google Patents

Abstract

PURPOSE: To provide the title apparatus which prevents implosion surely. CONSTITUTION: Pressure in a furnace 21 is properly held by controlling the opening of a moving blade 6a for a forced draft fan 6 and a moving blade 18a for an induced draft fan 18. When a signal to cut-off a main fuel is outputted from a boiler control system, the opening of the moving blade 6a is held in that state and the opening of the moving blade 18 is throttled. At the same time, the signal is outputted from a MFT signal transmitter 7 and a solenoid 31 is excited through an OR circuit 33. A controlling air line 30 is switched, an opening and closing valve 29 is opened, and outside air is thrown into the furnace 21. Since this process is carried out simultaneously with the output of the signal to cut off the main fuel, the outside air is quickly thrown thereinto and implosion can be surely prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler intrusion prevention device for preventing intrusion of a furnace that occurs when the main fuel to the boiler is shut off.

[0002]

2. Description of the Related Art During a boiler operation, for example, if a water supply system accident such as a water supply pump stoppage, a boiler steam leak, a turbine trouble, a fuel system pressure drop, etc. occurs, the boiler control system is used for main fuel cutoff (MFT). It outputs a signal and shuts off the main fuel that was being supplied to the boiler. When this main fuel cutoff occurs, the pressure of the furnace decreases, which causes the furnace to implode, which is dangerous. In order to prevent this, conventionally, a means for controlling the opening of the moving blades of the forced draft fan and the induction draft fan has been adopted. This will be described with reference to the drawings.

FIG. 3 is a block diagram of a conventional control device for a forced draft fan for preventing intrusion. In this figure, 1 is a secondary air pressure transmitter of the air preheater, 2 is a function generator that creates a set value of the secondary air pressure of the air preheater based on the air flow rate command, and 3 is a signal and function of the oscillator 1. A subtractor for calculating the deviation from the signal of the generator 2, 4 is a proportional integrator, 5 is an automatic / manual switcher, 6 is a forced draft fan, and 7 is a main fuel cutoff signal (MFT signal) transmitter.

FIG. 4 is a block diagram of a control device of a conventional induction draft fan for preventing intrusion. In this figure, 11 is a furnace pressure transmitter, 12 is a furnace pressure setting device, 13 is a subtractor for calculating the deviation between the signal of the furnace pressure transmitter 11 and the furnace pressure setting value, 14 is a proportional integrator, and 15 is automatic. / Manual switch, 7 is the same MFT signal transmitter as shown in FIG. 3, 16
Is an opening correction circuit for correcting the opening of the moving blade of the induction fan, 1
Reference numeral 7 is an adder, and 18 is an induction fan.

Next, the operation of the control means shown in FIGS. 3 and 4 will be described. The control means shown in FIG.
The manual switching device 5 is switched to the automatic side, and the subtractor 3
The opening degree of the moving blades of the forced draft fan 6 is appropriately controlled based on the deviation of the secondary pressure of the air preheater calculated in step 1. In the control means shown in FIG. It is switched to the automatic side, and the opening degree of the moving blade of the induction fan 18 is appropriately controlled based on the deviation calculated by the subtractor 13.

In this state, if the main fuel cutoff occurs, FIG.
In the means shown in (1), the automatic / manual selector 5 is switched to the manual side by the signal from the MFT signal transmitter 7, and the moving blade is fixed to the state at that time for a certain period of time. At the same time, FIG.
In the means shown in (1), the opening correction circuit 16 outputs a signal in the direction of narrowing down the moving blades of the induction fan 18 by the signal from the MFT signal transmitter 7 to suppress the induction of air in the furnace. As a result, the decline in the furnace pressure when the main fuel was shut off was prevented, and the intrusion was suppressed.

[0007]

However, while the main fuel cutoff occurs instantly, it takes a considerable amount of time to narrow down the moving blades of the induced draft fan 18, during which the furnace pressure is the pressure limit of the furnace. It was extremely dangerous as it could drop close to the value. On the other hand, for example,
As seen in Japanese Patent No. 58509 and Japanese Utility Model Laid-Open No. 61-58509, a means for introducing air into the furnace when the furnace pressure falls below a set value has been proposed. It is extremely difficult to select a value.

That is, since the furnace pressure fluctuates when the boiler is started or stopped, or when the load fluctuates during operation, if a set value high enough to suppress the intrusion is selected, the boiler will be operated. Unexpected air will be sent to the furnace, combustion will become large and unbalanced, and control of the boiler will be impossible. On the other hand, if the set value is selected to be low in order to avoid this, it becomes impossible to surely suppress the intrusion. in this way,
With the means described in the above publications, it is extremely difficult to properly select the set value.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a boiler intrusion prevention device capable of reliably suppressing intrusion.

[0010]

In order to achieve the above object, the present invention provides a pipe for supplying air directly from the atmosphere to a boiler furnace, an on-off valve for opening and closing this pipe, and a main fuel for the boiler. And a valve control means for opening the on-off valve to supply air to the boiler furnace when a main fuel cut-off signal for shutting off the fuel is output.

[0011]

When the main fuel cutoff signal is output in the boiler control system, the on-off valve opens immediately in response to this signal, and air from the atmosphere is introduced into the furnace through the pipe. When the main fuel cutoff occurs, intrusion will always occur, so that regardless of the furnace pressure at that time, air is quickly introduced into the furnace to reliably suppress the intrusion.

[0012]

The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a system diagram of a boiler intrusion prevention apparatus according to an embodiment of the present invention. In this figure, 21 is a boiler furnace, 22 is a wind box, 23 is a coal supply pipe from a mill, 24 is a coal burner, and 25 is an air preheater. 6 is a forced draft fan shown in FIG. 3, 6a is its moving blades, 18
Is an induction fan shown in FIG. 4, and 18a is its moving blade. Two
8 is a pipe for directly supplying the atmosphere into the furnace, 29 is a pipe 28
Is a control air pipe for guiding control air for opening and closing the open / close valve 29, and 31 is a solenoid for switching the control air pipe to either the open / close side. 7 is the MFT signal transmitter shown in FIGS. 3 and 4, 27 is an interlock control signal transmitter conventionally provided, and 33 is an OR.
A circuit, 34 is a NOT circuit.

The interlock control is a control for supplying air in order to prevent the coal burner 24 from being exposed to the high temperature in the furnace and being damaged when the coal burner 24 is stopped. The pipe 28, the on-off valve 29, The control air pipe 30, the solenoid 31, and the interlock control signal transmitter 32 that controls the solenoid 31 are existing ones.

Next, the operation of this embodiment will be described. During normal operation, neither the interlock control signal nor the MFT signal is output, and the opening degrees of the moving blades 6a of the forced draft fan 6 and the moving blades 18a of the induced draft fan 18 are appropriately controlled by the control means shown in FIGS. 3 and 4. The pressure inside the furnace 21 is properly maintained. When the main fuel cutoff occurs in this state, and the main fuel cutoff signal is output from the boiler control system, a signal is output from the MFT signal transmitter 7 and, as shown in FIG. 3 and FIG. The blade 6a is held at the opening degree at that time, and the moving blade 18a of the induced draft fan 18 is narrowed. At the same time, the signal from the MFT signal transmitter 7 excites the solenoid 31 on the side that opens the on-off valve 29 via the OR circuit 33 shown in FIG. 1 (the other solenoid is surely de-energized by the NOT circuit 34). The control air pipe 30 is switched to send control air to one chamber of the on-off valve 29 (a rod-side chamber in the figure) to open the on-off valve 29. As a result, the air from the atmosphere is piped 28
It is thrown into the furnace 21 through the through hole to prevent the pressure in the furnace 21 from decreasing and suppress the occurrence of intrusion.

When the signal from the MFT signal transmitter 7 disappears, the solenoid that has been excited until then becomes non-excited, the other solenoid is excited by the signal from the NOT circuit 34, and the on-off valve 29 is securely closed, so that the piping The air from 28 is shut off. The operation when the interlock control signal is output from the interlock control signal transmitter 32 is similar.

In this embodiment, when the MFT signal is output, the MFT signal is used to open the on-off valve to directly inject air from the atmosphere into the furnace, so that the air can be rapidly introduced. This makes it possible to surely suppress the intrusion. The effect of the implosion prevention device of this embodiment is shown in FIG.

FIG. 2 is a diagram showing changes in furnace pressure. In this figure, the horizontal axis represents time and the vertical axis represents furnace pressure. A
Is a curve showing the change in furnace pressure in the means of this embodiment, B
Is a curve showing the change in furnace pressure in the conventional means.
As is clear from the figure, when the main fuel cutoff occurs, in the conventional means shown in FIGS. 3 and 4, the furnace pressure rapidly approaches the furnace pressure limit value as shown by the curve B, which is dangerous. In the present embodiment, it can be seen that the furnace pressure changes gently in a pressure region much higher than the furnace withstand pressure limit value as shown by the curve A, and the intrusion can be surely suppressed. Further, in the present embodiment, since the existing interlock control device is used for supplying air, the device can be constructed at low cost.

In the description of the above embodiment, the on-off valve for switching and operating the control air pipe with the solenoid has been illustrated, but the present invention is not limited to this, and any valve can be used as long as the pipe 28 can be quickly opened and closed. A valve may be used.
Also, an example has been described in which the blades of the forced draft fan and the blades of the induction draft fan shown in FIGS. 3 and 4 are simultaneously controlled, but the controls shown in FIGS. 3 and 4 are not always necessary depending on the amount of air input. is not. Further, the air can be introduced independently of the existing interlock control device without using it.

[0019]

As described above, according to the present invention, when the main fuel cutoff signal for cutting off the main fuel to the boiler is output, the on-off valve is opened and the air is injected into the boiler furnace. Can be rapidly introduced, and thus the intrusion can be surely suppressed.

[Brief description of drawings]

FIG. 1 is a system diagram of a boiler implosion prevention device according to an embodiment of the present invention.

FIG. 2 is a diagram showing changes in furnace pressure.

FIG. 3 is a block diagram showing a conventional control means.

FIG. 4 is a block diagram showing a conventional control means.

[Explanation of symbols]

 6 Push-ventilator 6a Push-ventilator moving blade 7 MFT signal transmitter 18 Induction drafter 18a Induction drafter moving blade 21 Furnace 28 Piping 29 Open / close valve 30 Control air piping 31 Solenoid 32 Interlock control signal transmitter 33 OR circuit 34 NOT circuit

Claims (1)

[Claims] 1. A pipe for directly supplying air from the atmosphere to a boiler furnace, an on-off valve for opening and closing this pipe, and a main fuel shut-off signal for shutting off main fuel to the boiler. And a valve control means for opening and feeding air into the boiler furnace.