JP2002013730A - Equipment for controlling gas pressure in furnace at emergency stop of boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a breakage from being generated in a furnace by restraining a rapid reduction in a furnace gas pressure, immediately after generation of MFT(main fuel trip) depending upon a stop of a fan operation. SOLUTION: A boiler of a balanced draft system has a draft system which is provided with a forced draft fan for forcing combustion air in to the furnace and an induced draft fan for controlling a gas pressure in the furnace. A rotating blade of the induced draft fan in an idle running state due to the shaft inertia immediately after an emergency stop of the boiler or a damper opening in the inlet/outlet are controlled to restrain lowering of the pressure in the furnace, corresponding to the lowering of the in-furnace pressure measured by an in-furnace pressure gauge, in case of an emergency stop of the boiler caused by a stop of the forced draft fan or the induced draft fan.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler plant, and more particularly to a gas pressure control device in a furnace at the time of an emergency stop of a boiler accompanied by a stop of a ventilator installed on a boiler flue and a wind system, and more particularly to a single-line boiler. Suitable when installed on flue and air duct.

[0002]

2. Description of the Related Art FIG. 1 is a diagram showing a schematic configuration of a ventilation system of a balanced ventilation boiler plant, which comprises a single system boiler wind path and a flue. In the balanced ventilation type boiler plant, combustion air is sent into a furnace 2 by a forced draft fan (hereinafter, referred to as FDF) 1. During this time, the combustion air is heated by an air preheater (hereinafter, referred to as AH) 3 by heat exchange with the combustion exhaust gas from the furnace 2. The heated combustion air is burned together with the fuel in the furnace 2 to become a combustion gas, and after performing heat exchange with the combustion air in the AH 3, is guided to a chimney 5 by an induction ventilator (hereinafter referred to as IDF) 4. Released to the atmosphere. As the FDF or IDF, a centrifugal fan or an axial fan as shown in FIG. 6 is used. The structure of each fan has the structure as shown in FIG.

[0003] Here, the inlet pressure of the IDF 4 is adjusted to control the pressure of the combustion gas in the furnace. In particular, in a coal-fired boiler, the combustion gas in the furnace is maintained at a pressure lower than the atmospheric pressure (about -10 mmAq) by adjusting the pressure at the inlet of the IDF 4 in order to prevent ash leakage to the outside of the furnace. IDF4
The blade or inlet damper opening of the
4 The furnace pressure decreases due to the decrease in the inlet pressure,
As the opening is smaller, the furnace pressure increases due to an increase in the IDF4 inlet pressure.

The measured value of the furnace gas pressure measured by the furnace gas pressure measuring device 6 is sent to a subtractor 7 as a signal, where a deviation from the furnace pressure set value 8 is calculated. From the deviation, the rotor or inlet damper opening adjuster 9 adjusts the I
A blade opening adjustment signal for DF4 is created and sent to IDF4 to adjust the blade opening.

[0005] Boiler emergency stop in the prior art (hereinafter, referred to as
FIG. 2 shows the variation of the fuel flow rate, the exhaust gas flow rate, the furnace pressure, and the like with respect to the blade opening degree of the FDF 1 and the IDF 4 at the time of MFT (Main Fuel Trip).

In the MFT, a plant stop operation is performed by shutting off fuel supply.
4 needs to continue operation in order to remove unburned components remaining in the furnace and the ventilation system.

On the other hand, an MFT in which both the FDF 1 and the IDF 4 are stopped occurs when either the FDF 1 or the IDF 4 trips. Normally, FDF1 and ID
Since F4 is connected to each other by an interlock mechanism, if either one trips, the other ventilator also stops.

When an MFT occurs (FDF or IDF
2), the fuel supply is cut off (FIG. 2 (a)), so that the temperature of the combustion gas in the furnace rapidly decreases, and accordingly, the pressure of the combustion gas in the furnace rapidly decreases. (FIG. 2 (f)). At this time, FDF1 and IDF
If the operation of the DF4 is continued, the pressure of the combustion gas in the furnace can be adjusted by controlling the blade opening degree of the IDF4, so that the decrease in the combustion gas pressure immediately after the MFT is reduced to some extent. be able to.

[0009] However, when an MFT accompanied by the stoppage of both the FDF1 and the IDF4 occurs, it is not possible to control the combustion gas pressure in the furnace as in the case where the FDF1 and the IDF4 continue to operate. MF by fan trip
The TDF causes the FDF1 and the IDF4 to stop, but in fact, these fans continue to coast by inertia of the shaft thereafter, and the amount of air flowing into the furnace (FIG. 2 (c))
And the furnace pressure (FIG. 2 (f)). Immediately after entering the coasting state from the stop operation, FDF1 and IDF
The blade opening of No. 4 is switched from automatic operation to manual operation by the automatic / manual switch 10, and furthermore, the blade opening just before the switching operation stored in the manual operation device 11 is maintained for a certain time (3
After the pressure is held (about 0 seconds), an operation of gradually opening the rotor blades to a specified opening degree is performed in order to secure an air amount necessary for purging (removal of unburned components) ((b) of FIG. d)).

[0010] The reason why the blade opening of the fan is maintained for a certain period of time immediately after the MFT is that the unburned portion is ignited due to an increase in the amount of air flowing into the furnace when the FDF continues to operate after the MFT. The blade opening is MFT to prevent
It retains its previous state, which is also defined in the National Fire Service Standard (NFPA). From these facts, even at the time of the MFT when the FDF stops, the blade opening of the FDF is maintained at the state immediately before the MFT, assuming the same. Regarding the IDF, since the blade opening of the IDF is not directly related to the air flow rate of the furnace, there is no problem like the FDF, but the blade opening of the IDF in the normal operation state is the blade opening of the FDF. In the MFT at the time of a fan trip, the rotor blade opening of the IDF is also maintained at the state immediately before the MFT. As described above, the control of the combustion gas pressure in the furnace at the time of the MFT by the fan trip has not been conventionally performed.

FIG. 4 shows the relationship between the furnace pressure drop after MFT and the furnace design pressure. Usually MF by fan trip
Since the range of the decrease in the combustion gas pressure in the furnace at T is planned to be within the range of the design conditions related to the instantaneous fluctuation range of the furnace pressure, the furnace pressure immediately before the MFT due to the ventilator trip is set. There was no particular problem near the value (planned value) (see the solid line graph in FIG. 4). However, if the MFT due to a fan trip occurs in a state where the furnace pressure is lower than the set value for some reason, the furnace pressure may exceed the design pressure due to a subsequent decrease in the furnace pressure (see FIG. 4). In the worst case, the furnace may be damaged. The prior art does not take into account the effect of furnace pressure drop during MFT due to a fan trip when the furnace pressure is lower than a set value.

[0012]

As described above,
FDF installed on ventilation system in boiler plant
Further, when an MFT in which the IDF is stopped occurs, the fuel supply is cut off, and the gas temperature in the furnace rapidly decreases due to the rapid decrease in the gas temperature in the furnace, causing a sharp decrease in the furnace gas pressure.

If the MFT occurs when the pressure in the furnace is equal to or less than the set value, the pressure drop may exceed the design pressure of the furnace and may cause damage to the furnace (one point in FIG. 4). See the dashed line graph).

An object of the present invention is to provide an MF for stopping a ventilation fan.
It is an object of the present invention to provide a device for preventing damage to a furnace by adjusting a blade opening degree of an IDF in a coasting state immediately after the occurrence of T and suppressing a sharp decrease in furnace gas pressure.

[0015]

In order to solve the above problems, the present invention mainly employs the following configuration.

[0016] In a balanced ventilation type boiler provided with a ventilation system for feeding a combustion air into a furnace and a ventilation system for controlling a gas pressure in the furnace, the forced ventilation or induction ventilation is stopped. In response to the decrease in the furnace pressure measured by the furnace pressure measurement device at the time of the emergency stop of the boiler caused by the boiler, the moving blades or entrance / exit damper of the induction blower that is coasting due to the shaft inertia immediately after the emergency stop of the boiler is opened. A furnace gas pressure control device that controls the temperature and suppresses a decrease in furnace pressure.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for controlling gas pressure in a furnace during an emergency stop of a boiler according to an embodiment of the present invention will be described below with reference to FIGS. 1, 3, and 5. FIG. FIG. 1 is a diagram showing a general configuration of a ventilation system of a balanced ventilation boiler plant,
FIG. 3 shows the FDF and IDF after MFT in the present embodiment.
FIG. 5 is a diagram showing a change in air and gas flow rates and a furnace pressure with respect to a moving blade opening state, and FIG. 5 is a diagram showing a state of IDF moving blade opening adjustment in the present embodiment.

When an MFT due to an FDF or IDF trip occurs, both FDFs or IDFs are consequently stopped by an interlock, but these fans are still coasting due to axial inertia after the MFT, and The air flow and exhaust gas flow are maintained (FIG. 3 (c),
(E)). On the other hand, the fuel supply is cut off (FIG. 3A),
As a result, the temperature of the combustion gas in the furnace rapidly decreases, and accordingly, the pressure of the combustion gas in the furnace also starts to decrease (see FIG. 3).
(F)).

At this time, the blade opening of the FDF is switched from automatic operation to manual operation in order to avoid instability of the air flow into the furnace, and the opening is maintained in the state immediately before the MFT (FIG. b)), the blade opening of the IDF maintains the state of automatic operation even after the MFT. That is, the furnace pressure measured by the furnace pressure measuring device 6 installed in the furnace is subtracted by the furnace pressure set value 8 and the subtractor 7 to narrow the blade opening of the IDF according to the gradient of the furnace pressure decrease. Thus, the range of decrease in the furnace pressure is reduced (FIG. 3 (f)).

When the fluctuation of the furnace pressure is reduced, that is, when the pressure fluctuation is detected to be small, the IDF is detected.
The blade opening of the IDF is switched from automatic operation to manual operation, and the blade of the IDF is opened to a specified opening at which the amount of air required for purging can be secured.

[0021] As described above, the embodiment of the present invention is designed to reduce the pressure in the furnace at the time of MFT caused by the trip of the fan on the boiler ventilation system.
The blade opening of the IDF in the coasting state due to the shaft inertia immediately after was measured using the actual furnace pressure measured by the furnace pressure measuring device installed in the furnace, and the IDF of the IDF corresponding to the decrease in the furnace pressure was measured. The throttle amount of the blade opening is determined to suppress a decrease in furnace pressure.

Up to now, the opening degree of the moving blades of the induction blower has been described as an object of the gas pressure control in the furnace at the time of emergency stop of the boiler accompanied by the stoppage of the ventilation fan. The same effect can be achieved with the opening degree of the damper.

In the above description, a single boiler plant is used. However, the present invention can be applied to a plant having two systems in which both systems trip.
The specific implementation is the same as that described with reference to FIG.
Only one of the systems may be performed, and the remaining one is the same as the conventional one.

[0024]

According to the present invention, when the furnace pressure is lower than the set value for some reason and the FDF or IDF trips and the MFT with the FDF and IDF stop occurs, the design pressure of the furnace immediately after the MFT is exceeded. By suppressing a sharp drop in the combustion gas pressure in the furnace, it is possible to prevent the furnace from being damaged.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a ventilation system of a balanced ventilation boiler.

FIG. 2 shows FDF and IDF after MFT in the prior art.
It is a figure which shows the fluctuation state of air and gas flow rate, furnace pressure, etc. with respect to the moving blade opening degree state.

FIG. 3 is a diagram showing a variation state of a gas flow rate, a furnace pressure, and the like with respect to a blade opening state of an IDF after an MFT according to the present invention.

FIG. 4 is a diagram showing a relationship between a furnace pressure drop after MFT and a furnace design pressure.

FIG. 5 is a diagram showing a state of adjustment of an IDF blade opening degree in the present invention.

FIG. 6 is a diagram showing a schematic structure of a centrifugal fan and an axial fan used for an FDF or an IDF.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Push-in ventilator 2 Boiler furnace 3 Air heater 4 Induction ventilator 5 Chimney 6 Furnace pressure measuring device 7 Subtractor 8 Furnace pressure set value 9 Blade opening degree adjuster 10 Automatic / manual switching device 11 Manual operation device

Claims (1)

[Claims] An equilibrium ventilation type boiler having a ventilation system provided with a forced draft fan for feeding combustion air into a furnace and an induction draft fan for controlling gas pressure in the furnace, wherein the forced draft fan or the draft draft fan is provided. In response to the decrease in the furnace pressure measured by the furnace pressure measurement device at the time of the emergency stop of the boiler due to the stoppage of the boiler, the blade or damper of the induction blower in the coasting state due to the shaft inertia immediately after the emergency stop of the boiler is stopped. An in-furnace gas pressure control device characterized by controlling an opening degree and suppressing a decrease in a furnace pressure.