JPH11264536A - Flow rate controller of induced draft fan - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate an induced draft fan at all times without causing a surge. SOLUTION: The flow controller of an induced draft fan comprises an adder which receives the input of each signal form an air flow rate transmitter 2, a fuel flow rate transmitter 5, and a gas recirculation flow rate transmitter 15 and output an estimated flow rate signal to estimate the flow rate of exhaust gas passing through the induced draft fan, a exhaust gas flow rate function generator 18 which outputs a set flow signal to make the exhaust gas flow rate the lowest flow rate where surging does not occur, a flow rate controller 20 which outputs a flow rate adjustment signal to operate a chimney inlet damper 13 from the estimated flow rate signal and the set flow rate signal from the adder 19, and a high value selector 21 which performs the adjustment of operating, by comparing the flow rate adjustment signal with the inlet damper set signal from an inlet damper function generator 24 and transmitting a larger signal to the chimney inlet damper 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an exhaust fan, in which air supplied from a forced air ventilator and fuel supplied from a fuel pipe are burned in a furnace, is sucked by an induction ventilator and discharged to a chimney. Partial exhaust gas is recirculated to the furnace in response to fluctuations in the load of the boiler, and the induced draft is used to avoid the occurrence of surging in the induced draft fan used in the balanced ventilation boiler with gas recirculation that enhances thermal efficiency The present invention relates to a flow control device for a machine.

[0002]

2. Description of the Related Art In a ventilator such as an induced ventilator, if the relationship between the gas flow rate of the ventilator and the differential pressure of the ventilator becomes constant, surging may occur and the ventilator may be damaged. In other words, the lift curve of the ventilator rises to the right,
When the ventilator is operated in a part where the gas differential pressure that passes through the ventilator increases as the gas flow rate that passes through the ventilator increases, the ventilator is used even when the external force is not applied. Surging that causes severe periodic fluctuations in the discharge pressure and the discharge flow rate may occur, and the ventilator and peripheral devices of the ventilator may be damaged.

Therefore, when using the ventilator, it is necessary to avoid the operation where the lift curve of the ventilator rises to the right and to avoid such surging of the ventilator. In the past, attempts have been made to automatically control such that a large stress is applied to the fan and operation failure does not occur in ventilators used in other technical fields.

For example, in Japanese Patent Application Laid-Open No. 57-120122, "Blower control apparatus", a signal limiter in which a surging limit is set to a suction valve opening degree adjustment command output signal is added to a blower air volume control in a sewage treatment plant. When the blower does not operate below the surging limit, and when the air volume to be supplied becomes less than the surging limit, the differential air volume automatically opens the blow-off valve and blows air. A system is disclosed which operates at a surging limit or higher to avoid the occurrence of surging.

[0005] In Japanese Patent Publication No. 57-45447, "Waste gas treatment method for converter waste gas treatment apparatus", the throttle mechanisms of the primary dust collector and the induction blower are calculated based on the optimum flow rate set values. Controlled by the opening command, the throttle mechanism of the secondary dust collector is controlled by the opening command calculated based on the deviation between the optimum flow set value and the actual waste gas flow value, and the There is disclosed an apparatus which prevents operation and prevents the occurrence of surging of a ventilator.

However, the air supplied from the conventional forced draft fan and the fuel supplied from the fuel pipe are burned in a furnace, and the exhaust gas generated by the combustion is sucked from the furnace by an induction draft fan to a chimney. Discharge,
Surging of the induction ventilator used in so-called equilibrium ventilation boilers with gas recirculation, which recirculates part of the exhaust gas discharged into the chimney to the furnace in response to fluctuations in boiler load to increase thermal efficiency The actual situation is that the occurrence of the occurrence is conventionally performed by the operation of the induction ventilator determined by the operator.

FIG. 1 is a diagram showing a wind flue system of the above-mentioned balanced ventilation boiler with gas recirculation. As shown in the figure, the air A for combustion is sent into the furnace 8 through the air duct 4 while the flow rate is adjusted by the air flow control damper 3 from the forced draft fan 1. Further, the flow rate of the air A flowing in the air duct 4 is detected by the air flow rate transmitter 2, transmitted, and displayed on a display device provided in a control console or the like.

Further, a fuel flow control valve 6 is provided in the furnace 8.
The fuel F whose flow rate has been adjusted is sent in, and the supplied air A and fuel F are burned in the furnace 8 to generate heat energy and generate exhaust gas G. The fuel is discharged from a fuel pump (not shown),
The flow rate of the fuel F flowing through the fuel pipe 7 is also detected and transmitted by the fuel flow rate transmitter 5 and is similarly displayed on the display device.

Exhaust gas G generated in the furnace 8 is drawn out of the furnace 8 by the induction ventilator 9 and discharged to the chimney 26 through the gas duct 12. The flow rate of the exhaust gas G sucked from the furnace 8 by the induction ventilator 9 is also detected by the induction ventilator inlet pressure transmitter 10 and the induction ventilator outlet pressure transmitter 11 disposed before and after the induction ventilator 9. Is calculated from the difference between the transmission signals transmitted to the display device and displayed on the display device.

[0010] In the equilibrium ventilation type boiler 30 with gas recirculation as shown in the figure, the gas duct 12 is branched at the outlet side of the induction ventilator 9 in order to increase the thermal efficiency of the boiler 30, and as described above, the exhaust gas G some of, along with are released to the atmosphere as an exhaust gas G _1, the remaining exhaust gas G, through gas recirculation duct 16, and a structure in which again leads to the furnace 8 as recirculated exhaust gas G _2. Gas recirculation flow rate of the recirculated exhaust gas G ₂ which is recycled to the furnace 8, controls the discharge flow rate of the exhaust gas G ₁ to be discharged to the gas recirculation damper 14 and a chimney 26 provided in the gas recirculation duct 16 The opening degree of the chimney inlet damper 13 is controlled by controlling the opening degree as described later.

The gas recirculation flow rate flowing through the gas recirculation duct 16 is detected by a gas recirculation flow rate transmitter 15 installed in the gas recirculation duct 16 and transmitted to a display device for display. .

[0012] Figure 4 for controlling the gas recirculation flow rate of the recirculated exhaust gas G ₂ which is recycled to the furnace 8 as described above, the gas recirculation flow are conventionally employed control device 4
It is a figure which shows the control system of 0. As shown, the gas recirculation flow rate of recirculated exhaust gas G ₂ is, is set to a flow rate commensurate with the boiler load 22 by the recirculation flow rate function generator 23,
Accordingly, the chimney inlet damper 13 whose opening is set by the chimney inlet damper function generator 24 and the recirculation damper function generator 25 according to the flow rate similarly set by the recirculation flow function generator 23. The opening degree is controlled by operating the gas recirculation damper 14 in which the opening degree is set.

However, as shown in FIG. 4, the conventional gas recirculation flow rate control device 40 does not include a surging avoidance control device for the induction ventilator 9, and the recirculation exhaust gas G
_If the gas recirculation flow rate tends to be insufficient during the operation of returning the furnace ₂ to the furnace 8, the chimney inlet damper function generator 24 is operated so that surging of the induction ventilator 9 does not occur at the discretion of the operator. The opening degree of the chimney inlet damper 13 is changed, and the opening degree of the gas recirculation damper 14 is changed by operating the gas recirculation damper function generator 25 to increase the gas recirculation flow rate.

For this reason, the chimney inlet damper 13 may be closed too much, and if the chimney inlet damper 13 is closed too much, the outlet pressure of the induction ventilator 9 may increase. Occur. As described above, when the outlet pressure of the induction ventilator 9 rises, the induction ventilator 9 is operated in a portion where the head curve rises to the right, and the discharge pressure of the exhaust gas G discharged from the induction ventilator 9 is increased. In addition, so-called surging that causes a severe periodic fluctuation in the discharge flow rate may occur, and the impeller, shaft, or peripheral devices of the induction ventilator 9 may fail, and the boiler operation may not be able to continue.

[0015]

SUMMARY OF THE INVENTION The present invention is directed to a drawback of a conventional ventilator, particularly a drawback ventilator used for controlling a gas recirculation flow rate of an equilibrium ventilated boiler with gas recirculation. Since the ventilator is not provided with a surging avoidance control device, it is necessary to perform the opening operation of the chimney inlet damper and the gas recirculation damper at the discretion of the operator so that surging does not occur. Depending on the operation, the induction ventilator may be surging, causing the induction ventilator to fail, causing malfunctions such as inability to operate the balanced ventilation boiler with gas recirculation. The amount of exhaust gas passing through the ventilator is determined by the characteristics of the induced ventilator. Surging does not occur and operation control that ensures the minimum flow rate for safe operation is automatically performed. And to provide a flow control device of the machine.

[0016]

For this reason, the flow control device for an induced draft fan according to the present invention has the following means.

(1) Input a signal from the next transmitter,
An adder for calculating and transmitting an estimated flow rate signal for estimating the flow rate of the exhaust gas sucked by the induced draft fan is provided.

(A) Detecting a flow rate of air discharged into a furnace from a forced draft fan which supplies outside air as combustion air to a furnace for burning supplied combustion air and supplied fuel. (B) a fuel flow transmitter for detecting and transmitting a flow rate of fuel flowing through a fuel pipe discharged into a furnace for combustion with combustion air, and (c) a furnace flow The air and fuel discharged into the furnace burn, and a part of the exhaust gas that is sucked from the furnace by the induction ventilator and discharged to the chimney is recirculated into the furnace according to the load fluctuation of the boiler to improve the thermal efficiency. A gas recirculation flow transmitter that detects and transmits the flow rate of exhaust gas that is branched from the gas duct and recirculated into the furnace to increase the flow rate. (2) The flow rate of exhaust gas sucked from the furnace by the induced draft fan is determined by the induced draft fan. Minimum to avoid surging An exhaust gas flow rate function generator for outputting a set flow rate signal for setting the exhaust gas flow rate was provided.

(3) To set the exhaust gas flow rate of the induction ventilator to a flow rate that avoids the occurrence of surging from the estimated flow rate signal of the exhaust gas flow rate from the adder and the set flow rate signal of the exhaust gas flow rate from the exhaust gas flow rate function generator. In addition, there is provided a flow controller for operating the chimney inlet damper and outputting a flow control signal for controlling the flow rate of the exhaust gas sucked by the induction ventilator.

(4) a flow control signal from the flow controller;
The chimney inlet damper opening is set based on the load of the balanced ventilation boiler with gas recirculation, and the chimney inlet damper setting signal from the output chimney inlet damper function generator is compared to determine the chimney inlet damper opening. Override control that sets the larger of the flow control signal and the stack inlet damper setting signal so that the flow rate of exhaust gas sucked by the induction ventilator secures the minimum flow rate for safe operation determined by the characteristics of the induction ventilator. A high value selector for performing the above is provided.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a first embodiment of a flow control device for an induced ventilator according to the present invention, which has a surging avoidance control applied to the induced ventilator of the balanced ventilated boiler with gas recirculation shown in FIG. FIG. 3 is a schematic diagram of a gas recirculation flow control device, and FIG. 3 is a schematic diagram of a ventilator characteristic curve of the induced draft fan shown in FIG. 2, the same or similar members as those shown in FIGS. 1 and 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 2, the gas recirculation flow control device 50 of the induced draft fan according to the present embodiment employs a gas recirculation flow control device 50 for preventing the suction draft fan 9 from surging. The sum of the signals from the air flow transmitter 2, the fuel flow transmitter 5, and the gas recirculation flow transmitter 15 is added by an adder 19, and the flow rate of the exhaust gas passing through the induction ventilator 9 is estimated. From the difference between the signals transmitted from the induction ventilator inlet pressure transmitter 10 and the induction ventilator outlet pressure transmitter 11 installed before and after, respectively, and the calculated differential pressure before and after the induction ventilator 9, A flow controller 20 for securing the flow rate of the exhaust gas G set to prevent the occurrence of surging based on the surging occurrence relationship between the exhaust gas flow rate and the differential pressure across the induction ventilator 9. It is.

On the ventilator characteristic curve shown in FIG. 3, a dotted line 27 is a surging curve showing the relationship between the flow rate of exhaust gas in which surging occurs and the differential pressure across the induction ventilator 9.
In addition, a surging curve 27
Instead, a control line 28 having a sufficient flow rate is set in advance, and when the flow rate of the exhaust gas passing through the induction ventilator 9 approaches the surging curve 27 and surging is likely to occur, the control line 28 is used. The flow rate of the exhaust gas passing through the induction ventilator 9 is adjusted so that the flow rate of the exhaust gas reaches the specified level, thereby avoiding the occurrence of surging.

For this reason, as shown in FIG.
The differential pressure before and after the induction ventilator 9 is measured by the differential pressure gauge 17 by the induction ventilator inlet pressure transmitter 10 and the induction ventilator outlet pressure transmitter 11 provided before and after the induction ventilator. A set flow rate signal for setting the gas flow rate is generated by the exhaust gas flow rate function generator 18.

On the other hand, in the gas recirculation flow control device 50,
A set flow rate signal from the exhaust gas flow rate function generator 18;
An air flow transmitter 2 for detecting and transmitting the flow rate of air A discharged into the furnace 8 from a forced draft fan 1 for supplying outside air into the furnace 8 as combustion air A, and combusting the air A for combustion. Therefore, a fuel flow transmitter 5 for detecting and transmitting the flow rate of the fuel F flowing through the fuel pipe 7 discharged into the furnace 8, and the air A and the fuel F are burned, and the draft fan is introduced from the furnace 8. In order to recirculate a part of the exhaust gas G sucked in 9 and discharged to the chimney 26 into the furnace 8 according to the load fluctuation of the boiler, the exhaust gas G branched from the gas duct 12 and recirculated into the furnace 8 is A signal input from the gas recirculation transmitter 15 for detecting and transmitting the flow rate is added, and the estimated flow rate signal from the adder for estimating and transmitting the exhaust gas flow rate sucked by the induction ventilator 9 is compared. , The chimney inlet damper 13 by the flow controller 20 Generating an operation to flow rate control signal.

As described above, the operation signal of the chimney inlet damper 13 has been conventionally generated by the gas recirculation flow rate function generator 23 and the chimney inlet damper function generator 24 as described above. In the above, the set flow rate signal from the exhaust gas flow rate function generator 18 is compared with the estimated flow rate signal from the adder 19 for estimating the exhaust gas flow rate, and the flow rate control signal is generated by the flow rate controller 20.

Now, if the induction ventilator 9 tries to increase the gas recirculation flow rate due to a boiler load fluctuation, etc., in the boiler plant which was operating normally at the point x on the normal operation curve 29 in FIG. Circulating damper function generator 25
Gas recirculation damper 1 with gas recirculation damper setting signal from
4 moves in the opening direction, and the chimney inlet damper 13 moves in the closing direction by the chimney inlet damper setting signal from the chimney inlet damper function generator 24. For this reason, the differential pressure across the induction ventilator 9 increases, and the operating point x on the normal operation curve 29 of the induction ventilator 9 moves in the direction of the point y on the control line 28.

Further, when the differential pressure across the induction ventilator 9 becomes large, and the operating point x of the induction ventilator 9 exceeds the point E and approaches the z point on the surging curve 27, the chimney suitable for the boiler load is used. Since the chimney inlet damper setting signal from the chimney inlet damper function generator 24 that moves the inlet damper 13 in the closing direction is smaller than the flow control signal from the flow controller 20, the operation of the chimney inlet damper 13 is The control based on the chimney inlet damper setting signal from the function generator 24 is switched to the control based on the flow control signal from the flow controller 20, and the chimney inlet damper 13 does not move further in the closing direction. Is stopped at the y point, and the occurrence of surging of the induced draft fan 9 can be prevented.

As described above, when the differential pressure across the induction ventilator 9 rises and the operating point on the ventilation characteristic curve of the induction ventilator 9 approaches the surging curve 27, the stack inlet damper function generator 24 The flow rate control signal from the flow rate controller 20 is larger than the inlet damper setting signal from the controller, and the chimney inlet damper 13 is operated by the flow rate control signal from the flow rate controller 20 by the override control by the high value selector 21. Thus, the surging avoidance control becomes effective, and the flow rate of exhaust gas passing through the induction ventilator 9 is ensured, so that the occurrence of surging in the induction ventilator 9 can be prevented.

As described above, since the flow rate control device for the induced draft fan according to the present embodiment is configured as described above, the opening degree of the chimney inlet damper 13 is controlled by the flow rate of the induced draft fan 9 which can prevent the occurrence of surging. Can be avoided automatically due to the operation of always closing the chimney inlet damper 13 too close to the opening that can ensure the surging.
Breakage of the impeller, shaft, etc. of the induction ventilator 9 due to occurrence of surging or failure of peripheral devices can be prevented, and reliability and safety in boiler operation can be ensured.

[0031]

As described above, the flow rate control device for an induced draft fan according to the present invention pushes outside air as combustion air into a furnace that burns combustion air and supplied fuel. An air flow transmitter that detects and transmits the flow rate of air discharged into the furnace from the ventilator, detects and transmits the flow rate of fuel flowing through the fuel pipe discharged into the furnace for combustion with combustion air The fuel flow transmitter, and the air and fuel discharged into the furnace are burned, and a part of the exhaust gas that is sucked from the furnace by the induction ventilator and discharged to the chimney,
In order to recirculate in the furnace according to the boiler load fluctuation,
A signal from a gas recirculation flow transmitter that detects and transmits the flow rate of exhaust gas that is branched from the gas duct and recirculated into the furnace is input, and an estimated flow rate signal that estimates the exhaust gas flow rate sucked by the induced draft fan is input. Estimating from the adder to be transmitted, the exhaust gas flow function generator that outputs the set flow rate signal that sets the exhaust gas flow rate sucked from the furnace by the induction ventilator to the exhaust gas flow rate to avoid the occurrence of surging of the induction ventilator, and the adder From the flow rate signal and the set flow rate signal from the exhaust gas flow function generator, operate the chimney inlet damper to adjust the flow rate of exhaust gas sucked by the induced draft fan in order to set the exhaust gas flow rate to avoid the occurrence of surging of the induced draft fan. The flow control signal from the flow control device, the flow control signal from the flow control device, and the load of the balanced ventilation boiler with gas recirculation to set the opening of the chimney inlet damper,
The chimney inlet damper setting signal from the chimney inlet damper function generator to be output is compared with the chimney inlet damper setting signal, and the opening of the chimney inlet damper is set to the larger of the flow rate control signal and the chimney inlet damper setting signal, and suction is performed from the induction draft fan. A high value selector for performing an override control capable of securing a minimum flow rate for safe operation in which an exhaust gas flow rate is determined by characteristics of the induced draft fan is provided.

This makes it possible to prevent the occurrence of surging in which the flow rate and the discharge pressure of the exhaust gas discharged from the induced draft fan fluctuate sharply and periodically even when no external forced force is applied. , The opening degree of the chimney inlet damper is maintained, and the occurrence of surging due to the erroneous operation of closing the conventional chimney inlet damper too much can be reliably avoided. Of the impeller, the shaft, etc. or the failure of peripheral equipment can be prevented, and the reliability and safety in the operation of the boiler can be secured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a ventilation flue system of a balanced ventilation boiler with gas recirculation,

FIG. 2 shows a first embodiment of a flow control device for an induced draft fan according to the present invention, with a surging avoidance control applied to the induced draft fan of the balanced draft boiler with gas recirculation shown in FIG. System diagram of the gas recirculation flow control device,

FIG. 3 is a schematic diagram showing a ventilator characteristic curve of the induced draft fan shown in FIG. 1;

FIG. 4 is a system diagram showing a conventional gas recirculation flow control device for an induction ventilator of a balanced ventilation boiler.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 push-in ventilator 2 air flow transmitter 3 air flow control damper 4 air duct 5 fuel flow transmitter 6 fuel flow control valve 7 fuel pipe 8 furnace 9 induced draft fan 10 induced draft inlet pressure transmitter 11 draft outlet pressure Transmitter 12 Gas duct 13 Chimney inlet damper 14 Gas recirculation damper 15 Gas recirculation flow transmitter 16 Gas recirculation duct 17 Differential pressure gauge 18 Exhaust gas flow function generator 19 Adder 20 Flow controller 21 High value selector 22 Boiler load 23 Gas Recirculation flow function generator 24 Chimney inlet damper function generator 25 Gas recirculation damper function generator 26 Chimney 27 Surging curve 28 Control line 29 Normal operation curve 30 Balanced ventilation boiler 40 Gas recirculation flow control device 50 Gas recirculation flow controller a air F fuel for combustion G gas G ₁ exhaust gas G ₂ recirculation exhaust Scan

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masayuki Okamura 4-6-22 Kannonshinmachi, Nishi-ku, Hiroshima-shi Hiroshima Works, Mitsubishi Heavy Industries, Ltd.

Claims (1)

[Claims] 1. A furnace for burning air supplied from a forced draft fan and fuel supplied from a fuel pipe,
An equilibrium ventilation type boiler with gas recirculation, in which a part of exhaust gas sucked from the furnace and discharged to the chimney by the induction ventilator is recirculated to the furnace according to the load fluctuation of the boiler so as to increase thermal efficiency. In the flow control device of the induction ventilator used for controlling the gas recirculation flow rate, an air flow transmitter that detects and transmits the flow rate of the push-in ventilator, and the fuel flow rate that detects and transmits the flow rate in the fuel pipe A transmitter, and a signal from a gas recirculation flow transmitter that detects and transmits a flow rate of gas to be recirculated to the furnace is added, and an estimated flow rate signal is calculated by calculating a flow rate of exhaust gas sucked by the induced draft fan. An exhaust gas flow function generator that outputs a set flow rate signal that sets a minimum flow rate of the exhaust gas flow sucked by the induction ventilator; and a signal from the adder and the exhaust gas flow function generator. A flow controller for outputting a flow control signal for adjusting the flow rate of the exhaust gas, and a chimney inlet damper from a chimney inlet damper function generator for setting the opening of the chimney inlet damper in accordance with the flow control signal and the load variation of the boiler. A high value selector for selecting the larger one of the setting signals and setting the opening of the chimney inlet damper, and ensuring the minimum flow rate for safe operation in which the exhaust gas flow rate is determined by the characteristics of the induced draft fan. As described above, the flow control device for the induced draft fan is characterized in that the override control is performed to avoid the occurrence of surging of the induced draft fan.