JP6508515B2 - boiler - Google Patents

Description

  The present invention relates to a gas-fired boiler.

  Conventionally, as disclosed in FIG. 1 of Patent Document 1 below, in the duct (6) from the fan (5) to the burner (2), the combustion air from the fan (5) is supplied from the gas supply passage (10) There is known a boiler (1) which ejects and mixes the following gases and burns the premixed gas in a burner (2).

  In connection with a boiler of this type, the applicant has proposed a boiler capable of supplying the necessary amount of gas to the burner even if the gas supply pressure is relatively low, and has filed a patent application (Japanese Patent Application No. 2014-66252). In this prior invention, instead of mixing the gas into the air downstream of the blower, the gas is mixed into the air on the suction side to the blower. Specifically, a gas suction mechanism using a venturi pipe is provided at the suction port to the blower, and the gas is suctioned along with the suction of air into the blower and sent to the blower together with the air and mixed.

  In any case, in the gas-fired boiler, when the gas injection hole of the burner is clogged or the flue through which the exhaust gas passes is clogged, it is necessary to promptly detect this. In the case where multiple boilers are installed and exhaust gas from each boiler is discharged through a common flue (collective flue) and the number of operating boilers is changed according to the load (control of the number of boilers), There is also such a problem. That is, the boiler in standby mode (that is, combustion stopped) operates the blower and purges it in the furnace so that the exhaust gas does not flow back from the collective flue, but if any backflow occurs, this is detected promptly There is a need to.

  In relation to this point, as disclosed in Patent Document 2 below, based on the differential pressure before and after the damper (15) provided between the fan (10) and the burner (8), It is known to detect the backflow of the exhaust gas from the collective flues of However, as in the prior invention, when a gas is mixed into the air on the suction side to the blower and the mixture of air and gas is discharged from the blower, installing the damper in the duct from the blower to the burner The flammable mixture may leak to the outside from the shaft seal portion of the rotary shaft, and it takes time and money to cope with the problem. In addition, when the blower is stopped, it is desirable that the gas supply be reliably stopped.

Unexamined-Japanese-Patent No. 2006-266534 Patent No. 4059100

  The problem to be solved by the present invention is that the clogging of the burner or the flue and the backflow of the exhaust gas from the flue can be detected easily and reliably, and the gas leakage to the outside is surely prevented to provide high safety. It is to provide a boiler.

The present invention has been made to solve the above-mentioned problems, and the invention according to claim 1 is a main burner as a premix burner for heating a water pipe in a can, and a pilot for igniting the main burner. A burner, a blower for supplying combustion air to the main burner, and a venturi pipe provided at a suction inlet of air to the blower, and a gas supply passage is connected to a throat portion of the venturi pipe, A gas suction mechanism for drawing a gas from the gas supply passage and feeding the air together with the air to the suction opening as the air is drawn into the suction opening via the venturi tube, and a valve provided in the gas supply passage, the gas pressure at the outlet side of the valve, and a gas pressure control valve for opening adjustment to maintain the inlet side pressure force of the venturi tube, the inlet-side pressure and the throat portion pressure of the venturi And a differential pressure monitoring means for monitoring the differential pressure, the air inlet to the venturi, and an air filter is provided, the gas pressure adjusting valve, the gas pressure at the outlet side of the valve, the It is a boiler characterized by adjusting an opening so that it may maintain on the inlet side pressure of the venturi pipe in the lower stream side rather than an air filter .

According to the first aspect of the present invention, the gas suction mechanism using the venturi tube can suck and mix the gas as the air is sucked into the fan. Further, the gas pressure adjusting valve, the gas pressure at the outlet side, since the opening adjustment to maintain the inlet side pressure force of the Venturi tube, as long as the throat portion air is flowing in the forward direction to the venturi tube does not become negative pressure gas Can be prevented from flowing and gas leakage can be reliably prevented when the blower is stopped. Moreover, by maintaining the pressure on the outlet side of the gas pressure regulating valve at a predetermined level, the gas is stably mixed in the air at a desired flow rate according to the negative pressure generated in the venturi (in other words, the ventilation amount of the venturi). can do. Furthermore, by monitoring the differential pressure between the pressure on the inlet side of the venturi and the pressure at the throat by differential pressure monitoring means, clogging of the burner or the flue and backflow of the exhaust gas from the flue can be detected easily and reliably. can do.
Further, according to the invention of claim 1, when the air filter is clogged and the pressure on the inlet side of the venturi tube is lowered, the gas pressure on the outlet side of the gas pressure regulating valve is also lowered accordingly. Can be maintained at a predetermined air ratio.

  According to the invention as set forth in claim 2, a damper is not provided downstream of the blower in the duct to the main burner, and whether the air flow rate to the main burner is inverter-controlled the number of rotations of the blower And / or a damper is provided on the inlet side of the venturi tube, and the damper is used to change the damper.

  According to the second aspect of the present invention, since the damper is not installed downstream of the blower, there is no possibility that the air-fuel mixture leaks to the outside from the shaft seal portion of the rotary shaft of the damper. On the other hand, it is possible to inverter-control the rotational speed of the blower and / or provide a damper on the inlet side of the venturi tube and adjust the amount of air to the main burner by the damper. Moreover, the gas supply flow rate can also be changed by changing the ventilation amount of the venturi tube.

In the invention according to claim 3, when the differential pressure monitoring means detects that the differential pressure has become equal to or less than a set value, the combustion of each of the burners is stopped or instead of or in addition to this The boiler according to claim 1 or 2 , wherein a notification that the differential pressure has become equal to or less than a set value is output to a predetermined device.

According to the invention as set forth in claim 3, when the differential pressure between the inlet side pressure of the venturi and the throat pressure becomes lower than the set value, the fact is notified or the combustion of each burner is stopped, and the safety is achieved. It is possible to secure the sex.

Further, the invention according to claim 4, the gas supply passage to the venturi tube, the downstream of the gas pressure regulating valve, wherein the opening adjustable gas flow control valve is provided according It is a boiler of any one of claim 1 to 3 .

According to the fourth aspect of the present invention, the air ratio can be adjusted according to the amount of combustion by adjusting the degree of opening of the gas flow adjusting valve.

  According to the present invention, the clogging of the burner and the flue and the backflow of the exhaust gas from the flue can be detected easily and surely, and the gas leakage to the outside is surely prevented to realize a high safety boiler. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the boiler of one Example of this invention, and shows one part in a cross section.

  Hereinafter, specific embodiments of the present invention will be described in detail based on the drawings.

  FIG. 1 is a schematic view showing a boiler 1 according to an embodiment of the present invention, partially shown in cross section.

  The boiler 1 of this embodiment includes a can 2 having a large number of water tubes, a main burner 3 for heating the water tubes in the can 2, a pilot burner 4 for igniting the main burner 3, and a combustion for the main burner 3. , A gas suction mechanism 6 provided in the suction port 5a to the air blower 5 for mixing fuel gas into suction air, and gas pressure adjustment provided in the gas supply path 7 to the gas suction mechanism 6 A valve 8 and a differential pressure monitoring means 9 for monitoring a differential pressure at a predetermined location are provided as main parts.

  The can 2 is configured by connecting a plurality of water pipes between the upper and lower headers, and is covered with a can cover. Although the shape of the can 2 is not particularly limited, it is rectangular in the present embodiment. The can 2 is appropriately supplied with water from the lower header, and the water level in the can 2 is maintained as desired. The can body 2 is provided with the main burner 3 at one end, and the exhaust gas passage 10 is connected to the other end. The exhaust gas passage 10 is a flue and / or a chimney, and an economizer is optionally provided. The combustion gas (initially including the flame) from the main burner 3 exchanges heat with the water in each water pipe and then is discharged from the exhaust gas passage 10 as an exhaust gas. The water in each water pipe is heated by the combustion gas from the main burner 3 and is drawn out from the upper header through the steam separator 11 as steam.

  The main burner 3 is a premix burner which is supplied with a premixed mixture of combustion air and gas for combustion. In this embodiment, it is a completely premixed burner having a planar combustion surface (premixed gas ejection surface) having a large number of premixed gas injection holes. The main burner 3 may be switched on / off of the presence or absence of combustion, or the amount of combustion may be adjusted stepwise or continuously. For example, the main burner 3 can switch the amount of combustion at three positions of high combustion (100% combustion), low combustion (for example, 50% combustion) and stop. Alternatively, the main burner 3 can switch the amount of combustion at four positions of high combustion, medium combustion, low combustion and stop. Alternatively, the amount of combustion of the main burner 3 is continuously adjusted in proportion to the working load of steam. In any case, the main burner 3 is supplied with combustion air and gas according to the amount of combustion.

  The pilot burner 4 is provided close to the main burner 3. The pilot burner 4 is a pre-mixing burner in the present embodiment, but may optionally be a pre-mixing burner. In order to burn the gas in the pilot burner 4, the combustion burner 4 is supplied with combustion air and gas at a predetermined flow rate. The presence or absence of the supply of combustion air and gas to the pilot burner 4 can be switched separately from the presence or absence of supply of combustion air and gas to the main burner 3. The pilot burner 4 is ignited by an igniter (not shown), and the main burner 3 is ignited by the pilot burner 4.

  The blower 5 sucks in gas from the suction port 5a and discharges the gas to the discharge port 5b. The blower 5 is typically of a centrifugal type, rotates the impeller within the spiral casing, sucks in gas from the suction port 5a provided at the central portion of the casing, and discharges it from the discharge port 5b provided at the outer peripheral portion of the casing. Do. The suction port 5a of the blower 5 is provided with a gas suction mechanism 6 which sucks in gas as the air is drawn into the suction port 5a and sends the gas together with the air to the suction port 5a.

  The outlet 5 b of the blower 5 is connected to the main burner 3 via the duct 12. At this time, it is preferable not to install a damper in the duct 12. Since a flammable mixture of combustion air and gas is discharged from the blower 5 by the gas suction mechanism 6, if a damper is provided downstream of the blower 5, the shaft seal portion of the rotation shaft of the damper is flammable Measures are required to prevent the mixture from leaking out. However, by not installing the damper downstream of the blower 5 as in the boiler 1 of the present embodiment, there is no risk of gas leakage to the outside.

  The gas suction mechanism 6 includes a venturi 13 in this embodiment. The venturi tube 13 is provided with a taper part before and behind the throat part 13a as well known. Specifically, a gradually decreasing pipe 13b is provided on the upstream side of the throat portion 13a of the smallest diameter portion, and the diameter is gradually reduced as it goes downstream, while the diameter is increased as it goes downstream on the downstream side of the throat 13a. A gradually expanding tube 13c is provided. Then, the outlet side opening of the expansion pipe 13 c is directly connected to the suction port 5 a of the blower 5 (or connected via an appropriate pipe). Preferably, an air filter 14 is provided on the upstream side of the intake port to the venturi tube 13, in other words, the inlet of the gradually reducing tube 13b. In the illustrated example, an air filter 14 is provided in a straight tubular portion connected to the inlet side of the gradually reducing tube 13b.

  A gas supply passage 7 from a gas supply source (not shown) is connected to the throat portion 13 a of the venturi tube 13. A shutoff valve 15 and a gas pressure control valve 8 are provided in the gas supply passage 7 in the downstream direction. When the gas is supplied to the main burner 3, the valves 15 and 8 are opened, and when the gas supply to the main burner 3 is stopped, the valves 15 and 8 are closed. Therefore, the gas pressure control valve 8 functions in the same manner as the shutoff valve 15 in switching the presence or absence of the gas supply to the main burner 3.

  Furthermore, the gas pressure control valve 8 also has a function of maintaining the gas pressure on the outlet side (the downstream side of the gas pressure control valve 8) at a predetermined pressure when it is open. Specifically, in the present embodiment, the gas pressure adjusting valve 8 has the gas pressure at the outlet side, the inlet pressure of the venturi tube 13 (the venturi tube 13 at the downstream side of the air filter 14 when the air filter 14 is provided). The valve adjusts the opening to maintain the pressure on the inlet side of Here, the gas pressure adjusting valve 8 is a pressure equalizing valve that mechanically adjusts the opening degree by receiving the pressure on the inlet side of the venturi tube 13 (the pressure on the inlet side of the gradually reducing tube 13b) through the communicating tube 16 The pressure on the inlet side of the venturi 13 may be monitored by a sensor, and the valve may be a motorized valve that adjusts the opening based on the detection signal.

  Preferably, a gas flow control valve 17 is provided downstream of the gas pressure control valve 8 in the gas supply passage 7. The gas flow rate adjustment valve 17 is a motor-operated valve whose opening degree can be adjusted.

  The differential pressure monitoring means 9 comprises a pressure switch 18 in the present embodiment. The pressure switch 18 monitors whether or not the differential pressure (P1-P2) between the inlet pressure (P1) of the venturi tube 13 and the throat pressure (P2) is equal to or less than a set value.

  The boiler 1 is controlled by a controller (not shown). In the present embodiment, the controller performs combustion control and the like of the main burner 3 on the basis of the vapor pressure (the vapor pressure in the can 2 or at a position where the vapor is supplied therefrom).

  The controller is connected to a pressure sensor (or pressure switch) for detecting the vapor pressure, the motor of the blower 5, the shutoff valve 15, the gas pressure regulating valve 8, the gas flow regulating valve 17, the pressure switch 18 and the like. In addition, the controller is also connected to a touch panel, an operation button, a lamp, a buzzer, and the like as needed. Then, various controls as described below are executed.

  In order to burn the gas in the main burner 3, the blower 5 may be operated, the shutoff valve 15 (and the gas pressure control valve 8) may be opened, and ignition may be performed by the pilot burner 4. That is, first, after supplying predetermined combustion air and gas to the pilot burner 4 to ignite the pilot burner 4, the shutoff valve 15 is opened to ignite the main burner 3 and the combustion of the pilot burner 4 is stopped. Good. On the other hand, in order to stop the combustion in the main burner 3, the shutoff valve 15 may be closed to stop the supply of gas and the supply of combustion air from the blower 5 may be stopped. After the combustion of the main burner 3 is stopped, the fan 5 may be stopped. Alternatively or additionally, a damper is provided on the inlet side of the venturi tube 13 and the damper is closed or a damper is provided in the exhaust gas passage 10 The damper may be closed.

  When the blower 5 is operated to burn the gas in the main burner 3, the outside air through the air filter 14 is drawn into the suction port 5 a of the blower 5 through the venturi tube 13. When air is passed through the venturi 13, a negative pressure is generated in the venturi 13. Therefore, if the shutoff valve 15 is opened, gas is drawn from the gas supply passage 7 to the venturi 13. In this way, along with the suction of air into the suction port 5a of the blower 5, the gas can be sucked in the venturi tube 13 and sent to the suction port 5a together with air. Then, air and gas are mixed in the blower 5, and the mixture is supplied to the main burner 3 via the duct 12 and burned in the main burner 3.

  Since the suction of the air into the blower 5 is used to suck the gas in the venturi pipe 13, even if the gas supply pressure (the gas pressure upstream of the shutoff valve 15) is relatively low, the desired amount of gas can be Supply to the desired combustion. In addition, since the gas is mixed into the air and then supplied to the fan 5, the air and the gas can be reliably mixed in the fan 5.

  In addition, as described above, the gas pressure adjusting valve 8 maintains the gas pressure on the outlet side at a predetermined level, so that the desired flow rate according to the negative pressure generated in the venturi 13 (in other words, the ventilation amount of the venturi 13). Gas can be stably mixed into the air. Moreover, since the pressure on the outlet side of the gas pressure adjusting valve 8 is the pressure on the inlet side of the venturi tube 13, air flows in the forward direction in the venturi tube 13 and the gas does not flow unless the throat portion 13a has a negative pressure. Leakage of gas at the time of stop of 5 can be reliably prevented. Furthermore, when the air filter 14 is clogged and the pressure on the inlet side of the venturi tube 13 decreases, the gas pressure on the outlet side of the gas pressure adjusting valve 8 also decreases accordingly, so the air ratio of the boiler 1 is maintained at a predetermined level. be able to.

  Adjustment of the amount of combustion of the main burner 3 is performed by adjusting the flow rates of the combustion air and gas supplied to the main burner 3. Adjustment of the flow rate of combustion air is performed by changing the rotational speed of the motor of the blower 5 using an inverter, but instead or in addition to this, a damper is provided on the inlet side of the venturi tube 13 The position of the damper may be adjusted. Then, as described above, if the amount of air flow to the venturi tube 13 is changed, the flow rate of the gas is also changed, but in order to obtain an air ratio corresponding to the amount of combustion, the gas flow rate adjusting valve in the gas supply passage 7 to the venturi tube 13 17 should be provided. By changing the opening degree of the gas flow rate adjustment valve 17 according to the amount of combustion, it is possible to adjust to an air ratio according to the amount of combustion.

  By the way, there is a possibility that the main burner 3 may be clogged (more specifically, the mixture gas injection holes clogged) or the exhaust gas passage 10 may be clogged with the operation of the boiler 1, which is promptly detected. There is a need to. In the case where multiple boilers are installed, exhaust gas from each boiler 1 is discharged through a common flue (collective flue), and the number of operating boilers 1 is changed according to the load (number control) It is necessary to prevent the backflow of the exhaust gas from the collective flue to the boiler 1 during standby (that is, during combustion stop). Therefore, the boiler 1 on standby operates the blower 5 to purge the inside of the furnace with a flow rate that can prevent the backflow of exhaust gas, but should detect the backflow of exhaust gas promptly if it occurs. There is a need.

  Therefore, in the present embodiment, the controller monitors the differential pressure between the inlet side pressure of the venturi tube 13 and the throat pressure with the pressure switch 18. That is, the controller also functions as a differential pressure monitoring means together with the pressure switch 18. Then, when it is detected that the differential pressure has become equal to or less than the set value, there is clogging of the main burner 3 or the exhaust gas passage 10, or backflow of the exhaust gas from the exhaust gas passage 10 during standby in multi-can installation. It can be determined that

  When the controller detects that the differential pressure has become equal to or less than the set value, typically, when the main burner 3 is in combustion, the combustion is stopped, and when the pilot burner 4 is in combustion, Stop its combustion. For example, when it is detected that the differential pressure becomes lower than the set value while only the pilot burner 4 is burning, after the fuel supply valve to the pilot burner 4 is closed (or at the same time it is closed), combustion to the pilot burner 4 is performed. It also shuts off the air supply.

  Further, instead of or in addition to the stopping of the respective burners 3 and 4, the fact that the differential pressure has become equal to or less than the set value may be output to a predetermined device to notify the user. For example, it may be displayed on the touch panel, the lamp may be lit or blinked, or a buzzer may be sounded.

  Alternatively, when it is detected that the differential pressure has become equal to or less than the set value, the air flow may be increased. That is, when the number of rotations of the blower 5 is increased or the damper is provided on the inlet side of the venturi tube 13, the opening degree of the damper may be increased. Then, if the differential pressure exceeds the set value, the operation of the boiler 1 is continued, but otherwise, the combustion of each of the burners 3 and 4 is stopped or output to a predetermined device It may be notified to the user.

  By the way, in the present embodiment, the pressure switch 18 is used to monitor the differential pressure between the pressure on the inlet side of the venturi tube 13 and the pressure on the throat portion, but in some cases a pressure sensor may be used. That is, while the pressure on the inlet side of the venturi 13 is monitored by the first pressure sensor, the pressure at the throat of the venturi 13 is monitored by the second pressure sensor, and the controller detects the pressure difference based on the pressure detected by these pressure sensors. To perform the same processing as described above.

  When using a pressure sensor, the air flow rate to the main burner 3 can also be monitored based on the differential pressure. By monitoring the air blowing amount to the main burner 3, it can be monitored whether it is the supply amount of combustion air according to the combustion amount. For example, the controller can monitor whether combustion air according to high combustion is being supplied to the main burner 3 when the main burner 3 is in a condition where high combustion is to be performed. Moreover, when using a pressure sensor, the backflow of exhaust gas can also be easily detected based on the fact that the differential pressure becomes negative.

  In addition, as above-mentioned, the boiler 1 of a present Example may be installed in multiple cans. That is, a boiler system may be configured using a plurality of boilers 1. In this case, the boiler system includes a plurality of boilers 1 and a controller that controls the number of operating boilers 1 and the amount of each combustion. The steam from each boiler 1 is supplied to a steam header, and the steam in the steam header is sent to one or more of various steam using facilities. The working load of steam is monitored based on the pressure of the steam header, and the controller controls the number of operating boilers 1 and the amount of combustion so as to maintain the pressure of the steam header at the set pressure.

  When multiple boilers are installed, gas from a common gas supply source is supplied to the main burner 3 of each boiler 1 through the gas suction mechanism 6 provided in each boiler 1. In each boiler 1, since the gas suction mechanism 6 is used to suck gas, the gas supply pressure may be relatively low, and therefore, the number of installed cans of the boiler 1 can be increased. Further, as described above, the controller can also detect the backflow from the collective flue during the combustion stop based on the detection signal of the pressure switch 18.

  The boiler 1 of the present invention is not limited to the configuration (including control) of the above-described embodiment, and can be changed as appropriate. In particular, in a gas-fired boiler equipped with a premix burner (main burner), gas is sucked from the gas supply passage 7 along with suction of air into the suction port 5a of the fan 5 through the venturi pipe 13 and the suction port together with air. A gas suction mechanism 6 for feeding to 5a, a gas pressure adjusting valve 8 provided in the gas supply passage 7 to adjust the opening degree so as to maintain the gas pressure on the outlet side at a predetermined level, the pressure on the inlet side of the venturi tube 13 and the throat pressure If other differential pressure monitoring means 9 is provided to monitor the differential pressure between them, the other configuration can be changed appropriately.

  For example, in the above embodiment, the gas pressure adjusting valve 8 is a valve for adjusting the opening so as to maintain the gas pressure on the outlet side at the pressure on the inlet side of the venturi tube 13; It may be used as a valve. Specifically, the gas pressure control valve 8 may be a zero governor that mechanically adjusts the opening degree so as to maintain the gas pressure on the outlet side at atmospheric pressure. In this case, the installation of the communication pipe 16 can be omitted. Further, as in the above embodiment, since the air does not flow unless the air flows in the forward direction in the venturi 13 and the throat portion 13a becomes a negative pressure, the gas leakage when the blower 5 is stopped is surely prevented. it can. Moreover, by maintaining the pressure on the outlet side of the gas pressure adjusting valve 8 at a predetermined level, the gas can be stably supplied at a desired flow rate according to the negative pressure generated in the venturi pipe 13 (in other words, the ventilation amount of the venturi pipe 13). It can be mixed into the air.

  In the above embodiment, the boiler 1 in the standby mode continues the purge (blowing) in the case where multiple boilers are installed, but the pilot burner 4 may be continuously burned instead of the purge. . As a result, it is possible to maintain a certain furnace pressure and a draft (draft force) to the collective flue, and to prevent the backflow of the exhaust gas from the collective flue to the can. During this time (that is, during standby due to continuous combustion of the pilot burner 4), it is preferable to monitor the differential pressure of the venturi 13 and monitor the presence or absence of any reverse flow from the collective flue, as in the above embodiment. When the boiler 1 restarts and the combustion in the main burner 3 resumes, the combustion in the pilot burner 4 may be stopped. If the pilot burner 4 is continuously burned when the boiler 1 is on standby, pre-purge at the time of restarting the boiler 1 can be omitted, so that the heat radiation loss from the inside of the can 2 due to the pre-purge can be reduced.

  Furthermore, the can 2 of the boiler 1 is not limited to a square, but may be cylindrical, in which case the main burner 3 may be installed downward on the top of the can 2. And according to it, the composition of main burner 3 is changed suitably. Further, although the boiler 1 is a steam boiler in the above embodiment, it may be a hot water boiler or the like in some cases.

1 boiler 2 can 3 main burner 4 pilot burner 5 blower (5a: suction port, 5b: discharge port)
6 gas suction mechanism 7 gas supply passage 8 gas pressure adjusting valve 9 differential pressure monitoring means 10 exhaust gas passage 11 air-water separator 12 duct 13 venturi (13a: throat portion, 13b: gradually shrinking tube, 13c: gradually expanding tube)
14 air filter 15 shutoff valve 16 communicating pipe 17 gas flow control valve 18 pressure switch

Claims (4)

A main burner as a pre-mixing burner for heating a water pipe in the can,
A pilot burner for igniting this main burner,
A blower for supplying combustion air to the main burner;
A venturi pipe is provided at an air suction port to the blower, and a gas supply passage is connected to a throat portion of the venturi pipe, and along with suction of air to the suction port via the venturi pipe. A gas suction mechanism for drawing a gas from the gas supply path and feeding it with air to the suction port;
Wherein a valve provided in the gas supply passage, the gas pressure at the outlet side of the valve, and a gas pressure control valve for opening adjustment to maintain the inlet side pressure force of the venturi tube,
Differential pressure monitoring means for monitoring the differential pressure between the inlet side pressure of the venturi tube and the throat pressure ;
An air filter is provided at the air inlet to the venturi pipe,
The boiler, wherein the gas pressure adjusting valve adjusts the opening degree so that the gas pressure on the outlet side of the valve is maintained at the pressure on the inlet side of the venturi downstream of the air filter . In the duct to the main burner, no damper is provided downstream of the blower.
The air flow rate to the main burner is controlled by inverter control of the number of rotations of the fan and / or by changing a damper by providing a damper on the inlet side of the venturi tube. Boiler. When the differential pressure monitoring means detects that the differential pressure has become equal to or less than the set value, the combustion of each of the burners is stopped, or instead of or in addition to this, the differential pressure becomes equal to or less than the set value. The boiler according to claim 1 or 2 , wherein the boiler is notified that a predetermined device has been notified. The gas supply passage to the venturi tube, the downstream of the gas pressure regulating valve, according to any one of claims 1 to 3, characterized in that opening adjustable gas flow control valve is provided Boiler.

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