JP4144805B2 - Combustion device that prevents heating of main burner by pilot flame - Google Patents

Description

  The present invention relates to a combustion apparatus that prevents heating of a main burner by a pilot flame.

  As described in JP-A-11-351570, a combustion apparatus provided with a premixed main burner and a pilot burner is widely used. Since the main burner and the pilot burner are installed close to each other, when only the main burner is burning and the pilot burner is not burning, the pilot burner may be heated and burnt by the heat of the main flame. Therefore, in the invention of Japanese Patent Laid-Open No. 11-351570, a purge hole is provided on the side wall of the pilot fuel gas pipe in order to prevent the pilot burner from being heated. If the small hole for purge is opened, the combustion of the pilot burner stops, and when burning only with the main burner, the air flowing around the pilot burner enters the pilot burner through the small hole for purge, and the inside of the pilot burner Then, the fuel is injected from the pilot fuel injection hole. The air flowing in the pilot burner absorbs the heat of the pilot burner, so that the pilot burner can be cooled and the pilot burner can be prevented from being heated.

The pilot burner has a smaller combustion amount than the main burner, but the main burner may be heated by the pilot flame to cause burning. When combustion is performed by the main burner, since the fuel gas flows in the main burner, the main burner can be cooled by the fuel gas. However, when only the pilot burner is burned and the main burner is not burned for a long time, there is nothing to cool the main burner, so the main burner is heated by the pilot flame. As for the heating of the main burner by the pilot flame, since it is not possible to take in air by making a hole in the side wall of the main fuel gas pipe as in the case of the pilot burner in JP-A-11-351570, it prevents heating. This measure was necessary.
JP-A-11-351570

  The problem to be solved by the present invention is to prevent the main burner from being heated by the pilot flame generated by the pilot burner.

  The invention according to claim 1 has a main burner for supplying fuel through a main fuel gas pipe, a pilot burner for supplying fuel through a pilot fuel gas pipe, and a blower for supplying combustion air to the burner. The burner is a premixing method in which the fuel gas injected from the gas injection hole at the tip and the combustion air supplied from the blower to the front side of the burner through the blower passage are mixed on the front side of the burner and burned. In the combustion apparatus, a cooling air passage is provided in the middle of the air passage to send the air sent through the air passage into the main fuel gas pipe, and during pilot combustion in which combustion with only the pilot burner is performed for a relatively long time, At the time of main combustion in which air is supplied from the air passage into the main fuel gas pipe and combustion is performed by the main burner, And performing control to cut off the air supply to the in-fuel gas pipe.

  According to a second aspect of the present invention, in the combustion apparatus for preventing the main burner from being heated, a damper for controlling the flow passage area in the air passage is provided downstream of the cooling air passage installation portion of the air passage. In addition, it is characterized in that control is performed to close the damper during pilot combustion, and control is performed to open the damper during main combustion.

  According to a third aspect of the present invention, in the combustion apparatus for preventing the main burner from being heated, when the main combustion is shifted to the pilot combustion, after starting the control for supplying a part of the air from the blower into the main fuel gas pipe Control to close the damper is performed.

  By implementing the present invention, at the time of pilot combustion in which only the pilot burner is burned for a relatively long time, the tip of the main burner can be cooled by air sent into the main fuel gas pipe, thereby preventing heating of the main burner. be able to. In addition, if the cooling air is sent into the main fuel gas pipe, the main burner can be efficiently cooled, and the main burner can be prevented from being heated with a small amount of cooling air. And increase in exhaust gas loss can be suppressed.

  1 to 5 relate to a boiler embodying the present invention, FIG. 1 is a flow of fuel and air in a state where pilot combustion is being performed, and FIG. 2 is a fuel and air in a state where main combustion is being performed. Shows the flow. 3 is a longitudinal cross-sectional view of the tip of the burner during pilot combustion, FIG. 4 is a cross-sectional view taken along the line AA of FIG. 3, and FIG. 5 shows the operation status of the boiler combustion command and the cooling air valve and the like. It is a time chart.

  The boiler 11 has a combustion chamber 12 at the center, and a combustion device is installed above the combustion chamber 12. The combustion apparatus includes a cylindrical combustion cylinder 16 through which combustion air sent from the blower 8 passes, and a main fuel gas pipe 1 that is a concentric cylinder having a smaller diameter than the combustion cylinder 16 at the center of the combustion cylinder 16. . The main fuel gas pipe 1 is provided with a baffle plate 6 near the tip and a main fuel injection hole 5 further on the tip side than the baffle plate 6. The baffle plate 6 blocks an annular portion formed between the main fuel gas pipe 1 and the combustion cylinder 16, and openings 18 are provided at equal intervals on the outer edge of the baffle plate 6. Since the combustion air passing through the combustion cylinder 16 passes through the opening 18 of the baffle plate 6, the combustion air is divided and enters the combustion chamber 12.

  The other end side of the main fuel gas pipe 1 is connected to a fuel pipe 13 for supplying fuel gas, and a downstream portion of the main fuel gas pipe 1 serves as a main burner 2. Further, a pilot fuel gas pipe 3 is provided in the combustion cylinder 16 in parallel with the main fuel gas pipe 1, and a pilot fuel injection hole is provided on the tip side of the pilot fuel gas pipe 3 with respect to the baffle plate 6. The other end side of the pilot fuel gas pipe 3 is also connected to the fuel pipe 13, and the downstream portion of the pilot fuel gas pipe 3 is a pilot burner 4.

  The fuel pipe 13 is provided with a main fuel valve 15 in the middle, and a portion downstream of the main fuel valve 15 is a main fuel gas pipe 1. The pilot fuel gas pipe 3 is connected to a fuel pipe 13 upstream of the main fuel valve 15, and a pilot fuel valve 14 is provided in the middle of the pilot fuel gas pipe 3.

  The combustion air is supplied through the air passage 9 connected to the blower 8, and is supplied from the blower 8 through the air passage 9 and the combustion cylinder 16 to the combustion chamber 12. In addition, a cooling air passage 7 for sending air into the main fuel gas pipe 1 is connected to the air passage 9. The cooling air passage 7 connects the air passage 9 and the main fuel gas pipe 1, and a cooling air valve 10 is provided in the cooling air passage 7. A damper 19 for controlling the flow area in the air passage 9 is provided on the downstream side of the air passage 7 connecting portion of the air passage 9.

  The operation of the boiler is controlled based on a combustion command determined according to the load state such as a steam pressure value, and the combustion command is a main combustion in which the combustion is stopped by the main burner 2 to stop the combustion of the boiler completely. There are three patterns of pilot combustion in which the combustion of only the pilot burner 4 is continued in preparation for the next main combustion after the main combustion is stopped. Then, when shifting from the combustion stop to the main combustion, from the main combustion to the pilot combustion, and from the pilot combustion to the main combustion, steps of combustion start, pilot shift, and main shift are performed, respectively.

  In the time chart of FIG. 5, the opening / closing state of the fuel valve when the combustion command is output in the order of combustion stop, main combustion, pilot combustion, main combustion, and combustion stop are shown. When the combustion is stopped, the operation of the blower 8 is stopped, and the main fuel valve 15, the pilot fuel valve 14, the damper 19, and the cooling air valve 10 are closed. In this state, since the fuel and air are not supplied, the main burner 2 and the pilot burner 4 have stopped combustion.

  When a main combustion command is output from the state of combustion stop, a combustion start process is performed to start main combustion. In the process of starting combustion, first, the operation of the blower 8 and the control for opening the damper 19 are performed from the state where the combustion is stopped. At this time, the pilot fuel valve 14, the main fuel valve 15, and the cooling air valve 10 remain closed. When combustion is started from a combustion stopped state, it is necessary to ventilate the combustion chamber 12 for safety, and a pre-purge for a certain time is first performed. By supplying the fuel gas to the combustion chamber 12 by operating the blower 8 and controlling the opening of the damper 19 while the supply of the fuel gas is stopped, the inside of the combustion chamber 12 is ventilated.

  When the pre-purge is completed, the ignition device (not shown) is operated while the operation of the blower 8 and the opening control of the damper 19 are continued, and then the pilot fuel valve 14 is opened. By opening the pilot fuel valve 14, fuel gas is supplied to the pilot burner 4, and pilot fuel is injected from a pilot fuel injection hole provided at the tip of the pilot burner 4. On the front side of the pilot burner 4, the pilot fuel gas injected from the pilot burner 4 and the combustion air supplied from the blower 8 are mixed to become a combustible gas, and the electric spark generated in the ignition device is burned and spread. The pilot flame 17 is burned.

  When a predetermined time (several seconds) elapses after the combustion of the pilot flame 17 starts, the main fuel valve 15 is opened, and fuel gas supply to the main burner 2 is started. When the fuel gas is injected from the main fuel injection hole 5 provided at the tip of the main burner 2, the main fuel gas injected from the main burner 2 on the front side of the main burner 2 and the combustion air supplied from the blower 8. Are mixed to become combustible gas, and the combustion of the main burner 2 is started by burning and spreading the fire of the pilot flame 17.

  Immediately after the main combustion is started, the combustion by the main burner 2 and the combustion by the pilot burner 4 are overlapped, but during the main combustion, the combustion by the pilot burner 4 is unnecessary, so the combustion by the main burner 2 is performed. In this state, the pilot fuel valve 14 is closed and the combustion by the pilot burner 4 is stopped. When the main combustion is performed, the boiler is heated by the flame heat generated by the main burner 2, and steam is generated in the boiler.

  When steam pressure rises to the upper limit value due to steam generation by the boiler, the boiler stops main combustion and shifts to pilot combustion. In the pilot shift process, first, the pilot fuel valve 14 is opened, and fuel gas is also injected from the pilot burner 4, whereby combustion by the pilot burner 4 is performed in addition to combustion by the main burner 2. Next, by closing the main fuel valve 15, the fuel gas injection from the main burner 2 is stopped, and the combustion of the main burner 2 is stopped.

When shifting to pilot combustion due to an increase in the steam pressure, the pilot combustion is continued until the steam pressure value falls to the lower limit value, so that the combustion time of the pilot burner alone becomes longer than when the combustion is started. The pilot flame 17 by the pilot burner 4 is smaller than the main flame 20 by the main burner 2, but when the combustion is performed for a long time, the portion of the main burner 2 that is in close proximity is heated. Burning may occur in the main burner 2. Therefore, during pilot combustion, the cooling air valve 10 is opened to cool the main burner 2. When the combustion of the main burner 2 is stopped, no pressure is applied in the main fuel gas pipe 1, so when the cooling air valve 10 is opened, a part of the air sent to the combustion chamber 12 is branched from the blower passage 9. The air enters the cooling air passage 7 and enters the main fuel gas pipe 1 through the cooling air passage 7.

  When air is sent into the main fuel gas pipe 1, the air flows through the main fuel gas pipe 1, reaches the tip of the main burner 2, and flows into the combustion chamber 12 through the main fuel injection hole 5. At this time, the air flowing in the main burner 2 flows while absorbing the heat of the main burner 2, so that the main burner 2 can be cooled by the air.

  Further, the pilot combustion pilot flame 17 has a smaller combustion amount than the main combustion main flame 20, and therefore, the required amount of air is reduced. Supplying the same amount of air as in the main combustion greatly increases the amount of air required for the pilot flame 17, so that the amount of CO generated increases and the amount of exhaust gas loss increases. Therefore, by closing the damper 19, the air sent through the inside of the combustion cylinder 16 is shut off, and the air supply amount is reduced. Since the damper 19 is installed on the downstream side of the connection portion of the cooling air passage 7, air is sent through the cooling air passage 7 even when the damper 19 is closed, and the main burner 2 is cooled. When the air that has cooled the main burner 2 reaches the portion of the pilot burner 4, the air is burned as combustion air mixed with the fuel gas of the pilot burner. By concentrating the supply of air to the main fuel gas pipe 1, the air that does not contribute to the cooling of the main burner 2 is reduced, and the cooling effect of the main burner 2 is enhanced. Since the supply amount of air can be reduced, the CO generation amount and the exhaust gas loss amount are reduced.

  When the cooling air valve 10 is opened, the main fuel gas pipe 1 is filled with fuel gas. Therefore, when the cooling air valve 10 is opened, air starts to be injected from the main fuel injection hole 5. Sometimes there is a time difference. If the damper 19 is closed at the same time as the cooling air valve 10 is opened, the supply of combustion air to the pilot burner 4 portion temporarily stops, and the flame may disappear due to the lack of air amount. Is closed after a predetermined time has elapsed since the cooling air valve 10 is opened, so that the supply of combustion air is not interrupted.

  In the case of main transition in which combustion of the main burner is started from the state of pilot combustion, first, the damper 19 is opened and air supply through the combustion cylinder 16 is started. Next, the cooling air valve 10 is closed and the main fuel valve 15 is opened. When fuel gas is supplied to the main burner 2 through the main fuel gas pipe 1, the fuel gas injected from the main fuel injection hole 5 is mixed with air, and main combustion by the main burner is started. In the case of main transition that shifts from pilot combustion to main combustion, it is not necessary to ventilate the inside of the combustion chamber 12, so that main combustion can be started in a short time, and heat outflow due to pre-purge can be prevented. When the supply of air to the combustion cylinder 16 is stopped, the combustion exhaust gas generated in the combustion chamber 12 fills the combustion cylinder 16 and the wind box, and immediately after the damper 19 is opened, combustion occurs from the opening 18. It is conceivable that working air cannot be supplied. However, by controlling the air valve 10 for cooling after opening the damper 19, the combustion exhaust gas in the combustion cylinder 16 or the wind box is removed from the combustion chamber before the air supply from the main fuel gas pipe 1 is stopped. 12 and the supply of combustion air is started from the opening 18, the supply of combustion air is not interrupted.

  When the operation switch is turned off from the state where the main combustion is being performed, or when the steam pressure value has reached the set value for stopping the combustion when the pilot combustion is not performed, the combustion is stopped. In this case, the flame in the combustion chamber 12 is extinguished by closing the main fuel valve 15, and then the ventilation chamber 8 is ventilated by continuing to operate the blower 8 and opening the damper 19 for a predetermined time. Then, the blower 8 is stopped and the damper 19 is closed.

  By supplying air to the main fuel gas pipe 1 only in the case of pilot combustion in which combustion by the main burner 2 is not performed, the main burner 2 is heated during pilot combustion while maintaining the combustion state during main combustion appropriately. This can be prevented. Further, in the premixing method in which the fuel gas and air are mixed in advance, there is a possibility of backfire, but the problem of backfire does not occur by not sending air to the main fuel gas pipe 1 during main combustion.

Flow diagram of fuel and air during pilot combustion Fuel and air flow diagram with main combustion 1 is an enlarged cross-sectional view of the tip portion of the combustion device AA sectional view of FIG. Time chart showing boiler combustion commands and operating status of cooling air valves, etc.

Explanation of symbols

1 Main fuel gas pipe
2 Main burner
3 Pilot fuel gas pipe 4 Pilot burner
5 Main fuel injection holes
6 Baffle plate
7 Air passage for cooling 8 Air blower 9 Air passage 10 Air valve for cooling 11 Boiler 12 Combustion chamber 13 Fuel piping
14 Pilot fuel valve 15 Main fuel valve 16 Combustion cylinder 17 Pilot flame 18 Opening 19 Damper 20 Main flame

Claims (3)

A main burner for supplying fuel through a main fuel gas pipe, a pilot burner for supplying fuel through a pilot fuel gas pipe, and a blower for supplying combustion air to the burner. The main burner and the pilot burner are provided from a gas injection hole at the tip. In the combustion apparatus that is a premixing method in which the injected fuel gas and the combustion air supplied from the blower through the air passage to the front side of the burner are mixed at the front side of the burner and burned, in the middle of the air passage A cooling air passage is provided to send the air sent through the air passage into the main fuel gas pipe, and air is supplied from the air passage into the main fuel gas pipe at the time of pilot combustion in which combustion with only the pilot burner is performed for a relatively long time. During the main combustion, where the main burner performs combustion control, the main fuel gas pipe is empty. Combustion apparatus for preventing heating of the main burner by the pilot flame and performing control to cut off the supply. The combustion apparatus for preventing heating of the main burner according to claim 1, wherein a damper for controlling a flow passage area in the air passage is provided downstream of a cooling air passage installation portion of the air passage, and at the time of pilot combustion A combustion apparatus for preventing heating of a main burner by a pilot flame, wherein the damper is controlled to close and the damper is controlled to open during main combustion. The combustion apparatus for preventing heating of the main burner according to claim 2, wherein when the transition from main combustion to pilot combustion is started, control of supplying a part of the air from the blower into the main fuel gas pipe is started. A combustion apparatus for preventing heating of a main burner by a pilot flame, characterized by performing close control.

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