JP4926915B2 - Method and apparatus for preventing backfire of partially premixed burner - Google Patents

Description

  The present invention relates to a backfire prevention method and apparatus for a partial premixing type gaseous fuel burner (hereinafter referred to as a partial premixing burner) in which a part of a combustion fuel gas is premixed with combustion air.

Conventionally, as one method for reducing NOx generated by combustion of gaseous fuel, a premixing burner is known in which combustion is performed after a part (or all) of fuel gas is mixed with combustion air in advance. .
However, in the premixing burner, fuel is injected into the combustion cylinder in the wind box, etc., so that the combustible gas is mixed in the air-fuel mixture in the combustion cylinder in the wind box, especially when the combustion amount is low. When the air flow velocity in the windbox is low, the flame that is normally burned in the furnace enters the combustion cylinder in the windbox and ignites and burns the fuel gas injected into the combustion cylinder in the windbox. There is a risk of flashback.
For this reason, in the partially premixed burner, a wide turndown ratio cannot be obtained with a single burner, and combustion control for increasing excess air at a partial load is employed.

Conventionally, the burner casing is provided with temperature detecting means for detecting the temperature of the upstream surface with respect to the air-fuel mixture flow of the burner surface member, and based on the detected temperature, There is known a burner that includes a backfire detecting means for detecting, and a fuel shutoff means for shutting off the supply of all the fuel based on the detected pre-fire condition (see, for example, Patent Document 1).
Also, based on a signal from the backfire detection sensor for detecting abnormal combustion sound generated during backfire on one or both of the inner wall and / or outer wall of the cooling water passage communicating with the utility control device from the spray burner of the spraying device, and the detection sensor There is known a thermal spraying device having a flashback detection control device that determines the occurrence of flashback and a method of quenching flashback based on a signal from this device (see, for example, Patent Document 2).

Further, in the combustion apparatus, the flame holder for controlling the flame holding from the flame holding burner and the opening adjuster for controlling the ejection speed of the premixed gas from the main burner can be operated independently. Thus, it is known to prevent the rising flame and the blow-off by controlling the ejection speed of the premixed gas from the main burner (see, for example, Patent Document 3).
In addition, a plurality of pipes forming a flow path to which the premixed gas is supplied are detachably provided through a heat insulating material, and the tip of one of the plurality of pipes is positioned in the middle of the pipe for ignition. There is known a premix burner in which a rod is inserted and a flow path is configured to prevent backfire so that the flow velocity of the premix gas is higher than the combustion speed (see, for example, Patent Document 4). .
Although the prior art as described above has been searched, a technique for preventing backfire by cutting off the fuel gas supply for partial premixing or controlling the fuel gas supply amount has not been found.
JP 2000-274614 A (first page, FIG. 1) JP-A-8-277458 (first page, FIG. 1) JP 2006-242399 A (first page, FIG. 2A) Japanese Patent Laying-Open No. 2005-195206 (first page, FIG. 1)

  The problem to be solved is that the occurrence of flashback cannot be reliably prevented in the partially premixed burner.

  The present invention relates to a partial premix burner in which a fuel gas supply line is supplied to a premix nozzle for injecting fuel gas into combustion air in a combustion cylinder in a wind box, and a main combustion burner in a furnace. By providing two separate systems for supplying to the nozzle and cutting off the fuel gas supplied to the premixing nozzle or controlling the amount during combustion in the combustion load region where high backfire occurs, The main feature is to prevent the occurrence of flashback by reducing the air-fuel mixture in the combustion cylinder below the flammable limit concentration.

  In the present invention, in order to obtain a wide turndown ratio without causing a backfire in the partial premixing burner, two fuel gas supply lines are provided separately for the main nozzle and the premixing nozzle, of which the premixing nozzle is connected. The supply line is provided with an automatic valve that can be opened and closed by a command from the control panel. By setting this automatic valve to “close” or “reducing the opening” in the combustion load region where there is a high possibility of flashback (for example, the fuel is cut off when the combustion load is 50% or less) according to the combustion load. The fuel supply to the premixing nozzle is cut off, or the premixing amount of the fuel gas is controlled so that the air-fuel mixture does not enter the flammable range, thereby controlling to prevent backfire.

  The method of the present invention is a method for preventing flashback of a partially premixed burner, wherein the fuel gas for premixing is cut off during combustion in a combustion load region where there is a high possibility of flashback. .

  Further, the method of the present invention is a method for preventing backfire of a partial premixed burner, and changes the supply amount of fuel gas for premixing during combustion in a combustion load region where there is a high possibility of backfire. It is characterized by.

  Further, the method of the present invention is a method for preventing flashback when the partially premixed burner is a continuous combustion burner, wherein the fuel gas supply amount for premixing is controlled according to the combustion load factor of the burner. It is said.

  Further, the method of the present invention is a backfire prevention method in the case where the partial premixed burner is an intermittent control combustion burner, and is controlled by setting a premixed fuel gas supply amount at each stage of the intermittent control combustion. It is characterized by doing.

  Furthermore, when a backfire occurs in the partially premixed burner, the method of the present invention returns to normal combustion while continuing the combustion state by completely shutting off the supply of fuel gas for premixing. It is characterized by preventing.

  Further, the apparatus of the present invention provides a fuel gas main nozzle at the tip on the combustion furnace side of the combustion cylinder in the wind box in the partial premixing burner in which a part of the fuel gas is premixed with the combustion air. A premixing nozzle is provided inside the cylinder, a fuel gas main line is connected to the main nozzle, and a fuel gas premixing line with an automatic valve is connected to the premixing nozzle. Are connected to each other so that the automatic valve can be controlled by a signal from the control panel.

Since this invention is comprised as mentioned above, there exist the following effects.
(1) During combustion in a combustion load region where a partial premix burner is highly likely to generate backfire, the fuel gas supplied to the partial premix nozzle is cut off or the amount of fuel gas supplied is controlled. The air-fuel mixture in the combustion cylinder in the box can be made lower than the flammable limit concentration, and the occurrence of backfire can be reliably prevented, and safety and stability can be improved.

Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications.
FIG. 1 shows a backfire prevention device for a partially premixed burner according to an embodiment of the present invention.
Reference numeral 1 denotes a partial premixing burner. A fuel gas main nozzle 7 is provided at the tip of the combustion cylinder 3 in the wind box 2 on the combustion furnace 5 side, and a premixing nozzle 9 is provided inside the combustion cylinder 3. Yes.

A fuel gas main line 11 is connected to the main nozzle 7, and a fuel gas premixing line 15 having an automatic valve 13 is connected to the premixing nozzle 9. Further, the automatic valve 13 and the control panel 17 of the combustion furnace 5 are connected so that the automatic valve 13 can be controlled by a signal from the control panel 17. Note that the premixing line 15 branches from the main line 11.

  As described above, in the present embodiment, in order to obtain a wide turndown ratio without causing backfire in the partial premixing burner 1, two fuel gas supply lines, the main nozzle 7 and the premixing nozzle 9, are separately provided. Among these, the premixing line 15 that supplies the premixing nozzle 9 is provided with an automatic valve 13 that can be opened and closed by a command from the control panel 17. Then, depending on the combustion load, when the combustion load region where there is a high possibility of backfire, for example, when the combustion load becomes 50% or less, the automatic valve 13 is closed or the opening degree of the automatic valve 13 is reduced. In this way, control for preventing the occurrence of flashback is performed by cutting off the fuel supply to the premixing nozzle 9 or controlling the premixing amount of the fuel gas so that the air-fuel mixture does not enter the combustible range.

  In the above embodiment, the fuel gas supply amount for premixing is controlled by operating the automatic valve 13 by the command signal of the control panel 17 according to the combustion load factor of the partial premixing burner 1 which is a continuous combustion burner. However, as another embodiment, a fuel gas supply amount for premixing is set in advance for each stage of intermittent control combustion of a partial premixing burner which is an intermittent control combustion burner, and the automatic valve 13 is set according to a command signal from the control panel 17. There is also a case where it is controlled by operating.

  In the unlikely event of a backfire in the partial premix burner, the fuel gas supply for premixing is completely shut off with the automatic valve 13 fully closed, so that the burner 1 remains normal while the burner 1 continues to burn. Return to combustion to prevent subsequent flashback.

It is a systematic schematic block diagram of the backfire prevention apparatus of the partial premixing burner by embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Partial premix burner 2 Air box 3 Combustion cylinder 5 Combustion furnace 7 Main nozzle 9 Premix nozzle 11 Main line 13 Automatic valve 15 Premix line 17 Control panel

Claims (6)

A method for preventing backfire of a partial premix burner, wherein a fuel gas supply line is supplied to a premix nozzle for injecting fuel gas into combustion air in a combustion cylinder in a wind box, and in a furnace Partial premixing, characterized by providing two separate systems for supplying to the main nozzle to be burned, and cutting off the supply of fuel gas for premixing during combustion in the combustion load region where there is a high possibility of backfire Burner backfire prevention method. A method for preventing backfire of a partial premix burner, wherein a fuel gas supply line is supplied to a premix nozzle for injecting fuel gas into combustion air in a combustion cylinder in a wind box, and in a furnace Two parts of the system for supplying to the main nozzle to be burned are provided separately, and the amount of supply of the fuel gas for premixing is changed during combustion in the combustion load region where the possibility of backfire is high How to prevent backfire of premixed burner.   A method for preventing backfire when a partially premixed burner is a continuous combustion burner, wherein the fuel gas supply amount for premixing is controlled in accordance with the combustion load factor of the burner, and the reverse of the partially premixed burner Fire prevention method. This is a method for preventing flashback when the partially premixed burner is an intermittently controlled combustion burner in which multiple stages of combustion control are performed in multistage controlled combustion with multiple stages of combustion, for premixing at each stage of intermittently controlled combustion. A method for preventing backfire of a partial premixed burner, characterized in that the fuel gas supply amount is set and controlled in advance.   When backfire occurs in the partial premix burner, the fuel gas for premixing is completely cut off to return to normal combustion while continuing the combustion state, thereby preventing subsequent backfire. Backfire prevention method for partial premixed burners.   In a partial premix burner in which a part of the fuel gas is premixed with the combustion air, a fuel gas main nozzle is provided at the tip of the combustion cylinder side of the combustion cylinder in the wind box, and a premixing nozzle is provided inside the combustion cylinder. A fuel gas main line is connected to the main nozzle, a fuel gas premixing line with an automatic valve is connected to the premixing nozzle, and the automatic valve and the control panel of the combustion furnace are A device for preventing backfire of a partially premixed burner, wherein an automatic valve is connected in a controllable manner.