JPH09145013A - Low nox burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve low NOx operation irrespective of the amount of combustion by increasing the ratio of the amount of suction of waste gas with resect to the amount of air supply when the amount of combustion is turned down. SOLUTION: A plurality of waste gas sucking annular through holes H are formed in an air supply pipe 2, and a throat 5 is formed on an inner peripheral wall of the air supply pipe 2 for throttling an air passage cross section. The throat part 5 and the through holes 4 constitute an inspirator for sucking waste gas from a waste gas reflux passage 3 into the air supply pipe 2. In the throat 5, a movable plug 6 is slidably fitted over the outer periphery of a combustion supply pipe 1. The movable plug 6 is operated inter locking with the amount of fuel supply or the amount of air supply. When the amount of fuel supply is reduced, the movable plug is moved frontally through a lever 10 and a rod 9, and hence a flow velocity of combustion air passing through the inside of the through hole 4 is increased and the suction amount of the waste gas is increased into the air supply pipe 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low NOx type burner mainly used in industrial heating furnaces.

[0002]

2. Description of the Related Art A so-called self-exhaust gas recirculation burner has been conventionally known as a low NOx type burner of this type. FIG. 3 shows the structure thereof. An exhaust gas recirculation passage 3 having a tip opening into the furnace is formed further on the outer periphery of an air supply pipe 2 provided on the outer periphery of the fuel supply pipe 1, and a rear pipe of the air supply pipe 2 is formed. An inspirator for sucking exhaust gas is formed by the venturi effect of the through hole 4 formed in the wall and the throat portion 5 formed on the upstream side of the through hole 4. According to this configuration, the combustion air is mixed with a part of the exhaust gas in the furnace to reduce the oxygen concentration, so that the combustion becomes slow and the combustion temperature can be kept low, thereby generating NOx. There is an advantage that it can be suppressed, and in that case, the exhaust gas in the furnace can be recirculated using the momentum of the combustion air without using new pipes and auxiliary equipment, so it is small in size. And cost reduction can be achieved.

[0003]

However, in the above exhaust gas recirculation system, even when the combustion amount is increased or decreased,
The exhaust gas recirculation rate, that is, the ratio of the exhaust gas recirculation amount to the air supply amount can be maintained at a substantially constant value, but at low combustion, the momentum of the flame ejected into the furnace decreases,
The proportion of exhaust gas entrained in the flame is low, which results in a high flame temperature. Further, although flame holding is performed in order to prevent lift of the main flame, at the time of low combustion, this flame holding becomes excessive and acts to raise the flame temperature. Therefore, there is a drawback that the combustion temperature rises and the NOx generation amount increases at the time of low combustion. The present invention solves the above-mentioned problems, and in particular, in a heat treatment furnace that needs to be operated for a long time with a low combustion amount depending on the type of object to be treated, a gas burner that can maintain low NOx regardless of the amount of combustion. It is intended to provide.

[0004]

A low NOx burner according to the present invention comprises a fuel supply pipe 1 and an air supply pipe 2 surrounding the fuel supply pipe 1, and a through hole 4 is formed in a wall of the air supply pipe 2. In addition to providing the throat portion 5 on the upstream side of the through hole 4,
In the self-exhaust gas recirculation type low NOx burner which sucks the exhaust gas in the furnace into the air supply pipe 2 by the Venturi effect, a means for increasing the ratio of the exhaust gas suction amount to the air supply amount when the combustion amount is turned down is provided. It is a thing. As a means for increasing the amount of exhaust gas suctioned, the ventilation area of the throat portion 5 is reduced by the movable plug 6 as shown in FIG. 1, and the flow velocity of the air passing through the inside of the through hole 4 as the air supply amount decreases. 2, or the throat portion 5 is constituted by concentric double nozzles 5a and 5b, and the flow control valve 7 is provided in either one of the air supply paths to both nozzles. It is possible that it is inserted.

[0005]

1 shows an embodiment of a burner for an industrial furnace according to the present invention. An air supply pipe 2 is provided so as to surround a fuel gas supply pipe 1, and this air supply pipe 2 is provided. An exhaust gas recirculation passage 3 having a tip opening into the furnace is formed between the inner wall surface of the burner insertion hole formed in the furnace wall 8 and the outer peripheral surface of the air supply pipe 2. A plurality of through holes 4 for sucking exhaust gas are formed in an annular shape in the pipe wall of the air supply pipe 2, and an annular projection protruding from the inner peripheral wall of the air supply pipe 2 is provided slightly upstream of the through holes 4. The ventilation cross-sectional area is narrowed by the portion to form the throat portion 5, and the throat portion 5 and the through hole 4 form an inspirator for sucking the exhaust gas from the exhaust gas recirculation passage 3 into the air supply pipe 2. There is. Further, slightly behind the throat portion 5, a frustoconical movable plug body 6 is slidably fitted in the outer periphery of the fuel supply pipe 1 in the axial direction, and is operated back and forth by an operating mechanism including a rod 9 and a lever 10. The ventilating cross-sectional area of the throat portion 5 is increased / decreased by the forward / backward movement of the movable stopper 6.

The operation of the embodiment shown in FIG. 1 will now be described. When the fuel supply amount and the air supply amount are throttled and the burner combustion amount is turned down, the momentum of the flame decreases and the air is caught in the flame. The amount of exhaust gas in the furnace decreases, the oxygen concentration in the flame increases, and the combustion temperature rises. In general, flame holding holes are provided in the fuel nozzle to prevent the flame from lifting.However, when the fuel supply amount is decreased, the jetting speed of the main flame hole is markedly reduced and Is relatively excessive, which causes the combustion temperature to rise. Therefore, during low combustion, the ratio of the exhaust gas intake amount to the combustion air supply amount is increased compared to during high combustion, and as a result, the exhaust gas mixing ratio in the flame is maintained, and slow combustion is performed at the same level as during high combustion. Therefore, in this embodiment, the movable plug body 6 is operated in conjunction with the fuel supply amount or the air supply amount. That is, when the fuel supply amount is reduced, the movable plug body 6 is moved forward through the lever 10 and the rod 9, and the ventilation area of the throat portion 5 is reduced, so that the combustion air passing through the inside of the through hole 4 is reduced. The flow velocity is increased and the amount of exhaust gas sucked into the air supply pipe 2 is increased.

FIG. 2 shows another embodiment of the present invention, in which the throat portion 5 is a concentric double nozzle 5 as means for controlling the ratio of the exhaust gas suction amount to the air supply amount.
a, 5b, and air supply paths 11a, 1 to both nozzles
The flow rate control valve 7 is provided in either one of 1b. Also in this case, since the control for reducing the combustion air supply amount with the decrease in the fuel supply amount is performed only by the one air supply passage 11a, the momentum of the air passing through the entire throat portion 5 is equal to the fuel supply amount. Does not decrease, so both nozzles 5
By appropriately selecting the area ratio of a and 5b, the ratio of the exhaust gas intake amount to the air supply amount can be increased as the combustion amount becomes lower, and low NOx can be maintained even when the combustion amount is turned down. You can do it.
As an example, when the NOx value at the time of rated combustion was 92 ppm, it was conventionally increased to 200 ppm with a combustion amount of 1/4, but according to the present invention, it could be decreased to 62 ppm.

[0008]

As described above, according to the structure of the present invention, even if the fuel supply amount is decreased, the momentum of the air passing through the entire throat portion 5 is not decreased so much. , The ratio of the exhaust gas suction amount to the air supply amount 2 increases, whereby the surrounding exhaust gas is sufficiently caught in the flame even in the furnace, and the low NOx can be maintained even in the low combustion as in the high combustion. There is an advantage.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of the present invention.

FIG. 2 is a vertical sectional view of another embodiment of the above.

FIG. 3 is a longitudinal sectional view of a conventional example.

[Explanation of symbols]

 1 Fuel Gas Supply Pipe 2 Air Supply Pipe 3 Exhaust Gas Recirculation Channel 4 Exhaust Gas Suction Hole 5 Throat Section 6 Inspirator 7 Movable Plug 8 Furnace Wall 9 Rod 10 Lever

Claims (4)

[Claims] 1. A venturi effect, comprising a fuel supply pipe and an air supply pipe surrounding the fuel supply pipe, wherein a through hole is provided in a wall of the air supply pipe and a throat portion is provided upstream of the through hole. A self-exhaust gas recirculation type low NOx burner that sucks the exhaust gas in the furnace into the air supply pipe by means of providing a means for increasing the ratio of the exhaust gas suction amount to the air supply amount when the combustion amount is turned down. Low NOx burner to be. 2. The means for reducing the ventilation area of the throat portion increases the flow velocity of the air passing through the inside of the through hole to increase the ratio of the exhaust gas suction amount to the air supply amount. A low NOx burner according to claim 1 characterized. 3. A low N according to claim 2, wherein the ventilation area of the throat portion is increased or decreased by a movable plug body which is fitted into the outer periphery of the fuel supply pipe so as to be movable back and forth.
Ox burner. 4. The ratio of the exhaust gas suction amount to the air supply amount by constructing the throat part by concentric double nozzles and providing a flow control valve in either one of the air supply paths to both nozzles. The low NOx burner according to claim 1, wherein the low NOx burner is controlled.