JPH09145019A - Low nox burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low NOx burner in which an exterior wall body is not overheated, an area load rate is large, and stable combustion is provided. SOLUTION: A pair of thin gas combustion wall bodies 28 comprising porous ceramic plate provided along an exterior wall bodies 6 and a thick gas combustion plate 17 comprising porous ceramic plate which is horizontally disposed centrally between the lower parts of the wall bodies 28 are provided, and thick gas having low excess air ratio is burnt on the plate 17 to form a thick gas combustion flame 18 and thin gas having high excess air ratio is blown off from the wall bodies 28 to stabilize the flame 18, so that the thin gas blown off from the wall bodies 28 can be burnt in a stable state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burner which generates a small amount of nitrogen oxides (NOx) by burning gas having a high excess air ratio.

[0002]

2. Description of the Related Art Since a gas having a high excess air ratio cannot be stably burned alone, a gas having a low excess air ratio is burned, and the gas having a high excess air ratio is burned as flame holding. Burning.

A typical prior art burner 40 having such a flame holding mechanism is shown in FIG. A pair of left and right symmetrical combustion areas B1, B are placed between the parallel exterior wall bodies 41 facing each other.
2 are provided, and in each of the combustion areas B1, B2, a rich gas combustion wall 42 and a light gas combustion wall 43 are provided.
2 are arranged facing each other with the outer wall 2 facing the exterior wall 41. The rich gas flows from the rich gas supply pipe 44 to the dense gas flame port 46 through the communication path 45 and is ejected along the rich gas combustion wall 42. The secondary air for combustion flows from a blower (not shown) through a secondary air passage 47 to a secondary air discharge hole 48 provided along the vertical direction of the rich gas combustion wall 42,
It is ejected from here and burns together with the rich gas to form a rich gas flame 49. On the other hand, the lean gas having a large excess air ratio is produced by mixing the fuel gas supplied from the pipe line 51 with the air sent from the blower in the mixing chamber 52.
The gas is blown out from a flame hole 53 provided in a slit shape in the stainless steel light gas combustion wall 43 to form a light gas combustion flame 54. The light gas combustion flame 54 can continue burning stably due to the flame holding action of the dense gas combustion flame 49 located at the opposite position.

[0004]

The burner 40 has an N
The area of the rich gas combustion wall 42 is made smaller than the area of the light gas combustion wall 43 in order to increase the amount of light gas combustion with a small amount of Ox generated and reduce the total amount of NOx generated. Also, in order to make the flame holding effect of rich gas combustion work effectively,
The rich gas combustion wall 42 is relatively lower than the position of the lean gas combustion wall 43, that is, the lower ends of the rich gas combustion wall 42 and the lean gas combustion wall 43 are substantially the same height.
The upper end of 2 is at the middle height of the light gas combustion wall 43. Therefore, the portion 55 of the exterior wall body 41 directly facing the lean gas combustion wall 43 is exposed to the lean gas combustion flame. In order to prevent this, a part of the secondary air is blown out from the cooling air discharge hole 50 provided in the upper part of the rich gas combustion wall 42.
However, this alone does not sufficiently cool the exterior wall 41, and there is a problem in durability of the exterior wall 41.

[0005] The lean gas combustion wall 43 is formed by pressing a stainless steel plate to form a slit-shaped burner flame hole 53. The light gas combustion wall 43 preferably has a high area load in order to have a compact structure. However, if the area load is increased as long as a flame hole made of a stainless steel plate is used, the stainless steel plate is burned and deformed. There is a problem.

This also applies to the rich gas combustion wall 42. Since the rich gas combustion wall 42 is heated by the rich gas flame and by the radiant heat of the light gas combustion flame, the stainless steel plate undergoes burning deformation. Further, the flame holding effect of the rich gas combustion flame becomes insufficient especially when the combustion load is small. Therefore, low load (for example, less than 1/5 of the maximum combustion load) combustion is not stable, and when the load is low, only rich gas combustion is performed, and the amount of NOx generated at this time increases.

An object of the present invention is to provide a low NOx burner capable of stable combustion, preventing overheating of the exterior wall body, and having a large area load.

[0008]

DISCLOSURE OF THE INVENTION The present invention is a burner for burning fuel gas and air from a lower side to an upper side between a pair of parallel exterior wall bodies opposed to each other and burning the fuel gas and air along the exterior wall body. A pair of fresh gas combustion wall bodies, each of which has an upper end corresponding to the upper end of the exterior wall body and has a trapezoidal cross-section whose width becomes narrower toward the lower side and which is made of a ceramic porous plate, and the pair of fresh gas combustion wall bodies. It includes a rich gas combustion plate consisting of a ceramic porous plate formed in the lower central part of the chamber, ejects rich gas with a low excess air ratio from the rich gas combustion plate, forms a rich gas combustion flame on the combustion plate, and causes excess air. A low NOx burner characterized in that a high-purity fresh gas is ejected from a ceramic porous plate of a fresh gas combustion wall, and the rich gas combustion flame is used as a flame stabilizer to burn the fresh gas ejected from the ceramic porous plate. . According to the present invention, since the lean gas combustion wall is provided along the exterior wall, the exterior wall does not overheat. Further, since the light gas combustion wall and the rich gas combustion plate are made of a porous ceramic plate and are hardly deformed by heat, they can be burned with a high area load. Further, since the rich gas combustion plate is provided horizontally at the lower center of the lean gas combustion wall, the rich gas combustion flame has a larger flame holding effect. Therefore, low-load combustion can also be performed in a state in which the light gas combustion flame is maintained with the rich gas combustion flame, and low NOx is achieved in the entire combustion range.
Can be achieved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below more specifically with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of a low NOx burner 1 of the present invention, and FIG. 2 is a system diagram showing a fuel gas supply pipe. The fuel gas is supplied from the conduit 2 through the former cock 3, the solenoid valve 4, and the proportional valve 5, part of which is supplied to the rich gas conduit 11, and most of the other is supplied to the light gas conduit 21.

The rich gas pipe line 11 is connected to a rich gas distribution pipe 12 provided at the lower center of the burner 1. A gas discharge hole 13 is bored in the upper surface of the rich gas distribution pipe 12, and the fuel gas is discharged into the rich gas mixing chamber 14 through the gas discharge hole 13 to blow the gas.
It is mixed with the air sent from. Rich gas mixing chamber 14
In order to improve the mixing of fuel gas and air,
5 and baffle 16 are provided. The rich gas sufficiently mixed with air is ejected from the pores of the rich gas combustion plate 17 composed of the ceramic porous plate 20 and ignited by an ignition device (not shown) to form a rich gas combustion flame 18. The air mixing ratio of the rich gas is 1.05 to 1.1 times the theoretical air.

The fresh gas pipe 21 is branched into two and is connected to the fresh gas distribution pipes 22 provided at the lower portions on both sides of the burner 1. On the upper surface of the light gas distribution pipe 22, a gas discharge hole 23
Is drilled. The gas discharge holes 23 are provided more densely than the gas discharge holes 13 provided in the rich gas distribution pipe 12. The fuel gas discharged from the gas discharge hole 23 is used as the fresh gas mixing chamber 2
In the inside of 4, the air sent from the blower 31 is mixed with it to produce a light gas. The light gas mixing chamber 24 is also provided with a restrictor 25 and a baffle plate 26 in order to improve mixing of air and fuel gas. Further, a flow straightening plate 27 is provided downstream thereof. The rectified fresh gas is ejected from the pores of the fresh gas combustion wall body 28 constituted by the ceramic perforated plates 30 provided along both the exterior wall bodies 6 of the burner 1, and ignited by the rich gas combustion flame 18. The light gas combustion flame 29 is formed and burned.
The light gas combustion flame 29 is held by the rich gas combustion flame 18. The air mixing ratio of the light gas is 1.5 to 1.
6 times.

The air is supplied under pressure by the blower 31, is rectified by the first rectifying plate 32, and then is distributed by the distribution plate 33.
Is divided into air for rich gas and air for light gas, and sent to the mixing chambers 14, 24.

FIG. 3 is a front view of an example of the ceramic porous plate 20 constituting the rich gas combustion plate 17, and FIG. 4 is a front view of an example of the ceramic porous plate 30 constituting the light gas combustion wall body 28. . As the ceramic porous plates 20 and 30, a plurality of those carried for an infrared stove can be used side by side. The thickness 13 mm, the flame hole indicated by the black dot in FIG. 3 is 1.0 mmφ, and the flame hole indicated by the black dot in FIG. 4 is 1.25 mmφ.
Is commonly used. The area load of the ceramic porous plate is as large as 6.5 to 7.0 kcal / hmm ^2, and can be 1.5 to 2 times the area load of the slit flame hole 53 formed by processing a stainless plate.

FIG. 5 is an enlarged sectional view of the mounting portion of the ceramic porous plates 20 and 30. The ceramic porous plate 30
A support frame 37 fixed by two partition walls 35 and 36 provided between the rich gas mixing chamber 14 and the light gas mixing chamber 24.
Is supported via ceramic wool 38. The upper portion of the ceramic porous plate 30 is supported by the frame plate 8 fixed to the upper outer wall 7 with a space 9 left therebetween. The ceramic porous plate 20 has a support frame 3 whose both sides are fixed to one partition wall 36.
9 is supported via ceramic wool 38. Even if the ceramic porous plates 20 and 30 are heated in this way, heat is hardly transmitted to the support frames 37 and 39 and the frame plate 8 that support them, and these can be made of a material SUS plate that is easy to process.

As shown in FIG. 2, in the fuel gas supply pipe,
A solenoid valve 4 and a proportional valve 5 are connected in addition to the main cock 3.
The solenoid valve 4 gradually increases the amount of fuel gas and finally reaches the maximum load, and the proportional valve 5 controls the amount of air from the blower 31 in proportion to the amount of fuel gas. About 1/5 of the fuel gas is supplied to the rich gas line 11 and 2 to the light gas line 2.
2/5 each, for a total of about 4/5. In addition, the amount of air is distributed to the rich gas mixing chamber 14 by the distribution plate 33.
About 1/7 of the whole, 3/7 each in the light gas mixing chamber 24,
A total of about 6/7 is supplied.

FIG. 6 is a graph showing the relationship between the amount of combustion and the amount of gas supply. For a burner with a maximum load of 30,000 kcal / h, the proportional valve 5 is used to determine the amount of combustion by a straight line L1.
If the concentration is increased along the (solid line), the concentration of the concentrated gas increases along the straight line L2 (dashed line). The amount of the lean gas is represented by (L1−L2), and is always about 4/5 of the total fuel gas except when the load is extremely low near the combustion amount 0.

Therefore, the NOx generation amount in the burner 1 could be set to 20 ppm or less (18 ppm in the experiment by the inventor) in the entire combustion range as shown in FIG. In the conventional burner 40 shown in FIG. 8, when the combustion load is 20% or more of the maximum load, the NOx generation amount is 30 p
Although it can be made pm or less, when the load is less than 20%, only rich gas combustion is performed to stabilize the combustion, so the NOx generation amount exceeds 30 ppm, and in some cases 60 ppm. Note that the above NOx contents were all O ₂ = 0%
It is the value converted to.

[0019]

As described above, according to the present invention, a pair of lean gas combustion walls made of a porous ceramic plate is provided along the exterior wall, so that the area load due to the lean gas combustion wall is reduced. Even if it increases, the exterior wall body is not overheated, and a low NOx burner with a small area and a large combustion load can be obtained. Also, since the dense gas combustion plate is composed of a ceramic perforated plate and is provided horizontally below the center of the light gas combustion wall, the rich gas combustion plate is not subjected to heat distortion and has a large flame holding effect,
NOx reduction can be achieved in the entire combustion range.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a low NOx burner 1 according to an embodiment of the present invention.

FIG. 2 is a system diagram of a fuel gas.

FIG. 3 is a front view of a ceramic porous plate 20 constituting the rich gas combustion plate 17;

FIG. 4 is a front view of a porous ceramic plate 30 constituting the lean gas combustion wall body 28.

FIG. 5 is a partially enlarged sectional view of a mounting portion of the ceramic porous plates 20 and 30.

FIG. 6 is a graph showing the relationship between the supply amount of fuel gas and the combustion amount.

FIG. 7 is a graph showing the relationship between the combustion amount and the NOx generation amount.

FIG. 8 is a cross-sectional view of a prior art low NOx burner.

[Explanation of symbols]

 1 Low NOx Burner 6 Exterior Wall 12 Concentrated Gas Distribution Pipe 13 Concentrated Gas Gas Discharge Hole 17 Concentrated Gas Combustion Plate 18 Concentrated Gas Combustion Flame 20,30 Ceramic Perforated Plate 22 Light Gas Distribution Pipe 23 Light Gas Gas Discharge Hole 28 Light Gas combustion wall 29 Light gas combustion flame 31 Blower

Claims (1)

[Claims] 1. A burner for burning fuel gas and air by flowing from below to above between a pair of parallel exterior wall bodies facing each other, wherein the upper end of the exterior wall body is along the exterior wall body. And a pair of fresh gas combustion wall bodies made of ceramic perforated plates, which are formed in a trapezoidal shape in which the interval of the cross section becomes narrower toward the bottom, and a pair of fresh gas combustion wall bodies are formed in the lower central part of the ceramic body. Including a rich gas combustion plate consisting of a perforated plate, a rich gas with a low excess air ratio is ejected from the rich gas combustion plate,
A dense gas combustion flame is formed on the combustion plate, and a light gas having a high excess air ratio is jetted from the ceramic porous plate of the light gas combustion wall, and the gas jetted from the ceramic porous plate using the dense gas combustion flame as flame holding. Low N characterized by burning gas
Ox burner.