JPH08285235A - Low NOx combustion method of fuel gas using surface combustion and burner thereof - Google Patents

Abstract

(57) [Summary] [Purpose] A fuel gas is burned with low NOx while ensuring stable flame formation with a simple and low-cost structure. [Composition] A mixture of fuel gas and combustion air is jetted through the first porous body 4 and burned, and through a second porous body 6 provided downstream of the first porous body 4 in the burner axial direction. By ejecting the secondary fuel gas, two-stage combustion by surface combustion is performed. The fuel gas ejected through the second porous body 6 was set to 10 to 30% with respect to the total amount of the fuel gas ejected through both the first and second porous bodies 4 and 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel gas combustion method and a burner thereof in which a predetermined amount of fuel gas and combustion air are mixed, ignited and burned, and more particularly to a mixed gas of fuel gas and combustion air. The present invention relates to an object of reducing the NOx concentration in the combustion gas by improving an object using surface combustion that ejects and combusts through a porous body such as ceramics. The present invention relates to an industrial heating furnace, various melting furnaces, Used as combustion equipment such as heat treatment furnaces and boilers.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for reduction of nitrogen oxide (NOx) emissions in industrial burners from the viewpoint of global environmental protection.

Generally, NOx generated by combustion is
Thermal NOx, which is generated by the oxidation of nitrogen in combustion air and is more likely to occur as the combustion temperature increases.
And fuel NOx produced by the oxidation of nitrogen compounds in the fuel. These NOx are considered to be the cause of photochemical smog, etc., and therefore reduction measures thereof are urgently needed.

Conventional methods for reducing NOx in combustion include lean premixed combustion, exhaust gas recirculation, and rich / lean combustion.
Slow combustion, two-stage combustion of fuel, two-stage combustion of air, change of flame shape (split flame, thin film flame, etc.), water vapor injection and water injection are known, and various of them alone or in combination are known. A NOx reduction method has been proposed and put to practical use.

Of these, a combination of suppression means such as exhaust gas recirculation and water vapor injection is mainly used, centering on the method of two-stage combustion of fuel and air. For example, the two-stage combustion of air is a method in which the combustion air is divided into two stages and supplied, the primary air is made smaller than the theoretical air amount for combustion, and the rest is sent as secondary air. According to this, the flame temperature does not rise due to the division of air, and the oxygen concentration in the high temperature region decreases, so that the generation of NOx is suppressed.

[0006]

However, in the above-mentioned burner utilizing the two-stage combustion of air, in general, the fuel injection nozzle is arranged in the center and the jet ports of the combustion air are arranged in a divided manner around it. A rich fuel region is formed near the center axis of the burner, and the fuel near the center may be mixed unevenly with the air, resulting in non-uniform mixing, especially when burning at a low air ratio. There are drawbacks. (Here, the air ratio means the ratio of the amount of air used to the amount of air required to burn the fuel.) On the other hand, the combustion air is further divided into multiple stages to supply the fuel Some have tried to eliminate the non-uniformity of mixing with the combustion air, but the problem is that the supply system for combustion air is substantially increased, the structure is complicated and large, and the cost is increased. .

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a simple and low-cost structure, and yet to secure stable flame formation while reducing NOx. To burn fuel gas.

[0008]

The present invention for achieving the above object is constructed as follows for each claim. The structure of the invention according to claim 1 is a fuel using surface combustion, in which fuel gas and combustion air are supplied to one side of a porous body and combustion is performed on the other side that has passed through the porous body. In the gas combustion method, a mixture of fuel gas and combustion air is jetted through a first porous body to burn, and a fuel gas is passed through a second porous body provided on the downstream side of the first porous body, A combustion gas combustion method using surface combustion, characterized in that either combustion air or a mixture thereof is ejected.

According to a second aspect of the present invention, in the fuel gas combustion method using surface combustion according to the first aspect, the fuel gas ejected through the second porous body, combustion air, or One of these mixtures is characterized by being set to 10 to 30% with respect to the total amount of each of the first and second porous bodies ejected.

According to a third aspect of the present invention, the fuel gas and the combustion air are supplied to one side of the porous body so that the surface combustion is performed on the other side passing through the porous body. In the gas burner used, a first supply pipe for guiding a mixture of fuel gas and combustion air, a first porous body through which the mixture sent by the first supply pipe passes, fuel gas, combustion air, or A second supply pipe that guides one of these mixtures, a fuel gas that is provided on the downstream side of the first porous body and is sent by the second supply pipe, combustion air,
Alternatively, it is a gas burner using surface combustion having a second porous body through which any one of these mixtures passes.

According to a fourth aspect of the present invention, in the gas burner using surface combustion according to the third aspect, the first porous body has a cylindrical portion of the porous body and an inner hole of the cylindrical portion. A bottom plate of a porous body that closes one end of the second porous body, the second porous body is a tubular portion of the porous body, and is provided on the downstream side separately from the first porous body. Any of fuel gas, combustion air, or a mixture thereof ejected through the porous body, relative to the respective total amount ejected through both the first and second porous bodies,
It is characterized by being set to 10 to 30%.

According to a fifth aspect of the present invention, in the gas burner using surface combustion according to the third aspect, the first porous body is a disc of porous body having a central hole,
The second porous body is formed of a disc of a porous body, is separated from the first porous body and is provided on the downstream side, and
Any of fuel gas, combustion air, or a mixture thereof ejected through the porous body is 10 to 30 relative to the total amount ejected through both the first and second porous bodies. It is characterized by being set to%.

[0013]

In the present invention thus constructed, the mixture of fuel gas and combustion air is guided by the first supply pipe and supplied to one side of the first porous body. Next, the mixture is promoted to be mixed by passing through the first porous body, is uniformly ejected from the entire surface of the other surface of the first porous body, and is burned on the surface of the first porous body. And a primary flame is formed.

Further, either the fuel gas, the combustion air, or a mixture thereof is guided by the second supply pipe and supplied to one side of the second porous body, and the second porous body is supplied. It is uniformly ejected from the entire other surface through the body. Then, it is supplied onto the primary flame formed on the surface of the first porous body to form a secondary flame surface. Here, the secondary fuel gas ejected through the second porous body, the combustion air, or a mixture thereof is
It is set to 10 to 30% with respect to each total amount ejected through both the first and second porous bodies.

By carrying out surface combustion using such a porous body, a lean premixed combustion in which the fuel gas and air by the porous body are mixed and agitated and strengthened is ensured. As a result, the flame temperature is uniformly reduced and NOx is suppressed, and even at a low air ratio, a uniform and stable flame is formed from the entire surface, and NOx is further reduced. Moreover, the flame temperature is further lowered by the combustion in two stages, and the generation of NOx is further reduced.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of a gas burner using surface combustion according to an embodiment of the present invention.

As shown in FIG. 1, the gas burner 10 of this embodiment supplies fuel gas and combustion air to one side of a porous body and burns the other side after passing through the porous body. It is a gas burner that uses surface combustion to be performed.

The gas burner 10 includes a combustion air supply pipe 1 and a fuel gas supply pipe 2 coaxially arranged therein.
And have. A plurality of fuel gas supply holes 13 are formed in the vicinity of the downstream (left side in the figure) end of the fuel gas supply pipe 2. In this way, the fuel gas is supplied from the fuel gas supply hole 13 into the combustion air supply pipe 1, and the fuel gas and the combustion air are sufficiently mixed on the downstream side thereof. A mixing device 3 is provided in a direction perpendicular to the inner wall of the combustion air supply pipe 1. The mixer 3 is, for example, a porous disk having a central hole 3a, but is not limited to such a shape and material.

On the downstream side of the combustion air supply pipe 1, the first combustion air supply pipe 1 is integrally connected to the combustion air supply pipe 1.
A supply pipe 11 is provided. The mixture of the fuel gas and the combustion air mixed as described above is guided by the first supply pipe 11 and supplied to the outside of the first porous body 4.

The first porous body 4 is a cylindrical side surface combustion panel 4a as a cylindrical portion of the porous body, and a cylinder as a bottom plate of the porous body which closes one end of the inner hole of the cylindrical side surface combustion panel 4a. It consists of a bottom plate surface combustion panel 4b.

These surface burning panels 4a and 4b are ceramics or metal porous bodies, preferably porous bodies having a three-dimensional network structure and a high porosity (80 to 90%). Necessary conditions for the surface combustion panel are gas mixing and uniform ejection, heat resistance of the surface, and mechanical strength of the panel, and the optimum panel material is selected according to the usage conditions.

In the present embodiment, in particular, the second supply pipe 12 which is in communication with the fuel gas supply pipe 2 via the branch pipe 16 is provided. The second supply pipe 12 is provided so as to be coaxial with the first supply pipe 11 so as to cover the outer side thereof. Therefore, the fuel gas is supplied to the inner wall of the second supply pipe 12 and the first supply pipe 12. It is sent through between the outer wall of 11 and has a compact structure as a whole. In this way, the fuel gas is guided by the second supply pipe 12 and is supplied to the outer surface of the second porous body 6 as the tubular portion of the porous body.

The second porous body 6 is formed by the end plate 17 of the first supply pipe 11 on the downstream side of the first porous body in the burner axial direction.
It is provided so as to be separated from the porous body 4. The fuel gas guided by the second supply pipe 12 is the first porous body 4
The secondary flame is supplied as a secondary fuel gas on the gas flame formed on the inner surface of the burner tile 7, and a secondary flame surface is formed on the outlet side of the burner tile 7. Here, the secondary fuel gas G ₂ ejected through the second porous body 6 is 1 with respect to the total amount G _{T of the} fuel gas ejected through both the first and second porous bodies 4 and 6.
It is set to 0 to 30%.

As described above, the fuel system can be divided into two by only installing the partition in the single system of piping, and therefore, in the conventional two-stage combustion, substantially two burners are provided. However, two-stage combustion can be performed at a low cost with a simple structure. Then, by lowering the flame temperature by burning in two stages in this way, it is possible to further reduce the generation of NOx.

Here, a basic experiment was performed on a surface combustion burner alone (one-stage combustion of fuel and air) using a porous body, which is a characteristic configuration of the gas burner 10 according to the present embodiment. (FIGS. 2 to 5) will be described.

FIG. 2 is a graph showing the relationship between the combustion gas composition and the air ratio. The experimental condition in this case is fuel: LP
G, temperature: 1000 to 1100 ° C., porous body (surface combustion panel): 70 mm × 70 mm. From FIG. 2, it can be seen that the NOx concentration drops sharply at low air ratios.

FIG. 3 shows CO, CO under low air ratio combustion.
₂ is a graph showing _two concentrations. The experimental conditions in this case were as follows: fuel: LPG, temperature: 1000 to 1200 ° C., porous body (surface combustion panel): 130 mm × 130 mm. It can be seen from FIG. 3 that the CO and CO ₂ concentrations theoretically agree well up to the obtained air ratio of 0.55, and that the burner is completely combusted even under a low air ratio. Therefore, no soot is generated.

FIG. 4 is a graph showing the O ₂ concentration under low air ratio combustion. The experimental condition in this case is gas: CO
G, LPG, temperature: 850 to 1250 ° C. From FIG. 4, the O ₂ concentration shows an extremely low value of 20 ppm or less when the air ratio is 0.95 or less, and the premix (premix) type reducing burner A or the non-oxidizing burner B shown in the figure.
It can be seen that it is at the same level as.

FIG. 5 is a graph showing the gas composition distribution in the burner axis direction. The experimental conditions in this case are: furnace temperature: 1190
C, air ratio m: 0.8, gas: LPG. From FIG. 5, there is almost no change in each gas, and the combustion is completely combusted in a short distance, which is a characteristic of the premixed flame.

The present invention has conducted further earnest studies based on the finding that stable lean premixed combustion is ensured even at a low air ratio by surface combustion using such a porous body. The present invention has led to the realization of further suppression of NOx concentration in the gas burner.

Next, the operation of this embodiment will be described. When using the gas burner 10 of the present embodiment, the combustion air is sent from the supply port of the combustion air supply pipe 1,
It is sent toward the downstream side in the burner axial direction. On the other hand, the fuel gas is fed from the supply port of the fuel gas supply pipe 2, and is supplied into the combustion air supply pipe 1 from a plurality of fuel gas supply holes 13 formed in the vicinity of the downstream end of the fuel gas supply pipe 2. To be done. In this way, the fuel gas is mixed as the primary fuel gas G ₁ into the combustion air, and the both are sufficiently premixed by the action of the mixer 3 provided further downstream. The mixture of the fuel gas and the combustion air is supplied to the first supply pipe 11
And is supplied to the outside of the first porous body 4. Next, the mixture is further promoted to be mixed by passing through the first porous body 4, and is uniformly ejected from the entire inner surface of the first porous body 4 into the inner pores.
Combustion occurs on the inner surface of the to form a primary flame.

Further, the fuel gas is sent from the fuel gas supply pipe 2 to the second supply pipe 12 through the branch pipe 16, and the second gas is supplied to the second supply pipe 12.
It is guided by the supply pipe 12, is supplied to the outer surface of the second porous body 6, and is uniformly jetted inward from the entire inner peripheral surface through the second porous body 6. Then, it is supplied as secondary fuel gas on the primary flame formed on the inner surface of the first porous body 4, and a secondary flame surface is formed on the outlet side of the burner tile 7. Here, the secondary fuel gas G ₂ ejected through the second porous body 6 is 10 with respect to the total amount G _{T of the} fuel gas ejected through both the first and second porous bodies 4 and 6.
Set to ~ 30%.

By carrying out surface combustion using such a porous body, it is possible to secure lean premixed combustion in which the fuel gas and air by the porous body are agitated and strengthened. As a result, the flame temperature is uniformly reduced to suppress the generation of NOx, and even at a low air ratio, it is possible to form a uniform and stable flame from the entire surface.
Ox can be reduced. Moreover, the combustion temperature is further reduced by dividing the combustion into two stages and burning the NOx.
Can be further reduced. In addition, since the low air ratio combustion is easy, the turndown ratio (maximum heat input /
The minimum heat input can be as large as about 6.

FIG. 6 is a graph showing the gas composition distribution in the axial direction of the burner when the gas burner of this embodiment is used.
Here, NOx concentration indicates the value when changing the ratio to the fuel gas amount of secondary fuel gas (G ₂ / G _T) to _{0,10,30%, O 2, CO,} CO 2 concentration (G ₂
/ G _T) indicates the value when 0%.

Specifically, the combustion furnace (1.7 m × 2.0 m
The gas burner 10 of this example was installed on the side wall of 1.8 m in volume and about 6 m ³ in volume, and the combustion characteristics were measured. Further, the combustion conditions such as the fuel amount and the air ratio were changed, and the flame shape, in-furnace temperature distribution, combustion gas composition distribution, and NOx distribution were measured under steady conditions after about 3 hours. LP as fuel gas
Using G, combustion air was supplied so that the air ratio was 0.8 with respect to the total amount of fuel gas, and combustion was performed while maintaining the furnace temperature at 1190 ° C.

From FIG. 6, as the ratio (G ₂ / G _T ) of the secondary fuel gas to the total fuel gas increases, NOx increases.
It can be seen that the reduction effect is greatly exerted. However, the secondary fuel gas G _2, when (G ₂ / G _T) is increased to be larger than 30%, it becomes difficult to maintain the furnace temperature, therefore, the ratio of the fuel gas amount of secondary fuel gas ( G ₂ / G _T ) is preferably 30% or less.

FIG. 7 is a schematic sectional view of a gas burner using surface combustion according to another embodiment of the present invention. The same members as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof is partially omitted. According to the gas burner 20 of this embodiment, the primary fuel gas is supplied from the fuel gas supply hole 23 of the fuel gas supply pipe 2 into the air in the combustion air supply pipe 1. Then, the mixture of the fuel gas and the combustion air that has been sufficiently mixed and stirred in the mixer 3 is guided by the first supply pipe 11 to the first porous body 24 formed of a porous disc having a central hole. It is supplied and forms a primary flame through the first porous body 24. On the other hand, the secondary fuel gas is supplied by the fuel gas supply pipe 2 arranged on the burner shaft to the second porous body 26 formed of a porous disc provided at the downstream end, and the second fuel gas is supplied to the second porous body 26. The first porous body 2 passes through the porous body 26.
Supplied above the primary flame formed by 4. With this embodiment, the same effect as that of the above embodiment can be obtained.

As described above, the present invention utilizes the surface combustion by the porous body, and since the porous body is made of ceramics or metal, it can be easily molded, and the cylindrical body as in the above-mentioned embodiment. Panels can be formed into any shape such as a square shape (triangular shape, a square shape), a slit shape (elongated rectangular shape), a spherical shape, etc. Therefore, due to the flexibility of the shape of this porous body,
Flame formation of any shape is possible.

The above-described embodiments are described for facilitating the understanding of the present invention and not for limiting the present invention. Each disclosed element is intended to include all modifications belonging to the technical scope of the present invention.

For example, in the above-described embodiment, a part of the fuel gas is dividedly supplied and burned in two stages, but the present invention is not limited to this, and, for example, combustion air You may comprise so that a part may be dividedly supplied and burned in two steps. Furthermore, it is possible to divide and supply the mixture of the fuel gas and the combustion air to perform combustion in two stages.

[0041]

As described above, according to the present invention, since the surface combustion is performed using the porous body, the porous body enhances the mixing and stirring of the fuel gas and the combustion air. Lean premixed combustion can be secured. As a result, the flame temperature is uniformly reduced to suppress the generation of NOx, and even at a low air ratio, a uniform and stable flame can be formed over the entire surface, and NOx can be further reduced. Moreover,
By dividing the combustion in two stages and burning it, the flame temperature can be further lowered, and the generation of NOx can be further reduced. Further, since the low air ratio combustion is easy, a large turndown ratio can be adopted.

Further, by using the porous material, the supply system for fuel, air, etc. can be divided into two parts only by installing a partition in the piping of one system. Therefore, the conventional two-stage combustion is possible. However, in contrast to the fact that substantially two supply systems are required, two-stage combustion can be performed at a low cost with a simple structure. In addition, the flexibility of the shape of the porous body enables flame formation of any shape.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a gas burner using surface combustion according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a combustion gas composition and an air ratio in the case of a one-stage surface combustion burner.

FIG. 3 is a graph showing CO and CO ₂ concentrations under low air ratio combustion in the case of a single-stage surface combustion burner.

FIG. 4 is a graph showing O ₂ concentration under low air ratio combustion in the case of a single-stage surface combustion burner.

FIG. 5 is a graph showing a gas composition distribution in the burner axial direction in the case of a single-stage surface combustion burner.

FIG. 6 is a graph showing the gas composition distribution in the axial direction of the burner when the gas burner of this example is used.

FIG. 7 is a schematic sectional view of a gas burner using surface combustion according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Combustion air supply pipe, 2 ... Fuel gas supply pipe, 3 ... Mixer, 4,24 ... 1st porous body, 4a ... Cylindrical side surface combustion panel (cylindrical part), 4b ... Cylindrical bottom plate surface combustion panel (Bottom plate), 6, 26 ... Second porous body, 7 ... Burner tile, 10, 20 ... Gas burner, 11 ... First supply pipe, 12 ... Second supply pipe, 13, 23 ... Fuel gas supply hole, 16 ... Branch pipe, 17 ... End plate.

Claims (5)

[Claims] 1. A method of burning a fuel gas using surface combustion, in which fuel gas and combustion air are supplied to one side of a porous body, and combustion is performed on the other side that has passed through the porous body, The mixture of fuel gas and combustion air is used as the first porous material (4,2
4) through which it is jetted and burned, and through the second porous body (6, 26) provided on the downstream side of the first porous body (4, 24), fuel gas, combustion air, or a mixture thereof. A fuel gas combustion method using surface combustion, characterized in that any one of the above is ejected. 2. The fuel gas ejected through the second porous body (6, 26), combustion air, or a mixture thereof is used as the first and second porous bodies (4). , 6,2
4, 26) The method for burning fuel gas using surface combustion according to claim 1, wherein the amount is set to 10 to 30% with respect to each total amount ejected through both. 3. A gas burner using surface combustion in which fuel gas and combustion air are supplied to one side of a porous body and combustion is performed on the other side that has passed through the porous body. A first supply pipe (11) for guiding a mixture of working air, a first porous body (4, 24) through which the mixture sent by the first supply pipe (11) passes, fuel gas, combustion air , Or a second supply pipe (12) for guiding one of these mixtures, and a second supply pipe (1) provided on the downstream side of the first porous body (4, 24).
The second porous body through which the fuel gas sent by 2), the combustion air, or a mixture thereof passes.
A gas burner using surface combustion characterized by having (6, 26). 4. The first porous body (4) comprises a cylindrical portion (4a) of the porous body and a bottom plate (4b) of the porous body which closes one end of an inner hole of the cylindrical portion (4a). The second porous body (6) is composed of a tubular portion of the porous body, is separated from the first porous body (4) and is provided on the downstream side, and the second porous body (6) ) Is injected into the fuel gas, the combustion air, or a mixture thereof, with respect to the total amount of each of the first and second porous bodies (4, 6) ejected, The gas burner using surface combustion according to claim 3, which is set to 10 to 30%. 5. The first porous body (24) is made of a porous disk having a central hole, and the second porous body (26) is made of a porous disk, and One of the fuel gas, combustion air, or a mixture thereof, which is provided on the downstream side separately from the one porous body (24) and is jetted through the second porous body (26), is The gas burner using surface combustion according to claim 3, wherein the gas burner is set to 10 to 30% with respect to the total amount ejected through both the first and second porous bodies (24, 26).