JP2001124310A - Low nox combustion method and partial premixed gas low nox burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the further reduction of NOX, in a low NOX combustion method and a low NOX burner. SOLUTION: A film-form premixed air current is made in the downstream region of a premixed gas nozzle 9, using a partial premixing system of gas burner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a low NOx combustion method and a partially premixed gas low NOx burner.

[0002]

2. Description of the Related Art Conventionally, various proposals have been made to reduce harmful combustion exhaust gas in combustion equipment. However, recently, due to problems such as environmental pollution, reduction of NOx among harmful combustion exhaust gas has been particularly required. Attention is being directed. for that reason,
Many low-NOx combustion methods and low-NOx burners have been proposed in which a gaseous fuel containing less nitrogen is used as the fuel itself and thermal NOx (thermal NOx) is reduced in the combustion process. Further, in a burner that is used in a combustion space having a relatively small volume and requires a large output, such as a small-sized and simple-class boiler, it is difficult to reduce NOx. There is an increasing demand for combustion methods and low NOx burners.

[0003]

SUMMARY OF THE INVENTION The present invention provides a low NOx
In the combustion method and the low NOx burner, even lower NOx
Is to achieve

[0004]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and the invention according to claim 1 uses a partially premixed gas burner and uses a premixed gas injection port. It is characterized by forming a thin film premixed gas flow in the downstream area.

According to a second aspect of the present invention, a partially premixed gas burner is used to form a thin-film premixed gas stream in a downstream region of a premixed gas ejection port. It is characterized in that the secondary air for combustion is subdivided and ejected from the side.

According to a third aspect of the present invention, there is provided a fuel supply pipe for supplying fuel, a fuel supply pipe disposed on an outer periphery of the fuel supply pipe, and a fuel supplied from a fuel injection port provided in the fuel supply pipe. An inner cylinder that mixes the primary air, a premixed gas ejection port that ejects the mixed premixed gas, a thin film forming member that forms a thin film premixed gas flow downstream of the premixed gas ejection port, An outer cylinder disposed on the outer periphery of the inner cylinder and forming an annular flow path for secondary air for combustion between the outer cylinder and the outer wall of the inner cylinder, and a secondary air jet for combustion provided on the inner cylinder. It is characterized by that.

According to a fourth aspect of the present invention, the thin film forming member is disposed with a predetermined gap interposed between the thin film forming member and the inner cylinder.

Further, in the invention according to claim 5, the secondary air for combustion is subdivided from the secondary air jet for combustion into a thin premixed gas flow formed by the inner cylinder and the thin film forming member. And a small flame is formed from a portion where the secondary air for combustion and the premixed gas come into contact with each other.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A low NOx combustion method and a low NOx burner according to the present invention are implemented as a so-called partially premixed gas burner. In the low NOx combustion method according to the present invention, the secondary air for combustion is subdivided and ejected from a jet port into a premixed air in which a part of fuel and combustion air are premixed, and the premixed air and the combustion air are mixed. This is a combustion method in which a large number of small flames are formed in a portion where the secondary air comes into contact, and the surface area of the small flame is increased to lower the temperature of the small flame and reduce NOx. Further, the low NOx burner according to the present invention ejects a partial premixed airflow which is a mixture of primary air for combustion and fuel from the center side thereof, and ejects secondary air for combustion so as to surround the partial premixed airflow. It has a configuration. That is, the low NOx burner according to the present invention has an inner cylinder for ejecting a partially premixed airflow and an annular flow path for ejecting secondary air for combustion between the inner cylinder and the outer periphery of the inner cylinder. The outer cylinder is arranged substantially coaxially, and a thin-film forming member for forming a thin-film premixed airflow with a predetermined gap interposed between the outer cylinder and the inner cylinder is arranged at the tip of the inner cylinder.

[0010] According to this configuration, the fuel supplied from the fuel outlet provided in the fuel supply pipe and the primary air for combustion are mixed downstream of the primary air diffusion member disposed upstream of the fuel outlet, and the fuel is mixed. An annular premixed gas portion is formed between the outer wall of the supply pipe and the premixed gas sufficiently mixed in the annular premixed gas portion. The premixed gas flow passes through a predetermined gap, and has a thickness substantially equal to the thickness of the gap, and flows along the inner peripheral wall on the distal end side of the inner cylinder.

The secondary air for combustion is blown from the outside into the thin-film premixed airflow thus formed. This jet is subdivided into secondary air for combustion from a secondary air jet for combustion provided in the inner cylinder and is jetted toward the center of the burner. The secondary air jet for combustion is provided on the inner cylinder wall surface.
The secondary air jet for combustion is configured by arranging a number of small holes on the wall surface of the inner cylinder in order to form a number of jets at the tip of the inner cylinder. The arrangement of the small holes may be configured as a plurality of rows or a staggered arrangement. The shape of the small hole is a circle, a polygon, or the like, and is provided by piercing a steel plate or the like. Similarly, the means for subdividing the secondary air for combustion may be constituted by a punched metal plate, a wire mesh, or the like.

When the secondary air for combustion and the premixed gas are ignited by the igniting means arranged at a portion having an air ratio suitable for combustion, a small flame starts from the portion where the secondary air for combustion and the premixed gas come into contact with each other. To form When a small flame is formed by the ignition means, it burns off one after another, and a large number of small flames are formed. The large number of these small flames means that the flame surface area is increased, the flame is cooled, and no local high-temperature portion is generated, so that the thermal NOx can be reduced.
A large number of small flames with reduced thermal NOx merge into a flame, which is held at the tip of the burner and burns completely.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of a low NOx burner according to the present invention will be described in detail with reference to the drawings. Here, FIG. 1 is an explanatory sectional view showing an embodiment of a low NOx burner according to the present invention.

Now, the low NOx burner 1 shown in FIG.
An inner cylinder 2 for ejecting the partially premixed gas is provided inside the inner cylinder. On the outer peripheral side of the inner cylinder 2, an outer cylinder 4 forming an annular flow path 3 for ejecting secondary air for combustion between the inner cylinder 2 and the inner cylinder 2 is arranged substantially coaxially. The inner cylinder 2 and the outer cylinder 4
Are connected to an air duct 5 which is an air supply means. The air duct 5 is usually provided with a blower (not shown) on the upstream side. Inside the inner cylinder 2, a fuel supply pipe 6 is disposed substantially coaxially. This fuel supply pipe 6 is provided with fuel injection ports 7, 7,
... are formed. The position of each of the fuel injection ports 7 is such that the fuel and the primary fuel for combustion are located in an annular premixed air portion 15 which is an annular space formed between the fuel supply pipe 6 and the downstream side of the inner cylinder 2. The length is set so that the air and the air can be mixed uniformly. A primary air diffusing member 8 for diffusing the primary air for combustion is disposed upstream of each of the fuel outlets 7.

Further, a premixed gas injection port 9 is formed at the end of the fuel supply pipe 6 with a predetermined gap interposed between the fuel supply pipe 6 and the inner cylinder 2. At the tip of the fuel supply pipe 6, a disk-shaped thin film forming member 10 for forming a thin-film cylindrical pre-mixed gas flow in the downstream region of the pre-mixed gas jet port 9 is fixed. That is, the fuel supply pipe 6 holds the thin film forming member 10 at a predetermined position at the tip of the inner cylinder 2.

The thin film forming member 10 is located at the front end of the inner cylinder 2 in a state where the thin film forming member 10 is attached to the front end of the fuel supply pipe 6, but the positional relationship between the inner cylinder 2 and the thin film forming member 10 is set. Is as follows: First, the inner cylinder 2
Is located at a substantially central portion of the thin film forming member 10 in the axial direction. The relationship between the inner diameter of the inner cylinder 2 and the outer diameter of the thin film forming member 10 is based on
The outer diameter of 0 is slightly smaller than the inner diameter of the inner cylinder 2, and the gap formed by this difference constitutes the premixed gas outlet 9. Therefore, the thin film forming member 10 is disposed with a predetermined gap interposed between the thin film forming member 10 and the inner cylinder 2.

On the downstream side of the thin film forming member 10, an ignition means 11 and a flame detecting means 12 are arranged so as to penetrate the thin film forming member 10.

In the embodiment shown in FIG. 1, the inner cylinder 2 and the outer cylinder 4 are substantially flush with each other at the distal ends thereof. Is provided and shielded to form the annular flow path 3 for the secondary air for combustion. A large number of secondary air outlets for combustion 14, 14,... Communicating with the annular flow path 3 are formed in a staggered manner at the tip of the inner cylinder 2 within a predetermined width in the vertical direction. (See FIG. 2).

The amounts of the primary air for combustion and the secondary air for combustion are set as follows. That is,
The supply amount (flow rate) of the primary combustion air to the inner cylinder 2 is set to 0.4 to 0.8 of the total combustion air amount supplied to the burner 1.
Make it double. Here, the total amount of the primary air for combustion and the secondary air for combustion is an amount sufficient to burn the fuel.

The combustion operation of the low NOx burner having the above configuration will be described. First, primary air for combustion is supplied from the air duct 5 into the inner cylinder 2, and secondary air for combustion is supplied from the air duct 5 into the annular passage 3. In this state, when fuel is supplied from the fuel supply means (not shown) into the fuel supply pipe 6, the fuel is supplied from the fuel outlet 7 of the fuel supply pipe 6 to the space between the inner cylinder 2 and the fuel supply pipe 6. The fuel is jetted into the annular premixed gas portion 15 in the formed annular space, and is mixed with the primary air for combustion flowing in the inner cylinder 2 to form a partial premixed gas flow. Then, the partial premixed airflow is supplied to the inner cylinder 2 and the thin film forming member 10 at the distal end side of the inner cylinder 2.
Are ejected from the premixed gas ejection port 9 formed between the premixed gas and the premixed gas.

At this time, the flow direction of the partial premixed gas flow is regulated by the gap with the inner cylinder 2 according to the disk shape of the thin film forming member 10. It is ejected along the inner cylinder 2 in a state where the hollow thin film is formed in a substantially cylindrical shape. A large number of secondary air jets for combustion 14 and 1 provided in the inner cylinder 2 from the outside in the radial direction toward the thin-film cylindrical premixed gas flow.
From 4, the secondary air for combustion is subdivided and ejected.

When the secondary air for combustion and the premixed gas are ignited by the igniting means 11 arranged at a portion having an air ratio suitable for combustion, a small portion is formed from the portion where the secondary air for combustion and the premixed gas come into contact with each other. Forms a flame. When a small flame is formed by the igniting means 11, the flame burns one after another, and a large number of small flames are formed. The large number of these formed flames result in increased surface area, the flames are cooled, and no local hot spots are generated, thus reducing thermal NOx.

A large number of small flames having reduced thermal NOx merge into a flame, which is held at the tip of the burner 1 and completely burned. That is, the combustion with a large number of small flames increases the surface area of the small flames and prevents the formation of a local high-temperature region, thereby achieving low NOx.

[0024]

As described above, according to the present invention, the partial premixed airflow from the inner cylinder is jetted into a thin film by the thin film forming member, and the secondary air for combustion supplied from the annular passage is divided. By combining the small flames, combustion by a large number of small flames is performed, so that the surface area increases with respect to the volume of the small flames, and the heat radiation from the small flames is improved. Can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a development explanatory view illustrating a state in which a secondary air injection port for combustion is developed.

[Explanation of symbols]

 2 Inner cylinder 3 Annular flow path 4 Outer cylinder 6 Fuel supply pipe 7 Fuel ejection port 9 Premixed gas ejection port section 10 Thin film forming member 14 Secondary air ejection port for combustion

Claims (5)

[Claims] 1. A low NOx combustion method comprising forming a thin premixed gas flow downstream of a premixed gas outlet 9 using a partially premixed gas burner. 2. Using a partially premixed gas burner, a thin film premixed gas flow is formed downstream of the premixed gas injection port 9, and a secondary combustion gas is directed from the outside toward the thin film premixed gas flow. A low NOx combustion method, characterized in that air is segmented and jetted. 3. A fuel supply pipe 6 for supplying fuel, and fuel and primary air for combustion, which are arranged on the outer periphery of the fuel supply pipe 6 and are supplied from a fuel injection port 7 provided in the fuel supply pipe 6. , A premixed gas ejection port 9 for ejecting the mixed premixed gas, and a thin film forming member 10 for forming a thin film premixed gas flow downstream of the premixed gas ejection port 9
And an outer cylinder 4 arranged on the outer periphery of the inner cylinder 2 and forming an annular flow path 3 for secondary air for combustion between the outer cylinder 4 and the outer wall of the inner cylinder 2.
A partial premixed gas low NOx burner, comprising: a secondary air injection port for combustion 14 provided in the inner cylinder 2. 4. The partially premixed gas low NOx burner according to claim 3, wherein the thin film forming member is disposed with a predetermined gap interposed between the thin film forming member and the inner cylinder. 5. A secondary air for combustion is subdivided and jetted from the secondary air jet for combustion 14 into a thin premixed airflow formed by the inner cylinder 2 and the thin film forming member 10,
5. The partially premixed gas low NOx burner according to claim 3, wherein a small flame is formed from a portion where the secondary air for combustion and the premixed gas are in contact with each other.