JPS5892703A - Combustion apparatus - Google Patents

Abstract

PURPOSE:To decrease the generation rate of NOx during the primary combustion, as well as the secondary combustion, by lowering the temperature of primary combustion gas, by converting sensible heat of the primary combustion gas into radiant heat, by permeating the gas through a gas-permeable inner tube, provided in a combustion tube. CONSTITUTION:The primary combustion gas is fed into an inner tube 6 from a primary combustion chamber 8, permeating through the wall of an inner tube 6 as shown by arrow signs X. During this time, the inner tube 6, of which substantial surface area is large, is efficiently heated up to high temperature, which is as close as to the temperature of the primary combustion gas, by convection heat transfer. Then, the primary combustion gas is fed into a secondary combustion chamber 14, passing through the inner tube 6, being lowered its temperature by being deprived the sensible heat of the gas by a tube 4 by heat radiation. With such an arrangement, generation of NOx is suppressed during the primary combustion, because the resident time of the primary combustion gas in high temperature zone is shortened. Besides, the temperature of the gas is lowered by the secondary air, being fed from the secondary air feeding tube 15, during the secondary combustion, so that the rate of generation of NOx in the secondary combustion is made low, as well.

Description

[Detailed description of the invention] This invention relates to a combustion device.

Radiant tubes generally used in heat treatment furnaces, etc.
A burner is installed at the end of the tube, and the tube is heated by the high-temperature combustion gas obtained by burning fuel within the tube, so NOx (nitrogen oxides) are generated in the high temperature part of the flame of the burner. is likely to occur. So low N
Attempts were made to adopt a two-stage combustion burner, which is a type of oxidizing burner.

I'm here. This burner performs primary combustion of fuel by reducing the amount of air in the primary combustion chamber than the theoretically required amount of air,
The resulting primary combustion gas is supplied with the insufficient amount of air in the secondary combustion chamber to cause secondary combustion and complete combustion. Although this is intended to reduce the maximum flame temperature and suppress the generation of NOx, it has been difficult to achieve a sufficient reduction in Nqx.

This invention has been made in view of the above points, and is intended to provide a combustion device that can achieve a significant reduction in NOx.

The present invention will be described in detail with reference to FIGS. 1 and 2.

In the figure, 1 is a heating chamber of a heating furnace, 2 is a furnace wall, 3 is a radiant tube that is attached through the furnace wall, and 4 is a tube made of heat-resistant cast steel, which is the main body. Reference numeral 5 indicates a fuel conduit, and reference numeral 6 indicates an inner cylinder, both of which are disposed within the tube 4 concentrically with the tube. The inner cylinder 6 is made of a heat-resistant material such as metal or ceramic and formed into a cylindrical shape with an appropriate thickness by molding a heat-resistant material such as a mesh, honeycomb, perforated, or porous shape. 1. The substantial surface area in contact with the passing gas is sufficiently large. be. The inner cylinder 6 is provided in the inside of the heating chamber 1 of the tube 4, that is, at a position corresponding to the heating surface of the object to be heated, 7 is a seal ring provided between the tip of the inner cylinder 6 and the tube 4, and 8 is a seal ring. This is an annular primary combustion chamber formed between the inner cylinder 6 and the tube 4. Also 9
1 is a partition wall that partitions the inside of the inner cylinder 6 and the inside of the fuel conduit 5, IO is a plurality of fuel injection holes bored in the peripheral wall at the end of the fuel conduit 5, 11 is a fuel supply pipe communicating with the inside of the fuel conduit 5, and 12 is a fuel The inlet is connected to a fuel gas supply source (not shown). Further, 13 is a primary air inlet into the primary combustion chamber 8. A secondary combustion chamber 14 is formed in the tube 4 of the exhaust gas flow 1 from the inner cylinder d, and communicates with the inner cylinder 6. A secondary air supply pipe 15 is provided through the end wall of the tube 4 and the partition wall 9, and its tip is open toward the primary combustion chamber 84.
6 is the secondary air inlet.

In the apparatus configured as described above, fuel gas is supplied to the fuel inlet 12, secondary air for combustion and secondary air are supplied to the respective air inlets 13 and 16, and the secondary air and the fuel nozzle 10 are supplied.
When the mixture with the fuel gas flowing out is ignited by an ignition device (not shown), the fuel gas undergoes primary combustion (incomplete combustion) in the primary combustion chamber 8 using primary air that is less than the theoretically required air amount. The obtained primary combustion gas flows from the primary combustion chamber 8 through the wall surface of the inner cylinder 6 and into the inner cylinder 6 as shown by the arrow X in FIG. The inner cylinder 6 is efficiently heated to a high temperature close to the wet layer of the primary combustion gas by convection heat transfer, and the secondary combustion gas is heated to a high temperature close to the wet layer of the primary combustion gas.
Sensible heat is removed by heat radiation from the tube 4 to the tube 4, the temperature becomes low, and the temperature flows into the secondary combustion chamber 14 through the inner cylinder 6. Therefore, by shortening the residence time of the secondary combustion gas in the high temperature region, the generation of NOx in the primary combustion is suppressed, and the combustion temperature during secondary combustion is lowered by the secondary air from the secondary air supply pipe 15. Therefore, NOx in secondary combustion
The amount of generation is also small. On the other hand, since the heated inner cylinder 6 is a solid and has a much greater radiation emitting capacity than a gas, it radiates a large amount of radiation heat to the tube 4 and directly raises the temperature of the tube.

Furthermore, the unburned content in the primary combustion gas passing through the wall of the cylinder is heated almost uniformly by the radiant heat of the inner cylinder 6, and complete combustion can be achieved even if the excess oxygen ratio in the secondary combustion is low. The amount of NOx generated during secondary combustion is further suppressed.

As described above, through the action of converting the sensible heat of the primary combustion gas into radiant heat by the air permeable inner cylinder 6, reduction in NOx is achieved mainly by lowering the temperature of the primary combustion gas, but the inner surface of the inner cylinder 6 And/or if an active component such as platinum or palladium that acts as a NOx reduction catalyst is supported on the outer surface or the entire inner cylinder 6 to form a NOx reduction catalyst layer in the inner cylinder 6, the NOx generated by the secondary combustion can be reduced. Since it is reduced to N2 gas when passing through the inner cylinder 6, the overall amount of NOx generated can be further reduced.

It is possible to do this.

Next, FIG. 3 shows the results of the inventor's experiment (measured NO concentration in the exhaust gas of the radiant tube) using the radiant tube having the above configuration (178 kaku, 2000 twins in the furnace). The inner cylinder 6 is made of stainless steel wire mesh (wire diameter I
Curve D1 is the case where a catalyst layer is not formed on the inner cylinder 6, and NO is when a platinum-based metal is supported on the outer surface of the inner cylinder 6.
The case where the x reduction catalyst layer is formed is shown by curve D2. Curve D'' shows the case where a normal two-stage combustion burner is used.

As is clear from the figure, the NO concentration in the case of the present invention is significantly reduced by 50 to 60% of that in the case of using a conventional two-stage combustion burner at a furnace temperature of 900 DEG C., for example.

Although the present invention has been described above in the case where it is applied to a radiant tube, the present invention can also be applied to other combustion devices such as burners for various uses. Further, the tube 4 can be made of various materials such as heat-resistant steel, ceramics, and refractories.

As explained above, according to the present invention, the sensible heat of the primary combustion gas is converted into radiant heat by the air permeable inner cylinder provided in the tube, so that the primary combustion and The amount of NOx generated during secondary combustion is suppressed, and the tube is heated by radiation heat transfer from the inner cylinder, and secondary combustion heat can be efficiently radiated and effectively used to heat the tube. In addition, by forming a reduction catalyst layer on part or all of the high part, even lower N
Oxification can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical cross-sectional view of a radiant tube showing an embodiment of the present invention, and FIG. 2 is a NO concentration diagram in exhaust gas of the radiant tube. 3...Radiant tube, 4...Tube, 5...
... Fuel conduit, 6... Inner cylinder, 8... Secondary combustion chamber, 1
0... Fuel injection hole, 11... Fuel supply pipe, 14...
- Secondary combustion chamber, 15... secondary air supply pipe. Applicant: Daido Steel Co., Ltd. Agent: Yu Inui

Claims (1)

[Claims] 1. A cylinder having ventilation is provided in the tube, an annular primary combustion chamber is formed between the tube and the inner cylinder, and fuel and primary air are supplied to the secondary combustion chamber. A fuel supply path and a primary air supply path are provided for supplying the air, and the space inside the tube on the exhaust gas port side from the inner cylinder is used as a secondary combustion chamber, and the secondary combustion chamber is communicated with the inside of the cylinder. A combustion device comprising a secondary air supply path for supplying secondary air to the combustion equipment. 2. A fuel supply path for supplying fuel and primary air to the secondary combustion chamber by providing an inner cylinder with ventilation inside the tube to form an annular primary combustion chamber between the tube and the inner cylinder. and a primary air supply passage is provided, the space within the tube on the exhaust gas outlet side of the inner cylinder is used as a secondary combustion chamber, and the secondary combustion chamber is communicated with the inner cylinder, and secondary air is supplied into the secondary combustion chamber. In addition to providing a secondary air supply path that supplies
A combustion device comprising a NOx reduction catalyst layer formed in the inner cylinder.