JP2013178013A - Radiant tube burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiant tube with a configuration to simultaneously achieve reduction of heat discharged outside a radiant tube system as much as possible, and suppression of NOx generation by lowering a flame temperature of a burner by lowering a preheated air temperature after heat exchange.SOLUTION: A radiant tube burner provided with a tube body that projects from an inner wall of a furnace to the inside of the furnace has a burner on one end side of the tube body, and a heat exchanger on the other end side. A porous air permeable solid in which exhaust air can be distributed is disposed on an exhaust air introduction side of the heat exchanger. The air permeable solid is disposed downstream of the exhaust air relative to the inner wall of the furnace.

Description

  The present invention relates to a radiant tube burner used for indirectly heating an object such as a steel plate or steel material in a heat treatment furnace or the like, and in particular, an exhaust gas after combustion gas from a burner that burns fuel with air is used for heating. Further, the present invention relates to a radiant tube burner including a heat exchanger that recovers the heat of the exhaust gas by exchanging heat with air introduced into the burner.

Since the radiant tube burner indirectly heats the object, it is difficult to effectively use the combustion heat, and a lot of heat is discharged to the outside of the system. Therefore, it is common to collect exhaust heat via a heat exchanger.
For example, Patent Document 1 provides a partition wall made of a breathable solid, converts gas sensible heat passing through the partition wall into radiant heat, and adds radiant heat to the radiant tube and the heat exchanger, It is described that the heat transfer performance of the radiant tube and the heat recovery rate of the heat exchanger are improved.

  Patent Document 2 describes that by providing a heat exchange tube and forming a plurality of exhaust passages, two-stage air preheating by exhaust is possible, and the exhaust heat recovery rate is improved.

Japanese Patent Publication No.62-35013 JP 2006-29638 A

  In the radiant tube described in Patent Document 1, since the partition wall and the heat exchanger are arranged inside the furnace from the furnace wall, the heat of the burner combustion gas (effective heat) to be added to the tube portion in the furnace system Is partially extracted by the partition wall and the heat exchanger, and the thermal efficiency of the radiant tube is eventually lowered.

  The technique described in Patent Document 2 is focused on improving the recovery rate of the heat discharged to the outside of the furnace system and cannot reduce the outflow of the effective heat to the outside of the furnace system. On the other hand, although the exhaust heat recovery efficiency is improved, the combustion preheated air temperature supplied to the burner rises accordingly, so the flame temperature of the burner that burns using this preheated air also rises. . This increase in flame temperature leads to an increase in the amount of NOx generated.

  Therefore, the object of the present invention is to reduce the heat released to the outside of the radiant tube as much as possible, to lower the preheated air temperature after heat exchange and lower the flame temperature of the burner to suppress the generation of NOx, It is providing the radiant tube which has the structure for implement | achieving simultaneously.

  The inventors diligently investigated the means for solving the above-mentioned problems, and found that it is effective to appropriately install a breathable solid that shields radiant heat from the radiant tube system and sensible heat in the exhaust. As a result, the present invention has been completed.

That is, the gist configuration of the present invention is as follows.
(1) A radiant tube burner having a tube body protruding from the inner wall of the furnace into the furnace, having a burner on one end side of the tube body and a heat exchanger on the other end side, the heat exchanger A permeable tube that is porous and capable of circulating an exhaust gas is disposed on the exhaust introduction side of the exhaust gas, and the air permeable solid is disposed on the downstream side of the exhaust gas from the inner wall of the furnace. Burner.

(2) The radiant tube burner according to (1), wherein the breathable solid has the same end surface shape as a cross section orthogonal to the axial direction of the radiant tube.

(3) The radiant tube burner according to (1) or (2), wherein a plurality of the air-permeable solids are arranged.

(4) The breathable solid disposed on the exhaust upstream side among the plurality of breathable solids disposed has a lower density than the breathable solid disposed on the exhaust downstream side. Radiant tube burner.

(5) The radiant tube burner according to any one of (1) to (4), wherein the breathable solid is made of ceramics.

  According to the present invention, since the air-permeable solid and then the heat exchanger are arranged downstream of the inner wall surface of the furnace, it is possible to reduce the effective heat discharged outside the furnace system into the furnace, Further, it is possible to avoid the heat exchanger taking away effective heat. Therefore, the heat from the burner of the radiant tube can be effectively utilized in the system, and the preheated air temperature after heat exchange can be lowered to lower the flame temperature of the burner, thereby suppressing the generation of NOx.

It is a figure which shows the structure of the radiant tube burner of this invention. It is a figure which shows the radiation state in the air permeable solid provided in an exhaust path.

The radiant tube burner of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a radiant tube burner according to the present invention.
In the figure, reference numeral 1 denotes a burner of the radiant tube 2. In the burner 1, a flame formed by introducing air and burning fuel is discharged from the flame nozzle 1 a. Combustion gas accompanying the formation of the flame is supplied to the heat treatment furnace through the tube body 2a of the radiant tube 2 and then introduced into the heat exchanger 4 from the tube body 2a as the exhaust 3.

  The exhaust gas 3 introduced into the heat exchanger 4 is heat-exchanged in the heat exchanger 4 with the air 6 introduced into the heat exchanger 4 separately from the exhaust gas 3. The heat removal exhaust after the heat exchange in the heat exchanger 4 is discharged out of the system through an appropriate pipe. On the other hand, the preheated air 6a after heat exchange in the heat exchanger 4 is supplied to the burner 1 and contributes to combustion of fuel here.

  In the radiant tube burner described above, the air-permeable solid 5 a that is porous and capable of circulating the exhaust gas is installed in the introduction path 5 of the exhaust gas 3 leading to the heat exchanger 4. The breathable solid 5a absorbs the heat from the burner 1 of the radiant tube before reaching the heat exchanger 4, and prevents the radiant heat from the burner 1 of the radiant tube from reaching the heat exchanger 4 directly. In order to increase the effective heat into the furnace by refluxing into the radiant tube.

  The breathable solid 5a is a porous breathable solid having a predetermined thickness, and the radiant heat released from the burner 1 of the radiant tube and the sensible heat of the exhaust are shielded by the breathable solid 5a. Directly reaching the heat exchanger 4 can be avoided. In the air-permeable solid 5a that has received the radiant heat and the exhaust sensible heat, a temperature gradient as shown by a two-dot chain line in FIG. 2 is generated due to the shielding effect. That is, the radiant heat and exhaust sensible heat are converted to radiant heat in the breathable solid 5a and released to the exhaust upstream side and the exhaust downstream side, respectively, but the radiant heat to the exhaust downstream side is the thickness of the breathable solid 5a. Since it is shielded and attenuated accordingly, most of it is discharged upstream of the exhaust. Thus, the exhaust from the burner 1 passes through the air-permeable solid 5a with a significant temperature drop and flows toward the heat exchanger 4 side. Therefore, the exhaust gas supplied to the heat exchanger 4 has a low temperature, and the usage environment of the heat exchanger 4 is improved. As a result, the heat recovery performance can be maintained for a long time. On the other hand, the preheated air that has recovered the heat from the exhaust gas in the heat exchanger 4 has a lower temperature than before, so the temperature of the flame in the burner 1 is reduced and NOx generation can be suppressed. . Further, since the exhaust gas passes through the porous air-permeable solid 5a, a rectifying effect is obtained, and a uniform flow of exhaust gas is guided to the heat exchanger 4, so that the heat exchange efficiency can be improved.

  Here, as shown in FIG. 1, it is essential that the breathable solid 5 a be disposed on the exhaust downstream side of the inner wall of the heat treatment furnace in which the radiant tube 2 is installed, that is, the inner surface of the furnace wall 7. That is, since the breathable solid 5a and then the heat exchanger 4 are disposed downstream of the inner wall of the furnace, the radiant heat from the tube body 2a and the sensible heat of the exhaust are sufficiently consumed in the furnace, Heat is shielded by the air-permeable solid 5a on the inner wall of the furnace or outside the furnace system, and then heat exchange is performed in the heat exchanger 4. Therefore, it is possible to reduce the effective heat that has been exhausted outside the heat treatment furnace system in the past, and it is possible to prevent the heat exchanger 4 from taking away the effective heat more than necessary.

  Further, when the exhaust gas 3 passes through the porous air-permeable solid 5a, dust in the exhaust gas is removed, and dust adherence in the heat exchanger 4 is prevented. Can be suppressed.

  As for the arrangement of the breathable solid 5a and the heat exchanger 4, as shown in FIG. 1, the breathable solid 5a is arranged so as to be flush with the inner wall 7 of the heat treatment furnace in which the radiant tube 2 is installed. It is recommended that the vessel 4 be disposed outside or outside the furnace wall from the viewpoint of improving thermal efficiency.

  The predetermined thickness given to the air-permeable solid 5a is a thickness that can be optically shielded, specifically 10 mm or more, preferably 20 to 60 mm.

  Moreover, it is advantageous that the air-permeable solid 5a has the same end surface shape as the cross section orthogonal to the axial direction of the radiant tube. That is, when the air-permeable solid 5a is disposed in the introduction path 5 of the exhaust gas 3, there is no gap between the inner surface of the radiant tube and all of the exhaust gas 3 passes through the air-permeable solid 5a, 3 is reliably reduced into the furnace system through the breathable solid 5a.

Further, in FIG. 1, two of the breathable solids 5a are arranged apart from each other, but it is needless to say that one breathable solid 5a may be provided. By arranging a plurality, the effects of the above-described thermal reduction and rectification can be further enhanced, and it is effective to perform a plurality of additions in relation to the installation location.
For example, when arranging a plurality of breathable solids 5a, a low-density breathable solid 5a is disposed on the exhaust upstream side to form a heat shield, and a high-density breathable solid 5a is disposed on the exhaust downstream side. By ensuring the filter function, when a large amount of dust is contained in the exhaust gas, it is possible to make maintenance easier by replacing the breathable solid 5a on the exhaust downstream side as a filter.

The breathable solid 5a is not only silicon carbide and silicon nitride, but also boron nitride, alumina, silica, magnesia, zirconia, titania, hafnia, yttria, lantana, etc., and mullite and cordierite obtained by mixing them at an appropriate ratio. From the viewpoint of ensuring high-temperature durability, it is preferable to use ceramics having high durability such as rare earth oxide-stabilized zirconia.
Further, the pore diameter of the air-permeable solid 5a is a size that can have both shielding properties and air-permeability, and is specifically preferably 20 mmφ or less, more preferably 0.5 mmφ to 4 mmφ.

1 Burner 1a Flame nozzle 2 Radiant tube 2a Unheated exhaust introduction path 3 Exhaust 4 Heat exchanger 5 Path 5a Breathable solid 6 Air 6a Preheated air 7 Furnace wall

Claims (5)

  A radiant tube burner having a tube main body protruding from the inner wall of the furnace into the furnace, having a burner on one end side of the tube main body, and a heat exchanger on the other end side, the exhaust of the heat exchanger A radiant tube burner characterized in that a porous air-permeable solid capable of circulating an exhaust gas is disposed on the inlet side of the exhaust gas, and the air-permeable solid is disposed downstream of the exhaust wall from the furnace inner wall.   2. The radiant tube burner according to claim 1, wherein the breathable solid has the same end surface shape as a cross section orthogonal to the axial direction of the radiant tube.   The radiant tube burner according to claim 1 or 2, wherein a plurality of the breathable solids are arranged.   4. The radiant tube burner according to claim 3, wherein among the plurality of breathable solids arranged, the breathable solid arranged on the exhaust upstream side has a lower density than the breathable solid arranged on the exhaust downstream side.   The radiant tube burner according to any one of claims 1 to 4, wherein the air-permeable solid is made of ceramics.

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