JP2007032886A - Single end radiant tube burner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single end radiant tube burner capable of restraining NOx from being generated while having compactness. <P>SOLUTION: The single end radiant tube burner 1 includes, in a single end radiant tube 3 closed at one end 31, a gas lead-in tube 4 for leading combustion gas 71; a gas nozzle 41 disposed at the tip of the gas lead-in tube 4 to jet the combustion gas 71; an upstream inner tube 5 disposed to surround the gas lead-in tube 4 to lead combustion air 72; a tapered jet nozzle 51 extended from the tip of the upstream inner tube 5 and reduced in diameter ahead of a gas nozzle; and a downstream inner tube 6 disposed with a clearance between itself and the jet nozzle 51. The downstream inner tube 6 has inner diameter shape of directly or indirectly connecting a contracted part 61 reduced in diameter from the upstream end toward the lower reaches, and an enlarged part 62 enlarged in diameter toward the lower reaches. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a single end radiant tube burner capable of recirculating exhaust gas inside a single end radiant tube.

  Conventionally, a single end radiant tube burner is known as a burner used in industrial indirect heating such as carburizing. This single-end radiant tube burner performs combustion by mixing combustion air that is ejected through the burner body and combustion gas that is ejected from a gas pipe disposed on the inner peripheral side of the burner body. Then, the combustion gas is passed through a single end radiant tube connected to the burner body and heated by radiant heat from the single end radiant tube.

As shown in FIGS. 4 and 5, the conventional single-end radiant tube burner 9 has a radiant tube 97 whose one end (tip) 971 is closed, the inflow of combustion air 81 and combustion gas 82, and exhaust gas 89. Is a double tube structure that can be released in the vicinity of the other end (rear end) 972 of the radiant tube 97.
That is, the single-end radiant tube burner 9 includes a gas introduction pipe 94 extending from the burner body 92, a nozzle 95 provided at the tip thereof, and an inner pipe 96 provided so as to surround a flame 88 formed further ahead. The radiant tube 97 is provided as an outer tube surrounding the inner tube 96. The flame 88 formed in the inner pipe 96 makes a U-turn as exhaust gas, passes between the inner pipe 96 and the outer pipe (radiant tube 97), returns to the burner body 92 side, and burns as exhaust gas 89. It is configured to be discharged from the body 92 to the outside.

By the way, the single-end radiant tube burner having such a structure is required to suppress NOx (nitrogen oxide) emission as much as possible as in the case of burners having other structures.
Therefore, an external exhaust gas recirculation method in which an exhaust gas recirculation device 99 is installed outside the burner for reducing NOx has been reported (Patent Document 1).
However, when these external exhaust gas recirculation methods are adopted, there is a problem that the structure of the entire burner is increased by the amount of the exhaust gas recirculation device provided outside and the compactness is impaired.

Japanese Patent Application Laid-Open No. 07-217828

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a single-end radiant tube burner that has compactness and can suppress the generation of NOx.

The present invention is a single end radiant tube burner configured to emit a flame in a single end radiant tube closed at one end.
A gas introduction pipe for guiding combustion gas;
A gas nozzle that ejects the combustion gas disposed at the tip of the gas introduction pipe;
An upstream inner pipe that is disposed so as to surround the gas introduction pipe and guides combustion air;
A tapered ejection nozzle extending from the tip of the upstream inner pipe and having a diameter reduced in front of the gas nozzle;
Built in the single-end radiant tube with a downstream inner pipe disposed with a gap between the ejection nozzle,
The inner diameter shape of the downstream inner pipe has a shape in which a contracted portion that decreases in diameter as it goes downstream from its upstream end and a shape in which an expanded portion that increases in diameter as it goes downstream is connected directly or indirectly. The single end radiant tube burner is characterized (claim 1).

  The single-end radiant tube burner (hereinafter simply referred to as a burner) of the present invention has a structure in which the upstream inner pipe and the downstream inner pipe are separated from each other inside the single-end radiant tube (hereinafter simply referred to as a radiant tube). An inner pipe is provided. Therefore, the basic gas flow is that a mixture of combustion air and combustion gas flowing in the upstream inner pipe becomes a flame in the downstream inner pipe, and then the flame makes a U-turn as exhaust gas, and the upstream inner pipe And go through the radiant tube.

  Here, in the present invention, a jet nozzle is provided at the tip of the upstream inner pipe, and the jet nozzle has a tapered diameter in front of the gas nozzle. Therefore, it is possible to increase the flow rate of the air-fuel mixture during the combustion process and eject the mixture toward the downstream inner pipe.

  In addition, a gap is provided between the jet nozzle and the downstream inner pipe as described above. Thereby, combined with the effect of increasing the air-fuel mixture flow velocity due to the presence of the ejection nozzle, an action of taking a part of the exhaust gas that has passed between the downstream inner pipe and the outer pipe into the downstream inner pipe. Can be created.

  Moreover, the said downstream inner pipe has an internal diameter shape which connected directly or indirectly the shrinkage | contraction part diameter-reduced as it goes downstream from the upstream end, and the expansion part which diameter-expands as it goes downstream. Therefore, the pressure decreases and the flow velocity increases in the contraction portion, and the pressure and the flow velocity recover in the expansion portion. Therefore, the entrainment of the exhaust gas in the gap between the ejection nozzle and the downstream inner pipe can be further promoted.

Thus, in the present invention, the exhaust gas can be recirculated inside the radiant tube. By realizing this recirculation, NOx in the exhaust gas finally discharged to the outside can be greatly reduced as compared with the conventional case. Therefore, it is not necessary to provide an exhaust gas recirculation device as conventionally proposed.
Therefore, according to the present invention, a burner having compactness and capable of suppressing the generation of NOx can be obtained.

  As described above, the burner of the present invention has an ejection nozzle that extends from the upstream inner pipe and has a diameter reduced in a tapered shape in front of the gas nozzle. The degree of diameter reduction (taper) of the ejection nozzle is preferably set so as to be inclined in the range of 20 to 30 ° with respect to the axial direction. If the degree of diameter reduction is less than 20 °, the effect of increasing the air-fuel mixture flow rate in the combustion process may be reduced, while if it exceeds 30 °, the pressure loss may be too large.

  Moreover, it is preferable that the contraction part of the said downstream inner pipe is set so that the degree of the diameter expansion (taper) may incline in the range of 10-20 degrees with respect to an axial direction. If the degree of diameter expansion is less than 10 ° and exceeds 20 °, the exhaust gas may not be sufficiently sucked.

The inner diameter of the downstream inner tube is preferably such that a flat portion having a constant diameter is interposed between the contracted portion and the enlarged portion.
In this case, it is possible to obtain an effect that the exhaust gas flowing between the downstream inner pipe and the outer pipe in the gap between the ejection nozzle and the downstream inner pipe can be promoted.

It is preferable that the outer diameter shape of the downstream inner pipe has an outer taper portion whose diameter increases from the upstream end toward the downstream side.
In this case, there is an effect that the exhaust gas flowing between the downstream inner pipe and the outer pipe can be easily caught inside the downstream inner pipe.
Moreover, it is preferable to set the external taper part of the said downstream inner pipe so that the degree of the diameter expansion (taper) may incline in the range of 5-20 degrees with respect to an axial direction. If the degree of diameter expansion is less than 5 ° or more than 20 °, the exhaust gas may not be sufficiently sucked.

Hereinafter, embodiments of the single-end radiant tube burner 1 (hereinafter simply referred to as burner 1) of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the burner 1 of this example is configured to emit a flame 78 in a single-ended radiant tube 3 (hereinafter simply referred to as a radiant tube 3) whose one end (tip) 31 is closed. Yes.

  The burner 1 is disposed so as to surround the gas introduction pipe 4 that guides the combustion gas 71, the gas nozzle 41 that ejects the combustion gas 71 disposed at the tip of the gas introduction pipe 4, and the gas introduction pipe 4. An upstream inner pipe 5 that guides the combustion air 72, a tapered ejection nozzle 51 that extends from the tip of the upstream inner pipe 5 and has a diameter reduced in front of the gas nozzle 41, and between the ejection nozzle 51 The radiant tube 3 includes a downstream inner pipe 6 disposed with a gap therebetween.

  The inner diameter shape of the downstream inner pipe 6 is a shape in which a contracted portion 61 that decreases in diameter as it goes downstream from its upstream end and an enlarged portion 62 that increases in diameter as it goes downstream are connected by a flat portion 63 having a constant diameter. Have

This will be described in detail below.
As shown in FIG. 1, the burner 1 of this example has a burner body 2 having a gas inlet 21, an air inlet 22, and an exhaust gas outlet 29, and a radiant tube 3 and the like are disposed on the burner body 2. .
The gas introduction pipe 4 is connected toward the axial direction of the burner body 2 so as to communicate with the gas introduction port 21 that guides the combustion gas 71. The upstream inner pipe 5 is disposed so as to cover the outer peripheral side of the gas introduction pipe 4 so as to communicate with the air introduction port 22 that guides the combustion air 72. The radiant tube 3 is connected to the inner peripheral side of the burner body 2 in the axial direction of the burner body 2 so as to cover the outer peripheral side of the upstream inner tube 5.

  An inner tube having a structure separated into an upstream inner tube 5 and a downstream inner tube 6 is provided inside the radiant tube 3. The downstream inner pipe 6 is provided with a gap between the jet nozzle 51 and is inserted into the inner peripheral side of the radiant tube 3. Specifically, the downstream inner pipe 6 is fixed in a state where a gap is provided between them by connecting the tip of the upstream inner pipe 5, that is, the discharge nozzle 51 and the downstream inner pipe 6, with a coupling tool (not shown). It is.

A first exhaust passage 32 through which the exhaust gas 79 passes is formed between the downstream inner pipe 6 and the radiant tube 3, and between the upstream inner pipe 5 and the outer pipe radiant tube 3. The second exhaust passage 33 through which the exhaust gas 79 passes is formed.
A spark plug 42 used for ignition is provided inside the gas introduction pipe 4.

  Moreover, in this example, as shown in FIG. 2, the ejection nozzle 51 has a tapered shape that decreases in diameter as it goes forward as described above. The degree of this diameter reduction (taper) was set so that the angle α with respect to the axial direction was 27 °.

  Further, as described above, the downstream inner pipe 6 includes a contraction portion 61 whose diameter decreases as it goes downstream from its upstream end and an expansion portion 62 whose diameter increases as it goes downstream. It has a shape connected by the part 63. As shown in FIG. 2, the degree of diameter reduction of the contracting portion 61 was set such that the angle β with respect to the axial direction was 13 °. A flat portion 63 is connected to the downstream side of the contraction portion 61. The length L of the flat part 63 was 70 mm. Next, an enlarged portion 62 is connected downstream of the flat portion 63. The degree of diameter expansion of the enlarged portion 62 was set such that the angle δ with respect to the axial direction was 7 °. The downstream side of the enlarged portion 62 has a straight shape with a constant inner diameter up to the tip of the downstream inner tube 6.

  Further, the downstream inner tube 6 has an outer taper portion 64 whose diameter increases as the outer diameter shape goes downstream from the upstream end thereof. The degree of diameter expansion of the external taper 64 was set so that the angle γ with respect to the axial direction was 8 °. The downstream side of the external taper 64 has a straight shape with a constant outer diameter up to the tip of the downstream inner tube 6.

Hereinafter, the combustion operation in the burner 1 will be described, and the effects of the burner 1 will be described.
When combustion is performed in the burner 1, as shown in FIG. 2, the combustion gas 71 is caused to flow into the gas introduction pipe 4 and the combustion air 72 is caused to flow into the upstream inner pipe 5.
The combustion gas 71 flowing into the gas introduction pipe 4 is mixed with the combustion air 72 introduced into the gas nozzle 41 from the air introduction hole 415 to become an air-fuel mixture, and is provided inside the gas introduction pipe 4. It is ignited by the spark plug 42 (FIG. 1). Then, the air-fuel mixture becomes a flame 78 in the downstream inner pipe 6.

  In this example, the ejection nozzle 51 provided at the tip of the upstream inner pipe 5 has a diameter reduced in a tapered shape in front of the gas nozzle 41. Therefore, it is possible to increase the flow rate of the air-fuel mixture during the combustion process and eject the mixture toward the downstream inner pipe 6.

  The flame 78 makes a U-turn as the exhaust gas 79 and passes through the first exhaust passage 32. When the exhaust gas 79 passes from the first exhaust passage 32 to the second exhaust passage 33, in the gap between the ejection nozzle 51 and the downstream inner pipe 6, the above-described mixture flow velocity in the combustion process In combination with the rising effect, an action of taking a part of the exhaust gas 79 that has passed through the first exhaust passage 32 into the downstream inner pipe 6 can be created. Further, the exhaust gas 79 that has flowed into the second exhaust passage 33 is discharged from the exhaust gas outlet 29 to the outside of the burner 1.

  Further, in the downstream inner pipe 6, in the contracted portion 61 that decreases in diameter as it goes downstream from its upstream end and the flat portion 63 that has a constant diameter, the pressure decreases and the flow velocity increases, and the flow increases as it goes downstream. In the enlarged portion 62 having a diameter, the pressure and the flow velocity are recovered. Therefore, the entrainment of the exhaust gas 79 into the inside of the downstream inner pipe 6 in the gap between the ejection nozzle 51 and the downstream inner pipe 6 can be further promoted.

In the burner 1 of the present example, as described above, exhaust gas recirculation can be realized inside the radiant tube 3 by combustion. Therefore, the concentration of NOx in the exhaust gas finally discharged to the outside can be effectively suppressed. Further, unlike the prior art, it is not necessary to provide an exhaust gas recirculation device outside, and the compactness can be achieved.
Therefore, according to the radiant tube burner 1 of this example, while having compactness, generation | occurrence | production of NOx can be suppressed.

(performance test)
In this example, as the performance test of the burner 1, the NOx concentration of the exhaust gas after burning in the burner 1 was measured. For comparison, a radiant tube burner without exhaust gas recirculation was also measured in the same manner. The result is shown in FIG. In this figure, the horizontal axis represents the furnace temperature (° C.) and the vertical axis represents the NOx concentration (ppm), and the results of this example (symbol E) and the comparison results (symbol C) are plotted. .
The NOx concentration in the above measurement is represented by an oxygen concentration 11% equivalent value in the exhaust gas (that is, a value obtained by converting the NOx concentration under the actual oxygen concentration in the exhaust gas when the oxygen concentration in the exhaust gas is 11%). .

As can be seen from FIG. 3, the NOx concentration in the exhaust gas in the burner 1 of this example is lower than the NOx concentration in the exhaust gas of the radiant tube burner that does not recirculate the exhaust gas.
From this, it can be seen that the burner 1 of this example has a great effect of reducing the NOx concentration in the exhaust gas finally discharged to the outside.
Therefore, if the burner 1 of this example is employ | adopted, it turns out that it is not necessary to provide an exhaust gas recirculation apparatus like the conventional outside.

  As described above, the burner of the present invention has compactness and can suppress the generation of NOx.

Sectional drawing which shows the burner in an Example. Sectional drawing which shows the combustion part periphery of the burner in an Example. The graph which shows the relationship between the furnace temperature (degreeC) and NOx concentration (ppm) in an Example. Sectional drawing which shows the burner in a prior art. Sectional drawing which shows the combustion part periphery of the burner in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Burner 2 Burner body 3 Single end radiant tube 31 One end 4 Gas introduction pipe 41 Gas nozzle 5 Upstream inner pipe 51 Injection nozzle 6 Downstream inner pipe 61 Contraction part 62 Expansion part 71 Combustion gas 72 Combustion air

Claims (3)

In a single end radiant tube burner configured to emit a flame in a single end radiant tube closed at one end,
A gas introduction pipe for guiding combustion gas;
A gas nozzle that ejects the combustion gas disposed at the tip of the gas introduction pipe;
An upstream inner pipe that is disposed so as to surround the gas introduction pipe and guides combustion air;
A tapered ejection nozzle extending from the tip of the upstream inner pipe and having a diameter reduced in front of the gas nozzle;
Built in the single-end radiant tube with a downstream inner pipe disposed with a gap between the ejection nozzle,
The inner diameter shape of the downstream inner pipe has a shape in which a contraction portion that decreases in diameter as it goes downstream from its upstream end and a shape in which an expansion portion that increases in diameter as it goes downstream is connected directly or indirectly. Characteristic single-end radiant tube burner.   2. The single-end radiant tube burner according to claim 1, wherein the inner diameter of the downstream inner tube is such that a flat portion having a constant diameter is interposed between the contracted portion and the enlarged portion.   3. The single-end radiant tube burner according to claim 1, wherein the outer diameter shape of the downstream inner tube has an outer taper portion whose diameter increases from the upstream end toward the downstream.

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