JPH0335570B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a burner for radiant tubes that significantly reduces _NOx generation compared to conventional burners used in continuous annealing furnaces and the like.

[Conventional technology]

Generally, burners for radiant tubes in continuous annealing furnaces have a maximum tube temperature of 1100
It is used under harsh conditions that reach temperatures of
A function that can suppress the amount of _NOx generated below the regulatory value is required.

Therefore, a two-stage combustion type burner as disclosed in, for example, Japanese Unexamined Patent Publication No. 14106/1983 has been proposed to meet such requirements. This system supplies combustion air to the combustion chamber through two systems in order to achieve low _NOx combustion, and its outline is shown in FIGS. 3a, b, and c. In the figure, numeral 1 shows a part of the radiant tube, and the whole is as shown in FIG. 4. 2 is a burner inserted into this radiant tube 1. 3
3 is a gas supply port for combustion, and the gas supplied from this port to the gas chamber 4 passes through a gas lance 5 and is blown out from a gas nozzle 7 (see FIG. 3c) that opens into a burner head 6 and is combusted. 8 is burner head 6
A ring-shaped gap is formed between the flange and the radiant tube 1, and this serves as a primary nozzle 9. 10 is a combustion air supply port,
The air supplied from here enters the air chamber 11 (see Fig. 3a), which is a space inside the radiant tube 1 defined by the burner head 6, and a part of it is blown out from the primary air nozzle 9 and released together with the gas. A secondary combustion F ₁ is carried out, and on the other hand, the air blown out from the small cylindrical secondary air nozzle 12 provided in the burner head 6 carries out a secondary combustion F ₂ with the unburned gas from the primary combustion F ₁ (see Fig. 3). b), resulting in almost complete combustion, and the resulting high-temperature combustion gas
The entire radiant tube 1 shown in the figure is heated.

As shown in Figure 5, the amount of _NOx generated in a burner with the above configuration is greatly affected by the ratio of primary air to secondary air, so the cross-sectional area (opening area) of each air nozzle is constant. However, it is difficult to keep the diameter of the primary air nozzle 9 constant due to manufacturing errors in the inner diameter of the radiant tube 1.

Therefore, in order to keep the opening area of the primary air nozzle constant regardless of the inner diameter error of the radiant tube, the width between the radiant tube and the outer circumference of the burner flange should be uniform over the entire circumference, and the opening area should be kept constant over the entire circumference. A cylindrical body 20 has been developed which is arranged concentrically with the flange of the burner head (see FIGS. 2a, b, c), so as to form a gap of size, ie a primary air nozzle 29. In the figure, reference numeral 20 denotes a cylindrical body having a highly accurate inner diameter _D2 , and is provided on the burner 22 concentrically with the burner head 6. There is a width 1/2 (D ₂ −D ₁ ) between this cylindrical body 20 and the outer circumference of the flange 8 having an outer diameter D ₁ .
The primary air nozzle 29 is formed by a uniform gap.

[Problem that the invention seeks to solve]

However, when increasing the processing load in a continuous annealing furnace, it is necessary to increase the combustion amount of the burner in order to increase the heating amount by the radiant tube. There was a problem in that the temperature rose and the amount of thermal _NOx produced increased, making it difficult to meet environmental standards ( _NOx production of 150 ppm or less when the maximum temperature in the longitudinal direction of the radiant tube was 1050°C).

This invention has been made in view of the above-mentioned conventional problems.The above-mentioned problems are solved by using the annular gap between the through-hole provided in the burner head and the gas nozzle inserted therein as a primary air nozzle. The purpose is to resolve the issue.

[Means for solving problems]

This invention provides a radiant tube burner having a cylindrical body at the insertion part into the radiant tube, in which a small cylindrical secondary air nozzle is provided in the center of a disc-shaped burner head that is attached to close the open end of the cylindrical body. Furthermore, a plurality of through holes of the same diameter are arranged in the burner head at equal intervals on the same circumference that is concentric with the secondary air nozzle, and the open end of the gas lance is inserted into each of the through holes concentrically with the through hole. This provides a radiant tube burner in which a primary air nozzle is formed with an annular gap between the open end of the gas lance and the through hole.

[Effect]

Since the radiant tube burner according to the present invention is constructed as described above, the opening area of the annular primary air nozzle with a uniform width remains constant and does not change, so that the air is ejected from the primary air nozzle. Since the proportion of primary air to the total air amount can always be kept constant so that the amount of _NOx produced is the lowest, this burner can meet the environmental standards mentioned above.

〔Example〕

The present invention will be explained below based on the drawings. FIGS. 1a, b, and c are diagrams showing an embodiment of the present invention. Note that the same parts as in the conventional example are given the same reference numerals, and redundant explanation will be omitted.

First, the structure will be explained. Reference numeral 36 is a disk-shaped burner head, which is attached to close the open end of the cylindrical body 20 of the burner 32. 12 is a small cylindrical secondary air nozzle similar to the conventional example, and is attached to the center of the burner head 36. Reference numeral 31 denotes through holes, which are bored in the burner head 36 at equal intervals on the same circumference concentric with the secondary air nozzle 12 (four holes in this embodiment). A primary air nozzle 39 7 is an open end of the gas lance 5, and is inserted into the through hole 31 concentrically with the through hole to form an annular gap between the gas nozzle 7 and the through hole. is formed.
In the plurality of primary air nozzles, the inner diameters of the plurality of through holes 31 are equal to each other, and the outer diameters of the plurality of gas lances 5 are respectively equal to each other, so that the opening areas of the plurality of primary air nozzles are equal and constant.

Next, the effect will be explained.

Now, the combustion gas ejected from the gas nozzle 7 efficiently performs primary combustion F ₁ in the combustion chamber 13 while being surrounded by the primary air ejected in an annular shape from the primary air nozzle 39, and the primary air At this time, it is completely burned and consumed. Therefore, the primary combustion F ₁
is completed in the primary combustion zone, and the unburned gas at this time performs secondary combustion _F2 in the secondary combustion zone together with the secondary air supplied from the secondary air nozzle 12, so that the burner 32 is completely Performs two-stage combustion.

On the other hand, in the conventional example, the primary combustion is not completed in the primary combustion zone, and the primary air nozzle 2
The residual amount of the primary air ejected from the primary combustion F ₁ is sent to the secondary combustion zone, and the
Since it is added to the next combustion F ₂ , complete two-stage combustion is not achieved in this burner 22 .

This is clear from the comparison between Fig. 6 (embodiment) and Fig. 7 (conventional example), which are actual temperature distribution diagrams in the longitudinal direction of the radiant tube, in the F ₁ combustion zone of the embodiment. The temperature rises, and a cooling part is seen between the F ₂ combustion and the two-stage combustion is clear, whereas in the conventional example shown in Figure 7, the F ₂ combustion is hotter than the F ₁ combustion. .

Figures 8 and 9 are actual measurement diagrams of the amount _{of NO}
It is clear that it satisfies the environmental standard (150ppm or less at 1050℃) at 98ppm at 1050℃, and Figure 9 shows the difference between the conventional example shown in Figure 7.
This shows that _NOX exceeds environmental standards at 153ppm.

That is, in this embodiment, in order to maintain a constant size so that the opening area of the primary air nozzle can maintain a predetermined primary air ratio, unburned primary air is used as a residual amount in the primary combustion. It is not sent to the next combustion, that is, the primary combustibility is improved and the second stage combustion is almost completely performed.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to reduce the amount of _NOx produced during burner combustion to approximately two-thirds or less of the amount produced in the conventional example,
The effect is that the environmental standards regarding the amount of _NOx generated can be fully satisfied.

[Brief explanation of drawings]

Figure 1a is a side view with main parts cut away of an embodiment of the present invention, Figure 1b is a partially enlarged view of Figure 1a, Figure 1c is
2A is a side view of the conventional example with main parts cut away; FIG. 2B is a partially enlarged view of FIG. 2A; FIG. 2C is a view of FIG. Fig. 3a is a side view of another conventional example with main parts cut away, Fig. 3b is a partially enlarged view of Fig. 3a, Fig. 3c is a view taken along arrow A in Fig. 4b, and Fig. 4 is the entire radiant tube. Fig. 5 is a graph showing the amount of NO _x produced versus the primary air ratio, Fig. 6 is a graph showing the tube temperature of the embodiment, and Fig. 7 is a graph showing the tube temperature corresponding to the longitudinal position of the radiant tube of the conventional example. FIG. 8 is a graph showing the 11% O ₂ equivalent NO _X production value corresponding to the maximum temperature in the longitudinal direction of the radiant tube in the example and FIG. 9 in the conventional example. 1... Radiant tube, 2, 22... Burner, 6, 36... Burner head, 7... Gas nozzle (gas lance opening end), 9, 29, 39... 1
Secondary air nozzle, 12... Secondary air nozzle, 20...
...Cylindrical body, 31...Through hole.

Claims (1)

[Claims] 1. In a radiant tube burner having a cylindrical body at the insertion part into the radiant tube, a small cylindrical secondary air nozzle is provided in the center of a disc-shaped burner head that is attached to close the open end of the cylindrical body, and By arranging a plurality of through holes of the same diameter in the burner head at equal intervals on the same circumference that is concentric with the secondary air nozzle, and inserting the open end of each gas lance into the through holes concentrically with the through holes, A burner for a radiant tube, characterized in that a primary air nozzle forming an annular gap is formed between an open end of a gas lance and a through hole.