JP2776183B2 - Combustion control method for steel heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the combustion of a steel heating furnace, in particular, a steel strip heating furnace for forging pipes.

[0002]

2. Description of the Related Art Generally, whether a steel material is a strip steel or a shaped steel, it is heated to a predetermined temperature before processing to reduce so-called deformation resistance. For this purpose, a steel heating furnace is used. However, the combustion of the burner in such a heating furnace is usually performed at an air ratio of 1.1 to 1.2. Therefore, the atmosphere of the combustion gas is an oxidizing atmosphere containing excess oxygen. As a result, the material to be heated is heated while being exposed to the oxidizing atmosphere,
The amount of scale generated increased, and the resulting reduction in yield was large.

[0003] Also in the conventional, as a method to solve such a problem, JP 60 _- as disclosed in 215716 and JP-combustion method of the heating furnace has been proposed by two layers atmosphere. In this method, the area surrounding the material to be heated has an air ratio of 1.
By burning at less than 0 and burning the unburned gas generated in the combustion in this region in a region outside the region, it is intended to suppress the scale generated when the steel material is heated. This is the so-called reduction of scale loss.

[0004] However, in the combustion method using the two-layer atmosphere, it may be difficult to form the combustion zone in two layers. For example, in a steel forging pipe heating furnace (hereinafter simply referred to as a forging pipe heating furnace), a plurality of flue sections called off-takes are installed downstream of the heating zone. Since the size becomes large, the non-oxidizing atmosphere around the material to be heated is disturbed, and scale is generated at this position. In addition, there are about 300 burners in the forging tube heating furnace, and it is necessary to change all the burners to form a two-layer atmosphere, which requires very large equipment costs.

As a method for solving this problem, a method disclosed in Japanese Utility Model Laid-Open No. 3-45949 has been proposed. In this method, the furnace height in the combustion zone of the forging tube heating furnace is increased toward the off-take, so that the flow rate of the exhaust gas in the furnace is reduced to prevent disturbance of the non-oxidizing atmosphere around the steel material. However, this method has a drawback in that the equipment cost is extremely high as described above because the furnace body needs to be modified.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a steel material capable of suppressing a scale loss generated during heating of a steel material heating furnace such as a forged pipe heating furnace by 20 to 30% without incurring much equipment cost. It is to provide a heating method of a heating furnace.

[0007]

Means for Solving the Problems The present inventors have conducted various studies in order to achieve the object, and have found that the air ratio in the heating zone is 1.
Focusing on the advantage of combustion at less than 0, a combustion control system for stably forming a non-oxidizing atmosphere thereby has been completed, and the present invention has been completed.

[0008] Thus, it is an aspect of the present invention, the pre
Tropical and downstream of this pre-tropical zone
Heating zone having a plurality of combustion zones,
Smoke that connects the cloud and the tropics in communication
And a combustion control method for a steel heating furnace comprising a road section ,
Combustion in the combustion zone is performed at an air ratio of less than 1.0, and the amount of secondary combustion air required to completely combust the generated unburned gas is combined.
Calculated for each of the number of flue sections, and duplicated the calculated amount of secondary combustion air.
A combustion control method for a steel material heating furnace, characterized in that the supply is supplied to each of a number of flue sections.

[0009] In particular, when heating a steel plate for a forged pipe as a steel material, the pre-tropical zone is provided above the combustion zone and is connected at least partially by a vertically extending flue portion, and the secondary combustion air is provided. Will be injected diagonally upward into the pre-tropical zone in this vertical flue.

[0010]

Next, the operation of the present invention will be described more specifically with reference to the accompanying drawings. FIG. 1 is a schematic explanatory view of a forged pipe heating furnace used in the present invention, and FIG.
-A, and FIG. 3 is also BB of FIG.
FIG.

In the figure, the steel strip 1 enters in the direction of the arrow, enters the pre-tropical zone 3, makes a U-turn at the furnace end, exits the furnace once from the preheating furnace inlet, and is then introduced into the heating zone 2 for about 1200 After being heated to about ° C., it goes out of the furnace and is formed into a pipe shape by a pipe-making machine, and at the same time, the joining ends are pressed into a pipe.

In the heating zone 2, about 300 burners 5 are installed on both side walls of the combustion zones I to IV constituting the heating zone, and usually the furnace temperature is set to 1300 to 1350 ° C. . Since the exhaust gas from each heating zone is introduced into the pre-tropical zone 3 through the flue section 4, the steel strip 1 enters the pre-tropical zone at room temperature and enters the heating zone at about 500 to 600 ° C.

Here, it is known that it is effective to make the surrounding atmosphere of the material to be heated non-oxidizing in order to suppress the scale loss in the heating zone. Combustion is performed by adjusting the flow rates of the fuel pipe 6 and the combustion air pipe 7 so that the air ratio becomes 1.0 or less. At this time, the inside of the heating zone 2 becomes an atmosphere of O ₂ = 0% and CO> 0%, a non-oxidizing atmosphere is formed, and the generation of scale of the steel strip 1 is suppressed.

On the other hand, if the unburned gas generated in the heating zone 2 is discharged as it is, not only will there be a safety problem but also the fuel consumption rate will be deteriorated. Therefore, the air is discharged from the secondary combustion air pipe 8 to the flue section. And burn the unburned gas completely. As described above, the unburned gas is completely burned by the injection of the secondary combustion air, and the temperature of the exhaust gas rises. However, the sensible heat is recovered by the recuperator 10 downstream of the exhaust gas, and is discharged outside the furnace.

The amount of primary combustion air that makes the air ratio less than 1.0 and the amount of secondary combustion air that completely burns unburned gas are:
It is calculated by the calculator 9 based on the data from each of the flow meters 6-2, 7-2 and 8-2, and the control valves 6-1, 7-1 and 8-1 are operated by changing to predetermined electric signals. Let it. In addition,
Although not shown in FIG. 1, the secondary combustion air flow rate is adjusted.
Secondary equipped with valve 8-1 and secondary combustion air flow meter 8-2
The combustion air pipes 8 are provided in all the flue sections 4.

[0016] For example, the air quantity Q _b to be introduced from the secondary combustion air pipe is calculated by the arithmetic unit 9 by the following equation, it is controlling the flow rate by the flow rate regulating valve 8-1. _{Q b n = {(4.9~5.1)} × Q f n-Q a n} × Cn Q b: secondary combustion air flow rate Q _f: the fuel flow rate Q _a: combustion air flow C: subscript correction factor each symbol n: Fig. 2 shows the flue section provided downstream of the combustion zone and the connection of the pre-tropical zone, and Fig. 3 shows at least a part of the flue section extending vertically. The arrangement of the nozzle 8-3 for supplying combustion air is shown.

Here, the present inventors use a fluid model experiment or an actual heating furnace to determine the position and angle at which the secondary combustion air is injected when the secondary combustion air is injected in such a state. The following knowledge was obtained as a result of examining conditions for optimizing the mixing of the secondary combustion air and the unburned gas.

As shown in FIGS. 2 and 3, the nozzles 8-3 to inject secondary combustion air Q _b, upwardly disposed at an appropriate position of the peripheral wall of the preheating furnace side vertical portion 4-1 of the flue section 4 The angle θ is preferably about 30 to 60 ° upward from the horizontal direction, and the number of installed nozzles is preferably divided into 3 to 5 nozzles per flue portion. This is for the following reason.

First, as the position for charging the secondary combustion air,
Considering that it does not hinder the work of opening the heating furnace upper lid during regular furnace repair in the heating furnace, it is necessary to install a nozzle on the wall of the flue section 4 in the furnace length direction.

The secondary combustion air is injected from the drive side of the vertical section 4-1 of the flue section, ie, the wall facing the pre-tropical side, and the secondary combustion air is injected from the work side, ie, the wall opposite to the pre-tropical side. Looking at the situation with the introduction in the fluid model experiment,
When thrown in from the work side, the injected air is heated zone 2
It was found that they did not mix well with the more flowing exhaust gas, but flowed to the upper part of the flue with a split flow and stayed at the corner of the flue. However, when the secondary combustion air is injected obliquely upward from the drive side of the flue, the air can be sufficiently mixed with the exhaust gas. This is considered to be a characteristic of the flow direction of the exhaust gas and the shape of the flue.

The angle of the secondary combustion air injection nozzle 8-3 is
In the downward and horizontal directions, the flow of exhaust gas coming from the heating furnace is cut off, and the furnace pressure in the heating furnace increases.
An upward angle of 30-60 ° was found to be optimal for mixing the secondary combustion air with the furnace exhaust gas.

Experiments were also carried out on the number of secondary combustion air nozzles. As a result, it was found that the smaller the number of secondary combustion air nozzles, the better the mixing performance.
It is considered that about five divisions are appropriate. The knowledge obtained by this fluid model experiment was applied to an actual steel heating furnace, and its validity was confirmed by exhaust gas composition analysis and furnace pressure measurement.

As described above, the low-air ratio combustion in the heating furnace and the unburned gas secondary combustion in the flue section make it possible to easily and easily suppress the generation of scale in the forging tube heating furnace by using inexpensive means. Can be. Next, an example will be described in which the method for controlling combustion of a steel heating furnace according to the present invention exerts an actually excellent function.

[0024]

EXAMPLE In this example, the results of scale loss measurement when the steel strip for forging pipe was heated by using the forging pipe heating furnace shown in FIGS. 1 to 3 and changing the air ratio from 0.8 to 1.1 are shown. The dimensions of the steel and the heating conditions are as follows.

Heating material dimensions: 4.2t × 445W (mm) 速度 Speed: 80 m / min Heating zone temperature: 1300-1350 ° C Secondary combustion air injection nozzle: Angle 45 ° x 4 (per combustion zone) The results of are summarized in the graph shown in FIG. When the air ratio is less than 1.0, the scale loss is rapidly reduced, and based on the air ratio of 1.1,
A reduction of almost 20% was achieved with an air ratio of 0.8.

Next, Table 1 shows the results of measuring the CO% in the exhaust gas in the heating zone, in the flue, and in the pre-tropical zone when the heating zone was burned at an air ratio of 0.8. The numbers in the table indicate the measurement sites shown in FIG. As can be seen from these results, according to the present invention, a non-oxidizing atmosphere is stably formed in the heating zone, and the combustion of unburned gas is performed for the first time downstream from the flue, particularly in the pre-tropical zone. You can see that there is.

[0027]

[Table 1]

[0028]

According to the present invention, it is possible to suppress the scale generated in the forged pipe heating furnace at low equipment cost.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a forging tube heating furnace used in the present invention.

FIG. 2 is a view taken in the direction of arrows AA in FIG. 1, showing the shape and structure of a flue section connecting the heating zone and the pre-tropical zone.

FIG. 3 is a view taken in the direction of arrows BB in FIG. 2, showing an installation mode of a secondary combustion air injection nozzle.

FIG. 4 is a graph showing a result of an example of the present invention.

5 shows an explanatory view of a measurement site of the data of FIG. 4, FIG.
FIG.

[Explanation of symbols]

1: strip, 2: heated zone, 3: pre-tropical,
4: flue section, 5: burner, 6: fuel pipe,
6-1: fuel flow control valve, 6-2: fuel flow meter, 7: combustion air piping, 7-1:
Combustion air flow control valve, 7-2: fuel air flow meter,
8: Secondary combustion air piping, 8-1: Secondary combustion air flow control valve, 8-2: Secondary combustion air flow meter, 8-3:
Secondary combustion air injection nozzle, 9: arithmetic unit, 10: recuperator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C21D 1/00-11/00 105

Claims (2)

(57) [Claims] Claims: 1. A pre-tropical zone, wherein the pre-tropical zone is located downstream of the pre-tropical zone.
Zone with multiple combustion zones connected and connected
And a plurality of said combustion zones and said pre-
Steel heating furnace with a plurality of flue sections connected in a continuous manner
The combustion control method of the above, wherein the combustion in the combustion zone is performed at an air ratio of less than 1.0, the amount of secondary combustion air required to completely combust the generated unburned gas is discharged to each of the plurality of flue sections. Calculation
And transferring the calculated amount of the secondary combustion air to the plurality of flue sections.
A combustion control method for a steel material heating furnace, characterized in that it is supplied to each of them. 2. The secondary combustion air, wherein the steel material is a steel strip for a forged pipe, wherein the pre-tropical zone is provided above the combustion zone, and is connected at least partially by a vertically extending flue portion. 2. The combustion control method for a steel heating furnace according to claim 1, wherein the fuel is injected obliquely upward toward the pre-tropical zone in the vertical flue section.