JPH0499122A - Nonoxidative heating method for steel material - Google Patents

Abstract

PURPOSE:To subject steel material to nonoxidative heating at a high temp. and high speed by bringing the steel into contact with a high-temp. gas contg. a specific ratio of hydrogen radicals and heating the steel material CONSTITUTION:Gaseous fuel (for example, coke furnace gas) is burnt in a high-temp. gas generator 8 to generate a combustion gas of about 1100 deg.C. On the other hand, the hydrogen radicals of a high concn. are formed by a hydrogen radical generator 9 and are incorporated at >=100ppm into the high-temp. combustion gas. The high-temp. gas enriched with the hydrogen radicals is blown from blowing nozzles 10 provided on walls 2 of a heating furnace to a moving steel sheet 1 to heat the steel sheet 1. The nonoxidative heating of the steel sheet 1 is stably executed in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of heating steel materials to high temperatures at high speed without oxidation.

<Prior art and its problems> The "direct fire non-oxidation heating method", which heats steel by injecting high-temperature combustion gas from a burner, has been well known as one of the methods for heating steel materials to high temperatures without oxidation. There is.

FIG. 2 is a conceptual diagram illustrating an example of a conventional direct fire non-oxidation heating method. In Figure 2, suitably designed burners (3) are installed on the furnace walls (2) on both sides of the passage of the vertically moving thin steel plate (1). The fuel gas is combusted under the conditions of -0.9 to 0.95 to form a reduction flame (4), which is made to collide with the heated thin steel plate +11. Thereby, the thin steel plate (1) is heated without the surface being oxidized by the action of the reducing flame (4).

This direct-fire heating method has the great feature of being able to significantly increase the heating rate of steel compared to indirect heating using a radiant tube in a heating furnace whose atmosphere has been adjusted using reducing gas. Ta. However, in the case of this method, an essential condition to achieve non-oxidation heating is to use a burner that can guarantee good combustibility even if the air ratio during fuel gas combustion is less than 1. Patent No. 3320085 discloses a radiant cup burner with good performance used for the above purpose,
Also, as Special Publication No. 64-4408, air ratio 7 for the same purpose
A direct-fired reduction heating burner that burns at a temperature of 0.85 to 0.95 has been proposed.

However, such conventional direct flame heating methods have the following problems. In other words, for one thing, if the air ratio during gas combustion is made smaller than 1, the non-oxidation performance will improve, but the combustion heating efficiency will drop, and in order to maintain the non-oxidation performance, heating efficiency must be sacrificed. The problem is that it has to be done.

Furthermore, secondly, in non-oxidizing heating using a reducing flame, there is a limit to the heating temperature of the steel material, and the upper limit is 800 to 900 degrees Celsius, and if heated above this, the surface of the steel material to be heated will inevitably oxidize. The problem is pointed out.

Therefore, a method of injecting ultra-high temperature plasma gas into the flame was proposed as a means of increasing the flame temperature in order to improve non-oxidation heating performance (Japanese Patent Laid-Open No. 62-50
No. 416). This is an attempt to increase the flame temperature by injecting ultra-high temperature plasma gas into the flame, based on the experience that the higher the flame temperature when it collides with the steel material, the higher the non-oxidation heating limit temperature becomes.

Figure 3 shows "Flame temperature and non-oxidation heating limit temperature" from the experimental results of increasing flame temperature by injecting plasma gas, as shown in the above-mentioned Japanese Patent Application Laid-Open No. 62-50416.
This is a graph showing the relationship between According to FIG. 3, it can be seen that by raising the flame temperature by 400°C, the non-oxidation heating limit (upper limit) temperature also increases by 200 to 250°C.

However, the following problems were pointed out with this flame temperature increase type non-oxidation heating performance improvement measure.

For example, as described above, according to FIG. 3, in order to raise the non-oxidation heating limit temperature from 900°C to 1100°C, it is necessary to raise the flame temperature from 1600°C to 2000°C. Therefore, for this purpose, it is necessary to directly increase the heat content of the flame, and as is clear from the calculation formula (2000°C - 1600°C)/1600°C = 0.25, an increase in heat input of at least 25% is required. In order to deal with this problem by injecting plasma gas, the sensible heat amount of the plasma gas must be 25% or more larger than that of the combustion gas. However, in the plasma gas injection method, the increase in heat input must be covered by electrical energy, and moreover, the electrical energy required to generate plasma corresponding to the above value is 30% or more greater than the burner heat input. This leads to a significant increase in energy costs.

Moreover, there is also the fact that increasing the flame temperature will significantly reduce the durability of the burner, which is by no means a desirable method from an equipment engineering perspective, and may also increase the possibility of melting and damage to the steel being heated. Ta.

Therefore, the purpose of the present invention is to solve the problems pointed out in the conventional non-oxidation heating method, to achieve good combustion heating efficiency, and to provide a non-oxidation method without requiring excessive heat supply. The object of the present invention is to provide a non-oxidation heating means for steel materials that can increase the upper limit heating temperature.

<Means for Solving the Problems> As a result of extensive research to achieve the above object, the present inventors have discovered the following from a basic study, particularly regarding the properties of reduction flame:
The area where steel is reduced in flame corresponds to the area where the concentration of hydrogen radicals (atomic hydrogen) is high, and for non-oxidative heating and reduction of steel, it is necessary to have a high concentration of hydrogen radicals in the flame. They found that it is not necessary to raise the flame temperature.

Further investigation revealed that ``If 1,100 pp or more of hydrogen radicals exist as a component of the gas that heats the steel material, non-oxidation heating is possible regardless of the temperature of the heating gas (flame, etc.). We were also able to obtain the knowledge that

Figure 4 shows a simple experimental example that led to the above findings, in which a small-diameter wire (7) with an oxidized surface was inserted into a reducing flame (6) with a small air ratio produced by a Bunsen burner (5).
This shows how the area where the surface is reduced is examined on the flame axis. Through this experiment, it was confirmed that the area where the steel wire surface is reduced is from point a to point b on the flame axis. Furthermore, we investigated the "relationship between the distance on the flame axis, the concentration of hydrogen radicals, and the flame temperature" and obtained the results shown in Figure 5.
The region from point to point b” has a “concentration of hydrogen radicals of 11
It is also clear that the reduction of steel materials is not directly related to the flame temperature, but rather the composition of the flame gas (concentration of hydrogen radicals). I learned that enrichment is an important requirement.

The present invention has been made based on the above-mentioned findings, etc., and aims to achieve stable non-oxidation heating of steel materials by heating the steel materials by contacting them with a high-temperature gas containing 100 pp+n or more of hydrogen radicals. It has a major characteristic in that it has been

Here, the above-mentioned "high-temperature gas" refers to gas (including flame) heated to a general temperature applied for heating steel materials.
It is not limited to "a gas heated to a certain high temperature or higher."

Moreover, the hydrogen radicals can be formed, for example, by a plasma jet generator using hydrogen gas as a working gas. That is, in a plasma jet, as shown in FIG. 6, a phenomenon occurs in which two atoms of the working gas dissociate at a specific temperature, and in a plasma jet using hydrogen gas as the working gas, a large amount of hydrogen radicals are formed.

Therefore, if these hydrogen radicals are injected into a flame burning at a low air ratio, mixed, and sprayed to collide with and come into contact with the steel surface, the steel surface will be covered with a reducing atmosphere and protected from oxidation. At the same time, the temperature of the steel material increases to a predetermined temperature due to heat transfer from the flame gas.

A typical plasma jet generator has the structure shown in Figure 7, but if a "gas containing hydrogen but not containing oxidizing gas" is used as the working gas, hydrogen can be generated at rHz. -2HJ can be dissociated to generate hydrogen radicals.

Of course, hydrogen radicals can be generated not only by high-temperature plasma generation methods but also by low-temperature plasma generation methods.

In addition, in carrying out the method of the present invention, the following method can be adopted.

(a) Instead of flame, high-temperature gas containing hydrogen radicals collides with the steel material to heat the steel material.

(b) A "gas containing hydrogen radicals" is introduced into a normal combustion flame with a flame temperature of 1600° C. or lower without raising the flame temperature, and the steel material is heated by being brought into contact with the gas.

With these, the oxidation-free heating performance of the steel material can be improved without suffering the aforementioned "adverse effects associated with high flame temperatures."

Furthermore, when hydrogen radicals are injected into the flame (exhaust gas) in an existing "steel heating furnace equipped with a non-oxidizing heating burner that burns at an air ratio of 1.0 or less,"
Concentration of hydrogen radicals: 100pp As long as the pH is maintained at 1 or higher, oxidation of the steel will not occur even if the air ratio of the non-oxidizing heating burner is increased to nearly 1, and therefore the combustion heating efficiency can be stabilized while ensuring great benefits in terms of combustion heating efficiency. Non-oxidizing heating becomes possible.

Here, the hydrogen radical concentration can be measured by, for example, laser-induced fluorescence spectroscopy (LIFS method) or electron spin resonance method (
It goes without saying that this can be done relatively easily by a well-known method such as the ESR method.

Next, the present invention will be explained in more detail with reference to Examples.

<Example> As shown in Fig. 1, fuel gas (coke oven gas) is combusted in a high-temperature gas generator (8) to generate combustion gas at 1100°C, while a hydrogen radical generator (9) At the same time as generating high concentration hydrogen radicals, the two are mixed to obtain hydrogen radical-enriched high-temperature gas, which is then 0.8 f
A 1-thick IL steel plate (1) was blown onto the steel plate (1) to heat the steel plate.

At this time, first, the hydrogen radical concentration in the hydrogen radical-enriched high-temperature gas was adjusted to 300 ppm+, and the temperature was increased to 900°C in about 10 seconds.
As a result, there was no oxidation of the steel plate, confirming that stable oxidation-free heating was achieved.

Next, the temperature of the high-temperature gas was raised, and the mixing ratio of hydrogen radicals was also increased to reach a hydrogen radical concentration of 5000 pp.
As a result of similarly bombarding a 0.8 mm thick thin steel plate (1) with hydrogen radical-enriched high-temperature gas at 1250°C and heating it to 1100°C, the copper plate surface was not oxidized. It was confirmed that stable heating was possible.

Separately, if hydrogen radicals are injected into the flame of an existing non-oxidizing heating burner, the concentration of hydrogen radicals can be maintained at 1100 pp or more even if the air ratio of the non-oxidizing heating burner is increased to 0.98. It was also confirmed that no particular problem occurred in terms of non-oxidation performance. Furthermore, in this case, the air ratio of the non-oxidizing heating burner is set to 0.9 to 0.98.
By raising the temperature to 750℃, the 0.8mH thin steel plate was
It was found that the amount of fuel used was reduced by 12% when heated to

(Summary of Effects) As explained above, according to the present invention, the non-oxidation heating of steel materials can be stably performed without increasing energy costs or causing operational troubles, and with equipment that is significantly more compact than indirect heating methods. It becomes possible to implement
Industrially extremely useful effects are brought about.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of the non-oxidation heating method for steel material adopted in the example. FIG. 2 is a conceptual diagram illustrating an example of a conventional direct fire non-oxidation heating method. FIG. 3 is a graph showing the relationship between flame temperature and non-oxidation heating limit temperature. FIG. 4 is an explanatory diagram showing an experimental method for reducing an oxidized steel wire in a flame. FIG. 5 is a graph showing the relationship between hydrogen radical concentration and flame temperature at each position on the flame axis. FIG. 6 is a graph showing the relationship between the gas temperature, the amount of heat, and the state of the gas in a plasma generator using diatomic gas as the working gas. FIG. 7 is a schematic diagram showing an example of a plasma generation device. In the drawings: 1... Thin steel plate, 2... Furnace wall. 3... Burner, 4... Reduction flame. 5...Bunsen burner, 6...flame. 7... Steel wire, 8... High temperature gas generator. 9...Hydrogen radical generator. 10...Blowout nozzle.

Claims (2)

[Claims] (1) A non-oxidation heating method for steel, which is characterized by heating the steel by bringing it into contact with a high-temperature gas containing 100 ppm or more of hydrogen radicals. (2) In a heating furnace that uses combustion gas generated by combustion at an air ratio of less than 1.0, 100 ppm or more of hydrogen radicals are blown into the combustion gas, and the steel material is heated by contacting the hydrogen radicals with the hydrogen radicals. A non-oxidizing heating method for steel materials.