JP2000337776A - Method for improving secondary combustion rate and heating efficiency of melting furnace, or the like - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the secondary combustion rate and heating efficiency of a melting furnace, etc., without shortening the service lives of refractories, etc., and suppressing the flying out of slag, etc., by using a gas containing an oxygen gas more than a specific amount as a combustion supporting gas for secondary combustion. SOLUTION: The method for improving secondary combustion rate and heating efficiency of melting furnace, etc., uses a gas containing >=60% oxygen gas as a combustion supporting gas for secondary combustion. In order to heat the oxygen gas for secondary combustion to a high temperature, oxygen gas preheaters 5 are installed to the oxygen gas introducing sections of lances 2. Because of the preheaters 5, the oxygen gas can be heated to a temperature of about 1,100 deg.C and the temperature of the oxygen gas at the discharge ports of the lances 2 can be maintained at >=950 deg.C. In addition, the flow speeds of the oxygen gas discharged from nozzles are set at 100, 250, and 500 m/sec. Therefore, when the melting of a raw material is accelerated or the temperature in a melting furnace, such as the converter, electric furnace, etc., is raised at the time of melting the raw material in the furnace, the raw material can be melted by reducing the used amount of fuel or the combustion supporting gas without worsening the operability of the furnace nor damaging refractories by improving the heating efficiency of secondary compustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of burning a material to be melted or a substance to be burned in a fuel in a metal smelting furnace such as a converter and an electric furnace, or a metal smelting furnace such as a smelting reduction furnace of iron ore. Therefore, during the heating, melting and refining or smelting of the raw materials charged in the furnace, without deteriorating the operability of the furnace or damage to refractories, primary combustion gas generated in the furnace, especially The present invention relates to a technique for efficiently performing secondary combustion of CO gas, efficiently heating the generated secondary combustion heat to the molten material or molten metal in the furnace, and thus reducing the amount of fuel and supporting gas used. Things.

[0002]

2. Description of the Related Art In a converter, combustion techniques for increasing the dissolution rate and reduction rate of steel chips, manganese ore, and the like have been studied. For this purpose, an upper blowing lance for decarburization of molten iron is mainly used, and this lance is provided with a main nozzle for decarburization and a nozzle for injecting oxygen gas for secondary combustion around the lance and on the outer periphery of the lance. Can be That is, in addition to the main nozzle, the lance is provided with a nozzle for injecting oxygen gas for burning CO gas, which is the primary combustion gas generated by the decarburization reaction.
A part of the CO gas generated from the bath is secondarily burned to CO ₂ gas by these secondary combustion nozzles. However, since it is difficult to control the spatial region where the secondary combustion is performed, it is difficult to sufficiently increase the heat applied to the bath composed of the molten metal and the molten slag. If the secondary combustion is performed efficiently and the secondary combustion heat is to be efficiently radiated to the bath, an excessive supporting gas for secondary combustion must be supplied. As a result, Causes furnace wall damage.

On the other hand, in an electric furnace, oxygen gas is blown into the slag using a lance installed on the side wall of the furnace or a water-cooled lance inserted from a waste gate, and decarburization of the metal bath and its decarburization. The secondary combustion of the CO gas generated by the charcoal is performed simultaneously. A so-called carburizing material such as coke powder is also blown when the oxygen gas is blown to increase the generation of CO gas, or to foam slag to perform secondary combustion in the slag. The carburizing material injection in this case is originally a means for generating primary combustion heat for the purpose of replacing electric energy such as arc heat. In any case, CO gas generation by direct oxidation of the metal bath by blowing O2 gas is also indispensable for causing secondary combustion, but it is difficult to control a place where the secondary combustion is caused. Sufficient heat of the next combustion heat to the metal bath could not be realized. In some cases, a side-blown nozzle is used exclusively for secondary combustion.However, it is difficult to secure a secondary combustion space in the slag, and if a large amount of oxygen gas is added to increase combustion, a metal bath is required. Is inevitable, and it is similarly difficult to improve the secondary combustion rate and the heat transfer efficiency.

[0004] On the other hand, in the smelting reduction method, iron ore is heated and melted at a high speed and reduced to generate hot metal. Therefore, an increase in the amount of heat added is essential for promoting the reduction reaction. Various furnace-type processes have been proposed, and in the case of a furnace type similar to a converter, a method similar to the above-described top-blowing lance or a method of providing a lance or tuyere that can be inserted into the side wall of the furnace upper part. There is. When the ore is smelted and reduced, the oxygen in the ore becomes CO2
Although it is removed as a gas, the CO gas is subjected to secondary combustion with oxygen gas supplied from a separately provided lance or tuyere, and the combustion heat is used to compensate for the endothermic amount accompanying the reduction reaction and to heat the metal bath. Use for The gangue in iron ore used in the smelting reduction method is turned into slag, resulting in a large amount of slag.
The heat generated during the secondary combustion is transferred from the combustion gas to the slag, and then the metal bath is finally heated.
In order to increase the secondary combustion rate and the heat transfer efficiency, it is necessary to disperse the combustion and heat transfer sites to increase the combustion area and the heat transfer area, and generally increase the number of tuyeres and lances. Is done. However, an excessive increase in the number of blowing ports not only increases the size of the equipment but also causes a problem in controlling the added oxygen gas for secondary combustion.

Further, recently, when the supporting gas to be added is air, attempts have been made to raise the temperature of the air in advance to enhance the controllability of the air added from the blowing port. Like hot air from a blast furnace, transportation from the source to the furnace may be relatively easy, and techniques for blowing gas preheated to a high temperature into the furnace are limited to air. However,
Air has a low oxygen concentration and is disadvantageous not only with respect to an increase in the combustion rate, but also with the necessity of applying heat to a large amount of accompanying N ₂ gas, which is not necessarily superior in terms of total thermal efficiency.

[0006]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention considers the use of primary combustion gas in a melting furnace, a refining furnace, or a smelting furnace such as an electric refining furnace, a converter, or a smelting reduction furnace. When trying to increase the effective heat by secondary combustion, without shortening the life of refractory etc., which is an unstable factor in operation, and slag etc. popping out by introducing a large amount of gas It is intended to increase the secondary combustion rate and the heating efficiency while suppressing this.

In order to increase the heat applied to the object to be heated,
Burn in the vicinity of the metal bath to increase the effect of direct radiant heat transfer, or to increase the heat transfer from the molten slag at the top of the metal bath to the metal bath, first in the molten slag or immediately above the slag bath. It is effective to promote the heat transfer between the molten slag and the combustion gas by burning at the temperature.

As for the former, it is premised that such treatment in melting and refining involves generation of CO gas by decarburization, and in order to promote the treatment, bathing such as gas bottom blowing is required. Since it is common to use forced agitation, disturbance of the bath surface is inevitable. Therefore, when the fuel is burned in the vicinity of the metal bath, the direct oxidation of the effective components in the metal bath such as iron and manganese increases, and it is difficult to selectively burn the CO gas generated from the metal bath. Control of the slag composition becomes difficult, and the operation tends to be unstable due to damage to the refractory. For this reason, it is difficult to increase the final amount of heat by this method.

On the other hand, since the latter is burned in the molten slag or immediately above the slag bath, the reaction between the metal bath and oxygen gas can be easily avoided. However, it is essential to secure the combustion space and to increase the contact area of the combustion gas with the slag to promote heat transfer. For example, as described above, the heat transfer area is increased by increasing the number of lances, making the nozzle porous, dispersing the secondary combustion sites, or injecting the gas at a high speed from the pore nozzle, and moving the gas. Energy is used to enhance the agitation of the slag. However, such an attempt to promote heat transfer increases the heat load on the furnace wall refractory, increases the amount of molten slag and metal scattered outside the furnace, and further shortens the life of the nozzle. The operation stability is problematic. Furthermore, in such a melting method, quality control is also important, and in particular, in order to eliminate the problem of absorption of nitrogen into the metal bath, it is essential to use a supporting gas other than air containing a large amount of nitrogen. is there.

[0010]

In order to solve such a problem, the present inventors have increased the combustion rate in an appropriate limited space, and furthermore, efficiently realize the heat of the combustion heat. I thought that was effective. Furthermore, it was considered important to enable operation without any problem with respect to the properties of steel materials. That is,
Conventionally, pure oxygen gas at normal temperature has been used as a combustion supporting gas for combustion, but it has been found that the use of pure oxygen gas preheated to a high temperature in advance is effective to increase the combustion rate. The present inventors have studied in detail the combustion behavior of the fuel gas when the oxygen gas is added to the flow of the fuel gas such as the CO gas, and as a result, the combustion speed is increased by the oxygen gas preheated to a high temperature. It was confirmed that. Furthermore, it has been found that the use of oxygen gas preheated to a high temperature in advance is effective for improving the heat transfer efficiency.

It is important to contact and mix the combustion gas with the molten slag in order to increase the heat transfer efficiency, but it is necessary to increase the contact opportunity as much as possible within a limited time until the combustion gas goes out of the reaction system. is there. For that purpose, means for increasing the residence time of the oxygen gas jet for secondary combustion or the combustion gas in the molten slag is effective. The details of the discharge behavior of the high-temperature gas jet from the nozzle are complicated and not yet elucidated, but as a result of a detailed study by the present inventors, it has been found that the gas jet can be easily controlled by the following means. I found it. That is, by properly designing the nozzle,
It has been found that a desired nozzle characteristic can be obtained, for example, the width of control of the discharge flow velocity can be increased and extremely increased, and the spread of the jet can be easily controlled. For this reason, it becomes easy to enhance the combustion in the limited amount of molten slag and the stirring of the molten slag with oxygen gas and combustion gas, and to transfer heat from the combustion gas to the molten slag and from the molten slag to the metal bath. Heat transfer can be efficiently increased. Furthermore, it is possible to control the oxygen gas to be added to the optimal discharge condition while the conditions in the furnace of the bath such as the position of the metal bath surface, the amount of the slag and the fluidity change every moment. This is effective for improving the transmission efficiency of the vehicle.

Furthermore, the oxygen gas concentration in the above-described oxygen gas jet for secondary combustion is usually not 100% theoretically. There is basically no limitation on the oxygen gas concentration in the oxygen gas-containing gas as long as it meets the conditions for increasing the secondary combustion rate and the heat generation of the secondary combustion heat. Details are as follows.

When the amount of heat generated during the secondary combustion is used in a melting furnace or the like, it is necessary not only to increase the total heat value of the fuel but also to minimize the sensible heat of the exhausted combustion gas. When the oxygen gas concentration in the supporting gas changes, the total calorific value itself does not change if the oxygen amount is the same, but the sensible heat of the combustion gas changes. When the oxygen gas concentration decreases, part of the combustion heat is used to raise the temperature of gases other than oxygen gas, particularly gases that do not substantially react, such as nitrogen, and that gas is difficult to utilize in the furnace and is exhausted as it is. Will be. When a predetermined amount of a pure carbon source substance is burned with a predetermined amount of oxygen gas using a mixed gas of oxygen gas and nitrogen gas as the oxygen gas-containing gas, a part of the combustion heat is caused by the temperature rise of the nitrogen gas. Consumed and removed as sensible heat of nitrogen gas.
The heat loss increases as the oxygen gas concentration in the oxygen-containing gas decreases. Then, when the oxygen gas concentration falls below a certain value, the lost heat cannot be ignored. For example, oxygen gas concentration X containing 1 mole of oxygen gas
% Of the pure carbon source material is burned with
O ₂ is 1 mol product, the nitrogen gas becomes (1-X / 100) mole, ineffective heat is calculated by considering the specific heat of these gases increases as the oxygen gas concentration X% reduction. According to the study by the present inventors, the oxygen gas concentration needs to be at least 60% or more in order not to increase the ineffective heat, and it is advantageous that the oxygen gas concentration is as high as possible.
When the oxygen concentration becomes 90% or more, the ineffective heat becomes substantially negligible. On the other hand, in addition to achieving such high-temperature melting conditions for melting, refining, or fully exerting the function of the metal, it is necessary to consider restrictions from product quality. For example, from a practical viewpoint of keeping the nitrogen concentration affecting the quality of steel low,
In order to suppress the concentration to about 0 to 150 ppm or less, it is desirable that the nitrogen concentration in the mixed gas be 5 to 10% or less. From the viewpoint of industrial oxygen production methods, oxygen gas with impurities of several tens ppm or less can be used by a separation method (liquefaction method) by liquefaction of air, and an adsorption method (PS) containing several% of nitrogen can be used.
Method A: Pressure Swing Absorbt
General gas such as oxygen gas by the ion method) can also be used. However, when the oxygen production equipment becomes large in the case of large-volume use, or when economy is emphasized, a method of reducing the oxygen gas concentration at the time of these production, a method of mixing air with high-purity oxygen after production, etc. However, it is desirable that such a gas having a relatively low concentration of oxygen gas can be used without any problem.

For the reasons described above, the oxygen gas concentration in the oxygen gas-containing gas used in the present invention needs to be 60% or more, and preferably 90% or more.

Next, the temperature of the oxygen-containing gas will be described.

When the secondary combustion is performed in or near the slag, it is important to increase the dynamic pressure acting on the slag to increase the agitating flow of the slag and to enlarge the combustion space as much as possible. As a result of intensive examination of the discharge flow rate of the oxygen gas-containing gas to increase the stirring flow and widen the combustion space, the dynamic pressure and the stirring power that can act on the slag by preheating the oxygen gas-containing gas to a high temperature in advance, It was found that the combustion space could be expanded. In this case, if the temperature of the oxygen gas-containing gas is raised to 300 ° C. or more, the effect is large, and if the temperature is further increased to substantially 600 ° C., these effects are doubled as compared with the case where the room temperature oxygen is used. Therefore, it is more desirable to set the temperature higher than this temperature. Thus, the higher the temperature of the oxygen-containing gas,
Although the dynamic pressure, the stirring power and the control range of the combustion space can be widened, it is advantageous, but the temperature should be limited to 1300 ° C. or less in consideration of the heat resistance and safety of the piping and the increase of the pumping pressure. In particular, when using highly practical heat-resistant piping made of a high alloy, the temperature is slightly lower than when using special ceramics.
A temperature of 100 ° C. or lower is desirable because it is a condition for achieving stability. on the other hand,
Since the influence of the temperature of the oxygen gas-containing gas on the erosion of the refractory varies depending on the use environment, it is difficult to uniquely limit the temperature of the oxygen gas-containing gas. For example, conventionally, when combustion was performed only in a limited space in the slag, local high temperature in the slag occurred, or combustion did not complete in the slag and tended to occur also in the upper space of the slag. . In this case, the erosion of the refractory in contact with the slag by the high-temperature slag and the erosion of the refractory by the high-temperature combustion gas in the upper part of the slag tended to increase. In such a case, the combustion in the slag becomes uniform, and the refractory erosion can be reduced by suppressing the local high temperature.

Regarding the discharge flow rate of the oxygen gas-containing gas from the nozzle, a predetermined flow rate is necessary because the secondary combustion requires actions such as high dynamic pressure, high stirring flow, and reachability to a distant place as described above. And If the capacity of a practical electric furnace is about 50 to 200 tons and the melting and burning space is assumed, a furnace having a diameter of about 3 to 6 m is required. When applied to such a space, 150m
If it is not less than / s, it is possible to prevent not only the vicinity of gas introduction into the furnace, but also local heat deviation in this vicinity, damage to the furnace inner wall, and the like. Basically, since a flow velocity higher than the speed of sound can be applied, 300 m / s or more in a relatively low temperature range is required, depending on the temperature of the oxygen gas-containing gas. The upper limit of the discharge gas flow rate is determined by the ease of control into a limited space, the ease of increasing the pressure of gas, and the constraints of economics.
It can be applied without any problem up to about 00 m / s. On the other hand, regarding the influence of the discharge velocity of the oxygen gas-containing gas from the nozzle on the erosion of the refractory, as described above at the temperature of the oxygen gas-containing gas, it differs depending on the use environment,
Although it is difficult to uniquely limit the discharge flow rate of the oxygen gas-containing gas, the combustion space in the slag can be expanded by increasing the discharge flow rate, so that the erosion of the refractory can be reduced. .

As for the nozzles that can be used, the flow rate of the secondary combustion gas can be basically the same as the gas jet characteristics discharged from the conventional nozzle.
It can be used without problems from the conventional subsonic range to the supersonic range.

As described above, through the molten slag in a melting furnace or the like,
Although the case where the secondary combustion heat is added to the metal bath has been described, the above concept can be similarly applied to a raw material preheating process such as a melting furnace. In this case, secondary combustion is performed by supplying oxygen gas to the raw material packed bed, but the combustion rate and heat generation must be increased. By using oxygen gas preheated to a high temperature, the combustion space can be expanded, the combustion rate can be increased, and heat addition can be easily performed within a limited preheating layer.

The method for improving the secondary combustion rate and the heat transfer efficiency in the melting furnace and the like of the present invention has been made based on the above-mentioned various studies and findings, and the summary thereof is as follows.

According to the first aspect of the present invention, the primary combustion gas generated in a melting furnace, a smelting furnace or a smelting furnace is subjected to secondary combustion, and is used as effective heat in the melting furnace or the like. A method of using a gas-containing gas as the above-mentioned secondary combustion supporting gas, characterized in that a gas containing 60% or more of oxygen gas is used as the above-mentioned secondary combustion supporting gas. It is.

According to a second aspect of the present invention, there is provided the method for improving the secondary combustion rate and the heat transfer efficiency in the melting furnace or the like according to the first aspect, wherein the melting furnace or the like is a converter or an electric furnace for melting and / or refining iron. And a high-frequency melting furnace or a low-frequency melting furnace, or a smelting reduction furnace for smelting metal ore.

According to a third aspect of the present invention, in the method for improving the secondary combustion rate and the heating efficiency in the melting furnace or the like according to the first or second aspect, the temperature of the oxygen-containing gas is set at 30 degrees.
It is characterized in that the temperature is set to 0 ° C. or higher.

According to a fourth aspect of the present invention, in the method for improving the secondary combustion rate and the heat transfer efficiency in a melting furnace or the like according to any one of the first to third aspects, the oxygen-containing gas is discharged from a nozzle. At a flow rate of 150 m / s or more.

According to a fifth aspect of the present invention, in the method for improving the secondary combustion rate and the heat transfer efficiency according to any one of the first to fourth aspects, the oxygen-containing gas preheated to a high temperature is dissolved. It is characterized in that it blows into molten slag existing on a metal bath surface formed in a furnace or the like.

According to a sixth aspect of the present invention, in the method for improving the secondary combustion rate and the heat transfer efficiency according to any one of the first to fourth aspects, the oxygen-containing gas is formed in the melting furnace or the like. It is characterized in that it is blown into the raw material filling section that has not been completely dissolved.

According to a seventh aspect of the present invention, in the method for improving the secondary combustion rate and the heating efficiency according to any one of the first to sixth aspects, the step of preheating the oxygen gas-containing gas includes the step of supplying the oxygen gas-containing gas. In the oxygen gas-containing gas supply system between the apparatus and the oxygen gas-containing gas injection port to the melting furnace or the like, a predetermined fuel is burned to directly heat the oxygen gas-containing gas. It has a characteristic in a certain thing.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail.

FIG. 1 is a conceptual diagram of an arc heating electric furnace facility as an example of a melting furnace used for carrying out the present invention. The melting raw material and the slag-making material charged into the electric furnace are heated, melted and refined by the arc heat supplied from the electrode 1. First, in order to charge a solid iron source material such as steel scrap or cold pig into a furnace from a bucket, the furnace port has a structure in which an upper part can be opened. The furnace port is operated with the swiveling ceiling lid closed, and gas and dust generated in the furnace are discharged through the exhaust duct port. An inlet for auxiliary materials such as lime is also installed at the furnace port, and can be directly charged into the molten metal from the furnace port. On the other hand, the tip of the electrode 1 inserted from above the furnace port by the elevating device is stopped just above the surface of the molten metal, and the arc heating of the charged material is performed. Oxygen gas can be blown toward the molten metal surface from one or more nozzles on the lower surface side of the lance 2 fixed to the furnace side wall. In addition, the furnace bottom has one or more furnace bottom nozzles 3, and a stirring gas such as an inert gas is blown into the furnace bottom.
The furnace bottom nozzle 3 is made of a porous ventilation medium, and for example, a porous brick nozzle capable of injecting gas only when necessary, a metal single-tube nozzle or a concentric multi-tube nozzle is used. In the case of the latter metal tubular nozzle, since the molten metal enters the nozzle when the gas is stopped, it is necessary to continuously blow the gas from the time of charging the hot metal to the time of discharging the molten metal. As a melting furnace or the like, when a converter type reaction vessel furnace or the like is used in addition to the arc heating electric furnace, basically a furnace having functions of acid supply, stirring, charging of raw materials, and exhaust gas treatment is used.

In the case of using a converter type reactor, in addition to the material to be melted such as steel chips and the like, molten iron or a molten metal obtained by previously melting an iron source material in the furnace is fed while stirring with a bottom blow gas. The slag-making, melting, and heating of the metal bath are advanced by the heat energy generated by the acid and heat. Depending on the amount of heat required for melting, the supply of the carburizing material is also performed at the same time as the acid supply to supply the heat source. A variety of methods are available for the acid feeding method, but a lance is used for the acid feeding from above the metal bath surface.In general, a water-cooled lance is used to increase the durability, and an oxygen gas jet is injected from the nozzle hole at the tip. Is discharged at a high speed. The discharged oxygen gas jet collides with the metal bath surface while attenuating in the furnace, reacts with the metal bath, decarbonizes it, and generates CO gas. The CO gas generated in the vicinity of the metal bath surface or the like agitates the molten slag existing in a form covering the metal bath surface, rises and escapes, and is sucked into the exhaust gas treatment system through the furnace space and the furnace port. .

As described above, the CO gas, which is the primary combustion gas generated by the decarburization of the metal bath, is subjected to the secondary combustion by the oxygen gas. It is important that this secondary combustion be performed in a region as close as possible to the metal bath surface in order to increase the heat transfer efficiency to the metal bath.

The supply of an oxygen gas-containing gas to a melting furnace or the like is as follows.
Generally, a water-cooling lance from above the metal bath is provided with a supply line for oxygen gas for decarburization and a supply line for oxygen gas for secondary combustion. Therefore, an oxygen gas ejection nozzle is also provided separately. The secondary combustion nozzle is designed so that the oxygen gas is not directly blown onto the metal bath but is burned in a region slightly above the metal bath surface.

On the other hand, in a manner similar to the above, combustion is performed in a region slightly above the bath surface by a nozzle provided separately on the side wall of the furnace. Since it is important that such secondary combustion is performed over a wide area as described above, it is necessary to appropriately provide nozzles, lances, and tuyeres. As a method of preheating the gas containing the oxygen gas for secondary combustion to a high temperature before discharging it from the nozzle, the oxygen gas-containing gas pipe is passed through an atmosphere such as a high-temperature combustion gas used in various processes, A method of indirect heating through the pipe may be used, or a direct heating method of heating by burning a small amount of fuel in the oxygen gas pipe may be used. As the direct heating method, for example, a method disclosed in Japanese Patent Publication No. 6-29659 is used. Here, as described above, the heating temperature of the oxygen gas-containing gas is preferably as high as possible from the side of the secondary combustion reaction. However, the heating temperature is usually about 1300 ° C. due to the heat resistance of the heating device and restrictions on the transportation pipe of the gas after heating. It is desirable to do the following. In order to increase the secondary combustion rate, it is necessary to increase the temperature to at least 300 ° C.
The temperature is preferably set to 600 ° C. or higher.

In order to improve the heat transfer efficiency of the secondary combustion heat, it is particularly important to stir the metal bath and the slag bath. In this regard, electromagnetic stirring by arc heating of an electric furnace can be used, or an electromagnetic stirring coil can be provided on the furnace bottom or the furnace wall. In particular, in order to efficiently transmit the heat generated by the secondary combustion of CO gas to the metal bath, bottom-blown gas stirring from the furnace bottom side is effective, and various types of nozzles and bottom-blown gas types are used. Are possible. There are a multi-hole system in which a large number of nozzle holes are gathered, and a double-tube system including an inner tube for an oxygen-containing gas and an outer tube for a cooling gas. By using an oxygen gas-containing gas, a large amount of gas can be blown down at a low cost in some cases.However, in a low flow rate region, the reaction and thermal behavior in the bath are not much different from those of an inert gas, Both types are possible.

The gas jet from the bottom blow nozzle is controlled in view of measures against melt damage due to back attack by molten metal to the nozzle and measures against gas blow-through. In order to prevent back attacks on the nozzles, it is important to keep the gas discharge flow rate constant, and to prevent gas blow-through, it is important to reduce the flow rate per nozzle in accordance with the bath depth. Also in the present invention, it is necessary to design a nozzle in consideration of this point. Specifically, the number of nozzles and the nozzle diameter are designed according to the capacity of the processing furnace and the bath depth at the time of charging the molten metal.

[0036]

Next, the present invention will be described in more detail with reference to examples.

EXAMPLE 1 Six oxygen lances 2 for secondary combustion were provided on the side wall of a 50-ton AC arc electric furnace shown in FIG. The test consisted of Examples 1 to 9 performed under conditions within the scope of the present invention, and Comparative Examples 1 and 2 performed under conditions outside the scope of the present invention. As for the charging of the iron source raw material for melting, 50 t of an iron source raw material mainly composed of steel chips as a melting raw material were charged into a bucket in two parts, 30 t and 20 t, as in the case of ordinary melting. About 10 minutes after the second charge, the charge melted down and the metal 7 bath surface became apparently flat. At this stage, the lance 2 on the furnace side wall
The acid was fed at a more predetermined flow rate, and the CO gas generated from the metal 7 bath was secondarily burned, and the rate of temperature rise of the metal 7 bath was measured. Each secondary combustion lance 2 facing the center of the furnace had two nozzle holes at the tip, and the ejection angle was 20 ° downward with respect to the horizontal plane. The angle between two nozzle holes of the same lance is 20 ° and 110 °.
°, and lances having an angle between the nozzle holes of 20 ° and 110 ° were alternately arranged. Further, pure oxygen gas having an oxygen gas concentration of 99.5% was ejected from the nozzle. However, the oxygen gas jet does not interfere with the three electrodes 1,
The jetting direction of the jet with respect to the position of the electrode 1 was adjusted.
Oxygen gas flow rate is 1 in total from all 6 lances 2.
It was set to 500 Nm ³ / h. That is, the average flow rate per nozzle hole is 125 Nm ³ / h.

In order to preheat the oxygen gas for secondary combustion to a high temperature, an oxygen gas preheating device 5 is provided at an oxygen gas introduction portion to each lance 2. In this type, an oxygen gas pipe is passed through a small electric heater. The oxygen gas can be heated to about 1100 ° C. by the preheating device 5, and the temperature of the oxygen gas at the discharge port of the lance 2 can be maintained at 950 ° C. or more. The test was conducted at five levels of oxygen gas temperature: 250, 450, 650, 850 ° C. and room temperature. In addition, the diameter of each nozzle hole was determined in consideration of the oxygen gas temperature so that the flow rates of the oxygen gas discharged from the nozzles were 100, 250, and 500 m / s.

Supplying oxygen gas for secondary combustion under the above conditions
At the same time, insert a water cooling lance horizontally from the waste gate,
Carburizing and acid feeding from separate nozzles at the tip respectively
Was performed. Acid transfer rate is 1500Nm per hour^Threeso,
The coking was performed at a constant coke powder of 25 kg / min. Set
Since CO gas was constantly generated from the bath, the slurry on the bath surface
Slag 4 is in a so-called forming state, and slag 4 is
Standing, the height became about 60 cm or more. Side wall run
The oxygen gas from the slag 2 is high speed,
After penetrating inside, proceed inside the slag and reach near electrode 1
Meanwhile, the CO gas rising in the slag is burned.
Some or most of the CO gas is CO _TwoGas
You. Then, CO_TwoGas escapes from slag 4 and goes inside furnace
After passing through the internal space, it is treated by the exhaust gas collection system through the exhaust duct
Is done.

The power for heating the raw material by the electrode 1 was kept constant, and an electric power of 3800 kWh was supplied during the operation for 10 minutes. The operation was performed for 10 minutes under these conditions, and the secondary combustion rate was evaluated from exhaust gas analysis, and the heating efficiency was evaluated from the temperature measurement of the metal bath. Heating efficiency was based on an estimate of a heating rate of 15 ° C./min in the case where only normal forming operation was performed and electrode heating was performed without secondary combustion. As an estimate of the amount of heat when performing the secondary combustion, subtract the heating rate of the base from the heating rate after the time when the undissolved material completely disappeared,
This value was used as the actual sensible heat increase rate of the metal bath and the molten slag by the secondary combustion, and this was used as the above estimated value. The ratio of the sensible heat increase at this time to the theoretical combustion heat generated by the secondary combustion obtained from the secondary combustion rate was defined as the heat transfer efficiency. The conditions for carburizing and acid-supplying by a method in which a water-cooling lance is blown horizontally from a waste gate are common to Examples and Comparative Examples.

Further, as described above, the influence on the erosion of the refractory in the furnace was evaluated. If the location of the secondary combustion is too close to the side wall on the nozzle installation side, the refractory portion near the side wall where the nozzle is installed tends to be easily eroded. Therefore, the degree of erosion of the refractory portion immediately below the nozzle was evaluated.

The above test was conducted by changing the preheating temperature of the pure oxygen gas ejected from the nozzle of the lance on the furnace side and the discharge flow rate thereof as described above. Table 1 shows the test results.

[0043]

[Table 1]

From the above results, it can be seen that when oxygen for secondary combustion is supplied by the method of the present invention in the electric furnace steelmaking operation, the secondary combustion rate and the heating efficiency can be increased, and the melting loss of the refractory can be reduced. Was.

Example 2 In a 300 ton steelmaking converter, a preheating oxygen gas was used as a secondary combustion oxygen gas using a blowing lance (main lance), and secondary combustion and heat transfer efficiency were measured. Was tested. The test consisted of Examples 10 to 16 performed under conditions outside the scope of the present invention, and Comparative Examples 3 and 4 performed under conditions outside the scope of the present invention. The lance is of a double flow type having two systems of an oxygen gas pipe for decarburization and an oxygen gas pipe for secondary combustion. The decarburizing nozzle is the same as a normal blowing lance, and has a nozzle at the lower end of the lance that can supply a large amount of oxygen gas at room temperature. The nozzle hole used had one center hole and four holes around the center hole. The distance between the lower end of the lance and the surface of the molten metal (hereinafter referred to as the lance height) is 2.0 m.
000 Nm ³ / h was fed. For secondary combustion,
A plurality of nozzles provided on the outer peripheral surface at a height of 80 cm from the lower end of the lance were used.

As in the case of the converter blowing, after the charging of 110 tons of hot metal and 190 tons of hot metal, the blowing was started. From the initial stage of blowing, acid is supplied at a predetermined flow rate from the nozzle for secondary combustion, and while secondary combustion of the CO gas generated by decarburization, finally all of the cold iron dissolves, and furthermore, predetermined components and Blowing was performed until a temperature was obtained. The concentration of oxygen gas used for acid supply was 99.9%.
Pure oxygen gas. The discharge angle of the secondary combustion nozzle was set to 40 ° downward with respect to the horizontal plane. The oxygen gas flow rate for the secondary combustion was 12000 Nm ³ / h in total of all nozzles. Assuming that the total amount of oxygen gas for decarburization is CO gas, and of this CO gas, CO gas equivalent to the reaction equivalent to the total amount of oxygen gas for secondary combustion is converted to CO ₂ gas by secondary combustion, The combustion ratio CO ₂ / (CO + CO ₂ ) is 0.21. Actually, a part of the decarburizing oxygen gas is also consumed in the secondary combustion. Therefore, when the oxygen gas for the secondary combustion is completely burned, the secondary combustion ratio is higher than the above value of 0.21. Indicates a high value. Therefore, the evaluation of the secondary combustion ratio was not performed by comparing the absolute values, but by performing a relative comparison between the test conditions.

In order to preheat the oxygen gas for secondary combustion to a high temperature, a heating device for the oxygen gas was provided at the oxygen gas introduction section to each lance. The type is a method of directly burning the oxygen gas by burning a small amount of propane gas as fuel in the middle of the oxygen gas pipe. With this preheating device, the piping and nozzle were not damaged, and the oxygen gas temperature at the lance discharge port was 9
It can be secured to 00 ° or more. In this test, the oxygen gas temperature was set at five levels of 200, 400, 700, 900 and normal temperature. In addition, the nozzle hole diameter and the number of nozzle holes of each lance are considered in consideration of the discharge flow rate, and furthermore, in order to reduce the influence on the erosion of the refractory, the place where the secondary combustion is performed is not so close to the furnace wall. decided.

The carburizing agent was supplied simultaneously with the supply of the oxygen gas for secondary combustion. Coke powder was used as the carbonized material. Since CO gas was constantly generated from the metal bath, the slag on the metal bath surface was in a so-called forming state, the slag foamed, and its height became about 200 to 500 cm. Oxygen gas for secondary combustion from the lance is high-speed, penetrates into this forming slag, then proceeds in the slag, during which the CO gas rising in the slag is burned, and part of it becomes C oxygen gas . After that, it escapes from the slag, passes through the upper space in the furnace, passes through an exhaust duct, and is treated in an exhaust gas collection system.

Under the above-described conditions, the final molten steel C concentration is set to 0.1.
The operation is continued until the bath temperature reaches 1630 to 1640 ° C., the secondary combustion rate is determined from the total treatment time and exhaust gas analysis, and the components of the raw materials, metal bath components at the time of tapping and Using the tapping temperature, the heat transfer efficiency to the calorific value of the secondary combustion was evaluated based on the heat balance.

The above test was conducted by changing the preheating temperature and the discharge flow rate of the oxygen gas ejected from the main lance as described above. The test results are shown in Table 2.

[0051]

[Table 2]

From the above results, when the secondary combustion oxygen gas is preheated to a predetermined high temperature and used by the method of the present invention in the converter steelmaking operation, the secondary combustion site can be expanded and controlled, It was found that it was possible to increase the secondary combustion rate and the heating efficiency, and to reduce the erosion of the refractory.

[0053]

As described above, according to the present invention,
In melting furnaces such as converters and electric furnaces, the melting of raw materials can be promoted,
At the time of melting, which raises the temperature, without lowering the operability and the refractory damage, and increasing the heat-up efficiency of the secondary combustion heat,
It can be dissolved by reducing the amount of fuel or supporting gas used. Therefore, it contributes not only to reduction of the manufacturing cost but also to resource saving and energy saving. By providing such a method for improving the secondary combustion and accelerating the heat generation in the melting furnace, an industrially useful effect is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory conceptual diagram of an arc heating electric furnace facility used for carrying out the present invention.

[Explanation of symbols]

 Reference Signs List 1 electrode 2 lance 3 furnace bottom nozzle 4 slag 5 preheating device 6 oxygen gas supply device 7 metal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C22B 1/20 C22B 1/20 M 4K056 (72) Inventor Toshio Takaoka 1-chome 1, Marunouchi, Chiyoda-ku, Tokyo No. 2 Inside Nippon Kokan Co., Ltd. (72) Inventor Toshio Ishii 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term inside Nippon Kokan Co., Ltd. 4K001 AA10 BA22 BA23 FA10 GA06 GA16 GA17 GA19 GB03 JA01 4K002 AA01 AB01 AC05 AC07 AD02 BF01 BF03 4K012 CA04 CA06 CA09 CA10 4K014 AC04 AD00 CA01 CB01 CC01 CD18 4K045 AA04 AA05 BA02 DA04 RB02 RB16 RB17 4K056 AA02 BB01 CA02 CA20 FA13

Claims (7)

[Claims] 1. An oxygen-containing gas preheated to a high temperature is used for secondary combustion of a primary combustion gas generated in a melting furnace, a smelting furnace or a smelting furnace to be used as effective heat in the melting furnace or the like. A method for using as a combustion-supporting gas for secondary combustion, wherein a gas containing 60% or more of oxygen gas is used as the combustion-supporting gas for secondary combustion,
A method for improving the secondary combustion rate and heat transfer efficiency in a melting furnace or the like. 2. The melting furnace or the like may be any of a converter for melting and / or refining iron, an electric furnace, a high-frequency melting furnace or a low-frequency melting furnace, and a smelting reduction furnace for smelting metal ore. The method for improving the secondary combustion rate and the heat transfer efficiency in a melting furnace or the like according to claim 1, wherein: 3. The temperature of the oxygen-containing gas is 300 ° C.
The method for improving the secondary combustion rate and the heat transfer efficiency in the melting furnace or the like according to claim 1 or 2. 4. The secondary in a melting furnace or the like according to claim 1, wherein the flow rate of the oxygen-containing gas discharged from the nozzle is set to 150 m / s or more. A method for improving the combustion rate and heat arrival efficiency. 5. The method according to claim 1, wherein the oxygen gas-containing gas preheated to a high temperature is blown into a molten slag existing on a metal bath surface formed in the melting furnace or the like.
A method for improving a secondary combustion rate and a heat transfer efficiency in a melting furnace or the like according to claim 4. 6. The method according to claim 1, wherein the oxygen gas-containing gas is blown into a raw material filling portion formed in the melting furnace or the like and not completely melted. A method for improving the secondary combustion rate and heat transfer efficiency in a melting furnace or the like. 7. The preheating step of the oxygen-containing gas in the oxygen-containing gas supply system between the oxygen-containing gas supply device and an oxygen gas-containing gas injection port to the melting furnace or the like. The secondary combustion rate and heat transfer efficiency in a melting furnace or the like according to any one of claims 1 to 6, wherein the combustion is performed by directly heating the oxygen-containing gas by burning the fuel. How to improve.