JPH0368082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a metal raw material melting and refining method that is applied to a metal production process for smelting and reducing oxide metals, a process for melting reduced metals and scrap, and the like.

(Prior art) In the past, the mainstream steel production method was the open hearth method, which could melt large amounts of scrap, but it declined due to low productivity, and now pure oxygen top-blowing or bottom-blowing methods are being used instead. The converter method has become mainstream.

However, in these converter methods, the scrap ratio (scrap content ratio) is not as high as in the open hearth method.
It is at most 20%. Therefore, methods other than the converter method are becoming extremely important for scrap processing, which accounts for about 40% of raw steel raw materials.

And today, scrap as a raw material is used in blast furnaces.
In integrated steel mills using the converter method, much of it is consumed in electric furnaces.

The electric furnace method has low equipment costs, making it economically viable even in small-scale factories, and is also suitable for melting and refining reduced iron produced by direct reduction iron plants, which have been attracting attention in recent years. It is believed that it will continue to occupy an important position in the future.

However, the electric furnace method uses expensive electricity as a heat source to melt and refine the scrap, which puts it in an extremely difficult economical situation. There is a growing need for inexpensive scrap melting and refining methods.

Against this background, the development of new melting and refining methods has become an important issue in the steel industry, and the one that is attracting the most attention is the method that involves blowing coal and oxygen gas into a metal bath. This is a so-called metal bath process in which a partial oxidation reaction is carried out inside the tank, and the resulting heat is used to melt the scrap.

The following is an example of a process applied to iron-based raw materials. However, the main reaction within the iron bath in this process is shown by the following equation.

C+1/2O ₂ →CO (in coal) (injected gas, etc.) (1400℃ elution gas)
...1565Kcal/C-Kg (heat generation) Furthermore, the hydrogen contained in the coal becomes _H2 gas and is discharged from the iron bath as eluted gas.

(Problem to be solved by the invention) By the way, the biggest drawback of the basic iron bath process is that out of the heat added to the furnace, the amount of heat removed by the furnace gas is extremely large, and therefore the amount of coal consumed is extremely high. That's a big thing.

The reason for this is that most of the gas coming out of the iron bath
These are CO gas and _H2 gas, and this is because these gases possess a huge amount of chemical heat (latent heat of combustion).

In other words, out of the amount of heat added to the furnace (coal combustion heat),
80-90% of the heat leaves the iron bath as bath gas, and only 10-20% of the heat is absorbed into the furnace. (This value varies depending on the type of coal, etc.) In order to compensate for this drawback, conventional methods take the following two measures.

a Secondary combustion method Oxygen is blown into the upper gas layer in the furnace, a part of the bath gas is combusted in the furnace, and the heat generated at that time is transferred to the iron bath by radiation heat transfer method.

That is, this is a method of improving the overall thermal efficiency by circulating the energy dissipated as exhaust gas back into the bath.

b Scrap preheating method A method in which oxygen or air is blown into the flammable gas coming out of the furnace, a part of the gas is combusted to raise the temperature of the gas, and the gas is brought into contact with the scrap to preheat the scrap.

These conventional methods have the following drawbacks.

(a) Disadvantages of the secondary combustion method (1) If secondary combustion is simply carried out, unless the secondary combustion rate is large to some extent, the absorption rate of the heat generated by the secondary combustion within the iron bath will rapidly decrease. Most of the heat generated by the subsequent combustion merely increases the temperature of the furnace exit gas and exits outside the furnace as heat loss.

Moreover, this method not only causes an increase in heat loss, but also causes damage to the refractories in the furnace because the temperature of the exhaust gas and the upper space of the furnace increases significantly as described above.

Therefore, in this method, the secondary combustion rate is 10~
It is said that the limit is 20%.

In order to compensate for this drawback, as seen in the invention of JP-A-57-74390, a gas jet is blown onto the bath surface through the upper gas layer in the furnace, and as it passes through the gas layer, the gas jet burns the gas in the furnace. A method has also been proposed in which the heat generated by combustion of this gas is transferred to the iron bath, but even if this method is adopted, the secondary combustion rate is limited (approximately 20 to 30%). There is.

The reason for this is that this method uses a secondary blow (oxygen) jet flow to generate two gases in the furnace.
The mechanism is that the high-temperature combustion gas generated by the secondary combustion is entrained by the injector effect and transferred into the iron bath to transfer heat. Some of the CO ₂ gas and H ₂ O gas newly generated by secondary combustion come into contact with the carbon dissolved in the iron bath, and the following reaction (at 1400°C) causes CO 2 gas and H 2 O gas to be generated again. Gas or _H2
This causes the phenomenon of returning to gas. (The reaction at this time is an endothermic reaction) CO ₂ +C → 2CO
...3176Kcal/KgC (endothermic) H ₂ O + C → H ₂ + CO
...2583Kcal/KgC (endothermic) This is extremely inconvenient in light of the original purpose of secondary combustion. In other words, secondary combustion uses chemical energy (CO and _H2) in the exhaust gas.
) is converted into thermal energy (converts CO and H ₂ to CO ₂ and H ₂ O through combustion, increasing the temperature of the gas) and transfers that thermal energy to the bath, thereby converting the energy held in the exhaust gas into thermal energy. Even though the purpose is to reflux the bath, if the above reaction occurs, the converted thermal energy is converted back into chemical energy (CO,
This results in the inconvenience of returning to H ₂ ).

In addition, as mentioned above, since secondary combustion takes place in the space above the bath surface in the furnace, a considerable portion of the heat generated by combustion is dissipated into the upper furnace wall and exhaust gas by thermal radiation. .

As a result of these, the effect of secondary combustion is significantly weakened.

(2) The number of gas injection nozzles must be extremely large, making the furnace structure complicated.

(b) Disadvantages of the scrap preheating method Since it requires scrap preheating equipment, it not only requires huge equipment costs but also complicates operations. In addition, the gas becomes hot and mechanical friction with the scrap causes severe wear on the refractory materials, resulting in high operating costs and reduced operating efficiency due to repairs.

This invention was made in view of the above points, and involves intentionally retaining an extra amount of slag on a metal bath than conventionally required for metallurgy, and burning the gas eluted from the metal bath. An object of the present invention is to provide a metal raw material melting and refining method that effectively utilizes a medium and the heat generated by the medium as a heat transfer medium, and has significantly improved thermal efficiency.

(Means for Solving the Problems) In order to achieve the above object, the gist of the present invention is to introduce a carbon-containing fuel and an oxygen-containing gas into a metal bath, partially burn the fuel, and generate heat. At the same time, a flammable gas is generated from a metal bath, and a part of the gas is combusted by a secondary combustion oxygen-containing gas that is blown into the furnace from a system different from the oxygen-containing gas mentioned above to generate heat. In the method of melting and refining metal raw materials using the heat generated by the metal bath, a sufficiently larger amount of slag than required for metallurgy is intentionally kept on the metal bath, and the above-mentioned flammable gas generated from the metal bath or its A portion of the slag is combusted within the slag by secondary combustion oxygen-containing gas injected through a nozzle located within the slag, and the resulting high-temperature combustion gas is burned into the slag without contacting the metal bath. The heat generated by combustion is first transferred to the slag, and then the oxygen-containing gas for secondary combustion is blown into the slag to stir the slag bath, or it does not contain oxygen gas from another system. A metal raw material melting and refining method characterized in that heat retained in the slag is efficiently transferred to the metal bath or metal raw material by blowing gas into the slag bath so as to stir it.

(Example) Hereinafter, a case where an example of the present invention is applied to a scrap melting furnace will be described with reference to the drawings.

In the figure, reference numeral 1 denotes a scrap melting furnace whose inner surface is covered with refractory bricks 2, and a fuel injection nozzle 4 and an oxygen injection nozzle 5 are provided at the bottom of the furnace corresponding to the iron bath 3 in the furnace. Similarly, a gun outlet 6 is provided on the side wall of the furnace corresponding to the metal bath 3 in the furnace. Corresponding to the slag bath 7 above the iron bath in the furnace, an oxygen injection nozzle 8 for secondary combustion and a slag exhaust port 9 are provided on the furnace side wall, and an exhaust gas duct 10 is connected to the opening at the top of the furnace. A chute 11 is provided for charging scrap A and auxiliary fuel into the furnace.

(effect) In the above configuration, the operation will be explained next.

(a) Action in the iron bath Carbon C in the coal (pulverized coal) injected from the fuel injection nozzle 4 at the bottom of the furnace dissolves in the iron bath 3.

Further, the hydrogen H in the coal that is blown in here becomes hydrogen gas and comes out from the iron bath 3 into the slag bath 7.

On the other hand, carbon dissolved in the iron bath 3 reacts with oxygen blown in from the oxygen blowing nozzle 5 at the bottom of the furnace, becomes CO gas, and exits from the iron bath 3 into the slag bath 7 together with hydrogen gas.

On the other hand, the scrap A fed into the furnace through the chute 11 above the furnace undergoes the above reaction.
It melts due to the heat generated. Molten guns formed by melting the scrap A are sequentially taken out from a gun outlet 6 located at the bottom of the furnace.

(b) Action inside the slag bath The gas (mainly composed of CO and H ₂ ) that comes out from the iron bath 3 into the slag bath 7 as described above rises as it mixes into the slag bath 7 in the form of bubbles. However, during the rising process, this comes into contact with the secondary combustion oxygen blown into the slag bath 7 from the secondary combustion oxygen injection nozzle 8 on the furnace side wall, and a part of the slag combusts to generate heat. In addition, the slag bath 7 is vigorously stirred or refluxed by blowing oxygen for secondary combustion, and the above-mentioned heat generated in the slag bath 7 is transferred to the iron bath 3 through the interface between the slag bath 7 and the iron bath 3. This is said to be the case with iron-based raw materials.

In this way, the gas after secondary combustion in the slag bath 7 leaves the slag bath 7, rises in the furnace space, becomes exhaust gas, and is discharged to the outside of the furnace via the exhaust gas duct 10.

In addition, in the above process, slag is appropriately discharged from the slag discharge port 9 provided on the furnace side wall corresponding to the slag bath 7 in order to maintain the amount of slag in the furnace at a specified amount, and from the chute 11 at the upper part of the furnace. , scrap A, and auxiliary raw materials such as lime are charged as appropriate.

However, in this invention, oxygen-containing gas is injected into the slag to combust the gas coming out of the iron bath, but this injection of oxygen-containing gas for secondary combustion is carried out as described above. In addition to blowing through the furnace side wall that corresponds to the slag bath and contacts the slag bath, it is also possible to attach a secondary combustion oxygen-containing gas blowing nozzle to a lance inserted into the furnace from the top of the furnace, and blow through the lance. It is also possible to enter.

In addition, a plurality of the above-mentioned oxygen-containing gas blowing nozzles for secondary combustion are provided, some of which are oriented upwards from the horizontal level and others are oriented downwardly to blow gas into the slag bath, and these oxygen-containing gas blowing nozzles are By making the gas blowing direction from the filling nozzle eccentric rather than toward the center of the furnace, it is possible to improve the stirring effect of the slag bath or to form a steady reflux bath of the slag. Further, a gas other than the oxygen-containing gas for secondary combustion may be blown into the slag bath and the slag bath may be stirred.

Furthermore, liquid fuel such as heavy oil can also be used instead of coal.

In the above example, only the reduction of iron oxide was explained, but other metals such as Cr, Ni, Mn
Of course, it can be applied to iron-based raw materials in exactly the same way as iron-based raw materials.
Just change it to Cr.

Further, variations of this invention are as follows.

(1) When the blown oxygen-containing gas is air.

(2) When preheating the blown oxygen-containing gas.

(3) When preheating metal raw materials before charging them into the furnace.

(Effects) From the above explanation, the effects of this invention are as follows.

(1) Since the secondary combustion mainly takes place in the slag bath, the amount of heat generated by the secondary combustion dissipates is small, and most of the heat generated by the secondary combustion is absorbed into the slag bath, and this heat is transmitted into the metal bath through the metal raw material in contact with the slag bath or the interface of the metal bath. Therefore, the amount of chemical heat retained in the furnace gas is reduced, the heat absorption efficiency within the furnace is high, and the amount of fuel consumed is low.

According to the example calculation, 1 ton of iron scrap (1000
In comparing the amount of coal required to melt 1 kg), the conventional method required 200 kg, while the present invention required 160 kg.

Furthermore, in comparing the amount of coal required to melt and reduce 1 ton (1000 kg) of iron oxide, the conventional method required 1100 kg, while the method of the present invention required 860 kg.

(2) The slag bath acts as a physical and chemical buffer, making the secondary combustion process extremely stable and less susceptible to changes in operating methods. Therefore, operability is improved.

For example, in the case of the invention of JP-A No. 57-74390 mentioned above,
The blowing direction changes due to slag adhering to the secondary combustion air blowing nozzle installed at the top of the furnace or the refractory bricks being worn out, resulting in changes in the amount of blown gas and changes in the position of the metal bath surface. However, with the method of the present invention, such situations do not occur.

(3) Since the gas after secondary combustion does not come into contact with the metal bath, CO ₂ gas and H ₂ O contained in the combustion gas are removed.
Gas rarely changes back to CO gas or _H2 gas. Furthermore, since secondary combustion takes place within the slag, the amount of heat generated thereby is dissipated into the upper part of the furnace or into the exhaust gas is extremely small. As a result of the above, a high secondary combustion rate can be obtained.

[Brief explanation of drawings]

The drawing is a sectional view of a scrap melting furnace showing an embodiment of the present invention. 1... Scrap melting furnace, 2... Firebrick,
3...metal bath, 4...fuel injection nozzle, 5...
Oxygen injection nozzle, 6... Tapping port, 7... Slag bath, 8... Oxygen injection nozzle for secondary combustion, 9...
Slag outlet, 10...Exhaust gas duct, 11...Chute.

Claims (1)

[Claims] 1. A carbon-containing fuel and an oxygen-containing gas are introduced into a metal bath, the fuel is partially combusted to generate heat, and a flammable gas is generated from the metal bath, and the gas or the gas is A method in which a part of the oxygen-containing gas is combusted with a secondary combustion oxygen-containing gas blown into the furnace from a system different from the above-mentioned oxygen-containing gas to generate heat, and the metal raw materials are melted and refined using the heat. A sufficiently larger amount of slag than required is intentionally kept above the metal bath, and a portion of the flammable gases emanating from the metal bath are blown through a nozzle located within the slag. The slag is combusted with an oxygen-containing gas for secondary combustion, and the resulting high-temperature combustion gas is brought into contact with the slag without contacting the metal bath, and the heat generated by combustion is first transferred to the slag, and then Oxygen-containing gas for combustion is blown into the slag bath to stir it, or oxygen-free gas is blown into the slag bath from another system to efficiently transfer the heat retained in the slag to the metal bath. Or a metal raw material melting and refining method characterized by being transmitted to the metal raw material. 2. The metal raw material melting and refining method according to claim 1, wherein the nozzle is located on a furnace side wall that contacts a slag bath. 3. The metal raw material melting and refining method according to claim 1, wherein the nozzle is attached to a lance inserted into the furnace from the upper part of the furnace. 4. The metal raw material according to claim 1, wherein a plurality of secondary combustion oxygen-containing gas injection nozzles are provided, some of which are directed upward from the horizontal and the others are directed downward to blow the gas into the slag bath. Melting and refining method. 5. The metal raw material melting and refining method according to claim 1, wherein a plurality of the secondary combustion oxygen-containing gas injection nozzles are provided, and the gas injection direction thereof is not directed toward the center of the furnace but is eccentric. 6 Metal raw material melting and refining according to claim 1, in which an inert gas is blown into the slag bath, or into the slag bath and the metal bath, and the slag bath, or the slag bath and the metal bath are stirred or refluxed. Method.