JPS6312921B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to iron and steel metallurgy, and more particularly to a process for melting steel in a basic oxygen top-blown converter having an overhead-mounted oxygen lance.

The process of melting steel in a basic oxygen top-blown converter (BOF) involves refining the metal by blowing oxygen into a metal input that includes scrap metal, molten iron, and additives. An important feature of BOF technology in steelmaking is its scrap processing ability.

Scrap is a cheaper starting material for steelmaking than pig iron. Therefore, while 1.1 tons of scrap is sufficient to produce 1 ton of steel,
To produce one ton of steel from pig iron, two tons of ore must first be mined and processed in a blast furnace, a process that consumes about one ton of precious and expensive coking coal. The material cost of collecting and preparing one ton of scrap metal is 10 to 12 times less than the material cost of producing one ton of pig iron. Therefore, the use of scrap metal in steel making can result in significant savings both in critical materials and in the amount of labor required.

Taking into account the lower cost of scrap, the use of molten steel to increase the proportion of scrap metal and reduce the proportion of hot metal in the input metal part.
Various techniques have been recently introduced in BOF technology. One technique for increasing the scrap percentage is to preheat the scrap in a basic oxygen furnace. Accordingly, approximately one quarter of all BOF installations in the United States are equipped with fuel gas or fuel oil tuyeres for this purpose. According to available data (see Steel Times Magazine, Vol. 205, No. 11, 1977, pp. 133-137, 139-140), preheating the scraps to 800°C shows that with a heating time of about 10 minutes, The proportion of scrap can be increased by 10% of the total metal input weight. Steel melting techniques in which the scrap is preheated in basic oxygen furnaces to increase the scrap proportion of the metal input are widely practiced in the United States, United Kingdom, Belgium, Sweden, Japan, and France.

Prior Art The first attempt to heat and melt scrap without adding molten iron in a conventional basic oxygen furnace was
Voest-Alpine AG (Rinesch
(Refer to RF-J. Metals 1962, Vol. 14, No. 7, pp. 497-501).

U.S. Pat. No. 3,174,847 discloses a steel manufacturing method in which from 1.5 to 1.5 of the weight of pig iron and metal inputs previously placed in a basic oxygen furnace.
Put coke on top with steel scrap in the amount of 1.75%. The coke is then ignited by a gas burner and oxygen is blown through the charge, increasing as the charge melts.

Also, in a basic oxygen furnace, cold materials (crushed cast iron, steel scrap, fuel, iron alloys) are put into the furnace, and then they are melted and refined with oxygen, using flammable materials as fuel. Steel manufacturing methods are also known (see US Pat. Nos. 2,800,631 and 3,234,011).

However, implementing a steelmaking process that involves melting and smelting by supplying oxygen directly over inputs containing cold scrap and solid fuels can lead to ignition of the fuel, inefficient use of the fuel, and metallization. Difficulties were identified in high residual sulfur values in the furnace, short life of the refractory lining of the furnace, significant metal melting losses, and high loading of slag-forming substances. For these reasons, techniques for heating metal inputs have not been widely implemented.

Currently, the heating of scrap in basic oxygen furnaces with molten iron as the metal input composition is carried out by the heat generated by burning gaseous or liquid carbon-containing fuels in oxygen. This scrap heating technology uses fuel oil/
Steel mills such as Willing Pittsburgh with oxygen tuyeres, Allan with fuel gas/oxygen lances
Used in steel mills such as Wood.Wisconsin Steel.Inland Steel Co. Cockerill
Ougree uses oil as a liquid fuel (Blast Furnace and Steel Plant, 1969, Vol. 57, No. 12, pp. 1007-1012, Kemner WF; I.
Metals 1972, Vol. 24, No. 9, pp. 26-37;
Ironmaking and Steelmaking1976 Volume 8 No. 5
No. 252-258 Onuschek JW, Holmes R.
(See LW).

A steel mill of Nippon Steel Corporation uses a toroid-shaped kerosene/oxygen lance (Iron and Steel
Institute1973 Vol. 46 No. 4 No. 325-331
(See Chatterjee A.).

Known scrap preheating techniques operate as follows.
First, lime is introduced into the furnace to protect the furnace bottom from iron oxides released during scrap heating. After adding the lime, place the required amount of scrap into the furnace, pull the oxygen lance through the opening in the furnace hood, and replace it with the gas/oxygen lance. Set the furnace in the vertical position and lower the gas/oxygen lance until the tip of the lance reaches the opening in the hood. It is then ignited with a manual fuel gas torch. Subsequently, the lance is lowered to the scrap heating position and maintained at a distance of more than two to three times the depth of the melting bath during the heating operation.

In embodiments using liquid fuel, there is no particular need to ignite with a torch as the temperature of the refractory lining is sufficient to ignite the fuel. When the scrap preheating device is operated,
The lance is lowered into the furnace approximately 1 meter below the furnace mouth. If the lance gets too close to the scrap level, the tip of the lance will quickly be destroyed. On the other hand, if the lance is located too far from the scrap,
Heating efficiency is adversely affected. Moreover, with the techniques described above, the scrap is not heated uniformly;
The lighter pieces have already melted, but the heavier pieces have not yet been sufficiently heated. Following a scrap heating period of approximately 11-12 minutes, the fuel lance is raised and retracted to a non-use position, an oxygen lance is introduced in its place, the furnace is tilted, and molten iron is injected into it. Metal refining is carried out by blowing oxygen. At least 15% of the total amount of oxygen required for smelting operations
% and then set the lance in its working position.

However, the disadvantages of basic oxygen furnace operation using fuel gas/oxygen or fuel oil/oxygen to preheat the scrap are the complex construction with special equipment for supplying fuel to the lances and the difficulty of operating that equipment. the necessity of prolonging the scrap preheating time, and the generation of a liquid-phase molten region saturated with iron oxide after heating. Additionally, fuel/oxygen lance operation involves high levels of harmful frequency noise.

When used in basic oxygen furnaces, combustion of gaseous and liquid fuels in oxygen provides a lower heat utilization coefficient than solid carbonaceous fuels. Therefore,
The average temperature of BOF gas is 1440℃, and the heat utilization coefficients of natural gas and fuel oil combustion are 8.4, respectively.
% and 14.9%, while the heat utilization coefficients of anthracite and solid carbon are 22.5% and 23.2%, respectively (Baptizmanski, "Metal Scrap of Inputs in Basic Oxygen Furnaces", Moscow, USSR, 1982, p. 61). VI.
Boichenko BM; see Tretyakov EV).

The combustion of solid fuel (mainly coke) in a stream of oxygen is carried out using special lances with annular gaps. Powdered solid fuel is supplied to the lance from a special container via a corresponding pipe system with a flow of carrier gas (argon or nitrogen), meeting at the outlet of the annular gap of the lance with a flow of oxygen where it is combusted (Berg. &
Hu¨ttenman Mona¨tsh1960 Volume 105 No. 11 No. 303
Rinesch RF, p.-309; Rinesch RF, J. Metals 1962, Vol. 14, No. 7, pp. 497-501). This technology of scrap preheating is used, for example, by Klo¨ckner-Werke AG in West Germany, to melt steel from scrap in basic oxygen furnaces without using molten iron.
It is used in

High wear in the transport system is a major drawback of this method. Moreover, if a fuel with a volatile content of 8% or more is used, self-ignition is likely to occur, which limits the selection of carbonaceous fuels.

In all known methods of producing steel in basic oxygen furnaces using either solid or gaseous/liquid fuels, the method of heating the scrap is complicated and involves preparing the fuel and introducing it into the furnace. Considerable expense is required to install special equipment for supplying the water.

Problems to be Solved It is an object of the present invention to provide a steel melting process that makes the process of preheating the scrap simpler and cheaper, making use of readily available and relatively inexpensive heat sources.

Means for solving the problem The purpose is to introduce the scrap into a furnace; the scrap is heated with the heat generated by burning the carbon-containing fuel fed into the furnace in oxygen. A process for melting steel in a basic oxygen top-blown converter comprising steps of injecting molten iron and refining the metal by blowing oxygen, according to the present invention, the heating of the scrap is introduced as a stream. 8 to 8 per ton of scrap through a lance set at a height of 50 to 100 times the effective inside diameter of the lance, which supplies oxygen from the bottom level of the furnace. ^15Nm3 /
The flow of oxygen supplied in an amount of above the predetermined working height of the lance for the smelting operation.
beginning metal smelting by setting the lance at an altitude of 1.5 to 2.5 times, followed by setting the lance at a working altitude by gradually lowering the lance;
This descent begins after supplying 5 to 10% of the total amount of oxygen required for the smelting of the metal, and after supplying 20 to 25% of the total amount of oxygen required for the smelting of the metal. This is accomplished by a steel melting process in a basic oxygen top-blown converter, characterized by:

The steel melting process disclosed herein greatly simplifies the scrap preheating operation and makes it considerably less expensive. This is because the preheating of the scrap can be carried out in basic oxygen converters of conventional construction without any modifications and virtually without any investment.

Various grades of coal can be used as the solid carbonaceous fuel, including low-grade coal.

The refining process can be performed with high efficiency and high productivity under these conditions.

The features of the steel melting method disclosed herein will be better understood from the following description.

Operation The melting process takes place in a conventional basic oxygen top-blown converter furnace, ie, a furnace with an oxygen lance mounted overhead.

When the thermal products of the previous melting cycle (i.e. steel and slag) are removed from the furnace and the refractory lining of the furnace is maintained at a temperature of at least 800°C, the required amount of scrap (depending on the technology employed) is removed. into the furnace and set the furnace to its operating position. Lower the lance, set it at a height corresponding to a distance of 50 to 100 times the effective inside diameter of the lance from the level of the bottom of the furnace, and apply oxygen through the lance at a rate of 8 to 15 Nm ³ /min per ton of scrap. is supplied as a flow. The term "effective inner diameter" above means the diameter of a circle having an area equal to the sum of all areas at the level of the critical inner diameter of the nozzle of the lance. At the same time as oxygen is supplied into the furnace, solid carbonaceous fuel is supplied into the furnace in an amount of 8 to 45 kg of carbon per ton of scrap at a rate of 0.1 to 2 t/min.

The solid carbon fuel is supplied in a cross flow with the oxygen flow through conventional bulk input ducting. The angle defined by the oxygen flow and the solid carbonaceous fuel flow is between 10° and 30°. At the moment when the oxygen flow meets the carbonaceous fuel flow, due to the high temperature inside the furnace (at least 800 °C), the fuel will instantly ignite, causing the oxidation of carbon to carbon dioxide and the combustible components in the fuel, e.g. The combustion of hydrocarbons releases a large amount of heat. This ignition produces large flame tongues that heat the scrap.
The above technology for supplying carbonaceous fuel and oxygen allows them to be properly mixed and the unburnt particles of carbonaceous fuel are uniformly distributed over the whole scrap surface, where combustion is sustained and the scrap is removed. Can be heated. The duration of this scrap heating step is 3 to 8 minutes.

The setting of the lance at the height specified above is determined by the objective that it is necessary to heat as large an area of the heating surface of the scrap with the flame tongue as possible.

By setting the lance at a height less than 50 times the effective inside diameter above the furnace bottom level, the flow of carbonaceous fuel intersects the axis of the lance and the flow of solid fuel fed into the furnace crosses the oxygen flow. This is not allowed as it is incompatible with the condition that it intersects with

On the other hand, if the lance is set at a height greater than 100 times the effective inside diameter, the flame tongues will impinge on the refractory lining of the furnace, adversely affecting its strength.

The amount of oxygen supplied in the above range from 8 to 15 Nm ³ /min per ton of scrap to preheat the scrap is 8 Nm ³ /min per ton of scrap.
The decision is made because feeding at a lower rate will reduce the heat transfer from the flame to the scrap, worsening the secondary combustion conditions for the unburned solid fuel particles, and therefore resulting in lower scrap preheating.

On the other hand, supplying oxygen at a rate higher than 15 Nm ³ /min per tonne of scrap results in the formation of local liquid regions saturated with iron oxide in the scrap;
This area can splash out of the furnace when the next batch of molten iron is poured into the furnace.

Coal, coke, coking waste, and other similar materials of various compositional grades can be used as solid carbonaceous fuels. The impurities contained in the carbonaceous fuel have practically no effect on the refining process and do not impair the quality of the steel. The chunks of fuel used range from 1 to 3 centimeters. If larger particle size fuels are used, a significant amount of unburned fuel particles will remain in the furnace at the end of the scrap heating operation.

Once the scrap heating process is completed, lime is placed into the furnace and molten iron is poured into it.

After injecting the molten iron, the furnace is reinstalled in the operating position, the lance is lowered, and the lance is set at an altitude of 1.5 to 2.5 times the predetermined working altitude of the lance for the smelting operation. The term "working altitude" means the distance from the tip of the lance to the level of liquid metal in a virtual static state in the furnace.

The above lance position at the start of smelting is important to prevent metal and slag splashing due to the presence of large amounts of iron oxide formed during scrap heating. This position of the lance reduces the time to reset the lance to the working altitude.

If the lance is set below 1.5 times the working altitude, there is a risk that the tip of the lance will be damaged by the protruding unmelted scrap.

When the lance is set above 2.5 times the working altitude, a significant amount of iron oxide is formed in the slag and the next time the lance is lowered to the working altitude, the carbon oxidation reaction that develops removes the metal from the furnace. Slag will splash.

Next, 5 of the total amount of oxygen required for refining this metal.
After supplying an amount of 10% of oxygen, the lance is reinstalled in the working position by gradually lowering it from the above-mentioned initial position. Supply oxygen in an amount of 20 to 25% of the total amount required for the smelting operation and halt the lowering of the lance. Subsequent refining operations are conducted at a thermal efficiency suitable for melting the desired grade of steel.

If the lance is lowered from its initial position before 5% of the total oxygen required for the refining operation has been supplied, there is an increased risk that the lance tip will be damaged by protruding unmelted scrap.

On the other hand, if the lance is started lowering from its initial position after 10% of the total oxygen requirement has been supplied, the slag will become saturated with an excess amount of iron oxide. This must be avoided.

Similar precautions must be taken into account regarding the lowering of the lance and its installation at the working height. Lowering the lance too quickly, i.e., placing the lance at its working altitude before delivering 20% of the total amount of oxygen, may cause the lance to strike the scrap piece. However, it is undesirable to lower the lance too slowly and set it to the working altitude when more than 25% of the total oxygen has been supplied, as this increases the overall time of the refining operation.

The steel melting process described above offers a number of advantages, including:

The scrap heating operation can be simplified without making any practical additional investment in a Γ-basic oxygen top-blowing converter or a combined blowing furnace including top-blowing.

Γ Conventional equipment can be used without any structural improvements.

Γ Readily available and inexpensive thermal energy sources, ie, solid carbon fuels such as low-grade fuels, can be used without complex and expensive conditioning.

In order to better understand the invention described above, a practical example is given below.

WORKING EXAMPLE 1 350 with a refractory lining having a temperature of approximately 1000°C
After draining the molten steel and slag from the basic oxygen converter, 130 tons of scrap are placed into the furnace and the furnace is set in operating position. Lower the lance to a height of 8 meters (effective inner diameter) from the level of the bottom of the furnace.
85x). oxygen passes through the lance
1300Nm ³ /min (10N per ton of scrap
m ³ /min). Simultaneously with the oxygen supply, an amount of 3000 kg of low grade coal of the following composition is fed into the furnace through a bulk feed duct such that the flow of this fuel intersects the oxygen flow. By weight,
Combustible part 54.8%, ash 37.6%, moisture 7.6%. oxygen
Supply 6500Nm ³ and stop heating. Pour 15 tons of lime onto the preheated scrap. Raise the lance and tilt the furnace, C = 4.2%, Si = 0.7% by weight,
1400 including Mn=0.25% S=0.030%, P=0.06%
Pour 270 tons of molten iron into it. Reset the furnace to the operating position and place the lance 4 meters above the level of molten metal in virtual static conditions (at working altitude).
2.2 times) and then start oxygen supply. The lance is gradually lowered by supplying ^1300Nm3 of oxygen (8% of the total volume required for the scouring operation) and the molten metal level with the lance in a static state when ^3600Nm3 of oxygen is supplied (22% of the total volume) Set to a working altitude of 1.8 meters above the ground. This position of the lance remains substantially unchanged until the end of the refining operation, which is performed by standard techniques. The duration of the refining process is 12.5 minutes. At the end of the refining operation, the temperature of the produced steel is 1640 °C and its carbon content is 0.08%. The temperature of these steels and their carbon content data confirm that the thermal efficiency of the melting cycle was adequate.

Example 2 The sequence of operations is the same as Example 1, but the amounts of scrap and molten iron charged into the furnace are slightly changed, and the parameters of the scrap heating and refining processes are modified.

The amounts of scrap and molten iron introduced into the furnace are 100 tons and 230 tons, respectively. The lance is set at a height of 4.5 meters (50 times the effective inside diameter) to preheat the scrap. The oxygen supply rate for the heating process is 1500 Nm ³ /min (15 Nm ³ /min per ton of scrap). The total amount of coal fed into the furnace is 1920Kg. Supply 4500 Nm ³ of oxygen for the heating operation and stop heating the scrap. Ten tons of lime are placed on top of the preheated scrap and molten iron is poured into it. Metal refining is above the virtual level of molten metal in a static state.
Starting by setting the lance at a height of 2.5 meters, i.e. 1.5 times the working altitude, the oxygen supply is started and after supplying 865 ^Nm3 of oxygen (5% of the total amount required for the smelting operation): Gradually lower the lance,
When supplying 3460 Nm ³ of oxygen (20% of the total amount required for the refining operation), the lance is set at a working altitude of 1.7 meters above the virtual level of static molten metal.
At the completion of the smelting operation, the temperature of the produced steel is
It is 1635 degrees and its carbon content is 0.07%.
Scouring time is 11.5 minutes.

Example 3 The sequence of operations is the same as Example 1, but the amounts of scrap and molten iron charged into the furnace are changed, and the parameters of the scrap heating and smelting processes are modified.

The amounts of scrap and molten iron put into the converter are 140 tons and 260 tons, respectively. The lance is set at a height of 9.3 meters (100 times the effective inside diameter) to preheat the scrap. Oxygen is supplied for the heating process at a rate of 1120 Nm ³ /min (8 Nm ³ /min per ton of scrap). The total amount of coal fed into the furnace is 4200Kg. oxygen
Supply ^8960Nm3 and stop heating. Fifteen tons of lime are placed on top of the heated scrap, and molten iron is poured into the furnace. Start smelting by setting the lance at a height of 4.5 meters above the static molten metal level, i.e. 2.5 times the working altitude. ^1520Nm3
of oxygen (10% of the total amount required for smelting),
The lance is gradually lowered and, after supplying 3800 Nm ³ of oxygen (25% of the total required for the smelting operation), is set to a working altitude of 1.8 meters above the level of static molten metal. Refining time is 14 minutes. At the completion of refining, the temperature of the molten steel is 1635°C and its carbon content is 0.09%.

Example 4 The sequence of operations is the same as in example 1, but low-grade coal is replaced by coke containing 92% carbon.

The amounts of scrap and molten iron put into the furnace are 130 tons and 270 tons, respectively. The lance is set at a height of 8 meters (85 times the effective inside diameter) to preheat the scrap. The oxygen supply rate for the heating process is 1300 Nm ³ /min (10 Nm ³ /min per ton of scrap). The total amount of coke fed into the furnace is 2000Kg. oxygen
Supply ^6500Nm3 and stop heating. Fifteen tons of lime is placed on top of the heated scrap, and molten iron is poured into it. Refining operations are carried out at a height of 4 meters above the virtual level of static molten metal, i.e. at the working altitude.
Start by setting the lance at 2.2 times the height,
Having already supplied 1300 Nm ³ of oxygen (8% of the total amount required for the smelting operation), the lance was gradually lowered,
When ^3600Nm3 of oxygen (22% of the total amount) was supplied,
Set the lance to a static working altitude of 1.8 meters above the virtual level of molten metal. Refining time is 11.5 minutes. The temperature of molten steel at the end of the refining operation is 1620℃
and its carbon content is 0.06%.

Effects of the Invention The present invention significantly simplifies scrap heating and makes it possible to intensify the steel melting process in basic oxygen converters without substantial additional capital investment.

Claims (1)

[Claims] 1 Process of charging scrap into a furnace; Process of heating scrap with heat generated by burning carbon-containing fuel supplied into the furnace in oxygen; Process of pouring molten iron; a process of melting steel in a basic oxygen top-blown converter furnace, comprising the steps of: heating the scrap by burning a solid carbonaceous fuel introduced as a stream; A flow of oxygen and said fuel supplied in an amount of 8 to 15 Nm ³ /min per ton of scrap through a lance set at a height of 50 to 100 times the effective inside diameter of the lance supplying oxygen from bottom level. lime is poured over the heated scrap, and then molten iron is injected; above the level of molten metal in a static state, a predetermined amount for the smelting operation is ,
Metal smelting is started by setting the lance at an altitude of 1.5 to 2.5 times the working altitude of the lance, followed by setting the lance at the working altitude by gradually lowering the lance, and this lowering Start by supplying 5 to 10% of the total amount of oxygen required for refining the metal, and
A process for melting steel in a basic oxygen top-blown converter, characterized in that 20 to 25% oxygen is supplied and then discontinued.