KR20000026559A - Method for forming slags in electric furnace - Google Patents

Abstract

PURPOSE: A method for forming slags in an electric furnace is provided by which an electric consumption of operation can be reduced through the stabilization of slag-forming process and operating rate is enhanced. CONSTITUTION: In the method for forming slags in an electric furnace, after finishing issuance of steel, blowing 7kg/t-s carbon particles, of which size is within 2-4mm of cokes breeze and which is carried by over 10m3/t-s of air, with hot heels into a melted slag layer to reduce a slag-component layer(FeO) and P2O5 so that reduced P acts as a surface activation material to activate slag-forming.

Description

Furnace slag forming method

The present invention relates to a slag forming method of the furnace, in particular, during the refining of the electric furnace to improve the power source unit and production efficiency by blowing the powder carbon into the slag layer remaining with the residue after the tapping to improve the slag forming operation degree The present invention relates to an electric furnace slag forming method.

In general, slag forming in an electric furnace blows solid coke particles (usually 2 to 4 mm) into the slag layer using oxygen to a manipulator to generate slag forming, and the resulting CO gas raises the slag layer. It is to let. The slag foam generated at this time is dependent on the size of the bubble (bubble) of the generated CO gas and by the continuous generation of such droplets to maintain the CO gas stagnated in the slag layer. Slag foam generated at this time flows through the slag door (slag door), it is received by using a slag pot (slag pot) from the bottom. The slag forming method starts from the continuous loading and melting process of direct reduced iron (DRI) and is necessary to suppress heat dissipation loss when using arc or to improve thermal conductivity with a strong bath. One of the advantages of this work is the reduction of current and voltage deviation, and it is one of the important processes because it can reduce the noise caused by arcing and prevent the slag layer from absorbing from the atmosphere. In other words, the heat generated in the arc of the furnace is instantaneously higher than or equal to 3000 ° C and higher than the refractory melting point. Therefore, after the scrap and the charge is completely dissolved, the side wall portion of the furnace body is exposed to strong heat, and thus a method of suppressing the scrap is required.

In order to generate foaming, a method of blowing oxygen into molten steel and forming FeO was once proposed, but the method of blowing carbon proposed in Japanese Patent (昭 55-89414) was devised because of the problem of Fe loss caused by oxidation of steel. It is widely used. In other words, the carbon powder is blown into the slag layer on the molten steel surface using oxygen as a transport gas, and an arc is introduced into the foam to take advantage of the above-mentioned electric furnace work such as heat loss. This carbon injection improves the deoxidation of the steel and the reduction efficiency of FeO, which increases the thermal efficiency of the arc furnace and is also used for the recovery of valuable metals. The chemical reaction used at this time is as follows.

C _(S) + 1 / 2O ₂ = CO _(g) (+29,040 cal / mol) (1)

C _(s) + (FeO) = [Fe] + CO _(g) (-35,460 cal / mol) (2)

The method utilizes a phenomenon in which CO (g) generated in the chemical reaction is trapped in the slag and raised. Since the reduction reaction of FeO is endothermic, it is related to the maintenance of temperature as a basic condition of slag forming operation as a whole.

Therefore, as a foaming agent in consideration of sufficient supply of heat required for this endothermic reaction, Japanese Patent (昭 60-82607) uses SiC powder in place of a part of solid carbon, or divided use with solid carbon (Japanese Patent No. 60-67611, 60). -67612).

3 (FeO) + SiC = 3 [Fe] + (SiO ₂ ) + CO _(g) (+33,500 cal / mol) (3)

Although this method has a heat compensation aspect, it is effective only when 50% of SiC powder is used in terms of economical efficiency. Therefore, there is a limit in practicality.

As factors affecting slag forming, not only generation of CO gas in the slag layer, but also properties of the slag, that is, surface tension and viscosity, play an important role. To this end, US Patent 4528035 proposes a method of using a combination of quicklime (CaO) and coke breeze discharged from rotary kiln as a foaming agent that is introduced in advance to form as well as re-phosphorization It is known to have a side effect of preventing it. That is, the following equation was proposed based on the relative viscosity equation in which the apparent viscosity of slag is increased by the ratio of solid particles suspended in the slag layer.

η _e = η _o (1 + 5.5ε) (4)

Where ε is the fraction of suspended solid particles (%). This suspension is due to precipitated solid phases with temperature changes.

In addition, there is a method of causing foaming by using a CO gas by calcination using CaCO ₃ , but there is a problem that it is not practical.

An object of the present invention is to provide an electric furnace slag forming method that can improve the slag forming operation by a method of blowing the powdered carbon after it is blown to generate slag forming in the electric furnace.

The present invention for achieving the above object in the electric furnace slag forming method for blowing the powder carbon to generate slag forming in the electric furnace, the injection of the powder carbon to the slag layer remaining with the residual water at the same time after the tapping It is characterized by providing an electric furnace slag forming method to be blown.

1 is a diagram showing the effect of P ₂ O ₅ component and slag basicity change on the slag forming stability.

Hereinafter, the present invention will be described in detail.

The present invention focuses on surface active elements that lower the surface tension among physical factors affecting slag forming. The surface active material is easily adsorbed on the surface of the slag forming the foam, thereby lowering the activation energy required to form the foam, thereby facilitating easy bubble formation.

Among slag, P ₂ O ₅ , CaF ₂ and Fe ²⁺ / Fe ³⁺ ratio are known to play a role. The present invention was confirmed through the results according to the embodiment shown in Figure 1 that the surface active material has a great effect on the slag forming.

That is, the gas holdup index, which is an index for determining the degree of activity according to the slag basicity, indicates that the proper range of basicity is 2 to 2.5. Irrespective of the basicity, (P ₂ O ₅ ) component showed high foaming stability regardless of the basicity, so it was confirmed that the (P ₂ O ₅ ) component is a surface active material having a great influence on activating slag forming. However, the (P ₂ O ₅ ) component is a component that is difficult to increase because the presence of a large amount in the slag is decomposed and badly affects the quality of the steel. At present, about 1% by weight of slag (P ₂ O ₅ ) is present in the electric furnace. In the present invention, the slag flowing into the ladle by the vortex during the tapping in addition to the molten steel left when performing the operation of remaining the hot heel in a certain amount of the furnace for the purpose of strengthening the melting speed of the furnace charging scrap during tapping in the electric furnace It aims for stable forming operation by utilizing the remaining slag except for slag that flows out into the slag door during the forming operation. Detailed functions of the present invention are as follows. EBT (Eccetric bottom tapping), which is widely used in current operations, minimizes vortex by tapping molten steel toward the bottom of the bottom to minimize the mixing of slag during tapping. In the case of the residing operation in the electric furnace operation, the slag is discharged into the slag door during the forming operation, and the remaining slag remains in the furnace together with the remnant. The furnace slag left in the furnace cannot be quantitatively defined since the amount of the slag is not constant, but it is present in a liquid in the form of a certain layer on the top of the bath. Accordingly, in the present invention, the powder carbon is injected into the slag layer before the next dissolution operation is carried out to reduce the FeO component and (P ₂ O ₅ ) components in the slag to the molten steel side by the reaction formula as shown in the following formula (5) (6). Move it.

(FeO) + C _(s) = Fe + CO _(g) (5)

(P ₂ O ₅ ) + 5C _(S) = 2P + 5CO _(g) (6)

At the same time, the carbon bombarded into the slag layer increases the amount of dissolved carbon from the interface to the molten steel side as shown in the following equation (7) to increase the carbon concentration in the molten steel.

C _(S) = C (7)

The dissolved carbon delivered to the molten steel is lowered as the melting point decreases as the carbon concentration is increased, so that the dissolved carbon is dissolved even at a relatively low temperature during the dissolution of the added scrap, resulting in dissolution promotion.

Referring to the process of blowing the powdered carbon proposed in the present invention into the slag layer in more detail as follows. The powdered carbon injected into the slag layer reduces the (FeO) and (P ₂ O ₅ ) components remaining in the slag and transfers them to the molten steel side.In the case of reducing the (FeO) component, the molten steel error rate of the electric furnace is improved (P ₂ O ₅ ) Is reduced and increased by P concentration in molten steel and reoxidized by (FeO) component in gaseous oxygen and slag blown during melting. At this time, the reconstituted (P ₂ O ₅ ) component acts as a surface active material of the molten slag to activate the slag forming reaction as mentioned above. As a result, even when the optimum slag forming conditions are not established, the forming is activated early to stabilize the operation of the electric furnace. In addition, the increase in the amount of dissolved carbon is oxidized by the (FeO) component in the gaseous oxygen and slag blown as in the case of P to generate fine CO bubbles between the molten steel and the slag interface. The microbubbles generated in this way are a major gas source to stabilize the foaming, which also contributes to the stability of slag forming operation. Residual slag in the furnace due to the reduction of slag forming is discharged to the slag door side to suppress unnecessary slag retention, and additional generation of CO bubbles by dissolved carbon is applied to the CO gas bubbling. It is also effective to remove. Therefore, by injecting a certain amount of powder carbon proposed in the present invention into the remaining slag layer, the utilization of (P ₂ O ₅ ) activating slag forming during the subsequent dissolution and refining operations and the promotion of dissolution of scrap by increasing the amount of dissolved carbon, and dissolved It is expected to improve the refining capacity and forming ability due to the additional generation of CO bubbles in molten steel due to the increase in carbon content. The surface active material that is effective for slag forming can also make the best use of (P ₂ O ₅ ) and operate the electric furnace effectively by utilizing the remaining slag without additional work.

Hereinafter, the present invention will be described in detail through examples.

(Example)

In the 150-ton DC electric furnace operation, the particle size of the carbon powder to inject the powder carbon proposed in the present invention is 2 to 4 mm so as to be ejected to the lance discharge port of the current carbon / oxygen manipulator. Use to get out of the lance.

The time of use is blown into the molten slag layer remaining in the residue after tapping is completed. Since the blowing ratio of oxygen and carbon introduced for the normal slag forming operation is 22.7Nm ³ / ts: 15.5kg / ts level, the amount of carbon ash input for proper reduction of the remaining slag layer was added at 7kg / ts. .

For most bantangs, about 30 tons are common, so about 200 kg of powdered carbon is blown through the manipulator right after the tap. At this time, air was blown through oxygen lance as a transport gas so that the powdered carbon could be properly introduced into the slag layer, and the flow rate was blown at 10m ³ / ts, which is 1/2 of the normal level. The blown air and powdered carbon were introduced into the slag layer to reduce the (FeO) and (P ₂ O ₅ ) components in the slag, and then moved to Fe and P in the molten steel, respectively, contributing to the increase of iron recovery and dissolved P content in the slag. . As mentioned above, P in molten steel is re-oxidized during scrap cutting and after melting, in which coal and oxygen are blown at the same time after the introduction of new iron scrap, thereby reducing the surface tension so that the slag layer in which the goods are in progress is maintained in proper slag forming. Functioned.

In this example, the time taken for the first and second dissolution and the degree of activation of slag forming were measured during the entire treatment period, and compared with the case not according to the present invention. Since the size of slag forming in electric furnace operation is impossible to measure, the inventors and the like have observed through the slag forming measuring method invented in application number 97-35493 ("Measurement of gas retention ratio of foaming slag in slag forming electric furnace refining operation"). Compared with the method proposed in the present invention and the existing case as the degree of slag forming activation. As a method to measure gas holdup ratio and superficial gas velocity among physical indexes of slag forming generated during electric furnace operation, the slag collecting device can collect slag in foam state. Initially, it was manufactured in the shape of cube to know the total volume of collected slag. A handle is attached to secure the proper thickness to contain high temperature slag and to facilitate slag collection. The slag foam that overflows through the slag door is filled with slag through the slag collecting device and then quenched.

The quenched slag and other gases were discharged and finally the weight of slag remaining in the collecting device was measured, and the volume of the liquid slag in the container was measured by dividing by the total specific gravity of the separately collected collecting slag. This is calculated through the gas holdup ratio equation given in Equation 8.

Gas holdup ratio (ε _G ) = volume of gas / volume of liquid and gas (8)

In addition to the evaluation of the degree of activation of slag forming, in each case, in order to confirm the effects of the activation of slag forming as well as the shortening of the dissolution time due to the generation of additional CO bubbles due to the increase in the carbon concentration in molten steel, which is an additional expected effect by the present invention. The first and second dissolution times were compared.

Gas retention ratio and dissolution time by the present invention and conventional methods Experiment NO Hot water heel, hot heel Base prayer Leave (p ₂ o ₅ ) .wt% Primary dissolution time (minutes) Second melting time (minutes) Gas retention ratio (ε _G ) Carbon powder injection after class One 30 2.17 0.82 17 32 0.713 x 2 32 2.29 0.89 16 28 0.866 O (200 kg) 3 40 2.45 0.87 16 27 0.893 O (220 kg) 4 35 2.40 0.90 18 32 0.799 O (100 kg)

As shown in Table 1 above, when the slag layer blown into the slag layer proposed in the present invention is improved as described above, the dissolution rate of the scrap is improved as the carbon concentration in the molten steel is increased. Showed. In this case, the overall trend increased even with the gas retention ratio value. As a result, it was possible to obtain a result for forming activation and reduction of dissolution time by the method proposed by the present invention. The activation of slag foaming is believed to be due to the surface active material due to the reoxidation of the P component present in the molten steel and the generation of large amount of CO bubbles due to the carbon concentration in the molten steel. In the case of "4", which is a case where the powder blowing is cut in half, the result is no difference from that of no blowing. Therefore, a certain amount of powder carbon needs to be secured.

As described above, according to the present invention, it is possible to reduce the operating power unit through the stabilization of the slag forming, to obtain an economic effect that is expected to improve the overall operation degree, such as absorption of mass into molten steel and protection of the furnace body. In addition, there is a possibility to reduce the dissolution time and to remove nitrogen in the molten steel by CO gas boiling, which contributes to the operation of the electric furnace.

Claims (2)

An electric furnace slag forming method for injecting powdered carbon to generate slag forming in an electric furnace, wherein the blowing of the powdered carbon is performed after the tapping is completed and simultaneously blown into the molten slag layer remaining with the residue. How to form slag. The electric furnace according to claim 1, wherein the particle size of the powdered carbon to be blown is 2 to 4 mm in the particle size range of the powdered coke, and the blowing amount conveys 7 kg / ts or more as air of 10 m ^{3 '} / ts or more. Slag forming method.