KR100280595B1 - Electric furnace furnace protection method using seawater decarbonate sludge - Google Patents

Abstract

The present invention relates to an electric furnace operation method for manufacturing molten steel by dissolving scrap, the object of which is to provide a method for protecting the furnace body by charging the decarburized sludge pellets into the heated furnace of the tapping electric furnace. have.

In the present invention having such an object, in the electric furnace operating method of manufacturing molten steel by applying a current to a charged scrap to dissolve and injecting a slag preparation into the melt,

The technical gist of the electric furnace furnace protection method using the seawater decarbonation sludge comprising the step of tapping the molten steel of the electric furnace and putting the seawater decarbonation sludge pellet on the heated furnace, and then charging the scrap.

Description

Electric furnace furnace protection method using seawater decarbonate sludge

The present invention relates to a method of preventing damage to a furnace by scraps charged into an furnace, and more particularly, to a method of protecting an furnace using seawater decarbonate sludge.

The electric furnace of the steel mill applies and dissolves electric current to the charged scrap (scrap metal), adds slag preparation (coke powder, limestone, formation, etc.) to prepare the slag and deoxidizes and desorbs the molten steel by using the prepared slag. It is a kind of steel making equipment that manufactures. The furnace operation is severely damaged by the scrap because the molten steel is made in the furnace, tapped into ladles, and the scrap is charged into the heated furnace again. Currently, when a roche is damaged, the roche is repaired and used, but there is no known method to prevent damage to the roche.

On the other hand, magnesium oxide, which is generally used as a basic refractory raw material, is made of magnesium oxide (MgO) by extracting magnesium ions present in seawater to form magnesium hydroxide and calcining the magnesium hydroxide. In order to extract magnesium ions in seawater, hydrated lime (Ca (OH) ₂ ) is reacted with seawater so that the magnesium ions in seawater become magnesium hydroxide. At this time, in order to manufacture the required lime, first, calcined limestone is made of quicklime, and the quicklime is reacted with water to make calcined lime.

In this process, impurities such as unbaked limestone and SiO ₂ contained in limestone are removed and a high purity lime slurry (lime oil) is produced. This purified lime oil is reacted with purified seawater to produce magnesium hydroxide. In order to make purified seawater, seawater is taken out to remove impurities such as sand and seaweed contained in seawater, and then calcined limestone is added to seawater to remove carbonic acid from seawater components. If carbonate is not removed at this time, calcium carbonate is produced during the reaction of slaked lime and seawater, and this calcium carbonate is included in magnesium hydroxide, which leads to low concentration of magnesium oxide, which is an impurity. Therefore, in the seawater purification process, the carbonic acid process is necessarily performed.

In this deoxidation process, calcium carbonate and calcium hydroxide produced by the injection of quicklime and carbonate in seawater react to produce calcium carbonate and magnesium hydroxide, leaving some unreacted lime. If this is expressed as chemical reaction formula (1).

[Chemical Reaction Formula]

_{^{HCO -3 + 2Ca (OH) 2}} → CaCO 3 ↓ + Mg (OH) 2 ↓ + CaCl 2 + H 2 O + OH - ... (1)

Since calcium carbonate, magnesium hydroxide, and unreacted lime are removed to produce purified seawater, calcium carbonate, magnesium hydroxide, and unreacted lime are separated by filtration, in which carbonate sludge is generated.

Currently, this decarbonated sludge from Busan, Korea, is used as a neutralizing agent, but this is not always shipped, but it is shipped in spring and autumn, so it can be used for other purposes that can be processed continuously throughout the year. It is necessary to derive.

The present invention, as part of the study on the effective utilization of waste resources, to provide a method for protecting the furnace by using decarbonate sludge, the object thereof.

The furnace furnace protection method of the present invention for achieving the above object comprises the step of tapping the molten steel of the furnace and then injecting the dried seawater decarbonate sludge pellets into the furnace before charging the scrap into the heated furnace body.

Hereinafter, the present invention will be described in detail.

According to the present invention, when there is residual water at the bottom of an electric furnace where the endothermic reaction decarburized sludge is removed, that is, the bottom of the furnace, the residue is solidified while decarbonated sludge is decomposed by an endothermic reaction by the heat of the residue. Therefore, to prevent damage to the furnace due to scrap, there is a feature.

As mentioned above, in the manufacturing process of seawater magnesia clinker, a large amount of decarbonated sludge is generated, and typical chemical components of such decarbonated sludge are shown in Table 1 below. The particle size of the carbonic acid sludge showed that the average size was 13.24 µm and all were 60 µm or less.

division SiO ₂ CaO Al ₂ O ₃ MgO MnO P ₂ O ₅ TiO ₂ T-Fe K ₂ O Decarbonate sludge 2.72 45.47 0.49 13.02 0.06 Tr Tr 0.32 0.19

Among the components of the decarbonate sludge shown in Table 1, CaO3 is mostly in the actual state, and some of them are in the form of Ca (OH) 2. However, when CaCO3 or Ca (OH) 2 is heated, it is converted to CaO while absorbing heat. In other words, it takes away the surrounding heat and cools and converts it into CaO. Therefore, the present invention has developed a method for producing an electric furnace body protection material using such a phenomenon.

As can be seen from Table 1, the decarbonated sludge contains about 13% of magnesium oxide and about 45.47% of CaO. The present invention effectively utilizes the characteristics of such decarbonated sludge. That is, magnesium oxide may be more effective in protecting the furnace because it replaces magnesium oxide to be eluted from the magnesium oxide-based (MgO) furnace refractories. In addition, CaO in decarbonated sludge is useful because it can partially replace the amount of CaO preparation added as slag preparation during the operation of the electric furnace.

In the present invention, decarbonated sludge is pelletized and introduced into an electric furnace based on this aspect. First, pelletization is carried out as it is, without decalcifying sludge. Pellets are made by mixing dry decarburized sludge with cement. Mixing ratio of cement can be adjusted according to the required strength, and considering the strength and harmful components of cement, 5-10% of mixing is optimal condition. The reason is that when the amount of cement is less than 5%, it does not satisfy the condition of 50kgf or more, which is the commercial compressive strength required in actual use, and when it is 10% or more, there is a risk of excessively containing harmful components such as sulfur (S) in the steel. There is this.

The pellets are made by mixing decarbonate sludge and cement. The pellets should be less than 40mm in size. If the pellet is larger than 40 mm, the pellet may be cracked during drying together with the crack, and dust may be generated during transportation and use in actual field application. It is preferable to make the pellets in this way and then dry them. The reason for this is that when the pellet containing moisture is immediately charged into the furnace, the thermal explosion may occur while the moisture evaporates rapidly. Drying is advantageous in terms of time reduction when heated in a drier. For example, it may be dried for 3 hours in a dryer at 100 ℃.

When decarburized sludge pellets prepared according to the present invention are removed and put into the bottom of a heated electric furnace, the sludge is decomposed by the endothermic reaction due to the high heat of the furnace body and the high temperature of the residual water in the presence of the residue. By solidifying and also reducing the temperature of the bottom of the furnace, the softened floor can be cured to prevent erosion from the scrap charging.

At this time, the degree of temperature reduction of the furnace refractory material can be adjusted by adjusting the amount of pellets as necessary, but when the amount of the slag is less than 3% by weight based on the amount of quicklime added for the preparation of slag, the quality of the steel and the heat balance do not occur. In other words, more than 3% can cause problems such as hydrogen embrittlement in the steel, and if the bottom of the furnace body is cooled too much, there is a risk of increasing the electrical energy related costs for thermal compensation.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

10 kg of decarbonated sludge is prepared, the prepared sludge is dried and mixed by adding 5-10% of cement to the dried sludge, the mixture is prepared into pellets and dried in a drier at 100 ° C. for 3 hours, and then dried pellets. The change of shape was observed and the results are shown in Table 2 below.

Diameter of pellet (mm) Morphology change after drying 10 none 20 none 30 None, some cracks (5% or less) 40 Some cracks and some damages (less than 10%) 50 More than 30% damage

As shown in Table 2, when the diameter of the pellets is larger than 40 mm, the pellets are cracked and broken during drying, and there is a concern that dust is generated during transportation and use in actual field application.

Example 2

The pellets prepared in Example 1 were put on the electric furnace, and the scrap was added and the erosion of the furnace was examined. The input amount was a pellet weighing 1.5 kg for the final tapping amount of 1 ton corresponding to 3% of the quicklime input. MgO content of the slag generated in the conventional method without the injection of the pellet and the slag MgO content of the slag generated after the injection of the pellet was investigated.

division Slag by conventional method Slag generated during pellet injection MgO content 9.6% 7.5%

The change in the MgO content in the slag can be judged to be due to the suppression of erosion of the MgO-based refractory material, which is the main material of the bottom of the furnace. That is, compared with the conventional example in which no decarbonate sludge pellet is added, the hardened furnace has less erosion.

As described above, the present invention has the effect that it is useful to utilize the waste resources of the decarbonate sludge as a protective material for the furnace.

Claims (3)

In the electric furnace operating method of manufacturing molten steel by applying a current to the charging scrap to dissolve and injecting a slag preparation into the melt, A method for protecting an electric furnace using seawater decarbonate sludge, comprising tapping the molten steel of the electric furnace and adding seawater decarbonate sludge pellets to the heated furnace. The method of claim 1, wherein the pellets are 40 mm or less, characterized in that 5 to 10% by weight of cement is mixed with respect to 100% by weight of seawater decarbonate sludge. The method of claim 1, wherein the desalination sludge pellets are added to 3% by weight or less based on 100% by weight of quicklime added to the slag preparation.