JP2987277B2 - Water cooling structure of metal melting furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal melting furnace, such as an electric furnace or a metal melting furnace, which has a furnace wall or a bottomed furnace body which is opened above the melting furnace and into which raw materials are charged. To a water-cooled structure of a freely mountable furnace ceiling that closes the ceiling from above.

[0002]

2. Description of the Related Art In recent years, for example, the amount of crude steel produced by an electric furnace has been increasing, and as the amount of scrap steel, which is a main raw material, increases, the furnace capacity and power consumption increase in order to improve the melting capacity. Is planned. However, in the UHP (ultra high power) operation of a high power factor long arc in an electric furnace, the heat load on the furnace wall and the furnace ceiling is large, and in a furnace having a refractory structure using a refractory conventionally used, The refractories are severely worn and their life is reduced. For this reason, instead of using the refractory structure method, water cooling of the furnace wall and the furnace ceiling is performed for long life.

FIG. 10 shows a cross section of a typical prior art electric furnace. As shown in this figure, in the structure of the furnace ceiling 5 and the furnace wall 3 of the bottomed furnace body 2 which are generally water-cooled, the heat transfer tubes 8 for water cooling are positioned equidistant with respect to the direction of the central axis O in the furnace. In addition to being provided concentrically, the inside surface of the furnace has a planar structure with no access.

[0004]

However, when the inside of the furnace is water-cooled, heat loss from the inside of the furnace is large as compared with the conventional refractory structure system, and there is a disadvantage that the power consumption is deteriorated. In addition, since the heat loss in the furnace is large and the temperature control becomes unstable, there is a problem that the solubility and meltability of the main and auxiliary raw materials including metals and metallurgical reactions including various refining reactions are reduced. .

[0005] Further, in a furnace ceiling to be water-cooled (hereinafter referred to as a water-cooled furnace ceiling) and a furnace wall to be water-cooled (hereinafter referred to as a water-cooled furnace wall), thermal stress from a very high temperature to a low temperature (normal temperature) is repeated. Mechanical, local, and sudden wear and tear due to the fatigue of steel and physical and local contact with molten metal and scrap. Water leaks into the furnace not only destroys the function (action) of melting and melting the furnace and performs various reactions, but also has the danger of steam explosion. Required.

As a countermeasure, the basicity of the slag interposed with the metal and the molten metal in the furnace is reduced to 1.5 or less, and the powdering action of the slag is suppressed, and the surface of the water-cooled furnace ceiling and the water-cooled furnace wall is placed inside the furnace. There is a method of coating the flying slag. For example, the component composition of slag that coexists when smelting stainless steel is mainly composed of CaO—SiO ₂ and is composed of Cr ₂ O ₃ , MnO, MgO, Al ₂ O _3, etc. Is related to the phase transition of 2CaO—SiO ₂ . The phase transition of 2CaO—SiO _{2 represents} the following chemical formula 1 in the cooling process.

[0007]

Embedded image

At this time, α′-type and β-type are γ-type Ca ₂ Si
With a large volume expansion of about 14% when transforming to O ₄ ,
As a result, the entire slag powders and disintegrates. Therefore,
The slag adhered to the furnace wall is separated from the furnace wall by this powdering phenomenon, and therefore, slag coating on the furnace wall becomes impossible.

However, the slag powdering phenomenon is related to the basicity of the slag. When the basicity of the slag is increased to a high basicity of 1.5 or more, as the molar ratio of CaO: SiO ₂ approaches 2: 1, Since the ratio of the amount of 2CaO—SiO _{2 in} the slag increases, powdering of the slag occurs. vice versa,
When the basicity of the slag is 1.5 or less, the slag is prevented from being powdered, and the slag can be coated on the furnace wall. However, the basicity of slag has a great relationship with metallurgical reactions including various refining reactions in electric furnaces, and when the basicity of slag is 1.5 or less, desulfurization reaction during melting of stainless steel is difficult to be performed, There are drawbacks such as abnormalities in the hot metal component. However, under conditions where it is necessary to ensure that the desulfurization reaction during the melting of stainless steel is carried out, the water-cooled ceiling and the water-cooled There is a need to allow slag coating on the walls and not to easily peel off them.

[0010] Accordingly, an object of the present invention is to provide a slag coating on a water-cooled furnace ceiling and a water-cooled furnace wall even when the slag is operated in a high-basic state in a metal melting furnace, and to provide a stable slag so as not to be easily separated. By forming the coating layer, the heat removal from the furnace by the cooling water is reduced as much as possible, the power consumption is reduced, and the repeated fatigue due to thermal stress and the physical and local molten metal and Prevents mechanical, local and sudden wear and damage caused by scrap contact, extends the useful life of the furnace ceiling and the furnace wall of the furnace inside the furnace as much as possible,
An object of the present invention is to provide a water-cooling structure of a metal melting furnace capable of smoothly and advantageously performing a function of performing melting and various metallurgical reactions.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a metal melting furnace having a bottomed furnace body which is opened upward and into which raw materials are charged, and a mountable furnace ceiling which closes the furnace body from above. A heat transfer tube provided inside the furnace in close proximity to the steel shell forming the outer peripheral surface of the melting furnace and through which cooling water is circulated, and a space around the heat transfer tube along the inner surface of the steel shell facing the furnace internal space. And a slag coating layer formed by filling the heat transfer tubes in at least a part of two rows of staggered staggered staggered distances between adjacent tubes and the steel shell. The tube diameters of the first row of heat transfer tube groups closer to the center of the furnace are set to be smaller than the diameters of the second row of heat transfer tube groups closer to the steel shell. , A water cooling structure of a metal melting furnace, wherein a heat transfer tube is provided.

[0012]

Further, in the present invention, the sum of the cross-sectional areas of the heat transfer tube groups in the first row closer to the center of the furnace is closer to the steel bar in the space factor with respect to the cross-sectional area of the arrangement region of the tube groups. The heat transfer tubes are provided so as to be smaller than the same space factor of the heat transfer tube group in the second row.

[0014]

[0015]

[0016]

According to the present invention, a heat transfer tube is provided in the vicinity of the inner surface of the steel shell forming the outer peripheral surface of the metal melting furnace, and cooling water is circulated through the heat transfer tube. To form a slag coating layer. The heat transfer tubes are provided in a staggered arrangement, for example, in two rows so that the distances between adjacent tubes at different locations are different from the steel sheath. As a result, the amount of heat removed from the water-cooled furnace ceiling and the water-cooled furnace wall is reduced by removing heat to the cooling water circulating in the heat transfer tube by coating the heat transfer tube with slag with low thermal conductivity and forming a slag coating layer. Due to the restriction, the size is reduced, the heat dissipation loss is reduced, and the unit power consumption can be reduced.

Further, coating the slag on the water-cooled furnace ceiling and the water-cooled furnace wall reduces fatigue caused by thermal stress on the water-cooled furnace ceiling and the water-cooled furnace wall constituted by the heat transfer tubes and the heat transfer tube group. In addition, since the molten metal and scrap do not directly touch the heat transfer tubes, mechanical, local and sudden wear and breakage of the water-cooled reactor ceiling and water-cooled reactor walls are suppressed, and the service life of the entire furnace including these is extended. I do.

Further, the arrangement of the heat transfer tubes on the water-cooled furnace ceiling and the water-cooled furnace wall, and the cutoff of the areas where the heat transfer tube groups of the first row near the center in the furnace and the second row following the first row are arranged. Since the difference in occupancy relative to the area and the difference in tube diameter of the heat transfer tube group between the first and second rows are configured in a structure that is easy to coat and hard to peel even if the slag is easily weathered,
Problems such as the fact that slag weathering does not easily occur and that it is not necessary to operate under low basicity conditions that are disadvantageous to the desulfurization reaction, and that abnormal components occur due to insufficient refining reaction, are solved. Then, the function of performing melting and melting as well as various metallurgical reactions as a furnace can be smoothly, advantageously and safely performed, and the furnace can be brought into a state in which the original operation can be satisfied.

[0019]

FIG. 1 is a vertical sectional front view showing a state in which a furnace ceiling 5 of a metal melting furnace 1 according to one embodiment of the present invention is opened. In this embodiment, a metal melting furnace 1 is an AC arc type three-phase electric furnace, and has a bottomed furnace body 2 which is opened upward and into which main and auxiliary materials containing metal are charged, and a furnace body 2 having a bottom. And a freely mountable furnace ceiling 5 for closing from above. The furnace ceiling 5 is opened / closed by opening / closing means (not shown) for raising and lowering and turning as shown by the arrow A with respect to the bottomed furnace body 2 on which the furnace ceiling 5 is fixedly installed.

The furnace body 2 has a substantially cylindrical furnace wall 3 and a hearth 4, and an internal space 6 has a steel chip charged by an arc generated by energizing an electrode 7. The molten hot metal, molten metal, and slag that have melted and melted the main and auxiliary raw materials containing metals such as slag are stored. A secondary voltage from a transformer is applied to the electrode 7, and an arc is generated between the main and sub-raw materials charged in the internal space 6 to melt and melt the raw materials. Due to the generation of such an arc, the internal space 6 has a high temperature of, for example, about 1000 ° C., and has a high temperature range of 1500 to 2000 ° C. in a hot spot portion immediately below the electrode 7 which is directly subjected to the heat load of the arc.
During the operation of the metal melting furnace 1, the slag layer 15 floating on the stored hot metal or the molten metal is placed on the hearth 4 in the furnace body 2, that is, toward the furnace. Ceiling 5
The slag 16 is scattered toward the inner surface of the furnace wall 3 and the inner surface of the furnace wall 3.

FIG. 2 is a partially cutaway plan view of the furnace ceiling 5, and FIG. 3 is a sectional view taken along line AA in FIG. Furnace ceiling 5
Is formed substantially in a truncated cone shape, with the small ceiling 12 in which the electrode 7 is inserted and inserted in the center and the large ceiling 13 in which the heat transfer tubes 8 are provided surrounded by the small ceiling 12. Prepare together. The heat transfer tubes 8 provided in the large ceiling portion 13 are arranged in a concentric pattern with respect to the center of the furnace ceiling 5. The heat transfer tube 8 is formed by welding a curved tube 8A bent into an arc shape and a U-shaped tube 8C bent into a U shape by welding. For example, a steel tube made of ordinary steel is used. Is done.

As shown in the arrangement pattern of the heat transfer tubes 8 in FIG. 2, in the case of a three-phase electric furnace, the furnace ceiling 5 is aligned with the three electrodes 7 which are equally divided and arranged on the small ceiling 12. The heat transfer tubes are divided such that the large ceiling portion 13 is divided into three equal parts at a central angle of 120 ° with respect to the center of the central part, and a zigzag water flow path is formed in each of the divided partial rings. 8 Connect each other. At this time, it extends close to and substantially parallel to the inside of the furnace 1 (the inside of the furnace body 2) with the steel shell 9 as the outer plate of the furnace ceiling 5 and is adjacent to the steel shell 9 of the adjacent pipes 8. In the case where the distance is the one shown by the solid line and the one shown by the broken line in FIG. By connecting the flow paths of the cooling water formed in each partial ring in series in this manner, a single flow path of the cooling water is formed in the furnace ceiling 5. The slag coating layer 11 is formed by covering the heat transfer tubes 8 forming the flow path of the cooling water, as described later. In addition, these heat transfer tubes 8 group, L
It is bent into a shape and is attached to the steel shell 9 via a support member 14 having a concave semicircular groove for inserting the heat transfer tube 8 at a required location.

FIG. 4 is a front view of the furnace wall 2 of the furnace body 2 viewed from the side of the removed steel shell. FIG. 5 shows B in FIG.
FIG. 4 is a cross-sectional view taken along a line B. The furnace wall 3 is formed in a substantially cylindrical shape, and a heat transfer tube 8 is provided near an inner surface of the furnace 1 (in this case, the inside of the furnace body 2) with respect to a steel shell 10 as an outer plate thereof. The heat transfer tube 8 has a large ceiling 13
As in the case of the heat transfer tube 8 provided in the first embodiment, a curved tube 8B bent in an arc shape and a U-shaped tube 8C are joined by welding, and a steel tube made of ordinary steel is used.

6 and 7, the arrangement pattern of the heat transfer tubes 8 in the furnace wall 3 is shown in a horizontal sectional view and a perspective view, so that the central axis O of the cylindrical furnace wall 3 (that is, the center in the furnace 1) is shown. The furnace wall 3 is divided into eight equal parts, for example, at a central angle of 45 ° on the basis of the axis), and the large ceiling 1
The heat transfer tubes 8 are connected to each other so as to form a zigzag shape in the vertical direction in the same manner as in the case of 3, and to form an arrangement of two rows in a staggered manner in a vertical cross section to form a flow path of the cooling water. In this way, the cooling water flow paths respectively formed in the divided areas are connected in series, for example, in units of the respective areas to form eight cooling water flow paths, which are further paralleled by a header (not shown). To form a single cooling water flow path as a whole of the furnace wall 3.

The heat transfer tubes 8 forming the flow path of the cooling water are attached to the steel shell 10 by a support member 14 by means of fixing means such as screws, similarly to the case of the large ceiling portion 13. , The slag coating layer 11 is formed.

The water cooling structure of the embodiment having a two-row staggered arrangement pattern shown in FIG. 5 is characterized in that the amount of heat removed by cooling water is small and the life of the furnace wall 3 and the furnace ceiling 5 is prolonged. The validity will be described below.

[0027]

[Table 1]

[0028]

[Table 2]

Table 1 shows that the water-cooled ceiling 5 and the water-cooled wall 3 according to the present invention and the water-cooled ceiling and the water-cooled wall having the conventional structure are installed in a 90T (ton) electric furnace for comparison. The results obtained when the SUS-304 stainless steel is melted under the main and auxiliary raw material formulations shown in Table 2 and the operating conditions shown in Tables 1 and 2 are shown. In Comparative Example 1, a conventional water-cooled furnace ceiling and a water-cooled furnace wall were installed, and when these main and auxiliary materials were dissolved, the basicity of the slag was 2.0.
(High basicity). Comparative Example 2 is the result when the operation was performed with the basicity of the slag reduced to 1.5.

First, the desulfurization reaction will be described. The desulfurization capacity (S%) / [S%] in an electric furnace is affected by the basicity C / S. For example, the desulfurization reaction in a stainless steel electric furnace is represented by the following equation.

(CaO) + S = (CaS) + O (1) or O ²⁻ + S = S ²⁻ + O (2) where (CaO) and (CaS) are CaO in the slag. ,
CaS, and S and O are O and S in the metal. Therefore, the equilibrium constant K of the desulfurization reaction is

[0032]

(Equation 1)

From the third equation, the distribution of S is

[0034]

(Equation 2)

Or

[0036]

(Equation 3)

Here, the following is assumed.

A (S ²⁻ ) ≒ (% S), a (O ²⁻ ) ≒ N _cao (6) where N _cao is the molar fraction of CaO in the slag.
Substituting these into Equation 5, the distribution of S between slag and metal is

[0039]

(Equation 4)

## EQU4 ## According to this equation (7), theoretically, as the amount of CaO in the slag increases, or the amount of O in the metal increases.
It can be seen that the desulfurization reaction progresses as the amount of is reduced, that is, as the basicity increases.

In Comparative Example 2, since the slag is coated on the water-cooled furnace ceiling and the water-cooled furnace wall since the basicity is lower than that in Comparative Example 1, the service life can be extended and the power consumption can be reduced. Comparative Example 2 was unsuitable under the operating conditions of an electric furnace which required remarkable reduction in desulfurization.

In contrast, the present invention has a basicity of 2.0
(High basicity), so it can be applied to operating conditions that require desulfurization without lowering the desulfurization ability.

FIG. 8 shows the generation transition of the slag coating layer 11 formed on the water-cooled furnace wall 3 when operating under the conditions according to the present invention shown in Table 1. In the embodiment of the present invention, as shown in FIG. 5, the heat transfer tubes 8 in the first row and the heat transfer tubes 8 in the second row are alternately arranged in a two-row structure toward the central axis O in the furnace 1. Since the staggered two-row type is arranged so that the levels are different, even in a high basicity condition in which slag powdering is likely to occur and slag coating is difficult, the heat transfer tubes 8 in the second row close to the steel shell 10 can be formed. As shown in FIG. 8A, the slag that has scattered accumulates while being quenched as shown in FIG. 8A, and the slag continues to scatter from the slag layer at that portion. Since the degree of rapid cooling of the scattered slag is reduced, the slag powdering phenomenon due to phase transformation is suppressed, and because the heat transfer tubes 8 are in a staggered two-row type, slags having the same chemical composition are adhered to each other. Therefore, coating is easily performed sequentially.
By such repetition, the entire water cooling furnace wall 3 around the heat transfer tube group 8 is coated with slag as shown in FIG. 8B, and a stable slag coating layer 11 is formed.

As a result, the severe furnace atmosphere can be insulated, and as shown in the present invention 1 in Table 1, the power consumption is reduced by 20 KWH / T as compared with Comparative Example 1 of the prior art. Since the scrap does not directly touch the heat transfer tube 8, the life of the furnace wall 3 can be extended 500 times and the life of the furnace ceiling 5 can be extended 600 times.

FIG. 9 shows a staggered arrangement of groups of water cooling heat transfer tubes 8 provided on the furnace ceiling 5 and the furnace wall 3 of the furnace body 2 in the furnace inward direction with respect to the furnace center axis of the electric furnace. The group of heat transfer tubes 8 near the center is set as the first group of heat transfer tubes 8 and the furnace shell 10
When the group of heat transfer tubes 8 at a position close to the furnace is the second group of heat transfer tubes 8, the ratio of the area occupied by the group of second row heat transfer tubes 8 near the steel shell 10 is determined by the group of first row heat transfer tubes 8 near the center of the furnace. A larger arrangement is shown.

[0046]

That is, in FIG. 9, the total number of the heat transfer tubes 8 in both the first and second rows of heat transfer tubes 8 is substantially the same, 1 pipe diameter
It is arranged using a heat transfer tube 8 larger than that of the row.

Also in the arrangement structure shown in FIG. 9, since the slag coating ratio is increased and the stable slag coating layer 11 is formed, the heat extraction to the cooling water is reduced, the heat dissipation loss is reduced, and the power source is reduced. The unit can be reduced. Further, each life of the furnace wall 3 and the furnace ceiling 5 can be extended.

In the present invention 2 in Table 1, the arrangement of the water-cooled heat transfer tubes 8 in the furnace wall 2 and the furnace ceiling 5 is arranged in a staggered two-row arrangement as shown in FIG. Second row heat transfer tube 8
Results when the ratio of the area occupied by the group, that is, the space factor, was set to be larger than that of the first row of heat transfer tubes 8 near the center of the furnace, and the slag basicity was 2.0 (high basicity). It is. The present invention 2 is different from the present invention 1 in terms of electric power consumption by 5 units.
The KWH / T can be reduced, and the life of the furnace wall 3 and the furnace ceiling 5 can be extended 50 to 100 times.

[0050]

According to the present invention configured as described above, the following effects can be obtained, and the industrial value is very large. (A) Since the heat removal by the cooling water flowing in the water-cooled heat transfer tube is reduced, the power consumption can be reduced, the melting time can be shortened, and the productivity is improved. (B) In order to reduce the repetitive fatigue due to thermal stress on the furnace ceiling and the furnace wall composed of the water-cooled heat transfer tube group etc., and to prevent scrap, hot metal or molten metal from directly touching the water-cooled heat transfer tube. Mechanical, local and sudden wear and tear of the furnace ceiling and furnace wall can be suppressed, and their useful life is extended. (C) A stable slag coating layer is formed, which hardly causes powdering of the slag, and good temperature control can be performed. There is no need to operate under the conditions, and there is no problem such as an abnormal component composition due to insufficient refining reaction. (D) Since the ceiling of the water-cooled furnace and the wall of the water-cooled furnace are protected, water leakage into the furnace due to such damage is avoided, and the danger of steam explosion due to the water leakage can be prevented. (E) Therefore, the function (action) of performing melting and melting as well as various metallurgical reactions as a metal melting furnace is performed smoothly and very economically advantageously and safely, and the furnace's original operation is safely satisfied. Can be maintained. (F) The structure and arrangement of the water-cooled furnace ceiling and the water-cooled furnace wall are basically the same as those of the prior art, and only the arrangement of the water-cooled heat transfer tubes and the like is different. It can be remodeled without major remodeling, and the cost of remodeling can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional front view of an embodiment of the present invention.

FIG. 2 is a partially cutaway plan view of a furnace ceiling 5 shown in FIG.

FIG. 3 is a sectional view taken along line AA in FIG. 2;

FIG. 4 is a front view of the furnace wall 3 shown in FIG.

FIG. 5 is a sectional view taken along line BB in FIG. 4;

FIG. 6 is a horizontal sectional view showing an arrangement pattern of the heat transfer tubes 8 in the furnace wall 3 according to the embodiment of the present invention.

FIG. 7 is a perspective view showing an arrangement pattern of the heat transfer tubes 8 shown in FIG.

FIG. 8 is a longitudinal sectional view showing a generation transition of the slag coating layer 11 on the furnace wall 3 according to the embodiment of the present invention.

FIG. 9 is a longitudinal sectional view of a furnace wall 3 according to other embodiments of the present invention.

FIG. 10 is a sectional view of a furnace ceiling in a prior art electric furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal melting furnace 2 Furnace body 3 Furnace wall 4 Furnace floor 5 Furnace ceiling 6 Internal space 7 Electrode 8 Heat transfer tube 9,10 Iron shell 11 Slag coating layer

Claims (2)

(57) [Claims] 1. A metal melting furnace having a bottomed furnace body which is opened upward and into which raw materials are charged, and a mountable furnace ceiling for closing the furnace body from above, wherein an outer peripheral surface of the melting furnace is formed. Heat transfer tube provided inside the furnace in the vicinity of the steel shell to be cooled and through which cooling water is circulated, and slag formed by filling the space around the heat transfer tube along the inner surface of the steel shell facing the furnace internal space. A coating layer, wherein at least a portion of the heat transfer tubes are arranged in two rows in a staggered manner in which the distance between the adjacent tubes is different from each other in a staggered manner, and the heat transfer tubes are provided substantially parallel to the steel shell. The heat transfer tubes are provided so that each tube diameter of the first row of heat transfer tube groups closer to the inner center is smaller than each tube diameter of the second row of heat transfer tube groups closer to the steel shell. Characterized by water cooling structure of metal melting furnace. 2. The sum of the cross-sectional areas of the first row of heat transfer tube groups closer to the center of the furnace is equal to the space factor of the cross-sectional area of the area where the tube groups are disposed, which is closer to the steel shell. The water cooling structure of a metal melting furnace according to claim 1, wherein the heat transfer tubes are provided so as to be smaller than a similar space factor of the heat transfer tube group in the row.