JP2015007268A - Method of operating electric furnace and the electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of operating an electric furnace which can reduce the concentration of CO in exhaust gas from an electric furnace, in operating an electric furnace for refining of ferronickel.SOLUTION: In method of operating an electric furnace by charging burned ore into an electric furnace 1 of a diameter of 10-25 m and reduction-melting the burned ore, in refining ferronickel, a space 30 of height of 2.2-2.9 m including an ore layer composed of unmelted burned ore is formed over the melt layer 11 obtained by reduction melting of the burned ore.

Description

  The present invention relates to a method of operating an electric furnace and the electric furnace, and more particularly, the amount of CO gas generated in an electric furnace used in ferronickel smelting and flowing into an exhaust gas treatment facility provided after the electric furnace. The present invention relates to a method for operating an electric furnace that can be greatly reduced, and the electric furnace.

  In the electric furnace used in ferronickel smelting, the burned ore containing reducing coal obtained by calcining nickel oxide ore is reduced and melted, and the melt obtained by melting is ferronickel (metal). Specific gravity separation into slag. Further, the electric furnace exhaust gas generated from the electric furnace is sent to an exhaust gas treatment facility through an exhaust gas flue.

  Specifically, in a ferronickel smelting electric furnace, raw material ore (calcined ore) is reduced and melted using a carbonaceous material such as coal. At this time, in this electric furnace, the carbon in the coal as the reducing agent directly reduces the ore, and the ore is produced by the CO gas generated by combining the carbon in the coal with the oxygen in the air or the ore. Indirect reduction to reduce is in progress. Therefore, a large amount of CO gas is always present in the electric furnace.

  Regarding the exhaust gas discharged from the electric furnace (hereinafter also referred to as “electric furnace exhaust gas”), if the CO concentration in the electric furnace exhaust gas is as high as 6 to 8% as in the coke oven exhaust gas, for example, It can also be used as fuel in a combustion device or the like.

  Also, for example, in Patent Document 1, in a steelmaking electric furnace that melts scrap in a batch type, a gas containing oxygen is blown into the electric furnace using a nozzle to burn the CO gas in the electric furnace. Thus, a technology for increasing energy efficiency is disclosed.

  However, generally, the CO concentration in the electric furnace exhaust gas used in ferronickel smelting is relatively low, and it is difficult to reuse it in other combustion apparatuses. In addition, the steelmaking electric furnace technology disclosed in Patent Document 1 cannot be preferably applied to an electric furnace used in ferronickel smelting. Therefore, the electric furnace exhaust gas discharged from this ferronickel smelting electric furnace is purified, cooled, and rendered harmless, for example, by burning it at the tip of a chimney or in the middle of a flue, if necessary. It is common to release.

  However, the electric furnace exhaust gas discharged from the electric furnace may have a CO gas concentration exceeding about 12.5%, which is a limit concentration at which the CO gas does not explode, due to, for example, an abnormal reaction in the electric furnace. . For this reason, there is a risk that an explosion accident may occur due to the occurrence of sparks when there is a fire type in the exhaust gas treatment facility, particularly when dust removal is performed with an electric dust collector as the exhaust gas treatment facility.

  Also, even if the CO gas concentration in the electric furnace exhaust gas does not exceed the explosion limit, it is necessary to consider the possibility that workers etc. may be exposed to CO gas due to gas leakage from the exhaust gas treatment facility. Therefore, there are many safety and hygiene precautions when handling exhaust gas from electric furnaces.

  For this reason, it is preferable that exhaust gas with a CO gas concentration as low as possible be discharged in an operation in a ferronickel smelting electric furnace (reduction melting operation). Specifically, it is preferable that the CO concentration in the exhaust gas at the outlet of the electric furnace is not increased to 12.5% or more even when variation is taken into consideration.

Japanese Patent Laid-Open No. 10-317046

  Therefore, the present invention has been proposed in view of such circumstances, and effectively reduces the CO concentration in the exhaust gas discharged from the electric furnace in the operation of the electric furnace used in ferronickel smelting. An object of the present invention is to provide a method for operating an electric furnace.

  The inventors of the present invention have made extensive studies to achieve the above-described object. As a result, it is possible to promote the combustion of the CO gas generated in the electric furnace by forming a certain volume of space above the melt layer in the electric furnace, and the CO contained in the exhaust gas. The present inventors have found that the gas concentration can be effectively reduced and completed the present invention.

  That is, the operating method of the electric furnace according to the present invention is an operating method of the electric furnace in which calcination ore is introduced into an electric furnace having a diameter of 10 to 25 m and reduced and melted in ferronickel smelting, A space having a height of 2.2 to 2.9 m including an ore layer made of unmelted calcined ore is formed on the upper part of the melt layer obtained by reducing and melting the calcined ore.

  Here, in the electric furnace, air intake holes having a diameter of 50 to 300 mm are equally provided at 4 to 16 positions per electrode on a concentric circle centering on the electrode provided on the ceiling of the electric furnace. It is preferable.

  Further, in the electric furnace, the exhaust gas discharge holes having a diameter of 900 to 1800 mm are located away from the electrodes provided on the ceiling of the electric furnace and on a circumference that is concentric with the center of the electric furnace. It is preferable that 2-4 places are provided equally.

  Further, in the electric furnace, the firing ore is charged in a choke feed type through a throwing pipe for charging the raw calcined ore, and formed in the space above the melt layer. It is preferable that the done ore layer is in contact with the lower end of the thrown pipe.

  Further, the pressure of the space is preferably maintained in the range of −5 to −70 Pa.

  The electric furnace according to the present invention is an electric furnace having a diameter of 10 to 25 m for charging and reducing and melting calcination ore in ferronickel smelting and obtained by reducing and melting the calcination ore. A space having a height of 2.2 to 2.9 m including an ore layer made of unmelted calcined ore is formed on the upper part of the obtained melt layer.

  According to the present invention, since a space is formed in the upper part of the melt layer in the electric furnace, oxygen (air), which is a reduction object by CO gas, or an undissolved ore layer in the formed space. Can be effectively present, and combustion of CO gas generated in the electric furnace can be promoted. Thereby, the CO gas concentration contained in the exhaust gas generated in the electric furnace can be effectively reduced.

It is a cross-sectional schematic diagram explaining the state of the electric furnace at the time of reduction melting of the sinter in the reduction melting process. It is a schematic diagram for demonstrating the mechanism of CO gas reduction when forming desired space in the upper part of a melt layer. It is a schematic diagram when the ceiling part of an electric furnace is seen from the upper part.

  Hereinafter, a specific embodiment (hereinafter referred to as “the present embodiment”) of an electric furnace operating method according to the present invention will be described in detail in the following order. The present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present invention.

  The operating method of the electric furnace according to the present embodiment is an operating method of the electric furnace for introducing and reducing-melting the calcined ore (calcined ore) obtained by calcining nickel oxide ore in ferronickel smelting There is an operation method that makes it possible to significantly reduce the amount of CO gas in the exhaust gas discharged from the electric furnace (electric furnace exhaust gas).

[About ferronickel smelting]
First, the ferronickel smelting process will be outlined. The smelting method of ferronickel includes nickel oxide ore (hereinafter, also simply referred to as “ore”) as a raw material, a drying step of drying the ore, firing of the dried ore (dry ore) and partial reduction, and A partial reduction step, and a reduction melting step of reducing and melting the obtained calcined ore (calcination ore) in an electric furnace.

Although it does not specifically limit as a nickel oxide ore which is a raw material ore, A garnierite ore etc. are used preferably. As a typical composition of this garnierite ore, Ni grade is 2.1 to 2.5% by weight in terms of dry ore, Fe grade is 11 to 23% by weight, MgO grade is 20 to 28% by weight, SiO ₂ grade. Is 29 to 39% by weight, CaO grade is less than 0.5% by weight, and loss on ignition is 10 to 15% by weight.

  In the drying process, after mixing the raw material ore so as to obtain a predetermined blending quality, a part of moisture in the raw material ore is removed using a rotary dryer or the like. Specifically, for example, the moisture in the ore is adjusted to about 15 to 25%. The ore whose moisture has been adjusted is called dry ore.

  In the calcination and partial reduction process, the dry ore obtained through the drying process is charged into a rotary kiln, and a reducing agent such as coal and a melt as necessary are added, and the remaining moisture contained in the dry ore. Is completely removed, and the dried ore is partially reduced to obtain calcined ore (calcined ore).

  In the reduction melting process, the sinter produced in the calcination and partial reduction processes is transported into an electric furnace (reduction furnace), and the sinter is converted into an electric furnace using a coal (reducing agent) such as coal. Reduce and melt (melt). As will be described in detail later, this electric furnace is, for example, a three-phase AC electrode electric furnace, and sinter is charged through a sinter ore chute connected to a furnace bin. In the electric furnace, the supplied sinter is melted by the current applied to the electrodes, and metal (crude ferronickel) and slag are formed. The formed metal and slag are separated by the difference in specific gravity, and a metal layer (lower layer) is formed at the bottom of the electric furnace, and a slag layer (upper layer) is formed at the top.

[Electric furnace used in reduction melting process]
Here, in FIG. 1, the cross-sectional schematic diagram for demonstrating the state of the electric furnace at the time of the reduction melting of the sinter in the reduction melting process is shown. In addition, in this FIG. 1, the case where a three-phase alternating current electrode type electric furnace is used as an electric furnace 1 is mentioned as an example.

  The electric furnace 1 has a cylindrical shape with a diameter of about 10 to 25 m and a height (height from the furnace bottom to the top) of about 4 to 10 m. The interior is made of a refractory material. In the electric furnace 1, along with the reduction melting of the sinter, a melt layer (melt layer) 11 obtained by melting the sinter is formed therein. As described above, the melt layer 11 is composed of the bottom metal layer 11A separated by the specific gravity and the slag layer 11B present on the metal layer 11A.

  The electric furnace 1 is provided with a plurality of throwing pipes 21 for charging smelting ore for reducing and melting at the ceiling, and the sinter is continuously or intermittently input through the casting pipe 21. Is done. Therefore, at the time of operation, the surface of the above-described molten layer 11 (the surface of the slag layer 11B) is a smelted ore put through the casting pipe 21, that is, a layer (ore layer) 12 made of unmelted sinter. The state covered with is formed.

  The electric furnace 1 is provided with three electrodes 22 a to 22 c (for example, carbon electrodes) hanging from the ceiling of the electric furnace 1. In the electric furnace 1, the three electrodes 22a to 22c are immersed in the slag layer 11B and a three-phase alternating current is applied, thereby directly energizing the metal layer 11A and the slag layer 11B from the electrodes 22a to 22c to generate resistance heat. (Joule heat) is generated. And the ore which comprises the ore layer 12 formed in the upper part of the slag layer 11B is melted by the Joule heat from the melt, and a metal and slag generate | occur | produce. In melting the sinter, a method may be used in which an arc is generated in a state where the electrodes 22a to 22c are not immersed in the slag layer 11B, and the sinter is directly melted by the arc heat.

  Further, the electric furnace 1 is provided with a metal hole 23 and a slag hole 24 at a lower portion thereof. The metal hole 23 is provided corresponding to the position where the metal layer 11 </ b> A formed inside the electric furnace 1 exists, and the metal is extracted through the metal hole 23. The slag hole 24 is provided corresponding to the position where the slag layer 11 </ b> B formed inside the electric furnace 1 exists, and the slag is extracted through the slag hole 24.

  Furthermore, as shown in FIG. 1, the electric furnace 1 is provided with one or more combustion air intake holes 25 in the ceiling. The combustion air intake hole 25 is an air hole for taking in air for burning CO gas generated in the electric furnace 1 from the outside. As will be described in detail later, the plurality of combustion air intake holes 25 are equally provided on, for example, a concentric circle centered on the electrodes 22a to 22c suspended from the ceiling of the electric furnace 1.

  Moreover, as shown in FIG. 1, the electric furnace 1 is provided with one or more exhaust gas discharge holes 26 in the ceiling portion. The exhaust gas exhaust hole 26 is an exhaust port for exhausting exhaust gas discharged from the electric furnace 1 (electric furnace exhaust gas). Moreover, although mentioned later in detail, this exhaust gas discharge hole 26 is provided with two or more on the circumference of a concentric circle with respect to the center of the electric furnace 1, for example. Further, the exhaust gas exhaust hole 26 is provided with a CO concentration meter capable of measuring the CO concentration in the exhaust gas discharged from the electric furnace at a predetermined location. Based on the measured concentration value by the CO concentration meter. The conditions of detoxification treatment in the flue are determined and the safety of operation is ensured.

  Note that the electric furnace exhaust gas generated in the electric furnace 1 and discharged from the exhaust gas discharge hole 26 is sucked by an exhaust gas fan provided in the exhaust pipe, for example, to remove coarse dust contained in the exhaust gas. It is discharged from the chimney to the atmosphere through a dust chamber (Barun flue) and an electric dust collector for removing fine dust.

[Reduction of CO gas generated in the electric furnace]
In the reduction melting process of ferronickel smelting, as described above, CO gas is generated as the sinter is reduced and melted in the electric furnace 1. This CO gas is discharged as exhaust gas through the exhaust gas exhaust hole 26 provided in the ceiling portion of the electric furnace 1, but from the viewpoint of improving the operational safety or the efficiency of the detoxification treatment, It is desirable to reduce the CO gas that is contained in the exhaust gas as much as possible.

  Therefore, in the electric furnace operating method according to the present embodiment, in the electric furnace 1, an ore layer made of unmelted calcined ore is formed on the upper part of the melt layer 11 obtained by reducing and melting the supplied sinter. 12 is operated so as to form a space 30 having a predetermined height including 12 (dotted line encircled portion in FIG. 1).

  Specifically, it is important to form a space 30 having a height of 2.2 to 2.9 m including the ore layer 12 in the upper part of the melt layer 11. The “height” of the space 30 is the length of the space formed from the upper surface of the melt layer 11 to the top of the furnace in the direction from the bottom of the electric furnace 1 to the top of the furnace (the vertical direction of the electric furnace 1). In other words, by operating so that the height from the upper surface of the melt layer 11 to the top of the furnace becomes such a height, a space 30 having a constant capacity is formed in the electric furnace 1.

  In this electric furnace operating method, a space 30 having a constant capacity is formed in the upper part of the melt layer 11 in this way, so that oxygen (air) necessary for burning the generated CO gas in the space 30 is formed. ) And undissolved sinter can be effectively present.

  FIG. 2 is a schematic diagram for explaining the mechanism of CO gas reduction when a desired space 30 is formed above the melt layer 11. As shown in FIG. 2, when a predetermined space 30 including the undissolved ore layer 12 is formed in the upper part of the molten layer 11 (upper part of the slag layer 11B), the combustion air intake provided in the ceiling part of the electric furnace 1 A “place (space)” where the air taken in from the hole 25 can stay is born. Further, the formed space 30 is a space including the undissolved ore layer 12 and is a “place (space)” in which a burned ore that is undissolved and highly reactive can sufficiently exist.

  Then, the air and the unmelted sinter that have come to exist in this space 30 come to react positively with the CO gas generated in the electric furnace 1. That is, the air taken in from the combustion air intake hole 25 causes a combustion reaction with the generated CO gas, and the unmelted sinter stacked on the upper part of the melt layer 11 is indirectly generated by the generated CO gas. Reduced (indirect reduction). As a result, the CO gas generated in the electric furnace 1 is effectively burned and consumed by these air and unmelted sinter.

  In this way, by forming a space 30 having a predetermined height including the undissolved ore layer 12 above the melt layer 11, sufficient oxygen (air) or unmelted sinter is formed in the space 30. And the combustion of the CO gas generated in the electric furnace 1 can be promoted. When CO gas is burned and reduced in this way, the concentration of CO gas contained in the exhaust gas is inevitably reduced, and operation can be performed with high safety. In addition, the detoxification process when discharged into the atmosphere can be performed more efficiently.

(About the height of the space)
About the height of the space 30 formed in the upper part of the melt layer 11, it is necessary to set it as the height which can ensure sufficient capacity | capacitance for CO gas to be burned effectively.

  The condition for effectively burning CO gas depends not only on the capacity of the electric furnace 1 itself but also on the composition of the raw ore, the operation load of the electric furnace, and the like. Therefore, as the space 30 to be formed, the most appropriate height value exists for each electric furnace 1 to be used. In the electric furnace having a diameter of 10 to 25 m used in the reduction melting process of ferronickel smelting. As described above, the height of the space 30 is set to 2.2 to 2.9 m.

  If the height of this space 30 is less than 2.2 m, sufficient space for the presence of oxygen for burning the CO gas generated in the electric furnace 1 and undissolved ore cannot be obtained. The CO gas is not burned and mixed with the electric furnace exhaust gas. For example, the CO concentration in the exhaust gas exceeds 500 ppm as the reference concentration value.

  On the other hand, when the height of the space 30 exceeds 2.9 m, a sufficient space can be secured for the presence of oxygen and undissolved ore for burning the CO gas generated in the electric furnace 1. The CO gas concentration in the electric furnace 1 is effectively reduced, and the CO concentration in the exhaust gas from the electric furnace outlet can also be lower than the reference concentration value of 500 ppm. However, if the height exceeds 2.9 m or higher, the surface area of the furnace wall increases, so the heat dissipated in the electric furnace 1 increases and the furnace temperature is maintained within an appropriate range. This makes it difficult to perform efficient melting operations. Furthermore, as the height of the space 30 increases, the equipment cost for installing the electric furnace 1 also increases. Therefore, from the viewpoint of enabling efficient operation while effectively reducing the CO concentration, the upper limit value of the height of the space 30 to be formed is preferably 2.9 m or less.

(In-furnace pressure)
In the operation method of the electric furnace according to the present embodiment, the pressure in the electric furnace 1, that is, the pressure in the space 30 formed above the melt layer 11 as described above is −5 to −70 Pa. It is preferable to maintain the range.

  Here, in order to effectively burn the CO gas in the electric furnace 1, supply of oxygen necessary for the combustion is indispensable. Usually, in the case of an electric furnace used for ferronickel smelting, the CO gas generated in the electric furnace has a structure that does not leak to the outside of the electric furnace, and is formed by a combustion air intake hole 25 provided on the ceiling. Combustion air is introduced. At this time, by setting the pressure in the electric furnace 1 to a negative pressure, the combustion air can be efficiently taken in via the combustion air intake hole 25, and oxygen necessary for the combustion of the CO gas is supplied. Is possible.

  The pressure in the electric furnace 1 is adjusted, for example, by adjusting the inverter of an electric furnace exhaust gas fan, adjusting the opening of a damper in the middle of the electric furnace exhaust gas flue, or the like. In the present embodiment, the pressure in the electric furnace 1 is preferably maintained in the range of −5 to −70 Pa, more preferably in the range of −10 to −60 Pa by the pressure adjustment method as described above. The combustion air can be smoothly taken in from the combustion air intake hole 25, and the CO gas can be burned more effectively. As a result, the CO concentration in the exhaust gas discharged from the electric furnace 1 is more effective, for example, to the extent that safety and health problems such as explosions and CO gas poisoning do not occur, specifically to about 500 ppm or less. Can be reduced.

  If the pressure of the space 30 (in-furnace pressure) exceeds −5 Pa, there is a possibility that the required amount of combustion air cannot be taken in (sucked) from the combustion air intake hole 25 in order to efficiently burn the CO gas. . If the pressure is too high, there is a possibility that CO gas or the like in the electric furnace 1 will blow out from the combustion air intake hole 25 or the like.

  On the other hand, when the pressure in the space 30 (in-furnace pressure) is less than −70 Pa, the amount of air taken into the electric furnace 1 increases, so that the combustion of the CO gas in the electric furnace 1 sufficiently proceeds, The CO concentration will be effectively reduced. However, in this case, since a large amount of air enters the electric furnace 1, the sensible heat that is taken away by the exhaust gas increases. When the sensible heat increases in this way, the electric power for compensating the sensible heat increases and the energy efficiency deteriorates. Furthermore, since the suction power of the exhaust gas is increased, fine sinters present in the electric furnace 1 are scattered in the exhaust gas, and the actual yield of ferronickel due to reduction melting in the electric furnace is reduced.

(About the ore layer)
The space 30 formed in the upper part of the melt layer 11 includes the ore layer 12 made of unmelted calcined ore that is fed through the casting pipe 21. And as mentioned above, by making the height of the space 30 including the ore layer 12 2.2 to 2.9 m to form a sufficient space, the CO gas in the electric furnace 1 is changed to the ore layer 12. It is designed to react efficiently with the sinters that make up.

  For this reason, it is necessary that the unreacted (unmelted) sinter required for the reaction be effectively present on the upper part of the melt layer 11, and at least a thin sinter such as an oil film stretched on the water surface. It is sufficient that a layer of ore (ore layer) exists, and the CO concentration in the exhaust gas discharged from the electric furnace 1 is determined by the height of the space.

  However, from the viewpoint of more effectively reducing the CO gas concentration in the electric furnace 1, the ore layer 12 formed by the sinter is more preferably a thick layer. That is, in the space 30, it is preferable that the amount of sinter present is large.

  Here, as a method for supplying the burned ore put into the electric furnace 1, a batch feed method (formula) for feeding in batch while observing the molten state of the burned ore in the electric furnace 1, The slag supplied to the upper part of the generated melt (molten layer 11) through the casting pipe is charged until it comes into contact with the tip of the casting pipe, and a new amount corresponding to the amount of reduction melting is continuously added. There is a choke feed method (formula).

  In the electric furnace 1, the supplied sinter is reduced and melted by direct reduction using a carbonaceous material such as coal and indirect reduction using CO gas generated in the electric furnace 1. At this time, when the calcined ore is supplied by the batch feed method, the thickness of the ore layer 12 that will be present above the melt layer 11 in the electric furnace 1 is reduced, and the generated CO gas and the reduction target are reduced. There are fewer opportunities to contact a certain mine. On the other hand, when the sinter is supplied by the choke feed method, a new sinter corresponding to the melted amount is continuously supplied, so the ore layer 12 formed on the upper part of the melt layer 11 becomes thicker. In addition, the chances of contact between the generated CO gas and the calcination ore to be reduced increase.

  That is, when attention is focused on the CO gas in the electric furnace 1, the opportunity for the CO gas to come into contact with the sinter during the period from the generation of the CO gas to the exhaust gas flue with the exhaust gas exhaust hole 26 as an inlet (indirect reduction reaction) The chance of sinter is greater when the sinter is supplied by the choke feed method (see also FIG. 2). Therefore, the amount of the generated CO gas combusted by the reduction reaction with the sinter becomes larger when the sinter is supplied by the choke feed method.

  Therefore, in the operation method of the electric furnace according to the present embodiment, it is preferable that the sinter is continuously supplied into the electric furnace 1 by the choke feed method. As a result, the ore layer 12 that is as thick as possible can be present above the melt layer 11 in the electric furnace 1, and the ore layer 12 promotes the combustion of the CO gas generated in the electric furnace 1 and is discharged. The CO gas to be contained in the electric furnace exhaust gas can be reduced more effectively.

(Combustion air intake hole)
As described above, the CO gas generated in the electric furnace 1 is reduced and consumed by the reduction reaction with the sinter, and is burned by the air taken into the electric furnace 1. Therefore, it is preferable that the combustion air from the outside be taken into a position close to the electrodes 22a to 22c where CO gas is generated, that is, a position where the CO concentration is high.

  For this reason, it is preferable that the combustion air intake hole 25 that is an air hole for taking in air for burning CO gas from outside is provided around the electrodes 22a to 22c suspended from the ceiling. .

  Here, “around the electrode” differs depending on the electric furnace to be used depending on the structure of the beam or the like of the ceiling portion provided with the electrode, but is the position closest to the electrode, and the combustion air intake hole 25 is defined as The position where it can be installed. Specifically, as shown in the schematic diagram when the ceiling portion of the electric furnace 1 shown in FIG. 3 is viewed from above, each of the three electrodes 22a to 22c provided by being suspended from the ceiling portion of the electric furnace 1 is provided. It is preferable to equidistantly arrange on the circumference of a concentric circle as a center, in the vicinity of each of the electrodes 22a to 22c and where the intake holes can be installed.

  The size of the combustion air intake hole 25 is not particularly limited, but is preferably about 50 to 300 mm in diameter. Further, the number of combustion air intake holes 25 (the number of installation) is not particularly limited, but 4 to 16 places (4 to 16 places / electrode) are equally provided on the circumference of one electrode. preferable.

  If the size of the combustion air intake hole 25 is smaller than 50 mm in diameter or if the number of installed air holes is less than four, there is a possibility that the air necessary for the combustion of the CO gas cannot be taken in sufficiently. On the other hand, if the size of the combustion air intake hole 25 exceeds the diameter of 300 mm or if the number of installed air holes is larger than 16, the amount of air flowing into the electric furnace 1 increases, and the sensible heat taken away as exhaust gas. Is increased, and there is a possibility that the heat in the electric furnace 1 is insufficient, resulting in poor operation.

(About exhaust gas exhaust holes)
Now, for example, the combustion air introduced from the combustion air intake hole 25 installed around the electrode as described above reacts with the CO gas generated at the electrodes 22a to 22c, and then the inside of the electric furnace 1 is outside (electric furnace). It reacts with the remaining unreacted CO gas while flowing toward the inner wall side of 1). Therefore, in order to effectively react with unreacted CO gas, the longer the residence time of the combustion air in the furnace, the better.

  The combustion air is finally discharged as exhaust gas through a discharge hole (exhaust gas discharge hole) 26 provided in the electric furnace 1. Therefore, from the viewpoint of increasing the residence time of the combustion air in the furnace, the exhaust gas exhaust hole 26 for exhausting exhaust gas containing fuel air is a model when the ceiling portion of the electric furnace 1 shown in FIG. 3 is viewed from above. As shown in the figure, it is preferable to be away from the periphery of the electrode provided with the combustion air intake hole 25 described above. Further, the exhaust gas discharge holes 26 may be provided at equal positions on the circumference of a concentric circle with respect to the center of the electric furnace 1 in order to facilitate the flow of the exhaust gas in the electric furnace 1. preferable.

  Although it does not specifically limit as a magnitude | size of the exhaust gas discharge hole 26, It is preferable to set it as a diameter of about 900-1800 mm. Further, the number of the exhaust gas discharge holes 26 is not particularly limited, but the number of the exhaust gas discharge holes 26 is equally 2 to 4 on the circumference of the concentric circle with respect to the center of the electric furnace 1, and the position in contact with the inner wall of the electric furnace 1. It is preferable to provide it in a close position.

  If the size of the exhaust gas discharge hole 26 is smaller than 900 mm in diameter or if the number of the exhaust gas exhaust holes 26 is less than two, the exhaust gas is not discharged smoothly. Therefore, a sufficient amount of air necessary for combustion is introduced into the electric furnace 1. There is a possibility that it cannot be incorporated. On the other hand, if the size of the exhaust gas exhaust hole 26 is larger than 1800 mm in diameter, or if the number of the exhaust gas exhaust holes 26 is more than four, the amount of air entering the electric furnace 1 increases, and the sensible heat taken away as exhaust gas. Is increased, and there is a possibility that the heat in the electric furnace 1 is insufficient, resulting in poor operation.

  Further, for example, if the exhaust gas discharge hole 26 is provided at a position close to the center of the electric furnace 1 instead of a position in contact with or close to the inner diameter of the electric furnace 1, the combustion air taken in from the combustion air intake hole 25 It is not preferable because the residence time in the furnace is shortened and the time for the unreacted CO gas to react with the air to be reduced or unmelted sinter is insufficient.

  As explained in detail above, in the method for operating the electric furnace according to the present embodiment, the height of 2.2 to 2.9 m including the undissolved ore layer 12 above the melt layer 11 in the electric furnace 1. It operates so that the space 30 may be formed. As a result, oxygen (air) sufficient to react with the CO gas generated in the electric furnace 1 and unmelted sinter can be present in the space 30 and promote combustion of the CO gas. Can be made. As a result, the CO gas in the electric furnace 1 can be effectively reduced, the CO gas concentration in the exhaust gas can be reduced, and the operation can be performed with high safety.

  Examples of the present invention will be described below in comparison with comparative examples. In addition, this invention is not limited by these Examples.

Example 1
In ferronickel smelting, a reduction melting process was performed in which the sintered ore (calcined ore) obtained through the firing and partial reduction steps was reduced and melted in an electric furnace.

  An electric furnace having a size from the furnace bottom to the furnace top of 5.0 m and an inner diameter of 16.3 m was used. The electric furnace has four combustion air intake holes with a diameter of 50 mm on a concentric circle centered on each of the three electrodes provided on the ceiling at a position 300 mm away from the electrode surface. / An electrode was provided (see FIG. 3). In addition, the exhaust gas discharge holes were provided in two locations with a diameter of 900 mm so as to contact the inner diameter of the electric furnace (see FIG. 3).

  In Example 1, as the operating condition of the electric furnace, the depth (melt layer) of the melt obtained by reducing and melting the supplied sinter was 2.8 m, the liquid level of the melt (of the melt layer) The height from the top surface to the top of the electric furnace was 2.2 m. In addition, the upper part of the melt (the upper part of the melt layer) is continuously fed by a choke feed method through a throwing pipe into which the ore is charged so that an ore layer having a thickness of 1.7 m is formed. New mine was introduced. That is, a space of 2.2 mm including the ore layer was formed above the melt layer. At this time, the lower end of the thrown pipe is in contact with the ore layer. Moreover, the furnace pressure was maintained at -10 Pa.

  As a result of operating under the operating conditions of this electric furnace, the concentration of CO gas contained in the exhaust gas from the exhaust gas discharge hole at the outlet of the electric furnace was 400 ppm. This is thought to be because the CO concentration in the exhaust gas could be kept low by effectively reducing the CO gas in the electric furnace.

  The CO concentration in the exhaust gas was measured by a CO concentration meter (infrared gas analyzer, manufactured by Yokogawa Electric Corporation) provided in the exhaust gas discharge hole. The same applies to the following examples and comparative examples.

<< Example 2 >>
In Example 2, the height from the furnace bottom to the furnace top is 5.7 m in size as the electric furnace, the combustion air intake holes are provided at 16 locations / electrodes with a diameter of 300 mm, and the exhaust gas is further exhausted. A discharge hole having a diameter of 1800 mm and four places was used. The other electric furnace design conditions are the same as those in the first embodiment.

  In addition, as the operating conditions of the electric furnace, the height from the liquid level of the melt (upper surface of the melt layer) to the top of the furnace of the electric furnace is 2.9 m, that is, including the ore layer above the melt layer. An operation was performed in the same manner as in Example 1 except that a space of .9 mm was formed and the furnace pressure was maintained at -60 Pa.

  As a result of operating under the operating conditions of this electric furnace, the concentration of CO gas contained in the exhaust gas from the exhaust gas exhaust hole at the outlet of the electric furnace was 350 ppm. As in Example 1, it was considered that the CO concentration in the exhaust gas could be kept low by effectively reducing the CO gas in the electric furnace.

Example 3
In Example 3, as an operating condition of the electric furnace, a new calcined ore is introduced in a batch feed manner through a casting pipe for injecting a calcined ore so that the thickness of the ore layer becomes 0.1 m. I made it. At this time, the lower end of the thrown pipe is not in contact with the ore layer. Further, the furnace pressure was maintained at -5 Pa. Except for these, the operation was performed in the same manner as in Example 1.

  As a result of operating under the operating conditions of this electric furnace, the concentration of CO gas contained in the exhaust gas from the exhaust gas discharge hole at the outlet of the electric furnace was 480 ppm, although the concentration was slightly higher than in Example 1 and Example 2. The CO concentration in the exhaust gas could be effectively reduced.

Example 4
In Example 4, the electric furnace having a size of 5.7 m in height from the furnace bottom to the furnace top was used.

  In addition, as the operating conditions of the electric furnace, the height from the liquid level of the melt (upper surface of the melt layer) to the top of the furnace of the electric furnace is 2.9 m, that is, including the ore layer above the melt layer. A space of 9 mm was formed. In addition, new burned ore was introduced in a batch feed manner through the casting pipe into which the ore was put, so that the thickness of the ore layer became 0.1 m. At this time, the lower end of the thrown pipe is not in contact with the ore layer. Furthermore, the pressure in the furnace was maintained at -70 Pa. Except for these, the operation was performed in the same manner as in Example 1.

  As a result of operating under the operating conditions of this electric furnace, the concentration of CO gas contained in the exhaust gas from the exhaust gas discharge hole at the outlet of the electric furnace was 420 ppm, although the concentration was slightly higher than in Example 1 and Example 2. The CO concentration in the exhaust gas could be effectively reduced.

≪Comparative example 1≫
In Comparative Example 1, an electric furnace having a size of 4.4 m in height from the furnace bottom to the furnace top was used.

  Moreover, the operating condition of the electric furnace is 1.6 m from the liquid level of the melt (upper surface of the melt layer) to the top of the electric furnace, that is, including the ore layer above the melt layer. A space of 6 mm was formed. In addition, new calcined ore was continuously fed in a choke feed type through the casting pipe into which the calcined ore was charged, so that the thickness of the ore layer was 1.6 m. At this time, the lower end of the thrown pipe is in contact with the ore layer. Except for these, the operation was performed in the same manner as in Example 1.

  As a result of operating under the operating conditions of this electric furnace, the concentration of CO gas contained in the exhaust gas from the exhaust gas discharge hole at the outlet of the electric furnace was 680 ppm, exceeding the standard 500 ppm. This is because the space formed in the upper part of the melt layer was not of sufficient capacity, so that there was not enough oxygen or unmelted ore layer to burn the CO gas, This is probably because it could not be effectively reduced.

«Comparative example 2»
In Comparative Example 2, the height from the bottom of the furnace to the top of the furnace is 4.4 m as an electric furnace, and three combustion air intake holes with a diameter of 40 mm are provided / electrodes. A discharge hole having a diameter of 800 mm and one place was used. The other electric furnace design conditions are the same as those in the first embodiment.

  Moreover, the operating condition of the electric furnace is 1.6 m from the liquid level of the melt (upper surface of the melt layer) to the top of the electric furnace, that is, including the ore layer above the melt layer. A space of 6 mm was formed. In addition, new calcined ore was introduced into the upper part of the melt (upper part of the melt layer) so that an ore layer having a thickness of 1.6 m was formed by the choke feed method. At this time, the lower end of the thrown pipe is in contact with the ore layer. Further, the furnace pressure was maintained at −10 Pa. Except for these, the operation was performed in the same manner as in Example 1.

  As a result of operating under the operating conditions of this electric furnace, the concentration of CO gas contained in the exhaust gas from the exhaust gas discharge hole at the outlet of the electric furnace was 700 ppm, which was significantly higher than the standard 500 ppm. This is because the space formed in the upper part of the melt layer was not sufficient capacity, and a sufficient amount of oxygen (air) to burn the CO gas could not be taken in. This is thought to be because it could not be reduced to a certain level.

«Comparative Example 3»
In Comparative Example 3, the height from the bottom to the top of the furnace is 4.4 m as an electric furnace, and combustion air intake holes with a diameter of 350 mm are provided at 18 locations / electrode, and exhaust gas is further provided. A discharge hole having a diameter of 1900 mm and five holes was used. The other electric furnace design conditions are the same as those in the first embodiment.

  Moreover, the operating condition of the electric furnace is 1.6 m from the liquid level of the melt (upper surface of the melt layer) to the top of the electric furnace, that is, including the ore layer above the melt layer. A space of 6 mm was formed. In addition, new calcined ore was introduced into the upper part of the melt (upper part of the melt layer) so that an ore layer having a thickness of 0.1 m was formed by a batch feed method. At this time, the lower end of the thrown pipe is not in contact with the ore layer. The furnace pressure was maintained at -60 Pa. Except for these, the operation was performed in the same manner as in Example 1.

  As a result of operating under the operating conditions of this electric furnace, the concentration of CO gas contained in the exhaust gas from the exhaust gas discharge hole at the outlet of the electric furnace was 750 ppm, which was significantly higher than the standard 500 ppm. This is because the space formed in the upper part of the melt layer was not sufficient capacity, and the amount of undissolved ore that was indirectly reduced and melted by CO gas was small, effectively reducing CO gas. It is thought that it was not possible to make it.

<< Comparative Example 4 >>
In Comparative Example 4, as the electric furnace, the height from the furnace bottom to the furnace top is 4.4 m, the combustion air intake hole has a diameter of 40 mm, three places / electrodes, and exhaust gas A discharge hole having a diameter of 800 mm and one place was used. The other electric furnace design conditions are the same as those in the first embodiment.

  Moreover, the operating condition of the electric furnace is 1.6 m from the liquid level of the melt (upper surface of the melt layer) to the top of the electric furnace, that is, including the ore layer above the melt layer. A space of 6 mm was formed. In addition, new calcined ore was introduced into the upper part of the melt (upper part of the melt layer) so that an ore layer having a thickness of 1.6 m was formed by the choke feed method. At this time, the lower end of the thrown pipe is in contact with the ore layer. The furnace pressure was maintained at -2 Pa. Except for these, the operation was performed in the same manner as in Example 1.

  As a result of operation under the operating conditions of this electric furnace, the concentration of CO gas contained in the exhaust gas from the exhaust gas discharge hole at the outlet of the electric furnace was 800 ppm, which was significantly higher than the standard 500 ppm. This is because the space formed in the upper part of the melt layer was not sufficient capacity, and the furnace pressure was too high, so that a sufficient amount of oxygen (air) was introduced to burn the CO gas. This is probably because CO gas could not be effectively reduced.

  DESCRIPTION OF SYMBOLS 1 Electric furnace, 11 Molten layer, 11A Metal layer, 11B Slag layer, 12 Ore layer, 21 Throw pipe, 22 (22a, 22b, 22c) Electrode, 23 Metal hole, 24 Slag hole, 25 Combustion air intake hole 26 exhaust gas exhaust holes, 30 spaces

Claims (8)

In ferronickel smelting, an electric furnace operating method in which calcined ore is put into an electric furnace having a diameter of 10 to 25 m and the calcined ore is reduced and melted,
An electric furnace characterized by forming a space of 2.2 to 2.9 m in height including an ore layer made of unmelted calcined ore on the upper part of a melt layer obtained by reducing and melting the calcined ore Operating method.   The electric furnace is provided with 4 to 16 air intake holes having a diameter of 50 to 300 mm per electrode evenly on a concentric circle centered on the electrode provided on the ceiling of the electric furnace. The method for operating an electric furnace according to claim 1.   In the electric furnace, exhaust gas discharge holes having a diameter of 900 to 1800 mm are evenly spaced apart from electrodes provided on the ceiling of the electric furnace and on a concentric circle with respect to the center of the electric furnace. The method for operating an electric furnace according to claim 1 or 2, wherein 2 to 4 places are provided. In the electric furnace, the firing ore is thrown in a chalk feed type through a throwing pipe for feeding the raw firing ore,
The electricity according to any one of claims 1 to 3, wherein in the space, the ore layer formed on the upper part of the melt layer is in contact with a lower end of the thrown pipe. How to operate the furnace.   The electric furnace operating method according to any one of claims 1 to 4, wherein the pressure in the space is maintained in a range of -5 to -70 Pa. In ferronickel smelting, an electric furnace having a diameter of 10 to 25 m for charging and reducing and melting calcined ore,
A space having a height of 2.2 to 2.9 m including an ore layer made of unmelted calcined ore is formed on the upper part of the melt layer obtained by reducing and melting the charged calcined ore. Electric furnace.   The air intake hole having a diameter of 50 to 300 mm is provided at 4 to 16 positions per electrode evenly on the circumference of a concentric circle with the electrode provided on the ceiling of the electric furnace. Electric furnace.   Exhaust gas discharge holes with a diameter of 900 to 1800 mm are provided at 2 to 4 positions evenly on a concentric circle with respect to the center of the electric furnace at a position apart from the electrode provided on the ceiling of the electric furnace. The electric furnace according to claim 6, wherein the electric furnace is provided.

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