SK3942001A3 - Method for producing directly reduced metal in a multi-tiered furnace - Google Patents

Abstract

The invention relates to a method for producing directly reduced metal in a multi-tiered furnace, whereby metal oxides and a reducing agent are inserted into the furnace and the process heat required for the reduction of the metal oxides is generated by indirect heating of the individual tiers of said furnace.

Description

Process for producing directly reduced metal in a multiple-hearth furnace

Technical field

The invention relates to a process for the production of directly reduced metal in a multiple-hearth furnace.

Multiple crucible furnaces are used to produce metals from the corresponding metal oxides, wherein the metal oxide and the reducing agent are introduced into the multi crucible furnace and react at high temperature.

BACKGROUND OF THE INVENTION

DE-C-552 837 relates to a method for melting fine-grained iron ores in a six-hearth reduction furnace. The multiple-hearth furnace is divided into two zones. In the first zone formed by the upper two overheads, iron ore is first preheated. Any suitable hot neutral gases in controllable amounts are used for this purpose. Optionally, additional burners may also be used. The second zone comprising the four lower pads is sealed from the preheating zone. Therefore, there is no gas exchange between the two zones. The second zone is intended for the reduction of iron ore. For this purpose, the reducing gases are injected either into the lowest bottom or separately into each individual bottom. The top three of the reduction zone are equipped with muffles, each of which is equipped with a burner. Through these muffles and burners, fuel gases are supplied to the top three furnaces.

U.S. Pat. No. 2089782 discloses a multiple iron furnace for direct reduction of iron ore, in which a chamber containing hot melt and located below the furnaces indirectly heats the higher furnace (s).

Document D3 (LU-A-87890) discloses a rotary hearth furnace in which the pellets are reduced on a rotary platform divided into annular sections. Wherein these sections of the rotating platform are located between the fine-grained refractory mass concentrically rotating about the axis of rotation. The process temperature is provided by electric radiators located above a significant portion of the reactor segment. In order to minimize energy loss, the radiators are positioned only a few centimeters above the surface of said fine-grained material. The material to be reduced is directly heated to the desired temperature by the radiators. During the manufacturing process, the raw pellets remain in a stationary position, i.e. they do not participate in the corresponding circular movement

The metal oxides and reducing agents are charged into a multiple-hearth furnace, where they are swirled by rakes with a radius length running from the center to the periphery of the hearth, where they fall through several openings into the lower hearth. From there, the metal oxides mixed with the reducing agents are moved to the center of the crucible and then fall into the lower crucible. During the descent from the upper purge to the bottom of the multiple-hearth furnace, the metal oxides and reducing agents are gradually heated.

Since the reduction of metal oxides is an endothermic process, starting and maintaining this reaction requires the supply of a relatively large amount of energy. For this purpose, the multiple-hearth furnace is heated by gas or other burners and part of the reducing agent - generally the volatile components of the carbon carrier such as coal - is burned by injecting an oxygen-containing gas into the multiple-hearth furnace. The necessary process heat is obtained by burning coal and using gas burners to form carbon dioxide. Above a certain temperature, the carbon dioxide present in the hot gases reacts with the carbon in a multiple-hearth furnace according to the Boudouard reaction to form carbon monoxide. The carbon monoxide formed in this way reduces metal oxides to metal. The carbon monoxide content of the gases in the multiple-hearth furnace essentially determines their reduction potential.

The disadvantage of this is that oxidized gases and oxygen are introduced into the multiple-hearth furnace in which the reduction takes place. In addition, a large amount of waste gases is to be treated.

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In this type of multiple-hearth furnace, heated by hot flames from natural gas, it is difficult to establish and regulate a uniform temperature profile in the furnace cross-section Because the individual bands and crosses are interconnected, it is difficult to control the conditions in each bands independently of the others. Gases leaving one or the other affect the conditions in the next higher purer

It is therefore an object of the present invention to provide a process for the production of a directly reduced metal using less gas.

SUMMARY OF THE INVENTION

According to the present invention, this problem is solved by a method of producing directly reduced metal in a multiple-hearth furnace, characterized in that metal oxides are charged into the multiple-hearth furnace and reducing agents and process heat required to reduce metal oxides are generated by indirectly heating the metal oxides of the furnace or the housing of the multiple-hearth furnace by electric heating resistors under the individual hearths or on the housing of the multiple-hearth furnace and the individual hearths are indirectly heated independently of the others.

In the method of the invention, process heat is supplied to the multiple furnace furnace by radiation energy and not by combustion of the reducing agent in situ or by gas burners as in the known methods.

An important advantage of the present invention is that no oxygen or other oxidized gases need to be injected into the multiple-hearth furnace to achieve the necessary process heat. This greatly reduces the amount of gases circulating in the multiple-hearth furnace. The amount of waste gases to be re-treated is considerably less, thereby reducing the cost of the treatment

In addition, smaller gas volumes result in lower gas flow rates in the individual supports. Therefore, less turbulent waste dust is discharged from the multiple furnace furnace.

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Since no oxygen or other oxidized gases are injected into the multiple-hearth furnace, the reduction potential of the gases inside the multiple-hearth furnace is higher than in the already known multiple-hearth furnaces.

In addition, the method allows a more uniform heating of the multiple-hearth furnace and the substances contained therein.

The process can be carried out at a pressure of 1 to 5 bar, with the result that a multiple-hearth furnace can be of a more compact design.

In one preferred embodiment, gaseous reducing agents are used in addition to the solid reducing agents.

Metal oxides are, for example, iron ores, zinc ores, oil-containing wastes and iron oxides, and various forms of problem wastes such as the fraction of particulate iron containing iron oxides contaminated by zinc oxides and / or heavy metal oxides

The invention also relates to a multiple furnace comprising several furnaces placed one above the other for the production of directly reduced metal. The multiple furnace according to the invention is characterized by electric heating resistors for indirectly heating the individual furnaces which generate the process heat required to reduce metal oxides. underneath the individual hearths or on the shell of the multiple hearth furnace and the individual hearths are indirectly heated independently of the other

For example, the multiple-hearth furnace may be heated to the desired temperature and maintained at that temperature by electrical heating resistors installed within the multiple-hearth furnace.

Therefore, in each crucible, the temperature can be selectively adjusted without substantially affecting the conditions in the crucibles above and below. In contrast to traditional multiple crucibles, the conditions in the various crucibles can be regulated independently of the others.

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At the same capacity and at the same gas velocities in the pans, the multiple pan furnace for producing directly reduced metal may be smaller than the conventional multiple pan furnace according to the invention.

Indirect heating elements may be installed on the surface and / or under individual supports. They can also be fitted on the side walls.

This method is particularly suitable for direct reduction of iron ore.

Further advantageous embodiments are set forth in the dependent claims.

One embodiment of the invention is described below with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-section of a multiple-hearth furnace for the production of directly reduced metal.

Figure 2 is a schematic representation of electrical heating resistors in a multiple-hearth furnace.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a cross-section of a multi-hearth furnace 10 which comprises a plurality - in this case twelve - of the stack 12 placed one above the other. These self-supporting supports 12 are of refractory material as well as the jacket 14, the vault 16 and the bottom 18 of the multiple-hearth furnace 10.

The vault 16 of the multiple furnace 10 is provided with an exhaust 20 through which gases can be discharged from the multiple furnace and an opening 22 through which metal oxides and reducing agents are introduced into the upper hearth. However, metal oxides can also be charged lower and separately into the multiple furnace 10 from reducing agents

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B B B B B B B I B B B B B B. BBBBBBBB ··· ···· ·· ·· ·· ·

The shaft 24 provided with rakes 26 extending across the entire crates 12 is positioned in the middle of a multiple-hearth furnace The shaft 24 and the rakes 26 are cooled by air or water.

The rakes 26 are designed to swirl the material in a circumferential to center, and then in the lower, from the center to the circumference in a circular motion, so as to ensure that the material descends through the multiple furnace 10 from top to bottom.

The metal oxides are mixed with solid reducing agents such as lignite coke, petroleum coke or coal outside the multiple crucible furnace 10 and the mixture of metal oxides and reducing agents is subsequently charged to the upper crucible.

However, the metal oxides can also be fed separately into the upper crucible and then the solid reducing agents are fed into the multiple furnace 10 through the lower opening 30 in the housing 14.

The metal oxides may also be pre-dried outside the multiple crucible furnace 10 prior to mixing with the solid reducing agents.

After the mixture of the metal oxides and reducing agents has been introduced into the first crucible of the multiple crucible furnace 10, the mixture is swirled by the rakes 26 to the periphery of the crucible where it passes through several openings 28 provided for this purpose into the lower crucible. From there, the metal oxides mixed with the reducing agents are moved to the center of the crucible and then fall into the lower crucible. During the descent from the upper purge to the bottom of the multiple-hearth furnace, the metal oxides and reducing agents are gradually heated.

At the same time, moisture is removed from the metal oxides mixed with the reducing agents by contact with the crucible 12 and the rising hot gases. The upper supports in the multiple furnace 10 thus belong to the drying and preheating zone

In the side wall of the multiple-hearth furnace 10 - normally in its upper third - at least one intake opening 30 is provided through which reducing agents are introduced, unless they have been introduced into the multiple-hearth furnace 10

Ί · · · · · · · · · ··· ·· ·· ·· · together with metal oxides. Through this suction opening 30, either all reducing agents or only additional agents can be charged into the multiple-hearth furnace 10. These reducing agents may be in gaseous as well as in liquid or solid form. These reducing agents include, for example, carbon monoxide, hydrogen, natural gas, petroleum or petroleum derivatives, or solid carbon carriers such as lignite coke, petroleum coke, blast furnace dust, coal and the like.

The reducing agent, in this case coal, which is fed into the crucible located in the multiple crucible furnace 10 in the lower zone, is mixed here with the rakes 26 with the heated metal oxides. The metal oxides are gradually reduced by the high temperature and the presence of reducing agents in the descending transport by a multiple furnace 10.

The reduction of the metal oxides can be precisely controlled and its process carried out under optimal conditions by the controlled introduction of solid, liquid or gaseous reducing agents at various points in the multiple furnace 10 and by drawing off excess gases at critical points.

Nozzles 30 are disposed in the side walls for injecting oxygen-containing hot gases (250 ° C to 500 ° C) through which air or other oxygen-containing gas can be introduced into the multiple-hearth furnace 10. Due to the high temperatures and the presence of oxygen, combustible gases can be burned in the upper pans 12 of the multiple pan furnace 10 and the energy generated can be used to dry metal oxides and reducing agents

In the last bottom down or in the last two overheads, injection is provided for the gaseous reducing agent, for example carbon monoxide or hydrogen, by special nozzles 44. In the resulting atmosphere with increased reducing potential, the reduction of the metal oxides can be completed.

Subsequently, the produced metal is tapped together with the ash through the outlet 46 in the bottom 18 of the multiple-hearth furnace 11).

After tapping from the outlet 46, the metal is cooled in the cooler 48 together with ash and reducing agents which can be reused under appropriate circumstances. Po ····································

Hereby the reduced metal is separated from the ash by a separator 50 from reducing agents and reusable reducing agents 52.

The gas mixture from the multiple-hearth furnace 10 is discharged to a supplementary burner 54 via a withdrawal 20 to combust the combustible gases from the gas mixture. Thereafter, the gas mixture is introduced into a cooler 56 containing the coolant and cooled. Subsequently, the cooled gas mixture is purged by means of a cyclone filter 58 before being released to the atmosphere.

Of course, if the multiple furnace is operated under positive pressure, it is necessary to provide the holes 22 and 30 for the introduction of metal oxides and reducing agents as well as the exhaust 20 with pressure seals. Shaft bearings 24 and drain ´46 must also be sealed for hot material tapping.

However, the off-gases from the multiple furnace 10 can also be used to power an electricity generating turbine. In this case, it is necessary to omit the build-up inside the multiple-hearth furnace 10 and no oxygen-containing gas is injected into the multiple-hearth furnace 10.

This multiple furnace 10 allows the processing of iron ore, zinc ores, waste materials containing oil and iron oxide, and various problematic wastes such as dust containing iron oxide contaminated with zinc oxides and / or heavy metal oxides

Dust wastes and iron oxide containing sludges from electric or converter steel mills, which generally do not contain any carbon, or dust from blast furnace waste gas cleaning can therefore be fed into the multiple furnace 10 through a special opening 30. The reduction of residual materials can be precisely controlled and carried out under optimum conditions by the controlled introduction of solid, liquid and gaseous reducing agents at various points of the multiple-hearth furnace 10 and by drawing off excess gases at critical points

Because these ferric oxide-containing dust and liquid wastes are often contaminated with heavy metal oxides, a high proportion of gases may increase.

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As a result, it is possible to withdraw the dust and sludge containing heavy metal oxides from the furnace 10 under the furnace 10 by means of a pipe connector 60 located in the side wall and to reinject the furnace 10 through an opening 62 above said hearth. For example, in which dusts and sludges containing heavy metal oxides are introduced, the proportion of gas is small. The heavy metal oxides present in the dusts and sludges are reduced after being introduced into the furnace and the resulting metals are evaporated. Further, they can be withdrawn from the multiple furnace 10 as a small gas fraction by withdrawal 64 in the side wall.

This small volume of gas with a relatively high heavy metal content can then be cleaned separately. Small amounts of waste gas result in a low gas flow rate through the corresponding nozzles, so that only a small amount of waste dust is entrained with this waste gas. Therefore, the concentration of heavy metals in the waste gas is very high

Combustible gases withdrawn from the gaseous mixture are burned in the auxiliary burner 66. The remaining portion of the gaseous mixture is cooled in a condenser 68 and subsequently purified by a cyclone filter 70 before being released to the atmosphere.

The iron oxide present in the dust waste is reduced to iron together with the oil and iron oxide wastes

All gases produced, including the volatile components of the reducing agents, can be completely burned in the oven for residual materials containing heavy metal and iron oxide and, if necessary, for reducing agents outside the multiple furnace and the remaining heat of the furnace waste gases can be optimally used

Figure 2 shows a schematic representation of a crucible in a multiple crucible furnace 10 in which the heating resistors 72 and 74 are mounted on the side walls or housing 14 and below the crucible 12.

Claims (6)

PATENT CLAIMS Method for producing directly reduced metal in a multiple-hearth furnace, characterized in that metal oxides are charged into the multiple-hearth furnace and the reducing agents and the process heat required to reduce metal oxides are generated by indirectly heating the metal oxides solely by means of the furnace or sheath of the multiple-hearth furnace. electrical heating resistors installed below the individual pans or on the shell of the multiple pan furnace and the individual pans are indirectly heated, independently of each other. Process according to claim 1, characterized in that the process is carried out at a pressure of 1 to 5 bar. Method according to one of the preceding claims, characterized in that gaseous reducing agents are used. Method according to one of the preceding claims, characterized in that the metal oxides are iron ores, zinc ores, oil and iron oxide-containing wastes and various problematic wastes such as iron oxide-containing dust wastes contaminated with zinc oxides and / or other heavy metal oxides 5 Multiple crucible furnace containing several stacks placed one above the other for the production of directly reduced metal from metal oxides, characterized in that it is equipped with electric heating resistors installed under individual racks or on the casing of a multiple stack11 • ····· · · · »· ··· The process heat necessary for the reduction of metal oxides is generated by indirectly heating the metal oxides solely by electric heating resistors, the heating resistors being independent of each other. A multiple-hearth furnace according to claim 5, characterized in that the electric heating resistors have a protective shield.