MXPA01003080A - 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

PROCEDURE TO PRODUCE REDUCED METAL DIRECTLY IN A MULTI-SOLER OVEN DESCRIPTIVE MEMORY The invention relates to a process for producing reduced metal directly in a multiple sole oven. The multiple sole kilns are used for the production of metals from the corresponding metal oxides, with a metal oxide and a reducing agent being introduced into the multiple soleplate furnace and being reacted at an elevated temperature. DE-C-552837 relates to a process for the melting of fine iron ores in a reduction furnace with six screeds. The multiple sole kiln is divided into two zones. In the first zone, which comprises the two upper floors, the iron ore is preheated. For this purpose, inert hot gases are supplied in quantities that can be controlled. Burners could also be used. The second zone, which comprises the four lower solerails, is hermetically isolated from gases coming from the preheating zone. Therefore, there is no gas exchange between the two zones. The second zone is designed for the reduction of iron ore. For this purpose, reducing gases are supplied either in the lowest hearth or separately to each individual hearth. The three soleras The upper part of the reduction zone is provided with muffles, each equipped with a burner. The heating gases can be supplied to the three upper floors by means of these muffles and burners. The patent E.U.A. No. 2089782 discloses a multiple soleplate furnace for the direct reduction of iron ore, in which, below the solerails, a chamber containing a hot melt material indirectly heats the upper screeds. In document D3 (LU-A-87890), a rotary hearth furnace is described, in which the pellets are reduced in a rotating plate with annular sections, wherein the sections of the rotating plate are provided with fins of a material refractory which rotates concentrically around the axis of rotation. The heat of the processing is generated by electric radiators placed over a considerable proportion of the segment of the reactor. In order to reduce energy losses, the radiators are mounted only a few centimeters above the upper edge of the fins. The radiators directly heat the material that is going to be reduced to the required temperature. The pellets remain stationary, that is, without reciprocal movement throughout the entire process of handling in the reactor. The metal oxides and the reducing agents are introduced into the multiple soleplate furnace, they are circulated through rakes that extend through the individual solerails and from there they are transported towards the edge of the hearth, from where they fall through several openings provided for that purpose towards a lower hearth. From here the metallic oxides mixed with reducing agents are transported towards the center of the hearth and then fall towards the underlying hearth. During transport from the upper part down through the multiple soleplate furnace, the metal oxides and reducing agents are heated gradually. Because the reduction of metal oxides is endothermic, a relatively large amount of energy must be spent to initiate and maintain the reactions. To achieve this, the multi-solenoid furnace is heated by gas burners or the like and some of the reducing agents - generally the volatile part of a coal carrier such as coal - is burned by injecting a gas containing oxygen into the furnace. the oven of multiple soleras. The required processing heat is produced by combustion of coal and gas burners and carbon dioxide is formed. By above a specific temperature the carbon dioxide present in the hot gases reacts with the carbon in the multi-soleus furnace in order to form carbon monoxide in accordance with the Boudouard equilibrium. The carbon monoxide formed in this way reduces the metal oxides to the metal. The carbon monoxide content of the gases in the multiple soleplate furnace essentially determines the reduction potential. A disadvantage of this procedure is that oxidized gases and oxygen are introduced into the multi-solenoid furnace, in which the reduction takes place. In addition, a large amount of waste gases are produced which must be treated. In this type of multiple soleplate furnace, which is heated by a hot flame based on a natural gas, it is difficult to produce and maintain a uniform temperature profile. Because the different areas of the sole plates are connected to one another, it is difficult to control the conditions in the individual zones independently of one another.

Gases that leave a hearth influence the conditions of the next higher hearth. Accordingly, the task of the present invention is to propose a process for the production of directly produced metal that works with small amounts of gas. According to the invention, this problem is solved by a process for the production of reduced metal directly in a multiple soleplate furnace, characterized in that the metal oxides and reducing agents are introduced into the multiple hearth furnace and the heat of processing required for reduce metal oxides is produced by indirect heating of metal oxides only by means of the soleras or the shell of the multiple soleplate furnace by means of electric heating resistors mounted below the individual solerails or in the shell of the multiple soleplate furnace, and the individual hearths are heated indirectly independently of one another.

In the process according to the invention, the process heat is fed to the multiple soleplate furnace by radiant energy and not by combustion of the reducing agent in situ or by gas burners as in the known processes. An important advantage of the invention is that it is not necessary to inject oxygen or other oxidized gases into the multiple solenoid furnace in order to produce the required process heat. Therefore, the quantities of gases circulating in the multiple soleplate furnace are substantially reduced. Only significantly smaller amounts of waste gases need to be treated, with the result that the process is less expensive. In addition, the gas flow velocities in the individual hearths are smaller due to the smaller amounts of gas. A smaller amount of dust from the multi-sole oven is swirled and discharged. Because oxygen or other oxidized gases are not injected into the multiple soleplate furnace, the potential for gas reduction within the multiple soleplate furnace is greater than that of the already known multiple sole hearth furnaces. Furthermore, this method allows a more uniform heating of the multiple sole oven and its contents.

The process can be carried out at a pressure of 1 to 5 bars, with the result that the multiple-sole furnace can be of a more compact design. In addition to the solid reducing agents, gaseous reducing agents are used in a convenient embodiment. The metal oxides are, for example, iron ore, zinc ores, wastes containing oil and iron oxide and various forms of problematic wastes such as powders containing iron oxide contaminated with zinc oxides and / or some other oxides of iron. heavy metals. The invention also relates to a multiple-sole furnace comprising several sole plates one on top of the other for the production of reduced metal directly. The multiple soleplate furnace according to the invention is characterized by electric heating resistors for indirect heating of the individual hearths, which produces the heat of processing required to reduce the metal oxides, in which the heating resistors are installed by under individual solerails or on the shell of the multiple soleplate furnace, and individual solerails are indirectly heated independently of one another. The multi-solenoid furnace can, for example, be brought to the required temperature and maintained at that temperature by electrical heating resistors installed inside the multi-sole furnace.

Therefore it is possible to adjust the temperature in each hearth selectively without significantly affecting the conditions in the adjacent screeds. Contrary to the traditional multiple hearth furnaces, the conditions in the different hearths can be controlled independently of one another. With the same capacity and flow velocities of gas in the screeds, the multiple soleplate furnace for producing reduced metal directly by the process according to the invention may be smaller than a conventional multiple soleplate furnace. Indirect heating elements can be installed on the surface and / or below the individual screeds. However, these could also be mounted on the side wall. This process is particularly advantageous in the direct reduction of iron ore. Additional advantageous embodiments are listed in the dependent claims. Next, an embodiment of the invention is described with the help of the attached figure. Fig. 1 is a section through a multiple sole furnace for the production of reduced metal directly, Fig. 2 is a schematic arrangement of electric heating resistors in the multiple sole furnace.

Figure 1 shows a section through a multiple sole oven 10, which has several - in this case 12 - solerails 12 one on top of the other. These unsupported sills 12 as well as the shell 14, the cover 16 and the bottom 18 of the multiple sill furnace 10 are made from refractory material. An outlet 20 is provided through which gases from the multiple solenoid furnace 10, and an opening 22, can be evacuated, through which the metal oxides and reducing agents can be charged to the upper hearth, in the cover 16 of the multiple solenoid furnace 10. However, the metal oxides can also be introduced separately from the reducing agents a little lower in the multiple solenoid furnace 10. An arrow 24, on which the rakes 26 are mounted they extend through the respective solerails 12, they are installed in the center of the multiple solerail furnace. The arrow 24 and the rakes 26 are cooled with air or water. The rakes 26 are designed in such a way that they circulate the material on a hearth from the outside inwards and then from the inside outwards in the underlying hearth in order to transport the material from top to bottom through the multiple hearth furnace 10. The metal oxides can be mixed with solid reducing agents such as lignite coke, coal or petroleum coke outside the multi-sole furnace 10 or the mixture of metal oxides and reducing agents can subsequently be charged to the upper hearth.

However, the metal oxides can also be charged separately to the upper hearth and the solid reducing agents can be introduced into the multiple hearth furnace 10 a little further down through an entrance opening 30 in the shell 14. It is possible to pre-drying the metal oxides out of the multi-sole oven 10 before or after they are mixed with the solid reducing agents. After charging the mixture of metal oxides and reducing agents to the first sole plate of the multiple soleplate furnace 10, it is circulated through the rakes 26 and transported to the edge of the hearth, from where it falls through several openings 28 provided for the purpose in the underlying hearth. From here the metallic oxides mixed with the reducing agents are transported towards the center of the hearth and then fall into the underlying hearth. During transport, metal oxides and reducing agents gradually warm up. During this time the moisture of the metal oxides mixed with the reducing agents is eliminated by contact with the hearth 12 and the hot rising gases. Therefore, the upper screeds in the multi-sole oven 10 belong to the drying and preheating zone. At least one inlet opening 30 is provided, through which the reducing agents are introduced, if these have not yet been introduced into the multi-solenoid furnace 10 together with the metal oxides, in the side walls of the multi-sole oven 10 - normally in the upper third. All reducing agents or additional reducing agents can be introduced into the multiple sole oven 10 through this inlet opening 30. These reducing agents could be present both in the gaseous state and in liquid or solid form. These reducing agents are, for example, carbon monoxide, hydrogen, natural gas, petroleum or petroleum derivatives, solid carbon carriers such as lignite coal, petroleum coal, blast furnace dust, coke or the like. The reducing agent, in this case coal, which is introduced into a hearth a little lower in the multi-sole furnace 10, is mixed there with the hot metal oxides by the rakes 26. The metal oxides are gradually reduced to metal by the high temperature and the presence of reducing agents during the transport through the multiple solenoid furnace 10. The reduction of the metal oxides can be controlled in an exact way and the process can be carried out under optimal conditions controlling the supply of the solid reducing agents , liquid and gaseous at various points of the multiple solenoid furnace 10 and with the possibility of eliminating excess gases in liquid forms. On the side wall are provided nozzles 30 for the injection of hot gases (250 ° C to 500 ° C) containing oxygen, through which air or another gas containing oxygen can be supplied to the furnace of multiple solerails 10. As a result of the elevated temperatures and the presence of oxygen, the combustible gases can be burned in the upper solerails 12 of the multiple solenoid furnace 10 and the resulting energy can be used to dry the metal oxides and reducing agents . Provision is made in the last or in the last two sills to supply a gaseous reducing agent, for example, carbon monoxide or hydrogen, through the special nozzles 44. In this atmosphere with increased reduction potential, the reduction can be completed of metal oxides. The produced metal is subsequently discharged together with the ashes through the outlet 46 in the lower part 18 of the multi-solenoid furnace 10. The metal discharged at the outlet 46 is cooled in a coolant 48 with the ash and reducing agents, the which, in some circumstances, can be used again. The reduced metal is subsequently separated from the ash of the reducing agents, and any of the reducing agents 52, which can be reused, by means of a separator 50. The gas mixture coming from the multi-sole furnace 10 passes through the the outlet 20 and to a rear burner 54, in which the combustible gases of the gas mixture are burned. The gas mixture is fed to a refrigerant 56 supplied with a cooling medium and cooled. The cold gas mixture is subsequently cleaned with the help of a cyclone filter 58 before it is discharged into the atmosphere. If the multi-solenoid furnace 10 is operated under excessive pressure, it must, of course, be provided for pressure in the openings 22, 30 for supplying the metal oxides and reducing agents and at the outlet 20. The bearings of the arrow 24 must also be sealed and must be provided at exit 46 with an insurance to discharge the hot material. However, the waste gases from the multi-sole kiln 10 can be used to drive a turbine that generates electricity. In this case post-combustion must be dispensed into the multi-solenoid furnace 10 and oxygen-containing gases must not be introduced through the nozzles 32 into the multiple solenoid furnace 10. This multiple solenoid furnace 10 allows the use of iron ore, zinc ores, waste containing oils and iron oxide and various problematic wastes such as powders containing iron oxide contaminated with zinc oxides and / or other heavy metal oxides. Powders or sludges containing iron oxide from electric mills or steel converting mills, which could hardly contain any type of coal, dust from the cleaning of blast furnace waste gases can thus be introduced into the multi-solenoid oven 10 through a special opening 30. Reduction of waste materials It can be controlled in Exactly and the process can be carried out under optimal conditions by the controlled supply of solid, liquid and gaseous reducing agents at various points of the multiple solenoid furnace 10 and the possibility of eliminating excess gases at the critical points. Because these iron oxide-containing powders or sludges are often contaminated with heavy metal oxides, a large proportion of the gases flowing upward in the multiple solenoid furnace 10 can be removed from the multiple solenoid furnace 10. below the hearth in which the powders or sludges containing heavy metal oxides are charged, through an exhaust connecting piece 60 in the side wall and are re-injected into the multi-solenoid furnace 10 through a 62 entry above this hearth. Therefore, the amount of gas present in the screeds into which the powders or slurries containing heavy metal oxides are introduced is small. The oxides of heavy metals present in the powders or sludges are reduced after being introduced into the multiple soleplate furnace, and the metals formed evaporate. These can then be removed from the multiple solenoid furnace 10 in a relatively small amount of gas in this hearth through an outlet 64 in the side wall. The small volume of gas with a relatively high content of heavy metals can then be cleaned separately. As a result of the small amounts of waste gas, the flow velocities of the gases in the corresponding screeds are low, and from this Only small amounts of dust are discharged with this waste. Accordingly, a fairly high concentration of heavy metals is obtained in the waste gas. The combustible gases in the removed gas mixture are burned in a post-burner 66. The remainder of the gas mixture is cooled in a coolant 68 and subsequently cleaned by a cyclonic filter 50 before it is discharged into the atmosphere. The iron oxide present in the powders is reduced to iron with the waste containing oil and iron oxide. All the ascending gases, including the volatile constituents of the reducing agents, can be completely burned in the drying plant for the residual materials containing heavy metal and iron oxides and possibly for the reducing agents outside the multiple soleplate furnace and, of this, way it is used in waste heat from the waste gases of multiple sole kiln in an optimal way. Figure 2 shows a schematic representation of a hearth in the multi-sole furnace 10, in which the heating resistors 72, 74 are mounted on the side wall or on the shell 14 and below a hearth 12.

Claims (6)

NOVELTY OF THE INVENTION CLAIMS

1. - Process for producing directly reduced metal in a multiple soleplate furnace, characterized in that metal oxides and reducing agents are introduced in the multiple soleplate furnace and the processing heat required for the reduction of metal oxides is produced by heating Indirect metal oxides only through the hearth plate or shell of the multiple soleplate furnace by means of electric heating resistors installed below the individual solerails or on the shell of the multiple soleplate furnace, and the individual solerails are heated indirectly, independently of each other.

2. A method according to claim 1, further characterized in that the process is carried out under a pressure of 1 to 5 bars.

3. The process according to one of the preceding claims, further characterized in that gaseous reducing agents are used.

4. The process according to one of the preceding claims, further characterized in that the metal oxides are iron ore, zinc minerals, waste containing oil and iron oxide, and various problematic wastes such as, for example, iron oxide-containing powders contaminated with zinc oxides and / or other heavy metal oxides.

5. The multiple soleplate furnace comprising several sole plates one on top of the other to produce metal directly reduced from metal oxides, characterized in that it has electrical heating resistors which are installed under the individual solerails or on the shell of the oven. multiple sills, in which the heat of processing required to reduce the metal oxides is produced by indirect heat from the metal oxides by means of only the resistors for electric heating, and because the resistors for heating are independent of each other.

6. The multiple soleplate furnace according to claim 5, further characterized in that the resistors for electric heating have a protective sheet.