MXPA00005764A - Method for producing directly reduced iron in a layered furnace - Google Patents

Abstract

The invention relates to a method for producing reduced iron in a layered furnace comprising several superimposed layers, whereby ore is continually fed into the layered furnace, deposited on the uppermost layer, gradually transferred to the lower layers, and the reducing agent is deposited on the uppermost layer and/or layers thereunder and reacted with the ore in order to form directly reduced iron. The directly reduced iron and reducing agent residues are discharged in the vicinity of the lowest layer of the furnace.

Description

METHOD TO PRODUCE DIRECTLY REDUCED IRON IN A STRATIFIED OVEN The invention relates to a method for directly reducing iron production in a layered furnace. The production of the directly reduced iron is carried out in a direct reduction process by reducing iron oxide with solid or gaseous reducing agents. A carbon carrier, which reacts with carbon dioxide and forms the CO reduction gas at higher temperatures, for example, functions as a solid reducing agent. A process of this type can be carried out, for example, in a rotary crucible furnace, that is in a furnace with a rotary ring furnace bottom, which is coated with refractory material in the upper part and is inside a box. The burners, which penetrate the box and heat the inside of the box to the required reaction temperature above 1000 ° C, are mounted on the top of the box. The iron oxide is distributed together with the reducing agent at a specific point on the rotating crucible and is introduced by rotating the rotating crucible inside the box, where it reacts with the reducing agent because of the high temperatures and is present as iron directly reduced after approximately one revolution of the rotating crucible. In this process the iron oxide and the reducing agent after loading into the refractory lining of the rotating crucible must first be heated to the required reaction temperature before the actual reduction reaction can begin. This is carried out in the area surrounding the loading area of the rotary kiln in the direction of rotation by transferring heat from the hot waste gases from the burners to the charged materials. Due to the low thermal conductivity of the charged materials, the heating phase requires a considerable time before achieving the required reaction temperature within the layers of loaded material. The longer the heating phase, the lower the productivity of the rotary crucible furnace, because the heating rate determines the rotational speed of the rotating crucible. The reduction procedure depends on the concentration of the reduction gases, which are in contact with the ore. However, the gas composition in the individual zones of the furnace can hardly be affected, because all the furnace consists of only one process space. Therefore, in conventional processes, the diffusion of CO from the reducing agent to the mineral and the CO2 from the mineral to the reducing agents can not be affected. From a certain metallization level onwards, the speed of the reduction process decreases such that the process is usually interrupted when a metallization degree of 85 to 95% is achieved. A non-economic extension of the procedure time will be necessary to reduce the remaining oxides. DE 1 225 673 relates to a method for the dry reduction of iron ore in a layered furnace, which has several platforms one on top of the other. The iron ore is loaded on the upper platform and gradually transferred to the lower platforms. In the lower platforms (reduction platforms) a reducing gas is fed to reduce the iron ore. On the upper platforms, the iron ore is preheated to the reduction temperature required by the combustion of the reducing gas that rises. Prior to introduction into the stratified furnace, a solid reducing agent can be mixed with the iron ore. Part of the reducing gas from at least one of the upper reduction platforms is removed and fed into at least one of the lower reduction platforms. A process for the production of sponge iron in a stratified furnace is already known, which has several platforms, one on top of the other, of US 2,089,782. The iron ore is loaded on the upper platform and gradually transferred to the lower platforms. The solid reducing agent is loaded on one of the platforms below. The iron ore is reduced in the lower platforms (reduction platforms). The thermal energy required for the reduction is provided by an electrically heated molten material provided under the lower platform of the stratified furnace. On the upper platforms, the iron ore is preheated by the combustion of the reducing gas that rises from the reduction platforms. In this way, the task of the present invention is to propose an alternative process for the production of directly reduced iron. In accordance with the invention, this problem is solved by a process for the production of directly reduced iron in a stratified furnace having several platforms on top of one another, a high temperature prevailing in the lower platforms and where the ore is continuously introduced. to the stratified furnace and is deposited on the upper platform and gradually transferred to the lower platforms; the solid or liquid reducing agent is deposited on the highest platform and / or on one of the platforms below it; an oxygen-containing gas is fed into the lower platforms and reacts with the reducing agent to form a reducing gas, the reducing gas reacts with the ore to form directly reduced iron; The directly reduced iron is discharged together with the residues of the reducing agents in the area of the lower platform of the stratified furnace. An important advantage of the invention is that the process space is subdivided into different zones, the solids move continuously from the top down and the gases from the bottom up. By subdividing the procedure space into different zones, the process conditions can be measured and controlled in the different zones or even on each platform and selectively. Solid, liquid or gaseous reducing agents come into consideration as reducing agents. In this process, finely ground ore can be loaded and cake formation avoided by selective process control and continuous circulation. This is particularly useful if reducing agents that form ash are used. The separation of the ash from the reducing agent of the iron can be carried out easily. This separation can be carried out, for example, on the hot platform by screening. After a partial cooling below 700 ° C it is possible, on the other hand, to separate the directly reduced iron by means of magnetic separators from the ash and excess reducing agent. Therefore, this procedure can be used, because the continuous agitation in the layered oven prevents the formation of cake of the iron. The iron directly reduced in this way is produced in a finely ground form and is easily lifted by magnetic separators. The quality of the directly reduced iron obtained in this way is independent of the amount of waste of the reducing agent. The iron obtained subsequently can be processed into pellets or briquettes or introduced directly into a foundry furnace (electric furnace, etc.) and subjected to an additional procedure. If required, the reducing agent residues that are produced are burned in burners with any unused reducers and the resulting heat is fed into the furnace. In this way, a lower cost reducing agent having a relatively high ash content and / or carrying out the work without an excessive amount of reducing agent can be used. In cases where it is necessary to work with an excess of reducing agents it is useful to treat the waste to separate the unused reducing agents and reuse them. This can be done, for example by sieving the waste, in the event that the unused reducing agents are present in a sufficiently thick form. The unused reducing agents can be introduced directly into the stratified furnace. However, the loading of reducing agents can also be divided between several platforms. It is therefore possible to introduce coarse graining agents (1 to 3 mm) at a higher point into the layered furnace and fine grains reducing agents (<1 mm) to add them at a lower point. As a result, the discharge of the powder into the release gases is largely prevented and the reaction is accelerated by the fine reducing agent particles introduced in lower platforms. The loading of coarser particles reduces the consumption of reducing agents because small particles are consumed faster by waste gases in the upper platforms than is necessary for the reduction of iron ore. In accordance with a preferred embodiment, the ore is dried and possibly preheated by hot gases in the layered furnace before being fed into the layered furnace and in contact with the reducing agent. The ore is preferably heated to a temperature of at least 200 ° C, preferably at least 350 ° C. In this case, the heating and drying time should not exceed 10 to 20 minutes to avoid sticking the ore in a reducing atmosphere. However, the ore can be mixed with at least part of the required reducing agents before loading in the layered furnace. By the selective addition of reducing agents in the lower platforms of the furnace, the reducing agents in the furnace can be adjusted to an optimum concentration, thus achieving a better metallization degree. All the rising gases, including the constituents - volatiles of the reducing agents, can be burned completely in the upper part of the furnace or outside the stratified furnace in the drying plant for the ore and, if appropriate, for the agents reducers, and the waste heat from the waste gases of the kiln in this way can be used with maximum utility.

The ore continually circulates through vents mounted on each furnace platform and is gradually transported to the underlying platform. In this way the ore dries and heats up more quickly than in conventional ovens. The seams quickly mix the reducing agent under the ore and quickly heat up to the reaction temperature. The continuous circulation prevents the formation of cakes of the reducing agent and the mineral. The speed of circulation depends on many factors such as the geometry of the reefs, the thickness of the platforms, etc. The ore, any reducing agent present and the reduced iron directly on the platforms should circulate at least once each to three minutes to avoid agglomeration to a large extent. It is possible to selectively inject oxygen-containing gases into the platforms where the heat requirement must be met by combustion of the excess process gases. It is useful to use gases containing oxygen that have a temperature of at least 350 ° C. A gaseous reducing agent can additionally be injected into the lower platforms of the layered oven. Consequently, a more complete reduction of the mineral is achieved. According to a further useful embodiment, one or more platforms in the furnace that are below the platform into which the reducing agents are introduced are heated by burners. In order not to reduce the concentration of reducing gases in the lower part of the furnace by means of combustion gases of the ignition system, energy can also be indirectly supplied, for example by means of radiation heating. According to another modality that is preferred, the gases are expelled from the stratified furnace in one or more platforms. These hot gases can subsequently pass through a CO2 scrubber to reduce the amount of gas and increase the gas reduction potential or through an additional carbon-containing reactor, so that the carbon dioxide present in the hot gases react with the carbon to form carbon monoxide in accordance with the equilibrium of the production gas and increase the potential reduction of the gas. The gases enriched with carbon monoxide subsequently return to the stratified furnace. If necessary, additives are introduced in one of the platforms under the platform where the reducing agents are introduced. In this case, it is possible to expel gases on a platform superior to the platform where the additives are introduced. In accordance with a preferred embodiment, the gases are expelled from the stratified furnace below a specific platform and subsequently injected back into the furnace on this platform. The iron oxide powder containing carbon and heavy metals can be introduced into the furnace on this platform. The heavy metal oxides are reduced in that place, the heavy metals are volatilized and the gases produced in this platform are subsequently expelled separately. To achieve a greater increase in the productivity of the stratified kiln, it can be operated with a specific excess pressure. In contrast to a rotary kiln, which is sealed with hydraulic seals with a diameter of approximately 50 m, this can easily be done in a stratified kiln, which only has small seals on the drive shaft. In this case, the pressure closes the feed and the removal of the material must be provided. Next, an embodiment of the present invention will be described based on the appended figures. Figure 1: shows a section through a stratified furnace for the production of reduced iron directly; Figure 2: shows a section through an alternative type of a stratified furnace for the production of reduced iron directly. Figure 1 shows a section through a stratified oven 10, which has various platforms 12, in this case eleven, one on top of the other. These autonomous platforms 12 and the box 14, cover 16 and bottom part 18 of the furnace are made of a refractory material. An axis 20, in which the reefs 22 projecting on the respective platforms are fixed, is mounted in the center of the furnace. The seams 22 are designed in such a way that they circulate the material on a platform from the inside out and then on the underlying platform from the outside in to transport the material from the top down through the furnace. The ore can be loaded in the furnace either separately or together with the reducing agents. In this way, the ore can be dried out of the furnace and mixed with the reducing agents, the mixture is subsequently deposited on the highest platform, or the ore and reducing agents can be charged in the furnace separately and put in contact with the agents reducers in the first platform and / or in one of the underlying platforms. After the ore has reached the first platform it is circulated through the seams 22 and transported to the edge of the platform, from where it falls through various openings provided for the purpose of falling to the underlying platform. From there, the ore is transported to the center of the platform and then falls on the underlying platform. During this time the ore is heated by contact with the platform and by hot gases that rise to approximately 600 ° C to 1000 ° C. The shaft 20 and the seams 22 are cooled with air and the openings 24, through which the air can flow into the furnace and can be used later for a subsequent combustion, are provided in the seams. A chimney 26, through which the gases can be evacuated from the furnace, and an opening 28, through which the ore can be deposited on the upper platform, are provided in the cover 16 of the furnace 10.

At least one inlet opening 30, through which the reducing agents can be introduced into the furnace, is provided in the side walls of the furnace 10 normally in the third above. These reducing agents may be present in liquid form, gaseous form or solid form. The reducing agents are carbon monoxide, hydrogen, natural gas, petroleum and petroleum products or solid carbon carriers, such as lignite coke, petroleum coke, blast furnace dust, coal or the like. The carbon carrier, which is introduced into a lower platform of the furnace 10, is mixed with the mineral heated by the seams 22. The iron oxide present in the ore is gradually reduced to metallic iron by high temperature and the presence of carbon monoxide. carbon during transportation through the stratified furnace 10. Nozzles 32, through which air or other gas containing oxygen can be fed into the furnace 10, are provided in the lower half of the side wall for the injection of hot gases ( 350 ° C to 500 ° C) containing oxygen. As a result of high temperatures and the presence of oxygen, some carbon is burned to carbon dioxide, which in turn reacts with the carbon present in excess and becomes carbon monoxide. Finally carbon monoxide reduces iron oxide to metallic iron. As this reaction is predominantly endothermic, it is logical to mount burners 34 in the lower part of the furnace, which ensure a uniform high temperature in the lower platforms of the furnace. In this case, gas or pulverized coal burners can be used. These burners 34 can be fed with gas or coal sprayed with air for a preliminary heating and / or additional heating. As a result of the quantitative relationship between oxygen and fuel, an additional reducing gas can be produced, or in the case of excess air, a subsequent combustion of the process gases is achieved. The case of ignition with pulverized coal can produce an excess of carbon monoxide in the burner. With the external combustion chambers it can be avoided that the ash of the burned coal enters the furnace and mixes with the reduced iron directly. The temperatures in the combustion chambers are chosen in such a way that the slag produced can be emptied in liquid form and discarded in a vitrified form. The production of carbon monoxide reduces the consumption of solid carbon carriers in the furnace 10, and thus also the ash content in the finished product. Openings 36 are provided in the side wall of the furnace, through which the hot gases can be removed from the furnace, at the level of the platform that is in the middle of the furnace. A supply is made in the last or in the last two platforms for feeding a gaseous reducing agent, for example carbon monoxide or hydrogen, through the special nozzles 37. The reduction of the mineral can be carried out in this atmosphere with a potential of increased reduction.

The directly reduced iron is then discharged together with the ashes of the reducing agents through the outlet 39 in the lower part 18 of the furnace 10. It is possible to control the reduction of the ore in a precise manner and to develop the process under optimum conditions by feeding Controlled solid, liquid or gaseous reducing agents and gases containing oxygen at different points of the stratified kiln 10 and the ease of expelling excess gases at critical points. Figure 2 shows a stratified furnace 10 very similar to that shown in Figure 1. This furnace 10 also allows the use of problematic wastes such as contaminated iron-containing dust for the production of directly reduced iron. For example, contaminated powders containing iron oxide from power plants or steelmaking converters, which in fact contain hardly any carbon content, can be fed with the ore through the opening 28 in the cover 16 in the stratified furnace 10. Iron oxide containing dust and large amounts of carbon as waste containing oil of the grinder or dust from waste gas scrubbers or furnaces can be fed through a special opening 31 in the furnace 10. As these products containing carbon and iron oxide are often contaminated by heavy metals, a large proportion of Upwardly flowing gases can be removed from the furnace 10 below the platform where the carbon oxide powders containing carbon are deposited, by an ejector connecting piece 38 in the side wall and they are injected back into the furnace 10 through of an entry 40 on this platform. Consequently, the amount of gas in the platform to which the iron powder is introduced is small. The heavy metals present in the iron powder are reduced immediately after their introduction into the furnace and are volatilized. They can then be removed from the furnace 10 in a relatively small amount of gas in this platform through an inlet 42 in the side wall. The low volume of gas with relatively high content of heavy metals can be cleaned separately. As a result of the low amounts of waste gas, the gas flow rates in the corresponding stage are low and only a small amount of dust is discharged with the waste gas. As a result, an extremely high concentration of heavy metals in the waste gas is obtained. The iron oxide present in the powders is reduced with the ore fed in the iron furnace.

Claims (12)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for producing iron directly reduced in a stratified furnace having various platforms on each other, a high temperature prevailing in the lower platforms where ore is continuously introduced into the furnace laminate and is deposited on the upper platform and gradually it is transferred to the lower platforms; a solid or liquid reducing agent is deposited on the highest platform and / or on a platform below it; a gas containing oxygen through the lower half of the side wall inside the furnace laminated is fed and reacts with part of the reducing agent to form a reducing gas, the reducing gas reacts with the mineral to form iron directly reduced; The directly reduced iron is discharged together with the residues of the reducing agents in the area of the lower platform of the stratified furnace.

2. The method according to claim 1, further characterized in that one or more lower platforms are heated by burners arranged in the oven wall.

3. The method according to one of the preceding claims, further characterized in that the process is carried out under excessive pressure.

4. - The method according to one of the preceding claims, further characterized in that the reducing agents are introduced in platforms different from the stratified oven.

5. The process according to one of the preceding claims, further characterized in that an excess of reducing agents is introduced into the stratified oven.

6. The process according to one of the preceding claims, further characterized in that the reducing agent in coarse grains is introduced in the upper parts and reducing agent in fine grains in the lower platforms within the layered oven.

7. The process according to one of the preceding claims, further characterized in that a gaseous reducing agent, for example carbon monoxide or hydrogen, is fed through special nozzles (37) in the last or in the last two platforms.

8. The process according to any of the preceding claims, further characterized in that any unused reducing agents are separated from the waste after discharge from the stratified oven.

9. The method according to claim 8, further characterized in that the unused reducing agents are burned in external combustion chambers and the resulting heat is fed to the layered oven.

10. The method according to one of the preceding claims, further characterized in that one or more furnace platforms can be heated indirectly.

11. The process according to one of the preceding claims, further characterized in that the dust or sludge containing iron oxide heavy metal oxides is introduced into the furnace, the oxides are reduced there and the heavy metals volatilise .

12. The method according to claim 11, further characterized in that the volatilized heavy metals are extracted separately on the platform, where they are formed.