MXPA01001545A - Method for the thermal processing of residues containing heavy metals and iron oxide - Google Patents

Abstract

The invention relates to a method for the thermal processing of residues containing heavy metals and iron oxide, designed for use in a multiple-hearth furnace which comprises several hearths positioned on top of each other. According to said method residues containing heavy metals and iron oxide are continuously fed to the multiple-hearth furnace such that they are introduced into the topmost hearth and gradually transferred to the lower hearths. Reducing agents are introduced into the topmost and/or one of the lower hearths and react with the residues containing heavy metals and iron oxide such that heavy metals and directly reduced iron are produced. The heavy metals are discharged from the furnace with the waste gases and the iron is discharged together with reducing agent residues in the area of the lowest hearth of the multiple-hearth furnace.

Description

PROCEDURE FOR THERMAL STRENGTHENING OF RESIDUAL MATERIALS CONTAINING Q00 OF HEAVY METALS AND IRON DESCRIPTIVE MEMORY The invention relates to a process for the thermal treatment of waste materials containing heavy metal and iron oxide, such as powders from electric steelworks or sediments from converter steelworks. Large quantities of waste materials containing heavy metal oxide and iron in the form of dust or sediment are produced in electric or converter steelworks. Waste materials are separated by waste gas cleaning plants, such as dust or sediment. The disposal of this waste material is expensive or the final storage of these materials is problematic. Food is usually stored in artificial lakes in the open air, while the powders are stored underground in tunnels. Typical compositions of powders and sediments containing heavy metal from electric or converter steelworks are shown in the following table.

TABLE 1 In US 3,756,804, a process for thermal treatment of waste gas powders containing heavy metal and iron oxides in a multi-household furnace incorporating several homes one above the other is described. The waste gas powders containing heavy metal and iron oxides are mixed with reducing agents, which is transferred to the upper hearth of the multi-household furnace and is gradually transferred to the lower homes. This reducing agent reacts with the waste gas powders containing oxides of heavy metals and iron, in order to form heavy metals and directly reduced iron, vaporizing the heavy metals. A bypass line, located in the wall of the furnace at the level of the upper intermediate hearth, transfers the gases to a condenser cooler, in which the temperature of the gases is reduced, so that the heavy metals are condensed and deposited on plates in The condenser cooler. The gases liberated to a considerable degree from the vaporized heavy metals are subsequently heated and then introduced into the lower part of the furnace. iron and zinc), so that the separated fractions constitute supply materials for other procedures or can be returned to the existing production lines of the steelworks. Secondary products can be obtained from important constituents of the waste materials. The iron content can be returned to the production operations of the steel mill after going through the procedure. It concentrates the heavy metal oxides to such an extent that it can be used as a starting material for heavy metal recovery. Ash can remain, consisting essentially of inert materials such as S¡O2, AI2O3, MgO, and possibly an excess of reducing agents. As soon as the reducing agents have been supplied to the furnace, they are mixed with the rakes under the residual materials containing heavy metal oxide and iron and heated. As soon as their temperature level (approximately 900 ° C) has been reached, they begin to react with the heavy metal oxides, whereby heavy metals are formed, and they are evaporated and discharged together with the waste gases from the kiln. multiple homes. According to the present method, parts that flow up into the furnace under the hearths on the furnace are ejected from the furnace. ; j.Which heavy metals are vaporized, for example through an ejection connection in the side wall and re-injected in the furnace above their homes, for example through an inlet duct. In this way, the amount of gas present in households is kept small ^^^^ faith on which the oxides of heavy metals to heavy metals are reduced and vaporized. The heavy metals can then be expelled from the furnace through an outlet duct in the side wall in a relatively small amount of gas over these homes. The expelled gas mixture is subsequently heated, it is cooled in a cooling device and then cleaned with the help of a filter before discharging it to the outside. Due to the reduced amounts of waste gases, low gas flow velocities occur in the corresponding households and very little dust is discharged with this waste gas. In this way, a very high concentration of heavy metals is produced in the waste gas. Heavy metals are advantageously expelled from the homes in which they are formed and treated separately from the other waste gases. The waste gases are subsequently oxidized, for example in a subsequent combustion chamber, the heavy metals being converted into heavy metal oxides, which can then be separated from the waste gases in filtering equipment. At the same time or later, the iron oxides that remain in the multi-household furnace are reduced to metallic iron. The metallic iron produced in this way is discharged from the furnace together with the ash as liquid slag and the raw gas formed in the multi-household furnace is used as combustion or reducing gas. Accordingly, it is also possible to use a cheaper reducing agent with a relatively high ash content and / or to work with a relatively high excess of reducing agent, which prevents the agglomeration of the residual materials. When working with reducing agents in excess, it is possible to treat the waste in order to separate and reuse the unused reducing agents. This can be done, for example by screening the waste if the unused reducing agents are present in sufficiently thick form. Unused reducing agents can be returned directly to the multi-household furnace. However, the loading of reducing agent can also be distributed to several stages. It is thus possible to introduce coarse-grained reducing agents (1-3 mm) to higher levels in the multi-household furnace and fine-grained reducing agents (<; 1 mm) below. Accordingly, the discharge of dust with the waste gases is greatly prevented and the reaction is accelerated with the reducing agent particles introduced below. The consumption of reducing agents with the loading of coarser particles is reduced, because the small particles are quickly consumed by reaction with H2O and CO2 of the waste gas in the higher homes, on which an oxidizing atmosphere prevails. irUfcüritr »« 81 The procedure space is subdivided into different zones, the solids continuously move from top to bottom and the gases are led from the bottom to the top through the furnace. Subdividing the procedure space to different zones, you can > measure and selectively influence the conditions of the procedure in different areas or even for each household. However, residual materials containing heavy metal oxide and iron can also be mixed with at least a part of the reducing agents required before they are introduced into the multi-household furnace. This applies in particular in the case of the treatment of sediments, which are mixed with at least a part of the required reducing agents, before they are introduced into the furnace. The sediments usually have sticky consistency and can be introduced more easily into the furnace, if they are mixed with the reducing agents. Mixing with the reducing agents prevents the supply material from forming agglomerates during heating. By selective supply of the reducing agents in the lower furnace homes, the reduction gases in the furnace can be adjusted to an optimum concentration and thus a higher degree of metallization can be achieved. The residual materials containing heavy metal oxide and iron are continuously circulated with rakes mounted on each furnace hearth and gradually transferred to the underlying furnace.

The agglomeration of the particles with continuous circulation is avoided. The speed of circulation depends on many factors such as the geometrical configuration of the rakes, the thickness of the layers, etc. The residual materials that contain heavy metals and iron oxide, any reducing agents present and the iron directly reduced on the homes should be circulated, at least once every one to three minutes with the result that the agglomeration. Oxygen-containing gases can be injected into the home, in which the requirement of heat must be met with the combustion of excess process gases. It is advantageous to use gases containing oxygen with a temperature of at least 250 ° C. A gaseous reducing agent can be injected additionally into the lower homes of the multi-household furnace. This ensures a higher potential reduction of the atmosphere in the furnace and the most complete reduction of the oxides is achieved. According to a further advantageous embodiment, one or more furnace homes below the hearth on which reducing agents are introduced are heated with burners. In order to reduce the concentration of the reduction gases in the lower part of the furnace with duct gases from the heating system, energy can also be indirectly supplied here, ie by radiation heating. t ^^ & ^ iA,% ''. '? ^^ i, i According to another preferred embodiment, the gases from the multi-household furnace are expelled to one or more households. These hot gases can be subsequently passed through a CO2 scrubber to reduce the amount of gas and increase the reduction potential of the gas or through an additional reactor, in which carbon is present, so that the carbon dioxide present in the hot gases reacts with the carbon to form carbon monoxide according to the Boudouard equilibrium and thus increases the potential for gas reduction. The gases enriched with carbon monoxide are subsequently returned to the multi-household furnace. The multi-household furnace can be operated under a specific overpressure to achieve an additional increase in productivity. In contrast to a rotary kiln that is sealed with water seals with a diameter of approximately 50 m, this can be achieved very easily in multi-household furnaces, which have only small seals on the drive shaft. In such case, pressure loops must be provided for the supply and removal of material. According to another aspect of the present invention, the use of a multi-household furnace is proposed for the treatment of heavy metals and iron oxide-containing waste materials, such as powders and sediments from electric or converter steelworks in accordance with the procedure described.

Other advantageous embodiments are listed in the subclaims. A mode of the invention will now be described below with the help of the attached figure. Figure 1 is a section through a multi-household furnace for the thermal treatment of waste materials containing heavy metal and iron oxide, such as powders from electric or converter steelworks. Figure 1 shows a section through a furnace 10 of multiple hearths with several - in this case 12 - hearths 12 one above the other. These independent hearths 12, as well as the casing 14, the cover 16 and the bottom part 18 of the furnace are made of refractory material. An outlet duct 20, through which the gases from the furnace can be evacuated, and an opening 22, through which heavy metals and iron oxide-containing waste materials can be loaded onto the upper hearth, are provided. in the cover 16 of the furnace 10. An axle 24, on which the rakes 26 that extend over the respective hearths are secured, is mounted in the center of the furnace. The rakes 26 are designed in such a way as to move the material on a hearth from the interior to the exterior and then from the exterior to the interior on the underlying furnace before moving the material from the top down through the furnace. It is also possible to introduce the residual materials containing heavy metal oxide and iron and the reducing agents separately into the furnace. The waste materials are loaded onto the first home in this case, while the reducing agents are supplied to one of the underlying homes and put in contact there with the residual materials containing heavy metal oxide and iron. The waste materials containing heavy metal and iron oxide as well as the reducing agents are heated to approximately 600 ° C and up to 1000 ° C during transport. The shaft 24 and rakes 26 are air cooled and openings are provided on the rakes, through which air can flow into the furnace and can be used there for subsequent combustion. 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 - usually in the upper third. These reducing agents can be present both in gaseous form as well as in liquid or solid form. Reducing agents are for example carbon monoxide, hydrogen, natural gas, petroleum and petroleum derivatives or solid carbon carriers such as coke lignite, petroleum coke, blast furnace powders, coal or the like. The reducing agent, in this case coal, can also be introduced into the furnace even lower in the furnace 10, it is mixed there by the rakes 26 with the heated residual materials containing heavy metal oxide and iron oxide. The iron oxide present in the waste materials containing oil and iron oxide is normally reduced by the high temperature and the presence of carbon monoxide to metallic iron during transport through the multi-household furnace 10. The controlled supply of reducing agents solids, liquids and gases and gases containing oxygen at various points of the multiple kiln furnace 10 and the possibility of expelling excess gases at critical points allow precise control of the reduction of residual materials containing heavy metal oxide and iron and the completion of the procedure under optimal conditions. The oven allows a proportion of the gases flowing upwards in the furnace, through an ejection connection piece 60 in the side wall below the hearths, on which the heavy metals are evaporated and reinjected into the furnace 10 through the flue pipe. entrance 62 above these homes. Therefore, the amount of gas present on theH. homes on which heavy metals evaporate is small. They can be expelled from the oven 10 from a relatively small amount of gas on the hearth through an outlet duct 64 in the side wall. The small volume of gas with the relatively high content of heavy metals can then be cleaned separately. As a result of In these small amounts of waste gas, the gas flow velocities on the corresponding households are low and only small amounts of dust are thus discharged with this waste gas. Consequently, an extremely high concentration of heavy metals results in the waste gas. The waste gases are subsequently oxidized in a rear combustion chamber 66, the heavy metals being converted to heavy metal oxide and separated from the waste gases in a filter. 70. Before the waste gases enter the filter 70, they are cooled to the required temperature in a cooler 68. Nozzles 30 for the injection of hot gases (350 ° C to 500 ° C) are provided on the side wall. they contain oxygen, through which air or other gas containing oxygen can be supplied to the furnace. As a result of high temperatures and the presence of oxygen, part of the carbon is burned to form carbon dioxide, which reacts at the same time with the carbon present in excess and is converted into carbon monoxide. Carbon monoxide eventually reduces oxides. Since this reaction is predominantly endothermic, it is logical to install in the lower part the furnace burners 32 which ensure a uniform high temperature in the lower furnace homes. In this case, gas or pulverized coal burners can be used. Those burners 32 can be ignited with gas or coal OR sprayed with air for preheating and / or additional heating. An additional reduction gas can be produced for the quantitative ratio between the oxygen and the combustion material and the subsequent combustion of the process gases can be achieved in the case of excess air. In the case of excess ignition with pulverized carbon, carbon monoxide can be produced in the burner. In the case of external combustion chambers, charcoal ash can be prevented from entering the kiln and mixing with the iron. The temperatures in the combustion chambers are selected in such a way that the produced slag can be extracted in liquid form and eliminated in a vitrified form. The consumption of solid carbon carriers in the furnace 10 and therefore also the ash content in the finished product is reduced by the production of carbon monoxide. The supply of a gaseous reducing agent, for example carbon monoxide or hydrogen, is provided through special nozzles 44 at the last or the last two places. The reduction of iron oxides in this atmosphere can be completed with increased reduction potential. The produced iron is subsequently discharged through the outlet conduit 46 in the lower part 18 of the kiln 10 together with the ash. The iron discharged in the outlet conduit 46 is cooled with the ash and any reducing agents that can still be used in a cooler 48. The reduced iron is subsequently removed by a magnetic 50 separator from the ash of the reducing agents and any reducing agents that can still be used. The reducing agents 52 are then burned which can still be used in an external combustion chamber 34. The gases produced by combustion of the reducing agents can be introduced into the furnace 10, rf *

Claims (22)

NOVELTY OF THE INVENTION CLAIMS

1. - Procedure for the thermal treatment of waste materials containing heavy metal oxide and iron in a multi-household furnace with several homes one on top of the other, in which waste materials containing heavy metals and iron oxide are continuously introduced multi-household furnace, are discharged to the upper household and are gradually transferred to the lower households, the reducing agents are introduced to the upper part and / or one of the underlying homes and they are reacted with the residual materials they contain heavy metals and iron oxide to form heavy metals and iron directly reduced, the gases containing heavy metals are expelled separately on the homes on which it is vaporized and the iron is discharged together with the residues of the reducing agents in the area of the lower hearth of the multi-hearth furnace, exhausting the gases from the household furnace Tiples underneath the homes on which the heavy metals are vaporized and then reinjected back into the kiln of multiple hearths totally or partially above these kilns.

2. Method according to claim 1, further characterized in that the waste gases are treated in a subsequent burner, the heavy metals being converted into heavy metal oxides and separated from the waste gases in a filter.

3. Method according to one of the preceding claims, further characterized in that the gases are expelled on a hearth that is below the hearth to which the reducing agents are introduced.

4. Method according to one of the preceding claims, further characterized in that the directly reduced iron is cooled to less than 700 ° C after the discharge of the multi-household furnace and is subsequently separated from the waste of reducing agent with a magnetic separator.

5. Method according to claims 1 to 3, further characterized in that the directly reduced iron is separated from the waste of reducing agent in the hot state, sieving it after the discharge of the multi-household furnace.

6. Method according to claims 4 to 5, further characterized in that the treated directly reduced iron is treated further, forming pellets or small blocks.

7. Method according to one of the preceding claims, further characterized in that the directly reduced iron is melted with or without residues.

8. Method according to one of claims 4 or 5, further characterized in that any unused reducing agents are separated from the waste after discharge from the multi-household furnace.

9. Method according to claim 8, further characterized in that the waste of the reducing agent is used in a gasification reactor, the ash-forming constituents being separated as liquid slag, using only the crude gas formed in the multi-household furnace and supplying the resulting heat to the oven.

10. Method according to one of the preceding claims, further characterized in that the reducing agent is introduced in liquid, solid and / or gaseous form to the multi-household furnace.

11. Method according to one of the preceding claims, further characterized in that reducing agents are introduced to different homes in the multi-household furnace.

12. Process according to claim 11, further characterized in that coarse-grained reducing agents are introduced at higher levels into the multi-household furnace and the fine-grained reducing agents below.

13. Process according to one of the preceding claims, further characterized in that the excess reducing agent is introduced into the multi-household furnace.

14. Procedure according to one of the preceding claims, further characterized by mixing the heavy metal oxide and iron oxide containing materials and at least part of the required reducing agent with each other before they are introduced into the multi-household furnace.

15. Method according to one of the preceding claims, further characterized in that the oxygen-containing gases are injected selectively into different homes.

16. Method according to claim 15, further characterized in that the oxygen-containing gases have a temperature of at least 250 ° C.

17. Method according to one of the preceding claims, further characterized in that the agents are injected gaseous reducers to the lower homes of the multi-household furnace.

18. Method according to one of the preceding claims, further characterized in that one or more homes are heated directly or indirectly in the furnace.

19. Method according to one of the preceding claims, further characterized in that the gases are expelled from the furnace of multiple homes in one or more homes.

20. Method according to claim 19, further characterized in that the reduction potential of the exhausted gases is increased and the gases are subsequently introduced into the multi-household furnace.

21. - Method according to one of the preceding claims, further characterized in that the process is carried out under overpressure.

22. Use of a multi-household furnace for the thermal treatment of waste materials containing heavy metal oxide and iron by the method according to one of the preceding claims.