EP1114193A1

EP1114193A1 - Method for heat-treating recyclings containing oil and iron oxide

Info

Publication number: EP1114193A1
Application number: EP99947271A
Authority: EP
Inventors: Thomas Hansmann; Romain Frieden; Marc Solvi
Original assignee: Paul Wurth SA
Current assignee: Paul Wurth SA
Priority date: 1998-09-02
Filing date: 1999-08-30
Publication date: 2001-07-11
Also published as: KR20010073025A; WO2000014286A1; JP2004538122A; AU747819B2; BR9913608A; AU6079599A; TW452598B; SK2792001A3; US6391088B1; CA2339014A1; PL346336A1; CN1312863A; ZA200100948B; CZ2001755A3; LU90282B1; TR200101428T2

Abstract

The invention relates to a method for heat-treating recyclings containing oil and iron oxide in a multiple hearth furnace. Said oven has several superposed tiers. The recyclings containing oil and iron oxide are mixed with a solid reducing agent and continuously fed into the multiple hearth furnace, placed on the top tier and then gradually transferred to the lower tiers. The recyclings are dried on the uppermost tier. The oil is then evaporated and pyrolysed and the reducing agents react with the iron oxide to form directly reduced iron. The directly reduced iron is then discharged together with residues of the reducing agents in the area of the lowest tier of the multiple hearth furnace.

Description

Process for the thermal treatment of residues containing oil and iron oxide

The present invention relates to a process for the thermal treatment of residues containing oil and iron oxide, in the form of oil-containing sludges such as e.g. Sludges from steel mills.

In the rolling mills of the steel industry, large quantities of iron oxide-containing sludges are produced, which are produced when the cooling water is cleaned from the continuous casting plants or rolling mills. Depending on the granulometry of the iron components, these sludges are contaminated with oil or fat residues. The oil or fat content increases the finer the granulometry of the components. The fine fraction (<40μm), which can contain around 14% oil, has proven to be particularly oil-containing. Due to the high oil content, it is difficult to return these sludges to the existing production route. An attempt was made to use these sludges in sintering plants. However, such high levels of dioxins were measured in the combustion of these sludges that this type of treatment is neither economical nor ecological. These sludges are therefore deposited in artificial lakes and pose a potential environmental hazard because oil and other residues can get into the groundwater.

Typical compositions of these slurries are shown in the following table:

Table 1

In this context, “oil” means mainly lubricants and greases that are used when rolling steel. They are therefore mainly hydrocarbons containing various additives as are common in lubricants.

The object of the present invention is therefore to propose a method for the thermal treatment of such residues containing oil and iron oxide.

This object is achieved according to the invention by a method for the thermal treatment of oil and iron oxide-containing residues in a deck oven which has a plurality of superposed floors, the oil and iron oxide-containing residues being mixed with a solid reducing agent and continuously introduced into the deck oven and onto the top floor applied and gradually transferred to the lower floors, drying the residues containing oil and iron oxide on the top floors, then evaporating and pyrolyzing the oil and reacting the reducing agents with the iron oxides to form directly reduced iron, whereby directly reduced iron is discharged together with residues of reducing agents in the area of the bottom floor of the deck oven.

An important advantage of the invention is that valuable substances are produced from essential components of the oil and iron oxide-containing residues. After the process has been completed, the iron content can be returned to the steel mill's production process, the oil is pyrolyzed and the pyrolysis gases produced are burned. The oil thus helps to generate the necessary process heat. What may remain is ash, which essentially consists of inert substances such as SiO 2, I 2 O 3, MgO, ... and possibly an excess of reducing agents

In this process, sludge-like, oil- and iron oxide-containing residues can be added, whereby caking of the particles is avoided by a targeted process control and by constant circulation. Regardless of the consistency of the input material, the process delivers a fine-grained end product.

This is of particular advantage when ash-forming reducing agents be used. Since the solid end product is fine-grained, it is easy to separate the ash from the iron. This separation can e.g. B. in the hot state via classification.

After cooling below 700 ° C, on the other hand, it is possible to separate the reduced iron from the ashes and excess reducing agent using a magnetic separator. The quality of the directly reduced iron obtained in this way is almost independent of the amount of residues of the reducing agent.

The iron obtained can then be processed into briquettes or placed directly in a melting furnace (electric furnace, etc.) and processed further.

The resulting residues of the reducing agent can, if desired, be used in a separate gasification reactor with any unused reducing agents contained therein, the ash-forming constituents advantageously being separated out as liquid slag and the raw gas formed in the deck oven used as combustion or reducing gas. It is therefore also possible to use a cheaper reducing agent which has a relatively high ash content and / or to work with a relatively high excess of reducing agent, which prevents the agglomeration of the residues.

In the case where an excess of reducing agents is used, it is advantageous to prepare the residues in order to separate the unused reducing agents and reuse them. This can e.g. B. by sieving the residues when the unused reducing agents are in sufficiently coarse form. The unused reducing agents can be introduced directly into the deck oven.

However, part of the reducing agent required can also be applied to one or more floors, which are located below in the furnace. There is the possibility that coarse-grained reducing agents (1 -3 mm) are introduced further up in the deck oven and fine-grained reducing agents (<1 mm) are added below. As a result, the discharge of dust with the exhaust gases is largely avoided and the course of the reaction is accelerated by the fine reducing agent particles introduced below.

By charging coarser particles, the consumption of reducing agent is reduced, because on the upper floors where there is an oxidative atmosphere, the small particles are quickly consumed from the exhaust gas by reaction with H2O and CO2. Through the targeted addition of reducing agents in the lower levels of the furnace, the reducing gases in the furnace can be adjusted to an optimal concentration, whereby a better degree of metallization can be achieved.

The process room is divided into different zones, the solids move continuously from top to bottom and the gases are passed through the furnace from bottom to top. By dividing the process space into different zones, the process conditions in the different zones or even per floor can be measured and, if necessary, influenced in a targeted manner.

The oil and iron oxide residues are continuously circulated by rakes attached to each floor of the furnace and gradually transported to the floor below.

The constant circulation prevents the reducing agents and the oil and iron oxide-containing residues from caking together. The rate of circulation depends on many factors such as. B. the geometry of the rake, the thickness of the layers, etc. The oil and iron oxide-containing residues, the reducing agents and any reduced iron on the floors should be circulated at least once every one to three minutes, which largely prevents agglomeration.

It is possible to specifically blow in oxygen-containing gases on the floor where the heat requirement must be covered by burning the excess process gases. It is advantageous to use oxygen-containing gases that have a temperature of at least 250 ° C.

A gaseous reducing agent can also be blown in on the lowest floors of the deck oven. This achieves a more complete reduction in oxides.

According to a further advantageous embodiment, one or more floors in the furnace are heated by means of a burner.

So that the concentration of reducing gases in the lower part of the furnace is not reduced by flue gases from the heating, energy is supplied by radiant heating.

According to another preferred embodiment, gases are extracted from the deck oven on one or more floors. These hot gases can then either be passed through a CO 2 scrubber to reduce the amount of gas and increase the reduction potential of the gas, or passed through an additional reactor containing carbon so that it is contained in the hot gases Carbon dioxide reacts with the carbon to form carbon monoxide according to Boudoir's equilibrium, thereby increasing the reduction potential of the gas. The gases enriched with carbon monoxide are then returned to the deck oven.

If necessary, additives are added to one or more floors in the lower area of the furnace.

In such a case, it is advantageous to suck off gases on a floor above the floor on which additives are introduced. According to a preferred embodiment, gases are sucked out of the deck oven below a certain floor and then blown back into the oven above this floor.

Carbon and heavy metal-containing iron oxide dusts or sludges can be introduced into the furnace on this level. As soon as they have reached a certain temperature (approx. 900 ° C) the heavy metal oxides begin to react with the reducing agents, forming heavy metals which volatilize and are discharged together with the exhaust gases from the deck oven.

The heavy metals are advantageously extracted on the floors where they are formed and treated separately from the other exhaust gases.

The exhaust gases are then e.g. oxidized in an afterburning chamber, the heavy metals being converted to heavy metal oxides which can then be separated from the exhaust gases in a filter device. Typical compositions of heavy metal dusts and sludges from electrical or converter steelworks are shown in the following table.

Table 2

To further increase productivity, the deck oven can be operated under a certain excess pressure. In contrast to a rotary kiln, which is sealed over water cups with a diameter of approximately 50 m, this is very easy to achieve in a deck oven that only has small seals on the drive shaft. In such a case, pressure locks must be provided for the input and export of material.

According to another aspect of the present invention, the use of a deck oven for the thermal treatment of residues containing oil and iron oxide.

Further advantageous configurations are listed in the subclaims. An embodiment of the invention will now be described with reference to the accompanying figure. It shows: Fig. 1: a section through a deck oven for the thermal treatment of residues containing oil and iron oxide. Fig. 1 shows a section through a deck oven 10, which has several - in this case twelve - superposed floors 12. These self-supporting levels 12, as well as the jacket 14, cover 16 and the bottom 18 of the furnace 10 are made of refractory material.

In the cover 16 of the furnace 10, a vent 20 is provided through which the gases can be evacuated from the furnace and an opening 22 through which a mixture of residues and reducing agents containing oil and iron oxide can be applied to the top floor.

In the middle of the furnace there is a shaft 24 to which rakes 26 are fastened which protrude above the respective floors.

The rakes 26 are designed so that they roll the material from the outside inwards on one floor and then from the inside out on the floor below, so as to transport the material through the furnace 10 from top to bottom.

The residues containing oil and iron oxide are mixed with solid reducing agents such as e.g. Lignite coke, petroleum coke, or coal are mixed and then the mixture of residues containing oil and iron oxide and reducing agent is applied to the top floor. Because of the viscous, sticky consistency of the mixture, it is introduced into the deck oven by means of pumps (not shown).

The oil and iron oxide residues can possibly be pre-dried outside the oven before or after they are mixed with the solid reducing agents.

After the mixture of oil and iron oxide-containing residues and reducing agents has been applied to the first floor of the furnace 10, it is circulated by the rakes 26 and transported to the edge of the floor, from where it falls through a plurality of openings 28 provided therefor onto the floor below. From there, the oil and oil mixed with reducing agents residues containing iron oxide are transported to the middle of the floor and then fall to the floor below. During transportation, the residues containing oil and iron oxide and the reducing agents are gradually heated.

The shaft 24 and the rakes 26 are air-cooled and openings are provided on the rakes through which air can flow into the interior of the furnace and can be used there for afterburning.

During this time, moisture is removed from the oil and iron oxide-containing residues mixed with reducing agents through contact with the floor 12 and the rising warm gases. The top floors of the oven 10 thus belong to the drying and preheating zone. After most of the water has evaporated, the oil or hydrocarbons begin to evaporate and are carried away with the hot, rising gases. Due to the high temperatures and the presence of oxygen, part of the oil and possibly also part of the introduced reducing agents burn in the upper part of the furnace. The carbon dioxide produced during combustion reacts with the excess carbon of the reducing agents and is converted into carbon monoxide. This carbon monoxide reacts with the residues containing iron oxide and reduces the iron oxide to iron. At least one inlet opening 30 is provided in the side walls of the furnace 10, usually in the upper third, through which additional reducing agents can be introduced into the furnace. These reducing agents can be in gaseous form or in liquid or solid form. These additional reducing agents are, for example, carbon monoxide, hydrogen, natural gas, petroleum and petroleum derivatives, or solid carbon carriers such as e.g. around brown coal coke, petroleum coke, blast furnace dust, coal, etc.

The reducing agent, in this case coal, is placed on a lower part of the furnace

10 lying floor is introduced, there is mixed by the rake 26 with the heated oil and iron oxide-containing residues. Due to the high

Temperature and the presence of carbon monoxide and iron oxide-containing residues contained iron oxide gradually reduced to metallic iron during transport through the deck oven 10.

Through the controlled input of solid, liquid and gaseous reducing agents and oxygen-containing gases at various points in the deck furnace 10 and through the possibility of extracting excess gases at critical points, it is possible to precisely control the reduction of the residues containing oil and iron oxide, and that To perform procedures under optimal conditions. Nozzles 30 for blowing hot (250 ° C. to 500 ° C.) oxygen-containing gases are provided in the side wall, through which air or another oxygen-containing gas can be introduced into the furnace 10. Due to the high temperatures and the presence of oxygen, part of the carbon burns to carbon dioxide, which in turn reacts with the excess carbon and is converted to carbon monoxide. The carbon monoxide finally reduces the oxides.

Since these reactions are predominantly endothermic, it makes sense to install burners 32 in the lower part of the furnace, which ensure a consistently high temperature in the lowest levels of the furnace. Gas or coal dust burners can be used here.

These burners 32 can be fired with air for preheating and / or for additional heating with gas or coal dust. An additional reducing gas can be generated by the quantitative ratio between oxygen and fuel, or if the process gases are excess air, the process gases are re-burned. In the case of a coal dust combustion, an excess of carbon monoxide can be generated in the burner. With external combustion chambers, it can be avoided that the ashes of the burned coal get into the furnace and mix with the iron. The temperatures in the combustion chambers are chosen so that the slag can be drawn off in liquid form and can be disposed of in a glazed form. By producing carbon monoxide, the consumption of solid Reduced carbon carriers in the furnace 10 and thus also the ash content in the finished product.

The addition of a gaseous reducing agent, e.g. Carbon monoxide or hydrogen is provided through special nozzles 44. In this atmosphere with an increased reduction potential, the reduction of the iron oxides can be completed.

The iron produced is then discharged through the outlet 46 in the bottom 18 of the furnace 10 together with the ash.

The iron discharged at the outlet 46 is cooled in a cooling device 48 with the ash and possibly still usable reducing agents. The reduced iron is then separated from the ashes of the reducing agents and any reducing agents which can still be used by a magnetic separator device 50.

Reducers 52 that can be used are then burned in an external combustion chamber 34. The gases resulting from the combustion of the reducing agents can in turn be introduced into the furnace 10, while the residues of the reducing agents are discharged as ash or liquid slag through an outlet.

The gas mixture from the furnace passes through the exhaust 20 into an afterburner 54, where the combustible gases of the gas mixture are burned. The gas mixture is then introduced into a cooling device 56 to which a cooling medium is applied and cooled. The cooled gas mixture is then cleaned using a cyclone filter 58 before it is discharged to the outside. In addition to the treatment of wastes containing oil and iron oxide, this furnace 10 also allows various problem wastes, such as Recycle contaminated dusts containing iron oxide.

For example, iron oxide-containing dusts or sludges from electrical or

Converter steelworks, which contain hardly any carbon, or dust from the exhaust gas cleaning of blast furnaces, through a special opening 30 in the furnace 10 be introduced. Through the controlled input of solid, liquid and gaseous reducing agents and oxygen-containing gases at various points in the deck furnace 10 and through the possibility of suctioning off excess gases at critical points, it is possible to control the reduction of the residual substances precisely and the process under optimal conditions perform.

Since these iron oxide-containing dusts or sludges are often contaminated by heavy metal oxides, a large part of the gases which flow upwards in the furnace below the floor to which the dusts or sludges containing heavy metal oxides are applied can be removed from the furnace 10 through a suction nozzle 60 in the side wall vacuum and blow back into the furnace 10 through this inlet 62. As a result, the amount of gas present on the floors to which the heavy metal oxide-containing dusts or sludges are introduced is small. The heavy metal oxides contained in the dusts or sludges are reduced after they have been introduced into the furnace and evaporate. You can then be sucked out of the oven 10 in a relatively small amount of gas on this floor 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. Due to the small amounts of exhaust gas, low gas velocities occur on the corresponding floors, and so little dust is discharged with this exhaust gas. This results in a very high concentration of heavy metals in the exhaust gas.

The combustible gases of the withdrawn gas mixture are burned in an afterburner 66. The remaining part of the gas mixture is cooled in a cooling device 68 and then cleaned with the aid of a cyclone filter 70 before it is released.

The iron oxide contained in the dusts is reduced to iron with the waste containing oil and iron oxide. All rising gases, including the volatile constituents of the reducing agents, can be stored outside the deck oven in the drying system for the heavy metal and iron oxide-containing residues and, if necessary, for the reducing agents can be completely burned and the residual heat of the furnace exhaust gases can be optimally used.

Claims

PATENT CLAIMS

1.Process for the thermal treatment of oil and iron oxide-containing residues in a deck oven which has several superposed floors, the oil and iron oxide-containing residues being mixed with a solid reducing agent and continuously introduced into the deck oven and applied to the top floor and gradually transferred to the lower floors, drying the oil and iron oxide residues on the top floors, then evaporating and pyrolyzing the oil and reacting the reducing agents with the iron oxides to form directly reduced iron, with the directly reduced iron along with

Residues of reducing agents in the area of the bottom floor of the deck oven is discharged.

2. The method according to claim 1, characterized in that the reduced iron is cooled to below 700 ° C after discharge from the deck oven and then by a magnetic separator from the

Residues of the reducing agent is separated.

3. The method according to claim 1 or 2, characterized in that the directly reduced iron is separated after discharge from the deck furnace in the hot state by classification of the residues of the reducing agent.

4. The method according to any one of the preceding claims, characterized in that the reduced iron is processed into briquettes.

5. The method according to any one of the preceding claims, characterized in that the directly reduced iron with or without

Residues is melted.

6. The method according to any one of claims 2 or 3, characterized in that possibly unused reducing agents are separated from the residues after discharge from the deck oven.

7. The method according to any one of claims 2 to 6, characterized in that the residues of the reducing agent are burned in a gasification reactor, the ash-forming constituents being separated off as liquid slag and the raw gas formed being fed to the deck furnace as a combustion or reducing gas.

8. The method according to claim 1, characterized in that the reducing agent can be introduced in solid, liquid form and / or in gaseous form in the deck oven.

9. The method according to any one of the preceding claims, characterized in that the reducing agent on different floors of the

Can be placed in the deck oven.

10. The method according to claim 9, characterized in that coarse-grained reducing agent can be introduced further up and fine-grained reducing agent further down in the deck oven.

11. The method according to any one of the preceding claims, characterized in that an excess of reducing agent is introduced into the deck oven.

12. The method according to any one of the preceding claims, characterized in that oxygen-containing gases are blown in specifically on different floors.

13. The method according to claim 12, characterized in that the oxygen-containing gases have a temperature of at least 250 ° C.

14. The method according to any one of the preceding claims, characterized in that gaseous reducing agents are blown on the lowest floors of the deck oven.

15. The method according to any one of the preceding claims, characterized in that one or more floors of the furnace are heated directly or indirectly.

16. The method according to any one of the preceding claims, characterized in that gases are extracted from the deck oven on one or more floors.

17. The method according to claim 16, characterized in that the reduction potential of the extracted gases is increased and the gases are then introduced into the deck oven.

18. The method according to any one of the preceding claims, characterized in that gases are extracted from the deck oven below a certain floor.

19. The method according to claim 18, characterized in that the reduction potential of the extracted gases is increased and the gases are then introduced into the deck oven.

20. The method according to any one of the preceding claims, characterized in that heavy metal and iron oxide-containing dust or sludge are introduced into the furnace on one floor, are reduced there and the heavy metals evaporate.

21. The method according to claim 20, characterized in that the heavy metal gases are suctioned off separately on the floor where they arise.

22. The method according to any one of the preceding claims, characterized in that the method is carried out under excess pressure.

23. Use of a deck furnace for the production of iron according to the method according to any one of the preceding claims.

24. Use of a deck oven for the treatment of oil and iron oxide-containing residues according to the method according to one of claims 1 to 22.