WO2001048254A1

WO2001048254A1 - Method for the utilisation of plastic waste in the thermal treatment of metalliferous recyclings

Info

Publication number: WO2001048254A1
Application number: PCT/EP2000/011851
Authority: WO
Inventors: Romain Frieden; Marc Solvi; Thomas Hansmann
Original assignee: Paul Wurth S.A.
Priority date: 1999-12-23
Filing date: 2000-11-28
Publication date: 2001-07-05
Also published as: AU1705001A; TW436336B; LU90493B1

Abstract

The invention relates to a method for the utilisation of synthetic material in the thermal treatment of metalliferous recyclings in a multi-level furnace which is partitioned into three zones. Each zone is provided with several levels one on top of the other. The inventive method comprises the following steps: continually introducing the metalliferous recyclings into the top level of the first zone pertaining to the multi-level furnace, whereby the recyclings are gradually transferred to the second zone and are dried in the meantime; heating and calcining the recyclings at approximately 800 °C within the second zones, whereby the recyclings are gradually transferred to the third zone; continually introducing synthetic material to the top level of the third zone and heating the mixture to 1,000 °C to 1,200 °C in the third zone, whereby the metals are reduced; withdrawing the mixture from the multi-level furnace.

Description

Process for recycling plastic waste in the thermal treatment of metal-containing residues

The present invention relates to a method for recycling plastic waste in the thermal treatment of metal-containing residues such as Batteries of all kinds, oil and iron oxide-containing sludges from steel rolling mills, sludges from surface treatment, pickling and cleaning, metalization and tinning processes of metal parts, dust or sludge from blast furnaces, electrical or converter steelworks.

Used plastic packaging from households and small businesses is collected in various countries in Europe for recycling. The legislature of these countries stipulates that a certain percentage of the packaging placed on the market must be recycled. Proper recycling can be either that the plastics are cleaned, separated and then used for the production of new products, or that the plastics are broken down into their chemical components in order to obtain basic substances such as synthetic oil or methanol.

In recent years, plastics have increasingly been used in the automotive industry, which then have to be disposed of as so-called shredder light fraction after the motor vehicle has been scrapped.

On the other hand, there are large amounts of metal-containing residues in the form of sludge in industry. These residues fall e.g. when filtering the immersion baths and, in addition to large amounts of water, contain various metals such as Zinc, nickel, molybdenum, coblad, copper, iron in the form of oxides, hydroxides, chlorides and sulfates. The disposal of these residues is expensive and the disposal of these substances is problematic. The sludge is usually stored in special landfills.

An example of the composition of such metal-containing slurries is shown in the following table. Table 1

Large amounts of metal-containing residues in the form of dust or sludge accumulate in the blast furnaces, electrical steel or converter steelworks. Residual materials are separated from the exhaust gases as dust or as sludge by exhaust gas cleaning systems. The disposal of these residues is expensive and the disposal of these substances is problematic. The sludge is mostly stored in artificial lakes under the open sky, while the dust is deposited underground in tunnels.

Typical compositions of metal-containing dusts and sludges from blast furnaces, electrical or converter steelworks are shown in the following table.

Table 2

The object of the present invention is therefore to propose a resource-saving method for recycling plastic waste in the thermal treatment of metal-containing residues.

This object is achieved according to the invention by a method for recycling plastics in the thermal treatment of metal-containing residues in a deck oven, which is divided into three zones, each Zone has several superimposed floors and the method comprises the following steps:

Continuous introduction of the metal-containing residues onto the top floor of the first zone of the deck oven, the residues being gradually transferred to the second zone and being dried during this,

• heating up to approximately 800 ° C and calcining the residues within the second zones, the residues being gradually transferred to the third zone, • continuously introducing plastics to the top floor of the third zone and heating the mixture to 900 ° C until 1200 ° C in the third zone, where the metals are reduced,

• Discharge of the mixture from the deck oven.

An important advantage of the invention is that it is possible to reduce and separate the metal oxides, sulfates, chlorides etc. present as a mixture (in particular iron and zinc), so that the separated fractions are input materials for other processes and are used at the same time Recycle plastics. This means that valuable materials can be produced from residual materials. Any iron that is present can be returned to the production process of a steel mill after the process has been completed. The non-ferrous metal oxides are concentrated to such an extent that they can be used as raw materials for the extraction of non-ferrous metals. What remains are ashes, which essentially consist of inert substances such as SiO 2, Al 2 O 3, MgO. In the first zone, the metal-containing residues are heated up to about 200 ° C by contact with the hot floors, the gases rising in the deck oven and possibly by burners, so that the water evaporates completely and is then transferred to the second zone. In this zone, the metal-containing residues are heated to over 800 ° C and calcined. After the residues have reached a temperature of over 800 ° C the calcination is completed and the residues are entered into the third zone and plastics are continuously introduced to the top floor of the third zone and mixed with the residues and further heated. As soon as it has reached a certain temperature (from approximately 900 ° C to 1200 ° C), the metal oxides start to react with the plastics, whereby various non-ferrous metals evaporate and are discharged together with the exhaust gases from the deck oven.

In a preferred embodiment, the volatile non-ferrous metals can be extracted and treated separately from the other exhaust gases on the floors in the third zone where they are formed. These exhaust gases are then e.g. oxidized in a post-combustion chamber, the metals being converted to metal oxides, which can then be separated from the exhaust gases in a filter device.

At the same time or at a later point in time, the iron oxides, nickel oxides, etc. that may be present in the deck furnace are reduced to the corresponding metals. The non-volatile metals produced in this way are removed from the furnace together with the residues of the introduced material and the ashes.

In this process, either dust-like or sludge-like, metal-containing residues can be fed in, 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 particularly advantageous if the starting material contains iron oxides. Since the solid end product is fine-grained, the ash can be separated from the iron easily. This separation can e.g. B. in the hot state via classification.

Of course, this method is also suitable for the treatment of pellets and micropellets, which normally have a diameter of 0.5 to 3 mm. After cooling below 700 ° C, on the other hand, it is possible to separate the reduced iron from the ashes using a magnetic separator. The quality of that The directly reduced iron obtained is almost independent of the amount of ash and other residues of the starting material.

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

Resource-saving plastic waste can therefore be used to convert the metal oxides into metal and largely dispense with coal or other fossil fuels.

The process room is divided into different zones, the solids move continuously from top to bottom and the gases are from bottom to top i.e. passed in countercurrent through the furnace. By dividing the process space into different zones, you can measure and influence the process conditions in the different zones or even per floor.

In an alternative embodiment, the metal-containing residues can also be mixed with at least some of the required plastics before they are introduced into the deck oven. This is particularly true in the case of treatment of sludges with a high water content that with at least some of the required Plastics can be mixed before they are placed in the oven. The sludges usually have a sticky consistency and, when mixed with plastics, are easier to put in the oven. Mixing with the plastics reduces the tendency that the input material forms agglomerates when heated.

The metal-containing residues are continuously circulated by rakes attached to each floor of the furnace and gradually transported to the floor below.

The constant agitation prevents the particles 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 metal ones Residual materials 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 has to 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.

Plastic, carbon monoxide, hydrogen or natural gas can also be blown in on the bottom floors of the third zone of the deck oven. As a result, a higher reduction potential of the atmosphere in the furnace is realized and a more complete reduction of the oxides is achieved.

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 drawn off from the deck oven on each zone 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 can be passed through an additional reactor in which carbon is present, so that the carbon dioxide contained in the hot gases reacts with the carbon to form carbon monoxide according to the Boudoir equilibrium and thereby the reduction potential of the gas is increased. The gases enriched with carbon monoxide are then returned to the deck oven.

According to another embodiment, a part of the gases that are in the

Furnaces flow upwards below the levels on which non-ferrous metals evaporate and are extracted from the furnace through a suction connection in the side wall and above these levels through an inlet back into the furnace blow. As a result, the amount of gas present on the floors to which the nonferrous metal oxides are reduced to metals and volatilize is low. The metals formed can then be sucked out of the furnace in a relatively small amount of gas on these levels through an outlet in the side wall. The extracted gas mixture is afterburned, cooled in a cooling device and then cleaned with the aid of a filter before it is released.

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 metal concentration in the exhaust gas.

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 metal-containing residues according to the described method is proposed.

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 metal-containing residues. 1 shows a section through a deck oven 10, which consists of three zones 12, 14, 16 lying one below the other, each of which has a plurality of floors 18. These self-supporting levels 18, as well as the jacket 20, the cover 22 and the bottom 24 of the furnace are made of refractory material. In each zone 12, 14, 16 there is a suction nozzle 26, 28, 30 through which the gases can be evacuated from the furnace 10. The exhaust gases of the three zones 12, 14, 16 have a different composition so that it can be useful to treat the exhaust gases of the different zones 12, 14, 16 separately.

In the cover 22 there is an opening 32 through which the metal-containing residues, or a mixture of metal-containing residues and plastics, can be applied to the top floor of the first zone.

In the middle of the furnace there is a shaft 34 to which rakes are attached which protrude above the respective floors.

The rakes are designed so that they roll the material inside out on one floor and then outside in on the floor below, so that the material is transported through the furnace from top to bottom. The shaft 34 and the rakes 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.

The residues are usually applied to the first floor of the first zone 12 while the plastics are fed into the third zone 16 and are brought into contact with the metal-containing residues there. During the transport through the first zone 12, the metal-containing residues are heated to approximately 200 ° C. and dried.

In the jacket 20 of the deck furnace 10 - usually in the upper third of the third zone 16 - at least one inlet opening 36 is provided through which the plastics can be introduced into the furnace. The plastics that are introduced into the third zone 16 are mixed there by the rakes with the heated, metal-containing residues and suddenly cracked, with large amounts of hydrogen and carbon monoxide being released. Due to the high temperature and the presence of carbon monoxide and hydrogen, the oxides contained in the residues are reduced to metal during transport through the deck oven 10. Through the controlled input of plastics and oxygen-containing gases at various points in the deck oven 10 and through the possibility of suctioning off gases at critical points, it is possible to precisely control the reduction of the metal-containing residues and to carry out the process under optimal conditions.

Nozzles 38 for blowing hot (350 ° 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 deck oven 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 this reaction is predominantly endothermic, it makes sense to install burners 40 which ensure a constant high temperature in the levels of the furnace. Gas or coal dust burners can be used here.

These burners 40 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 afterburning of the process gases is achieved with excess air. 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 selected so that the slag can be drawn off in liquid form and can be disposed of in a glazed form. The generation of carbon monoxide reduces the consumption of plastics in the furnace 10 and thus also the ash content in the finished product.

On the last or the last two floors is the addition of plastics, carbon monoxide, hydrogen or natural gas through special nozzles intended. The reduction of the metal oxides can be completed in this atmosphere with an increased reduction potential.

Claims

1. Process for recycling plastics in the thermal treatment of metal-containing residues in a deck oven, which is divided into three zones, each zone having several superimposed floors and the method comprising the following steps: - Continuous introduction of the metal-containing residues onto the top one

Level of the first zone of the level furnace, the residues being gradually transferred to the second zone and being dried during this time,

heating and calcining the residues at approximately 800 ° C. within the second zones, the residues being gradually transferred to the third zone,

- Continuous introduction of plastics on the top floor of the third zone and heating of the mixture to 1000 ° C to 1200 ° C in the third zone whereby the metals are reduced, - discharge of the mixture from the floor furnace

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

3. The method according to any one of the preceding claims, characterized in that the metal-containing residues Lind at least part of the required plastic are mixed together before they are introduced into the deck oven.

4. The method according to any one of the preceding claims, characterized in that exhaust gases are extracted from the third zone and processed in an afterburner, the volatile contained therein

Metals are converted to metal oxides and separated from the exhaust gases in a filter device.

5. The method according to any one of the preceding claims, characterized in that iron is separated from the mixture after discharge from the deck oven.

6. 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.

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

8. The method according to claim 7, characterized in that the oxygen-containing gases have a temperature of at least 250 ° C.

9. Method according to one of the preceding; Claims characterized in that gaseous carbon monoxide, hydrogen and / or natural gas are blown in on the lowest floors in the third zone of the deck oven.

10. The method according to any one of the preceding claims, characterized in that gases are extracted from the deck oven on each floor of each zone.

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

12. Use of a deck oven for the thermal treatment of metal-containing residues according to the method according to any one of the preceding claims.