EP1137818A1

EP1137818A1 - Method for the heat treatment of residues containing heavy metals

Info

Publication number: EP1137818A1
Application number: EP99957993A
Authority: EP
Inventors: Jean-Luc Roth; Thomas Hansmann; Romain Frieden; Marc Solvi
Original assignee: Paul Wurth SA
Current assignee: Paul Wurth SA
Priority date: 1998-11-05
Filing date: 1999-11-04
Publication date: 2001-10-04
Also published as: CN1323359A; AU1551200A; AU750943B2; KR20010080042A; LU90315B1; CA2345412A1; PL348230A1; SK5962001A3; TW424004B; US6383252B1; TR200101253T2; JP2002529597A; BR9915309A; ZA200102662B; WO2000028094A1; CZ20011548A3

Abstract

The invention relates to a method for the heat treatment of residues containing heavy metals, carried out in a multiple-hearth furnace which is divided into three zones, each of which comprises several stacked levels. Said method consists of the following steps: continuous feeding of the heavy-metal residues into the top level of the first zone of the multiple-hearth furnace, the residues being gradually transferred to the second zone and dried during the transfer; continuous feeding of reducing agents and desulfurizers into the top level of the second zone, whereby the reducing agents and desulfurizers are mixed with the dried residues and the mixture is heated to approximately 800 DEG C, calcined during heating and gradually transferred to the third zone; heating of the mixture to approximately 1000 DEG C in the third zone, whereby the metals are reduced and the waste gases resulting in said third zone are drawn off and treated separately; and discharge of the mixture from the multiple-hearth furnace.

Description

Process for the thermal treatment of heavy metals

Residues

The present invention relates to a method for the thermal treatment of residues containing heavy metals, e.g. Sludges from surface treatment, pickling and cleaning, metalization and tinning processes of metal parts.

This process produces large amounts of heavy metal residues in the form of sludge. 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 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.

Typical compositions of such heavy metal containing slurries are shown in the following table.

The object of the present invention is therefore to propose a method for the thermal treatment of such heavy metal-containing residues.

This object is achieved according to the invention by a method for the thermal treatment of residues containing heavy metals in a multi-level furnace which is divided into three zones, each zone having a plurality of superimposed levels and the method comprising the following steps: • Continuous introduction of the heavy metal-containing residues on the top floor of the first zone of the deck oven, the residues being gradually transferred to the second zone and drying while, • Continuous introduction of reducing agents and desulfurization agents onto the top floor of the second zone, the Reducing agent and the desulfurizing agent are mixed with the dried residues, the mixture is heated to approximately 800 ° C. and calcined and gradually transferred to the third zone, • heating the mixture to approximately 1000 ° C. in the third zone, reducing the metals the exhaust gases that arise in this third zone are extracted and treated separately,

• Discharge of the mixture from the deck oven.

A major 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. In this way, valuable materials can be produced from essential components of the residual materials. After the process has been completed, the iron content can be returned to the production process of a steel mill. Heavy metal oxides are concentrated to such an extent that they can be used as raw materials for the extraction of heavy metals. What remains are ashes, which essentially consist of inert substances such as S.C> 2, Al2O3, MgO, ... and an excess of reducing agents.

In the first zone, the heavy metal-containing residues are heated indirectly by heating resistors or directly by burners to approximately 200 ° C., so that the water is completely evaporated and then transferred to the second zone. In this zone, reducing agent and desulfurizing agent are mixed with the heavy metal-containing residues and this mixture is heated up to approximately 800 ° C., during which the mixture is calcined. The carbonates and sulfates contained in the mixture are decomposed and converted to metal oxides, releasing carbonic acid and sulfur dioxide become. The sulfur dioxide reacts with the desulfurization agents so that the sulfur content in the gases inside the deck furnace remains low. After the mixture has reached a temperature of approximately 800 ° C, the calcination is complete and the mixture is introduced into the third zone and further heated. As soon as it has reached a certain temperature (from approximately 900 ° C) the metal oxides begin to react with the reducing agents, whereby the heavy metals evaporate and are discharged together with the exhaust gases from the deck oven.

The heavy metals are extracted on the floors in the third zone where they are formed and treated separately from the other exhaust gases. These 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.

At the same time or at a later point in time, the iron oxides remaining in the deck furnace are reduced to metallic iron. The metallic iron produced in this way is removed from the furnace together with the residues of the material introduced, the ashes of the reducing agents and any excess reducing agents that may be present.

In this process, sludge-like, heavy 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 of particular advantage when ash-forming reducing agents are 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 can be recycled with the unused reducing agents that may be contained in them in a separate gasification reactor, 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 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 agents, which prevents agglomeration of the residues.

In the event that an excess of reducing agents is used, it is possible 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 returned directly to the deck oven.

The charging of reducing agents can also be divided into several stages. There is the possibility that coarse-grained reducing agents (1-3 mm) are introduced further up in the second zone of the deck oven and fine-grained reducing agents (<1 mm) are added below. This largely avoids the discharge of dust with the exhaust gases and accelerates the course of the reaction through the fine reducing agent particles introduced below.

By charging coarser particles, the consumption of reducing agents 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 CC> 2. 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, you can measure and influence the process conditions in the different zones or even per floor.

The heavy metal-containing residues can, however, also be mixed with - at least some of the required - reducing agents or desulfurizing agents before they are introduced into the deck oven. This is particularly true in the case of treating sludges with a high water content which are mixed with at least some of the reducing agents or desulfurizing agents required before they are introduced into the furnace. This is because the sludge usually has a sticky consistency and, when mixed with a reducing agent or desulfurizing agent, is easier to put in the oven. Mixing with the reducing agents or desulfurizing agents prevents the input material from forming agglomerates when heated.

The heavy metal 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 heavy metal residues, any reducing agents and desulfurizing agents 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. A gaseous reducing agent 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, which are below the floor to which reducing agents are introduced, 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.

You can also remove part of the gases that flow upwards in the furnace below the floors on which heavy metals evaporate, suck them out of the furnace through a suction nozzle in the side wall and then blow them back into the furnace through an inlet. As a result, the amount of gas present on the floors to which the heavy metal oxides are reduced to heavy metals and volatilize is small. The Schwerme ^¬ metals can then be sucked off in a relatively small gas quantity on these floors through an outlet in the side wall of the oven. 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 concentration of heavy metals 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 residues containing heavy metals 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 residues containing heavy metals. 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 agbase of the three zones 12, 14, 16 have a different composition so that it makes sense 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 heavy metal-containing residues 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 applied to the first floor of the first zone 12, while the reducing agents and the desulfurizing agents are fed into the second zone 14 and are brought into contact with the residues containing heavy metals.

During the transport through the first zone 12, the heavy 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 second zone 14 - there is at least one inlet opening 36 through which the reducing agents and the desulfurizing agents can be introduced into the furnace. These reducing agents can be in gaseous form or in liquid or solid form. The reducing agents are carbon monoxide, hydrogen, natural gas, petroleum and petroleum derivatives, or solid carbon carriers, such as lignite coke, petroleum coke, blast furnace dust, coal, or the like. The desulfurizing agents contain, for example, lime (CaO), limestone (CaC0 ₃ ) and / or magnesite (MgO).

The reducing agents and the desulfurizing agents which are introduced into the second zone 14 are mixed there by the rakes with the heated, heavy metal-containing residues and heated to approximately 800.degree.

In the third zone 16, the mixture of heavy metal-containing residues, reducing agents and desulfurizing agents is heated to approximately 1000 ° C. Due to the high temperature and the presence of carbon mono- oxide, the oxides contained in the residues are gradually reduced to metal during transport through the deck furnace 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 suctioning off gases at critical points, it is possible to precisely control the reduction of the heavy metal-containing residues and the process under optimal conditions perform.

In the side wall, nozzles 38 are provided for blowing in hot (350 ° C. to 500 ° C.) oxygen-containing gases, through which air or another gas containing oxygen 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 through 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 burner, 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. 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. The addition of a gaseous reducing agent, for example carbon monoxide or hydrogen, through special nozzles is provided on the last or the last two floors. The reduction of the metal oxides can be completed in this atmosphere with an increased reduction potential.

Claims

PATENT CLAIMS

1. Method for the thermal treatment of heavy metal-containing residues in a multi-level furnace, which is divided into three zones, each zone having several superimposed levels and the method comprising the following steps: the residues are gradually transferred to the second zone and are dried,

• Continuous introduction of reducing agents and desulfurizing agents on the top floor of the second zone, the reducing agents and the desulfurizing agents being mixed with the dried residues, the mixture being heated to approximately 800 ° C. and being calcined and gradually transferred to the third zone heating the mixture to approximately 1000 ° C. in the third zone, the metals being reduced, the exhaust gases which arise in this third zone being suctioned off and treated separately,

• Discharge of the mixture from the deck oven.

2. The method according to claim 1, characterized in that the desulfurizing agents contain lime, limestone and / or magnesite.

3. The method according to any one of the preceding claims, characterized in that the reducing agent is introduced in liquid, solid form and / or gaseous in the deck oven.

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

5. The method according to any one of the preceding claims, characterized in that the heavy metal-containing residues and at least some of the required reducing agent are mixed together before they are placed in the deck oven.

6. The method according to any one of the preceding claims, characterized in that the exhaust gases from the third zone are processed in an afterburner, the volatile metals contained therein being converted to metal oxides and being separated from the exhaust gases in a filter device.

7. 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.

8. The method according to any one of the preceding claims, characterized in that unused reducing agents are separated from the mixture after discharge from the deck oven.

9. 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.

10. The method according to any one of the preceding claims, characterized in that oxygen-containing gases are blown in specifically on different floors. 11. The method according to claim 10, characterized in that the oxygen-containing gases have a temperature of at least 250 ° C.

12. The method according to any one of the preceding claims, characterized in that gaseous reducing agents are blown on the lowest floors in the third zone of the deck oven. 13. 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.

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

5. Use of a deck oven for the thermal treatment of residues containing heavy metals according to the method according to one of the preceding claims.