EP0910678A1

EP0910678A1 - Process for reusing dusts from metallurgical processes, such as steel converter dusts containing zinc

Info

Publication number: EP0910678A1
Application number: EP97929014A
Authority: EP
Inventors: Johann Lehner; Bertram Fritz; Peter Paschen; Kurt Antlinger
Original assignee: Voestalpine Stahl GmbH; Voestalpine Stahl Linz GmbH; Voest Alpine Industrienlagenbau GmbH
Current assignee: Voestalpine Stahl GmbH; Primetals Technologies Austria GmbH; Voestalpine Stahl Linz GmbH
Priority date: 1996-07-10
Filing date: 1997-07-07
Publication date: 1999-04-28
Also published as: ATA122496A; WO1998001590A1; AT405528B

Abstract

To avoid concentration of undesired metals and other associated elements in a metallurgical process and, nevertheless, to guarantee high yield of the product produced with the metallurgical process, the following procedures are used for recycling dusts which arise during the metallurgical process: the dusts are analyzed for their content of at least one metal undesirable for the metallurgical process, particularly zinc for steel production; if the threshold value of the metal is exceeded, at least a portion of the dusts with analysis values exceeding the threshold is separated from dusts with analysis values below the threshold; the separated dusts are subjected to a concentration treatment at least with regard to the analyzed metal, wherein a portion of the separated dusts with a high content of the analyzed metal and a portion with a content below the threshold is formed, and the portion with a low content of the analyzed metal dusts is fed into the metallurgical process and the portion with a high content of the analyzed metal dusts is fed into the process for reuse of this metal. A plant for carrying out this process consists of a metallurgical container (1), an exhaust gas cleaning device (2, 3), an analytic device (4) for measuring the zinc content, a separating device (5) for separating the dusts, a treatment device (11) for concentrating zinc, a conveyance device (14) for returning the treated dusts, and a return system (6) with a compacting device (6') for returning the untreated dusts.

Description

METHOD FOR RECYCLING DUST DURING METALLURGICAL PROCESSES, LIKE STEEL CONVERTER SPRAY CONTAINING ZINC

The invention relates to a method for recycling dusts produced in metallurgical processes, in particular in the manufacture of steel, and discharged with a process gas formed in the process, and a plant for carrying out the method.

In metallurgical processes, in particular in metallurgical processes for the production of steel or intermediate steel products, in which ores, pig iron and / or scrap are used, large amounts of dusts are generated which, together with the process gas formed in the metallurgical process, come from the metallurgical vessel in which the metallurgical Process is running, to be carried out. During the subsequent cleaning of the process gases, the dusts are separated either by dry and / or wet processes. These dusts contain relatively high percentages of metals and other accompanying elements, which are not only often undesirable for the metallurgical process and for the product produced here, but are also annoying and quality-reducing.

In order not to have to put the dust on landfill, it is known to recirculate the dust in the metallurgical process, but there is an accumulation of these metals and other accompanying elements, e.g. for an enrichment in zinc, lead, alkalis (K, Na), chlorine etc.

Especially when processing scrap, e.g. for the manufacture of steel, the enrichment can reach such an extent that one is forced to remedy it, e.g. Partial quantities of dust to be separated from the recirculation process and to be disposed of or otherwise used. This is particularly the case with increased recycling of galvanized sheets; there is - without countermeasures - a steady increase in the zinc content.

From EP-A - 0 275 863 and EP-B - 0 174 641 it is known to process metal-containing dusts, in particular zinc-containing or iron-containing dusts, such as occur in smelting processes, in such a way that the metals contained in the dusts are recovered is possible. To prepare the dusts, they are first subjected to pelletization, after which the pellets thus formed are dried and introduced into an induction furnace in which the iron, zinc and lead oxides contained in the pellets are reduced, whereupon the low-melting metals evaporate and in a condenser be put down. EP-A-0434 120 discloses a process for working up metallurgical residues containing zinc and lead, in which the residues are subjected to conditions which reduce temperatures at elevated temperatures, zinc and lead being volatilized and evaporated zinc and lead from the exhaust gas cooling can be separated. The thermal treatment at elevated temperatures takes place in a circulating fluidized bed

A problem arises with the recycling of the dusts in that the dusts are produced in very large quantities and recycling the dusts is only worthwhile if the contents of usable accompanying elements are high enough. In particular because the known recycling processes require a large amount of energy. There are therefore conflicting demands, on the one hand, to recycle the dusts as completely as possible in the metallurgical process by recirculation and to place the smallest possible quantities of the dusts in the landfill and, on the other hand, to prevent accumulation of unwanted metals and accompanying elements and to save energy in the processing or extraction of the To keep accompanying elements as low as possible, ie Only small amounts of dust with a very high content of undesirable metals and other accompanying elements can be used separately from the metallurgical process.

The invention therefore has as its object to provide a method and a plant for carrying out the method, which make it possible to prevent accumulation of undesired metals and other accompanying elements in the metallurgical process, but with a tolerable effort in the utilization of the dusts. In particular, it should be possible to recirculate most of the dust and still prevent an accumulation of unwanted metals and other accompanying elements.

In a method of the type described in the introduction, this object is achieved by combining the following features:

The dusts are analyzed with regard to a content of at least one metal which is undesirable for the metallurgical process, and in particular for zinc in the steel production,

• If a limit value for the analyzed metal is exceeded, at least a subset of the dusts with the analysis value above the limit value is separated from dusts with an analysis value below the limit value,

• The separated dusts are subjected to an enrichment treatment at least with regard to the analyzed metal, with a partial amount of the separated dusts with a high content of analyzed metal and a subset with a low content of the analyzed metal below the limit value and • the partial amount of the dusts with a low content of analyzed metal becomes part of the metallurgical process and the subset with a high content of analyzed metal the dust is recycled from this metal

Since it has been shown that the coarse fraction of the dusts contains far fewer fractions of undesirable metals or accompanying elements, only the fine fraction of the dusts produced in the metallurgical process is advantageously analyzed. For example, only the amount of dust deposited in an electrostatic filter is analyzed.

A high degree of recirculation can be achieved by returning the dusts to the metallurgical process if the content of the analyzed metal falls below the limit.

In order to be able to comply with the limit value of the undesired metal content in the metallurgical process as precisely as possible, the analysis of the content of at least one metal of the dusts is advantageously carried out continuously. Continuous is also understood to mean a mode of operation in which, for example, metals contained in the dust are analyzed at least once every five minutes. It is preferably analyzed five to twenty times per minute. A mean value is then expediently formed from a plurality of measurement results, and only when this exceeds the limit value is a separation of the dusts with analysis values above the limit value carried out.

The limit value for zinc between 5 and 40% by weight, preferably between 10 and 20% by weight, is expediently set for dusts from the steel industry.

In order to largely avoid the development of dust during the enrichment treatment, the dusts are compressed, in particular agglomerated, after the analysis has been carried out and before the enrichment treatment.

According to a preferred method, the enrichment treatment for at least the analyzed metal is carried out according to a pyrometallurgical method in which the dusts are subjected to a thermal treatment under reducing conditions, namely at a temperature at which at least the analyzed metal is evaporated, but the dust particles melt is avoided. O 98/01590

In order to separate further undesirable components of the dusts, the temperature and pressure are expediently kept in a range in which further undesired components, such as chlorides and alkalis, also evaporate.

In this case, the metal escaping during the evaporation is expediently either oxidized then cooled and filtered or condensed / sublimed

A system for carrying out the method according to the invention is characterized by the combination of the following features:

A metallurgical vessel, preferably a converter,

An exhaust gas purification device which is connected to the metallurgical vessel by means of a gas discharge leading from the metallurgical vessel to a process gas,

An analysis device for measuring the content of at least one metal contained in the dusts and undesirable in the metallurgical vessel,

A separating device for separating the dusts with a high content of analyzed metal from the dusts with a low content of analyzed metal,

A treatment device for the enrichment of at least the metal, the content of which has been analyzed,

A conveyor device downstream of the treatment device for returning a portion of the dusts with a low content of analyzed metal into the metallurgical vessel and

A further conveyor device arranged downstream of the treatment device for the removal of a partial quantity of the dusts with a high content of analyzed metal to a processing plant, in particular a metal extraction plant, for the analyzed metal.

In this case, the separating device is expediently followed by a compression device for the dusts with a high content of analyzed metal, in particular an agglomeration device.

The treatment device for enriching a metal preferably comprises a pyrometallurgical plant, the pyrometallurgical plant advantageously comprising a solid-state reactor, in particular a medium-frequency induction furnace.

A return line expediently leads from the cutting device to the metallurgical vessel, a compression device advantageously being provided in the return line. The invention is explained in more detail below with reference to a process sequence shown in the drawing in the block diagram, the exemplary embodiment relating to steel production. The method according to the invention can, however, be used for the entire metallurgical industry, for example in the pyrometallurgy of lead (lead shaft furnace and so-called direct reduction process, for example KIVCET). , copper (shaft furnace for secondary copper production, especially when using zinc-containing scrap and other materials) and tin (mixed tin production and recycling).

The metal compounds evaporating at the prevailing working temperatures are selectively volatilized and post-oxidized in the gas stream depending on the oxygen partial pressure. The separated dust particles can be adjusted in their content of valuable metals in such a way that an optimal further processing possibility is guaranteed depending on the subsequent process.

Pig iron, scrap metal, lime and other additives are used in a metallurgical vessel designed as a converter 1 for steel production. The exhaust gases generated when blowing the convector are fed to an evaporation cooler 2 for the coarse separation of dusts and further passed through an electrostatic filter 3 for the separation of the fine fraction (e.g. particle size below 100 μm) of the dusts. The dusts deposited in the electrostatic filter 3 are analyzed with respect to at least one metal which is undesirable for steel production, in particular with regard to the zinc content, by means of an analysis device 4. The analysis is preferably carried out continuously, with continuous measurements at shorter time intervals also being regarded as continuous. For example, five to twenty measurements can be carried out per minute. The analytical device 4 required for this is advantageously installed on a conveying means which continues the separated dusts, for example a nitrogen-flooded conveyor belt. Laser-induced plasma spectroscopy (LIPS) and X-ray fluorescence analysis can be used as the analysis device, for example.

About 16 kg of fine dust are deposited in the electrostatic filter per ton of crude steel produced. The coarse dust is already separated in the evaporative cooler 2.

A dust composition of the dusts separated in the electrostatic filter is given in Table 1 below as an example. Table I

Fe 40% by weight Zn 20% by weight α 1.3% by weight

Alkali 1.5% by weight

CaO, MgO, Al ₂ O ₃ , Pb 37.2% by weight

Downstream of the analysis device 4 is a separating device 5 for separating the dusts with a high content of analyzed metal from the dusts with a low content of analyzed metal. In the exemplary embodiment shown, this cutting device is designed as a flap 5. If, for example, the analyzed dust has the composition given in Table I - here the zinc content is above the predetermined limit value, which can be set between 5 and 40% by weight, preferably between 10 and 20% by weight - the dusts no longer become Via a return line 6 with agglomerating device 6 'or pelletizing device, in which external metallurgical dust (at 7) with a low zinc content can also be mixed into the metallurgical vessel 1, ie the converter 1, fed back, but fed via the flap 5 to a further treatment rail, which is generally designated 8. This treatment rail 8 is formed by a compression device 9, which is advantageously designed as an agglomeration device or as a granulation device - here, too, external metallurgical dust (at 10) with a high zinc content can be added - the treatment device 11 for the enrichment of at least the metal, the content of which has been analyzed is subordinate.

If the dusts generated during the metallurgical process and discharged with the exhaust gas from the metallurgical vessel 1 are separated using the wet process, for example in a wet scrubber, a swiveling trough is provided instead of the flap 5, with which the dust produced in the form of sludge is in one depending on the zinc content can be conveyed by two sedimentation containers. Chamber filter presses for dewatering the dusts are arranged downstream of the sedimentation containers, after which the agglomeration can be carried out with an agglomerating device. The agglomeration device is followed by drying, which is carried out, for example, in a drying oven in order to avoid the generation of hydrogen gas in the downstream treatment device 11.

The treatment device 11 is preferably a pyrometallurgical system, for example a medium-frequency induction furnace, in which the introduced dusts be subjected to a thermal treatment under reducing conditions, etc. at a temperature at which at least the analyzed metal and expediently also other undesired components such as chlorides and alkalis evaporate, but melting of the agglomerated dust particles is avoided.

In the pyrometallurgical treatment stage, the agglomerated dusts are inductively heated to over 900 ° C, i.e. via the evaporation points of Pb and Zn. The reducing gas to be introduced is also (previously) heated to over 1000 ° C. In the pyrometallurgical treatment stage, Zn oxide and Zn spinels (ZnO.Fe ₂ O) are reduced to Zn and evaporated. Agglomeration before the pyrometallurgical treatment stage is not absolutely necessary, but the fine dusts lead to an undesirable, unmanageable dust management

The metal escaping during the evaporation and the accompanying elements also evaporating in the process are oxidized in a post-treatment station 12, cooled and condensed and / or sublimed and finally filtered in a filter 13. The composition of the filtered material is shown in Table II below.

Table II

Fe 7% by weight

Zn 60% by weight α 3.8% by weight

Alkali 4.1% by weight

CaO, MgO, Al ₂ O, Pb 25.1% by weight

The filtered material is then available for removal to external processing for zinc production, such as a zinc smelter, etc.

The dusts not melted in the solid-state reactor 11 and freed from the evaporated constituents are discharged from the latter and returned to the converter 1 via a conveying device 14, such as a recirculation line 14. The composition of these dusts is shown in Table III below. O 98/01590

Table III

Fe 58% by weight

Zn 6% by weight

Cl 0.4% by weight

Alkalis 0.6% by weight

CaO, MgC), Al ₂ O ₃ . Pb 35% by weight

It can be seen in a comparison of Tables I and III that the zinc content has been significantly reduced, so that enrichment of the zinc in converter 1 can be avoided.

Of the 16 kg / t crude steel deposited in the electrostatic filter, about 2 kg / t crude steel of the dusts have an increased zinc content and are fed to the solid-state reactor 11. Of these 2 kg / t of crude steel, 1.3 kg / t of crude steel are returned to converter 1. Only about 0.55 kg of highly enriched material accumulates in the filter 13.

As an alternative to the pyrometallurgical treatment stage, the enrichment treatment can also be carried out in two stages, the temperature being kept below the vaporization point of Zn in the first stage, as a result of which only the spinels are cracked and the Zn oxides are reduced beforehand. The second stage is a hydrometallurgical reduction based on NH _. i or NaOH downstream.

The following advantages are achieved according to the invention:

• Due to the two partial quantity formation, etc. the first after the analysis has been carried out and the second, which takes place in the solid-state reactor 11, there is a greatly increased utilization of the dusts in the metallurgical process, i.e. in converter 1, and thus a high output of steel or steel raw material.

• No more landfill material is generated, since the iron components in the dust are almost entirely returned to the steel production process and the non-ferrous accompanying elements can also be used.

• Despite the almost complete return of the iron components in the steel production process, there is no negative influence on the steel quality, e.g. due to increased zinc content.

• The proportion of dust actually exported by the metallurgical process is extremely low, and it is characterized by a very high non-ferrous metal content and the lowest iron content.

• In the pyrometallurgical separation stage, ie the solid reactor 11, there is only a very small amount of substance to be treated, so that the solid reactor 1 1 is small can be kept and also requires little energy for its operation. The solid-state reactor 11, if it is operated with reducing gas, also enables the production of the smallest amounts of exhaust gas as well as waste-water-free operation.

Claims

O 98/01590 1 Patent claims:

1. Process for recycling dusts that are produced in metallurgical processes, in particular in steel production, and discharged with a process gas formed in this way, characterized by the combination of the following features:

• The separated dusts are subjected to an enrichment treatment at least as far as the analyzed metal is concerned, whereby a partial amount of the separated dusts with a high content of analyzed metal and a partial amount with a low, below the limit value of analyzed metal is formed and

• The subset of the dusts with a low content of analyzed metal are fed to the metallurgical process and the subset of the dusts with a high content of analyzed metal are used for recycling this metal

2. The method according to claim 1, characterized in that only the fine fraction of the dusts produced in the metallurgical process is analyzed.

3. The method according to claim 1 or 2, characterized in that when the limit of the content of the analyzed metal is undershot, the dusts are returned to the metallurgical process.

4. The method according to one or more of claims 1 to 3, characterized in that the analysis of the content of at least one metal of the dusts is carried out continuously, preferably at least once every five minutes, in particular five to twenty times per minute.

5. The method according to one or more of claims 1 to 4, characterized in that the limit value for zinc between 5 and 40 wt.%, Preferably between 10 and 20 wt.%, Is set for dusts from the steel industry.

6. The method according to one or more of claims 1 to 5, characterized in that the dusts are compacted, in particular agglomerated after carrying out the analysis and before the enrichment treatment.

7. The method according to one or more of claims 1 to 6, characterized in that the enrichment treatment for at least the analyzed metal is carried out according to a pyrometallurgical method in which the dusts are subjected to a thermal treatment under reducing conditions, at a temperature at at least the analyzed metal is evaporated, but melting of the dust particles is avoided.

8. The method according to claim 7, characterized in that the temperature and pressure are kept in a range in which further undesirable components, such as chlorides and alkalis, also evaporate.

9. The method according to claim 7 or 8, characterized in that the metal escaping during the evaporation is either oxidized, then cooled and filtered or is condensed / sublimed.

10. Plant for performing the method according to one or more of claims 1 to 9, characterized by the combination of the following features:

A metallurgical vessel (1), preferably a converter,

An exhaust gas purification device (2, 3), which is connected to the metallurgical vessel with a process gas discharge from the metallurgical vessel,

An analysis device (4) for measuring the content of at least one metal contained in the dusts and undesirable in the metallurgical vessel,

A separating device (5) for separating the dusts with a high content of analyzed metal from the dusts with a low content of analyzed metal,

A treatment device (11) for enriching at least the metal, the content of which has been analyzed,

• a conveyor device (14) arranged downstream of the treatment device (11) for returning a portion of the dust with a low content of analyzed metal into the metallurgical vessel (1) and

• A further conveyor device arranged downstream of the treatment device (11) for the removal of a partial quantity of the dusts with a high content of analyzed metal to a processing plant, in particular a metal extraction plant, for the analyzed metal. O 98/01590 ^{1 Z}

11. Plant according to claim 10, characterized in that the separating device (5) is a compression device (9) for the dusts with a high content of analyzed metal, in particular an agglomeration device, is arranged downstream

12. Plant according to claim 10 or 11, characterized in that the treatment device (11) for enriching a metal comprises a pyrometallurgical plant

13. Plant according to claim 12, characterized in that the pyrometallurgical plant comprises a solid-state reactor (11), in particular a medium-frequency induction furnace

14. Plant according to one or more of claims 10 to 13, characterized in that a return line (6) leads to the metallurgical vessel (1) from the separating device (5).

15. Plant according to claim 14, characterized in that a compression device (6 ') is provided in the return line (6).