WO1998040523A1 - Agglomerate for use as blast furnace feedstock - Google Patents

Abstract

The invention concerns an agglomerate which is formed from a mass for use as blast furnace feedstock consisting of a powdery to coarse-grained metal- or metal-oxide-containing fine material which has good resistance to abrasion and pressure. To that end, an agglomerate is proposed which contains more than 90 mass % of a metal- or metal-oxide-containing fine material and a silicate-like mineral sintering matrix in a structure of fine material particles. The fine material particles are embedded in vitrified molten silicate with mineral deposits and a porosity of between 20 and 50 vol % of the total volume, the portion of open pores being between 75 and 95 %.

Description

 Agglomerate for use as a blast furnace feed

The invention relates to an agglomerate for use as a blast furnace feedstock from a powdery to coarse-grained metal or metal oxide-containing fine material and a mineral binder which is hardened by thermal treatment.

In particular, the invention relates to an agglomerate of scale produced in rolling mills, in particular oil-containing scale scale.

The economical processing of mill scale into agglomerates, which can be fed to a blast furnace process as iron or iron oxide carriers, is of particular importance because of the large quantities of mill scale that arise. As is known, in the hot forming and heat treatment of steels, iron oxides form on the steel surfaces, the so-called mill scale, which is preferably fed to an iron and steel extraction process in order to recover its iron content.

For economic and metallurgical reasons, only iron oxides are considered for the blast furnace process, which are free from undesirable accompanying elements and, as hardened agglomerates, have sufficient pressure resistance and abrasion resistance. Known mill scale agglomerates do not meet these requirements sufficiently, so that the scale that is still present is often simply stored outdoors in so-called landfills. The resulting mill scale is generally highly oil-containing. For the production of agglomerates Therefore, people like to fall back on processes with controlled heat treatment in order to burn the proportion of hydrocarbons. Such a heat treatment of powder molded parts, which are preferably pre-pressed from mill scale, repeatedly leads to the breaking of individual molded parts, with the result that the reject fraction, in particular the dust emission, is high.

In the conventional sintering of agglomerates from fine-grained iron, as for example from BUCKEL, M. et al .; New developments in the production of sinters, in: Stahl und Eisen 110, 1990, No. 2, page 43 to 51, in particular page 50, right column, are not known, oil-containing mill scale slurries cannot be added at all due to the risk of filter fires in the required dedusting systems become.

It is also known from DE 196 29 099 A1 to form the generally powdery mill scale with the addition of a mineral binder, in particular a raw material containing clay minerals, as a ceramic molded body which is then dried and fired. However, the proportion of clay mineral-containing raw material required for the formation of ceramic moldings is too high to meet the purity requirement of iron oxide without undesired accompanying elements. A reduction in the proportion of raw material containing clay minerals to less than 10% by mass has so far not led to any usable agglomerates, since the shaped bodies produced from such mill scale mixtures do not have sufficient stability for a subsequent hardening process. The addition of additional strengthening materials fails due to the requirement to keep accompanying elements in the agglomerates as low as possible. Similar problems exist when agglomerating metal powders, grinding dusts and / or metal chips.

The object of the invention is therefore to create an agglomerate of a powdery to coarse-grained metal or metal oxide-containing fine material, in particular mill scale, which has good abrasion and pressure resistance and at the same time contains only a minimum of accompanying elements. This object is solved by the features of claim 1.

This creates an agglomerate that has a structural and higher load-bearing capacity. In particular, the hydrocarbon-enriched fine sludge, which is produced in the steel rolling process and in the steel processing industry and has previously been deposited, can be agglomerated in this way and then recycled. Organic components contained are destroyed by the thermal hardening process, so that the agglomerates also meet the purity requirement.

Further refinements of the invention can be found in the following description and the subclaims.

1 shows a preferred configuration of an agglomerate.

The invention relates to an agglomerate 1 with a proportion of more than 90% by mass of a metal or metal oxide-containing fine material and a silicate mineral sinter matrix in a structure of fine material particles of the fine material, which are embedded in a glassy solidified silicate melt with mineral excretion, and a porosity from 20 to 50 vol% of the total volume, the proportion of open porosity of which is 75 to 95%.

The structure of the agglomerates 1 is characterized by a glassy solidified silicate melt with mineral precipitation, which forms molten skins around the mill scale particles as well as fusible links between the mill scale particles, which leads to a reliable compacting of the mill scale grains. This gives mass bodies which have a desired, preferably high porosity after the hardening process. The agglomerate 1 is accordingly sintered via a silicate melt. The mineral excretion is preferably primary mullite. Even after wet sintering, the agglomerate 1 therefore has a pore fraction in the total volume of 20 to 50% by volume, in particular 35 to 45% by volume, more than 60% of this porosity being formed by an open porosity. Despite the compacting of the mill scale particles by means of a liquid phase, the proportion of open porosity is between 75 and 95%.

The shape of the agglomerate 1 can be selected and can take on flat or rounded shapes, the agglomerate 1 having square or rectangular bottom surfaces with a width B and a length L.

The agglomerate 1 is preferably given a stamping or piercing body shape with a crater depth 2 on the head side by means of a shaping process. The crater depth 2 can account for up to 70% of the total height of the body shape. Crater depths 2 of 50 to 60% of the total height are preferred. The crater depth 2 can have funnel widths of 50 to 80% of the diameter or the length L of the agglomerate 1. The crater depth 2 is also preferably formed centrally on the agglomerate 1 so that the agglomerate 1 has wall thicknesses that are as uniform as possible. Such a shape has a larger body surface and causes a change in the core tension, so that core cracks occur less frequently. Such a body shape also shortens the thermal treatment required.

A method for producing an agglomerate according to the invention is described below.

Agglomerates of a metal or metal oxide-containing fine material and a mineral binder are produced by mixing the fine material with a raw material containing clay minerals to form a mass, forming individual mass bodies and solidifying them to form an agglomerate.

The fine material is preferably obtained in rolling mills the tinder, especially the oil-containing roller tinder. The mill scale to be agglomerated can be added with particle sizes in the fine to coarse range, with up to 50% by mass in the range between 1 and 10 mm. The mill scale can also be added up to 90% as a powdery fine material, ie with grain sizes down to: 100 μm.

90 to 98 Ma of the mill scale are mixed with 2 to 10 Ma% of a raw material containing clay minerals in the grain size 0.5 μm to 200 μm with setting a mass moisture of 6 to 20% to a doughy mass. The desired moisture content can be adjusted depending on the moisture content of the metallic or metal oxide fines, possibly its oil content, as well as the moisture content of the clay mineral raw material by removing or adding water. The mill scale is generally in a sturdy, gritty / muddy, at least grain-digested form.

The proportion of mill scale in the batch can be partially replaced by another metal-containing fine material, such as, in particular, metallic grinding dust or chips.

The clay mineral-containing raw material is preferably added in very fine-grained form, in particular in the grain sizes 0.5 μm to 80 μm, with 50 to 80% of the proportion of the clay mineral-containing raw material preferably being added in the grain size between 20 and 60 μm. Furthermore, the clay mineral-containing raw material is preferably added with an essentially continuous grain size distribution.

The clay mineral-containing raw material preferably contains one or more two- and / or three-layer clay minerals as the main constituent. Clays whose cation exchange capacity is increased due to an at least low degree of diagenesis are preferred as two-layer clay minerals.

The mixture of mill scale and clay mineral raw material can 0.3 up to 1.5% by mass of additional solidifying agents, such as inorganic thickeners, in particular water glass, sugar solution, aluminum chromate or a phosphate, can be added. Minor proportions, preferably up to 0.5% by mass, of organic additives, in particular molasses, can also be added. A further additive to lower the hardening temperature are low-melting silicate substances, such as, in particular, a glass powder or phonolite, which can replace the clay-mineral-containing raw material by up to 10 to 40% of its proportion when mixed with mill scale.

The mixing of the batch into a doughy mass, in which the incorporated air is generally distributed over the smallest gas bubbles, is preferably carried out by means of a twin-shaft mixer. After the offset has been mixed into a mass, the mass is transported in blocks to a cutting tool, which divides the mass blocks into individual mass bodies, which are then hardened. The mass is not compressed at all or only slightly when it is transported in blocks.

Before the mass is fed to this blockwise transport, its processing consistency, i.e. their moisture content is checked again using water as the correction medium. This ensures that the mass with the desired mass moisture of 6 to 20% can get into a loading device for block transport.

The mass is preferably transported in blocks using a piston press which is only subjected to low pressures. Depending on the moisture content of the mass, the applied pressures are between 0.4 and 2.5 MPa.

An outlet nozzle of the piston press can divide the mass transported in blocks into individual lengths, from which individual mass bodies can be sheared off. Alternatively, the mass transported in blocks can be ejected in Hubein and then stamped and / or embossed. drive through.

It is always crucial that the mass is not subject to a mixing process during the shaping process, which would lead to the destruction of the stability of the mass.

The individual mass bodies are then thermally treated with a residual moisture content of greater than or equal to 3%. The mass bodies are preferably brought directly into a firing unit without drying. The thermal treatment serves to harden the mass bodies to form agglomerates, the hardening preferably being based on a sintering process with the formation of a silicate sintering matrix which has a glass phase and optionally a crystalline phase, in particular an ullitic phase. The silicate sintered matrix is then a glassy matrix in which crystalline particles are embedded, which are preferably a primary material.

The hardening process is preferably carried out by means of a thermal treatment at temperatures between 800 and 1200 ° C and a holding time of less than 90 min, so that the clay mineral-containing raw material can form a melting phase, which preferably consists of a glassy solidified sintered matrix with a crystalline fraction, in particular granular mullite or Primary mullite, in which the mill scale particles are embedded. The mass bodies are preferably fed directly to this baking firing, so that the heating phase lies in the initial phase of the baking firing. During this initial phase of the cooking or sintering firing, the mass bodies are given an outer, stable crust which leads to such inherent stability that the mass bodies can even be fired in a roller furnace.

The above statements apply accordingly if metal powder, metallic grinding dusts and / or metal chips are used as the metal or metal oxide-containing fine material, which preferably mixes fine-grained with the mineral binder and are processed into agglomerates as described above.

If the fine material containing metal or metal oxide is mill scale, coarse and medium-grain mill scale particles form indentations in the structure of the agglomerate, which are partially melted. Furthermore, a finely crystalline support matrix or a support structure in the sintered matrix has been created by collective crystallization of fine-grained mill scale particles, which leads to a further increase in the mechanical strength of the agglomerate.

Claims

claims 1. Agglomerate formed from a mass for use as a blast furnace feedstock with a proportion of more than 90% by mass of a powdery to coarse-grained metal or metal oxide-containing fine material as well as a silicate mineral sinter matrix in a structure made of fine particles which are embedded in a glassy solidified silicate melt with mineral excretion, and a porosity of 20 to 50 vol% of the total volume, the proportion of open porosity of which is 75 to 95%. 2. Agglomerate according to claim 1, characterized in that the mineral excretion of embedded, crystalline inclusions is formed from a primary armullite. 3. Agglomerate according to claim 1 or 2, characterized in that the metal or metal oxide-containing fine material is a granular mill scale. 4. Agglomerate according to claim 3, characterized in that the granular mill scale with fine to coarse grain mill scale particles is embedded in the sintered matrix, with up to 50% of the proportion of mill scale mill scale particles in the grain size range between 1 and 10 mm. 5. agglomerate according to claim 3, characterized in that the granular mill scale up to 90% consists of mill scale particles with a grain size less than 1 mm. 6. Agglomerate according to claim 1 or 2, characterized in that the metal or metal oxide-containing fine material consists of metal powder, metallic grinding dust and / or metal oil shavings. 7. agglomerate according to one of claims 1 to 6, characterized in that the agglomerate (1) has a punching or piercing shape with a head-side crater depth (2).