Fluxing agent, process of its production, agglomeration mixture and use of slug from secondary metallurgy

Abstract

The invention relates to fluxing agents for the agglomeration process based on slag from the secondary metallurgy, the use of these fluxing agents in the process of agglomeration in the manufacture of the agglomerate designed for the use as a metallic charge in blast furnaces and a process of production of fluxing agents based on slag from the secondary metallurgy or based on a mixture of slag from the secondary metallurgy with other materials.

Claims

1. A sinter mixture usable as a charge in an agglomeration process comprising (a) a metallic ore; (b) a fluxing agent; (c) a modified slag from secondary metallurgy produced by a process comprising (a) providing slag formed during a tapping and treatment operation in which crude steel is deoxidized with a deoxidizer comprising (i) aluminum, (ii) aluminum, silicon and manganese or (iii) silicon and manganese such that the slag comprises oxides of the deoxidizer, and (b) modifying the slag so that at least 90% by weight of the slag has a grain size under 100 mm; and (d) a fuel; wherein the modified slag from secondary metallurgy is present in the sinter mixture in an amount of less than 10% by weight, wherein the sinter mixture contains less than 8% by weight of Al.sub.2O.sub.3, and wherein the modified slag from secondary metallurgy comprises a mixture of oxides, including CaO, Al.sub.2O.sub.3, SiO.sub.2, MgO, MnO, and FeO and has a smelting temperature that is lower than 1600 C., wherein a total content of the oxides in the modified slag from secondary metallurgy is higher than 75% by weight, a content of CaO is higher than 40% by weight, a content of sulfur is lower than 2.5% by weight, and wherein the modified slag from secondary metallurgy has a content of FeO of not more than 5% by weight.

2. The sinter mixture according to claim 1, wherein the fluxing agent and the modified slag from secondary metallurgy together form a fluxing mixture, and the fluxing mixture comprises, in addition to the modified slag from secondary metallurgy, a waste material.

3. The sinter mixture according to claim 2, wherein a ratio of CaO/SiO.sub.2 by weight and CaO/Al.sub.2O.sub.3 by weight in the fluxing mixture is higher than 1.25.

4. The sinter mixture according to claim 1, comprising less than 5% by weight of Al.sub.2O.sub.3.

5. The sinter mixture according to claim 1, wherein the fluxing agent and the modified slag from secondary metallurgy together form a fluxing mixture.

6. A sinter mixture usable as a charge in an agglomeration process comprising (a) metallic ore; (b) a fluxing agent; (c) a modified slag from secondary metallurgy produced by a process comprising (a) providing slag formed during a tapping and treatment operation in which crude steel is deoxidized with a deoxidizer comprising (i) aluminum, (ii) aluminum, silicon and manganese or (iii) silicon and manganese such that the slag comprises oxides of the deoxidizer, and (b) modifying the slag so that at least 90% by weight of the slag has a grain size under 100 mm; and (d) a fuel; wherein the modified slag from secondary metallurgy is present in the sinter mixture in an amount of less than 10% by weight, wherein the sinter mixture contains less than 8% by weight of Al.sub.2O.sub.3, and wherein the modified slag from secondary metallurgy has a content of FeO of not more than 5% by weight.

7. A method for forming a sinter mixture usable as a charge in an agglomeration process, wherein the sinter mixture comprises (a) a metallic ore; (b) a fluxing agent; (c) a modified slag from secondary metallurgy produced by a process comprising (a) providing slag formed during a tapping and treatment operation in which crude steel is deoxidized with a deoxidizer comprising (i) aluminum, (ii) aluminum, silicon and manganese or (iii) silicon and manganese such that the slag comprises oxides of the deoxidizer, and (b) modifying the slag so that at least 90% by weight of the slag has a grain size under 100 mm; and (d) a fuel; wherein the modified slag from secondary metallurgy is present in the sinter mixture in an amount of less than 10% by weight, and wherein the sinter mixture contains less than 8% by weight of Al.sub.2O.sub.3, the method comprising the steps of: (i) preparing a fluxing mixture by modifying the slag from secondary metallurgy by gradually cooling the slag from secondary metallurgy at a cooling rate of up to 200 degrees Celsius per hour to cause spontaneous disintegration of part of the slag and then sizing or crushing a remainder of the slag such that at least 90% by weight has the grain size below 100 mm and mixing the modified slag from secondary metallurgy with the fluxing agent to form the fluxing mixture; and (ii) admixing the fluxing mixture with the metallic ore and the fuel and optionally another fluxing agent, waste material or both to form the sinter mixture, wherein the modified slag from secondary metallurgy is present in the sinter mixture in an amount of less than 10% by weight.

8. The method according to claim 7, wherein the sinter mixture is charged into a blast furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Explanation of the invention does not need FIGURES.

DETAILED DESCRIPTION OF THE INVENTION

(2) The method of production of the agglomerate, designed for the use as a charge into blast furnaces, can be used in accordance with the invention for various types of slag or slag mixtures of the secondary metallurgy as a substitution or a partial substitution for limestone, lime and dolomite or other steel or metal additives.

(3) The invention will be closer illustrated in the following examples of the implementation according to the invention:

Example 1

(4) Steel from a converter or from electric arc furnaces or similar devices, such as the hybrid device Conarc, is tapped into a ladle, and deoxidized through aluminium, silicon, manganese, or other deoxidizing elements. In such a way modified steel is processed in a secondary metallurgy device and after the processing it is ready for casting, for example on a device for a continuous casting or in the form of an ingot. After the casting, the remaining slag and the remnants of steel in the ladle are poured into a slag pot and after filling up thereof, they are transported on a slag deposit. After cooling and solidifying, coarse pieces of the remaining steel are removed mechanically. Slag disintegrates mostly spontaneously to a fine dust mass. Slag disintegrates, if the cooling rate is lower than 200 C. per hour. The slag, which does not disintegrate spontaneously, is mechanically crushed on the granulometry under 100 mm or it is utilised in a different manner. In such a way modified slag is ready for a further use as a raw material for the agglomeration process. Slags with lower contents of SiO.sub.2 (below 15%) are more appropriate for the above use.

(5) Slags and slag-forming materials are admixed to an agglomeration mixture so that the generation of unnecessary amount of slag in the blast-furnace process is prevented. The composition of fluxing agents in the agglomerate is carried out so that the resulting ratio of CaO/SiO.sub.2 in the agglomerate is higher than 0.5 and optimally around 0.8-1.5. Also the total content of Al.sub.2O.sub.3 is limited, namely by the value of 8%. For example, ores and ore concentrates have 4 to 10% SiO.sub.2 with the content of CaO around 2% and, therefore, it is necessary to add the corresponding amount of CaO so that the ratio of CaO to SiO.sub.2 matches a value of 0.8 to 2.5 in accordance with the practice of a particular blast furnace plant, advantageously in the range of 0.8 to 1.5. From these ratios and from the composition of slag from the secondary metallurgy or its mixture with other materials, it is simply possible to derive the necessary additions of the slag or the slag mixture. The respective slag from the secondary metallurgy constitutes a fluxing agent applicable in the agglomeration process.

Example 2

(6) Slag from the secondary metallurgy having the granulometry under 100 mm is mixed with other slag-forming materials such as lime, limestone, dolomite, dolomite limestone, magnesite, optionally with a fuel in the form of fine-grained coke. The mixture, prepared in such a way, is ready for the subsequent use as a fluxing agent for the agglomeration process.

Example 3

(7) The slug from the production of aluminium-killed steel is mixed with the slug from the steel killed by silicon or manganese. After mixing and adjustment of granulometry, the slug is ready for the subsequent use as a fluxing agent for the agglomeration process.

Example 4

(8) In the agglomeration process, a part or entire slag from the secondary metallurgy created in the respective steel-making plant is used, and in the case of low transport costs, it is possible to admix to this slag also slag from the secondary metallurgy of nearby steel-making plants, especially from electric steelworks. The respective slag from the secondary metallurgy constitutes a fluxing agent applicable in the agglomeration process.

Example 5

(9) After cooling, coarse metal pigs are first removed from the slag from the secondary metallurgy of the production of aluminium-killed steel, and, subsequently, the slag is graded on graders into individual fractions. For the direct use in the agglomeration process, the slag fractions with granulometry under 100 mm, conveniently under 20 mm are used. The remaining coarse pieces of slag are crushed to finer fractions for the use in the agglomeration process, or they are used in a different way. The slag mixture, processed in such a way, is evenly scattered into slag heaps, preferably in doses from 10 tonnes.

(10) Slag can be added to the charge in a single portion or in several portions in individual stages of the homogenization, however, at the latest into a pelletizing drum or into a device with the same function so that the total content of slag in the charge of the agglomeration process corresponds to a maximum of 10% of the total charge into the agglomeration.

Example 6

(11) The slag produced in accordance with the example 1 is further enriched with materials such as lime, limestone, dolomite, dolomite limestone, undersize coke, waste materials or by-products of metallurgical or cement industry. Slag or slag-forming mixtures with recycled materials can be added individually or in arbitrary mixtures, and they are added to the metallic charge in an arbitrary phase of homogenisation in a single portion or in several subsequent steps, however, at the latest into a pelletizing drum or into a device with the same function. The amount of slug from the secondary metallurgy is always lower than 10% by weight of the total weight of the charging materials of the agglomeration process.

Example 7

(12) This example consists in the utilisation of slags from the production of silicon and manganese-killed steel, the total content of SiO.sub.2+MnO+FeO of which is higher than 15% by weight. Also these slags can be used for the production of agglomeration mixtures or even added directly into such mixtures. Similarly as in the example 1 and 2, these slags are freed from the coarse pigs, subsequently sorted, possibly also crushed and prepared for the use. The fractions under 100 mm, conveniently under 20 mm are used. These slugs can be used directly or mixed with other materials similarly as described in the example 2.