GB2173213A - An iron bearing briquet - Google Patents

Abstract

A briquet consists essentially of, by weight, 50 to 90% direct reduced iron, 7 to 35% silica, 5 to 15% carbon and optionally a binder such as sodium silicate or a mixture of calcium hydroxide and molasses. The iron is preferably metallized iron fines and the carbon may be coke, coal, pitch or tar.

Description

SPECIFICATION An iron bearing briquet The present invention relates to a briquet having a metallic iron content for use in the manufacture of iron and steel.

In the manufacture of iron and steel, it is customary to make certain additions to the melting furnace, for example, various metalliferous products in the form of alloys such as ferrosilicon. Ferrosilicon normally contains a substantial amount of carbon.

According to the present invention there is provided an iron bearing briquet consisting essentially of, by weight, from 50 to 90% direct reduced iron, from 7 to 35% silica, and from 5 to 15% carbon.

In the briquets of the present invention, metallized iron, silica and carbon thus form the composition of a briquet which is of high value for foundry practice and other iron and steelmaking uses. The briquet avoids the requirement of expensive ferrosilicon additions in the foundry or steel making practice in which it is used.

The briquet of the invention preferably employs metallized iron fines as the basic ingredient in its composition. Previously known briquets employ iron oxide fines. The presence of metallized fines reduces the energy requirement for melting the invented briquet over what is required in prior briquets. Since the iron fines are in the metallized condition, the energy normally required for reducing iron oxide to iron is not a requirement in any process utilizing the invented briquets as feed material.

It is also a theory to which we subscribe, but do not wish to be held, that the iron contained in the invented briquet acts as a catalyst during reduction of the silican contained therein in the melting of the briquet. Of course, since the iron in the briquet need not be reduced before melting, the energy requirement is reduced.

Known prior art patents include Pietsch U.S. Patent 4,032,352. Rehder U.S. Patent 4,179,283, Merkert U.S.

Patent 4,395,284, Querengasser et al U.S. Patent 3,431,103 and Harrison U.S. Patent 1,134,128.

Pietsch teaches a binder composition for agglomerating direct reduced iron fines in order to prevent reoxidation of the metallized iron contained therein. Pietsch does not include granulated silica in his briquet.

Further, he does not include a carbonaceous reductant in the briquet for the purpose of reducing the silica.

His pitch component is present for use as a binder. It is noted that water is an essential ingredient in all of the binder compositions claimed by Pietsch.

Rehder teaches the briquetting of metal oxides only and has no direct reduced iron in his briquet. He utilizes two sources of carbon, a high reactivity and a low reactivity carbon.

Merkert teaches that iron and a binder are optional and are not essential ingredients. He prepares porous compacts for use as a feed material to an electric furnace, the material having an apparent low density and high internal porosity. Merkert states that up to about 15% of the silica weight can be iron particles.

Querengasser et al teach the production of ferro-silicon utilizing a briquet with iront contents as high as 8%. This is substantially lower than the iron contents of the briquet products of the present invention.

Harrison teaches a ferro-silicon product which has from 53 to 54.5% silicon. He states that regular alloys have from 25 to 60% silicon, which is the equivalent of 38 to 66% silica (SiO2), which is substantially more silican than that present in the invented briquet product.

The present invention differs from each of these prior art briquets as set forth above in that the invented briquets contain silica, carbon and iron which is over 60% metallized, when the briquets are made by hot compaction. When the briquets are made by cold compaction, a bonder such as sodium silicate or a mixture of calcium hydroxide and molasses is used.

There is thus a need for an iron-bearing briquet which includes silica, which briquet can be substituted for the more expensive ferrosilicon in various steel making and foundry practices, and for an iron-bearing briquet which contains silica, wherein the principal component is metallized iron fines from a direct reduction furnace.

The briquet of the invention can be either a cold compaction briquet, which requires the use of a bonder, or a hot compaction briquet, which requires no binder.

For a cold compaction briquet, the preferred binders are three parts lime and five parts molasses. Lime for the binder is in the form of hydrated lime, which is calcium hydroxide.

The range of components in the hot compaction briquet is, by weight, from 50 to 90 percent metallized iron fines, from 7 to 35 percent silica (SiO2), and from 5 to 15 percent carbon.

All of these components should be in the finely devided form, preferably less than 3 millimeters.

When preparing a cold compaction binder, from 85 to 99 parts of the mixture of finely divided material is blended with 1 to 15 parts of binder, the optimum cold compaction briquet containing 92 parts of finely divided material and 8 parts of binder.

An iron bearing briquet of the invention consists esssentially of, by weight, from 50 to 90% metallized iron, from 7 to about 35% silica and from 5 to 15% carbon. The iron in the composition is in the form of iron fines, preferably made by direct reduction of iron oxide, and at least 60% metallized, but usually more than 80% metallized. "Metallized", as used.throughout this specification does not mean coated with metal, but means nearly completely reduced to the metallic state, i.e., always in excess of 60% metal, and usually in excess of 80% metal in the material. Such metallized iron in many forms, including pellets, is well suited as feed material for steelmaking furnaces such as an electric arc furnace.Silica is present in fine or granulated form and the carbon is preferably a component of a solid fuel, such as coal or coke that alternatively could be pitch ortar.

Preferably, the particle size of all components is less than 3 millimeters, but most advantageously the particle size of all components will be less than 1.5 millimeters prior to briquetting.

A more advantageous range of components in the briquet is, by weight, from 50 to 70% metallized iron, 15 to 35% silica and 8 to 15% carbon.

The mixture set forth above can be briquetted by hot briquetting at a temperature of at least 6000C and a pressure of at least 6.895 N/mm2(1,000 pounds per square inch) to form a hot iron-bearing briquet. The compacting step is preferably carried out as a temperature of from about 650 to 750"C.

More commonly, it is expected that cold briquetting of the composition will take place wherein from 85 to 99 parts by weight of the composition will be mixed with from 1 to 15 parts of a binder. The preferrred binder is a mixture of calcium hydroxide and molasses in roughly equal parts, with an optimum composition of 3 parts lime to 5 parts molasses. However, each can be present in the amount of from 30 to 70% of the binder.

Alternative binders are sodium silicate, pitch, and tars, other organic or chemical binders, and cements.

The invented briquet product may be charged into a shaft furnace melter, such as a cupola or other melting furnace. Some of the silica in the briquet will be reduced during the melting process, and the metallic silicon will become available to the molten product as an alloying element. Thus it is seen that the present briquets can be substituted for the more expensive ferrosilicon.

In a cupola furnace, which is a melting furnace and not a reduction furnace, a loss in melting productivity results when reduction of both silica and iron oxide must be performed in the furnace. When only the silica must be reduced, that is if the iron oxide has already been reduced to the metallized iron form, the loss in melting productivity is minimized. In order to reduce silica in a briquet, iron must be present.

A briquet consists essentially of metallized direct reduced irons fines, fine or granulated silica, a carbon source such as coke breeze or coal fines, and a binder such as a mixture of calcium hydroxide and molasses.

After the mixture is compressed into a briquet, the briquet can be dried or cured at low temperature such as from 150 to 200"C (300 to 400"F) in order to remove any moisture and to improve the green strength. The green briquet should result in a reduced briquet having a high percentage of silicon, perhaps as much as 50% by weight The following tables compare the chemical analyses of various ferrosilicon compositions with equivalent invented ferrosilica briquets.

TABLE I Ferrosilicon Analysis Ferrosilicon FeSi 5 FeSi 10 FeSi 25 Designation Fe 94.5% 89.5% 74.5% Si 5.0 10.0 25.0 C 0.5 0.5 0.5 TABLE II Ferrosilica Briquet Composition Ferrosilicon FeSi 5 FeSi 10 FeSi 25 Equivalent Metallized 86.7% 75.9% 51.6% Iron Fines SiO2 7.8 15.7 33.5 C 5.5 8.4 14.9 TABLE Ill Ferrosilica Briquet Analysis FeSiS FeSilO FeSi25 Fe 73.5% 64.4% 43.7% FeO 8.3 7.3 4.9 C 6.8 9.5 15.7 SiO2 9.1 16.8 34.3 CaO 0.8 0.7 0.5 Other 1.5 1.3 0.9 The briquet could include additional carbon beyond the stoichiometric requirements in order to have a portion act as fuel to provide the heat of reaction for reduction and supply the necessary energy to heat and melt the reduced iron and silicon to tapping temperature (about 2700"F or 1500 C).

Alternative binders of the matrix type such as coal-tar pitch, petroleum asphalt, Portland cement, clay, or Gilsonite, or binders of the film type such as sodium silicate, plastic resins, starch, Bentonite, or glues, or binders of the chemical type such as hydrated lime and carbon dioxide, sodium silicate and calcium chloride, or sodium silicate and carbon dioxide are all envisioned to be suitable binders for this application.

Claims (10)

1. An iron bearing briquet consisting essentially of, by weight, from 50 to 90% direct reduced iron, from 7 to 35% silicon, and from 5 to 15% carbon.

2. A briquet according to claim 1, wherein the carbon is present as a component of a solid fuel.

3. A briquet according to claim 2, wherein the carbon is present as coke.

4. A briquet according to claim 2, wherein the carbon is present as coal.

5. A briquet according to claim 2, wherein the carbon is present as pitch or tar.

6. A briquet according to any one of claims 1 to 5, wherein the particle size of the components is less than 3 millimeters prior to briquetting.

7. A briquet according to claim 6, wherein the particle size of the components is less than 1.5 millimeters prior to briquetting.

8. A briquet according to any one of claims 1 to 7, wherein said metallized iron is at least 60% metallized.

9. A briquet according to claim 8, wherein metallized iron is at least 80% metallized.

10. An iron bearing briquet according to claim 1, substantially as hereinbefore described.