GB1600711A - Briquet and method of making same - Google Patents

Description

(54) BRIQUET AND METHOD OF MAKING SAME (71) We, MIDREX CORPORATION, a corporation of Delaware, United States of America, of One NCNB Plaza, Charlotte, North Carolina 28280, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a metallized briquet, and a method of making such a briquet.

In the field of agglomeration of mineral ores, there have been proposals for the agglomeration of directly reduced metallized particles or oxide fines. An extremely large number of binder compositions have been developed and patented over the years.

However, no binder is known to the Applicant to be suitable for agglomerating highly metallized finely divided particulates such as iron fines from a direct reduction process, a steel mill, a foundry or the like, either with or without metal oxide fines produced in similar plants or from ore treatment processes in the iron and steel industry, without oxidizing the metallic fines. A significant percentage of finely divided iron particulates or fines are produced in the operation of a direct reduction furnace whereby iron ore or pellets are reduced to highly metallized particles, such as pellets or lumps, by direct contact with a reducing gas. such as a mixture of hydrogen and carbon monoxide. These fines are normally discarded or stockpiled and constitute a waste material since heretofore there has been no suitable binder available for agglomerating these fines.Sintering or other treating method normally causes oxidation of the fines which thereupon require an additional reduction step. This is, of course, extremely inefficient inasmuch as the particulars are reduced twice.

Another method for utilizing fines that has been tried is to seal the fines into drums and charge the drums filled with fines into a steelmaking furnace. This is an extremely expensive method of recovering the fines because of high handling costs and drum expense. In addition, the finely divided particles constitute a health hazard for workers as well as a dust problem in the furnace.

Briquets have been found to be a very desirable charge material in iron or steelmaking.

They are particularly suitable for foundries. The high specific gravity enables briquets to penetrate the slag layer on a molten metal bath in an induction furnace more readily than other, lighter charge materials. The large size of briquets prevents them from trickling through a furnace charge as is common with fine materials, particularly when employed as a charge material for cupolas. The quality of the present binder allows the addition of coke breeze, ferro-alloys and other materials to the briquets, which can be stored and handled in the same manner as steel scrap. The high strength of the briquets, and the rust inhibiting properties of the binder allow outdoor storage and generally rough handling. The binder composition also makes it possible to tailor-make briquets for particular applications.

The present invention provides a metallised iron briquet consisting, by weight, essentially of from about 85 percent to about 95 percent directly reduced metallized iron and from about 5 percent to about 15 percent of a binder comprising only: a) from about 15 to about 40 percent hydrated lime, b) from about 15 to about 45 percent liquid sodium silicate, as herein defined, and c) up to 60 percent water.

The present invention also provides a briquet consisting, by weight, essentially of from about 85 to about 95 percent of particulate material selected from directly reduced finely divided metallized material, metal oxide fines, finely divided metal ores, and mixtures thereof and from about 5 to about 15 percent of a binder comprising only: a) from about 15 to about 4() percent hydrated lime, b) from about 15 to about 45 percent liquid sodium silicate, as herein defined, and c) up to 60 percent water.

The present invention further provides a method of making a briquet from particulate material selected from directly reduced finely divided metallized material, metal oxide fines, finely divided metal ores, and mixtures thereof, comprising: i) mixing from 85 to ')5 percent of particulate material with from about 5 to about 15 percent of a binder comprising only:: 1) about 15 to about 40 percent hydrated lime in powdered form, 2) about 15 to about 45 percent aqueous solution ol liquid sodium silicate, as herein defined, and '.) up to (1() percent witer to form a free flowing yet dense briquet feed material; b) densifving said feed material: ind c) forming said feed material into briquets.

U.S. Patent 2.205.043 teaches a binder of water glass i.c. sodium silicate, and limestone or dolomite. \Ne have determined that the invented binder is markedly superior to that of U.S. Patent No 2,205.(143 as is explained in gl-cntcr detail below.

The binder of the present invention consists essentially of liquid sodium silicate, hydrated lime. and water. The binder particularly disclosed herein has exceptional characteristics including high green strength tad rust inhibiting capability.

In a particular embodiment of the invention, the hinder material is mixed with finely divided metallized material such is directly reduced sponge iron fines to form a free flowing feed material. The feed material is mixed and predensified by apparatus such as a mix muller, then formed into briquets by known briquet formation equipment. Suitable briquetting machines are lautlht by U.S. Patent 3,897,183 and numerous other patents.

The broad range of the binder composition. by weight, is from about 15 to about 40 percent hydrated lime, front shout 15 to about 45 percent liquid sodium silicate and up to 60 percent water. The preíc rred r;inge is 15 to 30 percent hydrated lime, 30 to 45 percent liquid sodium silicate and remiiiitler water. Another suitable range which is very economical is from about 30 to about 4(1 pel cent hydrated lime, from about 15 to about 25 percent liquid sodium silicate and up to 55 percent water.

Liquid sodium silicate is an aqueous solution, having a concentration of 3(3 to 55 percent bv weight, depending on the type of sodium silicate. Sodium silicate is a generic term for a family of chemicals composed of sodium oxide (Na2O), silica (SiO2) and usually water(H2O). The proportion of Na2O to SiO2 in sodium silicates is expressed as a weight ratio with the alkali component held at unity. Commercial grades of liquid sodium silicate are usually concentrated for convenient handling. For instance, sodium silicate having a weight ratio of 3.22 can readily be handled up to a solids content of about 39.8 percent which is equivalent to approximately 43 degrees Barm6.

The liquid sodium silicate solution which is employed in the invention has a weight ratio of 3.22, a solids content of 37.6 percent by weight, a density of 41.0 degrees Baumé, and a viscosity of 180 centipoise. The term liquid sodium silicate" as used throughout this specification and claims refers to this 37.6 percent solids sodium silicate solution unless otherwise specified.

It is preferable to maintain the Na2O at the lowest possible ratio to SiO2. The 3.22 mixture, which is also the most readily available commercially, is the preferred ratio.

The sodium silicate solution brings to the binder composition the property of rendering the subsequent agglomerates or briquets rust resistant.

The hydrated lime of the binder composition is preferably in powdered form, and most preferably all minus 100 Tyler mesh. The hydrated lime produces plasticity of the mixture to be briquetted and improves briquet strength.

The dry component of the invented binder composition is metered into the briquet feed material together with the liquid binder component when the feed material is mixed before briquetting.

Three binder compositions were compared for effectiveness in bonding briquets: Composition A in accordance with U.S. Patent 2,205,043; Composition B in accordance with a prior art proposal; and Composition C in accordance with the present invention.

These binder formulations are as shown in Table 1.

TABLE I Component Composition A Composition B Composition C Sodium Silicate 21.2% 21.2So 21.2% Hydrated Lime -0- 18.2% 36.4No Powdered Pitch -0- 18.267c -0 Limestone 36.4% -0- -0 Water 42.4CHo 42.4% 42.4% Percentages are by weight.

All of the briquets were produced using the following conditions: Mulling time - 2 minutes: Briquet machine setting hydraulic pressure - 1600 p.s.i.g.

Accumulator pressure - 900 p.s.i.g.

The material leaving the briquetting rolls was screened on a one-half inch screen to determine the briquetting efficiency. The briquets were evaluated by drop tests of freshly produced briquets and of "aged" briquets about 24 hours after the time of production. Each sample consisted of 2 kilograms of briquets which were dropped 12 feet onto a steel plate.

Two batches of each type were tested and the results were averaged. The tests were repeated for Composition B.

The results of the comparison tests are shown on Table II below: TABLE II The mesh standard used is Tyler mesh.

Binder Composition A B B (Repeated) C briquetting efficiency (%2") 21.4aSs 20.9% 22.3% 18.0% 1 5 1 5 1 5 1 5 Fresh Briquets drop drops drop drops drop drops drop drops %+1/2" 68.8 18.2 62.4 16.8 73.4 20.3 84.1 36.1 %+3M 74.5 25.6 70.9 26.0 79.0 30.0 86.8 46.6 %+6M 79.0 31.8 76.1 33.6 83.4 38.9 89.9 54.9 %-6M 21.0 68.2 23.9 66.4 16.6 16.1 10.1 45.1 Briquets ] 5 1 5 1 5 1 5 Aged 24 hours drop drops drop drops drop drops drop drops 76.1 76.1 24.7 76.1 24.7 84.5 31.5 87.9 38.1 93.2 60.4 nxo+3M 80.9 30.5 87.5 41.3 90.9 49.4 94.7 67.2 %+6M 83.8 36.1 90.4 50.2 92.9 57.8 96.0 73.2 %-6M 16.2 63.9 9.6 49.8 7.1 42.2 4.0 26.8 Briquets made with the binder Composition C in accordance with the present invention clearly show test results superior to the binders of the prior art references. Note that the briquetting efficiency is greater as well as the green strength and aged strength of the briquets. In addition, briquets made with the invented binder are passivated against fresh water. Briquets wetted with fresh water and placed into an insulated vented 55 gallon drum for four days showed no heating during and no rusting at the end of the test. Further, briquets soaked in fresh water for three days did not rust during succeeding air drying.

From the foregoing, it is readily apparent that the binder composition particularly disclosed produced a briquet which has high green strength, high cured strength. high overall quality, and is insensitive to moisture.

WHAT WE CLAIM IS: 1. A metallized iron briquet consisting, by weight, essentially of from about 85 percent to about 95 percent directly reduced metallized iron and from about 5 percent to about 15

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE I Component Composition A Composition B Composition C Sodium Silicate 21.2% 21.2So 21.2% Hydrated Lime -0- 18.2% 36.4No Powdered Pitch -0- 18.267c -0 Limestone 36.4% -0- -0 Water 42.4CHo 42.4% 42.4% Percentages are by weight. All of the briquets were produced using the following conditions: Mulling time - 2 minutes: Briquet machine setting hydraulic pressure - 1600 p.s.i.g. Accumulator pressure - 900 p.s.i.g. The material leaving the briquetting rolls was screened on a one-half inch screen to determine the briquetting efficiency. The briquets were evaluated by drop tests of freshly produced briquets and of "aged" briquets about 24 hours after the time of production. Each sample consisted of 2 kilograms of briquets which were dropped 12 feet onto a steel plate. Two batches of each type were tested and the results were averaged. The tests were repeated for Composition B. The results of the comparison tests are shown on Table II below: TABLE II The mesh standard used is Tyler mesh. Binder Composition A B B (Repeated) C briquetting efficiency (%2") 21.4aSs 20.9% 22.3% 18.0%

1 5 1 5 1 5 1 5 Fresh Briquets drop drops drop drops drop drops drop drops %+1/2" 68.8 18.2 62.4 16.8 73.4 20.3 84.1 36.1 %+3M 74.5 25.6 70.9 26.0 79.0 30.0 86.8 46.6 %+6M 79.0 31.8 76.1 33.6 83.4 38.9 89.9 54.9 %-6M 21.0 68.2 23.9 66.4 16.6 16.1 10.1 45.1 Briquets ] 5 1 5 1 5 1 5 Aged 24 hours drop drops drop drops drop drops drop drops 76.1 76.1 24.7 76.1 24.7 84.5 31.5 87.9 38.1 93.2 60.4 nxo+3M 80.9 30.5 87.5 41.3 90.9 49.4 94.7 67.2 %+6M 83.8 36.1 90.4 50.2 92.9 57.8 96.0 73.2 %-6M 16.2 63.9 9.6 49.8 7.1 42.2 4.0 26.8 Briquets made with the binder Composition C in accordance with the present invention clearly show test results superior to the binders of the prior art references. Note that the briquetting efficiency is greater as well as the green strength and aged strength of the briquets. In addition, briquets made with the invented binder are passivated against fresh water. Briquets wetted with fresh water and placed into an insulated vented 55 gallon drum for four days showed no heating during and no rusting at the end of the test. Further, briquets soaked in fresh water for three days did not rust during succeeding air drying.

From the foregoing, it is readily apparent that the binder composition particularly disclosed produced a briquet which has high green strength, high cured strength. high overall quality, and is insensitive to moisture.

WHAT WE CLAIM IS: 1. A metallized iron briquet consisting, by weight, essentially of from about 85 percent to about 95 percent directly reduced metallized iron and from about 5 percent to about 15

percent of a binder comprising only: a) from about 15 to about 40 percent hydrated lime, b) from about 15 to about 45 percent liquid sodium silicate, as herein defined, and c) up to 60 percent water.

2. A briquet consisting, by weight, essentially of from about 85 to about 95 percent of particulate material selected from directly reduced finely divided metallized material, metal oxide fines, finely divided metal ores, and mixtures thereof and from about 5 to about 15 percent of a binder comprising only: a) from about 15 to about 40 percent hydrated lime, b) from about 15 to about 45 percent liquid sodium silicate, as herein defined, and c) up to 60 percent water.

3. A briquet according to claim 2 wherein said metal is iron.

4. A method of making a briquet from particulate material selected from directly reduced finely divided metallized material, metal oxide fines, finely divided metal ores, and mixtures thereof, comprising: a) mixing from 85 to 95 percent of particulate material with from about 5 to about 15 percent of a binder comprising only: 1) about 15 to about 40 percent hydrated lime in powdered form, 2) about 15 to about 45 percent aqueous solution of liquid sodium silicate, as herein defined, and 3) up to 60 percent water to form a free flowing yet dense briquet feed material, b) densifying said feed material, and c) forming said feed material into briquets.

5. A method according to claim 4 wherein said metal is iron.

6. A method according to claim 4 wherein the particle size of said hydrated lime is all minus 100 Tyler mesh.

7. A briquet when made by the method of any one of claims 4-6.