Combustible briquette especially for the iron and steel industry

Abstract

A briquette comprised of iron and steel industry waste materials and carbon as a fuel source thereby creating a self contained delivery system for the recovery of iron or steel. The briquette is held together by a binding system that can withstand the extremely high temperatures required to make iron and steel.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 60/158,670, filed on Oct. 8, 1999.

BACKGROUND OF THE INVENTION

[0002] Many waste materials are generated in the production of iron and steel. Some are listed as hazardous waste and must be disposed of at great cost, others must be hauled off and piled up or buried also at significant cost. Most of these waste materials contain high levels of iron oxides, the raw material from which iron and steel are made. Carbon and other valuable materials used in the iron and steel making processes are also present in some of these materials in recoverable quantities. The iron and steel industry has accordingly tried a wide variety of methods to recycle such wastes, including: loading or injection of iron oxides into the furnace, the use of a variety of binders including coal tar, molasses, pitch, sodium silicate and cement, all of which disintegrate on entering the furnace.

[0003] These attempts have used more energy, caused additional wear on electrodes (in the case of electric arc furnaces), caused additional wear on the fire brick as iron oxides attack the fire brick material, and increased the iron oxide content of the slag and furnace dust.

SUMMARY OF THE INVENTION

[0004] The present invention, in its preferred embodiment, provides the electric arc, blast furnace, blast oxygen furnace, and cupola with a briquette comprised of iron and steel industry waste materials and carbon as a fuel source thereby creating a self contained delivery system for the recovery of iron or steel. The briquette is held together by a binding system that can withstand the extremely high temperatures required to make iron and steel.

DETAILED DESCRIPTION OF THE INVENTION

[0005] To form the present inventive briquette in the tests, steel industry waste iron oxides and carbon in the form of coke breeze were homogeneously mixed with an aqueous sodium silicate binder, compressed into a 2″ in diameter by 3″ cylindrical shape, and cured until the moisture was gone and the briquettes were hard. The briquettes were added directly into the molten steel in an electric arc furnace at the beginning of the second charge, with scrap steel added on top of the briquettes. The addition of magnetic materials to the briquettes makes the briquettes themselves magnetic and is valuable for material handling purposes.

[0006] Carbon is a key ingredient. The stripping of the oxygen atom from the iron oxide molecule is an endothermic reaction which reduces it to molten iron. Then the bonding of the carbon atom with the oxygen atom it has stripped from the iron oxide molecule forms carbon monoxide gas which surrounds the briquette and acts as an insulating envelope, an exothermic reaction which produces considerable energy and allows the briquette to gradually decompose in the molten bath instead of falling apart. As the briquette dissolves, the carbon monoxide gas bubbles up through the molten iron or steel stripping nitrogen from the iron or steel and forming carbon dioxide, also an exothermic reaction producing even more energy. The net result is that these briquettes add substantial additional heat to the melt. This effect is sometimes referred to as “carbon boil”, and while the blast and blast oxygen furnace steel producers have achieved it, the electric arc steel makers have been trying to get it in their furnaces for many years, without success.

[0007] An example of the way the carbon to iron oxide ration is determined is as follows:

FeO+C→Fe+CO

72+12=6:1 ratio

Fe304+4C→3Fe+4CO

232+48=4.8:1 ratio

Fe203+3C→2FE+3CO

160+36=4.4:1 ratio

[0008] These ratios will change, for example, depending upon the types of iron oxides used, the extent to which the mixture is homogeneous, the extent to which the actual reaction mirrors the theoretical reaction, the desired delivery system for the introduction of carbon into the iron or steel making process (including the desired temperature at which the carbon is released into the melt), and the amount of carbon desired in the final iron or steel product. For example, for high carbon steel, more carbon can be added. If electrical energy costs are of no concern, less carbon can be added. Carbon content can also be adjusted to control the nitrogen content.

[0009] While the amount of carbon to be added is dependent on the above factors, an important aspect is that the amount of carbon exceed the stochiometric ration. In the tests 20% more carbon was added than was called for.

[0010] Carbon can be supplied by coke breeze, coal, petroleum coke and other materials as are known in the art, depending upon cost, availability, and the particle sizes of the carbon and the waste materials. The preferred binder is aqueous sodium silicate (such as “K” brand sodium silicate from the PQ Corporation) using between 5% and 20% sodium silicate by weight. The ultimate desired concentration is dependent on the moisture content and particle sizes of the specific waste materials used.

[0011] Once homogeneously mixed, the agglomerating mixture is then put into a die of the appropriate size and shape and compressed sufficiently to remove all air and voids from the briquette and to compact the material without driving the aqueous binder out. The briquette is then either cured from exposure to the air, or heat is applied to hasten its curing. The size of the briquette is important since it must be large enough to create the insulating envelope of carbon monoxide and small enough to be easily charged into the furnace. In our tests, 2″ in diameter by 3″ in height briquettes worked successfully, and further tests of varying sizes will be conducted.

[0012] This briquette has shown it converts the iron oxides to molten steel, adds energy to the melt, reducing melt time and increasing productivity, insulates the electrode, reducing wear, lowers the nitrogen content of the steel, reduces the amount of iron oxides in the slag, and does not affect the fire brick.

[0013] While preferred and alternate embodiments of the present invention have been shown, it is to be understood that the present inventive briquette and its method of manufacture can be altered, with the steps of the process changes and materials substituted without departing from the scope and spirit of the invention as disclosed herein.

Claims

1. A briquette comprising: an iron oxide and carbon mixed with an aqueous sodium silicate binder.

2. The briquette of claim 1, wherein the mixture is compressed to a desired shape and cured until hard.