US-12624406-B2 - Process and system for the production of iron nuggets

US12624406B2US 12624406 B2US12624406 B2US 12624406B2US-12624406-B2

Abstract

A hearth for a traveling hearth furnace for the production of pig iron grade nuggets, the hearth having a synthetic graphite material in direct contact with the process charge in producing a plurality of metallic iron nodules and slag. The process charge including iron containing oxide, a predetermined amount of a reductant and flux, which are carried into and through a reducing, melting and coalescing stages on the hearth, wherein resulting metallic iron nodules and slag are in direct contact with the synthetic graphite material and do not adhere to the synthetic graphite material of the hearth. The absence adherence and ease of removal minimizes any impurities in the pig iron grade nuggets and allows the hearth to be used more than one cycle without the need for any replenishment of the contact surface.

Inventors

John Simmons
Dale Hintsala

Assignees

Carbontec Energy Corporation

Dates

Publication Date: 20260512
Application Date: 20220323

Claims (15)

1 . A process for reducing iron containing oxides to produce a plurality of metallic iron nodules from a process charge including iron containing oxide, a predetermined amount of a reductant and flux, wherein the process charge is carried into a traveling hearth furnace for reducing, melting and coalescing stages to convert the process charge into the plurality of metallic iron nodules and slag components, the process comprising: providing a process charge on a hearth configured to be moved into and through the traveling hearth furnace, the hearth comprising a synthetic graphite material, wherein the process charge is in direct contact with an outer surface of the hearth consisting of the synthetic graphite material, such that the outer surface of the hearth is substantially devoid of a separate layer of carbonaceous material and natural graphite; and carrying the process charge on the hearth within the traveling hearth furnace during the reducing, melting and coalescing stages, wherein the process charge is in direct contact with the synthetic graphite material such that the plurality of metallic iron nodules and slag components are only in direct contact with the synthetic graphite material of the hearth, and wherein each of the plurality of metallic iron nodules contain a sulfur impurity level in an amount less than about 200 ppm.
2 . The process of claim 1 , wherein the synthetic graphite material has a thickness between about 2 mm and about 5 cm.
3 . The process of claim 1 , wherein the synthetic graphite material is configured as two or more layers forming the outer surface of the hearth.
4 . The process of claim 1 , wherein the hearth comprises a monolithic synthetic graphite material.
5 . The process of claim 4 , wherein the monolithic synthetic graphite material has a thickness between about 1 inch and about 12 inches.
6 . The process of claim 1 , wherein the plurality of metallic iron nodules and slag components do not adhere to the synthetic graphite material.
7 . The process of claim 1 , wherein the hearth is devoid of any carbonaceous material in direct contact with the process charge.
8 . The process of claim 1 , wherein the hearth is devoid of any natural graphite material in direct contact with the process charge.
9 . The process of claim 1 , wherein the sulfur impurity level of each of the plurality of metallic iron nodules in an amount less than about 80 ppm.
10 . The process of claim 1 , wherein the plurality of metallic iron nodules comprise pig iron grade nuggets.
11 . The process of claim 10 , wherein the hearth is capable of being used more than one time in a traveling hearth furnace for producing pig iron grade nuggets.
12 . The process of claim 10 , further comprising separating the pig iron phase from the slag phase by one or more of tumbling and/or magnetic separation.
13 . The process of claim 10 , wherein further comprising lauding the pig iron grade nuggets into rail cars, trucks, barges and/or ships for shipment.
14 . The process of claim 11 wherein the synthetic graphite material of the hearth does not need to be replenished for the hearth to be used in more than one cycle within the traveling hearth furnace for producing pig iron grade nuggets.
15 . The process of claim 1 , wherein the hearth comprises a raised edge to confine the iron and slag in a molten state within the hearth during processing, the raised edge preferably comprising synthetic graphite material.

Description

PRIORITY CLAIM This is a U.S. National Stage Application filing under 35 U.S.C. 37 of International Application No. PCT/US2022/021584, filed Mar. 23, 2022, which claims the benefit of U.S. Provisional Application No. 63/164,924, filed Mar. 23, 2021, each of which is hereby incorporated by reference in its entirety. TECHNICAL FIELD This invention relates to the production of pig iron grade nuggets. More specifically, the present invention is directed to the production of pig iron grade nuggets in traveling hearth furnaces by providing a hearth having synthetic graphite in direct contact with the process charge. BACKGROUND Currently, the most commonly used process for the production of pig iron is carried out in a blast furnace. It is well recognized that production of pig iron in that manner is a major contributor to the emission of unwanted gases into the atmosphere, particularly carbon dioxide. For that reason the iron and steel industry has moved in the direction of reducing the use of blast furnaces worldwide. In spite of that effort, virtually all merchant pig iron is still produced in a blast furnace. Merchant pig iron is defined as cold pig iron cast into ingots, granulated, or produced in the form of nuggets that are produced and sold on the market to third party users as ferrous feedstock, such as foundries and electric furnace steel makers, and to integrated steel making operations, which cannot produce sufficient pig iron to satisfy its requirement. In contrast to merchant pig iron produced in a blast furnace, pig iron grade nuggets can be produced in a traveling hearth furnace consuming 30% less energy or more and reducing carbon dioxide emissions. In a traveling hearth furnace, a hearth is moved into and through a reducing furnace carrying a mixture of a reductant, fluxes and iron containing oxides, e.g. iron ore and/or iron containing waste oxides from blast furnace or steel making operations. Currently, basically all merchant pig iron is produced in blast or shaft furnaces and little, if any, produced in hearth furnaces, i.e. linear (tunnel) or rotary hearth furnaces. That is believed to be the result of the complexity and cost of doing so in a traveling hearth furnace U.S. Pat. No. 7,695,544 contains a discussion of the state of the art relative to pig iron grade iron nugget production in a traveling hearth furnace. As disclosed therein, a hearth made from refractory material or has refractory material applied on the surface thereof carries a process charge, which comprises a mixture of a reductant, flux and iron containing oxides (e.g. iron ore), and is moved into, through and/out of a reducing and melting furnace. In the furnace, the process charge goes through drying, preheating, reduction, melting, and coalescence stages to convert the process charge into pig iron grade nuggets or nodules and slag. The disclosure contained in U.S. Pat. No. 7,695,544 is incorporated herein by reference in its entirety. In the prior art, the process charge of a traveling hearth furnace can be in the form of a pellet, briquette or like, carried on a hearth bed into and out of a reducing and melting environment generated in the furnace. As discussed in U.S. Pat. No. 7,695,544, the accepted conventional method is to provide a layer of carbonaceous material (a hearth layer) on the hearth to separate the process charge from the hearth surface. U.S. Pat. No. 7,695,544 teaches that the hearth layer provides separation of the process charge and the molten iron and slag from hearth bed to prevent the nuggets/nodules and slag from engaging the hearth surface. That separation prevents the molten iron and slag from reacting with the hearth to create an interface there between that would cause the solidified nuggets and/or the slag to adhere to the hearth. Such an adherence interferes with the removal of the metallic nuggets/slag form from the hearth at the end of the furnace process. The negatives of such an occurrence are (i) the adherence interferes with separating the metallic iron nuggets and slag from the hearth for post reduction processing to have it in the form of a discrete metallic iron nugget, the form useable in follow on iron foundry and steel making process; and (ii) the hearth could be damaged to the extent that it can't be reused in additional reduction cycles. Therefore, not only will part of the production be lost, but the hearth must be replaced, either of which contributing to increasing the cost of the pig iron grade iron nugget production. It should also be noted that the carbonaceous material as taught in U.S. Pat. No. 7,695,544 is coal, char and/or coke, which adds to the underlying cost of the process and also presents an additional carbon source available for the generation of carbon dioxide and other unwanted gases. The carbonaceous material is also a source of sulfur, the presence of which is to be avoided in steel making process. Sulfur will be absorbed into the produced pig iron grade iron