Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1999-11-10
2001-04-24
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S482000, C075S762000, C075S763000
Reexamination Certificate
active
06221127
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to the conversion of fine grained iron ore pellets into hardened iron oxide pellets suitable as a feed material for making steel. More specifically, the present invention relates to a rotary kiln useful in heat hardening the iron ore pellets while reducing the overall fuel consumption and NO
x
production. More generally, the present invention relates to a high temperature rotary kiln process where a longitudinal distribution of air and fuel along the length of the kiln enhances the processing condition of the solids being treated.
It is well known that most mineral ores in their natural state are low in concentration relative to a specific element and therefore require beneficiation which renders this material ore to a fine, powdery consistency. In the case of magnetite and hematite iron ores, this fine powdery state is unsuitable for transportation and many times unsuitable for further processing such as a feed to blast furnaces, open hearth furnaces or electric arc furnaces. A number of methods have been tried, with varying degrees of success, for agglomerating such fine ore particles to make the particles more suitable for handling, shipment and use in downstream processing equipment. In the following discussion, magnetite ore will be used as the feed material in the illustrations provided.
A well known agglomerating method involves converting the fine, powdery ore into balls or pellets that are transferred onto a traveling grate where the pellets are subjected to a cross-flow of hot gases to dry and pre-harden the pellets. While being heated, the iron ore pellets begin to oxidize, at which time the magnetite (Fe
3
O
4
) phase of iron begins to transform into hematite (Fe
2
O
3
). The pellets are then discharged from the traveling grate into a directly fired rotary kiln where the pellets are tumbled and subjected to further heating by a centerline burner in a counter-flowing oxidizing atmosphere with temperatures ranging between 2200-2450° F. The pellets are subsequently discharged into an annular cooler where they are further oxidized to the point of almost 100% oxidation. Since the oxidation of the ore is an exothermic reaction, the further oxidation of the product stream in the annular cooler raises the temperature within the cooler, which decreases its cooling efficiency.
The Rierson U.S. Pat. No. 5,248,330, incorporated herein by reference, improves upon the above-identified, generally known process by introducing an oxidizing gas, such as air, beneath the bed of pellets within the rotary kiln such that the oxidizing gas flows radially upward through the tumbling bed of pellets. The radially injected under-bed oxidizing gas intimately contacts the surface of the tumbling pellets and oxidation occurs. The process disclosed in the Rierson '330 patent causes nearly the entire oxidation to occur before the annular cooler, which relieves the burden on the downstream cooler, in which 30-40% of the oxidation previously occurred. The introduction of the oxidizing gas into the rotary kiln causes the oxidation to occur within the rotary kiln rather than in the annular cooler, which allows the annular cooler to operate more efficiently in cooling the iron oxide product.
Although the disclosure of the Rierson '330 patent has proved to be successful, a problem exists in the amount of NO
x
produced during the transformation of the magnetite into hematite. Specifically, the high temperature firing of the centerline burner required to maintain the temperature within the rotary kiln generates a significant amount of NO
x
, which is considered to be an environmental pollutant. The production of NO
x
occurs due to the high intensity firing of the centerline burner contained within the rotary kiln.
Therefore, it is an object of the present invention to decrease the amount of NO
x
produced during the oxidation of mineral ores such as magnetite. An additional object of the invention is to provide a system for oxidizing ores using a traveling grate and rotary kiln in which the ore is substantially oxidized prior to being discharged from the rotary kiln. Further, it is an object of the present invention to maintain the level of oxidation of iron ore prior to its introduction into the cooler while at the same time reducing the external fuel consumption and decreasing the NO
x
production.
SUMMARY OF THE INVENTION
The present invention is a method and apparatus for use in oxidizing an iron ore product stream. The rotary kiln of the invention includes a plurality of fuel distribution pipes that are positioned along a portion of the outer surface of the rotary kiln. The fuel distribution pipes are each associated with a supply pipe having a plurality of individual ports that provide a flow passageway from the fuel distribution pipe to the open interior of the rotary kiln.
Each of the fuel distribution pipes extending along the exterior of the rotary kiln is coupled to a common fuel distribution manifold through a fuel valve. The fuel valve can be selectively operated between a closed position to prevent the flow of fuel into the associated supply pipe and thus the open interior of the rotary kiln or an open position to allow the fuel to flow through the associated supply pipe and into the kiln interior.
In addition to the plurality of fuel distribution pipes, the rotary kiln of the present invention includes a plurality of air distribution pipes positioned adjacent to the fuel distribution pipes along the outer surface of the rotary kiln. The air distribution pipes are also each associated with one of the supply pipes having a plurality of individual ports that provide the flow passageway into the open interior of the rotary kiln. Thus, the ports serve the dual function of providing the flow passageway into the kiln for both fuel and air at different times during the rotation of the kiln.
Each of the air distribution pipes extending along the exterior of the rotary kiln is coupled to a second and independent air distribution manifold through an air valve. Each of the air valves can be selectively operated between a closed position to prevent the flow of air into the associated supply pipe and an open position to allow air to flow through the associated supply pipe and into the kiln interior. The fuel and air distribution systems discussed above are completely independent from each other and are designed to permit flow into the kiln's interior at different angular orientations as the rotary kiln rotates.
The air valves spaced around the circumference of the rotary kiln and positioned in the air distribution pipes are each operated in accordance with the invention to allow the oxidizing gas (air) to enter into the open interior of the rotary kiln when the rows of ports associated with the air distribution pipe are in the appropriate angular position(s). In the case where magnetite is being processed, air can be introduced when the rows of ports are oriented both under the bed and over the bed. When air is introduced under the bed, the oxidizing gas flows radially upward through the tumbling product stream to aid in the oxidation process of the product stream. When the oxidizing gas (air) is introduced above the bed, the air aids in the combustion of fuel added to the over bed space.
As the kiln continues to rotate, each of the fuel valves positioned in the fuel distribution pipes are opened to allow fuel to flow through the associated supply pipe and associated rows of ports when the fuel distribution pipe and rows of ports are positioned above the product stream bed. The fuel valve remains open to allow fuel to flow into the open interior during a predetermined fuel flow arc of travel. The introduction and distribution of fuel above the product stream causes the fuel to combust over the length of the ported zone and within the heated, oxidizing environment contained in the open interior of the rotary kiln.
Combustion of the fuel introduced, with air, through the rows of ports above the product stream bed length
Andrus Sceales Starke & Sawall LLP
King Roy
McGuthry-Banks Tima
Svedala Industries Inc.
LandOfFree
Method of pyroprocessing mineral ore material for reducing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of pyroprocessing mineral ore material for reducing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of pyroprocessing mineral ore material for reducing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2478105