Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1981-07-15
1983-09-06
Lewis, Michael L.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 3, 264117, C22B 7244
Patent
active
044027362
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a cold bonding process for pelletizing particles and more particularly for pelletizing ore fines.
The invention will herein be described with particular reference to its use in pelletizing iron ores, but it will be understood not to be limited to use in agglomerating that material.
BACKGROUND ART
Since the 1950's, pelletizing has been widely practised as a method of agglomerating iron ore fines as an aid to materials handling and transport. The first large plant in the United States with a capacity in excess of 6 million tons per annum commenced operation in 1955 and by 1975 iron ore pellet production in the United States was almost 60 million tons per annum. Pelletizing plants are now operated in many countries including Australia to facilitate intra and international transport of iron ores and their use in steel making.
The most widely used process is know as the "Fired Pellet", "Indurated" or "Hot Bonding" process and consists of two distinct operations; forming pellets at atmospheric temperature and then firing them at high temperature which is meant a temperature in the region of 2350.degree. F. (1300.degree. C.). In the first operation the pellets are first formed by rolling moist fine ore in either a horizontal drum, or more usually an inclined disk, to form spheres known as "green balls" or pellets. At this stage the pellets are required to have adequate strength to withstand handling to the firing stage and sometimes a minimum quantity of an inorganic or an organic binder is added to assist in achieving such adequate strength. In the second operation the pellets are fired. Firing is normally carried out in shaft furnaces, rotary kilns or travelling grate furnaces using gas or oil as fuel. The resulting fired pellets are typically spheroidal, of approximately 14-15 mm diameter, and have a cold compression strength of approximately of 500 lbs. force per pellet. "Cold compression strength" as herein used in a term familiar to those skilled in the art and is a measure of the load required to be applied to cause crushing of a substantially spherical pellet of predetermined diameter placed between two plates of an Instron tester or the like. As such they may be repeatedly bulk handled for example in loading to railway cars, unloading of railway cars, at port facilities, at steel works and the like, and withstand the rigours of transportion in bulk.
By virtue of the scale of throughput required by the industry, the capital investment in equipment necessary for the firing stage of pelletizing is major, and the energy consumption is high. The fuel costs of operating a typical installation are said to total millions of dollars per annum.
Many attempts have been made to find alternative agglomeration processes and in particular processes which would avoid the necessity for firing. To date no such process has proved satisfactory. The general requirements for good quality agglomerates include sufficient strength for handling and for long distance transportation, the ability to withstand outside storage without substantial detrimental effects, and complete reducibility in iron and steel furnaces without premature degradation or excessive swelling.
Numerous so called cold bonding processes have been developed in which inorganic binders such as cement, lime, magnesia, clays, bentonites and the like, or organic binder materials such as tars, petroleum residues, waxes, flours, paper industry by-products and polymers have been employed. In general the resulting pellets have been either too expensive to produce and/or have been deficient in strength, impact resistance or abrasion resistance. None of the organic and few of the inorganic binder cold bonding processes have warranted commercial production usage and of the latter none has achieved widespread acceptance.
An objective of the present invention is therefore to provide a method for pelletizing mineral fines which avoids the necessity to fire the pellets at high temperature while producing pellets of sufficient stre
REFERENCES:
patent: 2792298 (1957-05-01), Freeman
patent: 2833642 (1958-05-01), Barker et al.
patent: 2914394 (1959-11-01), Dohmen
patent: 2914395 (1959-11-01), Davies
patent: 3154403 (1964-10-01), Stickley et al.
patent: 3493642 (1920-02-01), Capes
Lewis Michael L.
N. B. Love Industries Pty. Limited
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