US2864687A - Pelletizing method - Google Patents

Description

Dec. 16, 1958 T. MYRON PELLETIZING METHOD Filed March 2'7, 1956 his Allarney PELLETIZING METHOD Thomas L. Myron, Pittsburgh, Pa., assignor to United States Steei tl'orporation, a corporation of New Jersey Application March 27, 1956, Serial No. 574,157

1 Claim. (Cl. 75-3) This invention relates to an improved method of pelletizing iron-bearing materials preliminary to fritting.

Before iron-bearing fines can be charged to a blast furnace, they must be formed into larger agglomerates which possess sufiicient mecheanical strength not to dis- :integrate during handling or in the furnace. One way of producing agglomerates involves pelletizing moist ironbearing fines and particles of solid fuel in a drum or disk ,pelletizer, and fritting the resulting pellets in a sintering machine or shaft furnace. A difficulty encountered in :such processes is that the pellets have poor green strength. Until they are fritted, they are extremely delicate and must be handled with great care. Prior to my invention .it has been recognized that the fines must have a distribution of sizes under about 100 mesh to form good pellets, since there are excessive voids in pellets formed of particles all the same size. It is also known that their green strength can be improved with additives such as bentonite or starch.

An object of the present invention is to provide an improved pelletizing method which produces pellets of higher green strength than heretofore.

A more specific object is to provide an improved pelletizing method in which the starting material contains a critcial proportion of relatively large particles that form solid nuclei in the individual pellets to increase their green strength.

In the drawing:

The single figure shows enlarged cross sections of several pellets formed by the method of the present invention.

According to my method, the starting material for pelletizing has a particle size distribution as follows:

Minus 100 mesh 15 to 25 Patented Dec. 16, 1958 This material can include ore particles, as well as reclaimed fines such as fiue dust, plus the usual proportion of solid fuel particles, which commonly are anthracite fines or coke breeze. It is moistened to produce a moisture content of 9 to 14 percent by weight and pelletized in any conventional drum or disk pelletizer, which can be operated in the usual way except there is no need to recirculate particles. Ordinarily no strengthening additive is needed, although one can be used if desired. As shown in the drawing, by inch particles become solid nuclei A on which accretions B of minus 100 mesh fines collect to form pellets. Some particles in the intermediate size range of inch to 100 mesh are included in an accretion of fines surrounding a large nucleus particle, as indicated at C; others themselves become nuclei of small pellets, as indicated at D. The resulting pellets have a solid interior and thus have a high green strength. They can be fritted in any usual way; if the fritting is accomplished in a sintering machine, the invention has the advantage of eliminating the need for including sinter returns in the feed thereto.

While I have disclosed only a preferred way of practicing the invention, it is apparent that modifications may arise. Therefore, I do not wish to be limited by the disclosure set forth, but only by the scope of the appended claim.

I claim:

A method of pelletizing iron-bearing materials preliminary to fritting comprising feeding a mixture of moist iron-bearing particles and solid fuel particles to a pelletizer, the moisture content being 9 to 14 percent by weight, said mixture of particles having a size distribution as follows:

Percent by weight by inch 45 to $5 by mesh 20 to 30 Minus 100 mesh 15 to 25 References Cited in the file of this patent UNITED STATES PATENTS Najarian Aug. 23, 1938 Firth Dec. 3, 1946

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