03_078
TRANSCRIPT
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Abstract
In order to reduce the heat loading in the Tilden Mine kilns caused
by burning coal, which in turn resulted in rapid and significant build-up
on the kiln lining, internal carbon was added to the green ball prior to
balling. Intensive laboratory testing led to three short-term full-scale
plant tests that were successfully conducted. Appropriate
environmental permits were obtained to allow Tilden to use internal
carbon on a continuous basis. Findings concerning carbon addition
rates, reductions in coal use, build-up reductions, fired pellet quality,
and environmental issues will be discussed.
Introduction
This paper discusses the successful use of internal fuel (coke
breeze) during the production of hematite fluxed pellets on the two
grate-kiln systems at the Tilden Mine. It is believed by the authors
that this is the first time that internal fuel has been used successfully
on grate-kiln systems in North America.
Cleveland-Cliffs, Inc is the largest supplier of iron ore products to
the North American steel industry. Subsidiaries of the company
manage and hold equity interest in five iron ore mines in North
America. These are the Empire and Tilden Mines in Michigan, the
Northshore and Hibbing Taconite (Hibtac) mines in Minnesota, and
the Wabush Mine in Labrador and Quebec, Canada.
The Companys wholly owned subsidiary, Cliffs Mining Services
Company (CMSC), operates a Research Laboratory in Ishpeming,Michigan. It also manages Engineering Services in Ishpeming. Both
Engineering Services and the Research Laboratory service all five
mines
Reason for Internal Carbon Study
Kiln ringing and build-up is a very significant and expensive
problem at Tilden when producing hematite fluxed pellets with 100%
coal firing. Straight grate indurating systems processing hematite
have used internal fuel to improve pellet quality, provide intimate heat
input and reduce heat consumption. Internal fuel additions generally
have approximated the quantity of heat evolved if the concentrate was
magnetite. It was theorized that if an internal fuel could replace the
heat provided by magnetite oxidation, the amount of heat required to
be supplied by the kiln burner would be significantly reduced. Tilden
experiences significantly less kiln build-up when processing
magnetite concentrate. To evaluate this concept, a series of pot
grate-batch kiln tests were conducted with Tilden hematite fluxed
concentrate with and without internal coke breeze addition. The pot
grate-batch kiln tests were successful, which led to a successful three
day plant test on Units 1 and 2 at Tilden.
Pot Grate Kiln Test Summary
Pot grate-batch kiln tests were conducted at Cliffs Technology
Center without internal fuel and at 0.5 and 1.0% addition levels. For
most of the tests the coke breeze was added to concentrate slurry and
pressure filtered before bench balling. Two of the tests had the coke
breeze added dry and mixed with the bentonite before bench balling.
The 1% internal coke breeze addition improved green ball,
preheat pellet, and fired pellet physical quality, except for fired pellet
compression strength, which was reduced slightly. It also, improved
pellet LTB and maintained reducibility. The total time required in
preheat was reduced by 0.44 minutes, which indicates that Tilden
may also get a slight production increase with internal coke breeze.
Bench balling with coke breeze was visually much easier and created
very little seed material compared to baseline balling. This was thecase with either slurry or dry addition. With hematite fluxed pellets a
1% internal fuel addition rate could reduce coal burning in the kiln by
around 35% or 7 ST per hour. Because of the success of the pot
grate kiln test program, Tilden ran a four-day plant test on both units
starting on October 1, 2001.
Plant Test Summary
On day shift on Monday, October 1, Tilden began introducing
coke breeze into the plant. The coke breeze was ground in the 1B
1 Copyright 2003 by SME
2003 SME Annual MeetingFeb. 24-26, Cincinnati, Ohio
Preprint 03-078
INTERNAL CARBON ADDITION DURING HEMATITE FLUXED PELLET PRODUCTION AT THE TILDEN MINE
M. J. HanninenT. E. SeppanenC. R. Sundberg
Cliffs Mining Svcs Co.Ishpeming, MI
P. J. SuardiniTilden Mining Co. L. C.
Ishpeming, MI
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