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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
