03_078

2003 SME Annual Meeting Feb. 24-26, Cincinnati, Ohio

Preprint 03-078

INTERNAL CARBON ADDITION DURING HEMATITE FLUXED PELLET PRODUCTION AT THE TILDEN MINE M. J. Hanninen T. E. Seppanen C. R. Sundberg Cliffs Mining Svcs Co. Ishpeming, MI P. J. Suardini Tilden Mining Co. L. C. Ishpeming, MI

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.

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.

Introduction

Pot Grate Kiln Test Summary

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 Company’s 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

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 the case 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.

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

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

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Copyright © 2003 by SME

2003 SME Annual Meeting Feb. 24-26, Cincinnati, Ohio pebble mill with the fluxstone, and added to the concentrate slurry tanks prior to filtering as part of flux addition. During the test, which lasted into afternoon shift on Thursday, October 4, Unit 1 burned 100% natural gas while Unit 2 burned 100% eastern coal. Summarized below are the findings of this short plant test. • Feed rates on both units were not affected with coke breeze addition. • Both units had slightly decreased fired pellet “Q” Index, compression and LTD. Pellet reducibility increased while porosity remained constant. • Both units experienced slightly increased bed pressures, which caused the process fan dampers to open up more. System temperatures remained constant throughout the test. • Green ball physical quality was equal on both units with and without internal coke breeze. On Unit 1 green ball sizing was equal, while on Unit 2 more 1/2” balls were produced. • Over 30% of the heat required to indurate the pellets was replaced with internal coke breeze on both units. As the test progressed total heat consumption was reduced significantly (50100,000 Btu/LTP) on both units at a 0.38% coke breeze addition rate. The test was not run long enough to determine if kiln build-up was reduced. • During the test waste gas stack NOx and CO emissions were measured on both units with and without internal coke breeze addition. Results showed a 38% reduction in NOx emissions on Unit 1 with natural gas firing. On Unit 2 with coal firing a 13% reduction in NOx emissions was measured. Both units saw around a 600% increase in CO emissions because of the coke breeze burning in the bed. Plant CO levels were also measured and were none detectable with and without internal coke breeze. Because of the success of this short plant test Tilden decided to run a longer 9-10 day test starting in early November 2001. During this test both units were burning 100% eastern coal. Plant operating conditions and fired pellet quality mirrored the results of the first plant test. During this longer test, Tilden noticed a definite reduction in kiln build-up on both units with 100% coal firing.

contributed to the magnitude of the problem and extent of the damage. By contrast, the most promising results of coke breeze is apparent when you look at the amount of time Tilden can run the units between scheduled flame-off shutdowns to remove the kiln build-up. Prior to internal fuel, when burning coal Tilden was averaging only 1421 days of flame-on operation (dependent on kiln spray and trim gas amounts). Since introducing the coke breeze, at a rate of 2-3 LTPH per unit (10-15% of the required fuel), Tilden has achieved between 30-40 days of flame-on operation, and has also been able to turn off the expensive kiln chemical spray. Future testing will involve doubling the amount of “trim gas” from 12% to 24% of the required kiln fuel. This will determine how many more days of run time that the units will achieve before being shutdown for the removal of kiln build-up. In summary, the internal coke breeze is not a magic solution. However, it does represent another valuable option in Tilden’s strategic fuel decisions. The challenge is to find the lowest cost fuel combination that protects the kiln and cooler refractory and associated steel; thereby allowing the Tilden pellet plant to achieve the high pellet unit availability required to make 8.0 MLT of pellets per year. Acknowledgments The authors would like to thank the Research technicians that conducted the laboratory testwork. We would also like to thank Tilden management and union personnel, who made the plant tests possible and successful. References 1. The Iron Ore Company of Canada’s Carol Mine Reference: CIM Bulletin, June 1991, Volume 84, No. 950 (Pellet Production – Carol pellet quality – a decade in review) by S. T. Vessey, J. Staples, D. Pearcey and V. Hedge 2. Companhia Vale do Rio Doce (CVRD) Mine in the Tubarao area in Brazi Reference: 25 Years Of Pelletizing At CVRD by L. A. Bandeira de Mello, J. M. Cunha, A.L. Piccolo and M. S. Klein 3. The Sidbec-Normines Pelletizing Plant at Port-Cartier, Quebec Reference: CIM Bulletin, August 1983 (Coke Breeze Addition To Fire Lake Pellets In Regular Operation) By C. Desmeules, Superindent – Production, Sidbes-Normines Inc. 4. Ferteco Mineracao S.A., Brazil Reference: World Iron Ore Conference, Nov 1-4, 1998 (Ferteco’s Pellet Plant, 20 Years Of Successful Operation) by Hans Heep, Industrial Director Ferteco Mineracao S.A., Brazil 5. Wabush Mines Pointe Noire Pellet Plant in Sept Isles, Quebec, Canada Reference: Wabush Mines Report W-47 dated March 9, 1978 (Pelletizing With Coke Breeze As An Internal Fuel Supplement( by C. Desmeules, E. Maes and M. Breech Jones

Long Term Internal Fuel Testing The air permit allowing Tilden to use internal coke breeze at a maximum rate of 5 LTPH per kiln on a continual basis was received from the Michigan DEQ in late June 2002. Testing on both units commenced in mid-July. The present plan is to add coke breeze only during the hematite runs (March through December each year). Eastern coal and coke breeze are much cheaper than natural gas. Thus far, in addition to some fuel cost savings, the other advantages of using internal fuel include: • Measured reductions in the rate of kiln build-up (as expected). • Considerable reduction in the nitrous oxide (NOx) emissions when burning either gas or coal. However, the use of internal fuel does have a number of possible issues associated with its use, which include: • Slightly reduced pellet strength. • Increased carbon monoxide (CO) emissions. • Hotter conditions on both the grate and cooler, which may reduce grate casting/chain life and increases the risk of fusing pellets in the cooler. Tilden continues to test various combinations of the three fuels (gas/coal/breeze), and is learning to alter their operating procedures, to maximize the advantages and mitigate the disadvantages/risks of internal fuel addition. For example, Tilden recently fused the Unit 2 cooler causing considerable downtime and cost, and coke breeze

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