Nitrogen in SL/RN direct reduced iron : origin and effect on the electric steelmaking process

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dc.contributor.advisor Pistorius, Petrus Christiaan
dc.contributor.postgraduate Erwee, M.W. (Markus Wouter)
dc.date.accessioned 2014-07-17T12:12:16Z
dc.date.available 2014-07-17T12:12:16Z
dc.date.created 2014-04-08
dc.date.issued 2014 en_US
dc.description Dissertation (MEng)--University of Pretoria, 2014. en_US
dc.description.abstract Direct Reduced Iron (DRI) is used as an alternative feedstock in electric arc furnaces, making up 50% or more of the total iron charge. DRI produced with coal based reductants (for example in rotary kilns) make up roughly 25% of DRI produced in the world. It was found that SL/RN DRI samples from a kiln cooler had high nitrogen contents (50-250ppm, depending on particle size), higher than DRI from gas-based reduction. The higher nitrogen content of SL/RN DRI would increase the levels of nitrogen of liquid steel produced in the EAFs. The problem is exacerbated by the fact that the SL/RN DRI contains virtually no carbon (which would aid in preventing nitrogen pickup). The proposed mechanism of nitrogen pick-up by the SL/RN DRI is one where nitrogen present within the atmosphere of the rotary cooler (where hot DRI, discharged at 1000°C from the rotary kiln, is cooled to approximately 100 °C in ca. two hours) penetrates the solids bed and nitrides DRI particles. Possible rate-determining steps for nitriding in the cooler have been evaluated. Nitriding of DRI particles is predicted to be rapid: the most plausible location for rapid nitrogen pickup is the first 5 meters of the rotary cooler, where the high temperature, nitrogen-rich gas atmosphere and rapid solids bed mixing are conducive to nitriding; solid-state and pore diffusion of nitrogen into DRI particles are predicted to be rapid too. The most plausible rate determining step for nitriding of DRI particles is that of nitrogen dissociation on the DRI surface, which can be further retarded by the presence of sulphur. A strong correlation was found between the amount of “melt-in” carbon in the liquid steel and the final tap nitrogen content, with 0.3% C resulting in nitrogen levels as low as 50 ppm (80 ppm or less is desired on the plant in question) at tap, even with DRI material that is high in nitrogen and contains virtually no carbon. Proposals to increase the melt-in carbon are included. en_US
dc.description.availability unrestricted en_US
dc.description.department Materials Science and Metallurgical Engineering en_US
dc.description.librarian gm2014 en_US
dc.identifier.citation Erwee, MW 2013, Nitrogen in SL/RN direct reduced iron : origin and effect on the electric steelmaking process, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/40830> en_US
dc.identifier.other E14/4/289/gm en_US
dc.identifier.uri http://hdl.handle.net/2263/40830
dc.language.iso en en_US
dc.publisher University of Pretoria en_ZA
dc.rights © 2013 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. en_US
dc.subject Direct Reduced Iron (DRI) en_US
dc.subject Electric Arc Furnace Steelmaking en_US
dc.subject Nitrogen en_US
dc.subject SL/RN DRI en_US
dc.subject Nitriding en_US
dc.subject Dusty-gas model en_US
dc.subject UCTD en_US
dc.title Nitrogen in SL/RN direct reduced iron : origin and effect on the electric steelmaking process en_US
dc.type Dissertation en_US


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