Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The pneumatic injection of reagent powder into molten iron has become
the preferred way to carry out iron and steel desulphurisation. It is
therefore essential to not only understand the thermodynamic
implications, but also the kinetic principles that govern the
desulphurisation process. Key variables that influence the kinetics of the
procedure are the condition and composition of the top slag and the
melt as well as the injection conditions. Notable injection parameters
include reagent flowrate, injection-lance depth and carrier gas flowrate.
Owing to sampling restrictions, the subsequent data from Saldanha
Steel®, South Africa does not provide adequate insight into the kinetic
behaviour of the desulphurisation process and it was therefore the focus
of this research to provide an improved quantitive comprehension of the
calcium carbide injection procedure at Saldanha Steel.
For this purpose a one-dimensional quasi-steady state model for
momentum, heat- and mass transfer in rising gas-liquid-powder plumes
has been developed for conditions relevant to the Saldanha Steel
refining process. Combined with a model predicting the contribution of
the topslag to the process, the overall rate of desulphurisation as a
function of time can be determined, thus affording the ability to
quantitatively explore and analyse the influence of the afore-mentioned
injection parameters, as well as the nature of both the topslag and the
melt, on the kinetics of the desulphurisation process.
Sensitivity analyses concluded that individual increases in the calcium
carbide flowrate, the depth of injection and the amount of carry-over
slag will result in a reduction in the injection time, while a decrease in the reagent particle diameter and the initial mass of iron in the ladle will
have the same effect.
Molten iron temperature losses brought about by prolonged injection
needs to be electrically recovered within a steelmaking furnace at a
high cost. Owing to the high cost of the desulphurising agent, any
reduction in the required injection time, while still maintaining product
specifications, will therefore result in diminishing overall production costs.
Although all the results contained in this study is of particular interest to
the Saldanha Steel scenario, it also provides invaluable information and
insights into the important variables and parameters playing a role in
injection desulphurisation processes in general, along with the influence
that changing conditions can have on the end result of such a
procedure. / AFRIKAANSE OPSOMMING: Die pneumatiese inspuiting van reagentpoeier is die populêrste
ontswawelingsmetode in die yster- en staal bedryf. Dit is dus van groot
belang dat die gepaardgaande termodinamiese en kinetiese beginsels
betrokke by die ontswawelingsreaksies baie goed verstaan word. Die
kondisie en samestelling van die bo-slak en die vloeibare yster, asook die
inspuitingkondisies is twee van die belangrikste veranderlikes wat die
kinetika van die ontswawelingsproses beïnvloed.
Beperkte monsternemingsgeleenthede het veroorsaak dat die relevante
data, soos voorsien deur Saldanha Staal®, nie die nodige kinetiese insig
in verband met die ontswawelingreaksie weergee nie. Dit is dus die doel
van hierdie werkstuk om ‘n verbeterde kwantitatiewe begrip van die
ontswawelingsproses by Saldanha Staal daar te stel.
Vir hierdie doeleinde is ‘n een-dimensionele, kwasi-gestadigde toestand
model vir stygende gas-vloeistof pluime ontwikkel. Die model
inkorporeer momentum-, hitte- en massaoordragsprinsiepe en is
verteenwoordigend van die ontswawelingsproses by Saldanha Staal. ‘n
Tweede model simuleer die bydrae wat die bo-slak tot die algehele
ontswawelingsproses maak en saam gee hierdie twee modelle die
algehele ontswawelingstempo weer as ‘n funksie van tyd. Die modelle
word ook gebruik om die invloed van die bogenoemde
inspuitingsveranderlikes op die proses te ondersoek.
Deeglike sensitiwiteitsanalise het gewys dat ‘n verhoging in die kalsium
karbied vloeitempo, asook die inspuitingsdiepte van die lans en die
hoeveelheid slak wat vanaf die boogoond na die ontswawelingseenheid
oorgedra word, ‘n vermindering in die vereisde inspuitingstyd te weeg
bring. Verkleining in die kalsium kardied partikels se gemiddelde diameter en vermindering van die hoeveelheid yster in die torpedokarre
aan die begin van die proses, het dieselfde uitwerking op die vereisde
inspuitingstyd.
Geweldig baie geld moet aan elektrisiteit spandeer word om die
temperatuur wat verlore gaan as gevolg van onnodige lang
inspuitingstye, in die staalmaakoonde te herwin. Gekombineerd met die
feit dat die kalsium karbied reagent baie duur is, beteken dit dat
reduksies in die vereisde ontswaweling inspuitingstyd groot besparings te
weeg kan bring.
Alhoewel die saamgevatte resultate van spesifieke belang is vir die
Saldanha Staal proses, verskaf hierdie studie waardevolle informasie oor
die belangrikheid van verskeie veranderlikes, asook die rol wat
veranderende toestande op die eindresultate van die
ontswawelingproses kan hê.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16424 |
| Date | 04 1900 |
| Creators | Scheepers, Emile |
| Contributors | Eksteen, J. J., Aldrich, C., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 201 leaves : ill. |
| Rights | University of Stellenbosch |
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