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Modeling of Gas Flows in Steelmaking Decarburization Processes
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The purpose of the current study is to increase the understanding of different steelmaking processes at the decarburization stages by use of mathematical modeling. More specifically, two De-Laval nozzles from a VOD (Vaccum Oxygen Decarburization) process, which is used for producing stainless steels with ultra-low carbon grades, was investigated for different vessel pressures. Moreover, the post combustion phenomena in a BOF or LD (Linz-Donawitz) process as well as an AOD (Argon Oxygen Decarburization) process were studied focusing on the decarburization stage.

Two industrial VOD nozzles were numerically studied and compared at different temperatures and ambient pressures. Flow patterns of the oxygen jet under different ambient pressures were predicted and the flow information at different positions from the nozzle was analyzed. In addition, the effects of different ambient temperatures on the jet velocity and the dynamic pressure were compared. The predictions revealed that a little under-expansion is somewhat helpful to improve the dynamic pressure. The jet dynamic pressure and its width for the specific nozzle geometry were also studied. It was observed that a variation in the ambient pressure can influence the jet momentum and its width. In addition, a high ambient temperature was found to have a positive effect on the improvement of the jet dynamic pressure. Furthermore, it was found that a change in ambient pressure has a stronger effect on the jet force than a change in the ambient temperature. In addition, it was proved that the profiles of the dynamic pressure at a certain blowing distance fit well to Multi-Gaussian distribution.

Post combustion in a BOF/LD and an AOD process during decarburization was also studied. Two mathematical models were created to show the post combustion phenomenon inside the converters, respectively. For the CFD modeling of the two processes, the realizable k-ɛ model, the species transport model and the discrete ordinate were adopted to calculate the turbulence, gas reaction and radiation present in the gas phase in the converter. For the BOF/LD modeling, a series of plant tests were conducted to collect data, which were used in the current model. These include the off-gas information, emissivity data, oxygen blowing parameters and the chemical composition

of steel. After the simulation, the predicted flow pattern and detailed information of the gases taking part in the post combustion were compared to plant data. Specifically, the off-gas data from the plant was used for the model verification. The measured CO2 concentration was 15-20 wt% and the predicted value from the modeling was 16.7 wt%.

For the AOD converter of interest in the current work, a fan is installed in the end of the AOD flue to help extract the off-gas from the converter. The influence of different fan gauge pressures as well as temperatures of the gas mixture, containing the generated CO and argon, on the post combustion in the whole AOD system was studied. It was indicated from the modeling results that the post combustion was only present in the flue for the present modeling conditions. Moreover, a critical fan gauge pressure (approx.. -550 Pa) was found which could yield a maximum post combustion in the flue gas.

For both two models (BOF/LD and AOD), simulations indicated that a change of the converter temperature from 1500 to 1700 °C did not influence the post combustion reaction to a large degree. In addition, these two models can be regarded as the first step for a future more in-depth modeling work of the post combustion.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , xiv, 64 p.
Keyword [en]
VOD, nozzle, jet, vacuum, BOF, LD, AOD, post combustion, flue, CFD
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-128541OAI: oai:DiVA.org:kth-128541DiVA: diva2:647968
Public defence
2013-09-19, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20130913

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2013-09-13Bibliographically approved
List of papers
1. Mathematical Modeling of VOD Oxygen Nozzle Jets
Open this publication in new window or tab >>Mathematical Modeling of VOD Oxygen Nozzle Jets
2011 (English)In: Steel Research International, ISSN 1611-3683, Vol. 82, no 3, 249-259 p.Article in journal (Refereed) Published
Abstract [en]

This study has focused on numerically exploring the oxygen flow in the convergent-divergent De Laval nozzle. The De Laval nozzle has been commonly used as oxygen outlet at the lance tip in the vacuum oxygen decarburization (VOD) process. The nozzle geometry used in an active VOD plant was investigated by isentropic nozzle theory as well as by numerical modeling. Since an optimal nozzle design is only valid for a certain ambient pressure, one VOD nozzle will be less efficient for a large part of the pressure cycle. Different ambient pressures were used in the calculations that were based on the De Laval nozzle theory. Flow patterns of the oxygen jet under different ambient pressures were studied and the flow information at different positions from the nozzle was analyzed. In addition, the study compared the effects of different ambient temperatures on jet velocity and dynamic pressure. The predictions revealed that the modeling results obtained with the CFD modeling showed incorrect flow expansion, which agreed well with the results from the De Laval theory. Moreover, a little under-expansion is somewhat helpful to improve the dynamic pressure. The jet dynamic pressure and its width for the specific nozzle geometry have also been studied. It has been observed that an altering ambient pressure can influence the jet momentum and its width. In addition, a high ambient temperature has a positive effect on the improvement of the jet dynamic pressure.

Keyword
VOD, De Laval nozzle, Mathematical modeling, turbulence, jet domain, ambient pressure, flow pattern, jet width, ambient temperature
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-32592 (URN)10.1002/srin.201000108 (DOI)000289061100013 ()2-s2.0-79952234188 (Scopus ID)
Note
QC 20110420Available from: 2011-04-20 Created: 2011-04-18 Last updated: 2013-09-13Bibliographically approved
2. Mathematical comparison of two VOD nozzle jets
Open this publication in new window or tab >>Mathematical comparison of two VOD nozzle jets
2011 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, no 10, 1637-1646 p.Article in journal (Refereed) Published
Abstract [en]

Studies of physical phenomena in a jet caused by VOD (Vacuum Oxygen Decarburization) nozzles have been carried out. The VOD process is a metallurgical process where the steel-making route is controlled under vacuum environment with oxygen top blowing. In this work, two VOD nozzle models have been employed for an investigation based on two real De Laval geometries used in industry. Numerical modeling was used to study oxygen blowing states of the nozzles at different temperatures and ambient pressures. The nozzle models were numerically computed with two dimensional domains, where vacuum conditions and temperatures were specifically defined. The modeling results showed that one of the nozzles was more applicably proper for lower pressures, displaying a more stable flow pattern. Furthermore, it was found that a change in ambient pressure has a stronger effect on the jet force than a change in ambient temperature. In addition, it was proved that the profiles of the dynamic pressure at a certain blowing distance fit well to Multi-Gaussian curves.

Keyword
VOD, modeling, jet, blowing, pressure, temperature
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-40801 (URN)000296267500011 ()2-s2.0-82455184395 (Scopus ID)
Note
QC 20111115Available from: 2011-09-20 Created: 2011-09-20 Last updated: 2017-12-08Bibliographically approved
3. A Study of Post Combustion in a BOF converter
Open this publication in new window or tab >>A Study of Post Combustion in a BOF converter
2013 (English)Report (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-128539 (URN)
Projects
Jernkontoret 21066: On line control of temperature and decarburisation in converter processes
Funder
VINNOVA
Note

QC 20130913

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-05-12Bibliographically approved
4. A study of post-combustion in an AOD flue
Open this publication in new window or tab >>A study of post-combustion in an AOD flue
2014 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 85, no 7, 1173-1184 p.Article in journal (Refereed) Published
Abstract [en]

An investigation on the post-combustion phenomena in an argon oxygen decarburization (AOD) system containing a converter and a flue has been conducted. An AOD converter is mainly characterized by nozzles installed at the lower side of the converter. The nozzles are intended to inject the decarburization gas of oxygen mixed with an inert gas such as argon. The injection promotes stirring and lowers the partial pressure of CO in the converter. For the AOD converter of interest in the current work, a fan is installed in the end of the AOD flue to help extract the off-gas from the converter. The influence of different fan gauge pressures as well as temperatures of the gas mixture, containing the generated CO and argon, on the post-combustion in the whole AOD system was studied. The realizable k-epsilon model was employed as the turbulence model. In addition, the reaction and radiation were also taken into account by use of the species transport model and the discrete ordinate model. It was indicated from the modeling results that the post-combustion was only present in the flue for the present modeling conditions. Moreover, a critical fan gauge pressure was found, which could yield a maximum post-combustion in the flue gas. Finally, no obvious change on the post-combustion was shown if the inlet gas mixture temperature was varied between 1500 and 1700 degrees C.

Keyword
CFD, AOD, flue, post-combustion, fan pressure
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-128540 (URN)10.1002/srin.201300307 (DOI)000338939300003 ()2-s2.0-84903826584 (Scopus ID)
Projects
Jernkontoret 21066: On line control of temperature and decarburisation in converter processes
Funder
VINNOVA
Note

QC 20150623. Updated from manuscript to article in journal.

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2017-12-06Bibliographically approved

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