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Evaluation of the flow pattern in a ladle with regard to stirring by argon through a porous plug using CFD
2002 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The steel industry nowadays has higher demands on the cleanliness of the products. The process must always be improved and deoxidation products must be better and faster separated from the steel. It is then necessary to understand what is happening inside the ladle to be able to improve the process and the quality of the steel. Therefore it is needed to evaluate the flow pattern in the ladle when stirring by argon gas through the porous plug is used. Computational Fluid Dynamics, CFD is used here to evaluate the flow pattern under real conditions at the steel plant of Saarstahl AG in Völklingen, Germany. Three different stirring intensities are used, which correspond to the process. The three intensities used are: without injection of argon, the flow is then only driven by the heat transfer to the surrounding. Secondly, a low stirring rate is used, 3 m3/h, and finally a high stirring rate is used, 27 m3/h. The results from the CFD calculations without injection of argon show large zones with slow mixing, stagnant zones, which results in a very slow deoxidation process. The calculations with low stirring rate show that the flow pattern, when gas is used, is independent on the temperature. The generated flow consists of a circulating loop with an upward flow driven by the injected gas and a downward flow along the walls. In this case, small stagnant zones are observed in the centre and close to the bottom of the ladle. From the calculations where a high stirring rate is used, a similar flow pattern is generated as in the case with low stirring rate. The average velocity and turbulence are higher in this case. Here, only a very small stagnant zone very close to the bottom is observed. The larger the gas flow rate is, the larger becomes the breakthrough zone, the open surface where the gas leaves the melt, but also the average velocity and turbulence become larger. The dependency of the gas flow rate on the average velocity and turbulence is not linear. A strong increase is observed at gas flow rates up to about 10 m3/h and a slighter increase thereafter. The differences between the minimum and maximum values of the flow variables are very high. This can indicate an unfavourable homogenisation due to very high values in the area of the rising gas and low values in the centre and close to the bottom of the ladle. Generally, the turbulence is lower the further down in the ladle.

Place, publisher, year, edition, pages
2002.
Keyword [en]
Technology, flow pattern, stirring, porous plug, turbulence, CFD
Keyword [sv]
Teknik
Identifiers
URN: urn:nbn:se:ltu:diva-52137ISRN: LTU-EX--02/210--SELocal ID: 947f96ba-bde4-47d7-b2c8-94d426027226OAI: oai:DiVA.org:ltu-52137DiVA: diva2:1025504
Subject / course
Student thesis, at least 30 credits
Educational program
Chemical Engineering, master's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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