Roberto Parreiras Tavares
◽
André Afonso Nascimento
◽
Henrique Loures Vale Pujatti
The RH process is a secondary refining process that can simultaneously attain significant
levels of removal of interstitial elements, such as carbon, nitrogen and hydrogen, from liquid steel.
In the RH process, the decarburization rate plays a very important role in determining the
productivity of the equipment. The kinetics of this reaction is controlled by mass transfer in the
liquid phase.
In the present work, a physical model of a RH degasser has been built and used in the study of the
kinetics of decarburization. The effects of the gas flow rate and of the configurations of the nozzles
used in the injection of the gas have been analyzed. The decarburization reaction of liquid steel was
simulated using a reaction involving CO2 and caustic solutions. The concentration of CO2 in the
solution was evaluated using pH measurements.
Based on the experimental results, it was possible to estimate the reaction rate constant. A
volumetric mass transfer coefficient was then calculated based on these rate constants and on the
circulation rate of the liquid. The logarithm of the mass transfer coefficient showed a linear
relationship with the logarithm of the gas flow rate. The slope of the line was found to vary
according to the relevance of the reaction at the free surface in the vacuum chamber. A linear
relationship between the volumetric mass transfer coefficient and the nozzle Reynolds number was
also observed. The slopes of the lines changed according to the relative importance of the two
reaction sites, gas-liquid interface in the upleg snorkel and in the vacuum. At higher Reynolds
number, the reaction in the vacuum chamber tends to be more significant.
The effect of aeration conditions, characterized by the volumetric mass transfer coefficient KLa, on the fermentation kinetics of Bacillus thuringiensis kurstaki
