1992 Volume 32 Issue 1 Pages 120-125
Fundamental experiments were carried out in order to accelerate the vacuum decarburization rate in low carbon range. As the results, it became clear that enlargement of interfacial area was more efficient than increase in overall mass transfer coefficient. One of the most practical methods to enlarge interfacial area was Ar injection into molten steel. Effect of Ar injection on decarburization rate was investigated in the 150 kg VIF. Ar injection was effective on decarburization rate, and the apparent decarburization rate constant with a two-holed nozzle was larger than that with a one-holed nozzle. Next, effect of Ar injection into a vacuum vessel of RH was investigated with a water model. CO2 desorption rate was measured to simulate decarburization rate. Gas injection nozzles were settled at the lowest part of the side wall in the vacuum vessel. The number of nozzles was 1, 8, or 16. An experiment without gas injection was also carried out as a reference. Gas injection into the vacuum vessel was effective on the CO2 desorption rate. In particular, increase in the number of nozzles was more effective at a constant total gas flow rate.
Finally, plant trials were carried out. Configuration of the nozzles was the same as the case of 8 nozzles in the water model. Gas flow rate into the snorkel for circulation was 2 500 NI/min. Gas flow rate into the vacuum vessel was 800 NImin. Inner diameter of the nozzles was 2 mmφ. As the result, it became possible to decrease the carbon content from 200 to 10 ppm within 10 min.
Interfacial area with Ar injection was evaluated to be 1.6 times larger than that without Ar injection.