전산모사기법을 활용한 Kroll 환원공정 열거동 해석

Abstract

Titanium with attractive properties which are corrosion resistance, light-weight, high specific strength has been used for purposes such as a high-technology of military and aerospace. Currently, the use of titanium in the non-aerospace fields like industry, medical, life is expanding. Most of the titanium used in the world is produced by Kroll process. In the Kroll process, titanium tetrachloride is reacted with liquid magnesium filled in the reactor at about 800℃ and titanium in the form of sponge is made. It is a reduction reaction which extracts titanium from titanium tetrachloride and generates very large heat. Efficient cooling system is needed because excessive heat generated by continuous reaction has a bad effect on reduction process. Therefore it is important to understand reaction mechanism of reduction process and change of temperature distribution with progression of process. Internal shape of the reactor is changed during the reduction process. Titanium formed on the crucible wall grows to the center on the liquid magnesium surface. And the amount of heat of reaction decreases when surface of liquid magnesium is covered by titanium is grown up. But heat of reaction changes when titanium sponges separated by high internal pressure are piled up on the bottom of reactor. Therefore internal temperature distribution is changed depending on the progress of process. Knowing temperature distribution with changes of reduction process factors is not easy. Because factors controlling the process are various and it is hard to measure temperature of internal reactor. Thus computational modeling method is used that is replaced experiment. Reactor of the same size compared with experiment is made and the boundaries conditions refer to the literature are set. Heat flows of various boundaries are investigated according to the progress of process and change of titanium length on the surface of liquid phase. Results of computational modeling indicate some patterns. When process progresses to the later state and titanium length is longer, the proportion of heat eliminated through lid and bottom is increasing but crucible wall is decreasing. Such a pattern suggests guideline of cooling system for the productivity and quality enhancement. To increase the proportion of wall, titanium length on the surface of liquid must be shorter. Thus, titanium sponge should be broken by increasing pressure of internal reactor and deposited on the bottom. And because the proportion of crucible wall eliminating heat is decreased by liquid level rising with progression of process, tapping should be used frequently to disturb rising of liquid phases in the reactor. Heat flows patterns can not be judged by only computational modeling results. Computational modeling results have trust if it is validated by comparing with experiment results. And computational model can be modified due to that various results unexpected occur at experiment. But before performing an experiment it is meaningful that can determine the flow of heat and set the cooling system in the reduction process.