Changkyu Lee

Modeling and simulation of solvent extraction processes for purifying rare earth metals with PC88A

A new simulation logic and thermodynamic equilibrium analysis algorithm combined with a new model simplification technique was developed to simulate the solvent extraction process for purifying rare earth metals from chloride solution with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) as a solvent. The proposed model simplification method significantly reduces the number of the nonlinear equilibrium equations to be simultaneously solved to overcome the initial guess problem and obtain numerically stable convergence pattern in solving the equilibrium analysis problem and performing the rigorous simulation of the extraction process. A new equilibrium analysis algorithm on the basis of the simplified nonlinear equilibrium equations is also proposed to estimate the equilibrium concentrations by solving the rigorous first principle extraction model. Finally, a solvent extraction simulator is developed to estimate all the concentrations of all the stages of the solvent extraction process by solving the equilibrium analysis problem at each stage in a sequential way. The proposed simulator doe not suffer from the initial guess problem and shows very robust convergence pattern without any numerical problems.

Adaptive monitoring statistics based on state space updating using canonical variate analysis

Abstract Recently monitoring techniques using canonical variate analysis (CVA) based state space model are proposed by several researchers. They discussed that canonical variate analysis based approach is superior to dynamic principal component analysis (PCA) based that for fault detection and identification. To apply canonical variate analysis base approach to time-varying systems, we proposed adaptive monitoring method via CVA based state space model updating. Forgetting factor is employed, to update current mean vector and correlation matrix and current state space model is recursively, estimated using Cholesky factor updating scheme. Two state space model based monitoring indices are proposed to detect process abnormalities. One is state monitoring index and the other noise process monitoring index. They are formulated using state prediction matrix and noise extraction matrix which are derived from current state space model and the statistics of them are also recursively determined using the η 2 distribution. To adjust forgetting factors according to variation of process state, the forgetting factor updating criterions are introduced. The proposed algorithm is applied to the continuous stirred tank reactor under operation condition change. Application results provide the expectation that the proposed algorithm can be applied to practical time-varying or transient processes.

Study on Electrolysis for Neodymium Metal Production

This study deals with research on the reduction process of neodymium oxide by molten salt electrowinning. Neodymium fluoride and lithium fluoride electrolyte were used for feed stock of electrolyte and neodymium oxide was added as precursor. Cell current was confirmed that cell potential was applied as constant potential of 4.5V. Argon gas injection into the electrolyte was carried out to confirm convection effect on current efficiency. Applied current was gradually decreased without argon flow, but applied current was kept within a certain range with argon flow in electrolyte.