Kwang Soon Lee

Novel shortcut estimation method for regeneration energy of amine solvents in an absorption-based carbon capture process.

Among various CO2 capture processes, the aqueous amine-based absorption process is considered the most promising for near-term deployment. However, the performance evaluation of newly developed solvents still requires complex and time-consuming procedures, such as pilot plant tests or the development of a rigorous simulator. Absence of accurate and simple calculation methods for the energy performance at an early stage of process development has lengthened and increased expense of the development of economically feasible CO2 capture processes. In this paper, a novel but simple method to reliably calculate the regeneration energy in a standard amine-based carbon capture process is proposed. Careful examination of stripper behaviors and exploitation of energy balance equations around the stripper allowed for calculation of the regeneration energy using only vapor-liquid equilibrium and caloric data. Reliability of the proposed method was confirmed by comparing to rigorous simulations for two well-known solvents, monoethanolamine (MEA) and piperazine (PZ). The proposed method can predict the regeneration energy at various operating conditions with greater simplicity, greater speed, and higher accuracy than those proposed in previous studies. This enables faster and more precise screening of various solvents and faster optimization of process variables and can eventually accelerate the development of economically deployable CO2 capture processes.

Bi-level optimizing control of a simulated moving bed process with nonlinear adsorption isotherms.

A bi-level optimizing control scheme originally proposed for a simulated moving bed (SMB) with linear isotherms has been extended to an SMB with nonlinear isotherms. Cyclic steady state optimization is performed in the upper level to determine the optimum switching period and time-varying feed/desorbent flow rates, and repetitive model predictive control is run in the lower level for purity regulation, taking the decision variables from the upper level as feed-forward information. Experimental as well as numerical study for an SMB process separating a high-concentration mixture of aqueous L-ribose and L-arabinose solutions showed that the proposed scheme performs satisfactorily against various disturbances. In contrast, an alternative scheme based on an SMB model with linear isotherms showed a limitation in the control performance; this scheme was apt to fail in purity regulation.

Extended Kalman Filter with Adaptive Grid Allocation for a Fixed-Bed Adsorption Process

Abstract Real-time knowledge of concentration profiles inside the adsorption bed is essential for feedback control of a pressure swing adsorption process. A difficulty encountered in developing an observer for this purpose is that the fixed-bed adsorption model is highly stiff and either a large number of grid points or an adaptive grid allocation is indispensable to accurately solve the model through discretization. The objective of this study is to present a nonlinear observer with adaptive grid allocation for an adsorption bed to estimate spatially distributed state. Experimental verification revealed that the proposed technique can accurately and rapidly predict the breakthrough curve in addition to other process variables despite the uncertainties in model parameters as well as the feed composition.

Repetitive Control and Cyclic Steady State Optimization of a Simulated Moving Bed Process

Abstract A two-tier optimizing control strategy for the simulated moving bed (SMB) process proposed in Kim et al.Kim (2010) has been studied experimentally as well as numerically. The strategy was designed to carry out repetitive model predictive control (RMPC) of average product purities in the lower tier and off-line cyclic steady state optimization of feed and desorbent flow rates and the length of switching period in the upper tier. Experimental studies have been conducted in a four zone SMB system to separate L-ribose and L-arabinose from their mixture dissolved in water for the linear isotherm case and numerical studies have been carried out for the nonlinear isotherm case. As a consequence, the optimizing control strategy is observed to satisfactorily attain the intended optimum while robustly regulating the product purities against various uncertainties.