Simulation and optimization of the physical absorption based carbon capture system with novel additives

Abstract

Reducing carbon dioxide emission has become an important social issue due to global warming. Therefore, developing technologies about carbon capture and storage has become an active research area. Various carbon capture technologies have been suggested to capture carbon dioxide such as post-combustion, pre-combustion and oxy-fuel combustion carbon capture system. Among various candidates for $CO_2$ capture, physical absorption based carbon capture system is relatively mature technology. Especial-ly, $Selexol^{TM}$ process, one of the pre-combustion carbon capture technology, has been commercialized and already adopted to some industries. Dimethyl Ethers of Polyethylene Glycol (DEPG) is used as physical ab-sorbent in this system. Extra cost for constructing and operating of carbon capture process is a main problem for applying it to real industries widely. In this study, employing novel additives to the Selexol process are suggested to reduce the economic loss of the Selexol process. Mixing additive with DEPG is expected to lead lower solvent purchasing cost compared to the Selexol process with pure DEPG while amount of captured $CO_2$ are same. In this work, the compounds are found that have similar $CO_2$ solubility with DEPG as well as cheaper than DEPG. The $CO_2$ solubility is can be represented as solvation energy of $CO_2$ in the additive materials. The additive candidates are selected by comparing solvation energies. Three compounds, dimethyl carbonate (DMC), diethyl carbonate (DEC), and triacetin (TAT), are chosen as the candidate additives. To estimate their economic feasibility, the Selexol processes with the three candidate additives are simulated using Aspen Plus®. The 1-stage Selexol process is developed instead of typical 2-stage Selexol process because only $CO_2$ capture is considered in this research. The feed gas stream for the 1-stage Selexol process is chosen from syn-gas generated by Integrated Gasification Combined Cycle (IGCC) power plant. Perturbed Chain Statistical Association Fluid Theory equation of state (PC-SAFT EOS) model is used for thermodynamics in the simula-tions. To obtain the amount of $CO_2$ capture using the additives in the simulation, the binary parameters be-tween $CO_2$ and the additives are needed. The parameters are obtained by regression tool in simulator using $CO_2$ solubility experimental data. Operating cost of the Selexol process with additives and pure DEPG are calculated. Then, equipment costs of the one candidate process which shows best economic performance among the additives and the Selexol process with DEPG are compared. Finally, optimal lean solvent tempera-tures that minimize the operating cost are found at various carbon capture rate. This thesis is written based on the published article “Economic assessment and optimization of the Selexol process with novel additives”