Numerical Analysis of Liquefaction and Vaporization Processes in a CO ₂ Capture System Recovered in the Form of Dry Ice

To develop a novel cryo-DAC system that directly captures CO2 from the atmosphere using the cryogenic heat of liquefied natural gas, we aim to obtain design and development guidelines for a cryo-DAC system that combines an amine absorption method and a cryo-sublimation pump. Previous studies have elucidated the process of CO2 cooling in the sublimation tank to produce dry ice. In this paper, we numerically analyze the process of liquefaction and vaporization of dry ice by heating using an unsteady lumped parameter system model with various analytical conditions, including physical assumptions, geometry of the heating tank, and operating conditions. Consequently, we clarified the effects of various analytical parameters on the different state changes and the kinetic characteristics of dry ice’s liquefaction and vaporization processes. We provided guidelines for designing advanced and high-performance systems. In particular, we found that if the ratio of the initial dry ice volume to the heating tank volume, i.e., the initial dry ice volume fraction xDI,0, was the same, the paths of state changes in the liquefaction and vaporization processes were the same. Moreover, we found that if the product of the specific surface area aC in the CO2 heating tank and the heat flux qW on the heating wall, aC･qW, was the same, the temporal changes of various quantities were the same, and that the speed of change was proportional to aC･qW.