We are developing a novel DAC system (Cryo-DAC system) that directly captures atmospheric CO2 using the cryogenic heat (-162 degrees C) of liquefied natural gas (LNG), and we aim to obtain design and development guidelines for a Cryo-DAC system combining an amine absorption method and a cryo-sublimation pump. In particular, it has been pointed out that when a non-phase-change gas such as N-2 mixes into the sublimation tank from the regeneration tower, it accumulates downstream of the sublimation tank and strongly inhibits dry ice production. Therefore, it is essential to elucidate the changes in the gas distribution in the sublimation tank and how the gas accumulation reduces the dry ice production rate. An unsteady lumped parameter system numerical model consisting of a regeneration tower, a connecting passage, and a sublimation tank divided into three parts was developed and numerically analyzed to investigate the influence of the non-phase-change gas on the temporal change of various quantities in the process and on the formation characteristics of dry ice. We set various analytical conditions for this process, such as the CO2 regeneration rate, the regeneration rate of the non-phase-change gas N-2, the cooling wall area, the amine absorption liquid temperature, the refrigerant temperature, the modification factor in the Lewis relationship and heat transfer coefficient of the dry ice surface. The previous report showed various process quantities' temporal variations when referencing the analytical conditions' parameters. Compared with this, we clarified the effects of various analytical parameters on unsteady variations of the pressure, temperature, CO2 regeneration rate in the regeneration tower, and CO2 solidification rate in the sublimation tank, and also on the dry ice production efficiency and production quantity.
