P07
固体吸着剤による CO2 除去システムの吸脱着プロセスの最適手法の検討
A Study on Optimization Methods in
Adsorption/Desorption Process of a Carbon Dioxide
Removal System Using Solid Adsorbent
新宮慧士 1, 松本 聡 2, 金子暁子 3,
Keito SHINGU1, Satoshi MATSUMOTO2 and Akiko KANEKO3
筑波大学大学院，University of Tsukuba
宇宙航空研究開発機構，JAXA
3 筑波大学，University of Tsukuba
12

1.

Introduction
In spacecraft such as the ISS (International Space Station), control of the environment, including water andair, is essential to maintain human life. A human emits 500 L of carbon dioxide per day1). In enclosed spaces,such as inside a spacecraft, carbon dioxide concentrations will increase and affect the human body if carbon
dioxide is not removed. Therefore, it is necessary to maintain appropriate carbon dioxide concentrations byremoving carbon dioxide. Carbon dioxide removal equipment on the ISS mainly uses CDRA (Carbon Dioxide
Removal Assembly) in US module and Vozdukh in Russian module. These carbon dioxide removal systems
use adsorbent to remove.
A typical system schematic of a four-bed temperature and pressure swing carbon dioxide removal system
is shown in Figure.1. Two are desiccant bed and the other two are carbon dioxide sorbent bed. Solid adsorbentssuch as zeolites are used for carbon dioxide adsorption, but they also adsorb water. Therefore, silica gel in thedesiccant bed first adsorbs the water in the air, and then adsorbs carbon dioxide. Adsorbent adsorption anddesorption are performed using temperature differences because the amount of adsorption varies depending
on temperature and pressure. Desiccant bed and carbon dioxide sorbent bed perform adsorption in one anddesorption cyclically in the other, enabling continuous treatment. During adsorption, the adsorption volume
is increased at a low temperature, and during desorption, the adsorbed components are heated by a heater toa high temperature for desorption. Need to set appropriate parameters such as temperature, cycle time, etc.
for efficient adsorption/desorption.

1 of 3

Figure 1.

Schematic diagram of carbon dioxide adsorption/desorption equipment

This study aims to optimize a carbon dioxide removal system using solid adsorbents. carbon dioxide
removal systems require the proper adjustment of various parameters such as temperature and pressure, andthese values are obtained from experience. Therefore, the final purpose is to model, derive optimal values, andintroduce them into the CO2 removal system. This paper describes an analytical model of silica gel for a
desiccant bed.
2.

Analysis Model
A schematic diagram of the system analyzed in this study is shown in Figure 2. The respective values inFigure 2 are shown in Table 1. These are analyzed for the vacuum case and the air case with convection. The
same is also done for the case where copper of the same diameter is introduced. The depth is not consideredin this case.

Figure 2.

Schematic diagram of silica gel adsorption bed

2 of 3

Table 1.

Various values for silica gel adsorption bed

𝐿10 [mm]𝑑𝑇ℎ1 , 𝑇ℎ2

0.5 [mm]
400 [K]𝑇𝑎𝑖𝑟

300 [K]The 1-D heat equation and Fourier's law equations are shown in equations (1) and (2).

𝑐𝜌

𝜕𝑇
𝜕
𝜕𝑇=(𝜆 )
𝜕𝑡 𝜕𝑥 𝜕𝑥𝑑𝑄 = −𝜆(1)

𝜕𝑇𝑑A
𝜕𝑛(2)

Where 𝑐 is specific heat, 𝜌 is density, 𝜆 is thermal conductivity, 𝑇 is temperature,𝜕𝑇𝜕𝑛is temperature

gradient, 𝑄 is amount of heat and 𝐴 is area. These equations are used to analyze heat transfer. In addition,
since thermal resistance such as thermal contact resistance must be taken into account, the thermal
conductivity is given by equation (3)2).

𝜆=𝐿
𝐴(𝑅𝑏𝑒𝑑 + 𝑇𝐶𝑅)

(3)

Where 𝑅𝑏𝑒𝑑 is thermal resistance of packed bed and 𝑇𝐶𝑅 is thermal contact resistance.
In the presentation, we will report on the analysis of temperature distribution for this analytical model.
References
1)

2)

Akira Yokohama, Shinsuke Suzuki, Masato Sakurai, Asuka Shima and Mitsuru Onishi: Effect of the heatertemperature on the quality of desorbed CO2 of the CO2 removal device for long-term space stay, SpaceUtiliz Res, 28 (2012) 105.
Mina Rouhani and Majid Bahrami: Effective thermal conductivity of packed bed adsorbers: Part 2 ─
Theoretical model, International Journal of Heat and Mass Transfer, Volume 123 (2018), DOI:
https://doi.org/10.1016/j.ijheatmasstransfer.2018.01.143.
© 2023 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

3 of 3