CARBON DIOXIDE CONTROL

On Earth, carbon dioxide levels in air have been rising since the advent of the Industrial Age. This has caused concern about the possibility of global warming induced by the atmospheric accumulation of anthropogenic 'Greenhouse Gases'. The current worldwide average airborne carbon dioxide level is approximately 350 ppm. Near sources of combustion such as automobile traffic, and in enclosed spaces, human beings are normally exposed to much higher levels. A recording of CO2 levels in the author's laboratory over several days is shown below:

In the above, the levels of peak CO2 concentration correspond to daytime, when several researchers are busily at work. The minima correspond to the evenings and weekends when the building is uninhabited. People can work without deleterious consequences in elevated CO2 levels. The original Space Station Freedom AR system was designed to maintain levels of 2000 ppm or less. The life support system for space suits worn during EVA is designed to maintain CO2 levels at or below 5000 ppm. Carbon dioxide generation rates are approximately 1 kg/person/day (2.2 lbs/person/day).

The ultimate means of CO2 control in a Bioregenerative Life Support System is the use of Green Plants to transform carbon dioxide into oxygen through photosynthesis. Information regarding this topic is provided under Advanced Life Support Systems (ALSS). Most primary physico-chemical CO2 removal systems for Life Support applications are sorption based. Molecular sieves are used to remove CO2 by adsorption (physi-sorption) within the porous structure of Zeolites. Additionally, several systems have been developed for the removal of carbon dioxide by chemisorption. These include lithium hydroxide (LiOH), silver oxide (Ag2O), and solid phase amines.

Once separated from air and concentrated, CO2 can be used to generate water in Bosch or Sabatier Reactors. Oxygen can also be produced directly from the electrolytic decomposition of CO2. A discussion of each of these systems can be accessed by the Links provided below.

LINKS TO SPECIFIC CO2 CONTROL METHODS

Copyright © 1996, James E. Atwater