Review of Two Methods to Remove CO2 Using Seawater From Submarines During Emergency Conditions

During normal operations, U.S. Navy submarines employ an electrically-powered regenerative scrubber system to remove carbon dioxide CO2 from the atmosphere using a water solution of monoethanolamine. A non-regenerative method of CO2 removal is also available onboard, using canisters of lithium hydroxide LiOH, that can be used as a backup to, and in conjunction with, the regenerative scrubber to increase the capability to remove CO2. However, under distress situations, where the submarine is disabled DISSUB and unable to surface, there is likely to be flooding and loss of AC power to run either system to remove CO2. Under these conditions, the current guidance recommends that the lithium hydroxide canisters be opened and the palletized material spread Out on the floor and other flat surfaces. However, there are significant problems related to the use of LiOH with or without electrical power. They include health concerns, limited stores that may not support the crew until rescue, and storage space requirements. Consequently, there is a strong need to develop an alternative CO2 scrubbing system for submarine use that uses either no power, limited human power, or the ships main batteries. This report reviews two methods and some recent testing of their effectiveness, for such removal of CO2 using seawater by 1 direct water contact with the air or 2 indirect contact in conjunction with a membrane system. Both methods were shown to be effective in removing CO2 from a closed-space atmosphere, thus offering the potential for greatly extending survivability during a DISSUB scenario. However, the feasibility of these techniques for the DISSUB, and the best way to design the system, remains to be investigated.