Living in an underwater habitat requires gas treatment; an input of oxygen, the disposal of carbon dioxide and pollutants, and one kind of ‘carrier’ or inert gas (nitrogen or helium). Industrial divers live in a pressure complex on a support vessel and all air treating is done outside the habitat on the vessel. It seems there are not too many references of air being treated inside an underwater habitat. If we are mistaken do not hesitate to comment this article accordingly.
Commercial Diving generally takes place in very deep water. Helium is used as inert gas, unscramblers are ‘translating’ the high frequency voices to an understandable level, the breathing medium has to be heated, the diving suits are equipped with circulating warm water and expensive decompression systems are available on expensive support vessels being operated by huge crews. Some example diving manuals are available in our Digital Library. We might get inspiration form their procedures, but since our projects are not supposed to be that deep and with a longer duration, we will be able to use more simple methods. Beside that we will not have a financial turnover as in a oil company leading to the conclusion that we will have to find systems, that would fit our demands, but would be unsuitable for commercial diving activities.
One of the best among the few sources ist Living and Working in the Sea by Ian Koblick and Jim Miller. This book from 1984 describes all underwater habitats of the 60’s and 70’s and comes up with all necessary conclusions. It is most likely that most of it is not outdated in general, though there might be developments in detail. Therefore we should use that file as a basement and double-check them with recent developments. By the way, Mart is currently translating the book to German and, most important, to the metric system. Keep in touch with our page to be updated.
- a constant flow of fresh air: air is pumped from the surface/shore into the habitat while redundant air bubbles out from the entrance pool. No filtering mechanism is necessary, but the flow of air has to be undisrupted. Since the fresh air travels through long pipes there should be preventive steps to avoid odours from the pipe material and moisture. The air inside the habitat should be exchanged all 60-90 minutes completely. Aquarius habitat uses compressors in the life support buoy pumping the air into the habitat.
- compressed air tanks: the air is stored in huge tanks to provide a constant flow of air. These tanks are generally located outside the habitat not to waste precious space, and due to difficulties and risks during refilling and handling, that might damage the integrity of the hull. The tanks can be filled via hoses from compressors on the surface or completely exchanged when empty. This system requires lots of tanks (the deeper the more) while its handling is difficult. On the other hand there is no carbon dioxide filtering necessary
- oxygen tanks: produced carbon dioxide is filtered out and replaced by oxygen stored in tanks. This system requires oxygen-clean equipment (since oxygen promotes rapid combustion, valves should be oil-free etc.) and atmosphere measuring/blending devices.
These solutions could be used for the first stages of the habitat. But after a while we should consider air treatment inside the habitat.
Here are some proposals for processing the atmosphere inside the habitat.
In standard dry scrubbers polluted air is led through a canister of absorbent like sodalime (see SodaSorb by Amron) which filters out the carbon dioxide and releases clean air. The absorbent has to be replaced frequently in huge amounts.
Aquanaut and adventurer Lloyd Godson used a biocoil for gas treatment in his BioSub project. In this system chlorella algae in a transparent tubeare supposed to convert carbon dioxide into oxygen. Though a very impressive idea the system failed to work satisfactory. See all details about the biocoil on our former article. Still the idea deserves to be followed-up. Maybe there is a way to make it function.
Amine Gas Treating
A typical amine gas treating process includes an absorber unit and a regenerator unit as well as accessory equipment. In the absorber, the downflowing amine solution absorbs H2S and CO2 from the upflowing sour gas to produce a sweetened gas stream (i.e., a gas free of hydrogen sulfide and carbon dioxide) as a product and an amine solution rich in the absorbed acid gases. The resultant “rich” amine is then routed into the regenerator (a stripper with a reboiler) to produce regenerated or “lean” amine that is recycled for reuse in the absorber. The stripped overhead gas from the regenerator is concentrated H2S and CO2. (Source: Wikipedia)
Systems like this are used in nuclear submarines like in the USS Nautilus. One major concern is the case of a leaky separator that would produce a chemical aerosol that might harm the aquanauts health.
Image Source: [GFDL (http://www.gnu.org/copyleft/fdl.html) oder CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons, User Mbeychok
Gas Treatment by using Sea Water
Another alternative we are just considering is the question if it would be possible to clean air by leading it through a spray of seawater? Seawater is available and disposable without limits.
to be continued…