Expeditionyacht.org

Since the last Ft. Lauderdale Boat show I’ve “dived” into the question of how to make Nitrox on board.  I visited the stand of Brownie’s at the show where they had the Triton sub on display and we got talking about their Nitrox solution.   Getting home I started doing a little more research.

There are basically two ways to make Nitrox: partial pressure blending and using a membrane.  For practical and safety reasons we stick to membrane systems.  And for reliability and maintenance reasons I stick to German-made compressor equipment.

To make Nitrox (officially ‘enhanced air nitrox’, you first use a low presssure compressor to pump air through a membrane which takes out part of the nitrogen and produces an ‘enhanced’ airmix that contains typically 32% or 36% oxigen.

It is then brought up to 4.500 psi (31o bar) with high pressure compresssors and put into the Nitrox storage tanks.  See the schematic drawing below. 

The problem with making Nitrox is that by compressing air with a low pressure compressor to push it through the membrane it gets a lot warmer.  In fact, some membrane filters need you to even heat the air before it enters the membrane.  This mean you can end up with Nitrox that’s warmer than the manufacturer of the high pressure (HP) compressor recommend it to be.  And hot Nitrox also shortens the service life of your filters pretty dramatically.  So how do you keep that Nitrox cool so it won’t ruin your compressor or loosing your warranty on your HP compressor? 

Another issue is getting the oil out of the air before it gets into the membrane.  Oil and nitrox membranes are not good friends: the first one shortens the life of the last one considerably.  I’ll be trying to find out how to take the most oil from the air before it reaches the membrane and how many hours I can expect from the membrane with a certain minimum oil content in the air.

Different companies, different solutions.  I’ll ‘dive’ more into that in my next post when I have received feedback from all the different providers.   I’m looking both into after market “yacht” products and adaptations as well as off-the-shelve industrial /commercial solutions.   And I checked into water cooled compressors – both after market like those of ‘Nitrox’ Bob Olson and industrial breathing air compressors.  It’s going to be an interesting comparison.