A local homebrewer showed me his setup yesterday (nice, 15 gal...) and he had an "oxygen concentrator" sitting there. I asked about it and he said he had access to a number of them.
It works by removing nitrogen from the air and concentrating the oxygen until it is at 90+%.
He runs it through a HEPA filter and then into a stone.
It can produce up to 5L / min. These were used for hospitals and are about 2.5' x 1' x 1.5' and resemble a little dehumidifier. It runs pretty quiet.
They have a runtime meter on them and are timed out for human usage but still produce above 90% concentration of O2.
Anyway, if anyone is interested I'll hook you up with the supplier.
