View source for Biogas CO2 scrubbing project

The biogas comes off the digester by its own pressure and comes through the
[[Biogas H2S Scrubbing|Sulphide stripper]], and is collected in a
gas bag which has a air pressure switch gotten from an automatic washing
machine, which clicks in at about 12" water gauge and out at about 2-3".
When the gas bag is full the switch clicks in and starts a  simple air
compressor which only needs to pump the gas up to   around  50-60psi.
although the compressor can go much more than that.  

The compressed gas is
then bubbled into the base of a vertical standing length of  6-10" pipe
about 4-6metres high and 2/3 full of water. The pipe can be anything though
PVC looks nice and clean.  If you are lucky enough to have a high mains
pressure for your supply, you just feed that in through a partially opened
tap.  The water level is controlled  by an exit float valve  which bleeds
off the highly gas charged water when the level gets beyond 2/3 to 3/4 way
up the pipe.  That water, when the pressure is released, will fiz just like
soda water.  

The gas then comes off the top of the vertical pipe through a
pressure release valve which controls the whole operation, and goes into a
pressure cylinder for storage at what we call '''intermediate pressure'''. If your
water supply is at low pressure, then  you will have to use an old piston
water pump or any type of positive displacement pump which can work at its
limit, say 150psi. It should be switched off and on along with the gas
compressor.  This means that the gas compressor can also work up to that
figure, and the whole system shifts up a cog in terms of its efficiency and
the gas comes out the stripping column for storage at that much higher a
pressure (150psi) and correspondingly less volume.  

We liked to get hold of old 500
litre LPG  cylinders from hotels and the like. One farmer I knew got hold of
an old railway locomotive boiler and used that.  He actually had two. One
alongside the biogas plant and another alongside his grain drier which was
about half a mile away.  They were connected together by 3/4" pvc water
pipe, which gave adequate gas transfer when the grain drier was working.
Just make sure that you have a water drain tap on the bottom of your storage
cylinder because everything gets warm and the gas will drop a lot of
moisture as it cools.