[Digestion] flex use biogas plant

[Zietsman, Rex]

Jason, Bjorn & Listers,
One of the best comments made on Digestion Digest, Vol 5, Issue 15 is
that the Internet provides so much help to one another. 
I am looking to build a digestor that will treat cow & pig manure with
the gas driving an engine to produce power. As we will have a small
dairy, we need cold. Instead of an absorption chiller, the engine
supplier I was in contact with via the Internet suggested that I bolt on
a car's A/C compressor and use that to generate cold. Not only is the
equipment proven, it is easy to maintain (second hand units are freely
available and relatively cheap). If you need more cooling than a car's
A/C compressor, get a bigger compressor as you will have a bigger engine
because you will have more cows generating more biogas! 
Another lister, Steve from New Zealand, sent me an article on using
water to remove CO2. Essentially, if you have a multi-stage compressor
to get up the pressures required for gas powered vehicles, you pull the
gas off after the first stage say at 5 bar, pass it through a column
irrigated by water and the water will absorb the CO2 just as in a fizzy
cooldrink. The CO2 loaded water is pumped to an open tank and irrigated
onto the surface. As the water depressurises, the CO2 escapes to
atmosphere. The water is then recycled to the scrubbing tower. The gas
in the meanwhile leaves the top of the tower and goes into the second
stage of the compressor. Just remember that there should be water traps
after each stage (anyone working with air compressors will also tell you
that). Finally, the beauty of the water scrubber is that if you add a
small about of alkali (lime, caustic, etc), you will also capture H2S!
This is a double win.
Cheers
Rex