[Digestion] compressing biogas

[Ken Calvert]

Dear Michael etal,  I think you have found the figures for LNG not CNG.  The 
only way to liquify Methane is at a very low temperature.  If you strip the 
CO2 and H2S out of biogas then to all intents you have Natural Gas, and CNG 
or compressed natural gas equipment operates at around 3,500psi, but it is 
still a gas.   If you are going to compress biogas at all,  then it is best 
to stick to the usual figures and then you can run you car  cook your food 
and warm your house with standard mass produced Global standard equipment 
from off the shelf of any hardware/heating store.  If you, and anyone else 
wants some plans as to how to do it as economically as possible then send me 
a private email and I will return mail you some  brochures put out by our 
Ministry of Agriculture  for  small  farm and hobby farm Biogas plant.
    In brief, you collect the gas in a plastic bag, and monitor the pressure 
with the filler guage out of a auto washing machine. The pressure switches 
on a  two cylinder air compressor which sucks the gas through one of a pair 
of barrels filed with rusty bashed up tin cans which are alternated one in 
line and the other left open to the air. The Iron sulphide in air then 
reverts to iron metal for reuse of the barrel, and the sulfur is left as 
elemental flowers of sulfur which is useful stuff. (beware heat problems) 
At around 150psi  the gas is bubbled through a vertical water column 
consisting of a six meter length of 6" 150mil  plastic pipe.  2metres as 
someone suggested is not enough.  Natural gas at 150psi can then be used in 
liu of LPG  if  it is metered through an LPG reduction valve and the jets in 
LPG stuff are opened out a smidgeon.  Storing a reasonable volume of methane 
at this pressure takes some ingenuity  but  it can be done.  To drive your 
car on CNG requires a pair of old double acting hydraulic cylinders off a 
bulldozer or some such. You can't  use one cylinder with a floating piston, 
because as already mentioned lubricating oil will take up methane under 
pressure   and hydraulic pumps don't work too well with oil foaming out the 
tank.   A single 3 ft stroke will take you up to 3000psi +  in one stroke, 
and normal DIY hydraulic equipment from  Northern Tool or other DIY stores 
operate at just the right pressures to make a  rather neat setup.  However,
let me say it again  spending the money to go this far is crazy if you do 
not clean up your gas first and  convert it into the Natural Gas which is a 
world wide commodity with so many appliances and equipment  matched to its 
use.
Ken C.


----- Original Message ----- 
From: "Michael Smith" <michael_1234 at msn.com>
To: "digestion" <digestion at listserv.repp.org>
Sent: Monday, September 03, 2007 8:31 AM
Subject: [Digestion] compressing biogas


> If the methane in pressurization is liquefied @ approx. 1100 psi what are 
> the consequences of the CO2 and Nitrogen at these pressures? I expect more 
> than enough electricity from wind power at various times to pressurize...2 
> to 4 cu. ft. per minute.
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> Beginner's Guide to Biogas
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>