[Digestion] Compressing Biogas into a Tank

[Tom Miles]

David,

In practical terms how much CO2 can be removed from the gas? What are
typical CO2 levels and what is a "scrubbed" level taking advantage of the
solubility and pressure?

Thanks

Tom


> -----Original Message-----
> From: digestion-bounces at listserv.repp.org [mailto:digestion-
> bounces at listserv.repp.org] On Behalf Of David Fulford
> Sent: Thursday, August 30, 2007 8:37 AM
> To: gp baron; Paul Harris
> Cc: digestion at listserv.repp.org
> Subject: Re: [Digestion] Compressing Biogas into a Tank
> 
> Gerry, Hi
> 
> Your systems sound typical of those used in places such as India and
> China.
> Some of the early work in India suggested that the gas production was
> higher at low pressures, so they used counter-balances with a floating
> drum
> to cause a negative gauge pressure. Unfortunately, if there is a leak
> in
> the system, air can mix with the gas and cause an explosive mixture. I
> have
> heard of a floating tank take-off when a farmer tried to demonstrate
> the
> flammability of the gas by lighting it as it came from the pipe in the
> top
> of the drum.
> 
> In fact, while the biogas production increases, the methane production
> does
> not. This is because the solubility of carbon dioxide in water varies
> with
> pressure, so a reduced pressure causes carbon dioxide to come out of
> solution. An increased pressure actually gives a better quality gas, as
> the
> carbon dioxide content is reduced. Dr Karve of ARTI claims that his
> floating drum system "pumps" carbon dioxide from the gas, as the
> pressure
> at the slurry surface in the narrow annulus outside the drum is lower
> than
> that of the biogas inside the drum, so the dissolved carbon dioxide
> bubbles
> out around this annulus.
> 
> Cheers,
> 
> David