[Digestion] Compressing Biogas into a Tank

Thu Aug 30 11:37:20 EDT 2007

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

At 06:36 30/08/2007 -0700, gp baron wrote:
>Komusta to all and thank you for responding to my inquiry.
>
>   My digesters are small units (in the 5 & 8 m3 size range.) They are 
> designed to produce cooking fuel from backyard farm animal manures. 
> Biogas produced overnite is typically used to cook breakfast. Gas 
> produced during the day is used for dinner.
>
>   I suspect, when biogas is produced, more is developed when pressure in 
> the container is low and less is produced when gas has accumulated and 
> pressure is higher. Is this true? Is biogas production affected by 
> pressure? Would negative (or vacuum) pressure produce more gas?
>
>   When biogas is used for cooking -- the flames begin strong, weaken and 
> make cooking difficult. By compressing biogas and regulating pressure to 
> a burner, a strong and constant flame can be maintained for faster and 
> more efficient cooking.
>
>   I have no plans to liquefy biogas but I would like to compress it to 
> say 50 psi and bubble it through a column of water (changed daily) before 
> containing it into a pressure tank. Would this effort help remove CO2 and 
> other impurities? Or are higher pressures of 10 bar (150 psi) necessary? 
> Are there other methods like passing the gas through wood chips, charcoal 
> and/or sand & stones available to make biogas a better cooking fuel?
>
>   Mabuhay & more power!
>
>   Gerry
>
>Paul Harris <paul.harris at adelaide.edu.au> wrote:
>   G'day Gerry,
>
>Biogas does react with mineral oil (we havd several destroyed
>compressors to attest to this!) but synthetic oil is apparently OK.
>
>Methane will not liquify at room temperatures and getting high pressures
>is very energy intensive.
>
>Hope this is some help,
>HOOROO
>
>gp baron wrote:
> >
> > Can biogas be compressed, using a regular air compressor, into a tank? 
> As biogas is 60% methane (CH4), would it have adverse reactions with oil 
> in an air compressor the way acetylene (C2H2) would?
> >
> > I have seen biogas stored in bladders, huge rubberized bags and 
> telescoping / floating metal tanks. I also remember some discussion in 
> this forum that biogas can be compressed and even be liquefied. These 
> options, however, are too bulky, non-transportable, complex and expensive.
> >
> > If biogas can be compressed using regular air compressors into a 
> stainless steel compressed air tank (if necessary) to minimize / avoid 
> corrosion -- it would be easier to use say for cooking, lighting, 
> heating, etc. The tank can be re-filled when needed and brought to where 
> the gas will be used. We can have a simple and practical way to make 
> better use of this fuel.
> >
> > Kindly share any information and/or experience you have. Thank you in 
> advance.
> >
> > Gerry
> > - -
> > Gerardo P. Baron
> > Philippine (Home Biogas System)
> > Email: gpbaron4091 at yahoo.com
> > Phone: +63 927 407 1142
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