[Stoves] Compact biogas plant

[Richard Stanley]

Dear Ad,
In yoru recent post to Kevin, I am left a bit puzzled .
Your note that the oldertanks made of meetal were heavy and provided  
a restiction to production can easily be understood.  If in fact you  
need weight with distance from the appliance, then it seems to me  
that ballast is indeed more sensible and less costly and more  
aesthetic way to go.  Our Tanzania cow dung digesters were indeed  
several hundred Kgs in weight. Even as spread  over a 2.5 mtr dia,  
this must have presented considerable constriction in production,  
which  we never knew about until you enlightneed us yesterday !.

Still the appliances we used required 2.5 to 3mm dia feed jets (at  
the base of each burner) in order to accept the gas. The added weight  
created about 3 inches of line pressure (as determined thru simple  
observation of the bubbling in the in line water trap). This  
increased delivery pressure was thought necessary becasue the science  
at the time held that was more viscous than LP gas. Our tanki was  
about 8 ft from the kitchen. If line resistance was a problem, one  
could simply increase line diameter no ?
I therefore wonder what kind of appliance you are using that it can  
burn such gas with what has to be a very reduced operating pressure.  
Do you have larger jets or ??

Richard

  represented a considerable reduction framee
On May 6, 2007, at 19:26, adkarve wrote:

> Dear Kevin,
> In the traditional models of biogas plants the movable dome, or gas  
> holder,
> is made of iron plates, either welded or riveted together. The gas  
> holder is
> therefore quite heavy.  In our case, the gas holder is made of moulded
> plastic. It is quite light. There were instances, when the gas  
> holder got
> dislodged by strong wind when it had telescoped fully out of the  
> digester.
> In order to avoid such a mishap, we fitted our biogas plant with a  
> framework
> that holds the gas holder in place. We do not put any weights on  
> top of the
> gas holder, if  the biogas plant is just outside the kitchen.  What  
> Richard
> had suggested was that if we put weights at the bottom of the gas  
> holder,
> the weights would stabilise the gas holder and that we then would  
> not need
> the framework that held the gas holder in place.
> Now I come back to your question. Normally, the weight of the gas  
> holder is
> enough to deliver the gas to the burner in the kitchen. But if the  
> biogas
> plant is more than 6 meters away from the burner, one has to put  
> weights on
> top of the gas holder so that the system develops enough pressure to
> overcome the resistance of the 10 meter long rubber tubing.  In all  
> such
> cases, we found that the amount of biogas produced under pressure  
> was less
> than the amount produced without the weight.
> Yours
> A.D.Karve
>
> ----- Original Message -----
> From: Kevin Chisholm <kchisholm at ca.inter.net>
> To: <adkarve at pn2.vsnl.net.in>
> Sent: Sunday, May 06, 2007 5:14 PM
> Subject: Re: [Stoves] Compact biogas plant
>
>
>> Dear AD
>>
>> I am surprised at this...
>>
>> Certainly, if one tried to make biomethane at "high pressure", say  
>> at 2
>> ATM pressure, one would expect a fall-off, but at the small increased
>> pressure required to deliver gas to the burner, there should only  
>> be a
>> small retardation in methane generation rate.
>>
>> This should certainly be the case, in the case of an "inorganic
>> reaction", where the Law of Mass Action, and its Pressure Equivalent
>> were at play.
>>
>> Is it perhaps a case that in a biological system, the rules for how
>> pressure governs a reaction are different?
>>
>> If so, in nature, would the rate at which methane is generated be
>> different in a "shallow" pond, of say 1" depth, versus a "deep"  
>> pond of
>> say 4 feet depth?
>>
>> If so, then a "deep" biogas reactor (4') would have a slower  
>> production
>> rate than would an agitated biogas reactor that would have an  
>> effective
>> depth of say 1".
>>
>> Note also, that basically, the pressure in the biogas reactor with  
>> the
>> system Richard proposes would not be changed... what he is  
>> proposing is
>> basically to support the same total weight of gas collector weights
>> inside the collector, at its base, rather than outside the  
>> collector on
>> its top. The advantage of his proposed system is that the  
>> collector is
>> inherently stable, and side supports are not necessary.
>>
>> Best wishes,
>>
>> Kevin.
>>
>
>
>
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