[Digestion] The relatively high cost of digesters.

Björn Dahlroth bjorn.dahlroth at telia.com
Wed Dec 8 10:43:47 CST 2010


Hello

More comments about efficiency.
When you are discussing efficiency and yield don't forget the energetic
efficiency. If you are working with industrial plants and large scale
digestion of various kinds of waste you must remember that the matter you
put in does have a an economical value even if it often is a negative value,
it also has a calorimetric heating value (=upper heating value) but only
some part of that can in theory be converted to gas. You must also no how
much electricity and heat you have to supply to the plant (the heat could
come from burning some of the gas) and you must now the energy content of
the net gas production.  Even if waste has a negative value you want to
squeeze out the maximum energy or the maximum business value from the stream
of material that you put in and if you are in a planning stage and have not
yet invested you must also consider all other treatment methods. It seems
that quite often it is not possible to get good information on the energetic
and economical efficiency and I have a feeling that the owners don't know
themselves. This is pity for all those who want to build digestion plants in
the future and it slows down development. 

About yield per cubic meter of volume one must remember that this also
depends on the residence time. A shorter residence time could increase the
yield per volume of a digester vessel and raise the economic efficiency but
it will decrease the gas yield per ton of digestible matter. Some digestible
matter or mixtures of matter need a longer residence time.

These things are rather important and deserves international discussion and
exchange of information. They are less important for small scale rural
digesters, which are important in countries with large rural populations
living at a fairly low economical level, but the new future for applied
digestion technology is in the larger and more sophisticated plants. One
reason for that there is not so much information on economic and
thermodynamic efficiency could be that it requires good knowledge about
composition of the material that goes in. It is not a pleasant job to dig in
the raw material, take samples regularly and analyse the composition in more
detail.

Bjorn Dahlroth
Sweden


-----Ursprungligt meddelande-----
Från: digestion-bounces at lists.bioenergylists.org
[mailto:digestion-bounces at lists.bioenergylists.org] För Hoysall Chanakya
Skickat: den 8 december 2010 06:29
Till: paul.harris at adelaide.edu.au; For Discussion of Anaerobic Digestion
Ämne: [Digestion] The relatively high cost of digesters.

Dear Paul (high digester costs),
Thanks for bringing it out succinctly - our narrow-focused obsession for
yields seen as gas production rate (m3 gas /m3 reactor /d) has led us to
this predicament of "sophisticated" and large digesters almost having
reached a point of no-return.  As we climb the yleld-rate ladder the
tolerance falls rapidly so the process can only be run with sophisticated
controls.  Loading so much controls makes it viable only at a large scale
- a catch-22 situation.

Many of us on this list have now moved towards a utility focused approach
- and in effect sacrificing a small bit on the "volumetric efficiency". 
What is interesting is in this exercise it also seems one could expand on
the feedstock variety - a vital requirement in tropical areas.  I am sure
like Dr.Karve, there are many more who have experimented and prioritized
with feedstock flexibility (especially agro-residues) with amazing
results.  IT would be nice to exchange more on this experience
best wishes
chanakya





  be "measured"
> G'day All,
>
> One reason for the "high" cost of digesters is that "Westerners" seem to
> have a preoccupation with complexity and large, centralised facilities -
> which "we" expect to inflict on the rest of the world.
>
> The small, simple, decentralised systems used extensively in China, India
> and more recently Columbia, Vietnam, Cambodia and Bolivia and reported by
> some members of this discussion group are making a big improvement to the
> environment by providing convenient, clean fuel without deforestation or
> fossil fuel depletion. They may not win on "biogas per unit digester
> volume"
> or "throughput per day" and will not make corporate profits but they do
> lift
> people from poverty, ease the grind of daily life and may well get more
> biogas per unit of VS/COD, compared to "our" large units.
>
> I agree you get what you pay for and there are bound to be improvements
> that
> may need to be done, but it's also "horses for courses".
>
> Happy digesting,
> HOOROO
>
> Mr. Paul Harris, Room S116b, Waite Main Building Faculty of Sciences, The 
> University of Adelaide, Waite Campus, PMB 1, Glen Osmond SA 5064 Ph    :
> +61
> 8 8303 7880      Fax   : +61 8 8303 4386
> mailto:paul.harris at adelaide.edu.au  
> http://www.adelaide.edu.au/directory/paul.harris
>
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> -----Original Message-----
> From: digestion-bounces at lists.bioenergylists.org
> [mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of Edgar
> Blanco-Madrigal
> Sent: Tuesday, 7 December 2010 10:51 PM
> To: For Discussion of Anaerobic Digestion
> Cc: digestion
> Subject: Re: [Digestion] The relatively high cost of digesters.
>
> In AD the universal principle applies:
> "You get what you pay for"
>
> You can build a cheap digester, and produce gas, etc. But you should not
> pretend this in any way will be helping the environment, because to do
> that
> money has to be committed in the whole operation.
>
> SNIP
>
> Please, do not peddle technology on the basis of its low cost, do it on
> the
> basis of quality!
>
>
>
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>
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-- 
Dr. Hoysall Chanakya
Centre for Sustainable Technologies
(Assoc. Faculty at Centre for Infrastructure, Sustainable Transport and
Urban Planning (CiSTUP) and Centre for Contemporary Studies)
Indian Institute of Science, Bangalore 560 012
ph 91-80-2293 3046; fax-91 80 2360 0683


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