[Digestion] Contents of digestion digest

[Alexander Eaton]

David, you are such a tease!  Bill, everything David says is correct, as
there is lots of complexity in how ER will be awarded for small digesters.
But, (without going into the details, and given you get lots of systems
together under similar conditions, and that you are using the gas
productively on-site for thermal energy and using a design that doesn't leak
excessively) we are able to commercialize credits that are based ONLY ON
ENERGY OFFSET at a rate of about 4.1-4.7 kg CO2/m3 of biogas.

It is difficult to get methane capture and destruction credits as baseline
conditions vary a lot across small farms, but (assuming that animal waste is
stored in a deep pit under anaerobic conditions for more than a month) that
would roughly be worth about 100-140 kg of CO2/pig/yr.  That same pig will
produce about 36 m3 of biogas over the course of the year worth about 0.81
GJ of energy which will offset about 150 kg CO2/yr.  This means that each
pigs waste that is managed by a digester (given credit for fuel displacement
AND methane capture) could in theory produce around 250-300 kg CO2/yr in
Emissions Reductions.

Again, we are only able to account for energy offsets at this time, so a
back of the envelope estimate for us is generally about 150 kg CO2/yr.  Cows
can be considered about six pigs.  Again, this is very rough, but it is nice
to have order of magnitude estimates sometimes!  As David says, each project
would have to be considered separately, and obviously all digesters and
wastes are not the same.

Cheers and Happy New Year to the Group!

A





On Sun, Jan 2, 2011 at 5:06 PM, David <david at h4c.org> wrote:

>
>
> Bill,
>
> On 1/1/2011 11:53 PM, Bill Rucks wrote:
>
> Some one must have a idea on that very simple equation 1000 - 10 m3 of biogas is equal to 1 tonne of co2 equivalents ??????  We will never build a large multiple of these system unless we have a idea on that ratio -  an surly building lots of small systems will benefit lots more people - than big companies - the big companies have got us into this predetermine that we find our selves in !!!
>
>
> Do forgive me if it was not clear, but if you consider my previous answer
> carefully, you will see that CO2 equiv is not a fixed metric-- there is no
> such fixed ratio between volume of biogas produced and CO2 equiv saved, *it
> does not and cannot exist*, to be quite clear about it-- but rather is
> situational. In order to earn carbon credits, one must demonstrate, in a
> rather specific way and for a specific situation, that a given digester or
> group of digesters is likely to be saving a certain tonnage of CO2 equiv.
> Explore the UNFCCC website, and if you can wade through the somewhat
> unsatisfactory search process provided, you can uncover a wealth of
> documents about small biogas digester projects that have gone through the
> process and produced their answers.
>
> My exploration of those documents and a wealth of other information leads
> me to believe that it should be possible in many situations to experience an
> annual CO2 equiv savings of a bit better than a tonne and a half per cu m
> digester, but so many factors intervene that one must also assert that the
> ballpark is rather large. For example, if the digesters built for a given
> project have a tendency to leak, then by rights the very powerful effect of
> methane as a GHG should be factored in to the calculations, and might even
> erase a major portion of the claimed savings.
>
> You've simply got to widen the scope of your question in order to come to
> any reasonable answer. What is the situation now, how many tonnes of CO2
> equiv are presently being produced, and, under the circumstances that
> apply-- weather, number of animals per family, size of digester, etc.,
> etc.-- how much of that can be offset by using the expected biogas?
>
>
>
>
> d.
> --
> David William House
>  "The Complete Biogas Handbook" www.completebiogas.com
> *Vahid Biogas*, an alternative energy consultancy www.vahidbiogas.com
>
>  "Make no search for water.       But find thirst,
> And water from the very ground will burst."
> (Rumi, a Persian mystic poet, quoted in *Delight of Hearts*, p. 77)
>
> http://bahai.us/
>
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> http://www.adelaide.edu.au/biogas/
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>
>
>


-- 
Alexander Eaton
Sistema Biobolsa
IRRI-Mexico
RedBioLAC

Mex cel: (55) 11522786
US cel: 970 275 4505

alex at irrimexico.org
alex at sistemabiobolsa.com

sistemabiobolsa.com
www.irrimexico.org
www.redbiolac.org
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