[Digestion] 5000 dairy cow AD system

[Rex Zietsman]

Gentlemen,

Your very valid reasons are appreciated. Would the argument hold if the
centralised AD were part of a large town's water treatment works. The idea
would be to take over the running of the existing works with the intention
of combining all the gas generation into one system. The main benefit is
that there would be a lot of existing infrastructure that would help reduce
the capital cost.

I come back to one of my questions though: does the FFA reside mostly in the
liquid or the solid phase prior to digestion? Or is it split? Paul has a
feeling that a lot of it is in the liquid and my experience indicates that
this is in fact the case. Consequently, local digestion would make far more
sense. Alternatively, the mobile unit could come into its own as there are
already lagoons at each farm. We also have many chicken farms that are
necessarily distributed to keep down the possibility of infection from one
location to another. Mobile units make sense for this application as well.

Many thanks for the help
Rex


Rex,

Another way to go would be to make a smaller mobile unit that would be
transported to the individual sites.  A unit that could handle a 1000
cows/pigs, 10000 birds as well as other agricultural concerns, would fit on
two flatbeds.  This would give a flexibility to demonstrate the success of
the process, and share the capital cost, with multiple users in the area.
 I've been involved in designing multiple mobile batch plants for other
industries and this is not as difficult as one might think.

On Sun, Jan 8, 2012 at 10:51 PM, Paul Harris
<paul.harris at adelaide.edu.au>wrote:

>  G?day Rex,****
>
> ** **
>
> Apparently a lot of the biogas comes from the fines/solutes in the liquid
> ? I noticed that with piggery effluent the raw effluent was almost
> impermeable to water (it would hold puddles for quite a while) but after
> treatment the solids were pretty free draining (water disappeared in
> minutes).****
>
> ** **
>
> I will also raise my usual point in favour of distributed systems ? why
> not put smaller (cheaper!) digesters at each farm and if necessary pipe
the
> biogas to a central generator (depending on distance)? You will be
spending
> a lot of energy on trucking waste in and then you have to truck the
> digestate out from the central facility again. The total capital cost may
> be higher, with more units to maintain, but you can start with one or two
> and spread the finances out a bit as well as helping local employment (I
> guess people will be working on digesters instead of driving trucks!).****
>
> ** **
>
> Happy digesting,****
>
> HOOROO****

I concur on Paul's preference for smaller systems.  I have seen a handful
of proposals based on trucking waste from a number of small to medium farms
where they have tried to show energy balance (all the trucks are methane
powered, etc.), but the numbers never add up.  Specifically, de-watering
this waste requires relatively well developed systems at each site, and
likely still leaves you with a serious amount of waste water treatment for
each site to achieve healthy discharge levels (in Mexico it is the water,
not the solids that is the treatment challenge).  The management system is
also more complex and requires a high level of coordination.  The
alternative de-centralized option will likely have similar initial capital
costs, but you can make a better case for farmer investment as they will
reap the benefits.  You then have much smaller long-term operating costs,
and all that energy for trucking can go to good use (or maybe still
trucking some effluent fertilizer to local fields).  As Paul mentioned, the
option to eventually pipe gas a larger distance for centralized use is an
option that may make sense (but I have not seen it outside of the European
context or large landfill gas context yet).

Cheers

A



Dear Rex,

I would suggest contacting Burdens who is distributing the "Portagester"
system in the UK and that could be useful for your intended use and scale.

Their web is
www.bioplex.co.uk/*portagester*.shtml<http://www.bioplex.co.uk/portagester.s
html>

Best regards,
Pablo.