[Digestion] AD for cow manure

[David Fulford]

Hello Rex and listers,

It depends if you want a set of small cheap systems or a large-scale
sophisticated system. Farms with >500 cows probably need the type of digester
that have been developed by various different German companies. They are
designed to generate power and use hot water from the engine to keep the
temperature in the digester at an optimum value (35 deg.C). They are designed
to be as automated as possible. They use both dung and silage as the main
feedstocks. The only disadvantage is cost.

In other parts of Africa there are small-scale systems that are much cheaper,
but rely on labour to run them. The majority of these systems use the
dung from just a few cattle to generate cooking fuel for a family. However,
there are much larger systems that can be used to run a generator.

I do know of installers based in Tanzania and Kenya, capable of making the
larger-scale cheaper units, if you would be interested in this approach.

Regards,

David F

Saturday, June 4, 2011, 7:42:52 AM, you wrote:

> Hi all,

> I am going to do something I swore I would never do. Unfortunately, I just
> don't have the time and know that the folks on this list know far more than
> me and can point me in the right direction.
> I live in a rural area where we are subject to occasional power cuts (power
> lines down mostly due to weather) but, more importantly, our power bills are
> rocketing as South Africa races to catch up to the rest of the world in
> terms of cost of power. Historically we had paid off coal fired power plants
> that gave us the lowest cost of power in the world. Anyway, now that power
> costs are rising, own generation is becoming an economic necessity.

> In my area we have a large number of dairy farms milking >500 cows. These
> are sizeable operations and the manure they produce is worth pursuing.
> Typically they all have slurry dams and they spread their manure from time
> to time (much to our temporary dismay while the odour kills us!). The
> question is: what is an economical way of producing gas? Bear in mind,
> efficiency is not an issue in this case. What we are talking about is
> getting gas that can be cleaned up and fed into motors to produce power. I
> am looking at using 3 litre petrol engines that will push out about 50kW
> tops. So, we are not looking for anything fancy. A plugflow system would
> make most sense as they can pump it into the one end while the processed
> material leaves the other. Heating suggestions? What about using the engine
> exhaust to heat water and circulate that around the reactor or use it to
> preheat the incoming feed? Here I was simply thinking of a double tank with
> hot water in the outer tank... any other suggestions?

> The other thing these farmers use a lot of is sileage (chopped maize that is
> stored and allowed to ferment). Has anyone had experience adding some of
> this to the AD?

> Looking forward to hearing from you all!
> Rex



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-- 
Best regards,
 David
  mailto:davidf at kingdombio.com
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Dr David Fulford CEnv MEI, 15, Brandon Ave, Woodley, Reading RG5 4PU
d.j.fulford at btinternet.com, Tel: +44(0)118 326 9779 Mob: +44(0)7746 806401
Kingdom Bioenergy Ltd, www.kingdombio.com, davidf at kindombio.com