[Digestion] AD for cow manure

[Rex Zietsman]

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