[Digestion] AD for cow manure

[Rex Zietsman]

David,

What I have seen down here which sounds and looks attractive is the use of
bladders. Effectively the "inventor" scraped hollows with adjacent walls and
put in heavy duty bladders that hold about 30m3. He has 11 of them and
empties and fills one a week with chicken litter. As the bladders are black,
they absorb heat from the sun which helps keep the temperature up. He then
uses two bladders as his gas storage system. By packing rocks onto the
bladder, he can pressurise them to deliver gas using PVC piping to his
generator. His H2S removal system was two 200 litre drums welded together
and filled with machining swarf. Catchpots served both as flash back
arrestors and as condensate drains. Each bag costs about $1500.

The benefit of this simple system is that it is easily tested at the one/two
bag size. If successful ie convinces the farmer that it works, it can easily
be expanded. At the same farm mentioned above, the farmer bought an old
scuba diving tank filling compressor and bought some old gas cylinders. He
then rigged his tractors and truck to take compressed biogas into their air
inlets and save diesel that way. So there are ways of extending the use of
biogas.

If anyone can add to this type of debate, I believe it would be helpful not
only to me but the list in general.

Kind regards
Rex 

-----Original Message-----
From: David Fulford [mailto:davidf at kingdombio.com] 
Sent: 04 June 2011 10:59 AM
To: Rex Zietsman
Cc: digestion at lists.bioenergylists.org
Subject: Re: [Digestion] AD for cow manure

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