[Digestion] energy calculations

[Anand Karve]

Dear Mr. Goonesekera,
 You have to assess the water content in the food waste to get a correct
estimate. Starch and sugar produce almost twice as much biogas as green
vegetable waste. So, the composition of the food waste is also important.
The rule of thumb followed by us is that a kg dry weight of human food waste
would produce about 600 to 700 litres of biogas and that it would replace
about 200 to 250 g LPG. Assuming your daily food waste to be 450 kg to have
a dry weight of 225 kg and that it contains some portion of leafy and
lignocellulosic vegetable waste, one would get daily about 225 X 200 =
45,000 g or 45 kg equivalent of LPG.
Yours
A.D.Karve .

On Fri, Mar 4, 2011 at 11:51 AM, Kshanika Goonesekera <
KshanikaG at masholdings.com> wrote:

>  Hi all,
>
>
>
> I’ve got a proposal for a biogas plant at our textile factory in Sri Lanka.
> I need to verify the energy per day to assess the feasibility of this
> project.
>
> The contractors propose a 90m3 plant (comprising of 3 tanks - 60m3, 20m3
> and 10m3) for a daily input of 450kg of food waste from the canteen.
>
>
>
> My question is will this plant supply enough gas to cover the present LPG
> consumption?
>
>
>
>
>
> *Present LPG consumption in the kitchen*:**
>
>
>
>  cylinders per day
>
> 3
>
>
>
> cylinders per month
>
> 60
>
>
>
> Gas weight per cylinder
>
> 37.5
>
> kg
>
> Energy requirement per day
>
> *4,950*
>
> *MJ/kg*
>
>
>
>
>
>
>
> food waste
>
> 450
>
> kg/day
>
>
>
>
>
>
>
>
>
>
>
> Assuming a food:biogas of 1:1,  450m3 of biogas will be produced per day.
> Of which 60% is CH4 hence, energy obtained = *13,500MJ/day* (calorific
> value of CH4 taken as 50.09MJ/m3)
>
>
>
> However, calculating the energy obtained using the equation below and
> taking 15% of the food waste as Carbon content,
>
> Coe/Co = 0.014T + 0.28
>
>
>
> Gives the energy per day as *3,763MJ/day*
>
> Which of these values am I to trust?
>
>
>
> Thanks and regards
>
> Kshanika Goonesekera
>
> Sri Lanka
>
>
>
>
>
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> for more information about digestion, see
> Beginner's Guide to Biogas
> http://www.adelaide.edu.au/biogas/
> and the Biogas Wiki http://biogas.wikispaces.com/
>
>
>


-- 
***
Dr. A.D. Karve
President, Appropriate Rural Technology Institute (ARTI)

*Please change my email address in your records to: adkarve at gmail.com *
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