[Digestion] energy calculations

Kshanika Goonesekera KshanikaG at masholdings.com
Sun Mar 6 23:05:43 CST 2011


Hi all,

Thank you Mr. Karve and Johan Carels for the valuable information. The contractor assures me that by reducing the input of water the CH4 content can be increased, and the 3 digesters will maximize biogas output further due to consecutive digestion. Is this possible?

Has anyone any experience with the 1:1, food(dry matter):biogas output?

Regards
Kshanika

________________________________
From: digestion-bounces at lists.bioenergylists.org [mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of Anand Karve
Sent: Sunday, March 06, 2011 8:30 AM
To: For Discussion of Anaerobic Digestion
Subject: Re: [Digestion] energy calculations

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

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