[Digestion] Small Scale Digester Heating
Jaime Marti Herrero
tallerbiogas at hotmail.com
Thu Oct 4 10:57:10 CDT 2012
i alli work mainly with cold climate low cost digesters. this means that during wintir we have to fight against -13ºC ambient temperature during the night. I work in bolivia.we do not use active heating systems because the cost and mantenience.we convert the digester in a solar heat collector with thermal inertia.we work with tubular plastic digester and the characteristics are:-black color plastic for the tubular tank-insulation into the ditch (straw or expanded polystyrene insulation) -small green house, with 'adobe' wallsof 30-40cm width
the amount of insulation characterize the temperature of the slurry. we have measure the temperature inside digesters (in the slurry) of 14ºC, and others with 20ºC. the difference is the width of the insulation (mainly, also sadhows from trees or buildings). here you can find a peper about this issue http://www.sciencedirect.com/science/article/pii/S096085241201187X
as we know that we are working at very low temperature insede the digester, we work with an HRT of 80-90 days in cold climate (45 days for warm climate, 35 for tropical one, and no greenhouse in both cases)
finally, the cost to heat a domestic digester is higher than the construction of a greenhouse and use of insulation. there are no maintenece for the greenhouse, and do not requires electricity.here you can find a video about how to install a cold climate tubular low cost digester, and at the end of the video you will find a 4.223 meters above sea level digester working http://es.youtube.com/watch?v=3Sl0XEN5Bgo
here you can find some general information of the digesters in bolivia, but you will find some more pictures of these kind of cold climate digesters: http://redbiolac.org/biblioteca/D_BDG_IDEASS_Marti_ENG
i hope this helpswe keep in touchjaime
-----
Jaime Martí Herrero
CIMNE (www.cimne.com). Building
Energy and Environment Group
Cochabamba · Bolivia
Tel. (+591)-73 090 621
BIOGAS AND BOLIVIA
-RedBioLAC:http://redbiolac.org/
-Taller Biogas Bolivia:http://tallerbiogas.blogspot.com
-Video: Biodigester installation in bolivian Altiplano:http://es.youtube.com/watch?v=3Sl0XEN5Bgo-Manual gratuito-Biodigestores familiares: Guía de diseño y manual de
instalación: http://grecdh.upc.edu/publicacions/llibres/documents/2008_jmh_guia_biodigestores.pdf
From: kyle at takamotobiogas.com
Date: Thu, 4 Oct 2012 17:25:53 +0300
To: digestion at lists.bioenergylists.org
CC: paul at takamotobiogas.com
Subject: Re: [Digestion] Small Scale Digester Heating
Dear Biogas List,
Thank you all for the advice and encouragement. It can be done which is good news.
Mr. Karve, could you explain your concept a little bit more? Is it passive or active (requires a pump)? and what is the name of the sponge rubber insulation material?
Manuel, you mention that electricity is required for control. It seems that a battery could be used for control and last for several years. Is this true? At most you could use a tiny solar panel to charge a battery for all of the control power you need. How much stirring is actually required? If you are heating the bottom of the digester then there should be some convection in the tank just from thermal differences. Even so, I think I have seen that stirring only increases gas production by around 20%.
Peter, how much power did your system require for pumping? Is there a way to do away with the pump? How much did a cloudy day affect the heating system? How much power was required to run your control system (if any)? It is good to hear that your mesophilic digester was able to produce better fertilizer than the ambient temperature digester. I have seen a website for a company in Australia called biobowser. Is that the same company? It looks like a beautiful technology all packaged into one easy (?) to install modular unit. Is there a reason why their smallest unit is for 100kg per day? Could their system be scaled down?
Paul, to better understand the rough spreadsheet you made, you found that one twelfth of the additional biogas was used for heating so the net effect was a significant increase in biogas to the user. Have you had bad experience with animals in your insulation? Would you recommend avoiding some kinds of insulation? Are there some insulations that a good for underground installations?
One of the ideas I proposed was to bubble a small amount of air through the digester so that there was a slight aerobic reaction that generates heat and keeps the digester warm. Is there any validity to this idea? Has it ever been done? Or would the amount of oxygen required to raise the temperature of a digester by 17C degrees kill the methanogenic bacteria?
All the best wishes,
Kyle
I built a 1000L small
scale digester about 10 years ago which incorporated chamber heating via solar
hot water circulation as well as a biogas fired heat-exchanger as a
back-up for cold nights.The system could readily
achieve blood temperature and maintain this with minimal management and a
small amount of electricity to drive the circulation pump intermittantly.A solar powered pump would
have been sufficient.I was not so interested in
the biogas component at the time as the unit was readily able to
produce 2 cubic meters of up to 90% methane per day and I had no other use for
this gas other than to flare it off.I used the gas
volume as an indicator of digestation reactivity and a
determinant for retention time.My interest was in the
spent digestate, particularly the colloidal nutrient contained within it. The bio-gas was a bonus,
the fertilizer was beyond compare.I split the digestate into
colloidal liquid and pelletized the remainder.The colloids were sprayed
as a foliar feeder and the pellets fed the soil and plant roots. Carbon content
of the soil was raised considerably. Plant growth was exceptional and the
fertilizer would enable the growth of vegetation on long term bare ground (at
least 20 years barren) which would not previously support any growth at
all. The full-scale plant (38,000L) was reproduced in India and achieved
22% better output results than I managed with the prototype. They called
it the BioBowser.
Peter Allison.
G'day Takamoto, You have to look at the tradeoff
between cost of a larger digester at ambient temperature (where you get all the
biogas to use!) and the cost (capital, operational and maintenance!) of
installing insulation (loved by birds and mice?) and a heating system on a
smaller digester. Of course you also have to consider the energy cost of
heating the digester - if you want more gas do you get it by using some of the
gas to heat the digester? Based on a steady state model (see http://biowattsonline.com/
for a web version) and a 4 cubic metre digester you should be able to go from 3
beef cattle to 11 beef cattle, so would get about 4 times the gas. My simple
Excel model shows the heater about halves the cost of biogas but nearly doubles
the digester capital cost and uses about 1/12 of the increased gas production
(about half of the ambient gas production - most of the gas is used to heat the
effluent if insulation is 50 mm thick) - I used 20 ambient and 35 digester
temperature. Happy Digesting,HOOROODear biogas technologists,you can heat a biogas digester using
a tube which forms a circle at the bottom of the biogas digester. Circulate hot
water through this tube. You can use a relatively small wood burning stove to
heat a water pot, from which the hot water is tapped for circulation through
the tube. For a small biogas plant, this is quite doable. Insulate the digester
with sponge rubber blanket, so that it remains warm. You can keep the biogas
digester indoors, with the water heating stove outside the house.YoursA.D.Karvenot only they have been tried but are
used from many many years agoyour numbers are real but as you
point it these kind of digester areof bigger costs because of the
technology involved the most important point is the
insulation used, bigger insulationthickness demands less energy but
costs are higher...you can heat it with solar heater and
the reminder energy if needed with biogasbut you cannot provide this kind of
digester to a small farm housewithout electric supply, for example
for control and mixingporpuses.....these "high tech" digester
are suitable for certain houses /locations/with all basic requirement
satisfied....... i work with these kind of digesters
.....if i can help you contact me SKYPE manuel.jimenezt Manuel
On Oct 4, 2012, at 5:37 AM, Paul Harris wrote:
G'day Takamoto,
You have to look at the tradeoff between cost of a larger digester
at ambient temperature (where you get all the biogas to use!) and
the cost (capital, operational and maintenance!) of installing
insulation (loved by birds and mice?) and a heating system on a
smaller digester. Of course you also have to consider the energy
cost of heating the digester - if you want more gas do you get it
by using some of the gas to heat the digester?
Based on a steady state model (see http://biowattsonline.com/ for
a web version) and a 4 cubic metre digester you should be able to
go from 3 beef cattle to 11 beef cattle, so would get about 4
times the gas. My simple Excel model shows the heater about halves
the cost of biogas but nearly doubles the digester capital cost
and uses about 1/12 of the increased gas production (about half of
the ambient gas production - most of the gas is used to heat the
effluent if insulation is 50 mm thick) - I used 20 ambient and 35
digester temperature.
Happy Digesting,
HOOROO
Mr Paul Harris BEng (Ag) (Melbourne)
Visitor at The University of Adelaide
On 3/10/2012 11:05 PM, Takamoto wrote:
Dear Biogas List,
I have been thinking about the biggest hurdles to producing
more gas from small scale biogas systems (4 cubic meters to 12
cubic meters) and by far the biggest barrier is heat. From the
literature I have read it seems that if you increase the
temperature of the digester from about 18C (the temperature of
our digesters) to 37C you can nearly double the gas yield per
unit of input and nearly halve the retention time which would
reduce the capital costs.
Does anyone know of tests that have been done or ideas that
have been put forth to heat small scale digesters in a
controlled manner? (For the moment assume that such a process
could be managed on many disparate, small scale biogas systems.
That is the next challenge.) The processes I was thinking of
were 1.) to heat the biogas system with biogas from the system
itself or 2.) to bubble a very slight amount of air through the
digester so that there was a slight aerobic reaction that
would produce heat and warm the digester. Or 3.) you could use
sunlight to warm the digester if you can warm the digester and
not the gas holder as warming the gas holder will only cause the
gas to expand and no heat will be transferred to the slurry.
These methods are probably most applicable to fixed dome and
floating drum.
Have either of these ideas been tried? Are there other ideas
out there?
Cheers,
Kyle
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and the Biogas Wiki http://biogas.wikispaces.com/
_______________________________________________
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to UNSUBSCRIBE or Change your List Settings use the web page
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for more information about digestion, see
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http://www.adelaide.edu.au/biogas/
and the Biogas Wiki http://biogas.wikispaces.com/
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