[Digestion] Small Scale Digester Heating

Thu Oct 4 10:33:22 CDT 2012

2012/10/4 Takamoto <kyle at takamotobiogas.com>
>
> 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%.

 Electricity helps if you want to obtain a perfect controlled process, i
mean a stable 37deg or 55deg, mixed reactor, but you can do without it but
you should invert money in insulation. (thera are calculation on this
topics but i don t expose them here)
i use not less than 15cm of polifan thick (similar to poliurethane foam)
and solar heater conecteted to a tubular (25mm diameter) helicoid 15-20
turns separete 30-50cm from inner reactor walls. These produce tiny
convection currents in reactor liquids (also depends on % solids). The
solar heater circulate thanks to termosyphon (solar heater should be
instaled below the hdpe top turns coil....)
if your point is a sunny place you will have a fluctuation of temp between
day and night. bacteria will be able to handle a smooth temp
fluctuation.........
as the result  your insulated reactor (we use here perfectly sealed
rotomoulded water tanks as reactor .......gasholder apart) will operate
near termophilic range (that have other problems......) in summer and in
mesophilic range in winter

insultaion is very importatnt
if there is a week or two cloudy your reactor will loss temperature but
very slowly...

(sorry my english)

Manuel

> 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,
>
> HOOROO
>
> Dear 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.
>
> Yours
>
> A.D.Karve
>
> not only they have been tried but are used from many many years ago
>
> your numbers are real but as you point it these kind of digester are
>
> of bigger costs because of the technology involved
>
>
>
> the most important point is the insulation used, bigger insulation
>
> thickness demands less energy but costs are higher...
>
> you can heat it with solar heater and the reminder energy if needed with
biogas
>
> but you cannot provide this kind of digester to a small farm house
>
> without electric supply, for example for control and mixing
>
> porpuses.....
>
> 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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> http://www.adelaide.edu.au/biogas/
> and the Biogas Wiki http://biogas.wikispaces.com/
>
>
>
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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/
>
>
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