[Digestion] Burning food waste

Tue Oct 9 14:25:34 EDT 2007

Zero organic waste?   Some say that over 50% is newsprint and other paper
products; some go up to 75%.

I've read a few advocacy pieces that indicate that AD is preferred to
burning for organics.

Frank J. Heller, MPA
KATAHDIN ENERGY WORKS
12 Belmont St.
Brunswick, ME 04011-3004
207.729.6090
http://mysite.verizon.net/fjheller/

-----Original Message-----
From: digestion-bounces at listserv.repp.org
[mailto:digestion-bounces at listserv.repp.org] On Behalf Of Duncan Martin
Sent: Wednesday, October 10, 2007 4:54 PM
To: Björn Dahlroth; 'mrcdb'; digestion at listserv.repp.org
Subject: [Digestion] Burning food waste

Yes, it might be reasonable to burn food waste at 40% H20. But that's not 
the scenario here.

The initial posting was about a landfill, which contains only a small % of 
organic waste (tending to zero in the EU). Landfills can burn, of course - 
but it's not recommended!

Duncan

----- Original Message ----- 
From: "Björn Dahlroth" <bjorn.dahlroth at telia.com>
To: "'mrcdb'" <mrcdb at charter.net>; <digestion at listserv.repp.org>
Sent: Wednesday, October 10, 2007 4:29 PM
Subject: Re: [Digestion] Digestion Digest, Vol 16, Issue 1

Hi
If you are not particularly interested in precisely methane for some special
purpose or in the N P K content of food waste but more in the energy
content, than it is more efficient to burn it in a large incineration plant
and produce hot water or steam and electric power. The total energy
efficiency will be higher than what you can achieve in a digestion plant.
The hot water can be used for district heating, steam can be used for
district heating or sold to some nearby industries. Electricity can be sold
on the market for electric power. However incineration plants can not be
very small and the moisture content can not be very high. Usually the
technical maximum limit for the moisture in the total waste stream going
into a modern incineration furnace is about 65% and above that you may have
problems with the ignition and the required temperature level (850 C) of the
combustion. Waste with a moisture content of 38-40% is very good fuel unless
most of it is inert material. If a limited waste stream in the municipal
solid waste has higher moisture content than approximately 65% you can still
extract a lot of heat from it by co-combustion with dryer waste followed by
flue gas condensation. Flue gas condensation is a common method for
increasing the heat production from combustion and standard equipment in
Scandinavia to day on incineration plants and plants for burning wood
residues (branches and tree tops) from the forest industry. The absolutely
theoretical upper moisture content limit for extracting heat from solid
waste in a co-firing plant is around 80%. It is above that limit that
digestion of food waste is most competitive from energy point of view. Also
it can be competitive for cases where the waste supply is small, where the
transport distance to a big incineration plant is too long and where the
methane market is willing to pay a high price (e g city busses) and where
there is no market for district heating. So when it is question about
municipal solid waste there is room for both incineration and digestion but
one has too look carefully at the market conditions in each case and also
consider the societal cost of separating food waste from other waste at the
source, which is necessary if you want to digest in closed containers.
Municipal solid waste is one of the most difficult energy sources to use
irrespective of method but anything is better than landfill without
treatment.  (Landfills can of course produce methane but the efficiency is
lower and the time required to complete the process is extremely long.) The
best use of digestion seems to be in agriculture and for treatment of high
moisture waste in the food industry.

Bjorn Dahlroth

-----Ursprungligt meddelande-----
Från: digestion-bounces at listserv.repp.org
[mailto:digestion-bounces at listserv.repp.org] För mrcdb
Skickat: den 8 oktober 2007 18:27
Till: digestion at listserv.repp.org
Ämne: Re: [Digestion] Digestion Digest, Vol 16, Issue 1

Hello All,

I am an Energy Consultant in Erie, MI,  USA

I have been researching anerobic digestion lately as related to Municipal
Solid Waste (MSW) landfills and landfill gas to electric plants.

I am a member of the Solid Waste Association of North America (SWANA) and
just completed their landfill gas ecourse.

Anyway, in their course they state that "a moisture content, of the
digestion material, of 38-40% is ideal for the most methane production" and
that "recirculating the leachate produces lots of gas"
They say that a moisture content much over 40% is a saturated condition, and

will slow or stop methane production!

So, it seems to me, that a digester full of water is not an efficient way to

produce methane?

Does anyone have any thoughts on this subject?

Thanks,

Charles Bagwell
President
Zerwell Energy
www.zerwellenergy.com
Erie, MI

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