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CMD - Complete Mix Digester - Methane Digester |
Once again, Selective Inc. is
on the cutting edge of technology. With a totally new
approach for the 21st century, we provide a unique,
state-of-the-art anaerobic digester, the Complete Mix
Digester (CMD) - that takes methane energy conversion to
a whole new level.
CMD systems are designed to
provide cost effective and reliable effluent treatment
of agricultural waste streams coming from a range of
sources including confined animal feeding
operations-CAFO's and food processing facilities.
CMD anaerobic digestion treatment, serves to
reduce the environmental impact of these waste streams
while producing renewable energy (methane) and high
quality soil amendments. The Complete Mix Digester
system is comprised of a series of independent - above
ground tanks, or cells, with the appearance of a classic
farm silo. CMD systems are modular and scaleable in
size, allowing the digester to grow incrementally with
the needs of the user without major alterations to the
existing facility.
CMD digesters are fully
automated, with a user friendly control system. The CMD
design is simple, extremely reliable and requires
minimal energy to run a largely passive, operation. A
high rate digester results in lower material storage
requirements. Combined with a vertical column design,
the CMD footprint is much smaller than what is
traditionally needed by other anaerobic digesters. With
a smaller footprint, CMD tanks can be housed in well
insulated, environmentally controlled buildings for more
consistent operation and protection from harsh, exterior
elements.
Using the above ground, small diameter
cell approach, the CMD offers greater modularity and
user flexibility than alternative in-ground systems or,
very large complete mix tanks. Completed CMD tanks are
delivered to the user site for fast and simple
installation and can be moved to another location at a
later date, if needed.
When maintenance is
required, a single tank can be taken off line without
affecting the overall system - and will continue to
operate without interruption. The CMD's operation is
mechanically simple with low maintenance requirements
and requires less energy consumption. The CMD,
computerized control system, monitors in real time and
controls the flow and temperature of all tanks and
peripheral plumbing devices. An optional service plan
allows us to monitor the digester using remote, computer
tracking systems.
Gas Production: Methane
gas production is directly related to solids
destruction. Digesters with comparable solids
destruction levels will produce comparable levels of
methane gas measured in BTU's. The actual gas volume
produced by a digester will vary somewhat with the
concentration of methane in the gas. On average, the CMD
converts 70cu.ft. per day from Holstein cow, from Jersey
cows, it converts 50cu.ft. per day.
Digesters
producing 50% methane gas (500 BTUs per cubic foot) must
produce a higher gas volume than a digester producing
65% methane gas (650 BTUs per cubic foot) in order to
achieve the same energy output (total BTU's). .
Not all digestible waste streams are equal in
terms of the potential for methane gas production, and
not all organic waste streams are suitable for anaerobic
digestion by themselves. Animal manure is well suited
for digestion by itself or as an excellent buffer for
other waste streams that are too acidic or basic for
processing on their own but that have high energy
potential.
Human waste can be processed into
methane with the CMD. The waste stream must be highly
consistent, with a balanced ph, no antibiotics,
chlorines, or other mechanisms that would other wise
inhibit or harm the live bacteria. By adding high energy
substrates to the waste stream, in the correct
proportion, methane gas production can be enhanced
significantly. The CMD system is well suited for the
controlled addition and digestion of supplemental
substrates.
Gas Utilization: Methane gas
from an anaerobic digester can often be used as a direct
replacement for natural gas. It is typically necessary
to make a simple modification to natural gas burners in
order to accommodate the lower BTU content of biogas
from methane digesters.
Compatibility is
enhanced when digesters produce gas with a higher BTU
content and lower H2S - Hydrogen Sulfide - content as in
the CMD system. When direct utilization of biogas is
employed, a fraction of the BTUs produced must be used
to heat the digestion process. On average this would be
less than 1/4th of the energy, depending on the climate.
Biogas is also suitable for use in a combustion
engine generator. The high BTU content and low H2S
content make the gas from the CMD digester well suited
for this application. The actual kilowatt production is
directly related to solids destruction as reflected in
BTUs generated by the digester as methane gas, and the
efficiency of the engine generation system.
Faster Digestion Times: The Complete Mix
Digester is a high rate digester, completing the
digestion process – HRT – Hydraulic Retention Time - in
less time than other digester types, typically in 5
days.
This is accomplished by creating a
bacteria rich environment through which the influent
stream must pass. With a greater bacteria concentration,
digestion of a given amount of feed material can be
effected in a shorter period of time. Covered lagoons
have a much longer, less efficient HRT, of typically
45-60 days
Please note : that temperature of the
effluent is directly impacted by the digester
temperature. For every 20 degrees below 95 degrees the
methane production is cut by 50%. Covered lagoons seldom
get to 95 degrees, except during the warm, summer
months. Along the coastal and cooler regions of the
world, these digesters will operate below ambient
temperatures year round.
Special features in the
CMD tank contribute to the retention of bacteria and
thus enrichment of the reactor. The vertical column
design of the CMD increases the length of the path of
concentrated bacteria through which material must
travel. More bacteria contact means more digestion.
Bacteria in the reactor thrive because of excellent
environmental controls and because they are constantly
being fed new material.
Methane Quality:
The quality of methane generated by a high rate system
is typically higher than gas produced by traditional
systems. The higher rate of digestion allows less time
for the other major component of biogas, CO2, to form.
The methane content of CMD gas is typically 65-70% vs.
50-60% from other systems. The H2S component is also
better, generally 800 ppm or lower. At Selective, Inc.
we offer:
- Project oversight and management
- Ongoing system management
- System maintenance services
- Assistance with grant and financing applications
- Assistance with Comprehensive Nutrient Management
Plans
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