Agrilab Technologies Inc. A unit of the Acrolab Group of Windsor, Ontario, Canada has
developed and designed a system for the extraction
thermal energy from the process of aerobic
decomposition (composting) of farm waste. The
system extracts energy from the hot water vapour
generated during the composting process. The
system then transfers that energy into an insulated
bulk storage water tank for farm heating and process
water applications. The system is essentially self
powered with the exception of a small amount of
electrical power needed to power four 120 VAC
motor driven inline air blowers using 1/8 hp motors.
In this particular application at Diamond Hill Custom
Heifers, the waste takes the form of cattle manure
and bedding materials. ( Fig 1)
System design: Diamond Hill Custom Heifers
decided to compost a portion of the manure and bedding
produced in its operation
both for on-farm use and sale of the compost end product and
to supplement the thermal energy requirements of the facility.
The composting facility ,collaboratively designed by Terry Magnan,
Joseph Ouellette, Brain Jerose and Bruce Fulford with input from Aaron Robtoy,
Paul Godin and Dan Carswell, produces on a large scale, high grade compost
approved for organic use. Further, the system extracts the thermal energy
generated as a product of the decomposition (composting) process.
The facility consists of a two bay composting barn
with an east and west composting floor separated by a central
enclosed hallway/gallery. Each of the composting
floors or bays is approximately 52 feet wide and 60
feet long. Each bay will permit active composting of
between 700 and 800 tons of materials at one time.
The four windrows in each bay routinely achieve and
maintain temperature of 120 to 165 degrees F. for four
to eight weeks after initial placement.
The floors are 6” to 10” poured reinforced concrete
over compacted sand and closed cell expanded
foam sheets typical of the type used in the
installation of “in floor” electric heating systems.
Below the concrete and above the insulation an
array of PVC pipes (Fig 2) have been placed. They
form four sections of four 8” pipes running under
the floor generally equidistant from each other and
oriented east to west for the full length of each bay
or pad. Additionally, these pipes are insulated by
being wrapped with a “Techfoil” material which
raises the insulation value around the pipes to
approximately R50 or R60.
These pipe arrays are manifolded together in groups of four contiguous pipes (Fig 4)
such that the manifolds, which are located in the
hallway separating the two bays, provide one outlet
per four pipes.
After the concrete floor has been poured to
approximately 6" to 10" in thickness, forms attached
to the upper surfaces of the pipes are removed
causing a chord of the pipe approximately 2.5” to 3”
wide, along the length of the pipe, to be exposed to
view. (Fig 3) That chord is then cut out leaving each
pipe with a slot the full 70' length of the pipe 2” to 3”
wide, 2” below the floor of the pad.
This allows for tractors and loading equipment to operate on the composting floor
without crushing or damaging the gutter pipes.
The manifolded pipes, (Fig 5) which are
in fact vapour collectors, have a 10" Fantech blower mounted vertically into 10"
flexible duct. the flex ducts are then attached to a large 24" PVC corrugated
conduct (Fig 6) in which an array of six
Isobar superthermal conductors is situated. The vapour from the compost windrows
is drawn through the gutters, through the ductwork and across the isolabs.
The resulting trough, with the pipe below it and the
opening centered along the length of the slot, is
then covered with a heavy-duty mesh screen along
the length of the trough.
These superthermal conductors known as Isobars reside within the
24” “condenser”(Fig 7)
conduit for 50 feet and then
immediately enter an insulated 800 gallon capacity
bulk tank extending through the tank and exiting out the other end.
(Fig 8 & 9) Note that
Figure 8 shows the Isobars ready for insersion into the bulk tank. Figure 7 shows the
Isobar array before the 24" conduit is fully installed.
The Isobars then exit the tank and extend roughly
6” beyond in an insulated enclosure welded to the
tank surface. These Isobar extensions facilitate
the charging valve train for the Isobars. (Fig 9)
A 24” discharge stack is “T”d into the condenser
conduit at or near the point where the conduit
bulkheads against the bulk tank wall. The stack is
vented up and outside of the hallway/gallery which
houses the system. Exhaust vapour is controlled
via a damper in the stack. Exhaust may be vented to the atmosphere. Plans are underway to duct
this spent vapour back into the composting bay
which will add water for irrigation and heat to the air drawn from above the composting
pile. This will increase the effectiveness of the energy generation as well as assist in
more efficient composting.
Four inline air blowers are attached to the outlet of the manifolds
(Fig 5) which in turn
connect the four slotted floor 8” pipe arrays The
warm vapour laden air is drawn through the slots
cut in the tops from the floor embedded PVC pipes
and is fed to the 24” condenser conduit containing
the Isobar superthermal conductors.
The manifolds, connecting conduits, condenser
conduit, and air blowers are all sealed to ensure
that no air leaks are present and then insulated to
Isobar Superthermal conductors are devices more technically defined as
evacuated two phase heat exchangers. Isobars,
( Fig 7, 8 & 9) in this
application are made of 3” stainless steel tube sections, sealed at each
end and charged with a working fluid.
The characteristics of Isobars
are such that any energy applied locally to any
random portion of the Isobar is immediately and at
exceptionally high speed transferred to all
remaining portions of the surface of the Isobar. As
an example if a propane torch flame was applied
to one end of the Isobar over an area of 3 square
inches, all the energy of that flame would
immediately be distributed across the remainder
of the Isobar at high speed to the point where you
could touch the area where the flame had been
applied seconds after the flame was removed.
Isobars are isothermal devices constantly
achieving uniform temperatures on the surface as a result of random heat inputs. In this
particular application, the hot water vapour condensing on the Isobars is immediately
transferred at near sonic speeds to that portion of the Isobar that is in contact with the
water in the bulk tank. As long as the water in the bulk tank is at a temperature below
that of the hot compost water vapour, transfer will take place. Isobars are self powered.
They do not require electrical power. They require no external energy source to activate
them other than a difference in temperature from one location on its surface to another.
Operation: A mixture of cattle manure and bedding plus other constituents as necessary
is blended to a specific recipe with the use of a feedmixer and loaded onto the floor to a
height of 10 feet roughly and covering the complete composting bay or floor. The
porosity of the blend is predictable. The natural composting process is enhanced by the
use of the air blowers drawing ambient air from the barn through the composting piles
from top to bottom where that air replaces water vapour at a temperature of from 90 to
150 F depending on the age and recipe of the materials.
The hot water vapour is drawn into the slotted 8” pipes embedded in the composting
floor and taken to the condenser conduit through insulated interconnected ducts. The
airflow through the system from the composting floor is controlled by the use of slide
gate valves in the pipes as well as through speed controls governing the RPM of the air
blowers. Because the duct and air blower system is highly insulated, once the system
achieves steady state the vapour being drawn from the composting materials will not
condense on the inner surfaces of the pipes, blowers and ducts which constitute the
vapour path of the system, but remain in vapour state until it is in contact with the Isobar
Isobar System Features: Once in contact with the Isobar array, the hot water vapour
generated by the composting reaction is drawn through the collector ducts and
manifolds via the air blowers. There it condenses and yields not only its latent heat but
also the energy associated with the temperature of the water condensate, which is at a
higher temperature than the Isobars. As long as the water in the bulk tank is at a lower
temperature than the hot water vapour, this heat transfer action will continue without the
need for outside power other than that needed to drive the four air blowers. In the
instance of a power outage, the Agrilab Heat Transfer System would continue to operate
at a reduced level as a result of the natural draft caused by the negative pressure in the
condenser duct created by the condensing vapour.
Isobar System Benefits: The Agrilab Isobar Heat Transfer System provides hot
process water contained in an insulated bulk storage tank for use either as an adjunct to
facility hot water heating systems or for direct hot process water.
The Agrilab Isobar Heat Transfer System can provide in some instances most if not all
process water heating needs without the use of external power sources.
Quantifiable results: At present
The Agrilab Isobar Heat Transfer System operating
at Diamond Hill Custom Heifers is functioning in a timer-controlled alternating
aeration cycle . The requirements of the system being to provide energy sufficient
to raise the temperature of well water to a process level of 120 F. A double tank
heat exchanger is connected to the 800-gallon bulk tank. This is an intermittent
or batch activity that places little demand on the system. Tests applied to the
system in this mode have indicated that a minimum transfer rate of 240,000 BTU/day
has been achieved. If the system is under significant demand such that the
temperature of the water in the insulated bulk tank is kept at a differential of
20 F with respect to the hot compost water vapour temperature, it is expected that
the heat transfer rate will be in the range of 500,000+ BTU s/day. Monitoring the
system for vapour temperatures and vapour flow rates will allow for better documentation
of BTU production, loss and utilization. The use of heated water in the radiant
floor heating system may significantly increase the value of the captured energy
from the composting system. This is being tested presently and may periodically
yield up to 3 million BTU/day or 120,000 BTU/hour.