"Earth, Science,Technology: Growing With You" 

Heat Extraction from Cattle Manure Composting / Remediation


Figure 1
Figure 2
Agrilab Technologies Inc. A unit of the Acrolab Group of Windsor, Ontario, Canada hasdeveloped and designed a system for the extractionthermal energy from the process of aerobicdecomposition (composting) of farm waste. Thesystem extracts energy from the hot water vapourgenerated during the composting process. Thesystem then transfers that energy into an insulatedbulk storage water tank for farm heating and processwater applications. The system is essentially selfpowered with the exception of a small amount ofelectrical power needed to power four 120 VACmotor driven inline air blowers using 1/8 hp motors.
In this particular application at Diamond Hill CustomHeifers, the waste takes the form of cattle manureand bedding materials. ( Fig 1)
Figure 3
System design: Diamond Hill Custom Heifersdecided to compost a portion of the manure and beddingproduced in its operationboth for on-farm use and sale of the compost end product andto 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 compostapproved for organic use. Further, the system extracts the thermal energygenerated as a product of the decomposition (composting) process.

The facility consists of a two bay composting barnwith an east and west composting floor separated by a centralenclosed hallway/gallery. Each of the compostingfloors or bays is approximately 52 feet wide and 60feet long. Each bay will permit active composting ofbetween 700 and 800 tons of materials at one time.The four windrows in each bay routinely achieve andmaintain temperature of 120 to 165 degrees F. for fourto eight weeks after initial placement.

Figure 4
The floors are 6” to 10” poured reinforced concreteover compacted sand and closed cell expandedfoam sheets typical of the type used in theinstallation of  “in floor” electric heating systems.Below the concrete and above the insulation anarray of PVC pipes (Fig 2) have been placed. Theyform four sections of four 8” pipes running underthe floor generally equidistant from each other andoriented east to west for the full length of each bayor pad. Additionally, these pipes are insulated bybeing wrapped with a “Techfoil” material whichraises the insulation value around the pipes toapproximately R50 or R60. 

Figure 5

These pipe arrays are manifolded together in groups of four contiguous pipes (Fig 4) such that the manifolds, which are located in thehallway separating the two bays, provide one outletper four pipes. 

After the concrete floor has been poured toapproximately 6" to 10" in thickness, forms attachedto the upper surfaces of the pipes are removedcausing a chord of the pipe approximately 2.5” to 3”wide, along the length of the pipe, to be exposed toview. (Fig 3) That chord is then cut out leaving eachpipe with a slot the full 70' length of the pipe 2” to 3”wide,  2” below the floor of the pad. 
Figure 6

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 arein 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 theopening centered along the length of the slot, isthen covered with a heavy-duty mesh screen alongthe length of the trough. 

These superthermal conductors known as Isobars reside within the24” “condenser”(Fig 7) conduit for 50 feet and thenimmediately enter an insulated 800 gallon capacitybulk tank extending through the tank and exiting out the other end.(Fig 8 & 9) Note thatFigure 8 shows the Isobars ready for insersion into the bulk tank. Figure 7 shows theIsobar array before the 24" conduit is fully installed.

Figure 7

The Isobars then exit the tank and extend roughly6” beyond in an insulated enclosure welded to thetank surface. These Isobar extensions facilitatethe charging valve train for the Isobars. (Fig 9)

A 24” discharge stack is “T”d into the condenserconduit at or near the point where the conduitbulkheads against the bulk tank wall. The stack isvented up and outside of the hallway/gallery whichhouses the system. Exhaust vapour is controlledvia a damper in the stack. Exhaust may be vented to the atmosphere. Plans are underway to ductthis spent vapour back into the composting baywhich will add water for irrigation and heat to the air drawn from above the compostingpile. This will increase the effectiveness of the energy generation as well as assist inmore efficient composting. 

Figure 8

Four inline air blowers are attached to the outlet of the manifolds(Fig 5) which in turnconnect the four slotted floor 8” pipe arrays Thewarm vapour laden air is drawn through the slotscut in the tops from the floor embedded PVC pipesand is fed to the 24” condenser conduit containingthe Isobar superthermal conductors.  

The manifolds, connecting conduits, condenserconduit, and air blowers are all sealed to ensurethat no air leaks are present and then insulated toR60+. 

Isobar Superthermal conductors are devices more technically defined asevacuated two phase heat exchangers. Isobars, ( Fig 7, 8 & 9) in thisapplication are made of 3” stainless steel tube sections, sealed at eachend and charged with a working fluid.
Figure 9
The characteristics of Isobarsare such that any energy applied locally to anyrandom portion of the Isobar is immediately and atexceptionally high speed transferred to allremaining portions of the surface of the Isobar. Asan example if a propane torch flame was appliedto one end of the Isobar over an area of 3 squareinches, all the energy of that flame wouldimmediately be distributed across the remainderof the Isobar at high speed to the point where youcould touch the area where the flame had beenapplied  seconds after the flame was removed. 

 Isobars are isothermal devices constantlyachieving uniform  temperatures on the surface as a result of random heat inputs.  In thisparticular application, the hot water vapour condensing on the Isobars is immediatelytransferred at near sonic speeds to that portion of the Isobar that is in contact with thewater in the bulk tank. As long as the water in the bulk tank is at a temperature belowthat 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 activatethem 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 necessaryis blended to a specific recipe with the use of a feedmixer and loaded onto the floor to aheight of 10 feet roughly and covering the complete composting bay or floor.  Theporosity of the blend is predictable. The natural composting process is enhanced by theuse of the air blowers drawing ambient air from the barn through the composting pilesfrom top to bottom where that air replaces water vapour at a temperature of from 90 to150 F depending on the age and recipe of the materials.

The hot water vapour is drawn into the slotted 8” pipes embedded in the compostingfloor and taken to the condenser conduit through insulated interconnected ducts. Theairflow through the system from the composting floor is controlled by the use of slidegate valves in the pipes as well as through speed controls governing the RPM of the airblowers. Because the duct and air blower system is highly insulated, once the systemachieves steady state the vapour being drawn from the composting materials will notcondense on the inner surfaces of the pipes, blowers and ducts which constitute thevapour path of the system, but remain in vapour state until it is in contact with the Isobarsuperthermal conductors.

Isobar System Features: Once in contact with the Isobar array, the hot  water vapourgenerated by the composting reaction is drawn through the collector ducts andmanifolds via the air blowers. There it condenses and yields not only its latent heat butalso the energy associated with the temperature of the water condensate, which is at ahigher temperature than the Isobars. As long as the water in the bulk tank is at a lowertemperature than the hot water vapour, this heat transfer action will continue without theneed for outside power other than that needed to drive the four air blowers. In theinstance of a power outage, the Agrilab Heat Transfer System would continue to operateat a reduced level as a result of the natural draft caused by the negative pressure in thecondenser duct created by the condensing vapour.
Isobar System Benefits: The Agrilab Isobar Heat Transfer System provides hotprocess water contained in an insulated bulk storage tank for use either as an adjunct tofacility hot water heating systems or for direct hot process water. 

The Agrilab Isobar Heat Transfer System can provide in some instances most if not allprocess water heating needs without the use of external power sources.

Quantifiable results: At presentThe Agrilab Isobar Heat Transfer System operatingat Diamond Hill Custom Heifers is functioning in a timer-controlled alternatingaeration cycle . The requirements of the system being to provide energy sufficientto raise the temperature of well water to a process level of 120 F. A double tankheat exchanger is connected to the 800-gallon bulk tank. This is an intermittentor batch activity that places little demand on the system. Tests applied to thesystem in this mode have indicated that a minimum transfer rate of 240,000 BTU/dayhas been achieved. If the system is under significant demand such that thetemperature of the water in the insulated bulk tank is kept at a differential of20 F with respect to the hot compost water vapour temperature, it is expected thatthe heat transfer rate will be in the range of 500,000+ BTU s/day. Monitoring thesystem for vapour temperatures and vapour flow rates will allow for better documentationof BTU production, loss and utilization. The use of heated water in the radiantfloor heating system may significantly increase the value of the captured energyfrom the composting system. This is being tested presently and may periodicallyyield up to 3 million BTU/day or 120,000 BTU/hour.

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Agrilab Technologies Inc
7475 Tranby Avenue
Windsor, ON
N8S 2B7
Tel: (519) 944-5900
Fax: (519) 944-9141