How animal carcass incinerators work
Animal carcass incinerators dispose of dead livestock, slaughterhouse condemned material and veterinary waste. Most are batch units: a large primary chamber with a hearth on which whole or cut carcasses are loaded, fired by diesel or gas burners at about 800 to 850°C, and a secondary chamber or afterburner at about 1,000 to 1,100°C. Carcasses are about two-thirds water and contain fat, so burn time is long and fat release causes sudden flare-ups. Smaller farm units rely on natural draft. Larger units add tempering air or a heat exchanger to cool the gas, then a cyclone or scrubber, and an ID fan to the stack. A combustion air blower supplies the chambers.
Where the FD fan sits
- Inlet screen
- FD fan
- Air header
- Primary chamber ports
- Afterburner air
- Chambers
The blower sits beside the incinerator and delivers ambient air through a header to dampered ports in the primary chamber, over and in some designs under the hearth, and to the afterburner. The support burners have their own integral blowers. The combustion air blower works against port and duct resistance, typically 100 to 250 mmWC. Because the hearth air ports sit close to the carcass load, they need to be placed where fat runoff cannot flood them.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C |
| Air at the chambers | Ambient, not preheated |
| Dust | Clean air; screen against debris near carcass handling |
| Pressure at the fan outlet | Typically 100 to 250 mmWC |
| Load profile | High during fat release, lower during burnout |
| Density at the design temperature | About 1.13 kg/m³ at 40°C, 94% of standard air. Pressure developed and power drawn scale with density, so the fan is selected at this condition and the motor is checked at the coldest operating or start-up condition. |
FD Fan selection for animal carcass incinerators
| Blade form | Backward curved or radial, compact |
| Material of construction | Mild steel, painted |
| Drive and arrangement | Direct mounted on the motor shaft |
| Bearings and cooling | Motor bearings |
| Flow control | Branch dampers and variable speed drive, set by chamber temperatures |
| Also specified | Air pressure switch interlocked with burners, inlet screen |
What this FD fan has to cope with
Smoke during fat release
When fat burns, oxygen demand rises sharply. Without enough air, smoke passes to the afterburner and stack. Air to the primary chamber is raised during this phase, under temperature control.
Overcooling during burnout
Supplying the full air flow after most of the carcass has burnt cools the primary chamber and slows final burnout of bone and residue. Air control on chamber temperature reduces flow as the burn progresses, which shortens the cycle and lowers support fuel use.
Hearth air port blockage
Rendered fat and ash can run into underhearth air ports and block them, so air reaches the load unevenly and parts of the carcass burn slowly. Port positions above the fat runoff level, regular cleaning between batches and a slight air purge during loading keep air distribution right.
Energy and control
The combustion air blower is small, but how it is controlled affects burner fuel use and cycle time far more than its own power. Matching air to the burn phase, high while fat is being released and lower through burnout, shortens the batch and saves support fuel, which is the main running cost of a carcass incinerator. A variable speed drive makes this practical without constant damper adjustment.
ID fan and FD fan in animal carcass incinerators
| ID fan | FD fan | |
|---|---|---|
| Position | After tempering and cyclone, at the stack | Beside the incinerator, feeding chamber ports |
| What it handles | Tempered hot gas with ash and soot | Ambient combustion air |
| Temperature at the fan | 250 to 350°C, up to 450°C upset | Ambient, 25 to 45°C |
| Main design concern | Heat resistance and fat flare-ups | Air matched to the burn phase |
| Control | Primary chamber pressure | Chamber temperatures |
See also the Induced Draft (ID) Fan for animal carcass incinerators.
Questions buyers ask
What does the combustion air blower do on a carcass incinerator?
It supplies air for burning the carcass in the primary chamber and for completing combustion in the afterburner. It is separate from the burner blowers and handles ambient air only.
How much air does a carcass incinerator need?
It varies through the batch. Air demand peaks when fat is released and burning, and falls during burnout. The blower is sized for the peak with control to reduce flow later.
Can one blower serve both chambers?
Yes, on most units, with dampered branches to the primary chamber and to the afterburner. Large units sometimes use separate blowers so that each chamber can be controlled independently and one blower can be maintained without stopping the other's duty.
Information needed to quote an FD fan for animal carcass incinerators
- Duty point. Combustion air quantity in m³/h or kg/h and the static pressure at the fan outlet, with the margins you want.
- Air condition. Site ambient temperature range and altitude, and whether the fan takes ambient air or air already heated.
- System. Boiler or furnace capacity and fuel, resistance of the air heater, windbox, grate or burner, and the existing fan curve or nameplate if this is a replacement.
- Mechanical. Drive arrangement, flow control (damper, inlet vanes or variable speed drive), noise limit, rotation and discharge orientation.
- Air ports. Number and location of primary chamber and afterburner air ports.
- Burner blowers. Whether burners have integral blowers or take air from the main blower.
Built and tested in Chennai
Adroit Fantech Engineers has designed and manufactured industrial fans at Ayanambakkam, Chennai since 2004. Each impeller, casing and shaft is built for the gas and temperature it will see, performance tested as per IS 4894 or BS 848 Part I, and balanced to grade G 6.3 or G 2.5 as per ISO 21940-11, with the records supplied with the fan. We also replace rotors and retrofit existing fans of any make.