How pet cremation incinerators work
A pet cremation incinerator is a compact two-chamber unit, typically handling 50 to 500 kg per cycle, fired on diesel, LPG or natural gas. Animals are placed on the hearth of the primary chamber, which runs at about 650 to 850°C, either one animal at a time for individual cremation or several together. The gas passes to a secondary chamber held at 850 to 1,000°C with a residence time of one to two seconds. Animal carcasses are 60 to 70% water with variable fat, so heat release and gas volume change sharply as fat ignites. Many small units discharge hot gas to a self-supporting chimney, using a dilution air inlet or an ID fan for draft; larger units add a heat exchanger or quench and a scrubber.
Where the ID fan sits
- Primary chamber
- Secondary chamber
- Dilution air or quench
- Scrubber (where fitted)
- ID fan
- Chimney
On many small pet cremators the fan is placed after a dilution air inlet that cools the gas from 900°C to 250 to 350°C so a heat-resisting or mild steel fan can handle it. On larger units with a quench and wet scrubber, the fan sees saturated gas at 55 to 75°C. Suction is typically 80 to 180 mmWC. Some small units use an eductor at the chimney base instead of an ID fan, so that no fan sits in the hot gas.
Gas at the ID fan
| Gas temperature, normal | 250 to 350°C after dilution; 55 to 75°C after a scrubber |
| Maximum or upset | Above 450°C during a fat flare-up with dilution damper slow to open |
| Dust at the fan | Low; fine ash and fur carbon |
| Moisture and dew point | High moisture from carcasses, 20 to 30% before dilution |
| Corrosive species | HCl and SO₂ from plastics in bedding and from protein sulphur |
| Density at the design temperature | About 0.62 kg/m³ at 300°C, 52% 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. |
ID Fan selection for pet cremation incinerators
| Blade form | Backward inclined or radial-tipped, compact for small flows at high temperature |
| Material of construction | Heat-resisting steel impeller for dilution duty; SS 316 for wet scrubber duty |
| Drive and arrangement | Belt drive or direct drive with a cooling disc and long shaft |
| Bearings and cooling | Shaft cooling disc and heat shield for dry hot duty |
| Flow control | Variable speed drive on chamber draft, linked to the dilution damper |
| Also specified | Insulated casing, high-temperature trip and an eductor alternative for very small units |
What this ID fan has to cope with
Fat flare-up overheats the fan
When a carcass with high fat content ignites, heat release can double within minutes, and the gas leaving the secondary chamber rises. If the dilution damper does not open fast, gas well above the design temperature reaches the fan. The impeller is rated for the flare-up temperature, and the dilution damper responds to fan inlet temperature directly.
Small fan, high temperature
A pet cremator may need only a few hundred cubic metres per hour of gas, yet at 300°C or more. Small, hot fans are prone to bearing overheating because the heat travels along a short shaft. A longer shaft with a cooling disc and heat shield keeps the bearings cool.
Odour complaints from poor draft
Pet crematoria are often close to residential areas or veterinary clinics, and any odour or smoke draws complaints quickly. Holding steady suction on both chambers, especially when the door opens to charge each new animal, prevents leakage. A fan selected with pressure margin at the door-open flow, with a drive that boosts on a door switch, achieves this.
Energy and control
Pet cremators often run several short cycles a day, charging one animal after another. Running the ID fan on speed control, slow between cycles and up to full only when charging and in the peak burn, saves power and, more importantly, reduces the diesel or gas used to reheat excess air. Dilution air should be added only as much as the fan temperature limit requires.
ID fan and FD fan in pet cremation incinerators
| ID fan | FD fan | |
|---|---|---|
| Position | After dilution or quench, at the chimney | On the incinerator frame |
| What it handles | Hot flue gas, dry or saturated | Ambient air |
| Temperature at the fan | 250 to 350°C dry, 55 to 75°C wet | Ambient |
| Main design concern | Fat flare-up temperature and bearing heat | Fast secondary air response |
| Control | Chamber draft and dilution | Chamber temperature |
See also the Forced Draft (FD) Fan for pet cremation incinerators.
Questions buyers ask
Does a pet cremation incinerator need an ID fan?
Small units can run on chimney draft or an eductor, but most pet cremation incinerators with a secondary chamber and any gas cleaning use an ID fan. It holds both chambers under suction, prevents odour leaks when the door opens, and overcomes the resistance of the quench and scrubber.
What temperature does the ID fan on a pet cremator see?
With dilution air the ID fan on a pet cremator typically sees 250 to 350°C, and more during fat flare-ups. With a quench and wet scrubber it sees 55 to 75°C saturated gas. The fan must be rated for the highest temperature that can reach it if the dilution damper or the water supply responds slowly.
What is an eductor and can it replace an ID fan?
An eductor uses a jet of air from a fan outside the gas stream to induce flow up the chimney. It keeps the fan out of the hot gas and suits very small units. It uses more power than an ID fan for the same draft and cannot overcome a scrubber.
Information needed to quote an ID fan for pet cremation incinerators
- Duty point. Gas volume in m³/h or Am³/h at the fan inlet and the static pressure the fan must develop, with the margin you want on each.
- Gas condition. Normal and maximum gas temperature at the fan, dust loading after the collector, moisture and any acid gases such as SO₂ or HCl.
- System. Boiler or furnace capacity and fuel, collector type and its pressure drop, and the existing fan curve or nameplate if this is a replacement.
- Mechanical. Drive arrangement, flow control (damper, inlet vanes or variable speed drive), rotation and discharge orientation, and a layout drawing or site photograph.
- Capacity and cycle. Kilograms per cycle, cycles per day and the largest animal handled.
- Gas cooling. Dilution air, quench or heat exchanger, and the temperature at the fan inlet.
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.