How electric crematoria work
An electric crematorium heats a refractory-lined chamber with resistance elements, typically to 650 to 800°C before the body is charged. There is no fuel burner; the body burns in air drawn into the chamber through controlled inlets, and the fat and tissue supply much of the heat once burning starts. Many units have an electrically heated or small burner-fired secondary chamber to finish the smoke. The gas volume is small compared with fuel fired crematoria, but it carries smoke, odour and moisture from the body. It passes a wet scrubber or cyclone and is drawn to the chimney by an ID fan. A cycle takes about 60 to 90 minutes, and the chamber is kept hot between cremations to save power.
Where the ID fan sits
- Electric primary chamber
- Secondary chamber
- Wet scrubber
- Mist eliminator
- ID fan
- Chimney
The fan is after the scrubber and mist eliminator, at the foot of the chimney. Upstream it has the primary chamber with its controlled air inlets, the secondary chamber, the flue and the scrubber, together typically 80 to 180 mmWC. The fan must hold a small suction in the primary chamber, about −2 to −5 mmWC, so that smoke does not escape when the door opens, while pulling no more air through the chamber than combustion needs.
Gas at the ID fan
| Gas temperature, normal | 45 to 70°C after the wet scrubber |
| Maximum or upset | 250 to 350°C if scrubber water fails |
| Dust at the fan | Very low; fine ash and calcium phosphate in droplets |
| Moisture and dew point | Saturated; body moisture is the main water source |
| Corrosive species | HCl from coffin furnishings, SO₂ and mercury from dental amalgam |
| Density at the design temperature | About 1.05 kg/m³ at 65°C, 88% 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 electric crematoria
| Blade form | Backward curved, small and efficient on low dust gas |
| Material of construction | SS 316 or FRP for the saturated, mildly acidic gas |
| Drive and arrangement | Direct drive, arrangement 4 |
| Bearings and cooling | Standard bearings with shaft seal |
| Flow control | Variable speed drive on chamber draft, with a door-open boost |
| Also specified | Casing drain, high-temperature trip, and quiet running for a hall location |
What this ID fan has to cope with
Too much suction wastes heater power
An oversized ID fan pulls cold air into the chamber through every gap, and the electric elements must reheat it. On an electric crematorium this shows directly in the power bill and in a longer cycle. A fan sized for the real gas flow, with speed control on a small fixed draft, keeps air ingress to what combustion needs.
Smoke at the door
With a small fan and low gas volume, the sudden inflow when the door opens can overwhelm the draft. A door switch that ramps the fan up for the charging minute, and a fan curve with spare pressure at the higher flow, keep smoke out of the hall.
Wet duty corrosion
Scrubber exit gas is saturated, and on an electric crematorium the fan often stands cold between cremations or overnight while the chamber is held hot. Condensate with dissolved chlorides pools in the scroll and attacks a mild steel casing from the inside. Stainless or FRP construction, a casing drain and a sloped outlet duct avoid early failure.
Element damage from aggressive draft
High air velocity across hot resistance elements oxidises them faster and can carry ash and fat residue onto them, shortening their life and causing hot spots. Holding a steady, low draft rather than a strong one, and placing the air inlets so that incoming air does not sweep directly across the elements, extends element life and reduces replacement cost.
Energy and control
The electric crematorium is the one type where fan control directly affects the main energy cost. Each unnecessary cubic metre of air drawn through the chamber must be heated by the elements to 700°C or more. A variable speed drive holding a small, steady draft, with a boost only during charging, reduces heater power per cremation. Between cremations the fan should drop to the minimum that keeps the chamber clear.
Questions buyers ask
Does an electric crematorium have an FD fan?
Usually not. There is no fuel burner, so the electric crematorium needs only the air for burning the body itself. The ID fan draws this in through controlled inlets on the chamber. Some designs use a small blower for secondary air, but the ID fan is the main and often the only fan.
What size ID fan is used on an electric crematorium?
Electric crematoria have small gas volumes, so the ID fan is smaller than on fuel fired units. The pressure is set by the secondary chamber, scrubber and flue, usually 80 to 180 mmWC. The flow should be sized for combustion air and door-open conditions, not with large margins.
Why is my electric crematorium using too much power?
One common cause is excess draft. The ID fan pulls more cold air through the chamber than combustion needs, and the electric elements must reheat it to 700°C or more. Reducing draft with a speed controlled fan, sealing door and peephole leaks, and running the fan slowly between cremations often reduces the power used per cremation.
Information needed to quote an ID fan for electric crematoria
- 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.
- Chamber and heaters. Heater rating, chamber volume and the secondary chamber arrangement.
- Draft and door. Required chamber suction and whether the fan must boost during charging.
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.