How e-waste thermal treatment furnaces work
E-waste thermal treatment furnaces burn or pyrolyse shredded printed circuit boards, cables and electronic scrap to remove plastics and recover copper and precious metals. Feed is charged to a rotary kiln, a batch pyrolysis chamber or a small smelting furnace at 500 to 900°C. The plastics, mainly epoxy and ABS with brominated flame retardants, give off a gas rich in organics, HBr and HCl. A secondary combustion chamber at about 1,100°C destroys the organics, after which the gas must be cooled quickly, by quench or heat exchanger, to below about 200°C to limit dioxin and furan reformation. Dry lime and activated carbon injection with a bag filter, often followed by a wet scrubber, cleans the gas before the ID fan.
Where the ID fan sits
- Kiln or pyrolysis chamber
- Afterburner
- Rapid quench
- Lime and carbon injection
- Bag filter
- Wet scrubber
- ID fan
- Stack
The fan is after the bag filter and, where fitted, the wet scrubber. With a dry system alone it handles gas at 140 to 180°C above the acid dew point; after a wet scrubber it handles saturated, acidic gas at 55 to 75°C. Total suction is high, often 400 to 600 mmWC, because the gas passes the kiln, afterburner, quench, reactor duct, bag filter and scrubber. Placing the fan last keeps every item under suction, so toxic gas does not escape.
Gas at the ID fan
| Gas temperature, normal | 140 to 180°C dry; 55 to 75°C after a wet scrubber |
| Maximum or upset | 250 to 300°C on quench water failure, before the bypass trips |
| Dust at the fan | Low after the bag filter; fine copper, lead and tin oxides if bags fail |
| Moisture and dew point | High after the quench; acid dew point raised by HBr and HCl |
| Corrosive species | HBr, HCl, SO₂ and bromine; dioxins at trace levels |
| Density at the design temperature | About 0.82 kg/m³ at 160°C, 68% 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 e-waste thermal treatment furnaces
| Blade form | Backward curved, for the high pressure on low dust gas |
| Material of construction | SS 316L or higher alloy for dry acid duty; rubber-lined or FRP for wet scrubber duty |
| Drive and arrangement | Direct drive, arrangement 8, with a sealed shaft entry |
| Bearings and cooling | Shaft cooling disc for dry duty; shaft seal against acid gas |
| Flow control | Variable speed drive on kiln or chamber pressure |
| Also specified | Casing drain, inspection door, acid-resistant coating inside and gas-tight casing joints |
What this ID fan has to cope with
Bromide and chloride corrosion
HBr and HCl from flame retardants and PVC condense as hydrobromic and hydrochloric acid when the gas falls below the acid dew point. Even SS 304 pits quickly. Keeping dry-system gas well above the dew point, and using SS 316L, higher alloys, rubber lining or FRP where the gas is wet, gives a usable life.
High system resistance
The gas cleaning train on an e-waste plant is long, and the bag filter resistance rises as the cake of lime, carbon and metal oxide builds. A fan selected only at clean conditions runs out of pressure and the kiln goes positive. Selecting for the fouled bag filter and the full train keeps suction.
Leakage of toxic fumes
Brominated organics and dioxins must not escape from the kiln seals, charging door or duct joints. The fan holds a steady negative pressure at the kiln with a fast control loop and enough margin for feed surges, when a batch of plastic-rich boards flashes off and the gas volume jumps within seconds. Losing suction then means visible fumes.
Metal oxide deposits
If a bag fails or a seal leaks in the bag filter, fine copper, lead, tin and zinc oxides reach the fan and deposit on the blades, causing imbalance and adding toxic dust to the stack. A broken-bag detector before the fan, and an inspection door on the casing, catch the problem early and allow safe cleaning.
Energy and control
Feed composition in e-waste treatment changes widely with the board type and the plastic fraction, so gas volume changes too. A variable speed drive on kiln pressure follows the real gas flow instead of throttling a fan sized for the worst batch. On a high-resistance system the fan is a significant load, so the bag filter cleaning cycle and the scrubber pressure drop are worth managing as part of energy control.
ID fan and FD fan in e-waste thermal treatment furnaces
| ID fan | FD fan | |
|---|---|---|
| Position | After bag filter and scrubber | Ahead of kiln and afterburner |
| What it handles | Cleaned gas with HBr and HCl traces | Ambient air |
| Temperature at the fan | 140 to 180°C dry, 55 to 75°C wet | Ambient |
| Main design concern | Halide corrosion and high system resistance | Afterburner air for organics destruction |
| Control | Kiln pressure | Afterburner oxygen and temperature |
See also the Forced Draft (FD) Fan for e-waste thermal treatment furnaces.
Questions buyers ask
What material is used for an ID fan handling HBr from e-waste burning?
HBr and HCl are very corrosive when they condense. For dry gas held above dew point, SS 316L or higher alloys are used. After a wet scrubber, the fan is usually rubber-lined steel or FRP. Mild steel and SS 304 are not suitable for e-waste thermal treatment exhaust.
Why is rapid quench needed before the ID fan in e-waste treatment?
Dioxins and furans can reform when the gas cools slowly through about 200 to 450°C in the presence of dust and chlorine or bromine. A rapid quench to below 200°C limits reformation, and also brings the gas to a temperature the bag filter and ID fan can handle.
What pressure does an e-waste furnace ID fan need?
The gas passes the kiln, afterburner, quench, dry reactor, bag filter and often a wet scrubber. Total suction is typically 400 to 600 mmWC, including the fouled bag filter. The e-waste furnace ID fan must also hold suction at the kiln during feed surges, so a pressure margin above the steady-state figure is needed.
Information needed to quote an ID fan for e-waste thermal treatment furnaces
- 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.
- Feed composition. Types of e-waste processed, plastic fraction and the halogen content of the feed.
- Gas cleaning train. Quench type, sorbent injection, bag filter and scrubber, with the pressure drop of each.
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.