How lead smelting and battery recycling work
A secondary lead plant breaks spent batteries, separates plastics, acid and lead-bearing paste and grids, and often desulphurises the paste before smelting. The lead is then smelted, usually in short rotary furnaces and sometimes in blast or reverberatory furnaces, at 1,000 to 1,200°C with fluxes and reductants. Bullion is refined and alloyed in gas-fired kettles at 350 to 600°C. The plant has two gas systems: process gas from the smelters, cooled by air or water coolers to bag filter temperature, and hygiene air from hoods over tapping points, kettles, charging and the breaker. Both go through bag filters to ID fans. Process gas carries SO₂, and often goes on to a scrubber.
Where the FD fan sits
- Inlet filter
- FD (combustion air) fan
- Air control valve
- Burner or tuyeres
- Smelter or kettle
Combustion air fans sit beside each furnace or kettle and feed the burner through a control valve; on a rotary furnace the air line enters through the burner end of the rotating body. A blast furnace instead uses a high pressure blower feeding a bustle pipe and tuyeres around the shaft. Burner fans work at 300 to 600 mmWC; blast furnace air blowers need much more pressure.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C |
| Dust | Lead-bearing dust in the plant air if the inlet is inside the building |
| Pressure at the fan outlet | 300 to 600 mmWC for burners; higher for blast furnace tuyere air |
| Turndown | Rotary furnaces cycle between high fire and holding; kettles fire intermittently |
| 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 lead smelting and battery recycling
| Blade form | Backward curved for burner air |
| Material of construction | Mild steel |
| Drive and arrangement | Direct coupled |
| Bearings and cooling | Standard bearings; no cooling needed |
| Flow control | Variable speed drive or modulating valve with burner ratio control |
| Also specified | Inlet taken from outside the building or through a filter |
What this FD fan has to cope with
Lead dust drawn into the fan
A combustion air fan with its inlet inside the smelter building draws lead-bearing dust, which builds up on the impeller and inside the air line and burner. The fan then becomes a source of lead contamination during maintenance. Ducting the inlet from clean outside air, or fitting a filter, solves both problems at little cost.
Oxy-fuel conversion
When a rotary furnace is converted to oxy-fuel firing, the existing combustion air fan is far larger than needed and runs throttled, or not at all. It can be replaced with a small fan for burner cooling or start-up air, or retired. The ID fan duty also falls sharply, which may allow its speed to be reduced.
Kettle burner stability
Refining kettles hold lead at 350 to 600°C and fire at low rates for long periods between alloying and drossing. A fan with stable low-flow behaviour, matched to the burner rather than oversized, and a good ratio control avoid flame outs, sooting and wasted gas during these long holding periods.
Energy and control
Combustion air demand follows the batch on rotary furnaces and the refining schedule on kettles. Variable speed drives on larger fans and ratio control on all burners avoid wasted air. Oxy-fuel firing removes most of the nitrogen from the gas, cutting both FD and ID fan power, though the cost of oxygen has to be weighed against the fuel and power savings.
ID fan and FD fan in lead smelting and battery recycling
| ID fan | FD fan | |
|---|---|---|
| Position | After the bag filters, before scrubber and stack | Beside each furnace and kettle |
| What it handles | Cooled process gas or hygiene air with lead traces | Ambient air |
| Temperature at the fan | 90 to 140°C | Ambient |
| Main design concern | Acid corrosion and leak-tight casing | Clean inlet air and burner stability |
| Control | Furnace and hood suction | Burner ratio |
See also the Induced Draft (ID) Fan for lead smelting and battery recycling.
Questions buyers ask
What is the FD fan in a lead smelter?
It is the combustion air fan supplying the burner on the rotary furnace or the refining kettles, or the air blast blower feeding the tuyeres on a blast furnace. In every case it handles ambient air and does not see process gas, so mild steel construction and a standard backward curved design are normal.
Does an oxy-fuel rotary furnace need an FD fan?
Not for combustion, since the burner uses oxygen instead of air. Some plants keep a small air fan for burner cooling, start-up, or mixed air and oxygen firing when oxygen supply is limited. The main forced draft duty largely disappears, and the gas volume at the ID fan falls too.
Why should the combustion air inlet be outside the building?
The air inside a lead smelter building carries fine lead dust from charging, tapping and drossing. Drawing it into the fan coats the impeller, contaminates the burner and air line, and exposes maintenance staff to lead. Taking the inlet from clean outside air avoids all of this.
Information needed to quote an FD fan for lead smelting and battery recycling
- 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.
- Firing system. Air-fuel, oxy-fuel or mixed, and the burner firing range for each furnace and kettle.
- Blast furnace air. Tuyere air flow and pressure, if a blast furnace is used.
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.