How copper anode and refining furnaces work
An anode furnace, usually a tilting rotary vessel, takes molten blister copper from the converter, or melts scrap in a refining furnace, and fire-refines it at about 1,150 to 1,250°C. The cycle has three stages: oxidation, where air is blown through tuyeres to remove sulphur and impurities; reduction or poling, where natural gas, LPG, diesel or ammonia lowers the oxygen content; and casting into anodes. The burner holds bath temperature throughout. Off-gas leaves the mouth at 1,100 to 1,250°C and goes through a post-combustion chamber, where unburnt reductant is burned, then a water-jacketed duct or evaporative cooler, a bag filter and the ID fan, often followed by an SO₂ scrubber or a link to the acid plant gas system.
Where the FD fan sits
- Inlet filter
- FD (combustion air) fan
- Air flow measurement
- Air control valve
- Burner
- Furnace
The fan sits on the operating floor beside the furnace, away from the tilting arc, and delivers air through a flexible or rotary joint to the burner at the end wall. Some furnaces preheat the air in a recuperator on the post-combustion chamber; the fan still handles cold air ahead of it. Its pressure covers the flow element, control valve, any recuperator and the burner, typically 300 to 700 mmWC.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C |
| Air after the recuperator | 300 to 450°C where fitted, downstream of the fan |
| Dust | Clean air if the inlet is taken away from the converter aisle |
| Pressure at the fan outlet | Typically 300 to 700 mmWC |
| Turndown | High firing during charging and heating; low firing while casting |
| 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 copper anode and refining furnaces
| Blade form | Backward curved for efficiency on clean air |
| Material of construction | Mild steel throughout |
| Drive and arrangement | Direct coupled, two-pole or four-pole speed depending on pressure |
| Bearings and cooling | Standard bearings; no cooling needed |
| Flow control | Variable speed drive holding air header pressure, with ratio control at the burner valve |
| Also specified | Inlet filter and silencer, and a flexible connection to the tilting furnace |
What this FD fan has to cope with
Dusty inlet air in the converter aisle
Copper smelter aisles carry fugitive fume and fine dust from converters, ladles and skimming. A fan that draws this air loads its inlet screen and coats the blades, and the flow falls away over months. Taking the fan inlet from outside the building, or through a simple panel filter, keeps the impeller clean and balanced.
Air-fuel ratio during poling
During reduction the operator often runs the burner slightly reducing to help the poling, and the air flow drops well below its design value. The air control must stay stable at this low flow. A fan with a steep curve and a variable speed drive gives finer and steadier control than a heavily throttled outlet damper.
Movement of the tilting furnace
The air line has to follow the furnace as it rotates for skimming, sampling and casting. Flexible hoses or rotary joints, rated for the full fan pressure and the radiant heat at the furnace end, avoid leaks that starve the burner of air and upset the ratio control.
Energy and control
Burner firing on an anode furnace follows the refining cycle, with long periods of reduced firing while anodes are cast. A variable speed drive that holds header pressure, with the burner valve setting the ratio, uses much less power than a damper. Preheating the combustion air from the post-combustion chamber saves more fuel than the fan saves in power, and the recuperator pressure drop is added to the fan duty.
ID fan and FD fan in copper anode and refining furnaces
| ID fan | FD fan | |
|---|---|---|
| Position | After the bag filter, before the scrubber or stack | Beside the furnace, feeding the burner |
| What it handles | Cooled off-gas with SO₂ and metal fume traces | Clean ambient air |
| Temperature at the fan | 120 to 180°C | Ambient |
| Main design concern | Acid dew point and stage-dependent volume | Stable burner air across the cycle |
| Control | Hood suction | Air header pressure and burner ratio |
See also the Induced Draft (ID) Fan for copper anode and refining furnaces.
Questions buyers ask
Is the FD fan on an anode furnace the same as the tuyere air blower?
No. The FD fan supplies combustion air to the burner that heats the bath. The oxidation air blown through tuyeres into the molten copper must overcome the metal head, so it needs much higher pressure and usually comes from a compressor or a multistage blower that is specified separately.
Does the combustion air fan on a copper refining furnace need special materials?
No. It handles cold ambient air, so mild steel construction is normal and the fan is a standard backward curved design. The only care needed is to take the inlet from a clean place, away from fume and dust in the converter aisle, and to protect the motor from radiant heat.
How much pressure does a copper furnace burner air fan need?
It depends on the burner design, the air line and any recuperator. Typical values are 300 to 700 mmWC at the fan outlet, with the higher figures for burners with preheated air. Send us the burner data sheet and the air line layout and we will calculate and confirm the duty.
Information needed to quote an FD fan for copper anode and refining furnaces
- 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.
- Burner data. Burner type, firing range and the air pressure required at the burner.
- Air preheat. Whether the combustion air passes a recuperator and its air side pressure drop.
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.