How copper smelter waste heat boilers work
Copper concentrate, mainly chalcopyrite, is smelted in a flash furnace or a bath smelting furnace with oxygen-enriched air, producing matte and slag, while converters then oxidise the matte to blister copper. The off-gas leaves the smelter at about 1,250 to 1,350°C, carrying a high SO₂ concentration and heavy, partly molten dust of oxides and sulphates. A waste heat boiler with a radiation chamber and convection section cools it to about 320 to 380°C, then a hot ESP removes the dust before the gas goes to wet gas cleaning and the sulphuric acid plant. The draft through the boiler is usually created by the acid plant main blower downstream. A hot gas fan after the ESP is used only on some layouts.
Where the ID fan sits
- Smelting furnace uptake
- WHB radiation chamber
- WHB convection section
- Hot ESP
- ID (hot gas) fan
- Wet gas cleaning and acid plant
Where fitted, the fan sits after the hot ESP, handling gas at about 320 to 380°C, and before the wet gas cleaning section. It holds the smelter uptake at a slight suction against the boiler and ESP, while the acid plant blower takes over from there. Placing it after the ESP keeps the sticky dust load low, and keeping the gas hot keeps it above the SO₃ dew point, so the fan works dry.
Gas at the ID fan
| Gas temperature, normal | 320 to 380°C after the boiler and hot ESP |
| Maximum or upset | Higher if boiler surfaces foul heavily, often limited by dilution air |
| Dust at the fan | Fine oxide and sulphate fume after the ESP; can be sticky |
| Moisture and dew point | SO₃ acid dew point can be high, often above 200°C, so the fan and duct must stay hot |
| Corrosive and toxic species | High SO₂ and some SO₃; leaks are a safety hazard |
| Density at the design temperature | About 0.57 kg/m³ at 350°C, 47% 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 copper smelter waste heat boilers
| Blade form | Backward curved or radial tipped, with blades that shed fine sticky fume |
| Material of construction | Heat-resisting steel impeller rated for the maximum gas temperature; casing in boiler quality steel with full insulation |
| Drive and arrangement | Direct coupled, arrangement 8, with sliding supports for thermal growth |
| Bearings and cooling | Water- or oil-cooled bearings and a shaft cooling disc |
| Flow control | Variable speed drive on furnace uptake pressure, coordinated with the acid plant blower |
| Also specified | Gas-tight shaft seals with sealing air or inert gas purge, insulated and heat-traced casing, no cold drains |
What this ID fan has to cope with
SO₂ leakage at the shaft
Smelter gas is toxic, and a fan working against a slight positive discharge pressure can leak at the shaft and joints. Multi-ring shaft seals with sealing air or inert gas purge and fully welded or gasketed casings keep the gas inside, and the area is monitored for SO₂.
Acid condensation on cold surfaces
SO₃ in smelter gas raises the acid dew point to well above 200°C in some conditions. Any cold spot, such as an uninsulated flange, door or drain, condenses acid and corrodes quickly. Full insulation, heat tracing on cold areas and keeping the fan running warm during short stops avoid it.
Sticky fume deposits
Fine sulphate and oxide fume that passes the ESP can stick to blades and build unevenly, especially when the ESP is upset. Blade forms that shed deposits, access doors for cleaning and in-situ balancing manage vibration between campaigns. Keeping ESP rapping and field voltages in good order is the first defence.
Coordination with the acid plant blower
The hot gas fan and the acid plant blower act on the same gas stream. If they fight, smelter draft swings and SO₂ escapes. A shared control strategy, with the hot gas fan holding furnace draft and the blower holding the acid plant inlet, keeps both stable.
Energy and control
Smelters run continuously, but gas flow changes with concentrate feed, oxygen enrichment and converter cycles. Speed control from uptake draft avoids throttling losses on the hot gas fan. Higher oxygen enrichment reduces the gas volume per tonne of concentrate, and the fan duty should be reviewed whenever the smelter changes its oxygen practice.
Questions buyers ask
Does a copper smelter waste heat boiler have an ID fan?
Often not as a separate machine. On many smelters, the acid plant main blower after the gas cleaning section pulls the gas through the boiler and ESP. A hot gas ID fan after the ESP is used on some layouts, especially where the gas path is long or the draft must be controlled close to the furnace.
Why must the copper smelter gas fan stay hot?
Smelter gas contains SO₃, which forms sulphuric acid below its dew point, often above 200°C. If the fan casing or drain cools below this, acid condenses and corrodes the steel rapidly. Insulation and heat tracing keep every surface above the dew point. Short stops are managed with the fan kept warm.
How is SO₂ leakage prevented at the fan shaft?
With multi-ring shaft seals supplied with sealing air or inert gas at a pressure above the gas inside the casing, and with gas-tight casing joints. The fan area is usually monitored for SO₂ as part of the smelter's safety system. Seal supply pressure is alarmed.
Information needed to quote an ID fan for copper smelter waste heat boilers
- 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.
- Gas composition. SO₂ and SO₃ content, oxygen enrichment, gas flow and temperature after the ESP.
- Gas handling system. Whether the acid plant blower or a hot gas fan controls the furnace draft, and the pressure at 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.