How calcined petroleum coke kilns work
Green petroleum coke from refinery cokers, with 8 to 12% volatile matter and 6 to 12% moisture, is calcined in a rotary kiln at about 1,200 to 1,350°C to drive off moisture and volatiles and raise its density and conductivity for anode and recarburiser use. The volatiles burn inside the kiln with air admitted through shell-mounted tertiary air fans, so the kiln needs little external fuel once running. The kiln exit gas, at about 900 to 1,100°C, still carries unburnt volatiles and coke fines, and passes to a pyroscrubber or incinerator where they burn out at 1,100 to 1,200°C. The gas then goes through a waste heat boiler, a bag filter or ESP, and often a desulphurisation unit, before the ID fan and stack. The calcined coke is cooled with water in a rotary cooler.
Where the ID fan sits
- Rotary kiln
- Pyroscrubber
- Waste heat boiler
- Bag filter or ESP
- FGD (if fitted)
- ID fan
- Stack
The fan sits after the waste heat boiler and gas cleaning, at the end of a long train. The suction at the fan covers the kiln, the pyroscrubber, the boiler, the collector and any scrubber, typically 300 to 500 mmWC. When the boiler or fan is out, an emergency stack at the pyroscrubber opens and the hot gas bypasses them, so the fan is protected from the 1,100°C gas but its trip is a major plant upset.
Gas at the ID fan
| Gas temperature, normal | 180 to 250°C after the waste heat boiler |
| Maximum or upset | Up to 350°C with boiler fouling or partial bypass |
| Dust at the fan | Low after the collector; fine coke and ash if it fails |
| Corrosive species | High SO₂ and some SO₃ from petcoke sulphur of 3 to 6% |
| Moisture and dew point | Acid dew point typically 130 to 160°C; wet and saturated after a wet FGD |
| Density at the design temperature | About 0.72 kg/m³ at 220°C, 60% 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 calcined petroleum coke kilns
| Blade form | Backward curved, on clean gas after the collector |
| Material of construction | Mild steel or corrosion-resistant low-alloy steel for dry gas; SS 316L or lined construction after wet FGD |
| Drive and arrangement | Direct coupled, variable speed drive, often with a standby fan |
| Bearings and cooling | Shaft cooling disc; bearings with temperature and vibration monitoring |
| Flow control | Variable speed drive on pyroscrubber or kiln hood pressure |
| Also specified | Insulated casing, drains, and purge sequence before shutdown |
What this ID fan has to cope with
Acid condensation
With 3 to 6% sulphur coke, the gas has a high acid dew point. Any cold spot in the fan casing, the inlet box or around the shaft seal condenses sulphuric acid and corrodes quickly. Insulation, keeping the gas above the dew point at low load, and corrosion-resistant materials in the cold zones reduce the risk.
Fan trip means plant upset
When the ID fan trips, the emergency stack opens and raw kiln gas is vented, the boiler loses steam, and the kiln may be stopped. A standby fan or a robust single fan with condition monitoring is common, because the cost of a trip is much larger than the cost of the fan.
Fines carry-over
Coke fines that escape a damaged bag or a weak ESP are hard and abrasive. They cut blade edges and unbalance the rotor. Collector monitoring and wear protection at the blade inlet handle this.
Wet gas after FGD
Where a wet scrubber is fitted before the fan, the gas is saturated and carries acidic droplets. A mist eliminator and stainless or lined construction are needed, or a fan placed before the scrubber.
Energy and control
Calcining kilns run continuously at steady output, so the ID fan runs near its design point most of the time. A correctly sized fan with speed control avoids damper losses, and the waste heat boiler makes the plant a net power producer, so fan efficiency directly affects exported power. Reducing air ingress at the kiln and pyroscrubber cuts both fan load and boiler losses.
ID fan and FD fan in calcined petroleum coke kilns
| ID fan | FD fan | |
|---|---|---|
| Position | After the boiler and gas cleaning | On the kiln shell and at the pyroscrubber |
| What it handles | Sulphur-laden flue gas | Ambient air |
| Temperature at the fan | 180 to 250°C | Ambient, with shell radiation |
| Main design concern | Acid dew point and trip consequences | Rotating mount and shell heat |
| Control | Pyroscrubber or kiln draft | Air per zone for volatile burn-off |
See also the Forced Draft (FD) Fan for calcined petroleum coke kilns.
Questions buyers ask
What temperature does a calcined petcoke kiln ID fan handle?
Typically 180 to 250°C after the waste heat boiler. The pyroscrubber gas at 1,100°C never reaches the fan; it goes to the emergency stack when the boiler or fan is out.
Why is acid corrosion a problem in petcoke calcining fans?
Petcoke carries 3 to 6% sulphur, which leaves as SO₂ and SO₃. The acid dew point can be 130 to 160°C, and any part of the fan cooler than that condenses acid. Insulation and suitable materials prevent attack.
Does a petcoke calcining plant need a standby ID fan?
Many plants fit one, because a fan trip vents raw kiln gas through the emergency stack and disrupts the boiler and the kiln. The decision depends on the plant's tolerance for these upsets.
Information needed to quote an ID fan for calcined petroleum coke kilns
- 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 train. Pyroscrubber, waste heat boiler and gas cleaning sequence, including any FGD.
- Coke sulphur. Sulphur in the green coke and the SO₂ at the fan inlet.
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.