How non-Recovery coke ovens work
A non-recovery or heat recovery coke oven carbonises coal in wide, horizontal ovens under suction, without collecting the by-products. The volatile matter burns in the oven crown above the coal and in the sole flues beneath it with air drawn in through ports, and the hot gas, at about 1,000 to 1,200°C, leaves through uptakes into a common tunnel. On heat recovery plants the gas goes to heat recovery steam generators, then to a flue gas desulphurisation unit, usually a spray dryer absorber with lime, and a bag filter before the ID fan and main stack. Emergency stacks on the tunnel open if the ID fan trips. Coking cycles are about 48 to 72 hours.
Where the ID fan sits
- Ovens and sole flues
- Common tunnel
- Heat recovery steam generators
- Spray dryer FGD
- Bag filter
- ID fan
- Main stack
The fan, usually one running and one standby or two at 50 to 60%, sits after the bag filter. Its suction covers the oven uptakes, the common tunnel, the heat recovery boilers, the FGD and the filter, typically 300 to 500 mmWC. The ovens themselves must stay under slight suction at all times, so the fan is critical to emissions. If it trips, the emergency stacks open and untreated hot gas is released.
Gas at the ID fan
| Gas temperature, normal | 140 to 170°C after the spray dryer and bag filter |
| Maximum or upset | Up to 250°C when the spray dryer water is off |
| Dust at the fan | Below 20 to 50 mg/Nm³ of fine lime, sulphate and ash after the filter |
| Moisture and dew point | Water vapour from the spray dryer adds to combustion water; dew point about 55 to 65°C |
| Corrosive species | SO₂ remaining after FGD; coal sulphur 0.5 to 1% gives high raw SO₂ |
| Density at the design temperature | About 0.83 kg/m³ at 155°C, 69% 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 non-Recovery coke ovens
| Blade form | Backward curved, for efficiency on low-dust gas |
| Material of construction | Mild steel with corrosion allowance and insulation; SS for the inlet box where gas is close to dew point |
| Drive and arrangement | Direct coupled, arrangement 8, with standby fan and isolation dampers |
| Bearings and cooling | Pedestal bearings with cooling disc and monitoring |
| Flow control | Variable speed drive on common tunnel draft |
| Also specified | Insulated casing, drains and fast changeover to standby |
What this ID fan has to cope with
Fan trip and emissions
If the fan trips, the ovens lose suction, the emergency stacks open and untreated gas is released. Standby fans with automatic changeover, a reliable power supply and condition monitoring are therefore essential. Emergency stack operation should be rare and short.
Variable oven gas
Each oven releases most of its gas early in the coking cycle. With staggered charging the total flow evens out, but charging several ovens at once gives peaks. The fan has flow margin and responsive speed control. The charging schedule is part of the fan duty.
Acid and moist deposits
Gas leaving the spray dryer is moist and carries fine calcium sulphite, sulphate and unreacted lime. If the fan casing cools, these stick to the blades and casing and absorb moisture, causing imbalance and corrosion. Insulation, a controlled spray dryer outlet temperature and cleaning at each opportunity prevent heavy build-up.
Energy and control
Heat recovery coke plants export steam or power, so ID fan power reduces net output. Variable speed control on tunnel draft adjusts to the charging pattern. Air ingress at oven doors and tunnel joints adds to the gas volume, so maintaining seals reduces fan load. Fan efficiency therefore matters in this plant.
Questions buyers ask
Why is the ID fan critical in a non-recovery coke oven?
It keeps every oven under suction. The process relies on that suction to draw combustion air into the ovens and keep gas from leaking out at the doors. If the fan stops, emissions escape and the emergency stacks open, so reliable standby fans with automatic changeover are needed.
What temperature does the ID fan handle in a heat recovery coke oven?
Typically 140 to 170°C after the spray dryer FGD and bag filter, with higher upset temperatures if the spray dryer water fails. The gas is moist and contains residual SO₂, so the fan is insulated and kept above dew point to avoid corrosion under acid deposits.
What is the difference between non-recovery and by-product coke ovens for fans?
A non-recovery or heat recovery coke oven relies on an ID fan to hold the ovens under suction and move the gas through the heat recovery boilers and FGD. A by-product battery uses natural draft for its heating system and gas exhausters for the raw gas, with ID fans mainly on emission control.
Information needed to quote an ID fan for non-Recovery coke ovens
- 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.
- Plant size. Number of ovens, charging pattern and heat recovery steam generators.
- FGD. FGD type and outlet temperature.
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.