How API process residue incinerators work
API manufacturing leaves process residues that are neither clean solvents nor ordinary solid waste: distillation still bottoms, tarry residues, spent carbon and filter aids, salt cakes from neutralisation and off-specification intermediates. Captive incinerators at API sites burn these in a static hearth, a small rotary kiln or a combined chamber with liquid injection for pumpable residues, followed by a secondary chamber at 1,100°C or more. The residues often contain nitrogen, sulphur, chlorine, bromine and fluorine, and some carry spent catalyst metals. Gas is quenched, scrubbed in a venturi and packed alkali column, passed through a mist eliminator and drawn by the ID fan. Combustion air fans serve the primary and secondary chambers.
Where the ID fan sits
- Primary chamber or kiln
- Secondary chamber
- Quench
- Venturi scrubber
- Packed alkali scrubber
- ID fan
- Stack
The fan sits after the packed scrubber and mist eliminator, at the base of the stack. It works against the chambers, quench, venturi and packed column, typically 400 to 700 mmWC, with the venturi taking the largest share. Keeping the fan at the end of the train keeps the chambers under suction during batch charging of drums or bags of residue, which can release gas suddenly, and keeps any scrubber leak drawing air inwards.
Gas at the ID fan
| Gas temperature, normal | 60 to 80°C, saturated after the scrubber |
| Maximum or upset | Hot gas on quench failure; protected by emergency vent and trips |
| Dust at the fan | Fine salt fume and droplets; traces of catalyst metal oxides |
| Moisture and dew point | Saturated, with free droplets |
| Corrosive species | Residual HCl, HBr and HF, and SO₂; halide salts in droplets |
| Density at the design temperature | About 1.03 kg/m³ at 70°C, 86% 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 API process residue incinerators
| Blade form | Backward curved or radial, with no liquid traps |
| Material of construction | FRP with a synthetic, non-glass veil for HF resistance, or rubber-lined mild steel; stainless steel is usually avoided |
| Drive and arrangement | Belt or direct drive with the motor outside the wet zone |
| Bearings and cooling | Pedestal bearings with sealed shaft entry |
| Flow control | Variable speed drive on chamber pressure |
| Also specified | Casing drain, wash nozzles, and temperature trip with emergency vent interlock |
What this ID fan has to cope with
HF attack on FRP
Hydrogen fluoride from fluorinated APIs and intermediates attacks the glass fibre in standard FRP, causing blistering and loss of strength. A synthetic veil and a resin selected for HF, or rubber lining on steel, give a much longer life.
Batch-to-batch gas changes
Residue composition changes with each campaign of the API plant. A fan selected for one product may face very different gas a month later. Selection is based on the full range of residues expected, especially worst-case halogen content.
Sticky tars from residues
Tarry still bottoms can burn incompletely during start-up or overload, and condensed organics reach the scrubber and fan. Keeping the secondary chamber at temperature before feeding, and wash nozzles on the fan, prevent build-up.
Energy and control
API residue incinerators often run on campaigns with batch feeding. A variable speed ID fan on chamber pressure handles charging surges and reduces power during low feed or hold periods. Venturi pressure drop is the largest share of fan power, so matching it to the actual particulate and salt fume load saves energy.
ID fan and FD fan in API process residue incinerators
| ID fan | FD fan | |
|---|---|---|
| Position | After the alkali scrubber | Beside the incinerator, feeding all chambers |
| What it handles | Saturated gas with HCl, HBr and HF | Ambient combustion air |
| Temperature at the fan | 60 to 80°C | Ambient, 25 to 45°C |
| Main design concern | Mixed halogen corrosion | Oxygen after batch charging |
| Control | Chamber pressure | Oxygen and chamber temperature |
See also the Forced Draft (FD) Fan for API process residue incinerators.
Questions buyers ask
What material should an ID fan be for a pharma waste incinerator with fluorinated residues?
FRP with a synthetic veil and an HF-resistant resin, or rubber-lined steel. Standard glass-veil FRP is attacked by HF, and stainless steel suffers from mixed halides in the wet gas.
Why is the ID fan after the scrubber on an API residue incinerator?
To keep the chambers and the scrubber under suction. API residues can release gas suddenly during charging, and suction prevents toxic or odorous gas from escaping at the feed door, the chamber seals or a leaking scrubber joint, which matters on a site with people working nearby.
What information is needed to size an ID fan for an API waste incinerator?
The range of residues and their composition, especially halogen content, the feed rate and method, the quench and scrubber design and pressure drop, and the expected gas volume at the fan. Existing fan nameplate data and measured suction help where an incinerator is being upgraded.
Information needed to quote an ID fan for API process residue incinerators
- 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.
- Halogen range. Expected range of chlorine, bromine and fluorine in the residues.
- Feed method. Drum, bag, screw or liquid injection feeding, and batch size.
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.