How pharmaceutical spray dryers work
Pharmaceutical spray dryers produce APIs, amorphous solid dispersions, excipients and inhalable particles, usually in small to medium chambers with two-fluid or pressure nozzles. Aqueous feeds dry in open-cycle units: HEPA-filtered air is heated by steam or electric heaters to about 120 to 200°C and leaves at 50 to 90°C through a cyclone and a cartridge or bag filter with a HEPA police filter. Feeds in organic solvents such as acetone, methanol or dichloromethane dry in closed-cycle units with nitrogen: the gas leaves the chamber, passes the cyclone and filter, is cooled in a condenser that recovers the solvent, and is reheated and recirculated by a single blower. Containment of potent compounds, product purity and, for solvents, oxygen levels and explosion risk set the design.
Where the ID fan sits
- Drying chamber
- Cyclone
- Product filter
- HEPA police filter
- Exhaust (ID) fan
- Condenser (closed cycle)
- Stack or recirculation
In open-cycle units the fan follows the product filter and HEPA police filter and discharges to atmosphere, holding the chamber at a slight suction for containment. In closed-cycle units the blower follows the filter and pushes nitrogen through the condenser and heater back to the chamber, with the loop held at a small positive pressure so oxygen cannot leak in. The fan pressure covers the cyclone, filters, condenser and heater.
Gas at the ID fan
| Air temperature, normal | 50 to 90°C in open cycle; often below 30°C after the condenser in closed cycle |
| Maximum or upset | Up to inlet temperature, typically 150 to 200°C, if feed is lost |
| Dust at the fan | Very low after the product and HEPA filters; any leakage is potent API |
| Moisture and solvent | Water vapour in open cycle; solvent vapour in closed-cycle nitrogen |
| Gas | Air in open cycle; nitrogen with oxygen held low in closed cycle |
| 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 pharmaceutical spray dryers
| Blade form | Backward curved, smooth and crevice-free |
| Material of construction | SS 316L for gas-wetted parts, polished finish, documented material certificates |
| Drive and arrangement | Direct driven, with a variable speed drive; gas-tight casing |
| Bearings and cooling | Bearings outside the gas, with a mechanical or nitrogen-purged shaft seal for closed cycle |
| Flow control | Variable speed drive on gas flow or chamber pressure |
| Also specified | Pressure-shock or vented design where required, earthing, flameproof motor for solvent duty, cleanable casing with drain |
What this ID fan has to cope with
Leakage of nitrogen or air in
In closed cycle, air leaking in at the shaft seal raises oxygen above safe levels with solvent vapour present. A gas-tight casing, mechanical or purged seal and a positive loop pressure keep the loop inert, with oxygen analysers interlocked to the heater.
Containment of potent compounds
A small amount of potent API passing a leaking filter can contaminate the fan and expose maintenance staff. The fan follows a HEPA police filter, is cleanable in place or easily dismantled, and has documented cleaning procedures.
Validation and documentation
Pharmaceutical users need material certificates, surface finish records, weld documentation and test reports for qualification. These are part of the fan specification from the start, not added at handover, because missing records can hold up installation and operational qualification.
Energy and control
Pharmaceutical dryers run in batches or short campaigns with frequent cleaning, so fan energy is modest. Closed-cycle units recover solvent and reuse nitrogen, which matters far more than the fan power. A variable speed drive lets one fan cover development and production rates, warm-up and the cleaning cycle. Running at reduced speed during cleaning also saves power.
ID fan and FD fan in pharmaceutical spray dryers
| ID fan | FD fan | |
|---|---|---|
| Position | After the product and HEPA police filters | After pre-filters, before heater and HEPA |
| What it handles | Moist air or solvent-laden nitrogen | Clean filtered air (open cycle only) |
| Temperature at the fan | 50 to 90°C open cycle; cool in closed cycle | Room temperature |
| Main design concern | Gas-tightness and containment | Repeatable flow |
| Control | Chamber pressure or loop flow | Gas flow |
See also the Forced Draft (FD) Fan for pharmaceutical spray dryers.
Questions buyers ask
What is a closed-cycle spray dryer?
A spray dryer that uses nitrogen in a closed loop to dry feeds in flammable organic solvents. The gas is cleaned, cooled in a condenser to recover the solvent, reheated and recirculated by a blower, so oxygen stays below the level that could support an explosion.
What seal does a pharma spray dryer blower need?
In closed-cycle nitrogen service, a mechanical seal or a nitrogen-purged labyrinth so nitrogen does not leak out and air does not leak in. For open-cycle aqueous duty, a good lip or labyrinth seal is usually enough.
Does a pharmaceutical spray dryer fan need to be SS 316L?
Usually yes for gas-wetted parts. SS 316L resists cleaning agents and solvents and is the common material for GMP equipment, with a specified internal surface finish and material certificates for each wetted part.
Information needed to quote an ID fan for pharmaceutical spray dryers
- 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.
- Cycle and gas. Open cycle with air or closed cycle with nitrogen, the solvents used and the oxygen limit.
- GMP documentation. Required material certificates, surface finish, seal type and any hazardous area classification.
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.