How egg powder spray dryers work
Liquid whole egg, yolk or albumen is filtered, pasteurised and, for albumen, often desugared by fermentation or enzymes before drying. The feed is dilute: whole egg is about 23 to 25% solids and albumen about 12%, so the dryer evaporates much more water per kg of powder than a dairy dryer. Egg proteins are heat sensitive, so inlet air is held at about 150 to 190°C and outlet at about 60 to 75°C, usually with steam or indirect heating. A rotary atomiser or nozzles spray the feed into a co-current chamber, and the powder may be hot-room pasteurised afterwards. Exhaust air passes cyclones and a bag filter; yolk and whole egg fines are rich in fat, which shapes how the exhaust side is cleaned.
Where the FD fan sits
- Air intake
- Pre-filter and fine filter
- FD (supply) fan
- Steam air heater
- Final filter
- Air disperser
- Drying chamber
The supply fan follows the filter house and feeds the steam heater, so it handles cool filtered air. Because inlet temperatures are moderate, steam coils can do all the heating and no high temperature heater is needed. Some plants add a final filter after the heater. The fan pressure covers the filters at their dirty condition, the steam coil, any final filter and the air disperser.
Air at the FD fan
| Air temperature at the fan | Ambient, 15 to 45°C |
| Air after the heater | 150 to 190°C, downstream of the fan |
| Dust | Filtered; fine filters protect the product |
| Humidity | Seasonal humidity reduces drying capacity at low inlet temperatures |
| Pressure | Filters, steam coil and air disperser |
| Density at the design temperature | About 1.13 kg/m³ at 40°C, 94% 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. |
FD Fan selection for egg powder spray dryers
| Blade form | Backward curved or aerofoil |
| Material of construction | Stainless steel or food-grade coated mild steel |
| Drive and arrangement | Direct driven with a variable speed drive |
| Bearings and cooling | Standard bearings outside the air stream |
| Flow control | Variable speed drive on air flow |
| Also specified | Food-grade flexible connections and inspection door |
What this FD fan has to cope with
Humid seasons cut output
At inlet temperatures below 200°C the drying capacity of the air depends strongly on its moisture. In humid seasons output falls unless the inlet air is dehumidified, which adds coil pressure drop to the fan duty.
Large volume, steady flow
The supply fan is large for the size of the dryer and runs at high load continuously. As the filters load, a fixed-speed fan drops flow and the powder moisture rises. Flow measurement and speed control hold the air constant between filter changes.
Hygiene of the air path
Supply air reaches the product directly, and egg powder is a high-risk food for microbial contamination. Clean, coated or stainless surfaces, no oil mist from bearings, and filters that are changed and recorded on schedule protect the powder.
Energy and control
Because the feed is dilute and the drying temperatures low, the supply fan moves a large volume of air per kg of powder for the whole campaign. A high-efficiency wheel and a variable speed drive repay quickly. Preheating the inlet air with heat recovered from the exhaust reduces steam use, at the cost of a coil pressure drop added to the fan duty.
ID fan and FD fan in egg powder spray dryers
| ID fan | FD fan | |
|---|---|---|
| Position | After the bag filter | After the filters, before the steam heater |
| What it handles | Cool humid air with fatty egg fines | Filtered ambient air |
| Temperature at the fan | 60 to 75°C | Ambient |
| Main design concern | Fat film, condensation and hygiene | Large steady air volume |
| Control | Chamber pressure | Drying air flow |
See also the Induced Draft (ID) Fan for egg powder spray dryers.
Questions buyers ask
Why do egg powder dryers use steam heating?
The inlet air temperature is moderate, usually below 190°C, which steam coils can reach. Steam heating is clean, has no combustion products and is easy to control, which suits a heat-sensitive, high-risk food product. It also keeps the supply fan on clean ambient air.
Does the egg dryer supply fan need stainless steel?
Many plants specify stainless steel for the whole product air path. A coated mild steel fan is also used where it meets the plant's hygiene standard and the fan is before the final filter.
How can egg dryer output be kept up in the monsoon?
By dehumidifying the inlet air with a chilled coil or desiccant wheel before the heater. Drier air evaporates more water at the same low inlet temperature. The supply fan must then have enough pressure for the extra coil or wheel, so this is best allowed for when the fan is selected.
Information needed to quote an FD fan for egg powder spray dryers
- Duty point. Combustion air quantity in m³/h or kg/h and the static pressure at the fan outlet, with the margins you want.
- Air condition. Site ambient temperature range and altitude, and whether the fan takes ambient air or air already heated.
- System. Boiler or furnace capacity and fuel, resistance of the air heater, windbox, grate or burner, and the existing fan curve or nameplate if this is a replacement.
- Mechanical. Drive arrangement, flow control (damper, inlet vanes or variable speed drive), noise limit, rotation and discharge orientation.
- Heater and filters. Steam pressure, heater pressure drop and filter grades.
- Dehumidification. Whether inlet air is dehumidified and the added pressure drop.
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.