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 ID fan sits
- Drying chamber
- Cyclones
- Bag filter
- Exhaust (ID) fan
- Odour control or stack
The fan follows the bag filter and holds the chamber at a slight suction. Because egg feeds are dilute and the outlet is kept low, the exhaust volume per kg of powder is large and its dew point is close to the outlet temperature, leaving little margin before condensation. The suction covers the chamber, cyclones and bag filter, typically 200 to 350 mmWC.
Gas at the ID fan
| Air temperature, normal | 60 to 75°C at the fan inlet |
| Maximum or upset | Up to about 110°C when feed is lost |
| Dust at the fan | Fine egg powder, fatty for yolk and whole egg, low after the bag filter |
| Moisture and dew point | High humidity, dew point about 40 to 50°C, close to the outlet temperature |
| Hygiene | Egg residues support bacterial growth; strict cleaning required |
| 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 egg powder spray dryers
| Blade form | Backward curved, smooth, fully welded blades without crevices |
| Material of construction | SS 304 or SS 316 for all wetted parts, ground welds |
| Drive and arrangement | Direct or belt driven, variable speed |
| Bearings and cooling | Bearings outside the air stream, shaft seal against moisture |
| Flow control | Variable speed drive on chamber pressure |
| Also specified | CIP nozzles, drain, insulated casing and quick-opening door |
What this ID fan has to cope with
Greasy film on the blades
Yolk and whole egg powders are high in fat, and fines that pass the filter leave a greasy film that collects more powder. Hot caustic CIP through nozzles in the casing removes it; dry brushing does not.
Condensation in the casing
With the outlet only 15 to 25°C above the dew point, any cold surface or slight overload brings condensation that wets the fines. An insulated casing, a drain and running the fan on dry air after shutdown prevent wet deposits.
Microbial risk
Wet egg residues in a fan casing are a breeding ground for bacteria, and fines can return to the product. Crevice-free construction, full drainage and CIP validated by swab tests protect the product.
Energy and control
Egg dryers handle a large air volume per kg of powder because the feed is dilute. Concentrating the feed by ultrafiltration before drying, where the product allows, and recovering heat from the exhaust to the inlet air reduce the air needed. A variable speed drive on the exhaust fan follows the evaporation rate.
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 Forced Draft (FD) Fan for egg powder spray dryers.
Questions buyers ask
Why does an egg powder spray dryer need such a large exhaust fan?
Liquid egg is dilute, especially albumen at about 12% solids, so much more water is evaporated per kg of powder. The low outlet temperature also limits the drying capacity of each cubic metre of air, so the air volume is large.
How is fat removed from an egg dryer exhaust fan?
By CIP with hot caustic solution through spray nozzles in the inlet and casing, followed by rinsing and drying. The fan must have a drain at the lowest point and no crevices where fat can collect.
What outlet temperature does an egg powder dryer use?
Usually about 60 to 75°C to protect the proteins and their functional properties. This keeps the exhaust humid and close to its dew point, which the exhaust fan design must allow for.
Information needed to quote an ID fan for egg powder 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.
- Product type. Whole egg, yolk or albumen, feed solids and fat content.
- Cleaning. CIP chemicals, temperatures and the hygiene standard followed.
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.