A paddle dryer is a combined blending and thermal drying reactor where a jacketed trough, hollow rotating shaft, and hollow paddles all circulate heating medium, maximising conductive heat transfer surface area. Operating under vacuum or atmospheric pressure, it dries wet cakes, filter press outputs, granules, and pastes to low residual moisture while simultaneously agitating the product bed for uniform drying throughout the batch.Â
Heating or cooling medium circulates simultaneously through the trough jacket and through the hollow shaft and paddle interiors via rotary unions at each shaft end. This dual heating path across both outer wall and internal paddles maximises heat transfer surface area and minimises radial temperature gradients across the product bed. A PLC-modulated control valve maintains product temperature within ±1°C throughout the blending cycle.
Challenges
Wet Product Sticking to Paddle Faces
Very wet cake adheres to paddle surfaces at high initial moisture, building up on paddle faces, increasing effective paddle diameter, and raising motor load progressively during early drying stages.
Dry Crust Formation at Drying Endpoint
A dry surface layer forms over residual wet core material near drying completion, reducing vapour diffusion and preventing moisture from reaching the heated surface efficiently.
Rotary Union Wear Under Combined Service Conditions
Rotary unions operating simultaneously under vacuum on the process side and heating medium pressure inside the hollow shaft experience accelerated seal face wear compared to single-service designs.
Heat Transfer Area-to-Volume Ratio Reduction at Scale
Larger production vessels have a lower ratio of heating surface area to batch volume than pilot scale, extending drying cycle time at production scale relative to pilot predictions.
Condenser Overload at Peak Evaporation Rate
The initial phase of drying generates the highest evaporation rate, which can exceed condenser capacity, causing vacuum pressure to rise and drying rate to fall during the critical early drying period.
Solutions
- PTFE-Coated Paddle Faces: Applying PTFE coating to all paddle contact surfaces prevents wet cake adhesion, allowing paddles to self-clean throughout the drying cycle and maintaining consistent paddle geometry and motor load from batch start to end.
- VFD-Programmed Paddle Speed Increase at Drying Endpoint: Programming the control system to increase paddle speed during the final phase of the drying cycle breaks the dry surface crust, exposing residual wet core material to the heated paddle and trough surfaces.
- Dual-Service Silicon Carbide Rotary Union: Specifying silicon carbide mechanical face rotary unions rated for simultaneous vacuum and heating medium pressure service provides adequate seal life under the combined loading conditions of paddle dryer operation.
- Supplementary Internal Heating Coil for Large Vessels: Installing an additional heating coil inside the vessel body compensates for the reduced surface-area-to-volume ratio at production scale, maintaining drying rate equivalent to pilot scale performance.
- Staged Vacuum Pull-Down with Oversized Condenser: Applying vacuum in defined steps during the initial high-evaporation phase, combined with a condenser sized above the calculated peak evaporation duty, prevents condenser saturation and maintains stable vacuum throughout the drying cycle.
Applications
- Pharmaceutical: API wet cake drying after filtration, granule drying, solvent recovery — GMP validated.
- Chemical: Specialty chemical wet cake and filter press output drying with full solvent recovery.
- Food & Beverage: Viscous food paste drying, starch drying, food ingredient wet intermediate processing.
- Nutraceuticals: High-value botanical extract drying, concentrated slurry drying, heat-sensitive ingredient.
- Agrochemical: Active ingredient wet cake drying and granule intermediate drying.
Models & Capacities
| Type 4 — Paddle Dryer: Models & Capacities (* At jacket surface temperature 80°C) | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Model | Scale | Net Vol. [L] | Batch Size [kg] | Shaft Speed [RPM] | Motor [kW] | Jacket Area [m²] | Hollow Paddle Area [m²] | Jacket Temp [°C] | Vacuum [bar abs.] | Max Evap. Water* [kg/h] | Max Evap. Ethanol* [kg/h] |  |  |  |
| PB-DR-050 | Lab | 30 | 9–22 | 5–30 VFD | 0.75 | 0.28 | 0.35 | 40–200 | 0.02–0.15 | 1 | 3 |  |  |  |
| PB-DR-100 | Lab/Pilot | 60 | 18–45 | 5–30 VFD | 1.1 | 0.45 | 0.55 | 40–200 | 0.02–0.15 | 2 | 5 |  |  |  |
| PB-DR-200 | Pilot | 120 | 36–90 | 5–25 VFD | 1.5 | 0.70 | 0.85 | 40–200 | 0.02–0.15 | 3 | 8 |  |  |  |
| PB-DR-300 | Pilot | 180 | 54–135 | 5–25 VFD | 2.2 | 0.95 | 1.15 | 40–200 | 0.02–0.15 | 5 | 12 |  |  |  |
| PB-DR-500 | Production | 300 | 90–225 | 4–20 VFD | 3.0 | 1.40 | 1.75 | 40–200 | 0.02–0.15 | 8 | 20 |  |  |  |
| PB-DR-750 | Production | 450 | 135–340 | 4–20 VFD | 4.0 | 1.95 | 2.40 | 40–200 | 0.02–0.15 | 11 | 27 |  |  |  |
| PB-DR-1000 | Production | 600 | 180–450 | 3–18 VFD | 5.5 | 2.50 | 3.10 | 40–200 | 0.02–0.15 | 14 | 35 |  |  |  |
| PB-DR-1500 | Production | 900 | 270–675 | 3–15 VFD | 7.5 | 3.50 | 4.30 | 40–200 | 0.02–0.15 | 20 | 50 |  |  |  |
| PB-DR-2000 | Production | 1,200 | 360–900 | 3–12 VFD | 11 | 4.40 | 5.50 | 40–200 | 0.02–0.15 | 26 | 65 |  |  |  |
| PB-DR-3000 | Large Prod | 1,800 | 540–1,350 | 2–10 VFD | 15 | 6.20 | 7.80 | 40–200 | 0.02–0.15 | 38 | 95 |  |  |  |
| PB-DR-5000 | Large Prod | 3,000 | 900–2,250 | 2–8 VFD | 22 | 9.00 | 11.5 | 40–200 | 0.02–0.15 | 58 | 145 |  |  |  |
| PB-DR-7500 | Large Prod | 4,500 | 1,350–3,375 | 2–6 VFD | 30 | 12.5 | 16.0 | 40–200 | 0.02–0.15 | 80 | 200 |  |  |  |
| PB-DR-10000 | Large Prod | 6,000 | 1,800–4,500 | 1.5–5 VFD | 45 | 16.0 | 20.0 | 40–200 | 0.02–0.15 | 100 | 250 |  |  |  |