A Wurster fluid bed coater is a bottom-spray fluidized bed system in which a cylindrical partition (Wurster column) inside a conical product container creates an organized, circulating particle flow. Particles rise through the column past a bottom-mounted spray nozzle and settle back through the surrounding annulus. Handling 0.5–600 kg, it applies precise functional coats to pellets, granules, crystals, and powders from 100 µm to 3 mm.
Heated air (40–80°C) enters through a distribution plate with higher open area under the partition, accelerating particles upward through the column. A two-fluid nozzle sprays upward, concurrent with particle flow, so droplets travel a short distance before impact. Particles dry in the expansion chamber and return through the annulus. Partition gap height (10–50 mm) sets circulation rate, and filters with automatic blow-back retain fines.
Challenges
Agglomeration
Excess spray rate or low air volume bonds wet particles inside the column.
Nozzle Blockage
Coating solids build up at the nozzle tip and distort the spray pattern.
Attrition of Fine Particles
High column velocity fractures fragile pellets and generates fines.
Electrostatic Charging
Dry fine particles cling to walls and filters during coating.
Filter Blinding
Fines and spray-dried coating clog filters, reducing airflow and fluidization.
Solutions
- Spray and Air Ratio Control: PLC links spray rate with fluidizing air volume and outlet humidity.
- Anti-Bearding Nozzle Cap: Microclimate air around the nozzle tip prevents solids build-up.
- Adjustable Partition + Plate Selection: Partition height and plate open area tuned for particle size and strength.
- Humidity Control + Full Earthing: Controlled inlet humidity and grounding reduce static charge.
- Automatic Filter Blow-Back: Sequential pulse cleaning maintains airflow throughout the batch.
Applications
- Pharmaceutical: MUPS pellets, enteric and sustained-release pellet coating, API taste masking.
- Nutraceuticals: Encapsulated vitamins, iron, and probiotic granules.
- Food: Flavour, acid, and nutrient encapsulation for controlled release.
- Agro & Chemical: Controlled-release fertilizer, enzyme, and catalyst granule coating.
Models & Capacities: Laboratory to Large Production
| Model | Scale | Chamber Ø [mm] | Wurster Inserts | Batch Size [kg] | Container Vol. [L] | Spray Rate [g/min] | Inlet Air [CMH] | Heater [kW] | Overall L×W×H [mm] | Weight [kg] |
|---|---|---|---|---|---|---|---|---|---|---|
| WFB-0.5 | Lab | 150 | 1 | 0.3–0.5 | 1 | 2–6 | 50 | 1.5 | 1250×1050×2200 | 300 |
| WFB-001 | Lab | 190 | 1 | 0.6–1 | 2 | 4–12 | 90 | 2 | 1300×1100×2350 | 410 |
| WFB-003 | Lab | 270 | 1 | 2–3 | 6 | 12–35 | 240 | 5.5 | 1500×1250×2700 | 710 |
| WFB-005 | Pilot | 320 | 1 | 3–5 | 9.5 | 18–55 | 380 | 8.5 | 1600×1300×2950 | 970 |
| WFB-010 | Pilot | 410 | 1 | 6.5–10 | 19 | 35–110 | 710 | 16 | 1800×1450×3350 | 1,550 |
| WFB-015 | Pilot | 460 | 3 | 9.5–15 | 30 | 55–160 | 1,050 | 25 | 1900×1550×3550 | 1,950 |
| WFB-030 | Production | 580 | 3 | 19–30 | 60 | 100–300 | 1,900 | 40 | 2200×1750×4100 | 3,200 |
| WFB-050 | Production | 690 | 5 | 30–50 | 95 | 160–490 | 3,050 | 65 | 2400×1900×4600 | 4,600 |
| WFB-075 | Production | 790 | 5 | 45–75 | 140 | 240–730 | 4,400 | 95 | 2650×2050×5050 | 6,150 |
| WFB-100 | Production | 870 | 7 | 65–100 | 190 | 320–950 | 5,700 | 130 | 2800×2200×5400 | 7,550 |
| WFB-150 | Production | 990 | 7 | 95–150 | 290 | 470–1,400 | 8,200 | 180 | 3100×2400×5950 | 10,000 |
| WFB-250 | Large Prod | 1,180 | 7 | 160–250 | 480 | 770–2,300 | 13,000 | 290 | 3500×2700×6800 | 14,600 |
| WFB-400 | Large Prod | 1,370 | 9 | 250–400 | 770 | 1,200–3,550 | 19,800 | 440 | 3900×3000×7650 | 20,300 |
| WFB-600 | Large Prod | 1,570 | 9 | 380–600 | 1,150 | 1,750–5,250 | 28,500 | 630 | 4350×3300×8550 | 27,300 |