A standard Agitated Nutsche Filter Dryer is a single closed pressure vessel integrating filtration, cake washing, and vacuum drying in one contained unit — a sintered stainless steel or filter cloth filter plate at the vessel base retains solid cake while an anchor or contra-rotating agitator smooths the cake during filtration, reslurries it during washing, and ploughs it during vacuum drying. Processing 5–4,000 L per batch at 0.01–2,500 kg product per batch, it eliminates multiple open-transfer steps between filter press, wash vessel, and tray dryer in GMP pharmaceutical and fine chemical manufacture.
Slurry is charged under pressure or gravity through the top inlet; filtration begins as vacuum or positive pressure (up to 6 bar) drives mother liquor through the filter plate into the filtrate receiver below. The agitator descends and smooths the cake surface — preventing cake cracking that creates preferential flow channels. Wash solvent floods the cake; the agitator reslurries to ensure uniform contact; re-filtration removes wash liquor. Jacket heating (30–160°C) combined with vacuum (10–50 mbar) dries the final cake — the agitator continuously ploughs, exposing fresh surface and preventing crust formation until target LOD is reached.
Challenges
Cake Cracking During Filtration Causing Channelling
Cracks across the cake surface create preferential liquid paths — mother liquor bypasses the cake, reducing washing efficiency and purity.
Agitator Seal Integrity Under Simultaneous Vacuum and Solvent Vapour
The rotating agitator shaft seal is exposed to both deep vacuum and solvent vapour simultaneously — failure releases containment and admits air.
Scale-Up of Wash Efficiency (Number of Wash Volumes vs. Impurity Removal)
Wash ratio and mixing intensity required to achieve target impurity level are not linearly predictable between pilot and production scale.
Cake Compaction at High Filtration Pressure (>3 bar)
Compressible cakes consolidate under high driving pressure — permeability collapses and filtration rate falls to near zero.
Residual Solvent in Compressed Heel at Drying Endpoint
Agitator cannot fully break the compressed wall zone around the blade sweep radius — residual LOD in heel region exceeds target.
Solutions
- Contra-Rotating Agitator with Downward Pressure Sensing: Agitator exerts controlled downward force on cake surface — seals cracks continuously throughout the filtration cycle.
- Double Mechanical Seal with Nitrogen Barrier Gas (5–10 mbar above Process Pressure): Positive barrier pressure higher than process vacuum — prevents inward air ingress and outward solvent vapour escape under all conditions.
- Pilot-Scale (0.1 m²) Wash Study with HPLC Inline Monitoring: Dedicated pilot wash study generates wash curve (impurity vs. wash volume) — defines production wash volumes from experimental data.
- Optimal Filtration Pressure Profile (Low Pressure Start, Progressive Ramp): Starting filtration at 0.3 bar and ramping to 2 bar allows initial cake structure to form before consolidation — preserves permeability.
- Heel Stirring Protocol (High-Speed Agitation at Drying Endpoint): Final drying stage uses maximum agitator speed to break and expose heel zone — achieves uniform LOD across entire batch.
Applications
- Pharmaceutical: API final isolation, controlled-substance processing, polymorph-sensitive crystalline intermediate isolation and drying.
- Fine Chemical: Specialty chemical filter-wash-dry in contained single-vessel operation — eliminates manual inter-stage transfer.
- Agrochemical: Herbicide and fungicide active ingredient filtration and washing with solvent recovery.
- Nutraceuticals: High-value botanical and fermentation-derived ingredient isolation and drying under containment.
- Biotechnology: Enzyme, fermentation intermediate, and biological active isolation from fermentation broth.
Models & Capacities
Standard ANFD — Models & Capacities (0.04 m² Lab to 20 m² Large Production) | |||||||||||||
Model | Scale | Filter Area [m²] | Working Vol. [L] | Batch Size [kg] | Agitator Type | Motor [kW] | Filtration Pressure [bar] | Vacuum [mbar] | Jacket Temp [°C] | Filter Plate Nominal [µm] | Overall Ø [mm] | Overall H [mm] |  |
ANFD-LAB-004 | Lab | 0.04 | 5 | 0.5–2 | Anchor | 0.12 | 0–5 | 10–200 | 20–160 | 5–100 | Ø225 | 900 |  |
ANFD-LAB-010 | Lab | 0.10 | 15 | 1–6 | Anchor | 0.18 | 0–5 | 10–200 | 20–160 | 5–100 | Ø360 | 1,100 |  |
ANFD-LAB-020 | Lab | 0.20 | 30 | 2–12 | Anchor | 0.25 | 0–5 | 10–100 | 20–160 | 10–60 | Ø510 | 1,300 |  |
ANFD-PIL-050 | Pilot | 0.50 | 80 | 5–30 | Anchor | 0.37 | 0–5 | 10–100 | 20–160 | 10–60 | Ø800 | 1,600 |  |
ANFD-PIL-100 | Pilot | 1.0 | 160 | 10–60 | Contra-rot. | 0.75 | 0–5 | 10–100 | 20–160 | 10–60 | Ø1,130 | 2,000 |  |
ANFD-PIL-200 | Pilot | 2.0 | 320 | 20–120 | Contra-rot. | 1.5 | 0–5 | 10–80 | 30–160 | 10–40 | Ø1,600 | 2,500 |  |
ANFD-P-040 | Production | 4.0 | 640 | 50–250 | Contra-rot. | 3.0 | 0–6 | 10–50 | 30–160 | 10–40 | Ø2,260 | 3,200 |  |
ANFD-P-060 | Production | 6.0 | 1,000 | 75–380 | Contra-rot. | 5.5 | 0–6 | 10–50 | 30–160 | 10–40 | Ø2,760 | 3,800 |  |
ANFD-P-080 | Production | 8.0 | 1,300 | 100–500 | Contra-rot. | 7.5 | 0–6 | 10–50 | 30–160 | 10–40 | Ø3,190 | 4,200 |  |
ANFD-P-100 | Production | 10.0 | 1,600 | 125–650 | Contra-rot. | 11 | 0–6 | 10–50 | 30–160 | 10–40 | Ø3,570 | 4,600 |  |
ANFD-LP-120 | Large Prod | 12.0 | 2,000 | 150–800 | Contra-rot. | 15 | 0–6 | 10–30 | 30–160 | 10–40 | Ø3,910 | 5,200 |  |
ANFD-LP-160 | Large Prod | 16.0 | 2,600 | 200–1,100 | Contra-rot. | 22 | 0–6 | 10–30 | 30–160 | 10–30 | Ø4,510 | 5,800 |  |
ANFD-LP-200 | Large Prod | 20.0 | 3,200 | 250–1,400 | Contra-rot. | 30 | 0–6 | 10–30 | 30–160 | 10–30 | Ø5,050 | 6,500 |  |