A rotary drum vacuum filter is a continuously operating filtration device in which a cylindrical drum covered with filter cloth rotates slowly (0.1–3 RPM) through a slurry trough — vacuum applied inside the drum draws filtrate inward through the cloth while solids deposit as a cake on the drum outer surface. Processing 0.5–200 m³/h of slurry at cake formation rates of 10–100 kg/m²/h, it provides the only fully continuous single-pass filter cake formation and discharge — the standard for large-volume pharmaceutical API filtration, mineral processing, and chemical dewatering.
The drum rotates through four sequential zones: the submersion zone (bottom, in slurry trough) where vacuum draws filtrate inward and cake forms on the cloth; the drying zone (rising side) where vacuum continues to remove residual filtrate; the wash zone (top, optional spray wash) where wash solvent rinses the cake while vacuum draws wash liquid through; and the discharge zone (fall-off side) where vacuum is cut and cake is removed by a doctor blade or string discharge. The drum surface is divided into vacuum sectors — vacuum is applied only to the sectors in the submersion and drying zones; the discharge sector is at atmospheric pressure or slight positive pressure.
Challenges
Thin Cake Formation on Highly Compressible or Gelatinous Slurries
Compressible solids form thin, dense cakes that block vacuum — cake forms too slowly and drops off incompletely.
Doctor Blade Scoring the Filter Cloth During Cake Discharge
Blade contact with cloth erodes cloth fibres — cloth life shortens; doctor blade gap requires frequent adjustment.
Wash Zone Efficiency Limited by Cake Crack Formation
Cake cracking during drying zone allows wash liquid to bypass through crack rather than washing cake uniformly.
Slurry Trough Sedimentation Causing Inconsistent Feed Concentration
Dense particles sediment in trough between drum passes — uneven slurry concentration causes variable cake thickness.
Vacuum System Moisture Carryover Into Vacuum Pump
Vacuum draws liquid and fine particles toward pump — liquid trap and coalescing filter required to protect pump.
Solutions
- Filter Aid Pre-Coat (Kieselguhr 500–2,000 g/m², Applied Before Slurry): Pre-coat creates permeable cake layer — compressible product cake forms on permeable pre-coat; prevents blinding.
- String Discharge (Fine Strings Through Cloth at Discharge Zone): Strings lift cake off cloth at discharge — cloth never contacts doctor blade; extends cloth life 5–10×.
- Rotary Drum Speed Optimisation (Thin Cake, 10–15 mm, for Compressible Product): Faster drum speed produces thinner, less compressed cake — higher specific permeability; better wash.
- Agitator in Slurry Trough (Pitched-Blade Paddle, 10–30 RPM): Gentle agitation prevents sedimentation — maintains uniform slurry concentration throughout trough.
- Vacuum Receiver + Liquid Knockout Vessel + Coalescing Filter Before Pump: Three-stage moisture protection: receiver collects liquor; knockout removes droplets; coalescing filter polishes air before pump.
Applications
- Pharmaceutical: API continuous cake filtration — continuous production where batch filter press impractical.
- Chemical: Titanium dioxide, starch, calcium carbonate, mineral acid salt continuous dewatering.
- Mining: Concentrate, tailings, and mineral slurry continuous large-volume filtration.
- Food: Starch, sugar, and fermentation by-product continuous dewatering.
- Environmental: Wastewater sludge continuous dewatering — high-volume, low operator intervention.
Models & Capacities
Type 5A — Rotary Drum Vacuum Filter (RDVF): Models & Capacities | ||||||||||||
Model | Scale | Drum Ø [mm] | Drum L [mm] | Filter Area [m²] | Slurry Flow [m³/h] | Cake Rate [kg/m²/h] | Drum Speed [RPM] | Vacuum [mbar abs.] | Vacuum Motor [kW] | Drive Motor [kW] | Overall W×L [mm] |
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RDVF-LAB-01 | Lab | Ø300 | 200 | 0.06 | 0.1–0.5 | 10–50 | 0.1–3 VFD | 300–650 | 0.25 | 0.04 | 600×500 |
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RDVF-PIL-05 | Pilot | Ø500 | 500 | 0.8 | 0.5–3 | 10–80 | 0.1–3 VFD | 300–650 | 0.75 | 0.09 | 1,000×900 |
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RDVF-PIL-20 | Pilot | Ø1,000 | 600 | 1.9 | 1–8 | 10–80 | 0.1–3 VFD | 300–650 | 1.5 | 0.12 | 1,800×1,200 |
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RDVF-P-050 | Production | Ø1,500 | 1,000 | 4.7 | 5–20 | 10–100 | 0.1–2 VFD | 300–650 | 3.0 | 0.25 | 2,500×2,000 |
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RDVF-P-100 | Production | Ø1,800 | 1,500 | 8.5 | 10–40 | 10–100 | 0.1–2 VFD | 300–650 | 5.5 | 0.37 | 3,200×2,600 |
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RDVF-P-200 | Production | Ø2,400 | 2,000 | 15.1 | 20–80 | 10–100 | 0.1–2 VFD | 300–650 | 7.5 | 0.55 | 4,200×3,400 |
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RDVF-LP-400 | Large Prod | Ø3,000 | 3,000 | 28.3 | 50–200 | 10–100 | 0.1–1.5 VFD | 300–650 | 15 | 0.75 | 5,500×5,000 |
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