Rotary Vacuum Disc Filter (RVDF) Filtration Calculator
Model continuous vacuum disc filter cake formation, dewatering kinetics, dry solids yield (t/m²·h), cake thickness, vacuum airflow demand, and drive kinematics for mineral slurries.
1. Disc Filter Geometry & Kinematics
2. Slurry Properties & Operating Vacuum
Filtration & Dewatering Performance
Disc Cross-Sectional Cycle Breakdown
5 Fatal Engineering Traps in Rotary Vacuum Disc Filter Design
1. Snap-Blow Distributor Misalignment & Trough Slurry Injection
The snap-blow cycle uses a 2–3 bar compressed air pulse channeled through the rotary trunnion valve to inflate sector bags and release cake. If valve bridge timing slips by even 10–15 degrees, the air pulse fires before the sector clears the slurry level in the filter vat. This injects abrasive mineral slurry directly backward through the filter cloth into the vacuum trunnion, contaminating the clean filtrate stream and eroding valve bridges.
2. Fines Blinding & Sector Bag Stretching
Ultra-fine slimes (<15 µm) penetrate monofilament or multifilament filter cloth weave, causing progressive irreversible blinding. When operators increase vacuum to compensate, the high differential pressure pulls the stretched filter fabric tightly into the radial drainage ribs of the sector core. This constricts internal filtrate channels, slashing effective drainage area by 30–40% and making cake discharge sluggish.
3. The High RPM Moisture Paradox & Vessel Liquefaction
Operating operators frequently ramp up disc RPM to clear bottlenecked concentrate surge tanks. While higher RPM boosts theoretical cycle count, it cuts vacuum drying time (tdry) proportionally. Dewatering coarse iron ore or copper concentrates with inadequate drying time raises cake moisture above the Transportable Moisture Limit (TML > 9.5%), presenting severe catastrophic cargo liquefaction and capsize risks during ocean shipping.
4. Slurry Vat Agitator Stalling & Heavy Mineral Bed Sanding
Heavy mineral concentrates (SG 4.2–5.2) settle out of suspension within 60–90 seconds if the reciprocating paddle agitator trips. Once a settled bed of dense iron ore forms in the rounded vat bottom, the rotating disc sectors plow directly into a compacted solid bed. This bends sector frames, shreds filter bags, and burns out the primary mechanical disc drive gearbox.
5. Inadequate Barometric Drop Leg Height & Vacuum Loss
RVDF vacuum receivers rely on a vertical barometric seal leg to gravity-drain liquid filtrate against a 65–75 kPa vacuum. Because 1 bar of vacuum corresponds to 10.33 meters of water head, the drop leg must have at least 10.5–11.0 meters of true vertical clearance into a submerged seal tank. Installing a shortened 7–8 meter pipe allows vacuum to siphon seal pit water back into the receiver tank, drowning the moisture traps and flooding liquid-ring vacuum pumps.
Mathematical Derivation & Filtration Hydraulics
Continuous rotary vacuum filtration is governed by the classic Ruth-Carman-Kozeny filtration equation for incompressible or slightly compressible cakes:
W = √[ (2 · ΔP · c · tform) / (μ · α) ]
Where:
W= Dry cake mass deposited per unit area per cycle (kg/m²)ΔP= Trans-cake vacuum driving pressure (Pa)t_form= Cake formation time during slurry immersion (seconds), wheret_form = (θ_form / 360°) × (60 / N_rpm)μ= Filtrate dynamic viscosity (Pa·s)α= Specific cake resistance (m/kg)c= Dry cake solids deposited per unit volume of filtrate (kg/m³):
c = [ ρL · Sfeed ] / [ 1 - Sfeed · (1 + Mcake / (100 - Mcake)) ]
Total dry solids production rate (filtration yield) across both faces of all discs:
Atotal = Ndiscs × 2 × [ π / 4 · (Douter² - Dinner²) ]
Ṁdry = (W × Atotal × Nrpm × 60) / 1000 (tonnes/hour)