In continuous rotary vacuum filtration, what is the typical pressure differential (vacuum level) maintained across the filter medium, expressed as an equivalent column of mercury (mm Hg)?

Introduction / Context:Rotary vacuum filters operate by maintaining a pressure differential across a porous medium to draw liquid through and form a cake. The achievable vacuum and corresponding pressure drop determine filtrate rate, cake formation, and moisture content.

Given Data / Assumptions:

• Standard industrial rotary drum vacuum filter with typical seal and vacuum pump performance.
• Filtration of slurries under ambient temperature without boiling.
• Vacuum expressed as equivalent mercury column (mm Hg).

Concept / Approach:Commercial systems generally maintain a vacuum corresponding to a pressure differential of a few hundred mm Hg. Too low a ΔP causes poor rates; too close to full vacuum is impractical due to leakage and hardware limits. The broadly accepted operating window is about 250–500 mm Hg for steady, economical filtration.

Step-by-Step Solution:Identify practical vacuum range for rotary vacuum filters.Select mid-range ΔP that balances rate and equipment capability.Hence, 250–500 mm Hg is typical.

Verification / Alternative check:Vendor curves and filtration handbooks show filtrate flux increasing with ΔP but leveling due to cake resistance and leakage; typical plants operate in the 0.33–0.66 bar range (~250–500 mm Hg).

Why Other Options Are Wrong:50–150 mm Hg: often insufficient for practical industrial rates.600–700 mm Hg: near equipment and seal limits for continuous service.900–950 mm Hg: unrealistic for continuous rotary systems due to leakage.

Common Pitfalls:Confusing gauge vacuum readings with absolute pressure.Ignoring cake compressibility and filtrate viscosity when setting ΔP.

Final Answer:250 to 500 mm Hg