Rotary drum vacuum filter: what is a typical operating drum speed at room conditions for filtration duty (order of magnitude, in rpm)?

Introduction / Context:
Rotary drum vacuum filters (RDVFs) are continuous filters widely used for slurries in chemicals, minerals, and wastewater treatment. Drum speed sets the residence time for cake formation, washing, and drying on each sector. Understanding the order of magnitude of drum rotational speed is essential to size filtrate piping, vacuum capacity, and cake washing times.

Given Data / Assumptions:

• Conventional rotary drum vacuum filter with segmented sectors, vacuum box, and discharge by scraper or belt.
• Room temperature service; non-explosive, non-foaming slurry.
• Question asks for typical speed magnitude, not the exact optimized value for a specific slurry.

Concept / Approach:
RDVFs operate slowly so that each sector experiences sufficient submergence, cake buildup, optional wash, and air-drying before discharge. Typical circumferential speeds are modest; hence rotational speeds are usually well below 10 rpm, commonly in the 0.2–6 rpm band depending on cake thickness and washing requirements. Very high speeds would reduce cake residence time and cause discharge and vacuum problems.

Step-by-Step Solution:
Recognize the need for long residence time for forming, washing, and drying → slow drum rotation.Industry practice: RDVFs often run around 0.5–3 rpm for many slurries; values near 1 rpm are very common.Therefore, pick the order-of-magnitude value closest to typical operation: 1 rpm.

Verification / Alternative check:
Vendors’ sizing curves and operating manuals routinely show sub-10-rpm operation, with 1 rpm frequently used in design examples for medium-thickness cakes.

Why Other Options Are Wrong:
50 rpm and 100 rpm: far too fast; would severely curtail cake residence time and disrupt vacuum sealing.500 rpm: unrealistic and mechanically unsuitable for a vacuum-filter drum.

Common Pitfalls:
Confusing RDVF with rotary vacuum precoat filters (still slow) or high-speed centrifuges; assuming higher speed always increases throughput—filtration is mass-transfer limited and needs residence time.

Final Answer:
1