Fine Sand Recovery System Selection: Flow, Solids and Particle Size

Two feeds with the same measured slurry flow can carry very different solids loads. The extra solids place different demands on the pump, cyclone and screen, even though the m³/h reading has not changed. Some of those solids may also be unsuitable for the intended sand product.

That is the limitation of selecting a fine sand recovery system from its flow rating alone. The enquiry needs to connect the incoming slurry, the particles worth recovering and the product grading. Flow volume, recoverable solids tonnage and the required cut point are separate selection parameters. [2]

What the flow rating leaves out

The WS / 2WS catalogue lists reference water-handling capacity in m³/h. This figure is not a sand production rate. It also should not be treated as total slurry feed flow in a calculation until its basis has been established.

With a measured slurry flow and a concentration stated in kilograms of dry solids per cubic metre of slurry, the incoming solids load can be calculated:

Dry solids loading (t/h) = slurry flow (m³/h) × concentration (kg dry solids/m³ slurry) ÷ 1,000

For a hypothetical feed of 150 m³/h at 80 kg dry solids/m³ slurry:

150 × 80 ÷ 1,000 = 12 t/h of dry solids

At the same hypothetical slurry flow, with concentration increased to 160 kg/m³:

150 × 160 ÷ 1,000 = 24 t/h of dry solids

These are incoming loads, not recovered sand outputs. The amount available as product depends on the feed grading, unwanted material and separation losses.

A report stating “20% solids” needs its measurement basis attached. Weight percentage and volume percentage are different quantities; neither can replace kg dry solids/m³ slurry in this formula without conversion and the relevant density information. Keep the normal and peak readings as well. An average alone can conceal the period that sets the equipment duty.

Which particles belong in the product?

A maximum feed size cannot show how much material lies around the required separation size. A particle size distribution provides that information. For an existing plant, sample the actual recovery stream and record where and under what operating conditions it was collected.

The target grading matters just as much. Recovered material might become a separate product or be blended back into the main sand. In the latter case, its effect on the combined grading needs to be checked. Useful fine sand, silt and clay can occur in the same effluent, so capturing more solids does not automatically increase saleable output. Product suitability still needs to be established. [1]

A hydrocyclone also does not separate particles as an ideal sieve would. Its d50 is the size with an equal probability of reporting to the underflow or overflow. Particles near that size divide between the two streams. Cyclone geometry influences the cut; increasing cyclone size can provide more flow capacity while producing a coarser separation. [3]

Specify the required recovery band and the unwanted fraction. A statement such as “recover fines” leaves the supplier without a clear product target.

The finest cut is not the only selection target

Smaller cyclones can make a finer separation, but the largest particles in the recovery stream still have to pass through their bottom outlets. Occasional coarse particles or debris can block a restrictive opening. Compare the expected recovery with the likely interruptions and access needed to clear a blockage. A finer nominal cut can lose its advantage when part of the stream is diverted to waste while a unit is blocked. [6]

The bottom outlet, called the apex or spigot, also affects how much water enters the underflow. Some fine particles travel with that water rather than separating solely according to size. A smaller spigot can reduce this bypass, but an opening too small for the solids load can produce a rope-like discharge, known as roping, and impair separation. A thick underflow is therefore not sufficient evidence of good recovery. The outlet must match the expected range of solids loading. [7]

Read pressure at the cyclone inlet

For comparable feed and equipment conditions, higher pressure generally produces a finer cut within the appropriate operating range. Feed concentration and slurry viscosity affect the result too. Clay-rich slurry can become more viscous and shift the cut towards a coarser size. [4]

Use pressure at the cyclone inlet when discussing the duty. A pump discharge reading can differ because of pipework losses and elevation. Send the measurement location with the reading, together with the pump details and pipe route.

The supplier should state the required inlet pressure and allowable variation for the proposed arrangement. A pressure change needs to be assessed with its effect on flow and the rest of the circuit. In a wet sand processing line, the overflow destination and downstream water handling also need to accommodate the selected arrangement.

Check the recovered material before promising moisture

The cyclone underflow still carries water. A dewatering screen can prepare it for conveying and stockpiling, but final moisture depends on the material. Finer particles and their surface characteristics affect how much water remains; a fine product may be drip-free while retaining more moisture than a coarse one. [5]

“Drip-free” describes handling behaviour. A specified moisture limit needs a measurement basis and sampling point. The quotation should relate any expected moisture to the proposed feed rather than apply one percentage to every sand.

Data to send with the enquiry

• Feed source, material type and existing process sketch.
• Normal and peak slurry flow, dry solids loading and concentration basis.
• Particle size distribution, sampling conditions and known contaminants.
• Maximum particle size, including occasional coarse particles or debris.
• Target product grading, recovery band and any blending requirement.
• Moisture limit or handling requirement, with its measurement basis.
• Pump details, inlet pressure location, pipe route and elevation.
• Overflow destination, screen drainage return and available installation space.
• Access to sample feed, underflow and overflow, and clearance to remove wear parts or clear a blockage.

Send these measurements and the process sketch with your project enquiry. Mark missing values as unknown so the supplier can distinguish measured conditions from assumptions.