Before crude palm oil ever hits a clarifier, mills that remove sand and fibers up front get faster separation, less wear, and measurable yield gains. The details are surprisingly specific: retention minutes, mesh sizes, and even pump types.
Industry: Palm_Oil | Process: Threshing_&_Pressing
Crude palm oil “press liquor” (the hot oil–water–solids slurry exiting the screw press) is not yet oil; it’s roughly 45–50% oil, about 45% water and around 5–10% solids such as fiber and dust (id.scribd.com). In one survey of press outputs the “crude oil” was ~48% oil, 45% water and 7% insolubles (id.scribd.com). Indonesia’s CPO quality standard (SNI 01-2901:2006) limits the combined water plus insoluble impurities to ≤0.5% by mass, meaning mills must strip out well over 90% of the incoming solids before clarification (kupdf.net).
Leaving heavy particles in the stream is costly: unremoved sand dramatically increases wear on pumps and valves, while fibrous debris raises viscosity and interferes with gravity settling because oil adheres to fibers (www.scribd.com). That is why pre‑clarification screening is essential for both product quality and downstream protection.
Composition and quality constraints
Typical screw‑press liquor runs ~48% oil, 45% water and 7% solids (higher solids if dilution is imperfect) (id.scribd.com). The national CPO spec allowing ≤0.5% combined water+solids makes that gap stark (kupdf.net). Mills respond with pre‑cleaning and heat: after screening, CPO is typically heated to ~90–95 °C to cut viscosity and maximize settling (www.scribd.com). One mill uses a 5 000 L hot‑oil tank for ~15 000 L/h feed—about 20 minutes retention—then reheats to ~95 °C before clarification (www.scribd.com; www.scribd.com).
Sand traps: quiescent settling design
Sand traps (desanders) are still tanks that slow the crude flow to near‑static conditions so dense grit settles by gravity (www.scribd.com). Heat is often applied before filling (to keep viscosity low), then steam is shut off during settling to avoid remixing (www.scribd.com). Solids collect at the bottom and are drained; skimmed oil is decanted onward to the vibrating screen chamber. One procedural guide is blunt: “Sand has a very high influence on the wear and tear of machinery” (www.scribd.com), and a student report warns that failing to trap sand first “will cause blockage of the sludge machine” (i.e., clarifier drain pumps) (id.scribd.com).
In practice, a properly sized trap removes the bulk of silts and sands. A three‑press mill running ~15 000 L/hr with a 5 m³ trap achieves ~20 minutes retention—enough that essentially all >50 μm (micrometre) particles settle out (www.scribd.com). Hydrocyclone sand separators are also used in large mills to complement traps. Typical design targets 20–30 minutes of retention; the 5 000 L for ~15 000 L/h example yielded ~20 minutes (www.scribd.com).
Temperature control matters. The crude is kept hot (~95 °C) for viscosity reduction, but steam must be off during settling to prevent turbulence; as the oil skims to the screens, it naturally cools, and many mills then reheat to ~90–95 °C before clarification (www.scribd.com; www.scribd.com). If traps are omitted or undersized, abrasive sand scours pumps, pipelines and rotors; operators note that positive‑displacement “Mohno” rotary pumps help move hot oil without remixing captured solids (www.scribd.com).
Vibrating screens: fiber and trash removal
Post‑desanding, vibrating or rotary screens remove coarse fibers and light debris. Commonly, two decks run in series: a coarser 20 mesh (~0.85 mm holes) above a finer 40 mesh (~0.42 mm) (www.scribd.com). A motor with an eccentric weight induces high‑frequency vibration; the cleaned oil passes through while coarser particulates remain on the screen and are discharged as “dirty oil” (www.scribd.com). These screens are not intended for sand removal unless mesh is extremely fine; their job is to remove fibrous material and other coarse matter and to shear the liquid to reduce viscosity (www.scribd.com).
Vendors describe screens that leave only the “dirty oil and sand” on the surface with cleaned oil passing through; installations commonly spray hot water onto the screens to prevent clogging (qualitative, as described in the same operating notes) (www.scribd.com). Capacity‑wise, a 60″ vibrating sieve may handle the ~15 000 L/hr from three presses at ~95 °C with a residence of a few minutes under vibration. In function, this continuous coarse removal resembles the duty of industrial units designed for continuous debris removal, such as an automatic screen. By stripping out fibers, screening reduces emulsion viscosity (oil‑in‑water dispersion) and prevents clogging at clarifier inlets; with fewer nuclei for oil‑in‑water emulsions, free oil separates more readily (www.scribd.com; www.scribd.com).
Operators report that adding screens enabled noticeable extraction yield lifts, with vendors citing single‑digit percentage gains from screens. In trials in Malaysia, installing high‑frequency screens was associated with ~10% higher oil recovery (www.scribd.com; www.researchgate.net).
Clarifier performance and warm, even feed
Continuous settlers (clarifiers—gravity settling tanks) work best with even, warm feed (www.scribd.com). Under ideal conditions—dilute, 90 °C, and 2–3 hours retention—a static clarifier can recover ≈99.3% of the oil by gravity alone (www.researchgate.net). In real mills, heavy solids upset that ideal; one study notes that 70–90% of a mill’s oil losses occur in the sludge (clarifier) step when turbulence or high solids impede settling (www.researchgate.net; www.researchgate.net).
Removing coarse debris upstream mitigates those losses. Cleaner feed separates faster, with less oil bound in sludge. A newly designed small‑scale clarifier at 85 °C and a 1:2 oil:water dilution achieved a 74.2% extraction efficiency, with improved results in trials when feed was uniform and warm (www.researchgate.net). In industrial terms, a gravity unit like a clarifier benefits directly when the pre‑cleaning steps have already skimmed off sand and fibers.
Uptime, wear, and yield impacts
Reducing solids load eases equipment wear and extends uptime: sand‑free oil spares pumps and pipework, while fiber‑free oil reduces clogging of sludge pumps and “sludge pads.” One operational note cautions that a positive‑displacement pump, which does not churn the oil, preserves heat and avoids remixing screen‑captured solids (www.scribd.com). Industry experience cited in operating notes is that a well‑screened crude charge raises yield by a few percentage points; trials in Malaysia reported ~10% higher oil recovery when high‑frequency screens were installed (www.scribd.com; www.researchgate.net). A 10% lift on a 30 T/h (tonnes per hour) mill corresponds to ~3 t/h extra oil—a significant business impact.
Notes on sources and parameters
Technical handbooks and mill studies underpin these parameters—CPO composition, mesh sizes, retention times, and oil losses. Chow & Ho (2000) and Borja & Banks (1994) align with the ~48% oil, 45% water, 7% insolubles press liquor composition (id.scribd.com). Industry operating notes detail sand‑trap design (settling, sizing, heating) and vibrating‑screen operation with 20/40 mesh decks and temperature practices, including reheating to ~95 °C (www.scribd.com; www.scribd.com). Clarifier throughput and efficiency figures (≈99.3% recovery potential at 90 °C and 2–3 h; 70–90% of oil losses occurring in sludge when upset; 74.2% extraction efficiency at 85 °C and 1:2 dilution) come from a recent small‑mill study (www.researchgate.net; www.researchgate.net). The Indonesian SNI 01‑2901:2006 standard codifies the ≤0.5% water+insolubles limit (kupdf.net).
