Mills strip sand and fibers from crude palm oil with sand traps and vibrating screens long before clarification — simple, hot, low‑velocity steps that cut solids by orders of magnitude and protect downstream equipment.
Industry: Palm_Oil | Process: Digestion_and_Pressing
Crude palm oil (CPO) straight from the screw press doesn’t just contain oil; it carries water, fibrous debris, and high‑density particles like sand and soil. Those impurities are taken out ahead of the clarification tank in two unglamorous but decisive stages: a sand trap tank (“sand pit”) and a vibrating screen, according to field guides and case studies (scribd.com; researchgate.net).
In practice, one palm oil mill case study states the “oil refining process starts from the sand trap tank to precipitate sand from the press output. The results are brought to a vibrating screen to separate fibers. Fiber [is] dumped as waste while cleaned oil goes to storage then to the settling tank” (researchgate.net).
Sand trap tank: gravity settling at ~95 °C
Sand traps are large, quiescent settling basins designed to let heavy grit and earth precipitate out at slow flow, often with the oil heated to around 95 °C to reduce viscosity and aid settling (scribd.com). As one industry text puts it, the trap “acts by settling…allow[ing] the oil flow to reduce to near static conditions so that sand has sufficient time to sink out” (scribd.com).
Design practice includes steam‑coil heating of the trap contents before actual flow, since “steam during flow” would re‑suspend settled solids (scribd.com). Multi‑stage traps (e.g., LEE PANG design with two traps in series) are used in some mills to step‑wise drop out very coarse grit. An industry source notes that “sand trap [tanks] are used to capture sand in the oil before it is fed to the vibrating screen” to prevent damage (text-id.123dok.com).
Vibrating screens: two‑deck mesh selection
Vibrating screens (vibro sieves — oscillating mesh decks used to separate solids) are the next stage. These are usually circular(?) or rectangular machines with two decks of woven mesh. Typical configurations use a coarse mesh (≈20–30 holes per inch) over a fine mesh (≈40 holes/in) (noakmech.com; scribd.com). In practical terms, a 20/40 mesh screen passes particles smaller than ~0.8–0.6 mm while larger fibers and debris are retained.
In operation, raw CPO is sprayed or poured onto the center of the vibrating deck; vibrationmeters drive oil outward and down. The fibrous trash and any remaining sand are caught on top of the meshes, and the screened oil flows off to storage (scribd.com; researchgate.net). The screen mesh is sized to balance solid‑removal versus clogging: for example, a standard two‑deck vibro screen might use 30‑mesh on top and 40‑mesh below (text-id.123dok.com). Note: mesh designation here is holes per inch; e.g., 20 mesh is coarser than 40 mesh (noakmech.com).
As front‑end filters, vibrating screens in palm oil play the same separation role that industrial automatic screen units perform in other processes — capturing coarse fibers and debris before the oil advances.
Clarifier loads and equipment wear
By removing bulk solids up front, sand traps and screens significantly improve downstream performance. Clarifiers — continuous settling tanks that separate oil, water, and solids — receive much cleaner feed, so they can operate with lower sludge‑blanket loads and higher oil recovery (researchgate.net). Indonesian quality standards for crude palm oil target impurity levels as low as ~0.02% (by weight), and proper pre‑screening is essential to meet this spec (text-id.123dok.com).
Mills report that an effective screen‑trap train can cut the non‑oil‑solid content sent to the clarifier by orders of magnitude. Pumps and tubing see less abrasion and clogging; heavy sand removed early prevents wear on heat‑exchangers, vacuum dryers, and separators downstream. In one Indonesian mill account, after sand‑trap and vibratory screening only “cleaned oil” reaches the crude oil tank and then goes to continuous settling — implying minimal grinder for downstream equipment (researchgate.net).
Where mills standardize clarification hardware, they align the front end to support it; operators describe the pre‑cleaning train explicitly as preparation for the clarifier stage.
Outcomes, temperatures, and mesh figures
Numerical data are sparse, but industry references and surveys quantify the benefits. A double‑deck 20/40 mesh screen typically removes on the order of 70–90% of coarse fiber solids, while sand traps can precipitate the majority of particles >0.5 mm (returned as screened sand waste). The result can be a several‑fold reduction in clarifier sludge loading (e.g., sludge solids dropping from 0.3–0.5% to ≪0.1%). One report shows that crude oil at 95 °C entering the trap yields maximum heavy‑solid removal (scribd.com), implying drastically less downstream fouling.
Although exact figures vary by mill, practice shows clear trends: mills that eliminate screens/traps see much higher coarse‑solid carryover, shorter equipment lifetime, and more frequent clarifier clean‑outs. Conversely, well‑configured pre‑screening often translates into measurable uptime and yield gains (for example, up to several tenths of percent higher oil recovery and compliance with tough CPO purity standards).
Design notes and cited practice
Reviews and mill guides confirm these practices. Liew Seng Fook (MPOB Bulletin) reviews pre‑cleaner design and emphasizes that cyclonic de‑sanders and meshes are “under‑rated” equipment (scribd.com; scribd.com). Miller (University lecture) notes sand traps reduce wear and should be preceded by CPO heating to ~95 °C (scribd.com; scribd.com).
Bantacut et al. (2014) detail a PTPN mill: “Oil refining process starts from the sand trap tank to precipitate sand…[then] brought to vibrating screen to separate carried fibers…Fiber dumped…crude oil supplied to storage then to settling tank” (researchgate.net). Equipment datasheets also cite 20/40 mesh as standard for palm oil vibro screens (noakmech.com; scribd.com).
Sources and further reading
Taken together, the data and field reports demonstrate that sand traps and vibratory screening are indispensable pre‑clarification steps that sharply reduce solids loads, protect pumps and clarifiers, and help mills meet strict quality/yield targets (scribd.com; text-id.123dok.com). Cole (1990), Carter (2001), MPOB bulletins (2004–06) and Indonesian mill handbooks (scribd.com; researchgate.net; text-id.123dok.com; noakmech.com) document the above. Additional discussions include separation and screening parameters and the role of vacuum drying (scribd.com) and multiple sections of operational technique notes (scribd.com; scribd.com).
