Palm oil mills live and die by the clean split between fiber and nuts. The depericarper—an air‑driven nut–fiber separator—makes that split, lifting boiler efficiency and kernel recovery in one pass.
In the segmented world of palm oil processing, one unsung machine governs a surprising portion of revenue: the depericarper. This nut–fiber separator strips fibrous mesocarp (“fiber”) from the pressed nut mix after oil extraction, routing clean nuts to the kernel line and clean fiber to the boiler house (ResearchGate).
The stakes are large. Large mills burn fiber and nut shells to make steam and power for the plant (FAO), and roughly 23–24% of fresh fruit by weight becomes crude palm oil in good Tenera varieties (FAO). The remaining ~75%—mostly fiber and shells—becomes fuel or feedstock (FAO). Even small gains in kernel recovery move the needle on oil output and boiler stability.
Airflow separation and machine architecture
A modern depericarper is built around three core units: a conveying chamber (often called a velocity box), an air separator (cyclone) with a fan, and a polishing drum. A cyclone is an air separator that uses centrifugal force to remove entrained solids from airflow; a polishing drum is a rotating cylindrical screen that scours off fiber and fines clinging to nuts. The feed is press cake—a mixed mass of nuts, broken shells, fiber, and dust—delivered by a cake breaker conveyor (Scribd; Kharisma Sawit).
Operation hinges on density and aerodynamics: a high‑capacity fan creates suction so lighter fiber is drawn to the fiber cyclone through a pneumatic airflow, while heavier nuts drop by gravity to the polishing drum (Kharisma Sawit; Scribd). In one design for a 60 t/h line, fan flow runs around 58,000–60,000 m³/h with a 70‑hp (≈52 kW) drive and an airlock feeder at the cyclone; a 45 t/h line targets ~43,566 m³/h on a 60‑hp (≈45 kW) fan (Scribd). Upstream, a destoner—an inline gravity separator—often removes stones and heavy debris to keep both equipment and the fiber stream clean (Kharisma Sawit). In liquid systems that deal with debris removal, an automatic screen plays a similar pre‑separation role.
Bench‑scale settings and efficiencies
Test work shows separation improves with well‑prepared feed and correct geometry. Running on dry press cake, at a 20° tilt and a 10 mm outlet gap, one separator delivered about 201 kg/h throughput and 96.3% separation efficiency (the share of nuts successfully discharged separately from fiber) (ResearchGate). A small‑scale unit at those settings produced ~0.2 t/h and achieved overall “quality” efficiency of 81.2% (ResearchGate).
Another design reported ~500 kg/h capacity at 92.5% efficiency (ResearchGate). Vendor data cited for a small separator powered by 7.5 HP showed ~0.5 t/h handling, illustrating how the same physics scale from lab rigs to factory duty (ResearchGate).
Full‑scale recovery and in‑plant checks
Full‑scale mills feed the depericarper with tens of tons per hour of press cake (for fruit throughput of 30–60 t/h, the press‑cake duty is on the order of 10–20+ t/h). Studies of kernel cracking and separation report overall palm kernel recovery efficiencies around 85–94% for good machines (ResearchGate).
When fans are undersized or screens clog, kernel losses rise—clear in the fiber stream. Factory practice counters this by grading nuts by weight or screening after the depericarper to confirm cleaning is complete (ResearchGate). Where post‑checks rely on screening, plants often prefer automated solutions; an automatic screen suits continuous operation.
Clean split, better boiler fuel
Clean separation pays twice. First, it maximizes kernel yield. A 60 t/h mill might generate ~3 t/h of nuts. If 2% slips into the fiber, that’s 0.06 t/h lost; across 8–10,000 operating hours, 480–600 tons of kernels disappear. At roughly $800/ton palm kernel oil (PKO; a specialty oil used in food and oleochemicals), that’s close to half a million dollars of output left in the dust (ResearchGate; ResearchGate). In small trials, separators delivered 92.5–96% nut removal; hand‑sorting in small mills is far less efficient (ResearchGate; FAO).
Second, it produces a predictable boiler fuel. Fiber and shells are the mill’s biomass fuel; contaminants and stray nuts destabilize combustion. A destoner step helps keep stones and heavy debris out of the fiber (Kharisma Sawit). Properly separated fiber has low, stable oil carryover—unlike the ~9–11% oil sometimes seen in poorly separated press cake (ResearchGate)—and mills target final nut shell content in the fiber of less than 6% by weight (Kharisma Sawit). Large mills then burn fiber and shells for steam and power (FAO). Utilities programs such as oxygen scavengers address the boiler’s water‑side chemistry; combustion stability still depends on clean, uniform fiber. Similarly, scale‑control measures protect water‑side heat exchange, but fuel quality is determined upstream—in the depericarper.
Economics, capacity, and the payoff
The depericarper’s features—fan/cyclone sizing, airflow paths, polishing drum, and air locks—are tuned to mill capacity, with high throughput and near‑complete nut removal the design intent (Scribd; Scribd). Modern separators routinely exceed 90% separation efficiency, producing “kernel‑pure” nuts (with <6% shell fragments) and a fiber stream ready for the boiler (ResearchGate; ResearchGate; Kharisma Sawit).
Costs are offset by kernel yield gains. Even small machines have shown strong returns: one small‑scale separator priced around N20,460 (≈$100 at 2010 prices) delivered more than 200 kg/h at 96% efficiency (ResearchGate). The principle scales up: better separation means more saleable kernel oil and steadier boiler fuel—two outputs from one critical split (FAO).
