Sterilizer condensate in wet‑process palm oil mills carries free oil and high‑grade heat. A purpose‑built collection, separation, and heat recovery train captures both value streams while easing POME treatment.
Start with the steam. Wet‑process palm oil mills sterilize fresh fruit bunches (FFB) with 2–3 bar steam (≈130–140 °C) at roughly 250 kg of steam per tonne FFB (www.researchgate.net). As that steam condenses, it produces 0.1–0.35 m³ of sterilizer condensate per tonne FFB (patents.google.com), or roughly 10–35 m³/h in a 100 t/h mill.
This hot stream (≈100–130 °C) is loaded with suspended solids and free oil. Left unmanaged, the oil washes into POME (palm oil mill effluent), driving up COD/BOD and losing product. Industry guidance calls for continuous condensate drainage to prevent flooding and oil carry‑over (www.scribd.com).
There is scale here. Raw POME contains only about 0.6–0.7% oil by weight (www.mdpi.com), but sterilizer condensate can be much oilier. With a ~30 Mt/year global CPO industry, the resulting POME volume is on the order of ~75 Mt (www.mdpi.com). Managing this stream at its source enables both resource recovery and pollution control.
Condensate fractions and flow characteristics
Mills report two distinct condensate fractions: a “rich” oil fraction of 0.02–0.07 m³/t FFB captured during full‑pressure steaming, and a “lean” fraction vented during pressure peaks (patents.google.com). Densities run 900–1100 kg/m³ (patents.google.com), reflecting high suspended content.
In aggregate, condensate volumes are 0.1–0.35 m³ per tonne FFB (patents.google.com). Continuous drainage during sterilization (www.scribd.com) keeps the system stable and reduces oil carry‑over.
Collection tank and pressure control design
The sterilizer should discharge to dedicated condensate drains (or a back‑pressure receiver) routed to a holding tank; two outlets or timed valves split “high‑oil” and “low‑oil” fractions so oil‑rich flow is diverted to recovery while water‑rich flow vents to atmosphere or the mill’s wastewater line (patents.google.com).
Size the collection tank for peak outflow (≈0.35 m³ per tonne × mill capacity). Include coarse screening and settling sections, plus degassing vents to manage flashing and avoid flash flooding. A back‑pressure valve or a vent to atmosphere via a flash tank handles safe depressurization; in practice, “blowoff” is often routed to an open flash tank (“chimney”) for that purpose (patents.google.com).
For coarse debris removal ahead of pumps, mills commonly deploy pre‑screens; where a compact, automated option is fit‑for‑purpose, an automatic screen helps stabilize downstream flows before separation.
Pretreatment: solids control and stabilization
Before oil separation, use a two‑chamber clarifier or trap to capture sand and fibers; a pH check is typically unnecessary because sterilizer condensate trends near‑neutral to slightly acidic. The stream is already hot, so no added heat is required in pretreatment.
If solubilized oil appears, flocculants or coalescers (e.g., tannin or alum) can improve oil‑drop aggregation; however, the oil is mostly free‑phase. A screening step below 1 mm protects pumps and separators; where fine protection is required, a cartridge filter can provide a defined cut‑off before the separator.
When the water‑rich fraction is directed toward the mill’s primary wastewater line, packaged equipment for screens, oil removal, and primary treatment can be incorporated as part of waste‑water physical separation to buffer loadings.
Where space or civil works are constrained, a compact clarifier provides detention volume for solids without disrupting condensate hydraulics.
Oil–water separation (API‑style gravity)
Free oil recovery is well served by a three‑chamber gravity separator (API‑style or baffled tank) that provides a forebay for heavy solids, a quiescent separation chamber, and an afterbay (www.researchgate.net). In the quiescent zone, palm oil (density ≈900 kg/m³) naturally rises at a rate 3× faster than water, forming a surface slick for skimming while clean water exits beneath a weir (www.researchgate.net).
With 10–30 minutes of retention, such separators remove about 90% of free oil droplets, especially larger ones above 100 µm (www.researchgate.net). Field reports indicate a well‑operated unit can recover several hundred kilograms of oil per hour in a medium mill. Example: if condensate contains 0.5% oil by volume, a 10 m³/h flow carries ~50 L/h; at ~90% efficiency, ~45 L/h (~40 kg/h) are reclaimed for return to the red oil system.
Performance improves with calm hydraulics, adjustable weirs, and coalescing media (plate packs or corrugated plates). For emulsified oil, dissolved‑air flotation (DAF) is an option, though gravity suffices for largely free oil; where DAF is selected, a packaged DAF system handles polishing beyond the gravity stage.
In palm mill service, an integrated oil‑water separator designed for free oil removal, such as an oil removal system, helps keep effluent oil and grease in check. That matters: Indonesian limits target approximately 25 mg/L oil & grease (www.pasirsilika.com).
Figure reference: a conventional layout showing forebay, separation chamber, and afterbay is outlined here (www.researchgate.net) — “Figure 1: Simplified API‑style separators employ a forebay (1), oil separation chamber (2) and afterbay (3). Oil rises and is skimmed off the top while clean water exits beneath a weir.”
Heat recovery to boiler feedwater (sensible heat)
Sterilizer condensate typically exits above 80 °C after flashing. Rather than dumping this heat, a heat exchanger can preheat boiler feedwater (make‑up water for steam generation), reducing fuel use. Palaniandy et al. note that ~70% of sterilizer steam input is lost as low‑pressure exhaust; for 1000 kg of FFB, 250 kg of steam are used and ~175 kg are lost (www.researchgate.net).
Quantified example: consider a 30 t/h mill (≈240 t/day FFB). At 250 kg steam/t, this is 7500 kg steam/day; ~70% (≈5250 kg) escapes. Assuming ~5000 kg of condensate at ~120 °C, sensible heat above 30 °C ambient is ~4.18 kJ/kg·K × 90 K × 5000 kg ≈ 1.88×10^6 kJ (~524 kWh). If a heat exchanger recovers half, that is ≈262 kWh daily (≈15,000 kJ per tonne FFB), which in practice could cut boiler fuel by ~10–20%.
Implementation uses a shell‑and‑tube or plate heat exchanger. Because condensate may carry oil droplets and fines, it is preferably routed through the separator first; the clean, hot condensate then preheats cooler feedwater. Illustrative duty: preheating feedwater from 40 °C to 100 °C using 0.5 m³ condensate/min (≈500 kg/h at 120 °C) transfers about 0.5 × 4.18 × 60 ≈ 125.4 kW continuously. Over 24 h, that is ~3 MWh (10.8 GJ). In larger mills (e.g., 100 t/h), the recovered heat can reach several megawatts.
Palaniandy et al. also demonstrate that combined steam‑recovery concepts can save ~20% energy (www.researchgate.net). A direct exchanger is simpler and leverages condensate’s sensible heat; even a 50–80% approach to heat exchange reduces fuel demand. For instance, saving 1.5 MW on a boiler (~50 GJ/day) reduces biomass fuel needs by ≈20%, and over a year this can translate to ~100–200 TJ saved (tens of thousands USD).
Outcomes, standards, and sizing notes
Oil recovery improves yield: even small fractions reclaimed (e.g., 0.1% of FFB oil) add up to hundreds of tonnes annually for a mid‑size mill. It also lightens POME loading, helping biological treatment and compliance with oil & grease limits near 25 mg/L (www.pasirsilika.com). Heat recovery lowers steam/wood use; for a 50 MW_th (thermal megawatts) boiler, reclaiming 1–2 MW_th saves about 3–6% fuel, which annualizes to ~100–200 TJ saved.
Separator sizing can follow API 421 practice; Water Research Center guidance cites ~3–10 minutes retention per chamber and proper overflow weir design (www.researchgate.net). Because condensate flows are intermittent (post‑cycle), use a buffer tank to smooth hydraulics. Pumps then transfer treated water to the POME collection pond or the boiler feed tank, with monitoring via level controllers and oil‑skimmer alarms.
Industrial case studies report >90% free‑oil removal by gravity separators in palm mills following these schemes, with oil clarifier effluent reaching single‑digit mg/L oil (www.researchgate.net; www.mdpi.com).
Bottom line: segregate, separate, and recover
Segregating sterilizer condensate for oil and heat recovery is a data‑backed upgrade. The equipment—drains, tanks, separators, and heat exchangers—pays back in reclaimed oil and lower fuel use. Designing for peak condensate throughput (during blow‑off) and employing robust, coalescing gravity separation (www.researchgate.net) helps mills meet Indonesian and international effluent standards while improving efficiency (patents.google.com; www.researchgate.net).
