In palm oil mills, mesocarp fiber and palm kernel shells — 16–21% of fresh fruit bunches — are more than waste. Fired in biomass boilers, they routinely supply 100% of steam and electricity, often with megawatt-scale surplus.
Indonesia processed 200.7 million tonnes of fresh fruit bunches (FFB — the harvested fruit clusters) in 2024, and with that came a mountain of press-side residue: roughly 26–30 million tonnes of mesocarp fiber and 12–16 million tonnes of palm kernel shell — over 40 million tonnes per year of biomass that is largely untapped (palmoilmagazine.com). In energy terms, total solid palm oil biomass (shell + fiber + other residues) could theoretically yield 40–59 TWh per year, outstripping Indonesia’s 2025 bioenergy target of 33 TWh (palmoilmagazine.com).
On the ground, mills have already turned this “waste” into baseload. Case studies show fiber and shells fuel boilers to generate high-pressure steam and electricity, covering all onsite needs — and often generating exportable surplus — while cutting costs and emissions (researchgate.net) (researchgate.net).
Solid press waste: yields and scale
Palm oil pressing produces two principal solids: mesocarp fiber and palm kernel shell. In Indonesian mills, fiber typically makes up 11–14% and shells 5–7% by weight of FFB (researchgate.net). A 30 t/h mill (t/h — tonnes per hour throughput) produces roughly 0.11–0.14 tonnes of fiber and 0.05–0.07 tonnes of shells per tonne of FFB processed (researchgate.net).
At national scale, Indonesia’s 200.7 Mt FFB in 2024 yielded on the order of 26–30 Mt fiber and 12–16 Mt shells annually (palmoilmagazine.com), and the broader solid biomass resource could deliver 40–59 TWh each year, exceeding the 33 TWh bioenergy target for 2025 (palmoilmagazine.com).
Fuel properties and moisture management
Shells pack heat: lower heating value (LHV — usable energy content) for dry palm kernel shells is around 20.7 MJ/kg (megajoules per kilogram), and even at 10% moisture they deliver ~17.3 MJ/kg (researchgate.net) (researchgate.net). Fiber (mesocarp) sits slightly lower at ~19.7 MJ/kg when dry, but high moisture — commonly 30–50% — can push usable energy down to ~8–11 MJ/kg; at 40% moisture, it’s ~10.8 MJ/kg (researchgate.net) (researchgate.net).
Shells are essentially clay‑free, minimizing clinker and ash issues; fiber has modest ash that exits as ash/char. For boiler service, mills often partially dry or shred fiber, while shells — typically ~10–15% moisture — can be fed relatively directly. Many operators mix the two to balance combustion: a typical grate mix is ~75% fiber and 25% shell by weight (researchgate.net).
Boiler pressure and turbine cogeneration
Modern palm oil mills run biomass‑fired boilers at ~18–21 bar (bar — unit of pressure) to drive back‑pressure steam turbines for electricity generation (researchgate.net). At Dolok Sinumbah (PTPN IV), a 30 t/h mill burning a 25% shell/75% fiber mix supplied 18 t/h of steam — covering process needs — and met its 734 kW (kilowatts) electricity demand solely from biomass (researchgate.net).
Another Indonesian site, Agro Mitra Madani (Jambi), generated 8,253 kWh (kilowatt‑hours) over a 7‑hour shift, exceeding its 4,900 kWh demand and leaving a 3,353 kWh surplus (researchgate.net). Surveys show surplus energy on the order of ~9.7 kW per tonne of FFB feed; for a 30 t/h mill, that’s ≈130–170 kW continuously (≈1.4–2.6 MWh in 20 hours) beyond onsite use (researchgate.net) (researchgate.net). Thai experience echoes this: a standard 45 t/h mill produced 2.83–4.22 MW of surplus electricity depending on operation mode (scijournals.onlinelibrary.wiley.com). Properly sized boilers (e.g., ~8–15 MW for 30 t/h mills) routinely generate multi‑megawatt surpluses while covering all steam loads.
Power output and efficiency metrics
Power scales with mill size: table data indicate a <30 t/h mill typically yields 3–7 MW, a 40–50 t/h mill about 13–16 MW, and a 60 t/h mill 17–20 MW (researchgate.net). In one 30 t/h case, fiber alone was estimated to supply ~542 kW and shells ~580 kW — comfortably covering a ~442 kW demand and leaving ~130–170 kW spare (researchgate.net) (researchgate.net). Over 20 hours, that implies ~1.4–2.6 MWh/day of excess, with ~648–686 kW (shells + other biomass) potentially sold externally (researchgate.net).
Cogeneration setups are efficient: specific energy consumption (SEC — electricity used per unit of FFB processed) can be as low as ~0.013 MWh/tFFB, roughly 30–50% better than earlier benchmarks in one report (researchgate.net). Combustion leaves little behind: in the Jambi shift above, 7 hours of firing produced only 654 kg of ash (~93 kg/h), which can be collected and repurposed or safely disposed — a near‑zero solid waste outcome (researchgate.net).
Economics and payback dynamics
Because fiber and shells are by‑products, their effective fuel cost is near zero. In the Jambi example, fiber + shell firing generated ~1.7× the mill’s electricity demand (researchgate.net), so the 3.353 MWh/shift surplus could be monetized; at IDR 1,000/kWh, that’s ~IDR 3.35 million per day (approximately $230/day). An efficiency upgrade in a 45 t/h mill increased off‑take power from 2.83 to 4.22 MW, directly lifting revenue potential (scijournals.onlinelibrary.wiley.com). Paybacks for cogeneration optimization can be short; one by‑product energy project reported a 3.16‑year payback (researchgate.net).
Operationally, biomass boilers can run continuously (many mills operate 20+ hours/day), reducing exposure to external electricity or gas disruptions. Residual value is already visible in markets: mills exported ~1.5 million tonnes of shells abroad annually in 2023, contributing 2–3 TWh per year (palmoilmagazine.com). For steam‑cycle upkeep, plants may rely on targeted chemistry and dosing; for example, operators can deploy boiler chemicals as part of routine protection and performance management.
Environmental and policy context
The carbon from fiber and shells was recently captured by the palms, making combustion effectively carbon‑neutral. Substituting biomass for coal or gas cuts emissions; co‑firing palm shells in coal power plants (potential ~5 GW capacity) could reduce CO₂ by ~10–15% per MWh generated (palmoilmagazine.com). One review warns that unused palm biomass leads to “severe environmental pollution” and threatens industry sustainability — a problem eliminated by using biomass as boiler fuel instead of open burning or decay (sciencedirect.com).
Lifecycle assessments indicate recycling oil palm biomass “is expected to contribute to the sustainability and economic success of the oil palm industry” and support Indonesia’s net‑zero 2060 target (sciencedirect.com). Diverting waste to energy reduces methane from rotting residues or effluent ponds and avoids deforestation (no extra land cleared for energy). Ash is the only by‑product and can be recycled as a soil amendment. Expanded biomass utilization, including fiber/shell, could add about $500 million to Indonesia’s GDP by 2030 and create hundreds of thousands of rural jobs, while cutting emissions (palmoilmagazine.com). Policy is aligned: the 23% renewables target by 2025 and Presidential Regulation 112/2022 aim to accelerate renewable electricity (esdm.go.id), while standards such as RSPO and ISPO favor zero‑waste operations. In practice, the fiber/shell boiler is described as the greenest choice: more efficient than open burning, displacing imported fuel, and ensuring that 100% of biomass is utilized.
Implementation steps and operating norms
Combustion systems are typically chain‑grate or fluidized‑bed boilers capable of handling coarse biomass. Key steps include fuel handling (fiber compacted or shredded; shells sized/screened; foreign objects removed), moisture control (fiber aerated or dried — sometimes via exhaust flue gases — to ~30%; shells at ~10–15% usually require no drying), and a steady firing mix (~75% fiber / 25% shell by weight) for stable combustion (researchgate.net). Boiler operation centers on ~18–21 bar steam with calibrated grate speed and air flow for complete burn; ash removal every shift (or continuously) prevents clinker build‑up (researchgate.net).
In cogeneration, high‑pressure steam feeds a turbine‑generator sized to the mill load; control systems regulate throttle bleed to satisfy both process steam and electricity demand. Excess steam can be condensed for export power, with condensate quality safeguarded by polishing where required — a role served by systems like a condensate polisher. Thermal efficiencies of 40–50% are typical with low unburned carbon losses. As engineering norms, heat content approximates 7–10 GJ per tonne of oven‑dry fiber and 9–11 GJ per tonne of dry shells, closely matching mill steam requirements.
Routine water‑chemistry control supports uptime in these 18–21 bar systems; accurate addition of treatment chemicals via a dosing pump and removal of dissolved oxygen using oxygen scavengers align with standard boiler practice to mitigate corrosion and scale in the steam cycle.
Zero‑waste mill, circular energy
The practical guide is circular: collect all press waste (fiber and shell), prepare fuel (remove contaminants and manage moisture), combust efficiently in a properly sized biomass boiler, generate steam and electricity, and route power to internal loads (or the grid). The result is a self‑powered mill with minimal fuel cost and strong environmental performance — a setup that peer‑reviewed studies and industry analyses say many mills already use to meet 100% of onsite energy needs from pressing waste, with documented cost savings and reduced emissions (researchgate.net) (researchgate.net) (scijournals.onlinelibrary.wiley.com) (researchgate.net) (palmoilmagazine.com) (researchgate.net) (sciencedirect.com).
