Full Published Article at: EUBCE 2025
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From Bagasse to Business: Integrating Pyrolysis at the Sugar Mill
Sugar mills sit on a goldmine of fibrous residue. A recent study by Bara Consultants and Regen Biofuels shows how slow pyrolysis, embedded inside the mill, can turn surplus bagasse into three sellable streams—biochar, bio-oil, and syngas—while improving waste management and economics.
What the testing proved
Under slow-pyrolysis conditions around 400 °C (inert atmosphere), dried bagasse split into roughly one-third char, one-third liquids, and one-third gas, with good mass balance closure. Moisture control mattered: insufficiently dried feed pushed more water into the condensate and slightly reduced organic liquid yield—reinforcing the value of on-site drying using low-grade steam.
The biochar came out energy-dense (~21 MJ/kg) with a standout BET surface area ~318 m²/g, opening options beyond fuel—adsorbents, soil carbon, even activated-carbon precursors.
The bio-oil naturally separated: a lighter pyroligneous acid (aqueous) layer rich in acetic acid and furfural, and a heavier phenolic tar suitable for burner fuel or resin precursors.
The syngas averaged ~35% CO₂, ~19% CO, ~2–3% CH₄ (balance N₂) with ~5–6 MJ/m³ heating value—ideal to loop back for process heat and make the unit self-sustaining after start-up.
Why integration at the mill wins
Because mills already have steam and heat sinks, integration is straightforward—and cheapest when you use existing HP steam for drying. In a direct comparison, energy cost came in at $1.21/GJ for HP steam vs $11.28/GJ for LPG and $16.33/GJ for electric heating; annual drying cost dropped from $116,610 (electric) to $8,637 (HP steam) in the modeled case.
Beyond drying, the team estimated total heating needs and found cost per kg of feed at $0.00091 (HP steam) vs $0.01011 (LPG) and $0.00590 (electric)—a decisive advantage for steam-integrated designs.
What the numbers look like
Assuming a typical 9-month milling season (~244 days) at ~90% availability, the modeled system processes mill bagasse and produces, per season: ~848.6 t pyroligneous acid, ~838.3 t biochar, and ~875.7 t syngas (mass basis).
At conservative product pricing, the study estimates $1.689 million in annual turnover ($0.81/kg for biochar; $1.19/kg for pyroligneous acid). Operating expenses tally $922,296/year, with CAPEX ~$2.54 million for a modest, low-complexity installation.
Here’s the kicker: even excluding any revenue from syngas, the HP-steam base case shows an annual profit ~$610k and a 24% ROI—beating LPG (13%) and electric (4.5%). The authors stress this is before counting carbon credits, fertilizer offsets, or advanced chemical recovery.
Product pathways that add resilience
- Biochar can cycle back to cane fields for soil health and potential carbon credits, or be upgraded to activated carbon—taking advantage of that ~318 m²/g surface area.
- Aqueous bio-oil (PA) contains furfural and acetic acid—platform chemicals that justify small-scale recovery where markets exist. The heavier phenolic tar can fuel kilns/burners or feed resin chemistry.
- Syngas closes the energy loop—combustion supplies drying/reactor heat so no flammable gases are vented and the unit can export heat to the mill.
Practical notes for mills
- Drying is non-negotiable. High moisture hurts liquid yield and efficiency; waste heat or LP steam at the mill can do this cheaply.
- Design for simplicity. The modeled system uses rotary drying and a rotary pyrolysis chamber—a low-complexity setup that fits existing utilities and O&M skill sets.
- Start with fuel uses; layer in chemicals. Early revenue from char and heat displacement de-risks the project; chemical recovery (e.g., furfural) can follow.
Bottom line
Integrating slow pyrolysis turns a disposal headache into bankable products and lower operating risk. With HP steam doing the heavy lifting on energy, the base case already pencils at ~24% ROI—before carbon and chemical upside. For mills seeking resilience against sugar-price swings, this is a pragmatic step toward a true biorefinery.