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Biomass Conversion

Biomass Fast Pyrolysis Bio-oil Yield Simulator

A process-design tool for fast pyrolysis, the high-heating-rate (>100 K/s), short-residence (<2 s) thermochemical conversion that turns wood, agricultural residues or microalgae into liquid bio-oil at 450-550 °C. Change feedstock, temperature, heating rate, residence time and reactor type and watch yields, mass balance, energy efficiency and CO₂ savings update in real time.

Parameters
Feedstock (biomass)
Sets volatile matter, ash, moisture and LHV
Pyrolysis temperature T
°C
Bio-oil yield peaks at 450-550 °C
Heating rate dT/dt
°C/s
>=100 K/s puts the unit into fast-pyrolysis regime
Vapour residence time τ
s
<=2 s suppresses secondary cracking
Feed rate (as-received)
kg/h
Reactor type
Fluidized bed is the commercial default
Results
—
Bio-oil yield (wt%)
—
Char yield (wt%)
—
Gas yield (wt%)
—
Bio-oil production (kg/h)
—
Energy efficiency (%)
—
CO₂ savings (kg/h)
—
Reactor schematic — fluidized-bed fast pyrolysis

Biomass enters the hot sand bed, vapours rise to the condenser where bio-oil is recovered, and char drops out the bottom. Colour reflects energy efficiency (green = high, orange = needs work).

Yield vs pyrolysis temperature
Bio-oil yield by feedstock (at current conditions)
Theory & Key Formulas

$$Y_{oil} = Y_{0} \cdot \frac{V}{V_{0}} \cdot \exp\!\left(-\left(\frac{T-T_{opt}}{100}\right)^{2}\right) \cdot f_{heating}$$

Bio-oil yield (wt%). Y₀ = 75 wt% is the ceiling, V is the volatile-matter content of the feed, V₀ = 80 wt% (pine reference), T_opt = 500 °C; f_heating = 1.0 in the fast-pyrolysis regime and 0.7 otherwise.

$$\eta_{E} = \frac{\dot{m}_{oil}\cdot LHV_{oil}}{\dot{m}_{biomass}\cdot LHV_{biomass}}\times 100\%$$

Energy efficiency η_E. Bio-oil LHV ≈ 17.5 MJ/kg; biomass LHV (dry) ranges 12-21 MJ/kg by feedstock.

$$\dot{m}_{CO_2,saved} = \dot{m}_{oil}\cdot LHV_{oil} \cdot 0.075 \;\;\text{[kg/MJ]}$$

CO₂ avoided by displacing fossil oil at an emission factor of 75 g-CO₂/MJ.

Biomass pyrolysis bio-oil yield — designing a fast pyrolysis unit

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Is "pyrolysing" biomass really different from just burning it? It feels like the same thing to me — heat goes in, smoke comes out.
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Good question, and the answer is yes, fundamentally different. Combustion needs oxygen and converts everything to CO₂ and water for heat. Pyrolysis explicitly excludes oxygen and heats the biomass to 350-700 °C, breaking it down into three families of products: liquid bio-oil, solid char and non-condensable gas. The aim is not heat — it is to recover molecules that can be used as fuel or chemicals. So instead of soot you get a valuable liquid energy carrier.
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OK so it's a chemical breakdown, not burning. If three products come out, which one dominates?
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That is where the operating conditions matter. Push the temperature and heating-rate sliders around and watch the bars move. Traditional charcoal kilns use slow pyrolysis — low heating rate, long residence — and get 30-35 wt% char. Modern fast pyrolysis is the opposite: heat the biomass past 450 °C in a fraction of a second and quench the vapours within two seconds. Under those conditions the bio-oil fraction climbs to 70-75 wt%. The tool flags "fast pyrolysis" automatically when heating rate >= 100 K/s and residence <= 2 s, and applies a yield bonus. Try dropping heating rate to 50 — you should see the verdict turn amber and the bio-oil yield collapse.
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Yes! It dropped from 75 % to 52 %. But if the conditions are that demanding, why bother with fast pyrolysis at all?
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Because we want a liquid. Char is a solid and gas cannot be stored in tanks, but bio-oil is a pourable, pumpable liquid that fits the existing fuel infrastructure — trucks, tanks, burner atomisers, pipelines. The strategic case is a carbon-neutral liquid that locally replaces fuel oil. Ensyn (RFO in North America), BTG-BTL (Empyro in the Netherlands) and Fortum (Joensuu in Finland) all run commercial fast-pyrolysis lines, typically 50,000-200,000 t/yr, feeding pulp mills and district heating.
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If I switch the feedstock to microalgae, the bio-oil yield drops but LHV and CO₂ savings look quite different. How should I interpret that?
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Sharp observation. Microalgae arrive with 80 % moisture, so only 200 kg/h of dry mass is actually pyrolysed for every 1,000 kg/h of feed. On the other hand its dry LHV is 21 MJ/kg thanks to high lipid content — energy per dry kg is large. In real projects algae fast pyrolysis is still pilot-scale because the dewatering/drying energy eats most of the upstream gains. Wood is the standard fast-pyrolysis feedstock precisely because it balances volatile matter, dryness and LHV. Toggle the feedstock dropdown and compare both bio-oil kg/h and efficiency to see how this plays out.
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Last one — can bio-oil be poured straight into a car's gasoline tank?
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Not as is. Bio-oil contains 35-40 wt% oxygen, is acidic (pH 2-3), holds 15-30 wt% water and slowly polymerises in storage, so it will corrode injectors and metal parts of an internal-combustion engine. Today the realistic uses are stationary fuels — boilers, kilns and district heat displacing heavy oil. To make true gasoline/diesel/jet substitutes you must upgrade by hydrodeoxygenation (HDO) or FCC catalytic cracking, which is exactly what IEA Bioenergy Task 34 and oil-major demonstration programmes are pushing on. With an LHV of 17 MJ/kg (about 40 % of petroleum) you always pay a volumetric penalty, so size your tanks and pipelines accordingly.

Frequently asked questions

Both heat biomass in the absence of oxygen to produce bio-oil, char and gas, but the operating windows are very different. Slow pyrolysis uses heating rates of 1-10 K/s and residence times of minutes to hours and is suited to char (charcoal) production, typically 30-35 wt%. Fast pyrolysis instead pushes heating rates above 100 K/s, keeps vapour residence below 2 s and operates at 450-550 °C; under these conditions bio-oil (liquid) yield rises to 65-75 wt%. This tool automatically flags 'fast pyrolysis' when heating rate >= 100 K/s and residence <= 2 s, and applies a yield bonus accordingly.
Depolymerisation of cellulose, hemicellulose and lignin becomes active around 400 °C, and primary vapours (which condense into bio-oil) are released most intensively between 400 and 550 °C. Above ~550 °C secondary cracking of these vapours dominates and produces non-condensable light gases (CO, CO2, H2, CH4), so bio-oil yield falls. Above 700 °C the process approaches gasification and bio-oil almost disappears. This tool models the temperature dependence as Y = Y0 * exp(-((T-500)/100)^2), which gives a clean maximum at 500 °C.
Not directly. Bio-oil contains 15-30 wt% water and 35-40 wt% oxygen, has a pH of 2-3, high viscosity and tends to polymerise and phase-separate in storage, so it cannot replace gasoline or diesel in passenger vehicles as is. Typical applications are stationary combustion in industrial boilers, kilns and Stirling engines. To make true gasoline/diesel/jet-fuel substitutes, bio-oil must be upgraded by hydrodeoxygenation (HDO) or catalytic cracking to remove oxygen. Its lower heating value (~17 MJ/kg) is about 40% of petroleum (42 MJ/kg), but it remains an attractive transport-ready liquid energy carrier derived from solid biomass.
The core requirement of fast pyrolysis is to deliver >100 K/s heating throughout the biomass particle. A fluidized bed achieves this by suspending hot heat-carrier particles (typically sand) in a gas stream and dropping small biomass particles (<3 mm) into the bed, which transfers heat almost instantaneously from particle surface to interior. The bed also smooths reaction heat and keeps temperature uniform. Commercial plants (Ensyn RFO, BTG-BTL Empyro, Fortum Joensuu) all use fluidized beds. This tool also includes auger, rotating-cone and ablative reactors that achieve the same goal by mechanical contact, centrifugal contact or sliding friction respectively.

Real-world applications

Replacing fuel oil in pulp mills and district heating: Fortum's Joensuu plant in Finland integrates a 50,000 t/yr fast-pyrolysis line into a CHP power station and uses the bio-oil to displace heavy fuel oil in district heating boilers. BTG-BTL's Empyro project in the Netherlands and Ensyn's RFO units in North America follow the same playbook: a fluidized-bed reactor producing bio-oil consumed locally, cutting both logistics costs and CO₂ at the same time.

Drop-in liquid fuels and Sustainable Aviation Fuel (SAF): Bio-oil can be upgraded via HDO, FCC or hydrotreating into gasoline, diesel or jet substitutes. For Sustainable Aviation Fuel in particular, woody bio-oil sits alongside used cooking oil and lipid residues as a promising pathway, with Honeywell UOP, Topsoe and ExxonMobil all operating demonstration units. The intermediate bio-oil can be transported to a central refinery for co-processing instead of moving bulky biomass.

Energy recovery from agricultural residues and MSW: Rice straw, husks, bagasse and MSW are awkward to burn directly because their ash (Si, K, Cl) attacks boiler tubes and forms slag. Fast pyrolysis converts them into a liquid that is easier to store, transport and co-process. Try MSW or rice straw in this tool and watch the bio-oil yield fall as the higher ash content reduces volatile matter available for cracking.

BECCS and biochar in soils: Fast pyrolysis always co-produces 10-25 wt% biochar. Burying that biochar in agricultural soil locks carbon away on a 100-year timescale and is recognised in IPCC AR6 as a Negative Emission Technology. Combine bio-oil combustion with CO₂ capture and you have BECCS plus biochar — a combined route to net-negative emissions.

Common misconceptions and pitfalls

The biggest pitfall is treating bio-oil's LHV as if it were petroleum. At ~17.5 MJ/kg bio-oil only delivers about 40 % of the energy density of crude oil (42 MJ/kg) or diesel (43 MJ/kg), because much of its mass is water (15-30 wt%) and oxygen (35-40 wt%) that is already "burnt". To deliver the same heat you have to handle roughly 2.5× the mass and volume — pipe diameters, pump capacities and storage tanks sized to fossil fuel will be undersized. Always check economics on an energy-equivalent basis before signing a fuel-replacement claim.

The second pitfall is confusing pyrolysis with gasification. They differ in oxygen (none vs partial), temperature range and target product. Gasification operates at 700-1,000 °C with air, oxygen or steam to produce syngas (CO + H₂), not bio-oil. If you push this tool past 800 °C you will see bio-oil yield crash because secondary cracking is pushing chemistry toward gasification. Pick the process and the temperature window to match the product you actually want.

Finally, do not pick a feedstock on yield alone. Microalgae looks attractive in this tool with high LHV (21 MJ/kg) and 70 wt% volatile matter, but its 80 wt% moisture means drying consumes 30-50 % of the upstream energy, often leaving woody biomass with a better lifecycle efficiency. MSW and rice straw carry 18-25 wt% ash that fouls reactors, poisons downstream catalysts and degrades char quality. Always evaluate on a cradle-to-gate LCA basis that captures availability, pre-treatment, ash handling and biochar end-use, not just bio-oil wt%.

How to Use

  1. Set pyrolysis temperature (°C): typical range 450–550°C for maximum bio-oil yield; higher temps favor gas production.
  2. Enter heating rate (K/s): values >100 K/s define fast pyrolysis; use 200–500 K/s for optimal liquid fraction.
  3. Specify residence time (s): keep <2 s to minimize secondary cracking; 0.5–1.5 s typical for bio-oil maximization.
  4. Input biomass feed rate (kg/h): realistic industrial scale ranges from 100–5000 kg/h depending on reactor size.
  5. Run simulation to obtain bio-oil yield (wt%), char yield, gas yield, hourly bio-oil production, energy efficiency, and CO₂ displacement.

Worked Example

Wood sawdust feedstock (pine, 12% moisture) at 500 kg/h, pyrolyzed at 500°C, heating rate 300 K/s, residence time 1.2 s yields approximately 45 wt% bio-oil (225 kg/h), 15 wt% char (75 kg/h), 40 wt% gas (200 kg/h). Energy efficiency ~65% (accounting for endothermic heat requirement). CO₂ savings: ~340 kg/h compared to conventional fossil fuel displacement equivalent. Char byproduct suitable for soil amendment or combustion heat recovery.

Practical Notes

  1. Temperature control is critical: each 10°C rise above 500°C reduces bio-oil yield by ~2–3 wt% as secondary decomposition accelerates.
  2. For agricultural residues (straw, bagasse), pre-dry to <15% moisture to prevent condensation losses and improve heat transfer efficiency.
  3. Residence time <0.8 s with fast heat-up favors liquid; operate fluidized-bed or circulating reactors for consistent contact.
  4. Bio-oil requires post-treatment (hydrotreating, blending) for fuel-grade use; raw yield represents unstabilized liquid at reactor exit.
  5. Gas co-product (CO, CO₂, CH₄, C₂H₄) can be recycled for process heating, increasing overall system efficiency by 15–25%.