# Thermochemical biomass conversion: Efficiency

Seconds or hours of heating: how speed decides the product

Source page: https://www.materialinsights.org/energy/e_bio_thermochem/efficiency/

What this tab covers How much of the energy available is actually captured or extracted, in per cent: theoretical limits, laboratory records, typical new equipment and in-service averages, each with exactly what is being measured.

Heating biomass with little or no oxygen splits it into gas, liquid and char: fast pyrolysis turns up to 65-75% of dry wood's mass into bio-oil, gasification about 85% into gas. Turning these into electricity or transport fuel leaves 25-40% as electricity or 14-18% of the mass as liquid fuel.

Chart: Efficiency ranges
 Commercial Record

#### Efficiency by measure

| Measure | Range | Type | What is measured |
|---|---|---|---|
| **Fast pyrolysis, bio-oil yield (commercial practice)** | 65% by mass^[1](https://old.etipbioenergy.eu/images/EIBI-4-torrefaction%20and%20pyrolysis.pdf) | Commercial | Bio-oil per unit of dry feed, about 1-2 seconds at around 500 C |
| **Fast pyrolysis, best liquid yield** | 75% by mass^[2](https://www.ieabioenergy.com/wp-content/uploads/2013/10/IEA-Bioenergy-Update-29-Task-34-Technology-Report.pdf)^[3](https://task34.ieabioenergy.com/?p=4482) | Record | Liquid per unit of dry wood feed (char 12%, gas 13%) |
| **Slow pyrolysis (carbonisation), char yield** | 35% by mass^[3](https://task34.ieabioenergy.com/?p=4482) | Commercial | Char per unit of dry wood at about 400 C over hours to days, with 30% liquid and 35% gas |
| **Gasification, gas yield** | 85% by mass^[3](https://task34.ieabioenergy.com/?p=4482) | Commercial | Gas per unit of dry wood at about 800 C, with 5% liquid and 10% char |
| **Torrefaction, solid yield** | 82% by mass^[3](https://task34.ieabioenergy.com/?p=4482) | Commercial | Torrefied solid per unit of dry wood at about 290 C for about 30 minutes (18% leaves as gas) |
| **Gasifier with gas engine, CHP** | 25 to 30%^[4](https://www.nachhaltigwirtschaften.at/resources/pdf/iea_ete03.pdf) | Commercial | Energy in biomass to electricity (0.2-1 MWe units) |
| **Biomass integrated gasification combined cycle (IGCC)** | 30 to 40%^[4](https://www.nachhaltigwirtschaften.at/resources/pdf/iea_ete03.pdf) | Record | Energy in biomass to electricity |
| **Gasification with Fischer-Tropsch synthesis** | 14 to 18% by mass^[5](https://www.dbfz.de/fileadmin/user_upload/Events/Sonstiges/2023/10_IEA_Workshop/07_IEA2023_vanDyk.pdf) | Commercial | Distillate fuel per tonne of agricultural (14%) or forest (18%) residue |
| **Microbial fuel cells, coulombic efficiency** | 55.6%^[11](https://pmc.ncbi.nlm.nih.gov/articles/PMC12065106) | Record | Share of electrons in the organic feed recovered as current, best reported under optimised laboratory conditions |

#### Where the energy is lost

| Step | Loss |
|---|---|
| **Pyrolysis char and gas (usually burned to heat the process)** | about 25% of feed mass (12% char, 13% gas)^[2](https://www.ieabioenergy.com/wp-content/uploads/2013/10/IEA-Bioenergy-Update-29-Task-34-Technology-Report.pdf)^[3](https://task34.ieabioenergy.com/?p=4482) |
| **Water carried in bio-oil** | about 25% of bio-oil by weight^[2](https://www.ieabioenergy.com/wp-content/uploads/2013/10/IEA-Bioenergy-Update-29-Task-34-Technology-Report.pdf) |

These processes break biomass into simpler fuels that are easier to store, ship or refine. Rapid heating to about 500 C for a second or two, with quick cooling of the vapours, gives mostly liquid; slow heating gives mostly char; higher temperatures with a little air or steam give mostly gas.

Bio-oil is not crude oil: it carries about 25% water and much oxygen, so it holds about 18 MJ per kg, roughly 40% of the energy of fuel oil by weight and 60% by volume, and must be upgraded with hydrogen before it can become transport fuel. Torrefaction (200-350 C) is a milder roasting that keeps about 82% of the mass as a dry, brittle 'bio-coal'. No quantitative efficiency data were found for hydrothermal liquefaction in the sources reviewed.

#### Sources

1. [Torrefaction and pyrolysis (European Industrial Bioenergy Initiative factsheet EIBI-4)](https://old.etipbioenergy.eu/images/EIBI-4-torrefaction%20and%20pyrolysis.pdf) ETIP Bioenergy
2. [IEA Bioenergy Update 29: Task 34 technology report on fast pyrolysis](https://www.ieabioenergy.com/wp-content/uploads/2013/10/IEA-Bioenergy-Update-29-Task-34-Technology-Report.pdf) IEA Bioenergy
3. [Fast pyrolysis: key points (table of product yields by pyrolysis mode)](https://task34.ieabioenergy.com/?p=4482) IEA Bioenergy Task 34 (Direct Thermochemical Liquefaction)
4. [Energy Technology Essentials ETE03: Biomass for Power Generation and CHP (2007 cost estimates)](https://www.nachhaltigwirtschaften.at/resources/pdf/iea_ete03.pdf) International Energy Agency (copy hosted by nachhaltigwirtschaften.at), 2007
5. [Progress in commercialisation of biojet / SAF (van Dyk, IEA Bioenergy workshop presentation)](https://www.dbfz.de/fileadmin/user_upload/Events/Sonstiges/2023/10_IEA_Workshop/07_IEA2023_vanDyk.pdf) IEA Bioenergy Task 39 (hosted by DBFZ), 2023
6. [Recent Applications, Challenges, and Future Prospects of Microbial Fuel Cells: A Review (Chakma et al., Global Challenges 9(5) 2500004)](https://pmc.ncbi.nlm.nih.gov/articles/PMC12065106) Wiley (open access, PubMed Central), 2025

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_bio_thermochem/index.md)
- [Overview](https://www.materialinsights.org/energy/e_bio_thermochem/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_bio_thermochem/correlation/index.md)
- [Techniques](https://www.materialinsights.org/energy/e_bio_thermochem/techniques/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_bio_thermochem/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_bio_thermochem/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_bio_thermochem/links/index.md)