THE ADVANCE OF STEAM TREATED PELLETS

WOOD PELLETS have been considered an alternative to fossil fuel for almost half a century.

The energy industry first used compressed sawdust as a fuel source in the early 1970s, when oil’s market price quadrupled and the fossil fuel was rationed. 

Ten years later, newly-developed plant equipment demonstrated wood being into a type of industrial charcoal through a process known as torrefaction. [1]

Unfortunately, at that time the primitive machinery and extreme dry heat used in torrefaction created a brittle end product – making its handling, transport and storage highly challenging at utility scale. 

However, the advent of steam explosion technology in bioenergy has brought about a new type of advanced black pellet as a viable and timely alternative to burning coal.

Steam-treated black pellets manufactured from a hydrothermal process, rather than from simple heat degradation, are a true direct ‘drop in’ replacement for coal. [2]

Steam explosion preserves and redistributes lignin in cellulosic materials – rather than degrades it – so granular woody mass can be bound together naturally and tightly to create outstanding mechanical strength under industrial compression. [3] [4] [5]

This reallocation of lignin – responsible in the natural world for waterproofing plant cell walls – creates a resilient, durable, energy-dense pellet capable of withstanding almost all weathers, knocks and abrasions.

In multiple ways, steam-treated black pellets exist and behave just like coal. Only, when burned, they have created just six percent of coal's carbon footprint, and they release minimal harmful local particulates.

The density and durability of steam-treated pellets are qualities that were seized upon in 2015, by Thunder Bay Generating Station in Ontario. The Canadian power plant became the first facility worldwide to fully convert its infrastructure from burning coal to burning steam-treated pellets. [6] [7] [8]

Only now though, as nations and regions approach hard deadlines for phasing out their use of coal, are steam-treated black pellets receiving the full attention and credit that they deserve.

Here are the five key reasons why energy companies and power stations around the world are turning to steam-treated black pellets as an ideal ‘drop in’ low-carbon replacement for coal:

Steam treatement alters the biomass structure of cellulosic materials. The high pressure and temperatures involved in the process causes energy-rich lignin to soften and disperse, so it can act as a natural binder during the pelletization of steam-treated black pellets. This gives steam-treated black pellets a greater mechanical strength than both torrefied and white wood pellets – enabling them to retain their bulk density and experience less fragmentation during handling. [5]

Steam treatement requires a maximum temperature of 260°C to produce steam-treated black pellets, while torrefaction needs roasting temperatures of 300°C and above. When produced on industrial scale for large energy utilities, this difference in treatment temperature represents a significantly higher energy use. Steam-treated black pellets can be mass produced for a lower cost than torrefied wood pellets, and with less harm to the environment. [9]

Steam treatement creates resilient, dense pellets with a tighter bind of granular organic mass than both torrefied and white wood pellets. This maximizes their energy payload per unit of volume, which falls between 14 and 18 GJ of energy per cubic meter. Light and brittle torrefied pellets typically provide 12-16 GJ of energy per cubic meter. Therefore, utilities shipping and stockpiling significant volumes of steam-treated pellets can reduce their operational expenses. [5]

Steam treatement gives black pellets a surface coating of lignin which makes them highly water resistant. Steam-treated pellets remain intact when submerged in water, where the pellet structures of torrefied and white wood pellets can disintegrate – as each pellet type has been shown to offer only partial and no water resistance respectively [10]. This quality enables utility companies to store steam-treated pellets outdoors without coverings, in all precipitation levels, and reduce capital expenditure costs.

Both steam-treated and torrefied black pellets offer excellent grindability for co-firing with pulverized coal and other materials. However, while steam-treated pellets require moderately more energy to pulverize, they grind more like coal – becoming granular again. When ground by industrial pulverizers, torrefied wood pellets tend to become powdery and can create a safety profile which often needs specific measures to prevent dust, off-gassing and combustion. [2] [11] [12]

[1] ECN Biomass. (2025, July). Bergman, Boersma, Zwart, Kiel. Torrefaction for biomass co-firing in existing coal-fired power stations - Biocoal (2.3, 2.4, 2.4.1). https://publications.tno.nl/publication/34628503/1cn2B7/c05013.pdf

[2] Valmet. (2017, October 24). A replacement for fossil coal in heat and power plants: steam treated black pellets. https://www.valmet.com/insights/articles/biofuels-and-biomaterials/black-pellets---a-replacement-for-fossil-coal-in-power-plants/

[3] BioPower Technologies. (2022, September 29) Chukwuka Onyenwoke, Lope G. Tabil, Tim Dumonceaux, Duncan Cree, Edmund Mupondwa, Phani Adapa, Chithra Karunakaran. Investigation of Steam Explosion Pretreatment of Sawdust and Oat Straw for Biofuel Pellets. https://www.mdpi.com/1996-1073/15/19/7168

[4] Frontiers in Chemistry (2021, November 11). Isabelle Ziegler-Devin, Laurent Chrusciel, Nicolas Brosse. Steam Explosion Pretreatment of Lignocellulosic Biomass: A Mini-Review of Theorical and Experimental Approaches. https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2021.705358/full

[5] Idaho National Laboratory. (2010, August) Jaya Shankar Tumuluru, Christopher T. Wright, Kevin L. Kenny, J. Richard Hess. A Review on Biomass Densification Technologies for Energy Application. https://sswm.info/sites/default/files/reference_attachments/Tumuluru%20et%20al.%202010%20A%20review%20on%20biomass%20densification_0.pdf

[6] Ontario Power Generation. (2015, February 9). OPG’s Thunder Bay Generating Station burns first advanced biomass pellets. OPG News Releases. https://www.opg.com/news-releases/opgs-thunder-bay-generating-station-burns-first-advanced-biomass-pellets/

[7] Power Enegineeering Magazine. (2018, March 30). World’s First Coal to Biomass Conversion Using Advanced Wood Pellets. https://www.power-eng.com/coal/world-s-first-coal-to-biomass-conversion-using-advanced-wood-pellets/ 

[8] Northern Ontario Business (2014, September 15). Thunder Bay Generating Station Test-Fires on Imported Pellets. https://www.northernontariobusiness.com/regional-news/thunder-bay/thunder-bay-generating-station-test-fires-on-imported-pellets-370704

[9] New Trends in Biofuels and Bioenergy for Sustainable Development. (2023, December 26). Chukwuka Onyenwoke, Lope G. Tabil, Tim Dumonceaux, Edmund Mupondwa, Duncan Cree, Xue Li, Onu Onu Olughu. Technoeconomic Analysis of Torrefaction and Steam Explosion Pretreatment Prior to Pelletization of Selected Biomass. https://www.mdpi.com/1996-1073/17/1/133

[10] VTT Technical Research Centre of Finland. Carl Wilén, Perttu Jukola, Timo Järvinen, Kai Sipilä, Fred Verhoeff, Jaap Kiel. Wood torrefaction – pilot tests and utilisation prospects. https://publications.vtt.fi/pdf/technology/2013/T122.pdf

[11] Chemical Engineering Transactions. (2016, January) Pedro Abelha, Michiel C. Carbo, Mariusz K. Cieplik. Explosivity Properties of Dusts from Torrefied Biomass Pellets. https://www.researchgate.net/publication/305375050_Explosivity_Properties_of_Dusts_from_Torrefied_Biomass_Pellets

[12] Chemical Engineering Transactions. (2017, August). Fahimeh Yazdanpanah, Roger Lindahl, Christoph Schilling. Off-Gassing of VOCs and Permanent Gases during Storage of Torrefied and Steam Exploded Wood. https://www.researchgate.net/publication/319301117_Off-Gassing_of_VOCs_and_Permanent_Gases_during_Storage_of_Torrefied_and_Steam_Exploded_Wood