Torrefaction: A Pathway Towards Fungible Biomass Feedstocks?

Torrefaction: A Pathway Towards Fungible Biomass Feedstocks?

by Alexander A. Koukoulas, Ph.D.

In June 2016, I gave an invited talk at the Advanced Bioeconomy Feedstocks Conference, which discussed the potential of low-cost forest biomass resources for accelerating the growth of the bioeconomy. My central theme focused on the availability of at least 68 million dry tons of forest residuals that could be sustainably harvested and used in the generation of biomass power and bio-based chemicals. Add to this at least 60 million dry tons of forest biomass that could be sustainably derived from forest management programs conducted on our National Forests and the amount of inherently low-cost biomass resource that could be used to drive the bioeconomy is enormous.

As with most biomass sourcing scenarios, forest biomass is challenged by the added cost of aggregating, handling, delivering and storing relatively low-density material across the supply chain. Compounding these challenges is the relatively high heterogeneity of the material in terms of its moisture content, chemical composition and energy density.

One promising approach to overcoming these challenges is torrefaction, a mild pyrolyis process that removes low-grade volatile materials from biomass to produce a relatively uniform energy carrier that can be used as a solid fuel. When densified, the energy density of torrefied biomass approaches the energy content of low-rank coal. An added benefit is that torrefaction imparts water resistance to the material, thus obviating the need for expensive storage solutions. The result is a bio-based energy carrier that can be used as a drop-in replacement for coal. While the U.S. is rapidly phasing out coal-fired power generation facilities, the opportunities for using torrefied biomass in existing coal-fired facilities, in either “super-peaker” or co-firing modes are enormous. Of course, export markets, like the EU, are especially excited about torrefied biomass as it has the potential of lowering transportation costs and dramatically reducing expensive capital improvements that are typical in non-torrefied biomass power generation.

Torrefaction removes water and low-energy volatiles from wood to create a water-resistant energy carrier with high energy density.

Biomass power generation is the only renewable option that can provide dispatchable, baseload energy delivery. Driving out cost through torrefaction could expand its use and adoption. Beyond power generation, torrefied biomass is finding applications as a specialty material, such as a component in advanced composites. Recent technical advances in torrefaction process technology and market demand for this material could drive a whole new industry based on renewable biomass resources.