The Value and Complexity of a Slash Pile

By Kolby Hoagland | January 31, 2014

Collectively, the bioenergy industry transforms an array of highly heterogeneous feedstocks into various energy products. Whether it is tree bark burned for heat in a pellet mill’s dryer or sewage sludge transformed in a hydrothermal liquefaction reactor to produce biochemicals, biogenic sources of fuel can provide a number of different energy products and services because of their varying nature. Their diversity allows for a range of opportunities, but the inherent variability in their composition also provokes complications. This week’s DataPoints Blog briefly delves into feedstock variability and the importance of uniformity.

In last week’s blog, I reported on a Western Forestry and Conservation Association conference and the need for the bioenergy industry in the Pacific Northwest to look more to forest residue as a fuel feedstock. One of the difficulties in using underutilized feedstock, such as forest residue after a logging or thinning operation, is often the heterogeneous nature of the residue that remains after the logs have been hauled away. Biomass feedstocks, in general, are comprised with highly varying states of moisture, composition, size, and density even within the same feedstock from a single harvest. For example, the concentration of ash forming minerals varies considerably between the outer bark and inner wood of the same tree. Compared to fossil energy sources, oil, natural gas, and coal remain relatively consistent over the lifetime of the well or mine that they’re extracted from. Fossil energy sources do require a certain amount of refining or processing to create uniformity, but the CAPEX, OPEX, and energy expended to process the fossil source is distinctly less than their bioenergy counterpart (Excluding oil from tar-sands, which requires significant processing and energy to extract the oil). Some technologies and segments of the bioenergy industry are capable at handling highly variable feedstock, but, for the most part, a uniform size, composition, and moisture content are insisted upon by bioenergy plant operators.

Low value, heterogeneous residue from forestry operations provides an excellent opportunity for the bioenergy industry in markets where competition for existing feedstock makes them unattainable. Finding cost effective, energy efficient means of extracting excess forest residue and processing it into a uniform feedstock is vital for the industry’s continued growth. The age-old practice of burning slash piles from forestry operations is a “nobody wins” outcome that only produces smoke. With the appropriate technologies and incentives, converting low value forest residue into a uniform, high value feedstock is an “everybody wins” strategy that generates greater revenue for the land owner and allows the bioenergy industry to grow.