Life-Cycle Greenhouse Gas Emissions from Forest Bioenergy Production at Combined Heat and Power Projects in Nova Scotia, Canada

Abstract

Forest bioenergy production can represent a renewable energy supply while benefiting the forest sector. However, greenhouse gas (GHG) reductions are often not immediate. The point of carbon parity where bioenergy starts delivering GHG benefits may be years to decades in the future. This study examined the life-cycle emissions associated with bioenergy production at combined heat-and-power (CHP) projects in Nova Scotia, Canada. We examined the effects and sensitivities of different feedstock mixes of chips from harvested roundwood and mill residues, the implementation of intensive and extensive silviculture strategies, and different market/supply-chain assumptions around additionality and product substitution. We found contrasting GHG outcomes for bioenergy, depending largely on additionality assumptions and biomass type. When primary biomass (roundwood) was used as the feedstock type, carbon parity was achieved within four to nine years when pulp and paper products were substituted, whereas carbon parity was achieved in 86–100 years or longer when biomass harvests were additional. Net GHG benefits were achieved in 10 years with the use of secondary biomass (mill residues) as the bioenergy feedstock, although they were delayed when at lower energy conversion efficiencies. Adoption of more intensive silvicultural practices (plantations) reduced the time to carbon parity because of increased yields, although uncertainties in long-term soil carbon storage exist. Study Implications: Our analysis shows that the use of forest biomass in local CHP facilities can deliver GHG benefits in the short term but there is substantial variability. Carbon parity times were the longest with the use of additional primary biomass feedstocks (i.e., roundwood) but were substantially reduced when biomass harvests substituted harvests for pulp and paper products and when secondary biomass (i.e., mill residues) was used. This study highlights the nuance of different forest management dimensions (e.g., silviculture) while also presenting novel findings on the importance of assumptions around biomass harvesting being additional to current practices or a substitution for declines in traditional forest products.