Influence of upstream, distributed biomass-densifying technologies on the economics of biofuel production

Authors: GUNUKULA, SAMPATH - University Of Maine; DAIGNEAULT, ADAM - University Of Maine; Boateng, Akwasi; Mullen, Charles; DESISTO, WILLIAM - University Of Maine; WHEELER, M - University Of Maine

Submitted to: Fuel
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2019
Publication Date: 3/29/2019
Citation: Gunukula, S., Daigneault, A., Boateng, A.A., Mullen, C.A., DeSisto, W.J., Wheeler, M.C. 2019. Influence of upstream, distributed biomass-densifying technologies on the economics of biofuel production. Fuel. 249:326-333. https://doi.org/10.1016/j.fuel.2019.03.079.
DOI: https://doi.org/10.1016/j.fuel.2019.03.079

Interpretive Summary: Utilization of bio-renewable resources as replacement for fossil fuels can decrease the net release of greenhouse gases and thereby mitigate climate change. One technological platform being studied for conversion of biomass to biofuels is pyrolysis, the heating of a material in the absence of oxygen. When applied to biomass, pyrolysis produces a liquid called “bio-oil” that can be refined via hydrotreatment to “green” gasoline, jet or diesel fuels that are identical to those produced from petroleum. Although this process is clearly attractive from an environmental standpoint, for the technology to be adopted commercially, it must produce products cost-competitively to petroleum refining. One challenge in biorefining is the need to supply large volumes of low density biomass feedstock, which results in high costs of transportation of the raw material. One way to mitigate these costs may be to densify the biomass to a more economically transported form close to its site of production. However, there is a tradeoff between the savings in transportation costs and the costs of the densification process and any effects on the refining process. This study examined these cost tradeoffs for three scenarios for biomass densification. The first two, using pelletizing or torrefaction produce denser solids to ship to the biorefinery for pyrolysis and hydrotreatment. The third performed the pyrolysis remotely to produce dense bio-oil, which is shipped to the refinery for hydrotreatment. Wood and switchgrass were considered as feedstocks. The results showed that densifying biomass reduced the transportation cost by at least 20%. However, the capital and operating costs required for densifying biomass increased the total cost of biofuel production by at least 3%. The plant size of a pelletizing facility is found to have a minimal impact on the cost of making pellets, and pelletizing can be economically competitive to make biofuel if less than ¼ of the land around the biorefinery is used to produce feedstock.

Technical Abstract: The low bulk density of biomass (switchgrass/wood) results in the requirement of transporting large volumes to feed biorefineries. The transportation volumes for bioenergy production can be reduced by densifying the biomass before it is processed to make renewable gasoline and diesel (RGD) fuels via integrated fast pyrolysis and hydrodeoxygenation. However, the additional costs of densifying the biomass, along with decreases in overall mass and energy yields, influence the overall economic performance of RGD production. This study investigated the techno-economic impacts of pelletizing, torrefying, or pyrolyzing the biomass at distributed facilities prior to upgrading the intermediates to RGD at a centralized facility. Eight scenarios were considered. Densifying biomass was shown to reduce the transportation cost by at least 20%. However, the capital and operating costs required for densifying biomass increased the total cost of RGD production by at least 3% as compared to that of RGD made from non-densified biomass. The plant size of a pelletizing facility was found to have a minimal impact on the cost of making pellets, and pelletizing can be economically competitive to make RGD when the fraction of land surrounding the biorefinery facility allocated to the cultivation of biomass is less than 0.25.