Production of Hydrocarbon Fuel Using Two-Step Torrefaction and Fast Pyrolysis of Pine. Part 2: Life-Cycle Carbon Footprint

Abstract

This study, as part II of two companion papers, investigated the environmental performance of liquid hydrocarbon biofuel production via fast pyrolysis of pine through two pathways: a one-step pathway via fast pyrolysis only, and a two-step pathway that includes a torrefaction step prior to fast pyrolysis. Fast pyrolysis in all cases took place at a temperature of 530 °C whereas for the two-step pathways, torrefaction was investigated at temperatures of 290, 310, and 330 °C. Bio-oil produced was then catalytically upgraded to hydrocarbon biofuel. Different scenarios for providing the required process heat either by using fossil energy or renewable energy, as well as the effect of heat integration, were also investigated. Our life cycle analysis indicated that using the energy allocation approach, a two-step heat integrated pathway with torrefaction taking place at 330 °C had the lowest global warming potential among all scenarios of about 29.0 g CO 2 equiv/MJ biofuel. Using the system expansion approach, significantly higher reductions in GHG emissions of about 56 to 265% relative to conventional gasoline were observed for the heat integrated processes. More modest percentage reduction in emissions of about 34 to 67% was observed across all scenarios using the energy allocation approach.

A review of thermochemical upgrading of pyrolysis bio‐oil: Techno‐economic analysis, life cycle assessment, and technology readiness

“…System expansion is a rule applied to coproducts in LCA that are assumed to displace existing products on the market, whose impacts are assumed displaced and therefore credited. Comparing the GHG emissions among studies on the basis of 1 MJ of fuel ranked from lowest to highest and benchmarked against the GWP of gasoline and diesel (Figure ), the two‐step torrefaction and fast pyrolysis of pine has the lowest GWP while the one‐step torrefaction and fast pyrolysis of pine (Winjobi, Zhou, et al, ) has the highest compared to conventional petroleum‐based fuels. A reason for this significant difference in GHG emissions between the highest and lowest processes is that the increase in temperature in the torrefaction process combined with it being a two‐step process (Winjobi, Zhou, et al, ) increases the quantity of coproduct (char), which is credited using system expansion and thereby significantly reduces the net GHG emissions compared to the one‐step lower temperature torrefaction process.…”

Effects of Coproduct Uses on Environmental and Economic Sustainability of Hydrocarbon Biofuel from One- and Two-Step Pyrolysis of Poplar

“…Full discussion of the biomass supply logistics can be found in detail in previous work by Winjobi 13 . The poplar is collected as forest logging residue.…”

“…The presence of a torrefaction pre-treatment step increases the guaiacol yield from fast pyrolysis. The upgrading of pyrolysis bio-oil to hydrocarbon transportation fuel was achieved by the hydrodeoxygenation of the model compounds contained in the bio-oil as outlined in previous studies 5,13,24 . Reaction pathways for the different model compounds were obtained from the literature [25][26][27][28][29] .…”

“…The upgrade is achieved by a stabilization step followed by a hydrotreatment step. The reaction pathways of the representative compounds are discussed in detail in previous work by Winjobi 13 . The emission inventories for this step include process heat requirements and cooling water used for cooling the highly exothermic hydrotreatment step.…”

“…A detailed description of the modeling of the biomass conversion can be found in previous work by Winjobi 13 .…”