Environmental assessments of woody biomass based jet-fuel
Dr. Indroneil Ganguly and Dr. Ivan L. Eastin, University of Washington, Seattle
Industrialization has resulted in much technological advancement. We have increased our
productivity using mechanized processes and have been able to utilize convenient, faster and
safer modes of transportation. However, much of this progress was centered on unsustainable
sources of energy and their corresponding environmental costs associated with it. Over the past
decade scientific research has shown that the continued burning of fossil fuels, with the attendant
release of CO2 into the atmosphere, will result in a change in the climate that will seriously affect
temperatures around the world and could eventually threaten the existence of civilization.
Fortunately, we do not have to rely on fossil fuels to maintain the conveniences of modern living
given that we are surrounded by renewable resources that are capable of substituting for fossil
fuels in the production of energy. The Northwest Advanced Renewables Alliance (NARA)
research project is exploring the possibility of converting woody biomass (in the form of forest
thinning and residue) into bio-jet fuel. To estimate the overall environmental burden caused by
converting woody biomass in bio-jet fuel, as well as the net reduction in emissions to the
atmosphere associated with avoiding the use of fossil fuel, a detailed Life Cycle Assessment
(LCA) is being performed.
Life Cycle Assessment (LCA) is a method to assess the environmental impacts of a product or
activity (a system of products) over its entire life cycle. In order to accurately estimate the
environmental footprint of woody biomass-based jet fuel, an integration of knowledge and
research from the fields of forestry, logistics (both transportation and process), energy economics
and chemical engineering is crucial. LCA is a computational tool that transcends disciplinary
boundaries and can be used to evaluate the environmental sustainability of a bio-jet fuel industry.
In this regard, we will perform an LCA starting from the forest to the delivery of the bio-jet fuel
to the pump at the airport. A simplified diagram of the biofuel process is depicted in Figure 1. In
the NARA project, LCA’s will be developed for the following modules: woody biomass
collection and processing within the forest including delivery to the pretreatment facility;
conversion of the woody biomass to isobutanol and delivery to the bio-jet fuel production
facility; conversion of isobutanol to jet fuel including transportation to the end-user; and
conversion of the by-products derived from the isobutanol and jet-fuel production processes into
useful co-products.
In the analysis we explore factors that drive the differences in estimates of the net emissions of
biofuels relative to fossil fuels and examine variations in key assumptions that have been
identified as sources of debate regarding the accuracy of biofuel LCA’s. The LCA team will also
investigate how terminology, life-cycle inventories and system boundaries define the framework
of an LCA and can influence the outcome of the LCA. Additionally, we will examine various
inherent assumptions for calculating the LCA of woody biomass and establish the significance of
the roles played by foresters, harvesters, biomass collectors and biomass transportation in the
ultimate LCA results. Finally, the LCA team recognizes the importance of transparency and
accuracy in calculation of the LCA of bio-jet fuel. Thus, to the extent possible, all data sources
will be documented and every effort made avoid the use of ‘black-box’ techniques.
Figure 1: Overall Scope of the LCA of woody biomass to bio-jet fuel
Avoided Environmental Burdens
Removing woody biomass derived from forest harvest operations greatly reduces the need for
slash pile burning. Similarly, conducting forest thinning operations to remove dead and dying
trees from the forest improves forest health and leads to a reduced risk of catastrophic forest fires
caused by an over-accumulation of fuels. Both of these activities reduce carbon emissions from
managed or unmanaged fires within the forest. The LCA team will conduct a consequential
LCA to evaluate the avoided environmental impacts associated with reducing the need for slash
pile burning as well as the avoided environmental cost of having fewer and less intense forest
fires as a result of regular thinning operations.
The Spatial and Temporal Aspects of System Boundary
Often system boundaries are perceived as unidirectional with a start and a finish point as
depicted in Figure 1. However, system boundaries can also be comprised of time and space. With
reference to the NARA regions, LCA estimates of woody biomass collected within the Inland
Empire region would look very different from that for woody biomass collected from western
Washington and Oregon. Even within each NARA region, differences in LCA results might
result from differences in forest management intensity or the type of forest ownership.
Considering the pre-treatment and liquid fuel conversion stages, the LCA of GHG emissions can
change due to the scale of the manufacturing production process and the efficiency of the
production system over time. The LCA team will address the spatial aspects of the LCA
estimates by conducting a sub-region specific analysis based on the existing forestry and
management practices used in the supply region associated with the location of the pretreatment
facility for both NARA communities.
There are two primary temporal aspects of LCAs; 1) developing a long-term impact assessment
of the various greenhouse gas emissions associated with the production process and 2)
considering the improved process efficiencies that may be attained within the production process
over time. Regarding the long-term impact assessment technique, the IPCC has suggested, and
the ISO has recognized, that the temporal scale of a biofuel process should be 100 years. The
LCA research team will also conduct a medium-term (less than 50 years) and a very long term
(500 years) impact assessment. Moreover, simulations will be conducted to predict the
improvements in LCA emissions that may be attained in the near future (10 to 20 years) from
process efficiencies in feedstock collection, transportation and treatment.
LCA is critical to the project’s success
The LCA results will be critical in demonstrating that bio-jet fuel produced from forest residuals
meets the greenhouse gas (GHG) reduction target specified in the US Energy Independence Act
of 2007. The US Energy Information Administration (EIA) requires that the overall GHG
emissions of cellulosic biofuel produce 60% lower carbon emissions (H.R.6:
http://www.gpo.gov/fdsys/pkg/BILLS-110hr6enr/pdf/BILLS-110hr6enr.pdf, Argyropoulos 2010:
http://www.eia.gov/conference/2010/session2/paul.pdf), relative jet fuel produced from fossil
fuel, in order to be considered for public procurement.