Lifecycle Analysis Finds Cellulosic Ethanol Produced by POET’s Project LIBERTY Will Reduce GHG Emissions 111% Over Gasoline
Cellulosic ethanol produced by grain ethanol producer POET’s Project LIBERTY (earlier post) first commercial cellulosic ethanol plant will reduce greenhouse gas emissions (GHG) by 111% relative to gasoline, an independent lifecycle analysis (LCA) compiled by Air Improvement Resource, Inc., has found. (I.e., the cellulosic ethanol will offset more greenhouse gas emissions than it produces.)
The reduction is somewhat less than the 130% calculated by the Environmental Protection Agency (EPA) in the RFS2 for the production of cellulosic ethanol from corn stover using a biochemical process. Air Improvement’s estimates of emissions from Project LIBERTY’s fuel and feedstock transport and fuel production (the last being the sum of storage, electricity, chemicals, waste disposal, and biogas production) are slightly higher than the corresponding elements in EPA’s analysis.
Project LIBERTY will produce approximately 25 million gallons of ethanol annually using the cobs and upper 25% of the stover as feedstock. Enzymatic hydrolysis will pretreat the biomass for subsequent fermentation. A key co-product from this biochemical ethanol refinery is a biogas that will be used to replace natural gas in POET’s collocated corn-based refinery, which has an annual output of 50 million gallons.
The analysis found that all the inputs into Project LIBERTY will emit 41.8 grams of carbon dioxide equivalent units per megajoule of energy produced (gCO2eq/MJ). The biogas exported as a co-product will offset 49.8 gCO2eq/MJ. EPA estimates for land use and agriculture changes offset an additional 1.7 gCO2eq/MJ, bringing Project LIBERTY’s total emissions to -9.7 gCO2eq/MJ.
EPA’s standard for gasoline emissions is 92.9 gCO2eq/MJ.
|Comparison of LIBERTY to EPA Corn Stover GHG Estimates in RFS2 (g/MJ)|
|Profess/activity||Project LIBERTY||EPA-RFS2 Corn Stover Bio-chemical|
|Net Domestic Agriculture||8.6||10|
|Net International Agriculture (EPA RFS2)||0||0|
|Domestic Land Use Change (EPA RFS2)||-10||-10|
|International Land Use Change||0||0|
|Fuel and Feedstock Transport||3.1||1.9|
|Total GHG Emissions||-9.7||-28.4|
|% Reduction of Gasoline||111%||130%|
It is important to note, Air Improvement said, that stover removal rates from fields around Project LIBERTY will not be more than 25% of total stover on the fields, so that additional fertilizer will not be necessary for the next corn crop. Consequently, it estimated no increase in agriculture emissions due to the stover removal for the Project LIBERTY facility.
The LCA highlighted a number of characteristics of POET’s process that lead to this large emissions reduction:
Project LIBERTY produces ethanol from agriculture waste. Because it uses a waste product from an existing crop, there are no additional inputs for planting and growing the feedstock.
Indirect Land Use Change, which creates an emissions penalty for grain-based ethanol, does not have any penalty associated with POET’s cellulosic ethanol.
The waste stream from POET’s process is fed into two anaerobic digesters to create biogas. Enough biogas is produced to completely power both Project LIBERTY and the adjacent grain-based ethanol plant. The natural gas that is displaced in this process is credited to the cellulosic ethanol plant.
The Project LIBERTY lifecycle analysis was conducted using the most current design elements available. POET said it will continue to learn from laboratory work and its pilot cellulosic ethanol plant currently operating in Scotland, SD As changes occur, the analysis will be updated.