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GHG Emission Analysis and Fuel Pathways

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Overview of GHG Requirements

Given that the lifecycle GHG emissions represent the most significant determinant of the various categories, the EPA’s approach to GHG analysis is central to understanding the proposed system.  The EPA provides detailed information regarding its approach to this analysis.  Overall, biofuel is assessed based on the feedstock and the production technology utilized.  For instance, ethanol produced from cornstarch using the same production technology receives the same GHG lifecycle assessment regardless of where the corn was grown or at what facility the fuel was produced.

The EPA’s analysis includes direct and “significant indirect” emissions.  Direct emissions are classified as those that are emitted from each stage of the full fuel lifecycle, including the growing of the feedstock, the distribution of the feedstock, the production of the fuel, the distribution of the fuel, and the use of the fuel in a transportation application.  Indirect emissions include other emissions impacts that result from fuel production or use, such as shifts in acreage between different crop types or land uses.  Indirect land use changes include changes in the usage of land, such as from forest to crop use.  NPRM at 275.  The EPA asserts that it is legally required to include the international indirect emissions that it determines are significant.  NPRM at 276.

Fuel Pathways

The GHG lifecycle analysis provides the basis for determining the feedstock, production technologies, and fuels that qualify for the various RFS 2 categories.  The EPA refers to these combinations as “fuel pathways.”  For each of the four categories of renewable fuel, the specific requirements imposed by EISA establish additional requirements for qualification.

In the category of Cellulosic Biofuel, the EPA has determined that cellulosic ethanol produced through an enzymatic hydrolysis process followed by fermentation using any eligible waste cellulosic feedstock will meet the 60 percent GHG threshold for Cellulosic Biofuel.  The EPA utilized switchgrass to arrive at this determination.  It invites comment as to whether this pathway should also include the feedstocks of miscanthus and planted trees.  Utilizing this methodology, the EPA developed the following fuel pathway chart that establishes which fuels will qualify for the various RFS 2 categories.  This same methodology will likely be utilized to determine whether biofuels produced from algae meet the specific category requirements.

 Applicable Categories for Each Fuel

Pathway Fuel Type

Feedstock

Production Process Requirements

Category

EthanolStarch from corn, wheat, barley, oats, rice, or sorghum- Process derived from biomassRenewable Fuel
EthanolStarch from corn, wheat, barley, oats, rice, or sorghum

- Dry mill plant
- Process heat derived from natural gas
- Combined heat and power(CHP)
- Fractionation of feedstocks
- Some or all distillers grains are dried

Renewable Fuel
EthanolStarch from corn, wheat, barley, oats, rice, or sorghum- Dry mill plant
- Process heat derived from natural gas
- All distillers grains are wet
Renewable Fuel
EthanolStarch from corn, wheat, barley, oats, rice, or sorghum

- Dry mill plant
- Process heat derived from coal
- Combined heat and power(CHP)
- Fractionation of feedstocks
- Membrane separation of ethanol
- Raw starch hydrolysis
- Some or all distillers grains are dried

Renewable Fuel
EthanolStarch from corn, wheat, barley, oats, rice, or sorghum

- Dry mill plant
- Process heat derived from coal
- Combined heat and power(CHP)
- Fractionation of feedstocks
- Membrane separation of ethanol
- All distillers grains are wet

Renewable Fuel
EthanolCellulose and hemicellulose from cornstover, switchgrass, miscanthus, wheat straw, rice straw, sugarcane bagasse, forest waste, yard waste, or planted trees- Enzymatic hydrolysis of cellulose
- Fermentation of sugars
- Process heat derived from lignin
Cellulosic Biofuel
EthanolCellulose and hemicellulose from cornstover, switchgrass, miscanthus, wheat straw, rice straw, sugarcane bagasse, forest waste, yard waste, or planted trees- Thermochemical gasification of biomass
- Fischer-Tropsch process
Cellulosic Biofuel
EthanolSugarcane sugar- Process heat derived from sugarcane bagasseAdvanced Biofuel
Biodiesel (mono alkyl ester)Waste grease, waste oils, tallow, chicken fat, nonfood grade corn oil- TransesterificationBiomass-Based Diesel
Biodiesel (mono alkyl ester)Soybean oil and other virgin plant oils- TransesterificationRenewable Fuel
Cellulosic dieselCellulose and hemicellulose from cornstover, switchgrass, miscanthus, wheat straw, rice straw, sugarcane bagasse, forest waste, yard waste, or planted trees- Thermochemical gasification of biomass
- Fischer-Tropsch process
- Catalytic depolymerization
Cellulosic Biofuel or Biomass-Based Diesel
Non-ester renewable dieselWaste grease, waste oils, tallow, chicken fat, nonfood grade corn oil- Hydrotreating
- Dedicated facility that processes only renewable mass
Biomass-Based Diesel
Non-ester renewable dieselWaste grease, waste oils, tallow, chicken fat, nonfood grade corn oil- Hydrotreating
- Coprocessing facility that also processes petroleum feedstocks
Advanced Biofuel
Non-ester renewable dieselSoybean oil and other virgin plant oils- Hydrotreating
Renewable Fuel
Cellulosic gasolineCellulose and hemicellulose from cornstover, switchgrass, miscanthus, wheat straw, rice straw, sugarcane bagasse, forest waste, yard waste, or planted trees- Thermochemical gasification of biomass
- Fischer-Tropsch process
- Catalytic depolymerization
Cellulosic Biofuel


For fuels that have not yet been assigned a pathway, the EPA proposes a regulatory mechanism whereby a producer can temporarily assign its renewable fuel to a category if it meets certain requirements.   This is referred to as utilizing default D codes.  The producer would utilize the D code that best represents its combination of fuel type, feedstock, and production process.


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