The Argonne National Laboratory’s Systems Assessment Center announced the 2021 release of the suite of GREET models and associated documentation. GREET (Greenhouse gases, Regulated Emissions, and Energy use in Technologies) is a life-cycle analysis (LCA) tool, structured to examine systematically the energy and environmental effects of a wide variety of transportation fuels and vehicle technologies in major transportation sectors (i.e., road, air, marine, and rail) and other end-use sectors, and energy systems.

Within the transportation sector, GREET covers road, air, water, and rail transportation sub-sectors. Recently, GREET was expanded to cover the building sector. Historically, GREET includes LCA of various materials such as steel, aluminum, cement, and different plastic types. Argonne has expanded and updated the model in various sectors in GREET 2021.

GREET offers two free platforms: the GREET.net model and the GREET Excel model.

Major expansions and updates were made to energy products, vehicles and materials.

Energy products. In addition to updating corn ethanol pathways to reflect the significant evolution of that industry over the past two decades, and to updating biodiesel/renewable diesel pathways (including adding carinata as a feedstock), the GREET team included the Supply Chain Sustainability Analysis (SCSA) fuel pathways for renewable gasoline, diesel, and hydrocarbon fuel pathways from lignocellulosic biomass and municipal wastewater sludge.

The SCSA tracks and demonstrates the progress of energy and environmental performances of the individual biofuel pathways that undergo continuous development, the GREET team noted.

For the GREET 2021 release, the team also added eight pathways for fuels for use in engines co-optimized with drop-in biofuel blends to improve engine efficiency performance and reduce engine-out emissions. (Co-Optima)

One pathway produces methanol from biomass gasification, which is blended with a petroleum gasoline blendstock and designed to improve engine efficiency for light-duty multi-mode (MM) engines. The other seven pathways, representing a combination of biochemical and thermochemical conversion technologies, produce bio-blendstocks capable of reducing engine-out emissions for mixing-controlled compression ignition (MCCI) engines in heavy-duty vehicles. These MCCI fuels are diesel-like bio-blendstocks blended with petroleum diesel.

GREET 2021 also adds eight sustainable aviation fuel (SAF) production pathways using the data in the CORSIA (Carbon Offsetting and Reduction Scheme for International Aviation) supporting document released by International Civil Aviation Organization (ICAO).

Further, a new co-processing module is intended to examine the impact of co-processing of bio-feedstocks in petroleum refineries. The GREET team used linear programming (LP) modeling of petroleum refineries to develop energy and mass balances of co-processing of renewable feeds in hydrotreaters, hydrocrackers, and fluidized catalytic crackers of conventional petroleum refineries.

The team examined three renewable feedstocks (soy oil, used cooking oil, and tallow) to hydrotreater and hydrocracker along with a case inserting pyrolysis oil into fluid catalytic cracker, all with 10% by volume of renewable feedstocks for each unit.

While the co-processing module is completed in the current release of GREET 2021, parametric assumptions are still undergoing research and review.The team plans to update the current placeholder parametric assumptions with actual assumptions in a new version of GREET after releasing a forthcoming report/paper documenting all key parameters and analysis results.

Based on discussion with National Renewable Energy Laboratory (NREL), the GREET team created three major updates of the parameters of various cellulosic ethanol production pathways in GREET 2021: ethanol yield, co-produced electricity, and material inputs. The feedstocks of cellulosic ethanol include corn stover, switchgrass, miscanthus, forest residue, willow, poplar, forage sorghum, and the biogenic portion of municipal solid waste (MSW).