A well-to-wheel life cycle assessment (LCA), conducted by synthetic fuels producer Greyrock and the National Renewable Energy Laboratory (NREL), has measured the potential reduction of greenhouse gases and criteria pollutant emissions from the use of synthetic fuels directly converted from flare gas.
A Greyrock flare gas-to-fuels conversion process at an Ohio oil well served as the base case for the study. The liquid fuel produced directly from methane and other wellhead gases (associated gas) that would otherwise be burned or flared gas primarily consists of premium synthetic diesel with a small amount of synthetic gasoline.
The Greyrock Ohio plant produces directly about 11,007 liters per day of fuel, resulting in an average plant thermal efficiency of approximately 58 percent or a conversion efficiency of approximately 44 percent when all gas inputs (including feedstock and gas for parasitic/burner loads) are used in the calculation. This fuel comprises 8,694 and 2,313 liters per day of synthetic diesel and synthetic gasoline, respectively.
The synthetic diesel and synthetic gasoline are blended at 20 and 10 volume percent with petroleum diesel and gasoline, respectively, in the LCA scenario. While the Greyrock synthetic diesel fuel can be used neat, a blend of 20 percent Greyrock synthetic diesel and petroleum-derived diesel was found to significantly improve engine performance, increase fuel economy and reduce emissions compared to the use of petroleum-derived diesel.
This blend was also found to reduce criteria air pollutant emissions by an average of 28, 18, 24 and 5.5 percent, respectively, for hydrocarbons, particulate matter, carbon monoxide and nitrogen oxides from 1996 to 2015 diesel vehicles.
There is a global potential to produce up to 71.1 billion liters (18.8 billion gallons) of synthetic fuel per year from flare gas. The analysis shows that the beneficial use of globally available flare gas for the production and use of synthetic fuel could reduce worldwide emissions of carbon dioxide and methane by up to 356 and 5.96 million metric tons per year, respectively. Criteria emissions could be reduced by up to 23.3, 0.37, 42.4, and 61.3 million metric tons per year globally for carbon monoxide, particulates, nitrogen oxides and hydrocarbons, respectively.
Research results are published in the International Journal of Energy and Environmental Engineering.