LIFE CYCLE ANALYSIS FOR BIOFUEL PELLET PRODUCTION ON RECLAIMED MOUNTAIN TOP COAL MINING SITES IN PIKE COUNTY KENTUCKY

Mountaintop coal mining and valley filling drastically disturbs soils and removes essentially all soil organic carbon (SOC) from sites. Growing crops for biofuels on these marginal lands could be a practical way to sequester and offset carbon emissions from coal production and consumption.

A life cycle model was developed to quantify the initial carbon density of the site and to determine the fuel to energy ratio, and the carbon benefits and losses associated with biofuel production on a reclaimed grassland mine site in Pike County Kentucky which was recently planted with several experimental biofuels crops-- corn, switchgrass, miscanthus, cottonwood, sycamore and black locust.

The model defines “Carbon benefits” as CO₂ emissions avoided from fossil fuels and carbon sequestered if uptake rate is greater than reclaimed grassland rate. “Carbon losses” are CO₂ emissions from production and carbon not sequestered if uptake rate is lower than reclaimed grassland rate. A 65% crop yield was assumed for all crops, and further long-term research is needed to constrain this estimate. Model inputs include crop production on the reclaimed mine sites, transported to pelleting station, pelletized, transported by truck to a river terminal, and transported by barge to coal plants to be burned for electricity. Initial carbon density is determined by collecting soil samples and determining the percentage of SOC using carbon 13 isotopic signatures. The SOC uptake rate of these crops is unknown, so rates less than, equal to and greater than reclaimed grassland and forest rates were used to provide a range of potential C sequestration rates associated with soils. A long-term soil sampling project has also been established to constrain these estimates.

The initial carbon density of the site was 11.6 Mg/ha. All crops had fuel to energy ratios greater than one and positive carbon savings if the SOC uptake rate was equal to the reclaimed grassland uptake rate. Crops with higher yields had greater fuel to energy ratios and greater carbon savings. The model heavily relied on estimates because of missing or inconclusive literature dealing with yields, pellet processing and SOC uptake rates. Results suggest promise for biofuel production however more refined measurements are needed for more conclusive results.