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NREL Biorefinery Air Pollutant Emissions Analysis Explores Mitigation Options

NREL’s Biofuel Air Emissions Analysis team led by Danny Inman and Garvin Heath is researching non-greenhouse gas air pollutant emissions of biorefineries. The novel research has garnered attention and Environmental Science & Technology, an ACS journal, has just published an article about the work. "Potential Air Pollutant Emissions and Permitting Classifications for Two Biorefinery Process Designs in the United States" by Annika Eberle, Arpit Bhatt, Yimin Zhang, and Garvin Heath describes the team's modeling of non-greenhouse gas air pollutant emissions for two feasibility-level biorefinery designs: (1) a biochemical technology pathway focused on biological conversion of cellulosic sugars and (2) a thermochemical pathway focused on fast pyrolysis of whole biomass.

The study shows that if both biorefineries were built as designed (size of 2,000 dry metric tons of biomass/day with specific unit processes and designed controls) they would likely be classified as major sources under the Clean Air Act’s New Source Review program. Because the major source classification can influence the duration of the permitting process and thereby impact the cost of capital and the fuel selling price, the authors explore technically feasible emission control technologies and process modifications that could allow the facilities to achieve minor source classification.

This work can assist biorefinery developers with the air permitting process and inform regulatory agencies about potential permitting pathways for novel biorefinery designs, leading to reduced costs of permitting and, ultimately, of the fuel produced.

One of the First Studies to Compare Air Emissions and Control Options for Multiple Biorefineries

Although the technical, economic, and regulatory feasibility of advanced biorefineries have been explored previously, no study has developed detailed estimates of air pollutant emissions for multiple early stage biorefinery designs using detailed engineering design software tools. By estimating air emissions for multiple emerging biofuel conversion pathways and by allowing biorefinery developers to better understand how these emissions impact their permitting requirements, this study could help mitigate uncertainty in the air permitting process.

"Demonstrating that the modeled biorefinery designs can achieve compliance with applicable federal air quality regulations is key to their viability," says Heath. "Add to that the facts that we're estimating the cost of achieving compliance and its effect on minimum fuel selling price and that we're investigating alternative pathways to achieving compliance and you have an important body of work–much of which has not been done before."

This article is one of a series of publications documenting NREL's research into the non-greenhouse gas air pollutant emissions of biorefineries. The team also conducts research about air emissions from other stages of the biofuel supply chain.  View the recent articles and reports and learn more about NREL's work in Analyzing Air Pollutant Emissions from the Biofuel Supply Chain.

—Kristi Theis