ENV-17-11 Finding a Correlation: FCCU Operating Parameters vs HCN Emissions – Round 2!

Description:

Hydrogen cyanide (HCN) emissions from fluid catalytic cracking units (FCCUs) were historically considered inconsequential and were not federally required to maintain separate permitting, emissions reporting, or regulatory requirements. In 2011, the United States Environmental Protection Agency (U.S. EPA) initiated an Information Collection Request (ICR) as part of their emission standard review and “residual risk” evaluation for existing refinery standards, including New Source Performing Standards (NSPS) and Maximum Achievable Control Technology (MACT) standards. The ICR included a stack testing component requiring 10 refineries to stack test FCCUs for select hazardous air pollutants (HAPs), including HCN. The results demonstrated that HCN emissions from FCCUs were higher than expected. In response, the U.S. EPA revised the published AP-42 emissions factor and updated MACT Subpart UUU to include an HCN stack testing requirement in addition to other changes. Currently, the U.S. EPA maintains that complete combustion is the best method to control HCN emissions, and they use carbon monoxide (CO) as a surrogate for limiting HCN emissions, since both are products of incomplete combustion. This approach is advantageous for industry since it does not require any additional controls, monitors, or best management practices outside of those required for CO. However, federal and state agencies may use the results of the required HCN stack tests to establish new emission standards or operating limitations if warranted by HCN testing data. In anticipation of the U.S. EPA performing a similar evaluation, TRICORD conducted a study in 2016 to evaluate HCN emissions compared to various FCCU operating parameters. In this 2017 follow up evaluation, TRICORD incorporates historical stack test results, new stack results, and other FCCU operating data to further evaluate potential correlations.