An overview of HCN emissions from FCCU’s and their potential impacts on human health

Report no. 1/19: This report provides an overview of the monitoring methods and abatement techniques available for hydrogen cyanide (HCN) emissions in fluid catalytic cracking units (FCCU’s). Recommendations are made for emission factors (EF’s) that can be used to estimate HCN emissions from European FCCU’s (for two different operating modes, namely full and partial coke burn) for E-PRTR reporting purposes. An overview of the potential health effects of HCN is given. The EPA OTM-29 wet chemistry method and the instrumental FTIR technique are the two HCN monitoring techniques used in refineries. Currently applied abatement techniques for flue gas cleaning at FCCU’s are not specifically designed for HCN emission control, but for particulate matter, NOx, SOx and CO reduction.

Emission factors for each mode of operation of an FCCU were developed using measurements undertaken on 10 FCCU’s in European refineries together with data reported by the US EPA. The emission factors derived are: 0.58 kg HCN/t coke burn for full burn FCCU’s, and 0.042 kg HCN/t coke burn for partial burn units. It is recommended that these be used for E-PRTR reporting purposes if measured values are not available. A dispersion modelling assessment was conducted to establish the potential risk that HCN emissions from FCCU’s could pose to human health. All runs showed that the predicted HCN ground-level concentrations were below the US EPA reference concentration (RfC) of 8 × 10-4 mg/m³ (0.8 μg/m3) for chronic inhalation exposure. This indicates that HCN emissions from the 10 European FCCU’s tested are not considered a potential risk for human health.