by John B. Cornwell and David W. Johnson
Abstract
Hydrogen fluoride (HF) is used in the petroleum industry as a catalyst in the alkylation process for producing high octane gasoline components. Over the past several years, an increasing awareness of the hazards associated with an accidental release of HF has resulted in a review of the potential hazards associated with the acid. In a typical alkylation unit, a release of anhydrous HF will result in an airborne aerosol cloud that contains HF vapor and HF droplets. Experiments (Goldfish tests, aerosol release [Blewitt, et al., 1987a]) and acci- dents (Marathon vapor release [EPA, 1993]) indicate that the formation of an aerosol may be one of the single most important parameters that determines the size of the hazard zone.
Over the past several years, different mitigation systems have been designed to reduce the impact of an HF release. The systems have varied from active systems that are designed to reduce the duration of an acid release or absorb acid out of the released cloud, to passive systems that alter the nature of the acid itself. In this paper, three current and proposed mitigation systems will be reviewed. Each system will have advantages and disadvantages relative to the others. For each system, a release from a generic HF alkylation unit will be evaluated. The effect of the mitigation system on the rate at which acid reaches the atmosphere, as well as the downwind travel distance to a toxic endpoint, will be calculated. The three mitigation systems to be evaluated are:
Several studies [Technica, 1990; Maher, Kaiser, and Alderman, 1994] have attempted to compare the risk of using HF as the alkylation acid to the risk associated with the use of sulfuric acid (H2SO4) as the alkylation acid. A key component to any risk analysis study is the accurate calculation of the source term. Considerably more information is now available for calculating the acid release rates. As a point of comparison, the release rates and dispersion distances for an equivalent release of H2SO4 will also be included in the analysis.