In situ optical measurements of hydrofluoric acid aerosols

Abstract

Abstract Large scale field tests were conducted to investigate the effectiveness of water spray mitigation on accidental releases of hydrogen fluoride (HF). This paper reports on a particular aspect of the test programme, namely the measurement of HF aerosol properties with an in situ optical instrument. Aerosol was generated by releasing HF through a sharp-edged orifice into the downwind direction of a large flow chamber. Release conditions were similar to conditions in an alkylation unit or a typical HF storage tank in summer weather. Aerosol properties were measured by inserting the probe at two downstream locations from the release point and at several radial positions within the emanating aerosol plume. A total of 86 usable aerosol data sets were obtained during the test period. As many as 10 data sets were acquired for a typical 11 min duration HF release. The PCSV-P optical instrument measured predominantly submicron aerosol particles near the release orifice. The aerosol then grew to larger particles further downwind. This points to the formation of the aerosol through vaporization-condensation as opposed to a conventional shear spray. HF release pressure and temperature, air humidity, radial position in the plume, and type of acid did not appear to have any significant effect on the measured size distributions for the range of conditions investigated. Understanding the size characteristics of the aerosol is particularly important in determining plume dispersion. The size distribution and dispersion characteristics are important both for design of water spray mitigation systems and as inputs for numerical models. Modelling simulates a broader range of release conditions than can be studied in a necessarily limited series of high cost experiments.