by David W. Johnson
Abstract
In the summer of 1991, an experimental program was conducted to determine the amount of equilibrium sulfuric acid that would pool, or fall to the ground, when the acid, both alone and as an emulsion with alkylation hydrocarbons, was released to the atmosphere. The acid/hydrocarbon emulsion was prepared in a highly agitated vessel and held at conditions that encompassed the normal range of alkylation unit operating conditions. The fluid was released to the atmosphere through square-edged circular orifices from 0.032 to 0.50 inches in diameter, circular tubes 0.25 and 0.5 inches in diameter, and a simulated flange gasket failure.
Thirty-six release runs were made, three runs using alkylation equilibrium acid (obtained from an operating commercial alkylation unit) and thirty-three runs using an acid/hydrocarbon emulsion. Usable data was obtained from thirty-one emulsion runs. The releases of equilibrium acid alone gave recoveries between 100.3 and 100.9 percent, indicating a small bias of recovery over release. Of the twenty-eight runs made by releasing an equilibrium acid/hydrocarbon emulsion, an average of 97.6 percent of the acid released was recovered (i.e., would have fallen to the ground). The capture percentages were grouped closely around the average, ranging from 92.5 to 100.4 with a standard deviation of 1.6.
Changes in release geometry, storage temperature, storage pressure, ratio of acid to hydrocarbon (for hydrocarbon/equilibrium acid emulsion releases), or the propane content of the hydrocarbon did not change the amount of acid recovered by more than the estimated experimental error of the measurements.
Small bubbles were observed to float above the capture equipment during all of the acid/hydrocarbon releases. These bubbles were suspected to be composed of a thin layer of equilibrium acid surrounding an inner core of hydrocarbon vapor.