Method for Simulating the Effect of Pressure in Transfer Lines on the Corrosivity of Hacs Available to Purchase

Abstract

The decrease of world reserves of conventional crude has led the oil industry to increase the percentage of so-called opportunity crudes in blends entering the distillation units. Among opportunity crudes are the high acid crudes, which cause corrosion problems in the temperature range 220-400⁰C. The heterogeneity in the chemical nature of naphthenic acids present in crude hinders the development of accurate predictive tools. Many studies have been done to evaluate the effect of temperature and hydrodynamic conditions on the corrosivity of naphthenic acids. However, the effect of pressure on the corrosivity of naphthenic acids, considering these compounds as a complex mixture, has not been studied. In this work, the effect of the pressure of the transfer lines on the distribution of the molecules of naphthenic acids in the vapor and liquid phases of crude oils was simulated. Considering that naphthenic acids are non-corrosive in the vapor phase, in this paper the variation of acidity in crudes due to evaporation processes in the transfer lines was evaluated. Using a process simulation program, the transfer lines between heating furnace and the atmospheric distillation tower were simulated. For this purpose, homologous series of naphthenic acids were introduced in process simulation as hypothetical compounds. To each crude oil from the distillation curves and the acidity of the cuts, the distribution profile of the naphthenic acids was determined. From this information the mole fractions of hypothetical compounds were calculated to simulate the distribution of naphthenic acids for each crude oil. With the proposed methodology, the reduction or increase of acidity in the liquid phase with the variation of pressure and/or temperature can be determined. It is observed that depending on the nature of the crude oil, the naphthenic acids may have a reduced acidity in the liquid phase up to 45%. This information can be used to improve strategies to control corrosion in distillation units during the processing of high acid crudes.