Ammonium Salt Crystal Deposition Prediction And Corrosion Behavior Of Petrochemical System

In recent years, with the further depletion of petroleum resources, the proportionof processed high-sulfur, chlorine contained and other low-quality crude oil increasedwhich sparked widespread equipments failure and seriously affected the refineryoperation safety and economic benefits. Ammonium salt deposition and corrosion astypical failure types of low-quality crude oil processing is closely related to theprocess, equipment construction and materials, etc. Because of the complicated failuremechanism, it is difficult to predict and control, and has long been the restrictivefactors of refinery long-period safe and stable operation.Aimed at the hydrogenation reaction effluent system, the ammonium salt crystalequilibrium curve was obtained and deposition mechanism in the heat exchanger wasanalyzed based on thermodynamic calculation. The multiphase equilibrium model oftypically hydrogenation reaction effluent cooling and separation system wasestablished by Aspen simulation software and composition which easy to crystallizewas analyzed. Based on the above, the ammonium salt crystal temperature and crystalrates calculation method was established. The ammonium salt crystal of differentfeedstock composition was calculated and the main factors affecting ammonium saltcrystal clarified.For the hydrogenation reaction effluent systems multiphase system, theammonium salt particles flow and deposition calculation model was establishedaccording to Eulerian-Lagrange method and the reaction effluent air cooler CFDnumerical calculations was realized by Fluent software. Based on the calculationresults, the distribution of multiphase and the deposition of ammonium salt particlesin each air cooler bundles were obtained. The quantitative prediction method ofammonium salt deposition was achieved and the air cooler danger areas of ammoniumsalt deposition were obtained. In order to verify the failure prediction results, other inservice air coolers were inspected using the infrared camera.The ammonium salt corrosion experiment apparatus was built to study thecorrosion resistance of five commonly used materials in under-deposit and saturatedsolution environment of ammonium chloride. Combined with the corrosion productsmorphology and composition analysis by scanning electron microscopy andspectroscopy, the under-deposit corrosion behavior was obtained under differenttemperature and humidity. The mechanism of ammonium salt under-deposit corrosion and corrosion forms conversion condition was proposed.The electrochemicalcorrosion behavior of five materials in saturated ammonium chloride solution wasstudied and the corrosion resistance was obtained by polarization curves andopen-circuit potential. The passivation characteristics and corrosion product filmbehavior of five materials under flow conditions was also studied by polarizationcurves and corrosion morphology analysis.The innovation of the paper is as follow: the ammonium salt crystal calculationmodel of complex petrochemical multiphase system was established and the mainfactors affecting ammonium salt crystal was clarified based on thermodynamiccalculation and process simulation. The ammonium salt deposition numericalsimulation method was established and the quantitative prediction ammoniumdeposition was achieved based on the inter-phase interaction of solid containedmultiphase. The ammonium salt corrosion experiment apparatus was built andunder-deposit corrosion and corrosion forms conversion conditions was obtained. Theresearch results are expected provide foundations for refinery ammonium salt crystaldeposition risk assessment, the design and materials selection of key equipment.