Development and Validation of a Reduced-Index Dynamic Model of an Industrial High-Purity Column

A depropanizer column is a high purity distillation unit, whose modeling is challenging due to its high nonlinear behavior and intricate dynamics. Also, depending on the assumptions, a differential algebraic equation (DAE) system of high index can arise in the modeling of the column. Such systems create significant difficulties to numerical simulation. Phenomenological hydraulic relationships can be used to avoid the index problems. However, these relationships may rely on unknown and arbitrarily assumed parameters and project details. This paper presents an alternative modeling approach called dynamic design using proportional action (DDPA), which is used to simplify the hydraulic and pressure drop relation for a distillation unit. The DDPA approach generates a reduced index dynamic model by adding equations similar to a proportional controller with arbitrarily large gain. A depropanizer column was modeled using DDPA, and the model was validated with real process data obtained in an industrial-scale depropenizer column located at Refinaria de Paulínia, Paulínia, São Paulo, Brazil, and owned by Petrobras S.A. The results show that the model with DDPA is able to predict the actual column dynamic behavior properly

Prediction of Crude Oil Properties and Chemical Composition by Means of Steady-State and Time-Resolved Fluorescence

Steady-state and time-resolved fluorescence measurements are reported for several crude oils and their saturates, aromatics, resins, and asphaltenes (SARA) fractions (saturates, aromatics and resins), isolated from maltene after pentane precipitation of the asphaltenes. There is a clear relationship between the American Petroleum Institute (API) grade of the crude oils and their fluorescence emission intensity and maxima. Dilution of the crude oil samples with cyclohexane results in a significant increase of emission intensity and a blue shift, which is a clear indication of the presence of energy-transfer processes between the emissive chromophores present in the crude oil. Both the fluorescence spectra and the mean fluorescence lifetimes of the three SARA fractions and their mixtures indicate that the aromatics and resins are the major contributors to the emission of crude oils. Total synchronous fluorescence scan (TSFS) spectral maps are preferable to steady-state fluorescence spectra for discriminating between the fractions, making TSFS maps a particularly interesting choice for the development of fluorescence-based methods for the characterization and classification of crude oils. More detailed studies, using a much wider range of excitation and emission wavelengths, are necessary to determine the utility of time-resolved fluorescence (TRF) data for this purpose. Preliminary models constructed using TSFS spectra from 21 crude oil samples show a very good correlation (<i>R</i>² > 0.88) between the calculated and measured values of API and the SARA fraction concentrations. The use of models based on a fast fluorescence measurement may thus be an alternative to tedious and time-consuming chemical analysis in refineries