Express estimation of crude oil TBP curves only from the viscosity of the crude oil

Express estimation of crude oil TBP curves only from the viscosity of the crude oil
G. Argirov, S. Ivanov, G. Cholakov
Argirov.Georgi.S@neftochim.bg
Bulgaria, 8104 Bourgas, Lukoil Neftochim Bourgas AD, Heavy Residue Upgrading Complex-Project
Abstract
Crude oil TBP curves are well recognized as an important characteristic, needed to determine the potential of fractions obtained by distillation, to monitor distillation units, to verify the identity of crude oil samples, etc. They can be obtained experimentally or calculated by a variety of methods, which have different precision. The precision of the particular method determines the applicability of the obtained TBP data.
Riazi’s two-parameter distribution model and experimental crude assay data for 117 crudes from all over the world have been used to derive a model for prediction of true boiling point (TBP) curves from the kinematic viscosity of the samples at 37,8 oC. The model was tested by prediction of the cumulative mass fractions of all studied crude samples.
It was found that the TBP distribution for fractions boiling up to 340 oC could be predicted with an average relative deviation of the order of 6 %. This is higher than the respective deviation of previously proposed models, e.g. - Riazi’s model, with an average deviation of 3.3 %. However, these models require experimental data for several properties, while in practical terms the precision of our model is sufficient to detect any significant upsets in the operation of refinery crude distillation units (CDUs), so its computerized procedure may be used as a quick tool for monitoring of the CDU operation.
INTRODUCTION [Excerpt]
For modern refineries frequent crude oil switching and disturbances in crude distillation unit (CDU) operations often propagate into bigger issues downstream. Managing the change of crudes and diminishing disturbances require regulatory control of the daily performance necessary to respond quickly and adequately to setpoint changes. The quality and value of a crude oil significantly depend on its TBP (“true” boiling point) distillation curve. Unfortunately, the experimental determination of TBP curves is costly and time consuming, so it is impractical to use them as a tool for daily monitoring of CDUs. This calls for the development of TBP calculation methods, requiring a minimum of experimental data, but having sufficient precision for daily monitoring of CDU operations. Riazi developed a three-parameter distribution model, which is widely used for estimation of the boiling points and other properties of C7+ fractions of petroleum fluids [1, 2]. It predicts TBP distributions with high precision, when at least three experimental points of the TBP curve of the crude are available [3]. Moreover, it can be used for predictions of the rest of the distillation curves, needed in petroleum processing (ASTM D 86, EFV, CD, etc.) If distillation data are not available, the values of at least three crude oil properties (molecular mass, density and refraction index) have to be known. Riazi’s method can not be used directly for daily monitoring of CDU operations, because of the need of significant amount of tests, but it gives the general lines along which this can be achieved. Stratiev et al. [4, 5] developed further Riazi’s ideas and showed that the boiling temperature and other property distributions can be calculated when experimental density and distillation data up to 300 oC are an available. The Lukoil Neftochim Bourgas AD (LNB) refinery has developed a data base of potential feedstocks - 117 crude oil assays, characterized by TBP curves, density, sulphur, viscosity, metals, Conradson carbon, and asphalthene content of crude oils and TBP cuts. The crude oils originate from different parts of the world . The aim of this work is to use the LNB database and Riazi’s ideas, for development of a model for crude oil TBP curve prediction from one routine measurement – the crude oil’s kinematic viscosity at 37.8 oC.
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