Molecular Characterisation of Petroleum Streams
Luyi Liu , Nan Zhang
The highly competitive market in the oil refining industry forces refiners look for more detailed information of both feedstocks and products to achieve the optimal economic performance. Due to stricter environmental legislations, the molecular level characterisation has been investigated by various researchers and shows promising advantages in modern refinery design, simulation and optimisation. Although various molecular characterisation methods have been developed, there is an unavoidable trade-off between keeping astronomical molecule details and practicality in industrial applications. In the meantime, many of these methodologies have different characteristics and different focuses according to the particular application purpose. Our aim is hence to tackle the problems of developing manageable and practical technical solutions for molecular characterisation of petroleum fractions from vary refinery processes.
The objective of this work is to provide a credible framework of light petroleum representation and correlate bulk properties with molecular composition information. Hence the contribution on properties from each molecular type of a refining stream can be quantitatively defined.
A pseudo-component based approach is developed within a modified MTHS (Molecular Type Homologous Series) matrix framework (Peng, 1999) to represent the molecular information of a particular refining stream. This proposed methodology incorporates both molecular type and pseudo-component information by the conjunction of homologous series and boiling points in the matrix framework. To increase the usability of this method, a 3-parameters gamma distribution is introduced to describe the composition of each structural molecular type. Typical PIONA (paraffin, iso-paraffin, olefin, naphthene, aromatic) analysis, ratios between each homologous types and the percentage of particular carbon type are considered as well as the distillation curve and the density of a stream. The proposed methodology is applied to a gasoline stream and a diesel stream in case studies to illustrate feasibility and reliability. The results show acceptable deviations in predicting molecular compositions and other bulk properties such as distillation profile, density, octane number of gasoline stream and centane index of diesel stream with measured data.
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