Modification of multisolid phase model for prediction of wax precipitation: a new and effective solution method

Problems related to precipitation and crystallization of waxes (solid paraffins) during production, transportation and processing of crude oil, cause major difficulties in these processes. This paper presents a modified multisolid phase model for predicting phase equilibria for oil mixtures taking into account the possible formation of a wax phase. This modified model is able to predict wax appearance point (WAP) and amount of precipitated wax in various oil samples. The vapor and liquid phases are described using the Peng–Robinson EOS. For the first three oil samples, heavy fraction properties are evaluated by use of the average properties method and for the second three oils PNA analysis is used. On the contrary to the original multisolid phase model which considers only liquid and solid(s) phases, this work considers vapor phase (in addition to liquid and solid(s) phases), and, therefore, because of this modification, prediction of pressure and composition effects on WAP will be possible. In this work, pressure effects on dead oil (stock-tank-oil, at above bubble point pressure, that there is not any gas) samples, have been studied and according to predictions suggested by previous works the WAP of oils raise as pressure increase. A second prediction based on the modified multisolid phase model refers to WAP decreases with increase of light component concentration. The calculation results obtained in this work, agree very well with experimental results and results obtained from other works.