Abstract
The prediction of phase equilibria for hydrocarbon/water blends in separators, is a subject of considerable importance for chemical processes. Despite its relevance, there are still pending questions. Among them, is the prediction of the correct number of phases. While a stability analysis using the Gibbs Free Energy of mixing and the NRTL model, provide a good understanding with calculation issues, when using HYSYS V9 and Aspen Plus V9 software, this shows that significant phase equilibrium uncertainties still exist. To clarify these matters, n-octane and water blends, are good surrogates of naphtha/water mixtures. Runs were developed in a CREC vapor–liquid (VL_Cell operated with octane–water mixtures under dynamic conditions and used to establish the two-phase (liquid–vapor) and three phase (liquid–liquid–vapor) domains. Results obtained demonstrate that the two phase region (full solubility in the liquid phase) of n-octane in water at 100 °C is in the 10−4 mol fraction range, and it is larger than the 10−5 mol fraction predicted by Aspen Plus and the 10−7 mol fraction reported in the technical literature. Furthermore, and to provide an effective and accurate method for predicting the number of phases, a machine learning (ML) technique was implemented and successfully demonstrated, in the present study.
Highlights
IntroductionSimulation software can be typically used in the oil and gas industry to provide a quick process analysis and to facilitate engineering decisions
The objectives of this work are as follows: (i) to establish the problems faced with estimating the number of phases in highly diluted octane/water mixtures when using HYSYS V9 and Aspen Plus V9, and (ii) to develop a methodology to predict the correct number of phases, using experimental data obtained in a new Chemical Reactor Engineering Center (CREC) vapor–liquid equilibrium (VL) Cell [10,11]
The three-phase equilibrium (VLL) of n-octane/water systems was first considered in the present study, using Aspen Plus V9 and HYSYS V9
Summary
Simulation software can be typically used in the oil and gas industry to provide a quick process analysis and to facilitate engineering decisions. When bitumen is extracted from oil sand and a naphthenic process is employed for froth treatment, the Naphtha Recovery Unit (NRU) is employed to recover naphtha from the tailings, for reuse in the process and to reduce the environmental impact of the process. This is an energy-intensive step, with environmental guidelines for naphtha recovery are required to be met [4]. While HYSYS V9 and Aspen Plus V9 software may be used with this objective in mind, the results regarding hydrocarbon/water mixtures from these simulations are not always reliable
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