Multiphase Behavior Simulation of Using the Supercritical Co2 to Extract Oil in Oily Sludge

Injecting supercritical CO 2 (SCCO 2 ) into the oily sludge to recover crude oil is an economical and effective method for oily sludge disposal. The SCCO 2 extraction process is accompanied by the components exchange between different phases(e.g., L 1 L 2 V) and ultimately reaches a multiphase equilibrium state, such as the L 1 L 2 two-phase equilibrium, under new thermodynamic conditions. Accurate prediction of phase behavior is crucial for determining the optimal extraction conditions and designing the SCCO 2 extraction process. However, the traditional cubic equation of state (EoS) ignores the hydrogen bond association between polar molecules such as asphaltene and H 2 O in crude oil, which lacks sufficient complex flexibility for capturing such complex phase behaviors. This paper proposed a new multiphase equilibrium model by developing a new characterization method for crude oil based on the cubic plus association equation of state (CPA EoS). A total of 34 sets of measured multiphase equilibrium data at temperatures from 280.45K to 362.55K are applied to validate the proposed model. Results show that this method enables to predict up to three-phase equilibrium, and the absolute average relative deviation between the predicted phase boundaries pressure and measured data is less than 11.81%, while the liquid volume fraction represents the oil extraction efficiency. Finally, three case studies are designed to research variations of liquid phase molar volume fraction with the pressure in the extraction system. It is found that the optimal extraction pressure required for the aqueous-containing system is higher than that of the aqueous-free system because the aqueous phase reduces the SCCO 2 solubility in crude oil. Hence, increasing the extraction pressure and the lasting time is worthwhile to improve the extraction efficiency for the aqueous-containing system.