Simulation of a supercritical carbon dioxide extraction plant with three extraction vessels

Although SuperCritical (SC) Fluid Extraction (SCFE) has been successfully applied commercially the last three decades, there is no systematic procedure or computational tool in the literature to scale-up and optimize it. This work proposes an algorithm to simulate dynamics in a multi-vessel (≥3) high-pressure SCFE plant where extraction vessels operate in batches, and is thus forced to use simulated-countercurrent flow configuration to improve efficiency. The algorithm is applied to a three-vessel SCFE plant using a shrinking-core model to describe inner mass transfer in the substrate. As example, the extraction of oil from pre-pressed seeds using SC CO₂ at 313 K and 30 MPa is simulated. After three cycles the process reaches a pseudo-steady-state condition that simplifies the estimation of plant productivity. Use of a three- instead of two-vessel SCFE plant increases oil concentration in the stream exiting the plant and decreases CO₂ usage at the expense of increasing extraction time.