Modeling and control of a leaching unit for sunflower oil extraction

In the leaching process alternative solvents to hexane have been studied to reduce the emissions of volatile organic compounds to the atmosphere. Ethanol is considered as an alternative solvent because it is cheap and it can be produced by fermentation from a large variety of biological materials using simple technology. In this paper a phenomenological-based semi-physical model (PBSM) for ethanolic extraction of oil from sunflower collets in a counter-current flow process is derived. In addition, a Proportional-Integral-Derivative (PID) controller and a Model Predictive Controller (MPC) are tested. The response of the controlled variable in both controllers to disturbance rejection, manipulating the ethanol flow, was compared. It was observed that the PID controller needs more than 1 hour to stabilize the controller response while the MPC does it in some minutes.

I. Introduction

Over the last five decades, the industrial oil extraction process has changed little, though there have been several technical developments regarding its optimization and better control. The conventional process procedure involves three main successive unit operations. Seed preparation includes cleaning, pre-heating, crushing, and cooking. Mechanical extraction produces a first oil fraction and a press cake, also called "oilcake", containing 16-24% of oil after continuous pressing, which depends on the variety of the treated seeds. Li et al. propose the counter-current flow extraction from ground oilcakes using n-hexane as a solvent [1]. However, residual traces of organic solvents are always found in the oil, especially when hexane is used, leading to a final purification step. For these reasons, alternative extraction processes are always under development for reducing environmental impact by decreasing the toxic residues and effluents and by increasing the use of the by-products [2]. One possibility is the use of ethanol instead of n-hexane [3].