(131c) Residual Solvent Release from Froth Treatment Tailings-Part 2

In oil sand processing, bitumen froth treatment tailings originating from tailings solvent recovery unit (TSRU) contain trace amounts of solvent. Currently, the TSRU tailings are deposited into tailings ponds under water. However, in future operation, the tailings will also be deposited on a beach. When the TSRU tailings are deposited part of the residual solvent inevitably evaporates and is released to atmosphere.  It is important to understand the behaviour of the solvent release from the TSRU tailings. We conducted a research program to study the solvent release from tailings for underwater deposition and aerial deposition (on beach). The study on solvent release from underwater deposition was presented in AIChE conference 2014. In this presentation, the study on solvent release from aerial deposition is reported.

In this work, we studied the solvent release from aerial deposited tailings in two approaches: 1) kinetic modeling, and 2) experimental testing. A kinetic model based on continuity equations was found to successfully model solvent release from unsaturated tailings under aerial conditions at ambient temperature. The calculated solvent mass transfer rate agreed well with the experimentally measured value. However, at temperatures above the solvent boiling point, boiling solvent generated bubbles and produced foam. The foam formation changed the characteristic of tailings and made the modeling very difficult. Therefore, at temperatures above boiling point of the solvent, the model becomes inapplicable due to foam formation and volume increase of vapour.  It seems that the mechanism of solvent release from aerially deposited tailings at high temperature is based on formation of pentane vapour bubbles and subsequent plug flow of the bubbles to the top of the deposit.