Use of Pipeline Pressure Gradients to Monitor Inline Polymer Flocculation of Oil Sand Fine Tailings

Abstract

In Canada’s oil sands industry, the processing and storage of fluid fine tailings is important because it directly impacts land usage and reclamation, water and thermal energy requirements as well as environmental stewardship and mine sustainability. A key technology used for this purpose is inline flocculation, wherein existing inventories of fluid fine tailings are withdrawn from tailings storage facilities and mixed with polymer flocculants. These flocculated tailings can be then sent through additional process stages (e.g. evaporation, centrifugation, filtration) to promote dewatering and improved geotechnical characteristics of the resulting deposits. The polymer type, dosage and inline mixing conditions primarily dictate the efficacy of the inline flocculation process. Presently, numerous measurements are taken to establish flocculation performance. Some of these require samples to be collected and analyzed, meaning that such measurements cannot be used for real-time process control. Others, such as online FBRM (focus beam reflectance measurement), can be used for real-time process control but are often challenging and expensive to deploy in a commercial operation. The present study represents a preliminary assessment of the use of pressure measurements to monitor flocculation performance using a pilot-scale inline flocculation rig. Tests were conducted at different flow rates and polymer injection rates/concentrations. The test rig was fitted with 4 differential pressure sensors positioned at different axial locations. The pressure gradients measured just downstream of the inline mixer were primarily dictated by the production, and subsequent break-up, of the shear-sensitive floc structures and thus were highly sensitive to changes in polymer dosage at any given fluid tailings feed rate. A relationship among conventional performance metrics (e.g. floc size from FBRM) and maximum pressure gradient measured downstream of the mixer was observed, i.e. the same optimal polymer dosage was indicated by conventional measures and peak pressure gradient.