Rotating cylinder technique for assessing the effectiveness of anti-scalants

• Novel technique for evaluating anti-scalants (AS).
• AS effectiveness analyzed from scale deposition tests on a rotating cylinder.
• In the absence of an AS scale deposition rate found to be mass transfer controlled.
• In the presence of effective AS dosage deposition shown to be independent of mass transfer rate.
• AS effectiveness assessed by dosage level providing surface deposition control.

A novel technique for evaluating the relative inhibition effectiveness of different anti-scalants is presented. The technique is based on the ability of anti-scalants to modify the scale deposition mechanism from mass transfer control to surface control. A rotating cylinder system which is known to provide well controlled mass transfer conditions is used to determine the scaling rate of a supersaturated solution dosed with various feed concentrations of an anti-scalant. Mass transfer conditions were characterized by turbulent flow at hydrodynamically smooth surface. In the absence of an anti-scalant, scale deposition is mass transfer controlled and scaling rate increases with rotation speed. With sufficient anti-scalant dosage, precipitation is modified to surface control and rotation speed has no effect on the scale deposition rate. Determination of the critical anti-scalant dosage enabling surface controlled precipitation provides a sensitive technique for comparing the relative effectiveness of different anti-scalants.