BUBBLE DETECTION IN FLOTATION COLUMNS BASED ON CIRCULAR HOUGH TRANSFORM
A bubble detection technique based on Circular Hough Transform (CHT) has been implemented for bubble size distribution (BSD) determination in two-phase (gas-liquid) systems. This technique allows overcoming issues related to the detection of large single bubbles as well as clusters. A high resolution CCD (charge-coupled device) camera is used to capture bubble images. The resulting digital images are automatically pre-conditioned to eliminate the background, eventual noises, and to enhance the contrast. Tests were carried out in a laboratory flotation column using different concentrations of frother and air flow-rates. Results were compared against manual (visual) count, as well as a commonly used bubble detection method based on circular particle detection (CPD). The CHT-based technique allows proper detection and measurement of bubble clusters, large bubbles, and also incomplete bubbles in the image frame. Results obtained are very similar to those resulting from manual counts. Compared to CPD algorithms, the CHT approach significantly improves D32 estimation (error of ~3% instead of ~18%) with a comparable processing time.
Bubble size distribution, Flotation process, Image processing, Hough transform.