Image analysis applied to a freeze-concentration water purification system

Freeze concentration is a promising water purification technology, specially due to the low levels of energy consumption when compared with other processes such as evaporation. Nevertheless, its development is still at pilot plant scale and more knowledge of the process is needed. One of the important parameters needed for design and control of the process is the growth velocity of the crystal, commonly known as the limit velocity. Above this velocity ice crystals will entrap solids and separation will not be successful. In this work, we describe a non-invasive technique to measure this limit velocity based on image analysis. Photographs were taken every 30 minutes in an experimental rig that allowed to freeze the sample unidirectionally. Back lighting was used in order to observe variations in luminosity at the samples surface. Image processing algorithms were used to segment the image, to identify the freezing front and to model its movement. Under the experimental conditions of this work, it was determined that the limiting freezing front velocity was 1.17 mm/h, which is a valuable information for the design and control of the process. © 2018 IMEKO-International Measurement Federation Secretariat. All rights reserved.