Field evaluation of coated plates of a compact heat exchanger to mitigate crystallization deposit formation in an MD desalination plant

The present study aims at investigating anti-fouling characteristics of various coated surfaces of a plate heat exchanger which were prone to crystallization deposition in a membrane-distillation plant. To do so, firstly various coatings were developed then subjected to harsh crystallization fouling conditions in a laboratory rest rig. The results showed that the deposition process was profoundly affected by altering the surface energy properties. In particular, increasing the electron donor component causes a significant reduction in fouling rate as well as weaker adhesion between deposit and the surface. For field evaluation, those coatings that performed best were chosen for utilization in a plate heat exchanger in the prototype desalination unit of the MEDESOL project where the coated plates were examined in two successive phases. The findings of the field tests were consistent to those of laboratory ones. No sign of fouling was observed in both phases, though in phase I, substantial flaking-off of the coatings occurred in particular around the inlet and outlet sections of the heat exchanger as well as the contact points between plates. In phase II, nonetheless, a thinner coating was applied on a more roughened surface which resulted in far better stickiness of coatings to the substrate.