Scaling control by using ultrasonic guided waves

Abstract

Fouling of heat exchanger surfaces is a major concern in the industry, resulting in performance losses through a decrease in the overall heat exchange coefficient. Control methods exist but are costly and have a strong environmental impact. Thus, the use of physical treatments is very promising, because the action is done on the clogged surface, in the bulk or in the solution. The present study shows the influence of ultrasonic guide waves on the crystallization of calcium carbonate inside a plate heat exchanger from scaled water. An experimental pilot was set up to study the scaling phenomenon. Several operating parameters such as flow rate, duration, and temperature were experimentally varied in order to identify their influence on the scale deposition in the heat exchanger. Subsequently, a thermodynamic prediction was performed by geochemical modeling using the Phreeqc software in order to get an idea of the nature of the deposit formed after the heating of scaled water. The main objective of this work was the determination of the impact of ultrasonic treatment on the mineral deposit, qualitatively and quantitatively. Therefore, four types of experiments lasting three days are presented in this paper to experimentally show the influence of ultrasound generated by a 35–50 kHz transducer on scale formation. The amount of solid deposited in grams/per day/area, the polymorphism of the formed crystals, and the number, size and size distribution of the particles were analyzed. Disassembly of the exchanger allowed access to the distribution of scale on the plates, and thus justified the choice of location for the 35–50 kHz transducer. It was also possible to estimate the thickness of the scale experimentally by 3D digital microscopy and to ensure the absence of microcrystals in the pores of the plate by analyzing the surface roughness. The results obtained were compared to the experimental measurements with and without the presence of the 35–50 kHz transducer. This allowed the evaluation of the effect of guided ultrasonic waves for the prevention of scale deposits. The presence of a single medium power transducer reduced mineral scale deposition in a plate and gasket heat exchanger by 76%.