Experimental Study of Deposits Removal in Thermal Desalination Plants by the Thermal Shock Technique

Abstract

Deposition of salts on heat transfer surfaces in thermal desalination plants can lead to operational failure. Scale removal can occur by applying a thermal shock, which is a sudden decrease in the heating process. The difference in thermal expansion between the heat transfer surface and the deposit layer plays a key role in the thermal shock process. The objective of this research is to determine experimentally the minimum temperature of the heating surface in desalination units, such that the thermal shock is still applicable. The minimum heating temperature is important for minimization of heat losses. An experimental setup has been designed and developed, and it consists of an oil tank in which oil is heated by electrical heaters. The heated oil is circulated by a gear pump to the steam generator, which contains the water to be desalinated, that is, a CaSO4 solution, at atmospheric pressure. The water is heated and converted into steam by the hot oil leaving the salts behind, that is, the fouling layer, on the tubes of the steam generator. A thermal shock is applied when the asymptotic behavior is approached, such that the flow of the hot oil is suddenly stopped for a short period of time before resuming it again. The minimum heating temperature has been determined for two types of tubes: stainless steel and copper, and at a salt concentration of 2 g/L. The minimum heating oil temperature that allows the applicability of the thermal shock is 130°C when using copper tubes, and 140°C for stainless-steel tubes.