EFFECT OF SUSPENDED PARTICLES ON CRYSTALLIZATION FOULING IN PLATE HEAT-EXCHANGERS

The presence of suspended particles in solutions significantly affects the crystallization rate. This study investigates the effects of calc ium sulphate (crystallizing) particles and alumina (noncrystallizing) particles on calcium sulphate crystallization fouling in a plate heat exchanger. Calcium sulphate particles are formed during the preparatio n of calcium sulphate solution due to breakage of calcium sulphate cry stals growing on the heat transfer surface. These suspended particles settle on the heat transfer surface and act as nuclei. The availabilit y of extra nucleation sites increases the crystallization rate signifi cantly. These particles can be removed with a filter, and the removal of the particles prevents this extra assistance available for crystall ization. Therefore, the crystallization rate is reduced markedly. Alum ina particles were purposely added during the preparation of calcium s ulphate solutions. These particles attach loosely to the heat transfer surface compared with crystalline deposits which adhere strongly. The refore, calcium sulphate crystals growing on these particles are remov ed easily. Also, alumina particles settling on the growth faces of cal cium sulphate crystals may act as a distorting agent. This slows down the growth of the crystals.