A 600-day experiments with polyphosphate as anti-scale agent in MSF distillers

Abstract

An experiment with polyphosphate as alkaline anti-scale agent was carried out over 600 days on a 16-stage MSF distiller at Umm Al Nar East Station (U.A.E.). During this period the distiller was subjected to two acid cleanings and one complete overhauling process. The operation of the distiller involved the measurement on regular basis of the temperature at the sea water intake, at the inlet and outlet of the heat rejection section, at the inlet and outlet of the brine heater, and the condensate temperature. The brine recirculation rate and the distillate output were determined on daily basis. The gained output ratio (GOR) and the heat transfer coefficient (HTC) were computed. Fouling in the distiller was qualitatively recognized from the decrease in the temperature at the brine heater inlet, and the corresponding increase in the condensate temperature. The tubes of both the brine heater and the cells in the heat rejection section were affected. Quantitative measures of the fouling were obtained from consideration of the variation of gained output ratio and of the heat transfer coefficient of the distiller. The two parameters decreased with the operation time. The variation of the GOR occurred in a stepwise manner This behaviour was qualitatively explained in terms of cyclic variations in the heat distribution pattern of the distiller. Conclusions regarding the behaviour of the distiller under polyphosphate dosingwere drawn.