Scale control inhibitor performance at 100°C under boiling conditions

Abstract

While numerous papers have presented information on successful trials using high temperature threshold additives to control alkaline scale deposits in MSF plants instead of continuous acid treatment, there has been little information reported on the performance of these chemicals in distillation plants which operate with boiling brine in contact with heat transfer surfaces at elevated temperatures. The high heat transfer coefficients achieved under such conditions using enhanced surface in combination with the higher thermodynamic efficiencies inherent in the multi-effect and vapor compression cycles make development of suitable threshold type chemical scale control systems particularly important now, and to the future generations of distillation equipment. This paper reports on trials of commercially available threshold chemicals using a packaged vapor compression distiller. This distiller uses vertical fluted tubes in an upflow natural circulation mode and operates just above atmospheric pressure. Some of the chemicals tried are those which have enabled a number of large MSF distillers to operate for thousands of hours between cleanings at terminal temperatures of over 100°C. Improvements made in chemical treatment as part of the test program have resulted in extending the time period between cleanings five fold. It is believed that these improvements can be used to make threshold type scale inhibition a practical reality in large scale high temperature multi-effect and vapor compression distillers as well as many MSF plants which have not responded favorably to conventional high temperature additives.