Using different types of anti-scalants at the Al-Jubail power and desalination plant in Saudi Arabia

Abstract

The purpose of this paper is to review the results of using different types of anti-scalant chemicals at the Al-Jubail Desalination Plant. A major problem in the desalination of sea-water is the scaling that takes place. During the desalination process brine flows inside heat transfer tubes causing a rapid growth of scale within the tubes which eventually results in a deterioration of plant performance. The desalination plant at Al-Jubail is considered to be the largest of its kind in the world and is capable of producing 240 migd at a low top brine temperature of 90°C and 281.6 migd at a high TBT of 112.8°C. Experience has shown that there are only two practical methods to prevent scale in a MSF plant, namely treatment of the scale by acid or by the use of chemical additives. The evaporators used at the plant were designed to use additive scale control method. Treatment of scale with an acid has not yet been used at the plant to clean the evaporators or Condensers. Two different types of anti-scalant treatments are used at the plant which are classified into three anti-scalant groups namely; poly-maleic acid, poly-phosphate and poly-phosphonate. This paper will compare the results experienced using the above chemicals. This paper will also discuss the necessity of anti-scalant selection for every operating mode in MSF evaporators. Factors will be reviewed to assess and evaluate the quality and performance the anti-scalant. Specifications of all the above chemicals is provided to assist in the selection of anti-scalants by other users without the need for expensive tests and trials.