Available safety margins of time and antiscalant dose rate

The Royal Commission power, desalination and seawater cooling complex at Madinat Yanbu Al-Sinaiyah (MYAS), Saudi Arabia includes six 380 m3/h multi-stage flash seawater desalination units. Each unit is designated for a top brine temperature of 121°C, employs a decarbonation method using sulfuric acid for scale control, and has a performance ratio of 19 kg of distillate per 1,000 Kcal heat input. The MYAS desalination units have been operated for over 15 years. The unitsʹ performance in terms of water production and energy consumption has remained satisfactory, however, various problems have been encountered, resulting in forced outages of varying duration. This paper discusses the performance of various components of the existing units, and highlights problems experienced and countermeasures adopted to eliminate or alleviate the problems. The existing unitsʹ operating experience and contemporary trends in the MSF desalination technology have been utilized to avoid similar problems on two new 570 m3/h units constructed recently. The paper also presents pertinent specifications for the two new units that demonstrate resolution of the problems noted on the existing units.