Thermal performance of multi-stage flash distillation plants in Saudi Arabia

Abstract

The Saline Water Conversion Corporation (SWCC) of Saudi Arabia is currently producing around 16% of the total worldwide capacity of desalted water [1]. The majority of SWCC desalination plants employs the multistage flash (MSF) distillation process which produce 94% of SWCC's total desalinated water. SWCC various MSF distillers are characterized by a wide range of operating and design conditions. The capacity of operating distillers ranges between 2.5 to 7.5 migd. Some large distillers of rated capacity up to 10 migd are under construction in Shoibah and Yanbu. The number of stages of these distillers varies between 16 and 34, while the operating top brine temperature varies between 90°C and 115°C. Design and operating parameters of various SWCC MSF distillers have been collected and effectively utilized to simulate and analyze the thermal performance of these distillers. The thermal performance of each distiller is quantitatively assessed using a computer program which is based on the first and the second law of thermodynamics. A comparative study on energy and exergy analyses is conducted for different MSF plants. This paper also presents a comprehensive micro-thermal analysis to identify the potential for improving plant efficiency. The exergy losses due to irreversibility in different subsystems of each MSF distiller are evaluated. Exergy destruction in the brine heater, heat recovery and heat rejection stages and friction in liquid paths are determined. The impact of different design and operating parameters such as top brine temperature and number of stages on the thermal performance of the MSF system is evaluated.