Multi-stage flash desalination: present and future outlook

Abstract

Multi-stage flash desalination (MSF) is currently the workhorse of the desalination industry with a market share close to 60% of the total world production capacity. As the turning point of the new millennium nears, the process faces many challenges dictated by industrial demands and public needs. The conservative nature of the desalination owner, as well as the strategic characteristics of the product, makes the MSF process favored over other competitive thermal desalination methods. In addition, the process has several merits, which include a large production capacity, proven reliability and well-developed construction and operation experience. This study offers an overview of the present and future developments in the MSF process, which aims to reduce the production cost. Special attention is given to the process fundamentals, which are the key elements for any serious and physically sound development of the MSF process. Also, a summary of the novel (MSF-M) configuration is given, which has recently been proposed by the authors. The process is based on the modification of operational MSF plants as well as the concept of once-through MSF. The modification involves removal of the heat rejection section and the addition of a mixing tank for the feed stream and the unevaporated brine recycle. This eliminates the amount of energy rejected in the cooling seawater stream and reduces the amount of energy rejected in the brine blowdown stream. Analysis of the MSF-M process shows an increase in the thermal performance ratio by a factor of 2–3 over conventional MSF.