Abstract

This work describes how the design and operation parameters of the Multi-Stage Flash (MSF) desalination process are optimised when the process is subject to variation in seawater temperature, fouling and freshwater demand throughout the day. A simple polynomial based dynamic seawater temperature and variable freshwater demand correlations are developed based on actual data which are incorporated in the MSF mathematical model using gPROMS models builder 3.0.3. In addition, a fouling model based on stage temperature is considered. The fouling and the effect of noncondensable gases are incorporated into the calculation of overall heat transfer co-efficient for condensers. Finally, an optimisation problem is developed where the total daily operating cost of the MSF process is minimised by optimising the design (no of stages) and the operating (seawater rejected flowrate and brine recycle flowrate) parameters.

Highlights

  • IntroductionThere is a shortage in the freshwater resources all over the world. About 40% of the world’s populations are suffering from the water crisis

  • At present, there is a shortage in the freshwater resources all over the world

  • Unlike Hawaidi and Mujtaba [9], we have proposed a fouling model [11,12] as a function of stage temperature which is incorporated into the Multi-Stage Flash (MSF) process model

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Summary

Introduction

There is a shortage in the freshwater resources all over the world. About 40% of the world’s populations are suffering from the water crisis. A recent study [4] shows that for a fixed design and operating conditions the production of fresh water from MSF process can significantly vary with seasonal variation of seawater temperature producing more water in winter than in summer. There is variation in water demand during 24 h of a day (peak and off-peak hours) [8] These variations in the seawater temperature will affect the rate of production of freshwater using MSF process during a day and throughout the year. Most recently, [9] provided a study on the design and operation of the MSF process with constant fouling resistance in the brine heater only and variable seawater temperature and freshwater demand during a day and throughout the year. For a different number of flash stages, operating parameters such as seawater rejected flow rate and brine recycle flow rate are optimised, while the total daily operating cost of the MSF process is selected to minimise

Dynamic Freshwater Demand
Seawater Temperature Dynamic Profiles
MSF Process Description
Steady State MSF Process Model
Storage Tank Level Control Model
Optimisation of MSF Parameters
Case Study
Findings
Conclusions
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