Optimisation Of A Liquid-Liquid Extraction Based Sustainable Water Desalination Process

CATEGORY: DESALINATION
Proceedings of the 6th International Conference on Process Systems Engineering (PSE ASIA)
25 - 27 June 2013, Kuala Lumpur.
Optimisation Of A Liquid-Liquid Extraction Based Sustainable Water Desalination Process
Eleftheria M. Polykarpou (a), Vivek Dua (b)*
v.dua@ucl.ac.uk
a School of Energy and Resources, UCL Australia, Adelaide 5000, Australia
b Department of Chemical Engineering, UCL, London WC1E 6BT, UK
Abstract
In this paper, a waste heat liquid-liquid extraction method is considered for the seawater desalination. The mathematical model is a result of mass and energy balances, phase behaviour and salt distribution in the two phases. Because of the high non-linearity of the phase behaviour and the salt distribution these are being approximated by the use of piecewise linear approximations methods and the solutions are presented. The results indicate that the quality of solution is not affected by the use of the approximation.
Introduction
Water is one of the most abundant resources on earth. Although, it covers almost 75% of the earth’s surface, only 3% of this is fresh water. This small percentage can be found in ground water, lakes and rivers, while the remaining 97% can be found in the oceans. The water shortage problem could be potentially addressed with the use of a sustainable seawater desalination process.
Separating salt from water and obtaining potable water is usually performed by methods that require large amounts of energy and are costly. The conventional methods of desalination are divided in thermal and membrane processes. The dominant thermal desalination method is the multi-stage flash distillation that requires external steam supply at 100OC, while the dominant membrane method is reverse osmosis and requires energy to power a pump that would increase the pressure up to 70bar. Multi-stage flash (MF) along with reverse osmosis (RO) account for 86% of the worldwide capacity of water desalination.
In this paper, a sustainable desalination method that uses waste heat is considered. This method is called the Puraq method and can produce fresh water by solvent extraction with a specially tailored liquid polymer solvent. These specially tailored polymers can pass from regions of complete miscibility into two phase separation when mixed with water. The Puraq process has two unique advantages over MF and RO because no membrane is necessary for the process and the temperature range is between 30 OC and 60OC. This makes the Puraq process a highly competitive process that is worthwhile being investigated.
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