Membrane desalination: concepts and perspectives related to thermodynamics and energy consumption
Department of Process Engineering, Stellenbosch University, South Africa
Abstract
Thermodynamics as a subject offers great opportunities for the development of deeper insight into our complex, entropy-enslaved universe. However, its usefulness is displayed in the common-sense engineering application of core principles, such as in the design of desalination plants.
Membrane desalination is a mature technology and many engineers and scientists have spent a substantial part of their careers on the development and implementation of related systems. With time, several hard and expensive, yet useful lessons have been learnt about the rather unforgiving behaviour of incorrectly designed, or poorly operated membrane plants.
Today, large plants are successfully operated world-wide, fulfilling a key function by securing reliable clean water supplies to many communities and industries. As with many other mature technologies, the refinement and improvement of related systems (in this case membrane materials, configurations, pre-treatment methods, etc.) will continue.
However, while those who are intimately involved with the operation of such plants are perhaps mostly focussing on the minimisation of membrane fouling and cleaning, one of the more popular public criticisms against desalination is that it is “energy intensive, expensive and unsustainable”. This is not unfounded criticism if one considers, for example, that the power consumption of a sea water reverse osmosis plant can contribute to more than 50% of related operating costs.
Therefore, this presentation will provide a bird’s eye view on some theoretical and practical aspects of power consumption during membrane desalination, also focussing on theoretical minimum energy requirements, energy efficient configurations and some energy recovery methods. The intention is not to bore the audience with rigid thermodynamic calculations, but rather to connect well-known theory with practical concepts related to the design or operation of membrane plants.