MED seawater desalination using a low grade solar heat source – SOLMED

SOLMED partnership merges specialists of thermal systems, polymers, design and engineering. Social aspects are taken into account through acceptability. During the project, a prototype will be operated during a year ; improvements, knowledge generation and showcase will be used to prepare the next step of demonstration.

Modelling of a SOLMED desalination unit and its coupling to solar or recovered heat source has been completed. A design study permits to reduce visual impact of a desalination unit. Different fabrications of flexible polymer tubes and ageing tests llowed to select the right process and material for the prototype. Optimized devices fixing the tubes in the tubular sheets have been designed nad are under fabrication. Construction of the prototype shell and utilities to operate it is quite terminated. In parallel, measurements of heat transfer in a single tube test rig confirm the validity of hypothesis adopted during the sizing phase. A material and energy balance has been carried out to be compared to traditional metallic solutions.

If objectives are reached, a demonstration step will follow the present project. Contacts are established and preparation is engaged.

Communication at « Desalination, for the environment, clean water and energy », Cyprus, 11-15 May 2014
Publication in Desalination and Water Treatment, 2014 1-10
2 patents in 2014, 2 others are examinated

The objective of SOLMED is to develop a seawater desalination system based on vertical tubes multi-effect distillation (MED) and powered by solar energy or low grade thermal wastes. The technology answers to main recommendations of Water Sciences and Technology Board (US NRC) and Middle East Desalination Research Center: capital and operating cost reduction, low environmental impact. To this effect, the developed technology is based on the use of polymer materials, even for the heat transfer surfaces making them cheaper than metallic ones, bringing corrosion resistance and mitigating strongly chemical rejects due to lighter or no pre-treatment. The use of thin wall tubes made of polymers as heat transfer surface allows reaching high heat transfer rates, equivalent or better than metallic surfaces ones. Distillation at moderate temperature, less than 70°C, makes usable a large panel of polymers and heat sources. SOLMED prototype will use solar energy, but coupling to thermal wastes is also examined.
This technology has yet been validated at laboratory scale and patented. The objective of SOLMED is to bring a proof of concept at a significant scale, able to be extrapolated to large production capacities - some hundred of cubic meters per day - without significant risk. It will be a first prototype before the industrialization step of an alpha tool, to be launched after the present project.

The challenges of SOLMED are:
- To find the best coupling and operating schemes between solar heat source and the distillation module, including heat storage option, through process models,
- To select among available raw polymers and thermal conductivity improved compounds the best material to realize the heat transfer surface, transform it into the suitable shape in industrial conditions, and realize safe connections between thin tubes and evaporator shell,
- To design and size properly a significant scale prototype, according to mechanical, hydraulic and thermal models to be developed, and manage the different fluid flows, especially non condensable gas flow,
- To build and operate the prototype coupled to a solar heat source,
- To show how this new desalination system is cost effective, has minor or no environmental impact and brings to public a new accepted feeling of this industrial activity.
- To manage innovation with an objective of exploitation by partners, through a dedicated structure or licencing.