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Low cost low energy technology to desalinate water into potable water

Final Report Summary - DESOL (Low cost low energy technology to desalinate water into potable water)

The rising demand of drinking water and climate change has caused a shortage of potable water in many regions of the world. Desalination of sea or brackish water is necessary to assure a reliable water supply. Most common desalination technologies require large amounts of fossil fuels and thus also have high CO2 emissions. The costs for standard desalination are continuously rising due to the development of the costs for fossil fuels.

The desalination technology is environmental friendly by using the sun as the only energy source. It is independent from fossil fuels and external electricity supply. A high efficiency can be achieved by using temperature at a low level. This becomes possible by applying a vacuum distillation process. The vacuum is produced and maintained, without a vacuum pump, by an innovative process using gravitation for vacuum production. By applying a multi-stage distillation process the energy is re-used internally and the specific heat energy demand is kept on a low level. The control and adjustment of the distillation system is fully automatic without the use of electronic components. Very low maintenance at a long life time is aspired. A modular design enables flexible adaptation to various water production capacities required by customers. This technology was used and further developed in the DESOL project.

At lab experiments (without insulation or energy recovery), it was already possible to achieve an efficiency of 80 % - 85 %. The vacuum generation by gravitation was possible down to very low pressures that enabled the usage of low temperatures for evaporation (< 50 degrees Celsius).

In parallel to the tests of the distillation tank and the vacuum generation principle a number of sub-systems were designed and independently tested. Besides the solar pump system and the measures against fouling and scaling the focus was on the automatic control and adjustment system. The objective was a self-adjusting system without using electronic components as actuators or sensors. Finally the result was a 100 % mechanical / thermo-mechanical control and adjustment system that reacts flexible to changing conditions of the distillation process (fluctuating heat supply, pressure changes, weather, etc).

In the second phase of the project the DESOL system was extended to a two-stage distillation system to decrease the energy demand and to prove that a multi stage process is possible.

Various tests were carried out:
- tests at Fraunhofer TEG Stuttgart, Germany (commissioning and optimisation of two-stage system);
- tests at the technology centre of CRIC in Terrassa, Spain (integration of sub-systems in complete system, such as thermal solar collectors, control and adjustment, pump system etc.);
- tests and demonstration at Hotel facility of Club Med, France (tests under real conditions to evaluate the performance of the system and to identify the potential for further optimisation - variation of process parameters and investigation of the impact on the systems performance).
At the end of the project the system was demonstrated at Club Med facilities in France. The dissemination activities will go on after the project.

The difference of the system to the current state of the art is that the technology is a low cost and low energy consuming technology. It is designed to provide water for single households up to small and medium enterprises (SMEs). The technological innovations are especially in the vacuum generation and the self adjustment without a complicated control system. It is no system known that produces the vacuum in a similar way.

The DESOL technology will be suitable to desalinate sea or brackish water effectively with low costs and low maintenance efforts. The system runs by solar energy and enables an autarkic water supply, independent from a public infrastructure. It has been experienced and evaluated by a market survey that the DESOL technology has a high potential to be used for decentralised water production in small and medium sized facilities. It is also possible to integrate the DESOL technology into renewable energy hybrid systems. Instead of heat from thermal solar collectors, waste heat from e.g. photovoltaic (PV) panels can be used.

The knowledge about the tank system developed in the DESOL project is, besides the application as a sub system of the DESOL technology, also suitable for other markets like water purification and chemical industry. This knowledge enables the SMEs involved to strength their market position and to enter new markets.