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Development of an Autonomous Low-Temperature Solar Rankine Cycle System for Reverse Osmosis Desalination (RO-SOLAR-RANKINE)

Final Report Summary - RO-SOLAR-RANKINE (Development of an Autonomous Low-Temperature Solar Rankine Cycle System for Reverse Osmosis Desalination)

The main objective of the project was the development, installation testing and performance evaluation of an innovative stand-alone, solar desalination system, generating mechanical work for Reverse osmosis (RO) desalination through a low temperature organic Rankine cycle.

Specific objectives were:
- the development and standardisation of the innovative desalination system;
- the optimisation of the thermal process and system size and components in order to achieve a cost effective and flexible technology with high adaptability to the desalination market's needs;
- extrapolating optimisation of the system design to a number of sites;
- the achievement of competitive fresh water price in comparison to other solar desalination technologies;
- the establishment of a high complementarity industrial consortium that guarantees the exploitation of the results after the programme end;
- the access of the involved SMEs to a new market;
- the definition of the range of the market to which the proposed technology aims at, and finally;
- the development of a competitive product.

Throughout the project duration all the objectives were met. The key factor to mitigate the objectives was the design, assembly, operation and monitoring of the prototype system.

The research concerned the development, design, assembly and installation, testing and monitoring and performance evaluation of a Low temperature Supercritical organic rankine cycle (SORC) system for sea water desalination. The prototype system consists of the following sub-systems and components:
1) high efficiency vacuum tube solar collectors' array, 100 kW;
2) circulator;
3) pre-heater (35 kW) and evaporator (73 kW);
4) condenser, 100 kW;
5) expander, 2 kW;
6) HFC-134a feed pump;
7) RO unit, 0.3 m3/h;
8) fresh water reservoir;
9) RO energy recovery system.

Towards the state–of-the art, the following aspects of innovations are pointed out:
-Low temperature thermal sources can be exploited efficiently for fresh water production.
- The solar energy is used indirectly and does not heat seawater; mechanical power is generated from organic fluid expansion through a Rankine thermodynamic cycle and drives the RO unit.
- The components of the system are tuned each other so that to achieved higher efficiency and consequently higher fresh water production rates.
- RO desalination plants are energised by electricity. In case the energy is produced by RES, PV or wind generators are used. The proposed system uses solely mechanical power generated by heat.
- Direct efficiency gain is achieved through no transformation of mechanical to electric power. In small scale motors the transformation efficiency is very low.
- The general RE desalinisation design eliminates the storage of energy, when reservoir of water is used.
- The energy recovery system of the RO unit is composed by axial type piston pumps co-axial connected making direct use of the generated shaft power of the expander.

The work performed and the results achieved are summarised in the following:
- overall coordination and management of the project;
- investigation of solar and other thermal sources potential and fresh water demand which resulted to the creation of a data base for possible applications of the developed technology;
- selection of the installation site and formulation of criteria for site selection;
- identification of possible sites for potential installation of the developed technology;
- assessment of water storage possibilities, technical and socio-economic evaluation of technology options and the support of design choices regarding water storage;
- communication of shortlist to water storage designing options;
- market survey on market available system's components;
- manufacturing of system components;
- procurement of system components not produced by the partners involved;
- infrastructure works in the installation site, which included the construction of concrete bases and metallic supporting frames of solar collectors, water and electricity supply, building construction for equipment housing, piping, wiring etc;
- assembly of the system components;
- start-up of the system and laboratory test realisation;
- start-up of the system and in site tests realisation;
- system monitoring and data acquisition;
- processing of experimental data;
- economic evaluation of the system;
- identification of environmental impacts;
- identification of socio-economic impacts;
- development of market penetration strategy;
- training activities;
- dissemination activities.