Within the framework of the Horizon 2020 DESOLINATION (DEmonstration of concentrated SOLar power coupled wIth advaNced desAlinaTion system in the gulf regION) project, CO₂-based mixtures will be used as the working fluid of the power cycle coupled with the desalination plant. Desalination technologies require temperatures above 50 ℃, therefore a fluid with a critical temperature above 70 ℃ is required to perform the compression step in the liquid phase, minimizing compression work and increasing cycle efficiency. Blending CO₂ with other fluids, such as SO₂, leads to an increase in the critical temperature of the mixture and makes it suitable for transcritical cycles in concentrated solar power applications, while preserving the advantages of pure CO₂ over steam cycles. Throughout the DESOLINATION project, CO₂ blends will be tested in the LUTsCO2 test loop to provide validation data for the design of heat exchangers. In this work, the adaptation of the test loop to the CO₂ blend is investigated. A dynamic model of the test loop is built in MATLAB-Simulink, which allows each component to be modeled independently and to realize a closed-loop cycle model coupled with a controller and real gas property tables. Steady-state simulations of the system are performed and the dynamic model of each component is verified with the design values. As a result, the study highlights the key performance and fluid dynamic differences which arise from the use of a CO₂ blend instead of pure CO₂.

This study analyses the concept of a novel multi-crystallization system to achieve zero liquid discharge (ZLD) for desalination plants using an innovative heat recovery system consisting of a heat transfer fluid and a compressor to reduce energy consumption. The main focus is to recover water and separately extract salts from seawater brines with high purity, including calcite, anhydrite, sodium chloride, and epsomite, which can be sold to the cement industry. The system is compared with a conventional brine treatment system. The energy demand and economic feasibility of both systems are assessed to evaluate profitability at a scale of 1000 kg/h. The results estimate that the utilization of a heat recovery fluid reduces energy consumption from 690 kWh_th/ton of feed brine to 125.90 kWh_th/ton equaling a total electric consumption of 60.72 kWh_e/ton. The system can recover 99.2% of water and reduce brine discharge mass by 98.9%. The system can recover 53.8% of calcite at near 100% purity, 96.4% of anhydrite at 97.7% purity, 91.6% of NaCl at near 100% purity, and 71.1% of epsomite at 40.7% purity. Resource recovery accounts for additional revenues, with halite and water accounting respectively for 69.85% and 29.52% of the income. The contribution of calcite and anhydrite to revenue is very low due to their low production. The levelized cost of water (LCOW) of the multi-crystallization system is 13.79 USD/m³ as opposed to 7.85 USD/m³ for the conventional ZLD system. The economic analyses estimate that the conventional ZLD system can achieve payback after 7.69 years. The high electricity cost, which accounts for 68.7% of the annual expenses, can be produced from renewable sources.