Comparison of Two Different Designs of a Scraped Surface Crystallizer for Desalination Effect and Hydraulic and Thermodynamic Numbers

Abstract

The design of a desalination plant is most important if the desired product purity has to be as high as possible. This is also true for freeze crystallization plants. A correct solid-to-liquid ratio has to be ensured when pressing is used as a post-treatment. Thus, the dependence of the overall plant design on the achieved ice quality but also on different hydraulic and thermodynamic numbers is important. In this research, a scraped screw crystallizer plant is presented and examined for two different screw designs. Experiments with a low initial concentration, as for the usage to desalinate groundwater to gain it as process water, were conducted. Furthermore, solutions with high initial concentrations simulating seawater to produce potable water were used as another set of test solutions. The findings showed that neither of the screw designs is more favorable than the other, but it is important to have a plant design fitting the existing parameters on site.

Brine rejection and hydrate formation upon freezing of NaCl aqueous solutions

“…This is due to the fact that the latent heat of freezing (334 kJ/kg) is significantly lower than that of evaporation (2257 kJ/kg) 2 . Despite the myths and misconceptions associated with this method 3 there have been several case studies that demonstrate the feasibility of this approach from small freezing units 4 to single-step desalination plants 5 , as well as for treating the waste water from Reverse Osmosis (RO) plants 6 . The energy consumption of freeze desalination has been estimated to be as low as 41.4 kJ/kg (11.5 kWh per 1000 kg of ice produced) 7 and 26.64 kJ/kg (7.4 kWh per 1000 kg of ice produced) 8 , which approaches the specific energy consumption of a RO plant, typically on the order of 7 kJ/kg (about 2 kWh/m 3 ) 9,10 .…”

Special Issue “Design, Control and Optimization of Desalination Processes”

“…This Special Issue also encompasses eleven research articles covering the optimal sizing of hybrid solar photovoltaic, fuel cells, hydrogen storage, and reverse osmosis seawater desalination system [4]; design of unconfined dense plunging jets used for brine disposal from desalination plants [5]; mode-based analysis and optimal operation of a multi-stage flash desalination system [6]; simulation analysis and optimization of a coupled reverse osmosis and membrane capacitive deionization plant for seawater desalination [7]; optimal operating parameters of a capacitive deionization desalination system via radial movement optimization [8]; design and thermodynamic analysis of a scraped surface crystallizer plant for freeze desalination [9]; design of a fault detection and isolation control system for industrial seawater reverse osmosis desalination plants based on structural analysis [10]; simulation and economic feasibility evaluation of an ocean thermal energy conversion system for electricity and freshwater production [11]; design and performance investigation of a closed-cycle humidification-dehumidification desalination system [12]; two-dimensional modelling approach and performance assessment of ionexchange membrane in membrane capacitive deionization [13]; and, advanced exergy, exergoeconomic, and exergoenvironmental analyses of a combined cycle power plant integrated with multi-effect distillation and reverse osmosis desalination units [14].…”