Modified ceramic membranes for the treatment of highly saline mixtures utilized in vacuum membrane distillation

Abstract

Membrane Distillation processes could enable the treatment of highly saline solutions and facilitate minimal (MLD) or zero liquid discharge (ZLD) applications. Ceramic membranes can be a robust alternative to polymeric membranes if they are chemically modified to exhibit hydrophobic qualities to prevent wetting, particularly for vacuum membrane distillation (VMD). This study found that the thin top layer of asymmetrically structured ceramic membranes is robust enough for highly saline and abrasive suspensions and that TiO2 membranes outperform Al2O3 membranes in respect to the mass transport due to their larger support pore size and lower thermal conductivity. A maximum permeate flux of 35 kg/(m2 h) with exceptionally high rejections were measured in VMD using a saline brine with a concentration of 350 g NaCl per kg H2O. Furthermore, a VMD mass transfer model was successfully adopted (based on the Dusty Gas Model) to facilitate the calculation of the mass transfer through asymmetrically structured TiO2 membranes. Model deficiencies such as the underestimation of polarization effects were discussed, and correction factors integrated accordingly. This was done to establish a mass transfer modelling fundament for asymmetrical ceramic membranes used in MD that can be extended in future works and possibly serve as a tool for membrane optimization.

https://doi.org/10.1016/j.desal.2023.116943

Authors:

  • J. Schnittger, T. Hoyer, M. Weyd, I. Voigt | Fraunhofer Institute for Ceramic Technologies and Systems (IKTS), Germany
  • Jeffrey R. McCutcheon | University of Connecticut, Department of Chemical & Biomolecular Engineering, United States of America
  • A. Lerch | TUD Dresden University of Technology, Germany

Characterization of the physical properties of the thermoresponsiveblock-copolymer PAGB2000 and numerical assessment of its potentialities in Forward Osmosis desalination

Abstract

Forward Osmosis is a promising strategy for desalination processes, however some aspects have to be better characterized to make it competitive with other affirmed technologies. One of these aspects is the selection of the draw agent, i.e., a polymeric solution that has to fulfill different requirements to guarantee both high membrane performances and good regeneration process. Previous studies have identified a thermoresponsive copolymer known as PAGB2000 as potential draw agent. However, in the open literature there is no information on the thermo-physical properties required for a fully characterization of the polymer itself, hence, different experimental campaigns have been conducted to quantify: phase behavior, osmotic pressure, density, dynamic viscosity, thermal conductivity, thermal diffusivity and isobaric specific heat capacity. These properties were then used in a computational model to simulate the whole desalination process. Recovery ratio, specific electric consumption and specific thermal consumption were compared with the ones obtained in a previous work, showing that a detailed characterization of the thermo-physical properties is required to get accurate and realistic predictions of the system performance.

Keywords: Polymer, Draw agent, Forward osmosis, Desalination.

Authors:

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Effects of Supercritical CO2 Fluid Properties on Heat Exchanger Design

Abstract

Supercritical CO2 (sCO2) in industrial applications is a promising solution for the reduction of equipment size and for the potential increasement of overall efficiency. The characteristics of CO2 near the critical point are advantageous for the heat transfer, with high specific heat capacity when compared to conventional liquid or gas coolants. Moreover, dopants can be mixed to CO2, in a blend, to further increase the heat transfer and elevate the critical point of the fluid. Under the framework of the Horizon 2020 DESOLINATION (DEmonstration of concentrated SOLar power coupled wIth advaNced desAlinaTion system in the gulf regION) project, a heat exchanger was designed using CO2 and blend as working fluids in an innovative power cycle bank of a concentrated solar power (CSP) plant coupled to a water desalination system. In this paper, the innovative heat exchanger is evaluated in terms of the geometry, focusing on heat transfer and turbulence, using computational fluid dynamic (CFD) simulations with SST k-ω turbulence model and real-gas models with REFPROP library for thermodynamic and transport properties. Within each fluid, the diameter of the channels varied from 1.8–2.2 mm and the results are compared to analytical models. The geometry with 1.8 showed a larger pressure drop, but also larger overall heat transfer coefficient. It is observed that both pressure drop and heat transfer decrease with the diameter. Blend as the hot fluid resulted in higher average temperature and heat transfer coefficient, but in lower pressure drop than pure CO2. Nusselt number correlations were compared, showing the decrease of its values with the diameter for pure CO2, while for the blend it was observed higher values for 2.0 mm of diameter, except for Fang and Xu correlation that showed the same trend as the CO2.

 

Keywords: supercritical CO2; heat exchanger; gas cooler; computational fluid dynamics

Authors:

Afonso Lugo
Lappeenranta-Lahti University of Technology, Lappeenranta, Finland
Jonna Tiainen
The Switch, Lappeenranta, Finland

Study on the Operation of the LUTsCO2 Test Loop with Pure CO2 and CO2 + SO2 Mixture Through Dynamic Modeling

Abstract

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.

Keywords:

  • CO2 mixtures
  • Transcritical refrigeration cycle
  • Dynamic model
  • Simulink
Authors:

Giuseppe Petruccelli
Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland

Teemu Turunen-Saaresti
Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland

Aki Grönman
Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland

Afonso Lugo
Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland

Techno-Economic Analysis of Brine Treatment by Multi-Crystallization Separation Process for Zero Liquid Discharge

Abstract

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 kWhth/ton of feed brine to 125.90 kWhth/ton equaling a total electric consumption of 60.72 kWhe/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.

Authors:
School of Water, Energy and Environment, Cranfield University, Bedford, Bedfordshire MK43 0AL, UK
Prof. Dr. Kumar Patchigoll
School of Water, Energy and Environment, Cranfield University, Bedford, Bedfordshire MK43 0AL, UK