Mechanistic modeling and experimental analysis of direct contact membrane distillation for seawater desalination

  • Mechanistische Modellierung und experimentelle Analyse der Direktkontaktmembrandestillation zur Meerwasserentsalzung

Al-Mahri, Badr Abdulla Salem Bin Ashoor; Marquardt, Wolfgang (Thesis advisor); Hasan, Shadi Wajih (Thesis advisor)

Düren : Shaker Verlag (2021)
Book, Dissertation / PhD Thesis

In: Berichte aus der Verfahrenstechnik
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

Membrane distillation (MD) is an emerging technology for seawater desalination. The main objectives of this research study were: (1) to design, fabricate, and install a pilot scale direct contact membrane distillation (DCMD) testing facility, (2) to carry out experimental investigations on the performance of the DCMD pilot scale facility in terms of distillate production rate, recovery ratio, and performance ratio, and identify the most important and optimum operating conditions using orthogonal experimental design approach to carry out experimental sensitivity analysis, (3) to carry out short- and long-term experimental investigations at transient conditions, (4) to develop a 2D spatio-temporal model of DCMD that consists of experimentally-validated parameters, and (5) to validate the 2D dynamic model at different operating conditions. Orthogonal experimental design, correlation analysis and response surface charts were used to identify the parameters influencing the operational efficiency of DCMD. The orthogonal array design method was used to optimize the number of experimental trials required for dependence analysis. The operating conditions studied were feed inlet properties (temperature, salinity, flowrate) and distillate inlet properties (temperature and flowrate). The impact of those operating conditions on three DCMD performance indicators - distillate production rate, performance ratio and recovery ratio – were investigated. and confirmed by using the Pearson product-moment correlation coefficients. The major foulants on the membrane surface were identified through membrane characterization. The characterization methods employed include scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, energy-dispersive X-ray spectroscopy (EDAX), streaming potential analysis, contact angle measurement, and membrane pore analysis. 2D dynamic model was developed from convective and diffusive heat and mass transfer to predict water flux across the membrane, temperature polarization, concentration polarization, and response of water flux to operational step changes. Aside the membrane module, the dynamic profiles of mass and temperature in the system peripheries, i.e. brine and distillate circulation tanks, were also modelled. Model parameters (kf, kp, αHeatloss, αCoil) were identified for different operating conditions using raw seawater and analytical grade NaCl solution; model accuracy was evaluated by comparing the model predictions before and after parameter estimation; and the calibrated model was compared with existing literature models to test model robustness. Higher accuracy of predictions for water flux across the membrane, relative to literature and experimental data, was achieved using the identified model. The 2D dynamic model was able to predict (i) 2D dynamic profiles of the temperature and concentration of the feed across the feed channel, (ii) 2D dynamic profile of temperature across the permeate channel, (iii) dynamic profiles of temperature and concentration polarization in the module and how the polarizations change along the flow direction, (iv) the dynamic profiles of temperature, concentration and mass in the peripheries, and (v) the dynamic profile of water flux in the module and how the profile changes along the flow direction.

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