Advanced membrane distillation technology for seawater desalination and brine treatment of desalination plants

The quest to find a sustainable solution to meet the potable water demands of increasing economies, populations, and industrial activities of countries is an ongoing challenge. Desalination technology provides 97% of water resources in Qatar. Currently, multi-stage flash (MSF), and multi-effect distillation (MED) provide 65 % of desalinated water in Qatar, while the remainder is desalinated by reverse osmosis (RO) technology. The compromise between thermal and membrane technology is subjected to many factors such as energy efficiency, reliability under harsh conditions, and lower unit costs. Realizing the benefits and the challenges of thermal and membrane technologies, hybrid (thermal/membrane) configurations are deemed to be a sustainable solution. A typical example of such a hybrid concept is the Um Al-Houl Power and Desalination plant (Qatar) in which a common seawater intake/brine outfall facility has been constructed for MSF and RO plants. The final product water is a blending of MSF and RO, however, both plants are running independently. Membrane distillation (MD) is an emerging technology-based hybrid thermal and membrane process. The membrane selectivity was designed to admit water vapor due to temperature difference (saturation pressure difference) across the membrane. However, the MD process suffers from some technical barriers that limit its upscale. Membrane pore structures and wetting, low productivity, and fouling build-up in high concentration are among some of the technical challenges and research questions faced using MD. Most of the studies available on MD have been conducted in lab-scale setups, making the cost analysis for scale-up uncertain. This project aims to develop a novel hybridized desalination process to reduce energy consumption with less environmental impact under highly saline and low-quality seawater. The integration of film evaporation-based heat transfer around hot tubes and evaporation-based mass transfer through a hydrophobic membrane will overcome the limitation of the individual processes. Fabricating a novel multi-layer MD membrane incorporating silane coated HNTs by electrospinning and simultaneous electrospinning + electro-spraying is proposed to improve the water flux and hydrophobicity. The electrospinning technique is proposed to control both pore size and surface properties. A new configuration of the MD is proposed in which the number of channels and module aspect ratio will be optimized to achieve a 40 m2 membrane surface area which will be larger than the current commercial module. Process simulation will be performed to design the capacity of the pilot plant and the upscaling of the commercial plant. As of the year 2020, in HBKU-QEERI, the LPI has installed an advanced Multi-Effect Distillation (MED) pilot plant which demonstrated a 40 % lower energy consumption rate than existing and traditional MED technology. This success motivated the research team to continue the pilot program including membrane distillation downstream of the MED brine. The project technical approach varies from bench scale to pilot testing. The project methodology varies from micro to macro investigation. Membrane fabrication will be conducted using an electrospinning tool for bench scale set up to verify the membrane flux and to conduct heat transfer and fouling studies. The characterization of the hydrophobic membrane addressing the microstructure, surface properties, and mechanical properties will enable optimizing the fabrication process. The process simulation will predict the system performance as well as build the bridge to fill the gap of the commercial-scale development. The prototype-based experimental and simulation outcome will guide the research team to prepare a recipe for fabricating a larger membrane surface area with high water flux. The MD pilot plant will be installed and be deployed in the brine of the existing MED pilot plant to validate and demonstrate the high Gain Output ratio (GOR). A techno-economic comparison between the novel and the traditional desalination plants will be performed to show the feasibility and to evaluate the unit water cost. Exploiting the results of lab tests and pilot plant tests of the new concept of the hybrid system (MED-MD) will provide reliable information to the stakeholder. A seamless channel for exchange knowledge and deliverables will be maintained among the project partners; Qatar Environment Research Institute (QEERI, Qatar) and both Istanbul Technical University and Gebze Technical University from Turkey. After the completion of this project, a novel desalination technology (TRL 4-5) based on in-house development will be demonstrated. The potential of filing a patent idea for new desalination and brine treatment system will be disclosed. Techno-economic optimization software will be in place for the detailed design of the desalination system. Several publications and dissemination of the results would create awareness around our technology. We will better understand the commercialization root since it would be suitable for harsh seawater conditions in the GCC countries. Implementing the hybrid MED-MD in the desalination technology portfolio would be an uplift direction to mitigate water security in Qatar and reducing the energy consumption which is in line with the environment and energy direction at HBKU and Qatar’s Vision 2030.

Hamad Bin Khalifa University (HBKU)