25 years of experience in operating thermal desalination plants

Novel Tri Hybrid Desalination Plants

Desalination is probably the only means for fresh water supply to countries in decertified climate. The majority of GCC counties rely on desalinated water for fresh water supply to major cities. Over 70% of the desalinated water in the GCC comes from thermal desalination plants including Multi Stage Flash (MSF) and Multi Effect Distillation (MED). The new trend in the desalination plant in the GCC is 30% Reverse Osmosis (RO) and 70% thermal. However, these percentages vary from one to another country depending on feed water quality and expertise. For example, Oman Sea has lower salinity than the Gulf water and hence Oman uses more RO for desalination than MED and MSF. This decision is also driven by economy as RO process less energy intensive and hence the produced water is less expensive as compared to thermal plants. On the contrary, Qatar and Kuwait use more MSF followed by MED due to the high salinity and low quality feed water. This is also because trials of RO in both Qatar and Kuwait were not successful because of the problems of membrane fouling and restrict pre-treatment requirements due to the quality of the water intake.The advantages of RO over thermal technologies are well known in terms of lower energy consumption and the cost of produced water; but are not yet taken advantage of in the GCC zone. One of the reasons is blamed on high feed water salinity and bad water quality; other reasons such as lack of experience, red tides and reliability are contributed to the dominance of thermal plants. However, field experience showed that good pretreatment and optimized RO design may overcome the problems of high feed salinity and bad water quality. Several RO plants, such as Fujairah in UAE, are good examples of a working RO technology in the harsh water environment. Good RO design includes design and optimization of both pretreatment and post-treatment. Field experience showed that most of RO plants failure was due to inefficient pretreatment which resulted in providing low quality water to the RO membrane that caused fouling. Fouling, including biological and scaling, can be handled once an efficient pretreatment process is available. Recent advances in pre-treatment techniques include the combination of Forward Osmosis (FO) with RO among other methods. Recent studies by the authors including commercial implantations have shown that the combination of FO with RO addresses the most technical challenge of RO process and that is fouling, which results in lower energy consumption and less chemical additives. Experience showed fouling in FO process in reversible, i.e. can be removed by backlashing while fouling in conventional RO process is irreversible.In this study, the feasibility of integrating FO with RO process for the desalting of the Gulf water in Qatar is presented. The results are expressed in terms of specific energy consumption, process recovery, produced water quality, chemical additives and overall process cost.The implementation of RO for desalination is not only reducing the cost of desalination but also the environmental impact. More R&D should be done to provide useful data about RO application and suitability for the Gulf water. The R&D should be focused on laboratory to market development of RO technology using rigorous lab scale and pilot plant testing program.

A review of hybrid desalination systems for co-production of power and water: analyses, methods, and considerations

The thermal desalination by Multi-Stage Flash (MSF) and Multi-Effect Distillation (MED) desalination plants are dominantly used in Qatar due to their maturity and reliability in dealing with the harsh seawater conditions of high (TDS, Seawater feed temperature, SDI, and HAB). Realizing the benefits and challenges of the thermal, there is a room of improvement to reduce energy consumption. Qatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University (HBKU) and Qatar Electricity and Water Corporation (QEWC) took initiative to improve the overall efficinecy and perfomance of thermal deslaintion plants in Qatar. In this work, a novel design and compact MED evaporator will be presented. The expected reduction in heat transfer area will reduce the capital cost of the evaporator as well as the footprint of the MED desalination plant. The present work describes a novel MED evaporator according to the GCC2016-31325 patent. The tubes are arranged in a way to allow generated vapor to flow in a smooth and minimized route to the following effect. The vapor route is designed to avoid shear losses and breakdown of film liquid around the tubes (dry zones) that will eliminate vapor entrainment, which will reduce brine carry over. Since there is no cross flow within tube bundle hence, eliminating the need for demister and vapor boxes. A well-developed Visual Simulation Program (VSP) is used to perform comparison between commercial MED desalination plant (63 MIGD, Rass Laffan, Qatar) and proposed novel design. The evaporator distillate production rate, seawater feed conditions (temperature and salinity), and heating steam conditions are specified as input to the software. The number of effects and the tube specifications are specified as input. The VSP software calculates the required steam consumption flow rate, the heat transfer area for each effect, the condenser and preheaters. The capital cost of the desalination plant was calculated using recent bidding of commercial desalination projects and the updated market material price. Process simulationm shows that, for a given gain output ratio of (GOR = 9), the required heat transfer area of novel evaporator is 20% less than of existing evaporators design due to thermal losses reduction. Moreover, the thermal losses reduction in novel evaporator were calculated via simulation and are in the range of 30% to 60%. Furthermore, removal of demister in novel MED evaporator decreases evaporator width by 65%. However, novel evaporator height is almost 1.25 times of the convnetional. In fact, the novel evaporator cost is 20 % less than that of the convnetional evaporator due to significant reduction of the evaporator width and vapor box. In addition to that, a 3D-CFD simulation have been conducted using COMSOL Multiphysics v.5.2a on the vapor route of the novel MED evaporator, to be compared with that of the convention MED evaporator. The engagement with QEWC to offer a site equipped with seawater intake/outfall, electricity will be highlighted. The detailed design of the pilot test, fabricate, installation, commission of MED pilot test of 25 m3/day at Dukhan will be used to develop the proof of concept.

In order to ensure long-term sustainability of the reservoir, the gas industry in Qatar is faced with the challenge of reducing the volume of produced and process water (PPW) sent to disposal wells by 50% [1-3]. Recently, Qatargas initiated a project to recycle process water and thus, reduce disposal volumes using commercial advanced water treatment technologies [4]. One emerging technology, “osmotic concentration” (OC) has been identified that offers a low-energy alternative to conventional thermal or membrane volume reduction methods. Osmotic concentration is a membrane filtration process that mimics first step in a forward osmosis (FO) system. It requires a high salinity draw solution (DS) which passes on one side of a semi-permeable FO membrane while the feed passes on the other side. Water from the feed is drawn through the membrane, via natural osmosis, reducing the feed volume and increasing the volume of the draw solution. This paper summarizes the results of bench-scale volume reduction tests wit...

Copper alloys are widely used for the heat exchanger tubes in both multi-stage flash (MSF) and multiple effect distillation (MED) thermal desalination plants. Millions of metres of such tubing have been used and, generally, the copper alloys give good performance. In the last few years the author has looked at a number of failures from thermal desalination plants in the Middle East. These are not from one location, but have occurred in different areas in different plants. The failure mechanisms are also different in each area. The common feature of the failures is that the corrosion mechanism for each one is well understood, and they could all have been prevented by using a corrosion engineer at the design stage. This paper presents some of the diverse range of case studies and explains how they could have been prevented.

Application of Membrane Distillation for desalting brines from thermal desalination plants

Corrosion of heat exchanger in thermal desalination plants and current trends in material selection

The design of new dual-purpose thermal desalination plants is a combinatory problem because the optimal process configuration strongly depends on the desired targets of electricity and freshwater. This paper proposes a mathematical model for selecting the optimal structure, the operating conditions, and sizes of all system components of dual-purpose thermal desalination plants. Electricity is supposed to be generated by a combined-cycle heat and power plant (CCHPP) with the following candidate structures: (a) one or two gas turbines; (b) one or two additional burners in the heat recovery steam generator; (c) the presence or missing a medium-pressure steam turbine; (d) steam generation and reheating at low pressure. Freshwater is supposed to be obtained from two candidate thermal processes: and (e) a multi-effect distillation (MED) or a multi-stage flash (MSF) system. The number of effects in MED and stages in MSF are also discrete decisions. Different case studies are presented to show the applicability of the model for same cost data. The proposed model is a powerful tool in optimizing new plants (or plants under modernization) and/or improving existing plants for desired electricity generation and freshwater production. No articles addressing the optimization involving the discrete decisions mentioned above are found in the literature.

Mega-scale desalination efficacy (Reverse Osmosis, Electrodialysis, Membrane Distillation, MED, MSF) during COVID-19: Evidence from salinity, pretreatment methods, temperature of operation

Impact of desalination plants fluid effluents on the integrity of seawater, with the Arabian Gulf in perspective

Field evaluation of membrane distillation technologies for desalination of highly saline brines

Libya, like many arid countries, relies heavily on groundwater resources, which are increasingly scarce. With a 1950 km Mediterranean coastline offering an abundant but highly saline water source (35,000 38,000 ppm), seawater desalination is essential to meet national water demands. This study presents a techno-economic evaluation of three desalination technologies—Reverse Osmosis (RO), Multi-Stage Flash (MSF), and Multi-Effect Distillation (MED)—for a 1200 m³/day plant. RO design was conducted using ROSA software, while MSF and MED were modeled thermodynamically.RO requires significantly lower seawater intake (117 m³/h) compared to MSF (475.7 m³/h) and MED (200 m³/h), with corresponding plant efficiencies of 43%, 10.5%, and 25%. RO produces potable water (190 ppm TDS), while MSF and MED yield ultra-pure water (~50 ppm TDS), necessitating remineralization. RO operates without steam input, unlike MSF and MED (7.3 m³/h steam), and demands 235 kW of electrical power versus 245 kW (plus steam) for MSF and 50 kW (plus 7.5 m³/h steam) for MED. RO’s high brine pressure (53.5 bar) enables energy recovery, whereas MSF and MED discharge warm brine at low pressure, posing environmental challenges. Economically, unit water costs are $0.37/m³ for RO, $1.52/m³ for MSF, and $1.21/m³ for MED. Overall, RO is the most technically and economically viable option for this capacity under Libyan conditions.

Evaluation of thermal desalination and reverse osmosis for the production of boiler feed water from sea water for coastal thermal power stations in India

Scale formation represents a major operational problem encountered in thermal desalination plants. In current installed plants, and to allow for a reasonable safety margin, sulfate scale deposition limits the top brine temperature (TBT) in multi-stage flash (MSF) distillers up to 110-112?C. This has significant effect on the unit capital, operational and water production cost. In this work, the influence of nanofiltration (NF) pretreatment on the scale deposition potential and increasing TBT in MSF thermal desalination plants is modeled on the basis of mass transfer with chemical reaction of solutes in the brine. Full and partial NF-pretreatment of the feed water were investigated. TBT can be increased in MSF by increasing the percentage of NF-treated feed. Full NF pretreatment of the make-up allows TBT in the MSF plant to be raised up to 175?C in the case of di hybrid NF-MSF and up to 165?C in the case of tri hybrid NF-RO-MSF. The significant scale reduction is associated with increasing flashing range, unit recovery, unit performance, and will lead to reduction in heat transfer surface area, pumping power and therefore, water production cost.