An evaluation of the energy requirements of desalination processes on the basis of the fuel-use performance ratio

Gaseous hydrocarbons and the development of producing countries: International days in Dijon, 17, 18, 19 May 1973

Novel Tri Hybrid Desalination Plants

A variety of industrial wastewater recovery technologies for different areas and applications has been developed over the years, including primarily thermal and membrane processes. The main thermal processes include atmospheric distillation, distillation with mechanical vapor compression, vacuum distillation, multi-stage flash distillation, multi-effect distillation with thermal vapor compression, etc. [1,2]. The membrane processes contain reverse osmosis, electrodialysis, and nanofiltration. The multi-stage flash distillation and reverse osmosis processes dominate in most applications. Wastewater recovery and re-use technologies have been expanding rapidly in recent decades. The market is also driven by the falling costs of wastewater recovery, which are due to the technological advances in the process. The costs of clean water produced by wastewater recovery process dropped considerably over the years as a result of reductions in price of equipment, reductions in power consumption and advances in system design and operating experiences. In this work state-of-the art and innovative wastewater recovery/re-use technologies are estimated and compared in their features and cost respects. The new technology is discussed that allows increasing in energy efficiency of the wastewater recycling and reduce electricity consumption associated with conventional methods. Successful development and implementation of the technology for food processing applications will provide large energy and water savings to the industry. These savings are tied to an energy efficiency increase and reduction in pumping power for process water supply. The ability to integrate waste heat recovery with wastewater reuse also leads to product cost reduction opportunities for producers.

The Pebble Bed Modular Reactor (PBMR), under development in South Africa, is an advanced helium-cooled graphite moderated high-temperature gas-cooled nuclear reactor. The heat output of the PBMR is primarily suited for process applications or power generation. In addition, various desalination technologies can be coupled to the PBMR to further improve the overall efficiency and economics, where suitable site opportunities exist. Several desalination application concepts were evaluated for both a cogeneration configuration as well as a waste heat utilization configuration. These options were evaluated to compare the relative economics of the different concepts and to determine the feasibility of each configuration. The cogeneration desalination configuration included multiple PBMR units producing steam for a power cycle, using a back-pressure steam turbine generator exhausting into different thermal desalination technologies. These technologies include Multi-Effect Distillation (MED), Multi-Effect Distillation with Thermal Vapor Compression (MED-TVC) as well as Multi-Stage Flash (MSF) with all making use of extraction steam from backpressure turbines. These configurations are optimized to maximize gross revenue from combined power and desalinated water sales using representative economic assumptions with a sensitivity analysis to observe the impact of varying power and water costs. Increasing turbine back pressure results in a loss of power output but a gain in water production. The desalination systems are compared as incremental investments. A standard MED process with minimal effects appears most attractive, although results are very sensitive with regards to projected power and water values. The waste heat utilization desalination configuration is based on the current 165 MWe PBMR Demonstration Power Plant (DPP) to be built for the South African utility Eskom. This demonstration plant is proposed at the Koeberg Nuclear site and utilizes a direct, single shaft recuperative Brayton Cycle with helium as working fluid. The Brayton Cycle uses a pre-cooler and inter-cooler to cool the helium before entering the low-pressure compressor (LPC) and the high-pressure compressor (HPC) respectively. The pre-cooler and intercooler rejects 218 MWt of waste heat at 73°C and 63°C, respectively. This waste heat is ideally suited for some low temperature desalination processes and can be used without negative impact on the power output and efficiency of the nuclear power plant. These low temperature processes include Low Temperature Multi-Effect Distillation (LT-MED) as well Reverse Osmosis (RO) with pre-heated water. The relative economics of these design concepts are compared as add-ons to the PBMR-DPP and the results include a net present value (NPV) study for both technologies. From this study it can be concluded that both RO as well LT-MED provide water at reasonable production rates, although a final study recommendation would be based on site and area specific requirements.

Utilization of waste heat in the desalination process

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.

Systematic Analysis Reveals Thermal Separations Are Not Necessarily Most Energy Intensive

Energy storage for desalination processes powered by renewable energy and waste heat sources

Multi-effect boiling systems from an energy viewpoint

Powering desalination by waste heat is often proposed to mitigate energy consumption and environmental impact; however, thorough technology comparisons are lacking in the literature. This work numerically models the efficiency of six representative desalination technologies powered by waste heat at 50, 70, 90, and 120 °C, where applicable. Entropy generation and Second Law efficiency analysis are applied for the systems and their components. The technologies considered are thermal desalination by multistage flash (MSF), multiple effect distillation (MED), multistage vacuum membrane distillation (MSVMD), humidification-dehumidification (HDH), and organic Rankine cycles (ORCs) paired with mechanical technologies of reverse osmosis (RO) and mechanical vapor compression (MVC). The most efficient technology was RO, followed by MED. Performances among MSF, MSVMD, and MVC were similar but the relative performance varied with waste heat temperature or system size. Entropy generation in thermal technologies increases at lower waste heat temperatures largely in the feed or brine portions of the various heat exchangers used. This occurs largely because lower temperatures reduce recovery, increasing the relative flow rates of feed and brine. However, HDH (without extractions) had the reverse trend, only being competitive at lower temperatures. For the mechanical technologies, the energy efficiency only varies with temperature because of the significant losses from the ORC.

wo rapidly growing reverse osmosis (RO) applications are seawater desalination and municipal wastewater reclamation. As water shortages increase, enhanced technology is improving the reliability of desalination processes and making produced water more affordable. RO Benefits RO technology continues to increase its market share in the desalination market because of the technology’s improved reliability and reduced energy requirements. Even in seawater applications, where high feed salinity requires high-pressure RO operation, energy requirements for RO processes are lower than the combined energy requirements of distillation processes (see figure below). In seawater desalination applications, high water permeability of today’s RO membranes, combined with increasingly higher salt rejection, enables users to optimize system operating parameters to minimize energy requirements. Additional energy reductions are possible with advanced energy recovery systems. However, further energy reductions will be minimal because of pressure limitations of the RO process and osmotic pressure of the concentrate stream. RO Options Forward osmosis (FO) is an emerging membrane desalination technology that does not have such pressure limitations. Although FO development is still in its early stages, the technology promises to significantly lower ener

The Nuclear Desalination Demonstration Project (NDDP) at Kalpakkam aims to demonstrate the safe and economic production of good quality water by desalination of seawater comprising 4,500 m³/d Multi-Stage Flash (MSF) and 1,800 m³/d Reverse Osmosis (RO) plant. The design of the hybrid MSF–RO plant to be set up at an existing nuclear power station is presented. The MSF plant based on long tube design requires less energy. The effect on performance of the MSF plant due to higher seawater intake temperature is marginal. The preheat RO system part of the hybrid plant uses reject cooling seawater from the MSF plant. This allows lower pressure operation, resulting in energy saving. The two qualities of water produced are usable for the power station as well as for drinking purposes with appropriate blending. The post treatment is also simplified due to blending of the products from MSF and RO plants. The hybrid plant has a number of advantages: part of high purity desalted water produced from the MSF plant will be used for the makeup demineralised water requirement (after necessary polishing) for the power station; blending of the product water from RO and MSF plants would provide requisite quality drinking water; and the RO plant will continue to be operated to provide water for drinking purposes during the shut down of the power station. Commissioning of the RO section is expected in 2002 and that of the MSF section in 2003. Useful design data are expected from the plant on the coupling of small and medium size reactors (SMR) based on PHWR. This will enable us to design a large size commercial plant up to 50,000 m³/d capacity. India will share the O&M experience of NDDP to member states of the International Atomic Energy Agency (IAEA) when the plant is commissioned. The development work for producing good quality water for power station from high salinity water utilizing low grade waste heat is presented. About 40 and 100 MWth low temperature waste heat is available in the moderator systems of the 220 and 500 MWe PHWR respectively. A significant part of this waste heat can be utilized for seawater desalination for in-house consumption. The Low Temperature Evaporation (LTE) technology for producing low conductivity water from seawater has been demonstrated at BARC on 30 m³/d scale by using waste heat. This plant is being connected to the CIRUS reactor for demonstration of coupling to a nuclear research reactor. The product water from this plant after minor polishing will meet the make up water requirement of the research reactor.

Retrofitting the combined-cycle producing electric power and desalted seawater to include district cooling in GCC

Coupling of a nuclear reactor to hybrid RO-MSF desalination plants

Hybrid Desalination Systems: Alternative Designs of Thermal and Membrane Processes.