Environmental impact of seawater desalination plants

On the brine re-utilization of a multi-stage flashing (MSF) desalination plant

Hybrid systems in seawater desalination-practical design aspects, status and development perspectives

Water scarcity is an alarming global problem for a growing population with depleting sources of fresh water. Desalination is thus becoming an important solution for water management to address such looming shortage of the municipal water supply. At present, several technologies dominate the desalination industry which can be categorized either as a thermal process such as multi-stage flash distillation or a membrane process such as that of reverse osmosis. New desalination systems are also being developed to make the process more cost-effective and energy efficient. Hence, this work proposes a systematic approach for optimal selection of desalination systems using fuzzy analytic hierarchy process (FAHP) and grey relational analysis (GRA). Fuzzy AHP addresses the vagueness involve in the trade-off of the criteria or attributes used in evaluating the alternatives. On the other hand, the GRA solves the multiple criteria decision problem by aggregating the entire range of performance attribute values for every alternative into a single score in spite of incomplete information. An illustrative case study was presented wherein five desalination systems namely reverse osmosis (RO), combined reverse osmosis and forward osmosis (RO-FO), electrodialysis (ED), multi-stage flash distillation (MSF), and combined forward osmosis and membrane distillation (FO-MD) were evaluated. These desalination systems were compared to each other with respect to energy requirement, land footprint, system efficiency, economic viability, and maturity of technology. Sensitivity analysis was also done to determine the robustness of the modeling results from the variation of weights of the criteria.

Novel Tri Hybrid Desalination Plants

Multi-criteria sustainability assessment of water desalination and energy systems — Kuwait case

Desalination technologies and their environmental impacts: A review

Oman is situated at the south-east of the Arabian Peninsula at the entrance to the Arabian Gulf, and its coastline stretches 1700 km along the Gulf of Oman in the north to the Arabian Sea in the south. Most of the population lives in the north-eastern coastal areas and in the capital area of Muscat. The climate of Oman is typically described as a tropical hyper-arid, with two distinct seasons: winter and summer. The winter period extends from late November to April, during which rains at irregular intervals occur. However, based on 27 years of rainfall data from 1977 (Kwarteng et al., 2009), the annual mean rainfall for the whole country is 117 mm. Hot weather with high humidity is experienced in the coastal areas during the summer months. The mean air temperature in northern Oman varies between 32 oC to 48 oC from May to September, and between 26 oC to 36 oC from October to April. The mean wind speeds range between 2 and 3.5 m/s, with high winds encountered during the summer months. Desalinated water has been used in Oman since 1976 when the Al-Ghubrah (co-location) power and seawater desalination plant using a thermal technology of multi-stage flash (MSF) was first commissioned in Muscat. To meet continuously growing water demand due to population growth and economic and social development and to reduce the reliance on groundwater resources, by 1999 the Al-Ghubrah plant had seven MSF desalination units installed. The first seawater desalination unit installed had a capacity of 22,750 m3/d, and the other six MSF units each have a capacity of 27,000 m3/d. Desalinated water usage in Oman is expected to increase further in the future, due to new industrial and tourismrelated developments. Desalination plants extract large volumes of seawater and discharge hot, hypersaline brine back into the marine environment. Therefore, the main concern of continuous brine discharges has been the potential impact upon the salinity of seawater (and possible thermal stress for discharges from MSF plants), and the resultant effects to marine communities around discharge outlets. Other occasional discharges from the plants include corrosion products, toxic antifoulants and antiscalants used in maintaining plant infrastructure (Roberts et al., 2010). As brine discharges are often denser and heavier than receiving marine waters, the brine streams tend to sink and spread further along the seabed than at the

Flaring of gas often having high heating value results in considerable economic and energy losses in addition to significant environmental impacts. Power generation through combined gas and steam turbine cycles may be considered as a suitable flare gas recovery process. Thermal sea-water desalination is a process that requires a considerable amount of heat; hence it may be used in downstream of power generation cycles. Energy is the largest section of the water generation cost of all desalination processes. The energy cost of thermal distillation sea-water plants is close to 50-60% of water generation costs. In the current study, the generation of power and desalinated water through the gas turbine cycle, steam cycle, and multistage flash (MSF) method using flare gas of cheshmeh khosh are investigated. The economic parameters related to the different scenarios considered for the production of power and water are evaluated in the current research. According to the economic evaluation carried out, the most economically profitable scenarios for the investigated co-generation plant is generating as much as possible power in the steam turbine and using the remaining heat in the low-pressure outlet steam in the MSF desalination process. The results show that by increasing steam turbine outlet pressure from 3 bar to 78 bar, power and water generation is changed from 697 to 581 MW and 1557 to 2109 m3/h, respectively. Also, by increasing the outlet pressure of the steam turbine from 3 to 78 bar, the total capital cost is changed from 1177 to 1192 MUSD, and the operating cost is changed from 117.85 to 117 MUSD/year. Finally, operating profit will decrease from 300 to 50 MUSD/year, and payback time will change from 3.92 to 4.75 years.

Despite being a mature process, production of fresh water using desalination is still a challenge. Desalination is broadly divided into two categories; thermal desalination processes, such as multi-stage flash, and semi-permeable membrane process, such as Reverse Osmosis (RO). This work is aimed at developing correlations for water permeability coefficient (Kw) and salt permeability coefficient (Ks) as a function of feed salinity and pressure using experimental data for a continuous RO process. For three different feed salinities of 15, 25, and 35 g/L at two different pressures of 40 and 45 bara experimental values of Ksand kwvalues are taken from the literature. Planar and ellipsoidal least square methods are used to correlate kwand Ksas a function of feed salinity and pressure, which are then embedded within the continuous RO process model to evaluate the process performance in terms of maximising the recovery ratio while optimizing the area and pressure to get the desired freshwater salinity. gPROMS model builder is used to simulate and optimise the process.

Thermoeconomic analysis of combined power cycle integrated with MSF/SWRO desalination plant

Improved productivity of the MSF (multi-stage flashing) desalination plant by increasing the TBT (top brine temperature)

Globally, energy is a dynamic element that makes people's major energy demands. There are a variety of energies; the one that is stupendous potential is solar. Solar energy is an efficient problem solving one to eliminate pollution from the environment and water scarcity. This review article provides the accomplishments in the progress of the solar pond, solar desalination and integration of both the systems in the recent years. The solar pool is one of the thermal energy storing systems which perform as a huge solar radiation collector to capture and store sun’s rays. The accumulated heat in the solar pool is weighed as the low category thermal energy. Hence, to enhance the performance upgrades are mandatory. Initially, use of unique salts and various additives is studied. And then, ingenious empirical works and several layers for minimizing the thermal losses from the upper and lower layers are exhibited. Heat removal techniques from the heat storage zone and mathematical model analysis are discussed. In addition, solar desalination unit is one of the possibilities for the effective production of sweet water from any form of polluted water (marine, brackish and contaminated water). Solar still is a trouble-free device utilized by condensation and evaporation processes to improve the limpidity of the water with the utilization of solar energy. This work made an attempt to classify various still designs with the greater volume of production. And also it analyzes the new innovations and thermal energy transfer process to reach at positive judgment. Desalination system performance is low for conventional approach, as desalination plant efficiency is relative to inlet water temperature, to upgrade it the solar pond coupled to desalination unit. With the exploitation of brine concentration and recovery system and multi-stage flash, fins and flat plate collector helps to elevate the beneficial solar pond and desalination output. This comprehensive review will guide the imminent researchers who desire to accelerate the performance of the pond and desalination units further.

Features of multi-effect evaporation desalination plants

Systematic Analysis Reveals Thermal Separations Are Not Necessarily Most Energy Intensive

Over the past decade, the author, Roger Francis, has looked at some very expensive corrosion failures in desalination plants. Avoiding Corrosion in Desalination Plants tells the reader how to avoid existing corrosion problems and how to avoid them in new builds. This book looks at corrosion problems specific to MSF, MED, and SWRO desalination plants, describing their causes, some solutions, and the relative performance of various materials. It gives advice on procuring materials for desalination plants to avoid quality problems. The world’s population is steadily increasing and with it is an increasing demand for water—for both drinking and irrigation. In many areas of the world, particularly in warmer climates, there are limited sources from rivers and wells, so desalination is being increasingly used to produce water to satisfy both requirements. Although desalination is sometimes carried out on brackish waters and highly saline well waters, most desalination plants generate fresh water from seawater. There are three main processes used in desalination plants, the oldest of which is multistage flash (MSF), where the water is essentially boiled at low pressure and the steam that flashes off is condensed for drinking water. The second process is multiple-effect distillation (MED), in which low-pressure steam is used to force evaporation of seawater and the vapor is then condensed for drinking water. Although actual MSF and MED plants (large-scale) are land based, small-scale units have been fitted to large ships, such as cruise liners, to generate fresh water. The third process is seawater reverse osmosis (SWRO), where chloride is selectively removed from water by forcing it at high pressure through a special membrane. This method involves no heat transfer but requires enough electricity to power the high-pressure pumps that are required. All three of these methods have advantages and disadvantages. This book looks at corrosion problems specific to MSF, MED, and SWRO desalination plants, describing their causes, some solutions, and the relative performance of various materials. It gives advice on procuring materials for desalination plants to avoid quality problems.