Evaporation desalination

Fig. 4. The 341,000-m /d multistage flash (MSF) evaporation desalination plant A1 Taweelah B in Abu Dhabi, United Arab Emirates. Courtesy of Italimpianti SpA. It is a dual-purpose plant, composed of six identical power and desalination units. The desalination units at 56,800 m /d each are currently (1997) the largest ia the world. They have 17 recovery and 3 reject stages and a Performance Ratio of 8 1. The plant also produces 732 MWe of...

W. J. Prince, Enhanced Tubes for Horizontal Evaporator Desalination Process, MS thesis in engineering, University of California, Los Angeles, 1971. 

Figure 3.30. A freezer/evaporator desalinator with H2O as the refrigerant.

Evaporation is generally carried out in one stage and the vapor is pure solvent, e.g. evaporative desalination of saline water produces pure water vapor. Following relation (10.1.39), the minimum heat required per mole of feed is... 

Desalination. Desalination of seawater and brackish water has been and, as of the mid-1990s, is the primary use of RO. Driven by a need for potable water in areas of the world where there is a shortage, this industry has developed. Desalination involves the reduction of the total dissolved soHds (IDS) concentration to less than 200 mg/L. RO offers several advantages over other possible desalination processes such as distillation (qv), evaporation (qv), and electro dialysis. The primary advantage of RO over the traditionally used method of distillation is the energy savings that is afforded by the lack of a phase change in RO. 

Desalination. A special case of distillation is water desalination. In places where energy is abundant but fresh water is not, eg, the Arabian Peninsula, water may be produced from seawater ia flash evaporators. Low pressure turbiae steam is extracted to provide heat for the evaporators. Coadeased steam is returned to the cycle. Such units may be particularly prone to corrosion by salts. Sizes vary, but a plant scheduled for completion in 1996 had six units and a total capacity of 345,600 m /d. Power generation was expected to be 17,500 MW (36). 

V. B. Chemo2ubov and co-workers, in Proceedings of the 1 st International Symposium on Water Desalination, Washington, D.C., Oct. 1965, p. 139. CIBA-Geigy Corp., The Application ofBelgardEU and Belgard EUN in Sea Water Evaporators, CIBA-GEIGY pamphlet DB 21. 

Evaporation. In most chemical industry evaporation systems, the objective is product recovery, although occasionally the objective is concentration of an organic waste from an aqueous solution, to facihtate incineration. Similar equipment is used extensively for desalination of salt or brackish water (see also Water, supply and desalination). 

Much as reverse osmosis (qv) can compete with evaporation in desalination appHcations, osmosis should also be considered as an alternative for process evaporation. Reverse osmosis is particularly attractive where the inlet stream is greater than 99% water. 

Ni-Si recovery of HP Processes involving cone. H2SO4 processes. Sulphur stripping columns. Distillation columns containing acidic chlorides. Handling acid sludges processes impellers, propeller shafts, fasteners. Demisters in desalination plants refrigerating brines. Salt production. Evaporators steel... 

Distillation processes, 26 61-73. See also Distillation(s) freeze-desalination, 26 71 materials and scaling issues in, 26 71-73 multi-effect distillation, 26 65-67 multistage flash evaporation, 26 61-65 vapor compression distillation, 26 67 Distillation reactors, 21 332 Distillation region diagrams (DRD), 22 302, 303, 331... 

Multistage flash (MSF) processes, 21 650 Multistage flash desalination, 26 59 Multistage flash evaporation, 26 61-65, 97 energy required by, 26 86 in hybrid desalination systems, 26 95-96 schematic flow and temperature diagram of, 26 62... 

The concentrations of seawater and brackish water can vary significantly, and as such there is a difference between the concentrate produced from seawater desalination plants and brackish water desahnation plants. Seawater typically has a level of total dissolved solids (TDS) between 33,000-37,000 mg/L. The average major ion concentration of seawater is shown in Table 2.1 along with water from the Mediterranean Sea, and water from Wonthaggi off the southern coast of Australia. Seawater sahnity increases in areas where water evaporates or freezes, and it decreases due to rain, river runoff, and melting ice. The areas of greatest salinity occur and latitudes of 30° N and S where there are high evaporation rates. 

Ahmed, M., Shayya, W.H., Hoey, D., Mahendran, A., Morris, R., Al-Handaly, J. Use of evaporation ponds for brine disposal in desalination plants. Desalination 130(2), 155-168 (2000) Mickley, M. Treatment of Concentrate, Desalination and Water Purification Research and Development Program Report No. 155. U.S. Department of the Interior, Bureau of Reclamation, Denver (2009)... 

The feasibility of an evaporation pond is determined by the volume of concentrate, the cost of land and the ambient evaporation rate. They are most cost-effective in areas with low rainfall, high evaporation rates, and where large expanses of land are available at low cost (Mickley 2009). This best suits inland desalination plants in regional and remote areas where these conditions can be met. 

Nicot, J.-P., Gross, B., Walden, S., Baier, R. Self-Sealing Evaporation Ponds for Desalination Facilities in Texas. Texas Water Development Board, Austin (2009)... 

The successful development of asymmetric cellulose acetate membranes by Loeb and Sourirajan in the early sixties, at the University of California, Los Angeles, has been primarily responsible for the rapid development of Reverse Osmosis (RO) technology for brack sh/sea water desalination. Reverse Osmosis approaches a reversible process when the pressure barely exceeds the osmotic pressure and hence the energy costs are quite low. Theenergy requirement to purify one litre of water by RO is only O.OO3 KW as against 0,7 KV required just to supply the vaporisation energy to change the phase of one litre of water from liquid to vapour by evaporation. Thus RO has an inherent capability to convert brackish water to potable water at economic cost and thus contribute effectively to the health and prosperity of all humanity. 

Fig. 2. Multistage flash evaporation process used in desalination...

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