Seawater reverse osmosis plants

The approximate operating costs for brackish and seawater reverse osmosis plants are given in Table 5.3. These numbers are old, but improvements in membrane technology have kept pace with inflation so the costs remain reasonably current. 

Table 5.3 Operating costs for large brackish water and seawater reverse osmosis plants [49]. Capital costs are approximately US 1.25 per gal/day capacity for the brackish water plant and US 4-5 per gal/day capacity for the seawater plant...

Co-location of a power plant and a seawater reverse osmosis desalination plant allows for the cooling water from a neighbouring power plant to be blended with the waste from a desalination plant before discharge (Voutchkov 2004). In such a process, seawater is used as the cooling water for the condensers in a power plant. This water is then used as both the feed for the desahnation process, and for blending to dilute the concentrate from the desalination plant. 

Reverse osmosis is now extensively used to reduce salt concentrations in brackish waters and to treat industrial waste water, for example, from pulp mills. Reverse osmosis has also proved economical (the cost can be as low as about 1 per 1000 liters) for large-scale desalination of seawater, a proposition of major interest in the Middle East, where almost all potable water is now obtained by various means from seawater or from brackish wells. Thus, at Ras Abu Janjur, Bahrain, a reverse osmosis plant converts brackish feedwater containing 19,000 ppm dissolved solids to potable water with 260 ppm dissolved solids at a rate of over 55,000 m3 per day, with an electricity consumption of 4.8 kilowatt hours per cubic meter of product. On a 1000-fold smaller scale, the resort community on Heron Island, Great Barrier Reef, Australia, obtains most of its fresh water from seawater (36,000 ppm dissolved salts) directly by reverse osmosis, at a cost of about 10 per 1000 liters. 

Desert countries like Saudi Arabia have built reverse osmosis plants to produce fresh water from seawater. Assume that seawater has the composition 0.470 M NaCl and 0.068 M MgCl2 and that both compounds are completely dissociated. 

Dalvi, A. G. I., Al-Rasheed, R., and Javeed, M. A. (2000) Studies on organic foulants in the seawater feed of reverse osmosis plants of SWCC. Desalination 132,217-232. 

Some of the largest plants for seawater desalination, wastewater treatment and gas separation are already based on membrane engineering. For example, the Ashkelon Desalination Plant for seawater reverse osmosis (SWRO), in Israel, has been fully operational since December 2005 and produces more than 100 million m3 of desalinated water per year. One of the largest submerged membrane bioreactor unit in the world was recently built in Porto Marghera (Italy) to treat tertiary water. The growth in membrane installations for water treatment in the past decade has resulted in a decreased cost of desalination facilities, with the consequence that the cost of the reclaimed water for membrane plants has also been reduced. 

Bou-Hamad, S., et al. (1997). Performance evaluation of three different pretreatment systems for seawater reverse osmosis technique. Desalination Int. Symp. Pretreatment of Feedwater for Reverse Osmosis Desalination Plants, March 31-April 2, 110, 1-2, 85-92. Elsevier Science B.V., Amsterdam, Netherlands. 

FIGURE 43.2 The three alignments suggested for the realization of a seawater reverse osmosis (SWRO) desalination plant between Israel and the Hashemite Kingdom of Jordan. (From http //www.mfa.gov.il/mfa.)... 

Both the brackish and seawater reverse osmosis product water costs are based on 1982 costs and they are indicative of specific plants in an assumed location in the southern United States. The cost of energy in the seawater system assumes that the reject from the first stage high pressure reverse osmosis system is sent to an energy recovery system which reduces the overall energy requirements for the total system by 31%. 

Pohland HW, Seawater desalination and reverse osmosis plant design. Desalination 1980, 32,157-167. 

V. Murugan, K. Rajanbabu, S.A. Tiwari, C. Balasubramanian, M.K. Yadav, A.Y. Dangore, S. Prabhakar, P.K.Tewari, Fouling and cleaning of seawater reverse osmosis membranes in Kalpakkam nuclear desalination plant, Int. J. Nucl. Desal. 2,2006,172-178. 

Commercial membrane separation processes include reverse osmosis, gas permeation, dialysis, electrodialysis, pervaporation, ultrafiltration, and microfiltration. Membranes are mainly synthetic or natural polymers in the form of sheets that are spiral wound or hollow fibers that are bundled together. Reverse osmosis, operating at a feed pressure of 1,000 psia, produces water of 99.95% purity from seawater (3.5 wt% dissolved salts) at a 45% recovery, or with a feed pressure of 250 psia from brackish water (less than 0.5 wt% dissolved salts). Bare-module costs of reverse osmosis plants based on purified water rate in gallons per day are included in Table 16.32. Other membrane separation costs in Table 16.32 are f.o.b. purchase costs. 

Kim, Y., Kang, M.G., Lee, S. et al. (2013) Reduction of energy consumption in seawater reverse osmosis desalination pilot plant by using energy recovery devices. Desalination and Water Treatment, 51 (4-6), 766-771. doi 10.1080/19443994.2012.705549... 

But what if you apply more pressure than is necessary to stop the osmotic process, exceeding the osmotic pressure Water is forced through the semipermeable membrane from the more concentrated side to the more dilute side, a process called reverse osmosis. Reverse osmosis is a good, relatively inexpensive way of purif5dng water. My local water store uses this process to purify drinking water (so-called RO water ). There are many reverse osmosis plants in the world, extracting drinking water from seawater. Navy pilots even carry small reverse osmosis units with them in case they have to eject at sea. 

A single pass reverse osmosis plant is used for the desalination of seawater (3.5wt% NaCl). 

Organization. A large reverse osmosis plant in Ashkelon, Israel, processes seawater to produce more than 330,000 cubic meters per day (330 million L/day) of fresh water. This is enough to provide 13% of the country s domestic consumer demand. The Kuwaiti and Saudi water purification plants that were of strategic concern in the Persian Gulf War use reverse osmosis in one of their primary stages. 

A desalination plant is assumed to be a standard option for the SPINNOR and VSPINNOR reactors. Seawater reverse osmosis (SWRO) system is targeted for use as described detail in [XXVI-8]. The specific energy consumption for potable water production is estimated at 6 kWh/m. The pressure in the SWRO section is assumed to be 3.8 4.6 MPa. 

To justify the assumptions, the estimated cost in power consumption, labor, and membrane replacement was compared with that in a seawater reverse osmosis desalination (SWRO) plant (Atikol et al., 2005). For SWRO, the reported cost for power was 0.04 US m, we estimated 0.022 US m for our system. The lower cost in energy consumption is mainly due to the low operating pressure and significantly higher water recovery in this system. The cost for pre-treatment was assumed to be lower than seawater plant due to the significantly much better water quality in the drinking water sources. The maintenance cost was adopted from the... 

System life time [years] 30 Assumption based on seawater reverse osmosis desalination plant... 

Reverse osmosis is used for desalination of seawater, treatment of recycle water in chemical plants and separation of industrial wastes. More recently the technique has been applied to concentration and dehydrogenation of food products such as milk and fruit juices. See ultrafiltralion. 

The first reverse osmosis modules made from cellulose diacetate had a salt rejection of approximately 97—98%. This was enough to produce potable water (ie, water containing less than 500 ppm salt) from brackish water sources, but was not enough to desalinate seawater efficiently. In the 1970s, interfacial composite membranes with salt rejections greater than 99.5% were developed, making seawater desalination possible (29,30) a number of large plants are in operation worldwide. 

Reverse osmosis processes for desalination were first appHed to brackish water, which has a lower I DS concentration than seawater. Brackish water has less than 10,000 mg/L IDS seawater contains greater than 30,000 mg/L IDS. This difference in IDS translates into a substantial difference in osmotic pressure and thus the RO operating pressure required to achieve separation. The need to process feed streams containing larger amounts of dissolved soHds led to the development of RO membranes capable of operating at pressures approaching 10.3 MFa (1500 psi). Desalination plants around the world process both brackish water and seawater (15). 

Concentration of Seawater by ED. In terms of membrane area, concentration of seawater is the second largest use. Warm seawater is concentrated by ED to 18 to 20% dissolved soHds using membranes with monovalent-ion-selective skins. The EDR process is not used. The osmotic pressure difference between about 19% NaCl solution and partially depleted seawater is about 20,000 kPa (200 atm) at 25°C, which is well beyond the range of reverse osmosis. Salt is produced from the brine by evaporation and crystallisa tion at seven plants in Japan and one each in South Korea, Taiwan, and Kuwait. A second plant is soon to be built in South Korea. None of the plants are justified on economic grounds compared to imported solar or mined salt. 

Industrial Wastes. Closely related to seawater concentration is the simultaneous concentration of industrial effluents and recycle of recovered water (see Wastes, industrial). These appHcations are expected to increase as environmental restrictions increase. Examples are the concentration of blowdown from cooling towers in power plants concentration of reverse osmosis blowdown and the processing of metal treatment wastes (11) (see... 

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