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4. SALINE WATER INTAKES AND PRETREATMENT
TABLE 4.2
Advantages
• Capital cost savings by avoiding the construction of separate intake pipeline and structure, and new discharge outfall.
• Decrease of the required RO system feed pressure and power cost savings as a result of using warmer water.
• Reduction of unit power cost by connecting directly to power plant generation facilities and avoiding power transmission charges.
• Accelerated permitting process as a result of avoidance of construction of new intake and discharge outfalls in the ocean.
• Reduction of marine organism impingement and entrainment because the desalination plant does not take additional seawater from the ocean.
• Reduction of the impact on marine environment as a result of faster dissipation of thermal plume and concentrate.
• Reduction of the power plant thermal discharge to the ocean because a portion of this discharge
is converted to potable water.
• Use of already disturbed land at the power
plant minimizes environmental impact.
Key Advantages and Disadvantages of Desalination Plant Collocation
Disadvantages
• Use of warmer seawater may accelerate membrane biofouling, especially if the source water is rich in organics.
• RO membranes may be exposed to iron, copper, or nickel fouling if the power plant condensers and piping are built of low-quality materials.
• Source seawater has to be cooled if its temperature increases above 40 C to protect RO-membrane integrity.
• Permeate water quality diminishes slightly with the increase of source water temperature.
• Use of warmer water may result in lower boron rejection and require feed water pH adjustment to meet stringent boron-water quality targets.
• RO-plant source water screening may be required
if the power plant disposes off its screenings through their outfall and the point of disposal is upstream of the desalination plant intake.
• Desalination plant operations may need to be discontinued during periods of heat treatment
of the power plant facilities.
estuaries as well. The impingement and entrainment effects of open intakes may be mitigated significantly if the source water velocity of the intakes is reduced below 0.15 m/s (0.5 fps).
4.3.8 Construction Costs of Open Intakes
4.3.8.1 Costs of Onshore Intakes
Fig. 4.13 depicts the construction costs of onshore open intakes as a function of the desali- nation plant intake flow. Because of the significant impact of the site-specific conditions of the actual intake costs, such costs may vary within 30% of the values indicated on this figure.
4.3.8.2 Costs of Offshore Intakes
The construction costs for intake systems with offshore inlet structures and HDPE pipe- lines, and with concrete tunnels are depicted on Fig. 4.14. These costs are presented as a func- tion of the plant intake flow and are expressed in US $ per meter of intake conduit. Similar to the onshore intake construction costs, the costs for these types of intakes will vary from one location to another and will be influenced by site-specific conditions such as water depth, geology, and currents, and they could be within a 30% envelope of the values indicated on Fig. 4.14. Analysis of this figure indicates that the construction of desalination plant intakes with deep tunnels is typically several times more costly than the installation of HDPE pipeline on the bottom of the source water body.