تصميم الابار الشاطئية بانواعها المختلفة

BEACH WELLS

GENERAL.DR

BAHAA BADR

Importance of Intake Systems in SWRO Plants

The amount and quality of feed water entering a desalination plant is greatly dependent upon the type and placement of the feed water intake
Raw water intake systems in SWRO plants

– Two main options: Open Sea Intake Vs Beach Wells systems.
– Design of the plant, equipment selection, process elements to be considered and the correct operation of the plant, as well as the operating costs, will depend of the Intake System selected.

Types of Sea Water Intake Systems

• Open Intakes
– Open Surface (1)
– Deep intake (2)

Types of Sea Water Intake Systems

• Beach wells
– Vertical (beach or coast) (3)
– Horizontal directional drilled(4)

Targets of the ideal Intake System

• Avoid suspended organic matter (solids, colloids, etc)
• Avoid dissolved organic matter (grease, oil, etc)
• Avoid biological activity (algae, plancton, etc)
• Keep permanent physicchemical characteristics (temperature, salinity)
• Avoid dissolved heavy metals and scaling compouds.

Targets of the ideal Intake System

• Optimum quality (prefiltered water).
• Constant feed flow (not decreasing in time).
• As close as posible to the site of the desalination plant (to optimize energy consumption).
• Flexibility to adjust the sea water flow to the required feed water flow to the RO trains (RO plants are modular installations).
• Environmental friendly, avoiding negative impacts over the environment (sea and coast).
• Viability (licenses and permits) to access to the
beach or coast.

Description of the different Systems

Surface Open Sea Water Intake Systems (1)

Open ocean intakes, or direct intakes, can be as simple as dredged channels through a nearshore region to draw in sea water.

This type of Intake systems, although used sometime in the past, they are not used nowadays because of the technical disadvantages:

normally they provide a low quality feed water resulting in nonprogramed stops of the installation with high inconveniences, mainly in industrial applicatons as mining; and environmental issues (hard visual impact in seashore)
Surface Open Sea Water Intake Systems (1)

• Advantages
– Low investment
– Permanent sea water feed flow guaranteed
– Possibility to get high sea water flows

• Disadvantages
– Low feed water quality, resulting in a high potential scaling and
higher operating costs
– Very rough pretreatment is required
– High content of TSS, colloids, TOC, oil and grease would increase the operating costs
– Complicated to get licenses and authorizations to consider this type of Intake
– Deep environmental impact afecting to the coast/beach

Deep Sea Water Intake Systems (2)

• It is a more sophisticated direct intake system that involve the construction of pipelines from shore to beyond the nearshore, out to waters deeper than 35 meters.

Deeper water is desirable in that the intake is less affected by waves and tidal action, but added pumping costs and pipeline costs limit the depth to which direct intakes can be practically placed. Direct intakes in general are fairly long lived in that they can have a service life of 3050 years.

They also provide an unlimited supply of seawater to a desalination plant as the seawater is pumped directly to the plant.

• In large desalination plants, more than one plastic pipe can be considered to feed sea water, working this way with smaller diameters.

• Submarine works to install the feed water pipes are very
complicated and always made by specialised companies in this type
of matters.

Deep Sea Water Intake Systems (2)

• It is very important to select the optimum point for the Deep Intake System to be installed. Commonly, selection of this point it is the result of a technical/economical balance.

• A sea water intake structure (tower, basket filter, screen…) has to be installed in the selected point.

• The deep selected to install the Intake System will pursuit two main objectives:

deep enough to avoid sunlight but, at certain heigh from the bottom to avoid sand and suspended particles coming into the system.

Deep Sea Water Intake Systems (2)

• Advantages

– Beach or coast are not affected (inland piping is normally underground)
– Possibility to get big sea water flows (commonly used in large
installations).
– Permanent feed flow guaranteed.

• Disadvantages

– Previous studies are required (cartographyc y bathymetryc).
– High investment (complex submarine works)
– Pretreatment with double pass filtration is highly recommended (planktonic organisms require additional filtration once the seawater arrives at the plant, driving up fresh water production costs)

– Complicated to get licenses and authorizations to consider this type of
Intake
– TSS, colloidal matter, TOC, oils and grease are not removed and can
produce operational problems
– Potential biological fouling of intake pipes
– Environmental impact afecting to the seabed

Vertical Beach Wells (3)

Consisting on vertical drillings made near a shoreline, typically very close to the nearshore in order to capture seawater filtering through the local nearshore geology.

Perforated plastics pipes are installed inside the well to avoid sand cloghing the well.

.The beach well is a subterranean reservoir that is sunk approximate
to sea level coupled to a pipe that is rammed outward from the bottom of the reservoir into the nearshore geological formation, the pipe has a plurality of throughholes for allowing the flow of seawater into the pipe.

• As water flows into the reservoir, it fills the reservoir until the level of
water in the reservoir is the same as at sea level. The water is then pumped from the reservoir to the desalination plant to be desalted.
Inside of every well there is a multistage, submersible pump installed to pump sea water.

• Vertical beach wells operate under the same filtration rate guidelines
as a slowsand filter, ensuring low maintenance required for the proper functioning.

• Advantages

– Potentially lower operations and maintenance costs due to the high and constant quality of the feed water

– Avoid issues related to volatile organic spills and lessen potentially
harmful algal blooms. Hence, the water quality provided by beach wells is excellent

• Disadvantages

– It use is limited to smaller systems due to the large number of wells that would need to be drilled in order to fulfill the pretreatment needs

– Not easy to identify the most suitable location to drill the wells
– Geological studies are required
– High number of wells are required to get medium flowrates
– Water supply produced by a beach well is totally dependent on
hydrogeologic conditions at the site
– Difficulties to know the evolution of the production flow
– Sometimes very deep wells are required (> 100 m depth)

• Beach wells (indirect intake systems) suffer from a shorter life span,
usually 1520 years, when compared with the 3050 years life span of direct intakes.

Further, the limitation in production capacity limits the use of indirect seawater intakes to only small desalination plants.

Also, due to the fact that indirect seawater intakes must be placed
near the nearshore, they are vulnerable to storm damage or damage
from beach erosion.

• Present seawater intakes require choices and compromises between high volume, long life direct intakes and low volume, shorter life, but higher water quality provided by indirect intakes.

Therefore a need exists for a seawater intake system that incorporates the high volume and long life of a direct intake while providing the high water quality of an indirect intake without being limited by surrounding
nearshore geology.

Horizontal directionaldrilled wells (4)

The inventive method is comprised of placing a subterranean reservoir
in communication with the first end of an intake pipe.

The reservoir is buried at a level approximate to sea level so that the inflow of water from the intake pipe occurs until the water in the reservoir reaches sea level.

Directional drilling methods are used to create a bore for the placement of an intake pipe.

Directional drilling can be used to place a single intake pipe30" or greater bore diameter).

(The large pipe in this case acts as a bore lining so that a plurality of intake pipes can be placed inside of the large pipe and connected to the reservoir.

This allows for the filtration of much higher volumes of seawater from the multiple intakes.

• Advantages

– Collecting very high sea water flows
– suspended solids, suspended biologies, debris and hydrocarbons
are either greatly reduced or eliminated altogether by the system,
therefore, high quality water is provided.
– Feed water quality is constant.
– No environmental affection during construction.
– Simple pretreatment
for the RO system is required
– In case it is required, in can be modified to be a Deep Water Intake

• Disadvantages

– Previous studies (cartographyc, geophysical and bathymetryc) are
required
– High investment
– New technique with no many references
– Microbiological quality is worse than using vertical beach wells.
Some organic matter can be present in feed water

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