Water Makers
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Water Makers
1:37 PM
• Consider the sea water feed is there any chance of
contamination from site discharge?
• Sewage ?
• Oil ?
• Oily Produced Water
• Are there Operating practices to minimise risk of
up take of seawater contamination
•
Does the seawater get used for anything else pre
water maker ?
•
E.g. equipment cooling ?
Raw Sea Feed - Contamination
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• The sea-water fed to the desalination plant shall
be free from contamination - sewage, process
fluids, solids, etc.
• If it is to be drawn from a line which provides
sea-water for other purposes such as plant
cooling, then the take off should be upstream of
any supplies to process equipment.
Raw Sea Feed - Contamination
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• Seawater intake may be chlorinated to prevent molluscs,
algae, slime and weed within the intake system.
Chlorination should also prevents sea shell deposition
within the feed system. It will however damage the water
makers so it should be removed.
Raw Sea Feed - Chlorination
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• Removes very large suspended
solids and sea creatures before the
sand filters
Raw Sea water filtration
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• Removes suspended solids down to
between 5 – 20 µm
• used as pre-filter when constituents in
raw water harm or reduce effectiveness
of other treatment devices – e.g.
Activated Carbon will remove Chlorine
which will damage RO Membranes
• “Media” can be variety of materials
• Maintenance involves periodic
backwashing
Raw Sea water filtration
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The media removes most
suspended particles down to
between 5 – 20 µm depending
on the filter type
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The feed water, free from large
suspended solids and dosed with
anti-scalant is passed
through 5 micron rated cartridge
filters and then 1 micron
Primarily for suspended solids
Maintenance involves periodically
replacing cartridges
Pre Water maker Filtration
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Pre Filters 20 to 1 µm (micron)
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Separate Activated Carbon Filter
Activated carbon filter necessary to
remove chlorine to prevent damage to
RO Membranes.
Sometimes a stand alone rather than as
part of the multi media sand filter.
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Activated Carbon Filter
Adsorption
– contaminant binds to
carbon
Honeycomb-like structure provides
enormous area for contaminants to
bind to
Effectiveness declines over time
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Water maker Full system - RO
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Water Makers
Distillation
Boiling and condensing
Gas Vent
Condensing Coil
Contaminated
Water
Coil water in
coil used to
condense
steam
Steam
Vapor
Heating Element
Cleaning
Drain
Distilled water to tank
May need to have
carbon filter
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Water Makers –
Flash/Vacuum Evaporation
The evaporation process normally
takes place around 70°C. The
evaporation effect is done at sub-
atmospheric conditions, where the
vacuum is created by means of
ejector
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Water Makers –
Flash/Vacuum Evaporation
Seawater From
Sea
Fresh Water To
Tank
Brine
Overboard
12
7
8
6
Compressor
10
9
11
4
5
2
Evaporator
1
Condenser
3
13
14
Seawater
Overboard
1.Vent condenser
2.Circulation pump
3.Brine pump
4.Compressor
5.Air ejector
6.Distillate pump
7.Brine / feed water pre-heater
8.Distillate / feed water pre-heater
9. Electrical heater
10.Filter
11.Sight glass
12.Filter
13.Evaporating chamber
14.14. Condenser chamber
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Water Makers –
Flash/Vacuum Evaporation
Vacuum
Cold
In
Pure Water OUT
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Water Makers Reverse Osmosis – RO
• Effective for a variety of contaminants
• Relies on pressure to force water through a membrane
• Reverse Osmosis forces water through the tiny holes of its membrane
which are up to 620,000 times smaller than the width of the human hair,
and which is also even smaller than the size of bacteria and other
microbes.
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Water Makers Reverse Osmosis – RO
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Water Makers Reverse Osmosis – RO
Membranes damaged by
• Chlorine
• Temperature 35°C +
• pH ‘s less than 2
• pH’s Greater than 11 (some may be damaged by 10+)
To prevent pH damage may want to invest in a pH meter and
calibration fluid to check the pH of Acid/Alkali cleaning solutions
before running a batch through the RO unit.
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Water Makers Reverse Osmosis – Scale
Membranes Scale
It is normal to add an anti scale / descalant/ scale inhibitor to
prevent membrane fouling
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Carbon dioxide in small amounts is present in all natural
waters.
In reverse osmosis membranes and flash evaporators
remove the alkalinity present in water but not the carbon
dioxide, because it is a gas.
The CO2 dissolves in water to give Carbonic Acid (H
2
CO
3
).
This creates reduces the pH in the product water.
It is common practice to adjust the pH and Re-harden /
Re-mineralise the water post water makers.
The Remineraliser works by slowly dissolving calcite into
the product water to add hardness and raise pH to near
neutral
pH Neutralisation media – Re Hardner / Re-mineraliser
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If water has a low pH and Low Alkalinity it will be corrosive and
will consume metal components in the plumbing system. This is
usually noted by green stains under any taps that may have slow
leaks.
The stain is a result of copper leaching from copper pipes and
from bronze and brass components in the water system.
These filters increase the hardness of water.
However high levels of hardness will cause scale deposits in hot
water systems
pH Neutralisation media – Re Hardener / Re-mineraliser
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If a water supply has a low (acidic) pH, it is common to use a sacrificial
neutralisation media to save plumbing and fixtures.
The most commonly used media are calcium carbonate (calcite) and
magnesium oxide (Corosex
®
).
Calcite (CaCO
3
) is converted to the bicarbonate (Ca(HCO
3
)
2
) by low
pH water and is effectively neutralized.
Magnesium oxide (MgO), is a much stronger base, simply acts as a
hydroxide to neutralize the acid. It may over correct particularly if the
flow is low through the filter.
pH Neutralisation media
– Re-Hardner / Re-Mineraliser
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NOTE : The filters are not fit and forget they will
need regular refilling with minerals when in use.
The tanks are filled with a sacrificial neutralization
media so check the levels regularly and top up if
required.
When Empty the filters become a nice breeding
ground for bacteria !
pH Neutralisation media
– Re-Hardner / Re-Mineraliser
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Neutralization media
Be careful if thinking of changing the blend or particle size of the Neutralisation media.
The media will have been selected by the OEM to suit the pH and flow of the water exiting
the water maker. They may also have chosen it because of the CO
2
injection.
A different blend will give a different pH
A smaller or larger granule size may give a significantly different pH.
Smaller granules have a larger surface area and will dissolve quicker and vice versa.
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