Ship's Fresh Water Generator (Distillation Plant) | Starting and Stopping Procedures | Chief MAKOi
Summary
TLDRThis video offers an in-depth look at the operation of a distillation plant aboard cargo ships, crucial for converting seawater into fresh water. It outlines the start-up and shutdown procedures, emphasizing the importance of the main engine's jacket water outlet as a heat source. The video explains the role of the ejector pump in creating a vacuum for boiling seawater at lower temperatures, the heat exchange process in the evaporator, and the collection of distilled water in the condenser. It also covers the critical steps of monitoring salinity with a salinometer and the disposal of non-evaporated seawater, ensuring the plant's efficient and safe operation.
Takeaways
- 🚢 Ocean-going ships use freshwater generators or desalination plants to convert seawater into fresh water due to the limited usability of seawater.
- 💧 The most common method for cargo ships is distillation, which requires the main engine to be running at navigation full speed.
- 🔥 The heating medium for distillation plants typically comes from the main engine's jacket water outlet, which is around 85-90 degrees Celsius.
- 🌊 It's important for ships to be in deep water and far from land to ensure the seawater used is clean and free of pollutants.
- 📦 The distillation process involves drawing seawater, creating a vacuum with an ejector pump, and heating the water to evaporate it in the evaporator.
- 🌡️ The boiling point of seawater is lowered inside the evaporator due to the vacuum created, allowing it to evaporate at temperatures below 100 degrees Celsius.
- 💧 The steam from the evaporator is condensed back into fresh water in the condenser, which is then collected and stored.
- 🔍 A salinometer is used to measure the salinity of the distilled water, ensuring it meets the required standards before being stored.
- 🚫 If the salinity is too high, an alarm is triggered, and the water is returned to the system to prevent contamination of the fresh water storage.
- 🛑 The shutdown process of the distillation plant is the reverse of the startup, ensuring the system cools down to prevent salt and scale buildup.
Q & A
Why do ocean-going ships need a freshwater generator?
-Ocean-going ships need a freshwater generator because seawater, despite being abundant, has high salinity which makes it unsuitable for most shipboard operations and human requirements.
What are the two main methods used to convert seawater into fresh water on ships?
-The two main methods used to convert seawater into fresh water on ships are distillation and reverse osmosis.
Which type of desalination plant is most commonly used on cargo ships?
-The most commonly used type of desalination plant on cargo ships is the distillation plant.
What is the source of heating for the distillation plant on most ships?
-The source of heating for the distillation plant on most ships is the jacket water outlet of the main engine, which typically has a temperature range between 85 to 90 degrees Celsius.
Why should the ship be far from land and in deep water when operating the distillation plant?
-The ship should be far from land and in deep water to ensure that the seawater drawn into the distillation plant is clean and free of pollutants.
What is the role of the ejector pump in the distillation process?
-The ejector pump creates a venturi effect, generating suction that helps maintain a vacuum inside the shell, which is necessary for the evaporation process to occur at lower temperatures than the boiling point of seawater.
How does the feed water line contribute to the efficiency of the distillation plant?
-The feed water line draws seawater from the upper part of the condenser, preheating the feed water and improving the efficiency of the distillation process.
What is the purpose of the salinometer in the distillation plant?
-The salinometer measures the salinity of the distilled water. If the salinity is higher than the set limit, an alarm is triggered, and the water is returned to the shell to prevent contaminated water from entering the freshwater storage tanks.
What happens to the salt that is not evaporated during the distillation process?
-The salt remains dissolved in the seawater that hasn't evaporated and is suctioned by the inductor and pumped out into the sea as part of the continuous flow system.
What is the procedure to stop the distillation plant before the ship arrives in port?
-The procedure to stop the distillation plant before the ship arrives in port involves switching off the dosing pump and salinometer, stopping the flow of heating into the evaporator, allowing the evaporator to cool down, stopping the ejector pump, closing all relevant valves, and opening the vacuum breaker.
Outlines
🚢 Starting and Stopping Procedures of a Ship's Distillation Plant
This paragraph explains the process of operating a freshwater generator, or desalination plant, aboard ocean-going ships. The freshwater generator is essential due to seawater's high salinity, which limits its use on ships. The most common type for cargo ships is the distillation plant, which converts seawater into fresh water by removing salt through distillation or reverse osmosis. The video will demonstrate the starting and stopping procedures of this plant. Distillation plants require the main engine to be running at full speed to operate, utilizing the engine's jacket water outlet as a heating medium. The starting procedure involves aligning the seawater line, opening various valves, and starting the ejector pump, which creates a vacuum effect to draw in seawater. The feed water line then introduces preheated seawater into the evaporator, where heat exchange occurs, and the process of converting seawater to fresh water begins.
🌡️ The Distillation Process and Salinity Control
This section delves into the distillation process, explaining how the feed water's temperature increases due to the heating medium from the main engine. Seawater's boiling point is slightly higher than pure water's due to its salinity, but the vacuum created by the ejector pump lowers the boiling point, allowing evaporation. The steam produced rises to the condenser, where it cools and condenses into distilled water. This water is collected and passed through a salinometer to ensure its salinity is below 5 ppm before being sent to the freshwater storage tank. The paragraph also addresses what happens to the salt left behind in the non-evaporated seawater, which is pumped out into the sea. In case of a malfunction or if the salinometer is switched off, a solenoid valve prevents untested water from entering the storage tanks. The video also touches on the continuous flow system and the importance of water treatment dosing pumps.
🛑 Safe Shutdown of the Distillation Plant
The final paragraph outlines the procedure for safely shutting down the distillation plant before the ship arrives in port. This involves turning off the dosing pump and salinometer, stopping the flow of heat to the evaporator, and allowing the evaporator to cool down to prevent salt and scale buildup. The shutdown process is essentially the reverse of the startup, with additional steps like closing the feed water valve, the condenser inlet and outlet valves, and the ejector pump inlet valve. A vacuum breaker is opened, and the ejector pump overboard valve is closed to complete the shutdown. If the ship is expected to stay in port for more than a day, it's recommended to drain the remaining feed water from the evaporator to maintain the plant's integrity.
Mindmap
Keywords
💡Freshwater Generator
💡Desalination
💡Distillation Plant
💡Ejector Pump
💡Venturi Effect
💡Condenser
💡Evaporator
💡Salinometer
💡Boiling Point
💡Combination Gas Law
💡Treatment Dosing Pump
Highlights
Seawater's high salinity limits its use on ships, necessitating freshwater generators.
Desalination plants convert seawater to fresh water through distillation or reverse osmosis.
Distillation plants are commonly used on cargo ships for freshwater production.
Operation of distillation plants requires the main engine to be running at full speed.
Heating medium for distillation comes from the main engine's jacket water outlet.
Ships should be in deep water and far from land for clean seawater intake.
The ejector pump creates a vacuum for seawater intake through the adductor's venturi effect.
Feed water line draws preheated seawater from the upper part of the condenser.
Evaporator tubes facilitate heat exchange with the heating medium.
The boiling point of seawater is lowered due to the vacuum created by the ejector pump.
Steam from the evaporator rises to the condenser, cooling and condensing into distilled water.
Distillate pump transfers distilled water from the condenser to the freshwater storage tank.
Salinometer measures salinity, ensuring water quality before storage.
Salt remains in the non-evaporated seawater, which is pumped out into the sea.
Distillation plant operation includes a treatment dosing pump for water quality.
Distillation plant must be stopped before the ship arrives in port and the main engine slows down.
Evaporator cooling is crucial to prevent salt and scale buildup.
Vacuum breaker is opened, and the ejector pump overboard valve is closed to stop the plant.
Draining the evaporator is recommended if the ship stays in port for more than a day.
Transcripts
ocean-going ships are always surrounded
by water
but ironically apart from being a steady
supply of cooling medium
seawater has very limited uses when it
comes to shipboard operations and human
requirements due to its high salinity
which is why ships are equipped with
what is called a freshwater generator
or a desalination plant
which is a machine that drastically
lowers the salinity of seawater
in simple terms it converts seawater
into fresh water by removing the salt
either through distillation or reverse
osmosis
for cargo ships the most commonly used
type is the distillation plan
and in this video you will see both the
starting and stopping procedures
for most ships distillation plants can
only be operated when the main engine is
running at navigation full speed
this is because the heating medium it
uses comes from the jacket water outlet
of the main engine
which typically has a temperature range
between 85 to 90 degrees celsius
although there are some distillation
plant designs which can also use steam
from the boiler as the heating medium
it is recommended that the ship should
be far enough from land and in an area
with deep water to ensure that the sea
water that will go into the distillate
plant
will be clean and potentially be free of
pollutants
you may recall that i have made a
previous video about the operating
principles of the distillation plant
here in this video i'll be showing you
the actual operating procedures
the first step is to line up the sea
water line and open the valves starting
from the ejector overboard valve
next is the seawater inlet valve to the
ejector pump
and then the condenser inlet and outlet
valves
these lines draw seawater from the main
seawater line coming from the sea chest
once the ejector and condenser lines are
established the ejector pump can now be
started
the ejector pump is basically just a
centrifugal pump
which delivers seawater through an
inductor
the velocity of the seawater passing
through the nozzle in the adductor
creates a venturi effect which then
generates suction in this line
this continuous suction causes the
pressure inside the shell to become
lower than atmospheric pressure or in
simple terms a vacuum
the next step is to let seawater
into the distillation plant
this feed water line draws seawater from
the upper part of the condenser
which in effect makes the feed water
preheated
once the valve is opened the feed water
enters from the bottom and into the
evaporator which is basically a series
of tubes encased in a compartment
where the heating medium flows thereby
facilitating heat exchange
here we can see the sea water flowing
from the evaporator
remember the doctor line
the seawater and any other particles
gets suctioned through this line and
gets ejected out into the sea
now that we have established a
continuous flow of feed water we have
good vacuum inside the shell
and a continuous flow of cooling sea
water through the condenser
it's time to heat things up
by diverting the flow of the main engine
jacket water outlet into the evaporator
as you can see he's doing it slowly so
it's not to cause sudden fluctuations in
the jacket water line pressure
once the evaporator heating is lined up
the temperature will start to rise
and we can observe the feed water
reacting to the increase in temperature
as we all know pure water has a boiling
point of 100 degrees celsius at
atmospheric pressure
seawater's boiling point will be
slightly higher
now as i mentioned earlier the jagged
water temperature is around 85 to 90
degrees celsius
under normal atmospheric pressure
that won't be enough to evaporate
seawater
but thanks to the ejector pump and the
adductor
the pressure inside the shell is
maintained below atmospheric in effect
the lower atmospheric pressure causes
the boiling point of the seawater to
also become lower
i won't bore you with the mathematical
details but if you want to learn more
about this a good starting point would
be the combination gas law which is
derived from boyle's law charles lowe
and gay lucex law
now since the feed water is already
boiling the steam rises up to the
condenser where it is cooled down and
condenses into distilled water
there is a water collecting tray just
beneath the condenser tubes and it leads
down to this pipe which is the suction
line of the distillate pump
the distillate pump delivers the
distilled water from the condenser to
the fresh water storage tank
but before it does the water needs to
pass through the salinometer which
measures its salinity
the alarm is usually set to 5 ppm if the
salinity is higher than that
an alarm is triggered and the solenoid
valve automatically opens and returns
the distilled water back into the shell
during startup it is normal for the
salinity to be high during the first few
minutes but eventually it will go down
to the required value
and distilled water will be delivered to
the freshwater storage tanks
if in case the salinometer malfunctions
or is switched off the solenoid valve
will remain open thereby preventing
untested water to go to the storage
tanks
in the previous video a lot of viewers
asked where does the salt go
as we have all seen this is a continuous
flow system meaning it never dries up
so the salt remains dissolved in the
seawater that hasn't evaporated
as soon as that sea water flows out of
the evaporator tubes and into the shell
it will be suctioned by the inductor and
pumped out into the sea
once fresh water production is stable
the last step is to switch on the
treatment dosing pump
for a detailed explanation of this water
treatment
you can check out this video
now the distillate plant needs to be
stopped before the ship arrives in port
specifically it needs to be stopped
before the main engine is slowed down
for maneuvering and while the ship is
still in deep water
it's basically just the reverse of
startup procedures but i still think
it's worth seeing it get done
first will be to switch off the dosing
pump and the salonometer
next will be to stop the flow of heating
into the evaporator
let the evaporator cool down thoroughly
this is to ensure that no more
evaporation will take place
in order to prevent salt and scale
buildup within the evaporator tubes
you can verify if it's sufficiently
cooled down if the evaporator
temperature is the same as the seawater
temperature
once cooled down
stop the ejector pump
close the feed water valve
close the condenser inlet and outlet
valves
and the ejector pump inlet valve
after that
open the vacuum breaker
finally close the ejector pump overboard
valve
additionally if the ship is expected to
stay in port for more than a day
it's good practice to drain the
remaining feed water in the evaporator
i hope you enjoyed the video and stay
tuned for the next one
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