Fresh Water Generator on Ship
The freshwater generator on the ship is used to convert the seawater or saltwater into freshwater. As we all know, there is a lot of use of fresh water in our daily life, for example, in cooking, drinking, washing, cleaning the tank, etc. This is why there is a need for a large amount of freshwater on the ship.
Per predictions, there is a need for about 100 liters of fresh water daily on the ship. The system required to generate the fresh water on the ship is called the freshwater generator, also known as the evaporator. There are three additional styles of methods utilized for generating reinvigorated water from saltish seawater.
These three methods are reverse(RO), boiling the water, or evaporating. Most marine vessels used either the method of RO or evaporators to produce fresh water. The plants of large desalination are connected with the steam circuit of the thermal power station, and then the steam is used to evaporate the seawater.
Below is an inventory of segments used in the freshwater elements.
- Connections of the hot and cold water.
- Pump for freshwater.
- Air-Purge Valve
- SRV Safety Relief Valve
- Temperature Monitoring Devices
- Water pump for freshwater.
Below All the Working Components Are Explained
The evaporator of the low-pressure flash is connected with the seawater and the hot water system. On the marine vessels, the seawater is directly acquired from the sea chest though hot water is AWG houses a plate of the condenser heat exchanger, yet the lower component houses an evaporator plate heat exchanger.
The condenser permits the sweater to go through the warmth exchanger in the impenetrable scheme. With the help of the evaporator, hot water goes through the exchanger of heat, which is in the closed system. The evaporator and the condenser do not fully seal the heat exchanger.
The seals are modified to authorize seawater to disappear from the evaporator containers and fresh water to crystallize on the condenser plates. A plate heat exchanger has two completely sealed methods, but in FWG, one procedure is closed, and the different is open in one heater. A demister gets installed between the condenser and the evaporator.
Within the FWG shell, the condenser, Demister, and evaporator are housed. From the FWG condenser, the freshwater gets pumped to the storage tank with the help of the freshwater pump(basically, it is a small centrifugal pump). They use an ejector and educator to create and maintain the vacuum in the shell.
This correspondingly assists in removing the brine from the inferior portion of the surface. Within the shell, its temperature, the system of the seawater, and the jack water are continuously monitored by using the thermometers and also by using the PT 100 sensors. The ventilation valve is mounted on the top of the housing. Vented should extend when FWG is not running and complete when FWG is running. A safety relief valve (SRV) is installed on the shelter of the casing to prevent overpressure.
The salinometer is used to measure the salinity of the generated freshwater. If the salinity of the freshwater is too high, it gets rejected. If the freshwater is within the limit, which is <10ppm, then it is allowed to pass to the tank of the freshwater.
Types of Freshwater Generator on Ships
Fresh water generators have two types: Reverse Osmosis and Distillation also. Distillation consists of two types one is plate type, and the second one is Tube type.
#1. Fresh Water Generator Plate Type
Whether the evaporator heat exchangers of a freshwater generator or the condenser are composed of plates, that type of freshwater generator is known as the plate type freshwater generator. The main parts are the evaporator heat exchangers and condenser, brain air ejector, sea water pump, salinometer, distillate pump, Demister, and the water flow meter.
1.1. Heat Exchangers
Evaporators and condensers are folded on titanium plates. These plates are folded with horizontal or corrugation of chevron pattern that helps to increase the heat exchange surface.
1.2. Brain Air Ejector
This brain air ejector is utilized to withdraw air and brainiac from the enclosure so that this enables the preservation of the vacuum.
1.3. Sea Water and Distillate Pump
Both pumps are outward. Distillate pumps help remove the carryover of the seawater droplets and spray water. It is made of wire which is layered knitted of Monel metal.
It is used to check the water salinity. The three-way valve is controlled with the help of the salinometer. If the salinity level in the water is high, then the water goes back into the evaporator inlet.
1.5. It’s Working
At the temperature of 80 degrees, the main engine jacket passes the water through the evaporator. The spread of sea water gets into the evaporator through the orifice at the dinner waterway. Because of the compartment’s low intimidation, the seawater simmers and contracts transformed into moisture.
To canary out, the droplets of the water and the spray of the water are removed by the Demister. The water droplets which get separated are collected as a brain that the ejector of the brain extracts.
The stem formed by boiling water gets cooled down to generate fresh water. With the help of the distillate pump, the freshwater gets pumped out from the condenser.
#2. Fresh Water Generator Tube Type
All are working, and the principle of the tube fresh water generator is the same as the plate type. The only difference is that it uses tubes instead of plates in the condenser and evaporators.
Working Principle of the Freshwater Generator
The basic principle of all low-pressure freshwater generators is that the boiling point of the water is reduced by reducing the pressure of the surrounding atmosphere in it. By preserving the low intimidation, water can be simmered at a low temperature which is approximately 50 breadth Celsius.
The heat source for the freshwater generator may be the rejected waste heat by the main engine jacket cooling water. Using energy from the heating coil and reducing the pressure into the shell of the evaporator, at about 40 to 60 degrees, boiling takes place. Such single-effect plants are designed to offer a better economy than those obsolete evaporators.
Arrangement of the Freshwater Generator
The freshwater generator’s main body consists of a large cylindrical body with two compartments. The compartments have two types: one condenser and the other one is another evaporator.
The freshwater generator also has an educator who helps generate the required volume. The ejector and the ship’s freshwater pump help transfer water from the freshwater generator.
The Process of Starting the Water Generator
Before beginning the freshwater generator, we require to substantiate that the ship is not in the overcrowded water aqueducts and is 20 navigational leagues away from the beachfront. It is done because the nearshore the effluents from the factories and the sewage are discharged into the sea and the freshwater generator.
Correspondingly, correspond whether the ship’s engine is maneuvering beyond 50 rpm. The reason behind this is that at the low rpm, the water jacket’s temperature, nearly 60 degrees, is insufficient for water evaporation. Correspond whether the gutter valve, which is current at the underside of the generator, is in a consolidated placement.
After this process, open the suction and discharge the seawater pump that will offer water for evaporation and cooling and educators for creating the vacuum. Release the seawater discharge valve from where water is sent back towards the sea after circulation inside the freshwater generator.
A closed vacuum valve is situated on the top of the generator. After it starts the pump of the seawater and checks whether the pump pressure is 3-4 bars or not, it postpones to produce up the emptiness. Essentially, the vacuum mandates at least 90% perceptible on the gauge attending to the generator. Generally, the vacuum generation process takes about 9 to 10 minutes. For the feed water treatment, open the valve when the vacuum is generated.
This is done to prevent the scale formation inside of the scale. Open the outlet valves and hot water slowly to half. Whenever you extend the valve, consistently extend the opening valve, preferably, and then the waterway valve. After it starts to increase, the opening of the valve opens fully.
After this process, the boiling temperature increases, and the vacuum drops. About 85% of the vacuum drop indicates that the evaporation gets started. From the freshwater pump to the drain, open the valve. To start it manually, switch it on the salinometer, but generally, it is on the auto start.
Then start the pump of the freshwater and taste the water which is coming out from the drain. When it starts to produce freshwater, it is seen that the boiling temperature starts dropping, and the vacuum comes back to its normal value. Check whether the water coming out from the salinometer is salty, and also check the salinometer reading.
This procedure is instructed to see if the salinometer is functioning appropriately and to discourage the reinvigorated water from contacting contaminated by salt water. Generally, the value of the salinometer is required below 10ppm.
After the methodology of inspecting the morsel of the water which arrives out of the salinometer, open the valve for the tank from the pump and shut the valve of the gutter.
The Process of Stopping the Water Generator
- Closed the inlet valve of the jacket water. Generally, it is required first to close the inlet and then the valve of the outlet.
- For the feed water treatment, close the valve.
- Stop the pump of fresh water.
- Turn off the salinometer.
- Stop the pump of seawater.
- Open the valve vacuum.
- Close the valve suction of the seawater and the valve overboard. Generally, it is not needed as it is a non-return valve. In case of leaking valves or damage, these valves need to be closed without failure.
Plate Type Fresh Water Generator
Design criteria of the plate type fresh water generator –-> the plate type of the freshwater generator is based on the scheme of the general design; the generator of the freshwater mainly consists of the condenser and an evaporator, ejector which is equipped for vacuum also the relevant accessories for the system.
Additionally, the whole control system is designed as a maker standard according to the purpose of the design.
#1. Components of the Plate Type Generator
This plate-type generator consists of condensing chamber, evaporating, and ejector to achieve vacuum and fresh water pump delivering distilled water to the storage tank.
The heat exchanger is made up of titanium. It is a device that saves energy using the heat jacket water, and the water boiling point is lower in the vacuum.
#2. Its Features
- Use a high-quality titanic plate for the condenser and evaporator.
- Use highly compatible with various heating sources such as thermal oil, jacket water, and steam.
- It controls the cabinet with the specialized meter of salinity.
- There are no moving parts, and they have less maintenance.
Frequently Asked Questions (FAQ)
Fresh Water Generator on Ships
Freshwater generators (FWG) convert seawater (saltwater) to fresh water. FWGs are a common site on many marine vessels as it allows them to generate the fresh water they need whilst at sea. The process of generating fresh water is achieved via distillation.
Types of Fresh Water Generator on Ships
- Freshwater generators (FWG) convert seawater (saltwater) to fresh water.
- There are three main methods employed for generating fresh water from seawater; these are boiling, evaporating, and reverse osmosis (RO).
Working Principle of Fresh Water Generator in Ship
Fresh Water Generator Working Principle. The basic principle of all low-pressure freshwater generators is that the boiling point of water can be reduced by reducing the pressure of the atmosphere surrounding it. By maintaining a low pressure, water can be boiled at low temperatures, say 50 degree Celsius.
Plate Type Fresh Water Generator
Plate Type Fresh Water Generator mainly consists of evaporating, condensing chamber, and ejector equipped to achieve. Vacuum, fresh water pump for delivering distilled water to storage tank. The heat exchanger is made of titanium.
Fresh Water Generator Starting Procedure
- First, we need to start the ejector pump.
- Intake of feed water.
- Start the chemical injection unit.
- Check the degree of vacuum in the evaporator to 0.9 bar.
- Injecting the hot water.
- Switch ON the power of the salinity indicator.
- Check the generated distillate.
Stopping Fresh Water Generator
- Open fully the hot water bypass valve.
- Close fully the hot water outlet valve.
- Close the hot water inlet valve.
- Stop the freshwater distillate pump by closing the outlet valve.
- Cool down the heater by running an ejector pump for 30 minutes to supply the feed water to the heater.