Master the Ship's Fresh Water Generator | Expert Tips

Table of Contents:

1. Introduction
2. The importance of freshwater on ocean-going ships
3. Types of freshwater generators
   • Distillation plants
   • Reverse osmosis plants
4. Operating principles of distillation plants
   • Heating medium
   • Vacuum effect
5. Starting procedures of a distillation plant
   • Lining up the sea water line
   • Starting the ejector pump
   • Letting seawater into the distillation plant
   • Diverting the flow of jacket water
6. Distillation process and heat exchange
7. Collection and storage of distilled water
8. Salinity measurement and control
9. Treatment dosing pump
10. Stopping procedures of a distillation plant
    • Switching off the dosing pump and salinometer
    • Cooling down the evaporator
    • Stopping the ejector pump and closing valves
11. Conclusion

The Process of Operating a Distillation Plant on an Ocean-Going Ship

Water is an essential resource for human survival, and its availability becomes crucial when it comes to operating ocean-going ships. Although surrounded by abundant seawater, the high salinity of this water restricts its usage for shipboard operations and human requirements. To address this issue, ships are equipped with freshwater generators, also known as desalination plants. These machines play a crucial role in converting seawater into freshwater by removing the salt content through distillation or reverse osmosis processes.

The Importance of Freshwater on Ocean-Going Ships

Ocean-going ships heavily rely on freshwater for various purposes, such as drinking, cooking, cleaning, and maintaining shipboard systems. While seawater acts as a constant cooling medium, its high salinity limits its usability. Therefore, having a freshwater generator on board is essential to ensure a steady supply of freshwater throughout the ship's journey.

Types of Freshwater Generators

Two main types of freshwater generators are commonly used on ocean-going ships: distillation plants and reverse osmosis plants. Distillation plants are the preferred choice for cargo ships. This article will specifically focus on the operating procedures of distillation plants.

Operating Principles of Distillation Plants

Distillation plants operate by utilizing a heating medium, typically obtained from the jacket water outlet of the ship's main engine. The heating medium, with a temperature range of 85 to 90 degrees Celsius, is circulated through the evaporator, causing the seawater to boil and form vapor. Through the process of condensation, this vapor is then converted back into distilled water. The distillation plant relies on a vacuum effect created by an ejector pump, which lowers the pressure inside the shell, enabling the seawater to boil at a lower temperature.

Starting Procedures of a Distillation Plant

Before initiating the distillation process, certain steps need to be followed to ensure the proper functioning of the system. First, the sea water line is lined up, and the valves for the ejector overboard, seawater inlet, and condenser inlet and outlet are opened. This allows seawater to be drawn from the sea chest and circulated through the evaporator. The ejector pump, a centrifugal pump responsible for delivering seawater through an inductor, is then started. The inductor creates a venturi effect, generating suction that maintains a vacuum inside the shell. Subsequently, the feed water valve is opened, allowing preheated seawater to enter the evaporator.

Distillation Process and Heat Exchange

Within the evaporator, heat exchange takes place between the seawater and the heating medium flowing through a series of tubes. The temperature gradually increases, causing the seawater to boil and form steam. The steam rises to the condenser, where it cools down and condenses into distilled water. A water collecting tray beneath the condenser tubes leads to a distillate pump, responsible for delivering the distilled water to the fresh water storage tank. To ensure the quality of the distilled water, it passes through a salinometer to measure its salinity.

Collection and Storage of Distilled Water

The distilled water, now free of salt, is collected in the fresh water storage tanks. It can then be used for various shipboard operations and meet human requirements. However, to maintain the desired salinity level, the system incorporates an alarm system in case the salinometer detects a salinity higher than the recommended value (usually 5 ppm). If triggered, an automatic solenoid valve opens, diverting the water back into the shell to prevent untested water from entering the storage tanks.

Treatment Dosing Pump

The treatment dosing pump is a crucial component of the freshwater generator system. It is responsible for injecting the necessary treatment chemicals into the water to prevent the growth of microorganisms and maintain the water's quality. The dosing pump is typically switched on during the operation of the distillation plant and should be properly calibrated to ensure the accurate dosage of treatment chemicals.

Stopping Procedures of a Distillation Plant

To ensure a safe shutdown of the distillation plant, specific procedures must be followed before the ship arrives in port. Firstly, the dosing pump and salinometer are switched off. The flow of heating medium into the evaporator is then stopped, allowing the evaporator to cool down completely. This step prevents salt and scale buildup within the evaporator tubes. Once the evaporator has sufficiently cooled down, the ejector pump is stopped, and all relevant valves are closed. Finally, the vacuum breaker is opened to release any remaining vacuum pressure, and the ejector pump overboard valve is closed. Additionally, if the ship is expected to stay in port for an extended period, it is advisable to drain the remaining feed water from the evaporator to prevent any potential issues.

In conclusion, freshwater generators, specifically distillation plants, are essential systems on ocean-going ships to ensure a steady supply of freshwater. Understanding the operating procedures of these plants is vital for ship crew members to effectively generate and manage the freshwater supply. By adhering to the proper startup and stopping procedures, the crew can maintain the functionality and longevity of the distillation plant, providing a reliable source of freshwater during the ship's journey.

Highlights:

• Ocean-going ships rely on freshwater generators to convert seawater into freshwater.
• Distillation plants are the most commonly used type of freshwater generator on cargo ships.
• Distillation plants operate by utilizing a heating medium and a vacuum effect to convert seawater into distilled water.
• The operating procedures for a distillation plant involve starting and stopping procedures, as well as the collection and storage of distilled water.
• The treatment dosing pump plays a crucial role in maintaining the quality of the freshwater.
• Following proper procedures is essential to ensure the efficient operation and longevity of the distillation plant.