How Ships Produce Fresh Water - Importance and Theory

Table of Contents

1. Introduction
2. What is a Freshwater Generator?
3. Categories of Usable Freshwater
   • Distilled Water
   • Drinking Water
4. Uses of Freshwater on Board
   • Engine Room Services
   • Cabin Use
   • Galley Services
   • Drinking Water
5. Overview of the Freshwater Generator
   • Heat Exchangers: Evaporator and Condenser
   • Main Engine Jacket Water
   • Sea Water Piping
6. The Importance of Vacuum in the Shell
7. The Role of Main Engine Jacket Water
8. Functioning of the Evaporator
9. The Distillate Water Pump and Salt Content
10. Making Distillate Water into Drinking Water
    • Reharden Filter
    • Ultraviolet Lamps
11. Adjusting Parameters for Maximum Efficiency
12. Common Problems and Maintenance
    • Deposits on Plates
    • Cleaning the SalaNa Meter Sensor
13. Recommendations for Fresh Water Source
14. Conclusion

Freshwater Generator: Producing Usable Water Onboard

Freshwater is a vital resource on any vessel, and one of the machines responsible for producing usable freshwater is the freshwater generator. In simple terms, usable freshwater can be categorized into two types: distilled water and drinking water. The distinction between them lies in their hardness, which is determined by the minerals present in the water, particularly calcium and magnesium. Distilled water has minimal hardness and is produced by evaporating seawater in the freshwater generator. Drinking water, on the other hand, has enough hardness to meet human consumption standards.

Onboard, distilled water generated by the freshwater generator serves a variety of purposes. In the engine room, it is used for general services such as cleaning and as feed water for the boiler and cooling water system, after undergoing necessary chemical treatment. Distilled water is also utilized in the cabins for toilets and showers. However, its taste may seem peculiar to some individuals. Drinking water, which is produced separately, is primarily used in the galley sinks where food is prepared, as well as other galley services like the water heater. The choice of drinking water can either be bottled water or water straight from the tap.

To understand the functioning of a freshwater generator, let's take a basic overview of its components. It consists of two crucial heat exchangers, namely the evaporator and condenser. The main engine jacket water and seawater piping play essential roles in the heating process. The system begins with the ejector pump, where seawater from outside the ship is sent to fill the system. The seawater initially enters the condenser, splitting into two streams; one goes to the ejector, creating a vacuum, while the smaller portion heads to the evaporator shell. Inside the evaporator shell, seawater will later be evaporated, facilitated by the vacuum generated by the ejector.

Creating a vacuum is imperative because the main engine jacket water, which is typically around 80 degrees Celsius, is not sufficient to evaporate the seawater. By reducing the pressure through the vacuum, the saturation temperature of water also decreases. Eventually, it drops below 100 degrees Celsius and even lower than 80 degrees Celsius, enabling the main engine jacket water to evaporate the seawater effectively. Once the vacuum is verified, the main engine jacket water enters the system through the evaporator, transferring heat to the seawater and causing it to evaporate inside the shell. As the seawater boils, a demister lowers carryover salt, ensuring the distillate water remains pure.

The heat exchangers, the evaporator, and condenser play vital roles in the freshwater generation process. The evaporator primarily utilizes the jacket water or steam to transfer heat to the seawater, allowing it to evaporate. The steam produced inside the shell of the evaporator is then condensed by cooling seawater from the pump. This condensed water is known as distillate water. The cooling seawater, which was heated during the process, enters the evaporator again to increase the efficiency of the freshwater generator, focusing on producing distillate water.

Once distilled water is produced, it undergoes further checks to ensure its suitability for consumption. A distillate water pump sends the water to a solidometer sensor, which measures the salt content. If the salt concentration exceeds 10 parts per million, the water is rejected through a solenoid valve back into the shell. However, if the salt content is within the acceptable range, the water is transferred to the distillate water tank. To transform distillate water into drinking water, it goes through a reharden filter filled with rocks that add minerals. Additionally, ultraviolet lamps are used to kill any bacteria present in the water, ensuring its safety for human consumption.

To achieve maximum efficiency in freshwater production, three parameters need to be adjusted: the heating jacket water, the amount of seawater allowed to pass from the condenser to the evaporator, and the vacuum. Finding the perfect balance between these parameters is crucial. For example, if too little seawater is allowed to enter the evaporator, the separation process will happen too quickly, resulting in low production rates. On the other hand, excessive seawater entry may lead to salt deposits on the plates, hindering heat transfer and reducing production efficiency. Regular maintenance, such as removing and cleaning the plates, helps to mitigate this problem.

When sourcing water for the freshwater generator, it is recommended to take it from a minimum distance of 20 nautical miles from the shore. Water from shore or ports tends to be more contaminated, and evaporating such water may not eliminate all bacteria. Therefore, for hygienic purposes, it is best to avoid showering or using contaminated water. By adhering to this practice, the likelihood of bacterial presence in the produced freshwater is significantly reduced.

In conclusion, the freshwater generator plays a crucial role in providing usable water onboard vessels. By understanding its functioning and maintaining optimal parameters, a reliable supply of distilled and drinking water can be ensured. The freshwater generator, along with supporting components and maintenance procedures, ensure the availability of safe and fresh water for various onboard needs.