Marine fresh water generators play a critical role in ensuring a continuous supply of clean, fresh water onboard ships and vessels.

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Regular maintenance and timely troubleshooting are essential to keep these systems in optimal working condition. In this article, we will explore the maintenance process and provide detailed insights into troubleshooting methods for two common types of marine freshwater generators: plate type and reverse osmosis systems.

Plate Type Freshwater Generator Maintenance

Pre-Maintenance Preparation

Before initiating the maintenance process, it is important to follow these preliminary steps:

• • • Shut down the freshwater generator system and isolate it from the power source.
    • Ensure all valves and pipes are closed to prevent water leakage.
    • Use appropriate personal protective equipment (PPE) such as gloves, goggles, and masks.

Cleaning the Plate Heat Exchanger

The plate heat exchanger is a critical component of plate type freshwater generators. Regular cleaning is necessary to maintain its efficiency. Follow these steps:

• • • Remove the end covers and access plates from the heat exchanger.
    • Measure the holding bolts distance from the end tip to the end plate in order to have a tightening reference.
    • Soak the plates into an mild acid base solution (e.g. Descalex, Descaling liquid etc.) and keep them soaked for few hours, as it will help to easily remove the salt scaling.
    • Use a soft brush or sponge to gently clean the plates, ensuring the removal of any fouling, scale, or corrosion.
    • Rinse the plates thoroughly with clean water to remove any residue.
    • Inspect for any signs of leakage or gasket damage. Replace damaged plates and/or gaskets if necessary. Use rubber glue if required for securing the gaskets.
    • Reassemble the heat exchanger, ensuring proper alignment and tightness of bolts.
    • Pressure test the plate assembly to ensure that there are no abnormal leaks detected.

Inspecting Valves and Pumps

Valves and pumps play crucial roles in regulating water flow. Regular inspection and maintenance are essential:

• • • Check all valves for proper functioning, tightness, and freedom from leakage.
    • Lubricate valve stems and ensure smooth operation.
    • Inspect pumps for signs of wear, leaks, or abnormal noise. Replace worn-out parts if necessary.
    • Verify pump impeller clearance and adjust if required.
    • Check and re-adjust, if necessary, the feed water regulating valve.
    • Check and clean, if required the feed water nozzle.

Maintaining Filters and Strainers

Filters and strainers prevent contaminants from entering the freshwater generator system. Regular maintenance is essential:

• • • Remove and clean intake filters, strainers, and mesh screens.
    • Inspect for clogs, damage, or excessive fouling.
    • Replace or clean the filters as per manufacturer guidelines.
    • Ensure proper alignment and tightness during reinstallation.

Troubleshooting Tips and Techniques

Insufficient Freshwater Production:

• • • Inspect Seawater Supply:
      • Check for clogged or malfunctioning seawater intake filters, valves, or strainers.
      • Check for feed water regulating valve adjustment
      • Check the water level in the sight glass.
      • Check the system vacuum and shell temperature.
      • Check the brine ejector for proper operation.
    • Monitor Pressure Gauges: Ensure proper pressure readings within specified ranges. Low pressure may indicate a blockage or fouling in the system.

High Energy Consumption:

• • • Fouled Heat Exchanger: Clean the heat exchanger plates/tubes to improve heat transfer efficiency.
    • Pump Malfunction: Check pump performance, impeller condition, and motor function. Repair or replace components as necessary.

Excessive Noise or Vibration:

• • • Misaligned Components: Check alignment of pumps, motors, and other rotating elements. Realignment may be required to reduce noise and vibration.
    • Loose Mounting: Inspect mounting brackets, bolts, and fasteners. Tighten as needed to minimize vibration.

Water Quality Issues:

• • • Fouled Filters: Clean or replace filters to ensure optimal filtration and maintain water quality.
    • Scaling or Fouling: If the water has a salty taste or is discolored, perform chemical cleaning or descaling procedures as recommended by the manufacturer.
    • Plate assembly leakage: Pressure test the plate assembly and re-tight as found necessary. Check for any damage gaskets and replace as found necessary.
    • Salinity sensor: Check salinity sensor, clean it and replace it as found necessary. Be aware that the sensor must be cleaned with a clean dry rag and must avoid to be touched by bare hands.
    • Brine ejector: Check the brine ejector for proper operation.

System Leakage:

• • • Check Connections: Inspect all connections, valves, and fittings for leaks. Tighten or replace damaged components.
    • Gaskets and Seals: Inspect and replace worn-out gaskets and seals to prevent leaks.

Electrical Malfunctions:

• • • Circuit Breakers and Fuses: Check and reset or replace tripped circuit breakers or blown fuses.
    • Control Panel: Inspect the control panel for error codes or abnormal readings. Consult the system manual for troubleshooting guidance.

Reverse Osmosis Freshwater Generator Maintenance

Pre-Maintenance Preparation

Before starting maintenance on a reverse osmosis (RO) freshwater generator, follow these preparatory steps:

• • • Isolate the system from the power source and shut off the seawater supply.
    • Open the system to relieve pressure.
    • Wear appropriate PPE to protect against chemicals and ensure safety.

Cleaning the RO Membranes

The RO membranes are the heart of the reverse osmosis system and require regular maintenance to optimize performance. Perform the following steps:

• • • Prepare a cleaning solution as recommended by the membrane manufacturer.
    • Flush the system with clean water to remove any loose particles.
    • Circulate the cleaning solution through the membranes for the recommended duration.
    • Rinse the system with clean water to remove residual cleaning solution.
    • Inspect the membranes for signs of fouling, scaling, or damage. Replace if necessary.

Inspecting High-Pressure Pumps

High-pressure pumps are vital for maintaining the required pressure in RO systems. Regular inspection and maintenance are crucial:

• • • Check the pump’s suction and discharge valves for proper operation and tightness.
    • Inspect the pump for leaks, vibrations, and unusual noises.
    • Verify the pump’s pressure and flow rates. Adjust as per manufacturer guidelines.
    • Lubricate pump bearings if required, following the manufacturer’s instructions.

Checking Instrumentation and Controls

Proper functioning of instrumentation and controls is essential for the overall performance of the RO system. Follow these steps:

• • • Inspect pressure gauges, flow meters, and control valves for accuracy and freedom from blockages.
    • Calibrate instrumentation devices if necessary.
    • Verify the performance of automatic control systems and alarms.
    • Test emergency shutdown systems to ensure their functionality.

Troubleshooting for Reverse Osmosis Systems

Marine reverse osmosis (RO) freshwater generators are prone to various issues, with membrane-related problems being one of the most common. Membranes play a crucial role in the RO process by separating salt and impurities from seawater.

Insufficient Freshwater Production

• • • Check the seawater flow rate and pressure. Adjust as required.
    • Inspect and clean clogged filters or strainers.
    • Evaluate the condition of RO membranes for fouling or scaling.
    • Over time, membranes can lose their efficiency due to wear and tear. Monitor the performance of the membranes and consider replacing them if they are significantly aged or damaged.

Excessive Freshwater Salinity

• • • Verify the system’s seawater flow and pressure. Adjust if needed.
    • Inspect the RO membranes for damage or fouling.
    • Review and adjust the operating parameters of the RO system, such as pressure, flow rate, and recovery rate, as per manufacturer guidelines. Optimizing these parameters can enhance the membrane’s performance in removing salt and TDS. If the salt or TDS levels remain high after adjusting the operating parameters, perform a thorough chemical cleaning of the membranes to remove any accumulated deposits that may be hindering their performance.
    • Check salinity sensor, clean it and replace it as found necessary. Be aware that the sensor must be cleaned with a clean dry rag and must avoid to be touched by bare hands.

Leakage or Water Purity Issues

• • • Inspect valves, pipes, and fittings for leakage or improper sealing. Repair or replace as necessary.
    • Check for loose or damaged connections.
    • Examine gaskets and seals for wear or degradation. Replace if needed.

Poor Permeate Quality

In some cases, the quality of the produced freshwater may not meet the desired standards. Troubleshoot as follows:

• • • Evaluate Feedwater Quality: Check the quality of the seawater being fed into the RO system. High levels of contaminants or unusual seawater conditions can affect the permeate quality. Address any issues with the feedwater source, such as pre-filtration or pretreatment, to improve the incoming water quality.
    • Inspect and Clean Pre-filtration Systems: Examine and clean the pre-filtration systems, including filters and strainers, to ensure they are effectively removing larger particles and contaminants before reaching the RO membranes.
    • Check Chemical Dosage: Review the dosage of chemicals, such as antiscalants or biocides, used in the RO system. Incorrect dosing or expired chemicals can impact the permeate quality. Follow the manufacturer’s recommendations for proper chemical dosage and replace expired chemicals.

Pressure Drop or Flux Decline

A sudden decrease in pressure or flux (water production rate) can indicate membrane issues. Troubleshoot using the following steps:

• • • Check for Fouling or Scaling: Inspect the membranes for fouling or scaling, which can cause a pressure drop or decline in water production. Clean the membranes using appropriate cleaning procedures.
    • Examine and Adjust Pre-treatment Systems: Ensure that pre-treatment systems, such as sand filters, cartridge filters, or media filters, are functioning properly. Clean or replace them if necessary to maintain optimum flow rates and pressure.
    • Verify Pump Performance: Inspect the high-pressure pump for any issues, such as clogging, leaks, or reduced performance. Address any pump-related problems promptly.

In conclusion, regular maintenance and prompt troubleshooting are essential for the reliable operation of marine freshwater generators. By following the outlined maintenance process and using the troubleshooting techniques mentioned above, ship owners, engineers, and crew members can ensure a consistent supply of high-quality fresh water onboard vessels. Remember to consult the manufacturer’s guidelines and seek professional assistance when faced with complex issues. With proper care and attention, marine freshwater generators can deliver reliable performance and contribute to the smooth operation of maritime vessels.

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