Onboard a marine vessel, one of the most critical systems is the fresh water generator, responsible for converting seawater into potable water for the crew’s daily needs. At the heart of this system lies the feed water regulating valve, an essential component that controls the flow of seawater into the fresh water generator.
Feed water regulating valve. Source and Credit: Alfa Laval
In this article, we will explore the operation, maintenance, and troubleshooting of the feed water spring-loaded regulating valve, as well as the role of onboard marine engineers in ensuring its proper functioning.
Feed water regulating valve operation
The feed water regulating valve is a crucial component of the marine fresh water generator system. Its primary function is to control the flow of feed water, which typically comes from seawater, into the evaporator.
Spring load diaphragm valve working animation. Source and credit: Chem media
The operation of this valve is finely tuned to maintain the desired pressure and flow rate, ensuring optimal conditions for the evaporator to produce fresh water through the process of distillation. The valve operates based on a preset loaded spring that monitors the system’s conditions, adjusting the flow of feed water as needed to maintain stable performance.
Its primary functions include:
Regulating Flow:The valve regulates the flow of seawater, ensuring it doesn’t exceed the system’s capacity or drop below the required feed rate for optimal performance.
Pressure Control: The spring-loaded mechanism allows the valve to adjust according to changes in system pressure, maintaining a steady flow regardless of variations in seawater pressure.
Preventing Overload: In the event of a sudden increase in seawater pressure, the valve can close partially to prevent overloading the fresh water generator.
Feed water regulating valve maintenance
Maintenance of the feed water regulating valve is essential to ensure the longevity and efficiency of the marine fresh water generator system. Marine engineers play a pivotal role in this aspect.
Spring loaded regulating feed water valve maintenance. Source and credit: Alfa Laval
Here are some key maintenance tasks:
Regular Inspection: Marine engineers should conduct routine inspections of the valve to check for signs of wear, corrosion, or damage. Any issues should be addressed promptly.
Lubrication: Lubricating the valve components, such as the spindle and seat, ensures smooth operation and reduces friction that can lead to wear.
Cleaning: Over time, the valve may accumulate marine fouling or deposits. Periodic cleaning is necessary to maintain its efficiency.
Calibration: Calibration of the valve is essential to ensure it operates within the specified parameters. This may involve adjusting the pressure settings or flow rates as needed.
Replacement of Parts: As with any mechanical component, parts of the valve may need to be replaced periodically due to wear and tear.
Feed water regulating valve troubleshooting
When issues arise with the feed water regulating valve, onboard marine engineers are responsible for diagnosing and addressing the problems promptly. Some common troubleshooting steps include:
Pressure Fluctuations: If pressure within the system fluctuates, engineers may need to inspect for leaks, blockages, or a malfunctioning valve.
Inconsistent Flow: Inconsistent feed water flow can be a result of valve wear or a misalignment of components. This requires a careful examination and possible adjustment.
Corrosion and Fouling: Engineers should check for corrosion and fouling regularly. If detected, cleaning and potential replacement of corroded parts are necessary.
Valve Sticking: If the valve sticks, it may not open or close as required. This could be due to debris or wear and may necessitate cleaning or repairs.
Leakage: Leakage is a serious concern and may require immediate action to prevent damage to the equipment and environmental contamination.
Role of Onboard Marine Engineers
Onboard marine engineers are indispensable when it comes to the operation, maintenance, and troubleshooting of the feed water regulating valve. Their roles include:
Regular Inspections: Conducting routine checks and inspections to ensure the valve is in optimal working condition.
Maintenance Planning: Planning and executing maintenance schedules to prevent unexpected breakdowns.
Prompt Response: Quick response to any issues with the valve to minimize downtime and ensure a constant supply of fresh water.
Training: Training the crew on basic troubleshooting and maintenance procedures to ensure everyone is prepared in case of emergencies.
In conclusion, the feed water regulating valve is a critical component of marine fresh water generator systems. Proper operation, maintenance, and troubleshooting are essential to ensure a continuous and reliable supply of fresh water on board. Marine engineers play a central role in safeguarding this vital resource, ensuring the safety and comfort of the crew and the vessel’s overall performance.
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Marine fresh water generators play a critical role in ensuring a continuous supply of clean, fresh water onboard ships and vessels.
For proper operation of fresh water generators please followTHIS LINK.
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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The steam condenser is a critical component on board vessels that plays a crucial role in the efficiency and operation of boiler and steam-powered systems. It enables the conversion of exhaust steam from the consumers or main propulsion or power generation systems back into water, allowing for reuse and maximizing energy efficiency. In this comprehensive article, we will delve into the correct operation of a steam condenser, highlight the importance of regular maintenance, and provide a troubleshooting guide for common operational malfunctions.
Correct Operation of a Steam Condenser
The correct operation of a steam condenser involves several key steps and considerations:
1.1. Cooling Water Circulation
Adequate cooling water circulation is vital for the efficient operation of the steam condenser. Cooling water is typically drawn from the sea or a freshwater source and circulated through the condenser tubes, absorbing the heat from the exhaust steam. It is crucial to ensure a sufficient flow rate and temperature difference for effective heat transfer.
1.2. Air Extraction
To maintain optimum performance, it is essential to remove non-condensable gases, such as air, from the condenser. This is achieved through air extraction systems that continuously remove air from the condenser, preventing its accumulation and reducing the risk of performance degradation.
1.3. Vacuum Creation
Maintaining a vacuum within the condenser is vital to enhance the efficiency of steam condensation. A vacuum is created by condensing steam, reducing its pressure, and evacuating the condensed water. Efficient vacuum creation is crucial for maximizing power generation and optimizing overall system performance.
Maintenance of a Steam Condenser
Regular maintenance is essential to ensure the reliable and efficient operation of a steam condenser. Neglecting maintenance can lead to reduced performance, increased energy consumption, and even catastrophic failures. Key maintenance activities include:
2.1. Tube Cleaning
Over time, fouling and scaling can accumulate on the condenser tubes, reducing heat transfer efficiency. Regular tube cleaning, using methods such as mechanical brushing, chemical cleaning, or high-pressure water jetting, is necessary to remove deposits and maintain optimal heat exchange.
2.2. Inspection and Repair
Routine inspections of the condenser, including visual checks and non-destructive testing, help identify any corrosion, tube leaks, or structural damage. Prompt repair or replacement of damaged components is crucial to prevent further degradation and ensure the condenser operates at its designed capacity.
2.3. Cooling Water Treatment
Effective treatment of cooling water is essential to prevent scaling, corrosion, and biological growth within the condenser. Regular monitoring and adjustment of water chemistry parameters, such as pH, alkalinity, and dissolved solids, help maintain water quality and prevent detrimental effects on condenser performance.
2.4. Air Extraction System Maintenance
The air extraction system must be inspected regularly to ensure proper functioning. This includes checking air extraction pumps, vacuum breakers, and associated valves for leaks or malfunctions. Any issues should be addressed promptly to maintain efficient air removal from the condenser.
Maintenance is of paramount importance for steam condensers due to the following reasons:
Efficiency and Performance: Regular maintenance ensures that the condenser operates at optimal efficiency, maximizing heat transfer and energy conversion. This results in improved overall system performance, reduced fuel consumption, and increased power generation or propulsion efficiency.
Equipment Longevity: Proper maintenance helps extend the lifespan of the steam condenser. Regular inspections, cleaning, and repair of components prevent premature wear, corrosion, and deterioration. This not only reduces the risk of costly breakdowns but also contributes to the longevity of the condenser and the entire steam system.
Energy Savings: A well-maintained steam condenser can significantly impact energy savings. When the condenser operates efficiently, more steam is converted back into water, reducing the need for additional steam generation. This leads to lower fuel consumption and operational costs, resulting in substantial energy savings over time.
3. Troubleshooting
Despite proper maintenance, steam condensers may experience operational malfunctions. Here is a troubleshooting guide for common issues:
3.1. Insufficient Cooling Water Flow:
Check the cooling water intake for any blockages or restrictions.
Verify that the cooling water pumps are operating correctly.
Inspect and clean the cooling water filters to ensure unrestricted flow.
3.2. Inadequate Vacuum:
Check for air leaks in the condenser or associated piping and repair any leaks.
Verify the proper functioning of vacuum pumps and vacuum breakers.
Ensure proper condensate removal to maintain the desired vacuum level.
3.3. Tube Fouling or Scaling:
Conduct a thorough cleaning of the condenser tubes using appropriate methods.
Review and adjust cooling water treatment to minimize scaling and fouling.
Consider implementing online cleaning systems for continuous tube maintenance.
3.4 Corrosion or Tube Leaks:
Perform regular inspections to detect any signs of corrosion or tube leaks.
Promptly repair or replace damaged tubes or components.
Consider using corrosion-resistant materials or protective coatings where applicable.
In conclusion, steam condensers are integral to the efficient operation of boilers and steam-powered systems on board vessels. Correct operation, regular maintenance, and timely troubleshooting are essential for optimal performance, energy efficiency, and prolonged equipment life. By following proper procedures, conducting routine maintenance activities, and promptly addressing operational malfunctions, ship engineers can ensure the reliable and efficient operation of their steam condensers, contributing to the overall success and safety of their vessels.
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Marine plate coolers, also known as heat exchangers (read more about their typical failures and remedies in HERE), play a crucial role in the cooling system of marine engines. These compact and efficient devices transfer heat from the engine oil or water coolant to the surrounding seawater or fresh water, helping to maintain optimal operating temperatures. In this blog post, we will explore the benefits and functionality of marine plate coolers, highlighting their importance in enhancing engine efficiency, preventing overheating, and ensuring reliable marine operations.
Example of plate coolers
Plate type heat exchangers are generally used as coolers for water cooling systems, lube oil coolers and as heaters for lube oil purifiers. They are characterized by a very compact structure and good heat transfer grading. By varying the number of plates, the performance can be adjusted and they have low filling capacity, low flow resistance and low thermal inertia. Fluids flow alternately through adjacent plate interspaces according with the counter flow principle and embossing on the plates provide good fluid turbulence and plate stability.
Efficient Heat Transfer: Marine plate coolers are designed with a series of stacked plates, allowing for increased surface area and improved heat transfer efficiency. As the engine coolant flows through the channels formed by the plates, heat is dissipated to the seawater passing through separate channels on the opposite side. This efficient heat exchange process helps to regulate the engine temperature, preventing overheating and maintaining optimal operating conditions.
Engine Performance and Fuel Efficiency: Maintaining the appropriate operating temperature is vital for engine performance and fuel efficiency. Marine plate coolers effectively remove excess heat from the engine coolant, ensuring that the engine operates within the optimal temperature range. By preventing overheating, plate coolers contribute to improved combustion efficiency, reduced wear and tear on engine components, and enhanced fuel economy. Consequently, vessel owners can enjoy longer operating hours and reduced fuel consumption, resulting in cost savings over time.
Corrosion Resistance and Durability: Marine plate coolers are constructed from materials that are highly resistant to corrosion, such as stainless steel, titanium, or cupronickel. These materials ensure the longevity and durability of the plate cooler, even in harsh marine environments where exposure to saltwater and contaminants is prevalent. The corrosion-resistant nature of plate coolers minimizes the risk of clogs, blockages, and other cooling system issues, thus contributing to the overall reliability of the engine.
Maintenance and Cleaning: Proper maintenance and regular cleaning are essential to maximize the performance and lifespan of marine plate coolers.
By understanding their operation and implementing proper maintenance practices is essential to maximize their effectiveness and prolong their lifespan. Further, we will explore the working principle of marine plate coolers and provide valuable maintenance tips to help you keep them running smoothly and reliably.
Working Principle of Marine Plate Coolers
As marine plate coolers are designed to transfer heat from the engine coolant to the surrounding seawater their operation can be summarized in the following steps:
Coolant Flow: The engine coolant is circulated through the plate cooler by a dedicated pump or the engine’s main cooling system. The coolant absorbs heat from the engine components, raising its temperature.
Heat Transfer: As the hot coolant flows through the channels formed by the stacked plates of the cooler, heat is transferred to the cooler’s plates. The large surface area of the plates facilitates efficient heat exchange.
Seawater Flow: Seawater is simultaneously circulated through separate channels on the opposite side of the plates. The cool seawater absorbs the heat from the plates and carries it away, effectively cooling the engine coolant.
Dissipation: The heated seawater is discharged back into the marine environment, while the now-cooled engine coolant returns to the engine, maintaining the desired operating temperature.
Essential Maintenance Practices for Marine Plate Coolers
Regular maintenance ensures optimal performance and longevity of marine plate coolers. Consider implementing the following maintenance practices:
Inspections: Conduct visual inspections of the plate cooler regularly. Look for signs of corrosion, scaling, or damage to the plates, seals, and connections. Address any issues promptly to prevent further damage.
Example of damaged plate cooler
Cleaning: Marine plate coolers can accumulate marine growth, sediment, and debris, affecting their performance. Clean the cooler regularly using appropriate cleaning solutions or marine-safe descaling agents. Follow the manufacturer’s recommendations or consult a professional for specific cleaning procedures. Typically, this involves flushing the plates and channels to remove deposits and maintain efficient heat transfer. Also, sometimes need to be opened and apply mechanical cleaning due hard deposits on the plates’ surfaces.
Back-Flushing: Periodically back-flush the plate cooler by reversing the water flow, to remove salt or impurities that may have accumulated during operation. This prevents the formation of scale and helps maintain the cooler’s performance. The correct back-flushing is done by removing the inner filter before operation.
Pressure Testing: The pressure tests must be performed on the plate cooler to ensure that there are no leaks or blockages that could compromise its effectiveness.
Gaskets and Seals: Inspect and replace gaskets and seals as necessary. Proper seals prevent coolant leaks and maintain the integrity of the plate cooler.
Example of replacing seals on the plate cooler
Coolant Quality: Ensure that the engine coolant used is of high quality and meets the manufacturer’s specifications. Improper coolant can lead to scaling, corrosion, and reduced cooling efficiency.(more about quality testing you can find in HERE)
Professional Servicing: Schedule regular servicing and maintenance with a qualified marine technician. They have the expertise and specialized equipment to perform in-depth inspections, cleaning, and testing of the plate cooler.
Troubleshooting
Plate cooler troubleshooting involves identifying and addressing issues that may arise with marine plate coolers. By diagnosing and resolving problems promptly, you can ensure the efficient operation of the cooling system and prevent potential damage to the engines and auxiliary equipment. Here are some common plate cooler troubleshooting tips:
Insufficient Cooling: If the engine temperature is higher than normal or the plate cooler seems to be providing inadequate cooling, consider the following:
Check for Blockages: Inspect the plate cooler for any blockages or obstructions that may be impeding the flow of coolant or seawater. Clear any debris or fouling that is restricting the flow. Usually this it happens inside filter which can choke in case the your MGPS doesn’t work properly.
Verify Coolant Flow: Ensure that the coolant flow rate is adequate. Insufficient flow can result from a faulty pump, clogged pipes, or a malfunctioning thermostatic valve. Address any issues with the coolant flow system.
Assess Seawater Flow: Check the seawater intake and strainer for blockages. Make sure the seawater pump is functioning correctly, and the intake valves are fully open. Clean or replace any clogged strainers.
Leakage: Leaks can compromise the efficiency of the plate cooler and lead to coolant loss or seawater contamination. Here’s what to do:
Visual Inspection: Inspect the plate cooler, connections, and fittings for any signs of leakage. Look for coolant or seawater stains or drips. Tighten loose connections and replace damaged or worn gaskets and seals.
Pressure Test: Perform a pressure test on the plate cooler to identify any leaks. Address any leaks promptly by repairing or replacing the affected components.
Corrosion and Scaling: Corrosion and scaling can reduce the effectiveness of the plate cooler.
Example of leaking cooler due corrosion and seal failure
Take the following steps to address these issues:
Cleaning: Regularly clean the plate cooler using appropriate cleaning solutions or descaling agents. This helps remove corrosion, scale, and marine growth that can impede heat transfer. Follow the manufacturer’s recommendations or consult a professional for specific cleaning procedures.
Corrosion Protection: Consider using corrosion inhibitors or coatings specifically designed for marine plate coolers. These products help prevent or reduce the risk of corrosion and extend the lifespan of the cooler.
Reduced Heat Transfer Efficiency: If you notice reduced heat transfer efficiency in the plate cooler, take the following actions:
Back-Flushing: Periodically back-flush the plate cooler with by reversing the flow in order to remove salt or impurities that may have accumulated during operation. This helps maintain optimal heat transfer efficiency.
Consult a Professional: If troubleshooting efforts do not improve the heat transfer efficiency, consult a qualified technician. They can perform in-depth diagnostics, including flow rate measurement, pressure testing, and visual inspections, to identify and address any underlying issues.
Remember, if you encounter complex or persistent issues with your marine plate cooler, it is advisable to seek the expertise of a professional technician or maker representative. They have the knowledge, experience, and specialized equipment to diagnose and resolve more complex problems, ensuring the efficient operation of your cooling system and engine performance.
In conclusion, marine plate coolers are crucial components for maintaining optimal engine temperatures in marine applications. Understanding their operation and implementing regular maintenance practices is essential to ensure their efficiency and longevity. By conducting visual inspections, cleaning, flushing, pressure testing, and engaging professional servicing, you can keep your marine plate cooler running smoothly and reliably. By prioritizing maintenance, you contribute to the overall performance and reliability of your marine engine, ensuring many hours of trouble-free vessel operation.
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If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World, Telegram Chief Engineer’s Log Chat or Instagram and will try to answer to all your queries. You can use the feedback button as well!
If you like my posts, please don’t forget to press Like and Share. You can also Subscribe to this blog and you will be informed every time when a new article is published. Also you can buy me a coffee by donating to this website, so I will have the fuel I need to keep producing great content! Thank you!
When it comes to maintaining efficient and reliable cooling systems, there are several crucial components that must be considered. One such component is the cooling water expansion tank.
Recently, I have been asked, by one of my followers, to write an article about cooling water expansion tank. I found the subject to be interesting and challenging as not many of us is really thinking about the importance of the expansion tank into the cooling water system. This is regarded, most of the time, as a simple tank with not so much importance.
If you want to learn more about engine cooling water system just follow the link in here and in here. Moreover, if you want to learn and understand more about vessel auxiliary equipment just click and have a look to Introduction to Marine Auxiliary Machinery.
Often overlooked, this vital piece plays a significant role in the overall performance and longevity of cooling systems. So, in this blog post, we will delve into the importance of cooling water expansion tanks, their function, and the benefits they offer in ensuring optimal cooling system operation.
Example of a cooling water expansion tank
Understanding the Function of Cooling Water Expansion Tanks
Cooling water expansion tanks are designed to accommodate the thermal expansion of water within a closed-loop cooling system. As water heats up, it expands, and without a proper means of accommodating this expansion, the system can experience excessive pressure buildup. Expansion tanks act as a reservoir for the expanding water, allowing it to safely expand and contract without compromising the integrity of the cooling system.
By providing a space for expanded water, cooling water expansion tanks help regulate system pressure. When the water expands, it enters the tank, reducing the pressure exerted on other components of the cooling system. This pressure regulation prevents potential damage to pipes, valves, pumps, and other system elements caused by excessive pressure. By maintaining a balanced pressure, expansion tanks contribute to the longevity and reliability of the entire cooling system.
Cooling water expansion tanks also play a crucial role in minimizing air and contaminant accumulation within the cooling system. The tanks are typically equipped with an air vent or an air separator, allowing trapped air to be released from the system. Removing air not only prevents airlocks but also enhances the efficiency of heat transfer, as air has a lower heat capacity compared to water. Additionally, expansion tanks can feature filtration systems that help capture contaminants and prevent their circulation within the cooling system.
Corrosion and oxidation pose significant threats to cooling systems, leading to reduced efficiency and potential system failures. Cooling water expansion tanks can include various internal coatings or linings that inhibit corrosion and oxidation processes. These protective measures help extend the lifespan of the expansion tank itself, as well as the overall cooling system.
Properly sized and installed cooling water expansion tanks contribute to enhanced system efficiency and performance. By maintaining optimal pressure levels, preventing airlocks, and reducing the risk of corrosion, expansion tanks ensure that the cooling system operates at its peak efficiency. This, in turn, translates to lower energy consumption, reduced maintenance needs, and increased overall system performance.
Example of expansion tank arrangement and fittings
Operation and Maintenance Guide for Cooling Water Expansion Tanks
Cooling water expansion tanks are crucial components of closed-loop cooling systems. To ensure the longevity and efficient operation of these tanks, proper operation and maintenance practices are essential. In the next paragraphs, we will explore the key aspects of operating and maintaining cooling water expansion tanks, providing valuable insights for engineers and operators.
Regular Inspections: Regular inspections of cooling water expansion tanks are necessary to identify any signs of wear, damage, or leaks. Inspect the tank’s exterior for physical damage such as dents or corrosion. Additionally, check the tank’s connections, including inlet and outlet pipes, for any signs of leakage. Early detection of issues can help prevent costly repairs or potential system failures.
Pressure Monitoring: Monitoring the pressure within the cooling water expansion tank is crucial for its proper operation. Utilize pressure gauges installed on the system to ensure the pressure remains within the recommended range. If the pressure consistently exceeds or falls below the recommended levels, it may indicate an underlying issue in the cooling system that requires investigation and correction.
Ventilation and Air Release: Cooling water expansion tanks often incorporate ventilation systems or air vents to remove trapped air from the system. Ensure that the vents are clear and functioning properly to prevent airlocks, which can hinder the cooling system’s performance. Regularly inspect and clean the vents to maintain their effectiveness and promote efficient heat transfer within the system.
Water Quality Maintenance: Water quality plays a vital role in the longevity and performance of cooling water expansion tanks. Implement appropriate water treatment methods, such as filtration and chemical treatment, to prevent the accumulation of contaminants that could lead to corrosion or blockages within the tank and the cooling system as a whole. Regularly monitor water quality parameters, such as pH levels and dissolved solids, and perform necessary maintenance and treatment actions based on the results.
Periodic Flushing and Cleaning: Over time, sediments, debris, and scale may accumulate within the cooling water expansion tank. Regular flushing and cleaning of the tank will help remove these deposits, ensuring optimal performance. Follow manufacturer guidelines and industry best practices when conducting flushing and cleaning procedures, and use appropriate cleaning agents that are compatible with the tank’s material.
Maintenance of Tank Supports and Mounting: Cooling water expansion tanks are typically supported by brackets or mounting systems. Periodically inspect these supports to ensure they are secure and in good condition. Any signs of wear, rust, or damage should be addressed promptly to prevent potential tank displacement or failure.
Proper operation and maintenance of cooling water expansion tanks are essential for the reliable and efficient performance of cooling systems. By conducting regular inspections, monitoring pressures, ensuring proper ventilation, maintaining water quality, and performing necessary cleaning and maintenance procedures, engineers can prolong the lifespan of the tanks and optimize the overall cooling system performance. Collaborating with maintenance professionals when needed will further enhance the effectiveness of the maintenance efforts, contributing to the long-term success of the cooling water expansion tank and the entire cooling system.
In conclusion, cooling water expansion tanks may be small in size, but their significance in cooling system operation cannot be overstated. From pressure regulation and system protection to minimizing air and contaminant accumulation, these tanks offer numerous benefits that help maintain the efficiency, reliability, and longevity of cooling systems. By understanding the importance of cooling water expansion tanks and incorporating them into cooling system designs and maintenance routines, engineers and operators can ensure optimal performance and maximize the lifespan of their systems.
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The evaporation of water into a gas results in the production of steam and in order for the process of vaporization to take place, the water molecules need to be provided with an adequate amount of energy so that the bonds that hold them together (hydrogen bonds, etc.) may be severed. The term “latent heat” refers to the heat that is released when a liquid is converted into a gas. That latent heat is transmitted and used by the medium being heated and after this has been released, the steam condenses. The condensate doesn’t posses the same heating capacity as the steam and if is not quickly removed from the steam piping or heat exchangers, the efficiency of the heating system will drastically drop. (more about steam system can be found by following this link).
I believe that many of you working onboard vessels have encountered, at least once, problems with the steam heating for different systems, problems that were mostly related to the steams traps installed along the steam lines, which most of the time are found to be rusty, seized and replaced with a regular ball-valve.
Steam traps are very important parts of the steam system and they are a form of automatic valve that are designed to prevent steam from escaping while simultaneously removing condensate (also known as condensed steam) and non-condensable gases such as air. Like in any other industry, steam onboard vessels is used for either the purpose of heating or as a driving force for mechanical power. In these kinds of applications, the usage of steam traps is necessary to prevent the loss of steam.
Example of steam trap. Source and credit: Sanmar Enteprises
As per ANSI/FCI 69-1-1989 the steam traps are defined as “self contained valve which automatically drains the condensate from a steam containing enclosure while remaining tight to live steam, or if necessary, allowing steam to flow at a controlled or adjusted rate. Most steam traps will also pass non-condensable gases while remaining tight to live steam.”
Using a ball-valve instead of a steam trap, it might look and sound like a “good” compromise, especially when you don’t have a spare steam trap, but because the valve opening is set to discharge a constant amount of fluid using this method, it is unable to correct for fluctuations in the load of condensate because of this arrangement. This is the method’s most significant drawback. In point of fact, the amount of condensate produced by a particular system is not a constant. When it comes to the piece of machinery in question, the load of condensate that is present during start-up is distinct from that which is present throughout normal operation. Variations in the product load also result in variations in the amount of condensate that is created as a byproduct of the process. Condensate that ought to be discharged will instead pool inside the equipment or the pipe, and the effectiveness of the heating system will suffer as a result, because the manual valve is unable to adapt to fluctuations in condensate load. On the other side, steam leakage will take place when there is a decreased condensate load, which will result in the loss of steam.
There are different types of steam traps used onboard vessel and those mainly are:
Example of mechanical steam trap. Source and credit: TLV CO. LTD
In contrast to other types of steam traps, which rely on either a change in temperature or a change in the velocity or phase of the steam, mechanical traps are steam traps that function according to the principle of specific gravity (more specifically, the difference between the specific gravities of water and steam). When it comes to mechanical traps, the movement of a float that rises and lowers in response to the flow of condensate is what causes the valve to open and close.
Example of float type steam trap. Source and credit: TLV Co. LTD
When using float traps, the amount of condensate in the trap has a direct influence on the location of the float inside the trap. The float is sensitive to the flow of condensate and adjusts its position to either open or close the valve in response. A float is typically fastened to the lever that operates the valve in designs known as lever floats. The float will become buoyant as condensate begins to enter the trap. This will cause the lever to move, which will then cause the trap valve to open. On the other hand, because the lever arm has a restricted range of motion, the head of the valve frequently remains in the direction of the flow of condensate. This might result in an additional pulling force being required to close the valve when there is a significant volume of flow.
Example of inverted bucket type. Source and credit: TLV Co. LTD
In steam traps that use an inverted bucket, the bucket itself is coupled to a lever that controls the opening and closing of the trap valve in reaction to the movement of the bucket. The steam causes the bucket to become buoyant and rise to the surface when air or steam enters into the underside of the inverted bucket and condensate surrounds it on the outside. When placed in this position, the bucket will bring about the closing of the trap valve. A vent hole is located at the top of the bucket, and it is there so that a small bit of the vapor can be released into the top of the trap, and then it can be discharged further downstream. When vapor is released through the vent hole, condensate begins to fill the interior of the bucket. This causes the bucket to sink, which enables the lever to open the trap valve and release any condensate that has accumulated.
Mechanical traps are able to function in precise response to the flow of condensate and their performance is unaffected by the majority of the environmental influences that may affect other types of traps. This is one of the distinguishing advantages they have over thermostatic and thermodynamic steam traps.
Steam traps of the thermodynamic type are highly sought after because of their small size and adaptability across a broad pressure range. They could have a straightforward structure and be able to function in either the horizontal or the vertical orientation.
Thermodynamic disc steam traps have an operating characteristic that is cyclical and intermittent at the same time. After opening to allow the discharge of condensate for a few seconds, the valve mechanism, which is made up of a disc and seat rings, subsequently closes for a generally longer period of time until the beginning of a new discharge cycle. The differential in the forces that are exerted on the top and bottom sides of the valve disc is what’s responsible for the opening and closing action that thermodynamic disc traps exhibit. Variations in the kinetic energy and pressure energy of the typical fluids involved, which include air, condensate, and steam, are the fundamental basis for these forces. At the beginning of the operation, incoming fluids at line pressure consisting of air and/or condensate (and even sometimes steam) exert an opening force (lifting force) on the bottom of the valve disc, which causes it to raise and open. Because of this opening force, the disc is lifted off of its seat to provide room for condensate passage.
There are several reason of why a steam trap doesn’t function properly and these can be (if you want to learn more about it follow this link):
negative pressure differential – the pressure drop across steam trap must be zero or positive in order steam to be discharged.
steam lock – steam locking occurs when the steam is trapped between condensate and the steam trap.
group trapping – collecting condensate from different sections of steam heated equipment with different condensate pressure into one condensate line with one steam trap.
high backpressure
debris or deposits
backward installation
etc.
As is the case with any mechanical device, a steam trap, regardless of how long-lasting it may be, will at some point require either repair or replacement. When a trap is used for a longer period of time, it has more of a chance to become worn. Because of this wear, the performance of the trap will deteriorate, and it may finally become impossible to use.
Because a trap’s lifecycle can be influenced by a number of factors, such as the steam trap type, application, pressure, condensate load, piping configuration, and steam/condensate quality, determining when a trap will fail is an extremely difficult task. This is due to the fact that a trap’s lifecycle can be influenced by a number of factors. Every vessel that uses steam should implement a steam trap management program to assist prevent premature trap failure and identify failures in a timely way.
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Source and Bibliography:
YouTube video credit: The Engineer Portal T.E.P; hararat
I believe that many of you have heard about PID, Temperature Control Valve (TCV), valve controller, step up controller etc. onboard vessel during your career. I know from my experience that many of the young engineers encounter problems to understand what exactly are those machinery items and how did they work.
So, in this post we will discuss about these equipment from operational point of view and I hope that after reading this post you will be able to understand what exactly are those machinery items and how did they work. I am not going to go into deep calculation formulas as this kind of theory you can find it into specialized engineering manuals or through a simple internet search.
A control loop feedback mechanism is referred to as a proportional-integral-derivative controller, or PID controller for short. The PID algorithm, as its name suggests, is comprised of three fundamental coefficients: proportional, integral, and derivative, all of which can be adjusted to achieve the best possible response.
Example of PID schematic
Regarding the operation of the PID, the key concept behind this algorithm is one of “manipulating the error,” and this idea underpins the entire thing.
Example of PID schematic as the Control System
It should be obvious that the difference between the Process Variable and the Setpoint is the source of the error.
These 3 modes are used in different combinations:
P – Sometimes used
PI – Most often used
PID – Sometimes used
PD – Very rare, useful for controlling servomotors.
The proportional corrects individual occurrences of error, the integral corrects the accumulation of error over time, and the derivative corrects the difference between the error that is currently occurring and the error that occurred the last time it was examined.
The derivative will have the effect of reducing the overshoot that is produced as a result of P and I.
When there is a significant amount of error, the P and the I will cause the controller output to be pushed. Because of this controller’s responsiveness, the error can vary very quickly, which in turn causes the derivative to more aggressively counteract the P and the I.
The mode of how your PID controller controls the valve involved it is best described in the controller manual, and therefore you need to read the manual carefully before any intervention or tuning attempt of the controller.
Adjusting the control parameters of a control loop to their optimal values in order to get a desired response is what is meant by “tuning” a control loop. These control parameters include the gain/proportional band, integral gain/reset, and derivative gain/rate.
When the Proportional Gain (KP) is set too high, it will cause values to oscillate and will have a tendency to induce an offset. The Integral Gain, often known as KI, will work to cancel out the offset. A higher value of KI indicates that the Setpoint will approach the PV too quickly, and if this event occurs very quickly, it increases the likelihood that the process variable will be unstable. This situation is kept under control by the Derivative Gain KD.
Manual PID tuning is done by setting the reset time to its maximum value and the rate to zero and increasing the gain until the loop oscillates at a constant amplitude. (When the response to an error correction occurs quickly a larger gain can be used. If response is slow a relatively small gain is desirable). Then set the gain of the PID controller to half of that value and adjust the reset time so it corrects for any offset within an acceptable period. Finally, increase the rate of the PID loop until overshoot is minimized.
Onboard vessels the PID controllers are mostly used for Temperature Control Valves (TCV) in cooling and heating systems (water cooling, purifiers’ heaters, FO heaters and LO coolers etc.).
Example of a LO cooler’s PID controlled temperature control valve
These valves are suited for use in vessel’s applications and process control situations in which fluids need to be mixed or redirected in order to obtain the desired temperatures. They can also be utilized in cogeneration systems to regulate temperatures within the heat recovery loop, so ensuring that the engine is cooled appropriately and making the most of the heat recovery process.
In most cases, the actuated control valve is a component of a comprehensive system that monitors changes in temperature with the assistance of an external probe.
Example of temperature probe
The valve ports are either opened or closed by an external power source after receiving a signal from the probe, which is sent to a control panel.
Example of control panels
Common sorts of systems include those that are electric, pneumatic, or a combination of the two.
Example of electric and pneumatic actuated valves
This kind of valve requires more components in order to function properly, but it does provide a number of advantages over other kinds. To begin, they are typically far more accurate, and because of this, they are the best choice when the application in question calls for extremely exact temperature control. Second, in contrast to thermostatic valves, these systems make it possible to make a flexible adjustment to the temperature range in the event that the working conditions shift.
As mentioned above actuated valves both work equally well for applications that require mixing fluids of two different temperatures or for diverting fluids to a cooler, heat exchanger, or radiator. They can can operate in any position, allowing you to mount the valves based on what works best with the existing pipework.
It is imperative that the temperature of the engine fluids be kept under control in order to guarantee the efficiency and performance of the equipment. Failure to maintain temperature constancy can, depending on the application, contribute to poor fuel consumption, high emission output, and smoke.
The temperature of the charge air inlet has a significant impact on the performance of the engine. For the combustion process to work properly, various grades and kinds of fuel need for varying temperatures at the air input. In addition, regulating the dew point helps cut down on corrosion and improve fuel economy.
The temperature of the jacket water can have an effect on the amount of NOx emissions, the efficiency of the engine, the amount of fuel consumed, and smoke. In this application, keeping the temperature at a high enough level is essential to load acceptance; on the other hand, keeping the temperature too low might result in cold corrosion, particularly during “slow steaming.” It is possible to recover waste heat from the HT system using technology known as smart valves, which can then be used to make the system more efficient as a whole. This is an additional benefit.
When valves are used for mixing service (e.g. Auxiliary Engine’s cooling system), Port C is the cold fluid inlet port from the cooler, Port B is the hot by-pass fluid inlet, and Port A the common outlet. Port A is the temperature sensing port and will mix the hot and cold fluids in the correct proportion to produce the desired outlet temperature leaving Port A.
When valves are used for diverting services, the inlet is Port A (temperature sensing port), with Port C being connected to the cooler, and Port B connected to the cooler by-pass line.
If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World and will try to answer to all your queries. You can use the feedback button as well!
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Every ship has a provision cooling plant, which can range from a refrigeration-cooling combination to 3 to 4 cold storage rooms depending on the ship size and type. Cold storage rooms on passenger ships can include up to 30 – 50 rooms, including dedicated storage rooms for wine, flowers, cigars, and so on. The purpose of cold storage rooms is to maintain optimal storage conditions in terms of temperature and air humidity. To avoid radiation losses, insulation layers are built on the ceilings, walls, and floors. Windows are not supplied, and special heat-insulated doors are fitted. Antechambers are installed to avoid cold loss during entry and leave.
The layout is determined by the vessel’s trading region and duration of voyage, as well as national and international legislation, classification society regulations, environmental regulations, and so on.
Example of a cold provision room onboard vessel
The refrigeration plant is fully automated, with two compressors (which can be scroll type or semi-hermetic reciprocating piston type), two condensers and each cooling and refrigerating room has an evaporator coil and an air circulation fan. A direct expansion Freon gas (usually R134a) system provides cooling for the cooling and refrigerating rooms. The expansion valve regulates the amount of liquid flowing to the evaporator in accordance with the current room temperature; if the temperature has risen, more liquid passes to the evaporator. The liquid travels through the expansion valve, converting to gas and absorbing heat from the evaporator. An electrically powered fan circulates air over the evaporator coil, cooling the provision room. The supply of refrigerant to the expansion valve is controlled by the provision room thermostat via a solenoid valve in the supply line. On some systems a suction line heat exchanger is fitted to protect the compressor from any refrigerant liquid droplets by vaporizing any droplets by the hot refrigerant liquid.
Refrigeration system working principle. Source and credit: Academic Gain Tutorials
The refrigeration unit is controlled by an electronic controller, which performs the following functions:
Setting of thermostat set points
Selection of defrost times
Selection of fan operating options during defrosting
Monitoring plant’s functions, such as room temperatures
System alarm indication and self-check functions
Temperature probe recalibration
Example of electronic controllers
Electric defrosting elements are installed in the refrigerating room evaporator. The frequency of defrosting is controlled by a timer that is part of the electronic control system of the refrigerating unit, but defrosting can also be initiated manually. Compressors function automatically and should not require any configuration changes. The cut-in, cut-out, and pressure differential settings on the controllers can be adjusted, although this should only be done if a new controller is installed. High pressure, low pressure, low lubricating oil pressure, and condenser cooling water failure cut off switches protect the compressors. Under typical circumstances, one compressor/condenser unit is in use, with the other ready for manual start-up. All valves on the standby unit should be closed until it is required for service. The compressor collects R134a gas from the cooling and refrigerating room evaporator coils and discharges compressed/hot gas to the condenser. Water circulating from the central cooling FW system cools the condenser, which cools the heated gas, which condenses into a cool liquid. The liquid refrigerant is returned to the evaporators in the cooling and refrigerating room via a dryer unit and filter.
Some compressors (scroll type) have additional cooling provided by the economizer which allows a small amount of refrigerant into the middle of the compression process. The refrigerant is allowed into the middle of the compressing scrolls by means of a capillary tube. The cooling effect of this refrigerant improves efficiency.
Provision compressor plant
A thermostat fitted in each room enables the liquid refrigerant solenoid valves to operate independently, this reduces the number of compressor starts and the running time of the compressors. It is important to note that the operation of the compressor plant is not designed for continuous parallel running. When one compressor is running, the standby compressor must be isolated from the system. If the valve in the liquid line is not shut, R134a in the system will accumulate in the standby condenser, which will be at the lowest pressure. This will result in the system to stop working due to the lack of refrigerant. Emptying the system of R134a will also transfer lubricating oil from the running compressor and damage the in-use compressor.
The expansion valves of the evaporators accept the refrigerant as a supercooled vapor and the temperature of the chamber being served by the evaporator determines the opening of the expansion valve. The vapours are then returned to the compressor after being heated by the evaporator. The room thermostats open and close the solenoid valves on the air coolers (evaporator units), allowing refrigerant gas to flow to the evaporator while open. With the solenoid valves closed, there is no gas flow to the evaporators; thus, there is no gas flow to the compressor suction, and the low pressure switch will shut down the compressor. The evaporator in the refrigeration room is equipped with electrical defrosting equipment, which comprises of electric heating components attached to the evaporator and drip tray. Any refrigerant gas escapes from the system will cause the system to become undercharged. Low suction and discharge pressures will indicate an undercharged system, which will eventually become useless. There will be bubbles seen in the liquid gas flow sight glass. When necessary, more refrigerant can be injected through the charging line after venting the connection between the refrigerant bottle and the charging connection to prevent air from entering the system through the connection pipe. Before the extra refrigerant enters the system, it is dried. Any trace of moisture in the refrigerant system will result in the thermostatic expansion valve icing over and being obstructed.
Refrigerant R134a is a hydrofluorocarbon (HFC) refrigerant and if gas is lost from the system, only R134a should be used to top the system up. To comply with the Montreal Protocol, the maximum annual leakage of this gas into the atmosphere should be restricted to 10% of the total system charge. To verify this and to monitor the number of times the system has to be recharged, a record has to be made in the Refrigerant Recharge Log. A regular system of leak detection to minimise gas leaks is to be implemented to ensure leaks are detected at an early stage.
The start and stop procedure of the system is similar with the one from the air conditioning system which has been explained on an earlier post which can be found here.
The procedure for defrosting the refrigerating room evaporator is usually as follow:
The evaporator in the refrigeration room is fitted with electrical defrosting equipment, i.e. the evaporator and drip tray are provided with electric heating elements. The frequency of defrosting is chosen by means of a defrosting relay built into the starter panel. The defrosting sequence is automatic and as follows:
The compressor stops and all the solenoid valves in the system are closed.
The fan in the refrigerating room stops working. The fan in the cooling room continues the circulation of the warm air over the coolers, in this way keeping the cooling surfaces free from ice.
The electric heating elements in the refrigerating room are switch on.
As long as the coolers are covered with ice, the melting takes nearly all of the heat supplied and the temperature of the cooler and the refrigerant is constantly kept near zero. When the ice has melted, the refrigerant temperature rises in the refrigerating room. When the temperature reaches the set point (approximately +10°C) of the defrosting thermostat, the heating elements are switched off.
The compressor will now restart and the solenoid valves will be opened according to operating conditions..
When the coil surface temperature has gone below the freezing point, the fan in the refrigerating room starts.
The system is now back on the refrigerating cycle again. If the defrosting is not completed at the expiration of the defrosting period, a new defrosting cycle will commence.
If the plant is to be shut down for maintenance or repair and it involves opening up the compressors or breaking into the refrigerant lines, the refrigerant must first be pumped down to the condenser and isolated in a similar way to that described in my previous post regarding air conditioning system which can be found in here. However, pumping down until the LP cut-out trips the machine will usually not capture all the refrigerant, which may be entrained in the lubrication oil in the compressor sump and around the system. To ensure that the entire refrigerant charge is pumped into the condenser, the system is run until the LP cut-out trips the compressor and the condenser is isolated. The low pressure in the system will allow any refrigerant to evaporate and the process of pumping down until the LP cut-out trips the compressor again. This process is repeated at hourly intervals until there is no rise in system pressure following LP cut-out.
When complete, the inlet and outlet valves must be kept closed until all maintenance work has been completed and the system returned to normal operation.
If more substantial repairs are to be undertaken, it may be necessary to remove all of the refrigerant gas/liquid from the system. Because this operation involves evacuating the condenser and pressurising recovery cylinders, it should only be undertaken by a member of ship’s staff trained in this operation, or by a qualified service engineer. Additionally, for safety reasons, reference should be made to the manufacturer’s operating manuals before undertaking this task.
The first stage in this process is to shut down the refrigeration plant in accordance with the previously described procedure. For full refrigerant evacuation, a designated gas recovery unit must be used together with dedicated gas recovery cylinders. Normally the cylinders used to charge the system cannot be used, as they will typically only have a single non-return valve on the top of the cylinder as opposed to a normal recovery cylinder that has two isolating valves, one for gas and one for liquid, and an internal dropper pipe from the liquid valve. The liquid valve from the recovery cylinder must first be connected via a flexible hose and isolating valve to the bottom of the condenser, and the gas valve of the cylinder connected in a similar manner to the suction side of the recovery pump. The discharge side of the recovery pump must then be connected to the top/gas side of the condenser. With the valves open to the recovery cylinder and recovery pump, the pump is to be run until all of the liquid refrigerant has been evacuated. The purpose of the pump is to compress gas evaporating from the top of the recovery cylinder, and use it to put a positive pressure inside the condenser on top of the liquid refrigerant. When all of the liquid has been expelled, the connections to the recovery pump need to be changed. The suction side of the pump now has to be connected to the condenser. The pump’s discharge should be connected to the liquid connection on the recovery cylinder, and the gas valve on the recovery cylinder either left closed or also connected to the inlet side of the recovery pump. Using this method, all of the gas is then removed from the condenser. The gaseous refrigerant passes through the recovery pump where it is condensed in its own air-cooled condenser and pumped into the liquid connection on the recovery cylinder. When the unit has been run sufficiently and allowed to pull a small vacuum on the main condenser, all of the refrigerant gas will have been removed. Switching off the pump and closing all of the valves will allow any necessary maintenance work to be undertaken. During this operation, a set of weighing scales must be used to ensure the recovery cylinders are not overfilled. It is important to ensure that any cylinder used is only filled to 80% capacity. The scales will also allow a record of the amount of gas recovered to be logged.
Example of gas recovering equipment and procedure
Before reintroducing any refrigerant into the system, all repair works must have been completed, and the pipelines and compressors visually checked for integrity. A vacuum pump, not the recovery pump, must then be used to create a vacuum in the system. A vacuum of 10 torr will be sufficient. This will allow leakage checks to be undertaken and also ensure any atmospheric moisture has been removed before refrigerant is introduced.
It is important to note that If there is water in liquid form in the system, rapid evacuation may cause the water to freeze. If this happens, there will be a rise in pressure (loss of vacuum) which could be confused with a pipework leak.
The vacuum is broken by flooding the system with dry nitrogen and again a pressure test, this time with positive pressure carried out. The nitrogen pressure is released to atmosphere until there is a slight positive pressure in the system and the vacuum pump then used to re-evacuate the system. The vacuum needs to be held for sufficient time to confirm that there is no leakage. Obviously the ship may not be carrying sufficient nitrogen for this process to be carried out, but it is the recommended practice.
The system is now ready to introduce refrigerant via a flexible hose into the condenser. The exact charge will be noted in the manufacturer’s handbook, and checked by suspending the refrigerant bottle from a set of scales. With modern refrigerants being gas mixtures, charging is always done via the liquid line as this ensures correct composition.
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This post is going to be short and concise as the sea water system is quite simple and easy to operate. Sea water is used onboard vessel mainly for cooling purpose, but also for fresh water production and adjusting vessel trim and its stability.
The sea water intake is possible through a crossover main pipe connected to the high and low sea chests located on each side of the ship. Each sea suction chest has an associated suction filter and this must be maintained in a clean condition, in order to ensure adequate water flow to the sea water crossover main pipe and each one of them is provided with air and steam connections for weed and ice clearing.
It is important to note that when lifting the cover off a suction filter casing the joint must be broken with nuts still attached to the cover as this allows the cover to be bolted back into position should sea water actually be leaking into the casing.
Sea chest suction on the ship side
Crossover main pipe inside view
A Marine Growth Prevention System (MGPS) is fitted inside each sea water filter, which provides chlorine and copper injection into the sea water suction main in order to inhibit marine growth in the system and must be operational at all times when a sea suction chest is operational and, on modern vessels, a flow switch at each sea chest monitors sea water flow and regulates operation of the MGPS for that sea chest.
The sea suction valves at each sea chest are manually operated, but on large vessels with big valves they are operated by means of local hydraulic actuators below floor plate level, same as the discharge valve for the main sea water circulating system. Which sea water suction is used depends upon operating circumstances. Normally at sea the low suction is used, but when operating in rivers, estuaries and harbors, where is a danger of drawing mud and silt into the suction manifold, the high sea suction is used.
The main cooling sea water pumps discharge to a common sea water pressure manifold which supplies sea water to the central fresh water coolers. The fresh water generator sea water pump operates the vacuum ejector on the FW generator, provides cooling water to cool the vapour produced during operation and supplies the FW generator with feed water. On container vessels, the reefer cooling sea water pumps supply sea water to the two container fresh water coolers. On some type of vessels the auxiliary sea water cooling pumps discharge to a common sea water pressure manifold which supplies sea water to the auxiliary central fresh water coolers, the sewage treatment system, the ballast water transfer system and the vacuum condenser sea water cooling pumps supply cooling sea water to the vacuum condensers and vacuum pump coolers.
All these pumps take suction from the sea water suction crossover main pipe. Other pumps taking suction from the sea water crossover main pipe are Fire pumps and Ballast pumps.
On some of the vessels one of the main SW cooling pump is provided with a priming unit because it has an emergency bilge suction, the valve spindle, which is painted red, extending above the floor plate level.
The SW cooling pumps are started and stopped remotely from the engine control room (ECR) or locally at the local selector switch panels. The pumps may be selected for RUN, OFF or ST.BY. When the selector switch is in the ST.BY position, the pump will start automatically should the running pump fail to maintain the correct system pressure. One of the SW cooling pumps will normally be selected as the standby pump to start if the operating pump cannot maintain the pressure. Pressure switches on the discharge side of the pumps provide the start signal for the standby pump, which would happen if the operational pump failed for any reason. On some systems there are high speed and low speed starting pushbuttons and the selected running pump may be started in the high or low speed condition as required and on modern vessels the pumps are equipped with frequency converters which will adapt the pump speed as required.
It is important to note that when starting any pump remotely from the ECR, ensure that the pump is operating on the system, and that all relevant suction and discharge valves are open. On the main switchboard, check the motor amps for pump load. On the monitoring system screen, check the suction and discharge pressures of the pump, if available.
At sea when the sea water temperature is below 26°C one of the main sea water cooling pump will be used at high speed as will provide enough sea water flow. If the sea water temperature exceeds 26°C both main sea water cooling pumps will be used at high speed giving a higher sea water output at a higher pressure.
The central fresh water coolers are fitted with a back flushing system on the sea water side and this is used to remove debris from the cooler surfaces in order to maintain them in a clean condition and should be carried out whenever the flow of sea water through the cooler is restricted. Basically the back flushing operation means shutting down the cooler and forcing sea water into the cooler through the outlet connection and allowing the sea water to flow overboard via the inlet connection. Valves are provided at each cooler to allow for back flushing. Back flushing should be carried out when the cooling load is low enough to enable one cooler to meet the cooling demand. To prevent damage to the sea water cooler line filter during backflushing, the filter insert must be removed. Before strainers are removed for cleaning the sea water inlet and outlet valves for the cooler must be closed and sea water in the cooler will be drained to the bilge.
Central fresh water coolers
Filter insert on central fresh water cooler
The interval between cleaning of the in-line filter (and backflushing) depends upon the nature of the sea water in which the vessel is operating. An increase in the sea water pressure drop across the cooler indicates fouling and cleaning of the in-line filter is necessary, but if this cleaning does not reduce the pressure drop, the cooler should be backflushed. In-line filter cleaning at monthly intervals should maintain the cooler sea water surfaces in a clean condition.
The procedure for backflushing of the Main Central Fresh Water Coolers is as follow:
Monitor the pressure drop across the cooler until increases to an unacceptable level. The pressure drop will increase when debris becomes lodged in the sea water channels of the cooler, this debris must be removed in order to restore the operational efficiency of the cooler.
To prevent damage to the sea water cooler line filter during backflushing, the filter insert must be removed. Ensure that the other cooler is in use, then isolate the sea water side of the cooler that need to be backflushed by closing the sea water inlet and outlet valves. Drain the cooler, remove the filter insert, and refit the filter housing cover.
Example of cooler’s backflushing diagram
With the auxiliary cooling sea water circulation system operating normally, open the cooler backflushing valves CW018 and CW019 for the cooler being backflushed (in this example No.1 cooler), and close the normal sea water inlet and outlet valves to the same cooler being backflushed, in this case, valves CW031and CW032.
The backflushing sea water will enter the cooler via the outlet pipe and leave the cooler via the inlet pipe. The backflushing water flows to the overboard discharge valve via the cooler outlet backflushing valve CW019.
Leave the backflush system operating for about 15 minutes.
When backflushing is complete, open the cooler’s inlet valve CW031 and outlet valve CW032, and close the cooler backflush valves CW018 and CW019.
Check the sea water flow through the cooler. The cooler is now back in operation and the other cooler may be backflushed, if required.
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The fresh water generator is an equipment installed onboard vessels which is used to produce fresh water from sea water. There are two major ways of producing fresh water onboard vessels: vacuum evaporation and reverse osmosis, of which the vacuum evaporation comprises of two types: tube type and plate type. Each system has its own pro and cons. The reverse osmosis type has the advantage that it can produce the designated amount of water even at anchorage or while vessel is drifting, but the equipment and its parts are very expensive. This system is mainly common for offshore vessels. Vacuum evaporation type is the most used onboard vessels, especially the plate type, as is reliable, efficient, easy to maintain and makes use of the energy generated by the main engine jacket cooling water system. The fresh water generator can be used for extended periods even at anchor by heating it with the main engine jacket water heater (of course the water production will be low and vessel must use more fuel in the boiler).
Vacuum evaporation plate type fresh water generator
The combined brine/air ejector, which is driven by the ejector pump, creates a vacuum in the system, lowering the feed water’s boiling temperature.
Brine/Air ejector
A spring-loaded regulating valve is used to introduce feed water into the fresh water generator.
Spring loaded regulating valve
Each second plate channel of the evaporator portion receives feed water. The remaining channels are filled with hot water from the jacket cooling system, which transfers its heat to the supply water in the evaporation channels.
Fresh water generator plate arrangement
Once the feed water reaches its boiling point (which is lower than the pressure at atmospheric pressure), it undergoes partial evaporation. The vapors and brine combination enters the separator vessel, where it is separated from the vapors and extracted using the combined brine/air ejector. After passing through a demister the vapors enter every second plate channel of the condenser section.
Demister
The remaining channels are filled with sea water supplied by the combination cooling/ejector water pump, which absorbs the heat from the vapour and condenses it into fresh water. The distillate pump extracts the produced fresh water and discharges it through a salinometer, which checks the water’s salinity. A flow meter is located at the distillate pump outflow. The distillate from the FW generator is routed through the re-hardening filter/neutralizing unit and the silver ion type electric sterilizer before being released into the fresh water storage tanks.
To continuously check the quality of the produced fresh water, a salinometer is provided, together with an electrode unit fitted on the fresh water pump delivery side. If the salinity of the produced fresh water exceeds the chosen maximum value, the dump valve and alarm are activated to automatically dump the produced water to the bilge tank.
In conclusion, the fresh water generator consists of the following components:
Evaporator section which consists of a plate heat exchanger and is enclosed within the separator vessel.
Separator vessel which separates the brine from the vapour.
Condenser section which like the evaporator section consists of a plate heat exchanger which is enclosed within the separator vessel.
The ejector extracts brine and uncondensed gases from the separator vessel.
The sea water supply pump is a single-stage centrifugal pump. This pump supplies the condenser with sea water, the brine/air ejector with jet water, and feed water for evaporation.
The distillate pump is a single-stage centrifugal pump. The distillate pump extracts the produced fresh water from the condenser and pumps the water to the fresh water tank.
The salinometer continuously checks the salinity of the produced water. The alarm set point is adjustable. The salinometer control panel is located at the fresh water generator side with LCD indicators ranging from 0.5 – 20ppm. The panel also contains a 10ppm test function and control buttons to set the alarm point.
The operating procedures for fresh water generator is described in the video below for a better understanding:
Source and credit: JJ AbelTasman
Reverse Osmosis. Source and credit: SA WaterCorp
It is very important that you do not operate the plant in polluted water. Fresh water must not be produced from polluted water, as the produced water will be unsuitable for human consumption. It is advisable and safe to start fresh water generator when the vessel is at least 20 nm from the shoreline.
Chemical treatment is added to the sea water feed in order to minimize foaming and restrict the formation of salt scale in the FW generator. It is essential that the correct dosage of chemical is used and frequent checks must be made on the dosing unit to ensure that the correct treatment is being applied.
The condensate produced in the FW generator is pumped to the storage tanks by the distillate pump. The distilled water may be pumped to the drain tank directly (for boiler feed water use), or it may be pumped to the fresh water tanks for domestic use throughout the ship.
Alfa Laval developed the new AQUA Blue S-type which maximizes energy efficiency and capacity-to-footprint ratio by making use of the vessel’s existing seawater cooling system pumps. This cuts electrical power needs by 70% compared to conventional freshwater generators, and it shrinks the already small AQUA Blue footprint by up to 15%. Because it makes use of the vessel’s seawater cooling system pumps, it employs a smaller ejector and a smaller, separately installed ejector pump. Likewise, the pipework can be both shorter and smaller in diameter.
Source and credit: Alfa Laval
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