Category Archives: Boilers

Steam boilers

Saturated vs. Superheated Steam on Board Vessels: Properties, Uses, and Safety

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Steam has been a cornerstone of maritime propulsion and industrial processes for centuries.  It is used in various applications onboard vessels, such as propulsion, power generation, heating, cooling, sterilization, and desalination. Steam can be classified into two main types: saturated and superheated.

Onboard vessels, understanding the differences between saturated and superheated steam is crucial for safe and efficient operation. In this article, we will explore where these types of steam are used, their properties, advantages, disadvantages, and the essential precautions to ensure the safety of both crew and equipment.

Saturated Steam: Properties and Uses

Saturated steam is steam that is in equilibrium with water at the same temperature and pressure. This means that saturated steam contains both water vapor and liquid water droplets.

Source and Credit: convergencetraining.com

The temperature and pressure of saturated steam depend on each other and are determined by the boiling point of water at that pressure. For example, at atmospheric pressure (101.3 kPa), the boiling point of water is 100°C, and the saturated steam has the same temperature. However, if the pressure is increased to 10 bar (1000 kPa), the boiling point of water rises to 180°C, and the saturated steam also has a higher temperature.

Advantages of Saturated Steam:

  • Relatively easy to produce and control.
  • Cost-efficient compared to superheated steam systems.
  • The main advantage of saturated steam is that it has a high heat transfer coefficient, which means that it can transfer a large amount of heat to a surface or a substance in a short time. This makes saturated steam suitable for:
    • heating applications, such as heating water, oil, or air
    • sterilization applications, such as sterilizing medical equipment or food products.
    • propulsion applications, such as driving reciprocating engines or low-pressure turbines.

Disadvantages of Saturated Steam:

  • The main disadvantage of saturated steam is that it has a low energy content per unit mass, which means that it requires a large mass flow rate to produce a given amount of work or power. This results in higher fuel consumption and lower efficiency.
  • Another disadvantage of saturated steam is that it can cause corrosion and erosion of metal surfaces due to the presence of liquid water droplets. These droplets can also damage mechanical parts, such as valves, pistons, or blades, by impacting them with high velocity and force.

Superheated Steam: Properties and Uses

Superheated steam is steam that has been heated to a temperature higher than its saturation temperature at the same pressure. This means that superheated steam does not contain any liquid water droplets and is completely dry, high-temperature steam with significantly more energy content.

Source and Credit: Imagination Station Toledo

Superheated steam can be produced by passing saturated steam through a separate heating device called a superheater, which transfers additional heat to the steam by contact or by radiation.

Superheated steam finds applications in specialized scenarios onboard vessels.

  • Steam Turbines: Superheated steam is ideal for powering high-performance steam turbines in applications where maximum efficiency and energy transfer are crucial.

  • Cargo Tank Heating: It is used to heat cargo tanks, such as those in liquefied gas carriers, as it can transfer heat efficiently and consistently.

Advantages of Superheated Steam:

  • Higher energy content and temperature, which means that it can produce a large amount of work or power with a small mass flow rate. This results in lower fuel consumption and higher efficiency.
  • Greater efficiency in power generation and propulsion, which means that can also be used for propulsion applications, such as driving high-pressure turbines or turbochargers. In industrial field, superheated steam can also be used for drying applications, such as drying paper or wood products.
  • Reduced risk of corrosion in pipelines due to dryness.

Disadvantages of Superheated Steam:

  • The main disadvantage of superheated steam is that it has a low heat transfer coefficient, which means that it can transfer only a small amount of heat to a surface or a substance in a long time. This makes superheated steam unsuitable for heating applications or sterilization applications.
  • More complex and costly to produce and maintain.
  • Requires precise control to prevent overheating and potential damage to equipment, which means that it can cause thermal stress and fatigue of metal surfaces due to the high temperature difference between the steam and the surface.

Safe Operation of Steam Onboard Vessels

Steam is a powerful and useful form of energy, but it can also be dangerous if not handled properly. Steam can cause severe burns, explosions, fires, or mechanical failures if it escapes from pipes, valves, boilers, turbines, or other equipment. Therefore, it is important to follow some safety precautions when operating steam onboard vessels.

Some of the safety precautions are:

  • Always wear protective clothing and equipment when working with or near steam systems.
  • Always check the pressure and temperature gauges before opening or closing any valves or vents.
  • Always use proper tools and procedures when repairing or maintaining any steam equipment.
  • Always follow the manufacturer’s instructions and specifications when operating any steam equipment.
  • Always inspect the steam equipment regularly for any leaks, cracks, corrosion, or wear.
  • Always report any abnormal conditions or malfunctions to the supervisor or engineer.
  • Develop and practice emergency procedures for steam-related accidents, including leaks, fires, and equipment failures.

In conclusion, saturated and superheated steam are both vital components of maritime operations, each with its distinct properties and applications. Saturated steam is versatile and cost-effective, making it suitable for various shipboard functions, while superheated steam excels in high-efficiency power generation and specialized heating tasks. Regardless of the type of steam used, safety must remain the top priority onboard vessels, with stringent maintenance, training, and emergency protocols in place to ensure smooth and secure operations. By understanding these principles and adhering to best practices, seafarers can harness the power of steam to navigate the world’s oceans safely and efficiently.

If you want to learn more about “Steam Theories in Marine Boilers“, please follow THIS LINK on Alison platform. The course is free and all you need to do is just to subscribe to their platform using the link above. This will be of a great help to me as well, as I will earn small commission. You can consider this as a reward for my effort to provide guidance and advices with regard to complex, challenging and rewarding marine engineering.

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!

Marine Boiler Burner Misfiring: Causes, Troubleshooting, and Safety Measures

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Marine boilers are specialized equipment used on ships and other maritime vessels to generate steam for various applications. If you want to learn and read more about “What is marine oil-fired boiler and how to correctly operate it?”, please follow THIS LINK.

Marine boiler burner misfiring can be a serious concern for vessel’s crew, as it can lead to decreased efficiency, increased fuel consumption, and potential safety hazards (e.g. furnace explosion). If you want to learn and read about “Why do Boiler Furnace Explosions Occur” please follow THIS LINK.

In this article, we will explore the possible causes of burner misfiring, discuss the troubleshooting process, and highlight the safety precautions and measures to be taken in the event of a misfiring incident.

Example of proper boiler burner firing flame

Causes of Marine Boiler Burner Misfiring

    • Insufficient Fuel Supply:
      • Clogged or blocked fuel filters – check and clean if required.
      • Incorrect fuel pressure or flow rate – The correct fuel pressure or flow rate on a boiler burner is essential for ensuring proper combustion and efficiency. If the fuel pressure is too low, the burner will not ignite properly or will produce a weak flame. If the fuel pressure is too high, the burner may ignite with a loud bang or produce a smoky flame.
      • Malfunctioning fuel pumps – A malfunctioning fuel pump can affect the firing process into the boiler burner in a number of ways, including: insufficient fuel delivery, unstable flame, clogged nozzle, damaged pump etc.
    • Ignition System Issues:
      • Faulty ignition electrodes or ignition transformer – Faulty ignition electrodes or ignition transformer can affect boiler burner firing in a number of ways, including: no spark, weak spark, misfire, carbon monoxide poisoning etc.
      • Improper spark plug gap or electrode alignment – The spark plug gap and electrode alignment are essential for the proper firing of a boiler burner. If the gap is too wide, the spark will be weak and will not have enough energy to ignite the fuel. If the gap is too narrow, the spark will be too hot and can damage the spark plug. The electrode alignment is also important, as the spark must jump between the electrodes in order to ignite the fuel. If the spark plug gap or electrode alignment is incorrect, the boiler burner may not ignite at all, or it may ignite with a weak or unstable flame. This can lead to a number of problems, including: low heat output, smoky flame, damage to the burner.

      • Damaged ignition cables or connectors
    • Combustion Air Supply:
      • Inadequate combustion air intake due to blockages or restrictions – this can affect boiler’s burner firing in a number of ways, including: incomplete combustion, smoky flame, low heat output, damage to the burner.
      • Malfunctioning air dampers or fans – Air dampers and fans are essential for controlling the flow of air to a boiler burner. If the air dampers or fans malfunction, it can affect the boiler’s burner firing in a number of ways, including: incomplete combustion, smoky flame, low heat output, damage to the burner, fire hazard.
      • Air leaks in the combustion air system
    • Fuel Quality:
      • Contaminated or degraded fuel – Contaminated or degraded fuel can affect boiler’s burner firing in a number of ways, including: incomplete combustion, smoky flame, low heat output, damage to the burner.
      • Incorrect fuel viscosity or flashpoint –  Same as above.
      • Inconsistent fuel composition – Same as above.

Safety Precautions and Measures

    • Emergency Shutdown:
      • Immediately shut down the boiler by activating the emergency stop button.
      • Close the fuel supply valves and isolate the burner from the fuel source.
    • Ventilation and Evacuation:
      • Ensure proper ventilation to prevent the accumulation of flammable gases or vapors.
      • Evacuate the affected area and establish a safe distance.
    • Firefighting Equipment:
      • Maintain firefighting equipment, including extinguishers, hoses, and blankets, in accessible locations.
      • Train crew members in proper firefighting procedures.
    • Communication and Alarm Systems:
      • Establish clear communication channels to inform relevant personnel about the incident.
      • Test and maintain alarm systems to promptly alert crew members in case of emergencies.

Boiler Burner Misfiring Troubleshooting

    • Check Fuel Supply:
      • Inspect fuel filters and clean or replace them if necessary.

        Example of an in-line fuel filter

      • Verify fuel pressure and flow rate, adjusting as per manufacturer’s specifications – The correct fuel pressure or flow rate will vary depending on the type of boiler and burner. However, there are some general guidelines that can be followed. To adjust the fuel pressure, you will need to locate the fuel pressure regulator. This is usually a small, cylindrical device that is attached to the fuel line. The regulator will have a set of adjustment screws that can be used to increase or decrease the fuel pressure.

Example of a fuel modulation module

To adjust the fuel flow rate, you will need to locate the fuel control valve. This is usually a butterfly valve that is located in the fuel line. The valve can be adjusted by turning the handle. When adjusting the fuel pressure or flow rate, it is important to make small adjustments and then test the burner to see how it performs. Once you have found the correct settings, you can tighten the adjustment screws or lock the fuel control valve in place.

      • Examine fuel pumps for any malfunction and repair or replace as needed.

        Example of a fuel booster pump on boiler burner

    • Inspect Ignition System:
      • Check ignition electrodes for wear, corrosion, or fouling, cleaning or replacing them if required.
      • Verify proper spark plug gap and alignment, adjusting as per manufacturer’s guidelines.

      • Inspect ignition cables and connectors for damage and replace if necessary.
    •  Evaluate Combustion Air Supply:
      • Inspect air intake for blockages, clean or remove obstructions, and ensure adequate air supply.
      • Verify proper functioning of air dampers and fans, repairing or replacing as needed.
      • Detect and seal any air leaks in the combustion air system to prevent disruptions.
    • Assess Fuel Quality:
      • Monitor fuel quality regularly and test for contaminants.
      • Ensure fuel meets specified viscosity and flashpoint requirements.
      • Establish a regular fuel testing and maintenance program.

In conclusion, marine boiler burner misfiring can arise due to various causes such as fuel supply issues, ignition system problems, combustion air supply limitations, and fuel quality concerns. It is crucial for vessel engineers to promptly troubleshoot misfiring incidents and take appropriate safety precautions to mitigate potential risks. By following proper maintenance procedures, conducting regular inspections, and implementing effective troubleshooting measures, marine engineers can ensure the smooth operation of boiler burners, optimize fuel efficiency, and prioritize the safety of the vessel and crew.

If you want to learn and get a “Diploma in Marine Boilers”, please follow THIS LINK on Alison platform. The course is free and all you need to do is just to subscribe to their platform using the link above. This will be of a great help to me as well, as I will earn small commission. You can consider this as a reward for my effort to provide guidance and advices with regard to complex, challenging and rewarding marine engineering. 

If you wish to learn about “Basics of  Marine Boiler Operations”, please follow THIS LINK.

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!

A Comprehensive Guide to the Operational Testing of Safety Valves for Boiler Safety

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Boilers are essential components of numerous industries, including marine operations, where they play a crucial role in generating steam for propulsion, power generation, and other onboard processes. Safety valves are critical elements of boiler systems, designed to protect against potentially hazardous conditions by relieving excess pressure. However, for safety valves to effectively perform their function, regular operational testing is essential. This article aims to emphasize the importance of testing safety valves, provide insights into their operation, maintenance, and testing procedures, and offer links to existing Class rules and regulations pertaining to safety valve live tests on marine boilers.

Safety valves act as the last line of defense against catastrophic boiler failures caused by excessive pressure. Their primary purpose is to ensure the pressure within the boiler remains within safe limits by discharging excess steam when the predetermined set pressure is exceeded. However, if safety valves are not periodically tested, their reliability may diminish over time, leading to potential risks such as boiler explosions or damage. Thus, regular testing of safety valves is critical to ensure the continued safety and proper functioning of the entire boiler system.

Safety valves are mechanical devices that rely on pressure to operate effectively. When the pressure inside the boiler reaches the predetermined setpoint, the safety valve opens to release excess steam and reduce pressure. This action helps prevent the pressure from surpassing the boiler’s maximum allowable working pressure (MAWP) and protects against potential over-pressurization hazards.

For boilers, the safety devices are to be tested and the safety valves are to be operated using the relieving devices. For exhaust gas heated economizers/boilers, the safety valves are to be tested at sea by the Chief Engineer and details recorded in the Log Book.

All safety valves are to be set under steam to a pressure not greater than the approved pressure of the boiler. As a working tolerance the setting is acceptable provided the valves lift at not more than 103 per cent of the approved design pressure. During a test of 15 minutes with the stop valves closed and under full firing conditions the accumulation of pressure is not to exceed 10 per cent of the design pressure. During this test no more feed water is to be supplied than is necessary to maintain a safe working water level.

To maintain the reliability and effectiveness of safety valves, regular maintenance is essential. Here are some key maintenance practices:

    1. Visual Inspection: Conduct routine visual inspections to identify any signs of damage, corrosion, or leaks. Ensure the valve is clean and free from debris that may obstruct its operation.

    2. Lubrication: Apply the recommended lubricants to moving parts to ensure smooth valve operation. However, it is crucial to use lubricants compatible with the valve’s construction materials.

    3. Testing: Regularly test safety valves to verify their performance and ensure they are operating within acceptable tolerances. This helps identify any issues with the valve’s lifting pressure, seat tightness, or disc movement.

The workshop bench testing procedure for safety valves, is done usually during dry dock inside yard workshop and,  typically involves the following steps:

    1. Preparation: Prior to testing, isolate the boiler from the system by shutting off the boiler and relevant valves. Follow proper lockout/tagout procedures to ensure the safety of personnel. Cool down and drain boiler pressure.

    2. Bench Testing: Remove the safety valve from the boiler and place it on a test bench. Connect it to an appropriate testing apparatus capable of accurately measuring pressure and flow rates.

    3. Set Pressure Verification: Verify the valve’s set pressure by gradually increasing the pressure until the valve starts to lift. Compare the observed set pressure with the manufacturer’s specified value.

    4. Seat Tightness Testing: After verifying the set pressure, gradually reduce the pressure until the valve reseats. This tests the tightness of the valve’s seating surfaces and ensures proper closure after relieving excess pressure.

    5. Overpressure Testing: Conduct an overpressure test to ensure the valve can handle pressures above the setpoint without any leakage or damage. This test provides an additional safety margin and evaluates the valve’s overall strength.

    6. Documentation: Record the test results, including the set pressure, lift pressure, reseat pressure, and any deviations or observations. Maintain a comprehensive maintenance log for each safety valve.

An in situ test of boiler safety valves, also known as a live test, involves testing the valves while the boiler is in operation. This procedure allows for the assessment of the safety valves’ performance under actual operating conditions. Here is a step-by-step description of the in situ test procedure for boiler safety valves:

Preparation:

      • Review the boiler system’s operating manual and safety valve manufacturer’s instructions to understand the specific requirements and procedures for testing the safety valves.
      • Ensure all necessary safety precautions are taken, such as wearing appropriate personal protective equipment (PPE) and following lockout/tagout procedures to isolate the boiler and associated equipment.
      • Verify that all required testing instruments and equipment, such as pressure gauges and flow measurement devices, are available and calibrated.

Isolation and Preparation for Testing:

      • Shut down any auxiliary equipment connected to the boiler and close relevant isolation valves.
      • Verify that the main steam valve and any other upstream valves are closed.
      • Confirm that the pressure within the boiler has dropped to a safe level before proceeding with the test.

Test Setup:

      • Identify the safety valve to be tested and visually inspect it for any signs of damage, corrosion, or leakage. Ensure it is clean and free from debris.
      • Attach or open pressure gauges to appropriate ports or connections to monitor the boiler pressure.
      • In some situations, mainly ashore, install flow measurement devices, such as an orifice plate or flowmeter, to measure the steam flow rate discharged by the safety valve during the test.
      • Ensure all connections and fittings are properly tightened and secured.

Testing:

      • Gradually increase the boiler pressure.
      • Monitor the pressure from inside boiler using the installed pressure gauges.
      • Observe the safety valve for signs of lifting, such as the discharge of steam and the movement of the valve’s disc.
      • Measure and record the lift pressure, which is the pressure at which the safety valve starts to open and discharge steam.
      • If required, continuously monitor and record the steam flow rate through the safety valve using the installed flow measurement devices.
      • Stop the boiler and allow the pressure to drop.
      • Once the valve has lifted and discharged steam, observe the valve’s reseating and make note of the reseat pressure, which is the pressure at which the valve closes after relieving excess pressure.

Evaluation and Analysis:

      • Compare the measured lift pressure and reseat pressure with the manufacturer’s specified values or any applicable regulatory requirements.
      • Assess the steam flow rate and ensure it is within the acceptable range for the specific safety valve and boiler system.
      • Evaluate the overall performance of the safety valve based on its response time, seat tightness, and ability to relieve excess pressure effectively.

Documentation and Maintenance:

      • Record all relevant test data, including the lift pressure, reseat pressure, steam flow rate, and any observations or deviations from expected performance.
      • Update the maintenance log or equipment records with the test results and note any necessary actions, such as adjustments, repairs, or replacement of the safety valve.
      • Follow any specific maintenance and reinstallation procedures recommended by the safety valve manufacturer or regulatory guidelines.

It is important to note that the specific procedure for conducting an in situ test of boiler safety valves may vary depending on the boiler system, safety valve type, and applicable regulations. Therefore, it is crucial to consult the boiler manufacturer’s instructions, regulatory guidelines, and industry best practices when performing these tests to ensure accurate and reliable results while prioritizing safety.

In the maritime industry, the operational testing of safety valves on marine boilers is governed by various regulatory bodies and classification societies. These organizations establish rules and guidelines to ensure the safe operation of vessels. Some relevant regulatory bodies and their associated regulations include:

    1. International Maritime Organization (IMO): The IMO sets global standards for safety and environmental performance, including boiler safety. The “International Convention for the Safety of Life at Sea” (SOLAS) contains regulations related to boiler safety on ships.

    2. Classification Societies: Classification societies such as the American Bureau of Shipping (ABS), Lloyd’s Register (LR), and DNV GL provide rules and guidelines for the construction, maintenance, and testing of marine boilers. These rules often include specific requirements for safety valve testing and maintenance.

To access the latest Class rules and regulations pertaining to safety valve live tests on marine boilers, please visit the respective websites of the classification societies mentioned above. They provide comprehensive information on safety standards and procedures.

In conclusion, the operational testing of safety valves is of paramount importance for ensuring the safe and reliable operation of boilers, particularly in marine applications. By conducting regular tests, adhering to maintenance practices, and following established regulations, vessel engineers can minimize the risk of boiler failures, protect onboard personnel, and safeguard marine environments. Prioritizing the testing and maintenance of safety valves contributes significantly to the overall safety culture and the longevity of boiler systems.

If you want to learn and get a “Diploma in Marine Electronics”, please follow THIS LINK on Alison platform. The course is free and all you need to do is just to subscribe to their platform using the link above. This will be of a great help to me as well, as I will earn small commission. You can consider this as a reward for my effort to provide guidance and advices with regard to complex, challenging and rewarding marine engineering. 

If you wish to learn about “Marine Electronics – Electric Circuits and Components”, please follow THIS LINK.

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!

Steam Condenser on Board Vessels: Operation, Maintenance, and Troubleshooting

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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.

    1. 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.

    1. 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.

If you want to learn and get a “Diploma in Marine Boilers”, please follow THIS LINK on Alison platform. The course is free and all you need to do is just to subscribe to their platform using the link above. This will be of a great help to me as well, as I will earn small commission. You can consider this as a reward for my effort to provide guidance and advices with regard to complex, challenging and rewarding marine engineering. 

If you wish to learn about “Beginner Steam Theories in Marine Boilers”, please follow THIS LINK.

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!

What to do in case of oil contamination of marine boilers

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Marine boilers play a vital role in powering vessels, providing heat and energy necessary for various operations at sea. However, the occurrence of oil contamination within these boilers can have severe consequences, jeopardizing both the safety and efficiency of maritime operations. In this blog post, we will explore the causes, impacts, and essential steps to address marine boiler oil contamination, ensuring the smooth operation of marine vessels.

Understanding Marine Boiler Oil Contamination

Marine boiler oil contamination refers to the unwanted presence of oil or oil-related substances within the boiler system. This contamination can arise from multiple sources, including fuel supply contamination, leakage from seals or pipes, improper maintenance practices, or even accidental spills. Regardless of the source, the effects of oil contamination can be detrimental and require prompt attention.

Many of you must’ve been heard or encounter an oil contamination of the boiler due different machinery or systems breakdown. The contamination has an immediate and consequential impact on boiler operation and is needless to say that the adverse effects of oil contamination on boiler steel and the plant can never be deemed overemphasized. In some situations, large areas of heat transfer lead to the development of cracks, which in turn leads to a loss of the material’s integrity. The majority of them lead to costly repairs that require a significant amount of time and effort, such as the replacement of pressure parts, chemical-mechanical cleaning, and downtime.

Boiler oil contamination

The most prevalent sources of oil pollution detected on boilers come from leaking heating coils fitting in fuel oil tanks, fuel/lube oil heaters, cylinder lube oil from reciprocating steam engines for pumps, and heating coils in DB tanks allocated for sludge/waste oil tanks. It is not unheard of for cargo tank heating coils and tank cleaning heaters installed on the cargo side to be a contributing factor in some instances of contamination.

On the other hand, main propulsion boiler plants that use a segregated saturated steam system as their primary source of heating medium have the lowest risk of oil contamination.

Minor cracks in HFO heating coils or in other heaters in the engine room or in other places on the ship where steam is utilized for heating can sometimes be the cause of oil leaks that become more severe over time. There are several different pathways by which oil can seep out of an engine room in today’s advanced machinery. It is not usually possible to see very thin coatings of oil. According to past experiences, oil pollution at a level of 15–20 ppm (parts per million) will not be noticeable. If there is an oil pollution level of 25 parts per million, then the steam drum will collect roughly 12 kilograms of oil every single day. The boiler has a capacity of 20 tons of steam per hour. There is a potential for localized overheating of the material and potential damage to the boiler if there are thin layers of oil on the tubes of the boiler or on any of the other directly heated surfaces of the boiler.

Example of oil heater

 

Impacts of Marine Boiler Oil Contamination

Foaming and carryover in oil-fired boilers due to increased tension at the water surface are two of the immediate effects of oil contamination. Other immediate effects of oil contamination include malfunctioning boiler water level controls and even protective shutdown systems. Carry-over of water and moisture with the steam may even reach the intensity of priming in the worst-case scenarios, wreaking widespread destruction on consumers such as turbines, super heaters, steam pipework, and associated gaskets.

The presence of severe oil pollution causes a decrease in the rate at which heat is transferred through the steel of the boiler, which contributes to the metal temperature being greater than the design value. Even an oil film or deposit as thin as 0.5 millimeters thick on the water side of an auxiliary boiler rated at 7 bar (g) can easily increase the metal temperature on the furnace side from the design value of 250 degrees Celsius to well above 600 degrees Celsius under normal operating conditions. This occurs when the metal temperature on the furnace side exceeds the design value of 250 degrees Celsius. Because of this, there is a domino effect that leads to an exponential decrease in the material’s yield strength. This continues until the pressure parts that are subjected to active heat transfer fail.

In circumstances in which the decrease in strength does not result in an immediate failure, the boiler steel may nevertheless be subjected to a time-dependent creep zone that is difficult to evaluate (if the temperature is higher than 380 degrees Celsius), unless alloying is taken into account during the design stage.

In the case of exhaust gas water tube boilers with an extended surface area that forms part of the system for the generation of steam by forced circulation, this may, in the worst cases, lead to soot fires due to a lack of heat transfer from the gas side and a rise in the temperatures of the metal due to the uncooled boundaries. In addition, this may cause a decrease in the efficiency of the steam generation system. As a result of the differential expansion of the overheated tubes in comparison to the shell, smoke tube exhaust gas boilers are prone to developing cracks on the tube terminations (see the image below for an example).

It is also important to be aware that other long-term impacts include local corrosion of the area that has been exposed to the acidic nature of oil deposits. This is something that should be kept in mind. When hydrocarbon deposits are subjected to high temperatures in the presence of water, they have a propensity to undergo an acidic transformation.

Addressing Marine Boiler Oil Contamination

As an immediate precautionary measure, derating the boiler’s steam generating capacity by reducing the firing rate/heat input in conjunction with the design working pressure is highly  recommended.

Depending of the degree of oil contamination on boiler, sometimes can lead to a requirement of the permanent restoration of the heat-transfer surfaces on the water and steam side prior to the boiler being put back into service.

Rebuilding boiler tube nest

To mitigate the negative impacts of marine boiler oil contamination, it is crucial to follow a systematic approach. Here are the key steps to be taken:

      1. Detection and Confirmation: Regular monitoring and analysis of water samples can help detect contamination. Suspicious characteristics or abnormal levels of impurities should be investigated further to confirm the presence and extent of the contamination.
      2. Isolate the Contaminated System: To prevent the spread of contamination, it is necessary to isolate the affected marine boiler system. This may involve shutting down the boiler or bypassing it temporarily until the issue is resolved.
      3. Identify the Source: Thorough inspection and investigation should be conducted to identify the root cause of the oil contamination. Addressing the source is essential to prevent its recurrence and implement appropriate preventive measures.
      4. Clean the System: Cleaning the contaminated marine boiler system is vital to remove oil residues and contaminants. The cleaning process typically involves flushing the system with specialized cleaning agents or solvents designed for marine boiler systems.
      5. Rinse and Drain: After the cleaning process, the system should be thoroughly rinsed with fresh water to eliminate any remaining cleaning agents or loosened contaminants. Complete drainage is necessary to ensure a clean and oil-free environment.
      6. Inspect and Replace Components: Inspect all components of the marine boiler system for damage or residual contamination. Replace compromised or heavily contaminated components to ensure the integrity and reliability of the system.
      7. Test and Restore: Thorough testing of the marine boiler system is necessary to ensure its proper functioning. Conduct pressure tests, verify temperature control, and monitor performance indicators to restore optimal operation.
      8. Preventive Measures: Implementing preventive measures is crucial to minimize the risk of future oil contamination incidents. This includes regular maintenance, monitoring, and sampling of the marine boiler system, along with adequate crew training in boiler operation and maintenance best practices is essential.

Boiling out the water side of the boiler using recommended chemicals and/or mechanical cleaning are normal procedures undertaken to facilitate satisfactory cleaning. This may be additionally supported by hardness checks and a hydrostatic pressure test at 1.5 times the design working pressure to ensure the expected safety factor at the design temperature.

Boil-out chemicals are highly caustic. Caustic Soda ash will produce a violent flash if introduced to water too rapidly. It is needless to say that the crew involved into this operation and handling the chemicals must wear protective equipment like, goggles, gloves, aprons, and an emergency shower should be nearby. Vinegar can be used as an antidote.

Below there is a recommended boil-out procedure that may be followed:

      1. If the boiler is equipped with prismatic type gauge glasses, replace them with the temporary boil-out glass to prevent chemical attack on the operational gauge glasses.
      2. Remove all manholes and handholes’ covers to verify that tubes and nozzles are not plugged with foreign materials.
      3. Wire brush any heavy scale on drum surfaces and remove them out.
      4. Close all inspection openings such as manholes, handholes, etc.
      5. Fill the boiler to the lower level of the water gauge glasses.
      6. Blow-down valves, scum valves, and gauge cocks should be checked and closed.
      7. Add the chemical and water mixture to the unit slowly and in small amounts to prevent excessive heat and turbulence. Add the mixture through the chemical feed or feed-water connections to a level just above the bottom of the gauge glass.
      8.  Fire the boiler at a very low firing rate.
      9. When the boiler begins to produce steam (as seen through the open vents), allow the unit to steam freely for at least four hours. Watch the level in the gauge glass and always maintain normal water level (midpoint of the gauge glass). It will be necessary to add more boil-out solution when the water level falls.
      10. Close all vents.
      11. Keep the drum pressure at aprox.1 bar.
      12. After 8 hours, increase the pressure up to 20 % of the nominal working pressure.
      13. Continue boil out for at least 48 hours. During this period, open the blowdown valve intermittently and drain an amount of solution equal to one-half of the gauge glass every eight hours. Then refill the unit to the midpoint of the gauge glass with the boil-out solution.
      14. The boil out procedure should be continued until clean blowdown is observed.
      15. If clean blow down is observed, the boiler should be stopped and cool down gradually.
      16. Drain the water in accordance with local, national and international rules and regulations.
      17. Flush the boiler with clean water for at least 2 times.
      18. Fill the boiler with clean distillated water and start the firing up procedure.
      19. Start using treatment chemicals as per manufacturers’ instructions.

For stubborn oil deposits or heavy contamination, manual mechanical cleaning may be required. Use appropriate brushes, scrapers, or cleaning tools to remove the oil residues from internal surfaces, tubes, and components. Be careful not to damage the boiler surfaces during this process.

It’s important to note that the above steps provide a general guideline, and the specific cleaning process may vary depending on the type of marine boiler and the severity of contamination. It is recommended to consult the vessel’s operational and maintenance manuals, follow manufacturer recommendations, and seek expert assistance to ensure a safe and effective cleaning process tailored to your specific marine boiler system.

In conclusion, marine boiler oil contamination poses a significant threat to the efficiency, safety, and environmental sustainability of maritime operation. Timely detection, isolation, and remediation are vital to address this issue effectively. By following a systematic approach and implementing preventive measures, vessel operators can safeguard their marine boilers, reduce operational costs, and ensure a safe and smooth voyage. Prioritizing the elimination of oil contamination is not just an imperative for individual vessels but also for the overall well-being of the marine industry.

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!

What you need to know about steam traps

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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:

    • mechanical traps: float type, inverted bucket type.
    • thermostatic type traps

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.

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!

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!

Source and Bibliography:

  • YouTube video credit: The Engineer Portal T.E.P; hararat
  • http://www.tlv.com
  • Photo credit: mentioned on every photo

What you need to know about steam boiler’s water level control onboard vessels

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It is imperative that the water level in a steam boiler be carefully managed in order to guarantee the production of high-quality steam in a manner that is risk-free, resource-friendly, and at the appropriate pressure.
Heat is produced by the combustion of fuel in a furnace, while waste heat from the main engine can also be used to produce steam. The heat is transferred to the water that is contained within the shell of the boiler, which subsequently evaporates to produce steam that is subjected to pressure.
In order to properly discharge steam from a boiler, there must be a particular amount of water surface area available. A certain height should also be allowed above the normal working level in order to allow the water level to rise with increasing load while still allowing sufficient area for the steam to be released without any carryover of water taking place. This should be done by allowing a certain height above the normal working level.

Example of water level sight glass arrangement. Source: chiefengineerlog.com

Because it is obvious that when steam is produced, the water in the boiler evaporates, and in order to keep the level consistent, the boiler has to receive a supply of water and it is imperative that the water be kept at the appropriate level at all times.
If the boiler is allowed to function with insufficient water, there is a possibility that severe damage may occur, and finally there is a chance of explosion.

For this reason, means of controls are required which will monitor and control the water level and detect if a low water level point is reached, and take appropriate action, like sounding an alarm, shutting down the feed water supply and shutting down the burner.

Example of boiler control panel. Source: chiefengineerlog.com

There are numerous standards that mandate the availability of two separated water gauges, which are made from a screen of tempered glass, which is typically attached to the front and sides of the water gauge glass that is attached to the steam or water drum or the boiler shell. Normally the high-pressure boilers will need water gauge glass that is made up of either flat or prismatic glass. The gauge glass device, which has withstood the test of time, is utilized on the overwhelming majority of boilers. This device is often designed to provide a visible range of water level that is both above and below the normal water level.

Example of water level gauge (sight glass) on auxiliary boiler. Source: chiefengineerlog.com

It is absolutely necessary to have a solid comprehension of what may be observed in a boiler gauge glass. Because the water surface in a steaming boiler is made up of a dense population of bubbles and has a robust horizontal circulation, it is not possible to precisely determine the height of the water within the drum. So, the gauge glass is filled with water, which does not experience current or agitation because of its location, does not have any steam bubbles within it and has a temperature that is lower than the actual water in the boiler. This indicates that the water found in the gauge glass (together with the water found in other external fittings) is of a higher density than the water found inside the boiler drum and as a consequence of this, the level gauge glass will display a level that is lower than the typical water surface level in the boiler drum.

When a boiler is operating at a high load, the vigorous circulation of the water within the boiler will generate differences in the water level at various points along the length of the boiler. There is also the chance that waves will form inside the boiler whenever there is a sudden change in the load and these waves, which can frequently be seen in the level gauge glass, are usually ignored by the water level controls.

There are three obvious applications for level monitoring sensors on a steam raising boiler, and they are as follows:

      • The purpose of the level control is to make sure that the boiler receives the appropriate quantity of water at the appropriate moment.
      • Alarm for low water level. If the water level in the boiler has decreased to or below a predetermined level, the alarm for low water level will sound, preventing the burning of fuel and ensuring that the boiler continues to function in a safe manner. In order to guarantee the user’s safety, rules and regulations require two separate low level alarms to be installed in steam boilers that are automatically controlled. In marine boilers, the burner will be “shut down and blocked” if the two low level alarms (low level and low low level) goes off, and it will be necessary to reset it manually in order to get the boiler back online.
      • Alarm for high water level. This alarm goes off if the water level gets too high, signaling to the boiler operator that they need to turn off the feed water supply.

There are different methods used to detect the water level in the marine steam boilers and these usually are:

      • floating sensors – This is a straightforward method of determining the level, where the boiler is equipped with a float of some kind, which might be in a chamber located outside the boiler, or it could be directly inside the boiler drum. As the water level in the boiler fluctuates, the float will move in an upward and downward motion.

Example of float control. Source: MirMarine

The buoyancy of the float causes it to move up and down in response to changes in the water level. The opposite end of the float rod has a magnet that rotates inside of a stainless steel cap. This magnet is located at the opposite end of the rod. The fact that the cap is made of stainless steel makes it (almost) non-magnetic and enables the lines of magnetism to travel through it without being disrupted. In its most basic manifestation, the magnetic force is responsible for the operation of the magnetic switches in the following manner:

        • The feed pump can be activated by using the switch located at the bottom.
        • The feed pump can be turned off using the switch on the top.

However, in most situations, a single switch will be sufficient to regulate the on/off status of the pump, and the second switch will be used for an alarm. Alarms for different levels can be generated with the help of the same setup. A more advanced method of providing modulating control will make use of a coil that is coiled around a yoke that is located inside the cap. As the magnet is moved up and down, there will be a change in the inductance of the coil. This change in inductance is then used to produce an analog signal to a controller, which is subsequently sent to the feed water level control valve.

      • differential pressure cells – on one side of the differential pressure cell there is always going to be a certain amount of water pressure. On the opposite side, there is a head that is adjustable in accordance with the amount of water in the boiler.

Example of differential pressure cells arrangement. Source: Fierce Electronics

An electrical level signal is generated by the measurement of a diaphragm’s deflection using one of three methods: variable capacitance, strain gauge, or inductive. These methods measure the deflection of the diaphragm in different ways.

The differential pressure cells are used in systems with water of a high quality that has been demineralized, where the conductivity of the water is extremely low, which may indicate that the conductivity and capacitance probes will not function in a dependable manner.

      • conductivity probes control – a point measurement can be obtained through the use of the conductivity principle. When the water level reaches the tip of the probe, it will cause an action to be taken by a controller that is associated with it.

Example of conductivity probe arrangement. Source: keepital.com

It’s possible that this action is to turn on or turn off a pump, open or close a valve, raise the alarm level and switch on or turn off a relay.
However, a single tip can only offer a single action, often known as a point action. Therefore, in order to turn on and off a pump at specific levels, a conductivity probe needs to have two tips attached to it. As soon as the water level drops and the tip at point “pump on” becomes visible, the pump will start operating. When the water level reaches the second tip close to point HW, the pump will be turned off because it has reached its maximum capacity.

      • capacitance probes – they consists of a conducting, cylindrical probe, which acts as the first capacitor plate. This probe is covered by a suitable dielectric material, typically PTFE. The second capacitor plate is formed by the chamber wall (in the case of a boiler, the boiler shell) together with the water contained in the chamber. Therefore, by changing the water level, the area of the second capacitor plate changes, which affects the overall capacitance of the system.

Example of capacitance probe. Source: Intempco

Onboard vessels, usually the boiler water level control is a modulating system which uses PID controllers (you can find and learn more about PID controllers, if you follow this link) .

In some cases, for measuring and control of the water level, the boiler is equipped with a differential pressure (DP) water level transmitter unit. The unit comprises a level electrode, mounted in a protection tube, and the level transmitter. The unit works by a capacitance measurement, with the electrode and protection tube forming a capacitor. If the level of the boiler water located between the two capacitor plates changes, the current flowing through the plates changes. The level transmitter produces a standard analogue output of 4-20mA, which is sent to the control system. The control system processes the signal from the DP transmitter and provides level alarms/shutdowns, and the control of the regulating feed water valve.

The boiler normally operates with two different set points for normal water level. This increases the volume available for shrink and swell during start and stop of the exhaust gas economizers. When the main engine is running and the exhaust gas economizer is in operation, the highest set point for normal water level will be active (NW2). When the main engine is stopped, then there will be a shrink in the auxiliary boiler water level, and the set point for the normal water level will switch to be at NW1.
A second independent safety device is fitted for the ‘too low water level’ shutdown function. The safety device consists of an electrode and level switch; when activated, the switch will cause the control system to shut down the burner. The electrode operates on the conductive measuring principle using the electrical conductivity of the boiler water for level signaling. When the electrode tip is submerged in the water, the imbalance of the level switch bridge circuit is positive. If the water level falls below the electrode tip, the electrode produces a negative imbalance of the bridge circuit. This causes a ‘too low water level’ shutdown signal to be generated and consequent shutdown of the burner.

The feed water is normally supplied to the boiler through the feed water automatic regulating valve, but it can also be supplied using a separate auxiliary line. The regulating valve is controlled by the level of water in the boiler, and will open and close to adjust the feed rate to maintain the correct level in the boiler. The auxiliary feed line is used if the automatic level control system is inoperative. The auxiliary feed water system requires manual control of the boiler inlet valves to maintain the correct level.

The automatic feed water valve operates on the boiler’s main feed line. The valve has a plug of parabolic form and the fluid flow direction is against the closing direction. The valve is operated by a pneumatic actuator which is mounted above the valve; the actuator (read more about this by following this link)  is controlled by a signal from the water level transmitter.

On other cases feed water supply to the boiler is handled by a single element control system, which is designed to maintain the boiler water level and provide an alarm and safety shutdown should the level not stay within set limits. A transmitter is mounted on the boiler, which sends a signal to the controller, which in turn regulates the opening of the feed water control valve.
The feed water control valve has a valve positioner for automatic operation, with
a handwheel for manual operation. The duty feed pump operates continuously and the feed control valve regulates the amount of water directed to the boiler, depending upon the current water level.

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!

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!

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Boiler operation, chemical scale control and defects

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On one of my previous posts, we have discussed about Boiler chemical dosing and control and explained how to test the water and dose the chemicals for water treatment. As the water treatment chemicals tend to settle the impurities, these will form deposits at the bottom of the boiler or will float at the surface of the water and need to be removed.

Always operate the boiler in accordance with the instructions provided by the manufacturer of the boiler, which should contain techniques for blowing down the boiler. The boiler will be equipped with either a surface skimmer valve or a bottom blowdown valve.

Example of boiler skimmer valve

In order to keep the operations of a boiler steady, it is vital to manage blowdown control in the appropriate manner and there are a number of different considerations that go into determining how blowdowns should be carried out. The following are the primary goals:

    • Bottom blowdown for the prevention and removal of sludge deposits in the boiler
    • Management of material that is floating on the surface – skimmer
    • Controlling dissolved solids, preventing carryover, and reducing corrosion are all achievable goals with either approach.

If the boiler operates, especially on shore water, calcium phosphate sludge deposits may form on the bottom of the boiler, making it necessary to perform periodic bottom blowdowns. These will frequently settle at the bottom of the boiler, and the periodic operation of the bottom blowdown will assist in the removal of any deposits that may have formed there. In the event that this is not done, the boiler runs the risk of developing excessive amounts of sludge deposits, as well as the potential for the heating surfaces of the boiler to get overheated.

Example of overheated areas in marine boilers

There is a possibility that not all boilers have surface skimmers. If the water is distilled or extremely soft, the requirement for bottom blowdowns may be reduced, and the surface skimmer may be able to control the amount of dissolved solids in the water instead. Conductivity in the boiler water can be automatically maintained by some boilers thanks to built-in automatic devices.

The word “Cycle of concentration” refers to the ratio of the amount of dissolved solids that is present in the feed water to the amount that is present in the boiler water. There are a few approaches to this calculation; one of the more prevalent methods involves measuring the levels of chlorine in both the feed water and the boiler water. A fundamental illustration of a boiler with a 5% blowdown can be seen in the figure below.

Example of cycle of concentration

In this particular scenario, there are a total of 20 cycles of concentration (10 t / 0.5 t). This figure will often fall somewhere in the range of 10 to 30 most of the time.

In addition to an adequate pre-treatment of the boiler feed water, controlled reserves of treatment chemicals need to be maintained in the boiler water. This is necessary in order to guarantee that any traces of deposit-forming compounds, such as salts of calcium, iron, silica, copper, and magnesium, are prevented from forming hard scales or baked-on sludges. Scale buildup can be avoided by the use of a variety of different treatment strategies.

The carbonate cycle control method of treatment is only suggested for package boilers up to 10 bar that do not have any external feed-water treatment. This might potentially provide us with calcium hardness in the feed water of approximately 40 ppm. By adding sodium carbonate, the objective is to keep the carbonate alkalinity in the boiler water at a level of no less than 250 ppm. Because of this, any calcium that may have been present will now precipitate in the majority of the boiler water rather than becoming baked-on scale on the heat transfer surfaces. After that, the fine precipitate is extracted using the blowdown of the boiler. An excessive amount of carbonate will eventually decompose, resulting in the formation of hydroxide, alkalinity, and carbon dioxide. In the event that silica is present in the boiler water, magnesium will either precipitate as magnesium hydroxide or magnesium silicate. It is essential to include dispersants in this program in order to guarantee that precipitated compounds will remain in suspension throughout the blowdown process. This will make the process more simpler.

The phosphate cycle control treatment approach relies on good quality pre-treatment, (usually sea water evaporators) plus the addition of soluble phosphate and hydroxide alkalinity to the boiler-water. These react with any trace calcium, magnesium and silica impurities to form fine precipitates of: Calcium Hydroxyapatite, Serpentine and Magnesium Hydroxide. These compounds have an exceptionally low solubility, which means that they will precipitate in the boiler water. They can then be removed by blowdown after they have done so. Again, it is essential to include dispersants as part of the treatment program to guarantee that precipitated compounds are kept in suspension throughout the treatment process and to make it easier to remove them using blowdown.

When the chemistry of the phosphate cycle is used, it is essential to keep enough amounts of OH alkalinity in the solution. This will ensure that magnesium will precipitate as either magnesium hydroxide or as hydrated magnesium silicate, both of which are inert compounds. In order for us to reach these circumstances, we need to work toward achieving an alkalinity ratio of 0.4:1 for silica to OH and a ratio of 1:10 for phosphorus oxide to OH. Overdosing of phosphate must also be avoided to prevent the formation of phosphate scales.

The application of polymeric conditioning treatments is able to more than adequately maintain control of deposition in situations in which one can rely on appropriate and constant pre-treatment of boiler feed-water. These are often formulated with long chains of negatively charged polymers and co-polymers, and they have an excellent stability at the high temperatures that are present in boiler fluids. These formulations are generally considered to be proprietary.

All polymer treatments can be described to inhibit scales by the following mechanisms:

    • Crystal modification – The dispersant acts on the surface of the scale as it is formed to prevent the formation of large angular crystals which are adherent to the heat transfer This action causes the scale to form in smaller, more rotund particles which are less adherent to surfaces.

  • Example of crystal modification

    • Dispersion – The negatively charged polymers attach to boiler metal and surround particles in the boiler-water. This mechanism sets up repulsive forces that inhibit the particles from agglomerating to form scale or sludge deposits.

  • Dispersation

    • Complexation – Negatively charged polymers can form weak sub-stoichiometric complexes with calcium, magnesium and iron which allow these impurities to exceed their normal solubility levels and acts to inhibit deposition at heat transfer surfaces. For best scale control it is important to maintain an adequate reserve of free polymer in the boiler water at all times.

Complexation

Typical boiler damages and defects and auxiliary boiler defects on pressure parts are typically related to mechanisms such as:

    • Active local pitting corrosion from the water/steam side
    • Overheating due to deposits, oil, scales, low water level, flame impingement, etc.
    • Poor workmanship during fabrication
    • Soot fires on fin/pin type water tube exhaust gas boilers
    • Cold corrosion from gas side

It has been observed that the majority of boiler defects that are reported are caused by corrosion, which arises out of probable factors related to an inferior water condition, most often as a result of insufficient maintenance. This is the case because corrosion arises out of probable factors related to an inferior water condition.

It would appear that the absence of a stable and passive magnetite layer (oxide) on the water/steam side of metal surfaces is the primary contributory mechanism that causes many of the documented faults.

Example of passive and stable magnetite layer

A smaller number of defects are related to other factors or operational issues.

It has been observed that many ships are struggling to allocate time and arrange acceptable materials and resources to repair the defects after they have occurred or are observed, making the situation even worse.

The following are the most significant things that have been learned as a result of inspections and surveys experience:

    • Enhanced focus on water treatment: The risk of active local and general corrosion of the internal surfaces (steam and water side) is reduced to a minimum by utilizing prescriptive methods to initiate and sustain a passive magnetite layer on steel surfaces, as well as by increasing the frequency of monitoring the water condition. This keeps the risk of corrosion to a minimum. In addition, the heat transfer barriers can be decreased by maintaining the ideal state of the heat transfer surfaces. This can be accomplished by avoiding the accumulation of scale and other impurities, for example. This therefore results in:
        • Improved fuel efficiency
        • Avoidance of thermal strains that could lead to cracks in the material
        • Preventing the wall of the furnace, the top plate, and the screening tubes from becoming overheated
    • Monitoring and maintenance of the boiler plant: Placing a greater emphasis on maintenance and conducting internal inspections reduces the likelihood that other contributing factors may result in a defect or make the likelihood of one occurring more likely (flame impingement from burner, etc.).
    • The risk of water side contamination/excessive dissolved oxygen and defects related to the gas side is minimized by optimizing the design of the feed water system (using things like salinometers, oil content sensors, and hotwell temperatures, for example), as well as monitoring the differential pressure across the exhaust gas boiler.
    • A more flexible class survey – As a consequence of this, a portion of the scope during each alternative boiler survey – which is not connected to the main class renewal survey – can be credited based on the chief engineer’s inspection report, which reflects evidence of a satisfactory internal examination. This is because the main class renewal survey is not connected to the alternative boiler survey.

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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Source and Bibliography:

  • WSS Water Treatment
  • DNV

Why do boiler furnace explosions occur?

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I believe that everyone of you have heard about or, unfortunately, witnessed at some point in your career a boiler explosion due different reasons. Unfortunately, despite all safety features, checklists and procedures in place this kind of accidents occur and they are mainly caused by human errors.

Example of a clean boiler burner

Explosions in boiler furnaces mainly happen when unburned fuel collected in the furnace or air box, vaporizes and mixes with other elements to create an explosive mixture. If this mixture of flammable vapours comes in contact with a source of heat, an explosion will happen.

Example of boiler fire due unburnt fuel collected into the air box

In a way similar to crankcase explosions, there is sometimes a primary explosion that breaks some part of the structure, followed by a much bigger secondary explosion as more air and fuel are vaporized by the first explosion.

So, where does the unburned fuel come from that causes a boiler furnace to explode?
Unburned fuel can build up in the furnace or air box if:

    • the boiler can’t be started, maybe because of a problem with the igniter or because the fuel isn’t mixed well enough;
    • fuel leaks past broken fuel oil shut-off valves while the boiler is off;
    • fuel spills into the furnace during maintenance;
    • the boiler doesn’t burn the fuel well enough while it’s running, causing unburned fuel to build up in cooler parts of the boiler. This could happen if someone tries to burn fuels in the boiler that it wasn’t made to burn, like sludge or very low-grade heavy fuel oils.

Now that we know where the fuel for an explosion can come from, let’s look at where the heat can come from.

    • When you try to light a boiler, you add a source of heat, which can cause an explosion if there is flammable vapour in the furnace;
    • If the boiler was just fired up, this could definitely be the source of the heat. This is because the refractory on the walls of the furnace will still be hot enough to both turn unburned fuel into vapor and start a fire;
    • When hot boiler furnaces were opened up for maintenance and fresh air rushed into the furnace, this can cause an explosion if unburnt fuel is present inside.

What are the conditions for a boiler to work correctly?

Let’s assume that everything is fine on the water and steam sides and that all the devices we need are working and set up correctly. For good combustion, we will need:

    • a good supply of fuel at the right pressure and temperature for atomization;
    • any other service needed to get atomization and this could be done by atomizing steam or by atomizing air from a supply fan.
    • a way to fire the boiler, which is usually a spark made by electricity from a pair of electrodes or something similar. In some situations, a pilot burner that uses distillate fuel is used to light the main burner.

Example of boiler ignition electrodes

Auxiliary boilers have a number of safety features that are meant to stop explosions in furnaces. These are:

    • The boiler purging sequence – before every attempt to light the boiler, an automated boiler will run through a “purge” sequence. This means that the combustion fan blows air through the furnace to remove any explosive present vapours. During the purge sequence, up to seven times the volume of air in the furnace is removed in order to ensure that any explosive vapours are pushed out of furnace.

  • Example of boiler modulation device

    • Double shut-off valves on the fuel oil system – these should prevent leakage of fuel oil into the boiler when the boiler is not meant to be firing.

  • View of double fuel oil shut-off valves

    • A low pressure trip for boiler fuel oil supply – this should stop the boiler in the event of low fuel oil pressure and help prevent poor atomization and combustion due to low fuel oil pressure.

  • Example of fuel line pressure switch

    • A low combustion air pressure trip – this should prevent poor combustion or flame failure in the boiler if the combustion air fan is damaged or not running. For boilers that use steam or air to assist atomisation, an alarm and trip will be fitted to prevent poor combustion or flame failure if the atomising medium is not present.

  • Example of primary and combustion air pressure switches

    • A flame detector – the flame detector may  have a number of roles. Its main purpose is to make sure that there is a flame in the furnace and to stop and cut out the boiler in the event of flame failure. This prevents fuel entering the furnace if the flame is extinguished for any reason. The flame detector  will also prevent burner start up if there is a flame already present in the furnace. This is partly a self check, to ensure that the “no-flame” condition can be identified by the detector. If there is a flame in the furnace before burner start up, this would indicate that there is unburned fuel, and therefore possibly an explosive fuel vapour mix. When flame failure occurs in the boiler, the safety shut-down solenoid valves shut off the fuel supply to the burner within few seconds and the control locks out the burner, requiring a manual reset.

Example of boiler flame detector

Automation is there to help prevent boiler furnace explosions, but when boiler is operated in manual or emergency mode, the operator should follow the procedure and operate the boiler with caution in order to keep everyone safe. In order to do so:

    • Make sure that there us enough time for purging the furnace, with the air dampers fully open to ensure that any dangerous vapours are pushed out.
    • Never try to reduce the purging time or bypass the purge sequence.
    • Carry out the correct boiler combustion equipment planned maintenance.
    • Only use fuel that the boiler is designed to use, and beware of fuels which have high wax points when in cold temperatures.
    • Make sure that the air fuel ration is correct and is giving complete combustion. Too much air, although inefficient, is safer than not enough.
    • Keep any heat exchangers or economizers fitted to the boiler clean.
    • Soot blow or water wash as required to avoid back pressure in the furnace.
    • Do not repeatedly reset the boiler after a flame failure. Find and fix the fault.

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.

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Exhaust gas economizers cleaning by cold cracking and water washing explained…

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In order to maintain a high thermal efficiency of the exhaust gas economizers and avoid excessive soot accumulations periodical soot blowing and cleaning must be carried out.

The goal of cold cracking is to cool and then heat the economizer steel structure. Because the coefficients of expansion of the boiler steel and the hard deposits differ, the deposits come loose during cold cracking. The carbon particles released during the process are burned off when the economizer is heated afterwards. This burn-off must not take place near coastal areas or in congested areas.

The economizer must be cleaned by soot-blowing on approach to the selected port for the cold cracking to be carried out, to minimize the subsequent burn-off.

The correct procedure for cold cracking process is, usually, as follow:

  • the cooling down process may be started on or during arrival. If the economizer is equipped with a by-pass damper than the cooling process can start during arrival when operating on the exhaust gas economiser bypass damper; if no by-pass damper then immediately after finish with engine.
  • close the steam supply to the heating coils in the drum if supplied.
  • keep the circulation pumps running during the procedure. If small soot fires occur, the circulating water will keep the exhaust gas economiser cool.
  • as an option to accelerate the cooling process, dumping steam can be carried out, but this must be done with care, and carried as below:
    • the steam can be dumped by opening the steam dump valve manually. The pressure drop must not exceed 0.3 bar/minute, to prevent the exhaust gas economiser circulating pumps cavitating, with the resulting pressure drop causing the standby pump to start.
    • open the vent valves on the steam drum.
    • stop the vacuum pumps if the vessel is equipped with the heat recovery system and turbo-generators.
  • open the hopper for the economiser to be cleaned. To increase the differential pressure across the economiser, the funnel fire flaps can be closed.
  • as an option, water spraying can be carried out as the water will accelerate the burn-off process. Water can be supplied from the hopper, or by using the water washing nozzles for a short period.
  • open the heating coil in the steam drums, if equipped, before vessel departure for slow warm up of the economizer.
  • close the hopper.
  • close the steam dump valve and keep the vent valve open.
  • after the start of maneuvering, open the exhaust gas damper (if equipped) to heat-up the economiser slowly and monitor the steam pressure and check if steam comes out through vent valve.
  • close vent valve.
Economizer opened for cold cracking procedure.

Water washing is recommended to be carried out during dry docking as frequent water washing
causes an external corrosion layer of steel on the economiser tubes, which with regular water washing will eventually cause tube leakage.

Water washing must be carried out when a main engine is stopped, but the economiser should be warm enough for the water to evaporate so that the tubes and fins will not remain moist after washing. Economizer washing must be done with fresh water only and where deposits are highly corrosive or bonded, a soaking spray with a 10% soda ash solution is advisable before washing.

When the water washing has begun, it must be continued until the heating surface is thoroughly washed and all deposits are removed, due to the fact that some types of coatings harden and get very difficult to loosen when they have been saturated and then dried out.

It must be ensured that all the washing water is drained away so that water will not enter the turbochargers. The dirty washing water is collected in a tank which is located beneath the economiser.

The economiser must be dried out immediately after water washing. This is because soot formations produced by the combustion process in the engine contain sulphur compounds. Any residual soot and water will therefore react chemically to form highly corrosive sulphuric acid.

Economizer water washing. Source and credit: Marine Engineer Work

The water washing is done utilizing a lance water pressure jet, but on some vessels there is a water washing system inbuild into economizer and the system consists of a number of water washing tubes installed on top of the evaporator sections inside the economiser. Each tube is equipped with spraying nozzles designed in such a way that the whole area of the heating surface will be covered.

Water washing must be carried out when the main engine is stopped and the economiser has been cooled down. However, the economiser should be warm enough for the water to evaporate, so that the tubes and fins will not remain moist after washing.

It is important to note that when the heating surfaces are water washed, there is a possibility of generating steam. To avoid a risk of scalding, the operators must remain outside the economiser casing.

The amount of water used for washing depends on the amount and condition of deposits and should be based on experience. The following procedure should be followed:

  • Open the economiser drain valves to the soot collecting tank and make sure that there is free drainage for the dirty water.
  • Open the drain valves at the main engine turbochargers and make sure that there is a free drainage from the casings.
  • Open the inspection doors above and below the economiser.
  • If there is a risk that the washing water will run into the exhaust gas pipe and down to the turbochargers, the exhaust gas pipe must be covered. Alternatively, the main exhaust gas damper (if equipped) may be closed, but this will not provide complete shut-off and washing water may also accumulate on the outlet side of the damper.
Measuring exhaust gas pipe for cover preparation.
  • Switch off the operational and standby water circulation pumps and close the outlet valves.
  • If the economizer is equipped with washing nozzles, open one of the water washing nozzle supply valves.
  • Open the main fresh water supply valves to the water washing system.
  • Crack open one or two water wash nozzle valves on the economiser. The flow should be sufficient to ensure that the drains are working properly. This will also result in having only a small amount of the soot deposits coming down. If a large amount of water is used, large amounts of soot deposits will loosen, which might block the drain system.
  • There is a time delay from washing water entering the economiser and to draining into the hopper tank. Under these circumstances, care must be taken to control the flow of washing water so that the hopper tank does not overflow if the drain becomes blocked. It is important to check that the drain and soot collecting system is working properly during the whole water washing procedure.
  • When it has been established that the washing water is running freely into the drain system, the water supply can be slowly increased to the full pressure for the water washing system. The nozzle supply valves should be opened as required to ensure that all the heating surfaces are covered. Check the nozzle spraying pattern and that it covers the whole heating surface.
  • When the whole surface has been cleaned, close the main fresh water supply valves and the nozzle valves.
  • When the water washing process has begun, it must be continued until all deposits have been removed and the heating surfaces are clean. This is due to the fact that some types of deposit will harden if they are saturated and allowed to dry out.
  • The soot-blowers may additionally be used during the water washing process. This will enhance the washing efficiency.
  • A fresh water hose may also be used to enhance the washing process.
  • Monitor the water level in the soot collecting tank.
  • When the economiser has been cleaned, it must be ensured that all the washing water is drained away so that water will not enter the turbochargers. The washing water supply valves should be closed and the soot collecting tank drain valves closed.
  • The economiser must be dried out immediately after water washing. This can be done by just having the natural air circulation through the economiser or by heating it up by circulating warm boiler water.
  • If the main exhaust damper was closed during water washing to prevent water from running back in the turbocharger, the damper should be inspected. Any water and soot accumulated at the damper should be removed and the damper properly dried. The condition of the damper and the soft seal can be checked at the same time.
  • Start the circulation pumps and hot water from the separator drums will slowly enter the economiser.
  • Slowly increase the flow through the economiser by opening the outlet valve for the operational circulation pump.
  • Close the inspection doors, close the drains, remove the covers for the exhaust gas pipe if used.
  • The economiser can now be brought back into normal service.

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