All About Boiler Water Blow Down And Procedures For Marine-Boilers

What is boiler water drum blow down in marine boilers?

In marine boilers, the boiler water drum blowdown refers to the process of removing a portion of the water contained in the boiler drum to control the concentration of dissolved and suspended solids. Blowdown is necessary to maintain the desired water quality and prevent the buildup of harmful impurities in the boiler.

During boiler operation, water is continuously evaporated to produce steam, leaving behind dissolved and suspended solids. If these impurities are allowed to accumulate, they can cause various problems such as scale formation, corrosion, and reduced heat transfer efficiency. Blowdown helps to remove these impurities and maintain optimal boiler performance.

The blowdown process involves opening a valve or a blowdown pipe to release a portion of the water from the bottom of the boiler drum. The amount of blowdown is carefully controlled to strike a balance between removing impurities and minimizing water and heat loss. The blowdown water is typically discharged to a suitable location, such as a blowdown tank or a sewage system, depending on the vessel’s design and regulations.

Blowdown frequency and quantity may vary depending on factors such as boiler design, water quality, operating conditions, and applicable regulations. It is crucial to follow the manufacturer’s guidelines, industry best practices, and regulatory requirements when performing boiler water drum blowdown in marine boilers to ensure safe and efficient operation.

Why blow down?

Blowdown is performed in boilers for several important reasons:

1. Control of dissolved and suspended solids: Blowdown helps control the concentration of dissolved and suspended solids in the boiler water. As water is continuously evaporated to produce steam, impurities such as salts, minerals, and other solids become more concentrated. If these impurities are allowed to accumulate, they can lead to scale formation on heat transfer surfaces, reduce heat transfer efficiency, and cause corrosion. By removing a portion of the water through blowdown, the concentration of these impurities is reduced, helping to maintain water quality within acceptable limits.
2. Prevention of scale formation: Blowdown plays a crucial role in preventing scale formation in the boiler. Scale refers to the buildup of mineral deposits on heat transfer surfaces, such as boiler tubes. Scale formation reduces heat transfer efficiency, restricts water flow, and can lead to overheating and mechanical failure. By controlling the concentration of impurities through blowdown, the likelihood of scale formation is minimized, thus preserving the integrity and performance of the boiler.
3. Corrosion control: Excessive concentrations of dissolved solids in the boiler water can promote corrosion of the boiler and associated equipment. Corrosion can result in the degradation of metal surfaces, leaks, and reduced boiler lifespan. Blowdown helps reduce the corrosive potential by maintaining appropriate water chemistry and minimizing the concentration of corrosive substances.
4. Maintenance of steam quality: High-quality steam is essential for various marine applications, such as propulsion and power generation. Impurities present in the boiler water can carry over into the steam, leading to contamination and potential damage to downstream equipment. By conducting regular blowdown, the level of impurities in the boiler water is controlled, improving steam quality and ensuring its suitability for use in critical systems.
5. Safety and compliance: Blowdown is necessary to ensure compliance with safety regulations and industry standards. Regulatory bodies establish guidelines for water quality in marine boilers to prevent hazards, protect equipment, and ensure the safety of the vessel and its occupants. By performing blowdown as prescribed, vessel operators can maintain compliance with these regulations and mitigate risks associated with poor water quality.

Overall, blowdown is a vital maintenance practice in marine boilers that helps control impurities, prevent scale formation and corrosion, maintain steam quality, and ensure safe and efficient operation.

Intermittent or Manual blowdown?

In marine boilers, both intermittent and manual blowdown methods are commonly used, and the selection depends on various factors such as boiler design, operating conditions, and regulatory requirements. Let’s discuss both methods:

1. Intermittent Blowdown: Intermittent blowdown involves the automatic discharge of a predetermined quantity of water from the boiler at regular intervals. This method is typically controlled by a blowdown valve that opens and closes automatically based on a timer or a preset pressure or conductivity level.

Advantages of intermittent blowdown:

• Regular and controlled removal of impurities, maintaining water quality within acceptable limits.
• Reduced dependency on manual operation, allowing for more consistent blowdown practices.
• Helps maintain a more stable water chemistry, minimizing the risk of scale formation and corrosion.
• Can be integrated into the boiler’s control system for automated operation and monitoring.

2. Manual Blowdown: Manual blowdown requires an operator to open a blowdown valve or a blowdown pipe to discharge a portion of the water manually. This method provides more flexibility in terms of timing and the amount of blowdown performed.

Advantages of manual blowdown:

• Allows operators to visually inspect the blowdown water for any abnormalities or indications of boiler condition.
• Provides flexibility to adjust the blowdown frequency and quantity based on specific operating conditions and water analysis results.
• Can be performed as needed during specific maintenance or operational activities.

The choice between intermittent and manual blowdown depends on various factors, including boiler type, automation capabilities, crew availability, and regulatory requirements. Many modern marine boilers are equipped with automatic blowdown systems that allow for intermittent blowdown. However, manual blowdown may still be required for certain maintenance tasks or during critical operating conditions.

It is essential to follow the manufacturer’s guidelines, industry best practices, and applicable regulations when performing blowdown, regardless of the method chosen. Regular monitoring of water quality and consultation with boiler experts or marine authorities can help determine the most appropriate blowdown method for a specific marine boiler.

Continuous blowdown and why?

Continuous blowdown is another method used in marine boilers for water treatment and impurity control. Unlike intermittent blowdown, which is performed at regular intervals, continuous blowdown involves the continuous discharge of a small amount of boiler water to maintain the desired water quality. Here are the reasons why continuous blowdown is employed:

1. Control of Total Dissolved Solids (TDS): Continuous blowdown helps control the concentration of Total Dissolved Solids (TDS) in the boiler water. TDS refers to the total amount of dissolved impurities, such as salts and minerals, in the water. By continuously removing a small fraction of the water, the concentration of TDS is controlled within acceptable limits. This prevents the accumulation of high concentrations of impurities, which can lead to scale formation, corrosion, and reduced boiler efficiency.
2. Steady Removal of Impurities: Continuous blowdown ensures a steady removal of impurities from the boiler water. By discharging a small amount of water consistently, the concentration of impurities remains relatively stable. This helps maintain a more consistent water chemistry and prevents rapid fluctuations in water quality that could otherwise occur with intermittent blowdown. It also helps in minimizing the potential for sudden increases in impurity levels and associated problems.
3. Heat Recovery: Continuous blowdown can be designed to include a heat recovery system. This allows the heat energy contained in the blowdown water to be recovered and utilized, improving overall energy efficiency. The recovered heat can be used for preheating feedwater or other processes, reducing the demand for additional fuel or energy sources.
4. Reduced Boiler Water Treatment Chemicals: By implementing continuous blowdown, the need for excessive amounts of boiler water treatment chemicals is reduced. By controlling the concentration of impurities through continuous blowdown, the usage of chemicals for water treatment can be optimized. This not only helps in cost savings but also reduces the environmental impact associated with the use and disposal of these chemicals.

It’s important to note that the continuous blowdown rate needs to be carefully determined to balance the objectives of impurity control and minimizing water and heat loss. Monitoring the water quality, maintaining appropriate blowdown rates, and following manufacturer recommendations and regulatory requirements are crucial for the successful implementation of continuous blowdown in marine boilers.

How to calculate the percentage of blowdown

To calculate the percentage of blowdown in a marine boiler, you need to determine the amount of blowdown water discharged relative to the total amount of feedwater entering the boiler. The formula to calculate the percentage of blowdown is as follows:

Percentage of Blowdown = (Blowdown Water Quantity / Feedwater Quantity) × 100

Here’s a step-by-step guide to calculating the percentage of blowdown:

1. Determine the Blowdown Water Quantity: Measure or calculate the actual amount of water discharged during blowdown. This can be done by measuring the blowdown water flow rate and the duration of the blowdown operation.
2. Determine the Feedwater Quantity: Measure or calculate the total amount of feedwater entering the boiler over the same time period as the blowdown. This can be determined by measuring the feedwater flow rate or by using other relevant parameters, such as steam production rate and steam-to-water conversion factors.
3. Apply the Formula: Divide the blowdown water quantity by the feedwater quantity and multiply by 100 to get the blowdown percentage.

Example calculation:

Let’s say during a specific time period, the blowdown water quantity is measured as 2,000 liters, and the feedwater quantity entering the boiler is determined to be 100,000 liters. Using the formula mentioned above:

Percentage of Blowdown = (2,000 / 100,000) × 100 = 2%

Therefore, the percentage of blowdown in this example is 2%.

Remember to use appropriate units and ensure consistency between the units used for blowdown water quantity and feedwater quantity in the calculation.

It’s essential to monitor and adjust the blowdown percentage based on water quality analysis, boiler condition, and any applicable regulatory requirements to maintain optimal boiler performance and water quality.

Procedure for Scumming and Bottom Blow Down

Scumming and bottom blowdown are two procedures performed in marine boilers to remove impurities from the surface and bottom of the boiler water. Here’s a step-by-step procedure for both scumming and bottom blowdown:

Scumming Procedure:

1. Ensure that the boiler is not under high pressure and the water level is below the scum valve opening.
2. Open the scum valve, which is usually located at the top surface of the boiler shell or near the steam space. This valve allows the removal of surface impurities, oils, and foaming substances.
3. Gradually open the scum valve to allow a small amount of water to flow out. This helps remove the scum layer from the water surface.
4. Observe the discharged water for any signs of oil, foam, or other impurities. If necessary, adjust the scum valve to control the flow rate and ensure effective scumming.
5. Close the scum valve once the scum layer is removed and the discharged water appears clear.

Bottom Blowdown Procedure:

1. Ensure that the boiler is not under high pressure and the water level is above the bottom blowdown valve opening.
2. Open the bottom blowdown valve, which is usually located at the lowest point of the boiler shell. This valve allows the removal of sediment, sludge, and other solid particles settled at the bottom of the boiler.
3. Slowly open the bottom blowdown valve to initiate a flow of water. This helps carry away the sediments and impurities settled at the bottom.
4. Monitor the discharged water for any indications of sediment, solids, or other impurities. Adjust the blowdown valve if needed to control the flow rate and ensure effective bottom blowdown.
5. Close the bottom blowdown valve once the water appears clear and the sediments are removed.

Important Notes:

• Ensure that the blowdown valves are in good working condition and not leaking.
• Follow the manufacturer’s instructions and recommended blowdown frequencies.
• Monitor the blowdown water quality and adjust blowdown procedures accordingly.
• Comply with applicable regulations and safety guidelines during scumming and bottom blowdown operations.
• Keep a record of blowdown activities for maintenance and regulatory purposes.

It’s crucial to consult the specific boiler manufacturer’s guidelines and adhere to vessel-specific procedures and safety protocols when performing scumming and bottom blowdown on marine boilers.

Steps for blow down procedure are as follows

Certainly! Here are the general steps for performing a blowdown procedure in a marine boiler:

1. Ensure Safety Precautions: Before starting any blowdown procedure, ensure that the boiler is not under high pressure, all safety devices are functional, and relevant safety precautions are followed. Wear appropriate personal protective equipment (PPE) as required.
2. Identify Blowdown Valves: Locate the blowdown valves in the boiler system. There are typically separate valves for bottom blowdown and surface blowdown (scumming), as well as separate valves for continuous blowdown and intermittent blowdown, if applicable.
3. Determine Blowdown Quantity and Frequency: Determine the required blowdown quantity and frequency based on boiler type, water quality analysis, operating conditions, and regulatory requirements. This information can be obtained from boiler manuals, manufacturer guidelines, or industry standards.
4. Continuous Blowdown (If Applicable): If the boiler has a continuous blowdown system, ensure that it is properly set up and functioning. Adjust the continuous blowdown rate as per the desired water quality parameters, ensuring that the heat recovery system, if installed, is also functioning correctly.
5. Intermittent Blowdown (Manual Blowdown): If intermittent blowdown is required, follow these steps: a. Determine the blowdown interval: Decide on the frequency at which blowdown will be performed based on the boiler’s operating conditions and water quality requirements. b. Confirm boiler water level: Ensure that the boiler water level is above the minimum safe level to avoid exposing heating surfaces. c. Open the blowdown valve: Gradually open the blowdown valve to release a small amount of water. Control the flow rate to prevent excessive water loss and maintain boiler water level stability. d. Monitor discharged water: Observe the discharged water for any signs of impurities, sediments, or abnormal conditions. Adjust the blowdown valve as needed to control the flow rate and maintain effective blowdown. e. Close the blowdown valve: After the desired blowdown duration or when the discharged water appears clear, close the blowdown valve to stop the flow.
6. Record Keeping: Maintain accurate records of blowdown activities, including the blowdown quantity, duration, frequency, and any observations made during the procedure. These records are essential for maintenance, troubleshooting, and regulatory compliance.
7. Safety Checks: After completing the blowdown procedure, ensure that all blowdown valves are tightly closed, and verify that the boiler is operating safely within desired parameters.

Remember to consult the specific boiler manufacturer’s guidelines, vessel-specific procedures, and any applicable regulations when performing blowdown in marine boilers. Regular monitoring of water quality and consultation with boiler experts or marine authorities will help ensure the effectiveness and safety of the blowdown procedure.

Advantages of boiler blowdown

Boiler blowdown offers several advantages in terms of maintaining water quality, improving boiler efficiency, and ensuring safe and reliable boiler operation. Here are some of the key advantages of boiler blowdown:

1. Impurity Control: Blowdown helps control the concentration of dissolved and suspended solids in the boiler water. By removing a portion of the water, blowdown reduces the accumulation of impurities that can cause scale formation, corrosion, and reduced heat transfer efficiency. Maintaining proper water quality through blowdown promotes optimal boiler performance and extends equipment lifespan.
2. Scale and Deposits Prevention: Blowdown plays a crucial role in preventing the formation of scale and deposits on boiler surfaces. Scale and deposits can hinder heat transfer, restrict water flow, and lead to overheating and mechanical failures. By controlling the concentration of impurities through blowdown, the likelihood of scale and deposits is reduced, resulting in improved heat transfer efficiency and reduced maintenance requirements.
3. Corrosion Mitigation: Excessive concentrations of dissolved solids and corrosive substances in the boiler water can lead to corrosion of boiler components. Blowdown helps maintain appropriate water chemistry, minimizing the risk of corrosion. By removing impurities, blowdown helps protect boiler internals, piping, and other equipment from corrosion-related damage and improves the overall reliability of the system.
4. Steam Quality Maintenance: Blowdown is essential for maintaining high-quality steam. Impurities present in the boiler water can carry over into the steam, leading to contamination of downstream equipment and processes. By controlling water quality through blowdown, steam quality is improved, ensuring its suitability for critical marine applications such as propulsion and power generation.
5. Energy Efficiency: Proper blowdown practices contribute to improved energy efficiency. By controlling the concentration of impurities, blowdown helps maintain clean heat transfer surfaces, ensuring efficient heat exchange and minimizing fuel consumption. Additionally, blowdown systems equipped with heat recovery capabilities allow for the utilization of waste heat, further enhancing energy efficiency.
6. Regulatory Compliance: Blowdown is necessary to comply with safety regulations and industry standards. Regulatory bodies establish guidelines for water quality in marine boilers to prevent hazards, protect equipment, and ensure the safety of the vessel and its occupants. By performing blowdown as prescribed, vessel operators can maintain compliance with these regulations and mitigate risks associated with poor water quality.

Overall, boiler blowdown is a vital maintenance practice that offers numerous advantages, including impurity control, scale prevention, corrosion mitigation, steam quality maintenance, energy efficiency, and regulatory compliance. It is crucial to follow recommended blowdown practices and consult industry guidelines and regulations to maximize these benefits and ensure safe and efficient boiler operation.

Disadvantages of boiler blowdown

While boiler blowdown is an essential procedure for maintaining water quality and ensuring efficient boiler operation, there are a few potential disadvantages associated with blowdown. These disadvantages include:

1. Water and Heat Loss: During blowdown, a portion of the boiler water is discharged, resulting in water and heat loss from the system. This loss requires additional makeup water to replenish the boiler, which may increase water treatment costs. Additionally, the discharged hot water carries away heat energy, reducing the overall boiler efficiency.
2. Environmental Impact: Blowdown water contains impurities and chemicals removed from the boiler, which may have environmental implications if not properly treated or disposed of. Discharging blowdown water directly into the environment can contribute to water pollution, especially if it contains high levels of chemicals or contaminants. Therefore, proper handling and treatment of blowdown water are necessary to minimize environmental impact.
3. Chemical Consumption: Blowdown helps control the concentration of impurities in the boiler water, but it may also increase the need for water treatment chemicals. Discharging water containing high concentrations of impurities requires more chemicals for water treatment and can result in higher chemical consumption, which may add to the operational costs of the boiler system.
4. Maintenance Considerations: Frequent blowdown can result in wear and tear on blowdown valves and associated equipment due to the flow of water and exposure to high temperatures. Proper maintenance and periodic inspection of blowdown valves are necessary to ensure their continued functionality and prevent leaks or failures.
5. Potential for Boiler Upsets: Improper blowdown practices, such as excessive or insufficient blowdown, can lead to operational issues and boiler upsets. Excessive blowdown can cause excessive water and heat loss, leading to reduced boiler efficiency and increased fuel consumption. On the other hand, insufficient blowdown can result in the accumulation of impurities, leading to scale formation, corrosion, and reduced boiler performance.

To mitigate these disadvantages, it is crucial to implement blowdown practices based on manufacturer recommendations, industry standards, and water quality analysis. Regular monitoring of water chemistry, optimization of blowdown frequency and quantity, and proper treatment and disposal of blowdown water can help minimize the potential drawbacks while reaping the benefits of effective boiler blowdown.

Requirements and Regulation

Requirements and regulations regarding boiler blowdown vary depending on the jurisdiction, type of vessel, and applicable industry standards. However, there are common requirements and guidelines that are generally followed to ensure safe and efficient boiler operation. Here are some key aspects of requirements and regulations related to boiler blowdown:

1. Water Quality Standards: Regulatory bodies and industry standards often establish water quality standards for marine boilers. These standards define acceptable limits for parameters such as total dissolved solids (TDS), alkalinity, pH, silica content, and specific conductance. Compliance with these standards helps ensure optimal boiler performance and prevents issues related to impurities and water chemistry.
2. Blowdown Frequency and Quantity: Regulatory guidelines or manufacturer recommendations often specify the frequency and quantity of blowdown required for marine boilers. These guidelines take into account factors such as boiler type, operating conditions, water quality, and steam production rates. Adhering to the recommended blowdown frequency and quantity helps maintain proper water quality and prevents excessive water and heat loss.
3. Blowdown Valves and Equipment: Boiler blowdown systems should be equipped with appropriate blowdown valves and related equipment. These valves should be properly sized, installed, and maintained to ensure reliable operation and accurate control of blowdown flow rates. It is important to follow manufacturer guidelines and industry best practices when selecting, installing, and maintaining blowdown valves.
4. Discharge and Treatment of Blowdown Water: Disposal of blowdown water should be done in accordance with local environmental regulations. In many cases, blowdown water must undergo appropriate treatment to remove impurities and chemicals before it can be discharged into the environment. Treatment methods may include filtration, chemical treatment, or other processes to ensure compliance with local discharge standards.
5. Record Keeping: It is common practice to maintain records of blowdown activities, including blowdown quantities, frequencies, and water quality measurements. These records serve as evidence of compliance with regulations, assist in troubleshooting, and support maintenance and operational decision-making.
6. Inspections and Audits: Regulatory bodies and classification societies may conduct periodic inspections and audits of marine boilers to ensure compliance with regulations and safety standards. These inspections may include checks on blowdown systems, water quality analysis, and documentation of blowdown procedures.

It is crucial to consult relevant regulatory bodies, classification societies, and industry standards applicable to your specific vessel and jurisdiction to ensure compliance with the requirements and regulations regarding boiler blowdown. Additionally, working closely with boiler manufacturers, water treatment experts, and experienced marine engineers can help ensure that blowdown procedures are conducted safely, efficiently, and in accordance with regulatory guidelines.

How to minimise boiler blowdown

Minimizing boiler blowdown is beneficial for conserving water, reducing energy loss, and minimizing the impact on water treatment processes. Here are some strategies to help minimize boiler blowdown:

1. Implement Proper Water Treatment: Effective water treatment can help reduce the need for excessive blowdown. Proper water treatment methods, such as using suitable chemicals and filtration systems, can help control impurities, prevent scale formation, and minimize the accumulation of dissolved solids in the boiler water. Conduct regular water quality analysis and work with water treatment experts to optimize the treatment process.
2. Optimize Boiler Operation: Proper boiler operation is crucial for minimizing blowdown. Ensure that the boiler is operated within its optimal operating range, including water level, steam pressure, and feedwater temperature. Maintaining stable operating conditions helps reduce fluctuations in water quality and minimizes the need for excessive blowdown.
3. Conduct Regular Water Quality Monitoring: Regular monitoring of water quality parameters allows for proactive management of the boiler system. Monitor key parameters such as TDS (Total Dissolved Solids), alkalinity, pH, and conductivity to identify trends and deviations. By identifying and addressing water quality issues promptly, you can reduce the frequency and quantity of blowdown required.
4. Use Blowdown Heat Recovery Systems: Blowdown heat recovery systems can help recover waste heat from blowdown water before it is discharged. These systems use heat exchangers to transfer heat from the blowdown water to the incoming feedwater. By recovering heat, blowdown water temperature is reduced, minimizing energy loss and reducing the need for additional heat input.
5. Optimize Blowdown Practices: Evaluate and adjust blowdown frequency and quantity based on water quality analysis, operating conditions, and regulatory requirements. It may be possible to optimize blowdown intervals and rates without compromising water quality or boiler performance. Consult manufacturer guidelines, industry standards, and experienced boiler operators to determine the most appropriate blowdown practices for your specific boiler system.
6. Implement Continuous Blowdown Systems: Continuous blowdown systems allow for continuous removal of a small amount of boiler water, maintaining water quality within acceptable limits. By continuously removing impurities, the need for intermittent blowdown can be reduced, resulting in less water and energy loss.
7. Train and Educate Boiler Operators: Proper training and education of boiler operators are crucial for optimizing blowdown procedures. Operators should be knowledgeable about the purpose of blowdown, water quality requirements, and the impact of blowdown on boiler efficiency. Regular training and refresher courses can help operators understand the importance of blowdown optimization and implement best practices.

By implementing these strategies, you can minimize boiler blowdown while maintaining water quality and ensuring efficient boiler operation. However, it is important to strike a balance between minimizing blowdown and maintaining safe and compliant boiler operation. Consult relevant regulations, manufacturer guidelines, and industry experts to ensure that blowdown practices are optimized for your specific boiler system and operational requirements.

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