Hotel Service Unit 18 Q1

An Oily Water Separator (OWS) is a piece of equipment used on ships to separate oil and water mixtures into their separate components.

It’s a crucial component of a ship’s pollution prevention system, ensuring that bilge water and other oily wastewater are treated to comply with MARPOL regulations before being discharged into the environment.

1. Oily Water Separators – Hints and Tips – Dromon Bureau of Shipping (DBS) – Home

2. Oily water separator (marine) – Wikipedia

Purpose:

• To remove oil and other contaminants from bilge water, oily waste, and other water mixtures generated onboard ships.   1. Oily water separator, bilge water separator – Wärtsilä www.wartsila.com
• To comply with MARPOL Annex I, which sets strict limits on the amount of oil that can be discharged into the sea.   1. Oily water separator – Further clarifications on requirements for sampling points – DNV www.dnv.com

Working Principle:

OWS systems utilize various physical and chemical processes to achieve oil-water separation:  

1. How Oil Water Separators Work – Ecologix Environmental Systems

1. Gravity Separation:

• The oily water mixture is first pumped into a settling tank or primary separation chamber.   1. What is an Oil/Water Separator? How Does an Oil/Water Separator Work? – Oil Skimmers, Inc. www.oilskim.com
• Due to the density difference, oil (being lighter) rises to the top, while water settles at the bottom.   1. What is an Oil/Water Separator? How Does an Oil/Water Separator Work? – Oil Skimmers, Inc. www.oilskim.com
• Baffles or plates may be used to enhance separation and prevent re-mixing.   1. Analysis and Research on the Automatic Control Systems of Oil–Water Baffles in Horizontal Three-Phase Separators – MDPI www.mdpi.com

2. Coalescence:

• The partially separated water then flows through a coalescing filter or pack.   1. How does an Oily Water Separator work? | 3D Animated Explanation – YouTube m.youtube.com
• This filter consists of specially designed media that encourages smaller oil droplets to coalesce (combine) into larger ones, making them easier to separate.   1. How Does a Coalescer Work & What is a Coalescing Filter? – Integrated Flow Solutions ifsolutions.com

3. Secondary Separation:

• The water, now with larger oil droplets, enters a secondary separation chamber.   1. How does an Oily Water Separator work? | 3D Animated Explanation – YouTube m.youtube.com
• Further gravity separation occurs, allowing the remaining oil to rise to the top for removal.   1. How does an Oily Water Separator work? | 3D Animated Explanation – YouTube m.youtube.com

4. Oil Removal:

• Skimming: The separated oil is skimmed off the surface using a skimmer or overflow system and collected in a sludge tank or oily waste holding tank.   1. Oil Skimming: Oil Removal Challenges in the Food Industry – Oil Skimmers, Inc. www.oilskim.com
• Adsorption: Some systems may also use absorbent materials or filters to further remove any residual oil from the water.

5. Oil Content Monitoring:

• An oil content meter (OCM) continuously monitors the oil content in the treated water before discharge.   1. Oily Water Separators – Hints and Tips – Dromon Bureau of Shipping (DBS) – Home www.dromon.com
• If the oil content exceeds the permissible limit (usually 15 ppm), the water is automatically diverted back to the holding tank for further treatment.   1. Understanding Oil in Water Monitoring – Rivertrace rivertrace.com

Types of OWS:

• Gravity Plate Separators
• Coalescer Separators   1. The different types of oil-water separators | CleanaWater cleanawater.com.au
• Centrifugal Separators   1. Centrifugal water–oil separator – Wikipedia en.wikipedia.org

Importance of OWS:

• Environmental Protection: By effectively removing oil from wastewater, OWS systems prevent marine pollution and protect the marine environment.   1. Oily Water Separator (OWS) Explained – saVRee www.savree.com
• Regulatory Compliance: They are essential for complying with MARPOL Annex I regulations and avoiding penalties or detentions.   1. Oily water separator – Further clarifications on requirements for sampling points – DNV www.dnv.com
• Operational Efficiency: By treating bilge water and other oily waste, OWS systems enable their safe and legal discharge, reducing the need for storage and disposal ashore.

Regular Maintenance:

• Proper maintenance, including cleaning, filter replacements, and calibration of the OCM, is crucial to ensure the OWS operates efficiently and meets regulatory requirements.   1. Maintaining An Oily Water Separator: 6 Key Parts to Replace on Time www.h2oinc.com

In conclusion, Oily Water Separators are vital components of a ship’s pollution prevention system, playing a crucial role in safeguarding the marine environment and ensuring compliance with international regulations.  

1. How Oil/Water Separators Preserve the Environment | Blog Vodaland Canada

Pumping of bilges refers to the process of removing water and other accumulated liquids from the bilge, which is the lowest compartment within the hull of a ship. This is a crucial operation to maintain the ship’s stability, prevent corrosion, and ensure the safe operation of machinery and equipment.  

1. Bilge pump – Wikipedia

Why Bilge Pumping is Necessary:

• Water Ingress: Ships inevitably experience some degree of water ingress due to various reasons, including:
  • Minor leaks or seepage through the hull or fittings   1. What Is a Bilge Pump and How Does It Work? – Fresh Water Systems www.freshwatersystems.com
  • Condensation within the hull
  • Rainwater or seawater entering through hatches or other openings   1. Water in the Bilge – Harbor Sailboats harborsailboats.com
  • Spills or leaks from machinery or equipment   1. Marine Bilge Pumps: The Ultimate Guide for Ships – Carver Pump www.carverpump.com
• Oil and Fuel Contamination: The bilge can also accumulate oil, fuel, or other fluids that leak from machinery or systems, creating a potential pollution hazard.   1. Risks associated with dirty engine room bilges – Shipowners’ Club www.shipownersclub.com
• Corrosion and Damage: If left unattended, the accumulated water in the bilge can promote corrosion of the hull structure and damage to equipment and systems.

Bilge Pumping System:

• Bilge Wells: The bilge is divided into several sections called bilge wells, strategically located throughout the ship.
• Bilge Suction Lines: A network of pipes and strainers connected to the bilge wells collects the accumulated liquids.
• Bilge Pumps: These pumps are responsible for drawing the bilge water from the suction lines and discharging it overboard or to a holding tank for further treatment.   1. Monitoring and controlling bilge water discharge – ABB Measurement & Analytics Blog new.abb.com
• Oily Water Separator (OWS): In compliance with MARPOL regulations, the bilge water may pass through an OWS to remove oil and other contaminants before discharge.   1. Oily water separator – Further clarifications on requirements for sampling points – DNV www.dnv.com

Pumping Procedure:

• Monitoring: The bilge levels in different wells are regularly monitored using gauges or alarms.   1. Monitoring and controlling bilge water discharge – ABB Measurement & Analytics Blog new.abb.com
• Operation: When the bilge water reaches a certain level, the bilge pump is activated to pump it out.   1. Bilge pump – Wikipedia en.wikipedia.org
• Discharge Control: Depending on the water’s content and the ship’s location, the discharge may be directed overboard (if it meets the permissible oil content limit) or to a holding tank for further treatment.

Regulations and Precautions:

• MARPOL Annex I: This international convention strictly regulates the discharge of oily mixtures from ships, including bilge water.   1. International Convention for the Prevention of Pollution from Ships (MARPOL) www.imo.org
• Oil Record Book: All bilge pumping operations must be recorded in the ship’s Oil Record Book, providing evidence of compliance with MARPOL regulations.
• Port State Control: Vessels are subject to inspections by port state control authorities to verify compliance with pollution prevention regulations, including bilge pumping practices.

Environmental Considerations:

• Responsible Discharge: It’s crucial to adhere to MARPOL regulations and discharge bilge water only when it meets the permissible oil content limits and at approved locations.
• Oil Spill Prevention: Proper maintenance of machinery and equipment, along with prompt response to leaks or spills, helps prevent oil contamination in the bilge and minimize the risk of pollution.

In conclusion, pumping of bilges is an essential operation on board ships to maintain stability, prevent corrosion, and protect the marine environment. By adhering to proper procedures and regulations, ship operators can ensure safe and responsible bilge water management.

While centrifugal pumps are widely used in various applications on ships, a positive displacement pump is generally preferred as the main bilge pump for several key reasons:

1. Self-Priming Capability:

• Positive displacement pumps are self-priming, meaning they can start pumping even if the suction line is not initially filled with liquid.   1. useful information on self-priming pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
• Centrifugal pumps, on the other hand, require priming to create a vacuum and draw the liquid into the pump. This can be problematic in bilge pumping, where the suction line may be partially filled with air or gases, hindering the centrifugal pump’s ability to start and function effectively.   1. Difference between centrifugal pumps and self-priming pumps – Viesse Pompe www.viessepompe.it

2. Ability to Handle Varying Water Levels and Viscosities:

• Bilge water can have fluctuating levels and varying viscosities due to the presence of oil, debris, and other contaminants.
• Positive displacement pumps can efficiently handle these variations, maintaining a consistent flow rate even with changing conditions.   1. Positive Displacement vs Centrifugal Pump – Dragon Products dragonproducts.com
• Centrifugal pumps are less efficient when dealing with low flow rates or high-viscosity liquids, potentially leading to reduced performance or even stalling.   1. The rotating stall in a centrifugal pump and its evaluation technique – ResearchGate www.researchgate.net

3. Ability to Run Dry:

• Positive displacement pumps can operate without liquid in the suction line for short periods without sustaining damage.   1. Centrifugal vs. Positive Displacement Pump – Gainesville Industrial Electric www.gainesvilleindustrial.com
• This is important in bilge pumping, where the pump may occasionally run dry as the bilge water level drops.   1. Centrifugal vs. Positive Displacement Pump – Gainesville Industrial Electric www.gainesvilleindustrial.com
• Centrifugal pumps are prone to damage if they run dry, as the impeller can overheat and seize due to lack of lubrication.   1. Marine Bilge Pumps: The Ultimate Guide for Ships – Carver Pump www.carverpump.com

4. Higher Suction Lift:

• Positive displacement pumps typically have a higher suction lift capability, meaning they can draw water from greater depths or distances.
• This is advantageous in large vessels with multiple bilge wells or where the pump is located far from the bilge.

5. Better at Handling Debris:

• While both types of pumps can be susceptible to clogging from debris, positive displacement pumps with specific designs, like diaphragm or progressing cavity pumps, are generally more tolerant of solid particles and debris often found in bilge water.

Disadvantages of Positive Displacement Pumps:

• Pulsating Flow: Positive displacement pumps produce a pulsating flow, which can cause vibration and noise issues.   1. Why Your Positive Displacement Pump System Needs a Pulsation Dampener – Blacoh www.blacoh.com
• Higher Maintenance: They generally require more frequent maintenance due to their more complex internal mechanisms and the presence of valves and seals.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk

Overall:

While centrifugal pumps offer advantages like higher flow rates and simpler construction, positive displacement pumps are more suited to the specific challenges of bilge pumping, including self-priming capability, ability to handle varying conditions, and tolerance to dry running. This makes them the preferred choice for main bilge pumps on many vessels, ensuring reliable and effective bilge water removal to maintain the ship’s safety and stability.  

1. Centrifugal vs. Positive Displacement Pump – Gainesville Industrial Electric

Exceeding the flow rate to an oily water separator (OWS) can have several detrimental consequences, impacting its efficiency and compliance with environmental regulations. Here’s why it’s important to stay within the specified flow rate:

1. Reduced Separation Efficiency:

• Overloading the System: An excessive flow rate overwhelms the OWS, reducing the time available for gravity separation and coalescence of oil droplets.
• Incomplete Separation: This leads to incomplete separation, with more oil remaining in the treated water, potentially exceeding the permissible discharge limit of 15 ppm.
• Carryover: High flow rates can cause oil droplets to be carried over into the clean water outlet, further contributing to pollution.

2. Increased Risk of Alarm Activation and Shutdown:

• 15 ppm Bilge Alarm: If the oil content in the treated water exceeds 15 ppm, the OWS’s oil content monitor (OCM) will trigger an alarm, potentially leading to an automatic shutdown of the discharge.
• Operational Disruption: This can disrupt bilge pumping operations and necessitate troubleshooting and corrective actions, causing delays and inconvenience.

3. Potential Damage to the OWS:

• Mechanical Stress: Excessive flow rates can put undue stress on the OWS components, such as pumps, valves, and filters, potentially leading to premature wear or damage.
• Filter Clogging: High flow rates can force more debris and solids into the filters, causing them to clog more quickly and requiring frequent cleaning or replacement.

4. Environmental Pollution:

• Exceeding Discharge Limits: The primary concern is the risk of discharging oily water with an oil content exceeding the permissible limit of 15 ppm, leading to marine pollution.
• Damage to Marine Life: Oil pollution can harm marine organisms, disrupt ecosystems, and have long-lasting environmental impacts.

5. Regulatory Non-Compliance:

• MARPOL Violations: Discharging oily water exceeding the 15 ppm limit is a violation of MARPOL Annex I regulations, which can result in fines, penalties, and detention of the vessel.

Therefore, adhering to the specified flow rate for the OWS is essential for:

• Ensuring effective oil-water separation and compliance with environmental regulations
• Preventing operational disruptions and equipment damage
• Protecting the marine environment and minimizing pollution risks

Operators should carefully monitor the flow rate during bilge pumping operations and adjust it as needed to stay within the OWS’s design capacity. Regular maintenance and inspections of the OWS are also crucial to ensure its optimal performance and compliance.

The discharge overboard line of an Oily Water Separator (OWS) should be higher than the OWS itself primarily to prevent backflow and ensure reliable operation of the system.

Here’s a breakdown of the reasons:

1. Preventing Backflow:

• Gravity-Based Operation: Many OWS systems rely on gravity for the separation of oil and water. If the discharge line is lower than the OWS, there’s a risk of backflow, where the treated water, potentially still containing some oil, flows back into the OWS.
• Disruption of Separation Process: This backflow can disrupt the separation process, leading to inefficient operation and potentially exceeding the permissible oil discharge limit.

2. Maintaining Positive Head:

• Positive Head Pressure: Keeping the discharge line higher than the OWS ensures a positive head pressure on the outlet side. This helps maintain a consistent flow rate and prevents air pockets from forming in the discharge line, which can impede flow and cause operational issues.

3. Facilitating Monitoring and Sampling:

• Oil Content Meter (OCM) Placement: The OCM, which monitors the oil content in the discharged water, is typically installed on the discharge line. Placing the line higher than the OWS allows for easier installation and access to the OCM for maintenance and calibration.   1. Oil content meter – Wikipedia en.wikipedia.org
• Sample Collection: The elevated position of the discharge line also makes it convenient to collect representative water samples for further analysis and verification of oil content.

4. Visual Inspection:

• Leak Detection: The visible section of the discharge line above the OWS allows for easy visual inspection for any leaks or signs of oil contamination. This enables prompt identification and correction of potential problems.

5. Regulatory Compliance:

• MARPOL Annex I: While not explicitly stated in the regulations, the practice of keeping the discharge line higher than the OWS is widely accepted as good engineering practice and helps ensure compliance with MARPOL Annex I discharge limits.

In summary, the elevated position of the discharge overboard line in relation to the OWS is crucial for:

• Preventing backflow and maintaining efficient separation.
• Ensuring a positive head pressure for consistent flow.
• Facilitating monitoring, sampling, and inspection.
• Aiding in compliance with environmental regulations.

By adhering to this design principle, ship operators can enhance the reliability and effectiveness of the OWS, minimize the risk of oil pollution, and contribute to the protection of the marine environment.

Detergents used for bilge cleaning can negatively impact the operation of an oily water separator (OWS) in a few key ways:

1. Emulsification:

• Formation of Stable Emulsions: Many detergents contain surfactants (surface-active agents) that reduce the surface tension between oil and water. This can lead to the formation of stable emulsions, where tiny oil droplets are dispersed throughout the water, making them difficult to separate by gravity or coalescence.   1. What are surfactants and how do they work? – Biolin Scientific www.biolinscientific.com
• Reduced Separation Efficiency: The OWS relies on the natural separation of oil and water based on their density difference. Emulsions hinder this separation, allowing more oil to pass through the system and potentially exceed the permissible discharge limit.   1. What is an Oil/Water Separator? How Does an Oil/Water Separator Work? – Oil Skimmers, Inc. www.oilskim.com

2. Foaming:

• Air Entrapment: Some detergents, especially those with high foaming properties, can create excessive foam in the OWS.
• Reduced Separation Efficiency: Foam can interfere with the gravity separation process and clog filters or coalescers, reducing the OWS’s ability to remove oil effectively.
• Operational Issues: Excessive foam can also lead to operational problems, such as overflow or difficulty in monitoring oil content in the treated water.

3. Chemical Interference:

• Coalescer Wetting: Certain chemicals in detergents can affect the wetting properties of the coalescer media, hindering its ability to capture and coalesce oil droplets.
• pH Changes: Some detergents may alter the pH of the bilge water, potentially impacting the OWS’s performance, especially if it relies on chemical coagulation or flocculation processes.

4. Increased Maintenance:

• Filter Clogging: The presence of detergents and emulsified oil can accelerate filter clogging, requiring more frequent cleaning or replacement.
• Cleaning Requirements: The OWS itself may require more frequent cleaning to remove detergent residues and prevent buildup that could affect its performance.

To mitigate these effects, it’s important to:

• Choose the Right Detergent: Use detergents specifically designed for bilge cleaning that are compatible with OWS systems and have low foaming properties. Look for “quick break” detergents that readily separate from oil and water, minimizing emulsion formation.
• Minimize Detergent Use: Use detergents sparingly and follow the manufacturer’s instructions for dilution and application.
• Separate Mop Water: Collect mop water and other cleaning solutions containing detergents separately and dispose of them responsibly ashore, avoiding their introduction into the bilge.
• Regular OWS Maintenance: Maintain the OWS according to the manufacturer’s recommendations, including regular cleaning and filter replacements, to ensure its optimal performance even in the presence of detergents.

By being mindful of detergent selection and adopting proper cleaning practices, ship operators can minimize the negative impact of detergents on OWS operation, ensuring compliance with environmental regulations and protecting the marine environment.

An air release valve, also known as a vent valve, is fitted to the top of the shell of an Oily Water Separator (OWS) for several important reasons:

1. Preventing Air Pockets and Vacuum:

• During operation, air can get trapped within the OWS, especially in the upper part of the shell or in the coalescer pack.
• These air pockets can disrupt the smooth flow of oily water, reduce separation efficiency, and cause fluctuations in pressure or level readings.
• The air release valve allows these trapped air pockets to escape, ensuring proper flow and preventing the formation of a vacuum that could impede operation or damage the equipment.

2. Facilitating Venting During Maintenance:

• When the OWS is opened for inspection, cleaning, or maintenance, the air release valve provides a means to vent any trapped gases or vapors that may have accumulated inside.
• This improves safety for personnel working on the OWS by preventing the sudden release of pressure or the inhalation of potentially harmful fumes.

3. Pressure Relief:

• In some cases, the air release valve may also act as a pressure relief valve, preventing excessive pressure buildup within the OWS.
• This is particularly important if there’s a blockage in the discharge line or if the pump is inadvertently run against a closed valve.
• The valve will open automatically at a preset pressure to release excess pressure and protect the OWS from damage.

4. Preventing Overfilling:

• While the primary function is air release, some designs of the valve may also incorporate a float or other mechanism to prevent overfilling of the OWS.
• If the water level rises too high, the valve will open to release excess water and prevent it from overflowing and potentially damaging other equipment or causing spills.

Overall, the air release valve on top of the OWS shell plays a vital role in ensuring its proper operation, safety, and maintenance. It helps maintain efficient separation, prevents pressure buildup, facilitates venting during maintenance, and can even act as a safeguard against overfilling.