The oily water separator (OWS) is a critical piece of equipment found in the engine rooms of ships, designed to separate oil from water mixtures before discharge into the sea. This function is not only essential for compliance with environmental regulations but also for the operational efficiency of marine vessels. The separation process is governed by principles of physics and engineering, and understanding its operation can significantly enhance the management of oily waste on board.
An oily water separator operates primarily by utilizing gravity and coalescence to separate oil from water. The device is essential for treating bilge water—water that accumulates in the lowest part of a ship’s hull, often mixed with oil and other pollutants. According to MARPOL Annex I regulations, ships must ensure that the oil content in discharged water does not exceed 15 parts per million (ppm). Failure to comply can result in severe penalties and environmental damage.
Construction and Working Principle
An oily water separator typically consists of several key components, each playing a specific role in the separation process:
- Separator Unit: This is the core component where the initial separation occurs. It includes:
- Coarse Separation Compartment: Here, the oily water mixture enters and undergoes gravity separation. Oil, being less dense than water, rises to the top.
- Fine Separation Compartment: After coarse separation, the remaining mixture flows into this compartment, where coalescing plates or filters further separate smaller oil droplets from water.
- Filter Unit: This unit is responsible for removing any remaining impurities after the initial separation. It typically includes:
- Coalescing Filters: These filters promote the merging of small oil droplets into larger ones, enhancing separation efficiency.
- Final Filtration Stage: This stage ensures that any residual solid pollutants or oil droplets are removed from the water before discharge.
- Control Unit: This component monitors and controls the operation of the OWS. Key features include:
- Oil Content Monitor (OCM): Continuously measures the oil concentration in the effluent. If levels exceed 15 ppm, it triggers alarms and redirects flow back to a holding tank.
- Control Valves: These valves manage the flow of separated oil and treated water, ensuring compliance with discharge regulations.
- Heating Coils: Some OWS units are equipped with heating coils to reduce the viscosity of oil and facilitate better separation by promoting smoother flow.
- Oil Skimmer: An optional but useful component that removes the oil layer from the surface of separated water, ensuring that only clean water is discharged.
Operational Considerations
The operation of an oily water separator involves several stages, each critical for effective separation:
- Initial Pumping: The oily bilge water is pumped into the separator unit through an inlet valve. The system is usually filled with clean seawater to aid in separation.
- Coarse Separation: In the coarse separation compartment, due to gravity, lighter oil rises to form a layer above the denser water. Heating coils may be activated to assist in reducing oil viscosity, allowing for more efficient separation.
- Oil Collection: As oil accumulates at the top, sensors detect its level and trigger a control valve that allows separated oil to drain into a designated sludge tank or dirty oil holding tank.
- Fine Separation: The remaining mixture flows into the fine separation compartment, where it passes through coalescing plates or filters. Here, smaller oil droplets merge into larger ones due to coalescence, further enhancing separation.
- Final Filtration: After passing through coalescing filters, almost oil-free water moves on to a final filtration stage where any remaining impurities are removed.
- Discharge Monitoring: The treated water exits through a discharge line equipped with an Oil Content Monitor (OCM). If the monitored ppm level is below 15 ppm, it can be discharged overboard; if not, it is redirected back to a holding tank.
The separated oil is collected in an oil collection chamber and is periodically discharged into an oily waste tank or sludge tank, while the treated water exits the separator for potential discharge overboard.
Case Studies and Examples
Case Study: MV Prestige IncidentOne notable example highlighting the importance of effective oily water separation occurred with the MV Prestige in 2002. The ship sank off the coast of Spain after suffering a hull breach, leading to a significant oil spill that caused extensive environmental damage. Investigations revealed that inadequate oily water separation practices contributed to this disaster, emphasizing how critical proper operation and maintenance of OWS systems are for preventing such incidents.Technological AdvancesRecent advancements have introduced new technologies aimed at improving oily water separation efficiency. For instance, some systems now utilize supercavitation techniques, which involve creating bubbles in a liquid to enhance separation processes. Research indicates that these methods can significantly reduce operational costs and improve compliance with environmental standards by achieving lower ppm levels more effectively than traditional methods.
Maintenance and Troubleshooting
Regular maintenance of oily water separators is essential for ensuring their effective operation. Common issues include:
- Clogged Filters: Over time, coalescing filters can become clogged with particulates, reducing efficiency. Regular cleaning or replacement is necessary.
- Sensor Malfunctions: The accuracy of OCMs is vital; faulty sensors can lead to incorrect readings and potential environmental violations.
- Pump Issues: The type and condition of pumps used can significantly impact performance. Using pumps that generate excessive turbulence can lead to poor separation.
A proactive maintenance schedule should include routine inspections, cleaning protocols, and prompt repairs to any identified issues.
Regulatory Compliance
Compliance with international maritime regulations regarding oily water discharge is non-negotiable for ship operators. MARPOL regulations require that all vessels are equipped with effective oily water separators and that crew members are trained in their operation and maintenance. Regular audits and inspections by port state control authorities ensure adherence to these standards.
The oily water separator plays a pivotal role in maritime operations by safeguarding marine environments from pollution while ensuring compliance with stringent regulations. Understanding its construction, working principles, operational requirements, and maintenance needs is essential for maritime professionals tasked with managing waste on board ships.As technology continues to evolve, innovations in oily water separation will likely enhance efficiency and effectiveness further, paving the way for more sustainable maritime practices. By prioritizing proper use and maintenance of OWS systems, ship operators can contribute significantly to protecting marine ecosystems while maintaining operational integrity within their fleets.
The Wärtsilä Senitec oily water treatment units use optimized emulsion breaking and separation technology that surpasses all existing regulations and guarantees an oil content in the cleaned water of below 5 ppm. In normal operation the actual levels have repeatedly been shown to be as low as 1 ppm, which gives a priceless safety margin to the IMO limit.
– Any combination of a separator, a coalescer or other means, and also a single unit designed to produce an effluent with oil content not exceeding 15 parts of oil per million parts of water by volume.
– Note: According to Resolution MEPC.107(49), a sampling point should be provided in a vertical section of the water effluent piping as close as practicable to the 15 ppm bilge separator. Re-circulating facilities should be provided after and adjacent to the overboard outlet of the stopping device to enable the 15 ppm bilge separator system, including the 15 ppm bilge alarm and the automatic stopping device, to be tested with the overboard discharge closed. One of the main causes of oilywater filtering equipment malfunction is the effect of bilge water containing cleaning agents. Detergent-based cleaning fluids can produce chemically stabilised oil emulsions which cannot be separated on board ship by the gravity alone. The best way to improve the performance of oily bilge water separating equipment is to avoid the use of surfactant-based cleaning materials.
1. Bilge water inlet
2. Oil separation stage
3. Emulsion tank
4. Chemical dosing pumps
5. Control panel
6. Oil and solids effluent
7. Chemical stage
8. Dissolved air inlet
9. Inlet to flotation stage
10. Overboard
11. Backwashing water outlet
12. Fresh water inlet (to filter stage)
13. Filter stage
14. Oil monitor
