Engine room oil and water waste
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Published: Mon, 5 Dec 2016
1.1 This report serves to explain the subject of oily water waste management. It explains the operation of the shipboard system and procedures specific to Bekulan, the vessel I served on.
1.2 The report identifies and explains the sources of oil and water within the engine room. It addresses the intentional and unintentional inputs to the system including leaks, spillages and wash down.
1.3 Oily water separators are used to process oily water waste to reduce its effects on the local ecology. This report covers the way the separator works to process this waste along with the requirements for ships to record, monitor and control their processing operations.
1.4 Oily water can be stored on board or discharged ashore or at sea. This report covers the requirements and regulations surrounding discharge operations in these situations. It also summarises ISO 14001 Standards for Environmental Management and the ‘Green Passport’ certification that is issued by the major Classification Societies.
1.5 The report explains the vessel’s engine room bilge system along with the alarms and automation that are required to comply with today’s demanding legislation.
Bekulan has five bilge wells and one dirty oil tank in the machinery space. Before any bilge water is pumped overboard it is first passed through the oily water separator.
The Heli-sep oily water separator onboard uses gravity assisted separation along with coalescence to separate and remove insoluble oil, solids and air from oily water bilges. The Oil Content Detector is mounted directly to the system and is provided to detect the oil content level of the processed water to be discharged.
The system incorporates three stages of oily water separation in the separator, these are;
1. Separation due to the difference in specific density between oil and water. A reduced flow rate of the oily water mix assists this process.
2. Coalescence of oil as it flows over a separating media of parallel corrugated plates.
3. Coalescence of residual oil droplets as fluid flows through a polishing pack of polypropylene beads.
The as well as alarms on the oily water separator (covered in section 7 of this report) the bilge system has two alarms. The first alarm is a high level bilge alarm. The second is a high high alarm that sounds if the bilge level rises further. Both alarms are controlled by float switches, one fitted above the aft bilge well, the other is fitted fwd under the main condenser. Each of these alarms is tested every Sunday as a weekly routine.
Design Principles Of The Oily Water Separator
The oily water separator is used to process oily waste by separating the oil from the water. It works on the principles of separation by gravity and coalescence.
The first stage of the separator works on the principle that oil is insoluble in water and since it is less dense a mixture of oil and water will naturally separate into layers. The rate at which these liquids separate is dependent on variables such as oil droplet size and flow rate. In the first stage of separation drops of oil are kept as large as possible and the flow rate is also kept low.
Under normal conditions, the small droplets coalesce (combine) to form larger droplets which rise to the oil layer at the top of the water. When droplets are small, the molecular action of the water is sufficient to prevent them from coalescing and a mechanical emulsion is formed.
With the separator in operation processed water is pumped overboard via the oil content monitor and oil is discharged to the dirty oil tank. The oily water separator is designed to remove all air and oily wastes except synthetic oils.
As long as the oil content monitor measures an oil content below 15 ppm the discharge may take place. When the oil content in the water rises up to 15 ppm the system automatically shuts the overboard valve and shifts the system into the recirculation mode until the oil content once again falls below the 15 ppm.
Operation Of The Oily Water Separator
The oily water mixture is drawn into the separator by a progressive cavity (mono) pump. The pump is located on the outlet of the separator to prevent the formation of a mechanical emulsion. Emulsified oils are very difficult to separate from water so every effort is made to ensure the flow is smooth.
The fluid enters the separator near the bottom of the vessel, also known as the sludge collecting chamber. Most of the oil separates from the water immediately due to the differences in specific density and reduced flow rate inside the separator.
The fluid flows upwards through the separating media while solids and sludge drop to the bottom of the cylinder. The path taken maximises the surface area of fluid that is in contact with the separating media. This further enhances the coalescence of oil and hence increases the likelihood of solid and sludge fallout.
The fluid exits the separating media near the top of the cylinder. At this point oil continues to flow to the top of the cylinder (the oil collecting chamber) due to the difference in specific density between oil and water. Water is at this stage drawn downward through the polishing pack of polypropylene beads. The polishing pack coalesces any residual oil that may be left in the water until drops large enough to break loose and rise up to the oil collecting chamber.
When a sufficient volume of oil has collected in the collecting chamber the oil sensing probe creates a signal to stop the pump and open the clean water inlet valve. Pressurised water entering from the bottom of the separator flows upwards through the polishing pack and displaces the accumulated oil which is then discharged through the oil discharge line. After the oil has been removed and the oil sensing probe is again immersed in water, the separator returns to separating mode.
A slip stream of processed water is fed to the OCD to continuously monitor the oil content in parts per million (ppm). The OCD then controls the processed water discharge, which is dependant on the oil content, by opening or closing solenoid valves. If the oil content is less than 15ppm the processed water is allowed to discharge normally and an overboard discharge solenoid valve is opened. If greater than 15ppm the processed water is re-circulated to be processed again via a re-circ solenoid valve and the overboard solenoid valve is closed. The operation of the oily water separator is clearly shown in figure 4.1 below.
Sources Of Oil And Water
The oily waste system provides a means for the collection of lube oil, fuel oil, and oil contaminated water through the use of drainage funnels and drip pans piped directly into the dirt oil tank.
Water in the bilges can be produced intentionally from washing the deck and draining various pieces of equipment such as instrument and control air receivers. Unintentional water input can come from spillages and leaking equipment such as freshwater coolers and steam pipes. A major contributor is the water drained from steam lines used for de-super heaters, ballast pumps and the turbo alternators. Distilled water tanks also overflow to the bilges.
No oil is intentionally put into the bilges. Oil should be disposed of by pouring it into a drainage funnel leading directly to the dirty oil tank. Oil can enter the bilge wells as a result of wash-down from a piece of machinery that has an oil leak on it.
The Progressive Cavity Pump
The progressive cavity pump is used for bilge pumping operations as it produces a smooth flow is important for the oily water separator. As previously discussed emulsified mixtures are more difficult to separate. The operation of the progressive cavity pump is clearly shown in figure 6.1 below.
Fluid enters the pump at the top and moves right to left as the rotor revolves inside the stator. The stator is twisted in a cavity with an oval shape cross-section. As the rotor turns a series of cavities are continuously formed that progress down the rotor until discharge.
Monitoring Processing Operations
Monitors and alarms for oily water separators ensure that the waste water sent overboard does not produce a visible sheen on the water. OPNAVINST 5090.1A (Pollution Prevention Afloat) states that the maximum ppm of oil allowed to be discharged from vessels is 15 ppm. To ensure oil is not discharged above this limit an oil content detector is used.
The oil content detector has a built in sample chamber. The chamber remains closed when the oily water separator is secured. The monitor activates automatically when the separator starts. A sample is taken continuously via a slipstream from the processed water outlet. The sample is exposed to a high intensity light source. The intensity of the transmitted light is measured by two photocells that convert light energy to electrical signals. This signal through the control panel operates the solenoid valves for discharge either overboard or back to the oily waste holding tank. The monitor transmits the signal to the main control panel.
The main control panel provides a digital readout of the oil content in ppm. When the maximum set point of 15 ppm is reached the system automatically goes to the recirculating mode sending oily water back to the dirty oil tank.
Oil Record Book
The Oil Record Book, ORB, is a legal document and must be completed with extreme care. Every entry in the ORB is signed and dated by the engineer responsible for relevant operations. Entries are into the ORB include;
1. Bilge pumping operations, whether overboard or to the dirty oil tank.
2. Bulk fuel and lube oil transfers
3. Operations by which liquids are pumped in or out of the dirty oil tank
4. Maintenance of the OWS, its monitor and/or pipelines
5. Records of all periods for which the OWS is out of action for whatever reason.
6. A weekly record of the contents of the dirty oil tank
7. Disposal of cooking oils, oils used in cleaning etc are also recorded.
When making entries all the relevant details specified at the front of the ORB must be complied with. The quantities recorded must not exceed the specified rate of the equipment for the amount of time running. The oil record book is handed to the Chief Engineer for signing on the completion of each page.
Rules relating to oily water waste were referenced from;
Reed’s General Knowledge for Marine Engineers, 2006 Edition. ISBN 978-0-7136-6736-3. References on page 9 on 4th May 2009
How to pump bilges on Bekulan referenced from;
B-Class engine room information book, 08/03/06 Edition. References on pages 12 and 13 on 9th May 2009
Information concerning ISO 14001 was referenced from;
http://www.iso.org/iso/iso_catalogue/management_standards/iso_9000_iso_14000/iso_14000_essentials.htm, At 10:09 on 8th June 2009
(i) The Bilge System
All bilges are first pumped to the aft bilge well before being pumped to the oily water separator.
The ships location at the beginning and end of all bilge pumping operations must be recorded.
(ii) Rules Governing Oily Water Waste
Protecting the environment is a deeply held value within the Shell group. Regulations set out by IMO Resolution A393 and MARPOL regulations 9 1b and 10 3b (Correct as of September 2004) are summarized below and are strictly adhered to in order to minimize shipping’s impact on the environment.
1. The ship must be ‘en route’
2. The ship must have 15ppm equipment with an automatic stopping device. The equipment must work
3. The water must not be ‘diluted’
4. In the case of an oil tanker, the bilges must not have been contaminated with cargo ie from the pumproom.
5. If these conditions cannot be met in full, then absolutely no overboard discharge is permitted. (…unless a serious emergency is threatening the safety of the ship )
6. When in special areas absolutely no oil is permitted to be pumped overboard.
7. There is no 12 mile rule for machinery space bilges within MARPOL
8. If bilges are not to be pumped overboard for whatever reason, it is prudent to keep the level below the alarm and so it may be necessary to move the bilges to the dirty oil tank.
(iii) ISO 14001
ISO 14001 is a standard for environmental management systems, EMS, which can be implemented in shipping and any other business. The aim of the standard is to reduce the environmental footprint of a business and to decrease the pollution and waste a business produces.
An EMS meeting the requirements of ISO 14001:2004 is a management tool enabling an organization to:
1. Identify and control the environmental impact of its activities, products or services
2. Improve its environmental performance continually
3. Implement a systematic approach to setting environmental objectives and targets, to achieving these and to demonstrating that they have been achieved.
ISO 14001 does not specify levels of environmental performance. If it specified levels of environmental performance, they would have to be specific to each business activity and this would require a specific EMS standard for each business.
The intention of ISO 14001 is to provide a framework for a holistic, strategic approach to the organization’s environmental policy, plans and actions. ISO 14001 can also be used to meet some of the external objectives listed below;
1. Provide assurance on environmental issues to external stakeholders such as buyers, inspectors and classification societies.
2. Comply with environmental regulations as set by Marpol.
3. Support the organization’s claims about its own environmental policies, plans and actions
(iv) Green Passport
The International Maritime Organization’s Guidelines on Ship Recycling were introduced in 2003 to improve standards of safety and reduce environmental pollution resulting from the scrapping of ships. The guidelines introduced the concept of the Green Passport, an inventory of materials present in a ship’s structure, systems and equipment that may be hazardous to health or the environment.
Prior to scrapping, details of additional hazards in stores and wastes are added, and the document can then be used to help the recycling yard formulate a safer and more environmentally sound plan for decommissioning the ship. As well as being an invaluable tool for the ship recycling yards, the Green Passport also helps to raise crew awareness of the materials onboard a ship that may require special handling.
Lloyd’s Register was the first classification society to issue an independently verified Green Passport, in 2004. As well as facilitating safer and more environmentally sound dismantling of ships, the Green Passport provides a formal summary of hazards, which can help to promote better hazard management aboard ship, enhancing safety and enabling better long-term liability planning
The Green Passport can demonstrate a company’s commitment to improving environmental standards. It provides measurable and achievable objectives for ISO 14001 certified companies and, since it is voluntary, may also help to boost reputation in the market.
STASCOs entire fleet of 25 LNG carriers has been awarded Green Passports.
(v) Instructions for Pumping Bilges on Bekulan
The instructions below detail every operation that is required for pumping bilges aboard Bekulan. Numbers refer to valves that can be seen in the system diagram on page 13.
1. Open bilge suction valves x 3. (One on a well, the suction from bilge main on manifold and separator inlet).
2. Open pump discharge (27) and overboard valves.
3. Open oil outlet valve (14).
4. Open FW flushing valve (9) (before solenoid) and small freshwater flushing line to PPM sensor.
5. Turn separator power switch (20) to ON position.
6. Turn operation switch (21) to FLUSH position, and open check cock (10). When clear water is flowing out of the cock shut it and turn operation switch (21) to RUN position (shut the PPM sensor flushing cock now as it can draw in air).
7. NB It may take a long time to flush the separator using this method alone. If so you can flush using the SW flushing. This valve is located on the suction manifold. If you are to use this method of flushing only open valve slightly and take care not to over pressurise the system.
8. The separator should now work automatically.
9. If oil/air is sensed at the top of the separator it will automatically go into a flush cycle. The pump stops and the flushing water solenoid opens. At this time it may be better turn the operation switch (21) to FLUSH and open the seawater flushing carefully as per note above.
10. Please note if the PPM meter (26) is reading above 15ppm it is pumping to the dirty oil tank.
1. Turn operation switch (21) to FLUSH
2. Open manual vent (10).
3. When clear water is flowing out, shut the vent and turn the operation switch (21) to OFF.
4. Shut fresh water flushing valve (9).
5. Shut oil discharge valve (14).
6. Shut pump discharge (27) and overboard valves.
7. Shut bilge main suction on manifold, suction valve on well and separator suction.
Solids And Sludge Removal
1. If in operation, stop the system pump by placing the operation switch (21) in the OFF position. Allow solids to settle for a few minutes.
2. Open Drain/Solids dump valve (4).
3. Place operation switch (21) in the FLUSH position, for 2 to 5 minutes to expel solids.
4. Place the operation switch (21) in the OFF position.
5. Open the top sample valve (10). Allow the solids to dump for 25 to 30 seconds or until the oil discharge light is illuminated.
6. Close the top sample valve (10).
7. Close the Drains/Solids dump valve (4) and return to normal operation.
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