OWS/Pollution prevention Flashcards
What is the problem with bilge water content on modern vessels?
The bilge water content on modern vessels not only contains diesel oil and water but also lube oil, hydraulic oil, heavy fuel oil and oil additives. This sort of mixture has to be separated into three distinct phases. Oil, water and sludge.
The other problem is the presence of emulsions, which are mixtures of immiscible liquids such as tiny oil droplets mixed into the bilge water. This is normally able to be dealt with by gravity, which will cause these droplets to separate from the water but if the bilge water contains chemicals from cleaning products used on board will then these will prevent this process from happening.
Why is the type of pump used for delivering oily water mixture important?
The type of pump used for delivering the oily water mixture is important because it controls considerably the degree of contamination in the effluent (liquid waste/sewage). The best type of pumps to use are the positive displacement pumps for example reciprocating pumps or gear pumps, which enable better performance from the OWS as they will not produce large quantities of small oil droplets. As oppose to for example centrifugal pumps which churn the oily water and produce small oil droplets dispersed throughout the water
Draw a cross-sectional diagram of an oily-water separator system suitable for oil discharges of less than 15ppm. Indicate on the diagram the flow of fluid through the separator and label all major component parts.
/Or,
Sketch an Oily-water separator system that complies with present legislation.
SEE EOOW ORAL/IAMI Sketch Pack for drawing
With reference to the disposal of bilge water from the machinery spaces:
a) Explain when it is not permissible to discharge the bilge water overboard,
even via an oily water separator; (8)
b) State the maximum permissible oil content of the overboard discharge. (2)
c) Identify the documentation to be completed and state by whom, following such an operation. (6)
a.) it is not permissible to discharge bilge water overboard, which contains oil from ships of 400GT and above in the event of the following circumstances
if the ship is within the Antarctic area.
if the ship is NOT proceeding en route (in other words, the vessel is alongside, anchored, or at rest).
if the oil content exceeds 15ppm.
if the oily mixture originated from cargo pump-room bilges on oil tankers.
if the oily mixture, in the case of oil tankers, is mixed with oil cargo.
If less than 12 miles offshore.
if the vessel is not in compliance with MARPOL: Annexe 1. (Regulations for the prevention of pollution by oil)
if the oil-water mixture hasn’t been processed through approved oil filtering equipment.
b.) 15 ppm (parts per million).
c.) Following such an operation, an entry has to be made in the Oil Record Book. The officer-in-charge has to complete an entry and sign after each completed operation, and the Master then countersigns every completed page and the C/E. Then, fill out the ER Log book, which is also signed by the watch-keeper and chief engineer and the master
a) Describe the procedure for operating the oily water separator (12)
a.) 1. the OWS overboard discharge valve is kept locked and keys are kept with the C/E, therefore the the first step is to inform the bridge and C/E that you wish to discharge the bilge water via the OWS. you can also then verify with the bridge if the vessel is in compliance marpol annex 1 regualtions, like for example the vessels position to check if its at least 12miles from shore and not in any special area and proceeding en route. the chief engineer has overall authority on the OWS system and therefore must supervise the EOOW to ensure hes operating the system correctly.
- Fill the OWS with fresh water to flush both 1st stage and 2nd stage compartment and test the OCM alarm ensuring the discharge stops during alarm state.
- Sound bilge holding tank and record results.
- Open all the other valves of the system including recirculation line/discharge to bilge.
- Open the desired bilge tank valve from which the oily water mixture is to be discharged from OWS.
- Open air if the control valves are air operated. then Switch on the power supply of the control panel and OCM unit.
- Fill the separator and filter unit with fresh or sea water to prime the system and flush out any oil.
- Start the OWS supply pump, which is a laminar flow pump that will supply the oily water mixture to OWS
- Observe the OCM for ppm value and keep checking sounding level of bilge holding tank from where OWS is taking suction and also of the OWS sludge tank. also monitor the three-way control valve for correct operation. this valve should automtically close the O/B discharge line and direct the bilge water through the recirculation line back to bilge holding tank should the oil content exceed 15ppm.
- OWS is put in full auto control and the O/B discharge valve is opened start suction from bilge holding tank, directing the bilge water overboard and constantly recording the results. at the same time as the O/B discharge valve is opened you need to ensure you log the time when the discharge is started as well the starting volume of the bilge holding tank and the position of vessel.
- During discharge operation observe the level of bilge tank from where OWS is taking suction and of the OWS sludge tank by sounding the tanks. also monitor the sample valve which is provided just before overboard valve and after the 3-way valve. Keep a check on the sample for any effluent and clarity
- After discharge quantity is reached so the operation is finished, stop OWS supply pump and close O/B discharge valve. then Flush OWS with clean water. Sound bilge holding tank for the final volume and make records in ER logbook and ORB.
- After the operation, switch off the power, close all valves and ensure the overboard valve is closed and locked. Inform bridge and C/E that operation finished and then Keys for O/B dicharge valve are handed over to the Chief Engineer
- An entry in the Oil Record Book (ORB) is made by C/E with his signature and Operating Officers signature and the Master for every completed page. the Oil record Book must be filled out correctly and in the correct format as its a legal document.
State TWO ways that the separator could be made to operate more
efficiently. (4)
- adding a tube skimmer to prevent oil build up, continuously remove oil from the surface, and keep your oil water separator working as designed.
- Install Dust Filter: While using OWS for discharging bilge mixture containing dust and sand, it will be difficult for the coalescer filter to pass dust and sand due to size. installing this filter will reduce the operating hours of the filter and in-turn the efficiency of the OWS.
State the effect that EACH of the following would have on the efficiency of the separator:
i) The addition of heat to the separator (4)
ii) Agitating the bilge water before it is pumped. (4)
b.) i.) slightly increasing the temperature of the bilge water would give better separation because it will reduce viscosity. increasing temperature will increase the specific density differential of the oil and water, which would aid in the separation.
ii.) The larger the oil droplets, the faster the rate of separation. Agitating it will mix the water and oil, making the droplets smaller, making separation more difficult. Also, it can lead to turbulent flow inside the OWS, resulting in a fall in OWS capacity due to the formation of emulsion.
With the aid of a sketch describe a two stage OWS
see sailors notebook
What is Oily Water Separator ?
The oily water separator (OWS) is a very important piece of equipment / device carried on board to separate the mixtures of oil and water into their separate components.. An oily water separator is used to treat the oil — water mixture from bilge spaces , oil in any compartment in the ship which has accumulated water ,before discharging into the sea. Oily water separator is used on ship to prevent the discharge of oil overboard mainly when pumping out Bilges. It is used for de ballasting or cleaning oil tanks.
On Which Principle Oily water separator Works?
Oily water separator Works on the Principle of Separation by Gravity Differential between the oil and water.
why we use oily water separator ?
1.Because free oil and oily emulsions discharge in the water way can interfere with the natural process such as photosynthesis and re-aeration and induced the destruction of algae and plankton so essential to fish life .
2.Inshore discharge of oil can cause damage to birds life and Mass pollution of beaches .
difference between oily water separator and centrifuge?
-Oily water separator are required to handle large quantity of water from which usually a small amount of oil must be removed
-centrifuge is required to remove usually a small quantity of water from much larger amount of oil
what is the working principle of the OWS?
The fundamental principle of separation by which oil / water separators work is the difference of gravity between oil and water. The oil exists in oily water mixtures as a collection of globules (small particles) of various sizes. The force acting on such a globule which causes it to move in the water is proportional to the difference in weight between the oil particle and an equal volume water particle. The resistance to movement of the globule depends on its size and the the fluid viscosity. In the case of small particles moving under streamline flow conditions, the relationship between these properties can be expressed in Stoke ‘s Law.
What are ways of improving and speeding up the operation?
a high separation rate is encouraged by the large size of the oil globule, the elevated system temperature (which increases the specific gravity differential of oil and water and reduces the viscosity of the oil) and the use of seawater. Turbulence or agitation should be avoided as it causes the oil to be mixed and causes a large amount of small oil droplets. Laminar or streamlined flow (uninterpted flow, flow rate is the same and direction remain unchanged at all times) is beneficial for good operation of OWS. In addition, the heating coils can provided to improve separation by increasing temperature and reducing viscosity.
Most systems are fitted with a back flushing connection. Backflushing allows the separator to be filled with clean water before and after operation and backflushing should be carried out each time the
separator is used. The separator should also be backflushed after a malfunction such as high oil
content in the water discharge. The water and oil from backflushing is normally discharged into the
bilge waste tank. According to regulations there MUST be a procedure for operating the OWS
posted next to the machinery.
what is meant by Stoke ‘s law?
Stoke’s Law is a mathematical equation that expresses the settling velocities of the small particles in a fluid medium. it consider the forces acting on a particular particle as it sinks through the liquid under the influence of gravity. the velocity or rise and hence the separation rate is directly proportional to the
difference in density of the oil and the continuous fluid, and the size of the droplets of oil. It also states that rate of rise is inversely proportional to the
viscosity of the surrounding fluid.
what 3 units does the OWS consist of
1.Separator unit
2. coalescing Filter unit
3.control unit (oil content monitoring)
