Oily Water Separator: Construction and Working and Operating Procedure

Oily Water Separator: Construction and Working

Construction and Working of OWS

OWS consists of mainly three segments:

Separator unit

§  This unit consists of catch plates which are inside a coarse separating compartment and an oil collecting chamber.

§  Here the oil having a density which is lower than that of the water, which makes the former rise into the oil collecting compartment and the rest of the non-flowing oil mixture settle down into fine settling compartment after passing between the catch plates.

§  After a period of time more oil will separate and collect in the oil collecting chamber. The oil content of water which passes through this unit is around 100 parts per million of oil.

§  A control valve (pneumatic or electronic) releases the separated oil in to the designated OWS sludge tank.

§  Heater may be incorporated in this unit for smooth flow and separation of oil and water.

§  First stage helps in removing some physical impurities to achieve fine filtration in the later stage.

The Filter unit

§  This is a separate unit whose input comes from the discharge of the first unit.

§  This unit consists of three stages – filter stage, coalescer stage and collecting chamber.

§  The impurities and particles are separated by the filter and are settled at the bottom for removal.

§  In second stage, coalescer induces coalescence process in which oil droplets are joined to increase the size by breaking down the surface tension between oil droplets in the mixture.

§  These large oil molecules rise above the mixture in the collecting chamber and are removed when required.

§  The output from this unit should be less than 15 ppm to fulfil legal discharge criteria.

§  If the oil content in water is more than 15 ppm then maintenance work such as filter cleaning or renewal of filters is to be done as required.

Oil Content Monitor and Control Unit

§  This unit functions together in two parts – monitoring and controlling.

§  The ppm of oil is continuously monitored by Oil Content Monitor (OCM); if the ppm is high it will give alarm and feed data to the control unit.

§  The control unit continuously monitors the output signal of OCM and if alarm arises, it will not allow the oily water to go overboard by means of operating 3 way solenoid valve.

§  There are normally 3 solenoid valves commanded by control unit. These are located in the first unit oil collecting chamber, second unit oil collecting chamber and one in discharge side of the oily water separator which is a 3 way valve.

§  The 3 way valve inlet is from the OWS discharge, where one outlet is to overboard and second outlet is to OWS sludge tank.

§  When OCM gives alarm, 3 way valve discharges oily mixture in the sludge tank.

How to Operate an Oily Water Separator (OWS) on Ship?

An oily water separator clears the bilge water of oily content to bring it inside the acceptable range to discharge it overboard. An oily water separator is machinery for such importance that it is handled by only the 2nd or chief engineer. (However, the duty engineer might also be asked to operate under supervision)

Operating an Oily Water Separator

An oily water separator can only be operated when the ship is sailing and en route. According to MARPOL, the oily water separator can only be operated when the ship is 50 nautical miles away from the shore and is en route. In case of failure to follow any of the above mentioned rules, the ship will be fined and stopped, and the chief or 2nd engineer can even be imprisoned.

Because of such high risks, operating an oily water separator should be done with utmost 

precision to minimize the risks of marine pollution. Though a “How to Operate?” guide is always

posted near the oily water separator, there are few points to be kept in mind and followed to 

prevent any mistake.

Operating Procedure

The following points are to be followed while operating OWS.

1) OWS overboard manual discharge valve is to be kept locked and keys are to be kept with the chief engineer. Open the lock and overboard valve. Open all the other valves of the system.

2) Open the desired bilge tank valve from which the oily water mixture is to be discharged from OWS.

3) Open air if the control valves are air operated.

4) Switch on the power supply of the control panel and OCM unit.

5) Fill the separator and filter unit with fresh or sea water to clean up and prime the system till the water comes out from vent of second stage.

6) Start the OWS supply pump which is a laminar flow pump and one that will supply the oily water mixture to OWS.

7) Observe the OCM for ppm value and keep checking sounding of bilge tank from where OWS is taking suction and of the OWS sludge tank.

8 ) A skin valve/sample valve is provided just before overboard valve and after the 3-way valve. Keep a check on the sample for any effluent and clarity.

9) Keep a watch on the ship side at the overboard discharge valve.

10) After the operation, Switch off the power and shut and lock the overboard valve. Keys to be handed over to the chief engineer.

11) Entry to be made by chief engineer in the Oil Record Book (ORB) with signature of operating officer, chief engineer and the master.