Construction of Oily Water Separator

OWS consists of mainly three segments:

1. Separator unit

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

Here the oil density is lower than water, which makes the former rise into the oil collecting compartment and the rest of the non-flowing oil mixtures 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 into the designated OWS sludge tank.

The heater may be incorporated in this unit for smooth flow and separation of oil and water.

A heater may be incorporated in this unit either on the middle or sometimes in the bottom part of the unit (depending upon the area of operation and capacity of the separator equipment) for smooth flow and separation of oil &water.

The first stage helps in removing some physical impurities to achieve fine filtration in the later stage.

2.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 the 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.

A freshwater inlet connection is also provided to the filter unit to clean and flush the filter. This is usually done before and after the operation of an oil separator unit.

3.Oil Content Monitor and Control Unit

Functions of this unit: Monitoring and controlling.

The ppm of oil is continuously monitored by Oil Content Monitor (OCM); if the ppm is high it will give an 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 the control unit. These are located in the first unit oil collecting chamber, second unit oil collecting chamber and one in the 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 the second outlet is to OWS sludge tank.

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

A small pipe connection of fresh water can be provided to the OCM unit for flushing. Whenever this line is in use, an alarm is sounded and recorded in the OCM log, ensuring a record to check the discharge valve was shut during this period.