Sizing oily water separators.

[DavidCR]

We have two dikes with AST for fuel oil #2(One dike with two tanks, and another with three, 5000m3 each API 650 fixed cone roof AST), the instalation is quite old and just have a simple drainage system with a fixed oil trap.

We have dimensioned a separator considering a ten year return period rain. The plant operators have asked for a capacity of this rain plus the water and foam fire system demand at full capacity in the worst fire escenario. For us this is too big, but the operators want us to size following their criteria.

They don´t want to see that this implies a very big separator but we want to base the design on a rational basis, and we want to know what is the criteria to define the capacity to size the separator considering the fire system water demand, any help on this.

 

[IFRs]

API 421 Design and Operation of Oil-Water Separators might help. Available from

http://www.api.org

 

[Hadeed]

It is very important to know the fuel oil you process(type & density) since it maters to seperate from water. Moreover, fuel oils are considred dry, so that they have high specific gravity i.e .95, otherwise it is diffcult to seprate. However, the fire water & foam, will be used in case of fire they should not be counted in calculating the capacity of the seperartor design since in case of fire or rain(ten years cycle)(usually it is 5 years return in order to be considred in design) should drain away from the dikes to drainge channels then to the designated surface draiange area of the plant( faded away by means of nutural evaporation). Finally, since a separter is only paratical if you process a daily oily water with appreciable quantity of product to recover; therefore, you need to quantify the daily generated oily water before determining the seperator capacity.