How to design oil-water separator?
An oil/water separator is a widely used device for separating oily waste from wastewater flow. These are typically installed in industrial and maintenance areas such as aircraft and vehicles, maintenance and cleaning and other activities including petroleum and lubricants (POL).
An oil water separator is a device for treating wastewater that allows safe discharge to approved discharge points that are further sentin the sewer. It removes oils and hydrocarbons, leaving only harmless water. After that, the wastewater can be safely disposed of in the sewer.
There are various types of oil-water separators. Each has different skills and is used in a variety of commercial and industrial applications. They are used to treat various pollutants in water, such as suspended oils, emulsified oils, dissolved oils, and suspended solids.
Types of oil / water separators:
There are three main types of oil / water separators: gravity separators (traditional gravity), parallel plate gravity separator and flotation separator.
The oil / water separator used is a traditional gravity separator. Gravity separator process relies on different densities of oil, water, and solids for successful operation. Gravity oil / water separator is available in two versions. These separators use free and emulsified fats and oils as a pre-treatment method mainly before discharging to the sewer or in the septic tank system.
Example of design of oil/water Separator:
Understanding the design of oil water separator with the help of an example:
Question:
Design an oil water separator for a vehicle maintenance facility with 2 hose bibs which are used for wash down. Each hose bib is rated at 1 L/s. (Usually only 1 maintenance bay will be rinsed at a time, but all three may be at the same time during a spill clean-up).
Solution:
Step 1-Average Flow = 1 * 1 L/s.
Step 2-Required Volume for Average Flow = 30 min * 1 L/s * 60 sec/min = 1800 L = 1.8 m3
Step 3-Peak Design Flow = 2 *1L/s = 2 L/s
Step 4-Required Volume for Peak Flow = 15 min * 2 L/s * 60 sec/min = 1800L = 1.8 m3
The required separator must have a minimum volume of 1.8 m3.
Step 5-Calculate Separator Dimensions:
Horizontal Velocity = 0.91 m/min,
Therefore, Depth x Width = 0.09 m3/min= 0.91 m/min = 0.1 m2
If assume Width:Depth = 3:1, then W = 3D
Therefore,
m2 = D * 3D.
Depth = 0.18m and Width = 0.54 m
If assume Length: Width = 2:1, then
L = 2W, and Length = 1.09 m
Calculated Separator Dimensions:
D = 0.18 m, W = 0.54 m, and L = 1.09 m
Calculated Separator Volume:
V=1.8 m3
A separator with dimensions of D = 0.20 m, W = 0.6 m and L = 1.1 m will meet the separator dimensional design requirements, but this separator does not meet the minimum AED separator requirements.
Therefore, the separator required for this application would be D = 1 m, W = 2 m, L = 3 m which would have a volume of 6 m3, and a detention time of 200 minutes at the average flow when using 1 hose bib.
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