Oil-water separators

Numerous processes and service operations generate oily wastewater, the disposal of which is usually subject to legislatory and environmental requirements. Tankering to some other place is the simple answer, whereby a contractor is paid to collect the wastewater and dispose of it but this can prove to be the least cost effective disposal method, and in any case it only transfers the basic problem from one site to another. On-site treatments are therefore almost always to be preferred, but need to be matched to the kind and proportion of oil contaminant, its condition (i.e. whether free or emulsified), and to the presence of other contaminants. 

Incineration is a possible (although never a popular) on-site treatment. The achievement of successful incineration may demand me use of special incinerating equipment wim gas or fuel oil present in me waste. Emulsified wastes, aimough containing a significant proportion of water, are often more readily incinerated man heavier oily wastewater. 

Slop oil compartment Effluent transfer pipe Oil spill-over weir Separation chamber 

The American Petroleum Institute recommends various minimal horizontal and vertical cross-section areas and depm-to-widm ratios. These minima are based on the formula version of Stokes s law, which relates me rate of rise of an oil droplet through a tank of water to (among omer things) me difference between me liquid densities and the square of me droplet diameter. 

It is important to know me oil globule size because me rate of rise of me globule increases as me square of me diameter. Considering two applications, when in which all factors are me same except for oil globule size, when me following will hold true mat a 150 pm oil droplet will rise nine times faster than a 50 pm one (150/50 = 3, and 3 = 9). 

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This type of clarifier is used in apphcations such as prehminaiy oil-water separations in refineries and clarification of waste streams in steel mills. When multiple units are employed, common walls are possible, reducing construction costs and saving on floor space. Overflow clarities, however, generally are not as good as with circiilar clarifiers, due primarily to reduced overflow weir length for eqmvalent areas. 

The chemical propjerties of the contaminants have to be considered when selecting separation techniques. Some of the liquids are absolutely immiscible in water, and if the process stream involves water and the contamination is liquid/liquid, then the separation technique can greatly reduce the volume of contaminated water. For example, if acetone is the contaminant of concern, a simple vap>or stripping technique can be effective in making a separation. In the case of refined oil, which has a solubility limit of approximately 50 ppm, one of the oil/water separation techniques could be effective. Some general guidelines to consider are ... 

In general, when sepiarating two liquids, they must be immiscible and have different spiecific gravities before a separation technique-such as oil/water separation-would be effective. In the case of finely dispersed liquids or finely dispersed solids, if the dispersed material is below one micron in particle size, centrifuging should be considered. The use of centrifugal force on the differing densities of the material can facilitate the separation technique. 

A eoaleseer aehieves separation of an oily phase from water on the basis of density differences between the two fluids. These systems obviously work best with non-emulsified oils. Applications historically have been in the oil and gas industry, and hence the most famous oil/water separator is the API separator (API being the abbreviation for the American Petroleum Institute). 

Figure 29. Underground installation of an oil/water separator. Source Tanks Direct from their website http //oilwaterseparators.com/process.htm...

The grand-thermodynamical potential is, like the temperature, calculated in units of b. Macroscopically, b is related to the critical temperature of the oil-water separation by kT = 3(1 — p )b. The coupling constants of O2 re... 

Car-washing wastewater Carwash water Kuwait Separation tank/oil water separator/ Alters... 

Appendix B presents the U.S. EPA data on a full-scale treatment of aluminum forming wastewater by emulsion breaking and ultrafiltration. After emulsion breaking, various oil-water separation... 

FIGURE 5.1 Typical gravimetric API oil-water separator. (Source Wikipedia Encyclopedia, API Oil-Water Separator, http //en.wikipedia.org/wiki/API oil-water Separator.)... 

API stands for the American Petroleum Institute and TEB stands for Thermal Emulsion Breaking. Figures 5.1 and 5.2 show two typical types of oil-water separators, gravimetric and parallel plate.7 A dissolved air flotation (DAF) clarifier is commonly used for polishing the effluent from an oil-water separator.8"1013... 

BDL, below detection limits NM, not meaningful. a API, American Petroleum Institute oil-water separator. b TEB, thermal emulsion breaker. c Approximate value. 

APPENDIX A Full Scale Treatment of Aluminum Forming Wastewater by Emulsion Breaking and Oil-Water Separation Removal Data Sampling Three 24-Hour or One 72-Hour Composite ... 

Oil-Water Separation, Biological Treatment, Powdered Activated Carbon Adsorption, and Clarification... 

Removal of Total Toxic Organics and Oil and Grease from Coil Coating Wastewater by Oil-Water Separation... 

Under optimum conditions, an oil-water separator can reduce the hydrocarbon emulsion in water down to 15 mg/L. The separator is most effective when the gasoline plume is relatively small and the rate of water flow is slow enough to allow for complete separation. 

If it is desirable to reuse the oil, then more efficient oil-water separators utilizing heating and nebulization techniques will be needed. U.S. patents issued to Weber and colleagues42 and Wang and colleagues43 make use of such techniques. 

Wang, L.K. and Mahoney, W.J., Treatment of storm runoff by oil-water separation, flotation, filtration and adsorption, Part A, The 44th Purdue Industrial Waste Conf. Proc., Lewis Publishers, Chelsea, MI, 1990, pp. 655-666. 

Since 1995, the sparks solvent/fuel site located in Sparks, Nevada, a remediation system consisting of MPE, air sparging, and SVE, has been operational. The treatment system consists of 29 MPE wells, an oil-water separator, and a fluidized bed bioreactor, with an influent flow rate of 23.3 L/s (370 gpm) and a retention time of 8 min. Vapors are sent through a condenser, followed by a thermal oxidizer, before its release to the atmosphere. Condensate is sent back through the oil-water separator. Performance data, available for the first 650 days of site operation, showed a reduction in MTBE concentration across the bioreactor from 2400 to 55 pg/L. No data were provided for reduction of MTBE concentrations in the aquifer.51... 

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