Emulsion Breaking Methods

Several physical methods can separate oils and SS from wastewater, including gravity separation, dissolved air flotation, centrifugation, filtration, and electrical dehydration. Selecting the method depends on the nature of the wastewater and the degree of treatment required. Chemical methods of breaking water-oil emulsions are based on the addition of chemicals that destroy the protective action of hydrophobic or hydrophilic emulsifying agents and allow the water globules and oil to coalesce.

Figure 7.34.19 shows a typical API separator. This two-stage separator can be expanded to include additional sections. Figure 7.34.20 shows a common treatment arrangement that uses a combination of mechanical process and a chemical process. System operation is as follows:

1. Piping design and feeding facilities allow the operator to pump into either or both tanks and add an emulsion-breaking chemical to either tank or to the waste enroute from the API separator.

2. Steam coils are in both tanks since heat improves the speed and efficiency of phase separation after emulsion resolution.

3. This system fills one tank with waste from a bottom inlet until an upper-level limit is reached. The flow then switches to the other tank. The filled tank is allowed to settle for about 60 min and is then inspected.

4. The system pumps any oil that has risen to the top to reclaimed oil storage. It draws water from the bottom and routes it to the separator inlet. After this step, normally about three-fourths of a tank of w/o emulsion are left.

5. The system heats the emulsion with the steam coils. After the proper temperature is reached, it mixes it by rolling the tank with gas. The emulsion-breaking chemical is added during the mixing.

6. After thorough mixing, this system shuts off the gas and steam so that the treated emulsion can cool and settle until phase separation is complete.

7. The water phase, containing some SS but virtually oil-free, is routed to a settling pond. The oil goes to re-claimed-oil storage and is recycled to the refinery crude unit at a steady rate.

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