Acoustic separation of liquid hydrocarbons from wastewater

Abstract

A process for separating liquid hydrocarbons from a wastewater using acoustic energy below cavitation is disclosed. The wastewater containing the residual hydrocarbons is introduced into a vessel which has at least two groups of acoustic transducers attached to it. Acoustic energy is applied to the fluid at an intensity below cavitation level and sufficient to induce at least one standing wave in the fluid. The liquid hydrocarbons are allowed to coalesce within the vessel to a coalesced droplet size of about 20 microns. These coalesced hydrocarbons are then separated from the wastewater.

What we claim is: 
     
       1. A process for separating liquid hydrocarbons from wastewater; said process comprising the steps of: introducing a continuous flow of said wastewater into a vessel sized to accommodate a large volume of wastewater; said vessel further having at least two groups of acoustic transducers attached thereto, wherein each of said acoustic transducer groups comprises two transducers attached to said vessel at positions opposite each other in the radial direction of said vessel; and wherein each of said transducer groups are positioned axially along said vessel;   applying acoustic energy to said wastewater within said vessel at an intensity below cavitation level and sufficient to induce at least one standing wave within said wastewater;   allowing a portion of said liquid hydrocarbons to coalesce within said vessel; and   separating at least a portion of said resulting coalesced hydrocarbons from said wastewater.   
     
     
       2. The process of claim 1 wherein said liquid hydrocarbons in said wastewater comprise oil and oil-in-water emulsions. 
     
     
       3. The process of claim 1 wherein said vessel is a pipe and wherein each of said acoustic transducer groups are attached to said pipe at the maximum amplitude of vibration locations along said pipe. 
     
     
       4. The process of claim 1 wherein said liquid hydrocarbons coalesce at at least one of said pressure antinodes of said standing wave. 
     
     
       5. The process of claim 1 wherein said liquid hydrocarbons coalesce at at least one of said pressure nodes of said standing wave. 
     
     
       6. The process of claim 1 wherein, prior to application of said acoustic energy, about 95% of said liquid hydrocarbons have a droplet size of less than about 10 microns, and wherein at least about 50% of said resulting coalesced hydrocarbons have a droplet size of at least about 20 microns. 
     
     
       7. The process of claim 1 wherein, prior to application of said acoustic energy, said liquid is hydrocarbons have a droplet size in the range of about 1.0 microns to about 150 microns, and wherein a majority of said resulting coalesced hydrocarbons have a droplet size of at least about 20 microns. 
     
     
       8. The process of claim 1 further comprising, prior to the application of acoustic energy, pretreating the wastewater to reduce surface charge repulsion between said droplets. 
     
     
       9. The process of claim 8 wherein said pretreatment step comprises adding chemical coagulants to said wastewater. 
     
     
       10. The process of claim 8 wherein said pretreatment step comprises applying an electric field to said wastewater.