Desalter emulsion separation by emulsion recycle

Abstract

A petroleum desalting process in which fluid from interfacial boundary layer between the settled water layer and the settled oil layer or emulsion-water layer in the vessel is withdrawn from the desalter and recycled to the crude oil inlet of the desalter to improve separation of the oil and water phases.

1 . A petroleum desalting process which comprises:
 mixing a crude oil to be desalted with desalting water and passing the mixture of oil and water to a desalter vessel to form (i) a settled water layer containing salts dissolved from the oil in the lower portion of the vessel, (ii) a settled supernatant, desalted oil layer in the upper portion of the vessel and (iii) an emulsion layer formed from the oil and the water comprising emulsified oil and water at the interface between the settled water layer and the settled oil layer,   removing a stream of emulsion comprising fluid from the boundary layer at the interface between the settled water and the emulsion layer,   recycling a portion of the removed emulsion to the crude oil to be desalted and mixing the recycled emulsion with the crude oil feed.   
     
     
         2 . A desalting process according to  claim 1  in which the stream of emulsion withdrawn from the desalter vessel includes oil-wet solids from the oil-water or emulsion-water layer in the vessel. 
     
     
         3 . A desalting process according to  claim 1  in which the withdrawn emulsion stream is settled to effect a partial separation of water and oil from the emulsion to form a water stream and an emulsion stream which is recycled and mixed with to the crude oil feed. 
     
     
         4 . A desalting process according to  claim 1  in which the recycled emulsion is mixed with the crude oil feed in a proportion up to 0.03:1 v/v of the crude. 
     
     
         5 . A desalting process according to  claim 4  in which the recycled emulsion is mixed with the crude oil feed in a proportion of 0.005:1 to 0.025:1 v/v of the crude. 
     
     
         6 . A desalting process according to  claim 1  in which a demulsifying additive is added to the emulsion stream removed from the desalter vessel. 
     
     
         7 . A desalting process according to  claim 1  in which a hydrocarbon diluent is added to the emulsion stream removed from the desalter vessel. 
     
     
         8 . A desalting process according to  claim 7  in which the hydrocarbon diluent added to the emulsion stream removed from the desalter vessel has a boiling range from 200 to 400° C. 
     
     
         9 . A desalting process according to  claim 8  in which a hydrocarbon diluent comprising a light cycle oil is added to the emulsion stream removed from the desalter vessel. 
     
     
         10 . A desalting process according to  claim 7  in which the hydrocarbon diluent is added to the emulsion stream in a proportion of 3:1 to 20:1 v/v. 
     
     
         11 . A desalting process according to  claim 1  in which the position of the interface between the settled water layer and the settled oil layer or emulsion-water layer in the vessel is detected by means of a level detector. 
     
     
         12 . A desalting process according to  claim 1  in which the emulsion layer includes emulsion-stabilizing solids. 
     
     
         13 . A petroleum desalter which comprises:
 a desalter vessel having a crude oil feed inlet for admitting a mixture of crude oil to be desalted with desalting water to form (i) a settled water layer containing salts dissolved from the oil in the lower portion of the vessel, (ii) a settled supernatant desalted oil layer in the upper portion of the vessel and (iii) an emulsion layer formed from the oil and the water and comprising oil and water formed between the settled water layer and the settled oil layer,   a water outlet conduit at the bottom of the vessel for removing water from the water layer,   an oil outlet conduit at the top of the vessel for removing desalted oil from the oil layer,   at least one emulsion outlet for removing an emulsion stream from the interfacial boundary layer between the settled water layer and the settled oil layer or the emulsion-water layer in the vessel,   a recycle conduit connecting the emulsion outlet to the crude inlet.   
     
     
         14 . A desalter according to  claim 13  in which the desalter vessel has a plurality of vertically spaced emulsion withdrawal points connected to the emulsion withdrawal port. 
     
     
         15 . A desalter according to  claim 13  in which the emulsion outlet of the desalter vessel is connected to a settling drum having an upper outlet and a lower outlet, to settle the emulsion and remove water from the emulsion, to form an emulsion stream to be withdrawn from the settling drum through its upper outlet and passed to recycle conduit. 
     
     
         16 . A petroleum desalter which comprises:
 a desalter vessel having a crude oil feed inlet for admitting a mixture of crude oil to be desalted with desalting water to form (i) a settled water layer containing salts dissolved from the oil in the lower portion of the vessel, (ii) a settled supernatant desalted oil layer in the upper portion of the vessel and (iii) an emulsion layer formed from the oil and the water and comprising oil and water formed between the settled water layer and the settled oil layer,   a water outlet conduit at the bottom of the vessel for removing water from the water layer,   an oil outlet conduit at the top of the desalter vessel for removing desalted oil from the oil layer,   a level detector for detecting the position of the interface between the settled water layer and the settled oil layer or the emulsion-water layer in the vessel,   at least one emulsion outlet for removing an emulsion stream from the interfacial boundary layer between the settled water layer and the settled oil layer or the emulsion-water layer in the vessel,   a conduit connecting the emulsion withdrawal port to a settling drum having an upper outlet and a lower outlet, to settle the emulsion and remove water from the emulsion, to form an emulsion stream to be withdrawn from the settling drum through its upper outlet,   a second conduit connecting the upper outlet of the settling drum to a recycle conduit connecting the upper outlet of the settling drum to the crude oil feed inlet.   
     
     
         17 . A desalter according to  claim 16  which includes an inlet for a hydrocarbon diluent to the recycle conduit.