Abstract:
A separator inlet includes a spiral channel in a channel housing and having an open top. Fluid flows in tangentially and out of a central outlet of the channel housing, or in a reverse direction.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns an inlet for a separator (separator tank) in a process plant, for example a plant for processing a fluid consisting of oil, water and/or gas. 
     The inlet arrangement in a separator in a process plant usually has several purposes. First, the inlet reduces the impulse to incoming fluid to prevent the inlet flow from disturbing the steady flow conditions required in the separator. Second, the inlet prevents sand or similar material in the process flow from being deposited in places where this is undesirable. Thirdly, the inlet prepares the process flow so that the conditions for good separation are optimal. 
     In practice, impulse reduction is usually the guiding factor for the design of an inlet in a separator. A widely known impulse reduction solution is based on the use of a flow interruption plate arranged just outside the separator inlet. The fluid flow meets the plate and is spread outwards and possibly backwards if the plate is curved. Another impulse reduction solution is based on the use of a U-shaped pipe in connection with the inlet to “return” the flow towards the separator wall. A third solution is based on the use of a T-pipe section in connection with the inlet to interrupt the fluid flow and steer it sideways. 
     However, all of these solutions create a greater or lesser degree of spray, agitation and disturbance to the surface of the fluid, which means that the conditions for good separation are not achieved or are poor. If the fluid supply flow consists of oil and water, large shear stresses, for example as a result of pressure loss across a valve or sudden changes of speed, can lead to the oil and/or water being turned into small drops and a so-called emulsion being formed. In its simplest form, the emulsion is either oil-in-water (oil drops in water) or water-in-oil (water drops in oil). Surfactants in the oil can stabilize the emulsion and make it difficult to separate the oil and water. Water-in-oil emulsions are considered to be more difficult to break down than oil-in-water emulsions. 
     If the fluid supply flow contains free gas in addition to oil and water, shear stresses to which the fluid supply flow is exposed can lead to the formation of small gas bubbles which are mixed with the fluid phases. These gas bubbles can have an emulsion-stabilizing effect like the surfactants in oil. 
     SUMMARY OF THE INVENTION 
     The present invention represents an inlet to a separator in which the fluid inlet flow is not exposed to unnecessarily large shear stresses (plunging, sudden changes of speed), and in which free gas which may be present in the fluid supply flow is released before the fluid flow is exposed to shear stresses. Moreover, the present invention represents an inlet which produces steady flow conditions in the separator and prevents any sand or other particulate contaminants from being deposited in places where this is undesirable. 
     The present invention is characterized in that the separator inlet is designed as a spiral channel open at the top in a channel housing. The fluid flows in tangentially and flows out through a central outlet in the housing downwards. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described in the following in further detail with reference to the attached drawings, in which: 
     FIG. 1 shows a separator inlet in accordance with the present invention arranged in a separator tank; 
     FIG. 2 shows, in the form of a schematic diagram, an outline of the separator inlet; 
     FIG. 3 is a schematic diagram of the same inlet seen from above; and 
     FIG. 4 is a schematic diagram of the inlet shown in FIG. 2 during operation, i.e. filled with a fluid, for example oil/water containing gas. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows, as stated, a separator inlet  1  in accordance with the present invention arranged in a separator tank  2 . The separator inlet is placed in connection with the surface of the fluid, and the fluid is supplied to the separator inlet from outside via a supply line  3 . 
     The separator inlet  1  comprises, as shown in FIG.  2  and FIG. 3, a channel housing  4  with channels  10  open at the top which run from a tangentially-located connection line (first line)  5  for the supply line  3  in a spiral path to an outlet line (second line)  6  which is arranged centrally in the housing  4 . 
     The housing  4  may expediently be made of a disc-shaped plate  7  and inward-sloping plates  8 ,  9  arranged on this disc-shaped plate  7  which run in a spiral path and form walls in a channel  10 . A circular, pipe-shaped part with openings  11  to the channel  10  may also expediently form the outlet  6  in the housing. The housing  4  may be equipped with a lid over the channel, but any lid must be provided with openings for the evacuation of gas. 
     In order to trap any gas bubbles which are released at the outlet line (second line)  6  in the housing  4 , it is preferable to arrange a funnel-shaped gas trap  12  which is connected to the housing via mounting pieces  13 . The gas trap  12  is designed to extend slightly below the second line  6  to just above the surface of the fluid outside the housing  4 . 
     The separator inlet works in the following way. The fluid is introduced into the channel  10  in the housing  4  from the pipe  5  and flows in spiral path through the channel  10  in the housing to the outlet  6  while releasing any gas. The fluid then flows downwards through the outlet  6 , and any remaining gas will be trapped by the funnel-shaped trap  12  and conveyed to the surface. Alternatively, the flow can be in the opposite direction (i.e., the inflow can be via the centrally-located second line  6  from above, and the outflow can be tangential via the first line  5 , which will be immersed in the fluid in the separator). 
     The housing may expediently be made by casting or of welded plates of a corrosion-resistant material, for example stainless steel. 
     EXAMPLE 
     Comparative tests were performed in a Plexiglas model of a separator in the scale 1:4.5. Water, Exxol D80® and air were used for the three phases in the fluid, which was supplied to a separator inlet in accordance with the present invention and to a well known separator inlet of the impulse type with two sets of plate packs in the water phase. The tests for the two separator types were performed under the following conditions. 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Water cut (percentage content of water) 
                 60% 
               
               
                   
                 Gas/fluid ratio (volume) 
                 1.2 
               
               
                   
                 Mixing speed (inflow speed of fluid) 
                 6 mls 
               
               
                   
                   
               
             
          
         
       
     
     Oil in water was measured with a Horiba® IR instrument. 
     The following results were obtained: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Oil in water at 
                 Oil in water at 
               
               
                   
                 inlet of separator 
                 outlet of separator 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Widely known impulse type inlet 
                 110-140 ppm 
                 400-500 ppm 
               
               
                 Inlet in accordance with the present 
                 100-150 ppm 
                 220-300 ppm 
               
               
                 invention 
               
               
                   
               
             
          
         
       
     
     As the results show, the separator inlet in accordance with the present invention produces a much lower content of oil in water (better water quality) at the separator outlet than the well known inlet.