Abstract:
An apparatus for treating a suspension that includes liquid and solid particles of varying sizes has a first decanter type centrifuge that discharges the solids onto a dryer/filter element that further separates the liquid from the solids in the suspension.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention disclosed and claimed in this application relates to a decanter centrifuge which is typically utilized in a variety of industrial processes where it is necessary to separate out solids that are suspended in a liquid medium. As an example, decanter centrifuges are used in oil and gas well drilling to separate out solid particles that are recirculated back to the surface as a result of drilling through the formation. Such drilling fluids are commonly referred to as mud. Other well treating processes also may result in fluids being returned to the surface. These fluids may also be treated using decanter centrifuges. 
         [0003]    2. Description of Related Art 
         [0004]    U.S. Pat. No. 4,731,182 is an example of typical decanter centrifuge. It consists of an outer bowl  33  within a casing  34 . Positioned within the bowl is a screw conveyor having a core  15  and helical vanes  15   a  and  15   b.  Sludge or drilling mud is directed into the interior of core  15  and exits through ports  35  into bowl  33 . Bowl  33  and the screw conveyor are driven at different speeds. The heavier phase accumulates at the inner surface of bowl  33  by centrifugal force and is moved by vanes  15   b  to outlet  39  while the lighter phase is discharged through outlets  36 . 
         [0005]    U.S. Pat. No. 6,823,605 discloses an apparatus that includes a baffle cone  14  that intercepts the larger particles from outlet  11  and directs them into a hot gas stream for drying the particles. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention enhances the performance of typical decanter centrifuges by adding a dryer mechanism at the output area for the heavier particles. The dryer is designed to remove liquid and some smaller particles as the larger solids pass over the dryer filter. 
         [0007]    This arrangement eliminates the need for separate centrifugal dryers that are typically used to treat the heavier particles separated out by the decanter centrifuge, thus saving money and the extra space needed for the dryers at the well site. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0008]      FIG. 1  is a cross sectional view of a combined decanter centrifuge and dryer according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    Referring to  FIG. 1 , an embodiment of the invention includes a decanter centrifuge  1  including a support housing  11  and a cover  2  pivotably mounted on the housing. A transmission mechanism  21  is provided to rotate inner cone shaped screw conveyor  4  and outer bowl  3  at different rotational speeds as is known in the art. A suitable drive mechanism including motor  31  and pulley  51  is connected to transmission mechanism  21 . Screw conveyor  4  includes a hollow frustoconical end portion  12  and a solid portion  13 . Helical vanes  5  are located on the outer surface of the screw conveyor  4 . The liquid/solid mixture to be processed is directed into the interior portion  12  of the screw conveyor by inlet tube  19 . Interior portion  12  of screw conveyor  4  is provided with a plurality of outlets  10  which allow for the liquid/solid mixture to be flung outwardly against the inner surface of bowl  3 . As explained above, due to centrifugal force the heavier particles in the mixture will congregate at the inner surface of bowl  3  and be directed towards outlet area  14  by vanes  15 . Liquid with some fine solid particles will congregate at the outer surface  25  of the screw conveyor  4 , and will exit through outlet openings  9  in annular member  26 . 
         [0010]    Screw conveyor  4  is driven by shafts  42  and  49  which are secured to solid portion  13 . Outer bowl  3  and dryer  7  are driven by shaft  41  through annular members  56 ,  26 , and  55  which are secured to each other and shaft  41 . Bowl  3  includes a plurality of discs  51  and spacers  52  and a terminal ring member  53  which are held together in a suitable manner. Dryer  7  is held in place by a flange  8  extending from ring  53  and a groove provided in one of the discs  51  positioned at the outlet of bowl  3 . Housing  11  includes supports  43  which support annular members  47 ,  48 , which in turn support cylindrical member  45 . Member  45  is the support housing for the main bearings (not shown) that support shaft  41 . 
         [0011]    Attached to the discharge outlet portion  14  of bowl  3  is a dryer filter  7  in the form of an outwardly expanding conical ring. As the heavier particles are discharged over end portion  14  of bowl  3 , they are directed over filter medium  7 . Liquid and some remaining fine particles smaller than a pre-selected size, for example less than 200 microns, pass through the filter medium  7  and are collected in a suitable reservoir  29 . Larger solid particles pass over the filter medium  7  and are discharged over the outer portion of the dryer filter and are collected in a suitable manner. 
         [0012]    Thus it can be seen that the invention includes treating the slurry or mud in two distinct ways in one apparatus. Liquid with fine particles is first separated from a suspension of heavier particles. The remaining mixture of heavier particles and liquid is then passed over a rotating dryer filter where the heavier particles are further separated from any remaining liquid and smaller particles. The liquid recovered from the first and second stage may then be recycled for use in the process such as a drilling process. 
         [0013]    Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.