Abstract:
Polymer mixing apparatus strips oil from polymers in an oil phase continuous emulsion and at least partially hydrates the polymers by injecting the emulsion and a pressured aqueous solution into a mixing zone. The emulsion and solution are passed through a confined space, where the oil is stripped from the polymer molecules and at least partially hydrated. The resulting solution is removed from the confined space without recirculation through the confined space.

Description:
[0001]     This invention relates to polymer mixing devices, and more particularly, to devices that invert an oil phase continuous (reverse) emulsion containing polymer molecules to a water phase continuous (straight) emulsion, effectively removing the oil from the polymer molecules and hydrating the molecules, so the polymer molecules can be activated and used in purifying water.  
       BACKGROUND OF THE INVENTION  
       [0002]     The use of liquid (emulsion) polyelectrolytes in water, wastewater and papermaking applications began to proliferate in the early  1980 &#39;s. Polyelectrolytes are useful for removing fine particulate matter from water.  
         [0003]     Initially, traditional batch systems were used to dilute and activate the new polyelectrolytes, commonly called polymers. Typical batch systems use one or more 50-5000 gallon tanks. A measured amount of polymer in an oil-based emulsion is dumped or pumped into the tanks, which contain water, with a propeller mixer running. The mixing action of the propeller strips some of the oil from the polymer molecules, called inversion, allowing the molecules to absorb water. After some period of time (10-30 min.) the mixer is turned off and the solution is allowed to “age” for an additional 30-60 minutes. Aging allows the polymer molecules to open and extend, called activation, exposing ionic sites to the water.  
         [0004]     After aging, the solution is dosed into water containing suspended solids. The ionic sites attract and grasp suspended particles in the water, and the particles settle to the bottom of the water, leaving the water in a cleaner condition. Batch systems have several problems, though. Inversion is incomplete, and the impact of the propeller damages many of the polymer molecules. Activation is slow and cumbersome, and the process is inefficient overall.  
         [0005]     In-line systems for activating the new liquid polymers began to appear in about 1982 and gained fairly rapid acceptance in the marketplace. In-line systems invert the emulsion and activate the polymer, fairly continuously moving the inverted solution until it leaves the system. In-line systems do not use aging tanks and offer savings in space required, installed cost and cost of operation. While they address some of the problems found in batch systems, though, they only solve them to some extent, as the shear forces they create lack uniformity, which limits the degree of activation achieved.  
         [0006]     Thus, there is a need for a polymer mixing apparatus that more uniformly inverts an oil-phase continuous polymer emulsion to a water phase continuous emulsion, more fully exposing the polymer molecules to activating water.  
         [0007]     Accordingly, one object of this invention is to provide new and improved polymer mixing devices.  
         [0008]     Another object is to provide new and improved polymer mixing devices that more fully and uniformly strip oil from polymers, which allows the polymer to hydrate in an aqueous solution.  
         [0009]     Still another object is to provide new and improved polymer mixing devices which cause less damage to the polymer molecules in the process of inversion and activation.  
       SUMMARY OF THE INVENTION  
       [0010]     In keeping with one aspect of this invention, apparatus for stripping oil from polymers in an oil phase continuous emulsion and at least partially hydrating the polymer molecules injects the oil-based emulsion and a pressurized aqueous solution into a mixing zone. The resulting solution is passed from the mixing zone through a confined space, where the oil is stripped from the polymer molecules and the polymer molecules are at least partially hydrated. The solution is removed from the confined space without recirculation through the confined space. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above mentioned and other features of this invention and the manner of obtaining them will become more apparent, and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:  
         [0012]      FIG. 1  is a cross-sectional view of a polymer mixing device made in accordance with the present invention;  
         [0013]      FIG. 2  is a partially cut-a-way detail view of the water conduit, stator disk and impeller used in the device of  FIG. 1 ;  
         [0014]      FIG. 3  is a perspective view of an impeller which can be used in the device of  FIG. 1 ;  
         [0015]      FIG. 4  is a perspective view of another embodiment of an impeller, which is shown in the device of  FIG. 1 ;  
         [0016]      FIG. 5  is a perspective view of another embodiment of an impeller, which can be used in the device of  FIG. 1 ; and  
         [0017]      FIG. 6  is a cut-a-way view of a portion of the device of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0018]     Referring to  FIGS. 1 and 2 , the polymer mixing apparatus  10  has one inversion stage  12  and an activating stage  14 . The inversion stage  12  includes a stator disk  16  and impeller disk  18 . The stator disk  16  and impeller  18  are generally flat, and the impeller does not have the paddles found in the impellers of some known polymer mixing devices. The impeller disk  18  is rotated by a motor  20  through a seal  22  and a threaded hub  23 .  
         [0019]     The stator  16  includes protrusions  25  extending from its outside wall or edge  27 . The protrusions  25  maintain the general position of the stator within a housing  26 , and also create an outlet  42  of the inversion stage  12 . The outlet  42  is formed in the space between the outer wall  27  of the stator  16  and the housing  26 , as defined by the protrusions  25 . Three or four preferably equally spaced protrusions can be used, as desired.  
         [0020]     The activation stage  14  includes one or more baffles  24 . The inversion stage  12  and the activation stage  14  are enclosed in the housing  26 , and an end cap  28  is provided at the top of the activation stage  14 . A bottom cap  29  closes the lower end of the inversion stage  12 .  
         [0021]     Polymer in an oil-based continuous phase emulsion enters the apparatus  10  through a polymer inlet  30 . The polymer-in-oil emulsion passes through a polymer column  32  to an injection check valve  34 , located in the inversion stage  12 . The check valve  34  has a valve stem  35  for operating the check valve  34 .  
         [0022]     A pressurized aqueous solution such as water enters the apparatus  10  at a water inlet  37 , and passes through a water conduit  36  to the inversion stage  12 . O-rings  39  seal the water inlet  37 , yet allow some axial movement of the water conduit  36 , which is attached to the stator  16 . Upward (axial) movement and rotational movement of the stator  16  is limited by a keyed collar  41  and a stop  43 . Water pressure without impeller rotation pushes the stator away from the impeller. Impeller rotation creates lower pressure, though, which draws the stator closer to the impeller.  
         [0023]     Water is delivered by externally applied pressure through an adjustable flow control device (not shown) into the mixing zone. Polymer-in-oil emulsion is delivered to the mixing zone by separate adjustable pumping apparatus (not shown). Rotation of the impeller  18 , which can rotate up to perhaps 3450 rpm, draws the resulting solution through the mixing zone  38  and then through an inversion zone  40 . The inversion zone  40  is a confined space, which will be described in more detail.  
         [0024]     In the inversion zone (confined space)  40 , oil is stripped from the polymer molecules and emulsified in the diluting water, exposing the polymers to the water. The polymer molecules then begin to be hydrated by the aqueous solution.  
         [0025]     The inverted polymer molecules leave the inversion zone at the outlet  42 , and the resulting solution, which is under pressure, passes through the activation stage  14 , following the arrows shown in  FIG. 1 , in mild turbulence with low shear. However, the solution does not circulate back through the inversion stage  12 . Hydration and extension can continue in the activation stage, exposing numerous ionic activation sites which can attract and capture particulate matter in wastewater.  
         [0026]     The solution leaves the apparatus  10  at an outlet  44 , and can be stored for later use or immediately placed in water to be treated. When placed in the water, the ionic activation sites capture particulate matter. The particles captured in the water add weight to the polymer molecules, and the particle-laden molecules sink to the bottom of the water, cleaning the water. The resulting particles are easily removed by various known techniques.  
         [0027]     The impeller  18  rotates in the inversion zone  40 , generating centrifugal force which adds pressure to the solution as it passes through the activation stage  14 . The movement of the impeller  18  creates relatively high shear turbulence in the inversion zone  40 , but the impeller  18  and stator disk  16 , which form the confined space or inversion zone  40 , strip and hydrate the polymer molecules by subjecting them to a substantially uniform frictional force, without generating substantial impact forces against the polymer molecules.  
         [0028]     The confined space  40  extends both axially and radially between the stator and the impeller. The axial (Z) dimension is small compared with the radial dimension. The axial dimension can be typically 0.025 inches or less, while the radial dimension of the impeller can be about 5 inches, extending through both the X and Y dimensions. The mixing zone can have a radius of about 0.5 inches. In this example, the confined space  40  extends radially for about 4.5 inches.  
         [0029]     The polymers are in the inversion zone  40  for a very short time, perhaps 25 milliseconds. In the inversion zone, the molecules are subjected to a uniform shear force for this predetermined time. The polymers do not recirculate through the inversion zone, though, because the centrifugal force generated by the impeller directs the polymers immediately through the exit  42 , through the continuous uniform volume of the confined space  40 , and the activation stage is isolated from the inversion stage by the stator. While the shear force might increase from the inside to the outside of the confined space, the shear force is substantially uniform, because the impeller surface and the stator disk surface are substantially flat.  
         [0030]     The lowered pressure generated by the rotating impeller draws the stator closer to the impeller, limited by the solution in the inversion zone, and the stop  41 . The stop  41  is particularly helpful if water pressure at the water inlet  37  is inadvertently interrupted, which would produce excessive lowered pressure in the inversion zone and might allow contact between the impeller and the stator.  
         [0031]     The impeller  18  can take various forms, including those shown in  FIGS. 3, 4 , and  5 . In  FIG. 3 , an impeller  46  has a flat surface  48  with openings  49  for mounting the impeller to the hub.  
         [0032]     In  FIG. 4 , an impeller  50  also has a generally flat surface, with a plurality of circumferentially spaced vanes  52 . The vanes  52  extend from an entrance  54 , which is a predetermined distance from an axis  56 , to a predetermined point short of an outer edge  58  of the impeller  50 . The outer edge  58  is the end of the inversion zone  40 .  
         [0033]     In  FIG. 5 , an impeller  60  also has a flat surface  62 , and a plurality of vanes  64 . The vanes  64  extend from an inlet  66  to an outlet  68 . The vanes  52 ,  64  can have any suitable shape, but preferably are recessed and tapered in two axes. Since the vanes are recessed, the polymer-in-oil solution is dispersed more rapidly throughout the inversion zone  40 , and enters the more confined space between vanes on the flat surfaces  58 ,  62 .  
         [0034]     The vanes  52  ( FIG. 4 ) and  64  ( FIG. 5 ) are recessed so that the polymer molecules can extend and travel radially through the impeller and disperse more evenly along the surface of the impeller when they leave the vanes. The vanes provide a convenient way to control the time the polymer molecules are subjected to shear forces in the confined space, and disperse the polymer solution more quickly.  
         [0035]     After inversion in the confined space  40 , the oil is substantially stripped from the polymer molecules, and the polymer molecules become hydrated both in the confined space  40  and in the activation zone  14 .  
         [0036]     While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.