Abstract:
An impeller vane assembly for blending liquids with solid particulate matter in which a center drive shaft extends through a housing having a solid particle inlet and a liquid inlet together with an outlet, and upper and lower impeller vanes are aligned respectively with the particle inlet and liquid inlet to cause intermixing of the solids and liquids by counterflow of the liquid into the upper impeller region, the upper and lower vanes being separated by a common divider plate, and the vanes are characterized by being curved in the direction of rotation of the impeller and having outer radially extending tips which terminate at the outer peripheral edge of the common divider plate, the vanes being operative to balance the point at which the solids and liquid are intermixed between the solid particle inlet and annular space surrounding the impeller. In one embodiment, expeller blades are employed in inner concentric relation to the upper impeller vanes to accelerate the flow of solid particles into the upper impeller region, and baffle plates or deflector members are employed above and below the upper and lower impellers to prevent any leakage of liquid into the center of the impeller.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of patent application Ser. No. 10/428,276 filed May 2, 2003, now U.S. Pat. No. 6,974,246, for METHOD AND APPARATUS FOR BLENDING LIQUIDS AND SOLIDS INCLUDING NOVEL AND IMPROVED IMPELLER ASSEMBLY by Jorge O. Arribau and Michael G. Dubic, incorporated by reference herein. 
    
    
     BACKGROUND AND FIELD OF INVENTION 
     This invention relates to blenders as well as pumping apparatus; and more particularly relates to a novel and improved method and apparatus for blending liquids with solid particulate materials, and still further relates to a novel and improved impeller assembly which is conformable for use with blenders as well as centrifugal pumps. 
     Numerous types of blenders have been devised for intermixing and pumping large volumes of liquid/solid slurries. For example, downhole operations in oil and gas fields, such as, fracturing and cementing operations utilize a blender in which liquids and solids are introduced into a housing, a rotor within the housing, upper and lower impeller portions for intermixing the materials and throwing or advancing the materials outwardly into an annulus surrounding the rotor from which the resultant intermixture or slurry can be discharged into the well. A representative blender is that set forth and described in U.S. Pat. No. 5,904,419 to Jorge O. Arribau, one of the inventors of this invention which patent is incorporated by reference herein (hereinafter referred to as the &#39;419 patent). Other representative patents are U.S. Pat. No. 4,239,396 to Arribau; U.S. Pat. Nos. 3,256,181 and 3,326,536 to Zingg; U.S. Pat. No. 4,850,702 to Arribau and U.S. Pat. No. 4,460,276 to Arribau. 
     In the &#39;419 patent, liquids were introduced through mixing apertures intermediately between the rotor and annulus for mixing with the solid particles prior to introduction into the relatively high pressure annulus. 
     There is a continuing but unmet need for a blender of simplified construction which can regulate the balance or mixing point between the solids and slurry in a region radially inwardly of the annulus and be capable of pumping the slurry under a substantially constant pressure over a wide range of mass flow rates. There is similarly a need for an impeller assembly in which impeller vanes are designed to regulate the slurry pressure as well as to prevent liquid or slurry leakage back into the central expeller area. Still further, to decrease the depth of vanes required for the upper impeller region by encouraging more immediate outward flow of sand to achieve the same capacity or mass flow rate as deeper vanes. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide for a novel and improved method and apparatus for blending liquids and solid particles by counterflow of the liquid with respect to the direction of solid flow through an impeller region. 
     It is another object of the present invention to establish a balance point between liquid and solid particle intermixture in an impeller for a blender and to control the pressure and velocity of liquid/solid flow by regulating the size, length and configuration of the impeller vanes. 
     It is a further object of the present invention to prevent backflow of liquids or solid particles around impeller zones of a blender apparatus. 
     It is a still further object of the present invention to provide in a pumping system for an impeller design capable of maintaining substantially constant pressure of a liquid/solid slurry over a wide range of mass flow rates. 
     In accordance with the present invention, there is provided in apparatus for blending liquids with solid particles in which a housing has an upper solid particle inlet and lower liquid inlet, a center drive shaft in said housing and outlet communicating with an annular space in outer spaced surrounding relation to the drive shaft, the invention characterized by having upper impeller vane means mounted for rotation on the shaft whereby to direct solid particles from the inlet toward the annular space, lower impeller vane means mounted for rotation on the drive shaft whereby to direct liquid from the liquid inlet through the annular space to intermix by counterflow of the liquid with the solid particles, and a plate interposed between the upper and lower impeller vane means. In the preferred form, the upper impeller means includes inner and outer concentric vanes, the inner vanes being operative to force the solid particles into the outer impeller vane region at a rate sufficient to substantially reduce the height of the outer vanes necessary to intermix the desired ratio of solid particles to liquids and prevent any tendency of the solid particles to back up into the center inlet region. In another preferred form of invention, the radial tips of the upper impeller vanes are lengthened to discourage return flow of the liquids or slurries toward the center of the impeller region. 
     The above and other objects, advantages and features of the present invention will become more readily appreciated and understood from the following description of preferred and modified forms of invention when taken together with the accompanying drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal section view of a preferred form of invention taken vertically through the apparatus. 
         FIG. 2  is a top plan view partially in section of the preferred form of invention shown in  FIG. 1 ; 
         FIG. 3  is a view in detail of inner concentric impeller vanes employed on the upper impeller of the invention; 
         FIG. 4  is a cross-sectional view taken about lines  4 - 4  of  FIG. 1 ; 
         FIG. 5  is a somewhat perspective view of the impeller vanes illustrated in  FIG. 3 ; 
         FIG. 6  is a fragmentary side elevational view of the preferred form of invention mounted on a truck; 
         FIG. 7  is a longitudinal section view of a modified form of invention; 
         FIG. 8  is a cross-sectional view taken about lines  8 - 8  of  FIG. 7 ; 
         FIG. 9  is a sectional view taken about lines  9 - 9  of  FIG. 7 ; 
         FIG. 10  is a fragmentary view of another preferred form of invention illustrating modifications to the vanes of the impeller assembly; and 
         FIG. 11  is a cross-sectional view taken about lines  11 - 11  of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings, a preferred form of blender apparatus is illustrated in  FIGS. 1 to 5 , and  FIG. 6  illustrates a typical mounting of a blender apparatus on a truck T whether the apparatus be of the preferred form of blender apparatus  10  illustrated in  FIGS. 1 to 5  or the modified form of apparatus  10 ′ illustrated in  FIGS. 7 to 9 . In oil and gas operations, such as, fracturing or cementing wells, the apparatus  10  or  10 ′ is mounted on a truck bed B including an engine E with a drive mechanism D to impart rotation via speed reducer mechanism M to a central drive shaft  12 . The solid particulate matter, such as, sand is delivered from a storage area S by means of an auger system represented at A to the upper end of a hopper  14 . There, the sand is permitted to advance by gravity into the apparatus  10  or  10 ′. The sand is thoroughly mixed with a liquid which is introduced through an inlet line L 2  into the inlet port  16 ; and the resultant slurry is discharged via outlet port  18  through a delivery line L 1  with sufficient pressure to be delivered to other trucks for delivery to a well head. The speed reducer M is a right angle drive as shown to enable the blender apparatus  10  to be oriented vertically in order to receive the sand and other dry chemicals under gravity flow through the hopper  14 . The sand screw assembly or auger A has the capability of introducing sand from the storage area S to a point at least 10″ above the inlet of the hopper  14  so that the mass flow rate of sand downwardly through the hopper is sufficient to produce the desired flow rate of sand through the discharge port. While the apparatus is described and shown as being truck-mounted, it will be appreciated that it can be as readily mounted on a fixed support and be oriented vertically or canted at an angle, such as, in the manner disclosed in hereinbefore referred to U.S. Pat. No. 5,904,419. 
     The apparatus  10  of the preferred form of invention is illustrated in more detail in  FIGS. 1 to 5  and will be seen to be broadly comprised of a base mount  20  including a bearing to support the lower end of the drive shaft in journaled relation to the mount, a cylindrical wall or casing  22  extending upwardly from the base mount  20  into an enlarged housing area  24  for the speed reducer mechanism M, and an intermediate casing  26  includes a bearing  27  to which an intermediate portion of the drive shaft  12  is journaled. The upper end of the casing  26  terminates in a flange  28  which is attached by suitable fasteners  29  to a substantially flat underside  30  of an upper impeller housing  32  for an impeller assembly generally designated at  34  within the housing  32 . The underside  30  is of annular configuration and disposed in outer spaced concentric relation to the drive shaft  12 , the impeller assembly  34  being mounted for rotation on the drive shaft in a manner to be described. 
     The impeller housing  32  has a substantially flat top side  36  of annular configuration parallel to the underside  30  and joined to the underside  30  by an outer continuous wall  38  of generally convex or toroidal cross-sectional configuration. The hopper  14  converges downwardly through a central opening in the top side  36  and is centered with respect to the drive shaft  12 . An upper flat, annular connecting plate  40  is attached by suitable fasteners to the top side  36  and has an inner thickened ring-like portion  42  attached by suitable fasteners to the top side  36  and wedged against a necked down portion  44  of the hopper  14 . A butterfly valve  48  with suitable hand control arm  49  is mounted in the hopper to seal off the mixer when desired and can assist in regulating the flow rate of sand into the impeller housing  32 . The discharge port  18  extends tangentially away from the outer wall  38  of the housing  32 , and the inlet port  16  extends radially into the housing  26  immediately below the expeller housing  32 . 
     An important feature of the present invention resides in the impeller assembly  34  which is comprised of upper impeller vanes  50  and lower impeller vanes  52  interconnected by a common plate  54  which is centered for rotation on the upper end of the drive shaft  12  by means of a cup-shaped retainer  56 . The upper impeller vanes  50  are bounded by a cover plate  58  having radially extending, circumferentially spaced expeller vanes  60 . The plate  58  is of annular configuration and mounted in surrounding relation to the lower edge  44  of the hopper  14 . The top side  36  of the housing  32  has a downwardly projecting, circular rib  62  extending into a circular slot  64  in the cover plate  58  as well as the vanes  60 , as best seen from  FIGS. 1 and 2 . The rib or baffle plate or deflector  62  cooperates with the expeller vanes  60  in minimizing any return flow of slurry or liquids toward the center region of the impeller. 
     The lower vanes  52  are similarly bounded by a bottom cover plate  66  having spaced expeller vanes  68  to discourage return flow of slurry or liquids around the underside of the housing. A rib  30 ′ projects upwardly from the underside  30  of the housing  32  radially inwardly of the inner terminal edges of the plate  66  and vane  68  to cooperate in discouraging the return flow of slurry or liquids. 
     The upper vanes  50  are shown in detail in  FIG. 4 , each having an inner edge or tip  70  substantially tangent to the inner radial edge of the cover plate  58  and curving radially and outwardly in a trailing direction to define a generally arcuate or concavo convex curvature at  71 , then turning in a radial direction to terminate in outer tips  72  which are perpendicular to the direction of flow. The direction of curvature of the upper vanes  50  presupposes that the vanes are rotating in a clockwise direction when viewed upwardly. The vanes diverge gradually outwardly from one another and terminate in the tips  72  at the edge of the common plate  54  but inwardly of the outer edge of the cover plate  58 . 
     As further illustrated in  FIGS. 3 to 5 , a plurality of expeller blades  80  are mounted on a base plate  81  which is affixed to the plate  54  at the eye of the impeller. The blades are keyed to the drive shaft  12  by a central fastener  82  threaded onto upper end portion of the shaft  12 . Each of the blades  80  includes a flat radial portion  84  extending vertically and upwardly from the plate  81  and terminates in an upper curved or rounded portion  85  having a top machined or flattened surface  86 . Preferably, the blades  80  correspond in number and spacing to the vanes  50  and are oriented or aligned with the entrances between the tips  70  of adjacent vanes  50  so as to redirect the incoming sand from the hopper  14  in a radial direction into the upper passages between the impeller vanes  50 . The upper curved ends  85  are curved in the direction of rotation of the shaft  12  so as to confine the flow of the sand in an outward radial direction. 
     The lower vanes  52 , as shown in  FIG. 9 , are of the same configuration as the upper vanes  50  including inner somewhat tangential tips  74 , arcuate portions  75  and outer radial tips  76  which also terminate at the outer edge of the common plate  54  and are rotating at the same rpm but will oppose the entrance of liquid into the upper impeller region. Nevertheless, the liquid is under sufficient pressure to undergo counterflow into the upper impeller region until it reaches a balanced pressure condition with the sand being driven outwardly between the upper impeller vanes  50 . As the upper vanes  50  approach the discharge port  18  the sand/water slurry will be driven outwardly under sufficient force by the vanes  50  as to overcome the counterflowing liquid and be discharged to the well head. The balance point or condition established between the sand and slurry is regulated to some extent by the relative length of the vanes  50  and  52 . For example, as illustrated in  FIGS. 4  and  9 , the upper vanes  50  are substantially longer than the lower vanes  52  and in cooperation with the expeller blades  80  of sufficient velocity while maintaining the necessary high pressure condition to overcome the water pressure and be discharged through the port  18 . Further, the combined use of the expeller blades  80  with the longer impeller vanes  50  will create greater pressure to push the water back at a balance point beyond the midpoint of the upper impeller vanes  50 ; and at the same time the height of the upper vanes  50  may be reduced to obtain the same capacity or mass rate of flow as substantially higher vanes, for example, as shown and described in the modified form of  FIGS. 7 to 9 . Maintaining the balance point at least beyond the midpoint of the upper vanes will help also to discourage leakage of water past the sand into the central inlet or eye of the impeller  34 . 
     The following working example is given for the purpose of illustration in the utilization of the blender method and apparatus of the preferred form of invention in mixing sand and water and delivering continuously to a well head: The inlet end of the impeller at the lower reduced end  44  of the hopper  14  is 12″ less the diameter of the center fastener  82  for the expeller blades  80 , and the sand is delivered at a constant rate through the auger A to a point no less than 10″ above the inlet in order to reach the design criteria of 30,000 lbs. of sand per minute through the opening. Again, in order to reach the design criteria of 30,000 lbs. of sand per minute through the outlet  18 , the expeller blades  80  and impeller vanes  50  and  52  are greater than 0.62″ in depth and are rotated at 1050 rpm. The water will enter the blender apparatus  10  through a 10″ to 12″ diameter inlet  16  and will not be accelerated until it reaches the vanes  52  whose inner tips are at a radius of 9″. The water is accelerated by the vanes  52  until it reaches the outer tips of the vanes at a radius of 14″ whereupon the liquid is driven into the annulus and energized to a pressure of approximately 100 psi. The liquid will then occupy the entire annulus and begin to invade the upper set of impeller vanes  50  which are rotating at the same rpm as the lower vanes and therefore opposing the entrance of the liquid into the upper section of the impeller. Once the liquid has reached a point 9″ from the center of the upper vanes  50  it will have dissipated its energy somewhat, and any tendency of the liquid to reach the eye of the impeller will be overcome by the length of the upper vanes  50  which will be on the order of 8″ compared to the lower vanes which are on the order of 5″. Accordingly, the eye of the upper impeller will be free of liquid so as not to interfere with the introduction of the sand from the auger A. 
     The expeller blades  80  will impart a velocity on the order of 660″ per second as a result of which it is not necessary to have a higher depth of sand expeller vane  50  than the depth of the lower water vanes  52 . Thus, the depth of the upper vanes  50  may be more on the order of 0.6″ to 1.0″ and therefore considerably more compact for the mass rate of flow of sand being handled. In addition, the expeller blades  80  reduce the area of the vanes which must be exposed to the pressurized liquid and therefore reduces the torque required to maintain the requisite rpm and correspondingly reduces the horsepower required on the engine. It will be evident that the size of the inlet may be reduced depending upon the amount or capacity of sand and water being discharged and therefore minimize the net positive suction head required. 
     Another preferred form of invention is illustrated in  FIGS. 10 and 11  in which like parts are correspondingly enumerated to those of  FIGS. 1 to 7 ,  8  and  9 . Specifically, the upper vanes  50 ″ have the same configuration as the vanes  50  and  50 ′ of the preferred and modified forms hereinbefore described, but outer radial tips  72 ″ are lengthened to extend to the outer peripheral edge of the common plate  54  in order to most effectively discourage the return flow of slurry or liquids toward the expeller blades  80 . 
     Detailed Description of Modified Form of Invention 
       FIGS. 7 to 9  illustrate a modified form of blender apparatus  10 ′ in which like parts are correspondingly enumerated with prime numerals. As shown in  FIGS. 8 and 9 , the vanes  50 ′ and  52 ′ are separated by a common plate  54 ′ and are of corresponding configuration to the vanes  50  and  52  of the preferred form of invention. However, the upper vanes  50 ′ are substantially increased in depth to compensate for the absence of the expeller blades  80  rapidly discharging the sand from the eye into the impeller vanes  50 ′. Thus, as represented, the increased depth of the inlet area beneath the hopper  14 ′ as well as the increased depth and size of the upper impeller occupied by the vanes  50 ′ may be varied and will enable greater amounts of sand to be introduced but at a much lower rate of flow. Furthermore, referring to the working example given with respect to  FIGS. 1 to 5 , in order to move a corresponding amount of sand would require an impeller vane  50 ′ of a depth six to eight times greater than that of the preferred form. Nevertheless, the modified form of invention is similarly capable of delivering the mixture or slurry under the same pressure over a wide range of mass flow rates. 
     The vane configuration devised for the preferred and modified forms of invention enable close control over the pressure of the solid and liquid materials in order to achieve optimum performance. For example, when the vanes are curved in the same direction as the direction of rotation, the pressure increases as the rate of flow of the materials increases and, in curving away from the direction of rotation, the pressure will decrease. However, any tendency to decrease can be overcome by adding the straight radial portions  72  or  76  to the radially outer ends of the vanes.  FIGS. 10 and 11  illustrate the lengthening of the blade tips  72 ″ to be flush with the outer edges of the plate  54 . As seen from  FIGS. 4 and 9 , the degree of curvature of the portions  71  and  75  as well as the relative length of the tips  72  and  76  can be varied to achieve different flow and pressure characteristics for a given rpm or speed of rotation of the vanes. It is therefore to be appreciated that the preferred and modified forms of invention are readily conformable for use in mixing various solids and liquids. It will be further evident that the vane configuration of the impeller vanes  50  and  52  is conformable for use in numerous applications other than blender apparatus and for example are adaptable for use in centrifugal pumps or in virtually any application where it is desirable to control the pressure of liquid or solid particles by regulating the curvature of the impeller vanes. 
     It is therefore to be understood that while preferred and modified forms of invention have been herein set forth and described, various modifications and changes may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.