Abstract:
An eductor for mixing liquids and solid particles includes a nozzle, an initial mixing chamber, a first diffuser, an intermediate mixing chamber and a second diffuser. The nozzle includes a semicircular nozzle outlet that is offset from a centrally-located first axis. Motive flow is accelerated through the nozzle through a first and second acceleration segment. Solid particles are added to the motive flow in the initial mixing chamber and directed to the first diffuser. Each diffuser includes an acceleration and a deceleration segment separated by an elliptically-shaped throat. The intermediate mixing chamber is located between the first and second diffusers. A method for mixing liquids and solids includes introducing a motive flow into an initial mixing chamber, creating a vacuum in the initial mixing chamber to induce solids into the motive fluid, providing a region of turbulence to enhance mixing of the motive flow and solid particles, and diffusing the motive flow to further increase boundary flow separation conducive to mixing.

Description:
This application claims priority to U.S. Provisional application 60/532,159 filed on Dec. 23, 2003, entitled “Device and Methodology for Improving Liquid/Solid Mixing,” hereby incorporated by reference. 
    
    
     BACKGROUND OF INVENTION 
     Efficient mixing of fluids and solids is essential for many industry sectors. The means by which this mixing is undertaken are many, the choice of which is dependent upon the nature of the materials being mixed and the degree and rate of mixing required. 
     Numerous concepts and frequent efforts have been made to improve the efficiency and effectiveness of liquid and solid mixing systems. Several notable methods that have met with relative success, depending upon the nature of the materials being mixed, have included: nozzle geometry distortion, motive flow pulsation, and the introduction of a diffuser as part of the system. 
     Nozzle distortion attempts to create turbulent flow by altering the geometry of the interaction of the motive flow with the nozzle surface, as shown in  FIGS. 1   a  and  1   b . The result of such an alteration is to change the velocity of the motive fluid as it exits the outlet of the nozzle creating vortices in which liquid-liquid or liquid-solid mixing can occur. Referring to  FIG. 2   a , typical geometries generate a narrow circular or near circular jet  300  that minimizes solids entrainment, hence minimizing the mixing effectiveness of liquid-liquid or liquid-solid vortices. As shown in  FIGS. 2   a - d , nozzle distortions  300  will quickly decay and eventually return to a circular or near circular shape. In addition, when solids  310  are introduced from the top by gravity into a larger cavity containing the liquid jet stream  300 , only a small portion of the solids make contact with the liquid. 
     Referring to  FIG. 3 , a fluid velocity profile is shown for a prior art nozzle. The liquid jet stream  300  emanating from the initial mixing chamber reaches an upper range of 53.6 to 67.0 ft/sec, depicted as reference  320 . As can be seen, this high velocity pierces through the solids that are introduced from above. Slower fluid velocities in the range of 40.2 to 53.6 ft/sec are depicted as reference  322  and are present ahead of the higher velocity stream  320  and in a boundary layer around stream  320 . The fluid velocity slows even more downstream to a range of 26.8 to 40.2 ft/sec as depicted by reference  324 . Upon entrance to the constricted area  312 , and the diverging area  314 , the velocity is slower, in the range of 13.4 to 26.8 ft/sec, shown by reference  326 . It is in this entrance to the constricted area  312  that the velocity profile shows a single mixing zone  330 . The slowest velocity, 0.00 to 13.4 ft/sec, shown by reference  328 , is present along the edges of diverging area  314  as well as in initial mixing chamber where solids  310  are added at an angle normal to, or nearly normal to, the direction of fluid through the nozzle. 
     In motive flow pulsation, pulsating the velocity of the motive flow, either with or without a nozzle, does change the velocity that creates turbulent flow, but will not permit the maintenance of a vacuum conducive to consistent and rapid induction of the secondary solid. Furthermore, such efforts require additional control systems and external energy reducing the efficiency of the process. 
     A third methodology which has seen more positive results is that of the motive flow utilizing the combination of nozzle and diffuser. This combination is referred to as an eductor. The relative velocity of the motive flow passing through the void on the outlet of the nozzle effectively maintains the vacuum required to permit induction of the secondary solids, but does not create recirculation zones sufficient in size and intensity to permit optimal mixing. 
     The action of the motive flow through the nozzle into the void space at the outlet of the nozzle carries the secondary solid into the eductor but does not succeed in mixing the two to any great extent. All nozzle geometries create vortices at the micro level downstream of the nozzle. It has been suggested that some nozzle geometries, such as lobed nozzles, can create these vortices faster (i.e. at a lower pipe diameter lengths) for liquid in liquid applications. However, the intensity of the vortices does not change and applications to induced solids in liquid are unknown._ Furthermore the speed at which the micro vortices are created in eductor based liquid-solid mixing applications is not critical as several pipe diameters are available prior to discharge. 
     The creation of a vacuum to induce solids into the motive fluid and large eddy current vortices is necessary to entrain and mix the solids with the motive fluid. Therefore, without the addition of a downstream diffuser which is used to create vacuum and create short and intense large eddies, mixing is limited and solids are simply carried along the plane of the motive flow only to be inefficiently mixed several pipe diameters downstream at a very slow rate. 
     One effective method of controlling the location of large eddies and recirculation mixing zones created between the nozzle outlet and the diffuser inlet is through nozzle and diffuser geometry and position. Through the combination of these geometries and positions, several large eddies are generated that maximize solids induction and solid-liquid interface while limiting pressure drop. Typically, nozzles with or without distorted geometries are placed in the center of the motive flow and produce only limited contact with the solids and motive fluid. Therefore the turbulence and consequent mixing along the linear axis of the motive flow are limited. Further, protruding nozzles can be an impediment to the induction of the solids. Such an impediment will reduce the induction rate and negatively impact mixing performance. 
     This problem has been addressed with the introduction of a multi-lobed circular nozzle in conjunction with a lightly tapered single throat diffuser. While effective, this concept can be improved upon in such a manner so as to increase the rate at which secondary solids can be induced into the motive flow, improving the solids-liquid surface contact through a flat profile jet stream, improve the generation of three large eddy currents through the use of diffuser geometry, maintain turbulent flow throughout the mixing body through nozzle and diffuser geometry, increase and maintain the vacuum which facilitates the rapid induction of solids, reduce the pressure loss through the eductor system through nozzle geometry and improve overall mixing performance as measured by rate of hydration of secondary solids. 
     SUMMARY 
     In one aspect, the claimed subject matter is generally directed to an improved in-line liquid/solid nozzle. The present invention provides an improved fluid mixing nozzle that achieves one or more of the following: accelerates the motive fluid; provides improved mixing of fluids and secondary solids; utilizes a unique semicircular nozzle geometry; improves the vacuum in the void between the nozzle outlet and diffuser inlet; improves the rate of induction of secondary solid; allows the use of a shorter diffuser section ; utilizes a diffuser section with non-uniform diffuser inlet angles; utilizes a diffuser with a primary mixing zone plus two additional mixing zones in the diffuser; improves pre-wetting of solids in the primary mixing zone; creates a turbulent flow zone; induces macro and micro vortices in the motive flow; improves rate of hydration of solids; increases motive flow rates through the nozzle; permits consistent performance with low or inconsistent line pressure; reduces pressure drop through the eductor, in addition to other benefits that one of skill in the art should appreciate. The eductor includes a nozzle, an initial mixing area, and a segmented diffuser. The nozzle is a semi-circular orifice that is off-center from a central axis. The nozzle outlet feeds motive flow into the initial mixing area. The solid material is also directed into the initial mixing area. The initial mixing area is of a size sufficient to create a temporary vacuum within the area, enhancing mixing in this first mixing zone. From the initial mixing area, the combined motive flow and entrained solid are fed into the segmented diffuser. The diffuser has two segments, the first of which contains a sloped inlet converging to a throat and a sloped outlet diverging to an intermediate cavity. The diffuser throat is elliptical, consistent with the shape of the jet stream. The second segment inlet is also sloped, converging to a throat while the outlet is sloped, diverging to the eductor outlet. The intermediate cavity serves as a second mixing zone, while the exit of the second diffuser serves as a third mixing area. 
     Another illustrated aspect of the claimed subject matter is a method for liquid/solid mixing. A liquid fluid acting as a motive flow passes through a nozzle into a void. The motive flow through the nozzle into the void creates a temporary vacuum, which permits the enhanced induction of a separate solid entrained into the motive flow external to the nozzle. The flat profile of the jet stream allows for improved entrainment of solids. A large turbulent region having turbulent intensity at minimal pressure loss is produced by the nozzle. This region of turbulence is conducive to mixing the motive flow and the induced solid. The motive flow carries the induced solid into the diffuser section. In each of the diffuser cavities, large eddy currents and recirculation mixing zones are created as velocity increases and boundary flow separation occurs. In these recirculation mixing zones and diffuser convergent sections, there exists areas of turbulent flow conducive to mixing. The mixed fluid is discharged from the diffuser unit. 
     Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  and  1   b  are views of a prior art nozzle. 
         FIGS. 2   a  through  2   d  are contours of volume fractions of solids through a prior art nozzle. 
         FIG. 3  is a computer-generated velocity profile of fluid through a prior art nozzle and downstream addition of a solid. 
         FIG. 4  is a back view of the inventive nozzle. 
         FIG. 5  is a cutaway side view of the inventive nozzle. 
         FIG. 6  is a front view of the inventive nozzle. 
         FIG. 7  is a cutaway side view of a mixing apparatus including the nozzle. 
         FIGS. 8   a  through  8   d  are contours of volume fractions of solid particles through the eductor. 
         FIG. 9  is a side view of the contour of volume fraction of solid particles through the eductor. 
         FIG. 10  is a computer-generated velocity profile of fluid through the inventive eductor with solid particles added downstream from the nozzle. 
         FIG. 11  is a side view of a prior art nozzle. 
         FIG. 12  is a front view of a prior art nozzle. 
     
    
    
     DETAILED DESCRIPTION 
     The claimed subject matter relates to a eductor  100  and a method for mixing liquids with solids. Referring to  FIG. 7 , the eductor  100  includes a nozzle  110 , an initial mixing chamber  150 , a hopper  154 , a first diffuser  160 , an intermediate mixing chamber  168 , and a second diffuser  170 . 
     Turning to  FIGS. 4-6 , three views of an embodiment of nozzle  110  are depicted. A motive flow is introduced into initial mixing chamber  150  through nozzle  110 . A nozzle inlet  112  is circular about a first axis  102  and has a nozzle inlet diameter  114 . In an entrance segment  116  of nozzle  110 , the inner surface  118  has an inner diameter  120 , which is equal to nozzle inlet diameter  114 . Nozzle  110  has a nozzle outlet  134 , wherein an upper outlet edge  136  is flat and a lower outlet edge  138  is semicircular. The upper and lower outlet edges  136  and  138  share common side points  142  and  144  and lower outlet edge  138  extends nozzle outlet height  146  from upper outlet edge  136  at the lowest point. The upper outlet edge  136  is offset from first axis  102  by an offset distance  140 . Between nozzle inlet  112  and nozzle outlet  134 , a first acceleration segment  122  is defined by a gradually reducing cross sectional area, wherein an upper portion  124  of inner surface  118  gradually flattens and slopes toward a plane that is offset distance  140  below first axis  102 , aligned with upper outlet edge  136 . In a second acceleration segment  128  of nozzle  110 , the radial length  130  between a lower portion  132  of the inner surface  118  and the first axis  102  also decreases to match the shape of the lower outlet edge  138 . 
     A standard round nozzle  200  may be incorporated into eductor  100  instead of nozzle  134 . As shown in  FIGS. 11 and 12 , round nozzle  200  has an outlet  210  that is circular about a nozzle axis  212 . When inert solids, such as bentonite, are mixed with a fluid, the semicircular nozzle  134  may be used. As will be discussed, when more active and partially hydrophilic solids, such as polymers, are added to a fluid, round nozzle  200  is preferred. 
     Returning to  FIG. 7 , initial mixing chamber  150  receives both motive flow and solid particles. The motive flow is received from nozzle outlet  134  or  210  through a chamber first inlet  152  while the solid particles are received from hopper  154  through a chamber second inlet  156 . A first mixing zone  220 , shown in  FIGS. 9 and 10 , is created within initial mixing chamber  150 . When semicircular nozzle  134  is used to direct fluid into initial mixing chamber  150 , first mixing zone  220  is more turbulent than when round nozzle  210  is used to direct fluid into the initial mixing chamber  150 . First mixing zone  220  often extends into chamber second inlet  156  when semicircular nozzle  134  is used, due to the fluid velocity created by nozzle  134 . For this reason, when active and partially hydrophilic solids are added to the motive flow, the round nozzle  210  is preferred to minimize the fluid entry to and the build up of solid particles within chamber second inlet  156 . When more inert solid particles are added to the motive flow, semicircular nozzle  134  may be used. 
     A chamber outlet  158  directs the initial mixture of motive flow and solid particles into the diffuser segments of the eductor  100 . Chamber outlet  158  is aligned with nozzle outlet  134 , thereby minimizing energy lost by the motive flow as the solid particles are received into initial mixing chamber  150  at an angle substantially normal to stream of the motive flow. 
     Chamber outlet  158  feeds the initial mixture into a first diffuser  160 . First diffuser  160  includes a first converging section  162  and a first diverging section  166 , between which is a first throat  164 . First throat  164  has an elliptical cross-sectional shape (not shown), consistent with the shape of the jet stream. The converging and diverging sections  162 ,  166  of first diffuser  160  serve to induce turbulence into the flow, enhancing the mixing of the motive flow and solid particles. 
     The first diverging section  166  feeds the initial mixture into intermediate mixing chamber  168 , which is in alignment with the first diffuser  160 . Within intermediate mixing chamber  168 , a second mixing zone  222 , shown in  FIGS. 9 and 10 , is created by eddies forming therein prior to the motive fluid and solid particles being directed further downstream. 
     From the intermediate mixing chamber  168 , the intermediate mixture is fed into a second diffuser  170 . The second diffuser  170  is similar to the first diffuser  160 , having a second converging section  172 , a second throat  174 , and a second diverging section  176 . Additional mixing is enhanced by the turbulence created by the second diffuser  170 . Downstream from second diffuser  170 , a third mixing zone  224  forms, as shown in  FIGS. 9 and 10 , causing additional mixing of the fluid and the solids. 
     Referring to the cross-sectional views of the flow through the eductor  100  shown in  FIGS. 8   a - 8   d , the extent of mixing at points throughout the eductor  100  may be seen.  FIG. 8   a  shows the contour of motive flow fluid  180  coming through the nozzle outlet  134  (shown in  FIG. 5 ). Such fluid is virtually solids-free and is denoted as reference  180  throughout this description. The addition of solids from hopper  154  to the motive flow is shown in  FIG. 8   b , with reference number  188  denoting a cross-sectional area that is primarily solids. It is understood by one skilled in the art that there may be a traces of solids in the fluid  180  throughout the eductor  100  while there may be traces of fluids in the areas that are primarily solids  188 . 
     For this description, additional increments of the mixture between the solids-free fluid  180  and the solids  188  are included. Reference  184  refers to a mixture, wherein the solids are effectively entrained in the fluid. Boundary layers of ineffectively mixed fluid  182  and ineffectively mixed solids  186  are also depicted. 
     In  FIG. 8   b , it can be seen that an area of effective mixing  184  has begun to form centrally between the solids-free fluid  180  and the solid particles  188 . A boundary layer of ineffectively mixed solids  186  is located around the area of effective mixing  184  while a boundary layer of ineffectively mixed fluid is located below the solids-free fluid  180 . 
     Referring to  FIG. 8   c , the areas of effective mixing  184  include the area toward the center of the cross sectional area and above the fluid stream  180  emanating from the nozzle  110 . Primarily solid particle streams  188  are present along the sides of the cross sectional area. Other boundary layers of effectively mixed fluid  184  are present at the top and bottom of the cross sectional area and around the solids-free fluid stream  180 . Boundary layers of ineffectively mixed solids  186  are present around the solid particle streams  188 . 
     Referring to  FIG. 8   d , the solids free fluid stream  180  has been elongated around much of the cross-sectional area. The solid particle stream  188  has merged into a single stream that is slightly off-center. A boundary layer of ineffectively mixed solids  186  surround the solid particle stream  188 . A ring of effectively mixed fluid  184  surrounds the ineffectively mixed solids  186 . A boundary layer of ineffectively mixed fluid  182  is between the boundary layer of effectively mixed fluid  184  and the solids-free fluid  180 . 
     Referring to  FIG. 9 , it can be seen more clearly that the solid particle stream  188  and the solids-free fluid stream  180  are mixed in the initial mixing chamber  150 . Downstream, the solids-free layer  180  gradually decreases in height and flows near the bottom of the eductor  100 . Further mixing eddies can be seen in intermediate mixing chamber  168 . 
     The computer-generated water velocity profile, shown in  FIG. 10 , has several ranges of fluid velocity depicted. Reference  190  depicts fluid velocity in the range of about 33.1 to 41.4 ft/sec. The range depicted by  190  includes the fluid flow out of nozzle  110  and through initial mixing chamber  150 . From the profile, it appears that the fluid velocity remains in this higher range until into first throat  164 . The velocity range depicted by reference  192  is about 24.9 to 33.1 ft/sec. The range shown by reference  192  is in a boundary layer around range  190  as well as in second throat  174 . Reference  194  shows fluid velocity in the range of 16.6 to 24.9 ft/sec. Range  194  is present in a boundary layer around range  192  and through first diffuser  160 , intermediate mixing chamber  168  and second diffuser  170 . The fluid velocity range depicted by  196  is in the range of 8.29 to 16.6 ft/sec, which is primarily in mixing eddies of the initial mixing chamber  150  and the intermediate mixing chamber  168 , as well as downstream of second diffuser  170 . Fluid velocity in the range of 0.0164 to 8.29 ft/sec. is shown as reference  198  and is in the area where solid particles are added at an angle at or nearly normal to direction of fluid flow from nozzle  110 . The slower fluid velocities  194 ,  196 ,  198  through first diffuser  160 , intermediate mixing chamber  168  and second diffuser  170  help enhance mixing of the liquid and solids by creating turbulence. 
     Test 
     A test was conducted using a variety of powdered materials representative of solids that would be mixed with base liquid to form a drilling mud. The same hopper was utilized with the exception that the mixing nozzles indicated were used. Bentonite, polyanionic cellulose, and XC polymer were each introduced to the base liquid through the various nozzles. Such particles are representative of other particles having the same or similar densities. 
     Rheological properties of the resulting drilling muds were measured and recorded. Such properties included fisheyes, yield point, and funnel viscosity. Fisheyes are known by those of skill in the art to be a globule of partly hydrated polymer caused by poor dispersion during the mixing process. The yield point is the yield stress extrapolated to a shear rate of zero. The yield point is used to evaluate the ability of a mud to lift cuttings out of the annulus of the well hole. A high yield point implies a non-Newtonian fluid, one that carries cuttings better than a fluid of similar density but lower yield point. The funnel viscosity is the time, in seconds for one quart of mud to flow through a Marsh funnel. This is not a true viscosity, but serves as a qualitative measure of how thick the mud sample is. The funnel viscosity is useful only for relative comparisons. The comparison of each of these rheological properties may be seen in Table 1 below: 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Rheological Properties 
               
             
          
           
               
                   
                 Fisheyes 
                 Yield Point 
                 LSRV 
                 Funnel Viscosity 
               
             
          
           
               
                   
                 Bentonite 
                 PAC 
                 XCD 
                 Bentonite 
                 PAC 
                 XCD 
                 XCD 
                 Bentonite 
                 PAC 
                 XCD 
               
               
                 Nozzle 
                 lb/100 bbl 
                 lb/100 bbl 
                 lb/100 bbl 
                 YP 
                 YP 
                 YP 
                 cp 
                 sec 
                 sec 
                 sec 
               
               
                   
               
               
                 Invention 
                  14 
                 66 
                 1.9 
                 6 
                 28 
                 11 
                 6,599 
                 31 
                 112 
                 35 
               
               
                 Prior Art 
                  22 
                 56 
                 0.1 
                 4 
                 26 
                 13 
                 3,399 
                 34 
                  86 
                 35 
               
               
                 #1 
               
               
                 Prior Art 
                 109 
                  2 
                 0.6 
                 4 
                 45 
                  7 
                 1,700 
                 18 
                 N/A 
                 33 
               
               
                 #2 
               
               
                 Lab 
                   
                   
                   
                 6 
                 57 
                 67 
               
               
                   
               
             
          
         
       
     
     As can be seen, the fisheyes in the mud made from bentonite mixed with the inventive nozzle weighed less per volume than that mixed with the prior art nozzles. Further, the mud yield point was higher than the mud mixed with the prior art nozzles. 
     Mechanical properties of the resulting drilling muds were also measured and recorded. These properties included mixing energy, pressure drop, motive flow, vacuum, and solids induction. 
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                   
               
               
                 Mechanical Fluid Properties 
               
             
          
           
               
                   
                   
                 Pressure 
                 Motive 
                   
                 Solids 
               
               
                   
                 Mixing Energy 
                 Drop 
                 Flow 
                 Vacuum 
                 Induction 
               
               
                 Nozzle 
                 kW/m3/hr 
                 psi 
                 gpm 
                 in of Hg 
                 lb/hr 
               
               
                   
               
               
                 Invention 
                  95 
                 49.2 
                 578 
                 26.6 
                 25,992 
               
               
                 Prior Art #1 
                 106 
                 55.7 
                 515 
                 21.5 
                 26,173 
               
               
                 Prior Art #2 
                 110 
                 57.3 
                 488 
                 16.5 
                 13,846 
               
               
                   
               
             
          
         
       
     
     From the table, it is seen that the eductor  100  can entrain nearly the same volume of solids per hour into the motive stream at a lower mixing energy than the prior art mixer. 
     A method of mixing solid particles with a motive flow includes introducing a motive fluid to an initial mixing chamber  150 . This may be done through the nozzle  110 , previously described. Inside initial mixing chamber  150 , a vacuum is created by the motive flow. Solids are introduced into initial mixing chamber  150  and are induced into the motive fluid by the vacuum that has been created. A region of turbulence is provided to initially mix the motive flow and the induced solids. The motive flow, now carrying the induced solids is diffused to further entrain the solid particles. The initial mixture is further mixed in an intermediate mixing chamber. The intermediate mixture is then diffused again to provide additional turbulence to enhance mixing. Prior to each diffusion, the mixture may be subjected to an increased flow rate by reducing the cross sectional area through which the mixture flows. 
     While the claimed subject matter has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the claimed subject matter as disclosed herein. Accordingly, the scope of the claimed subject matter should be limited only by the attached claims.