Abstract:
The application relates to a metering apparatus for introducing a powdery medium into a fluid, comprising a guide device for guiding the fluid and a metering device, said metering device being arranged above the guide device such that the powdery medium released by the metering unit is scattered onto the surface of the fluid.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2010/003224, filed May 27, 2010, which designated the United States and has been published as International Publication No. WO 2010/139418 and which claims the priority of German Patent Application, Serial No. 10 2009 023 546.9, filed May 30, 2009, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a metering apparatus for introducing a powdery medium into a liquid fluid. The invention also relates to a mixing system with a metering apparatus of this type for mixing a drilling fluid, as well as a method for introducing a powdery medium into a liquid fluid. 
     It is known to use a drilling fluid for supporting the drill feed when constructing ground drill holes and in particular horizontal drill holes. The drilling fluid is used to soften the ground in advance of the drill head of the drilling apparatus in order to improve the cutting performance of the drill head. The drilling fluid can also be used to lubricate the drill head and the drill rods, which are rotatably driven in the drill hole, so as to reduce friction with the ground. In addition, the drilling fluid can be used to flush out the soil removed by the drill head through the annular gap between the drill rod and the wall of the drill hole or through an annular gap of dual drill rods. 
     The drilling fluid is typically a mixture of water and bentonite, and sometimes several additives. Bentonite is a mixture of different clay materials, with the largest component being montmorillonite (generally with a content of 60% to 80%). Additional accompanying materials may be quartz, mica, feldspar, pyrite and sometimes also calcite. Due to the montmorillonite content, bentonite has strong water absorption and swelling capability. 
     Water into which bentonite is stirred can have thixotropic characteristics, so that it behaves like a fluid when in motion, but like a solid structure when at rest. Because of this behavior, a drilling fluid composed of water and bentonite can also be used for supporting the wall of the drill hole, thereby preventing a collapse. 
     The introduction of bentonite into water poses a particular challenge, because the bentonite has the tendency to lump together in contact with water. In the state-of-the-art, the drilling fluid is typically stirred in large storage vessels with dynamic mixing apparatuses and thereafter transported in batches to the construction site where the drilling fluid is to be used. However, such batch-wise mixing is quite cumbersome. In addition, after the drill hole has been completed, the unused portion of the last batch must be disposed of, which is complex and expensive. 
     Another conventional method and a corresponding mixing apparatus are known, which eliminate this disadvantage of batch-mixing of a drilling fluid. With this approach, the bentonite is introduced directly in the water in the region of a high-pressure pump, which is provided for transporting the drilling fluid through the drill rod to the drill head of a horizontal drilling apparatus, in order to take advantage of the turbulences produced in the water by the high-pressure pump for mixing the bentonite with the water. A swelling section can be arranged downstream of the high-pressure pump, where the bentonite-water-mixture is given time to swell before it is transported through the drill rod to the drill head. 
     Such method for continuous mixing of a drilling fluid and a corresponding continuous flow mixing system are disclosed in DE 199 18 775 B4. However, this document does not disclose the manner in which the powdery bentonite is actually introduced into the water. 
     Starting from the aforedescribed state-of-the-art, it was an object of the invention to provide an improved metering apparatus for introducing a powdery medium into a fluid, with which the problem associated with the powdery medium lumping together upon contact with the fluid, known from the state-of-the-art, can at least be reduced. According to the invention, a corresponding method and a mixing system for mixing a drilling fluid will also be described. 
     SUMMARY OF THE INVENTION 
     This object is attained with a metering apparatus for introducing a powdery medium into a fluid, which includes a housing, a guide device for guiding the fluid and forming a continuous flow of the fluid in the housing, wherein the fluid has a fluid surface, and a metering device arranged above the guide device and dispensing the powdery medium. The metering device is constructed to scatter the powdery medium onto the fluid surface. The obiect is also attained with a method for introducing a powdery medium into a fluid, with the steps of providing a continuous flow of the fluid. forming a fluid surface from a fluid film guided inside a housing, metering the powdery medium, and scattering the metered powdery medium onto the fluid surface by gravity. The obiect is further attained with mixing system for mixing a drilling fluid, which includes the claimed metering apparatus, a bentonite feed operatively connected with the metering device, a water feed operatively connected with the guide device, and a pump. 
     The core of the invention is directed to improving mixing of the powdery medium with the fluid by scattering the powdery medium onto the surface of the fluid in a metered form. Scattering the powdery medium onto the surface of the fluid results in a fine distribution of the individual particles of the powdery medium already at the time of the first contact with the fluid, thereby effectively preventing lumping. 
     In the context of the invention, “scattering” refers to dispensing the particles of the powdery medium from the metering device and/or applying the powdery medium on the fluid surface as finely distributed as possible. Scattering according to the invention can occur through gravity; however, pressure-aided dispensing, for example in conjunction with compressed air or other auxiliary means for accelerating a particle may also be included in the term “scattering” according to the invention. However, a combination of gravity-fed and pressure-aided scattering is also feasible. 
     A particularly fine distribution of the powdery medium on the fluid surface can be achieved with a continuous flow of the fluid through the guide device, as is the case, for example, in a continuous flow mixing apparatus for producing a drilling fluid. 
     According to the invention, the distribution of the powdery medium in the fluid can advantageously be further improved by designing the guide device below the metering unit so that a fluid film is created with a width that is a multiple of its depth. With this configuration of the metering apparatus according to the invention, the powdery medium can already be so finely distributed on or in the fluid that complex mixing with static or dynamic mixing units may no longer be necessary. 
     Advantageously, the metering apparatus according to the invention may be provided with a pump; this particularly applies when a metering apparatus according to the invention is integrated in a continuous flow mixing system for a drilling fluid, wherein a pump is typically already installed for transporting the mixed drilling fluid through a drill pipe to a drill head. 
     According to the invention, the metering device may form a metering gap, with which the powdery medium can be distributed over a large-area on the fluid surface. With the metering apparatus according to the invention, the metering gap may advantageously have a length which corresponds substantially to the width of the guide device. The powdery medium can thus be scattered according to the invention over the entire surface of the fluid film. 
     In a preferred embodiment of the metering apparatus according to the invention, the metering gap may be formed by a (first) metering roller and a corresponding counter element. By providing a metering roller, the powdery medium can be continuously dispensed even if the metering gap is very small; the metering roller(s) may dissolve lumps of the powdery medium, thereby preventing clogging of the metering gap. With the rotating motion of the metering roller, a fine film of the powdery medium can be formed and pushed through the metering gap. This may cause the film of the powdery medium to adhere to the surface of the metering roller. The metering roller may have a suitably formed (e.g. roughened) surface which aids a continuous formation of a film of the powdery medium on the surface of the metering roller. 
     To detach a film of the powdery medium adhering to the surface of the metering roller, so that this film may be scattered according to the invention on the fluid surface, the film may be detached from the surface of the metering roller with a stripping element. 
     In another preferred embodiment of the metering apparatus according to the invention, the counter element may also be constructed as a (second) metering roller. In this way, a particularly fine film of a powdery medium can be obtained on the surface of one or both metering rollers. This applies particularly to the preferred embodiment of the metering apparatus according to the invention, wherein the two metering rollers are driven for rotation in the same direction, forming opposing tangential velocity components in the metering gap. 
     In another embodiment, the metering gap may be formed by two plates facing each other, preferably with a conical orientation. The two conically oriented opposing plates may form an intermediate reservoir in form of a funnel and thus enable very finely metered dispensing of the powdery medium, which can then be scattered on the fluid surface. 
     Clogging of the metering gap formed by the plates by lumps that may be present in the powdery medium can be prevented by moving the plates cyclically with a drive in opposing directions. The finely metered powdery medium can then be continuously dispensed. The direction of the cyclical relative movement of the two plates may preferably be parallel to the gap, because the gap width is then not changed in spite of the relative movement of the flaps. However, it will be understood that other movement directions are also feasible. 
     According to another preferred embodiment of the metering apparatus according to the invention, a metering brush may be provided to further separate and, if desired, also accelerate the particles of the powdery medium. In particular, the metering brush may be constructed as a roller, with a rotation of the roller-shaped metering brush enabling a continuous motion. For example, the metering brush may be provided to brush off a film of the powdery medium formed on a metering roller, whereby the particles are scattered in finely metered form on the liquid surface. 
     In a preferred embodiment of the metering apparatus according to the invention, the powdery medium may be supplied to the metering device with a feed screw. It will be understood that other feed devices may also be used, for example a funnel, through which the powdery medium can be gravity-fed to the metering device. 
     The metering apparatus according to the invention is particularly suited for introducing bentonite into an aqueous fluid and in particular into (pure) water. 
     The method according to the invention for introducing a powdery medium into a fluid is characterized in that the powdery medium is scattered on the fluid surface in metered form. 
     A mixing system according to the invention for mixing a drilling fluid includes a metering apparatus according to the invention as well as a bentonite feed operatively connected with the metering device of the metering apparatus, a water feed operatively connected with the guide device of the metering apparatus according to the invention, as well as a pump. 
     Preferably, the pump of the mixing system according to the invention may be a high-pressure pump, enabling the construction of a continuous flow mixing system, because a high pressure pump generates a pressure that is sufficient for transporting the drilling fluid through a hollow drill pipe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention will now be described in more detail with reference to exemplary embodiments illustrated in the drawings. 
       The drawings show in: 
         FIG. 1  in an isometric view, the front side of a metering apparatus according to the invention in a first embodiment; 
         FIG. 2  in an isometric view, the rear side of the metering apparatus of  FIG. 1 ; 
         FIG. 3  in an isometric view, a detailed view of a mixing swing arm used with the metering apparatus according to  FIG. 1 ; 
         FIG. 4  in an isometric view, a detailed view of the stripper used with the metering apparatus according to  FIG. 1 ; 
         FIG. 5  the stripper of  FIG. 4  in a disassembled state; 
         FIG. 6  in an isometric view, a detailed view of the water inlet of the metering apparatus according to  FIG. 1 ; 
         FIG. 7   a  in a side view, the water inlet of  FIG. 6  in a first operating position; 
         FIG. 7   b  in a side view, the water inlet of  FIG. 6  in a second operating position; 
         FIG. 8  in an isometric view, a detailed view of the mixed material outlet of the metering apparatus according to  FIG. 1 ; 
         FIG. 9  in an isometric view, a metering apparatus according to the invention in a second embodiment; and 
         FIG. 10  in an isometric view, a metering apparatus according to the invention in a third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a first embodiment of a metering apparatus according to the invention in an isometric view. The metering apparatus includes a housing  1 , a funnel  2  for a powdery medium, in particular a bentonite, detachably connected with the housing  1 , a water inlet  3  and a mixed material outlet  4 . 
     The housing  1  which is accessible, as illustrated in  FIG. 1 , by disassembling a side wall, surrounds the individual elements of the metering device of the metering apparatus according to the invention. The metering device includes a large metering roller (transport roller  5 ), a small metering roller  6 , a brush roller  7  and a stripper  8 . The transport roller  5  and the smaller metering roller  6  are positioned with respect to each other so as to form a small gap therebetween. A side face of the stripper  8  adapted to the shape of the envelope of the transport roller rests against the transport roller and is otherwise wedge-shaped. The brush roller  7  is arranged such that the tips of the brushes contact a section of the stripper  8 . 
     The transport roller  5 , the metering roller  6  and the brush roller  7  are connected via drive shafts with electric drives that are flanged to the rear side of the housing  1  (see  FIG. 2 ). The electric drives each include an electric motor  9  and a gear  10  for imparting a rotation on the transport roller  5 , the metering roller  6  and the brush roller  7 . The transport roller  5  and the metering roller  6  share an electric drive which operates on the driveshaft of the transport roller  5 . The drive power of this electric drive is partially transmitted from the driveshaft of the transport roller  5  by way of a toothed belt  11  to the drive shaft of the metering roller  6 . The transport roller  5  and the metering roller  6  then have identical rotation directions. 
     The metering apparatus illustrated in  FIG. 1  operates as follows: the powdery medium (bentonite) is stored in the funnel  2  and fed to the metering device arranged in the housing  1  through a metering opening disposed in the bottom of the funnel. The bentonite powder thereby drops into an intermediate space  12  which is delimited, on one hand, by the upper halves of the transport roller  5  and the metering roller  6  and, on the other hand, by the sidewalls of the housing  1 . The bentonite powder is temporarily stored in this intermediate space  12 . A small quantity of the temporarily stored bentonite powder is transported onward with the transport roller  5  through the gap formed between the transport roller  5  and the metering roller  6 . This occurs in form of a bentonite film forming on the surface of the transport roller  5 , with the thickness of the formed film corresponding approximately to the thickness of the gap between the transport roller  5  and the metering roller  6 . The bentonite film is detached again from the surface of the transport roller  5  below the gap formed by the transport roller  5  and to metering roller  6  by using the wedge-shaped stripper  8 , whereafter the bentonite powder is captured by the brushes of the brush roller  7  and accelerated towards the bottom side of the housing  1 . The brush roller  7  thus causes substantial separation of the particles of the powdery bentonite, whereby the bentonite is scattered onto the surface of a water film flowing below. 
     For forming the water film, the water (or another fluid to be mixed with the powdery medium) is discharged through the water inlet  3  and a slit-shaped outlet opening  25  formed in the water inlet  3  (see  FIG. 6 ). The slit-shaped metering opening  13  has a width that substantially corresponds to the interior width of the housing  1 . The water then flows along the surface of the inclined bottom plate  14  of the housing  1 ; the water is hereby mixed with the bentonite powder according to the invention. The bentonite-water mixture is then discharged from the metering apparatus through the mixed material outlet  4 . 
       FIGS. 3 to 6  show the structural details of several components of the metering apparatus according to  FIG. 1 . 
       FIG. 3  shows the individual elements of a mixing swing arm used with the metering apparatus according to  FIG. 1 . The mixing swing arm has a rectangular mixing element  15  made of a wire, which substantially prevents bridge or chimney formation of the bentonite powder in the funnel  2  through a cyclical pivoting motion inside the funnel  2 . The cyclical pivoting motion of the mixing element  15  is implemented with an eccentric drive. The eccentric drive includes a Y-shaped swing arm  16  having two fingers which cooperate by way of an adjustable roller  17  with an excenter ring  18  which is in turn connected with the driveshaft of the transport roller  5 . An eccentric segment of the excenter ring  18  operates alternatingly with a phase shift of 180° on a respective one of the adjustable rollers  17  of the fingers of the swing arm  16 , causing alternatingly deflection of the swing arm  16  in both directions in the course of one revolution of the excenter ring  18  or the driveshaft of the transport roller  5 . The cyclical deflection of the swing arm  16  is transmitted to the mixing element  15  via a swing shaft  19 . 
       FIGS. 4 and 5  show details of the stripping device of the metering apparatus according to  FIG. 1 . The wedge-shaped stripper  8  is connected by way of a shaft  20  with a lever  21  which due to its weight produces a torque about the shaft  20 ; the wedge-shaped stripper  8  is thereby pressed with a substantially constant pressing force against the transport roller  5 . The wedge-shaped stripper  8  is subjected to increased wear due to the direct contact with the rotating transport roller  5 . To cause mainly the wedge-shaped stripper  8  and not the transport roller  5  to be worn down, the stripper  8  is preferably made of plastic, whereas the transport roller may be made of steel. A potentially required exchange of the wedge-shaped stripper  8  due to wear may be performed without using a tool by way of a simple plug connection, as illustrated in  FIG. 5 . To this end, the stripper  8  has a groove  22  and can be placed on a corresponding spring element  23  (with a rectangular cross section) connected with the shaft  20 . To prevent unintentional detachment of the stripper  8 , the connection between the stripper  8  and the spring element  23  may be formed as a clamping (force-locked) connection. 
       FIG. 6  shows the details of the water inlet  3  of the metering apparatus according to  FIG. 1  in an isometric view. The water inlet  3  includes a tube  24  which is closed off on one side and extends with the closed end into the housing  1 . In the section extending into the housing  1 , the tube  24  has a slit-shaped outlet opening  25 , wherein the width of the outlet opening  25  can be varied with a closure element  26  that is movable on the tube in the circumferential direction. To this end, the closure element  26  has two longitudinal openings  27 , with two screws  28  connected with the tube  24  extending through the openings  27 . The closure element  26  can be moved relative to the tube  24  within the limits defined by the size of the longitudinal openings  27 , allowing the width of the outlet opening  25  to be varied. The tube  24  and the closure element  26  are each provided with a guide plate  29  for deflecting the flow of the exiting water into the desired direction.  FIG. 7   a  shows a position of the closure element  26  wherein the width of the slit-shaped outlet opening  25  is very small, allowing only a small amount of water to be discharged (small arrow). Conversely,  FIG. 7   b  shows a position of the closure element  26  with a wide outlet opening  25  and consequently greater water discharge (large arrow). Alternative to the manual adjustment, the closure element  26  may also be adjusted, for example, electrically, electromagnetically, pneumatically and/or hydraulically, wherein the adjustment may be initiated manually or may occur automatically, depending on the required quantity of water. 
       FIG. 8  shows the mixed material outlet  4  through which the mixed material, i.e., the bentonite-water-mixture, is discharged from the metering apparatus. The mixed material outlet  4  includes a substantially vertical tube  30  (in the operating position of the metering apparatus illustrated in  FIG. 1 ), wherein a total of eight guide plates  31  which are oriented in the longitudinal direction of the first tube are arranged on the interior side of the tube  30 . The bentonite-water mixture entering the mixed material outlet  4  from above flows downward along the guide plates  31  through the first tube  30 , where it enters in a second, substantially horizontal tube  32  (in the operating position of the metering apparatus illustrated in  FIG. 1 ) of the mixed material discharge  4 . A calming zone  33  for the mixture is thereby formed in the region of the transition from the first tube  30  to the second tube  32 . The configuration of the mixed material outlet  4  with the guide plates  31  arranged inside the first tube  30  and of the calming zone  33  at the transition from the first tube  30  to the second tube  32  produces a substantially bubble-free bentonite-water mixture. 
       FIG. 9  shows an alternative embodiment of a metering apparatus according to the invention. This metering apparatus corresponds in principle substantially to the metering apparatus of  FIG. 1 , and therefore has a transport roller  105 , a metering roller  106  and a brush roller  107  which are arranged inside a closed a housing  101  and are driven by electric drives. Unlike the metering apparatus of  FIG. 1 , the embodiment according to  FIG. 9  does not include a funnel for storing the bentonite powder and introducing the bentonite powder into the metering device in metered form; instead, the metered bentonite powder is fed with a metering screw  134 .  FIG. 9  shows clearly the formation of the very thin water film on the top side of the inclined bottom plate  114  of the housing. 
       FIG. 10  shows another alternative embodiment of a metering apparatus according to the invention, wherein the particles of the bentonite powder are separated based on a principle that is different from the principle of the metering apparatuses according to  FIG. 1  and  FIG. 9 . Like in the metering apparatus according to  FIG. 9 , the bentonite powder in the metering apparatus according to  FIG. 10  is fed with a metering screw  134 , whereafter the bentonite powder drops into an intermediate space  212  with a tapered-down cross-section, where the bentonite powder is temporarily stored. The intermediate space  212  is formed by two (angled) metering plates  235  which are inclined relative to each other, with the lower edges of the to metering plates  235  forming a narrow gap through which the bentonite powder trickles (i.e., is scattered) on the water film flowing below (according to the principle of an hourglass). 
     For forming the water film, the water is fed via an inlet tube  236  having an (unillustrated) slit-shaped opening and a width that corresponds substantially to the width of the housing  201  of the metering apparatus. The inlet tube  236  may, like the water inlet  3  of  FIG. 1  or  FIG. 6 , include an adjustable opening. The water exiting the slit-shaped opening flows in form of a thin film along the inclined bottom plate  214  of the housing  201  where it is mixed with the bentonite powder falling down from the metering unit. The bentonite-water mixture is then discharged from the metering apparatus through an outlet tube  237 . 
     To support a continuous discharge of the bentonite powder through the gap formed by the metering plates  235 , the two metering plates  235  are moved cyclically relative to one another (with opposite phases), as shown in  FIG. 10  by the arrows. The movement directions of the two metering plates  235  are parallel to the gap formed by the metering plates  235 . The cyclical movements of the metering plates  235  are generated by an electric motor  238  which is connected with the respective metering plate  235  by way of a drive disk  239  and a plunger  240  which is eccentrically mounted on this drive disk. 
     The structural and functional details of the aforedescribed exemplary embodiments cannot only be applied in the respective actually disclosed combination, but can be applied in any combination also with other embodiments according to the invention.