Abstract:
The present invention is directed to an apparatus and method for accurately metering and conveying a dry powder or granular material to a blender in a substantially closed system. The apparatus includes a storage tank adapted to hold the dry powder or granular material, a hopper disposed inside of the storage tank; and a conveyor at least partially disposed inside of the storage tank, which delivers the dry powder or granular material to the hopper. The apparatus also includes a metering feeder adapted to deliver the dry powder or granular material at a substantially uniform density from the hopper to a blender located outside of the storage tank. The apparatus is a substantially closed system, thus minimizing the risk that the dry powder or granular material will become airborne.

Description:
BACKGROUND  
       [0001]     The present invention relates generally to apparatuses and methods for metering and conveying dry powder or granular materials to a blender, and more particularly to an apparatus and method for accurately metering and conveying dry powder or granular materials to a blender in a substantially closed system.  
         [0002]     In conventional oil field operations, dry powder and granular materials are transported in sacks to the well location. The sacks are then manually moved to a metering feeder mounted on a fluid blending device. The metering feeder has a hopper to collect the dry powder or granular material and to serve as a reservoir. The hopper is kept full by opening sacks of the dry powder or granular material and dumping them into the hopper. The amount of dry powder or granular material must be kept at a constant level in the hopper so as to maximize the accuracy and repeatability of the metering feeder. The accuracy and repeatability of the metering feeder is dependent on having a constant material bulk density at the screw auger.  
         [0003]     Fluctuating levels of powder or granular material in the hopper can alter the bulk density of the material, and thus negatively affect the desired quality of the oil field service fluid. However, it is difficult to maintain a constant feed of material to the hopper when the hopper is being filled manually. Thus, the drawback of such systems is that there is a likelihood the hopper will be either overfilled in which case dry powder or granular material is spilled, or underfilled in which case the bulk density will be altered, which in turn will reduce the quality of the oil field service fluid. In the case where the dry powder or granular material is spilled, material is lost and clean up is necessary, which translates into lost revenue. This method also generates a lot of dust since the hopper is open to the outside air.  
         [0004]     Alternate methods have been proposed, which also have drawbacks of their own. One such method is to transport the dry powder or granular material to the well location in a large bulk tank and to convey the material pneumatically or mechanically to the metering feeder on the fluid blending device. This method, however, requires the conveying device to be controlled either automatically with level sensors and control loops, or manually in order to keep the dry powder or granular material at a constant level in the metering hopper for maximum accuracy and repeatability. Vehicle roading and equipment vibrations tend to compact the powder or granular material and cause significant variations in the bulk density of the material which affects the accuracy and repeatability of the metering feeder. This process is also labor intensive, susceptible to sensor failures and likely to generate dust.  
       SUMMARY  
       [0005]     The present invention is directed to an apparatus and method that eliminates or at least minimizes the drawbacks of conventional dry powder and granular material metering and conveying systems.  
         [0006]     In one embodiment, the present invention is directed to an apparatus for accurately metering and conveying a dry powder or granular material to a blender. The apparatus comprises a tank adapted to store the dry powder or granular material, a hopper disposed inside of the tank, and a conveyor that delivers the dry powder or granular material from the tank to the hopper in a substantially enclosed environment. The apparatus further comprises a metering feeder disposed at least partially within the tank and adapted to deliver the dry powder or granular material from the hopper to the blender at a substantially uniform density.  
         [0007]     In another aspect, the present invention is directed to a method of accurately metering and conveying a dry powder or granular material to a blender comprising the steps of storing the dry powder or granular material in a tank; metering dry powder or granular material out of the tank to the blender at a substantially uniform density with a metering feeder; and supplying the metering feeder with dry powder or granular material in a substantially enclosed environment.  
         [0008]     The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the exemplary embodiments, which follows.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, which:  
         [0010]      FIG. 1  is a schematic diagram of an apparatus for accurately metering and conveying a dry powder or granular material to a blender in accordance with the present invention.  
         [0011]      FIG. 2  is a schematic diagram of an alternative embodiment of an apparatus for accurately metering and conveying a dry powder or granular material to a blender in accordance with the present invention.  
     
    
     DESCRIPTION  
       [0012]     The details of the present invention will now be described with reference to the accompanying drawings. Turning to  FIG. 1 , an apparatus for accurately metering and conveying a dry powder or granular material  1  in accordance with the present invention is shown generally by reference numeral  10 . The apparatus  10  comprises a bulk material tank  12 , which is generally cylindrical or rectangular in shape in its upper portion and generally funnel shaped in its lower portion. The bulk material tank  12  is generally a closed container. It has a sealable opening (not shown) for injecting dry powder or granular material into the tank and an outlet for discharging the dry powder or granular material, which is described in more detail below. The bulk material tank  12  is designed to be mobile, i.e., to be transportable to a work site, such as an oil and gas well, for example.  
         [0013]     The apparatus  10  further comprises a conveyor  14 , which has a horizontal section  16  attached at the base of the bulk material tank  12  and a vertical section  18 , which couples to the horizontal section  16  at a junction box  20  located outside of the bulk material storage tank. In one certain embodiment, the horizontal and vertical sections  16 ,  18  of the conveyor  14  are screw augers, e.g., Martin Sprocket and Gear—Type 1 Super Screw Conveyor. In another embodiment, the vertical section  18  is a bucket elevator, e.g., Martin Sprocket and Gear—Series 100. The vertical section  18  of the conveyor  14  comprises a chute  22  for directing the dry powder or granular material  1  into a hopper  24  described in more detail below.  
         [0014]     In one certain embodiment, the conveyor  14  is an enclosed and sealed structure. In this embodiment, the dry powder or granular material being transported by the conveyor  14  is not exposed to the outside environment. This is accomplished by forming the conveyor  14  with an outer housing that surrounds the augers or other conveying mechanisms and sealing the areas where the conveyor attaches to the bulk material tank  12  with elastomeric O-rings, brazing or other similar means. Alternatively, the outer housing of the conveyor  14  is integrally formed with the housing of the bulk material tank  12 . In such an embodiment, the horizontal and vertical sections  16  and  18  are also sealed to the junction box  20  in much the same way, i.e., either by employing elastomeric seals, brazing or integral formation. As those of ordinary skill in the art will appreciate, alternate ways of enclosing and sealing the conveyor  14  may be employed. Those of ordinary skill in the art will also appreciate that the objectives of the present invention will be substantially met even if the conveyor  14  is not completely enclosed and sealed. Furthermore, those of ordinary skill in the art will also recognize that the conveyor  14  may be any known volumetric or mass conveyor system.  
         [0015]     Turning to the hopper  24 , it is essentially an open container, which temporarily collects the dry powder or granular material  1  and feeds it to metering feeder  26 . The hopper  24  is mounted in the upper cylindrical portion of the bulk material tank  12 . The hopper  24  is mounted above the fill line of the dry powder or granular material  1  in the tank and preferably as close to the top of the bulk material tank  12  as possible. The hopper  24  is open on the top to receive the dry powder or granular material  1  being ejected from the chute  22 . In one certain embodiment, the hopper  24  is an Acrison Model  140 . However, as those of ordinary skill in the art will appreciate, other devices may be used to temporarily collect the dry powder or granular material  1  and feed it to the metering feeder  26 .  
         [0016]     The metering feeder  26  is provided for metering the dry powder or granular material I out of the bulk material tank  12 . In one certain embodiment, the metering feeder  26  is a high tolerance screw feeder that is capable of metering precise volumes of dry powder or granular material. In one embodiment, the metering feeder  26  is an Acrison Model 140. However, as those of ordinary skill in the art will appreciate, other similar precise metering devices can be employed. The metering feeder  26  is preferably attached to the base of the hopper  24 . As can be seen from the figure, metering feeder  26  is partially disposed inside of the bulk material tank  12  and partially outside of the tank. Like conveyor  14 , metering feeder  26  is also preferably enclosed and sealed. Metering feeder  26  comprises a chute  28 , which operates to discharge the dry powder or granular material  1  from the bulk material tank  12 . In certain embodiments, the metering feeder  26  discharges the dry powder or granular material  1  into mixing blender  30  for further processing. That is the case in oil and gas well applications. In one such application, the dry powder or granular material  1  is a ground guar or guar-derivative bean and is used in forming a completion gel. In another application, the dry powder or granular material  1  is any one or more of the dry components used in forming a downhole cement slurry. As those of ordinary skill in the art will recognize, however, the dry powder or granular material  1  may be any material and used in any application requiring one or more material components in a dry powder or granular form.  
         [0017]     The apparatus  10  may optionally be provided with a vibrator, agitator system or other similar device  32  designed to assist gravitational force inducing dry powder or granular material  1  into the conveyor  14 . The vibrator  32  is preferably secured at or near the bottom of the bulk material tank  12 , as shown in the figure.  
         [0018]     The operation of the apparatus  10  will now be described as follows. First, the horizontal section  16  of the conveyor  14  draws dry powder or granular material  22  from the base of the bulk material tank  12  and conveys it to the junction box  20 , as shown by the large arrow in the figure. Because the dry powder or granular material  1  is drawn from the bottom of the bulk material tank  12 , it has a tendency to clump together (densify) due to compacting. The rotational movement of the auger, however, breaks up (loosens) these clumps and thereby returns the material to its original powder or granular state.  
         [0019]     The vertical section  18  of the conveyor  14  then transports the dry powder or granular material  1  from the junction box  20  to the hopper  24  through chute  22 , as again indicated by the large arrow in the figure. The conveyor  14  is designed and operated to convey the dry powder or granular material  1  to the hopper  24  at a bulk rate that exceeds the maximum rate at which the metering feeder  26  is capable of transporting the dry powder or granular material out of the bulk material tank  12 . Because the hopper  24  is located above the fill line of the dry powder or granular material in the bulk material tank  12 , the overflow of the dry powder or granular material  1  being delivered to the hopper by the conveyor  14  spills back into the tank. Therefore, the hopper  24  continuously overfills and spills over. The excess powder or granular material is then recycled back to the conveying system while the hopper  24  remains at a consistent powder or granular level and consistent material density. Any dusting is confined to the bulk material tank  12 .  
         [0020]     The metering feeder  26  then meters the dry powder or granular material  1  out of the bulk material tank  12  in very precise volumetric amounts. Because the dry powder or granular material  1  is in a powder or granular state when it is fed into the metering feeder  26  and the hopper  24  is always kept full so that a constant volume of dry powder or granular material  1  is always being drawn by the metering feeder  26 , the apparatus  10  is capable of delivering the dry powder or granular material  1  out of the bulk material tank  12  at a substantially uniform density. Also, because the apparatus  10  is substantially closed, i.e., it is only open at the discharge chute  28 , the apparatus is able to deliver the dry powder or granular material  1  to mixing blender  30  substantially dust free.  
         [0021]     In an alternate embodiment according to the present invention, the vertical section  18  of the conveyor  14  is disposed completely outside of the bulk material tank  12 , as shown in  FIG. 2 . In this embodiment, the metering hopper  24  is disposed above the rest of the bulk material tank  12 , so that the dry powder or granular material is permitted to overflow into the main portion of the tank. In this embodiment, the top of the bulk material tank  12  housing has a raised section for accommodating the hopper  24 . This design permits the bulk material tank  12  to be filled virtually to the top and, thus maximize the storage capacity of the tank, while at the same time achieving the benefits of the present invention.  
         [0022]     Therefore, the present invention is well-adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While the invention has been depicted, described, and is defined by reference to exemplary embodiments of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. The depicted and described embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.