Abstract:
An apparatus and method is disclosed to automatically maintain a desired back pressure on a slurry to facilitate the proper operation of pumping equipment and to eliminate or diminish scaling or other buildup in piping and related equipment.

Description:
FIELD OF THE INVENTION 
     The present invention provides an apparatus and method for dispensing a slurry and facilitates the prevention of scaling or sedimentation in feed lines. While specific problems encountered in the dispensing of a lime slurry are discussed, the invention should be understood to apply to the dispensing of slurries generally. 
     BACKGROUND OF THE INVENTION 
     Slurries are used industrially for a variety of applications. By way of example, the physical properties of slurries may be utilized for polishing various industrial surfaces. Alternatively, chemical properties of a slurry may be important in applications such as waste treatment or water purification. In general terms, slurries are created by mixing solids, such as a powder, with liquids. While solvation may occur, typically slurries include particles of a solid suspended or present throughout the liquid phase. 
     The presence of the solid particles typically associated with slurries creates numerous processing challenges, particularly with pumping and flow through piping. For example, solid particles from the slurry may be abrasive and prone to settling out of the liquid phase when not constantly agitated or maintained at certain minimal velocities in processing systems. Abrasiveness can cause excessive wear on the components of a particular process. The settling out of various particles can clog piping as well as various instruments and components of a piping system. 
     Because of the abrasive nature of a typical slurry, positive displacement pumps are frequently utilized for pumping operations. Compared to other type of pumps available, positive displacement pumps offer enhanced pump life when using abrasive slurries. An undesirable consequence, however, of utilizing positive displacement pumps for the delivery of slurry is frequently a pulsing output pressure and/or velocity. The fluctuating changes in pressure and velocity may frequently result in undesirable settling of solid particles. This problem may be exacerbated as the diameter of output piping is decreased or the length of travel between the positive displacement pump and delivery point is increased. Furthermore, a back pressure generally must be maintained against a positive displacement pump to ensure its proper operation. Otherwise, slurry may be undesirably siphoned through the pump or clogging of the pump may occur. 
     Lime is a substance having a variety of useful applications. For example, as set forth in U.S. Pat. No. 5,277,491, which is incorporated in its entirety herein by reference, lime may be used to treat drinking water and waste water. The addition of lime can increase the alkalinity of water that has an undesirably low pH. Frequently, slurries created with lime and water are used for the delivery and application of the lime. Such lime slurries offer material handling challenges in addition to those discussed above with regard to slurries generally. 
     For example, to maintain a back pressure against a positive displacement pump being used to meter a slurry, a fluid such as water may be introduced under pressure at or near the discharge of the pump. While water under pressure can maintain the desired back pressure against the pump, with lime slurries undesirable scaling or calcification may occur as the water reacts with the lime in the slurry from the pump. The amount and rate of scaling will vary depending upon the pH and content of the water and lime slurry being used. For some applications, periodic maintenance may be required to remove the scale from certain equipment such as the piping or tubing being used to delivery the slurry. In addition, due to the possibility of problems with scaling, calcification, or other build-up, it was previously believed that piping or tubing with diameters smaller than approximately ¾ inches could not be used without undue problems. Undesirable limitations on the lengths of piping or tubing to transport lime slurry were also observed in an effort to minimize the effect of the build-up. 
     SUMMARY OF THE INVENTION 
     In accordance with one form of the present invention, there is provided an apparatus or process for delivery of a slurry. In certain embodiments, the present invention allows for slurry delivery over greater distances and allows the use of piping or tubing having smaller diameters than was previously believed acceptable. By way of example only, with the present invention, piping and tubing diameters of approximately ⅜″ have been successfully tested with lime slurries. In addition, feed lines over 800 feet long have been successfully tested for lime slurries with the present invention. The frequency of maintenance previously required to remove buildup in equipment has been substantially reduced or even eliminated. 
     In accordance with one exemplary embodiment of the invention, a tank is provided for receiving the slurry. The tank has an outlet for release of the slurry and an agitator associated with the tank for providing agitation to the slurry. A conduit is provided in fluid communication with outlet of the tank and is used for delivering slurry from the tank to a pump. The slurry is pumped from the tank to a flexible member that has an interior surface in contact with slurry passing through the flexible member. The flexible member also has an exterior surface. The flexible member is located in a housing and together the flexible member and housing form a chamber for the receipt of a gas. The chamber receives gas for applying a pressure upon the exterior surface of the flexible member. The pump may be a positive displacement pump. The conduit may be inclined upwardly from the outlet of the tank to help maintain agitation of the slurry in the conduit. More specifically, the conduit may be inclined at an angle of at least 30 degrees from horizontal. Rubber may be used as a material of construction for the flexible member. 
     In another exemplary embodiment of the present invention, a vessel is provided that contains a slurry. The vessel has an opening for the flow of the slurry from the vessel to a pump. The pump has an inlet and an outlet. Means are provided in fluid communication with the pump and are adapted for using a gas to apply a pressure against slurry flowing from the outlet of the is pump. A conduit may be connected to the opening of the vessel to connect the vessel to the inlet of the pump. The conduit may be inclined upwardly from the opening of the vessel. An agitator may be provided with the vessel for agitating the contents of the vessel. 
     In still another embodiment, a tank is provided for receipt of the slurry. The tank has an upper portion and a lower portion. A lower portion has an outlet which is connected to a pump by a conduit. The conduit has an initial portion that is inclined upwardly from the point where the conduit connects to the outlet of the tank. An expandable member is provided that is in fluid communication with the pump. The expandable member has an interior surface forming a channel through which slurry flows and also has an exterior surface. The expandable member is configured so as to provide a back pressure on slurry being delivered from the pump. The expandable member may be received into a housing so as to form a chamber between the housing and the expandable member. Gas may be held in the chamber and used to apply pressure to the exterior surface of the expandable member. Means may be provided for monitoring the pressure of the gas in the chamber, and the tank may be equipped with an agitator for agitating the contents of the tank. Such agitator may include one or more propellers. The conduit may have a portion that is inclined upwardly from the outlet of the tank at an angle of at least 30 degrees or more from the horizontal. 
     In another embodiment of the present invention, there is provided a process for delivering a slurry. The process includes applying slurry to a pump. The pump has an inlet and an outlet. Slurry is discharged from the outlet of the pump to a flexible element that expands or contracts so as to provide a back pressure against the slurry discharging from the outlet of the pump. Pressure may be applied to the exterior surface of the flexible element using a gas. The amount of expansion and contraction of the flexible element due to changes in the slurry being fed through the flexible element may be adjusted by adjusting the pressure of the gas. In certain embodiments, the pump may be a positive displacement pump. Rubber may be used as a material of construction for the flexible element. After feeding the slurry through the flexible element, the slurry may be further transported for treatment, use, or storage. 
     In still another embodiment of the present invention, there is provided a process for dispensing a slurry that includes agitating the slurry within a vessel having an outlet. The slurry is fed from the outlet of the vessel using a pump that has an inlet and a discharge. The slurry is then pumped to means for using a gas to apply pressure back against the discharge of the pump. The slurry is then delivered to a desired application. 
     In still another exemplary embodiment of the present invention, there is provided a process for dispensing a slurry from a vessel to a remote location where the slurry may be stored, treated, or applied. The process includes pumping the slurry from the vessel using a pump. The slurry is then fed through a flexible member that is located downstream from the pump and configured for applying pressure to the pumped slurry. The size of the flexible member is then automatically adjusted in order to maintain a back pressure on slurry discharging from the pump. The slurry from the flexible member is then supplied to the remote location. The slurry may be agitated while present in the vessel. 
     These and other embodiments, features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments, or portions thereof, of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic representation of an embodiment of an apparatus forming a part of the present invention. 
     FIG. 2 is a partially exploded view of an embodiment of an apparatus forming a part of the present invention. 
     FIG. 3 is a partial sectional side view of an embodiment of an apparatus forming a part of the present invention. 
     FIG. 4 is a partial sectional side view of an embodiment of an apparatus forming a part of the present invention. 
     FIG. 5 is a partial schematic and diagrammatic representation of an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although preferred embodiments of the invention are described herein using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or the scope of the present invention, which is set forth in the following claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein. 
     An exemplary embodiment of an apparatus  10  forming a part of the present invention for dispensing a slurry as shown in FIG.  1  and FIG. 2. A housing  12  is provided and contains flexible element or member  14 . Inlet flange  16  and outlet flange  18  assist in securing flexible member  14  into a position inside housing  12 . Flexible member  14  includes seals  20  and  22  that are secured between inlet flange  16  and housing flange  24  and outlet flange  18  and housing flange  26 , respectively. Flexible member  14  is expandable and is constructed of any material or composite capable of expanding and contracting as will be described. By way of example, such materials may include rubber, various polymers, or combinations. One such flexible member  14  that may be used is constructed of Hypolon rubber and may be obtained from The Rubber Mill of Liberty, N.C. or Pulsafeeder Company of Rochester, N.Y. A plurality of flange bolts  28  are received into threaded holes  29  and are torqued so as to secure inlet flange  16  and outlet flange  18  as shown. 
     Inlet flange  16  is configured with an inlet nipple  17  having male threads  30 . Accordingly, a dispensing apparatus  10  can be connected by inlet flange  16  to piping or other equipment supplying slurry to apparatus  10 . In analogous fashion, outlet flange  18  is configured with outlet nipple  19  having female threads  32 . Accordingly, apparatus  10  may be connected to downstream piping or other equipment to which slurry will be fed from apparatus  10 . Housing flanges  24  and  26  are shown connected to housing  12  using welds  33 , however, such flanges could be formed as a unitary part of housing  12 . Using the teachings enclosed herein, one of ordinary skill in the art will understand that apparatus  10  can be connected within a system using components other than flanges  16  and  18  and such are depicted by way of example only. 
     For the exemplary embodiment depicted in FIGS. 1 and 2, a gas supply line  34  is shown connected to housing  12 . Inlet valve  36  is used to admit or release gas from chamber  12 . Alternatively, gas supply line  34  could be connected directly to a gas source such as a compressor, gas cylinder, or regulated gas supply. Apparatus  10  is equipped with pressure gauge  38  that is shown connected to gas supply line  34  using tee  35 . Gauge  38  allows an operator to determine whether the desired gas pressure is present in housing  12  and also allows the observation of any pressure fluctuations during operation of apparatus  10 . In addition, apparatus  10  is shown optionally equipped with an electronic sensor  40  connected by wires  42  to a local or remote display  44  as desired. Sensor  40  is shown connected to gas supply line  34  using tee  46 . Any electronic sensor  40  suitable to the particular application and pressures in use may be utilized. One such sensor  40  that may be used is provided by Endress &amp; Hauser, of Maulburg, Germany having a pressure range of 0 to 150 PSI. Accordingly, apparatus  10  may be equipped to display the pressure of gas in chamber  12  at a location remote from apparatus  10  as may be desirable in certain applications. In addition, apparatus  10  may be equipped with a controller that takes certain predetermined action based on the pressure in housing  12 . For example, such controller could be used to start, stop, or otherwise control a pump feeding slurry to apparatus  10  based on the pressure being detected and changes thereof. While any gas suitable for materials of construction and environment of use may be used to supply pressure to housing  12 , frequently air is used because equipment for providing the same is readily available or obtained. A cover  37  may be placed over valve  36  and gas supply line  34  and secured into position using a bolt  39 . Cover  37  thereby helps prevent tampering with valve  36  once the pressure of gas in housing  12  has been set. 
     Referring now to FIG. 3, flow arrows  48  indicate the flow of slurry into housing  12  during operation of apparatus  10 . Slurry enters through inlet nipple  17  and flows through inlet flange guide  50 . Slurry then flows through flexible member  14  and exits apparatus  10  by passing through outlet flange guide  52  and outlet nipple  19 . The length of inlet nipple  17  and/or outlet nipple  19  can be varied to ensure proper placement and operation of flexible member  14 . A chamber  54  is formed by the exterior surface  56  of flexible member  14  and the inside wall  58  of housing  12 . As represented by arrows  60 , chamber  54  is filled with a gas and set to a desired pressure using gauge  38  or remote display  44  and inlet valve  36 . The gas then exerts a pressure on the exterior surface  56  of flexible member  14 , which in turn exerts a pressure on the slurry in flexible member  14  through interior surface  62 . By adjusting the pressure using valve  36 , the pressure exerted on the slurry through interior surface  62  may be determined. 
     As shown in the exemplary embodiment depicted in FIG. 4, flexible member  14  changes shape based on changes in the pressure or flow of slurry present therein. FIG. 4 shows flexible member  14  in a contracted state as would occur when the pressure of gas in chamber  54  exceeds the pressure of the slurry inside flexible member  14 . By way of example, if slurry is being siphoned from apparatus  10  through outlet nipple  19 , flexible member  14  will contract to maintain the upstream pressure of the slurry in contact with inlet nipple  17  as is depicted by arrows  64 . As the flexible member  14  contracts, the amount of slurry within member  14  decreases. Alternatively, should the pressure of slurry entering apparatus  10  begin to increase, flexible member  14  can expand within housing  12  to dampen the pressure increase of the slurry. During the expansion, the amount of slurry in flexible member  14  increases. 
     For certain applications, flexible member  14  can be used to dampen fluctuations in the pressure of the slurry without using a gas to apply pressure to the exterior  56  of member  14  and such an embodiment is within the spirit and scope of certain claims of the present invention. In these applications, the flexibility or resiliency of the flexible member  14  acts without assistance of the gas pressure to dampen pressure or flow fluctuations in the slurry. To compensate for differences in pressures and flow from application to application, the flexibility or resiliency of member  14  is varied by changing the composition of the materials of construction and/or the physical dimensions of flexible member  14 . By way of example only, for applications where higher pressures or flow are anticipated, a flexible member  14  having a thicker wall  66  and/or a material capable of absorbing larger pressure changes could be used. Accordingly, members  14  having varying degrees of flexibility or resiliency could be substituted into apparatus  10  until the desired performance was obtained based on the pressure of the slurry being fed to apparatus  10  and the fluctuations in such pressure. 
     Alternatively, by using flexible member  14  within a housing  12  as is shown in the exemplary embodiment depicted in FIG. 3 or FIG. 4, the responsiveness of apparatus  10  to changes in the pressure or flow of slurry can be adjusted by varying the pressure of the gas in chamber  54  using gas supply line  34  and inlet valve  36 . For example, by increasing the pressure of the gas in chamber  54 , more pressure is applied to the exterior surface  56  of flexible member  14 . This increase in pressure is passed through wall  66  and is exerted on the slurry by interior surface  62 . Accordingly, the increased gas pressure in chamber  54  allows apparatus  10  to maintain a greater pressure on slurry within flexible member  14 . In addition, the increased gas pressure decreases the flexibility or expandability of the member  14  at a given pressure. Similarly, by decreasing the pressure in chamber  54 , the pressure exerted on slurry within member  14  is also decreased and the flexibility or expandability of member  14  is increased at a given pressure. Therefore, the use of a gas or other compressible fluid to exert a pressure on the exterior of flexible member  14  allows apparatus  10  to be adjusted or tuned for proper operation in different applications or under varying operating conditions. 
     An exemplary embodiment of an apparatus  68  for dispensing a slurry is shown in FIG. 5. A vessel or tank  70  is provided having an upper portion  72  and a lower portion  74 . Tank  70  is equipped with an agitator  76  that includes a motor  78  that drives propeller  80  using shaft  82  to agitate slurry in tank  70 . Although not shown, tank  70  can be equipped with baffles, which may be preferable with certain types of slurry. The presence of slurry in tank  70  is depicted generally by surface line  84 . Tank  70  includes an outlet  86  in the lower portion  74 . Connected to outlet  86  is a tube or conduit  88 . A portion of conduit  88  near the connection to outlet  86  is inclined upwardly in the exemplary embodiment depicted in FIG.  5 . More specifically, if conduit  88  is maintained at an angle of at least 30 degrees with respect to horizontal, gravity will cause slurry particles in conduit  88  to fall back into tank  70  where agitation can occur. Conduit  88  is equipped with valve  90  to control the flow of slurry from tank  70 . 
     Inlet line  92  provides a feed of slurry from tank  70  to positive displacement pump  94 , which is driven by motor  96 . Pump  94  has an inlet  98  for feeding in slurry, and a discharge or outlet  100  for pumping slurry out. An acceptable positive displacement pump that may be used with apparatus  68  is a Pulsa pump available from the Pulsafeeder Company of Rochester, N.Y. As described in U.S. Pat. No. 5,277,491, which is incorporated by reference, pump  94  has a straight flow through path  102  constructed from a tube preferably made of tetrafluoroethylene to further reduce flow restrictions and clogging. In the exemplary embodiment of FIG. 5, apparatus  10  is shown connected by inlet flange  16  to the outlet  100  of pump  94 . The present invention does not require apparatus  10  to be directly connected to outlet  100  and, using the teachings disclosed herein, one of ordinary skill in the art will understand that apparatus  10  may be connected further downstream from pump  94 . Through outlet flange  18 , apparatus  10  is connected to a slurry feed line  104 , which is then used to transport the slurry to further treatment, storage, or use. 
     For cleanout and maintenance, a fluid supply line  106  is shown connected to inlet line  92 . Line  106  connects a fluid supply  108  to line  92 . Valve  110  is used to control the flow of fluid from supply  108  and back flow preventer  112  precludes the contamination of supply  108  with slurry from line  92 . Accordingly, after extended periods of operation or after a shutdown, valve  90  is closed and valve  110  is opened to allow fluid from supply  108  to be fed into inlet line  92 . The fluid can then be transported through pump  94  and apparatus  10  to clean out any particles that have accumulated. In the case of lime slurries, the fluid used for fluid supply  108  is typically water. 
     Continuing with the exemplary embodiment of FIG. 5, during operation a slurry is received and/or stored in tank  70 . If necessary, the concentration of slurry can be adjusted by the addition of a fluid, such as water, from supply line  114 . Using agitator  76 , the slurry is maintained by constant agitation. By opening valve  90 , slurry is fed through outlet  86  in the lower portion of tank  74 , through conduit  88 , and on to pump  94  through line  92 . Pump  94  then acts on slurry as it passes through path  102  to pump the slurry downstream to apparatus  10 . As slurry flows through apparatus  10 , the flexible member  14  contracts and expands to provide a pressure on the slurry as described above. Accordingly, when pump  94  is in suction mode or is turned off, apparatus  10  provides a back pressure against slurry discharging from the outlet  100  of pump  94  to ensure proper operation of the pump  94  and the metering of slurry therefrom. Therefore, back pressure is provided by apparatus  10  rather than by introducing a source of fluid under pressure at a point downstream from the outlet  100  of pump  94 . In the case of lime slurries, the scaling or calcification that occurs by using water downstream of pump  94  to provide such back pressure is eliminated. In addition, because apparatus  10  operates to dampen the pulsations from positive displacement pump  94 , settling and sedimentation of the slurry downstream of pump  94  is minimized. Because these problems are minimized or eliminated, the diameter of piping or tubing used for line  104  can be reduced to diameters previously believed to be ineffective due to problems with settling, scaling, calcification, clogging, or the like. In addition, the operation of apparatus  10  allows slurry to be pumped from pump  94  over greater distances than were previously obtainable due to such problems. 
     Where a gas is used with apparatus  10  to provide a pressure on the exterior surface  56  of flexible member  14 , the pressure in chamber  54  can be tuned or adjusted so as to provide the desired amount of expansion and contraction of flexible member  14  and the desired amount of back pressure. By way of example, referring to FIG.  1  through FIG. 5, additional gas can be admitted to chamber  54  using valve  36  and gauge  38  if additional back pressure is needed. Alternatively, gas can be bled from chamber  54  using valve  36  if less back pressure is desired. The amount of back pressure needed can vary from application to application depending on factors such as the volume of slurry flow, the pressure of slurry flow, the rate of slurry flow, the size of piping used, the size of pump  94 , and other factors that will be apparent to one of ordinary skill in the art using the teachings disclosed herein. 
     From the foregoing description of exemplary embodiments of the present invention, it will be apparent using the teachings disclosed herein that there are other embodiments of the invention and that modifications to the invention may be made without departing from the spirit and scope of the invention.