Patent Publication Number: US-2010111680-A1

Title: Delivery Pump

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of international patent application no. PCT/EP2008/002767, filed Apr. 8, 2008 designating the United States of America and published in German on Nov. 6, 2008 as WO 2008/131846 A1, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application no. DE 10 2007 020 218.2, filed Apr. 28, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a delivery pump with a variable-speed drive, the delivery pump being designed as a single-stage centrifugal pump with a radial impeller ( 2 ) of centrifugal type of construction, arranged rotatably in an impeller chamber of a pump casing ( 1 ), for delivering a fluid between a pump inlet ( 4 ) and a pump outlet ( 13 ), the radial impeller ( 2 ) being connected to a drive motor variable in speed into the five-digit range of revolutions per minute, the radial impeller ( 2 ) receiving the flow centrally, being provided with delivery ducts ( 3 ) and, in the case of an outside diameter of up to 55 mm, delivery heads of up to 300 m. 
     In the field of research and development processes in the chemical and pharmaceutical industries, there is the demand for ever faster developments at lower costs. The production of such substances requires more flexible, smaller-scale and more environmentally friendly processes. This leads to the use of process engineering components which are sometimes operated with very low filling volumes and with a continuous substance flow. On account of the demand for a flexible use of such plants, it is necessary to be able to scavenge the entire plant, together with the assemblies mounted in it, with the aid of special scavenging media. 
     Such plants require an accurate, constant, freely adjustable and pulsation-fee volume flow of liquid substances. For high-precision continuous volume flows in the range of zero milliliters per minute up to a three-digit number of liters per hour, positive-displacement pumps in the form of micro-annular and gear pumps and also in the form of diaphragm and piston pumps are employed. Such positive-displacement pumps have the disadvantage of the lack of reliability due to friction between the components to be sealed off, moved in relation to one another, and their pulsating delivery stream. A resulting outlay in terms of maintenance and the costs for wearing parts and for exchanging these are detrimental to rapid research and development work and appreciably disrupt a production process. 
     A centrifugal pump, designed as a canned motor pump, for the circulation of supercritical hydrocarbons is known from WO 2005/052365 A2. The drive motor has a can made from polyaryletheretherketone (PEEK), within which is arranged a rotor protected by a high-grade steel covering. Ceramic bearings of the pump shaft and of the drive rotor are lubricated by a part stream of the delivery fluid, said part stream being extracted from the pump casing. The impeller of open design has a diameter of between 1 and 2 inches, and the impeller-driving rotor of the rolling bearing-mounted direct-current motor has a diameter of between 1.5 and 2 inches. The single-stage pumping arrangement with the open impeller is intended to reach maximum rotational speeds of up to 60,000 rpm. The suction connection piece, the pressure connection piece and a type of spiral chamber following the impeller are arranged in an outer pump casing part, while an inner pump casing part has the overhung-mounted impeller and a fastening for a variable-speed direct-current canned motor as a drive motor. 
     The disadvantage of this canned motor design is the multiplicity of gaps which, because of the complex flow routing between the pump and canned motor, seriously impede the cleaning of the pump. Since part of the delivery fluid flows permanently through the motor and its gap space, a high introduction of heat into the delivery fluid occurs due to the frictional heat of the rolling bearings and to the heat loss from the canned motor. Consequently, this pump can be operated only in the immediate vicinity of an undefined optimal operating point. If this pump were operating under part load, an inadmissibly high introduction of heat would take place very quickly. This would result not only in damage to the fluid, but also in a failure of the pump as a result of cavitation or dry running. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an improved delivery pump for delivery and/or metering of liquid substances. 
     Another object of the invention is to provide a delivery pump for the delivery and/or metering of milliliter amounts of liquid chemical, pharmaceutical and/or cosmetic components. 
     A further object of the invention is to provide a pump unit having a delivery rate which is variable, pulsation-free and accurately adjustable over a wide range for delivering differing media having different properties. 
     An additional object of the invention is to provide a delivery pump which which can be cleaned easily for rapid product changes. 
     These and other objects have been achieved in accordance with the present invention by providing a delivery pump as described and claimed hereinafter. 
     A metering pump in the form of a centrifugal pump having a centrifugal pump construction is produced. This is designed as a delivery pump for use in a process engineering plant for nominal operation in the form of continuous centrifugal pump part-load operation with delivery rates in the range of 0 ml/min to 7000 ml/min, nominal operation being characterized by a centrifugal pump part-load-specific rotational speed nq  TL ≧0.05≦10, and the impeller chamber being provided on the circumference with one or more pump outlet ducts arranged at an acute angle to or tangentially to the radial impeller outside diameter. 
     In complete contrast to all current centrifugal pump design rules or provisions, this centrifugal pump is designed for extreme part-load operation, with the result that small quantities are delivered, pulsation-free. For this purpose, the delivery pump preferably has a centrifugal pump part-load-specific rotational speed nq TL ≧0.05≦3 (l/min). It also has proved advantageous to design the delivery pump for a centrifugal pump part-load operating range nq TL &lt;2.5 has also proved advantageous. The radial impeller may have a maximum outside diameter of up to 70 mm. 
     According to further embodiments, the pump casing, with a radial impeller arranged in it, preferably has a residual volume lower than 30 milliliters. This has the considerable advantage that the delivery pump is easily scavengable. In addition, as a result of the low residual volume and the minimum number of gaps, when a fluid to be pumped is changed in the pump, only low product losses occur during a cleaning or scavenging of the delivery pump. Furthermore, an inside diameter of the impeller chamber is designed to be a maximum of 4% larger than an outside diameter of the radial impeller. Also, by reducing the size of the impeller chamber surrounding the radial impeller, the dynamic pressure prevailing at the pump outlet duct is increased. In this case, the inlet ports of one or more pump outlet ducts are constructed in the form of pressure tubes or similarly to a pressure tube. 
     According to another embodiment of the delivery pump, the pump is provided with a thermal control device, preferably for nominal operation at a centrifugal pump part-load-specific rotational speed nq TL ≧0.05≦1 (l/min). 
     This device improves the delivery of sensitive fluids and/or of fluids with a low boiling point by means of the delivery pump capable of being operated in a wide nq TL  range. 
     According to another embodiment, a seal is arranged between the impeller chamber and the radial impeller and/or its shaft. A design is likewise possible in which a hermetically leaktight magnet-coupled drive transmits a torque to the radial impeller. Also, a bearing for the shaft is arranged on the pump casing, on the thermal control casing and/or on a bearing casing. Moreover, the delivery pump may be constructed as a modular assembly with a flanged-on motor. 
     Depending on the drive used, the delivery pump is characterized by constant delivery operation or by metered dosing operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawing figures, in which: 
         FIG. 1  shows a longitudinal sectional view of a delivery pump according to the invention; 
         FIG. 2  shows a perspective view of the pump unit; 
         FIG. 3  shows a perspective view of an impeller; 
         FIG. 4  shows a sectional view of the impeller; 
         FIG. 5  shows a cross-sectional view through the delivery pump, and 
         FIG. 6  shows the position of the delivery pump in an nq graph. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a delivery pump having a single-stage pump construction. A radial impeller  2  of centrifugal type of construction is arranged rotatably in the pump casing  1 . The radial impeller  2  has delivery ducts  3  and receives the flow centrally through a pump inlet  4 . The radial impeller  2  is connected in a force-transmitting manner to a variable-speed drive  5  and has an outside diameter D LA  which may amount to up to 70 mm. The radial impeller rotates in an impeller chamber  6 , the inside diameter D LRI  of which is designed to be only a maximum of 4% larger than the outside diameter D LA , of the radial impeller  2 . 
     The pump casing  1  is provided with a thermal control device  7  which in this illustrative embodiment is integrated in the pump casing. Other forms of construction are also possible. Cooling spaces  7 . 1  to  7 . 3  surround the impeller chamber  6  and also a seal casing  8  contiguous to the pump casing  1 . Within the seal casing  8  is arranged, as a type of shaft seal, a seal  9  which is illustrated in the illustrative embodiment as a lip sealing ring. Depending on the delivery fluid used, the seal  9  may also be constructred as a floating ring seal. The seal  9  may bear sealingly against the impeller  2 , against an impeller hub  2 . 1  or against the shaft  10 , depending on the selected connection between the impeller and a shaft  10  of the drive. The thermal control spaces  7 . 1  to  7 . 3  are acted upon by external coolant. As a result, the parts of the pump casing which are touched by the delivery fluid are reliably cooled, since the centrifugal pump is designed for continuous operation in a part-load operating point map, the delivery rate limits of which lie in the range of 0 milliliters/min to 3600 milliliters/min in the case of a delivery head limit of 20 meters-300 meters. As a result of the high rotational speed of the drive  5  necessary for this purpose, additional coolant  11  is arranged on the outer circumference of the drive  5 . The drive  5  is also connected or attached in a force-transmitting manner to the thermal control device  7 . 
     The area of the pump inlet  4  is defined by a bearing face  12  which is located in the immediate vicinity of the pump interior and against which a line to be connected for a delivery fluid bears sealingly. A similar construction is present at the pump outlet  13  which here is located below the drawing plane and can be seen only partially as a semicircle. The fastening of pump lines, not shown here, which are to be connected thereto takes place in a known manner, for example via union nuts. By a pump line being led directly up to the impeller chamber  6  and because of the small diameter differences between the impeller outside diameter D LA  and the inside diameter D LRI  of the impeller chamber  6 , the residual volume for delivery fluid inside the pump casing with the radial impeller mounted therein is less than or equal to 50 milliliters. This very small quantity has the advantage that only the least possible losses arise when the valuable delivery fluids are changed. 
     The pump inlet  4  and the pump outlet  13  are clear from  FIG. 2  which is a perspective view of the delivery pump constructed as a unit. The thermal control device  7  is integrated into the pump casing  1 , and the pump inlet  4  and pump outlet  13  extend through the thermal control device  7  as far as the impeller chamber. 
     External thermal control means, for example coolants, are supplied to and discharged from the thermal control spaces  7 . 1  to  7 . 3  via the axial or radial connections  14 ,  15  which can be used selectively. A pump unit and drive motor  5  are combined into a structural unit and are held in a carrying element  16 . The carrying element  16  satisfies the precondition for modular construction or installation into an existing plant. 
       FIG. 3  shows a perspective view of a radial impeller  2 . The radial impeller  2  is of disk-shaped configuration and in this example is provided with a hub  2 . 1 . A force-transmitting connection to the shaft  10 , not shown, of the drive  5  takes place within the hub  2 . 1 . Delivery ducts  3  are arranged inside the radial impeller  2 . In addition, a plurality of delivery depressions  18 , which are configured in the form of blind bores, are arranged on the impeller circumference  17 . With the aid of these delivery depressions, the pressure coefficient of the centrifugal pump impeller is improved. 
     In one possible configuration, the pressure-side and suction-side cover disks  19 ,  20  have a plurality of radially extending delivery grooves  21 . The delivery grooves  21  likewise improve the pressure coefficient of an impeller installed according to  FIG. 1  in an impeller chamber  6 . Compensating bores  22  which extend through the impeller in the axial direction serve for pressure compensation within the pump casing and at the same time as a mounting aid when a connection to the drive is being made. 
       FIG. 4  shows a sectional view through an impeller  2  in which four delivery ducts  3  are used. Their diameter is coordinated such that they do not intersect an adjacent delivery duct in the region of the impeller inlet  23 . This ensures that a defined impeller inlet diameter is maintained. The depth T of the delivery depressions  18  is selected as a function of the desired residual volume of a ready-assembled pump. 
     Instead of the delivery depressions  18 , shown here, in the form of bores, any other form, for example grooves, slots or the like, by means of which energy transmission is possible in the region of the impeller outside diameter, may also be employed. 
       FIG. 5  shows a cross section through the delivery pump of the invention. Due to the generously dimensioned thermal control space  7 . 2  which is operatively connected to the other thermal control space, continuous extreme part-load operation is ensured. The pump outlet duct  13  may be configured as a simple bore or, as illustrated, it may be formed by an insert  24  resembling a pressure tube and having an inlet port  25 . The latter makes simple adaptation to varied design requirements possible. 
     Due to the minimized impeller chamber  6 , a radial gap width which lies in the single-digit millimeter range is obtained between the outside diameter D LA , of the radial impeller and the enveloping surrounding diameter D LRI  of the impeller chamber  6 . In a practical centrifugal pump, the radial gap between the impeller and casing lies in the region of 2 mm. The gap between the impeller and casing lies in a similar order of magnitude in the region of the axial impeller sides. As a result of this configuration of the casing region having a minimal residual volume, the pump can be cleaned very quickly and reliably by a scavenging medium. The pump can also be adapted to changed delivery conditions or plants with the lowest possible losses of parts of the delivery product. Due to the continuous rotation of the centrifugal impeller  2 , pulsation-free operation of this delivery pump is achieved. 
     As a result of the minimized gap between the impeller outside diameter and impeller chamber, the circumferential component of the impeller simultaneously approaches the circumferential speed, and, in combination with a pump outlet  13  arranged at an oblique angle, preferably tangentially, to the impeller  2 , a maximum possible dynamic pressure is obtained for this centrifugal pump at its outlet port. In conjunction with the variable-speed motor, high delivery heads, along with a minimal residual volume within the pump casing, can be achieved. 
     The contact-free arrangement of the impeller within the impeller chamber avoids frictional surfaces bearing sealingly one against the other. This measure prevents the generation of mechanical frictional heat, prevents frictional wear and resulting contamination of a delivery fluid with abraded particles and improves operational reliability due to substantially prolonged service lives. Moreover, sealing gaps which adversely affect cleanability are avoided. 
     In  FIG. 6 , the nq values of centrifugal pumps are compared with those of positive-displacement pumps in an nq graph in characteristic maps depicted by unbroken lines. The novel delivery pump, with its characteristic map, illustrated in gray, of the centrifugal pump part-load-specific rotational speed nq TL , covers the range between these two opposite pump types for the first time. 
     The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.