Patent Publication Number: US-6655930-B2

Title: Insulation means for a centrifugal pump

Description:
BACKGROUND TO THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a centrifugal pump for handling liquefied gases and very low temperature fluids. More specifically, the present invention relates to a centrifugal pump including a pump with an impeller, and a motor for driving the impeller. 
     2. Description of the Related Art 
     Specialized pumps exist for handling low temperature fluids such as liquefied natural gas, liquefied petroleum gas, and other liquified gases. In general, these pumps each include a pump portion and a motor portion. The pump portion includes an impeller which imparts speedy motion to the fluid. The motor includes an electric motor which operates the impeller. 
     Since the operating temperatures for these specialized pumps are very low, it is necessary to adequately insulate the inside and outside of the pump and take other steps to minimize heating effects. For this reason, an insulating jacket typically surrounds these specialized pumps in an attempt to provide adequate heat insulation. Many of these insulating jackets operate ineffectively as well as detrimentally increase the size of the pump. 
     To assist heat insulation, it is preferable to have a pump with a small surface area. When starting the pump, it is necessary to have adequate cooling of the pump temperature so that the low temperature fluid does not inappropriately volatilize. Thus, a pump with a small heat capacity is needed for speedy cooling. The known pumps have high heat capacity and therefore provide ineffective and slow cooling prior to operation. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a pump which overcomes the drawbacks of the related art noted above. 
     It is another object of the present invention to provide an efficient centrifugal pump. 
     It is another object of the present invention to provide a pump which easily handles very low temperature fluids. 
     It is another object of the present invention to provide a pump which includes adequate heat insulation and has a small heat capacity. 
     It is another object of the present invention to provide a pump with a speedy start up. 
     The present invention relates to a centrifugal pump including a motor portion and a pump portion. The motor portion, which is coaxial with the pump portion, drives an impeller to pump a low temperature fluid. A pot is sealed to the pump portion to receive the low temperature fluid. The low temperature fluid contacts only the pump portion in the pot to thereby reduce the overall heat capacity of the centrifugal pump and thus reduce start time. A heat insulating jacket is in tight contact with the motor portion. A vent pipe extends from the pot, through the pump portion and within the heat insulating jacket, to a rear of the motor portion to increase safety and provide double-insulation to the vent pipe. The heat insulating jacket reduces the size and surface area of the centrifugal pump to resist heat flow and increase safety. 
     According to an embodiment of the present invention there is provided a centrifugal pump, for pumping a low temperature fluid, comprising: a pump portion, a motor portion on the pump portion, the pump portion including an impeller having a first rotation axis, the motor portion including a motor having a second rotation axis, the first rotation axis in coaxial alignment with the second rotation axis, the motor driving the impeller during an operation of the centrifugal pump to drive the pump portion and pump the low temperature fluid, insulating jacket means for thermally insulating at least the motor portion, the insulating jacket means surrounding at least the motor portion, at least a first vacuum jacket in the insulating jacket means, and the first vacuum jacket including at least a low pressure vacuum between a motor outer surface and an inner surface of the first vacuum jacket, whereby tight contact between the insulating jacket means and the motor portion and the coaxial alignment provides increased thermal efficiency, reduced size, and simplified construction. 
     According to another embodiment of the present invention there is provided a centrifugal pump, further comprising: a pot, the pot sealed around a lower portion of the pump portion, the pot solely receiving the low temperature fluid during the operation, an intake pipe in the lower portion extending away the pump portion along the first rotation axis into the pot, the intake pipe and the impeller in fluid communication, and the intake pipe and the impeller transporting the low temperature fluid from the pot during the operation, thereby restricting direct contact of the low temperature fluid to the pump portion and providing a reduced pump surface area with an improved startability. 
     According to another embodiment of the present invention there is provided a centrifugal pump, further comprising: a flow straightening plate, the flow straightening plate in the pot opposite the intake pipe, and the flow straightening plate having a shape preventing formation of a rotational flow of the low temperature fluid in the pot during the operation. 
     According to another embodiment of the present invention there is provided a centrifugal pump, further comprising: a release pipe, the release pipe in sealed communication between the motor portion and an external portion of the centrifugal pump, and the release pipe providing an easy release of any the low temperature fluid and a vapor of the low temperature fluid which has improperly entered the motor portion, thereby increasing reliability of the centrifugal pump. 
     According to another embodiment of the present invention there is provided a centrifugal pump, further comprising: a vent pipe, the vent pipe in vapor communication between the pot and the release pipe, and at least a first portion of the vent pipe within the first vacuum jacket, whereby the first vacuum jacket provides easy double-service thermal insulation of the motor portion and the vent pipe to reduce size while increasing safety. 
     According to another embodiment of the present invention there is provided a centrifugal pump, wherein: the release pipe extends from a rear side of the motor portion away from the first vacuum jacket. 
     According to another embodiment of the present invention there is provided a centrifugal pump, wherein: the at least a first portion of the vent pipe includes the entire vent pipe, whereby the first vacuum jacket provides easy double-insulation of the motor portion and the entire vent pipe while reducing size and increasing safety. 
     According to another embodiment of the present invention there is provided a centrifugal pump, wherein: at least the first portion of the vent pipe is greater that one half of an overall length of the vent pipe, whereby the first vacuum jacket provides easy double-insulation of the motor portion and the first portion while reducing size and increasing safety. 
     According to another embodiment of the present invention there is provided a centrifugal pump, wherein: the flow straightening plate includes at least a first and a second plate extending away from a bottom of the pot toward the intake pipe, and the first and the second plates perpendicular to each other. 
     According to another embodiment of the present invention there is provided a centrifugal pump, further comprising: a front end partitioning wall between the motor portion and the pump portion, a rear end partitioning wall on the motor portion opposite the front end partitioning wall, and the motor portion sealed between the front end partitioning wall and the rear end partitioning wall thereby separating the motor portion from the first vacuum jacket and allowing easy creation of the first vacuum jacket. 
     According to another embodiment of the present invention there is provided a centrifugal pump, wherein: the release pipe is in sealed communication between the rear end partitioning wall on motor portion and an external portion of the centrifugal pump. 
     According to another embodiment of the present invention there is provided a centrifugal pump, further comprising: at least a second vacuum jacket in the insulating jacket means, and the second vacuum jacket including at least a low pressure vacuum between a pot outer surface and an inner surface of the second vacuum jacket, whereby tight contact between the insulating jacket means and the pot and coaxial alignment provides increased thermal efficiency, smaller size, and simplified construction. 
     According to another embodiment of the present invention there is provided a centrifugal pump, for pumping a low temperature fluid, comprising: a pump portion, a motor portion on the pump portion, the pump portion including an impeller having a first rotation axis, the motor portion including a motor having a second rotation axis, the motor driving the impeller during an operation of the centrifugal pump to drive the pump portion and pump the low temperature fluid, the first rotation axis coaxial with the second rotation axis, insulating jacket means for thermally insulating at least the motor portion, the insulating jacket means surrounding at least the motor portion, at least a first vacuum jacket in the insulating jacket means, the first vacuum jacket including at least a low pressure vacuum between a motor outer surface and an inner surface of the first vacuum jacket, whereby tight contact between the insulating jacket means and the motor portion and coaxial alignment provides increased thermal efficiency, reduced size, and simplified construction, a pot, the pot sealed around a lower portion of the pump portion, the pot solely receiving the low temperature fluid during the operation, an intake pipe in the lower portion extending away the pump portion along the first rotation axis into the pot, the intake pipe and the impeller in fluid communication, the intake pipe and the impeller transporting the low temperature fluid from the pot during the operation and restricting direct contact of the low temperature fluid to the pump portion thereby providing a reduced pump surface area and an improved startability, a release pipe, the release pipe in sealed communication between the motor portion and an external portion of the centrifugal pump, the release pipe providing an release of any of the low temperature fluid and a vapor of the low temperature fluid which has improperly entered the motor portion, a vent pipe, the vent pipe in vapor communication between the pot and the release pipe, and at least a first portion of the vent pipe is located within the first vacuum jacket, whereby the first vacuum jacket provides easy double-service thermal insulation of the motor portion and the vent pipe. 
     According to another embodiment of the present invention there is provided a centrifugal pump, for pumping a low temperature fluid, comprising: a pump portion, a motor portion on the pump portion, an impeller in the pump portion, a motor in the motor portion driving the impeller during an operation of the centrifugal pump and pumping the low temperature fluid, the motor portion is coaxial with the impeller, a heat insulating jacket on the centrifugal pump, and the heat insulating jacket including a first insulating portion in tight contact around the motor portion, thereby reducing the centrifugal pump in size while increasing thermal efficiency. 
     The above, and other objects, features, and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic diagram of a centrifugal pump according to an embodiment of the present invention. 
     FIG. 2 shows a schematic diagram of a centrifugal pump according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, a centrifugal pump  10  is primarily divided into a pump portion  12  and a motor portion  14 . Motor portion  14  drives pump portion  12 , as will be described. Pump portion  12  includes an impeller  18  which rotates inside a casing  16 . Pump portion  12  is beneficially positioned inside a pot  20 , as will be explained. 
     Pot  20  is surrounded on three sides by a lower outer cylinder  22  and a bottom plate  24 . A bottom section (not shown) of outer cylinder  22  is sealed to bottom plate  24 . Casing  16  is joined to and sealed to pot  20 . During assembly, a lower vacuum jacket  26  is constructed by reducing the pressure in the space between pot  20 , lower outer cylinder  22 , and bottom plate  24 . Lower vacuum jacket  26  provides beneficial heat insulation to pump portion  12  while easily allowing for reduced size, as will be explained. Lower outer cylinder  22  has a predetermined and specified spacing away from pot  20 . 
     An inlet pipe  28  provides sealed fluid access to pot  20 . During operation, inlet pipe  28  transports the fluid to be handled (i.e., a very low temperature fluid) into a fluid container portion  2  inside pot  20 . 
     An intake pipe  30  extends away from pump portion  12  toward fluid container portion  2  in pot  20 . Intake pipe  30  aids in pumping the low temperature fluid collected inside pot  20  to a discharge pipe  32 . During operation, impeller  18 , in pump portion  12 , draws the low temperature fluid into intake pipe  30  and discharges the low temperature fluid out discharge pipe  32 . Intake pipe  30  and impeller  18  are both located in casing  16 . 
     A straightening plate  33  is disposed below intake pipe  30  in pot  20 . Straightening plate  33  includes multiple plates designed and arranged to prevent the formation of circling flow inside pot  20  during use. In the present embodiment, the plates in straightening plate  33  are cross-shaped plates which extend perpendicular to intake pipe  30 . One skilled in the art will readily recognize that alternative embodiments of the instant invention may include additional or different arrangement of the cross-shaped plates or the use of different designs and baffles at different angles to prevent circling flow 
     Motor portion  14  includes an electric motor  40  having a stator  34  and a rotor  38 . Rotor  38  is unitarily formed with a rotor shaft  36  inside stator  34 . Rotor shaft  36  extends away from motor portion  14  to pump portion  12  where it is affixed to an end of impeller  18 . During operation, rotor shaft  36  transmits torque from motor portion  14  to pump portion  12  to pump the low temperature fluid. 
     Electric motor  40  is sealed inside a motor outer cylinder  42 , as will be explained. Motor outer cylinder  42  is in close contact on the outer perimeter of stator  34 . A set of front and a rear end partitioning walls  44 ,  46  seal and close both ends of motor outer cylinder  42 . 
     Front end partitioning wall  44  is a partitioning wall on a pump portion side of electric motor  40 . Front end partitioning wall  44  is a part of casing  16  in pump portion  12 . Rear end partitioning wall  46  is opposite front end partitioning wall  44  in electric motor  40 . 
     A fluid release pipe  48  joins to a back end of motor  40  to release any low temperature fluid that has undesirably entered motor portion  14 . A power line duct  50  is joined to the back end of motor  40 . Power line duct  50  receives power lines (not shown) for transmission of power to the coils of stator  34 . Fluid release pipe  48  and power line duct  50  are sealed to rear end partitioning wall  46  opposite pump portion  12 . 
     An upper outer cylinder  52  surrounds motor outer cylinder  42  and back end partitioning wall  46 . Upper outer cylinder  52  is sealed to a flange  56  on a pump side end, and to an outer surface of power line duct  50  and to fluid release pipe  48 . Flange  56  is sealed to casing  16  during assembly. Upper outer cylinder  52  has a predetermined and specified spacing away from motor outer cylinder  42 . 
     During assembly, an upper vacuum jacket  54  is formed by reducing the pressure between upper outer cylinder  52  and motor outer cylinder  42 . Upper vacuum jacket  54  provides simple heat insulation in a minimum space with efficient parts usage. 
     A vent pipe  58  extends through casing  16 , inside upper vacuum jacket  54 , to fluid release pipe  48 . Vent pipe  58  provides a sealed release path to release low temperature fluid that has vaporized inside pot  20 . 
     Upper vacuum jacket  54  is in close contact with the outer perimeter of motor portion  14 . This positioning provides desirable design and space benefits because the outer diameter of upper vacuum jacket  54 , (the outer diameter of upper outer cylinder  52 ) is small. This reduction in size correspondingly reduces the overall centrifugal pump  10  surface area. One particular benefit of the present invention is the use of motor portion  14  itself as an integral part of the insulating system of centrifugal pump  10 . 
     The external shape of centrifugal pump  10  both easily accommodates and protects vent pipe  58  inside upper vacuum jacket  54  thus providing further size reduction and safety. The position of vent pipe  58  within upper vacuum jacket  54  provides easy double-service heat insulation without additional equipment. 
     Casing  16  serves in part as a partitioning wall between pump portion  12  and motor portion  14 . 
     During operation, low temperature fluid accumulates in pot  20  before being suctioned into pump portion  12 . Pot  20  is solely around pump portion  12 , below casing  16 , and is sealed to casing  16 . This beneficially reduces minimum pot  20  capacity and increases efficiency and speed of centrifugal pump  10 , as will be explained. 
     Since pot  20  surrounds only pump portion  12 , pot  20  limits low temperature fluid contact solely to pump portion  12 . This beneficially limits the portion of pump portion  12  that must be cooled prior to start. In other words, this reduction in size correspondingly reduces the heat capacity (thermal mass) of the portion of pump portion  12  that must be cooled by the low temperature fluid prior to starting. The reduction in heat capacity allows cooling to an operable temperature of pump portion  12 . One skilled in the instant art will therefore understand that by limiting the direct contact of low temperature fluid to only pump portion  12 , the ‘startability’ (speed-to-start time) of pump portion  12  is improved 
     Referring now to FIG. 2, an alternative embodiment of the present invention includes a centrifugal pump  60  having electric motor  40 . Motor outer cylinder  42  closely surrounds electric motor  40 . A front and a back end partitioning wall  64 ,  66  close and seal both ends of motor outer cylinder  42 , as will be explained. 
     A casing back surface  62  separates pump portion  12  and motor portion  14  in centrifugal pump  60 . Front end partitioning wall  64  also serves as a partitioning wall on the pump portion  12  side of electric motor  40 . Front end partitioning wall  64  is sealed to casing back surface  62  and divides and separately secures pump portion  12  and motor portion  14 . Pump portion  12  is located below casing  16 . 
     A fluid release pipe  68  extends through back end partitioning wall  66 , as will be explained. One end of fluid release pipe  68  opens at a surface on electric motor  40 , and from there, fluid release pipe  68  extends radially toward a side surface of centrifugal pump  60 . Fluid release pipe  68  allows beneficial release of low temperature fluid which has entered motor portion  14 . 
     A through hole  70  allows sealed power line access through back end partitioning wall  66  to the coil of stator  34 . The power line provides operational power to electric motor  40  to drive pump portion  12 . 
     Motor outer cylinder  42  closely surrounds motor  40  and is sealed to respective front and back end partitioning walls  64 ,  66 . An upper outer cylinder  72  surrounds outer cylinder  42  at a predetermined spacing. A lower end of upper outer cylinder  72  is sealed to front end partitioning wall  64 . An upper end of upper outer cylinder  72  is sealed to a flange  76 . Flange  76  is sealed to and extends from an upper end of motor outer cylinder  42 . 
     An upper vacuum jacket  74  is created by depressurizing the space between motor outer cylinder  42  and upper outer cylinder  72 . Upper vacuum jacket  74  provides beneficial thermal (heat) insulation to centrifugal pump  60  within a minimal space, as noted above. 
     A vent pipe  78  passes through casing  16  and front end partitioning wall  64  and extends inside upper vacuum jacket  74  to a back end of motor portion  14 . Vent pipe  78  exits upper vacuum jacket  74  before reaching back end partitioning wall  66  where it joins fluid release pipe  68 . Vent pipe  78  releases vaporized low temperature fluid from inside pot  20 . 
     An end cap  80  extends above end partitioning wall  66 . A terminal box  82  is fixed to an upper end of end cap  80 . Terminal box  82  includes an external power supply terminal which links an external power supply to the power cables passing through end cap  80  and through hole  70  to electric motor  40 . To additionally aid thermal insulation of motor portion  14 , end cap  80  may retain a vacuum adjacent back end partitioning wall  66 . 
     As with the previous embodiment, upper vacuum jacket  74  tightly contacts an outer perimeter of motor portion  14 . This beneficial design reduces the outer diameter of upper outer cylinder  72  and reduces the overall surface area of centrifugal pump  60 . Vent pipe  78  both receives beneficial thermal (heat) insulation from upper vacuum jacket  74  and also contributes to the reduction in overall surface area of centrifugal pump  60 . 
     As with the embodiment described above, before operating centrifugal pump  60 , low temperature fluid accumulates in pot  20  before being suctioned into pump portion  12 . Pot  20  is only around pump portion  12  below casing  16  and is sealed to casing  16 . This reduces minimum pot  20  capacity and increases efficiency and speed of centrifugal pump  10 , as will be explained. 
     Since pot  20  surrounds only pump portion  12 , pot  20  limits low temperature fluid contact to pump portion  12 , and the design beneficially limits the portion of pump portion  12  that must be cooled prior to start. This reduction in size correspondingly reduces the heat capacity of the portion of pump portion  12  that must be by the low temperature fluid prior to start-up. The reduction in heat capacity allows a faster cooling of pump portion  12  to an operable temperature. One skilled in the instant art will therefore understand that by limiting the direct contact of low temperature fluid to pump portion  12 , the ‘startability’ of pump portion  12  is improved and increased in speed. 
     As will be understood by a reader skilled in the art, the embodiments presented above provide multiple benefits, particularly in the areas of reduced pump size, faster pump start speed (startability), increased thermal efficiency, faster vapor recovery, and construction simplicity. 
     Although only a single or few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiment(s) without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the spirit and scope of this invention as defined in the following claims. In the claims, means- or step-plus-function clauses are intended to cover the structures described or suggested herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, for example, although a nail, a screw, and a bolt may not be structural equivalents in that a nail relies entirely on friction between a wooden part and a cylindrical surface, a screw&#39;s helical surface positively engages the wooden part, and a bolt&#39;s head and nut compress opposite sides of at least one wooden part, in the environment of fastening wooden parts, a nail, a screw, and a bolt may be readily understood by those skilled in the art as equivalent structures. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.