Screw pump rotor and method of reducing slip flow

Abstract

A pump rotor for a screw pump includes a shaft, a first set of threads disposed on a portion of an outer surface of the shaft, at least one thread of the first set of threads including a groove disposed on an end portion thereof, and a ring seal disposed on the groove such that the ring seal is configured to protrude outwardly from the groove and to rest against an inner surface of a liner of the screw pump, and the groove is sized so as to allow the ring seal to move radially with respect to the plurality of threads as the rotor is deflected.

1 . A pump rotor for a screw pump, the pump rotor comprising:
 a shaft;   a first set of threads disposed on a portion of an outer surface of the shaft, at least one thread of the first set of threads comprising a groove disposed on an end portion thereof; and   a seal disposed on the groove.   
   
   
       2 . The pump rotor according to  claim 1 , wherein the seal is a brush seal. 
   
   
       3 . The pump rotor according to  claim 1 , wherein the seal is a ring seal. 
   
   
       4 . The pump rotor according to  claim 3 , wherein the ring seal is configured to protrude outwardly from the groove and to rest against an inner surface of a liner of the screw pump, and the groove is sized so as to allow the ring seal to move radially with respect to the at least one thread as the rotor is deflected. 
   
   
       5 . The pump rotor according to  claim 3 , wherein the ring seal is configured to rotate with the shaft. 
   
   
       6 . The pump rotor according to  claim 5 , further comprising: first and second pins disposed in the groove, a first end of the ring seal being disposed against the first pin and a second end of the ring seal being disposed against the second pin. 
   
   
       7 . The pump rotor according to  claim 6 , wherein the ring seal and the first set of threads are helical. 
   
   
       8 . The pump rotor according to  claim 1 , further comprising:
 a second set of threads disposed on another portion of the outer surface of the shaft, at least one thread of the second set of threads comprising a groove disposed on an end portion thereof, the first set being separate from the second set, and a second ring seal being disposed on the groove of the at least one thread of the second set;   first and second pins disposed in the groove of the at least one thread of the first set, a first end of the ring seal being disposed against the first pin and a second end of the ring seal being disposed against the second pin; and   third and fourth pins disposed in the groove of the at least one thread of the second set, a first end of the second ring seal being disposed against the third pin and a second end of the second ring seal being disposed against the fourth pin.   
   
   
       9 . The pump rotor according to  claim 8 , wherein circumferential positions of the first and second pins and circumferential positions of the third and fourth pins are different from each other. 
   
   
       10 . The pump rotor according to  claim 3 , wherein the ring seal is a sacrificial wear component of the pump rotor. 
   
   
       11 . A twin-screw pump, comprising:
 a casing having an inlet and an outlet;   a liner disposed inside of the casing; and   two rotors disposed inside of the liner, each rotor comprising, a shaft;
 a set of threads disposed on a portion of an outer surface of the shaft, at least one thread of the first set of threads comprising a groove disposed on an end portion thereof; and 
 a ring seal disposed on the groove. 
   
   
   
       12 . The pump according to  claim 11 , wherein each ring seal is configured to protrude outwardly from the groove and to rest against an inner surface of the liner, and the groove is sized so as to allow each ring seal to move radially with respect to the at least one thread of the first set of threads as the rotor is deflected. 
   
   
       13 . The pump according to  claim 12 , wherein the ring seal is configured to rotate with the respective shaft. 
   
   
       14 . The pump according to  claim 13 , wherein each rotor further comprises first and second pins disposed in the groove, a first end of the ring seal being disposed against the first pin and a second end of the ring seal being disposed against the second pin. 
   
   
       15 . The pump according to  claim 14 , wherein the ring seal and the set of threads are helical. 
   
   
       16 . The pump according to  claim 11 , wherein for each rotor the set of threads is a first set of threads, each rotor further comprising,
 a second set of threads disposed on another portion of the outer surface of the shaft, at least one thread of the second set of threads comprising a groove disposed on an end portion thereof, the first set being separate from the second set, and a second ring seal being disposed on the groove of the at least one thread of the second set;   first and second pins disposed in the groove of the at least one thread of the first set, a first end of the ring seal being disposed against the first pin and a second end of the ring seal being disposed against the second pin; and   third and fourth pins disposed in the groove of the at least one thread of the second set, a first end of the second ring seal being disposed against the third pin and a second end of the second ring seal being disposed against the fourth pin.   
   
   
       17 . The pump according to  claim 11 , further comprising:
 variable speed drives; and   a clearance control logic configured to control the speed of the drives.   
   
   
       18 . A method of reducing slip flow in a screw pump having a casing having a low-pressure inlet and a high-pressure outlet, a liner disposed inside of the casing, and a rotor disposed inside of the liner having a shaft and a first set of threads disposed on a portion of an outer surface of the shaft, the method comprising:
 forming a groove on end portions of each thread Of the first set of threads;   disposing a ring seal on the groove, the ring seal being configured to protrude outwardly from the groove and to rest against an inner surface of the liner of the screw pump, the groove being sized so as to allow the ring seal to move radially with respect to the first set of threads as the rotor is deflected, and the ring seal being configured to reduce the slip flow from the high-pressure outlet to the low-pressure inlet.   
   
   
       19 . The method according to  claim 18 , further comprising rotating the ring seal when the shaft is rotated. 
   
   
       20 . The method according to  claim 19 , further comprising preventing the ring seal to rotate with respect to the shaft by placing first and second pins in the groove, a first end of the ring seal being disposed against the first pin and a second end of the ring seal being disposed against the second pin.