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EP-4483062-B1 - A MULTI-STAGE CENTRIFUGAL PUMP COMPRISING AN ASSEMBLY FOR COMPENSATING AXIAL FORCES

EP4483062B1EP 4483062 B1EP4483062 B1EP 4483062B1EP-4483062-B1

Inventors

  • Tiitinen, Kalle
  • KOIVIKKO, MATTI
  • Vartiainen, Jouni

Dates

Publication Date
20260506
Application Date
20230224

Claims (14)

  1. A multi-stage centrifugal liquid pump (100) comprising an assembly (10) for compensating axial forces in the multi-stage centrifugal liquid pump (100), comprising - a housing (12), - a shaft (14) arranged rotatably to the housing (12), to which shaft (14) the impellers (14.1) of the pump (100) are coupled, - a balancing drum (16) arranged to the shaft (14) inside the housing (12), - the balancing drum (16) having a first axial end surface (16.1) and a second axial end surface (16.2), wherein the first axial end surface (16.1) is in flow communication with a stage of the pump adjacent to the balancing drum (16), - the balancing drum (16) is a multistage balancing drum, which comprises at least two drum sections (16', 16"), and there is a circumferential axial space (16.3) arranged between the drum sections (16', 16"), the drum sections having a first radius (R1), wherein ∘ the circumferential axial space (16.3) has a first axial length (L1) and a bottom, which bottom has a second radius (R2), which is smaller than the first radius (R1) - the assembly comprises in the housing (12) at least one ring element (20) at an axial position of the circumferential axial space (16.3), extending radially into the axial space (16.3) to a proximity of the bottom of the axial space (16.3), wherein ∘ the at least one ring element (20) has a radial inner surface having a third radius (R3), greater than the second radius (R2), ∘ the at least one ring element (20) has a second axial length (L2), which is less than the first axial length (L1) - the assembly comprises a first pressure chamber (22) between a first side wall of the circumferential axial space (16.3) and a first side wall of the ring element, - the assembly comprises a second pressure chamber (24) between a second side wall of the circumferential axial space (16.3) and a second side wall of the ring element, wherein the first pressure chamber (22) is nearer to the pump than the second pressure chamber (24), - the assembly comprises a first annular flow path between the first pressure chamber (22) and the second pressure chamber (24) via the bottom of the circumferential axial space (16.3) and the inner surface of the ring element (20), - the assembly comprises a second annular flow path extending out from the first pressure chamber (22) and from the second pressure chamber (24) via the outer surface of the drum sections (16',16‴) and the inner surface of the housing (12), characterized in that - the assembly comprises a first flow communication path extending from the stage of the pump (100) nearest to the balancing drum (16) to the second pressure chamber (24), and - the assembly comprises a second flow communication path extending from the stage of the pump (100) farthest from the balancing drum (16), to the first pressure chamber (22).
  2. A multi-stage centrifugal liquid pump (100) according to claim 1, characterized in that at least one of the drum sections (16',16",16‴) of the balancing drum (16) and opposing inner surface of the housing (12) comprise a slide bearing between the balancing drum (16) and the housing (12).
  3. A multi-stage centrifugal liquid pump (100) according to claim 2, characterized in that the slide bearing between at least one of the drum sections (16',16",16‴) and opposing inner surface of the housing (12) is configured to bear radial forces by means of a liquid film of pumped liquid between the surfaces, when in use.
  4. A multi-stage centrifugal liquid pump (100) according to claim 2, characterized in that all of the drum sections of the balancing drum (16) and opposing inner surfaces of the housing (12) comprise a slide bearing between the balancing drum (16) and the housing (12).
  5. A multi-stage centrifugal liquid pump (100) according to claim 1 or 2, characterized in that the balancing drum (16) comprises at least three drum sections (16', 16") and circumferential axial spaces (16.3) arranged between the drum sections (16', 16", 16‴), wherein - the balancing drum (16) has drum sections (16',16",16"') at both sides of each one of the axial spaces (16.3), - each one of the axial spaces (16.3) have a cylindrical bottom having a second radius (R2), - there is a ring element (20) in connection with each one of the axial spaces (16.3), - the second annular flow path is provided between the second pressure chamber (24) and the first pressure chamber (20) via outer surface of each drum section (16',16',16") of the balancing drum (16) and inner surface of the housing (12).
  6. A multi-stage centrifugal liquid pump (100) according to claim 5, characterized in that the balancing drum (16) comprises three axial spaces (16.3) and four drum sections.
  7. A multi-stage centrifugal liquid pump (100) according to claim 5, characterized in that the circumferential axial spaces (16.3) are identical and that the ring elements (20) are identical.
  8. A multi-stage centrifugal liquid pump (100) according to claim 1, characterized in that an axial length of the circumferential axial space is 1,05 - 2 times an axial length of the ring element (20).
  9. A multi-stage centrifugal liquid pump (100) according to claim 2 or 3, characterized in that the slide bearing has a bearing clearance arranged between cylindrical surfaces of the drum sections and a cylindrical inner surface of the housing (12).
  10. A multi-stage centrifugal liquid pump (100) according to claim 9, characterized in that the bearing clearance is less than 0,15mm.
  11. A multi-stage centrifugal liquid pump (100) according to claim 2 or 3, characterized in that the cylindrical counter surfaces of the balancing drum section and opposing housing comprise steel - silicon carbide counter surfaces.
  12. A multi-stage centrifugal liquid pump (100) according to claim 2 or 3, characterized in that the cylindrical counter surfaces of the balancing drum section and opposing housing comprise coated steel - polyether ether ketone counter surfaces.
  13. A multi-stage centrifugal liquid pump (100) according to claim 2 or 3, characterized in that the cylindrical counter surfaces of the balancing drum section and opposing housing comprise silicon carbide - silicon carbide counter surfaces.
  14. A multi-stage centrifugal liquid pump (100) according to claim 1, characterized in that radial gap between the bottom of the circumferential axial space (16.3) and inner surface of the ring element is provided with a mechanical sealing.

Description

Technical field The present invention relates to a multi-stage centrifugal pump comprising an assembly for compensating axial forces in a multi-stage centrifugal liquid pump according to the preamble of the first independent claim. Background art Centrifugal multi-phase centrifugal liquid pumps are provided with impeller wheels arranged into a housing by means of a rotatably supported shaft. During the operation of such centrifugal flow machines axial forces are subjected to the shaft. Such axial forces can be minimized by suitably designing the pump. Remaining forces are transmitted to the housing via a thrust bearing. Balancing axial forces is particularly relevant to multi-stage centrifugal flow machine where each stage results in an axial force component i.e., thrust to the system. The net axial thrust of an impeller is the difference between forces acting on back and front shrouds. There are number of hydrodynamic effects that can alter these forces. For instance, ring leakage or impeller axial positioning relative to the volute or diffuser can alter the pressure distribution between the impeller and sidewall gaps. Relatively small changes in pressure are greatly magnified by the large projected shroud surface areas. The result can be very large shifts in axial thrust in either direction. It is known as such to use a so-called balancing drum of minimizing the axial forces subjected to the bearings. Balancing drum is a part connected to a drive shaft of the machine, which drum has a cylindrical outer surface parallel with a center axis of the shaft of the centrifugal flow machine. The housing of the centrifugal flow machine is provided with a cylindrical space for the balancing drum. There is a clearance gap arranged between the balancing drum and the space in the housing. The purpose of the gap is to provide a flow restriction providing a pressure difference over the balancing drum. However, the clearance gap makes it possible for the process liquid to flow through the gap to some extent and therefore the efficiency of the centrifugal flow machine is decreased. Thus, it is often so that using the balancing drum cannot totally eliminate the need of a thrust bearing. The balancing drum provides an axial force which is based on hydraulic properties of the pump, dimensional proportions and prevailing operating point of the pump. Production tolerances, number impeller wheels and actual shape of pumps components cause deviation from designed compensating force of the balance drum. Thus, actual residual axial force may be considerably greater than the dimensioned one, which effects on dimensioning, lifetime and/or service interval of bearings. Publication JP 01-237394 discloses a balance piston provided in a centrifugal gas compressor. Document discloses a sealing ring attached to the inner peripheral surface of the casing is divided into three pieces in the axial direction and are arranged apart from each other. A high-pressure side sealing ring provided near the high-pressure gas chamber is opposed to a large-diameter portion of the balance drum. A low-pressure side sealing ring provided near the low-pressure gas chamber faces also the large-diameter portion of the balance drum. There is a middle sealing ring provided in the center portion which is opposed to the middle diameter portion of the balance drum. In this way, the annular space interposed between the sealing rings at both ends is partitioned into the low-pressure auxiliary chamber and the high-pressure auxiliary chamber by the middle sealing ring. A communication passage is provided to guide the high pressure of the high-pressure chamber to the high-pressure auxiliary chamber and keep the internal pressure of the high-pressure auxiliary chamber at high pressure. There is also disclosed a communication path which is provided to guide the low pressure of the low-pressure chamber to the low-pressure auxiliary chamber and keep the internal pressure of the low-pressure auxiliary chamber at the low pressure. Publication provides a balance piston for a gas compressor where distinct sealing rings separate the auxiliary chambers. DE 681 087 C discloses a device on centrifugal pumps for relieving axial thrust. Several relief disks are arranged one behind the other so that each relief disk is arranged in a special working chamber and that individual working chambers are separated from each other by circumferential sealing disks. An inflow chamber is arranged in front of the relief disk and an outflow chamber behind it. Relief fluid is fed into the former at a pressure that is higher than the pressure in the outflow chamber, which is separated from the adjacent relief disk by a circumferential sealing disk. An object of the invention is to provide an assembly for compensating axial forces in a multi-stage centrifugal liquid pump which performance is considerably improved compared to the prior art pumps. An object of the invention is to provide a multi-stage c