Pump Comprising a Balance Arrangement and a Related Method

Abstract

A pump (110) is disclosed comprising: an inlet (114) being in fluid communication with an inlet cavity (115); an outlet (118) being in fluid communication with an outlet cavity (119); a motor (120) being arranged in a motor cavity (121); a pump axis (122) being rotatably drivable by the motor; impellers (124) being positioned between the inlet cavity and the outlet cavity and being actuatable by the pump axis to cause a differential pressure across the inlet cavity and the outlet cavity; and a balance arrangement (126) configured to at least partially offset an axial thrust affected upon the axis by the impellers when the pump is in operation, the balance arrangement comprising: a balance cavity (132); a balance drum (128) arranged between the outlet cavity and the balance cavity; and a balance line (134) extending between and fluidly connecting the balance cavity and the inlet cavity. The inlet is in fluid communication with the inlet cavity via the balance cavity and the balance line. A related method is also disclosed.

Claims

1. A pump comprising: an inlet in fluid communication with an inlet cavity; an outlet in fluid communication with an outlet cavity; a motor arranged in a motor cavity; a pump axis rotatably drivable by the motor; a number of impellers positioned between the inlet cavity and the outlet cavity and being actuatable by the pump axis to cause a differential pressure across the inlet cavity and the outlet cavity; and a balance arrangement configured to at least partially offset an axial thrust effected upon the axis by the impellers when the pump is in operation, the balance arrangement comprising: a balance cavity; a balance drum arranged between the outlet cavity and the balance cavity; and a balance line extending between and fluidly connecting the balance cavity and the inlet cavity; wherein the inlet is in fluid communication with the inlet cavity via the balance cavity and the balance line.

2. The pump according to claim 1, wherein the motor cavity is separated from the balance cavity by a rotary seal through which the axis runs.

3. The pump according to claim 2, wherein the rotary seal is configured to allow leakage of a barrier fluid from the motor cavity to the balance cavity.

4. The pump according to claim 1, wherein the balance arrangement is configured to allow leakage of a balance fluid from the outlet cavity to the balance cavity.

5. A method of pumping an inlet fluid using a subsea pump, the subsea pump comprising: an inlet in fluid communication with an inlet cavity; an outlet in fluid communication with an outlet cavity; a motor arranged in a motor cavity; a pump axis rotatably driven by the motor; a number of impellers positioned between the inlet cavity and the outlet cavity and being actuatable by the pump axis to cause a differential pressure across the inlet cavity and the outlet cavity; and a balance arrangement configured to at least partially offset an axial thrust effected upon the axis by the impellers when the pump is in operation, the balance arrangement comprising: a balance cavity; a balance drum arranged between the outlet cavity and the balance cavity; and a balance line extending between and fluidly connecting the balance cavity and the inlet cavity; wherein the method comprises directing the inlet fluid to the inlet cavity via the balance cavity and the balance line.

6. The method according to claim 5, further comprising: separating the motor cavity from the balance cavity using a rotary seal through which the axis extends; leaking a balance fluid through the balance arrangement from the outlet cavity to the balance cavity; and leaking a barrier fluid through the rotary seal from the motor cavity to the balance cavity; wherein the inlet fluid, the balance fluid and the barrier fluid are mixed in the balance cavity prior to being directed to the inlet cavity via the balance line.

Description

DESCRIPTION OF THE DRAWINGS

[0044] Following drawings are appended to facilitate the understanding of the invention:

[0045] FIG. 1 schematically illustrates a prior art pump; and

[0046] FIG. 2 schematically illustrates an embodiment of a pump according to the present invention.

[0047] In the drawings, like reference numerals have been used to indicate common parts, elements or features unless otherwise explicitly stated or implicitly understood by the context.

DETAILED DESCRIPTION OF THE INVENTION

[0048] In the following, a specific embodiment of the invention will be described in more detail with reference to FIG. 2. However, it is specifically intended that the invention is not limited to the embodiments and illustrations contained herein but includes modified forms of the embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system and/or business related constraints, which may vary from one implementation of the invention to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication and manufacture for the skilled person having the benefit of this disclosure.

[0049] According to the present invention, accumulation of deposits on the surfaces in the balance cavity area is at least reduced by increasing the flow through the balance cavity. This will have a mechanical flushing effect and also cause the dilution of leaked barrier fluid.

[0050] An embodiment of a pump 110 according to the present invention is schematically illustrated in FIG. 2.

[0051] The pump 110 comprises an inlet 114 which is in fluid communication with an inlet cavity 115 and an outlet 118 which is in fluid communication with an outlet cavity 119. The pump 110 further comprises a motor 120 which is arranged in a motor cavity 121, a pump axis 122 which is rotatably drivable by the motor 120.

[0052] The pump 110 also comprises impellers 124 which are positioned between the inlet cavity 115 and the outlet cavity 119 and which are actuatable by the pump axis 122 to cause a differential pressure across the inlet cavity 115 and the outlet cavity 119, i.e. across the inlet 114 and the outlet 118.

[0053] The pump 110 further comprises a balance arrangement 126 configured to at least partially offset an axial thrust effected upon the axis 122 by the impellers 124 when the pump 110 is in operation. The balance arrangement 126 comprises a balance cavity 132, a balance drum 128 arranged between the outlet cavity 119 and the balance cavity 132, and a balance line 134 extending between and fluidly connecting the balance cavity 132 and the inlet cavity 115.

[0054] The inlet 114 is in fluid communication with the inlet cavity 115 via the balance cavity 132 and the balance line 134 allowing the inlet fluid to be routed to the inlet cavity via the balance cavity and the balance line. In other words, the entire inlet flow of the pump 110 is routed through the balance cavity 132 on its ways to the inlet cavity 115.

[0055] As previously stated, this will reduce temperature and accumulation of deposits (e.g. scaling) in the balance cavity 120, which will increase the reliability of the pump.

[0056] The motor cavity 121 may be separated from the balance cavity 132 by a rotary seal 136 through which the axis 122 runs, which rotary seal 136 may be configured to allow leakage of a barrier fluid from the motor side of the seal 136, i.e. from the motor cavity 121, to the balance cavity 132. Since the inlet flow is routed through the balance cavity 132 on its way to the inlet cavity 115, the inlet flow will reduce the operating temperature at the mechanical seal 124, thus allowing alternative mechanical seal designs to be used, which also may increase seal reliability.

[0057] The balance arrangement 126 allows leakage of a portion of the pumped fluid from the outlet cavity 119 to the balance cavity 132, allowing the leaked fluid to act as a balance fluid.

[0058] In operation of the pump 110, the inlet fluid is directed to the inlet cavity 115 via the balance cavity 132 and the balance line 134.

[0059] The balance fluid being leaked through the balance arrangement 126 from the outlet cavity 119 to the balance cavity 132, and the barrier fluid being leaked through the rotary seal 136 from the motor cavity 121 to the balance cavity 132 will mix in the balance cavity 132 prior to being directed to the inlet cavity 115 via the balance line 134. As a consequence, the inlet fluid will cool the balance cavity 132 and also dilute the balance and barrier fluids, thus cooling the balance cavity 132 and its surroundings (including the seal 136) and prevent build-up of deposits, e.g. scale.

[0060] In the preceding description, various aspects of the apparatus according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the apparatus and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the apparatus, which are apparent to person skilled in the art to which the disclosed subject-matter pertains, are possible within the scope of the present invention as defined by the following claims.