Rotary pump for conveying process fluid

Abstract

A rotary pump for delivering a process fluid is proposed, comprising: a pump housing having an inlet for receiving the process fluid, an outlet for discharging the process fluid; a pump shaft configured to rotate about an axial direction; and a hydraulic unit for conveying and pressurizing a process fluid wherein the hydraulic unit comprises at least one impeller fixedly mounted on a pump shaft, the pump further comprising a balancing device for balancing an axial thrust generated by the hydraulic unit, the balancing device comprises a balancing disc fixedly connected to the pump shaft and having a rotary sliding surface, and a stationary part fixedly connected to the pump housing and having a stationary sliding surface, where the rotary sliding surface and the stationary sliding surface face each other, and where a radial bleed channel is provided between the rotary sliding surface and the stationary sliding surface. Each of the rotating sliding surface and the fixed sliding surface includes at least 30% diamond by volume.

Description

Technical Field

[0001] The invention relates to a rotary pump for conveying process fluids according to the preamble of the independent claim. Background Art

[0002] Rotary pumps for conveying fluids, for example liquids such as water, are used in many different industries. Examples are the oil and gas industry, the power generation industry, the chemical industry, the water industry or the pulp and paper industry. The rotary pump has at least one impeller and a pump shaft for rotating the impeller. The at least one impeller can be configured, for example, as a radial impeller, or as an axial or semi-axial impeller, or as a helical axial impeller. Furthermore, the impeller can be configured as an open impeller or as a closed impeller, wherein a shroud is arranged on the impeller, the shroud at least partially covering the blades of the impeller.

[0003] A rotary pump can be designed as a single-stage pump with only one impeller mounted to the shaft, or as a multistage pump comprising a plurality of impellers, wherein the impellers are arranged one behind the other on the shaft. The impellers can be arranged in either an in-line arrangement, wherein the axial thrust generated by a single impeller is directed in the same direction for all impellers, or a back-to-back arrangement, wherein the axial thrust generated by a first set of impellers is directed in the opposite direction to the axial thrust generated by a second set of impellers.

[0004] Many rotary pumps are provided with at least one balancing device or balancing system for at least partially balancing the axial thrust generated by the impeller(s) during operation of the pump. The balancing device at least reduces the axial thrust that must be carried by the axial bearing or thrust bearing. Known balancing devices include, for example, balancing drums or balancing discs.

[0005] The balancing drum is fixedly connected to the pump shaft of the pump in a torque-proof manner and is further fixedly connected to the pump shaft relative to the axial direction. A discharge channel is arranged between the balancing drum and a fixed part fixed relative to the pump housing. The discharge channel extends from the front side of the balancing drum to the rear side of the balancing drum in the axial direction. At the front side, high pressure prevails, such as the discharge pressure of the pump. The rear side is usually connected to the suction side or low-pressure position of the pump by means of a balancing line. Therefore, during the operation of the pump, the balancing drum generates an axial force that counteracts the axial thrust generated by the impeller (s).

[0006] Other known balancing devices include a balancing disc. The balancing disc works similarly to a balancing drum, however, the discharge channel usually extends in a radial direction perpendicular to the axial direction or in a direction oblique to the axial direction. The balancing disc is fixedly connected to the pump shaft in a torque-proof manner. In addition, the balancing disc is fixedly connected to the pump shaft relative to the axial direction. The balancing disc cooperates with a counterpart arranged to face the balancing disc. The counterpart is a fixed part, which is fixedly connected to the pump housing. The front side of the balancing disc (which is the side facing the fixed counterpart) is exposed to high pressure (e.g., the discharge pressure of the pump or a reduced discharge pressure), while the rear side of the balancing disc is connected to low pressure (e.g., the suction pressure of the pump). Sometimes a throttle valve is arranged between the high-pressure side and the front side of the balancing disc and / or between the rear side of the balancing disc and the low-pressure side of the pump.

[0007] Typically, the balancing disc comprises a rotating sliding surface, and the fixed part comprises a fixed sliding surface facing the rotating sliding surface. The discharge channel is arranged between the rotating sliding surface and the fixed sliding surface. If no measures are taken, the fixed sliding surface and the rotating sliding surface abut against each other when the pump is stationary (i.e., when the pump does not generate any pressure). When the pump starts to generate pressure, the higher pressure at the front side of the balancing disc pushes the balancing disc and the pump shaft away from the fixed part, so that the radial discharge channel opens between the fixed sliding surface and the rotating sliding surface.

[0008] The advantage of a balancing disc compared to a balancing drum lies in the fact that the balancing disc is self-adjusting and completely balances the axial thrust generated by the impeller(s), so that no axial bearing is required for the pump shaft. When the pump is operated, for example, at its nominal speed, the radial discharge channel has a nominal width, for example of about 100 micrometers. If now for any reason the pressure at the front side increases, the balancing disc moves in the axial direction away from the fixed part, which in turn increases the width of the radial discharge channel. As a result, the pressure drop across the balancing disc decreases and the balancing disc moves in the axial direction towards the fixed part. In this known manner, the balancing disc is self-adjusting and can completely balance the axial thrust generated by the rotating impeller(s).

[0009] One problem with balancing disks is dry running, in particular during pump startup and also during shutdown. If there is no fluid film between the rotating sliding surface and the fixed sliding surface or the fluid film is not sufficiently developed, dry friction or mixed friction occurs between these sliding surfaces. Dry friction or mixed friction causes severe wear and a large generation of heat, which in turn leads to severe thermal stresses in the balancing disk, the fixed part and other parts of the pump.

[0010] Many material pairings have been used for rotating and stationary sliding surfaces, such as high performance plastics sliding along hardened surfaces (such as polymers PEEK (polyetheretherketone), or SiC (silicon carbide) sliding along SiC, hardened metal sliding along hardened metal, or many other material combinations. However, all these material pairings have not provided truly satisfactory results.

[0011] In order to solve these problems, it has been proposed to provide a lift-off device which bridges the critical phases during startup and shutdown to avoid direct physical contact between the balancing disc and the fixed part. In order to ensure contactless startup and shutdown of the pump, the lift-off device generates a displacement of the pump shaft in the axial direction so that the rotating sliding surface and the fixed sliding surface do not touch each other. The displacement of the pump shaft can be generated, for example, by magnetic force generation or by mechanical means using spring force to displace the pump shaft. Such a mechanical lift-off device is disclosed, for example, in EP 3832143 A1.

[0012] However, providing the pump shaft with a lifting device requires additional equipment, which increases the manpower and cost for manufacturing the pump. Summary of the invention

[0013] Starting from this prior art, the object of the present invention is therefore to propose a rotary pump for conveying process fluids, which has a balancing device with a balancing disk, wherein the balancing device is exposed to low wear without reducing the balancing of axial thrust forces acting on the pump shaft during operation of the pump.

[0014] The subject matter of the invention which meets this object is characterized by the features of the independent claims.

[0015] Therefore, according to the present invention, a rotary pump for conveying a process fluid is proposed, the rotary pump comprising: a pump housing having an inlet for receiving the process fluid, an outlet for discharging the process fluid; a pump shaft configured to rotate about an axial direction; and a hydraulic unit for conveying and pressurizing the process fluid, wherein the hydraulic unit comprises at least one impeller fixedly mounted on the pump shaft, the pump further comprising a balancing device for balancing the axial thrust generated by the hydraulic unit, the balancing device comprising a balancing disc fixedly connected to the pump shaft and having a rotating sliding surface, and a fixed part fixedly connected to the pump housing and having a fixed sliding surface, wherein the rotating sliding surface and the fixed sliding surface face each other, and wherein a radial discharge channel is provided between the rotating sliding surface and the fixed sliding surface. Each of the rotating sliding surface and the fixed sliding surface comprises at least 30% diamond by volume.

[0016] By providing both the rotating sliding surface of the balancing disc and the fixed sliding surface of the fixed part with a diamond content of at least 30% by volume, the two sliding surfaces have excellent wear resistance and a very low friction coefficient, so that the two sliding surfaces can slide along each other without significant wear even under dry running conditions. Therefore, even if the rotating sliding surface and the rotating sliding surface abut against each other, so that there is dry friction or mixed friction between the two sliding surfaces, there is no significant wear, which is due to the very low friction coefficient of diamond and the high wear resistance of diamond. In addition, the high compressive stress strength of diamond ensures that even if the two sliding surfaces slide along each other in direct physical contact with each other, these sliding surfaces will not be damaged.

[0017] In many applications, the fluid film between the rotating sliding surface and the fixed sliding surface consists of a process fluid, i.e. the balancing device is lubricated by the process fluid. For these applications, diamond-containing fixed and rotating sliding surfaces have the following advantages: the process fluid can contain abrasives (e.g. sand) without endangering the correct and reliable operation of the balancing device.

[0018] Furthermore, it is no longer necessary to provide a lifting device for producing a displacement of the pump shaft in the axial direction (particularly during start-up and shut-down) in order to avoid direct physical contact between the balancing disc and the fixed part. The rotary pump according to the invention can be started and stopped with direct physical contact between the fixed sliding surface and the rotating sliding surface.

[0019] According to a preferred embodiment, each of the rotating sliding surface and the fixed sliding surface is configured as an annular surface.

[0020] There are several preferred possibilities for providing the rotating sliding face and the stationary sliding face with a diamond content of at least 30% by volume.

[0021] In some embodiments, each of the rotating sliding surface and the fixed sliding surface is configured as a diamond surface. In these embodiments, the rotating sliding surface and the fixed sliding surface are completely composed of diamond, for example, a thin diamond layer is provided on a substrate to form the rotating sliding surface and the fixed sliding surface, respectively. The thickness of the diamond layer can be several microns, for example, two microns.

[0022] In some embodiments, each of the rotating sliding surface and the stationary sliding surface comprises polycrystalline diamond.

[0023] According to a preferred embodiment, each of the rotating sliding surface and the fixed sliding surface comprises diamond-grain reinforced silicon carbide (hereinafter referred to as diamond-SiC). Diamond-SiC is a matrix composite material in which diamond grains are embedded in a matrix of silicon carbide (SiC). In addition to its excellent hardness and strength, diamond-SiC also has a very high thermal conductivity, for example up to 500 Watts / meter × Kelvin (W / m*K). High thermal conductivity is conducive to reliably removing heat generated, for example, between the rotating sliding surface and the fixed sliding surface. In addition, diamond-SiC has a very low tendency to fretting.

[0024] Particularly preferably, each of the rotating sliding surface and the fixed sliding surface is composed of silicon carbide (diamond-SiC) enhanced by diamond particles. Due to the excellent hardness of diamond, the physical contact between the rotating sliding surface and the fixed sliding surface is at least similar to pure diamond-diamond contact. If the contact between the rotating sliding surface and the fixed sliding surface is also based on non-diamond material (e.g., SiC) at the beginning, the non-diamond material is eroded quite fast, so that the diamond material then protrudes from the rest of the corresponding sliding surface. Therefore, the remaining contact between the two sliding surfaces is completely based on diamond-diamond contact.

[0025] In some embodiments, the balancing disc includes a rotating ring arranged in an annular groove and forming a rotating sliding surface, wherein the fixed part includes a fixed ring arranged in the annular groove and forming a fixed sliding surface. The balancing disc includes an annular groove, which is arranged in the surface facing the fixed part. The fixed part includes an annular groove, which is arranged in the surface facing the rotating part. These annular grooves are aligned with each other, so that the rotating ring arranged in the annular groove of the balancing disc is aligned with the fixed ring in the annular groove of the fixed part. The surface of the rotating ring facing the fixed ring forms the rotating sliding surface, and the surface of the fixed ring facing the rotating ring forms the fixed sliding surface.

[0026] Preferably, the rotating sliding surface of the rotating ring and the stationary sliding surface of the stationary ring are made of diamond particle reinforced silicon carbide (diamond-SiC).

[0027] In some embodiments, the entire rotating ring and / or the entire stationary ring consists of diamond-SiC. In other embodiments, both the rotating ring and the stationary ring include a carrier on which a diamond-SiC layer is provided, wherein the carrier is made of a material different from diamond-SiC, such as SiC.

[0028] In some embodiments, the rotating ring comprises an annular recess extending along the circumference of the rotating ring, wherein a rotating inlay is arranged in the annular recess, the rotating inlay forming a rotating sliding surface.

[0029] In some embodiments, the fixing ring comprises an annular recess extending along the circumference of the fixing ring, wherein a fixing inlay is arranged in the annular recess, the fixing inlay forming the fixing sliding surface.

[0030] According to a preferred configuration of the embodiment having a rotating ring with an annular recess and a fixed ring with an annular recess, the rotating ring and the fixed ring are made of silicon carbide.

[0031] Preferably, the rotating inlay and the fixed inlay are made of diamond particle reinforced silicon carbide (diamond-SiC). In this configuration in which the fixed inlay and the rotating inlay are made of diamond-SiC, the diamond-SiC inlay is embedded in the SiC ring.

[0032] It is particularly preferred that each of the rotating sliding surface and the fixed sliding surface comprises at least 50% by volume of diamond.

[0033] Due to the excellent tribological, mechanical and thermal properties of diamond, it is possible to configure the rotary pump so that the nominal width of the radial discharge channel is significantly smaller than that of conventional rotary pumps. In the rotary pump according to the invention, it is possible that the radial discharge channel is configured to be at most 80 microns, preferably at most 50 microns during operation of the rotary pump. Of course, the width of the radial discharge channel may change during operation, however, the width of the radial discharge channel has a nominal value, which is, for example, the width of the radial discharge channel or an average value of said width when the pump is operated at a nominal speed.

[0034] With regard to the efficiency of the rotary pump, a smaller width of the radial bleed channel is advantageous. Leakage of process fluid through the bleed channel results in a decrease in the hydraulic performance or efficiency of the pump. Therefore, reducing the width of the radial bleed channel improves the efficiency of the pump.

[0035] Nowadays, in many applications, efforts are made to utilize pumps most efficiently. It is desirable to have the highest possible ratio of power delivered by the pump (especially hydraulic power) to the power required to drive the pump. This desire is mainly based on an increased awareness of environmental protection and the responsible handling of available resources and on the increasing energy costs. Therefore, an advantage of the rotary pump according to the invention is that the radial discharge gap can be constructed with a smaller width.

[0036] In some embodiments, the rotary pump is configured as a multi-stage centrifugal pump. In a multi-stage centrifugal pump, the hydraulic unit comprises at least a first-stage impeller and a final-stage impeller, and optionally at least one intermediate-stage impeller, wherein each impeller is fixedly mounted on a pump shaft.

[0037] Further advantageous measures and embodiments of the invention are apparent from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention will be explained in more detail below with reference to embodiments of the invention and with reference to the accompanying drawings. The accompanying drawings are shown in schematic representation:

[0039] Figure 1 is a schematic cross-sectional view of an embodiment of a rotary pump according to the present invention,

[0040] Figure 2 is an enlarged cross-sectional view showing a balancing device,

[0041] Figure 3 is a schematic cross-sectional view of a first embodiment of a rotating ring and a fixed ring of a balancing device,

[0042] Figure 4 is a schematic cross-sectional view of a second embodiment of a rotating ring and a fixed ring of a balancing device, and

[0043] Figure 5 is a schematic cross-sectional view of a third embodiment of a rotating ring and a fixed ring of a balancing device. DETAILED DESCRIPTION

[0044] Figure 1 A cross-sectional view of an embodiment of a rotary pump according to the invention is shown, which is designated as a whole by reference numeral 1. The pump 1 is designed as a centrifugal pump for conveying a process fluid, for example a liquid such as water.

[0045] The rotary pump 1 comprises a pump housing 2 having an inlet 3 and an outlet 4 for the fluid to be conveyed. The inlet 3 is arranged on the suction side and receives the process fluid with a suction pressure SP. The outlet 4 is arranged on the discharge side and discharges the fluid with a discharge pressure DP, wherein the discharge pressure DP is greater than the suction pressure SP. The pump 1 further comprises a hydraulic unit 5 for conveying the process fluid from the inlet 3 to the outlet 4 and for pressurizing the process fluid from the suction pressure SP so that the fluid is discharged at the outlet 4 at the discharge pressure DP.

[0046] The hydraulic unit 5 comprises at least one impeller 51 , 52 , 53 for acting on a fluid.

[0047] The pump further includes a pump shaft 6 for rotating each impeller 51, 52, 53 about an axial direction A. The axial direction A is defined by the axis of the pump shaft 6. The direction perpendicular to the axial direction A is referred to as the radial direction. The pump shaft 6 extends from a drive end 61 to a non-drive end 62. In this embodiment of the pump, the drive end 61 of the pump shaft 6 is located outside the pump housing 2 and can be connected to a drive unit (not shown) for driving the pump shaft 6 to rotate about the axial direction A. The drive unit may include, for example, an electric motor. Each impeller 51, 52, 53 is mounted to the pump shaft 6 in a torque-proof manner and is further fixedly connected to the pump shaft 6 relative to the axial direction A.

[0048] In the following description, reference is made by way of example to an embodiment suitable for many applications, namely that the rotary pump 1 is configured as a multistage pump 1, wherein the hydraulic unit 5 comprises a plurality of impellers 51, 52, 53, namely at least a first-stage impeller 51, a final-stage impeller 52, and optionally at least one intermediate-stage impeller 53, wherein each impeller 51, 52, 53 is fixedly mounted on a pump shaft 6. The impellers 51, 52, 53 are arranged one after another on the pump shaft 6. Reference numeral 51 denotes a first-stage impeller, which is arranged closest to an inlet 3 for receiving a process fluid having a suction pressure SP. Reference numeral 52 denotes a final-stage impeller 52, which is the impeller 52 closest to an outlet 4. The final-stage impeller 52 pressurizes the fluid so that the fluid is discharged through the outlet 4 at a discharge pressure DP. Reference numeral 53 denotes an intermediate-stage impeller 53. When viewed in the direction of increasing pressure, each intermediate-stage impeller 53 is arranged between the first-stage impeller 51 and the final-stage impeller 52.

[0049] Figure 1 The embodiment shown in FIG. 1 has three stages, i.e. the hydraulic unit 5 comprises a first stage impeller 51, a final stage impeller 52 and an intermediate stage impeller 53. Of course, the number of three stages must be understood as exemplary. The plurality of impellers 51, 52, 53 may be arranged in a straight line configuration (e.g. Figure 1 In the case of the embodiment of the pump 1 as a single-stage pump, the hydraulic unit is provided with only one impeller, which constitutes the first-stage impeller 51 or the last-stage impeller 52, respectively.

[0050] Figure 1 The multi-stage rotary pump 1 shown in FIG. 1 is designed as a horizontal pump, which means that during operation the pump shaft 6 extends horizontally, ie the axial direction A is perpendicular to the direction of gravity.

[0051] It has to be understood that the invention is not limited to this type of rotary pump 1. In other embodiments, the rotary pump may for example be designed as a vertical pump, which means that during operation the pump shaft 6 extends in the vertical direction, which is the direction of gravity.

[0052] The rotary pump 1 includes bearings on both sides (with respect to the axial direction A) of the hydraulic unit 5, i.e. the rotary pump 1 is designed as a between-bearing pump. A first radial bearing 81 and a second radial bearing 82 are provided for supporting the pump shaft 6. The first radial bearing 81 is arranged adjacent to the drive end 61 of the pump shaft 6. The second radial bearing 82 is arranged adjacent to or at the non-drive end 62 of the pump shaft 6. An embodiment of the rotary pump 1 has no axial bearings, because the axial thrust generated by the impellers 51, 52, 53 is completely compensated by the balancing device 7. In other embodiments, the rotary pump 1 is configured with at least one axial bearing.

[0053] The radial bearings 81 , 82 are configured to support the pump shaft 6 in a radial direction perpendicular to the axial direction A. A radial bearing such as the first radial bearing 81 or the second radial bearing 82 is also referred to as a “journal bearing”.

[0054] All bearings 81, 82 are preferably configured as antifriction bearings, such as ball bearings. Of course, it is also possible that some or all bearings 81, 82 are configured as liquid hydrodynamic bearings. Bearings 81, 82 can be configured as process fluid lubricated bearings 81, 82, which are also referred to as process lubricated bearings (PLBs). The term "process fluid lubricated pump" refers to a pump in which the process fluid conveyed by pump 1 is used to lubricate and cool the components of the pump (e.g., bearings 81, 82). Therefore, the process fluid lubricated pump 1 uses the process fluid itself or the process fluid modified (e.g., by filtering process) to lubricate and / or cool the pump components. There is no separate lubricant (e.g., oil) required for lubricating and cooling the pump components (e.g., bearings 81, 82). The advantage of the process fluid lubricated pump 1 is that it does not require a separate oil or fluid lubrication system, while in other types of pumps, a separate oil or fluid lubrication system is required. When the pump is not lubricated by a process fluid or a modified process fluid, a shaft seal is required which separates the process fluid from both the environment and the lubrication system filled with a lubricant different from the process fluid.

[0055] The rotary pump 1 further comprises a balancing device 7, which will be referred to as Figure 2 Explaining the balancing device in more detail, the figure shows an enlarged cross-sectional view of the balancing device 7. The balancing device 7 is configured to balance the axial thrust generated by the hydraulic unit 5, more precisely, by the impellers 51, 52, 53. The balancing device 7 comprises a balancing disc 70 fixedly connected to the pump shaft 6 and having a rotating sliding surface 75. The balancing device 7 further comprises a fixed part 90 fixedly connected to the pump housing 2 and having a fixed sliding surface 95, wherein the rotating sliding surface 75 and the fixed sliding surface 95 face each other. The radial discharge channel 79 (see also Figure 3 ) is arranged between the rotating sliding surface 75 and the fixed sliding surface 95.

[0056] The provision of a balancing disc 70 for compensating the axial thrust generated by the impellers 51 , 52 , 53 is known per se in the art and will therefore only be briefly explained here.

[0057] The balancing disc 70 is fixedly connected to the pump shaft 6 in a torque-proof manner and is further fixed to the pump shaft 6 relative to the axial direction A, so that the balancing disc 70 cannot move relative to the pump shaft 6 relative to the axial direction A. Therefore, the axial thrust generated by the impellers 51, 52, 53 can be compensated by the balancing disc 70. The balancing disc 70 is arranged between the hydraulic unit 5 and the non-drive end 62 of the pump shaft 6. The balancing disc 70 defines a front side 71 and a rear side 72. Both the front side 71 and the rear side 72 are configured as annular chambers. The front side 71 is a side or space facing the hydraulic unit 5. The rear side 72 is a side or space facing away from the hydraulic unit 5. The balancing disc 70 is arranged adjacent to the fixed portion 90, so that the fixed portion 90 is arranged between the hydraulic unit 5 and the balancing disc 70 with respect to the axial direction A.

[0058] The pump shaft 6 is configured to be movable relative to the axial direction A so that a radial relief passage 79 is formed between the rotating sliding surface 75 and the fixed sliding surface 95 . The radial relief passage 79 forms an annular gap between the fixed sliding surface 95 and the rotating sliding surface 75 .

[0059] The radial drainage channel 79 is also referred to as a "radial gap" or a "radial labyrinth". The term "radial" indicates that the drainage channel 79 extends in a radial direction, so that the process fluid passing through the radial drainage channel 79 flows in a radial direction. It should be noted that in other embodiments, the radial drainage channel does not extend exactly in a radial direction (i.e., perpendicular to the axial direction A), but may also be inclined both relative to the axial direction A and relative to the radial direction.

[0060] When the rotary pump 1 is at rest, the rotating sliding surface 75 abuts against the fixed sliding surface 95. When the pump 1 is started, it generates pressure. Reference is now made to the operating state, in which the pump 1 is operating at its nominal speed, so that the discharge pressure DP prevails at the outlet 4 and the suction pressure SP prevails at the inlet 3.

[0061] The front side 71 is in fluid communication with the rear side of the final impeller 52, where essentially the discharge pressure DP prevails. It is possible to arrange the first throttle valve channel 10 in said fluid communication so that the pressure P1 prevailing at the front side 71 is less than the discharge pressure DP. The rear side 72 is in fluid communication with a low-pressure location, for example, a location where the suction pressure SP prevails. It is possible to arrange the second throttle valve channel 11 in said fluid communication so that the pressure P2 prevailing at the rear side 72 is higher than the suction pressure SP. Of course, the pressure P2 prevailing at the rear side 72 is less than the pressure P1 prevailing at the front side 71. Therefore, it is

[0062] DP≥P1>P2≥SP.

[0063] The pressure difference P1-P2 across the balancing disk 70 generates a pressure acting in the axial direction A and directed from the front side 71 to the rear side 72 (ie, according to Figure 2 This force counteracts and compensates the axial thrust generated by the impellers 51, 52, 53 during operation of the pump 1. Figure 2 As shown in FIG. 1 , the axial thrust generated by the impellers 51 , 52 , 53 is directed from right to left.

[0064] The balancing disc 70 is self-adjusting, as known to those skilled in the art. Therefore, it is not necessary to describe the self-adjustment.

[0065] According to the invention, each of the rotating sliding surface 75 and the fixed sliding surface 95 comprises at least 30% by volume of diamond. Preferably, the diamond content of both the rotating sliding surface 75 and the fixed sliding surface 95 is at least 50% by volume.

[0066] According to a preferred embodiment, Figure 2 As shown in FIG, the balancing disc 70 includes a rotating ring 76 arranged in an annular groove 77 and forming a rotating sliding surface 75. In addition, it is preferred that the fixed part 90 includes a fixed ring 96 arranged in an annular groove 97 and forming a fixed sliding surface 95. The rotating ring 76 and the fixed ring 96 are aligned with each other so that the rotating sliding surface 75 abuts against the fixed sliding surface 95 when the pump 1 is stationary.

[0067] The annular grooves 77 and 97 may be provided with a sealing element 13 to prevent the process fluid from entering the respective annular grooves 77, 97. The sealing element 13 is configured as an O-ring, for example.

[0068] There are several possibilities for providing the rotating sliding surface 75 and the stationary sliding surface 95 with a diamond content of at least 30% by volume.

[0069] Figure 3 A schematic cross-sectional view of a first embodiment of the rotating ring 76 and the fixed ring 96 of the balancing device 7 is shown.

[0070] As in Figure 3 As shown in the cross-sectional view of the rotating ring 76 and the fixed ring 97 in FIG. 1 , it is possible to construct the rotating ring 76 as a one-piece part composed entirely of the same material. In addition, it is possible to construct the fixed ring 96 as a one-piece part composed entirely of the same material, which can be the same or different material as the material that constitutes the rotating ring 76.

[0071] In particular, the rotating ring 76 and the stationary ring 96 may be composed of polycrystalline diamond (PCD) or diamond particle reinforced silicon carbide (diamond—SiC).

[0072] Figure 4A schematic cross-sectional view of a second embodiment of the rotating ring 76 and the fixed ring 96 of the balancing device 7 is shown.

[0073] As in Figure 4 As shown in the cross-sectional view of the rotating ring 76 and the fixed ring 96 in FIG. 1 , it is also possible to construct the rotating ring 76 and / or the fixed ring 96 with a base 771, 971 on which a layer 772, 972 having a diamond content of at least 30% by volume is arranged. The layers 772, 972 form the rotating sliding surface 75 or the fixed sliding surface 95, respectively. Each of the layers 772, 972 can completely cover (e.g. Figure 4 ) or partially covers the corresponding substrate 771, 971.

[0074] Each layer 772, 972 may be configured as a diamond face, which is generated, for example, by a chemical vapor deposition (CVD) process. When layers 772 and / or 972 are configured as diamond faces, the thickness of layers 772, 972 is typically in the range of a few microns, such as two microns.

[0075] It is also possible that layer 772 and / or layer 972 consists of diamond-SiC.

[0076] When the layer 772 or 972 is made of diamond-SiC, it is preferred that the corresponding base body 771 , 971 consists of SiC.

[0077] Figure 5 A schematic cross-sectional view of a third embodiment of the rotating ring 76 and the fixed ring 96 of the balancing device 7 is shown.

[0078] The rotating ring 76 includes an annular recess 773 extending along the circumference of the rotating ring 76 , and a rotating inlay 774 is arranged in the annular recess 773 , the rotating inlay forming the rotating sliding surface 75 .

[0079] The fixing ring 97 comprises an annular recess 973 extending along the circumference of the fixing ring 97 and wherein a fixing inlay 974 is arranged in the annular recess 973 , the fixing inlay 974 forming the fixing sliding surface 95 .

[0080] Preferably, the extension of the annular recess 773 of the rotating ring 76 in the radial direction is smaller than the extension of the rotating ring 76 in the radial direction. In addition, it is preferred that the annular recess 773 is arranged in the middle of the rotating ring 76 with respect to the radial direction.

[0081] Furthermore, it is preferred that the annular recess 973 of the fixing ring 96 extends in the radial direction less than the extension of the fixing ring 96 in the radial direction. Furthermore, it is preferred that the annular recess 973 is arranged in the middle of the fixing ring 96 with respect to the radial direction.

[0082] It is particularly preferred that both the rotating inlay 774 and the fixed inlay 974 are made of diamond-SiC.

[0083] When the fixed inlay 974 or the rotating inlay 774 is made of diamond-SiC, the rotating ring 76 and the fixed ring 96 are made of silicon carbide, which means that the rotating ring 76 and the fixed ring 96 are made of SiC, wherein the rotating inlay 774 and the fixed inlay 974 are made of diamond-SiC.

[0084] Due to the excellent tribological, mechanical and thermal properties of diamond, it is possible to configure the rotary pump 1 so that the nominal width W of the radial discharge channel 79 is significantly smaller than that of conventional rotary pumps. In the rotary pump 1 according to the present invention, it is possible that the radial discharge channel 79 is configured to be at most 80 microns, preferably at most 50 microns during operation of the rotary pump. Of course, the width W of the radial discharge channel can change during operation, however, the width W of the radial discharge channel 79 has a nominal value, which is, for example, the width W of the radial discharge channel 79 or an average value of the width W when the pump is operated at a nominal speed.

Claims

1. A rotary pump for conveying a process fluid, the rotary pump comprising: A pump housing (2) having an inlet (3) for receiving the process fluid, an outlet (4) for discharging the process fluid; a pump shaft (6) configured to rotate about an axial direction (A); and a hydraulic unit (5) for conveying and pressurizing the process fluid, wherein the hydraulic unit (5) comprises at least one impeller (51, 52, 53) fixedly mounted on the pump shaft (6), and the pump further comprises a balancing device (7) for balancing the axial thrust generated by the hydraulic unit (5), the balancing device (7) comprising a balancing device (7) fixedly connected to the hydraulic unit (5). A balancing disc (70) connected to the pump shaft (6) and having a rotating sliding surface (75), and a fixed part (9) fixedly connected to the pump housing (2) and having a fixed sliding surface (95), wherein the rotating sliding surface (75) and the fixed sliding surface (95) face each other, and wherein a radial discharge channel (79) is provided between the rotating sliding surface (75) and the fixed sliding surface (95), characterized in that each of the rotating sliding surface (75) and the fixed sliding surface (95) comprises at least 30% by volume of diamond.

2. The rotary pump according to claim 1, wherein: Each of the rotating sliding surface (75) and the fixed sliding surface (95) is configured as an annular surface.

3. A rotary pump according to any one of the preceding claims, wherein: Each of the rotating sliding surface (75) and the fixed sliding surface (95) is configured as a diamond surface.

4. A rotary pump according to any one of the preceding claims, wherein: Each of the rotating sliding surface (75) and the fixed sliding surface (95) comprises polycrystalline diamond.

5. The rotary pump according to any one of claims 1 to 2, wherein: Each of the rotating sliding surface (75) and the fixed sliding surface (95) includes diamond particle reinforced silicon carbide.

6. The rotary pump according to claim 5, wherein: Each of the rotating sliding surface (75) and the fixed sliding surface (95) is composed of diamond particle reinforced silicon carbide.

7. A rotary pump according to any one of the preceding claims, wherein: The balancing disc (70) comprises a rotating ring (76) arranged in an annular groove (77) and forming the rotating sliding surface (75), and wherein the fixed part (90) comprises a fixed ring (96) arranged in an annular groove (97) and forming the fixed sliding surface (95).

8. The rotary pump according to claim 7, wherein: The rotating sliding surface (75) of the rotating ring (76) and the fixed sliding surface (95) of the fixed ring (96) are made of silicon carbide reinforced with diamond particles.

9. The rotary pump according to any one of claims 7 to 8, wherein: The rotating ring (76) comprises an annular recess (773) extending along the circumference of the rotating ring (76), and wherein a rotating inlay (774) is arranged in the annular recess (773), the rotating inlay (774) forming the rotating sliding surface (75).

10. The rotary pump according to any one of claims 7 to 9, wherein: The fixing ring (96) comprises an annular recess (973) extending along the circumference of the fixing ring (96), and wherein a fixing inlay (974) is arranged in the annular recess (973), the fixing inlay (974) forming the fixing sliding surface (95).

11. The rotary pump according to claim 10, comprising the rotating ring (76) with the annular recess (773) and the fixed ring (96) with the annular recess (973), wherein: The rotating ring (76) and the fixed ring (96) are made of silicon carbide.

12. The rotary pump according to claim 11, wherein The rotating inlay (774) and the fixed inlay (974) are made of silicon carbide reinforced with diamond particles.

13. A rotary pump according to any one of the preceding claims, wherein: Each of the rotating sliding surface (75) and the fixed sliding surface (95) comprises at least 50% diamond by volume.

14. A rotary pump according to any one of the preceding claims, wherein: The radial bleed passage (79) is configured to be at most 80 microns, preferably at most 50 microns during operation of the rotary pump.

15. The rotary pump according to claim 1, which is designed as a multi-stage centrifugal pump.

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