Mechanical seal device

Abstract

The invention relates to a mechanical seal arrangement (16) for a centrifugal separator (1), the mechanical seal arrangement (16) comprising: a first seal ring (18) comprising a first sealing surface (20); a second seal ring (22) comprising a second sealing surface (24), wherein the first sealing surface (20) and the second sealing surface (24) are configured to face each other to form a seal (50); at least one channel (26) for a cooling fluid is arranged in the first seal ring (18), wherein the at least one channel (26) comprises an inlet (28) and an outlet (30). The outlet (30) of the at least one channel (26) is arranged at the first sealing surface (20) of the first seal ring (18). The invention further relates to a centrifugal separator (1) comprising a mechanical seal arrangement (16).

Description

TECHNICAL FIELD

[0001] The present invention relates to a mechanical seal arrangement for a centrifugal separator according to the appended claims. The present invention also relates to a centrifugal separator comprising a mechanical seal arrangement according to the appended claims. BACKGROUND

[0002] A centrifugal separator is configured to separate liquid, gas and solid particles from each other. In addition, different densities of liquids mixed together can also be separated from each other in a centrifugal separator. Different densities of gases mixed together can also be separated from each other in a centrifugal separator. The centrifugal separator should be sealed in order to prevent liquid, gas or solid particles from leaking out of the centrifugal separator. Since some parts of the centrifugal separator rotate, leakage can occur between rotating parts and stationary parts. Therefore, a mechanical seal can be arranged between rotating parts and stationary parts in the separator. Due to the relative rotational movement between the rotating parts and the stationary parts, heat can be generated between the sealing surfaces of the mechanical seal arranged between these rotating parts and stationary parts. In some centrifugal separator applications, the mechanical seal can provide a gas-tight seal.

[0003] Document US 2020 / 016610 A1 discloses a seal assembly for a centrifugal separator. The seal assembly comprises two seal rings arranged such that a double contact seal is formed when the two seal rings are engaged. Chambers in one or both seal rings can be supplied with cooling fluid. The chambers can be used to detect leakage in the seal assembly. Furthermore, fluid under pressure can be supplied to the chambers in order to prevent leakage in the seal assembly.

[0004] Document US 4654023 A discloses a mechanical seal for a casing of a centrifugal separator. Two seal rings are pressed against each other in the axial direction, one being rotatable and one being non-rotatable, in order to seal the interior of the casing from connection with the space around the radial bearing via an opening in the bottom of the casing. SUMMARY

[0005] The heat generated in a mechanical seal due to the relative movement between the sealing surfaces can shorten the lifetime of the mechanical seal. In addition, the heat generated in the mechanical seal can cause seal failure and leakage. Furthermore, large temperature differences in different areas of the mechanical seal can cause seal failure and leakage, and shorten the lifetime. Therefore, there is a need to develop a mechanical seal arrangement for a centrifugal separator which has a long lifetime and provides a tight seal without seal failure and leakage. Furthermore, there is a need to develop a mechanical seal arrangement for a centrifugal separator in which the temperature differences in the seal are small. In addition, there is a need to develop a centrifugal separator provided with a mechanical seal arrangement which has a long lifetime and provides a tight seal without seal failure and leakage.

[0006] It is therefore an object of the present invention to develop a mechanical seal arrangement for a centrifugal separator which has a long lifetime and provides a tight seal without seal failure and leakage. Furthermore, it is an object to develop a mechanical seal arrangement for a centrifugal separator which provides an air-tight seal. Furthermore, it is an object to develop a mechanical seal arrangement for a centrifugal separator wherein the temperature difference in the seal is small. In addition, it is an object to develop a centrifugal separator provided with a mechanical seal arrangement which has a long lifetime and provides a tight seal without seal failure and leakage.

[0007] This is achieved by a mechanical seal arrangement for a centrifugal separator according to the appended claims. This is also achieved by a centrifugal separator comprising a mechanical seal arrangement according to the appended claims.

[0008] According to one aspect of the present invention, a mechanical seal arrangement for a centrifugal separator is provided. The mechanical seal arrangement comprises a first seal ring comprising a first sealing surface; a second seal ring comprising a second sealing surface, wherein the first sealing surface and the second sealing surface are configured to face each other to form a seal of the seal rings; the first seal ring has a first central axis and the second seal ring has a second central axis, wherein the first central axis of the first seal ring is configured to coincide with the second central axis of the second seal ring; at least one channel for a cooling fluid is arranged in the first seal ring, wherein the at least one channel comprises an inlet and an outlet; the outlet of the at least one channel is arranged at the first sealing surface of the first seal ring, wherein the outlet of the at least one channel is arranged at a radial distance from the first central axis which is larger than an outer radius of the formed seal.

[0009] Thus, the seal assembly is a mechanical seal which can form an air-tight seal. The seal assembly is used to form a seal between a stationary part and a rotatable part. This mechanical seal arrangement has a long lifetime and will provide a tight seal with a reduced risk of seal failure and leakage. Furthermore, the temperature difference in the mechanical seal arrangement will also be small.

[0010] According to the present disclosure, the outlet of the at least one channel is arranged at a radial distance from the first central axis which is larger than an outer radius of the formed seal. Thus, the outlet of the at least one channel will be arranged radially outside the formed seal of the seal arrangement. No further seal is formed in the mechanical seal arrangement in the same axial plane radially outside the outlet of the channel.

[0011] The cooling fluid absorbs heat in the mechanical seal arrangement and thus reduces the temperature in the mechanical seal arrangement. Furthermore, since the outlet of the at least one channel is arranged at (i.e. near or next to) the first sealing surface of the first seal ring, the cooling fluid will pass adjacent to the first sealing surface and thus adjacent to the formed seal. Heat generated by the relative movement of the first and second sealing surfaces can be absorbed by the cooling fluid when the cooling fluid flows in the at least one channel. The at least one channel is configured to equalize the temperature in the seal ring. The equalized temperature in the seal ring can prevent cracking and deformation of the seal ring and the first and second sealing surfaces. When the cooling fluid flows out of the at least one channel, the cooling fluid flows to the area of the first and second sealing surfaces since the outlet of the at least one channel is arranged at (i.e. near or next to) the formed seal of the seal arrangement between the first and second sealing surfaces. When the cooling fluid has a fluid connection to the first and second sealing surfaces, heat generated by the relative movement of the first and second sealing surfaces can be absorbed by the cooling fluid. This will reduce the temperature of the first and second sealing surfaces.

[0012] According to an aspect of the present invention, there is provided a centrifugal separator. The centrifugal separator comprises a mechanical seal arrangement as disclosed herein.

[0013] Such centrifugal separators provided with a mechanical seal arrangement as disclosed herein will have a long lifetime and will also provide a tight seal with reduced risk of seal failure and leakage.

[0014] Other objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and by practicing the invention. Although the following description sets forth the present invention, this description is not intended to limit the application of the invention to the specific details described. Those skilled in the art will recognize and appreciate that other applications, modifications, and combinations can be made of the teachings of the present invention. BRIEF DESCRIPTION OF DRAWINGS

[0015] For a more complete understanding of the present disclosure and its further objects and advantages, the detailed description set forth below should be read in conjunction with the accompanying drawings, in which: Figure One Upon reading the following detailed description, it is intended that the application is not limited to the details outlined in the specification. There is a disclosure of other applications, modifications and combinations within the scope of the present application for those skilled in the art who have the benefit of the teachings of the present specification.

[0016] Figure 1 schematically illustrating a centrifugal separator according to an example,

[0017] Figure 2 schematically illustrating a cross-sectional view of an inlet and outlet arrangement of a centrifugal separator according to an example,

[0018] Figure 3 schematically illustrating a cross-sectional view of an inlet and outlet arrangement of a centrifugal separator according to an example, Figure 2a cross-sectional view of the line I-I in Fig. 1, and

[0019] Figure 4 a detailed view of Figure 2 is schematically shown. DETAILED DESCRIPTION

[0020] According to the present disclosure, a mechanical seal arrangement for a centrifugal separator is provided. The mechanical seal arrangement comprises a first seal ring comprising a first sealing surface and a second seal ring comprising a second sealing surface, wherein the first sealing surface and the second sealing surface are configured to face each other to form a seal of the mechanical seal arrangement. The first seal ring has a first central axis and the second seal ring has a second central axis, wherein the first central axis of the first seal ring is configured to coincide with the second central axis of the second seal ring. This means that the first seal ring and the second seal ring can have a common central axis. At least one channel for a cooling fluid is arranged in the first seal ring, wherein the at least one channel comprises an inlet and an outlet. The outlet of the at least one channel is arranged at, i.e. close to or next to, the first sealing surface of the first seal ring. The outlet of the at least one channel is arranged at a radial distance from the first central axis that is greater than an outer radius of the formed seal.

[0021] Hence, the formed seal of the mechanical seal arrangement is located radially inwards of the outlet of the channel. The mechanical seal arrangement does not form a further seal or sealing interface between the opposing surfaces of the first and second seal rings in the same axial plane as the first and second surfaces extending radially, i.e. radially outwards of the channel for the cooling fluid. Hence, the formed seal is of the single-contact seal type.

[0022] The mechanical seal arrangement can be arranged between a rotating part and a stationary part in a centrifugal separator. Alternatively, the mechanical seal arrangement can be arranged between two rotating parts having different rotational speeds. The mechanical seal arrangement can be configured to prevent a fluid or a gas from passing the seal. However, a very thin film of a fluid or a gas can form between the sealing surfaces of the seal. This thin film has a lubricating effect on the sealing surfaces.

[0023] The mechanical seal arrangement can provide a gas-tight seal preventing any fluid or gas from passing the seal.

[0024] A centrifugal separator can be configured for separating fluids and gases having different densities. The separator can comprise a rotor forming a separation chamber within itself, in which centrifugal separation of fluids or gases takes place during operation. The separation chamber is provided with a stack of truncated conical separation discs for efficient separation of fluids or gases. The stack of truncated conical separation discs is an example of surface augmenting inserts and is fitted centrally and coaxially with the rotor. During operation of the separator, the fluid or gas to be separated is brought into the separation space. Depending on the density, different phases in the fluid or gas separate between the separation discs. The heavier components of the fluid or gas move radially outwards between the separation discs, while the phase of lowest density moves radially inwards between the separation discs and is forced through outlets arranged at the radially innermost layer in the separator. Alternatively, the higher density components are forced outwards through outlets at a larger radial distance. Any possible solids or sludge in the fluid will accumulate at the periphery of the separation chamber and be emptied intermittently from the separation space through a set of radial sludge outlets that are opened, whereupon the sludge is discharged.

[0025] The first sealing ring can have a diameter and an axial extension that are suitable for the type and size of the centrifugal separator. The first sealing surface of the first sealing ring has a circular configuration. The first sealing surface has a smoothness that provides an effective sealing of fluids and gases.

[0026] The second sealing ring can have a diameter and an axial extension that are suitable for the type and size of the centrifugal separator. The second sealing surface of the second sealing ring has a circular configuration. The second sealing surface has a smoothness that provides an effective sealing of fluids and gases.

[0027] The first sealing surface and the second sealing surface are configured to face each other. The contact area between the first sealing surface and the second sealing surface constitutes the seal of the mechanical seal device. Alternatively, the interface provided by a thin film of fluid or gas between the first sealing surface and the second sealing surface constitutes the seal of the mechanical seal device.

[0028] The first sealing surface and the second sealing surface can have the same or different areas. The first sealing surface and the second sealing surface can have the same or different smoothness.

[0029] An actuator can be arranged to push the first sealing surface and the second sealing surface together. Such an actuator can be a spring, such as a coil spring.

[0030] Due to the relative rotational movement between the first sealing surface and the second sealing surface, heat can be generated in the sealing surfaces and in the first sealing ring and the second sealing ring. In addition, the fluid and gas to be separated in the centrifugal separator can have a high temperature, which can increase the temperature in the first sealing ring and the second sealing ring. The at least one channel arranged in the first sealing ring is configured to reduce the temperature in the mechanical seal arrangement. In addition, the at least one channel is configured to equalize the temperature in the first sealing ring. The equalized temperature in the first sealing ring can prevent cracks and deformations in the first sealing ring and the first sealing surface. In addition, the at least one channel is configured to equalize the temperature in the second sealing ring. The equalized temperature in the second sealing ring can prevent cracks and deformations in the second sealing ring and the second sealing surface.

[0031] The cooling fluid can be provided from a cooling fluid source connected to the centrifugal separator and to the at least one cooling channel of the mechanical seal arrangement. The cooling fluid can be cooled in the cooling fluid source. The cooling fluid can have a certain initial temperature when it enters the centrifugal separator, which is suitable for the specific separation process in the centrifugal separator. The cooling fluid can be a liquid, a gas or a powder. The cooling fluid can have lubricating properties. The cooling fluid absorbs heat in the mechanical seal arrangement and thus reduces the temperature in the mechanical seal arrangement. A pump can be arranged for generating a flow of cooling fluid in the at least one channel. Gravity can generate a flow of cooling fluid in the at least one channel.

[0032] The at least one channel comprises an inlet and an outlet arranged in the first sealing ring. The cooling fluid is configured to enter the at least one channel through the inlet and to exit the at least one channel through the outlet. Thus, the at least one channel can form a cooling channel.

[0033] Since the outlet of the at least one channel is arranged at (i.e. next to) the first sealing surface of the first sealing ring, the cooling fluid will pass adjacent to the first sealing surface. When the cooling fluid flows in the at least one channel, the heat generated by the relative movement of the first sealing surface and the second sealing surface can be absorbed by the cooling fluid. When the cooling fluid flows out of the at least one channel, the cooling fluid flows to the area of the first sealing surface and the second sealing surface. When the cooling fluid has a fluid connection to the first sealing surface and the second sealing surface, the heat generated by the relative movement of the first sealing surface and the second sealing surface can be absorbed by the cooling fluid. This will reduce the temperature of the first sealing surface and the second sealing surface.

[0034] Furthermore, since the outlet of the at least one channel is arranged at a radial distance from the first central axis which is larger than the outer radius of the formed seal, the outlet of the at least one channel will be arranged radially outside the outer radius of the first sealing surface of the first sealing ring. This configuration will reduce the temperature in the sealing rings and also in the first sealing surface and the second sealing surface.

[0035] According to one aspect, the outlet of the at least one channel is arranged in fluid connection with the first sealing surface of the first sealing ring and the second sealing surface of the second sealing ring.

[0036] According to one aspect, the outer radius of the second sealing surface of the second sealing ring is larger than the outer radius of the first sealing surface of the first sealing ring, and wherein the outlet direction of the at least one channel is towards the second sealing surface of the second sealing ring. Thus, the outlet of the at least one channel is at least partially arranged and positioned radially inside the outer radius of the second sealing surface of the second sealing ring. This will result in that the cooling fluid is flowing over the part of the second sealing surface that is positioned radially outside the outer radius of the first sealing surface of the first sealing ring. When the cooling fluid has direct fluid connection with the second sealing surface, the heat generated in the second sealing ring can then be efficiently absorbed by the cooling fluid. This will reduce the temperature of the second sealing surface. Furthermore, when the cooling fluid is flowing over the part of the second sealing surface that is positioned radially outside the outer radius of the first sealing surface of the first sealing ring, the cooling fluid can easily enter between the sealing surfaces and form a very thin film between the sealing surfaces. This thin film has a lubricating effect on the sealing surfaces.

[0037] According to one aspect, a restriction is arranged in or at the at least one channel for restricting the flow of cooling fluid.

[0038] The restriction will reduce the flow rate of the cooling fluid in the at least one channel. In addition, the volume flow of the cooling fluid in the at least one channel will be reduced by the restriction. The restriction can be a part of the at least one channel having a reduced diameter. The entire length of the at least one channel can be provided with a reduced diameter in order to achieve a reduced flow rate and volume flow.

[0039] According to one aspect, the restriction is configured to at least partially cover the inlet opening of the at least one channel.

[0040] The restriction can be a component arranged to partially cover the inlet opening and thus restrict the cooling fluid from entering the inlet opening. The restriction can be a component arranged in the inlet opening and in the at least one channel for partially covering the inlet opening. The restriction can be a component arranged on the outside of the inlet opening and thus on the outside of the at least one channel for partially covering the inlet opening. The restriction will reduce the flow rate and volume flow of the cooling fluid in the at least one channel.

[0041] According to one aspect, the restriction is a grommet element configured to rest on the first sealing ring and configured to at least partially cover the inlet of the at least one channel.

[0042] The inner diameter of the grommet element can be larger than the inner diameter of the first seal ring. The inlet of at least one channel in the first seal ring can be partly covered by the inner periphery of the grommet element. The outer diameter of the grommet element can be smaller than the outer diameter of the first seal ring. The inlet of at least one channel in the first seal ring can be partly covered by the outer periphery of the grommet element. The inner periphery or the outer periphery of the grommet element can be provided with a bevel adapted such that the grommet element partly covers the inlet of the at least one channel. Alternatively, the grommet element can comprise a through hole having a smaller diameter than the inlet of the at least one channel.

[0043] According to an aspect, the at least two channels are evenly distributed around the first seal ring.

[0044] The even distribution of the channels around the first seal ring can distribute the flow of cooling fluid evenly through the channels. This will equalize the temperature in the first seal ring and thus avoid any temperature gradients in the first seal ring.

[0045] According to an aspect, the number of channels evenly distributed around the first seal ring can be in the interval 2-10, such as 4-8, e.g. 6. Thus, sufficient cooling can be provided around the periphery of the seal ring, while not negatively affecting the mechanical properties. However, a large centrifugal separator provided with a mechanical seal arrangement having a large diameter can comprise a larger number of channels evenly distributed around the first seal ring.

[0046] The even distribution of the channels around the first seal ring can distribute the flow of cooling fluid evenly through the channels. This will equalize the temperature in the first seal ring and thus avoid any temperature gradients in the first seal ring.

[0047] According to an aspect, the material in the second seal ring is harder than the material in the first seal ring.

[0048] Since the first sealing surface of the first seal ring can slide on the second sealing surface of the second seal ring during the relative movement between the first seal ring and the second seal ring, wear of the surfaces can occur. Since the material in the second seal ring is harder than the material in the first seal ring, the wear will essentially occur in the first seal ring. Thus, only the first seal ring can be replaced during maintenance of the mechanical seal arrangement.

[0049] According to an aspect, the material in the second seal ring comprises silicon carbide and the material in the first seal ring is graphite.

[0050] The silicon carbide in the second seal ring is harder than the graphite in the first seal ring. Thus, the wear will essentially occur in the first seal ring. Thus, only the first seal ring can be replaced during maintenance of the mechanical seal arrangement. The first seal ring made of graphite can be manufactured at a low cost. Thus, the replacement of the first seal ring can be done at a low cost.

[0051] According to an aspect, the material in the second sealing ring has a greater thermal conductivity than the thermal conductivity of the material in the first sealing ring.

[0052] The greater thermal conductivity in the second sealing ring can absorb heat from heat generation in the relative movement of the sealing surfaces and transfer the heat away from the second sealing surface. As the at least one channel is arranged in the first sealing ring, the generated heat will be transferred away from the first sealing ring by means of the cooling fluid.

[0053] According to an aspect, the at least one channel in the first sealing ring has an extension parallel with the first central axis.

[0054] By arranging the first sealing ring in a position such that the first central axis has a vertical extension in the centrifugal separator, the at least one channel in the first sealing ring will also have a vertical extension. If the channel has a vertical extension, the cooling fluid can flow in the at least one channel by means of gravity.

[0055] According to an aspect, the first sealing surface of the first sealing ring has a first normal and the second sealing surface of the second sealing ring has a second normal, and wherein the directions of the first normal and the second normal are parallel with the direction of the first central axis of the first sealing ring and with the second central axis of the second sealing ring.

[0056] The first sealing surface and the second sealing surface are configured to face each other to form a seal. Thus, the first normal and the second normal directions of the sealing surfaces are towards each other. This arrangement will result in a tight seal without seal failure and leakage. The contact area of the first sealing surface and the second sealing surface will be defined by the inner diameter and the outer diameter of the first sealing ring and the second sealing ring.

[0057] According to an aspect, the first sealing ring is configured to be arranged stationary and the second sealing ring is configured to be arranged rotatably.

[0058] The stationary first sealing ring can simplify the arrangement of guiding the cooling fluid through the at least one channel.

[0059] According to the present disclosure, a centrifugal separator is provided. The centrifugal separator comprises a mechanical seal arrangement disclosed herein.

[0060] Such a centrifugal separator provided with a mechanical seal arrangement disclosed herein will have an extended lifetime and will also provide a tight seal with a reduced risk of seal failure and leakage. In addition, the maintenance of the mechanical seal arrangement in the centrifugal separator will be simplified and done at low cost.

[0061] The mechanical seal arrangement for a centrifugal separator and the centrifugal separator comprising the mechanical seal arrangement will now be described with reference to the accompanying drawings, in which Figure One The mechanical seal arrangement for a centrifugal separator and the centrifugal separator comprising the mechanical seal arrangement will now be described with reference to the accompanying drawings, in which The mechanical seal arrangement for a centrifugal separator and the centrifugal separator comprising the mechanical seal arrangement will now be described with reference to the accompanying drawings, in which

[0062] Figure 1 A centrifugal separator 1 according to an example is schematically illustrated. The separator 1 comprises a rotor 2 which forms a separation chamber 4 within itself in which centrifugal separation of a fluid or gas takes place during operation. The separation chamber 4 is provided with stacked conical separation discs 6 to facilitate efficient separation of the fluid or gas. During operation of the separator, the fluid or gas to be separated is brought into the separation chamber 4 by means of inlet and outlet means 8 of the centrifugal separator 1. Depending on the density, different phases in the fluid or gas separate between the separation discs. The heavier components of the fluid or gas will move radially outwards between the separation discs 6, while the least dense phase will move radially inwards between the separation discs 6 and be forced through a first outlet 10 arranged at the radially innermost layer in the separator 1 and further to the inlet and outlet means 8. The higher density components are forced outwards through a second outlet 12 at a larger radial distance, which components will be intermittently emptied from the separation chamber 4. The inlet and outlet means 8 comprises a first inlet 14 for the fluid or gas to be separated.

[0063] Figure 2 A cross-sectional view of the inlet and outlet means 8 of the centrifugal separator 1 according to an example is schematically illustrated. The inlet and outlet means 8 comprises the first inlet 14 and the first outlet 10. A mechanical seal arrangement 16 is arranged in the inlet and outlet means 8. The mechanical seal arrangement 16 comprises a first seal ring 18 with a first seal surface 20 and a second seal ring 22 with a second seal surface 24. The first seal surface 20 and the second seal surface 24 are configured to face each other to form a seal. Channels 26 for a cooling fluid are arranged in the first seal ring 18. Each channel 26 comprises an inlet 28 and an outlet 30. The outlet 30 of each channel 26 is arranged at, i.e. next to, the first seal surface 20 of the first seal ring 18. Each channel 26 is arranged in fluid connection with the first seal surface 20 of the first seal ring 18 and the second seal surface 24 of the second seal ring 22. The cooling fluid is provided by a cooling fluid source 32 which is connected to a second inlet 34 of the centrifugal separator 1. The first seal ring 18 is configured to be stationary arranged in the inlet and outlet means 8. The second seal ring 22 is connected to a rotatable member of the centrifugal separator 1 and is thus configured to be rotatably arranged.

[0064] The first seal ring 18 has a first central axis 36 and the second seal ring 22 has a second central axis 38. The channels 26 in the first seal ring 18 extend in parallel with the first central axis 36. The first central axis 36 of the first seal ring 18 coincides with the second central axis 38 of the second seal ring 22.

[0065] A cooling fluid enters the centrifugal separator 1 through the second inlet 34. The cooling fluid flows from the second inlet 34 into a cavity 39 in which an actuator 41 is arranged for pushing the first sealing surface 20 and the second sealing surface 24 together. In Figure 2 the actuator 41 is a spring.

[0066] Figure 3 a cross-sectional view along the line I-I in Figure 2 is schematically shown. Six channels 26 are arranged in the first sealing ring 18. The channels 26 are evenly distributed around the first sealing ring 18 so that the cooling fluid flow through the channels 26 is evenly distributed. The evenly distributed channels 26 in the first sealing ring 18 will equalize the temperature in the first sealing ring 18 and thus avoid any temperature gradients in the first sealing ring 18.

[0067] Figure 4 a detailed view of Figure 2 is schematically shown. The detailed view shows the mechanical seal arrangement 16 in more detail. The gasket element 40 is configured to rest on the first sealing ring 18 and to at least partly cover the inlet 28 of the channel 26. The gasket element 40 will limit the cooling fluid flow in the channel 26. By associating a gasket element or other restriction of this type with each channel, the cooling fluid flow through the channels 26 can be evenly distributed.

[0068] The first sealing surface 20 of the first sealing ring 18 has a first normal 42 and the second sealing surface 24 of the second sealing ring 22 has a second normal 44. The directions of the first normal 42 and the second normal 44 are parallel with the direction of the first central axis 36 of the first sealing ring 18 and with the second central axis 38 of the second sealing ring 22. A seal and / or sealing interface 50 of the mechanical seal arrangement 16 is formed between the first sealing surface 20 and the second sealing surface 24.

[0069] Figure 4 the arrow 46 in Figure 2 represents the direction and path of the cooling fluid flow. The cooling fluid enters the centrifugal separator 1 through the second inlet 34 (see ) and further into the cavity 39. The cooling fluid flows from the cavity 39 through a circular passage formed between the gasket element 40 and the stationary element 48 of the inlet and outlet arrangement 8 of the centrifugal separator 1. Thereafter, the cooling fluid flows into the inlet 28 of the channel 26 and towards the outlet 30.

[0070] The outlet 30 of the channel 26 is arranged at a radial distance D from the first centre axis 36 which is greater than the outer radius Rl of the first sealing surface 20 of the first sealing ring 18. As a seal is formed between the first sealing surface 20 and the second sealing surface 24, the outer radius Rl also forms the outer radius Rl of the formed seal 50. Thus, the outlet 30 of the channel 26 will be arranged radially outside the outer radius Rl of the first sealing surface 20 of the first sealing ring 18. The outlet 30 of the channel 26 is arranged at, i.e. next to, the first sealing surface 20 of the first sealing ring 18. Thus, the cooling fluid will pass next to the first sealing surface 20 and thus next to the seal 50 of the mechanical seal arrangement. As can be seen from the drawings, no further seal is included radially outside the seal 50 between the first and second sealing surfaces of the first and second sealing rings.

[0071] The outer radius R2 of the second sealing surface 24 of the second sealing ring 22 is greater than the outer radius Rl of the first sealing surface 20 of the first sealing ring 18, and in this way, the outlet 30 of the at least one channel 26 can be directed towards the second sealing surface 24 of the second sealing ring 22. In this way, the cooling fluid will thus flow over the part of the second sealing surface 24 which is positioned radially outside the first sealing surface 20 of the first sealing ring 18 having the outer radius Rl. Thus, a small part of the cooling fluid flow can enter between the sealing surfaces 20, 24 and form a very thin fluid film between the sealing surfaces 20, 24. However, after passing the first and second sealing rings 18, 22, the majority of the cooling fluid will be discharged through an outlet port (not shown) of the centrifugal separator 1.

[0072] The foregoing description of examples of the disclosure has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the described examples and variations. Many modifications and variations will be apparent to those skilled in the art. The examples have been chosen and described in order to best explain the principles of the disclosure and its practical application to thereby enable others skilled in the art to best utilize the disclosure for a variety of examples and with various modifications as are suited to the particular use contemplated.

Claims

1. A mechanical seal arrangement (16) for a centrifugal separator (1), the mechanical seal arrangement (16) comprising: - a first seal ring (18) comprising a first seal surface (20); - a second seal ring (22) comprising a second seal surface (24), wherein the first seal surface (20) and the second seal surface (24) are configured to face each other to form a seal (50) of the mechanical seal arrangement; - the first seal ring (18) has a first central axis (36) and the second seal ring (22) has a second central axis (38), wherein the first central axis (36) of the first seal ring (18) is configured to coincide with the second central axis (38) of the second seal ring (22); - at least one channel (26) for a cooling fluid is arranged in the first seal ring (18), wherein the at least one channel (26) comprises an inlet (28) and an outlet (30); - the outlet (30) of the at least one channel (26) is arranged at the first seal surface (20) of the first seal ring (18), wherein the outlet (30) of the at least one channel (26) is arranged at a radial distance (D) from the first central axis (36) that is greater than an outer radius (R1) of the formed seal (50), - wherein a restriction portion (40) is arranged in connection with the at least one channel (26) for restricting the flow of cooling fluid.

2. The apparatus (16) of claim 1, wherein, - the outlet (30) of the at least one channel (26) is arranged in fluid connection with the first seal surface (20) of the first seal ring (18) and the second seal surface (24) of the second seal ring (22).

3. The apparatus (16) of claim 1, wherein, - an outer radius (R2) of the second seal surface (24) of the second seal ring (22) is greater than an outer radius (R1) of the first seal surface (20) of the first seal ring (18), and wherein the outlet (30) of the at least one channel (26) is directed towards the second seal surface (24) of the second seal ring (22).

4. The apparatus (16) according to any one of claims 1-3, wherein, - the restriction portion (40) is configured to at least partially cover the inlet (28) of the at least one channel (26).

5. The apparatus (16) according to any one of claims 1-3, wherein, - the restriction portion (40) is a grommet element (40) configured to rest on the first seal ring (18) and configured to at least partially cover the inlet (28) of the at least one channel (26).

6. The apparatus (16) according to any one of claims 1-3, wherein, - there are at least two channels (26) evenly distributed around the first seal ring (18).

7. The apparatus (16) according to any one of claims 1-3, wherein, - the number of channels (26) is in the interval 4-8, which channels (26) are evenly distributed around the first seal ring (18).

8. The apparatus (16) according to any one of claims 1-3, wherein, - the material in the second seal ring (22) is harder than the material in the first seal ring (18).

9. The apparatus (16) according to any one of claims 1-3, wherein, - the material in the second seal ring (22) comprises silicon carbide and the material in the first seal ring (18) is graphite.

10. The apparatus (16) according to any one of claims 1-3, wherein, - the material in the second seal ring (22) has a greater thermal conductivity than the thermal conductivity of the material in the first seal ring (18).

11. The apparatus (16) according to any one of claims 1-3, wherein, - at least one channel (26) in the first seal ring (18) has an extension parallel to the first central axis (36).

12. The apparatus (16) according to any one of claims 1-3, wherein, The first sealing surface (20) of the first sealing ring (18) has a first normal line (42) and the second sealing surface (24) of the second sealing ring (22) has a second normal line (44), and wherein the directions of the first normal line (42) and the second normal line (44) are parallel to the direction of the first central axis (36) of the first sealing ring (18) and to the direction of the second central axis (38) of the second sealing ring (22).

13. The apparatus (16) according to any one of claims 1-3, wherein, The first sealing ring (18) is configured to be stationary and the second sealing ring (22) is configured to be rotatable.

14. A centrifugal separator (1) comprising a mechanical seal arrangement (16) according to any one of claims 1-13.

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