Centrifugal separator with discharge control system

Abstract

A centrifugal separator (100) is disclosed, comprising a rotor (110) for separating a feed mixture into at least a first liquid fraction and a solid fraction. The rotor comprises a discharge outlet (120), which is controlled by an opening element to provide intermittent discharge of the solid fraction. The opening element is actuated by a pressurised liquid provided by a discharge control system (200) comprising a liquid channel (220) configured to fluidically connect the opening element to a reservoir with pressurised fluid, a control valve arrangement (230) operable to selectively open and close the liquid channel, and a control unit (240) configured to control the control valve arrangement to supply the opening element with the pressurised liquid. The discharge control system is configured to actuate the opening element based on a duration for which the control valve arrangement remains open.

Description

Technical Field

[0001] The present invention relates to centrifugal separators, and particularly to centrifugal separators comprising a discharge control system.Background

[0002] Centrifugal separators are used to separate feed mixture components with different densities by accelerating the feed mixture to high rotational speeds. Denser components move outward towards the perimeter of the separator's separation space, forming one or more heavy fractions, while less dense components remain closer to the centre, forming one or more light fractions. If the feed mixture comprises solid particles or heavier impurities, a denser layer, known as a solid fraction or sludge, may accumulate at the outer periphery of the separation space.

[0003] To enable continuous operation, sludge may be automatically removed through a discharge system which intermittently expels the sludge via discharge outlets. This system may include a sliding bowl bottom or movable slide that vertically opens or closes the discharge outlets. During regular operation, the slide covers these outlets to prevent discharge. When actuated, it uncovers the outlets, allowing sludge expulsion. The slide's movement may be controlled by a hydraulic system using pressurised liquid to operate the sliding mechanism.

[0004] Precise control over the hydraulic system's operation is desirable, as this may help optimising the discharge process, reducing waste and ensuring efficient discharge.Summary

[0005] It is an object of the present disclosure to provide a technology that addresses at least some of the above concerns.

[0006] According to a first aspect of the present invention, there is provided a centrifugal separator comprising a rotor, an opening element, and a discharge control system actuating the opening element. The rotor defines a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, wherein a radially outer portion of the rotor comprises a controllable discharge outlet for intermittent discharge of the solid fraction from the separation space. The opening element is arranged within the rotor and configured to control opening and closing of the discharge outlet. The discharge control system is configured to actuate the opening element by means of a pressurised liquid, and comprises a reservoir for accommodating the pressurised liquid. The discharge control system further comprises a liquid channel fluidically connecting the reservoir and the opening element, a control valve arrangement for selectively open and close the liquid channel, and a control unit for controlling the operation of the control valve arrangement to supply the opening element with the pressurised liquid actuating the opening element. The discharge control system is configured to actuate the opening element based on a duration for which the control valve arrangement remains open.

[0007] According to a second aspect, there is provided a method of operating a centrifugal separator comprising a rotor defining a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, and a controllable discharge outlet for intermitted discharge of the solid fraction from the separation space. The method comprises providing, by a reservoir, a pressurised liquid and opening, by a control valve arrangement, a liquid channel fluidically connecting the reservoir and an opening element in the rotor. The method further comprises actuating the opening element by supplying the opening element with the pressurised liquid, and opening, by the opening element, the discharge outlet to discharge the solid fraction from the separation space. The opening element is actuated based at least in part on a duration for which the control valve arrangement remains open.

[0008] According to a third aspect, a method of operating a centrifugal separator is provided. The separator comprises a rotor defining a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, and a controllable discharge outlet for intermittent discharge of the solid fraction from the separation space. The method comprises separating, in the separation space, a volume of the solid fraction from the feed mixture, generating a sequence of pressure pulses actuating an opening element arranged within the rotor and configured to control and closing of the discharge outlet, and discharging, by the sequence of pressure pulses opening and closing the discharge outlet, the volume of the solid fraction through the discharge outlet.

[0009] In the above aspects, the discharge control system is used to actuate the opening element, which then controls the discharge outlet, either directly or indirectly. The opening element is actuated by a flow of pressurised liquid, which also may be referred to as an opening liquid, or pressurised opening liquid. The opening liquid may be supplied as a pulse of pressurised liquid provided by the control valve arrangement. The pulse may be initiated when the control valve arrangement opens the liquid channel between the reservoir and the opening element, and terminated when the control valve arrangement closes the liquid channel. The length of the discharge, and thereby the volume of the discharge, is thus determined by the duration of the pulse actuating the opening element, which in turn is determined by the time the control valve arrangement remains open. In other words, the timing of the valve's open state may directly determine how long the discharge outlet remain uncovered by the opening element. This timing can be precisely controlled using, for example, electronic controllers, enabling fine-tuning of the discharge process.

[0010] This approach offers an advantage over prior art systems that control discharge by the volume of pressurised fluid supplied to actuate the mechanism controlling the discharge outlets. In those systems, the discharge is controlled based on the assumption that a specific volume of fluid will correspond to a particular degree of movement in the mechanism controlling the discharge outlets, thereby controlling the duration and extent of the discharge.

[0011] By controlling the discharge based on the time the control valve arrangement remains open, a faster response time and a more precise actuation of the opening element can be achieved. This method also facilitates the generation of shorter pulses and, in some cases, a series of smaller discharge pulses, enhancing the overall efficiency and control of the separation process.

[0012] In some examples, the control valve arrangement comprises a first valve and a second valve in series along the liquid channel, forming a dual-valve arrangement. These valves may work together to generate a pressure pulse that actuates the opening element. The valves may form a complementary pair, with the first valve being a normally-closed (NC) valve, which opens when actuated and closes when deactivated, and the second valve being a normally-open (NO) valve, which closes when actuated and opens when deactivated. This configuration allows the control unit to initiate the supply of pressurised liquid by actuating the NC valve and terminate the supply by actuating the NO valve.

[0013] Such a dual arrangement may be particularly beneficial for valves with asymmetric response characteristics, that is, valves that have different actuation and deactivation speeds. In the present example, the valves may actuate faster than they deactivate. Consequently, the NC valve may operate as a quick-opening, slow-closing valve, and the NO valve function as a quick-closing, slow-opening valve. By combining these two valve types, the arrangement leverages the fast-actuating behaviour of both valves to achieve a relative quick initiation and termination of the pressure pulse.

[0014] Beneficially, the time it takes for the control valve arrangement to open or close the fluid passage may be significantly shorter than the duration of the discharge, ensuring precise and repeatable control of the opening element. In some examples, the control valve arrangement may be configured to be actuated (i.e., opened or closed) in a few milliseconds, such as 5 milliseconds or less, while the duration of the discharge may be in the order of 100 milliseconds.

[0015] The valve arrangement may, for example, be controlled by solenoid actuators, pneumatic actuators, hydraulic actuators, or motorised actuators. Additionally, these actuators may be combined with spring-return mechanisms, allowing the valve to be moved in one direction by the actuator (e.g., solenoid, pneumatic, or hydraulic) and returned by the spring force. It should be noted, however, that these are merely illustrative examples, and that other configurations and actuations mechanisms may also be possible.

[0016] The opening element may be configured to control the discharge outlet either directly or indirectly. In the latter case, the opening element may serve as an intermediary control element, such as a pilot valve, controlling the operating of another mechanism such as a slide or sliding bowl bottom. The slide can be arranged in a first position along a rotation axis of the rotor to close the discharge outlet and in a second position along the rotation axis to open the discharge outlet. An operating chamber may be provided between the slide and a body of the rotor, configured to accommodate an operating liquid that maintains the slide in the first position and therefore may be referred to as a closing liquid. The opening element may be arranged to control the position of the slide by discharging closing liquid from the operating chamber. This may cause the slide to be displaced from the first position to the second position to open the discharge outlet.

[0017] In some examples, the opening element comprises an operating slide, which may be arranged axially below the sliding bowl bottom (i.e., the slide that opens and closes the discharge outlet). The operating slide may be operable to control the position of the slide by means of the closing liquid, which may be supplied to and discharged from the operating chamber as discussed above.

[0018] The use of a pilot valve may enable finer control over the discharge process, as a relatively small adjustments in the pilot valve position can result in a more precise regulation of the flow of closing liquid. This allows a smaller flow of opening liquid to control a larger flow of closing liquid, using a relatively small amount of force.

[0019] The closing liquid may be supplied from the reservoir, which hence may be configured to provide both the opening liquid controlling the opening element and the closing liquid controlling the position of the slide. The opening liquid and the closing liquid may, for example, be formed of water that is kept under pressure in the reservoir. In some examples, the control valve arrangement comprises an operating valve configured to control the supply of the pressurised liquid to the operating chamber.

[0020] The control unit may be configured to open the operating valve after initiating the supply of pressurised opening liquid to the opening element. This ensures that the discharge outlet may be closed again (by the supply of closing liquid) after it has been opened (by the opening liquid actuating the opening element).

[0021] Using the pressurised liquid from the reservoir, which is already employed to actuate the opening element, as the closing liquid for maintaining the slide in its closed position offers a simplified system design. There may be a reduced need for separate reservoirs, pumps, or supply lines for different liquids, reducing the overall complexity of the system. Furthermore, fewer components may translate to lower initial costs for producing and installing the equipment.

[0022] The reservoir may be a hydraulic accumulator, which is configured to store pressurised fluid and release the fluid when needed to perform work in the system, such as actuating an opening element or displacing a slide. The hydraulic accumulator may be formed of a chamber that is divided into two or more section by a separating element. The separating element can be a flexible membrane, diaphragm, bladder, or piston, depending on the specific design. The section filled with the liquid (such as closing liquid or opening liquid) may be kept under pressure and readily available to be supplied to the opening element or operating chamber as needed. The other side of the separator may be filled with a pressurised gas (such as air or nitrogen), which servers to maintain the pressure on the liquid side. The gas may act as a spring, compressing when the liquid is forced into the accumulator and expanding when the liquid is drawn out, thus maintaining a consistent pressure in the system. The pressurised gas provides the energy needed to quickly supply the liquid to the opening element or the operating chamber when the control valve arrangement is opened, ensuring a rapid and efficient response.

[0023] In some examples, the centrifugal separator comprises a pump unit for replenishing the reservoir with liquid. The pump unit may be configured to draw water from a regular water supply system, such as a building's municipal water supply, or a dedicated water source. The water supply system is typically operated at a lower pressure than required by the reservoir. The pump unit, therefore, may increase the pressure of the incoming water to meet the specific needs of the reservoir. Furthermore, the pump unit may allow for a continuous replenishing of the reservoir with pressurised liquid, ensuring that the system can operate without interruption. This is particularly beneficial in processes requiring continuous or frequent actuation of components, such as in high-throughput centrifugal separation processes. The ability to draw from a regular water supply and convert it into a high-pressure fluid source means that the centrifugal separator is not reliant on specialised fluids or fluid sources, making the separator more versatile and easier to maintain.

[0024] The separator may be equipped with sensors and a control system that automatically detects when the liquid level or pressure in the reservoir drops below a certain threshold. When this occurs, the pump may be activated to draw in water and pressurise it, replenishing the reservoir without the need for manual intervention.

[0025] The discharge control system may be operated to provide either a partial discharge or a full discharge of the sludge (solid fraction). During a full discharge, the discharge outlets remain open long enough to ensure that all, or substantially all, of the accumulated sludge is expelled from the separation space. In a partial discharge, the discharge outlets may be opened only briefly, allowing just a portion of the sludge to be expelled before they are closed again. In some examples, a full discharge can be achieved through a series of partial discharges. In other words, a specific volume of the accumulated sludge may be discharged by generating a sequence of pressure pulses that cause the discharge outlets to open and close repeatedly, until the desired volume has been expelled through multiple partial discharges.

[0026] The rotor may comprise a plurality of controllable discharge outlets, or openings, which may be arranged along a circumference of the rotor and extending in a plane orthogonal to the rotation axis. The discharge outlets may be evenly spaced around the perimeter to allow the sludge to be expelled evenly, reducing the risk of imbalance in the rotor and promoting smooth operation. Other configurations are however possible, such as segmented arrays in which openings are grouped into segments with gaps between each segment, or staggered arrangements in which the outlets are slightly offset from each other along the perimeter. The staggered design may ensure that not all openings are exposed to the maximum concentration of sludge simultaneously, reducing the risk of clogging and promoting smoother and more consistent discharge.

[0027] The shape of the discharge outlets may be customised based on the specific requirements of the separation process. Example shapes include circular, elliptical, and slot-like openings.

[0028] The centrifugal separator may be a high-speed centrifugal separator, with the rotor rotating at several thousand rotations per minute, typically ranging from 3,000 to 12,000 rpm during operation.

[0029] The separation space may comprise a stack of separation discs, such as a stack of frustoconical separation discs, as known in the art. Thus, the centrifugal separator may be a disc-stack centrifugal separator.

[0030] The rotor may be arranged inside a stationary housing of the centrifugal separator and driven to rotate about a rotation axis by a drive arrangement, such as an electric motor. In some examples, the rotor body may comprise two or more separate parts, including a sliding bowl bottom that delimits a lower portion of the separation space.

[0031] When the centrifugal separator is positioned for use, the rotation axis may be oriented vertically. Accordingly, the rotor may have an upper portion and a lower portion. The term axial, radial, and rotational relate to the rotation axis: an axial direction extends parallel to the rotation axis, while a radial direction extends perpendicular to the rotation axis.

[0032] During use, a liquid feed mixture may be supplied into the separation space along the rotation axis. A separated light phase, or fraction, may be led out of the separation space along the rotation axis or radially close to the rotation axis. The sludge, or sludge fraction, may be separated from the feed mixture and discharged through the outlet openings in the radial direction. In some examples, a separated heavy phase may also be led out of the separation space along the rotation axis or radially close to the rotation axis.

[0033] Throughout this document, the term "sludge" is used to refer to the denser portion of a feed mixture that is separated during the centrifugal process and discharged through the designated discharge outlets. This portion may also be referred to as the "solid fraction", "solid phase", "sludge phase", or "sludge fraction", depending on the specific context. These terms are intended to be interchangeable and encompass any high-density materials that are separated out from the feed mixture, including but not limited to solid particles, heavier impurities, or any other components with greater density relative to the light liquid fractions.

[0034] It should be understood that these terms are used broadly to describe the dense material separated by the centrifugal separator, and their usage is not intended to impose any limitations the scope of the invention as defined by the appended claims. The terms "sludge", "solid fraction", "solid phase", and "sludge fraction" should be interpreted to cover any material that exhibits the characteristics of being denser or heavier than the lighter liquid fractions, and which is desired to be discharged through the discharge outlets.

[0035] The term "pressurised liquid" typically denotes the liquid actuating the opening element and may thus be referred to as "opening liquid" or "control liquid". Similarly, the term "operating liquid", as used in some examples, typically denotes the liquid maintaining the slide in its closed position. The operating liquid may hence be referred to as "closing liquid".

[0036] Further features and advantages of the invention will become apparent from the following description of preferred embodiments, given by way of example only, which is made with reference to the accompanying drawings.Brief Description of the Drawings

[0037] Various aspects and examples of the present disclosure will be readily understood from the embodiments discussed in the following detailed description and the accompanying drawings, in which: Figure 1 shows schematically a cross section of a centrifugal separator according to some examples. Figures 2A and 2B show schematically a cross section of a portion of a centrifugal separator. Figures 3 and 4 as schematic diagrams illustrating discharge control systems according to some examples. Figures 5A and 5B are flow charts of methods of operating a centrifugal separator. Detailed Description

[0038] Figure 1 is a schematic cross-section of a centrifugal separator 100 according to some examples. The centrifugal separator 100 comprises a rotor 110 defining a separation space 111, in which a feed mixture can be separated into separate components based on their densities as the rotor rotates around a rotation axis X extending vertically through a centre of the separator 100. Heavier constituents, such as solid particles and heavy liquid components, may be accumulated at a radially outer portion of the rotor 110 and intermittently discharged through a series of discharge outlets 120. The accumulated, heavier constituents may be referred to as a solid fraction, or sludge. The discharge outlets 120 may be closed during regular operation of the separator to prevent the contents of the rotor 110 from being expelled, and opened during a discharge process in which the sludge is to be expelled from the separation space 111.

[0039] The opening and closing of the discharge outlets 120 may be controlled, either directly or indirectly, by an opening element 130. The opening element 130 may, for example, be a valve that actuates a mechanism that opens and closes the discharge outlets 120, as will be discussed in further detail with reference to figures 2A and B.

[0040] The opening element 130 may be actuated by a discharge control system 200 of the separator 100. In some examples, the discharge control system 200 is a hydraulic control system that actuates the opening element 130 by means of a pressurised liquid, in the following referred to as an opening liquid. An example of such a discharge control system 200 is described in further detail in connection with figures 3 and 4.

[0041] The rotor 110 may form the rotating component of the separator 100 that spins at high speeds to generate the centrifugal force needed for the separation process. The rotor may be arranged within a stationary housing or body 105 of the separator 100 and accommodate the separation space 111 in which the separation process takes place. Sometimes, the rotor 110 may comprise other elements such as a drive shaft or spindle 112, and bearings 114. The rotor 110 may comprise a bowl, or separator bowl, which may be the part of the rotor 110 where the actual separation of the feed mixture occurs.

[0042] The rotor 110 is arranged to rotate around the rotation axis X during operation. A plurality of separation members 116, such as a stack of frustoconical separation discs 116, may co-rotate with the rotor 110 to separate the liquid feed mixture into the different fractions.

[0043] The feed mixture may be supplied to the separation space 111 via a flow path that passes through a hollow interior of the spindle 112, onto which the rotor 110 may be attached. The spindle 112 may be rotatably supported by the bearings 114 and driven to rotate about the rotation axis X by a motor, such as an electric motor 113, to cause the rotor 110 and the separation members 116 to rotate. The feed mixture may be supplied to the flow path through an inlet opening 103 arranged at a lower end of the spindle 112.

[0044] The separated fractions, such as the light fraction and a heavy fraction, may leave the separation space 111 through one or more outlets 101, 102 of the rotor 110, whereas the sludge, or solid fraction, may be intermittently discharged through the discharge outlets 120, which may be arranged at a periphery of the separation space 111 and controlled by the discharge control system 200.

[0045] An example of an opening element 130 and a control mechanism for controlling opening and closing of the discharge outlets 120 will now be discussed with reference to figures 2A and B. Figures 2A and B schematically illustrate cross sections of a portion of a centrifugal separator 100, which may be configured similarly to the centrifugal separator 100 shown in figure 1.

[0046] As already mentioned, the centrifugal separator 100 comprises a rotor 110 arranged to rotate around the rotation axis X to separate a feed mixture into at least a first liquid fraction and a solid fraction. The solid fraction may accumulate in radially outer portion, such as the periphery, of the separation space 111 during operation. One or more controllable discharge outlet 120 are provided in a wall of the rotor 110 to allow the accumulated solid fraction, or sludge, to be discharged from the rotor 110.

[0047] The discharge outlet 120 may be opened and closed by a control mechanism that includes a movable component located within the rotor 110. The movable component may include a slide 140 designed to move along the rotation axis X. In a first position along the axis X, which may be referred to as its default operating position, the slide 140 may be positioned to abut against an upper part 142 of the rotor body 110 to seal the discharge outlet 120, preventing the release of sludge. This position is shown in figure 2A. When the discharge is required, the slide 140 may be actuated to move to a second position along the rotation axis X, uncovering the discharge outlet 120 and allowing the sludge to be expelled from the separation space 111. This position is shown in figure 2B.

[0048] The movement of the slide 140 along the rotation axis X may be actuated by a pressurised operating liquid, such as water, which may be controlled by the discharge control system 200. In the following, the operating liquid is referred to as closing liquid. The supply of closing liquid may be managed by the discharge control system 200, which includes an opening element, such as a pilot valve 130, configured to control the flow of the pressurised closing liquid out of an operating chamber 150 beneath the slide 140. When pressurised closing liquid enters the operating chamber 150, it displaces the slide 140 along the rotation axis towards the first position, closing the discharge outlets 120. When the closing liquid is released from the operating chamber 150, the slide 140 moves towards the second position, opening the discharge outlet 120.

[0049] The closing liquid may be supplied via a supply channel 152 and released from the operating chamber 150 through a discharge channel 154 controlled by the pilot valve 130. The supply channel 152 may be fluidically connected to a closing liquid supply system, which in some cases may be provided by the discharge control system 200.

[0050] The pilot valve 130 may be actuated by a pressurised liquid, also referred to as an opening liquid, which in the present example may be water. The opening liquid may be provided as a pressure pulse through an opening liquid channel 138 that extends at least partially through the rotor 110.

[0051] The opening liquid channel 138 is arranged to supply the opening liquid to a valve body 131 of the pilot valve 130, which is movable to open and close the discharge channel 154. In figure 2A, the valve body 131 is arranged in a closed state, in which it seals against a sealing surface 132 of the pilot valve 130 and closes the discharge channel 154 to allow the closing liquid to fill the operating chamber 150. The valve body 131 may be maintained in the closed position by a biasing means, such as a compression spring 136, pushing the valve body against the sealing surface 132. In some examples, the rotation of the rotor 110 may generate a centrifugal force that urges the valve body 131 towards the sealing surface 132. Accordingly, in some examples a separate biasing means may not be required.

[0052] When the pilot valve 130 is actuated, opening liquid may be supplied through the opening liquid channel 138 to exert a pressure on an actuation pressure receiving area 134 of the valve body 131, displacing the valve body 131 into an open position to open the discharge channel 154 and allow the operating fluid to be released from the operating chamber 150. As illustrated in figure 2B, the opening liquid may force the valve body 131 to move away from the sealing surface 132, overcoming the biasing force provided by the compression spring 136 and / or the centrifugal force generated by the rotation of the rotor 110.

[0053] It should be appreciated that a certain threshold pressure, or "cracking pressure", may be required to actuate the opening element 130, such as the pilot valve shown in figures 2A and B. In other words, the pulse of opening liquid provided by the discharge control system 200 may need to generate sufficient pressure to overcome any forces keeping the opening element 130 in the closed state, such as the biasing force exerted by the compression spring 136 in the example illustrated in figures 2A and B. Therefore, the discharge control system 200 may be configured to provide a pressure pulse of opening liquid with an amplitude that exceeds the cracking pressure of the opening element 130.

[0054] The valve body 131 can be returned to the closed position by the discharge control system 200 either shutting off the flow of opening liquid or reducing the flow to a level that allows the biasing force and / or centrifugal force to move the valve body 131 towards the sealing surface 132.

[0055] The pilot valve 130 described above, which is actuated by a pulse of pressurised liquid, is merely an illustrative example provided to explain the inventive concept. Other mechanisms and means for controlling the opening and closing of the discharge outlets 120 are possible and may be employed within the scope of the inventive concept. These alternatives may include different types of valves and control mechanisms, which may be actuated by a pulse of pressurised liquid provided by a discharge control system 200, which will now be discussed in further detail below.

[0056] Figure 3 is a diagram schematically outlining a discharge control system 200, which may be configured similarly to any of the discharge control systems discussed above in connection with figures 1, 2A, and 2B. The system 200 may be configured to provide the opening element 130 of the rotor 110 with a pressurised liquid, or an opening liquid, for controlling the discharge of sludge through the discharge outlets 120.

[0057] The example system 200 comprises a reservoir 210 accommodating the opening liquid, such as pressurised water, a liquid channel 220 fluidically connecting the reservoir to the opening element 130, and a control valve arrangement 230 operable to selectively open and close the liquid channel 220 to control a flow of opening liquid therethrough.

[0058] The reservoir 210 may be a tank or vessel comprising a pressure mechanism, such as a flexible bladder or diaphragm, a spring mechanism, or a piston, allowing a consistent supply of pressurised liquid to be maintained. The reservoir 210 may be fluidically connected to the opening liquid channel 138 (shown in figures 2A and B) via the liquid channel 220 and the control valve arrangement 230.

[0059] The control valve arrangement 230 may comprise one or more valve elements, including solenoid valves, pneumatic valves, and hydraulic valves. Other types of valves are however possible. The control valve arrangement 230 may be used to control a flow of opening liquid supplied to the opening element 130, such as one or more pulses propagating through the liquid channel 220.

[0060] The control valve arrangement 230 may be controlled by a control unit 240, or controller, which may be communicatively coupled to the control valve arrangement 230 via a wired or wireless communication channel. The control unit 240 may be configured to control the time the control valve arrangement remains open, which in turn may determine the volume of the discharge. The control unit 240 may comprise a microcontroller or a programmable logic controller (PLC), as well as a user interface such as a touchscreen or control panel, allowing operators to set parameters, select operating modes, and monitor system performance. The control unit 240 may also comprise communication interfaces allowing it to communicate other control systems, remote monitoring systems, and one or more sensors monitoring the status of the control valve arrangement 230 or other parts of the separator 100.

[0061] Figure 4 is a schematic outline of a discharge control system 200 according to an example, which may be configured similarly to the discharge control system 200 of figure 3. This example shows a control valve arrangement 230 comprising a first valve 231 and a second valve 232 arranged in series along the liquid channel 230. The valves 231, 232 may cooperate to generate a pulse of opening liquid actuating the opening element 130. The first valve 231 may be a normally-closed (NC) valve that opens when actuated and closes when deactivated, while the second valve 232 may be a normally-open (NO) valve that closes when actuated and opens when deactivated. The first and second valves 231, 232 may hence form a complementary pair, which can be individually controlled to initiate, maintain, and terminate a pulse of opening liquid. By controlling the timing of the actuation of the valves 231, 232, a pulse of a desired length may be provided. It should be noted that the order of the valves 231, 232 may be reversed, such that the first valve 231 is arranged upstream of the second valve 232, i.e., closer to the reservoir 210.

[0062] In some examples, the first and second valves 231, 232 may actuate faster than they deactivate. Specifically, the NC valve 231 may open faster than it closes, while the NO valve 232 may close faster than it opens. These asymmetries may be leveraged by using the fast-opening first valve 231 to initiate the pulse and the fast-closing second valve 232 to terminate it. Thus, the discharge of sludge may be controlled by opening the first valve 231 to allow the pressurised opening liquid to flow to the opening element 130. The first valve 231 may be kept open for a duration that corresponds to the desired length of the discharge, after which the discharge may be terminated by closing the second valve 232 to stop the flow of opening liquid. The duration of the discharge process may hence be determined by the duration for which the control valve arrangement 230 remains open to supply the opening element 230 with opening liquid.

[0063] The reservoir 210 may be a hydraulic accumulator comprising a separating element, such as a diaphragm or piston 215, dividing an interior of the accumulator into a liquid chamber 212 accommodating the opening liquid and a gas chamber 211 comprising a pressurised gas. The separating element 215 is provided to ensure that the gas and the opening liquid remain separate. The pressurised gas, typically nitrogen or air, provides the necessary fore to maintain the opening liquid under pressure. This gas can be replenished when needed through a gas supply system, such as a valve 260, connected to the reservoir 210.

[0064] The volume of opening liquid in the liquid chamber 212 may be substantially larger than the volume consumed to generate a single pulse for operating the discharge outlets 120. This to ensure that multiple pulses, and thus multiple discharges, can be generated without the need to refill the reservoir 210.

[0065] The opening liquid can be replenished when its volume decreases to a predetermined lower limit. This replenishment can be managed through a liquid refill system connected to the reservoir 210, which refills the liquid chamber 212 to the required volume. The liquid refill system may include one or more valves and / or one or more pumps 250 to increase the pressure of the supplied liquid to match the pressure in the reservoir 210. The opening liquid may, for example, be water drawn from a building's municipal water supply.

[0066] The gas pressure in the gas chamber 211, as well as the volume of opening liquid in the liquid chamber 212, may be monitored by one or more sensors. Data from these sensors may be fed to the control unit 240, which may determine when the pressure and / or volume of the opening liquid falls below a predetermined lower limit. If the pressure and / or volume drops below this limit, the control unit 240 may send instructions to the gas supply system and / or liquid refill system to replenish the gas and / or the opening liquid.

[0067] The reservoir 210 may further be configured to supply the closing liquid, i.e. pressurized water (closing water) keeping the slide 140 in its closed position. Hence, the closing liquid may be from the same source as the opening liquid actuating the opening element 130. An example of such a configuration is shown in figure 4, wherein the reservoir 210 is fluidically connected to the supply channel 152 of the rotor 210 through a channel 225 controlled by an operating valve 233. The operating valve 233 may form part of the control valve arrangement 230. Further, the operating valve 233 may be controlled by the control unit 240, similar to the first and second valves 231, 232 regulating the flow of opening liquid to the opening element 130.

[0068] The control unit 240 may be configured to determine an open time of the valve arrangement 230, which in turn may determine the length of the discharge process and, consequently, the volume of solid fraction expelled during the discharge. The control unit 240 may use this open time to generate control signals that actuate and deactivate the valve elements of the valve arrangement 230, such as the first and second valves 231, 233 depicted in figure 4.

[0069] In some examples, the control unit 240 may be configured to generate control signals - i.e., commands for opening and closing the valve arrangement 230 - based on a desired discharge volume and / or discharge time. The desired discharge volume or discharge time may serve as input for determining the appropriate open time of the valve arrangement 230, which may be achieved by timing the opening and closing of the NC valve 231 and the NO valve 232 to create a pulse of opening liquid with the desired pulse length.

[0070] Figure 5A is a flow chart schematically illustrating a method of operating a centrifugal separator 100 according to any of the examples described above. Reference is made to figures 1, 2A and 2B, 3, and 4 for examples of structural elements of the centrifugal separator 100.

[0071] The centrifugal separator 100 may operate by spinning its rotor 110 around rotation axis X to separate 310 a solid fraction from a feed mixture. The solid fraction, or sludge, may accumulate at the outer, peripheral portion of the separation space 111, from where it may be intermittently discharged during continuous operation of the separator 100. The solid phase may be discharged through a plurality of discharge outlets 120, which may be controlled by a hydraulically actuated opening element 130.

[0072] In this example method, the control valve arrangement 230 opens 320 the liquid channel 220 to fluidically connect the reservoir 210 comprising the pressurised liquid, or opening liquid. This action initiates the supply of opening liquid to the opening element 130, which is actuated 330 by the opening liquid, causing the discharge outlets 120 to open 340. The volume of solid fraction expelled during the discharge process may be determined at least in part by the time the control valve arrangement 230 remains open. The discharge can be terminated by stopping 350 the supply of the opening liquid.

[0073] In some examples, where the control valve arrangement 230 comprises a first valve 231 and a second valve 232 in series along the liquid channel 220, the supply of the opening liquid may be initiated 320 by actuating the first valve 231 to open the liquid channel 220 and terminated 350 by actuating the second valve 232 to close the liquid channel 220.

[0074] Figure 5B illustrates an example method wherein a certain volume of solid fraction is separated 310 from the feed mixture and discharged through multiple partial discharges. This process involves generating 325 a sequence of pressure pulses of opening liquid, which actuates the opening element 130 accordingly, allowing the solid fraction to be discharged 345 in a series of repeated discharges. Consequently, the discharge valve arrangement 230 may be operated to generate a pulse train of pressure pulses, with each individual pulse having a duration shorter than the time required to discharge the entire volume of accumulated solid fraction. It is to be noted that the length of each pulse, dictating the length of each partial discharge, and the separation time between individual pulses of the sequence, can vary depending on several factors, including operational parameters, the design of the centrifugal separator, and properties of the solid fraction. The duration of each individual pulse may typically be a few ten milliseconds, such as 10-100 milliseconds. The separation time may be of the same order, such as a few ten milliseconds.

[0075] As mentioned above, the centrifugal separator 100 may be controlled by the controller, or control unit 240, which may be incorporated in the separator 100 or arranged at another location, physically separate from the separator 100. The control unit 240 may generally comprise one or more processors and one or more non-transitory computer-readable media storing first computer executable instructions that, when executed by the one or more processors, cause the separator 100 to perform at least parts of the actions discussed in connection with figures 5A and B. Generally, the control unit 240 may comprise circuitry which is configured to implement (using one or more non-transitory computer-readable media) the functionality described herein. Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors or cores, of any kind of computer. The processors can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). Those skilled in the art will understand that the above-described exemplary embodiments may be implemented in any suitable software, hardware, or firmware configuration or combination thereof. An exemplary hardware platform for implementing the exemplary embodiments may include, for example, an Intel x86 based platform with compatible operating system, a Windows OS, a Mac platform and MAC OS, a mobile device having an operating system such as iOS, Android, etc. In a further example, the exemplary embodiments of the above-described method may be embodied as a program containing lines of code stored on a non-transitory computer readable storage medium that, when compiled, may be executed on a processor or microprocessor.

[0076] The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, other, mechanisms than the slide can be employed to control the opening and closing of the discharge outlets. Example mechanisms may, for example, include valves, such as sliding gate valves or piston valves that are actuated by the opening liquid provided by the discharge control system. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Examples

Embodiment Construction

[0038]Figure 1 is a schematic cross-section of a centrifugal separator 100 according to some examples. The centrifugal separator 100 comprises a rotor 110 defining a separation space 111, in which a feed mixture can be separated into separate components based on their densities as the rotor rotates around a rotation axis X extending vertically through a centre of the separator 100. Heavier constituents, such as solid particles and heavy liquid components, may be accumulated at a radially outer portion of the rotor 110 and intermittently discharged through a series of discharge outlets 120. The accumulated, heavier constituents may be referred to as a solid fraction, or sludge. The discharge outlets 120 may be closed during regular operation of the separator to prevent the contents of the rotor 110 from being expelled, and opened during a discharge process in which the sludge is to be expelled from the separation space 111.

[0039]The opening and closing of the discharge outlets 120 ma...

Technical Field

[0001] The present invention relates to centrifugal separators, and particularly to centrifugal separators comprising a discharge control system.Background

[0002] Centrifugal separators are used to separate feed mixture components with different densities by accelerating the feed mixture to high rotational speeds. Denser components move outward towards the perimeter of the separator's separation space, forming one or more heavy fractions, while less dense components remain closer to the centre, forming one or more light fractions. If the feed mixture comprises solid particles or heavier impurities, a denser layer, known as a solid fraction or sludge, may accumulate at the outer periphery of the separation space.

[0003] To enable continuous operation, sludge may be automatically removed through a discharge system which intermittently expels the sludge via discharge outlets. This system may include a sliding bowl bottom or movable slide that vertically opens or closes the discharge outlets. During regular operation, the slide covers these outlets to prevent discharge. When actuated, it uncovers the outlets, allowing sludge expulsion. The slide's movement may be controlled by a hydraulic system using pressurised liquid to operate the sliding mechanism.

[0004] Precise control over the hydraulic system's operation is desirable, as this may help optimising the discharge process, reducing waste and ensuring efficient discharge.Summary

[0005] It is an object of the present disclosure to provide a technology that addresses at least some of the above concerns.

[0006] According to a first aspect of the present invention, there is provided a centrifugal separator comprising a rotor, an opening element, and a discharge control system actuating the opening element. The rotor defines a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, wherein a radially outer portion of the rotor comprises a controllable discharge outlet for intermittent discharge of the solid fraction from the separation space. The opening element is arranged within the rotor and configured to control opening and closing of the discharge outlet. The discharge control system is configured to actuate the opening element by means of a pressurised liquid, and comprises a reservoir for accommodating the pressurised liquid. The discharge control system further comprises a liquid channel fluidically connecting the reservoir and the opening element, a control valve arrangement for selectively open and close the liquid channel, and a control unit for controlling the operation of the control valve arrangement to supply the opening element with the pressurised liquid actuating the opening element. The discharge control system is configured to actuate the opening element based on a duration for which the control valve arrangement remains open.

[0007] According to a second aspect, there is provided a method of operating a centrifugal separator comprising a rotor defining a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, and a controllable discharge outlet for intermitted discharge of the solid fraction from the separation space. The method comprises providing, by a reservoir, a pressurised liquid and opening, by a control valve arrangement, a liquid channel fluidically connecting the reservoir and an opening element in the rotor. The method further comprises actuating the opening element by supplying the opening element with the pressurised liquid, and opening, by the opening element, the discharge outlet to discharge the solid fraction from the separation space. The opening element is actuated based at least in part on a duration for which the control valve arrangement remains open.

[0008] According to a third aspect, a method of operating a centrifugal separator is provided. The separator comprises a rotor defining a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, and a controllable discharge outlet for intermittent discharge of the solid fraction from the separation space. The method comprises separating, in the separation space, a volume of the solid fraction from the feed mixture, generating a sequence of pressure pulses actuating an opening element arranged within the rotor and configured to control and closing of the discharge outlet, and discharging, by the sequence of pressure pulses opening and closing the discharge outlet, the volume of the solid fraction through the discharge outlet.

[0009] In the above aspects, the discharge control system is used to actuate the opening element, which then controls the discharge outlet, either directly or indirectly. The opening element is actuated by a flow of pressurised liquid, which also may be referred to as an opening liquid, or pressurised opening liquid. The opening liquid may be supplied as a pulse of pressurised liquid provided by the control valve arrangement. The pulse may be initiated when the control valve arrangement opens the liquid channel between the reservoir and the opening element, and terminated when the control valve arrangement closes the liquid channel. The length of the discharge, and thereby the volume of the discharge, is thus determined by the duration of the pulse actuating the opening element, which in turn is determined by the time the control valve arrangement remains open. In other words, the timing of the valve's open state may directly determine how long the discharge outlet remain uncovered by the opening element. This timing can be precisely controlled using, for example, electronic controllers, enabling fine-tuning of the discharge process.

[0010] This approach offers an advantage over prior art systems that control discharge by the volume of pressurised fluid supplied to actuate the mechanism controlling the discharge outlets. In those systems, the discharge is controlled based on the assumption that a specific volume of fluid will correspond to a particular degree of movement in the mechanism controlling the discharge outlets, thereby controlling the duration and extent of the discharge.

[0011] By controlling the discharge based on the time the control valve arrangement remains open, a faster response time and a more precise actuation of the opening element can be achieved. This method also facilitates the generation of shorter pulses and, in some cases, a series of smaller discharge pulses, enhancing the overall efficiency and control of the separation process.

[0012] In some examples, the control valve arrangement comprises a first valve and a second valve in series along the liquid channel, forming a dual-valve arrangement. These valves may work together to generate a pressure pulse that actuates the opening element. The valves may form a complementary pair, with the first valve being a normally-closed (NC) valve, which opens when actuated and closes when deactivated, and the second valve being a normally-open (NO) valve, which closes when actuated and opens when deactivated. This configuration allows the control unit to initiate the supply of pressurised liquid by actuating the NC valve and terminate the supply by actuating the NO valve.

[0013] Such a dual arrangement may be particularly beneficial for valves with asymmetric response characteristics, that is, valves that have different actuation and deactivation speeds. In the present example, the valves may actuate faster than they deactivate. Consequently, the NC valve may operate as a quick-opening, slow-closing valve, and the NO valve function as a quick-closing, slow-opening valve. By combining these two valve types, the arrangement leverages the fast-actuating behaviour of both valves to achieve a relative quick initiation and termination of the pressure pulse.

[0014] Beneficially, the time it takes for the control valve arrangement to open or close the fluid passage may be significantly shorter than the duration of the discharge, ensuring precise and repeatable control of the opening element. In some examples, the control valve arrangement may be configured to be actuated (i.e., opened or closed) in a few milliseconds, such as 5 milliseconds or less, while the duration of the discharge may be in the order of 100 milliseconds.

[0015] The valve arrangement may, for example, be controlled by solenoid actuators, pneumatic actuators, hydraulic actuators, or motorised actuators. Additionally, these actuators may be combined with spring-return mechanisms, allowing the valve to be moved in one direction by the actuator (e.g., solenoid, pneumatic, or hydraulic) and returned by the spring force. It should be noted, however, that these are merely illustrative examples, and that other configurations and actuations mechanisms may also be possible.

[0016] The opening element may be configured to control the discharge outlet either directly or indirectly. In the latter case, the opening element may serve as an intermediary control element, such as a pilot valve, controlling the operating of another mechanism such as a slide or sliding bowl bottom. The slide can be arranged in a first position along a rotation axis of the rotor to close the discharge outlet and in a second position along the rotation axis to open the discharge outlet. An operating chamber may be provided between the slide and a body of the rotor, configured to accommodate an operating liquid that maintains the slide in the first position and therefore may be referred to as a closing liquid. The opening element may be arranged to control the position of the slide by discharging closing liquid from the operating chamber. This may cause the slide to be displaced from the first position to the second position to open the discharge outlet.

[0017] In some examples, the opening element comprises an operating slide, which may be arranged axially below the sliding bowl bottom (i.e., the slide that opens and closes the discharge outlet). The operating slide may be operable to control the position of the slide by means of the closing liquid, which may be supplied to and discharged from the operating chamber as discussed above.

[0018] The use of a pilot valve may enable finer control over the discharge process, as a relatively small adjustments in the pilot valve position can result in a more precise regulation of the flow of closing liquid. This allows a smaller flow of opening liquid to control a larger flow of closing liquid, using a relatively small amount of force.

[0019] The closing liquid may be supplied from the reservoir, which hence may be configured to provide both the opening liquid controlling the opening element and the closing liquid controlling the position of the slide. The opening liquid and the closing liquid may, for example, be formed of water that is kept under pressure in the reservoir. In some examples, the control valve arrangement comprises an operating valve configured to control the supply of the pressurised liquid to the operating chamber.

[0020] The control unit may be configured to open the operating valve after initiating the supply of pressurised opening liquid to the opening element. This ensures that the discharge outlet may be closed again (by the supply of closing liquid) after it has been opened (by the opening liquid actuating the opening element).

[0021] Using the pressurised liquid from the reservoir, which is already employed to actuate the opening element, as the closing liquid for maintaining the slide in its closed position offers a simplified system design. There may be a reduced need for separate reservoirs, pumps, or supply lines for different liquids, reducing the overall complexity of the system. Furthermore, fewer components may translate to lower initial costs for producing and installing the equipment.

[0022] The reservoir may be a hydraulic accumulator, which is configured to store pressurised fluid and release the fluid when needed to perform work in the system, such as actuating an opening element or displacing a slide. The hydraulic accumulator may be formed of a chamber that is divided into two or more section by a separating element. The separating element can be a flexible membrane, diaphragm, bladder, or piston, depending on the specific design. The section filled with the liquid (such as closing liquid or opening liquid) may be kept under pressure and readily available to be supplied to the opening element or operating chamber as needed. The other side of the separator may be filled with a pressurised gas (such as air or nitrogen), which servers to maintain the pressure on the liquid side. The gas may act as a spring, compressing when the liquid is forced into the accumulator and expanding when the liquid is drawn out, thus maintaining a consistent pressure in the system. The pressurised gas provides the energy needed to quickly supply the liquid to the opening element or the operating chamber when the control valve arrangement is opened, ensuring a rapid and efficient response.

[0023] In some examples, the centrifugal separator comprises a pump unit for replenishing the reservoir with liquid. The pump unit may be configured to draw water from a regular water supply system, such as a building's municipal water supply, or a dedicated water source. The water supply system is typically operated at a lower pressure than required by the reservoir. The pump unit, therefore, may increase the pressure of the incoming water to meet the specific needs of the reservoir. Furthermore, the pump unit may allow for a continuous replenishing of the reservoir with pressurised liquid, ensuring that the system can operate without interruption. This is particularly beneficial in processes requiring continuous or frequent actuation of components, such as in high-throughput centrifugal separation processes. The ability to draw from a regular water supply and convert it into a high-pressure fluid source means that the centrifugal separator is not reliant on specialised fluids or fluid sources, making the separator more versatile and easier to maintain.

[0024] The separator may be equipped with sensors and a control system that automatically detects when the liquid level or pressure in the reservoir drops below a certain threshold. When this occurs, the pump may be activated to draw in water and pressurise it, replenishing the reservoir without the need for manual intervention.

[0025] The discharge control system may be operated to provide either a partial discharge or a full discharge of the sludge (solid fraction). During a full discharge, the discharge outlets remain open long enough to ensure that all, or substantially all, of the accumulated sludge is expelled from the separation space. In a partial discharge, the discharge outlets may be opened only briefly, allowing just a portion of the sludge to be expelled before they are closed again. In some examples, a full discharge can be achieved through a series of partial discharges. In other words, a specific volume of the accumulated sludge may be discharged by generating a sequence of pressure pulses that cause the discharge outlets to open and close repeatedly, until the desired volume has been expelled through multiple partial discharges.

[0026] The rotor may comprise a plurality of controllable discharge outlets, or openings, which may be arranged along a circumference of the rotor and extending in a plane orthogonal to the rotation axis. The discharge outlets may be evenly spaced around the perimeter to allow the sludge to be expelled evenly, reducing the risk of imbalance in the rotor and promoting smooth operation. Other configurations are however possible, such as segmented arrays in which openings are grouped into segments with gaps between each segment, or staggered arrangements in which the outlets are slightly offset from each other along the perimeter. The staggered design may ensure that not all openings are exposed to the maximum concentration of sludge simultaneously, reducing the risk of clogging and promoting smoother and more consistent discharge.

[0027] The shape of the discharge outlets may be customised based on the specific requirements of the separation process. Example shapes include circular, elliptical, and slot-like openings.

[0028] The centrifugal separator may be a high-speed centrifugal separator, with the rotor rotating at several thousand rotations per minute, typically ranging from 3,000 to 12,000 rpm during operation.

[0029] The separation space may comprise a stack of separation discs, such as a stack of frustoconical separation discs, as known in the art. Thus, the centrifugal separator may be a disc-stack centrifugal separator.

[0030] The rotor may be arranged inside a stationary housing of the centrifugal separator and driven to rotate about a rotation axis by a drive arrangement, such as an electric motor. In some examples, the rotor body may comprise two or more separate parts, including a sliding bowl bottom that delimits a lower portion of the separation space.

[0031] When the centrifugal separator is positioned for use, the rotation axis may be oriented vertically. Accordingly, the rotor may have an upper portion and a lower portion. The term axial, radial, and rotational relate to the rotation axis: an axial direction extends parallel to the rotation axis, while a radial direction extends perpendicular to the rotation axis.

[0032] During use, a liquid feed mixture may be supplied into the separation space along the rotation axis. A separated light phase, or fraction, may be led out of the separation space along the rotation axis or radially close to the rotation axis. The sludge, or sludge fraction, may be separated from the feed mixture and discharged through the outlet openings in the radial direction. In some examples, a separated heavy phase may also be led out of the separation space along the rotation axis or radially close to the rotation axis.

[0033] Throughout this document, the term "sludge" is used to refer to the denser portion of a feed mixture that is separated during the centrifugal process and discharged through the designated discharge outlets. This portion may also be referred to as the "solid fraction", "solid phase", "sludge phase", or "sludge fraction", depending on the specific context. These terms are intended to be interchangeable and encompass any high-density materials that are separated out from the feed mixture, including but not limited to solid particles, heavier impurities, or any other components with greater density relative to the light liquid fractions.

[0034] It should be understood that these terms are used broadly to describe the dense material separated by the centrifugal separator, and their usage is not intended to impose any limitations the scope of the invention as defined by the appended claims. The terms "sludge", "solid fraction", "solid phase", and "sludge fraction" should be interpreted to cover any material that exhibits the characteristics of being denser or heavier than the lighter liquid fractions, and which is desired to be discharged through the discharge outlets.

[0035] The term "pressurised liquid" typically denotes the liquid actuating the opening element and may thus be referred to as "opening liquid" or "control liquid". Similarly, the term "operating liquid", as used in some examples, typically denotes the liquid maintaining the slide in its closed position. The operating liquid may hence be referred to as "closing liquid".

[0036] Further features and advantages of the invention will become apparent from the following description of preferred embodiments, given by way of example only, which is made with reference to the accompanying drawings.Brief Description of the Drawings

[0037] Various aspects and examples of the present disclosure will be readily understood from the embodiments discussed in the following detailed description and the accompanying drawings, in which: Figure 1 shows schematically a cross section of a centrifugal separator according to some examples. Figures 2A and 2B show schematically a cross section of a portion of a centrifugal separator. Figures 3 and 4 as schematic diagrams illustrating discharge control systems according to some examples. Figures 5A and 5B are flow charts of methods of operating a centrifugal separator. Detailed Description

[0038] Figure 1 is a schematic cross-section of a centrifugal separator 100 according to some examples. The centrifugal separator 100 comprises a rotor 110 defining a separation space 111, in which a feed mixture can be separated into separate components based on their densities as the rotor rotates around a rotation axis X extending vertically through a centre of the separator 100. Heavier constituents, such as solid particles and heavy liquid components, may be accumulated at a radially outer portion of the rotor 110 and intermittently discharged through a series of discharge outlets 120. The accumulated, heavier constituents may be referred to as a solid fraction, or sludge. The discharge outlets 120 may be closed during regular operation of the separator to prevent the contents of the rotor 110 from being expelled, and opened during a discharge process in which the sludge is to be expelled from the separation space 111.

[0039] The opening and closing of the discharge outlets 120 may be controlled, either directly or indirectly, by an opening element 130. The opening element 130 may, for example, be a valve that actuates a mechanism that opens and closes the discharge outlets 120, as will be discussed in further detail with reference to figures 2A and B.

[0040] The opening element 130 may be actuated by a discharge control system 200 of the separator 100. In some examples, the discharge control system 200 is a hydraulic control system that actuates the opening element 130 by means of a pressurised liquid, in the following referred to as an opening liquid. An example of such a discharge control system 200 is described in further detail in connection with figures 3 and 4.

[0041] The rotor 110 may form the rotating component of the separator 100 that spins at high speeds to generate the centrifugal force needed for the separation process. The rotor may be arranged within a stationary housing or body 105 of the separator 100 and accommodate the separation space 111 in which the separation process takes place. Sometimes, the rotor 110 may comprise other elements such as a drive shaft or spindle 112, and bearings 114. The rotor 110 may comprise a bowl, or separator bowl, which may be the part of the rotor 110 where the actual separation of the feed mixture occurs.

[0042] The rotor 110 is arranged to rotate around the rotation axis X during operation. A plurality of separation members 116, such as a stack of frustoconical separation discs 116, may co-rotate with the rotor 110 to separate the liquid feed mixture into the different fractions.

[0043] The feed mixture may be supplied to the separation space 111 via a flow path that passes through a hollow interior of the spindle 112, onto which the rotor 110 may be attached. The spindle 112 may be rotatably supported by the bearings 114 and driven to rotate about the rotation axis X by a motor, such as an electric motor 113, to cause the rotor 110 and the separation members 116 to rotate. The feed mixture may be supplied to the flow path through an inlet opening 103 arranged at a lower end of the spindle 112.

[0044] The separated fractions, such as the light fraction and a heavy fraction, may leave the separation space 111 through one or more outlets 101, 102 of the rotor 110, whereas the sludge, or solid fraction, may be intermittently discharged through the discharge outlets 120, which may be arranged at a periphery of the separation space 111 and controlled by the discharge control system 200.

[0045] An example of an opening element 130 and a control mechanism for controlling opening and closing of the discharge outlets 120 will now be discussed with reference to figures 2A and B. Figures 2A and B schematically illustrate cross sections of a portion of a centrifugal separator 100, which may be configured similarly to the centrifugal separator 100 shown in figure 1.

[0046] As already mentioned, the centrifugal separator 100 comprises a rotor 110 arranged to rotate around the rotation axis X to separate a feed mixture into at least a first liquid fraction and a solid fraction. The solid fraction may accumulate in radially outer portion, such as the periphery, of the separation space 111 during operation. One or more controllable discharge outlet 120 are provided in a wall of the rotor 110 to allow the accumulated solid fraction, or sludge, to be discharged from the rotor 110.

[0047] The discharge outlet 120 may be opened and closed by a control mechanism that includes a movable component located within the rotor 110. The movable component may include a slide 140 designed to move along the rotation axis X. In a first position along the axis X, which may be referred to as its default operating position, the slide 140 may be positioned to abut against an upper part 142 of the rotor body 110 to seal the discharge outlet 120, preventing the release of sludge. This position is shown in figure 2A. When the discharge is required, the slide 140 may be actuated to move to a second position along the rotation axis X, uncovering the discharge outlet 120 and allowing the sludge to be expelled from the separation space 111. This position is shown in figure 2B.

[0048] The movement of the slide 140 along the rotation axis X may be actuated by a pressurised operating liquid, such as water, which may be controlled by the discharge control system 200. In the following, the operating liquid is referred to as closing liquid. The supply of closing liquid may be managed by the discharge control system 200, which includes an opening element, such as a pilot valve 130, configured to control the flow of the pressurised closing liquid out of an operating chamber 150 beneath the slide 140. When pressurised closing liquid enters the operating chamber 150, it displaces the slide 140 along the rotation axis towards the first position, closing the discharge outlets 120. When the closing liquid is released from the operating chamber 150, the slide 140 moves towards the second position, opening the discharge outlet 120.

[0049] The closing liquid may be supplied via a supply channel 152 and released from the operating chamber 150 through a discharge channel 154 controlled by the pilot valve 130. The supply channel 152 may be fluidically connected to a closing liquid supply system, which in some cases may be provided by the discharge control system 200.

[0050] The pilot valve 130 may be actuated by a pressurised liquid, also referred to as an opening liquid, which in the present example may be water. The opening liquid may be provided as a pressure pulse through an opening liquid channel 138 that extends at least partially through the rotor 110.

[0051] The opening liquid channel 138 is arranged to supply the opening liquid to a valve body 131 of the pilot valve 130, which is movable to open and close the discharge channel 154. In figure 2A, the valve body 131 is arranged in a closed state, in which it seals against a sealing surface 132 of the pilot valve 130 and closes the discharge channel 154 to allow the closing liquid to fill the operating chamber 150. The valve body 131 may be maintained in the closed position by a biasing means, such as a compression spring 136, pushing the valve body against the sealing surface 132. In some examples, the rotation of the rotor 110 may generate a centrifugal force that urges the valve body 131 towards the sealing surface 132. Accordingly, in some examples a separate biasing means may not be required.

[0052] When the pilot valve 130 is actuated, opening liquid may be supplied through the opening liquid channel 138 to exert a pressure on an actuation pressure receiving area 134 of the valve body 131, displacing the valve body 131 into an open position to open the discharge channel 154 and allow the operating fluid to be released from the operating chamber 150. As illustrated in figure 2B, the opening liquid may force the valve body 131 to move away from the sealing surface 132, overcoming the biasing force provided by the compression spring 136 and / or the centrifugal force generated by the rotation of the rotor 110.

[0053] It should be appreciated that a certain threshold pressure, or "cracking pressure", may be required to actuate the opening element 130, such as the pilot valve shown in figures 2A and B. In other words, the pulse of opening liquid provided by the discharge control system 200 may need to generate sufficient pressure to overcome any forces keeping the opening element 130 in the closed state, such as the biasing force exerted by the compression spring 136 in the example illustrated in figures 2A and B. Therefore, the discharge control system 200 may be configured to provide a pressure pulse of opening liquid with an amplitude that exceeds the cracking pressure of the opening element 130.

[0054] The valve body 131 can be returned to the closed position by the discharge control system 200 either shutting off the flow of opening liquid or reducing the flow to a level that allows the biasing force and / or centrifugal force to move the valve body 131 towards the sealing surface 132.

[0055] The pilot valve 130 described above, which is actuated by a pulse of pressurised liquid, is merely an illustrative example provided to explain the inventive concept. Other mechanisms and means for controlling the opening and closing of the discharge outlets 120 are possible and may be employed within the scope of the inventive concept. These alternatives may include different types of valves and control mechanisms, which may be actuated by a pulse of pressurised liquid provided by a discharge control system 200, which will now be discussed in further detail below.

[0056] Figure 3 is a diagram schematically outlining a discharge control system 200, which may be configured similarly to any of the discharge control systems discussed above in connection with figures 1, 2A, and 2B. The system 200 may be configured to provide the opening element 130 of the rotor 110 with a pressurised liquid, or an opening liquid, for controlling the discharge of sludge through the discharge outlets 120.

[0057] The example system 200 comprises a reservoir 210 accommodating the opening liquid, such as pressurised water, a liquid channel 220 fluidically connecting the reservoir to the opening element 130, and a control valve arrangement 230 operable to selectively open and close the liquid channel 220 to control a flow of opening liquid therethrough.

[0058] The reservoir 210 may be a tank or vessel comprising a pressure mechanism, such as a flexible bladder or diaphragm, a spring mechanism, or a piston, allowing a consistent supply of pressurised liquid to be maintained. The reservoir 210 may be fluidically connected to the opening liquid channel 138 (shown in figures 2A and B) via the liquid channel 220 and the control valve arrangement 230.

[0059] The control valve arrangement 230 may comprise one or more valve elements, including solenoid valves, pneumatic valves, and hydraulic valves. Other types of valves are however possible. The control valve arrangement 230 may be used to control a flow of opening liquid supplied to the opening element 130, such as one or more pulses propagating through the liquid channel 220.

[0060] The control valve arrangement 230 may be controlled by a control unit 240, or controller, which may be communicatively coupled to the control valve arrangement 230 via a wired or wireless communication channel. The control unit 240 may be configured to control the time the control valve arrangement remains open, which in turn may determine the volume of the discharge. The control unit 240 may comprise a microcontroller or a programmable logic controller (PLC), as well as a user interface such as a touchscreen or control panel, allowing operators to set parameters, select operating modes, and monitor system performance. The control unit 240 may also comprise communication interfaces allowing it to communicate other control systems, remote monitoring systems, and one or more sensors monitoring the status of the control valve arrangement 230 or other parts of the separator 100.

[0061] Figure 4 is a schematic outline of a discharge control system 200 according to an example, which may be configured similarly to the discharge control system 200 of figure 3. This example shows a control valve arrangement 230 comprising a first valve 231 and a second valve 232 arranged in series along the liquid channel 230. The valves 231, 232 may cooperate to generate a pulse of opening liquid actuating the opening element 130. The first valve 231 may be a normally-closed (NC) valve that opens when actuated and closes when deactivated, while the second valve 232 may be a normally-open (NO) valve that closes when actuated and opens when deactivated. The first and second valves 231, 232 may hence form a complementary pair, which can be individually controlled to initiate, maintain, and terminate a pulse of opening liquid. By controlling the timing of the actuation of the valves 231, 232, a pulse of a desired length may be provided. It should be noted that the order of the valves 231, 232 may be reversed, such that the first valve 231 is arranged upstream of the second valve 232, i.e., closer to the reservoir 210.

[0062] In some examples, the first and second valves 231, 232 may actuate faster than they deactivate. Specifically, the NC valve 231 may open faster than it closes, while the NO valve 232 may close faster than it opens. These asymmetries may be leveraged by using the fast-opening first valve 231 to initiate the pulse and the fast-closing second valve 232 to terminate it. Thus, the discharge of sludge may be controlled by opening the first valve 231 to allow the pressurised opening liquid to flow to the opening element 130. The first valve 231 may be kept open for a duration that corresponds to the desired length of the discharge, after which the discharge may be terminated by closing the second valve 232 to stop the flow of opening liquid. The duration of the discharge process may hence be determined by the duration for which the control valve arrangement 230 remains open to supply the opening element 230 with opening liquid.

[0063] The reservoir 210 may be a hydraulic accumulator comprising a separating element, such as a diaphragm or piston 215, dividing an interior of the accumulator into a liquid chamber 212 accommodating the opening liquid and a gas chamber 211 comprising a pressurised gas. The separating element 215 is provided to ensure that the gas and the opening liquid remain separate. The pressurised gas, typically nitrogen or air, provides the necessary fore to maintain the opening liquid under pressure. This gas can be replenished when needed through a gas supply system, such as a valve 260, connected to the reservoir 210.

[0064] The volume of opening liquid in the liquid chamber 212 may be substantially larger than the volume consumed to generate a single pulse for operating the discharge outlets 120. This to ensure that multiple pulses, and thus multiple discharges, can be generated without the need to refill the reservoir 210.

[0065] The opening liquid can be replenished when its volume decreases to a predetermined lower limit. This replenishment can be managed through a liquid refill system connected to the reservoir 210, which refills the liquid chamber 212 to the required volume. The liquid refill system may include one or more valves and / or one or more pumps 250 to increase the pressure of the supplied liquid to match the pressure in the reservoir 210. The opening liquid may, for example, be water drawn from a building's municipal water supply.

[0066] The gas pressure in the gas chamber 211, as well as the volume of opening liquid in the liquid chamber 212, may be monitored by one or more sensors. Data from these sensors may be fed to the control unit 240, which may determine when the pressure and / or volume of the opening liquid falls below a predetermined lower limit. If the pressure and / or volume drops below this limit, the control unit 240 may send instructions to the gas supply system and / or liquid refill system to replenish the gas and / or the opening liquid.

[0067] The reservoir 210 may further be configured to supply the closing liquid, i.e. pressurized water (closing water) keeping the slide 140 in its closed position. Hence, the closing liquid may be from the same source as the opening liquid actuating the opening element 130. An example of such a configuration is shown in figure 4, wherein the reservoir 210 is fluidically connected to the supply channel 152 of the rotor 210 through a channel 225 controlled by an operating valve 233. The operating valve 233 may form part of the control valve arrangement 230. Further, the operating valve 233 may be controlled by the control unit 240, similar to the first and second valves 231, 232 regulating the flow of opening liquid to the opening element 130.

[0068] The control unit 240 may be configured to determine an open time of the valve arrangement 230, which in turn may determine the length of the discharge process and, consequently, the volume of solid fraction expelled during the discharge. The control unit 240 may use this open time to generate control signals that actuate and deactivate the valve elements of the valve arrangement 230, such as the first and second valves 231, 233 depicted in figure 4.

[0069] In some examples, the control unit 240 may be configured to generate control signals - i.e., commands for opening and closing the valve arrangement 230 - based on a desired discharge volume and / or discharge time. The desired discharge volume or discharge time may serve as input for determining the appropriate open time of the valve arrangement 230, which may be achieved by timing the opening and closing of the NC valve 231 and the NO valve 232 to create a pulse of opening liquid with the desired pulse length.

[0070] Figure 5A is a flow chart schematically illustrating a method of operating a centrifugal separator 100 according to any of the examples described above. Reference is made to figures 1, 2A and 2B, 3, and 4 for examples of structural elements of the centrifugal separator 100.

[0071] The centrifugal separator 100 may operate by spinning its rotor 110 around rotation axis X to separate 310 a solid fraction from a feed mixture. The solid fraction, or sludge, may accumulate at the outer, peripheral portion of the separation space 111, from where it may be intermittently discharged during continuous operation of the separator 100. The solid phase may be discharged through a plurality of discharge outlets 120, which may be controlled by a hydraulically actuated opening element 130.

[0072] In this example method, the control valve arrangement 230 opens 320 the liquid channel 220 to fluidically connect the reservoir 210 comprising the pressurised liquid, or opening liquid. This action initiates the supply of opening liquid to the opening element 130, which is actuated 330 by the opening liquid, causing the discharge outlets 120 to open 340. The volume of solid fraction expelled during the discharge process may be determined at least in part by the time the control valve arrangement 230 remains open. The discharge can be terminated by stopping 350 the supply of the opening liquid.

[0073] In some examples, where the control valve arrangement 230 comprises a first valve 231 and a second valve 232 in series along the liquid channel 220, the supply of the opening liquid may be initiated 320 by actuating the first valve 231 to open the liquid channel 220 and terminated 350 by actuating the second valve 232 to close the liquid channel 220.

[0074] Figure 5B illustrates an example method wherein a certain volume of solid fraction is separated 310 from the feed mixture and discharged through multiple partial discharges. This process involves generating 325 a sequence of pressure pulses of opening liquid, which actuates the opening element 130 accordingly, allowing the solid fraction to be discharged 345 in a series of repeated discharges. Consequently, the discharge valve arrangement 230 may be operated to generate a pulse train of pressure pulses, with each individual pulse having a duration shorter than the time required to discharge the entire volume of accumulated solid fraction. It is to be noted that the length of each pulse, dictating the length of each partial discharge, and the separation time between individual pulses of the sequence, can vary depending on several factors, including operational parameters, the design of the centrifugal separator, and properties of the solid fraction. The duration of each individual pulse may typically be a few ten milliseconds, such as 10-100 milliseconds. The separation time may be of the same order, such as a few ten milliseconds.

[0075] As mentioned above, the centrifugal separator 100 may be controlled by the controller, or control unit 240, which may be incorporated in the separator 100 or arranged at another location, physically separate from the separator 100. The control unit 240 may generally comprise one or more processors and one or more non-transitory computer-readable media storing first computer executable instructions that, when executed by the one or more processors, cause the separator 100 to perform at least parts of the actions discussed in connection with figures 5A and B. Generally, the control unit 240 may comprise circuitry which is configured to implement (using one or more non-transitory computer-readable media) the functionality described herein. Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors or cores, of any kind of computer. The processors can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). Those skilled in the art will understand that the above-described exemplary embodiments may be implemented in any suitable software, hardware, or firmware configuration or combination thereof. An exemplary hardware platform for implementing the exemplary embodiments may include, for example, an Intel x86 based platform with compatible operating system, a Windows OS, a Mac platform and MAC OS, a mobile device having an operating system such as iOS, Android, etc. In a further example, the exemplary embodiments of the above-described method may be embodied as a program containing lines of code stored on a non-transitory computer readable storage medium that, when compiled, may be executed on a processor or microprocessor.

[0076] The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, other, mechanisms than the slide can be employed to control the opening and closing of the discharge outlets. Example mechanisms may, for example, include valves, such as sliding gate valves or piston valves that are actuated by the opening liquid provided by the discharge control system. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Examples

Embodiment Construction

[0038]Figure 1 is a schematic cross-section of a centrifugal separator 100 according to some examples. The centrifugal separator 100 comprises a rotor 110 defining a separation space 111, in which a feed mixture can be separated into separate components based on their densities as the rotor rotates around a rotation axis X extending vertically through a centre of the separator 100. Heavier constituents, such as solid particles and heavy liquid components, may be accumulated at a radially outer portion of the rotor 110 and intermittently discharged through a series of discharge outlets 120. The accumulated, heavier constituents may be referred to as a solid fraction, or sludge. The discharge outlets 120 may be closed during regular operation of the separator to prevent the contents of the rotor 110 from being expelled, and opened during a discharge process in which the sludge is to be expelled from the separation space 111.

[0039]The opening and closing of the discharge outlets 120 ma...

Claims

1. A centrifugal separator (100), comprising: a rotor (110) defining a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, wherein a radially outer portion of the rotor comprises a controllable discharge outlet (120) for intermittent discharge of the solid fraction from the separation space; an opening element (130) arranged within the rotor and configured to control opening and closing of the discharge outlet; and a discharge control system (200) configured to actuate the opening element by means of a pressurised liquid, the discharge control system comprising: a reservoir (210) configured to accommodate the pressurised liquid, a liquid channel (220) configured to fluidically connect the reservoir and the opening element, a control valve arrangement (230) operable to selectively open and close the liquid channel, and a control unit (240) configured to control the operation of the control valve arrangement to supply the opening element with the pressurised liquid actuating the opening element; wherein the discharge control system is configured to actuate the opening element based on a duration for which the control valve arrangement remains open.

2. The centrifugal separator according to claim 1, wherein the control valve arrangement comprises a first valve (231) and a second valve (232) arranged in series along the liquid channel.

3. The centrifugal separator according to claim 2, wherein: the first valve is a normally-closed valve; the second valve is a normally-open valve; and the control unit is configured to initiate the supply of the pressurised liquid by actuating the normally-closed valve and terminate the supply of the pressurised liquid by actuating the normally-open valve.

4. The centrifugal separator according to any of the preceding claims, wherein the opening element is a pilot valve.

5. The centrifugal separator according to any of the preceding claims, further comprising: a slide (140) arrangeable in a first position along a rotation axis of the rotor to close the discharge outlet and in a second position along the rotation axis to open the discharge outlet; and an operating chamber (150) provided between the slide and a body of the rotor; wherein the operating chamber is configured to accommodate an operating liquid maintaining the slide in the first position; and wherein the opening element is arranged to control a discharge of the operating liquid from the operating chamber to displace the slide from the first position to the second position.

6. The centrifugal separator according to claim 5, wherein: the operating chamber is fluidically connected to the reservoir; and the operating liquid is provided by the pressurised liquid accommodated by the reservoir.

7. The centrifugal separator according to claim 6, wherein: the control valve arrangement comprises an operating valve (233) configured to control the supply of pressurised liquid to the operating chamber; and the control unit is configured to open the operating valve subsequent to initiating the supply of the pressurised liquid to the opening element.

8. The centrifugal separator according to any of the preceding claims, wherein the discharge outlet is one of an array of discharge outlets arranged along a circumference of the rotor and extending in a plane orthogonal to the rotation axis.

9. The centrifugal separator according to any of the preceding claims, wherein the reservoir is a hydraulic accumulator comprising a separating element (215) separating the liquid from a pressurised gas.

10. The centrifugal separator according to any of the preceding claims, further comprising a pump unit (250) configured to replenish the reservoir with liquid.

11. A method of operating a centrifugal separator comprising a rotor defining a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, and a controllable discharge outlet for intermittent discharge of the solid fraction from the separation space, the method comprising: opening (320), by a control valve arrangement, a liquid channel fluidically connecting a reservoir and an opening element in the rotor, the reservoir comprising a pressurised liquid; actuating (330) the opening element by supplying the opening element with the pressurised liquid; and opening (340), by the opening element, the discharge outlet to discharge the solid fraction from the separation space; wherein the opening element is actuated based at least in part on a duration for which the control valve arrangement remains open.

12. The method according to claim 11, comprising: separating (310), in the separation space, a volume of the solid fraction from the feed mixture; generating (325) a sequence of pressure pulses of the pressurised liquid actuating the opening element; and discharging (345), by the sequence of pressure pulses actuating the opening element, the volume of the solid fraction from the separation space.

13. The method according to claim 11, comprising: initiating (320) the supply of the pressurised liquid to the opening element by actuating a first valve of the control valve arrangement; and terminating (350) the supply of the pressurised liquid to the opening element by actuating a second valve of the control valve arrangement.

14. The method according to any of claims 11-13, comprising: discharging, by the opening element, an operating liquid from an operating chamber provided between a slide and a body of the rotor; displacing, by the discharged operating liquid, the slide from a first position along a rotation axis of the rotor to a second position along the rotation axis to open the discharge outlet.

15. The method according to claim 15, comprising: providing operating liquid to the operating chamber; displacing, by the operating liquid, the slide from the second position to the first position to close the discharge outlet.

16. A method of operating a centrifugal separator comprising a rotor defining a separation space for separating a feed mixture into at least a first liquid fraction and a solid fraction, and a controllable discharge outlet for intermittent discharge of the solid fraction from the separation space, the method comprising: separating, in the separation space, a volume of the solid fraction from the feed mixture; generating a sequence of pressure pulses actuating an opening element arranged within the rotor and configured to control opening and closing of the discharge outlet; and discharging, by the sequence of pressure pulses opening and closing the discharge outlet, the volume of the solid fraction through the discharge outlet.

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