Field of the Invention
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The present invention relates to the field of centrifugal separators, and more specifically to a method of operating a high-speed centrifugal separator.
Background of the Invention
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High speed centrifugal separators are generally used for separation of liquids and/or for separation of solids from a liquid. During operation, liquid mixture to be separated is introduced into a rotating bowl and heavy particles or denser liquid, usually water, accumulates at the periphery of the rotating bowl whereas less dense liquid accumulates closer to the central axis of rotation. This allows for collection of the separated fractions, e.g. by means of different outlets arranged at different distances from the rotational axis.
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However, during operation of a centrifugal separator, large volumes of water is generally consumed. This may be water used for cooling parts of the separator, such as the hood or the motor. Further, if the centrifugal separator is hermetically sealed with mechanical seals, water may also be needed and consumed for cooling the seals. Also, some centrifugal separators are equipped with nozzles or intermittent discharge ports at the periphery of the separator bowl. These are used for discharging - continuously or intermittently - accumulated sludge from the bowl to a space between the rotating bowl and the stationary hood. Such space may need to be flushed with water in order to prevent build-up of discharged sludge within the hood.
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Thus, there is a need in the art for methods and systems for decreasing the water consumption of a centrifugal separator.
Summary of the Invention
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It is an object of the invention to at least partly overcome one or more limitations of the prior art. In particular, it is an object to provide a method of operating a centrifugal separator that leads to a reduced water consumption during use of the centrifugal separator. As a first aspect of the invention, there is provided a method of operating a centrifugal separator, wherein the centrifugal separator comprises
- a centrifuge bowl arranged to rotate around an axis of rotation (X) and in which the separation of a liquid mixture takes place,
- a stationary hood which defines at least part of a surrounding space in which the centrifuge bowl is arranged,
- a drive member configured to rotate the centrifuge bowl around the axis of rotation (X), wherein
- the centrifuge bowl further comprises an inlet for receiving the liquid mixture to be separated and at least one liquid outlet for discharging a separated liquid phase,
- wherein the method comprises the steps of
- a) separating the liquid feed mixture into at least one separated liquid phase in the centrifuge bowl;
- b) collecting contaminated water from at least one unit of the centrifugal separator; and
- c) resupplying the contaminated water to the centrifugal separator to flush the surrounding space.
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The centrifugal separator may be a disc-stack centrifugal separator, e.g. as disclosed in
US20210107014 .
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The method is a method for decreasing the water consumption during operation of the centrifugal separator.
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Step a) of separating the liquid feed mixture may comprise supplying the liquid feed mixture to the inlet of the centrifugal separator and discharging at least one separated liquid phase from the outlet the centrifugal separator. Step a) may comprise separating the liquid feed mixture into two liquid phases of different density. Step a) may also comprise separating the liquid feed mixture into a solid phase and at least one liquid phase. Step a) mat also include discharging the separated solid phase, either continuously or intermittently, from the bowl to the surrounding space.
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Step b) of collecting contaminated water may be performed continuously and during step a). The contaminated water may comprise operating water that has been supplied to at least one unit of the centrifugal separator; in which unit the operating water has been contaminated. "Operating water" is thus not the liquid feed mixture that is separated, but water used by different units of the centrifugal separator and which water may be contaminated, e.g. by constituents in the feed. Hower, in some embodiments, the collected water in step b) is parts of a separated phase that has been discharged from the separator.
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Step b) may comprise collecting contaminated water from a plurality of units of the centrifugal separator, and operating water may have been supplied to at least one or all of those units.
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Step c) of resupplying the contaminated water to flush the space surrounding the centrifuge bowl may comprise flushing one or several surfaces present in the surrounding space, such as the outer surface of the centrifuge bowl or a sludge channel in the surrounding space. The sludge channel may be arranged for capturing a solid phase that is ejected to the surrounding space from the centrifuge bowl and direct that sludge to a vessel used for accommodating discharged sludge.
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The resupplied water in step c) may be pressurized water, such as having a pressure of above 1.5, such as above 2 bar.
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In embodiments of the first aspect, steps b) and c) are performed during step a) i.e. during the separation of the liquid feed mixture.
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The first aspect of the invention is based on the insight that contaminated water may be reused for a specific task in the centrifugal separator, i.e. flushing the surrounding space of the centrifugal bowl. This space is usually already contaminated, e.g. by product, and the inventors have found that this part of the centrifugal separator may be flushed with slightly contaminated water without affecting the quality of the separation process. With such a solution, the water consumption of the centrifugal separator will be highly reduced.
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However, in some embodiments, and depending on the origin and concentration of contaminants in the collected water, the water may need to be diluted with before flushing. Consequently, in embodiments of the first aspect, step c) further comprises diluting the contaminated water before resupplying the contaminated water to the centrifugal separator to flush the surrounding space.
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The dilution may be performed by dilution with fresh water.
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In embodiments of the first aspect, step c) further comprises filtering the contaminated water before resupplying the contaminated water to the centrifugal separator to flush the surrounding space.
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The filtering may be for removing solid particles in the collected water. Such particles may need to be removed before flushing the surrounding space with the contaminated water.
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In embodiments of the first aspect, step b) comprises collecting the contaminated water from a plurality of units in a collection tank and step c) comprises resupplying contaminated water from the collection tank.
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Thus, all collected streams of contaminated water may be collected in the same tank. This may facilitate handling and a possible dilution of the collected contaminated water. As an example, step c) may comprises diluting the contaminated water in the tank before resupplying the contaminated water to the centrifugal separator to flush the surrounding space.
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In embodiments of the first aspect, the contaminated water has been contaminated with constituents of the liquid feed mixture of step a).
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Thus, the contaminants may originate from the liquid feed mixture, one or several separated liquid phases and/or a separated solid phase from the liquid feed mixture.
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In embodiments of the first aspect, the concentration of contaminants in step c) is less than 15 % (volume) when the surrounding space is flushed.
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Thus, if the concentration of contaminants is higher than this when the contaminated water is being collected, it may be diluted to a concentration of below 15% (vol) before being used as flushing water in step c).
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As an example, the contaminants may comprise a separated phase from the liquid feed mixture, and this phase may be present in a concentration of less than 15% (vol), such as less than 10% (vol) during flushing in step c).
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As an example, at least one unit from which contaminated water is collected may be a mechanical seal that is used for sealing the inlet or a liquid outlet of the centrifugal separator, and wherein the contaminated water is sealing water used for the mechanical seal.
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Thus, the inventors have found that the sealing water, or cooling water used for a mechanical seal, may be collected and used for another purpose in the centrifugal separator, i.e. flushing of the surrounding space.
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The cooling or sealing water may be used for creating a liquid film at the interface between the rotating and stationary portions of the mechanical seal.
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Consequently, step a) may also comprise supplying sealing liquid to at least one mechanical seal, and step b) may comprise collecting such sealing liquid from the sela as contaminated water.
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In embodiments of the first aspect, the at least one unit comprises the hood, and wherein the contaminated water is water that has been used to flush the surrounding space. Thus, contaminated water may be collected from the inside of the hood, i.e. from the surrounding space surrounding the hood, which is where for example water that has used to flush the underside of the centrifuge bowl may be collected. Thus, when one of the units is the hood, contaminated water may be collected via a nozzle or opening in the lower part hood, and that water may be water that has flown or trickled down in the surrounding space to the inside of the hood.
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The collected water in step b) does not have to be contaminated operating water used for different functions of the centrifugal separator, but it may originate from a phase that has been separated and discharged phase from the separator.
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Therefore, in embodiments of the first aspect, the unit comprises a vessel of the centrifugal separator that is arranged for collecting discharged solid phase, and wherein the contaminated water comprises water that has been discharged together with the solid phase.
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The discharged solid phase is often in the form of a sludge phase, i.e. solids together with an amount of water. This water is collected together with the solid phase in a vessel, and such water may thus be collected and reused for flushing the surrounding space in step c).
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As an example, the vessel may be in the form of a cyclone.
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Furthermore, the water that has been collected may be filtered before being reused in step c).
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In embodiments of the first aspect, the least one unit comprises an intermittent discharge system of the centrifugal separator that is arranged for discharging a separated solid phase from the centrifuge bowl to the surrounding space, and further wherein the contaminated water is operating water used by the intermittent discharge system.
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An intermittent discharge system of a centrifugal separator often uses operating water for controlling a sliding bowl bottom for closing and intermittently opening solid outlets that are arranged in the periphery of the bow. In this way, the solid phase (together with some water) may be discharged to the surrounding space. Operating water may leak or may be constantly consumed by the intermittent discharge system and thus be collected. As an example, operating water used by the intermittent discharge system may be transported to the surrounding space and be collected from the surrounding space via the hood.
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The centrifugal separator may thus also be arranged for discharging a solid phase, i.e. a separated solid phase that may also contain some liquid, to the surrounding space around the centrifuge bowl. This is performed by an intermittent discharge system comprising sludge outlets at the periphery of the centrifuge bowl. The sludge outlets may be in the form of a set of ports arranged to be opened intermittently during operation. The centrifugal separator may be arranged for emptying a partial content of the bowl during such an intermittent discharge (partial discharge) or arranged for emptying the whole content of the centrifuge bowl during intermittent discharge (full discharge).
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The intermittent discharge system thus controls the opening of the sludge outlets. For this purpose, the intermittent discharge system may comprise a an operating slide that is movable between a closed position, in which the sludge outlets are closed, and an open position, in which the sludge outlets are open. Keeping the operating slide in a closed position may be effected by supplying operating water via a channel to a closing chamber to hold the operating slide in the closed position. The intermittent discharge system may further comprise an opening chamber, to which water is supplied when to change the operating slide to its open position. The intermittent discharge system may thus comprise sludge outlets and an operating slide arranged within the centrifuge bowl to open and close the sludge outlets.
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As an example, the operating water use by the intermittent discharge system may originate from an operating water module (OWM) of the intermittent discharge system. Such an OWM may be arranged to supply an amount of water to the centrifugal separator to open and/or close the sludge outlets.
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In embodiments of the first aspect, at least one unit comprises a pump of the centrifugal separator that is arranged for decreasing the air pressure in the surrounding space, and further wherein the contaminated water is operating water used by the pump.
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A pump used for creating a lower pressure in the surrounding space, such as a vacuum pump, may consume some water that thus may be collected and reused in step c).
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As a second aspect of the invention, there is provided a centrifugal separation system for separating at least one liquid phase and a solid phase from a liquid feed mixture, the separation system comprising a centrifugal separator and a recirculation unit; wherein the centrifugal separator comprises
- a centrifuge bowl arranged to rotate around an axis of rotation (X) and in which the separation of the liquid mixture takes place,
- a stationary hood which defines at least part of a surrounding space in which the centrifuge bowl is arranged,
- at least one flushing member arranged for flushing the surrounding space with water;
- a drive member configured to rotate the centrifuge bowl around the axis of rotation (X),
- wherein the centrifuge bowl further comprises an inlet for receiving the liquid mixture to be separated and at least one liquid outlet for discharging a separated liquid phase,
- and further wherein the recirculation unit comprises
- a collection tank for collecting contaminated water from at least one unit of the centrifugal separator,
- wherein the at least one nozzle is connected to the collection tank so that contaminated water collected in the collection tank may be used to flush the surrounding space.
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This aspect may generally present the same or corresponding advantages as the former aspect. Effects and features of this second aspect are largely analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect.
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The centrifugal separator may be operated according to the method of the first aspect. The centrifugal separator is for separation of a liquid feed mixture. The liquid feed mixture may be an aqueous liquid or an oily liquid. As an example, the centrifugal separator may be for separating solids and one or two liquids from the liquid feed mixture.
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The centrifuge bowl encloses by rotor walls a separation space. The separation space, in which the separation of the fluid mixture takes place, may comprise separation members, such as a stack of separation discs. The separation discs may e.g. be of metal. Further, the separation discs may be frustoconical separation discs, i.e. having separation surfaces forming frustoconical portions of the separation discs. The separation discs may be arranged coaxially around the axis of rotation (X) at a distance from each other such that to form passages between each two adjacent separation discs.
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The centrifuge bowl of the separator may be arranged to be rotated around vertical axis of rotation, i.e. the axis of rotation (X) may extend vertically. The centrifuge bowl is usually supported by a spindle, i.e. a rotating shaft, and may thus be mounted to rotate with the spindle. Consequently, the centrifugal separator may comprise a spindle that is rotatable around the axis of rotation (X). The centrifugal separator may be arranged such that the centrifuge bowl is supported by the spindle at one of its ends, such at the bottom end or the top end of the spindle.
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The stationary hood defines at least a portion, such as the upper portion, of the surrounding space in which the centrifuge bowl is arranged. The stationary hood is thus a non-rotating part.
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The drive member may be a drive motor for rotating a spindle onto which the centrifuge bowl is mounted. The drive member may be connected to the spindle via a transmission means in the form of a worm gear which comprises a pinion and an element connected to the spindle in order to receive driving torque. The transmission means may alternatively take the form of a propeller shaft, drive belts or the like, and the drive motor may alternatively be an electric motor, which may be connected directly to the spindle.
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The flushing member may for example be a nozzle arranged for flushing water to walls defining the surrounding space. The nozzle may be arranged through of the stationary hood that surrounds the centrifuge bowl.
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The centrifugal separator also comprises an inlet for liquid mixture to be separated (the liquid feed mixture). This inlet may be arranged for receiving the liquid feed mixture and be arranged centrally in the centrifuge bowl, thus at rotational axis (X). The centrifuge bowl may be arranged to be fed from the bottom, such as through a spindle, so that the liquid feed mixture is delivered to the inlet from the bottom of the separator. However, the centrifuge bowl may also be arranged to be fed from the top, such as through a stationary inlet pipe extending into the bowl.
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Further, also one or two liquid outlets may be arranged at the top or the bottom of the centrifugal separator and a sludge outlet.
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The recirculation unit comprises a collection tank. This tank may be arranged for collecting contaminated water from several units of the centrifugal separator. The recirculation unit may comprise pipes connected to the unit or units from which contaminated water is collected, and a pipe connected to the flushing member. Further, the recirculation unit may further comprise a pump for pumping the collected water from the tank to the flushing member.
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In embodiments of the second aspect, the at least one flushing member is connected to the collection tank via a piping system. The piping system and/or the collection tank may further comprise a valve for introducing fresh water to the collection tank and/or piping system for diluting the contaminated water before reaching the at least one flushing member.
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Furthermore, the recirculation unit may comprise a pump connected to the piping system for pumping water from the collection tank to the flushing member.
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In embodiments of the second aspect, the recirculation unit further comprises a filter unit arranged for filtering contaminated water from at least one unit of the centrifugal separator before reaching the collection tank.
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In this way, the amount of solids in the contaminated water may be decreased in the tank.
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In embodiments of the second aspect, the centrifugal separator further comprises an intermittent discharge system for discharging a separated solid phase from the centrifuge bowl to the surrounding space. The intermittent discharge system may be as discussed in relation to the first aspect above.
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The centrifugal separator may further comprise a vessel, such as a cyclone, for collecting the discharged solid phase. The filter unit may be arranged for filtering contaminated water originating from the vessel used to collect the discharged solid phase before this contaminated reaches the collection tank.
Brief description of the Drawings
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The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.
- Figure 1 shows a schematic drawing of a centrifugal separator according to an embodiment of the present invention.
- Figure 2 shows a schematic drawing of a centrifugal separation system according to an embodiment of the present invention.
- Figure 3 shows a flow chart of a method of operating a centrifugal separator.
Detailed Description
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The method and the centrifugal separation system according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.
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Fig. 1 show a cross-section of an embodiment of a centrifugal separator 1 which in this embodiment is arranged to separate a solid phase, a liquid heavy phase, and a liquid light phase from a liquid feed mixture.
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The centrifugal separator 1 comprises a centrifuge bowl 10 which is arranged to rotate around an axis of rotation (X) together with spindle 7 onto which the bowl 10 is mounted. The spindle 7 is supported a bottom bearing 5 and a top bearing 6. The centrifuge bowl 10 is attached to the upper portion of the spindle 7 and forms within itself a separation chamber in which centrifugal separation of the liquid feed mixture takes place during operation. The separation chamber within the centrifuge bowl 10 may be provided with a stack of frustoconical separation discs in order to achieve effective separation of the liquid feed mixture, such as separation discs disclosed in
EP3315203 .
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Further, the separator 1 comprises a stationary hood 2 that surrounds at least the upper portion of the centrifuge bowl 10. The hood 2 thus defines at least part of a surrounding space 3 in which the centrifuge bowl 10 is arranged.
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The spindle 7 is in this example a hollow spindle that is used for introducing the liquid feed mixture to the inlet 11 of the centrifuge bowl 10. The inlet is sealed by an inlet seal 19 to a stationary inlet pipe (not shown). The centrifuge bowl 10 further comprises a liquid outlet 12 for discharging a separated liquid light phase and a liquid outlet 13 for discharging a liquid heavy phase. The liquid light phase outlet 12 is arranged at a smaller radius than the liquid heavy phase outlet 13. There is further a stationary outlet pipe 12a connected to the liquid light phase outlet 12 for receiving the separated liquid light phase, and a stationary outlet pipe 13a connected to the liquid heavy phase outlet 13 for receiving the separated liquid heavy phase.
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The centrifuge bowl 10 further comprises a solid phase outlet 14 for discharging a separated solid phase to the surrounding space 3, which is sealed relative the surroundings of the hood 2. The solid phase outlet 14 takes the form of a set of intermittently openable sludge outlets arranged at the outer periphery of the centrifuge bowl 10 for discharge of sludge from a radially outer portion of the separation chamber within the bowl 10 to the surrounding space 3. The solid phase outlets 14 form part of the intermittent discharge system 30. The opening of the sludge outlets 14 of the intermittent discharge system 30 is controlled by means of an operating slide (not shown) arranged within the bowl 10 and actuated by operating water supplied to the centrifuge bowl by an operating water module (OWM) 40. The operating slide is movable between a closed position in which the sludge outlets 14 are closed, and an open position, in which sludge outlets 14 are open. During operation, operating water in the form of closing water supplied by the OWM 40 may act on the operating slide to close the outlets 14. The draining of the water and thereby opening of the sludge outlets 14 may also be initiated by introducing operating water, such as opening water, from the OWM 40.
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Discharged solid phase is collected under the hood 2 in sludge channel 21 and is further directed to vessel 20. The vessel 20 is in the form of a cyclone and thus arranged for collecting the separated solid phase discharged from the centrifuge bowl 10. The vessel 20 is further connected to a discharge device 25 in the form of a sludge pump for discharge of sludge and liquid present in the vessel 20. The sludge pump may be provided with a check valve function which prevents flow into the vessel 20 via the sludge pump.
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The centrifugal separator 1 further comprises a drive motor 4 configured to rotate the centrifuge bowl 10 in relation around the axis of rotation (X). The drive motor 4 may be connected directly to the spindle 7 or connected to the spindle 7 via a transmission means.
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Consequently, during operation of the separator in Fig. 1, the centrifuge bowl 10 is caused to rotate by torque transmitted from the drive motor 4 to the spindle 7. Via the stationary inlet pipe 7a (see Fig 2), liquid mixture is supplied to the hollow spindle 7 and inlet 11. Thus, the liquid mixture to be separated is brought into the separation chamber within the centrifuge bowl 10 and further between the separation discs of the stack fitted in the separation chamber. A separated liquid light phase moves radially inwards between the separation discs and is discharged via the liquid light phase outlet 12 to the stationary outlet pipe 12a, whereas separated liquid heavy phase is discharged via the liquid heavy phase outlet 13 to the stationary outlet pipe 13a. Heavier components in the liquid mixture, e.g. solid particles and/or heavy phase, move radially outwards between the separation discs and accumulate at the periphery of the separation space 21. The separated solid phase is emptied intermittently from the solid phase outlets 14 by supplying hydraulic fluid to the intermittent discharge system 30 from the OWM 40.
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The surrounding space 3 is sealed relative the surroundings of the hood 2 by means of an upper seal 15 and a lower seal 16. The upper seal 15 may be an outlet seal that seals the liquid outlets from the surroundings. If the centrifugal separator 1 is arranged with a stationery inlet pie extending into the centrifuge bowl from the top, the upper seal 15 could also be the seal that seals the inlet from the surroundings.
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The upper seal 15 could for example be a mechanical seal or a liquid seal. Also the lower seal 16 could be a mechanical seal or a liquid seal. One or both of the upper 15 and lower seal 16 could be a hermetic seal.
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In this example, the separator 1 further comprises a pump 26, which may be a vacuum pump, for creating a pressure lower than atmospheric pressure in the surrounding space 3. This may reduce the energy consumption of the centrifugal separator 1.
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The centrifugal separator 1 further comprises a first 17 and second 18 flushing member in the form of nozzles that extend through the hood 2. The first nozzle 17 is for flushing the surrounding space 3 and especially the sludge channel 21 with flushing water supplied via channel or pipe 42. This may be performed after discharge of a solid phase through solid phase outlets 14 and to further facilitate transport of the discharged solid phase to the vessel 20 and to clean the sludge channel 21.
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The second nozzle 18 is used to flush the underside of the centrifuge bowl 10 with water supplied via channel or pipe 45.
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According to the method of the present invention, contaminated water may be collected from the centrifugal separator 1, e.g. from one or several of the below units:
- Operating water in the form of sealing water may be supplied to the inlet seal 19 via channel 29. Such sealing water may be contaminated by constituents of the liquid feed mixture and may be collected, as indicated by arrow 52.
- Operating water in the form of sealing water may further be supplied to the outlet seal 15 via channel 28. Such sealing water may be contaminated by constituents of a separated liquid phase and may be collected, as indicated by arrow 50.
- Operating water used by the OWM may leak or end up in the bottom of the hood 2. Also flushing water used for flushing the underside of the centrifuge bowl 10 may end up in the bottom of the hood 2. Water from the bottom of the hood may thus be contaminated and collected, as indicated by arrow 53.
- Operating water used by vacuum pump 26 may be supplied via channel 27 and then be collected, as indicated by arrow 51.
- The discharged solid phase usually contains amounts of water from the liquid feed mixture. Thus, the vessel 20 may comprise water contaminated by the discharged solid phase. Such contaminated water may be collected from the bottom of the vessel 20, as indicated by arrow 54.
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The collected water may then be used for flushing the bowl, as will be further described in relation to Fig. 2 below.
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Fig. 2 illustrates a centrifugal separation system 200 comprising the centrifugal separator 1 discussed in relation to Fig. 1 above. The separation system 200 further comprises a recirculation unit 80, which comprises a collection tank 60. The collecting tank 60 is arranged to collect contaminated water from at least one unit of the centrifugal separator 1. In this example, the collection tank 60 is arranged to collect contaminated water from all of the above exemplified units, i.e. to collect contaminated water from inlet seal 19 via line 52, contaminated water from the hood via line 53, contaminated water from the vacuum pump 26 via line 50, contaminated water from the outlet seal 15 via line 50 and contaminated water from the vessel 20 via line 54. However, in other examples, the collection tank 60 may be arranged for collecting contaminated water from only one or a selection of the above-exemplified units.
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Since the collected contaminated water from the vessel 20 may comprise a large amount of solids, the separation system 200 further comprises a filter unit 65 arranged for filtering contaminated water - i.e. decrease the amount of solids - from the vessel 20 before this water reaches the collection tank 60.
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The first flushing member 17 is connected the collection tank 60 via a piping system 70 that connects an outlet 63 of the collection tank 60 to the inlet line 42 of the first flushing member 17. In this way, contaminated water collected in the collection tank 60 may be used to flush the surrounding space 3, and especially the sludge channel 21, as discussed in relation to Fig. 1 above. In some examples, contaminated water is also used to supply the second nozzle 18 with water to flush the underside of the bowl 10, which means that also flushing water inlet line 45 may be connected to the piping system 70.
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The collected contaminated water may need to be diluted before being used as flushing water. For this purpose, the piping system 70 further comprises a valve 61 for introducing fresh water from pipe 62 to the piping system 70 for diluting the contaminated water before reaching the at least one flushing member 17. However, freshwater line 62 and valve 61 may be connected directly to the collection tank 60.
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As an example, the water used as flushing water by first nozzle 17 may have, or be diluted to, a concentration of less than 15 % (volume) of contaminants in the water.
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The separation system 70 further comprises a pump 71 used for pumping and/or pressurizing the contaminated water that is being reused as flushing water. In Fig. 2, the pump is arranged in connection to the piping system 70, but it may as well be directly coupled to the collection tank 60 to pressurize and pump contaminated water from the collection tank 60 into the piping system 70.
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An embodiment of the method 100 of the present invention that is used for operating the centrifugal separator 1 is further illustrated by the flow chart in Fig. 3. The method 100 comprises step a) of separating 101 the liquid feed mixture into at least one separated liquid phase in the centrifuge bowl 10. The liquid feed mixture is for example an aqueous feed mixture. The method 100 further comprises a step b1 of supplying 102 operating water to a unit of the centrifugal separator 1. This step may comprise supplying sealing water to an inlet and/or outlet seal or operating water to a vacuum pump. The method 100 further comprises the step b) of collecting 103 contaminated water from at least one unit of the centrifugal separator 1. Contaminated water may be collected from a unit to which operating water has been supplied in step b1, and/or from the hood 2, from the vessel 20 for collecting a discharged solid phase. The contaminated water may have been contaminated with constituents of the liquid feed mixture during step a). The method 100 further comprises a step c) of resupplying collected contaminated water to the centrifugal separator 1 to for flushing 106 the surrounding space 3. In some examples, a step b2) of filtering 104 the collected contaminated water is performed before resupplying in step c). In some examples, the step b) of collecting 103 the contaminated water comprises collecting contaminated from a plurality of units in a collection tank 60. Step c) may the comprise resupplying 106 contaminated water from the collection tank 60. In some examples, a step b3) of diluting the 105 the collected contaminated water is performed before resupplying in step c). The concentration of contaminants in step c) may be diluted to a concentration of less than 15 % (volume) when the surrounding space 3 is flushed. In other examples both steps b2) of filtering 104 the collected contaminated water and b3) diluting the 105 the collected contaminated water is performed before resupplying in step c).
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The invention is not limited to the embodiment disclosed but may be varied and modified within the scope of the claims set out below. The invention is not limited to the orientation of the axis of rotation (X) disclosed in the figures. The term "centrifugal separator" also comprises centrifugal separators with a substantially horizontally oriented axis of rotation. In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.