Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04B—CENTRIFUGES
  • B04B1/00—Centrifuges with rotary bowls provided with solid jackets for separating predominantly liquid mixtures with or without solid particles
  • B04B1/20—Centrifuges with rotary bowls provided with solid jackets for separating predominantly liquid mixtures with or without solid particles discharging solid particles from the bowl by a conveying screw coaxial with the bowl axis and rotating relatively to the bowl
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04B—CENTRIFUGES
  • B04B1/00—Centrifuges with rotary bowls provided with solid jackets for separating predominantly liquid mixtures with or without solid particles
  • B04B1/20—Centrifuges with rotary bowls provided with solid jackets for separating predominantly liquid mixtures with or without solid particles discharging solid particles from the bowl by a conveying screw coaxial with the bowl axis and rotating relatively to the bowl
  • B04B1/2016—Driving control or mechanisms; Arrangement of transmission gearing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04B—CENTRIFUGES
  • B04B11/00—Feeding, charging, or discharging bowls
  • B04B11/02—Continuous feeding or discharging; Control arrangements therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04B—CENTRIFUGES
  • B04B1/00—Centrifuges with rotary bowls provided with solid jackets for separating predominantly liquid mixtures with or without solid particles
  • B04B1/20—Centrifuges with rotary bowls provided with solid jackets for separating predominantly liquid mixtures with or without solid particles discharging solid particles from the bowl by a conveying screw coaxial with the bowl axis and rotating relatively to the bowl
  • B04B2001/2066—Centrifuges with rotary bowls provided with solid jackets for separating predominantly liquid mixtures with or without solid particles discharging solid particles from the bowl by a conveying screw coaxial with the bowl axis and rotating relatively to the bowl with additional disc stacks

Definitions

• the present invention relates to the field of centrifugal separators for separating solid particles from a liquid mixture, and especially to a method for ejecting solid particles from a centrifugal separator.
• Centrifugal separators such as decanter centrifuges, are used for separating solid particles from a liquid mixture.
• WO 2008/140378 discloses a centrifugal separator initially defined for purifying a fluid from contaminating particles.
• the particles separated from the fluid deposit themselves on the inside of the rotor body in the form of a layer of sludge, wherein the screw conveyor is arranged for transporting the sludge towards and out of the outlet.
• this layer of sludge may be difficult to transport due to the viscosity of the sludge (the viscosity may be too high or low for good transportation characteristics).
• the sludge transportation problem may be worsened.
• the resulting high centrifugal forces have a compressing effect on the sludge making it more difficult to transport out of the sludge outlet. Failure to discharge the sludge from the rotor body will cause a relatively solid sludge phase to grow radially inwards towards the axis of rotation, impairing the degree of separation and ultimately rendering continued separation impossible because of obstruction.
• a main object of the present invention is to provide a method and a centrifugal separator for effectively separating solid particles, such as sludge, from a liquid mixture and further transporting separated solid particles out of the separator.
• a method for separating solid particles from a liquid mixture in a centrifugal separator wherein the separator comprises a rotor body which is rotatable around an axis of rotation (R), the rotor body having a separation chamber for separating solid particles from the liquid mixture and an inlet for the liquid mixture and a screw conveyor adapted to rotate in the rotor body around the axis of rotation (R) for transporting the separated solid particles in the separation chamber towards and out of a sludge outlet, the method comprising rotating the rotor body and the screw conveyor at different speeds and the steps of
• the method further comprises rotating the rotor body at a first speed during the separation phase and at a second speed, which is lower than the first speed, during the ejection phase.
• the first aspect of the invention is based on the insight that introducing or injecting an ejection liquid during the period when solid particles are ejected or discharged from the separator has several advantages.
• the introduction of additional liquid during the period when solid particles are discharged leads to improved removal of solid particles.
• the inventors have found that by introducing a liquid during discharge, the effect of the centrifugal forces on the solid particles is reduced during the discharge.
• the force required for discharging the solid particles may increase exponentially to the decrease in liquid level in the separator, and by introducing an ejection liquid the force for ejecting the solids may accordingly be decreased.
• the force for discharging the solids may be about 1/10 of the force required if the ejection liquid was not present.
• the rotor body is usually rotating at high speed, whereby solid particles are effectively separated from the liquid mixture in the separation chamber of the rotor body. These separated particles are deposited on the inside of the rotor body. At such a high rotational speed the deposited particles, such as sludge, may be difficult to discharge from the separator, at least in a sufficient amount. Hence, with time the deposited particles will cause a sludge layer to grow radially inwards towards the axis of rotation.
• an ejection liquid is introduced in the separation chamber as the screw conveyor may transport the sludge towards and out of the sludge outlet.
• the ejection phase of step b) may be regarded as a particle discharge phase. More sludge is thus ejected out from the sludge outlet during the ejection phase compared to the separation phase. However, also some sludge may be ejected during the separation phase.
• the method comprises switching from a separation phase to an ejection phase, i.e. the separation phase and the ejection phase are not performed at the same time but instead take place during different times, i.e. are temporary separated.
• the liquid level in the decanter is prevented from decreasing, and as discussed above, this has been found to facilitate the removal of sludge.
• a larger amount of solid particles, such as sludge may be removed and additionally, the risk of clogging the separator decreases.
• a higher efficiency of the separation process may be achieved.
• step b) may comprise introducing ejection liquid in such amount such that the liquid level in the separator is substantially maintained at the same level during discharge of the solid particles.
• ejection liquid may be introduced such that the liquid level is substantially the same during the separation phase and the ejection phase.
• the method further comprises rotating the rotor body at a first speed during the separation phase and at a second speed, which is lower than the first speed, during the ejection phase.
• the difference in rotational speed between the rotor and the screw conveyor i.e. the differential speed, may be about 1 -5 rpm, such as 1 -2 rpm, during the separation phase.
• the liquid mixture may comprise different liquid phases in addition to the solid particle.
• the liquid phases may have different density.
• the liquid mixture may comprise oil, an aqueous phase and solid particles. Consequently, step a) may further comprise separating the liquid mixture into a first liquid phase and a second liquid phase, wherein the density of the first liquid phase is higher than the density of the second liquid phase.
• the first liquid phase may be an aqueous phase and the second liquid phase may be oil.
• the solid particles may for example be sludge.
• the ejection liquid introduced in step b) is introduced via the inlet for the liquid mixture that is to be separated.
• the weight of the ejection liquid introduced in step b) is about the same or less than the maximum weight of the solid particles that is ejected in step b).
• the weight of the ejection liquid introduced does not have to be higher than the amount of solid particles that can possibly be removed during step b). Thus, this may optimize the amount of ejection liquid that is used in step b).
• the density of the ejection liquid may be equal or less than the solid particles or sludge that is ejected during step b).
• the feed of the liquid mixture into the separation chamber is lowered or interrupted during the ejection phase.
• the feed of feed through the inlet during the ejection phase may be interrupted or lowered during step b). Further, if the rotor rotates at a lower speed during the ejection phase compared to the separation phase, the separation performance of the centrifugal separator may be reduced, which means that the liquid mixture may be introduced into the separation chamber at a reduced rate during the ejection phase.
• the method is further comprising rotating the screw conveyor at a different speed than the rotor body during both step a) and b).
• the screw conveyor may be rotated at a different speed than the rotor body during both the separation phase and the ejection phase, which facilitates discharge of solid particles.
• the differential speed between the screw conveyor and the rotor body is activated exclusively during the ejection phase of step b).
• the screw conveyor may distribute and work on the solid particles or sludge deposited on the inside of the rotor body to reduce some negative effects caused by the centrifugal forces.
• One of those negative effects is that compressing the solid particles or sludge may make it more difficult to discharge.
• Another negative effect is that compressed sludge may be unevenly distributed in the rotor body, causing an unbalance with harmful vibrations of the centrifugal separator during operation.
• the method is further comprising lowering also the rotational speed of the screw conveyor during step b) compared to step a). This may further aid in ejecting the sludge.
• the method is further comprising increasing the differential speed between the screw conveyor and the rotor body in step b) compared to step a).
• the differential speed during the ejection phase may be 3-10 rpm, such as 3-6 rpm.
• the solid particles may be discharged at a relative high rate to make the ejection or discharge phase short in duration.
• step b) the differential speed between the screw conveyor and the rotor body in step b) compared to step a) also may be decreased.
• the method is further comprising repeating steps a) and b) for any number of cycles.
• the method of the first aspect of the invention may be a cyclic method, i.e. the repetition of cycles comprising the separation phase of step a) and the ejection phase of step b).
• the ejection phase may thus be initiated before the growing layer of solid particles or sludge becomes a problem. If the rotor body is rotating at a first speed during the separation phase and at a second speed, which is lower than the first speed, during the ejection phase, the rotor body may be accelerated back to high speed rotation for the separation phase of the next operating cycle when essentially all of the solid particles or at least a sufficient amount of solids has been discharged from the separator. Furthermore, if needed by the process, the feed may be stopped until full rotor speed is re-established. When the rotor body is rotating at full speed with the increased separation performance in the separation phase, the feed rate may be re-established.
• the switch from step a) to step b) and/or from step b) to step a) may be performed after a predetermined period of time.
• step a) may be performed during a predetermined period of time
• step b) may be performed during a predetermined period of time or both steps a) and b) may be performed during a predetermined period of time.
• the ejection phase may be initiated, whereby the sludge is discharged.
• the centrifugal separator may switch back to the separation phase.
• the predetermined times of the separation phase and/or the ejection phase could be manually set by an operator. However, predetermined times could also be calculated from operating parameters of the centrifugal separator measured by various sensors.
• the time of the separation phase may be calculated from sensors registering a feed rate and concentration of particles in the feed through the inlet.
• the ejection phase may be calculated from parameters as the accumulated sludge amount, the differential speed between the screw conveyor and the rotor body, the type of sludge and viscosity of the sludge etc.
• both the ejection phase and separation phase may be controlled by combining the above described predetermined time and the threshold value of one or several operating parameters.
• the separation phase and ejection phase could for example have set default predetermined times combined with measured threshold values, whereby an ejection phase would be initiated in advance if the threshold value was reached before the default predetermined time had lapsed.
• the switch from step a) to step b) and/or from step b) to step a) may be dependent on one or several operating parameters.
• any other parameter may be a torque of the centrifugal separator.
• the torque may be measured by a torque measuring arrangement for the screw conveyor, which torque may be measured directly through a torque sensor or by calculating the torque using the current consumed by the electric motor of the screw conveyor. Consequently, when the torque increases above a specific threshold value, the ejection phase may be initiated.
• Another operating parameter may be the turbidity, such as the turbidity measured by a turbidity sensor associated with at least one liquid outlet. Thus, the ejection phase may be initiated when the turbidity of the purified liquid increases above a specific threshold value.
• Another possible operating parameter is the capacity, such as the capacity measured by a capacity sensor arranged in a liquid outlet for a liquid having a relatively low density.
• the concentration of heavy liquid e.g. water
• the concentration of heavy liquid may be measured by means of capacity in the outlet for a liquid having a relatively low density, such as oil, when separating two different liquid phases.
• the ejection phase may be initiated when the measured concentration of heavy liquid reaches a certain threshold.
• the pressure in the liquid outlet may also be utilized to trigger the ejection phase.
• the ejection phase may be initiated.
• the pressure may for example be measured by sensors located in the liquid outlet.
• the ejection liquid is an aqueous liquid.
• the ejection liquid may be a liquid of relatively high density that aids in maintaining a high pressure in the separation chamber.
• the ejection liquid may be water or comprise water.
• the ejection liquid may be the feed itself, i.e. the liquid mixture itself.
• the separation chamber comprises a stack of separation discs.
• the separation discs may be truncated, conical separation discs.
• a stack of separation discs further facilitates separation of the liquid mixture.
• centrifugal separator for separating solid particles from a liquid mixture, the centrifugal separator comprising
• a rotor body which is rotatable around an axis of rotation (R), the rotor body having a separation chamber with an inlet for the liquid mixture, - at least one liquid outlet for a separated liquid from the liquid mixture,
• a screw conveyor adapted to rotate in the rotor body around the axis of rotation (R), at a speed differing from the rotational speed of the rotor body, for transporting the separated solid particles in the separation chamber towards and out of the sludge outlet,
• control unit adapted to switch the operation of the separator between a separation phase, in which solid particles are separated from the liquid mixture, and an ejection phase, in which separated solid particles are transported towards the sludge outlet and further ejected out of the sludge outlet and wherein more sludge is ejected out of the sludge outlet during the ejection phase compared to the separation phase,
• control unit is further adapted to control the introduction of an ejection liquid to the separation chamber during the ejection phase, and wherein the control unit is further adapted to control the drive arrangement to rotate the rotor body at a first speed during a separation phase and at a second speed, which is lower than the first speed, during the ejection phase
• the centrifugal separator of the second aspect of the invention may thus be adapted to perform the separation method according to the first aspect discussed above. Accordingly, the centrifugal of the second aspect of the invention may facilitate improved removal of solid particles from the liquid mixture due to the introduction of additional liquid during the period when solid particles are discharged.
• the control unit may be adapted to regulate a valve such that ejection liquid is introduced into the separator during the ejection phase.
• the drive arrangement may for example include one or several electrical motors for rotating the rotor body and the screw conveyor.
• the control unit may thus also include a device for driving such electrical motors. As discussed in relation to the first aspect above, rotating at a lower speed during the ejection phase facilitates removal or ejection of solid particles from the separator. In other words, the control unit may cause the rotor body to rotate at a slower speed during ejection, whereby the
• centrifugal forces are decreased so that the screw conveyor may transport the sludge towards and out of the sludge outlet more easily.
• a difference in speed between the screw conveyor and the rotor body may be activated by the control unit exclusively during the particle discharge phase.
• the control unit is adapted to control the drive arrangement to rotate the screw conveyor at a different speed than the rotor body during both the separation phase and the ejection phase.
• the control unit may be adapted to control the drive arrangement to change, preferably increase, the differential speed between the screw conveyor and the rotor body in the ejection phase compared to the separation phase.
• the sludge may be discharged at a rate that is suitable.
• the sludge may be discharged at a relative high rate by increasing the differential speed to make the discharge phase short in duration.
• the control unit may further be adapted to also lower the rotational speed of the screw conveyor during the ejection phase.
• the centrifugal separator is arranged to reduce or interrupt a feed of the mixture through the inlet during the ejection phase. Consequently, the liquid mixture may be introduced into the separation chamber at a reduced rate during the ejection phase.
• the control unit may decrease the rotational speed during ejection and if needed by the process, the feed may be stopped until full rotor speed is re-established.
• the separator may re-establish the feed.
• control unit is adapted to control the drive arrangement to rotate the rotor body at the first speed during the separation phase for a predetermined time, wherein the first speed is higher than the second speed at which the rotor rotates during the ejection phase.
• control unit may be adapted to control the drive arrangement to rotate the rotor body at the second speed during the ejection phase for a predetermined time.
• the predetermined time may be as discussed in relation to the first aspect above.
• control unit is adapted to initiate an ejection phase when receiving a threshold value from an arrangement for measuring an operating parameter of the centrifugal separator.
• the operating parameter may be as discussed in relation to the first aspect above.
• an arrangement for measuring an operating parameter may for example be include a torque measuring arrangement for the screw conveyor, a turbidity sensor associated with at least one liquid outlet, a capacity sensor arranged in a liquid outlet, and/or pressure sensors measuring the pressure in a liquid outlet.
• the rotor body is rotatably supported only at its one end through a rotor shaft, which is arranged so that the axis of rotation extends substantially vertically.
• This type of centrifugal separator is typically more light weight than for example a decanter centrifuge, which comprises a relatively heavy rotor body with a horizontal axis of rotation.
• the rotor body according to this embodiment is more suitable to accelerate back and forth between a separation phase and discharge phase.
• Such a separator will many times include a stack of truncated conical separation discs in the separation chamber, whereby the separation efficiency is improved.
• the inlet of such a separator would preferably include an inlet pipe, which extends into the rotor body at its one end, the liquid outlet for separated liquid including at least one outlet channel, which extends out of the rotor body at its one end, and the sludge outlet for separated solids situated at the opposite other end of the rotor body.
• the drive arrangement includes a so called Harmonic Drive gear device, also known as a strain wave gearing device, arranged between the rotor body and the screw conveyor.
• the screw conveyor comprises a conveyor shaft which extends axially through the rotor shaft, the rotor shaft and the conveyor shaft being coupled together through a gear device.
• the gear device may include three co-operating members, of which a first gear member is connected with the rotor shaft and a second gear member is connected with the conveyor shaft.
• the three gear members may be adapted for rotation relative to each other around a prolongation of the axis of rotation (R).
• the inlet pipe may extend centrally through the gear device.
• the gear device may be a strain wave gear device including the first gear member in the form of a stiff cylindrical gear member, which is rotatable around the axis of rotation (R) and has a first number of cogs or teeth distributed around this centre axis, the second gear member in the form of a flexible gear member, which extends around the same axis of rotation (R) and has a different second number of cogs or teeth distributed around the centre axis, which are adapted successively to be brought into and out of engagement with the cogs or teeth of the cylindrical gear member, and the third gear member in the form of a wave generator which is adapted gradually to deform the flexible gear member and thereby accomplish the teeth engagement between the gear members.
• the separation chamber comprises a stack of separation discs.
• the separation discs may be truncated, conical separation discs.
• a stack of separation discs further facilitates separation of the liquid mixture.
• a computer program product comprising computer-executable components for causing a device to perform any one or all of the method steps recited in relation to the first aspect of the invention when the computer-executable components are run on a processing unit included in the device.
• the device may for example be a control unit as discussed in relation to the second aspect above.
• Figure 1 shows schematically a section view of a centrifugal separator according to an embodiment of the invention.
• Figure 2 shows a section view of a schematically drawn separator and the level of solid particles before and after ejection.
• Fig. 1 discloses a centrifugal separator according to an embodiment of the invention.
• the centrifugal separator includes a rotor body 1 , which is rotatable at a speed around a vertical rotational axis R, a screw conveyor 2 arranged in the rotor body 1 and rotatable around the same rotational axis R.
• the screw conveyor 2 is rotatable at a speed differing from the rotational speed of the rotor body 1 .
• a drive arrangement 3 is adapted for rotation of the rotor body 1 and the screw conveyor 2 at their respective speeds.
• the drive arrangement 3 includes two electric motors 3a and 3b and a gear device 3c.
• the rotor body 1 has a cylindrical upper rotor body portion 4 which is connected with a conical lower rotor body portion 5 by means of bolts 6. Alternative connection members can of course be used.
• the cylindrical rotor body portion 4 includes an extension axially upwards in the form of a hollow rotor shaft 7, which is connected to the electric motor 3a for rotating the rotor body 1 around the axis of rotation R.
• a further hollow shaft, the conveyor shaft 8, extends into the rotor body 1 through the interior of the hollow rotor shaft 7.
• the shaft 8 supports the screw conveyor 2 by means of screws 9.
• the hollow shaft 8 drivingly connects electric motor 3b with the screw conveyor 2 via the gear device 3c.
• the screw conveyor 2 comprises an upper cylindrical part 10 which extends axially inside the cylindrical rotor body portion 4, a lower conical part 1 1 which extends axially inside the conical rotor body portion 5, and a conveying thread 12 which extends in a screw-like manner along the upper cylindrical part 10 and the lower conical part 1 1 of the screw conveyor 2.
• the screw conveyor 2 may of course have more than one conveying thread, such as two, three or four conveying threads, which may all extend in a screw-like manner along the inside of the rotor body 1 .
• An inlet pipe 13 for a liquid mixture to be treated in the rotor body 1 extends through the conveyor shaft 8 and leads on into a central sleeve 14 in the interior of the screw conveyor 2.
• the central sleeve 14 delimits an inlet chamber 15 for the liquid mixture, wherein the inlet chamber 15
• a number of wings 18 are distributed around the axis of rotation R and extend into a lower part of the inlet chamber 15 and further define radially extending side walls of the distribution channels 17.
• the wings 18 are arranged to cause the liquid mixture in the inlet chamber 15 and the distribution channels 17 to rotate with the screw conveyor 2.
• the distribution channels 17 are arranged between the wings 18.
• the separation chamber 16 is an annular space that surrounds the inlet chamber 15 and comprises a stack of truncated conical separation discs 19.
• the stack is fitted radially inside the cylindrical part 10 of the screw conveyor 2 and arranged coaxially with the axis of rotation R.
• the conical separation discs 19 are held together axially between an upper conical support plate 20 and a lower conical support plate 21 .
• the lower conical support plate 21 is formed in one piece with the central sleeve 14.
• the separation discs 19 comprise holes which form channels 22 for axial flow or distribution of liquid through the stack of separation discs 19 in the centrifugal separator.
• the lower support plate 21 comprises a corresponding hole, whereby the distribution channels 17 communicate with the channels 22 for axial flow of liquid in the stack of separation discs 19.
• the upper conical support plate 20 comprises a number of holes 23 which connect a radially inner annular space 24, within the stack of separation discs 19, with a relative lower density or light liquid outlet chamber 25.
• Such liquid of lower density, or light liquid may for example be oil.
• a so called paring disc 26 for discharging purified light liquid is disposed within the outlet chamber 25.
• the paring disc 26 is stationary and firmly connected to the inlet pipe 13, wherein the paring disc 26 is communicating with an outlet channel 27 extending in an outlet pipe which surrounds the inlet pipe 13.
• the cylindrical part 10 of the screw conveyor 2 radially surrounds the stack of separation discs 19, wherein the cylindrical part 10 comprises a number of axially extending apertures 28 which are distributed round the axis of rotation R.
• the axially extending apertures 28 are provided to allow for separated solid particles or sludge from the liquid mixture to pass through and deposit on the inside of the cylindrical wall of the rotor body 1 . Liquid may of course also be able to pass through the apertures 28 in the cylindrical part 10.
• the conveyor shaft 8 comprises a number of holes 29 which connect an annular space 30 situated radially outside the cylindrical part 10 with a heavy liquid outlet chamber 31 for liquid of relative higher density. Such heavy liquid may for example be water.
• a paring disc 32 for discharging heavy liquid is disposed within this outlet chamber 31 , wherein the paring disc 32 communicates with an outlet channel 33 for the heavy liquid.
• the heavy liquid outlet channel 33 extends in an outlet pipe which surrounds the outlet pipe and channel 27 for the light liquid.
• the rotor body 1 has at its lower end a central and axially directed outlet 34 for separated solids particles, such has sludge.
• This sludge outlet 34 defines the initially mentioned sludge outlet for solid particles.
• the rotor body is surrounded by device 35 for intercepting sludge which leaves the sludge outlet 34.
• the sludge is disclosed in the drawing in the form of accumulations at the radially outer portion of the conveying thread 12, on the latter's side which faces toward the sludge outlet 34.
• the screw conveyor 2 may be made in one piece of plastic material, and may further be fibre-reinforced.
• the conical part 1 1 may have a hollow interior or cavity, which is either sealed or open to the surrounding. If desired, the cavity being possibly filled with some material having a relatively low density, such as cellular plastic or the like.
• the rotor body 1 is supported through the rotor shaft 7 by two axially separated bearings 36 and 37, respectively. These bearings are supported in turn by a sleeve 38, which is resiliently connected to a frame (not shown).
• the rotor shaft 7 supports a belt pulley 39, around which a driving belt 40 extends.
• the driving belt 40 is connected to the electric motor 3a for rotating the rotor body 1 .
• the gear device 3c may for example be a Harmonic Drive gear device, which is also known as a strain wave gearing device.
• Gear device 3c comprises a stiff cylindrical first gear member (not shown), which is firmly connected with the pulley 39 and, thereby, is also firmly connected with the rotor shaft 7.
• the cylindrical first gear member has internal cogs or teeth, which are formed on the inside of a ring, which constitutes a part of the cylindrical first gear member.
• a second gear member (not shown) is situated radially inside of the cylindrical first gear member and includes a thin flexible sleeve.
• the second gear member is supported through a supporting member by the conveyor shaft 8 and has on the flexible sleeve external cogs or teeth situated opposite to the internal cogs or teeth on the ring of the surrounding cylindrical first gear member.
• the teeth-provided flexible sleeve is circular-cylindrical and it has a smaller pitch diameter than the teeth-provided ring.
• the flexible sleeve has a smaller number of teeth than the ring.
• the gear device also includes a third gear member in the form of a so-called wave generator, which surrounds the rotational axis R and supports a belt pulley 41 .
• a belt 42 extends around the belt pulley 41 and is connected to the electric motor 3b for rotating the screw conveyor 2.
• the wave generator has an elliptically formed surrounding portion provided with two end portions or protuberances placed diametrically each on one side of the rotational axis R, the protuberances being dimensioned such that they locally deform the flexible sleeve, i.e. the second gear member, so that the external teeth of the sleeve are kept locally in engagement with the internal teeth of the surrounding stiff first gear member, i.e. the ring.
• Other parts of the gear members are situated radially spaced from each other in the areas of their respective teeth and, thus, are not in engagement with each other more than in the areas of the protuberances.
• a difference in rotational speed, between the rotor body 1 and the screw conveyor 2 may be accomplished by rotating the wave generator with the electric motor 3b and belt 42 around the rotational axis R at a speed differing from that by which the wave generator is entrained by the rotor body.
• a bearing 43 is arranged between the conveyor shaft 8 and the surrounding rotor shaft 7. There is another bearing inside the gear device 3c, whereby this bearing and bearing 43 constitute the two bearings by means of which the screw conveyor 2 is supported in the rotor body 1 .
• the drive arrangement 3 in this case comprising the two electrical motors 3a and 3b as well as gear device 3c, is arranged for driving the rotor body 1 and the screw conveyor 2, respectively.
• control unit 44 that is adapted to drive the electrical motors 3a and 3b, respectively.
• the control unit may be adapted to drive the electrical motors 3a and 3b at varying speeds.
• the electrical motors 3a and 3b in the disclosed embodiment have a common control unit 44. It is however evident that each one of the two motors 3a and 3b may be controlled by an individual control unit.
• the control unit 44 is in this example connected through signal cables
• the motors 3a and 3b may be a direct- current motor or an alternating-current motor; either a synchronous motor or an asynchronous motor.
• the control unit 44 may be designed in many different ways self-evident for a person skilled in the art of electrical motors.
• the control unit 44 includes a device for driving its electrical motors 3a and 3b at different speeds; either so that a limited number of speeds can be obtained or so that a continuous change of the motor speed can be performed.
• Different kinds of devices for speed regulation of motors are well known and need no closer description here.
• For a direct-current motor a simple device for voltage control may be used.
• For an alternate-current motor various kinds of frequency control equipment may be used.
• the control units 44 is connected to one or several different sensors on the centrifugal separator and adapted to treat the signal(s) coming from the sensor(s).
• the incoming signal(s) is depicted in Fig. 1 with an arrow 54 pointing at the control unit 44. Consequently, the control unit 44 will treat the signal(s) and produce a control signal in signal cables 45a and 45b for the driving of the electrical motor 3a and 3b.
• the signal(s) from the sensor(s) may be used in an automatic control of the centrifugal separator in order to initiate the separation phase and the ejection phase, respectively. Thus, both the separation phase and the ejection phase may be initiated on the basis of a sensed value.
• the signal(s) may also be used to control optimize rotor body speed and screw conveyor speed in both the separation phase and the ejection phase.
• a software, or computer program product may be used for e.g. causing the control device 44 to switch between separation phase and ejection phase and to drive the rotor 1 and the screw conveyor 2 at different speed.
• the control device may comprise a processing unit on which the computer- executable components of the software are run.
• control unit 44 may include a manual operation, wherein an operator programs the control unit 44 for operation of the electrical motors 3a and 3b by means of manually programmed control signals.
• the operator may set parameters such as separation phase time (duration in minutes or hours), ejection phase time (duration in seconds or minutes), rotor body speed (rpm) during the separation phase, rotor body speed (rpm) during ejection phase, and differential speed (rpm) between rotor body and screw conveyor during separation phase and ejection phase, respectively.
• the signals by means of which for example the speed of the electrical motors 3a and 3b should be controlled or adjusted, may be a function of many different variable factors.
• one or more of the following factors may be included, for instance: the turbidity of the liquid in the light and/or the heavy liquid outlet, which may indicate a growing layer of sludge being accumulated in the rotor body
• the vibration amplitude of the rotor body which may relate to an unbalance in the separator
• the control unit is further adapted to control three-way valve 50, as depicted by arrow 53 in Fig. 1 .
• a signal cable similar to cables 45b and 45a may be used.
• the control unit sets three-way valve 50 so as to let feed of liquid mixture from pipe 52 enter the separator via inlet pipe 13.
• the control unit may switch three-way valve 50 so as to interrupt the feed from pipe 42 and instead let ejection liquid, such as water, from pipe 50 enter the separator via inlet pipe 13.
• the centrifugal separator operates in the following manner:
• the pulleys 39 and 41 are kept in rotation, by means of the motors 3a and 3b with belts 40 and 42, around the rotational axis R in the same rotational direction but with somewhat different angular velocities. Thereby, the rotor body 1 and the screw conveyor 2 are kept in rotation at somewhat different rotational speeds.
• the rotor body 1 initially doesn't contain any sludge and so the separation phase of the operating cycle is initiated, whereby the rotor body 1 is accelerated by its motor 3a to high speed rotation at a predetermined speed (e.g. at 7500 rpm) through a control signal from the control unit 44.
• the screw conveyor 2 being rotated at a somewhat different speed (e.g. a differential speed of 1 - 2 rpm) by means of the motor 3b and the gear device 3c, whereby the differential speed is set through a control signal in the signal cable 45b from the control unit 44.
• the control unit 44 further adjusts the three-way valve 50 such that the mixture of liquid and particles is introduced into the rotor body 1 from above through the inlet pipe 13.
• the mixture flows into the inlet chamber 15 and further through the distribution channels 17, in which it is brought into rotation by the wings 18, thereby subjecting the mixture to a centrifugal force.
• a free liquid surface is formed after a while in the rotor body 1 at the radial level 46, the position of which is determined by the radial position of the holes 23 in the upper support plate 20 at the light liquid outlet chamber 25.
• the liquid(s) and particles are separated in the separation chamber 16 comprising the stack of separation discs 19.
• the separated heavy liquid i.e. the liquid with high density, flows through the radially outer annular space 30, through the holes 29 in the conveyor shaft 8 and out of the centrifugal separator through the heavy liquid outlet chamber 31 by means of the paring disc 32.
• the separated light liquid flows through the radially inner annular space 24, through the holes 23 in the upper support plate 20 and out of the centrifugal separator through the light liquid outlet chamber 25 by means of the paring disc 26.
• the separated solids deposit on the inside of the surrounding wall of the rotor body 1 . Even if the screw conveyor 2 doesn't discharge any sludge during the separation phase, the screw conveyor 2 through the differential speed may at least distribute and work on the sludge inside the rotor body 1 to reduce some negative effects caused by compressed and uneven distributed sludge. With time the deposited particles will cause the sludge layer to grow radially inwards towards the axis of rotation R. Before the growing layer of sludge becomes a problem, the control unit 44 will initiate the ejection phase, or particle discharge phase, of the present invention. This may be initiated after a predetermined time or after a sensed operating parameter of the centrifugal separator has reached a threshold value.
• control unit 44 switches three-way valve 50 such that ejection liquid, in this case water, from pipe 51 is directed into the separator via inlet pipe 13.
• ejection liquid in this case water
• the separated particles are transported in the form of sludge along the surrounding wall downwardly and out through the outlet 34, which is also referred to as the initially mentioned sludge outlet 34 for solid particles.
• the control unit 44 may control the screw conveyor motor 3b to increase the differential speed, e.g. to a differential speed of 3 - 6 rpm, whereby the sludge will be discharged at an increased rate.
• the control unit 44 will switch back to separation phase by instructing the motors 3a and 3b to accelerate the rotor body 1 and the screw conveyor 2 back to high speed rotation with the differential speed and further switch valve 50 so that feed of liquid mixture again is introduced into the separator.
• the separator may contain ejection liquid. This further facilitates turning the separator off after an ejection phase since problem with clogging etc. of the separator, such as clogging due to solid particles left in the separator when the separator is not operating, may be avoided.
• Figure 2 further schematically shows radial levels of solid particles in a section of the rotor body 1 .
• the radial level of solid particles, measured from rotational axis X, at the end of the separation phase is denoted by A.
• the radial level of solid particles has increased to level C.
• the ejected amount of solid particles is thus represented by amount B.
• the amount of ejection liquid that is introduced into the separator may be less or about equal to amount B in terms of volume or weight.
• centrifugal separator also comprises centrifugal separators with a substantially horizontally oriented axis of rotation.
• the invention is not limited to the drive arrangement including the specific gear device 3c. Other known gear devices such as planetary gear dives may also be used.
• the drive arrangement may also comprise a direct drive adapted to rotate the screw conveyor, wherein direct drive includes a motor stator connected to the rotor body and a motor rotor connected to the screw conveyor shaft.

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• 2013
  • 2013-05-02 EP EP13166245.4A patent/EP2799146B1/en active Active
• 2014
  • 2014-04-29 CN CN201480024582.5A patent/CN105188947B/zh active Active
  • 2014-04-29 KR KR1020157033860A patent/KR20160005061A/ko active Application Filing
  • 2014-04-29 WO PCT/EP2014/058751 patent/WO2014177579A1/en active Application Filing
  • 2014-04-29 KR KR1020187009516A patent/KR20180037328A/ko not_active IP Right Cessation

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