Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
  • D21D5/18—Purification of the pulp suspension by mechanical means; Apparatus therefor with the aid of centrifugal force
  • D21D5/24—Purification of the pulp suspension by mechanical means; Apparatus therefor with the aid of centrifugal force in cyclones
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
  • B03B13/00—Control arrangements specially adapted for wet-separating apparatus or for dressing plant, using physical effects
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04C—APPARATUS USING FREE VORTEX FLOW, e.g. CYCLONES
  • B04C5/00—Apparatus in which the axial direction of the vortex is reversed
  • B04C5/08—Vortex chamber constructions
  • B04C5/103—Bodies or members, e.g. bulkheads, guides, in the vortex chamber

Definitions

• the present invention relates to a method of treating a contaminated pulp suspension, in which relatively heavy contaminants are separated from the pulp suspension by pumping the latter through a multihydrocyclone unit containing a multiplicity of hydrocyclones, each of which is provided with turbulence creating means adapted to counteract formation of fibre network in radially outer liquid layers in the hydrocyclone.
• the pulp suspension separated from heavy contaminants is dewatered in a pulp wet machine.
• the invention also relates to a plant for treating a contaminated pulp suspension, comprising a multihydrocyclone unit of the kind stated above, a pump for pumping the pulp suspension through the multihydrocyclone unit, and a pulp wet machine for receiving cleaned pulp suspension.
• the pulp wet machine also called pulp drying machine, constitutes a last treatment step, in which the pulp is dewatered to a fibre concentration which makes the pulp suitable for drying and storing or for further transportation to a factory for paper production.
• the pulp which is dewatered in the pulp wet machine usually contains no filling compounds (so called filler) or insignificantly small amounts of filling compounds if the pulp is produced from recycled paper.
• filler filling compounds
• Such a pulp free from filling compounds has the property that fibre network in the form of flocks of fibres easily are formed, since the pulp is particularly easy to dewater, which can disturb the hydrocyclone cleaning of the pulp by the flocks clogging the outlets of the hydrocyclones for contami- nants.
• Hydrocyclones with parti- cularly efficient turbulence creating means in the form of radially outwardly directed steps in the separation chambers of the hydrocyclones, as disclosed in WO 93/10908, are marketed by Alfa Laval Celleco AB under the designation StepReleaseTM .
• a plant comprising a multihydrocyclone unit for separating heavy contaminants, a thickening device and a pulp wet machine are known from EP-B-0 422 314.
• the fibre concentration of the pulp suspension which is supplied to the multihydrocyclone unit is at least 0,9 %. It has surprisingly been proved that the hydrocyclones with the turbulence creating means are capable of cleaning a pulp suspension with the relatively high fibre concentration of 0,9 % without the cleaning efficiency becoming un- acceptably low. As a matter of fact, the cleaning efficiency can be satisfactorily maintained with increasing fibre concentration, up to about 1,5 %.
• the fibre concentration of a pulp suspension which can be increased from for example 0,45 % to 0,9 % thanks to the invention thus results in a reduction of the flow through the multihydrocyclone unit by 50 % .
• the halved flow in turn results in that the number of hydrocyclones in the multihydrocyclone unit can be halved.
• fibres are recovered from the reject flow from the multihydrocyclone unit by means of a number of stages of hydrocyclones connected in cascade. Since the reject flow also is reduced thanks to the invention, the number of hydrocyclones connected in cascade in this example can be reduced by about 30 % .
• the pulp suspension separated from light contaminants is pumped from said additional multihydrocyclone unit to the first mentioned hydrocyclone unit.
• light contaminants also comprise particles which in themselves are heavier than fibres but because of their shape behave as lighter than fibres in the hydrocyclones.
• light contaminants may be separated from the pulp suspension by means of said additional multihydrocyclone unit after that the heavy contaminants have been separated from the pulp suspension by means of the first mentioned multihydrocyclone unit and before the pulp suspension is dewatered in a pulp wet machine.
• the pulp suspension separated from heavy contaminants is conducted from the first mentioned multihydrocyclone unit via a pump to said additional multihydrocyclone unit.
• the object of the present invention is also obtained by the plant mentioned initially, which is characterized in that means are arranged to keep the fibre concentration of the pulp suspension which is fed into the multihydrocyclone unit at at least 0,9 %.
• the multihydrocyclone unit is directly connected to the pulp wet machine via a transport conduit for transporting separa- ted pulp suspension from the multihydrocyclone unit to the pulp wet machine.
• said means are arranged to affect the fibre concentration of the pulp suspension such that pulp suspension which is fed to the multihydrocyclone unit has a fibre concentration which is at least 1,0 % and 3 % at maximum, preferably 1,5 % at maximum.
• an additional multihydrocyclone unit for separating relatively light contaminants from the pulp suspension is arranged upstream of the first mentioned multihydrocyclone unit and downstream of said pump.
• Said additional multihydrocyclone unit is suitably connected to the first mentioned multihydrocyclone unit via a connection conduit with an additional pump for transferring pulp suspension separated from light contaminants .
• a return conduit for cleaned pulp suspension extends from said transport conduit to the suction side of said pump and a control device is adapted to control a control valve in the return conduit in response to the pressure in the inlet box of the pulp wet machine.
• connection conduit Upstream of said additional pump and downstream of said additional multihydrocyclone unit said connection conduit is preferably provided with a counterpressure device adapted to maintain a constant counterpressure in an outlet for an accept fraction of said additional multihydrocyclone unit.
• the counterpressure device enables a return flow with recovered fibres from the reject fraction of the first mentioned hydrocyclone to be transferred back to the first mentioned multihydrocyclone unit without loading said additional multihydrocyclone unit with said return flow.
• figure 2 shows a flow chart of a plant according to a first embodiment of the invention
• figure 3 shows a modification of the embodiment according to figure 2
• figure 7 shows a modification of the embodiment accor- ding to figure 6
• FIG 1 there is shown a diagram, in which the dependence of the cleaning efficiency ⁇ upon the fibre concentration C of a pulp suspension for an older conventional regular hydrocyclone is illustrated by a continuous curve line and for a newer regular hydrocyclone, which is provided with turbulence creating means of the kind shown in WO 93/10908, is illustrated by a dotted curve line.
• the pressure difference dP between the inlet and the accept outlet of each hydrocyclone in this case is 120 kPa.
• FIG 2 there is shown a plant according to a first embodiment of the invention comprising a container 1 for a pulp suspension, which contains relatively heavy contaminants, a pulp wet machine 2 with an inlet box 3 for receiving cleaned pulp suspension, and a white water container 4 for receiving white water from the pulp wet machine 2.
• a conduit 5 extends to a multihydrocyclone unit 6, which comprises hydrocyclones with turbulence creating means of the kind shown in WO 93/10908 coupled in parallel.
• Each hydrocyclone in the multihydrocyclone unit 6 is conical with an inlet 6a for pulp suspension, an apex outlet 7 for a reject fraction containing relatively heavy contaminants and a base outlet 8 for an accept fraction containing cleaned pulp suspension.
• a transport conduit 9 extends directly to the inlet box 3 of the pulp wet machine 2.
• the conduit 5 is provided with a pump 10 and a protective screen 11 situated downstream of the pump 10. From the container 1 a conduit 12, which is connected to the conduit 5, extends upstream of the pump 10. Also the conduit 12 is provided with a pump 13, the capacity of which is controlled by a control device 14 in response to the basis weight of dewatered pulp leaving the pulp wet machine 2. The basis weight is sensed by a means 14a somewhere after the pulp wet machine. The capacity of the pump 10 is controlled by a control device 15 via a signal conduit 16.
• the control device 15 comprises pressure sensors, which sense the pressure in the inlet 6a via a signal conduit 17 and the pressure in the outlet 8 via a signal conduit 18.
• a return conduit 19 for separated pulp suspension extends from the transport conduit 9 to the conduit 5.
• the return conduit 19 is provided with a control valve 20, which is controlled by a control device 21 adapted to sense the pressure in the inlet box via a signal conduit 22.
• the reject fraction flowing through the apex outlet 7 of the multihydrocyclone unit 6 contains some fibres which are recovered by a multihydrocyclone unit 23 comprising hydrocyclones of the same kind as in the multihydrocyclone unit 6 coupled in parallel.
• the fibres in the reject fraction are usually recovered by several stages of multihydrocyclone units coupled in cascade, but for reasons of simplicity only one such stage is shown here ) .
• pulp suspension is pumped from the container 1 by the pump 13 to the suction side of the pump 10 where the pulp suspension is diluted with white water from the white water container, so that the fibre concentration of the pulp suspension becomes at least 0,9 % and at most 3 %.
• the capacity of the pump 13 is controlled by the control device 14 so that the desired basic weight of the dewatered pulp in the pulp wet machine is achieved.
• the diluted pulp suspension is further pumped by the pump 10 via the protective screen 11 to the multihydrocyclone unit 6.
• the protective screen 11 separates possible coarse contaminants from the pulp suspension.
• the capacity of the pump 10 is controlled by the control device 15, so that the desired pressure difference between the inlet 6a and the base outlet 8 for operating the multihydrocyclone 6 at an optimum is maintained.
• the pressure difference between the base outlet 8 and the apex outlet 7 of the multihydrocyclone unit is kept at a desired value by the control device 28 which controls the opening degree of the control valve 27.
• the reject fraction from the apex outlet 7 is diluted with the white water in the conduit 24 and is pumped by the pump 25 to the multihydrocyclone unit 23, which delivers an accept fraction with recovered fibres through the base outlet 31 and a reject fraction with heavy contaminants through the apex outlet 33.
• the accept fraction is conducted through the conduit 32 back to the pump 10.
• the fibre concentration of the pulp suspension which is fed into the multihydrocyclone unit 6 is controlled by the control devices 14, 15 and 21. According to the invention these control devices 14, 15 and 21 cooperate so that the fibre concentration of the pulp suspension which is fed into the multihydrocyclone unit 6 is kept at at least 0,9 %.
• FIG 3 there is shown the same plant as in figure 2 but with modified control devices.
• the capacity of the pump 10 is controlled by a control device 34 in response to the pressure in the inlet box 3.
• a control device 35 the opening degree of the control valve 20 is controlled in response to the pressure difference between the inlet 6a and the base outlet 8 of the multihydrocyclone unit 6.
• the control devices 14, 34 and 35 cooperate so that the fibre concentration of the pulp suspension which is fed into the multihydrocyclone unit 6 is kept at at least 0,9 %.
• FIG 4 there is shown a plant according to a second embodiment of the invention which basically differs from the plant according to figure 2 by the fact that a multihydrocyclone unit 36 for separating relatively light contaminants from the pulp suspension is arranged upstream of the multihydrocyclone unit 6 and downstream of the pump 10.
• the multihydrocyclone unit 36 comprises a multiplicity of hydrocyclones of reverse type coupled in parallel, for instance Tripac 90 ReverseTM marketed by Alfa Laval Celleco AB and having an apex outlet 37, which via a connection conduit 38 is directly connected to the inlet 6a of the multihydrocyclone unit 6, and a base outlet 39, which is connected to a drain conduit 40.
• Tripac 90 ReverseTM marketed by Alfa Laval Celleco AB
• the capacity of the pump 10 is not controlled to achieve a desired pressure difference in the multihydrocyclone unit 6. Instead said pressure difference is achieved by means of a control device 41, which controls the opening degree of a control valve 42 in the drain conduit 40, in response to the pressure in the inlet 6a and the pressure in the base outlet 8 of the multihydrocyclone unit 6.
• the pulp suspension is diluted with white water so that the fibre concentration of the pulp suspension which is supplied to the multihydrocyclone unit 36 becomes about 0,7 %, which gives a fibre concentration of about 1,5 % at the pulp suspension flowing through the apex outlet 37.
• the control device 41 controls the control valve 42 so that the desired pressure difference for operating the multihydrocyclone unit 6 at an optimum is maintained. In this case the fibre concentration becomes about 1,49 % at the pulp suspension flowing through the base outlet 8.
• the light reject fraction from the base outlet 39 is diluted with white water in the conduit 44 and is pumped by means of the pump 45 to the multihydrocyclone unit 43, which gives an accept fraction with recovered fibres through the apex outlet 46 and a light reject fraction with light contaminants through the base outlet 48.
• the accept fraction is conducted through the conduit 47 back to the pump 10.
• the plant according to figure 4 is operated in the same manner as the plant according to figure 2.
• a level control means 55 is adapted to control the control valve 42 in response to the liquid surface level in the second container 54, so that said level is below the overflow 53.
• the capacity of the pump 49 is controlled in this case by a control device 56 in response to the pressure in the inlet box 3.
• the control valve 20 is controlled by a control device 57 in response to the pressure difference between the inlet 6a and the base outlet 8 of the multihydrocyclone unit 6. Thanks to the open container 54 the accept fraction with recovered fibres can be conducted via a return conduit 58 from the multihydrocyclone unit 23 to the container 54, whereby the pump 10 and the ultihydro- cyclone unit 36 do not need to be loaded by said accept fraction.
• the return conduit 58 is connected to the conduit 32 via a valve 59. There is also a valve 60 in the conduit 32. By means of the valves 59, 60 desired flows in the return conduit 58 and the conduit 32 can be adjusted.
• the plant according to figure 6 corresponds to the plant according to figure 5.
• FIG 7 there is shown a modification of the plant according to figure 6.
• the return conduit 19 is replaced by a return conduit 61 extending from the transport conduit 9 via a control valve 62 to the open container 54.
• a control device 63 is adapted to control the control valve 62 in response to the pressure difference between the inlet 6a and the base outlet 8 of the multihydrocyclone unit 6.
• the cleaned pulp suspension which is returned from the transport conduit 9, to load the pump 10 and the multihydrocyclone unit 36.
• the fibres in the light reject fraction from the multi- hydrocyclone unit 64 is recovered by a recover stage comprising a multihydrocyclone unit 73 of the same kind (but having fewer hydrocyclones) as the multihydrocyclone unit 64.
• a conduit 74 with a pump 75 extends from the conduit 5 to the multihydrocyclone unit 73.
• a drain conduit 76 with a control valve 77 is connected to the conduit 74 upstream of the pump 75.
• the control valve 77 is controlled by a control device 78 in response to the pressure in the transport conduit 70.
• An apex outlet 79 of the multihydrocyclone unit 73 is via a conduit 80 connected to the conduit 5 and to the suction side of the pump 66.
• the multihydrocyclone unit 6 is supplied with a pulp suspension having a fibre concentration in the range of 0,9 - 1,3 %.
• the pulp suspension separated from heavy contaminants will have a fibre concentration in the range of 0,85 - 1,25 % and is diluted with the accept fraction from the multihydrocyclone unit 73 to a fibre concentration in the range of 0,6 - 0,7 %.
• the pulp suspension diluted in this manner is pumped by the pump 66 to the multihydrocyclone unit 64, which via the apex outlet 71 delivers a fraction of the pulp suspension separated from light contaminants with a fibre concentration in the range of 1,3 - 1,7 %.
• Via the transport conduit 70 the pulp suspension separated from heavy and light contaminants is transported directly to the inlet box 3 of the pulp wet machine 2.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)
• Cyclones (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=20403880

Family Applications (1)

Country Status (9)

Cited By (1)

Families Citing this family (5)

Family Cites Families (5)

• 1996
  • 1996-09-16 SE SE9603345A patent/SE507387C2/sv not_active IP Right Cessation
• 1997
  • 1997-09-08 CA CA002235384A patent/CA2235384A1/en not_active Abandoned
  • 1997-09-08 EP EP97942332A patent/EP0870084A1/en not_active Withdrawn
  • 1997-09-08 ID IDW980009D patent/ID21089A/id unknown
  • 1997-09-08 BR BR9706751A patent/BR9706751A/pt not_active IP Right Cessation
  • 1997-09-08 JP JP10513558A patent/JP2000500832A/ja active Pending
  • 1997-09-08 WO PCT/SE1997/001503 patent/WO1998011297A1/en not_active Ceased
  • 1997-09-08 KR KR1019980703435A patent/KR19990067424A/ko not_active Ceased
• 1998
  • 1998-05-15 NO NO982225A patent/NO982225L/no not_active Application Discontinuation

Non-Patent Citations (1)

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