CA2233193A1 - Method and plant for treating a contaminated pulp suspension - Google Patents
Method and plant for treating a contaminated pulp suspension Download PDFInfo
- Publication number
- CA2233193A1 CA2233193A1 CA002233193A CA2233193A CA2233193A1 CA 2233193 A1 CA2233193 A1 CA 2233193A1 CA 002233193 A CA002233193 A CA 002233193A CA 2233193 A CA2233193 A CA 2233193A CA 2233193 A1 CA2233193 A1 CA 2233193A1
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- Prior art keywords
- pulp suspension
- multihydrocyclone unit
- multihydrocyclone
- unit
- separated
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 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
Abstract
With the aid of hydrocyclones, relatively light and heavy contaminants are separated from a pulp suspension. According to the invention, at first light contaminants are separated from the pulp suspension and the fibre concentration of the pulp suspension is substantially increased by means of a first multihydrocyclone unit (6) comprising a multiplicity of parallelly coupled hydrocyclones designed for separating light contaminants, and thereafter heavy contaminants are separated from the pulp suspension with the increased fibre concentration by a second multihydrocyclone unit (13) comprising a multiplicity of parallelly coupled hydrocyclones designed for separating heavy contaminants.
Description
W O 98/11296 PCTtSE97/01437 Metho~ ~nd pl~nt for tre~ting ~ cont~min~te~
~ lls~n~ion The present invention relates to a method of treating a pulp suspension containing relatively light and heavy contaminants, the contaminants being separated ~rom the pulp suspension with the aid of hydrocyclones. The invention also relates to a plant for treating such a pulp suspension comprising a first multihydrocyclone unit having a multiplicity of parallelly coupled hydro-cyclones designed for separating light contaminants from the pulp suspension under substantial thickening of ~he pulp suspension, and a second multihydrocyclone unit having a multiplicity of parallelly coupled hydrocyclo-nes designed for separating heavy contaminants from thepulp suspension. The plant further comprises at least one pump for pumping the pulp suspension to be separated to the multihydrocyclone units. With the expression "relatively light and heavy contaminants" is meant such contaminants which are light and heavy relative to the ~ibres of the pulp suspension. In this connection, relatively light cont~m;n~nts also comprise particles which in themselves are heavier than fibres but because of their shape behave as lighter fibres in the hydro-cyclones.
Conventionally, light and heavy contAmin~nts areseparated from pulp suspensions by first removing the heavy contaminants by means of a "regular" type of hydrocyclone, whereafter the light contaminants are separated by means of a "reverse" type of hydrocyclone.
A hydrocyclone plant comprising such a regular hydrocyclone and such a reverse hydrocyclone arranged downstream of the ragular hydrocyclone is disclosed in for instance CA l 203 778.
-Since the density of light cont~m~n~nts, such as plastic and glue fragments, is close to the density of wood fibres, the concentration of fibres of a pulp suspension which is separated from such light cont~m;n~nts by a reverse hydrocyclone has to be relatively low, about 0.4 - 0.7 %, (the fibre concentrations mentioned throughout the text all relate to weight percentage) in order to make the separation efficiency good. For this reason, the regular hydrocyclone is conventionally fed with a pulp suspension having a fibre concentration in the range of 0.4 - 0.75 %, which gives an outgoing pulp suspension which is suitable for feeding the reverse hydrocyclone, since the regular hydrocyclone somewhat dilutes the pulp suspension. Thus, the flows of pulp suspension which are supplied to the regular hydrocyclone and the reverse hydrocyclone are of about the same sizes, which makes it advantageous to utilize one single pump to pump the pulp suspension both through the regular hydrocyclone and the subsequent reverse hydrocyclone, see for instance EP-B-0 422 314.
The investment and operation costs ~or plants of the kind described above are significant, since the multi-hydrocyclone units have to be dimensioned for very large flows, between 40 000 and 180 000 litres/minute is usual.
The object of the present invention is to provide a method and a plant of the kinds here presented, which in comparison with the above described conventional tech-ni~ue results in substantially reduced flows of the pulp suspension which is treated, whereby investments and operation costs are substantially reduced.
This object is obtained by the method stated initially, which is characterized in that at first light contami-nants are separated from the pulp suspension and the fibre concentration of the pulp suspension is substan-tially increased by means of a first multihydrocycloneunit comprising a multiplicity of parallelly coupled hydrocyclones designed for separating light contami-nants, and therea~ter heavy contaminants are separated from the pulp suspension with the increased ~ibre con-centration by means of a second multihydrocyclone unitcomprising a multiplicity of parallelly coupled hydrocyclones designed for separating heavy contami-nants. As a result, the number of hydrocyclones in the second multihydrocyclone unit can be substantially reduced, since the flow of pulp suspension, which is separated from light contaminants, from the first multi-hydrocyclone unit is substantially smaller than the flow of pulp suspension which is fed into the first multi-hydrocyclone unit. The reduced flow through the second multihydrocyclone unit also results in a reduced need for energy to pump the flow. For instance, it is quite possible to increase the fibre concentration of a pulp suspension from 0.4 ~ to 0.8 ~ by means of the first multihydrocyclone unit, which reduces the necessary number of hydrocyclones in the second multihydrocyclone unit by 50 %, since the flow through the second multi-hydrocyclone unit is halved.
The pulp suspension with the increased fibre concentra-tion is advantageously conducted from the first multi-hydrocyclone unit via a pump to the second multihydro-cyclone unit.
Each hydrocyclone of the second multihydrocyclone unit is preferably provided with turbulence increasing means adapted to counteract the formation of fibre net-work in radially outer liquid layers in the hydrocyclone, and the fibre concentration of the pulp suspension is increased to at least 0.9 ~ by the first multihydro-cyclone unit before the pulp suspension is separated bythe second multihydrocyclone unit. It has surprisingly been proved that hydrocyclones with such turbulence creatin~ means are capable of separating a pulp suspen-sion from relatively heavy contaminants without the separation efficiency becoming unacceptably low. As a matter of fact the separation efficiency can be satis-factorily maintained with increasing fibre concentra-tion, up to about 1.5 %. Hydrocyclones with particularly efficient turbulence creating means in the form of radially outwardly directed steps in the separation chambers of the hydrocyclones, as shown in W0 93/10908, are marketed by Alfa Laval Celleco AB under ~he designa-tion Step~eleaseTM.
The object of the present invention is also achieved by means of the plant described initially, which is charac-terized in that the pump is adapted to pump the pulp suspension to be separated through the first multihydro-cyclone unit, and that the first multihydrocyclone unit is connected to the second multihy~.rocyclone unit for supplying thickened pulp suspension., which is separated from light contaminants, to the second multihydrocyclone unit.
Preferably, each hydrocyclone of th.e second multihydro-cyclone unit is provided with turbulence creating means adapted to counteract the formation of fibre net-work in radially outer liquid layers in the hydrocyclone, and the first multihydroc~clone unit is adapted to thicken the pulp suspension to a fibre concentration of at least 0.9 %, preferably at least 1.0 ~ and m;~xim~lly 1,5 96.
The first multihydrocyclone unit is advantageously con-~ 5 nected to the second multihydrocyclone unit via a con-nection conduit with an additional pump, for transfer-ring said thickened pulp suspension from the first to the second multihydrocyclone unit. The energy consump-tion of said two pumps will be substantially less than the energy comsumption of a single pump which is uti-lized to operate the first and the second multihydro-cyclone unit.
Upstream of said additional pump and downstream of the first multihydrocyclone unit, said connection conduit can advantageously be provided with a counter pressure device adapted to maintain a constant counter pressure in an outlet for accept fraction of the first multi-hydrocyclone unit. The counter pressure device enables a return flow with recovered fibres to be transferred from the reject fraction of the second multihydrocyclone unit back to the second multihydrocyclone unit without loa-ding the first multihydrocyc~one unit with said return flow.
Further advantageous features of the plant according to the invention are defined in the attached claims.
The invention is described more closely in the ~ollowing with reference to the accompanying drawings, in which figure l is a diagram showing how the cleaning effi-ciency depends on the fi~re concentration of the pulp suspension at hydrocyclones with and without turbulence creating means, W O 98/11296 PCTISE97/~1437 figure 2 shows a flow chart of a plant according to a first embodiment of the invention, and figure 3 shows a flow chart of a plant according to a second embodiment of the invention.
~n the figures identical components have been provided with the same reference numerals.
In figure 1 there is shown as an example 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 W0 93/10908, is illustrated by a dotted curve line. The pressure difference dP
between the inlet and the accept outlet of each hydro-cyclone is in this case 120 kPa. As is evident from the diagram the cleaning efficienc~ of a conventional hydrocyclone decreases from about 92 % at a fi~re con-centration of 0.5 % to about 87 % at a fibre concen-tration of 0.9 ~, whereas the cleaning efficiency of the newer hydrocyclone still is as high as about 92 % at a fibre concentration of O.g %. This means that only 8 ~
contaminants are left in a pulp suspension, which has a fibre concentration of 0.9 % and which has been separa-ted by the newer hydrocyclone, whereas 13 % contaminants are left in the same pulp supension which has been sepa-rated by the older hydrocyclone. Conseguently, the olderhydrocyclone allows about 60 % more contaminants to pass through than the newer hydrocyclone when separating pulp suspensions with 0.9 % fibre concentration.
As is evident from the diagram, the cleaning efficiency of the newer hydrocyclone at a higher fibre concentra-tion of 1.0 ~ is still about 92 %, whereas the cleaning efficiency of the older hydrocyclone has decreased further to about 85 %. At higher ~ibre concentrations than 0.9 ~ the risk of clogging of the apex outlet of the older hydrocyclone with fibre net-work is drama-tically increased, and for this reason in practice the older hydrocyclone is only utilized for pulp suspensions with a fibrè concentration less than 0.9 % The newer hydrocyclone, on the other hand, can be utilized for separating pulp suspensions with a fibre concentration of up to 1.5 %, without risk for clogging. The limiting factor here is the poorer cleaning efficiency, not the 1~ risk of clogging.
It should be noted that the diagram accordin~ to ~igure 1 relates to a certain kind of pulp suspension. Other kinds of pulp suspensions of course give other curve lines in the diagram, but the principal differences which are evident from the example above are also valid for such other kinds of pulp suspensions.
In figure 2 there is shown a plant according to a first embodiment of the invention comprising a feed conduit 1 for a pulp suspension, which contains relative light and heavy cont~m;n~nts, a machine 2 ~or receiving and dewa-tering separated pulp suspension, e.g rotary filter, bow sieve or paper machine, and a container 3 ~or receiving water from the machine 2. From the container 3 a conduit 4 with a pump 5 extends to a multihydrocyclone unit 6, which comprises a multiplicity of parallelly coupled conical hydrocyclones of reverse type, e.g. Tripac 90 ReverseTMwhich are marketed by Alfa Laval Celleco AB.
The multihydrocyclone unit 6 has an inlet 7 for pulp suspension, an apex outlet 8 for an accept fraction containing pulp suspension separated from relatively light contaminants and a base outlet 9 for a light reject fraction containing relatively light conta-minants. From the apex outlet 8 a connection conduit 10with a pump 11 extends to an inlet 12 of a multihydro-cyclone unit 13, which comprises parallelly coupled conical hydrocyclones with turbulence creating means of the kind shown in W0 93/10908. The multihydrocyclone unit 13 has an apex outlet 14 for a heavy reject fraction containing relatively heavy contaminants and a base outlet 15 for an accept fraction containing pulp suspension separated from relatively heavy contaminants.
From the base outlet 15 a transport conduit 16 extends directly to the machine 2.
A return conduit 17 for separated pulp suspension extends from the transport conduit 16 to the conduit 4.
The return conduit 17 is provided with a valve 18 for adjusting the return flow in the return conduit 17.
The heavy reject fraction flowing through the apex out-let 14 of the multihydrocyclone unit 13 contains some fibres which are recovered by means of a multihydro-cyclone unit 19 comprising parallelly coupled hydro-cyclones of the same kind as in the multihydrocyclone unit 13. (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 a stage is shown here).
A conduit 20, which is connected to the conduit 4 upstream of the connection between the latter and the conduit 17~ extends to the multihydrocyclone unit 19. Tn the conduit 20 there is a pump 21. The apex outlet 14 of the multihydrocyclone unit 13 is connected via a conduit ~2 to the conduit 20 upstream of the pump 21. A base outlet 23 in the multihydrocyclone unit 19 is connected via a conduit 24 to the conduit 4 downstream of the connection between the conduit 4 and the conduit 20, for supplying recovered fibres to the pump 5. An apex outlet 25 of the multihydrocyclone unit 19 is connected to a container, not shown, for separated heavy contaminants.
The light reject ~raction flowing through the base out-let of the multihydrocyclone unit 6 contains some fibres which are recovered by a multihydrocyclone unit 26 comprising parallelly coupled conical hydrocyclones of the same kind as in the multihydrocyclone unit 6. (The 1~ fibres in the light reject fraction are usually re-aovered by several stages of multihydrocyclone units coupled in cascade, but for resons of simplicit~ only one such a stage is shown here). A conduit 27 with a pump 28 extends from the conduit 20 upstream of the connection between the conduits 20 and 22 to the multi-hydrocyclone unit 26. A drain conduit 29 from the base outlet 9 is connected to the conduit 27 upstream of the pump 28. An apex outlet 30 of the mu~tihydrocyclone unit 26 is r.~n~e.nted via a conduit 31 to the conduit 4 down-stream of the connection between the conduit 4 and theconduit 20, for supplying recovered fibres to the pump 5. A base outlet 32 of the multihydrocyclone unit 26 is connected to a container, not shown, for separated light contaminants.
During operation of the plant according to figure 2 the pulp suspension which comes in via the feed conduit 1 is deluted with water from the container 3 so that the fibre concentration of the pulp suspension supplied to the multihydrocyclone unit 6 becomes about 0.6 %, which CA 02233l93 l998-04-23 gives a fibre concentration of about 1.2 % at the accept fraction of the pulp suspension flowing through the apex outlet 8. The light reject fraction from the base outlet 9 is deluted with the water in the conduit 27 and is pumped by the pump 28 to the multihydrocyclone unit 26, which gives an accept fraction with recovered fibres through the apex outlet 30 and a light re~ect fraction with light contaminants through the base outlet 32. The accept fraction is condueted via the conduit 31 back to the pump 5.
From the base outlet 15 of the multihydrocyclone unit 13 an accept fraction, which contains pulp suspension sepa-rated from relatively heavy contaminants and whieh in this case has a fibre concentration, of about 1.15 ~, is conducted to the machine 2. Depending on the capacity of the machine 2 the valve 18 is adjusted so that a part flow of the flow in the transport conduit 16 is returned to the pump 5.
The heavy reJect fraction from the apex outlet 14 of the multihydrocyclone unit 13 is deluted with water in the conduit 20 and is pumped by the pump 21 to the multi-hydroeyclone unit l9, which gives an accept fraction with reeovered fibres through the base outlet 23 and a reject fraetion with heavy cont~m1n~nts through the apex outlet 25. The aecept fraction is conducted via the conduit 24 baek to the pump 5.
In figure 3 there is shown a plant according to a second em~odiment of the invention, which is identical to the plant according to figure 2, except that means are arranged to bring back the accept fraction with reco-vered fibres from the multihydrocyclone unit 19 without loading the pump 5 and the multihydrocyclone unit 6, and CA 02233l93 l998-04-23 th~t suitable control devices are implemented. Conse-quently, the connection conduit 10 comprises a first part lOa extending upwardly from the apex outlet 8 of the multihydrocyclone unit 6 to a first open container 33 with an overflow 34 and a second part lOb extending from a second open container 35 to the pump 11, the container 35 being arranged to receive pulp suspension from the container 33 via the overflow 34.
The contalners 33 and 35 and the overflow 34 constitute a counter pressure device adapted to maintain a constant counter pressure in the apex outlet 8.
A level control means 36 is adapted to control a control valve 37, which is arranged in the drain conduit 29 from the base outlet 9 of the multihydrocyclone unit 6, in response to the level of the liquid surface in the second container 35, so that said level is below the overflow 34. A return conduit 38 extends from the con-duit 24 via a valve 39 to the container 35. A valve 40 is arranged in the conduit 24. By the valves 39 and 40 desired part flows of the accept fraction from the multihydrocyclone unit 19 can be adjusted in the con-duits 38 and 24. For instance, a major part flow or the entire accept fraction may be conducted via the return conduit 38 to the container 35, whereby energy can be saved for the operation of the pump 5 and the number of hydrocyclones in the multihydrocyclone unit 6 can be reduced.
A control device 41 is adapted to control the capacity of the pump 5 in response to the pressure in the inlet 7 of the multihydrocyclone unit 6. Since it exists a constant counter pressure in the apex outlet 8 of the multihydrocyclone unit 6, because of the arrangement W 098/112~6 12 PCT/SE97/01437 with the open container 33, which is located at a certain height above the apex outlet 8, the eontrol device 41 only needs to control the pressure in the inlet 7 in order to maintain a desired differenee pressure between the inlet 7 and the apex outlet 8.
A control device 42 is adapted to control the capacity of the pump 11 in response to the difference pressure between the inlet 12 and the base outlet 15 of the multihydroeyclone unit 13. A control valve 43 is arranged in the eonduit 22 and is eontrolled by a control device 44 in response to the pressure difference between the accept outlet 15 and the apex outlet 14 o~
the multihydroeyelone unit 13.
Since the accept fraetion with recovered fibres from the multihydrocyclone unit 19, during operation of the plant according to figure 3, is supplied to the pulp suspen-sion from the multihydrocyclone unit 6 via the container 35 the fibre coneentration of the pulp suspension is increased to about 1.3 ~ before the pulp suspension is pumped into the multihydrocyelone unit 13. As a result, the fibre eoncentration of the pulp suspension separated from relatively heavy contaminants and flowing through the base outlet 15 of the multihydroeyelone unit 13 beeomes about 1.15 ~.
In addition to this, the plant aeeordin~ to figure 3 is operated in the same manner as the plant aceording to figure 2.
As an alternative, one of or both of the eontrol devices 42 and 44 of the plant aeeording to figure 3 may also be installed in the plant according to figure 2.
~ lls~n~ion The present invention relates to a method of treating a pulp suspension containing relatively light and heavy contaminants, the contaminants being separated ~rom the pulp suspension with the aid of hydrocyclones. The invention also relates to a plant for treating such a pulp suspension comprising a first multihydrocyclone unit having a multiplicity of parallelly coupled hydro-cyclones designed for separating light contaminants from the pulp suspension under substantial thickening of ~he pulp suspension, and a second multihydrocyclone unit having a multiplicity of parallelly coupled hydrocyclo-nes designed for separating heavy contaminants from thepulp suspension. The plant further comprises at least one pump for pumping the pulp suspension to be separated to the multihydrocyclone units. With the expression "relatively light and heavy contaminants" is meant such contaminants which are light and heavy relative to the ~ibres of the pulp suspension. In this connection, relatively light cont~m;n~nts also comprise particles which in themselves are heavier than fibres but because of their shape behave as lighter fibres in the hydro-cyclones.
Conventionally, light and heavy contAmin~nts areseparated from pulp suspensions by first removing the heavy contaminants by means of a "regular" type of hydrocyclone, whereafter the light contaminants are separated by means of a "reverse" type of hydrocyclone.
A hydrocyclone plant comprising such a regular hydrocyclone and such a reverse hydrocyclone arranged downstream of the ragular hydrocyclone is disclosed in for instance CA l 203 778.
-Since the density of light cont~m~n~nts, such as plastic and glue fragments, is close to the density of wood fibres, the concentration of fibres of a pulp suspension which is separated from such light cont~m;n~nts by a reverse hydrocyclone has to be relatively low, about 0.4 - 0.7 %, (the fibre concentrations mentioned throughout the text all relate to weight percentage) in order to make the separation efficiency good. For this reason, the regular hydrocyclone is conventionally fed with a pulp suspension having a fibre concentration in the range of 0.4 - 0.75 %, which gives an outgoing pulp suspension which is suitable for feeding the reverse hydrocyclone, since the regular hydrocyclone somewhat dilutes the pulp suspension. Thus, the flows of pulp suspension which are supplied to the regular hydrocyclone and the reverse hydrocyclone are of about the same sizes, which makes it advantageous to utilize one single pump to pump the pulp suspension both through the regular hydrocyclone and the subsequent reverse hydrocyclone, see for instance EP-B-0 422 314.
The investment and operation costs ~or plants of the kind described above are significant, since the multi-hydrocyclone units have to be dimensioned for very large flows, between 40 000 and 180 000 litres/minute is usual.
The object of the present invention is to provide a method and a plant of the kinds here presented, which in comparison with the above described conventional tech-ni~ue results in substantially reduced flows of the pulp suspension which is treated, whereby investments and operation costs are substantially reduced.
This object is obtained by the method stated initially, which is characterized in that at first light contami-nants are separated from the pulp suspension and the fibre concentration of the pulp suspension is substan-tially increased by means of a first multihydrocycloneunit comprising a multiplicity of parallelly coupled hydrocyclones designed for separating light contami-nants, and therea~ter heavy contaminants are separated from the pulp suspension with the increased ~ibre con-centration by means of a second multihydrocyclone unitcomprising a multiplicity of parallelly coupled hydrocyclones designed for separating heavy contami-nants. As a result, the number of hydrocyclones in the second multihydrocyclone unit can be substantially reduced, since the flow of pulp suspension, which is separated from light contaminants, from the first multi-hydrocyclone unit is substantially smaller than the flow of pulp suspension which is fed into the first multi-hydrocyclone unit. The reduced flow through the second multihydrocyclone unit also results in a reduced need for energy to pump the flow. For instance, it is quite possible to increase the fibre concentration of a pulp suspension from 0.4 ~ to 0.8 ~ by means of the first multihydrocyclone unit, which reduces the necessary number of hydrocyclones in the second multihydrocyclone unit by 50 %, since the flow through the second multi-hydrocyclone unit is halved.
The pulp suspension with the increased fibre concentra-tion is advantageously conducted from the first multi-hydrocyclone unit via a pump to the second multihydro-cyclone unit.
Each hydrocyclone of the second multihydrocyclone unit is preferably provided with turbulence increasing means adapted to counteract the formation of fibre net-work in radially outer liquid layers in the hydrocyclone, and the fibre concentration of the pulp suspension is increased to at least 0.9 ~ by the first multihydro-cyclone unit before the pulp suspension is separated bythe second multihydrocyclone unit. It has surprisingly been proved that hydrocyclones with such turbulence creatin~ means are capable of separating a pulp suspen-sion from relatively heavy contaminants without the separation efficiency becoming unacceptably low. As a matter of fact the separation efficiency can be satis-factorily maintained with increasing fibre concentra-tion, up to about 1.5 %. Hydrocyclones with particularly efficient turbulence creating means in the form of radially outwardly directed steps in the separation chambers of the hydrocyclones, as shown in W0 93/10908, are marketed by Alfa Laval Celleco AB under ~he designa-tion Step~eleaseTM.
The object of the present invention is also achieved by means of the plant described initially, which is charac-terized in that the pump is adapted to pump the pulp suspension to be separated through the first multihydro-cyclone unit, and that the first multihydrocyclone unit is connected to the second multihy~.rocyclone unit for supplying thickened pulp suspension., which is separated from light contaminants, to the second multihydrocyclone unit.
Preferably, each hydrocyclone of th.e second multihydro-cyclone unit is provided with turbulence creating means adapted to counteract the formation of fibre net-work in radially outer liquid layers in the hydrocyclone, and the first multihydroc~clone unit is adapted to thicken the pulp suspension to a fibre concentration of at least 0.9 %, preferably at least 1.0 ~ and m;~xim~lly 1,5 96.
The first multihydrocyclone unit is advantageously con-~ 5 nected to the second multihydrocyclone unit via a con-nection conduit with an additional pump, for transfer-ring said thickened pulp suspension from the first to the second multihydrocyclone unit. The energy consump-tion of said two pumps will be substantially less than the energy comsumption of a single pump which is uti-lized to operate the first and the second multihydro-cyclone unit.
Upstream of said additional pump and downstream of the first multihydrocyclone unit, said connection conduit can advantageously be provided with a counter pressure device adapted to maintain a constant counter pressure in an outlet for accept fraction of the first multi-hydrocyclone unit. The counter pressure device enables a return flow with recovered fibres to be transferred from the reject fraction of the second multihydrocyclone unit back to the second multihydrocyclone unit without loa-ding the first multihydrocyc~one unit with said return flow.
Further advantageous features of the plant according to the invention are defined in the attached claims.
The invention is described more closely in the ~ollowing with reference to the accompanying drawings, in which figure l is a diagram showing how the cleaning effi-ciency depends on the fi~re concentration of the pulp suspension at hydrocyclones with and without turbulence creating means, W O 98/11296 PCTISE97/~1437 figure 2 shows a flow chart of a plant according to a first embodiment of the invention, and figure 3 shows a flow chart of a plant according to a second embodiment of the invention.
~n the figures identical components have been provided with the same reference numerals.
In figure 1 there is shown as an example 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 W0 93/10908, is illustrated by a dotted curve line. The pressure difference dP
between the inlet and the accept outlet of each hydro-cyclone is in this case 120 kPa. As is evident from the diagram the cleaning efficienc~ of a conventional hydrocyclone decreases from about 92 % at a fi~re con-centration of 0.5 % to about 87 % at a fibre concen-tration of 0.9 ~, whereas the cleaning efficiency of the newer hydrocyclone still is as high as about 92 % at a fibre concentration of O.g %. This means that only 8 ~
contaminants are left in a pulp suspension, which has a fibre concentration of 0.9 % and which has been separa-ted by the newer hydrocyclone, whereas 13 % contaminants are left in the same pulp supension which has been sepa-rated by the older hydrocyclone. Conseguently, the olderhydrocyclone allows about 60 % more contaminants to pass through than the newer hydrocyclone when separating pulp suspensions with 0.9 % fibre concentration.
As is evident from the diagram, the cleaning efficiency of the newer hydrocyclone at a higher fibre concentra-tion of 1.0 ~ is still about 92 %, whereas the cleaning efficiency of the older hydrocyclone has decreased further to about 85 %. At higher ~ibre concentrations than 0.9 ~ the risk of clogging of the apex outlet of the older hydrocyclone with fibre net-work is drama-tically increased, and for this reason in practice the older hydrocyclone is only utilized for pulp suspensions with a fibrè concentration less than 0.9 % The newer hydrocyclone, on the other hand, can be utilized for separating pulp suspensions with a fibre concentration of up to 1.5 %, without risk for clogging. The limiting factor here is the poorer cleaning efficiency, not the 1~ risk of clogging.
It should be noted that the diagram accordin~ to ~igure 1 relates to a certain kind of pulp suspension. Other kinds of pulp suspensions of course give other curve lines in the diagram, but the principal differences which are evident from the example above are also valid for such other kinds of pulp suspensions.
In figure 2 there is shown a plant according to a first embodiment of the invention comprising a feed conduit 1 for a pulp suspension, which contains relative light and heavy cont~m;n~nts, a machine 2 ~or receiving and dewa-tering separated pulp suspension, e.g rotary filter, bow sieve or paper machine, and a container 3 ~or receiving water from the machine 2. From the container 3 a conduit 4 with a pump 5 extends to a multihydrocyclone unit 6, which comprises a multiplicity of parallelly coupled conical hydrocyclones of reverse type, e.g. Tripac 90 ReverseTMwhich are marketed by Alfa Laval Celleco AB.
The multihydrocyclone unit 6 has an inlet 7 for pulp suspension, an apex outlet 8 for an accept fraction containing pulp suspension separated from relatively light contaminants and a base outlet 9 for a light reject fraction containing relatively light conta-minants. From the apex outlet 8 a connection conduit 10with a pump 11 extends to an inlet 12 of a multihydro-cyclone unit 13, which comprises parallelly coupled conical hydrocyclones with turbulence creating means of the kind shown in W0 93/10908. The multihydrocyclone unit 13 has an apex outlet 14 for a heavy reject fraction containing relatively heavy contaminants and a base outlet 15 for an accept fraction containing pulp suspension separated from relatively heavy contaminants.
From the base outlet 15 a transport conduit 16 extends directly to the machine 2.
A return conduit 17 for separated pulp suspension extends from the transport conduit 16 to the conduit 4.
The return conduit 17 is provided with a valve 18 for adjusting the return flow in the return conduit 17.
The heavy reject fraction flowing through the apex out-let 14 of the multihydrocyclone unit 13 contains some fibres which are recovered by means of a multihydro-cyclone unit 19 comprising parallelly coupled hydro-cyclones of the same kind as in the multihydrocyclone unit 13. (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 a stage is shown here).
A conduit 20, which is connected to the conduit 4 upstream of the connection between the latter and the conduit 17~ extends to the multihydrocyclone unit 19. Tn the conduit 20 there is a pump 21. The apex outlet 14 of the multihydrocyclone unit 13 is connected via a conduit ~2 to the conduit 20 upstream of the pump 21. A base outlet 23 in the multihydrocyclone unit 19 is connected via a conduit 24 to the conduit 4 downstream of the connection between the conduit 4 and the conduit 20, for supplying recovered fibres to the pump 5. An apex outlet 25 of the multihydrocyclone unit 19 is connected to a container, not shown, for separated heavy contaminants.
The light reject ~raction flowing through the base out-let of the multihydrocyclone unit 6 contains some fibres which are recovered by a multihydrocyclone unit 26 comprising parallelly coupled conical hydrocyclones of the same kind as in the multihydrocyclone unit 6. (The 1~ fibres in the light reject fraction are usually re-aovered by several stages of multihydrocyclone units coupled in cascade, but for resons of simplicit~ only one such a stage is shown here). A conduit 27 with a pump 28 extends from the conduit 20 upstream of the connection between the conduits 20 and 22 to the multi-hydrocyclone unit 26. A drain conduit 29 from the base outlet 9 is connected to the conduit 27 upstream of the pump 28. An apex outlet 30 of the mu~tihydrocyclone unit 26 is r.~n~e.nted via a conduit 31 to the conduit 4 down-stream of the connection between the conduit 4 and theconduit 20, for supplying recovered fibres to the pump 5. A base outlet 32 of the multihydrocyclone unit 26 is connected to a container, not shown, for separated light contaminants.
During operation of the plant according to figure 2 the pulp suspension which comes in via the feed conduit 1 is deluted with water from the container 3 so that the fibre concentration of the pulp suspension supplied to the multihydrocyclone unit 6 becomes about 0.6 %, which CA 02233l93 l998-04-23 gives a fibre concentration of about 1.2 % at the accept fraction of the pulp suspension flowing through the apex outlet 8. The light reject fraction from the base outlet 9 is deluted with the water in the conduit 27 and is pumped by the pump 28 to the multihydrocyclone unit 26, which gives an accept fraction with recovered fibres through the apex outlet 30 and a light re~ect fraction with light contaminants through the base outlet 32. The accept fraction is condueted via the conduit 31 back to the pump 5.
From the base outlet 15 of the multihydrocyclone unit 13 an accept fraction, which contains pulp suspension sepa-rated from relatively heavy contaminants and whieh in this case has a fibre concentration, of about 1.15 ~, is conducted to the machine 2. Depending on the capacity of the machine 2 the valve 18 is adjusted so that a part flow of the flow in the transport conduit 16 is returned to the pump 5.
The heavy reJect fraction from the apex outlet 14 of the multihydrocyclone unit 13 is deluted with water in the conduit 20 and is pumped by the pump 21 to the multi-hydroeyclone unit l9, which gives an accept fraction with reeovered fibres through the base outlet 23 and a reject fraetion with heavy cont~m1n~nts through the apex outlet 25. The aecept fraction is conducted via the conduit 24 baek to the pump 5.
In figure 3 there is shown a plant according to a second em~odiment of the invention, which is identical to the plant according to figure 2, except that means are arranged to bring back the accept fraction with reco-vered fibres from the multihydrocyclone unit 19 without loading the pump 5 and the multihydrocyclone unit 6, and CA 02233l93 l998-04-23 th~t suitable control devices are implemented. Conse-quently, the connection conduit 10 comprises a first part lOa extending upwardly from the apex outlet 8 of the multihydrocyclone unit 6 to a first open container 33 with an overflow 34 and a second part lOb extending from a second open container 35 to the pump 11, the container 35 being arranged to receive pulp suspension from the container 33 via the overflow 34.
The contalners 33 and 35 and the overflow 34 constitute a counter pressure device adapted to maintain a constant counter pressure in the apex outlet 8.
A level control means 36 is adapted to control a control valve 37, which is arranged in the drain conduit 29 from the base outlet 9 of the multihydrocyclone unit 6, in response to the level of the liquid surface in the second container 35, so that said level is below the overflow 34. A return conduit 38 extends from the con-duit 24 via a valve 39 to the container 35. A valve 40 is arranged in the conduit 24. By the valves 39 and 40 desired part flows of the accept fraction from the multihydrocyclone unit 19 can be adjusted in the con-duits 38 and 24. For instance, a major part flow or the entire accept fraction may be conducted via the return conduit 38 to the container 35, whereby energy can be saved for the operation of the pump 5 and the number of hydrocyclones in the multihydrocyclone unit 6 can be reduced.
A control device 41 is adapted to control the capacity of the pump 5 in response to the pressure in the inlet 7 of the multihydrocyclone unit 6. Since it exists a constant counter pressure in the apex outlet 8 of the multihydrocyclone unit 6, because of the arrangement W 098/112~6 12 PCT/SE97/01437 with the open container 33, which is located at a certain height above the apex outlet 8, the eontrol device 41 only needs to control the pressure in the inlet 7 in order to maintain a desired differenee pressure between the inlet 7 and the apex outlet 8.
A control device 42 is adapted to control the capacity of the pump 11 in response to the difference pressure between the inlet 12 and the base outlet 15 of the multihydroeyclone unit 13. A control valve 43 is arranged in the eonduit 22 and is eontrolled by a control device 44 in response to the pressure difference between the accept outlet 15 and the apex outlet 14 o~
the multihydroeyelone unit 13.
Since the accept fraetion with recovered fibres from the multihydrocyclone unit 19, during operation of the plant according to figure 3, is supplied to the pulp suspen-sion from the multihydrocyclone unit 6 via the container 35 the fibre coneentration of the pulp suspension is increased to about 1.3 ~ before the pulp suspension is pumped into the multihydrocyelone unit 13. As a result, the fibre eoncentration of the pulp suspension separated from relatively heavy contaminants and flowing through the base outlet 15 of the multihydroeyelone unit 13 beeomes about 1.15 ~.
In addition to this, the plant aeeordin~ to figure 3 is operated in the same manner as the plant aceording to figure 2.
As an alternative, one of or both of the eontrol devices 42 and 44 of the plant aeeording to figure 3 may also be installed in the plant according to figure 2.
Claims (17)
1. A method of treating a pulp suspension containing relatively light and heavy contaminants, the contaminants being separated from the pulp suspension with the aid of hydrocyclones, c h a r a c t e r i z e d i n that at first light contaminants are separated from the pulp suspension and the fibre concentration of the pulp suspension is substantially increased by a first multihydrocyclone unit (6) comprising a multiplicity of parallelly coupled hydrocyclones designed for separating light contaminants, and thereafter heavy contaminants are separated from the pulp suspension with the increased fibre concentration by a second multihydrocyclone unit (13) comprising a multiplicity of parallelly coupled hydrocyclones designed for separating heavy contaminants.
2. A method according to claim 1, c h a r a c t e r i z e d i n that the pulp suspension with the increased fibre concentration is conducted from the first multihydrocyclone unit (6) via a pump (11) to the second multihydrocyclone unit (13).
3. A method according to claim 1 or 2, c h a r a c t e r i z e d i n that each hydrocyclone of the second multihydrocyclone unit (13) is provided with turbulence creating means adapted to counteract the formation of fibre net-work in radially outer liquid layers in the hydrocyclone, and that the fibre concentration of the pulp suspension is increased to at least 0.9 % by the first multihydrocyclone unit (6) before the pulp suspension is separated by the second multihydrocyclone unit.
4. A method according to claim 3, c h a r a c t e r i z e d i n that the fibre concentration of the pulp suspension is increased to at least 1.0 % and maximally 1.3 % by the first multihydrocyclone unit (6) before the pulp suspension is separated by the second multihydrocyclone unit (13).
5. A method according to anyone of claims 1-4, c h a r a c t e r i z e d i n that the pulp suspension separated from light and heavy contaminants is conducted from the second multihydrocyclone unit (13) directly to a machine (2) for dewatering the pulp suspension.
6. A plant for treating a pulp suspension containing relatively light and heavy contaminants, comprising a first multihydrocyclone unit (6) having a multiplicity of parallelly coupled hydrocyclones designed for separating light contaminants from the pulp suspension under substantial thickening of the pulp suspension, a second multihydrocyclone unit (13) having a multiplicity of parallelly coupled hydrocyclones designed for separating heavy contaminants from the pulp suspension, and at least one pump (5) for pumping the pulp suspension to be separated through the multihydrocyclone units, c h a r a c t e r i z e d i n that the pump (5) is adapted to pump the pulp suspension to be separated through the first multihydrocyclone unit (6), and that the first multihydrocyclone unit is connected to the second multihydrocyclone unit (13) for supplying thickened pulp suspension, which is separated from the light contaminants, to the second multihydrocyclone unit.
7. A plant according to claim 6, c h a r a c t e r i z e d i n that each hydrocyclone of the second multihydrocyclone unit (13) is provided with turbulence creating means adapted to counteract the formation of fibre network in radially outer liquid layers in the hydrocyclone, and that the first multihydrocyclone unit (6) is adapted to thicken the pulp suspension to a fibre concentration of at least 0.9 %.
8. A plant according to claim 7, c h a r a c t e r i z e d i n that the first multihydrocyclone unit (6) is adapted to thicken the pulp suspension to a fibre concentration of at least 1.0 % and maximally 1.5 %.
9. A plant according to anyone of claims 6-8, c h a r a c t e r i z e d i n that the second multihydrocyclone unit (13) is directly connected to a machine (2) for dewatering the pulp suspension via a transport conduit (16) for transporting pulp suspension separated from heavy contaminants from the second multihydrocyclone unit to said machine.
10. A plant according to claim 9, c h a r a c t e r i z e d i n that a return conduit (17) for separated pulp suspension extends from said transport conduit (16) to the suction side of said pump (5).
11. A plant according to anyone of claims 6-10, c h a r a c t e r i z e d i n that the first multihydrocyclone unit (6) is connected to the second multihydrocyclone unit (13) via a connection conduit (10) with an additional pump (11), for transferring said thickened pulp suspension from the first to the second multihydrocyclone unit.
12. A plant according to claim 11, c h a r a c t e r i z e d i n that the second multihydrocyclone unit (13) comprises an inlet (12) for pulp suspension to be separated and an outlet (15) for an accept fraction, and that a control device (42) is adapted to control the capacity of said additional pump (11) in response to the pressure difference between said inlet and said outlet for accept fraction of the second multihydrocyclone unit.
13. A plant according to claim 11 or 12, c h a r a c t e r i z e d i n that upstream of said additional pump (11) and downstream of said first multihydrocyclone unit (6) said connection conduit (10) is provided with a counter pressure device (33-35) adapted to maintain a constant counter pressure in an outlet (8) for an accept fraction of the first multihydrocyclone unit (6).
14. A plant according to claim 13, c h a r a c t e r i z e d i n that the counter pressure device comprises a first open container (33) with an overflow (34), and a second open container (35), which is arranged to receive pulp suspension flowing across said overflow (34).
15. A plant according to claim 14, c h a r a c t e r i z e d i n that said connection conduit (10) comprises a first part (10a), which extends upwardly from the first multihydrocyclone unit (6) to the first container (33), and a second part (10b), which extends from the second container (35) via said additional pump (11) to the second multihydrocyclone unit (13).
16. A plant according to claim 15, c h a r a c t e r i z e d i n that the first multihydrocyclone unit (6) comprises an outlet (9) for a light reject fraction, that a drain conduit (29) with a control valve (37) extends from the outlet for light reject fraction, and that a level control means (36) is adapted to control the control valve (37) in response to the level of the suspension surface in the second container (35), such that said level is below the overflow (34).
17. A plant according to anyone of claims 14-16, c h a r a c t e r i z e d i n that the second multihydrocyclone unit (13) comprises an outlet (14) for a heavy reject fraction connected to at least one multihydrocyclone unit (19) for recovering fibres from the heavy reject fraction, and that a return conduit (38) is adapted to transfer an accept fraction with recovered fibres from said multihydrocyclone unit (19) for recovering fibres to said second open container (35).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9603346-9 | 1996-09-16 | ||
| SE9603346A SE507386C2 (en) | 1996-09-16 | 1996-09-16 | Process and plant for treating a contaminated pulp suspension |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2233193A1 true CA2233193A1 (en) | 1998-03-19 |
Family
ID=20403881
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002233193A Abandoned CA2233193A1 (en) | 1996-09-16 | 1997-08-28 | Method and plant for treating a contaminated pulp suspension |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0874936A1 (en) |
| JP (1) | JP2000500831A (en) |
| KR (1) | KR19990067425A (en) |
| BR (1) | BR9706750A (en) |
| CA (1) | CA2233193A1 (en) |
| ID (1) | ID18266A (en) |
| NO (1) | NO982224L (en) |
| SE (1) | SE507386C2 (en) |
| WO (1) | WO1998011296A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI20055073A (en) * | 2005-02-17 | 2006-08-18 | Metso Paper Inc | A method and apparatus for removing finely divided impurities from a fibrous suspension |
| FI119999B (en) | 2008-01-28 | 2009-05-29 | Andritz Oy | Method and apparatus for treating pulp |
| JP5465638B2 (en) * | 2010-09-02 | 2014-04-09 | 住友重機械エンバイロメント株式会社 | Sediment separation system and water separator for sand basin |
| IN2014DN09180A (en) * | 2012-04-03 | 2015-07-10 | Ovivo Luxembourg Sarl | |
| CN104328706A (en) * | 2014-11-17 | 2015-02-04 | 东莞理文造纸厂有限公司 | Heavy residue removal system for papermaking |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE406713B (en) * | 1977-07-18 | 1979-02-26 | Celleco Ab | HYDROCYCLOSE SEPARATOR WITH SLIDES IN THE CIRCULAR CYLINDRICAL PART OF THE SEPARATION CHAMBER |
| US4153558A (en) * | 1978-03-08 | 1979-05-08 | Ab Celleco | Hydrocyclone separator |
| ATE104382T1 (en) * | 1989-10-10 | 1994-04-15 | Nils Anders Lennart Wikdahl | METHOD AND APPARATUS FOR MAKING AN IMPROVED QUALITY CELLULOSE PULP. |
| SE469511B (en) * | 1991-12-02 | 1993-07-19 | Celleco Hedemora Ab | HYDROCYCLON WITH TURBULENCING ORGAN |
| AU7865894A (en) * | 1994-09-01 | 1996-03-22 | Kvaerner Pulping Ab | Separator for removing impurities from a fluid |
-
1996
- 1996-09-16 SE SE9603346A patent/SE507386C2/en not_active IP Right Cessation
-
1997
- 1997-08-28 KR KR1019980703436A patent/KR19990067425A/en not_active Application Discontinuation
- 1997-08-28 WO PCT/SE1997/001437 patent/WO1998011296A1/en not_active Application Discontinuation
- 1997-08-28 BR BR9706750A patent/BR9706750A/en not_active IP Right Cessation
- 1997-08-28 JP JP10513548A patent/JP2000500831A/en active Pending
- 1997-08-28 EP EP97936918A patent/EP0874936A1/en not_active Ceased
- 1997-08-28 CA CA002233193A patent/CA2233193A1/en not_active Abandoned
- 1997-09-15 ID IDP973179A patent/ID18266A/en unknown
-
1998
- 1998-05-15 NO NO982224A patent/NO982224L/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1998011296A1 (en) | 1998-03-19 |
| BR9706750A (en) | 1999-07-20 |
| EP0874936A1 (en) | 1998-11-04 |
| NO982224D0 (en) | 1998-05-15 |
| SE9603346L (en) | 1998-03-17 |
| NO982224L (en) | 1998-07-14 |
| JP2000500831A (en) | 2000-01-25 |
| ID18266A (en) | 1998-03-19 |
| SE9603346D0 (en) | 1996-09-16 |
| SE507386C2 (en) | 1998-05-25 |
| KR19990067425A (en) | 1999-08-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |