CA1110411A - Recycling by repulping wax and resin impregnated paperboards in black liquor - Google Patents
Recycling by repulping wax and resin impregnated paperboards in black liquorInfo
- Publication number
- CA1110411A CA1110411A CA316,508A CA316508A CA1110411A CA 1110411 A CA1110411 A CA 1110411A CA 316508 A CA316508 A CA 316508A CA 1110411 A CA1110411 A CA 1110411A
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- CA
- Canada
- Prior art keywords
- paperboard
- black liquor
- pulp
- pulper
- weak
- 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.)
- Expired
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/64—Paper recycling
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Abstract
ABSTRACT OF THE DISCLOSURE
The present invention relates to method and apparatus for recovering and recycling paperboard for reuse as pulp, more particularly re-pulping and re-using waste paperboard resulting from various packaging and other paperboard coverting processes, which paperboard has been, in such processes, impregnated with wax or resin for the purpose of imparting wet strength and imperviousness to liquid.
Essentially, the invention comprises process and apparatus for re-pulping the wax or resin impregnated paperboard in weak kraft black liquor produced in the conventional kraft cooking process and then washing the re-pulped material in a brown stock washer along with the virgin kraft pulp produced in the conventional cook, in order to clean the re-pulped material and recover and reuse the weak kraft black liquor used in the re-pulping process.
When recovered by the process and apparatus of the present invention, such pulp can be uses in manufacture of corrugating medium and linerboard, for instance, for use in the manufacture of corrugated paperboard boxes. The process and apparatus have economic value in the recovery of paperboard pulp from the waste product not only as the inherent benefit of using a material otherwise wasted, but also because the process liquid, weak kraft black liquor, is itself a relatively inexpensive by-product of the original virgin kraft pulping process and thus provides a low cost treatment liquid for the process of the invention when temporarily diverted from the kraft recovery process for that purpose.
The present invention relates to method and apparatus for recovering and recycling paperboard for reuse as pulp, more particularly re-pulping and re-using waste paperboard resulting from various packaging and other paperboard coverting processes, which paperboard has been, in such processes, impregnated with wax or resin for the purpose of imparting wet strength and imperviousness to liquid.
Essentially, the invention comprises process and apparatus for re-pulping the wax or resin impregnated paperboard in weak kraft black liquor produced in the conventional kraft cooking process and then washing the re-pulped material in a brown stock washer along with the virgin kraft pulp produced in the conventional cook, in order to clean the re-pulped material and recover and reuse the weak kraft black liquor used in the re-pulping process.
When recovered by the process and apparatus of the present invention, such pulp can be uses in manufacture of corrugating medium and linerboard, for instance, for use in the manufacture of corrugated paperboard boxes. The process and apparatus have economic value in the recovery of paperboard pulp from the waste product not only as the inherent benefit of using a material otherwise wasted, but also because the process liquid, weak kraft black liquor, is itself a relatively inexpensive by-product of the original virgin kraft pulping process and thus provides a low cost treatment liquid for the process of the invention when temporarily diverted from the kraft recovery process for that purpose.
Description
SUMM~RY OF TJIE INVENTION
This invention has to do with recycling by the recovery and re-use of waste paperboard as pulp which can be used by itself or mixed with virgin pulp in the kraft (sulphate) pulping system and in which the ~waste consists of paperboard which has previously been impregnated with waxes or resins or both in a previous converting process such as wet strength packaging or furniture component manufacture.
In an ordinary re-pulping operation, fiber separation to form pulp is relatively easy because khere is no lignin present binding the Eiber together as in the case oE wood to be pulped, which would require the use oE
strong cooking chemicals in the form of white li~uor, high heat of the order of 350 degrees F., pressure of the order of 100 pounds per square inch and time. But the waste paperboard of the type to which this invention applies has its fiber bound together again by the wax or resin with which it is impregnated in order to give the converted product, Eor instance a paperboard for packaging, the properties of strength and wet resistance required for use of the material, for instance as a container for very wet material such as iced poultry. Thus, the waste paper-board again has properties approaching those of wood, with the wax or resin as a binder like the original lignin, so that re-pulping in the conventional manner with water became impossible. On the other hand, if original kraft cooking liquor (white liquor) is used, the process becomes too expensive to be economically practical in a manufacturing field such as pulp and papermaking where cost facts have to be carefully balanced.
, \/ 2 ~ b,~ ~ ~
In khe process and apparatus of the invention the paperboard is re-pulped and the fibers are separated from each other and from the impregnating material so that the material treated iR thus made ready for re-use as pulp.
The commercial ànd sociological benefits of the invention lie in the fact that hundreds of thousands of tons of what would otherwise be waste paperboard material can be recycled. It is an additional benefit that the process material is the effluent by-product of a prior pulping process i.e. it is the weak black liquor ~rom the kraft (sulpha~e) proce4s for mak1ng pulp by cooking wood chips undex heat and pressure in a solution of sodlum hydroxide and sodium ~ulphide. SuGh weak kraft black liquor or spenk liquor contains residual sodium salts and sodium organic derivatives mixed with the lignin compounds which are cooked out of the wood chips to leave wood fibers for paper and paperboard manufacture.
In the standard kraft or sulphate process the weak black or spent liquor washed out o the pulp coming rom the digestor or cooker i9 sent to an evaporator for concentra~ing so that it can be burned to produce energy and the residual sodium salts which are recovered for re-use in the kraft cooking proces by combining them with carbonaceous matter in a furnace and then dissolving the ingredients in water to form "green li~uor." Calcined lime ~from a lime kiln) is combined with the green liquor to form sodium sulphide and sodium hydroxide as original cooking liquor ~white liquor) used in the sulphate process.
4~
In the present invention some of the weak black or spent liquor otherwise disposed of in the above described usual manner is diverted for use as a processing liquor for re~pulping the waste wax or resin impregnated paperboard thus providing a relatively inexpensive processing liquor in the form before it is recovered and re-combined with other ingredients to produce original cooking liquor (white liquor).
The essence of our invention is the discovery that, whereas the use of chemical additives to separate the wax and/or resin contaminated fiber has not been generally successful and the use of original white cooking liquor has been relatively too expensive, the use of relatively inexpensive weak kraft black liquor is both practical and economical for re-pulping the wax and resin contaminated waste, particularly when coupled with the step Of washing the re-pulped stock along with the pulp stock produced in an original virgin kraft cook thereby conserving the black liquor for its original use to produce heat, energy and recovered cooking chemicals.
Thus,-the invention in one aspect provides the method of recycling waste paperboard for re-use as pulp, which paperboard has been impregnated with wax or resin up to fifty percent by weight o~ the total, which comprises re-pulping said paperboard by immersing it in weak sulphate black liquor.
In a further aspect the invention provides apparatus for recycling waste paperboard for re-use as pulp which comprises a brown stock washer for separating weak sulphate black liquor from pulp, a re-pulper for re-pulping said waste paperboard, means to supply weak black liquor from said washer to said re-pulper, '.
:. ............................. :
, 4~L
and means to control the flow of said black liquor to said re-pulper in response to the amount of waste paperboard immersed in the black liquor in said re-pulper.
Thus, the invention provides means for recycling and 5 re-using large tonnages of material which would otherwise be waste and is thus increasingly important at a time when increasing demand and cost and decreasing supply of pulpwood, papermaking chemicals and other components makes recycling economically and ecologically beneficial.
Consequently the objective of the invention is to provide a method and apparatus by which wax and resin contaminated waste paperboard material can be economically recovered and re-used.
a -~' :.
.. . .
'' '` .
i ~' The drawing, Figure 1, is a schematic diagram 1-showing on the left hand side of the vertical dashed ¦~
line L-L the essential components o the conventional kraft pulp manufacturing system and on the right hand side of the vertical dashed line L-L the added sy~tem of the invention by which the contaminated waste paper- ~;~
board material is re-pulped and recovered for re-use ' as pulp and in which, in combination with the aonven-tional system, the impregnating materials, waxes and resins, are washed out o the re-pulped material to a sufficient degree for practiaal purposes and be~ome part of the weak black liquor in th~ system.
DETAI~ED DESCRLP~XON ~ND SP~CIFICATION OF THE INVENTION
Referring to Figure 1., a conven~ion kraft pulp digester is shown at 10 into which wood chips are introduced as at ll and cooking liquor (white liquor) is introduced as at 12 and in which the wood chips are cooked ~or a period of time under heat and pressure to separate the wood fibers to produce so called vir~in kraft pulp. At the end of the aook, the contents o~ the digester including pulp and spent cooking liquor tblack liquor) are discharged through the line 15 into a blow tank 16 for temporary retention.
From the blow tank 16 the pulp and black liquor are discharged as unwashed pulp through the line 17 into a brown stock washer 20 ~he unc~ion of which is to wash the impurities comprising mainly spent liquor (black liquor) out of the pulp. In a conventional kraft system th~re are usually a series of brown stock washers 20 with the pulp going from a first washer, the ona indicated in the drawing, to successive washer~ and being washed in progressively cleaner water with the wash water ';
moving countercurrently against the progression of the pulp from washer to washer so that the cleanest pulp is washed with the cleanest water in the last washer and the dirtiest pulp with the dirtiest water in the first washer.
The effluent from the latter is weak kraft black liquor which passes through a conduit indicated at 22 into a weak black liquor storage tank indicated at 23. From the storage tank 23 the weak black liquor can be trans~erred as by a pump 25 through a line 26 into the evaporator 30 from which it emerges through the line indicated at 32 a~ concenkraked black li~uor ready for burning to produce heat energy and recovered sodium chemicals for re-use in the original cooking liquor.
On the xight hand side of the dashed vertical line L-L is located a conventional re~pulper apparatus indicated at 35. Bales of the wax or resin impregnated paperboard are introduced into the re-pulper 35 as indicated at 36 whexe they are immersed in a bath of weak black llquor indicat~d at 36a which is constantly being agitated in the usual manner as by an impeller indicated at 38.
Continuous agitation o the paperboard bales in the weak black liquor causes the fibers of the paperboard to separate from each other and from the wax or resin with which the paperboard is impregnated. Some of the separated wax or resin is washed out of the re-pulped material in the subsequent washing step to be desc;ibed, and some of it is retained in the pulp without harmful effect.
Weak black liquor may be introduced into the re-pulper 35 directly fxom the brown stock washer 2Q through the line 22 and .its extension 22a, 22b and 22c or else by way o the weak black liquor storage tank 23, the pump 25 and the branch 26a of the line 26 and thence into the line extensions 22b and 22c. Valves 40, 41 and 42 determine the path and volume of flow of black liquor from the brown stock washer and its effluent line 22 to the eventual flow line 22c and into the re-pulper 35. Normally and while the brown stock washer 20 is in operation the flow of weak black liquor would be directly through the lines 22, 22a, 22b and 22c into the re-pulper 35 with the valves 41 and ~2 open and the valve ~0 closed. But if the brown stock washer were ~or any xeason not operating tempora.rily, weak black liquor could be drawn from the storage tank 23 and through the lines 26 and 26a into the lines 22b and 22c with the valve 40 open.
The re-pulped paperboard is removed from the re-pulper 35 by means of a pump 45 which moves it through a line 46 and into a centrifugal cleaner 48 convenien~ly placed and ln which impurities such as metal particles may be removed from the pulp. The impurities are drawn off through a line 49, The pulp flows away through a line 50, the sensing component 52 of a conventional consistency regulating device 54 and a three way flow diversion valve 55. The coupling between the sensing component 52 and the regulations device 54 is indicatecl at 53. The valve 55 is arranged so that it may allow at least some of the pulp to recirculate into the re-pulper 35 by way of the line 56. Thus when no new b~les o~
paperboard and no new weak black liquor are introduced into the xe-pulper 35, the pulp which is :Eormed in the re-pulper continues to recirculate back illtO the re-pulper.
When new bales of paperboard are introduced into the re-pulper 35 the consistency or percentage of solid content of the pulp in the re-pulper beyins to rise. 5ince it is always desirable to maintain the consistency at a predetermined level it then becomes necessary to introduce more weak black liquor into the re-pulper 35 by way o~
the line 22c. For this purpose the sensing component 52 of the consistency regulating device 5~, sensing the ri~e in consistency of the pulp, actuates the consi.stency rogulator 54 which in turn opens the valve ~2 ~o aclmit more black liquor into the re-pulpex until the consistency of the stock in the re pulper returns to the desired level.
The introduction o more paperboard and more black liquor into the re-pulper 35 also tends to raise its liquid level higher than the pre-determined desired location.
For the purpose of re-establishing khe liquid level in the re-pulper, a liquid level sensing device 60 aatuates a controller 61 which in ~urn moves the valve 55 so as to release some of the pulp and black liquor into a line 65 through which it 10ws either toward the blow tank 16 from which it may later flow into the brown stock washer 20 or directly into the brown stock washer 20 either through the lines 66 or 67 depending upon the operating conditions of the valves 68 and 69 as determined by the requirements o~ the system.
~l~f~4D~
Thus while no bales o paperboard are introduced into the re-pulper the system continues to recirculate in a state of stability without producing new re-pulped material.
~ owever, as soon as additional bales o paper-board are introduced into the r0-pulper 35 the system balances itsel both with respect to the consistency of the pulp in the re-pulper and also with respect to the liquid level in the re-pulper. And this addition of paperboard bales under these conditions produces new re-pulped paperboard material which goes back to the brown stock washer 20 as above described whexe ~he pulp iB
washed aloncJ with the viryin kraf~ pulp rom the digester.
Xn general, the re-pulping may be aarried out at a pulp consistenay o~ the order o~ 2~, in a temperature range of 150 - 200F. and at time intervals o 20 to 60 minutes, The wax materials with which the re-pulped paper-board is impregnated consist essentially o~ paraffins but apparently paperboard treated with other types of waxes may also be re-pulped. Examples inalude Chevron Research Corporation's 1~6/130 White Scale Wax, City Service Oil Co.'s IPS Nos. 1, 2 and 5 and Pacemaker Nos. 30, 35, 40 and 42, Exxon's Parvan 2730, Mobil Oil Corporation's Wax Rex 53D and Mobil Wax 130 and National Wax Co.'s 6603 -and 133/5.
The resins with which the re-pulped paperboards were treated included B staged Urea Formaldehyde PolyVinyl Acetate resins in which the resins solids to bone dry fiber ratio was appr~ximately ~2 percent but could be as high as 50 percent. Some of the resin impregnated samples also included paraffin wax.
The re-pulping proce~s using weak black liquor causes essentially complete defiberization of the waste paperboard. The amount of residual resins or waxes left in the pulp after washing depends on the thoroughness of the wash in standard brown stock washers.
Ordinarily complete wax or resin freedom is not essential for ~he production o the components of corruyated paperboard packaging material.
While for some purposes a new paperboarcl sheet can be,made en~irely of the re-pulped waste materials, it i~ al50 usual to blend the repulped material with virgin kraft to produce a paperboard of superior strength pro-perties. Such blends might be 90% virgin kraft pulp ~, and 10~ re-pulped material.
Since the highest properties require the most expensive processing it will be understood that the degree of re-pulping and of washing of the re-pulped material and the blending with virgin kra~ ma~erial will depend on the purposes for which the stock i8 intended.
~o
This invention has to do with recycling by the recovery and re-use of waste paperboard as pulp which can be used by itself or mixed with virgin pulp in the kraft (sulphate) pulping system and in which the ~waste consists of paperboard which has previously been impregnated with waxes or resins or both in a previous converting process such as wet strength packaging or furniture component manufacture.
In an ordinary re-pulping operation, fiber separation to form pulp is relatively easy because khere is no lignin present binding the Eiber together as in the case oE wood to be pulped, which would require the use oE
strong cooking chemicals in the form of white li~uor, high heat of the order of 350 degrees F., pressure of the order of 100 pounds per square inch and time. But the waste paperboard of the type to which this invention applies has its fiber bound together again by the wax or resin with which it is impregnated in order to give the converted product, Eor instance a paperboard for packaging, the properties of strength and wet resistance required for use of the material, for instance as a container for very wet material such as iced poultry. Thus, the waste paper-board again has properties approaching those of wood, with the wax or resin as a binder like the original lignin, so that re-pulping in the conventional manner with water became impossible. On the other hand, if original kraft cooking liquor (white liquor) is used, the process becomes too expensive to be economically practical in a manufacturing field such as pulp and papermaking where cost facts have to be carefully balanced.
, \/ 2 ~ b,~ ~ ~
In khe process and apparatus of the invention the paperboard is re-pulped and the fibers are separated from each other and from the impregnating material so that the material treated iR thus made ready for re-use as pulp.
The commercial ànd sociological benefits of the invention lie in the fact that hundreds of thousands of tons of what would otherwise be waste paperboard material can be recycled. It is an additional benefit that the process material is the effluent by-product of a prior pulping process i.e. it is the weak black liquor ~rom the kraft (sulpha~e) proce4s for mak1ng pulp by cooking wood chips undex heat and pressure in a solution of sodlum hydroxide and sodium ~ulphide. SuGh weak kraft black liquor or spenk liquor contains residual sodium salts and sodium organic derivatives mixed with the lignin compounds which are cooked out of the wood chips to leave wood fibers for paper and paperboard manufacture.
In the standard kraft or sulphate process the weak black or spent liquor washed out o the pulp coming rom the digestor or cooker i9 sent to an evaporator for concentra~ing so that it can be burned to produce energy and the residual sodium salts which are recovered for re-use in the kraft cooking proces by combining them with carbonaceous matter in a furnace and then dissolving the ingredients in water to form "green li~uor." Calcined lime ~from a lime kiln) is combined with the green liquor to form sodium sulphide and sodium hydroxide as original cooking liquor ~white liquor) used in the sulphate process.
4~
In the present invention some of the weak black or spent liquor otherwise disposed of in the above described usual manner is diverted for use as a processing liquor for re~pulping the waste wax or resin impregnated paperboard thus providing a relatively inexpensive processing liquor in the form before it is recovered and re-combined with other ingredients to produce original cooking liquor (white liquor).
The essence of our invention is the discovery that, whereas the use of chemical additives to separate the wax and/or resin contaminated fiber has not been generally successful and the use of original white cooking liquor has been relatively too expensive, the use of relatively inexpensive weak kraft black liquor is both practical and economical for re-pulping the wax and resin contaminated waste, particularly when coupled with the step Of washing the re-pulped stock along with the pulp stock produced in an original virgin kraft cook thereby conserving the black liquor for its original use to produce heat, energy and recovered cooking chemicals.
Thus,-the invention in one aspect provides the method of recycling waste paperboard for re-use as pulp, which paperboard has been impregnated with wax or resin up to fifty percent by weight o~ the total, which comprises re-pulping said paperboard by immersing it in weak sulphate black liquor.
In a further aspect the invention provides apparatus for recycling waste paperboard for re-use as pulp which comprises a brown stock washer for separating weak sulphate black liquor from pulp, a re-pulper for re-pulping said waste paperboard, means to supply weak black liquor from said washer to said re-pulper, '.
:. ............................. :
, 4~L
and means to control the flow of said black liquor to said re-pulper in response to the amount of waste paperboard immersed in the black liquor in said re-pulper.
Thus, the invention provides means for recycling and 5 re-using large tonnages of material which would otherwise be waste and is thus increasingly important at a time when increasing demand and cost and decreasing supply of pulpwood, papermaking chemicals and other components makes recycling economically and ecologically beneficial.
Consequently the objective of the invention is to provide a method and apparatus by which wax and resin contaminated waste paperboard material can be economically recovered and re-used.
a -~' :.
.. . .
'' '` .
i ~' The drawing, Figure 1, is a schematic diagram 1-showing on the left hand side of the vertical dashed ¦~
line L-L the essential components o the conventional kraft pulp manufacturing system and on the right hand side of the vertical dashed line L-L the added sy~tem of the invention by which the contaminated waste paper- ~;~
board material is re-pulped and recovered for re-use ' as pulp and in which, in combination with the aonven-tional system, the impregnating materials, waxes and resins, are washed out o the re-pulped material to a sufficient degree for practiaal purposes and be~ome part of the weak black liquor in th~ system.
DETAI~ED DESCRLP~XON ~ND SP~CIFICATION OF THE INVENTION
Referring to Figure 1., a conven~ion kraft pulp digester is shown at 10 into which wood chips are introduced as at ll and cooking liquor (white liquor) is introduced as at 12 and in which the wood chips are cooked ~or a period of time under heat and pressure to separate the wood fibers to produce so called vir~in kraft pulp. At the end of the aook, the contents o~ the digester including pulp and spent cooking liquor tblack liquor) are discharged through the line 15 into a blow tank 16 for temporary retention.
From the blow tank 16 the pulp and black liquor are discharged as unwashed pulp through the line 17 into a brown stock washer 20 ~he unc~ion of which is to wash the impurities comprising mainly spent liquor (black liquor) out of the pulp. In a conventional kraft system th~re are usually a series of brown stock washers 20 with the pulp going from a first washer, the ona indicated in the drawing, to successive washer~ and being washed in progressively cleaner water with the wash water ';
moving countercurrently against the progression of the pulp from washer to washer so that the cleanest pulp is washed with the cleanest water in the last washer and the dirtiest pulp with the dirtiest water in the first washer.
The effluent from the latter is weak kraft black liquor which passes through a conduit indicated at 22 into a weak black liquor storage tank indicated at 23. From the storage tank 23 the weak black liquor can be trans~erred as by a pump 25 through a line 26 into the evaporator 30 from which it emerges through the line indicated at 32 a~ concenkraked black li~uor ready for burning to produce heat energy and recovered sodium chemicals for re-use in the original cooking liquor.
On the xight hand side of the dashed vertical line L-L is located a conventional re~pulper apparatus indicated at 35. Bales of the wax or resin impregnated paperboard are introduced into the re-pulper 35 as indicated at 36 whexe they are immersed in a bath of weak black llquor indicat~d at 36a which is constantly being agitated in the usual manner as by an impeller indicated at 38.
Continuous agitation o the paperboard bales in the weak black liquor causes the fibers of the paperboard to separate from each other and from the wax or resin with which the paperboard is impregnated. Some of the separated wax or resin is washed out of the re-pulped material in the subsequent washing step to be desc;ibed, and some of it is retained in the pulp without harmful effect.
Weak black liquor may be introduced into the re-pulper 35 directly fxom the brown stock washer 2Q through the line 22 and .its extension 22a, 22b and 22c or else by way o the weak black liquor storage tank 23, the pump 25 and the branch 26a of the line 26 and thence into the line extensions 22b and 22c. Valves 40, 41 and 42 determine the path and volume of flow of black liquor from the brown stock washer and its effluent line 22 to the eventual flow line 22c and into the re-pulper 35. Normally and while the brown stock washer 20 is in operation the flow of weak black liquor would be directly through the lines 22, 22a, 22b and 22c into the re-pulper 35 with the valves 41 and ~2 open and the valve ~0 closed. But if the brown stock washer were ~or any xeason not operating tempora.rily, weak black liquor could be drawn from the storage tank 23 and through the lines 26 and 26a into the lines 22b and 22c with the valve 40 open.
The re-pulped paperboard is removed from the re-pulper 35 by means of a pump 45 which moves it through a line 46 and into a centrifugal cleaner 48 convenien~ly placed and ln which impurities such as metal particles may be removed from the pulp. The impurities are drawn off through a line 49, The pulp flows away through a line 50, the sensing component 52 of a conventional consistency regulating device 54 and a three way flow diversion valve 55. The coupling between the sensing component 52 and the regulations device 54 is indicatecl at 53. The valve 55 is arranged so that it may allow at least some of the pulp to recirculate into the re-pulper 35 by way of the line 56. Thus when no new b~les o~
paperboard and no new weak black liquor are introduced into the xe-pulper 35, the pulp which is :Eormed in the re-pulper continues to recirculate back illtO the re-pulper.
When new bales of paperboard are introduced into the re-pulper 35 the consistency or percentage of solid content of the pulp in the re-pulper beyins to rise. 5ince it is always desirable to maintain the consistency at a predetermined level it then becomes necessary to introduce more weak black liquor into the re-pulper 35 by way o~
the line 22c. For this purpose the sensing component 52 of the consistency regulating device 5~, sensing the ri~e in consistency of the pulp, actuates the consi.stency rogulator 54 which in turn opens the valve ~2 ~o aclmit more black liquor into the re-pulpex until the consistency of the stock in the re pulper returns to the desired level.
The introduction o more paperboard and more black liquor into the re-pulper 35 also tends to raise its liquid level higher than the pre-determined desired location.
For the purpose of re-establishing khe liquid level in the re-pulper, a liquid level sensing device 60 aatuates a controller 61 which in ~urn moves the valve 55 so as to release some of the pulp and black liquor into a line 65 through which it 10ws either toward the blow tank 16 from which it may later flow into the brown stock washer 20 or directly into the brown stock washer 20 either through the lines 66 or 67 depending upon the operating conditions of the valves 68 and 69 as determined by the requirements o~ the system.
~l~f~4D~
Thus while no bales o paperboard are introduced into the re-pulper the system continues to recirculate in a state of stability without producing new re-pulped material.
~ owever, as soon as additional bales o paper-board are introduced into the r0-pulper 35 the system balances itsel both with respect to the consistency of the pulp in the re-pulper and also with respect to the liquid level in the re-pulper. And this addition of paperboard bales under these conditions produces new re-pulped paperboard material which goes back to the brown stock washer 20 as above described whexe ~he pulp iB
washed aloncJ with the viryin kraf~ pulp rom the digester.
Xn general, the re-pulping may be aarried out at a pulp consistenay o~ the order o~ 2~, in a temperature range of 150 - 200F. and at time intervals o 20 to 60 minutes, The wax materials with which the re-pulped paper-board is impregnated consist essentially o~ paraffins but apparently paperboard treated with other types of waxes may also be re-pulped. Examples inalude Chevron Research Corporation's 1~6/130 White Scale Wax, City Service Oil Co.'s IPS Nos. 1, 2 and 5 and Pacemaker Nos. 30, 35, 40 and 42, Exxon's Parvan 2730, Mobil Oil Corporation's Wax Rex 53D and Mobil Wax 130 and National Wax Co.'s 6603 -and 133/5.
The resins with which the re-pulped paperboards were treated included B staged Urea Formaldehyde PolyVinyl Acetate resins in which the resins solids to bone dry fiber ratio was appr~ximately ~2 percent but could be as high as 50 percent. Some of the resin impregnated samples also included paraffin wax.
The re-pulping proce~s using weak black liquor causes essentially complete defiberization of the waste paperboard. The amount of residual resins or waxes left in the pulp after washing depends on the thoroughness of the wash in standard brown stock washers.
Ordinarily complete wax or resin freedom is not essential for ~he production o the components of corruyated paperboard packaging material.
While for some purposes a new paperboarcl sheet can be,made en~irely of the re-pulped waste materials, it i~ al50 usual to blend the repulped material with virgin kraft to produce a paperboard of superior strength pro-perties. Such blends might be 90% virgin kraft pulp ~, and 10~ re-pulped material.
Since the highest properties require the most expensive processing it will be understood that the degree of re-pulping and of washing of the re-pulped material and the blending with virgin kra~ ma~erial will depend on the purposes for which the stock i8 intended.
~o
Claims (10)
1. The method of recycling waste paperboard for re-use as pulp, which paperboard has been impregnated with wax or resin up to fifty percent by weight of the total, which comprises re-pulping said paperboard by immersing it in weak sulphate black liquor.
2. The method of claim 1 which includes elevating the temperature of the said paperboard and black liquor to at least 150 degrees Fahrenheit.
3. The method of claim 1 which includes immersing the said paperboard in the said black liquor with a major portion of said paperboard being so immersed for at least about 20 minutes.
4. The method of claim 1 which includes washing the black liquor out of the re-pulped material.
5. The method of claim 4 which includes recovering the said black liquor.
6. The method of claim 1 which includes washing the re-pulped material along with pulp stock produced in an original virgin kraft cook.
7. Apparatus for recycling waste paperboard for re-use as pulp which comprises a brown stock washer for separating weak sulphate black liquor from pulp, a re-pulper for re-pulping said waste paperboard, means to supply weak black liquor from said washer to said re-pulper, and means to control the flow of said black liquor to said re-pulper in response to the amount of waste paperboard immersed in the black liquor in said re-pulper.
8. In the apparatus as set forth in claim 7, means to recirculate at least part of the re-pulped waste paperboard and weak black liquor from the re-pulper back into the re-pulper.
9. In the apparatus as set forth in claim 8, means to control the rate of said recirculation in response to variations in a predetermined level of material in the re-pulper.
10. In the apparatus as set forth in claim 8, said means to recirculate including a selector valve which operates to divert for re-use as pulp and weak black liquor that part of the re-pulped waste paperboard and weak black liquor from the re-pulper which is not recirculated into the re-pulper.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US90574178A | 1978-05-15 | 1978-05-15 | |
| US905,741 | 1978-05-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1110411A true CA1110411A (en) | 1981-10-13 |
Family
ID=25421387
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA316,508A Expired CA1110411A (en) | 1978-05-15 | 1978-11-20 | Recycling by repulping wax and resin impregnated paperboards in black liquor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1110411A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5147503A (en) * | 1991-03-01 | 1992-09-15 | Domtar Inc. | Recycling waste cellulosic material with sodium sulphide digestion |
| AU665559B2 (en) * | 1992-04-23 | 1996-01-11 | Domtar Inc. | Wood-free pulp and white paper product |
| US5503709A (en) * | 1994-07-27 | 1996-04-02 | Burton; Steven W. | Environmentally improved process for preparing recycled lignocellulosic materials for bleaching |
| US5538594A (en) * | 1992-04-06 | 1996-07-23 | Westvaco Corporation | Method for producing a blade coated paper from recycled, high lignin content, waste paper |
| US6017415A (en) * | 1997-09-05 | 2000-01-25 | International Paper Company | Method for co-pulping waste cellulosic material and wood chips |
-
1978
- 1978-11-20 CA CA316,508A patent/CA1110411A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5147503A (en) * | 1991-03-01 | 1992-09-15 | Domtar Inc. | Recycling waste cellulosic material with sodium sulphide digestion |
| US5538594A (en) * | 1992-04-06 | 1996-07-23 | Westvaco Corporation | Method for producing a blade coated paper from recycled, high lignin content, waste paper |
| AU665559B2 (en) * | 1992-04-23 | 1996-01-11 | Domtar Inc. | Wood-free pulp and white paper product |
| US5503709A (en) * | 1994-07-27 | 1996-04-02 | Burton; Steven W. | Environmentally improved process for preparing recycled lignocellulosic materials for bleaching |
| US6017415A (en) * | 1997-09-05 | 2000-01-25 | International Paper Company | Method for co-pulping waste cellulosic material and wood chips |
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