CA2013011C - Method and means for treating pulp - Google Patents
Method and means for treating pulpInfo
- Publication number
- CA2013011C CA2013011C CA002013011A CA2013011A CA2013011C CA 2013011 C CA2013011 C CA 2013011C CA 002013011 A CA002013011 A CA 002013011A CA 2013011 A CA2013011 A CA 2013011A CA 2013011 C CA2013011 C CA 2013011C
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- screening
- thickening
- thickener
- pressure
- 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 - Fee Related
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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
Abstract
Method and means is disclosed for treating pulp, in particular fiber suspensions of the pulp and paper industry, and more specifically, for improvement of pulp mill screening plants, to make their operation more effective and to reduce the need for equipment to reduce the investment costs etc. In the known screening process it is usually desirable to increase the pulpconsistency after the screening to a range of 10 to 15% for storing or after-treatment. It is also desirable to handle rejects by either refining or some other method, but usually at consistency which is higher than that of screening. In other words, the pulp flows always have to be thickened after screening. The present invention comprises a method and means for screening pulp in a pressurized, closed space by means of screens in a consistency range of 1 to 5% and by means of centrifugal cleaners in a consistency below 1%. The various pulp screening and/or cleaning stages are effected in a pressurized state in a closed space in the screening plant. Access of air to the treated pulp is prevented by carrying out the thickening stages in a pressurized state, at the initial pressure corresponding to that of the preceding screening and/or cleaning stage.
Description
METHOD AND APPARATUS FOR TREATING PULP
The present invention relates to a method and apparatus for treating pulp. In particular, it is suitable for treating fiber suspensions of the pulp and paper industry and more specifically, it is related to the development of the 5 screening plants in pulp mills, making their operation more effective and reducing their need for equipment, thus enabling a considerable reduction in the investment costs.
Wood pulp is manufactured with various methods in the pulp and paper industry. Pulp can be manufactured chemically by cooking or mechanically by 10 grinding and refining. It is also manufactured from waste paper by defiberingit in a pulper. It is common to all pulp manufacturing methods that the pulp contains more or less impurities which have to be removed therefrom.
Pulp is cleaned in a screening plant by means of screens and cleaners.
The screen is apparatus in which pulp is screened by either a slotted screen or 15 a perforated screen in the consistency range of 1 to 5%. The cleaner, normally a so-called centricleaner, is apparatus in which pulp is cleaned by centrifugal force in a low, usually less than 1% consistency.
However, screening involves two problems. Firstly, it is usually desirable after screening to increase the pulp consistency to a range of 10 to 15% for 20 storing or after-treatment. Secondly, handling of the reject is also desirable by either refining or some other method, but usually in a higher consistency than that of screening. In other words, the pulp flows always have to be thickened after screening.
There have been attempts to completely resolve this problem, for 25 example, by raising the consistency to 8 - 15% in the screening equipment.
Efforts have been made in developing both screens and cleaners which would operate in a consistency of about 10%. However, this has succeeded only partially. Screening and cleaning as such are fairly successful in a high consistency, but the separation efficiency of the screens and cleaners 30 substantially decreases when the consistency rises. It can be said therefore that these attempts have replaced one problem with another, i.e. they have eliminated the need for thickening at the cost of reducing the cleaning efficiency.
The present invention comprises a method and apparatus for screening 5 pulp in a pressurized, closed space by screens in the consistency range of 1 to 5% `and by centricleaners in a consistency of less than 1%.
According to the invention and in one aspect thereof, the method is provided of treating pulp in a screening plant of a pulp mill, in which method impurities containing fraction is separated from defibered pulp by screening 10 and/or cleaning, the defibered pulp accepted in such a manner is thickened toa consistency of 10 to 20% and is further fed into further processing, said impurities containing fraction is further treated in the screening plant by screening and defibering to recover from said fraction acceptable fiber materialfor further screening and thickening and for removing non-acceptable impurities 15 from the screening plant after various screening stages. In accordance with the invention, the various pulp screening and/or cleaning stages are effected in a closed, pressurized space in the screening plant and that access of air to the pulp treated is prevented by effecting the thickening stages in a pressurized state at pressure prevailing in the screening and/or clèaning stage immediately 20 preceding said thickening stage or stages, whereby no separate pump is required for thickener or thickeners used in said thickening stage or stages.
The present invention could also be defined in general terms as a method of treating pulp suspension in a s plant of a pulp mill, comprising the steps of:
fractionating said suspension by s or cleaning to produce an impurities 25 containing fraction and an accepted pulp fraction; thickening the accepted pulp fraction to a consistency of about 10 to about 20%; feeding the accepted pulp fraction for further processing thereof; further treating said impurities containing fraction in the s plant by s the fraction in order to obtain acceptable fraction and non-acceptable impurities; thickening the acceptable fraction;
30 removing non-acceptable impurities from the s plant; said s or cleaning beingeffected in a closed, pressurized space in the s plant; preventing access of air B
~3~ 2 0 13 011 to the accepted pulp fraction and to said acceptable fraction by effecting the step of thickening in a pressurized state and at a pressure corresponding to that of the stage immediately preceding the step of thickening, thus eliminatingthe need for a separate pump for pressurizing thickener or thickeners used in 5 said thickening steps.
The present invention also provides apparatus for treating pulp in a screening plant of a pulp mill, said apparatus being comprised of a plurality ofpulp treatment devices, wherein said treatment devices are each closed to ambient atmosphere and are arranged to operate in a pressurized state, the 10 plurality of pulp treatment devices including a pump/thickener combination inwhich the over-pressure required in the thickener of said combination is derivedgenerally solely from the pump of the combination.
The term "apparatus" in describing the present invention may refer to one or more devices disposed in a screening plant.
The method and apparatus according to the invention will be described in closer detail below, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a basic scheme of a screening plant according to the prior art, and Fig. 2 is a scheme of a screening plant according to the method and apparatus of the invention.
Fig. 1 is a basic scheme of a screening plant which is commonly used today. Its construction and operation are described more in detail below. Many other screening diagrams exist, which considerably differ from the details of the diagrams shown in Fig. 1, but Fig. 1 presents the commonly used basic principle of screening. In the accompanying drawings, pumps used in pulp feeding are generally marked with a reference letter P because the pumps themselves have no substantial significance as to the invention.
-4~ 201~011 Pulp is fed in a consistency of about 5% from a pulp storage 1 through a knotter 2 and intermediate tank 3 to screens 4 - 8, which in the embodiment of Fig. 1 are divided into two stages, the first being comprised of screens 4 and 5 and the second of screens 6, 7 and 8. The cleaned pulp from the last 5 screens 6, 7 and 8 is taken to one or more suction filters 9. In the knotter 2, knots and large pieces or the like are separated from the pulp and are further taken to the knot scrubber 10, where acceptable fiber material is separated from the knot pulp and is returned to the intermediate tank 3. The knot material is removed from the knot scrubber 10 and is taken to further 10 treatment, in the embodiment of Figure 1, through a knot silo 11.
Shives, fiber bundles and small impurities or the like are separated from the pulp in screens 4 - 8. The reject from screens 4 and 5 is led into a secondary screen 12 and the accept from said screen 12 is led back into screens 4 and 5 of the first screening stage and the reject directly to a reject15 thickener 14, wherefrom it is further conducted by means of a feed screw 15 to a refining stage 16. Refined pulp from the refiner 15 is led to another secondary screen 17, whose accept is led to cleaners 18. The accept from the cleaners 13 is conducted to either the intermediate tank 18 or directly to the first secondary screen 12. The accept pulp from the screens enters the suction 20 filter in a consistency of 1 to 2%, which prevails aftèr screening, because the suction filter is not capable of handling pulp of a higher inlet consistency, and the pulp is thickened to a consistency of 10 to 15% by drawing water therefrom by means of a gravity-operated drop leg. The inevitable result of thisis that the pulp mill must have, at least for the disposition of suction filters, a 25 storey at a height of about 10 m. Other components of the equipment are disposed in various storeys according to need and space.
Screening as described above involves some problems. Firstly, in thickening of pulp with filters 4 and 8 and also in transfer of pulp, plenty of air is mixed with the pulp and the filtrates, which causes, for example, foaming.
30 Also the building height required by said filters can be considered a significant drawback. If the screening plant could be of pressurized construction and ~5- 2013011 hydrauiically closed so as to prevent any air from mixing with pulp, all above-mentioned drawbacks could be eliminated.
Secondly, a great number of apparatuses is needed. For example, screens are disposed in two successive stages, the first stage comprising two 5 screens connected in parallel and the second stage three screens connected in parallel. A great number of apparatuses are needed because as high as possible separation efficiency is aimed at in each apparatus. In other words, the desiredfraction is attempted to be separated completely from the undesirable fraction, i.e. the idea is to keep the reject ratio as low as possible. This results in that 10 pulp is circulated for a relatively long time in the apparatus, whereby only a fractional part of the maximum capacity of the apparatus is used.
Thirdly, the low consistency of the suspension to be treated constitutes a problem. The low consistency in itself requires a big filter, even if it were not taken into account that the suction filter is by no means the most efficient type 15 of filter when comparing the operating efficiencies of filter surfaces. It can be assumed, for example, that the consistency of the pulp entering the filter is 1.5% and is then raised to 15% at the filter. For the production of 15 tons of dry fiber pulp by the filter, one has to take a total of 100 tons of 15%
suspension out of it. For this result, 900 tons of liquid has to be removed from20 the 1.5% pulp entering the filter. If the consistency of the pulp entering the filter is 3%, only 400 tons of liquid has to be removed and if the inlet consistency is 4.5%, only 233 tons of liquid has to be removed. Thus, if the nominal thickening capacity of the filter remains unchanged, it is possible, by tripling the inlet consistency, to manage with the apparatus whose thickening 25 area is only about a fourth of the thickening area of the thickening apparatus required by low consistency.
Fig. 2 illustrates more in detail a method according to a preferred embodiment of the invention and apparatus needed therefor. Pulp is fed from tank 1 via pump 101 to knotter 2 and through a pump 102 and a screen 21 30 further to a drum thickener means 23. Screening takes place in a consistency range of 1 to 5%, normally in a consistency range of 3 to 5%. The drum -6- 2013~11 displacement means 23 is a drum provided with cells in which the pulp is thickened to a consistency of 10 to 15% at the pressure of inlet pulp. Ambient air is not allowed to enter in the pulp processed. An embodiment of the drum thickener means is disclosed in, for example, US patent 4,502,171.
The reject pulp from the first screen 21 is fed, via pump 103 directly to the second screen 22 whose accept is returned to the first screen 21 and the reject is led, in the embodiment shown, via pump 104 to a pressurized, closed thickener 24 wherefrom pulp in a pressurized state flows without a feed screw to a refiner 25 (also referred to as a ~fiberizer-refiner". Pulp is fed in a low consistency into the thickener 24 and filtrate is removed during turbulence effect. Selection of holes of a suitable size (of diameter 1 - 2 mm) contributesto primary fibers being discharged with the filtrate, and the remaining, thickened reject pulp then flows further to the refining stage. Thus, the refining and thickening of the reject pulp is made at a pressurized condition and no air is mixed with the pulp. An example of the thickener 24 is disclosed in the published Fl patent application 874854. The filtrate from thickener 24 and the filtrate from the drum thickener means 23 are fed by pump 105 together with the pulp to be cleaned to the cleaners 18, and the fraction accepted by these cleaners is conducted to a thickener 26, whose filtrate is also fed to the cleaners 18. Thickener 26 is a pressurized water separator disclosed in the published Fl patent application 873020. Thus, also the pulp cleaning and thickening effected thereafter are provided in a pressurized and closed state.
It is apparent from the above that the arrangement according to the present invention presents certain combinations, series or groupings. For instance, the pump 104 and the thickener 24 present an embodiment of a ~pump/thickener combination." It can be appreciated from the drawing of Fig.
2 that overpressure required at the thickener 24 of said combination is derived solely by the pump 104 of said combination.
Similarly, the combination referred to in the preceding paragraph forms a part of an embodiment of a closed pump 104 / thickener 24 / fiberizer-refiner 25 group so arranged and disposed that the pressure at the fiberizer-refiner 25 B
- ~7~ 2013011 of said group substantially equals an initial pressure at the thickener 24 of said group.
Also, the pump 103, screen 22, cleaner 18, thickener 26, can generally be defined as a pump/screen/cleaner/thickenerseries so arranged and disposed 5 that overpressure required for the operation of the thickener 26 of the seriesis derived solely from the pump of the respective series despite the fact that in the embodiment of Fig. 2 an additional pump 105 may also be employed if desired .
When comparing the equipment illustrated in Fig. 2 above with the 10 equipment of Fig. 1, it can be seen that there are differences in both the number of screens and the methods of thickening. When filtrate is removed in small pressurized thickeners, the layout of the mill is compact and, according to estimate, the required building volume is less than half of the building volume required by a conventional screening plant. The reject handling 15 equipment according to Fig. 1 comprises a suction filter, a feed screw and a refiner itself. Now, the reject handling is managed with a thickener of a considerably smaller size and without a feed screw. The number of cleaners has not substantially changed. The only addition compared with the equipment of Fig. 1 is the thickener 26 for the accept received from the cleaners. It 20 thickens the suspension from the consistency level required by the cleaners to that required by screening. The thickening means are disposed last in the screening plant. According to the present system, two such means, i.e. suction filters, are needed. They shall be of the size 4 x 8 m, where the drum diameter is 4 m and the drum length 8 m. In the system according to the present 25 invention, only one 3.5 x 5 m thickening means is needed.
The function of the system according to the invention is, on the other hand, based on that the screens themselves are dimensioned and the capacity optimized so that the capacity is at its maximum, whereby the reject ratio is relatively high, about 20 to 30%. Thus, the accept from the screens is 30 absolutely clean and suitable as such to be fed directly into the thickener, excluding the secondary screening stage. The task of the second screen 22 is to handle the reject from the first screen 21, i.e. the suspension, which still includes a great amount of acceptable fiber fraction which is returned to the first screen. Thus, screen 22 in a way corresponds to the screen 12 of Fig. 1, which treats the reject from the screens of the first stage.
On the other hand, the function of the method and apparatus according to the invention is based on that the entire screening can be accomplished at an over-pressure so that no external air is allowed to enter the process. This has been achieved by arranging only a few key points of the system with a pumping facility in order to pressurize the treated suspension so that it will be transferred from one means to another by said pressure. More specifically, the screening plant is divided into a number of pump - screen/ cleaner - thickener combinations, in which the feed pressure of each pump is sufficient to maintain over-pressure so that, on one hand, no external gas is allowed to the system and, on the other hand, even the pressure difference required for thickening comes from the pump unit of each combination.
The economical advantages referred to in the beginning of this description are best seen when reviewing the results of the following comparative calculations.
- The energy consumption in a screening plant applying the method and apparatus according to the invention is about 34% less than in a conventional screening plant, - the costs of building and equipment in a pulp mill are distributed asfollows if the reference number 100 refers to costs in a conventional screening plant.
Object Conventional Invention olant pipes 100 61 service platforms 100 60 valves 100 49 pumps 100 74 mixers 100 00 building 100 29 total 100 52 Thus, it will be appreciated that apart from the energy consumption being cut down by a third, the costs of equipment and building, excluding 5 electrification, instrumentation and main equipment, the inclusion of which inthe calculation would cause too much inaccuracy and uncertain estimates, are only about half of corresponding investments in a conventional pulp mill.
As a conclusion, the above describes a process for screening and cleaning pulp in a closed, pressurized space so that the consistency need not 10 be raised at a cost of the cleaning efficiency. No equivalent process has been earlier disclosed, where pulp is screened, cleaned, and reject handled in a closed space so that the cleaning operations themselves are effected in a consistency optimal to them, the pulp still being in a high consistency when it is led to the after-treatment stage. The method and apparatus of the invention 15 are not limited to the embodiment described above, but they cover all the embodiments within the scope of the accompanying claims.
The present invention relates to a method and apparatus for treating pulp. In particular, it is suitable for treating fiber suspensions of the pulp and paper industry and more specifically, it is related to the development of the 5 screening plants in pulp mills, making their operation more effective and reducing their need for equipment, thus enabling a considerable reduction in the investment costs.
Wood pulp is manufactured with various methods in the pulp and paper industry. Pulp can be manufactured chemically by cooking or mechanically by 10 grinding and refining. It is also manufactured from waste paper by defiberingit in a pulper. It is common to all pulp manufacturing methods that the pulp contains more or less impurities which have to be removed therefrom.
Pulp is cleaned in a screening plant by means of screens and cleaners.
The screen is apparatus in which pulp is screened by either a slotted screen or 15 a perforated screen in the consistency range of 1 to 5%. The cleaner, normally a so-called centricleaner, is apparatus in which pulp is cleaned by centrifugal force in a low, usually less than 1% consistency.
However, screening involves two problems. Firstly, it is usually desirable after screening to increase the pulp consistency to a range of 10 to 15% for 20 storing or after-treatment. Secondly, handling of the reject is also desirable by either refining or some other method, but usually in a higher consistency than that of screening. In other words, the pulp flows always have to be thickened after screening.
There have been attempts to completely resolve this problem, for 25 example, by raising the consistency to 8 - 15% in the screening equipment.
Efforts have been made in developing both screens and cleaners which would operate in a consistency of about 10%. However, this has succeeded only partially. Screening and cleaning as such are fairly successful in a high consistency, but the separation efficiency of the screens and cleaners 30 substantially decreases when the consistency rises. It can be said therefore that these attempts have replaced one problem with another, i.e. they have eliminated the need for thickening at the cost of reducing the cleaning efficiency.
The present invention comprises a method and apparatus for screening 5 pulp in a pressurized, closed space by screens in the consistency range of 1 to 5% `and by centricleaners in a consistency of less than 1%.
According to the invention and in one aspect thereof, the method is provided of treating pulp in a screening plant of a pulp mill, in which method impurities containing fraction is separated from defibered pulp by screening 10 and/or cleaning, the defibered pulp accepted in such a manner is thickened toa consistency of 10 to 20% and is further fed into further processing, said impurities containing fraction is further treated in the screening plant by screening and defibering to recover from said fraction acceptable fiber materialfor further screening and thickening and for removing non-acceptable impurities 15 from the screening plant after various screening stages. In accordance with the invention, the various pulp screening and/or cleaning stages are effected in a closed, pressurized space in the screening plant and that access of air to the pulp treated is prevented by effecting the thickening stages in a pressurized state at pressure prevailing in the screening and/or clèaning stage immediately 20 preceding said thickening stage or stages, whereby no separate pump is required for thickener or thickeners used in said thickening stage or stages.
The present invention could also be defined in general terms as a method of treating pulp suspension in a s plant of a pulp mill, comprising the steps of:
fractionating said suspension by s or cleaning to produce an impurities 25 containing fraction and an accepted pulp fraction; thickening the accepted pulp fraction to a consistency of about 10 to about 20%; feeding the accepted pulp fraction for further processing thereof; further treating said impurities containing fraction in the s plant by s the fraction in order to obtain acceptable fraction and non-acceptable impurities; thickening the acceptable fraction;
30 removing non-acceptable impurities from the s plant; said s or cleaning beingeffected in a closed, pressurized space in the s plant; preventing access of air B
~3~ 2 0 13 011 to the accepted pulp fraction and to said acceptable fraction by effecting the step of thickening in a pressurized state and at a pressure corresponding to that of the stage immediately preceding the step of thickening, thus eliminatingthe need for a separate pump for pressurizing thickener or thickeners used in 5 said thickening steps.
The present invention also provides apparatus for treating pulp in a screening plant of a pulp mill, said apparatus being comprised of a plurality ofpulp treatment devices, wherein said treatment devices are each closed to ambient atmosphere and are arranged to operate in a pressurized state, the 10 plurality of pulp treatment devices including a pump/thickener combination inwhich the over-pressure required in the thickener of said combination is derivedgenerally solely from the pump of the combination.
The term "apparatus" in describing the present invention may refer to one or more devices disposed in a screening plant.
The method and apparatus according to the invention will be described in closer detail below, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a basic scheme of a screening plant according to the prior art, and Fig. 2 is a scheme of a screening plant according to the method and apparatus of the invention.
Fig. 1 is a basic scheme of a screening plant which is commonly used today. Its construction and operation are described more in detail below. Many other screening diagrams exist, which considerably differ from the details of the diagrams shown in Fig. 1, but Fig. 1 presents the commonly used basic principle of screening. In the accompanying drawings, pumps used in pulp feeding are generally marked with a reference letter P because the pumps themselves have no substantial significance as to the invention.
-4~ 201~011 Pulp is fed in a consistency of about 5% from a pulp storage 1 through a knotter 2 and intermediate tank 3 to screens 4 - 8, which in the embodiment of Fig. 1 are divided into two stages, the first being comprised of screens 4 and 5 and the second of screens 6, 7 and 8. The cleaned pulp from the last 5 screens 6, 7 and 8 is taken to one or more suction filters 9. In the knotter 2, knots and large pieces or the like are separated from the pulp and are further taken to the knot scrubber 10, where acceptable fiber material is separated from the knot pulp and is returned to the intermediate tank 3. The knot material is removed from the knot scrubber 10 and is taken to further 10 treatment, in the embodiment of Figure 1, through a knot silo 11.
Shives, fiber bundles and small impurities or the like are separated from the pulp in screens 4 - 8. The reject from screens 4 and 5 is led into a secondary screen 12 and the accept from said screen 12 is led back into screens 4 and 5 of the first screening stage and the reject directly to a reject15 thickener 14, wherefrom it is further conducted by means of a feed screw 15 to a refining stage 16. Refined pulp from the refiner 15 is led to another secondary screen 17, whose accept is led to cleaners 18. The accept from the cleaners 13 is conducted to either the intermediate tank 18 or directly to the first secondary screen 12. The accept pulp from the screens enters the suction 20 filter in a consistency of 1 to 2%, which prevails aftèr screening, because the suction filter is not capable of handling pulp of a higher inlet consistency, and the pulp is thickened to a consistency of 10 to 15% by drawing water therefrom by means of a gravity-operated drop leg. The inevitable result of thisis that the pulp mill must have, at least for the disposition of suction filters, a 25 storey at a height of about 10 m. Other components of the equipment are disposed in various storeys according to need and space.
Screening as described above involves some problems. Firstly, in thickening of pulp with filters 4 and 8 and also in transfer of pulp, plenty of air is mixed with the pulp and the filtrates, which causes, for example, foaming.
30 Also the building height required by said filters can be considered a significant drawback. If the screening plant could be of pressurized construction and ~5- 2013011 hydrauiically closed so as to prevent any air from mixing with pulp, all above-mentioned drawbacks could be eliminated.
Secondly, a great number of apparatuses is needed. For example, screens are disposed in two successive stages, the first stage comprising two 5 screens connected in parallel and the second stage three screens connected in parallel. A great number of apparatuses are needed because as high as possible separation efficiency is aimed at in each apparatus. In other words, the desiredfraction is attempted to be separated completely from the undesirable fraction, i.e. the idea is to keep the reject ratio as low as possible. This results in that 10 pulp is circulated for a relatively long time in the apparatus, whereby only a fractional part of the maximum capacity of the apparatus is used.
Thirdly, the low consistency of the suspension to be treated constitutes a problem. The low consistency in itself requires a big filter, even if it were not taken into account that the suction filter is by no means the most efficient type 15 of filter when comparing the operating efficiencies of filter surfaces. It can be assumed, for example, that the consistency of the pulp entering the filter is 1.5% and is then raised to 15% at the filter. For the production of 15 tons of dry fiber pulp by the filter, one has to take a total of 100 tons of 15%
suspension out of it. For this result, 900 tons of liquid has to be removed from20 the 1.5% pulp entering the filter. If the consistency of the pulp entering the filter is 3%, only 400 tons of liquid has to be removed and if the inlet consistency is 4.5%, only 233 tons of liquid has to be removed. Thus, if the nominal thickening capacity of the filter remains unchanged, it is possible, by tripling the inlet consistency, to manage with the apparatus whose thickening 25 area is only about a fourth of the thickening area of the thickening apparatus required by low consistency.
Fig. 2 illustrates more in detail a method according to a preferred embodiment of the invention and apparatus needed therefor. Pulp is fed from tank 1 via pump 101 to knotter 2 and through a pump 102 and a screen 21 30 further to a drum thickener means 23. Screening takes place in a consistency range of 1 to 5%, normally in a consistency range of 3 to 5%. The drum -6- 2013~11 displacement means 23 is a drum provided with cells in which the pulp is thickened to a consistency of 10 to 15% at the pressure of inlet pulp. Ambient air is not allowed to enter in the pulp processed. An embodiment of the drum thickener means is disclosed in, for example, US patent 4,502,171.
The reject pulp from the first screen 21 is fed, via pump 103 directly to the second screen 22 whose accept is returned to the first screen 21 and the reject is led, in the embodiment shown, via pump 104 to a pressurized, closed thickener 24 wherefrom pulp in a pressurized state flows without a feed screw to a refiner 25 (also referred to as a ~fiberizer-refiner". Pulp is fed in a low consistency into the thickener 24 and filtrate is removed during turbulence effect. Selection of holes of a suitable size (of diameter 1 - 2 mm) contributesto primary fibers being discharged with the filtrate, and the remaining, thickened reject pulp then flows further to the refining stage. Thus, the refining and thickening of the reject pulp is made at a pressurized condition and no air is mixed with the pulp. An example of the thickener 24 is disclosed in the published Fl patent application 874854. The filtrate from thickener 24 and the filtrate from the drum thickener means 23 are fed by pump 105 together with the pulp to be cleaned to the cleaners 18, and the fraction accepted by these cleaners is conducted to a thickener 26, whose filtrate is also fed to the cleaners 18. Thickener 26 is a pressurized water separator disclosed in the published Fl patent application 873020. Thus, also the pulp cleaning and thickening effected thereafter are provided in a pressurized and closed state.
It is apparent from the above that the arrangement according to the present invention presents certain combinations, series or groupings. For instance, the pump 104 and the thickener 24 present an embodiment of a ~pump/thickener combination." It can be appreciated from the drawing of Fig.
2 that overpressure required at the thickener 24 of said combination is derived solely by the pump 104 of said combination.
Similarly, the combination referred to in the preceding paragraph forms a part of an embodiment of a closed pump 104 / thickener 24 / fiberizer-refiner 25 group so arranged and disposed that the pressure at the fiberizer-refiner 25 B
- ~7~ 2013011 of said group substantially equals an initial pressure at the thickener 24 of said group.
Also, the pump 103, screen 22, cleaner 18, thickener 26, can generally be defined as a pump/screen/cleaner/thickenerseries so arranged and disposed 5 that overpressure required for the operation of the thickener 26 of the seriesis derived solely from the pump of the respective series despite the fact that in the embodiment of Fig. 2 an additional pump 105 may also be employed if desired .
When comparing the equipment illustrated in Fig. 2 above with the 10 equipment of Fig. 1, it can be seen that there are differences in both the number of screens and the methods of thickening. When filtrate is removed in small pressurized thickeners, the layout of the mill is compact and, according to estimate, the required building volume is less than half of the building volume required by a conventional screening plant. The reject handling 15 equipment according to Fig. 1 comprises a suction filter, a feed screw and a refiner itself. Now, the reject handling is managed with a thickener of a considerably smaller size and without a feed screw. The number of cleaners has not substantially changed. The only addition compared with the equipment of Fig. 1 is the thickener 26 for the accept received from the cleaners. It 20 thickens the suspension from the consistency level required by the cleaners to that required by screening. The thickening means are disposed last in the screening plant. According to the present system, two such means, i.e. suction filters, are needed. They shall be of the size 4 x 8 m, where the drum diameter is 4 m and the drum length 8 m. In the system according to the present 25 invention, only one 3.5 x 5 m thickening means is needed.
The function of the system according to the invention is, on the other hand, based on that the screens themselves are dimensioned and the capacity optimized so that the capacity is at its maximum, whereby the reject ratio is relatively high, about 20 to 30%. Thus, the accept from the screens is 30 absolutely clean and suitable as such to be fed directly into the thickener, excluding the secondary screening stage. The task of the second screen 22 is to handle the reject from the first screen 21, i.e. the suspension, which still includes a great amount of acceptable fiber fraction which is returned to the first screen. Thus, screen 22 in a way corresponds to the screen 12 of Fig. 1, which treats the reject from the screens of the first stage.
On the other hand, the function of the method and apparatus according to the invention is based on that the entire screening can be accomplished at an over-pressure so that no external air is allowed to enter the process. This has been achieved by arranging only a few key points of the system with a pumping facility in order to pressurize the treated suspension so that it will be transferred from one means to another by said pressure. More specifically, the screening plant is divided into a number of pump - screen/ cleaner - thickener combinations, in which the feed pressure of each pump is sufficient to maintain over-pressure so that, on one hand, no external gas is allowed to the system and, on the other hand, even the pressure difference required for thickening comes from the pump unit of each combination.
The economical advantages referred to in the beginning of this description are best seen when reviewing the results of the following comparative calculations.
- The energy consumption in a screening plant applying the method and apparatus according to the invention is about 34% less than in a conventional screening plant, - the costs of building and equipment in a pulp mill are distributed asfollows if the reference number 100 refers to costs in a conventional screening plant.
Object Conventional Invention olant pipes 100 61 service platforms 100 60 valves 100 49 pumps 100 74 mixers 100 00 building 100 29 total 100 52 Thus, it will be appreciated that apart from the energy consumption being cut down by a third, the costs of equipment and building, excluding 5 electrification, instrumentation and main equipment, the inclusion of which inthe calculation would cause too much inaccuracy and uncertain estimates, are only about half of corresponding investments in a conventional pulp mill.
As a conclusion, the above describes a process for screening and cleaning pulp in a closed, pressurized space so that the consistency need not 10 be raised at a cost of the cleaning efficiency. No equivalent process has been earlier disclosed, where pulp is screened, cleaned, and reject handled in a closed space so that the cleaning operations themselves are effected in a consistency optimal to them, the pulp still being in a high consistency when it is led to the after-treatment stage. The method and apparatus of the invention 15 are not limited to the embodiment described above, but they cover all the embodiments within the scope of the accompanying claims.
Claims (18)
1. A method of treating pulp in a screening plant of a pulp mill, in which method impurities containing fraction is separated from defibered pulp by screening and/or cleaning, the defibered pulp accepted in such a manner is thickened to a consistency of 10 to 20% and is further fed into further processing, said impurities containing fraction is further treated in the screening plant by screening and defibering to recover from said fraction acceptable fibermaterial for further screening and thickening and for removing non-acceptable impurities from the screening plant after various screening stages, characterized in that the various pulp screening and/or cleaning stages are effected in a closed, pressurized space in the screening plant and that access of air to the pulp treated is prevented by effecting the thickening stages in a pressurized state at pressure prevailing in the screening and/or cleaning stage immediately preceding said thickening stage or stages, whereby no separate pump is required for thickener or thickeners used in said thickening stage or stages.
2. The method as claimed in claim 1, characterized in that the consistency of the pulp being treated is maintained within the range of about 2% to about 5% during the screening stage.
3. The method as claimed in claim 1, characterized in that the pulp is thickened after the cleaning stage prior to being supplied to the screening, thethickening of the pulp being effected at a pressure corresponding to an outlet pressure of the cleaning stage.
4. The method of claim 1, wherein the pulp coming from the screening is thickened at a pressure corresponding to an outlet pressure of the screening,from the consistency of about 2 - 5% to the consistency of about 10 - 20%.
5. The method of claim 1, wherein the reject from the screening and/or cleaning stages is fed at an outlet pressure of the respective screening and/or cleaning stage through a thickening stage and therefrom to a refining stage, the refining stage being carried out at a feed pressure corresponding to an outlet pressure of the thickening stage.
6. The method of claim 1, wherein all thickening operations of the screening plant are carried out at an over-pressure without a suction effect.
7. A system for treating pulp in a screening plant of a pulp mill, said system comprising a plurality of devices including screens, cleaners, thickenersand pumps, characterized in that all said devices are so arranged and disposed in said system that the pulp passing therethrough is isolated from the atmosphere surrounding the system and is maintained under pressure, said system including at least one pump/thickener combination, wherein overpressure required at the thickener of said combination is derived solely by the pump of said combination.
8. The system as claimed in claim 7, further comprising at least one closed pump/thickener/fiberizer-refiner group so arranged and disposed that the pressure at the fiberizer-refiner of said group substantially equals an initial pressure at the thickener of said group.
9. The system of claim 7, further comprising a plurality of pump/screen/cleaner/thickener series so arranged and disposed that overpressure required for the operation of the thickener of the series is derived solely from the pump of the respective series.
10. A method of treating pulp suspension in a screening plant of a pulp mill, comprising the steps of:
(a) fractionating said suspension by screening or cleaning to produce an impurities containing fraction and an accepted pulp fraction;
(b) thickening the accepted pulp fraction to a consistency of about 10 to about 20%;
(c) feeding the accepted pulp fraction for further processing thereof;
(d) further treating said impurities containing fraction in the screening plant by screening the fraction in order to obtain acceptable fraction and non-acceptable impurities;
(e) thickening the acceptable fraction;
(f) removing non-acceptable impurities from the screening plant;
(g) said screening or cleaning being effected in a closed, pressurized space in the screening plant;
(h) preventing access of air to the accepted pulp fraction and to said acceptable fraction by effecting the step of thickening in a pressurized state and at a pressure corresponding to that of the stage immediately preceding the step of thickening, thus eliminating the need for a separate pump for pressurizing thickener or thickeners used in said thickening steps.
(a) fractionating said suspension by screening or cleaning to produce an impurities containing fraction and an accepted pulp fraction;
(b) thickening the accepted pulp fraction to a consistency of about 10 to about 20%;
(c) feeding the accepted pulp fraction for further processing thereof;
(d) further treating said impurities containing fraction in the screening plant by screening the fraction in order to obtain acceptable fraction and non-acceptable impurities;
(e) thickening the acceptable fraction;
(f) removing non-acceptable impurities from the screening plant;
(g) said screening or cleaning being effected in a closed, pressurized space in the screening plant;
(h) preventing access of air to the accepted pulp fraction and to said acceptable fraction by effecting the step of thickening in a pressurized state and at a pressure corresponding to that of the stage immediately preceding the step of thickening, thus eliminating the need for a separate pump for pressurizing thickener or thickeners used in said thickening steps.
11. The method of claim 10, wherein the fractionating includes screening, the consistency of the treated pulp being maintained in the range of 2 to 5% during the step of s.
12. The method of claim 10, wherein the fractionating includes the steps of sscreening by screens and cleaning by vortex cleaners, wherein accepted suspension discharged from the cleaners is thickened prior to being fed to the screens, at a pressure corresponding to an outlet pressure at said cleaners.
13. The method as claimed in claim 10, wherein the accepted pulp fraction coming from a screen or screens of the plant is thickened at a pressurecorresponding to that at a discharge end of said screen or screens.
14. The method as claimed in claim 10, wherein the rejects from a screen or screens of the plant are passed, at the pressure corresponding to thatat a discharge end of said screen or screens, through a thickening stage and therefrom to a refining stage such that the pressure at the refining stage corresponds to the pressure at an outlet of the thickening stage.
15. The method of claim 10, wherein all thickening operations of the plant are carried out at an over-pressure while preventing a suction effect at the stock being thickened, whereby air is prevented from penetrating into the stock thickened.
16. Apparatus for treating pulp in a screening plant of a pulp mill, said apparatus being comprised of a plurality of pulp treatment devices, wherein said treatment devices are each closed to ambient atmosphere and are arranged to operate in a pressurized state, the plurality of pulp treatment devices including a pump/thickener combination in which the over-pressure required in the thickener of said combination is derived generally solely from the pump of the combination.
17. Apparatus as claimed in claim 16, wherein the screening plant comprises at least one closed group comprised of a pump, a thickener and a fiberizer/refiner said group being arranged for operating in a pressurized state, the group being so arranged and disposed that feed pressure at the refiner of said group substantially equals the inlet pressure of the thickener of said group.
18. Apparatus as claimed in claim 16, wherein the screening plant comprises a number of closed combinations, each closed combination comprising a pump, a screen or a cleaner or both, a thickener, each closed combination being so arranged and disposed that the over-pressure needed in each respective thickener is derived from the pump unit of respective combination.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI891484A FI82082C (en) | 1989-03-29 | 1989-03-29 | FOERFARANDE OCH ANORDNING FOER BEHANDLING AV MASSA. |
| FI891484 | 1989-03-29 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2013011A1 CA2013011A1 (en) | 1990-09-29 |
| CA2013011C true CA2013011C (en) | 1995-09-26 |
Family
ID=8528130
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002013011A Expired - Fee Related CA2013011C (en) | 1989-03-29 | 1990-03-26 | Method and means for treating pulp |
Country Status (5)
| Country | Link |
|---|---|
| US (2) | US5112444A (en) |
| EP (1) | EP0390403A3 (en) |
| JP (1) | JPH086273B2 (en) |
| CA (1) | CA2013011C (en) |
| FI (1) | FI82082C (en) |
Families Citing this family (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5794791A (en) * | 1987-11-30 | 1998-08-18 | Genesis Research Corporation | Coal cleaning process |
| CA1327342C (en) * | 1987-11-30 | 1994-03-01 | James Kelly Kindig | Process for beneficiating particulate solids |
| DE4041105A1 (en) * | 1990-12-21 | 1992-06-25 | Toepholm & Westermann | METHOD FOR PRODUCING INDIVIDUALLY ADAPTED OTOPLASTICS OR EARPIECES TO THE CONTOURS OF AN EAR CHANNEL |
| US5405499A (en) * | 1993-06-24 | 1995-04-11 | The Procter & Gamble Company | Cellulose pulps having improved softness potential |
| US5453159A (en) * | 1993-11-04 | 1995-09-26 | International Paper Company | Deinking of recycled pulp |
| US5575395A (en) * | 1994-07-15 | 1996-11-19 | A. Ahlstrom Corporation | Method and apparatus for screening fibrous suspensions |
| US5679218A (en) * | 1994-07-29 | 1997-10-21 | The Procter & Gamble Company | Tissue paper containing chemically softened coarse cellulose fibers |
| CA2158522C (en) * | 1994-09-19 | 2001-04-10 | Daniel R. Roll | Mixer for mixing multi-phase fluids |
| US6174410B1 (en) * | 1995-02-14 | 2001-01-16 | Julia Innotec Gmbh | Process apparatus for recovering raw materials from paper mill effluents |
| FI97736C (en) * | 1995-03-07 | 1997-02-10 | Ahlstrom Machinery Oy | Method and apparatus for handling filler-containing material, such as recycled fiber |
| MY112041A (en) * | 1995-04-21 | 2001-03-31 | Matsushita Electric Ind Co Ltd | A method for managing defects in an information recording medium, and a device and information recording medium using said method |
| FI112385B (en) * | 1998-09-23 | 2003-11-28 | Andritz Oy | Method and apparatus for treating pulp |
| FI109548B (en) * | 2000-04-19 | 2002-08-30 | Pom Technology Oy Ab | Paper pulp cleaning arrangement |
| KR20030010485A (en) * | 2002-03-28 | 2003-02-05 | 주식회사 피엠시코리아 | Automatic Modular Cleaner System |
| SE528924C2 (en) * | 2004-11-16 | 2007-03-20 | Metso Paper Inc | Method of treating a fiber suspension |
| US20100175840A1 (en) * | 2007-06-12 | 2010-07-15 | Hart Peter W | High yield and enhanced performance fiber |
| US20080308239A1 (en) | 2007-06-12 | 2008-12-18 | Hart Peter W | Fiber blend having high yield and enhanced pulp performance and method for making same |
| WO2008153565A1 (en) | 2007-06-12 | 2008-12-18 | Meadwestvaco Corporation | A fiber blend having high yield and enhanced pulp performance and method for making same |
| FI123023B (en) * | 2009-09-01 | 2012-10-15 | Andritz Oy | Method and apparatus for separating soap |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1933609A (en) * | 1932-02-17 | 1933-11-07 | J O Ross Engineering Corp | Multiple stage pulp washer |
| US3237763A (en) * | 1962-07-06 | 1966-03-01 | Wikdahl Nils Anders Lennart | Method and apparatus for concentrating fibrous suspensions |
| CA887765A (en) * | 1969-11-21 | 1971-12-07 | Cowan Ben | Pulp screening machine |
| DE2701737B2 (en) * | 1977-01-18 | 1980-03-20 | Hermann Finckh Maschinenfabrik Gmbh & Co, 7417 Pfullingen | Process for the preparation and cleaning of fiber material as well as an installation for carrying out such a process |
| FI62872C (en) * | 1978-06-06 | 1983-03-10 | Ahlstroem Oy | ANORDNING FOER SILNING AV FIBERSUSPENSIONER |
| CA1173603A (en) * | 1980-12-31 | 1984-09-04 | Kamyr, Ab | Pressure diffuser controlling |
| SE431571C (en) * | 1982-07-02 | 1985-04-21 | Nils Anders Lennart Wikdahl | SET FOR CLEANING A FIBER SUSPENSION |
| FI65829C (en) * | 1982-08-06 | 1984-07-10 | Enso Gutzeit Oy | FORM OF CELLULOSE TV |
| SE451736B (en) * | 1983-09-19 | 1987-10-26 | Nils Anders Lennart Wikdahl | WHEN WATERING A WATER SUSPENSION CONTAINING CELLULOSA FIBERS |
| DE3605259C1 (en) * | 1986-02-19 | 1987-07-02 | Finckh Maschf | Process and installation for removing color particles from a fiber suspension obtained from waste paper |
| CA1330174C (en) * | 1987-07-08 | 1994-06-14 | Toivo Niskanen | Method and apparatus for thickening fiber suspension |
| SE461104B (en) * | 1988-05-05 | 1990-01-08 | Kamyr Ab | DEVICE FOR DIVISION OF A SUSPENSION OF A FIBER-CELLULOUS CELLULOSAMASSA |
| SE464640B (en) * | 1988-06-16 | 1991-05-27 | Kamyr Ab | DEVICE FOR SILENCE OF A SUSPENSION OF A FIBER CELLULOSAMASSA |
-
1989
- 1989-03-29 FI FI891484A patent/FI82082C/en not_active IP Right Cessation
-
1990
- 1990-03-20 EP EP19900302992 patent/EP0390403A3/en not_active Ceased
- 1990-03-26 CA CA002013011A patent/CA2013011C/en not_active Expired - Fee Related
- 1990-03-28 US US07/500,475 patent/US5112444A/en not_active Expired - Fee Related
- 1990-03-29 JP JP2082895A patent/JPH086273B2/en not_active Expired - Lifetime
- 1990-08-24 US US07/573,388 patent/US5147504A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0390403A3 (en) | 1991-09-18 |
| FI82082B (en) | 1990-09-28 |
| JPH0351390A (en) | 1991-03-05 |
| JPH086273B2 (en) | 1996-01-24 |
| FI891484A0 (en) | 1989-03-29 |
| US5112444A (en) | 1992-05-12 |
| FI82082C (en) | 1991-12-10 |
| US5147504A (en) | 1992-09-15 |
| EP0390403A2 (en) | 1990-10-03 |
| CA2013011A1 (en) | 1990-09-29 |
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Legal Events
| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |