Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
  • D21B1/00—Fibrous raw materials or their mechanical treatment
  • D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
  • D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
  • D21B1/14—Disintegrating in mills
  • D21B1/16—Disintegrating in mills in the presence of chemical agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone

Definitions

• the present invention relates to a method for manufacturing mechanical pulp.
• Publication Fl 61926 and corresponding publication DE 2444475 disclose a process in which pulp is treated with ozone. It is possible that the pH of the pulp is adjusted after the ozonation.
• Publication Fl 67412 and corresponding publication CA 1083870 disclose a process in which pulp is fractionated and one fraction, possibly the coarse fraction, is treated with ozone. During the ozonation alkali is fed into the process.
• a problem related to the ozonation process is that it produces strong organic acids.
• the organic acids lower the pH of the pulp, which causes problems in a bleaching process, e.g. by precipitating ferrous substances from the process water.
• the organic acids also deteriorate process devices by causing corrosion.
• the above-mentioned drawbacks can be overcome by the method of the invention.
• the method comprises
• raw material of the mechanical pulp is introduced in a process.
• the raw material can be softwood species, such as pine (Pinus sylvest ⁇ s), Southern pine (genus Pinus, several different species), spruce (Picea abies), or mixtures of pine and spruce. Hardwood species and their mixtures with softwood species are also possible raw materials.
• the raw material can be in form of wood chips.
• the starting raw material can also be logs which are ground in a PGW (pressure groundwood) process.
• the raw material such as wood chips, which are dewatered in order to reach a consistency which is from 25 % to 35 %, typically 30 %, is fed in a refiner in which it is refined in a first refining stage.
• the refiner can be a disc refiner or a disc refiner with a conical section.
• the raw material is refined at an elevated temperature and under pressure in the refiner in order to form mechanical pulp.
• the first refining stage can also be accomplished by a hammer mill.
• the preferred raw material is pine because the method of the invention is the most advantageous compared to other processes when the raw material is pine. It is commonly known that the refining ability of pine is poor. However, by using ozone it can be improved. Pulp treated with ozone contains less fines and shives compared to pulp which is not treated with ozone. The ozone treatment has also a beneficial effect on a pitch removal which is important in connection with the pine raw material.
• the first stage refining is rather mild; the pulp is refined to a freeness of 600 - 700 ml CSF.
• the upper limit can be even higher than 700 ml CSF.
• the pulp can be sorted to a first accepted stock and a first rejected stock, and the rejected stock is led to the alkali treatment reactor.
• the whole mechanical pulp is led to the alkali treatment reactor in order to achieve a certain pH level.
• the mechanical pulp is treated with alkali, such as sodium hydroxide (NaOH), sodium bicarbonate (Na 2 CO 3 ), magnesium hydroxide (Mg(OH) 2 ), or calcium hydroxide (Ca(OH) 2 ).
• alkali such as sodium hydroxide (NaOH), sodium bicarbonate (Na 2 CO 3 ), magnesium hydroxide (Mg(OH) 2 ), or calcium hydroxide (Ca(OH) 2 ).
• the process in the alkali treatment reactor is arranged so that there is a process delay, i.e. the pulp stays in the reactor for at least 0.5 hours, typically from 1 to 2 hours.
• the process delay is necessary because the alkali should penetrate from the surface of the fibers of the pulp to the inner parts of the fibers (or fiber aggregates, depending on how coarse the pulp is), i.e. also the inner parts of the fibers and/or fiber aggregates shall
• the pulp After the pulp is treated in the alkali treatment reactor, it is led to a sorter, such as a screen or a cyclone.
• the pulp is sorted to a first accepted stock and a first rejected stock.
• the sorting step takes place in a consistency of from 0.5 to 1.5 percent, typically about one percent, and the first accepted stock remains in that consistency after sorting.
• the ratio accepted stock / rejected stock may be approximately 20/80.
• the ratio accepted stock / rejected stock may also be 60/40 or 50/50.
• the accepted stock may be between 20 and 60 percent of the total amount of the pulp, or even between 15 and 65 percent of the total amout of the pulp.
• the first rejected stock is first dewatered so that the consistency of the first rejected stock is preferably higher than 30 %.
• the consistency is more preferably higher than 35 %.
• Excess liquid is circulated back to the process.
• the first rejected stock is led in the above-mentioned consistency to an ozone reactor in which the first rejected stock is fluffed and ozonated.
• the ozonation process is arranged so that the amount of ozone is between 0.5 and 10 % and preferably between 1 and 4 % of the weight of the pulp.
• the process temperature is between 20 and 90 0 C. Strong organic acids form in the ozonation process, but the alkali by which the first rejected stock has been treated neutralizes those strong organic acids.
• the strong organic acids and the alkali form a buffer solution whose pH can be kept on a certain level for a long time although the ozonation process constantly produces organic acids.
• the pH of the rejected stock is between 5 and 7, which is a beneficial range in regard to the following process steps.
• the first rejected stock is refined in a main line refining which may comprise sequential refiners. It is possible that that the first rejected stock is sorted to a second accepted stock and a second rejected stock.
• the second rejected stock can be conveyed for further refining, i.e. to a third refining stage, but it is also possible that it is just removed from the process. If there is the third refining stage it is accomplished in the same manner as the preceding refining stages.
• the first accepted stock and the accepted amount of the first rejected stock are combined after the above-mentioned process stages.
• the accepted amount of the first rejected stock refers to all accepted stocks which have been obtained after the pulp has been sorted to the first accepted stock and the first rejected stock.
• the first accepted stock is treated with ozone and the ozone treated pulps are combined. It is also possible that some alkali is added to the first accepted stock after it has been treated with ozone. The alkali may be the same that is added before the ozonation. Further, it is possible that the accepted stock which has not been ozonated is treated with the alkali before it is combined with the accepted amount of the first rejected stock.
• the freeness of the resulting stock may be between 90 and 150 ml CSF but it is also possible that the lower limit is 30 or 40 ml CSF. Naturally, the above- mentioned freeness depends on the desired paper quality.
• the pulp is sorted in a sorter, such as a screen or a cyclone, to a first accepted stock and a first rejected stock.
• the consistency in the sorter is between 1 and 2 %.
• the ratio accepted stock / rejected stock may be approximately 20/80.
• the ratio accepted stock / rejected stock may also be 60/40 or 50/50.
• the accepted stock may be between 20 and 60 percent of the total amount of the pulp, or even between 15 and 65 percent of the total amount of the pulp.
• the first rejected stock is treated with alkali, such as sodium hydroxide (NaOH), sodium bicarbonate (Na 2 CO 3 ), magnesium hydroxide (Mg(OH) 2 ), or calcium hydroxide (Ca(OH) 2 ), in an alkali treatment reactor.
• alkali such as sodium hydroxide (NaOH), sodium bicarbonate (Na 2 CO 3 ), magnesium hydroxide (Mg(OH) 2 ), or calcium hydroxide (Ca(OH) 2
• the pH of the first rejected stock is elevated to a level which is between 9 and 11 depending on the ozone amount to be applied and the raw material to be treated.
• After that liquid is removed from the first rejected stock so that a consistency which is preferably higher than 30 % is achieved.
• the consistency is more preferably higher than 35 %. Excess liquid is circulated back to the process.
• the first rejected stock is led in the above-mentioned consistency to an ozone reactor in which the first rejected stock is fluffed and ozonated.
• the ozonation process is arranged so that the amount ozone is between 0.5 and 10 % and preferably between 1 and 4 % of the weight of the pulp.
• the process temperature is between 20 and 90 0 C.
• Strong organic acids form in the ozonation process, but the alkali by which the first rejected stock has been treated neutralizes those strong organic acids.
• the strong organic acids and the alkali form a buffer solution whose pH can be kept on a certain level for a long time although the ozonation process constantly produces organic acids.
• the pH of the rejected stock is between 5 and 7, which is a beneficial range in regard to the following process steps.
• the first rejected stock is led to a refiner in order to accomplish a second refining stage.
• the first rejected stock is conveyed from the refiner to a sorter which sorts the first rejected stock to a second accepted stock and a second rejected stock.
• the freeness of the accepted stocks i.e. the stock consisting of the first accepted stock and the second accepted stock, may be between 90 and 150 ml CSF but it is also possible that the lower limit is 30 or 40 ml CSF. Naturally, the above-mentioned freeness depends on the desired paper quality.
• the second rejected stock can be conveyed for further refining, i.e. to the third refining stage, but it is also possible that it is just removed from the process. If there is the third refining stage, it is accomplished in the same manner as the preceding refining stages.
• the first accepted stock may be removed from the process and used for other purposes, but it is also possible that the first accepted stock and the second accepted stock are combined so that they can be led as one stock to the following process step, which is usually a bleaching step.
• the stock obtained from the second refining stage has a pH that is between 5 and 7, and the first accepted stock has about the same pH, so no further steps are required to adjust the pH level.
• Harmful wood extractives are soluble in the water in which the alkali is added.
• the mechanical pulp obtained from the present method (the above- mentioned first and second main options) is utilized in a paper product manufacturing process.
• the paper product may be a paper containing mechanical pulp, such as a printing paper containing mechanical pulp, or it may be a cardboard.
• Fig. 1 shows a schematic view of a first process
• Fig. 2 shows a schematic view of a second process
• Fig. 3 shows schematic views of third and fourth processes
• Fig. 4 shows tensile index as a function of SEC (specific energy consumption).
• Fig. 5 shows tear index as a function of tensile index.
• Points 1 and 2 correspond to the results achieved from a normal TMP refining in which pine is used as the raw material.
• Point 5 in Figs. 5 and 6 corresponds to the results achieved from a process in which an ozonated pine reject is mixed with a non-ozonated pine accept. No alkali is added.
• Point 7 in in Figs. 5 and 6 corresponds to the results achieved from a process in which an ozonated pine reject is mixed with an ozonated pine accept. No alkali is added.
• Raw material of mechanical pulp is first dewatered, for example, in a thickener 1 , such as a screw press, and after that the raw material is fed into a refiner 2, in which the raw material, such as pine chips, is refined in a first stage refining at an elevated temperature and under pressure in order to form mechanical pulp.
• the consistency during the refining is about 30 %.
• the preferred raw material is pine because the method of the invention is the most advantageous compared to other processes when the raw material is pine.
• the first stage refining is rather mild; The pulp is refined to a freeness of 600 - 700 ml CSF. It is possible that the freeness value is even higher than 700 ml CSF.
• the pulp is treated with an alkali, such as sodium hydroxide, in an alkali treatment reactor 3.
• the pH of the first rejected stock is elevated to a level which is between 9 and 11.
• There is a delay in the alkali treatment reactor 3 so that the pulp remains inside the alkali treatment reactor for at least 0.5 hours, typically from 1 to 2 hours.
• the pulp is also diluted in the alkali treatment reactor so that its consistency is between 0.5 and 1.5 %.
• the pulp is sorted in a sorter 4, such as a screen, to a first accepted stock A1 and a first rejected stock R1.
• a sorter 4 such as a screen
• the ratio accepted stock / rejected stock is approximately 20/80, but also other ratios, which are described in the general description, are suitable .
• the first rejected stock R1 is led to a thickener 5, such as a screw press, which removes liquid from the stock in such a manner that a consistency which is higher than 35 % has been achieved. Excess liquid 9 is circulated back to the process.
• the first rejected stock R1 is led in the above-mentioned consistency to an ozone reactor 6 in which the first rejected R1 stock is ozonated. Strong organic acids form in the ozonation process but the alkali by which the first rejected stock has been treated neutralizes those strong organic acids.
• the strong organic acids and the alkali form a buffer solution whose pH can be kept on a certain level for a long time although the ozonation process constantly produces organic acids.
• the pH of the rejected stock is between 5 and 7, which is a beneficial range in regard to the following process steps.
• the first rejected stock R1 is led to a refiner 7.
• the first rejected stock R1 has been treated with ozone, its properties have been changed so that the refining stage consumes much less energy compared to stocks which are not treated with ozone.
• the first rejected stock R1 may be conveyed from the refiner 7 to another refiner 8. It is also possible that the first rejected stock is led to a sorter (not shown) which sorts the first rejected stock to a second accepted stock and a second rejected stock.
• the second rejected stock can be conveyed for further refining but it is also possible that it is just removed from the process.
• the first accepted stock and the accepted amount of the first rejected stock may be combined after the first rejected stock has been treated in the above- mentioned manner so that they can be led as one stock to the following process step, which is usually a bleaching step.
• the obtained stock has the pH which is between 5 and 7.
• Raw material of mechanical pulp is first dewatered, for example, in a thickener 1 , such as a screw press, and after that the raw material is fed into a refiner 2, in which the raw material, such as pine chips, is refined in a first stage refining at an elevated temperature and under pressure in order to form mechanical pulp.
• the consistency of the pulp is about 30 %.
• the preferred raw material is pine because the method of the invention is the most advantageous compared to other processes when the raw material is pine.
• the first stage refining is rather mild; the pulp is refined to a freeness of 600 - 700 ml CSF.
• the pulp is treated with an alkali, such as sodium hydroxide, in an alkali treatment reactor 3.
• the pH of the first rejected stock is elevated to a level which is between 9 and 11.
• the pulp is diluted to a consistency which is between 0.5 and 1.5 %.
• the pulp is sorted in a sorter 4, such as a screen, to a first accepted stock A1 and a first rejected stock R1.
• a sorter 4 such as a screen
• the ratio accepted stock / rejected stock is approximately 20/80, but also other ratios are suitable.
• the first rejected stock R1 is led to a thickener 5, such as a screw press, which removes liquid from the stock in such a manner that a consistency which is higher than 35 % has been achieved. Excess liquid 9 is circulated back to the process.
• the first rejected stock R1 is led in the above-mentioned consistency to an ozone reactor 6 in which the first rejected R1 stock is ozonated.
• the amount of ozone is between 0.5 and 10 % and preferably between 1 and 4 % of the weight of the pulp.
• the temperature during the ozonation is between 20 0 C and 90C°.
• the first rejected stock R1 is led to a refiner 7.
• the first rejected stock R1 may be conveyed from the refiner 7 to another refiner 8. It is also possible that the first rejected stock is led to a sorter (not shown) which sorts the first rejected stock to a second accepted stock and a second rejected stock.
• the second rejected stock can be conveyed for further refining, but it is also possible that it is just removed from the process.
• the first accepted stock A1 is led to an ozone reactor 11 at a consistency which is between 0.5 and 1.5 %.
• the first accepted stock A1 is ozonated in the ozone reactor 11. Ozone may be injected to the first accepted stock A1.
• the first accepted stock A1 and the accepted amount of the first rejected stock R1 are combined after the first stocks have been treated in the above- mentioned manner so that they can be led as one stock to the following process step, which is usually a bleaching step.
• the obtained stock has a pH which is between 5 and 7.
• the third process is similar to that in example 2, except that the first accepted stock is treated with alkali after the ozonation in a mixing reactor 13.
• the amount of the alkali was 0.5 wt.-% of the total amount of the dry first accepted stock (for example, 0.5 wt.-% of 100 % NaOH).
• a process delay is arranged to the mixing reactor 13. The pulp stays in the reactor 13 at least for 0.5 hours.
• Point 8 in Figs. 4 and 5 corresponds to the result which is achieved from the above-described process option.
• the fourth process is described by referring to Fig. 3.
• the fourth process is similar to that in example 2, except that the first accepted stock is treated with alkali after the ozonation in a mixing reactor 13.
• the amount of the alkali was 2 wt.-% of the total amount of the dry first accepted stock (for example, 2 wt.-% of 100 % NaOH).
• a process delay is arranged to the mixing reactor 13. The pulp stays in the reactor 13 at least for 0.5 hours.

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• 2006
  • 2006-12-28 FI FI20065860A patent/FI119062B/fi not_active IP Right Cessation
• 2007
  • 2007-12-27 CA CA2633800A patent/CA2633800C/en not_active Expired - Fee Related
  • 2007-12-27 WO PCT/FI2007/050721 patent/WO2008081078A1/en active Application Filing
  • 2007-12-27 EP EP07858372.1A patent/EP2097582A4/de not_active Withdrawn
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