Classifications

• • 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
  • D21C9/001—Modification of pulp properties
  • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
  • D21C9/004—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives inorganic compounds
• • 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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D1/00—Methods of beating or refining; Beaters of the Hollander type
  • D21D1/20—Methods of refining
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/70—Inorganic compounds forming new compounds in situ, e.g. within the pulp or paper, by chemical reaction with other substances added separately

Definitions

• the invention relates to a method for reducing the energy consumption at the refining of a pulp suspension in a papermaking process and use of non- stoichiometric sodium bicarbonate in this papermaking process.
• Refining is one of the most important unit operations when preparing papermaking fibers for high-quality papers or paperboards. Refining is of importance both to the properties of mechanical pulp and to those of chemical pulp.
• the chemical environment, like pH and various metal ions etc. during refining and sheet forming, is known to have an influence on the final sheet properties.
• US 5,007,985 discloses a process using alkali with the cellulose-containing material for neutralizing acid groups bonded to the fiber wall for reducing the energy consumption during the refining.
• US 5,454,907 discloses a method for treatment of chemical pulp in the papermaking wherein the energy consumption is reduced by using a refining assisting agent comprising sulfonated chitosan.
• WO 2004/053224 discloses a method for treatment of chemical pulp wherein a refining assisting agent comprises a complexing agent.
• An object of the present invention is to provide the refining of a pulp suspension in a papermaking process wherein the refining is an energy efficient process.
• Another object of the invention is to provide for the refining a papermaking pulp suspension having a decreased calcium hardness value.
• An object of the invention is also to provide for the refining a pulp suspension having a controlled pH which is maintained at a desired level.
• a further object of the invention is to enable refining at optimum conditions regarding pH, ion concentration and related electrical properties of the pulp suspension.
• An object of the invention is also to provide a refining which improves the paper quality as regards strength and/or porosity.
• the present invention relates to a method for reducing the energy consumption at the refining of a pulp suspension in a papermaking process.
• the method is characterized in that a pulp suspension containing solid calcium carbonate is treated with non-stoichiometric sodium bicarbonate for providing in said pulp suspension, as it enters said refining a calcium hardness value below 10 °dH.
• the reducing of the energy consumption is provided by treating said pulp suspension with sodium bicarbonate. Due to the treatment with sodium bicarbonate the calcium hardness value of the said pulp suspension is decreased to a level having an advantageous effect on the energy consumption and at the same time the pH value is adjusted and maintained at the desired level in the refining and preferably also throughout the subsequent paper making.
• the hardness value of a pulp suspension is, after a diluting with process water, 10 °dH or higher. This has been found to cause increased energy consumption at refining.
• the process water from the paper machine used in the diluting contains some solid calcium carbonate used as filler when the paper was produced. For instance, in a non-integrated mill, dry pulp is slushed using process water for dilution. The process water is circulated to slushing. Each time the water comes into contact with the acidic pulp or acidic process chemicals dissolve, which leads to fioormation of free calcium ions. The accumulation of calcium ions due to recirculation of process water causes an even increasing hardness value. This, in turn has been found to increase the energy consumption at refining.
• the calcium hardness value can be decreased below 10 °dH, preferably below 7 °dH, by treating the pulp suspension with non-stoichiometric sodium bicarbonate solution.
• the treatment of the pulp suspension with non-stoichiometric sodium bicarbonate is performed before the refining.
• the sodium bicarbonate solution is produced by reacting gaseous carbon dioxide and aqueous sodium hydroxide.
• the ratio is typically between 0.5 and 2.0, preferably between 1.2 and 1.7, and most preferably 1.4 and 1.6, respectively.
• the carbon dioxide and sodium hydroxide feeds may be added to the pulp suspension in a pulper or a storage tower, or to the process water used in the dilution.
• the sodium bicarbonate comprises non-stoichiometric sodium bicarbonate produced by adding carbon dioxide and sodium hydroxide separately or simultaneously to the pulp suspension.
• the suspension may, for instance, be treated as it flows in a pipe leading to a pulp dumping chest or the like.
• the feeding of sodium bicarbonate obtained by the addition of carbon dioxide and sodium hydroxide in this way corresponds to the one obtainable by an addition of dissolved sodium bicarbonate, but has the advantage that the space consuming and messy handling of solid sodium bicarbonate is avoided.
• Sodium hydroxide is a chemical which is abundantly available in the paper mill since it is used for many other purposes. Carbon dioxide gas may be generated on site or may be bought as desired. Feeding of carbon dioxide into the suspension is technically clean and easy.
• the carbon dioxide is preferably in gaseous form, although it may be added as an aqueous liquid by dissolving gaseous or solid carbon dioxide in water. Carbon dioxide and sodium hydroxide may be added separately or simultaneously to the pulp suspension or to the process water used in the dilution.
• a further advantage resides in the treatment with non-stoichiometric sodium bicarbonate in that the pH value can be adjusted and maintained also by providing a suitable ratio of carbon dioxide to sodium hydroxide.
• the ratio should be sufficient to provide a significant buffering effect at a pH value between 6.0 and 8.0.
• Processes for stabilizing the pH of a pulp suspension at a desired pH level are disclosed in US 6,991,705 and US 7,175,759. These processes are suitable for adjusting the pH value also in the present invention.
• the pulp suspension is preferably buffered by carbon dioxide and sodium hydroxide combination to a pH value below 8.0 and above 6.0, preferably below 7.3 and above 6.8.
• the electrical properties of the pulp suspension will also change.
• the pH and reduced calcium carbonate dissolution affects not only the cation concentration (Ca 2+ ) but also influences other electrical properties such as the z-potential of the pulp suspension.
• the reduced amount of positively charged calcium ions which compete with cationic chemicals to absorb onto the fibers, the amount of cationic chemicals which can be adsorbed onto the fibers increases and thus, e.g. it will be easier to apply the desired amount of cationic starch to the paper.
• the energy consumption at the refining may be reduced by 25 to 70 % compared to the refining of a similar suspension having the same pH but without being treated with said non- stoichiometric sodium bicarbonate.
• Refining is used by mills e.g. to improve the strength of the fibers and thus the strength of the paper produced from the refined pulp suspension.
• the porosity of the paper may be controlled by refining the pulp. Papermakers may set a target porosity to obtain paper having a desired printability and/or coating hold-out.
• the pulp suspension may be bleached or unbleached, chemical or mechanical pulp.
• Calcium carbonate may advantageously be used as filler for the pulp after the refining, since the stabilized pH will ascertain that the filler remains in solid form in the suspension. Less dissolved calcium carbonate also provides a paper with less problems with pinholes since there is less gas formed in the process. Solid calcium carbonate may also enter the process by being added as filler or enters the process as filler and/or coating pigment of reclaimed fiber. The reclaimed fiber typically comprises also broke.
• the present invention also relates to a method for reducing the energy consumption at the refining of a pulp suspension in a papermaking process, said method comprising the steps of: - providing a pulp suspension containing solid calcium carbonate at a first pH value;
• the present invention relates also to the use of non-stoichiometric sodium bicarbonate for reducing the energy consumption at the refining of a pulp suspension in a papermaking process and furthermore to the use of non-stoichiometric sodium bicarbonate for increasing the strength of paper produced from a refined pulp suspension.
• the invention also relates to the use of sodium bicarbonate for decreasing the porosity of paper produced from a refined pulp suspension.
• the hardness value is clearly reduced by using sodium bicarbonate at refining.
• the results significantly show that the energy consumption at the refining is reduced.
• a laboratory refining trial was performed to test the influence of the reduced hardness obtainable by sodium bicarbonate.
• 500 g of hardwood kraft pulp was soaked and disintegrated in water.
• the hardness of the aqueous pulp was adjusted so that the final hardness was 3 or 22 °dH, respectively.
• the pH of both pulps was 6.8.
• the conductivity was the same for both hardness levels.
• Refining was performed on pulp samples of each hardness level at 0.5 kW during O, 3, 6 and 10 minutes. This corresponds to a specific refining energy of 0, 50, 100 and 166.7 kWh/t, respectively.
• the samples were diluted with soft fresh water for sheet forming. Prior to sheet forming, the hardness of the samples was adjusted so that they all had the same hardness at sheet forming.
• a paper mill produces high quality paper for printing from kraft pulp.
• the pulp is refined before web forming in order to increase the surface strength of the paper.
• the paper strength is monitored and the refining is adjusted to reach a desired surface strength, which will ensure that there will be no problems with picking during printing.
• Calcium carbonate is used as filler in the paper production.
• a non-stoichiometric NaHCO 3 solution is produced from carbon dioxide and sodium hydroxide in a reactor and the solution is added to the pulp suspension before refining.
• the addition of sodium bicarbonate reduces the concentration of calcium ions in the suspension due to reduced dissolution of solid filler CaCO 3 .
• Sodium bicarbonate is added in an amount which provides, in the resulting pulp suspension, a hardness value below 10 °dH. When the reduced hardness pulp is refined, the energy consumption at refining to the same paper surface strength as before the sodium bicarbonate addition is reduced.
• the desired surface strength is achieved with significantly less refining energy.
• the savings in refining energy vary between 12 and 30%, depending on paper grade.
• Example 4 A mill controls the porosity of its paper by refining the pulp to obtain a target porosity.
• the pulp is refined in 3 refiners.
• Calcium carbonate is used as filler and some of it is dissolved as a result of the pulp being slightly acidic and some process chemicals being acidic.
• the hardness of the pulp varies between 15 and 20 °dH during refining. In the short circulation the hardness is even higher.
• the mill changes its process and starts adding sodium bicarbonate according to the invention into the process in order to reduce the number of refiners and the energy of the refining.
• the sodium bicarbonate is adjusted so as to provide a hardness value between 4 and 8 °dH during refining.
• the hardness in the short circulation is also lowered to below 10 °dH.
• the paper has significantly less problems with pinholes since there are fewer problems with gas formed in the process.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Inorganic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=38009954

Family Applications (1)

Country Status (3)

Families Citing this family (11)

Family Cites Families (9)

• 2007
  • 2007-04-30 FI FI20075301A patent/FI120651B/fi not_active IP Right Cessation
• 2008
  • 2008-04-30 WO PCT/EP2008/055340 patent/WO2008132228A1/en active Application Filing
  • 2008-04-30 EP EP08749924A patent/EP2140064A1/de not_active Withdrawn

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events