Patent Publication Number: US-2007119561-A1

Title: Method and apparatus of the prepartion of a fibrous stock suspension

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This is a continuation of PCT application No. PCT/EP2005/005863, entitled “METHOD AND DEVICE FOR PREPARING A FIBROUS MATERIAL SUSPENSION”, filed Jun. 1, 2005. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to SC paper which is produced from a fibrous stock suspension containing fibers which are partially loaded with ash. The invention also relates to news print and to wood-free uncoated (WFU) papers which are also produced from a fibrous stock suspension containing fibers which are partially loaded with ash.  
      2. Description of the Related Art  
      With papers which are produced in accordance with the current state of the art the observation is made that the ash retention in the wire section clearly decreases with increasing ash content. This creates an undesirable contamination of the water circuits inside the machine and the requirement for additional retention agent increases, thus affecting the formation of the paper. Also, the initial wet-strength diminishes with increasing ash content. This limits the rate with which the fiber web can be produced.  
      Another disadvantageous aspect is the dusting of the paper during offset or laser printing, especially with uncoated papers (SC-paper, newsprint, WFU paper). This causes contamination of the print units, thereby necessitating regular clean-up and down-times of the printing press or the copier.  
      Methods for the processing of a fibrous stock suspension according to the Fiber-Loading-Technology are already known from DE 101 13 998 A1 and DE 102 04 254 A1.  
      What is needed in the art is to increase the ash content in the above referenced paper types, however without the occurrence of the previously described negative paper characteristics.  
     SUMMARY OF THE INVENTION  
      For SC paper of the type described at the beginning, the present invention provides that the ash content in the SC-paper fiber web which was produced from the fibrous stock suspension is higher than 35%, preferably higher than 39%.  
      For newsprint of the type described at the beginning, the present invention provides that the ash content of the news print fiber web which was produced from the fibrous stock suspension is higher than 15%, preferably higher than 19%.  
      For wood-free paper of the type described at the beginning, the present invention provides that the fiber web of the wood-free, uncoated paper which was produced from the fibrous stock suspension is higher than 15%, preferably higher than 19%.  
      The present invention permits maximization of the ash content in a paper, thereby providing economic and qualitative advantages. Ash is cheaper than fibrous stock and at the same time advantageous for the optical characteristics of whiteness and opacity.  
      It has been found that, given the same retention agent application the ash content is up to twenty percentage points higher than can be achieved under the current state of the art, due to the improved adhesion of the ash on the fibers. In addition, the initial wet strength is also increased by up to 20% with the same ash content. The dusting tendency of the paper is reduced by more than half. This permits the ash content in the paper to be clearly increased. Alternatively, an equivalent paper may be produced with a lower basis weight.  
      According to an embodiment of the present invention, relative to, but not limited to, the above referenced papers, a method includes the following process steps: 
          Adding calcium hydroxide in liquid or dry form, or of calcium oxide into the fibrous stock suspension;     Adding gaseous carbon dioxide into the fibrous stock suspension;     Precipitating calcium carbonate through the carbon dioxide;     Refining the fibrous stock suspension during the loading process; and     Washing the fibrous stock suspension prior to the crystallization process and/or the refining process and/or during the refining process and/or after the refining process.        

      According to another embodiment of the present invention, a method includes the following process steps: 
          Adding calcium hydroxide in liquid or dry form, or of calcium oxide into the fibrous stock suspension;     Adding gaseous carbon dioxide into the fibrous stock suspension;     Precipitating calcium carbonate through the carbon dioxide; and     Washing the fibrous stock suspension before delivering said fibrous stock suspension into a head box chest which is located downstream when viewed in the direction of the fibrous stock suspension flow and/or into a machine for further processing of the fibrous stock suspension. Depending on what is required of the end product, the Fiber-Loading-Technology will be applied either before or after the refining process.        

      The present invention provides a method for the production of fiber loaded precipitated calcium carbonate (FLPCC), especially for the production of chemical pulp or the use of chemical pulp in paper production. The fiber raw material which is to be loaded is produced for example from recycling paper, from DIP (de-inked paper), from secondary fiber stock, bleached or unbleached chemical pulp, wood pulp of all types, raw paper pulp of all types, bleached or unbleached sulfate pulp, broke, linen, cotton and/or hemp fibers (used predominantly for cigarette paper) and/or all other types of paper raw material which can be used in a paper machine.  
      The inventive method may be utilized independent of whether the end product contains a filler which was produced through a precipitation process in a batch reactor or through a refining process (GCC=ground calcium carbonate), or in which talcum, silicon, titanium dioxide (TiO2) are used.  
      In the FLPCC process described below, the filler material which is used in other manufacturing processes is being replaced with the filler material which is being produced by the fiber loading process technology. The scope of the filler produced according to the fiber loading process technology extends to the paper production and to the areas of application for all paper types, including wrapping papers, which possess a filler content of between 1 and 60%, or which have a white liner that has a filler content of between 1 and 60%.  
      The scope of the current invention is not limited to the use of these fillers in paper manufacturing processes; the invention may be utilized in any paper manufacturing process or related processes including the manufacture of chemical pulp. A completely new product including new and improved characteristic compared to products already on the market will result if a fibrous stock suspension is treated with the fiber loading technology during the paper manufacturing process. The process described below permits precipitation of a filler (calcium carbonate) which is evenly distributed and deposited only on and in the fibrous stock, especially the paper fiber to occur directly in the stock preparation section in a paper mill.  
      By way of a combination or by way of an individual application of the design forms of the current invention which are described below, only fibrous stock loaded with precipitated calcium carbonate is produced, whereby the calcium carbonate is attached on or in the fibers, or is embedded in them; this prevents the formation of loose precipitated calcium carbonate (PCC). An additional wash cycle before a refining process and/or after the refining process and/or before the crystallization process in a crystallizer and/or before the headbox chest or prior to delivery into the paper machine or recycling the press filtrate to a header tank or to another storage arrangement located on the infeed side provides that a constant calcium hydroxide content is adjusted or regulated in the infeed system of the fiber loading apparatus. The calcium hydroxide can be added directly in a fiber stock pulper. The press filtrate can be recycled into the pulper system. Calcium hydroxide which does not attach on or in the fibers is recycled back to the upstream processes.  
      Only that filler which is not attached on or in the fibers, in other words loose precipitated calcium carbonate, is washed out. The fibers themselves which are provided with filler on the inside and the outside do not lose said filler through the wash process and the recycling of the press filtrate, so that the positive effects of the fiber loading technology are maintained.  
      In addition to the design forms of the current invention which are described in more detail below, we also refer you to the design examples which are described in further detail in U.S. Pat. No. 6,413,365, DE 101 07 448 A1 and DE 101 13 998 A1 and with which the inventive method can also be implemented.  
      The present invention provides a method according to which the fibrous stock suspension is fed into a press arrangement intended to squeeze out a filtrate. Subsequently, the filtrate is recycled back, at least partially into an arrangement for pulping of the fibrous stock suspension, specifically into a reservoir which is located on the infeed side, for example a header tank. The calcium hydroxide is added at least partially in the arrangement for pulping of the fiber stock. In the complete pulper system, specifically in the arrangement for pulping of the fibrous stock, a pH value of between 7 and 12, especially between 9 and 12 is maintained.  
      In accordance with the current invention, aqueous fibrous stock material, especially aqueous paper stock having a consistency of 0.1 to 20%, preferably between 2 and 8%, can be used as primary raw material.  
      Calcium hydroxide in aqueous or in dry form, or calcium oxide are mixed into the aqueous paper fiber stock in a range of between 0.01 and 60% of the existing solids content. A static mixer, a header tank or a pulper system are utilized for the mixing process; a pH value in the range of between 7 and 12, preferably between 9 and 12, is applied. The reactivity of the calcium hydroxide is between 0.01 seconds and 10 minutes, preferably between 1 second and 3 minutes. Dilution water is added according to predetermined parameters.  
      Carbon dioxide is added into the moist paper stock suspension according to the reaction parameters. In doing so calcium carbonate precipitates in the carbon dioxide atmosphere.  
      At the same time a refining energy in the range between 0.1 and 300 kWh/ton dry paper pulp is applied. Compared to conventional processes for the production of a fibrous stock suspension, the current invention provides energy efficient attainment of a higher level of freeness; according to the current invention as much as 50% of refining energy can be saved. This affects especially all paper grades which undergo a refining process during their production cycle and particularly those that have a high or very high freeness value, for example FL-cigarette papers (FL=Fiber Loading), FL B&amp;P papers, FL kraft sack papers and FL filter papers. With these papers which do not require fillers, loose filler which is not deposited on or in the fibers can be removed before the refining process or prior to feeding the fibrous stock suspension into the headbox chest or prior to entry into the paper machine. The fibers themselves however, are loaded inside and outside with filler, so that the positive effects of the fiber loading technology are maintained.  
      The high mechanical strengths in the end product which are achieved through the high freeness value positively affect the production of all paper grades since, due to process based mechanical loads in the various sections of the paper machine, such as in the press section, the dryer section or in the section where the web is wound, the produced intermediate product and the end product which is to be produced bear a high mechanical load due to utilization of winders, rewinders and converting machinery.  
      The inventive pre-treatment of the fibrous stock suspension also creates the basis for improved drying, thereby increasing the efficiency level in the production of all paper grades. Residual moisture contents in the range of 1 to 20% are advantageous.  
      With the current invention greater brightness and/or higher optical values of around 15 or more lightness points are also achieved on all grades of paper, cardboard or in various cardboard applications including the white liner on a cardboard layer.  
      The energy supply during the refining process, specifically the heat volume and the resulting warming effect are controlled. Crystals in various forms can be produced, according to the control.  
      In an additional embodiment, the current invention relates to a method which provides that a static mixer, a refiner, a disperger and/or a fluffer FLPCC reactor are utilized as a reactor, whereby the fibrous stock content, especially the paper content is between 0.01 and 15% in the instance of a static mixer, at between 2 and 40% in the instance of a refiner and a disperger, especially between 2 and 8% for LC refining and between 20 and 35% for HC-refining and between 15 and 60% in the instance of a fluffer-FLPCC-reactor.  
      The current invention also relates to a method according to which an expenditure of energy of between 0.3 and 8 kWh/t, especially between 0.5 and 4 kWh/t, is used for the precipitation reaction, especially if no refining process is utilized.  
      The process temperature is preferably between −15° C. and 120° C., especially between 20 and 90° C. Rhombohedral, scalenohedron and spherical crystals are formed, whereby the crystals measure between 0.05 and 5 μm, especially between 0.3 and 2.5 μm.  
      Static and/or moving, especially rotating mixing elements are utilized for the production of a fibrous stock suspension which is loaded with calcium carbonate.  
      The process is preferably conducted in a pressure range of between 0 and 15 bar, especially between 0 and 6 bar. Also, the process is carried out at a pH value that is preferably between 6 and 10, especially between 6.5 and 9.0. The reaction time is between 0.01 seconds and 1 minute, especially between 0.05 seconds and 10 seconds.  
      An additional advantage when utilizing the inventive technology with the above referenced paper grades is that these can also be further processed in a calender. Blackening is avoided due to the fact that when using the fiber loading technology, fiber loading particles are deposited in, around and on the fibers.  
      Compared to a fibrous stock which is produced according to conventional methods, a fibrous stock produced in accordance with the fiber loading combination process technology possesses a superior dewatering capacity which is in the range of between 5 to 100 ml CSF or 0.2 to 15° SR, depending upon the required level of freeness and filler content. This fibrous stock possesses a lower water retention capacity of approximately 2 to 25%, depending upon the raw material that is used in the paper manufacturing process. Compared to conventional fibrous stock the water can be removed more quickly from the fibrous stock suspension, and the fibrous stock dries accordingly faster. This also has a positive effect on remoistening which, as a result, is diminished in the paper manufacturing process, and upon the printability of the produced paper grades.  
      The current invention also relates to an apparatus for the implementation of one of the methods described above.  
      According to the current invention the apparatus is characterized in that it includes a static mixer, a processing unit for the addition of calcium oxide or calcium hydroxide, a press or dewatering screw, an equalizing reactor or an equalizing screw, a container serving as crystallizer, an additional static mixer, a carbon dioxide storage tank or an additional device for the recovery of carbon dioxide.  
      One advantageous embodiment provides for a high consistency refiner and/or a carbon dioxide heater and/or a storage tank for press water or for water which was removed in the dewatering screw.  
      It is also advantageous if fiber stock suspension filtrate which is recovered in the dewatering screw is returned via a line to a header tank or to another upstream device for the preparation of the fibrous stock suspension.  
      An additional washer unit for cleansing of the fibrous stock suspension after the crystallizer is also advantageous. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
       FIG. 1  is a schematic illustrating the preparation of a fibrous stock suspension for application in a machine for the production of a fiber web; and  
       FIGS. 2-4  are schematics illustrating embodiments of paper machines for the production of SC paper, news print or wood-free uncoated paper. 
    
    
      Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a pipe line system  1  that is equipped with control valves  2 ,  3  and that is provided for a fibrous stock suspension. The control valve  2  is located in a line  4  through which the pipe line system  1  is connected with a static mixer  5 . Dilution water is added to the mixer  5  via a valve  6 . A tank  7  or a container for storage of the fibrous stock suspension is located following the mixer  5 , viewed in direction of the fiber stock flow direction. From the tank  7  the fibrous stock suspension is pumped via a pump  8  to an additional static mixer  9 . Dilution water is also added to the mixer  9  via a valve  10 . Likewise, the inflow of a calcium hydroxide suspension is controlled through a valve  11  which is located in a line  12 .  
      This is supplied by a processing unit  13  where solid calcium oxide or calcium hydroxide is added to water. For this purpose the processing unit  13  is supplied with water via a line  14  which is equipped with a valve  15 . The suspension that is produced in the processing unit  13  is supplied through a pump  16  into the line  12 .  
      The fibrous stock suspension to which calcium hydroxide was added flows from the mixer  9  into a line  17  which is equipped with a valve  18  to a dewatering screw  19  where water is removed from the fibrous stock suspension. Said water can, for example be returned through a line  20  to the mixer  5  as dilution water. Alternatively, or in addition, the water that was removed in the dewatering screw  19  may also be routed to a storage tank  21  for the fibrous stock suspension, or it is returned to the mixer  9 . Due to the return flow of calcium hydroxide containing water the pH value can be increased and adjusted in all instances in the units that are located preceding the dewatering screw  19 .  
      In order to equalize the fibrous stock suspension, said suspension is delivered via a line  22  from the dewatering screw  19  to an equalizing screw  23 . A downstream container  25  (crystallizer) is connected through a line  24  with said equalizing screw. For the purpose of supplying carbon dioxide this container is connected with a carbon dioxide storage container  30  via a line  29  which is equipped with valves  26 ,  27  and a pump  28 .  
      Carbon dioxide is supplied from this container into the crystallizer  25  in order to produce the desired precipitation reaction of calcium hydroxide and carbon dioxide for the formation of calcium carbonate as a filler in the fibers of the fiber stock.  
      In addition the carbon dioxide storage container  30  is connected with the equalizing screw  23  via an additional line  31  which is equipped with a valve  32  and which branches off line  29 . Carbon dioxide can herewith also be supplied to the equalizing screw in order to achieve at least a partial precipitation already at this point.  
      Line  29  is also connected via an additional valve  33  with a static mixer  34 . This serves to add additional carbon dioxide to the fibrous stock suspension which is flowing from the crystallizer  25  via a line  36  which is equipped with a valve  35 .  
      The fibrous stock suspension flows from the mixer  34  into a mixing chest  37 . A storage tank  38  which additionally serves as a filtration unit may be provided between the mixer  34  and the mixing chest  37 . From the storage tank  38  the filtrate which has been enriched with calcium carbonate is recycled back into the header tank  7  or into another upstream unit for the processing of the dilution water or the fibrous stock suspension. The mixing chest  37  is equipped with a rotor  39  to thoroughly mix the fibrous stock suspension. The fibrous stock suspension then flows from the mixing chest  37  either immediately to a head box in a paper machine, or will be subjected to additional mechanical processing, for example in a refiner feed chest.  
      Fibrous stock suspension to which calcium hydroxide has not yet been added can also be supplied to the mixing chest  37  through a pipe line system  1  via the valve  3  and a line  40  in which said valve is installed.  
      It is further provided that white water or process water which has been recovered from the machine for the production of the fibrous stock suspension, especially from the paper machine, for example in the wire area of the paper machine or, as already described previously, for the fibrous stock suspension from the dewatering screw  19 , is supplied to the tank  21 . Dilution water may for example be supplied to this tank through a line  41  which is equipped with a valve  42 .  
      From the container  21  dilution water which is mixed with process water flows through a line  43 , a pump  44  and a valve  45  to the crystallizer  25 . According to the design of an arrangement for loading of the fibrous stock suspension with a filler, especially with calcium carbonate as depicted in  FIG. 1 , a multitude of possibilities arise to influence the composition of the fibrous stock suspension that is being produced in various stages of the manufacturing process.  
      The installation of a high consistency refiner  46  inside line  4  is advantageous. A heater  47  for the carbon dioxide which is supplied by the storage tank  30  is optional. The heater  47  operates with superheated steam which is supplied via an inlet  49  and discharged via an outlet  48 .  
      A machine as illustrated in  FIG. 2  is suitable for the production of a SC paper web (SC=super-calendered) or magazine type paper. The machine includes a twin wire former  50 , a press section  51  with two press nips arranged in tandem, a single row dryer section  52 , calender  53  with a multitude of soft and hard rolls, as well as a winder  54 .  
      A machine ( FIG. 3 ) is provided for the production of newsprint, including a twin wire former  55 , a press section  56  and two press nips arranged in tandem, a single row dryer section  57  and two calendars  58 ,  59  whereby each is equipped with one soft and one hard roll. The paper web is wound on a winder  60 .  
      A machine ( FIG. 4 ) for the production of WFU-paper includes a twin wire former  61 , a press section  62  with two press nips arranged in tandem, a single row dryer section  63  within which a coating unit  64  is located, a two-row dryer section  65 , two calenders  66 ,  67  each of which is equipped with one pair of rolls, and a winder  68 .  
     Component Identification Listing  
     
         
         
           
               1  Pipe line system  
               2  Control valve  
               3  Control valve  
               4  Line  
               5  Static mixer  
               6  Valve  
               7  Header tank  
               8  Pump  
               9  Static mixer  
               10  Valve  
               11  Valve  
               12  Line  
               13  Processing unit  
               14  Line  
               15  Valve  
               16  Pump  
               17  Line  
               18  Valve  
               19  Dewatering screw  
               20  Line  
               21  Storage tank  
               22  Line  
               23  Equalizing screw  
               24  Line  
               25  Container  
               26  Valve  
               27  Valve  
               28  Pump  
               29  Line  
               30  Carbon dioxide storage tank  
               31  Line  
               32  Valve  
               33  Valve  
               34  Static Mixer  
               35  Valve  
               36  Line  
               37  Mixing chest  
               38  Storage tank  
               39  Rotor  
               40  Line  
               41  Line  
               42  Valve  
               43  Line  
               44  Pump  
               45  Valve  
               46  High consistency refiner  
               47  Heater  
               48  Inlet  
               49  Outlet  
               50  Twin wire former  
               51  Press section  
               52  Dryer section  
               53  Calender  
               54  Winder  
               55  Twin wire former  
               56  Press section  
               57  Dryer section  
               58  Calender  
               59  Calender  
               60  Winder  
               61  Twin wire former  
               62  Press section  
               63  Single row dryer section  
               64  Coating unit  
               65  Two-row dryer section  
               66  Calender  
               67  Calender  
               68  Winder