Abstract:
A method to make pulp adapted for forming a corrugated medium, the method includes: cooking chips in a cooking vessel using a caustic carbonated pulping soda/caustic (SC) cooking liquor injected into the cooking vessel; fiberizing the chips discharged from the cooking vessel to form a pulp, and removing lignin from the pulp or oxidizing lignin in the pulp by injecting oxygen (O 2 ) into the fiberized pulp.

Description:
CROSS RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/353,489, filed on Jun. 10, 2010, the entirety of which application is incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a method of manufacturing pulp and more particularly to a method of manufacturing pulp to be used for making corrugated medium. 
     A wide range of methods exist for manufacturing semi-chemical pulp to be used for making a corrugated medium. For example, the high yield hardwood pulps used in manufacturing corrugating medium may be produced using semi-chemical pulping processes including soda/caustic pulping, neutral sulfite semi-chemical (NSSC) pulping, and green liquor pulping. Depending on the manufacturing method used, the pulp yield generally varies from 75 percent (%) to 82% for NSSC pulping and up to 85% to 86% for green liquor and soda/caustic pulping. Typically low yields pulps result from treatment with sulfur containing cooking chemicals, which provide better pulp quality than high yield pulps. 
     Standard soda/caustic (SC) pulping is a popular method for puling. SC pulp manufacturing is attractive due to inexpensive cooking chemicals and a relatively easy and simple chemical recovery process. The pulp quality from standard soda/caustic pulping tends to be inferior to the pulp quality generated by NSSC pulping. The pulp quality is a major disadvantage for soda/caustic pulping, especially for paper grades requiring high results for the ring crush test and corrugated medium test (CMT). 
     BRIEF DESCRIPTION OF THE INVENTION 
     A new method and system for soda/caustic pulping has been developed that provides high quality pulp, e.g., higher ring crush and CMT values than typically obtained with the standard soda/caustic pulping. The new method and system may also have the same easy and simple chemical recovery of standard soda/caustic pulping and thereby minimize the environment pollution. 
     A method has been conceived to make pulp comprising: cooking chips, e.g., wood chips, in cooking vessel using a soda, caustic or green cooking liquor injected into the cooking vessel; fiberizing the chips discharged from cooking vessel to form a pulp, and removing lignin from the pulp or oxidizing lignin in the pulp by injecting oxygen (O 2 ) into the fiberized chips (pulp). The fiberized chips may be washed to form the pulp adapted to form, for example, a corrugated medium. The method may use cooking liquor that includes one or more of soda (NaOH) and soda ash (Na 2 CO 3 ). The method may also include a mechanical fiberizing process. The pulp may be refined after removing or oxidizing the lignin and used to form corrugated medium. The step of removing or oxidizing the lignin may be performed at a temperature in a range of 120 degrees Fahrenheit (deg. F.) to 300 deg. F. and for a period in a range of 5 minutes to 120 minutes. 
     A method has been conceived to make pulp comprising: cooking chips in a cooking vessel using a caustic carbonated pulping cooking liquor injected into the cooking vessel; fiberizing the chips discharged from the cooking vessel to form a fiberized pulp; removing lignin from the pulp or oxidizing lignin in the pulp by injecting oxygen (O 2 ) into the fiberized pulp, and washing the fiberized pulp to form the pulp. The cooking liquor may include at least one of a soda, caustic or green cooking liquor. Further, the cooking liquor may include one or more of soda (NaOH), soda ash (Na 2 CO 3 ) and sodium sulfide (Na 2 S). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram of a method to manufacture pulp. 
         FIG. 2  is a table of Pulp Physical Properties resulting from various pulping processes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a flow diagram of a method  10  to manufacture pulp. The new method comprises soda or soda ash (or both) cooking followed by multistage delignification, for manufacturing corrugated medium from wood chips. 
     Wood chips  12  (or other comminuted cellulosic fibrous material—collectively referred to as “chips”) may be a mixed-blend of wood from various species of hardwood, deciduous trees including, but not limited to, ash, aspen, beech, basswood, birch, black cherry, black walnut, butternut, buckeye, chestnut, cottonwood, dogwood, elm,  eucalyptus, gmelina , hackberry, hickory, holly, locust,  magnolia , maple, oak, poplar, red alder, redbud, royal  paulownia, sassafras , sweetgum, sycamore, tupelo, willow, yellow-poplar, and combinations thereof. The wood chips may also comprise wood from various varieties within the species of trees. It is contemplated that other species of hardwood, deciduous trees may be used. It is also contemplated that a single species of hardwood, deciduous trees may be used. Bagasse, straw, kenaf, hemp, and combinations thereof may also be used to form the chips. It is contemplated that the chips may include wood from hardwood, deciduous trees in combination with non-wood fibers including those discussed above. The chips may be supplied from a wood yard or a wood room in a pulping mill. 
     The chips are fed using a conventional chip feed system  14  to a cooking vessel  16 , such as a batch digester, a continuous digester, and a Pandia type digester. The chip feed system  14  may add steam  18  and liquor  15 , e.g., water, to the chips being transported through the chip feed system to the cooking vessel. 
     The chips are treated in cooking vessel  16  with, for example, regular soda ash (Na 2 CO 3 ) which is added in amount approximately 10% of the bone dry weight (bdw) of the chips added to the vessel  16 . The regular soda ash is added from a liquor supply  20  that injects the soda ash, with the cooking liquor, into the vessel of the cooking system  16  or into the chip feed system  14  upstream of the vessel. 
     The chips and cooking liquor are heated in the vessel  16 , such as with steam  18  injected to the vessel to a temperature in a range of 330 degrees (deg.) Fahrenheit (F.) to 380 deg. F., or in a range 360 deg. F. to 370 F. The chips are retained in the vessel for a period such as two (2) to fifteen (15) minutes, or 4 to 10 minutes. The chips are mechanically fiberized in a chip fiberizing vessel  17 , such as defiberator or refiner vessel, to a shines content of, for example, 10% to 50%, or 30% to 45%. 
     The fiberized chips are discharged from the fiberizing vessel  17  and directed to one or more stages  22  of delignification, such as a continuous or batch chemical reactor(s)  24 . The delignification stages may remove or oxidize the lignin in the fiberized chips using oxidizing agents  26  such as one or more of oxygen, hydrogen peroxide and ozone. 
     The fiberized chips from the vessel  17  may be optionally washed  25  using a wash liquid, e.g., water, before entering the delignification stage(s)  22  and washed between each of the individual delignification stages  24 .  FIG. 1  shows by the branch “or” in the flow path that the washing or pressing stages  25  are optional, and may precede the delignification stage(s)  22  and be between the individual delignification stages  24 . In particular,  FIG. 1  shows alternative flow paths branching at the “or”. The delignification stages  22  may be the same in both braches of the flow path. In particular, each of the delignification stages  22  may add one or more of oxygen (O 2 )  26 , steam  18  and alkaline solutions  23  to one or more of the individual delignification stages  24 . 
     Each of the delignification stages(s)  24  may treat the fiberized chips with oxygen (O 2 ) and maintain the chips at a temperature of, for example, 120 deg. F. to 300 deg. F. or 200 deg. F. to 230 deg. F. These stage(s)  24  may maintain the chips under pressures of 60 pounds per square inch (psig) to 110 psig for a period of 5 to 120 minutes or 20 minutes to 40 minutes at 5% to 45% (or even 10% to 30%) consistency of pulp to liquor. 
     The fiberized chips  17  may have a shives content of 35% to 45% after treatment with oxygen (O 2 )  26  in the delignification stage(s)  22 . The pH level in each of the delignification stages  24  may be alkaline pH. The target pH of the chips being discharged from the delignification stages may be in a range of 7 pH to 12 pH or 8 pH to 10 pH. Downstream of the delignification stages  22 , the oxygen delignified pulp, which may have a shives content of 35% to 45%, is washed  28  and refined  30  before entering a paper machine  32  that forms the pulp into corrugated paper or other corrugated medium. 
     Preliminary results have been obtained using the pulping process described above. These results are shown in the table of  FIG. 2 . The results indicate a significant improvement in pulp quality using the novel SC pulping process described above. Major physical pulp properties such as Ring Crush, CMT, Mullen, Tensile, and Tear strength were improved by 25% to 40% as compared to standard one stage carbonate pulp for final pulp yields of 75% to 80%. There is a strong correlation between pulp quality improvement and the final yield as well as pulp consistency and degree of pulp washing prior oxygen treatment. 
     The oxygen delignification process is described above in the context of a soda, caustic or green (soda/caustic/green) liquor cooking process. This oxygen delignification process is not limited to soda/caustic/green cooking. The oxygen delignification described above may also be applied to all other cooking processes to produce pulp, such as for a corrugated medium. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.