Abstract:
An impregnation vessel including: a vessel container including an upper inlet to receive cellulosic material; a lower discharge port to discharge the cellulosic material from a discharge section of the vessel container; a convergence section internal to the vessel through which passes a flow of the cellulosic material in the vessel; a cavity between an internal wall of the vessel and the convergence section, wherein the cavity has a lower opening to the cellulosic material in the vessel and an upper section shielded from the flow of cellulosic material in the vessel, and an input port in the vessel and opening to the cavity, wherein the input port is connectable to a source of hot liquid to be added to the cellulosic material in the vessel.

Description:
CROSS RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/949,987 filed Jul. 16, 2007, the entirety of which is incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to an impregnation vessel used with continuous cooking (such as but not limited to Kraft or soda cooking processes) of cellulosic material (such as wood chips and non-wood materials such as annuals, bagasse, etc.) to produce pulp. In particular, the invention relates the addition of a hot liquid, e.g., liquor or steam, to add heat to the cellulosic material in an impregnation vessel. 
         [0003]    Impregnation vessels pretreat cellulosic material before the material is fed to, for example, a digester vessel. While in the impregnation vessel, the cellulosic material is immersed in liquor and/or steam to heat the material. Examples of conventional vessels suitable for impregnation vessels are shown in U.S. Pat. No. 4,746,400, which discloses a vessel having a bottom scraper and hot liquid injection below the scraper to flush cellulosic material out from the vessel, and U.S. Pat. Nos. 5,500,083 and 5,628,873, which disclose vessels having a bottom section having a one-dimensional and two-dimensional convergences with a side relief device, currently marketed as the Diamondback® Chip Bin by Andritz, Inc. of Glenn Falls, N.Y., USA. 
         [0004]    Cellulosic material flows from an impregnation vessel to a digester vessel that generally operates at a higher temperature than does the impregnation vessel. Heat is added to the cellulosic material in the digester. While some heating of cellulosic material occurs in the impregnation vessel, the material in the impregnation vessel is conventionally heated in the digester vessel. 
         [0005]    Increasing the temperature of the cellulosic material in an impregnation vessel could reduce the heat needed to be added to the material in the digester vessel. If hot liquid is added to a downstream portion of an impregnation vessel, the added hot liquor may form currents of hot liquid flowing up through the impregnation vessel. Such currents could disrupt the desired uniform treatment of the cellulosic material flowing down through the vessel. Accordingly, adding a heated liquid to the impregnation vessel is not conventional. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    An impregnation vessel has been developed that includes: a vessel container including an upper inlet to receive cellulosic material; a lower discharge port to discharge the cellulosic material from a discharge section of the vessel container; a convergence section internal to the vessel through which passes a flow of the cellulosic material in the vessel; a cavity between an internal wall of the vessel and the convergence section, wherein the cavity has a lower opening to the cellulosic material in the vessel and an upper section shielded from the flow of cellulosic material in the vessel, and an input port in the vessel and opening to the cavity, wherein the input port is connectable to a source of hot liquid to be added to the cellulosic material in the vessel. 
         [0007]    The convergence section may converge in only a single direction within the impregnation vessel and include a tapered wall having an upper section sealed to the internal wall of the vessel and a lower section positioned radially inward of the internal wall, wherein the cavity is between the internal wall of the vessel and the tapered wall of the convergence section. The cavity may be below a liquid level in the vessel and arranged in the middle third elevation of the vessel. The source of hot liquid may supply hot liquid at a temperature, e.g., at least 120 degrees Celsius, above a discharge temperature of the cellulosic material from the impregnation vessel. 
         [0008]    An impregnation vessel has been developed comprising: a vessel container including an upper inlet to receive cellulosic material; a lower discharge port to discharge the cellulosic material from a discharge section of the vessel container; a one-dimensional convergence section internal to the vessel through which passes a flow of the cellulosic material in the vessel; a cavity between an internal wall of the vessel and the convergence section, wherein the cavity has a lower opening to the cellulosic material in the vessel and an upper section shielded from the flow of cellulosic material in the vessel, and an input port in the vessel and opening to the cavity, wherein the input port is connectable to a source of hot liquid to be added to the cellulosic material in the vessel and the hot liquid is added to the cavity at a temperature above an average temperature of the cellulosic material in the vessel. 
         [0009]    A method has been developed for heating cellulosic material in an impregnation vessel having an internal convergence, the method comprising: introducing cellulosic material to an upper inlet port in the impregnation vessel; adding a heated liquid to the vessel and forming a liquid level in a upper section of the vessel; heating the cellulosic material with the heated liquid as the cellulosic material flows downward through the vessel; funneling the flow of the cellulosic material below the liquid level and in the vessel through the internal convergence; introducing a hot liquid to a cavity in the vessel and behind the convergence, wherein the hot liquid is introduced to the cavity at a temperature above a temperature of the heated liquid; adding the hot liquid from the cavity to the flow of cellulosic material downstream of the internal convergence; heating the flow of cellulosic material downstream of the internal convergence with the hot liquid, and discharging the cellulosic material from a discharge port in a lower section of the vessel below the cavity and internal convergence. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic side view diagram of an impregnation vessel with a single direction convergence. 
           [0011]      FIG. 2  is a top down, cross-sectional diagram of the impregnation vessel having a single direction convergence. 
           [0012]      FIG. 3  is a schematic side view diagram of an impregnation vessel with orthogonal direction convergence. 
           [0013]      FIG. 4  is a top down, cross-sectional diagram of the impregnation vessel having a orthogonal direction convergence. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1  is a schematic diagram of an impregnation vessel  10  for pretreatment of cellulosic material, referred to herein as chips. The vessel may be a metallic cylinder having a height of 100 feet (30 meters) or more, a diameter of 70 inches (2 meters) or more, and may process 700 metric tons per day (700 mtpd) of pulp. The chips may flow continuously and simultaneously into, through and out of the impregnation vessel. The pretreated chips from the impregnation vessel  10  may flow to an upper inlet of a continuous digester vessel  46 . 
         [0015]    Chips may be supplied to the impregnation vessel  10  from a chip source  12  which may be a chip bin or a presteaming vessel or merely a holding location for the chips (such as if no chip bin is used). The impregnation vessel has an upper chip inlet  14  that receives the chips and optionally may receive the chips in a slurry that includes liquor. Within the impregnation vessel, a chip level  16  and a liquid level  18  is form, where the chip level is likely to be above the liquid level. The liquid level  18  in the vessel may be formed by the addition of flashing liquor (such as white or black liquor) and/or steam with the purpose of heating the chips from a source  19  of heated liquid and/or steam. The gaseous volume  20  of the vessel above the liquid level  18  is preferably maintained at a temperature of about 100 degrees Celsius (° C.) and at atmospheric pressure. The heated liquid and/or steam may flow directly into the gaseous volume  20  of the impregnation vessel  10 . 
         [0016]    A one dimensional convergence  22  is formed in the vessel in a liquid section  24  of the vessel below the liquid level  18 . Preferably, the convergence  22  is in the bottom half of the vessel and above the bottom rotating scraper  25  or other device to move chips into the bottom discharge outlet  27 . For example, the convergence  22  may be in the middle third elevation of the vessel and, preferably is below mid-elevation of the vessel and above the lower third elevation of the vessel. 
         [0017]    The one dimensional convergence  22  may be embodied as a hollow transition section  26  having a substantially circular cross-section open top  28  and a substantially rectangular cross-section open bottom  30 . The convergence  22  includes a transition section  26  having opposite non-vertical gradually tapering sidewalls  29  that may form an angle with respect to the vertical, typically of about 20 to 35 degrees, and preferably 25 to 30 degrees. The sidewalls  29  may extend straight across the vessel. The walls may be straight in a direction perpendicular to an axis of the vessel  10  and tapered (continuously or in segments) in a direction parallel to the axis and along the transition section  26 . 
         [0018]    Opposite side edges of the sidewalls  29  may attach to the interior walls vessel  32 . The open top  28  of the transition section  26  may be curved to conform to the vessel wall  32  and welded to the vessel wall to provide a continuous fluid-tight seal between the vessel and the convergence  22 . One dimensional convergence structures for chip vessels are disclosed in U.S. Pat. Nos. 5,500,083 and 5,628,873. Support braces or ribs  31  may extend from the vessel wall  32  and to the tapered walls  27  of the transition section to support the convergence within the vessel. 
         [0019]      FIG. 2  is a top down, cross-sectional diagram of the impregnation vessel  10  to show the convergence  22 . The opposing sidewalls  29  of the convergence are tapered and may include an upper tapered sidewall section  50 , a straight vertical sidewall section  52 , and a lower tapered sidewall section  54 .  FIG. 2  shows the one dimensional nature of the convergence in that the bottom of the transition section is narrower than the top  28  in one direction and is as wide as the top  28  in a perpendicular direction. 
         [0020]    The one dimensional convergence  22  of the transition section promotes flow of chips down through the vessel and through the transition section  26 . The convergence may provide flow rate regulation of the chips in the vessel and promote adequate retention time of the chips in the vessel  10 . Further, the one dimensional convergence  22  is less susceptible to chips clogging or bridging in the transition section than are conical convergence sections which converge in two-dimensions. 
         [0021]    A cavity  34  is formed between the inside vessel wall  34  and the sidewall(s)  29  of the transition section  26 . The cavity  34  is a shielded region in the vessel behind the sidewall  29  of the transition section  26 . The cavity  34  is shielded by the sidewall from the downward flow of chips in the vessel. Because the cavity is below the tapered transition sidewall  29 , the wall prevents heat currents flowing upward from the cavity and above the transition section  26 . There may be two cavities  34  in the vessel on opposite sides of vessel, wherein one cavity is behind each of two sidewalls  29  of the convergence  22 . 
         [0022]    The cavity  34  provides a region into which additional hot liquid, such as black liquor or white liquor, can be added without the liquid flashing in the upper regions of the vessel  10 . The hot liquid enters the cavity  34  and mixes with the liquids and chips that flow up into the cavity from below the outlet  30  of the transition section. Heat currents formed by the hot liquid cannot flow upward through the vessel because the cavity is capped by the tapered sidewall  29  of the transition section. 
         [0023]    A source of hot liquor  42  ( FIG. 1 ) feeds a pipe  40  that conveys the hot liquor to the cavity  34 . The liquor source  42  may be excess hot liquor from the digester vessel  46 , and specifically hot wash liquor extracted from a lower section of a digester vessel  46 . If sufficient excess black liquor is not available, low pressure steam  48  may be used to heat the liquor  42  pumped through pipe  40  to the cavity  34 . Additionally, other liquids having sufficient heat can be introduced into the cavity  34 . 
         [0024]    The temperature of the liquor fed to the cavity  34  may be maintained at a temperature, such as 120 degrees Celsius, which may be higher than the temperature in the vapor area  20  of the vessel. If allowed to flow into the vapor area  20 , the heated liquid and/or steam may flash. Introducing the hot liquid in the cavity allows the sidewalls  29  to block any upward flow of the liquid. 
         [0025]    The hot liquid from the liquid source  42 , which is preferably black or white liquor, is introduced into the cavity  34  and preferably at an elevation above the outlet  30  of the transition section  26 . Introduction of liquor into the cavity does not disrupt the flow of chips down through the vessel, because the chips are funneled through the convergence  22  and away from the cavity  34 . The cavity  34  allows the liquid  42  to enter the vessel in the relatively quite, e.g., stagnant, flow of the cavity. From the cavity, the hot liquid diffuses into the chip flow being discharged  30  from the transition section. 
         [0026]    The liquor  42  added to the cavity  34  preferably has a temperature above the average temperature of the chips in the vessel  10 , and the temperature of the chips passing through the discharge outlet  38 . The added liquor  42  heats the chips in the impregnation vessel  10 . The heating is desirable for chips to be conveyed to a digester vessel  46  that typically operates at a higher temperature than the impregnation vessel. 
         [0027]    The introduction of hot liquid  42  in the cavity  34  does not interfere with a conventional discharge devices  25 , such as a scraper or other mechanical devices which may include a sluice system, to assist in the movement of the chips through the discharge  38  of the vessel. 
         [0028]    The cavity  34  allows liquid  42  to flow into the vessel  10  without causing channeling or heat currents to form and rise through the chips in the vessel. Another advantage of adding hot liquid  42  to the cavity  34  is that it makes efficient use of excess hot liquid available in a pulp plant, which may include liquids at temperatures above 100 degrees Celsius. 
         [0029]    If the hot excess liquid were added to the impregnation vessel  10  without the use of a convergence  22  with a sidewall, channeling (areas where there is a disruption in the homogeneity and uniformity of the chips) could occur as would heat currents. To add hot liquids from an inlet of the vessel directly to the chip flow through the impregnation vessel may cause heat currents in the chip flow that, in turn, may produce heat risers through the chip column and result is less efficient heating of the chips. 
         [0030]    The addition of the liquid into the cavity  34  allows the hot liquid to mix with other liquids in the cavity and diffuse over a wide area to the chip flow exiting the outlet  30  to the transition section. Further, a stream of hot liquid entering a sidewall of the vessel and directly entering the chip stream in the vessel could disrupt the uniform movement and treatment of the chips through the impregnation vessel. Introducing hot liquid in the cavity  34  avoids creating a hot liquid stream in the chip flow and minimizes the risk of disrupting the uniform movement and treatment of chips through the vessel. 
         [0031]      FIG. 3  is a schematic side view diagram of a portion of an impregnation vessel  50  with orthogonal direction convergence  52 .  FIG. 4  is a top down, cross-sectional diagram of the impregnation vessel  50  having a orthogonal direction convergence  52 . The orthogonal direction convergence has a transition section  54  that reduces the flow path through the vessel in two orthogonal directions. The flow path reduces from the cross-sectional area of the entire vessel at the top of the transition section  54  to a smaller circular cross-sectional area of the output  56  of the convergence. Preferably, the transition section  54  includes diamond shaped side-panels  58  that are joined by curved side panels  60 . A hot liquid inlet  62  to allow hot liquid, e.g., hot liquor and/or steam  64 , is arranged in the annular cavity  66  between the inner sidewalls  68  of the vessel  50  and the outer surfaces of the side-panels  58 ,  60  of the convergence  52 . The cavity provides a region of the impregnation that is out of the direct flow path of the chip and liquid flowing downward through the vessel. As they flow from the outlet  54  of the convergence  52 , the chips and liquid mix with the hot liquid flowing down from the cavity. The hot liquid heats the chips as the chips flow further down in the vessel  50  to a discharge device  70 , such as a scraper, and to the outlet  72  of the vessel. 
         [0032]    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.