Abstract:
A flash tank including: a closed interior chamber; a gas exhaust port coupled to an upper portion of the chamber; a liquid discharge port coupled to a lower portion of the chamber; an inlet nozzle attached to an inlet port of the chamber, wherein the inlet nozzle includes a flow passage, and a movable valve plate in the flow passage, wherein the valve plate has a first position which defines a first throat in the flow passage and a second position which defines a second throat having a smaller cross-sectional area than the first throat.

Description:
CROSS RELATED APPLICATION 
     This applications claims priority to U.S. Provisional Patent Application Ser. No. 61/598,112 filed Feb. 13, 2012. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to flashing fluids extracted from pressurized reactor vessels and particularly to flash tanks for flashing black liquor from a pressurized reactor vessel in a pulping or biomass treatment system. 
     Flash tanks are generally used to flash a high pressure fluid liquor stream including steam and condensate. A flash tank typically has a high pressure inlet port, an interior chamber, an upper steam or gas discharge port and a lower condensate or liquid discharge port. Flash tanks safely and efficiently reduce pressure in a pressurized fluid stream, allow recovery of heat energy from the stream, and collect chemicals from the stream in condensate. 
     Flash tanks may be used to recover chemicals from chemical pulping systems, such as Kraft cooking systems. Flash tanks are also used in other types of cooking systems for chemical and mechanical-chemical pulping systems. To pulp wood chips or other comminuted cellulosic fibrous organic material (collectively referred to herein as “cellulosic material”), the cellulosic material is mixed with liquors, e.g., water and cooking chemicals, and pumped in a pressurized treatment vessel. Sodium hydroxide, sodium sulfite and other alkali chemicals are used to “cook” the cellulosic material such as in a Kraft cooking process. These chemicals degrade lignins and other hemicellulose compounds in the cellulosic material. The Kraft cooking process is typically performed at temperatures in a range of 100 degrees Celsius (100° C.) to 170° C. and at pressures at or substantially greater than atmospheric. 
     The cooking (reactor) vessels may be batch or continuous flow vessels. The cooking vessels are generally vertically oriented and may be sufficiently large to process 1,000 tons or more of cellulosic material per day. The material continuously enters and leaves the vessel, and remains in the vessel for several hours. In addition to the cooking vessel, a conventional pulping system may include other reactor vessels (such as vessels operating at or near atmospheric pressure or pressurized above atmospheric pressure) such as for impregnating the cellulosic material with liquors prior to the cooking vessel. In view of the large amount cellulosic material in the impregnation and cooking vessels, a large volume of black liquor is typically extracted from these vessels. 
     The black liquor includes the cooking chemicals and organic chemicals or compounds, e.g., hydrolysate, residual alkali, lignin, hemicellulose and other dissolved organic substances, dissolved from the cellulosic materials. The black liquor is flashed in a flash tank to generate steam and condensate. The cooking chemicals and organic compounds are included with the liquid condensate formed when the liquor is flashed. The steam formed from flashing is generally free of the chemicals and organic compounds. The condensate is processed to, for example, recover and recausticize the cooking chemical. The steam may be used as heat energy in the pulping system. 
     In conventional flash tanks, the black liquor enters flash tanks through an inlet pipe having a fixed inlet diameter. The inlet is not variable or otherwise controllable to adjust the size of the black liquor flow passage. Changes to the flow passage at the inlet to a conventional flash tank for black liquor have been made by changing the inlet piping to the flash tank. Conventional flash tanks do not have a means for adjusting the flow passage; controlling of the volume or the velocity of the black liquor flow into the flash tank, pressure drop in the flash tank, or regulating the pressure in the conduits containing black liquor connected to the inlets to the flash tanks. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An inlet for a flash tank has been conceived where the flow passage area of the inlet to the flash tank is varied to allow for control of the flow passage area of the inlet to the flash tank without changing of physical or mechanical components of the inlet or flash tank. The flow passage area is adjusted by a pivoting hinged plate in the inlet to the flash tank. This movable, hinged plate may be located at, near or after the junction between piping and the inlet to the flash tank. At this junction, the piping typically transitions from piping having a rectangular cross-section to piping circular in cross-section. 
     The movable, hinged plate changes of the cross-sectional area of the inlet to adjust the flow passage area through which hot black liquor flows from fully open to smaller area or from a smaller area to a larger area. This adjustment of the inlet opening size provides a means to control the velocity of the fluid into the tank. 
     The movable, hinged plate may be operated by a pneumatic or electro-mechanical actuator. A formable seal may be provided on either the movable hinged plate or the interior of the pipe to prevent leaking of hot black liquor out of the pipe or past the side edges of the plate. 
     A flash tank has been conceived including: a closed interior chamber; a gas exhaust port coupled to an upper portion of the chamber; a liquid discharge port coupled to a lower portion of the chamber; an inlet nozzle attached to an inlet port of the chamber, wherein the inlet nozzle includes a flow passage having a throat, and a movable valve plate in the flow passage, wherein the valve plate has a first position which defines a first throat area in the flow passage and a second position which defines a second throat area having a smaller cross-sectional area than the first throat area. 
     The valve plate may be a rectangular plate having planar surfaces bounded by edges and the flow passage may have a rectangular cross-section. The rectangular plate may be attached to a hinge attached to a sidewall of the flow passage. The hinge may be attached to an upstream end of the valve plate and creates a pivoting axis for the valve plate. 
     The valve plate may have an actuator connected to the valve plate, wherein the actuator moves the valve plate between the first and second positions. 
     The valve plate may be moved by an actuator having an extendible shaft connected to the valve plate, wherein the actuator moves the valve plate between the first and second positions. 
     A method has been conceived to flash a pressurized liquor comprising: feeding a pressurized liquor to an inlet nozzle of a flash tank; flashing the pressurized liquor as the liquor flows from the inlet nozzle into an interior chamber of the flash tank; exhausting a gas exhaust formed by the flashing through an upper portion of the chamber; discharging a liquid formed by the flashing from a lower portion of the chamber, and adjusting a cross-sectional area of a flow passage in the inlet nozzle by moving a valve plate in the flow passage. 
     The step of feeding may include a first feeding step in which the pressurized liquor flows through the flow passage while the valve plate is at a first position which defines a first throat area in the flow passage and a second feeding step in which the pressurized liquor flows through the flow passage while the valve plate is in a second position which defines a second throat area having a smaller cross-sectional area than the first throat area. Additional valve plate positions may also exist where the valve plate in multiple positions along the flow passage define multiple throats having smaller cross-sectional areas than the first throat area. 
     The method may include adjusting the cross-sectional area of the flow passage in the inlet nozzle allows for control of the volume of flow of black liquor entering the flash tank. Adjusting of the cross-sectional area of the flow passage inlet nozzle may also allow for control of the flow velocity of the black liquor entering the flash tank. Additionally, adjusting the cross-sectional area of the flow passage in the inlet nozzle allows for a degree of control over the pressure drop in the flash tank. Adjusting the cross-sectional area of the flow passage in the inlet nozzle may also ensure sufficient pressure in the conduits upstream of the inlet nozzle to the flash tank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a conventional flash tank receiving black liquor extracted from a pressurized reactor vessel. 
         FIG. 2  is cross-sectional view of the flash tank taken along a horizontal line, wherein the inlet nozzle is attached to the tank along a tangent to tank. 
         FIG. 3  shows a perspective and partially cut-away view of the inlet nozzle to illustrate the valve plate and the connection of the nozzle to the sidewall of the flash tank. 
         FIG. 4  is a cross-sectional schematic view of the inlet nozzle taken along a vertical plane to illustrate the valve plate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic diagram of a pulping system including a flash tank  10  coupled to a vessel  12 , e.g., an impregnation vessel or a cooking vessel. A slurry of cellulosic material  14  and liquor flow to an upper inlet  15  of the vessel  12 . White liquor  16  may be added to the vessel  12  such as through center inlet pipes  18 . Screen assemblies  20  at various elevations in the vessel  12  extract black liquor from the cellulosic material moving down through the vessel  12 . The material is discharged as pulp  22  from the bottom  24  of the vessel. 
     The black liquor extracted from the vessel  12  may flow to the flash tank  10  through conduits  26  fluidly coupling the screen assemblies  20  to a respective flash tank  10 . The number of flash tanks  10  and whether one flash tank  10  receives black liquor from multiple screen assemblies  20  are design choices. The number, size and arrangement of flash tanks  10  may also depend on the design choice of whether to have heat exchange equipment in the conduits  26  leading to the flash tanks  10 . 
     Black liquor flashes in the flash tank  10  to form steam  28  and condensate  30 . The steam  28  flows out upper outlets  17  of the flash tanks  10 . The condensate  30  flows as a liquid from bottom discharges  19  of the flash tanks  10 . 
       FIG. 2  is a cross-sectional view of the flash tank  10 , wherein the cross-section is along a horizontal plane bisecting the inlet piping system to the flash tank  10 . The conduits  26  transporting the black liquor to be flashed may be cylindrical pipes. The inlet nozzle  34  to the flash tank  10  may be rectangular in cross-section. An end outlet  32  of the conduits  26  connects to the inlet nozzle  34  attached to the flash tank  10 . The inlet nozzle  34  may be tangential to a cylindrical portion  38  of the flash tank  10 . 
     The flash tank  10  need not be cylindrical and the inlet nozzle  34  need not be tangential to the flash tank  10 . The flash tank  10  may have planar sections in its sidewall. Other suitable configurations of the inlet nozzle  34  may be oriented vertically and attached to the top of the flash tank  10  or to the side of the flash tank  10  without being tangential to the sidewall of the flash tank  10 . 
     The flow passage  40  through inlet nozzle  34  may be rectangular, e.g., square, in cross-section. The rectangular cross section allows a valve plate  42  in the flow passage  40  to move, e.g., pivot, within the flow passage  40 . The valve plate  42  regulates the velocity of the flow stream of black liquor to the flash tank  10 . 
     A transition section  44  at the upstream end of the inlet nozzle  34  may convert a round inlet to a rectangular cross section of the remainder of the flow passage  40  through the inlet nozzle  34 . The inlet of the transition section  44  connects to the end of the conduit  26 . The outlet of the transition section  44  connects to the inlet nozzle  34 . The transition section  44  may include a flange coupling  31  to attach to an end outlet  32  of the conduit  26 . 
       FIG. 3  illustrates an exemplary valve plate  42  in the inlet nozzle  34 . The inlet nozzle  34  extends tangentially to the cylindrical portion  38  of the flash tank  10 . The valve plate  42  may be attached to a hinge  46  fixed to a sidewall  48  of the flow passage  40  through the inlet nozzle  34 . An upstream end  50  end of the valve plate  42  is fixed to the hinge  46  and may be adjacent the sidewall  48 . 
     Pressurized black liquor flows through the flow passage  40  and, specifically, between the valve plate  42  and an opposite sidewall  52  of the inlet nozzle  34 . The valve plate  42  may extend downstream such that the downstream edge  54  of the valve plate  42  is proximate to an opening  56  in the side of the cylindrical portion  38  of the flash tank  10 . 
     The valve plate  42  pivots, see arrow  58 , about the vertical axis of the hinge  46 . The range of angles through which the valve plate  42  pivots is a design parameter to be selected during the design of the inlet nozzle  34 . The range of angles may swing the valve plate  42  from being adjacent to the sidewall  48  (a zero angle position) to a maximum angle position where the downstream edge  54  abuts the end of the opposite sidewall  52 . 
     The downstream edge  54  of the valve plate  42  will form an edge of the throat area (T in  FIGS. 2 and 4 ) of the flow passage  40 . The throat area T is the narrowest cross-sectional area of the flow passage  40 . The throat area T is directly related to the capacity, quantity of black liquor the flow passage  40  is capable of passing to the flash tank  10 . The throat area T of the flow passage  40  is widest and has a maximum capacity when the angle of the valve plate  42  is zero and the valve plate  42  is adjacent the sidewall  48 . The throat area T of the flow passage  40  is narrowest and has a minimum capacity, which may be a zero flow rate, when the valve plate  42  is at a maximum angle the downstream edge  54  nearest the opposite sidewall  52  of the flash tank  10 . 
     The downstream edge  54  of the valve plate  42  may have a replaceable or hardened strip  60 , e.g., soft metal such as copper or a plastic material capable of withstanding the abrasive conditions such as those from the black liquor, which may be available to act as a seal between the downstream edge  54  of the valve plate  42  and the opposite sidewall  52  or interior wall of the flash tank  10 . A similar strip  60  may be along the upper and lower side edges of the valve plate  42 . 
       FIG. 4  is a cross-sectional schematic diagram of the inlet nozzle  34  taken along a vertical plane and showing a side of the flash tank  10 .  FIG. 4  shows a view looking directly into the inlet nozzle  34  in a downstream direction of the flow passage  40 . The rectangular cross-sectional shape of the flow passage  40  is evident as is the oval or circular shape of the opening  56  to the flash tank  10 . The valve plate  42  is shown extending partially across the flow passage  40  and forming a rectangular throat area (T). The valve plate also extends across and blocks a portion of the opening  56  to the flash tank  10 . 
     The area of the flow passage  40  and portion of the opening  56  blocked or closed off by the valve plate  42  depends on the position of the valve plate  42  and particularly on the position of the downstream edge  54  (see  FIG. 3 ) of the valve plate  42 . The valve plate  42  may extend completely across the flow passage  40  and cover the entire flow passage  40 , from top to bottom and side to side. On the other hand, the valve plate  42  may be positioned to be parallel and adjacent the sidewall  48  and thereby open the flow passage  40  and opening  56 . 
     The motion of the movable, hinged valve plate  42  is controlled by a pneumatic or electro-mechanical actuator  62 , such as a pneumatic piston pump. The actuator  62  may have a cylindrical body  64  attached to the side of the flash tank  10  and a reciprocating shaft  66  driven by a piston in the cylindrical body  64 . A distal end of the shaft  66  is pivotable and is attached to the backside of the valve plate  42 . The actuator  62  may extend and retract the shaft  66  to move the valve plate  42  to open the throat area T or close the throat area T of the flow passage  40 . The shaft  66  extends through a port  67  in the sidewall  48  of the inlet nozzle  34 . The port  67  may include a seal to prevent leakage of black liquor. 
     A controller  68 , e.g., a computer or manual adjustment, determines the extension of the shaft  66  and the position of the valve plate  42 . The controller  68  may extend the shaft  66  to set the position of the valve plate  42  and achieve a desired throat area T for the flow passage  40 . The controller  68  may be adjusted manually to change or adjust the position of the valve plate  42 . Alternatively, the controller  68  may adjust the position of the valve plate  42  by computer, manual adjustment or other suitable means based on, for example, comparison between a desired pressure in the flow passage  40  and a sensed pressure in the flow passage  40 . 
     Hot black liquor extracted from the screens  20  of a vessel  12  flows through the inlet nozzle  34  and enters the flash tank  10 . The throat area T of the inlet nozzle  34  determines volume of flow or flow velocity using backpressure in the flow passage  40  which restricts the flow of black liquor entering the flash tank  10 . Because the throat area T is determined by the position of the valve plate  42 , the controller  68  can move the valve plate  42  to adjust the throat area T and consequently the velocity or volume of flow through the flow passage  40 . 
     Controlling the volume of flow or flow velocity in the inlet nozzle  34  allows for the velocity and volume of black liquor entering the flash tank  10  to be regulated, provides a degree of control over the pressure drop in the flash tank  10  and ensures a sufficient pressure in the conduits  26  upstream of the inlet nozzle  34 . 
     As the black liquor enters the flash tank  10 , the liquor flashes to produce steam  28  and condensate  30 . The steam  28  may be used as heat energy in the vessel  12 , in an impregnation vessel (not shown), in a chip feed bin (not shown), in a chip steaming vessel (not shown), in a tank holding fresh cooking liquor, e.g., white liquor, or other locations in the mill where steam is needed. The condensate  30  may flow to additional flash tanks  10  or other chemical recovery equipment (not shown), e.g., a recovery boiler, an evaporation system or other chemical recovery system. 
     The orientation of the valve plate  42  in the inlet nozzle  34  is a design choice. The hinge  66  for the valve plate  42  may be attached to either sidewall  48  or the top or bottom walls of the flash tank  10 . 
     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.