Patent Document

BACKGROUND OF THE INVENTION 
     The present invention relates to discharge ports in a pressurized vessel used to process biomass feed materials. In particular, the present invention relates to an assembly of valves and nozzles in a discharge port of a pressurized vessel. 
     Biomass feed material is typically processed in a vertical pressurized vessel. The feed material enters an upper inlet of the vessel, is cooked or otherwise processed in the vessel and is discharged from a port at the bottom of the vessel. The biomass feed material may be pre-treated in the vessel, such as by steaming or by hydrolysis, or the vessel may digest the biomass feed material to convert the biomass to fibers or otherwise process the biomass. In addition, the pressurized vessel may be a steaming and pressurizing device wherein the nozzle in the discharge port causes the biomass feed material to undergo steam explosion pulping. 
     Biomass feed material general includes one or more of cellulosic feed material, e.g., wood chips, shredded agricultural residues like straws or corn-stover, fuel energy crops like switchgrass, biomass sorghum or miscanthus, paper pulp and comminuted biomass materials. In addition, the feed material as it flows through the discharge port of the pressurized vessel may be in a slurry including cooking chemicals (which tend to be corrosive) and a large quantity of steam. 
     Steam explosion pulping typically involves steam used to break apart the cellulosic fiber structure (explosion pulping) of cellulosic biomass feed material. Steam explosion pulping has been used, for example, for enzyme hydrolysis. In steam explosion pulping, pulp is produced from cellulosic biomass feed material by pressurizing feed material with steam and subsequently rapidly reducing the pressure of the feed material impregnated with the steam. The rapid pressure reduction causes steam in the cells of the biomass feed material to expand and burst the cells to produce pulp. The pulp is further processed, for example, with enzymes to convert the pulp to sugars. 
     In steam explosion pulping, the rapid pressure reduction of the biomass feed material may be performed using a blow-valve at an outlet of a pressurized cooking vessel or conduit. Upstream of the blow-valve, the biomass feed material is pressurized to, for example, 6 bar to 25 bar, and infused with steam. Upstream of the blow-valve, the cellulosic biomass feed material may also be impregnated with chemicals, such as acids, added to a cooking reactor in which the pulp is steamed and held under pressure. 
     A conventional swept orifice discharge assembly includes a single ball valve or segmented ball valve connected to each discharge outlet at the bottom of a pressurized vessel. The biomass feed material flows through the ball valve and the discharge outlet directly to a blow tank. The ball valve or segmented ball valve is adjustable to control the flow of biomass feed material through the discharge outlet. The flow rate of the biomass feed material from the pressurized vessel is regulated by the ball or segmented ball valve in a conventional orifice discharge assembly. 
     The biomass feed material frequently contains solid material, e.g., dirt, sand and other hard particles, that wear and damage the components of an orifice discharge assembly. The ball or segmented ball valve of a conventional swept orifice discharge assembly is particularly susceptible to wear and damage from the solid material in the biomass feed material. The adjustability of the ball or segmented ball valve, the large pressure differential across the valve and the solid material in the biomass feed material cause excessive wear to the valve and result in frequent replacement of the valve. 
     To replace conventional ball valves and segmented ball valves requires the pressurized vessel to be shut down and the flow of biomass feed material to be temporarily stopped while the valve is replaced. In addition to the cost of lost biomass production, the cost of material and labor to replace or repair a ball or segmented ball valve is expensive. Discharge assemblies having multiple adjustable valves and nozzles have been used to provide alternative nozzles and valves for use when one nozzle and valve becomes clogged. The discharge assemblies with multiple valves and nozzles have adjustable valves with each nozzle that are prone to the same wear and damage described above. There is a long felt need for a pressurized vessel discharge assembly that is resistant to solid material in biomass feed material, may be repaired without interrupting the production of biomass feed materials, and is inexpensive to repair or replace. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An assembly of valves and nozzles has been developed to replace the single ball valve and nozzle conventionally used at the discharge port of a pressurized vessel. The assembly may include multiple pairs of nozzles and valves arranged on and attached to the outer periphery (sidewall or underside) of the discharge assembly coupled to the bottom of a pressurized vessel or other conduit of biomass feed material. The valves may be conventional on-and-off valves that are more resilient to wear and less prone to damage as compared to ball or segmented ball valves. The valves may be each attached directly to a discharge port of the outer periphery of the discharge assembly. The valves may be arranged at the upstream inlet to the nozzles. The nozzles may be each attached between a valve and a conduit for directing the biomass feed material to a subsequent processing station. 
     The multiple nozzles may have different flow capacities, e.g., different throat diameters, such that the rate of biomass feed material flowing through each nozzle is a different rate than the rate flowing through one or more of the other nozzles. The flow rate of biomass feed material is selected by directing the biomass feed material through the nozzle having the desired flow capacity. In addition, a nozzle may be repaired or replaced by directing the biomass feed material through another nozzle and servicing the nozzle while the biomass feed material continues to flow through the other nozzle. 
     A valve and nozzle assembly has been conceived for a discharge assembly comprising: a plurality of discharge openings in the discharge assembly; a plurality of valves each coupled to one of the openings, and a plurality of nozzles each coupled to one of the valves within the plurality of discharge openings, wherein a first nozzle may have a greater flow capacity than a second nozzle. 
     A discharge assembly has been conceived including: a chamber having an sidewall extending around a perimeter of the chamber, an open upper region, an flange coupling at an upper region of the sidewall and extending around the upper region and a bottom, wherein the chamber receives a rotating impeller; a plurality of discharge openings in at least one of the sidewall and bottom of the chamber; a plurality of valves each coupled to one of the discharge openings, and a plurality of nozzles each coupled to one of the discharge openings and downstream in the opening to the valve for the opening. 
     A method has been conceived for discharging feed material from a discharge assembly of a pressurized vessel, the method comprising: coupling each of a plurality of valves to each of a plurality of discharge openings of the discharge assembly; coupling each of a plurality of nozzles to one of the valves, wherein the plurality of nozzles may include a first nozzle and a second nozzle having a greater flow capacity than the first nozzle; selecting the first nozzle or second nozzle based on a desired flow rate or pressure drop of the biomass feed material flowing through the discharge assembly, and, opening one of the valves corresponding to the selected first or second nozzle and closing the other valve to allow biomass feed material to flow through the open valve and selected first or second nozzle and preventing a flow of biomass feed material through the other valves. The feed material may include biomass feed material. The multiple discharge openings may be arranged at the periphery of an impeller, and the method further comprises the rotation of the impeller to move the feed material into an open discharge opening(s). 
     In the method, the plurality of nozzles may each have a throat having a cross-sectional area different than that of the throat of the other nozzles, and the step of selecting the first nozzle or second nozzle includes selecting a nozzle based on a desired flow rate for discharging the material. 
     The plurality of nozzles may each have a replaceable nozzle liner. The step of replacing the nozzle liner may be performed while feed material is discharged through another discharge openings, nozzle and valve arrangement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a bottom discharge assembly for a pressurized vessel. 
         FIG. 2  is a perspective view of the discharge assembly with the interior visible of the conical housing to show the impeller. 
         FIG. 3  is a perspective view of a cross-section of the discharge assembly showing cut-away views of a housing, valve and nozzle. 
         FIG. 4  is a perspective view of a discharge assembly connected to a conduit via a cylindrical coupling. 
         FIG. 5  is a perspective view of a discharge assembly having nozzle and valve pairs at a bottom surface of the assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a discharge assembly  10  attached to the bottom discharge of a pressurized cylindrical vessel  12  (shown schematically), such as a chemical digester, a pre-treatment vessel, pressurized cooking reactor, hydrolyzing vessel and a steam explosion device. The discharge assembly  10  includes multiple assemblies of valves  13 ,  43  ( FIG. 3 ) and nozzles  14 . The valves  13 ,  43  ( FIG. 3 ) may each be conventional on-off valves  15  turned manually by a handle  17  or automatically by remote control of an actuator. 
     The valves may be upstream of the nozzles  14  (see valve  43  in  FIG. 3 ) and, optionally, between the nozzles  14  and an inlet to a blow line  16  (valve  13  in  FIG. 1 ). The discharge of each nozzle or valve is connected to a blow line  16 , only one of which is shown in  FIG. 1 . The blow line  16  may be a pipe or other conduit that transports biomass feed material from the pressurized vessel  12  to a collection vessel, such as a cyclone, a blow tank or other vessel. 
     The discharge assembly  10  includes an upper frustoconical or cylindrical housing  18  between a bottom of the pressurized vessel  12  and an annular assembly  20  of valves and nozzles. Annular flanges  21  on the conical housing and the nozzle valve assembly are connected together by fasteners, such as bolts. A motor and gearing assembly  22  rotates an internal vertical shaft  24  that turns an impeller in the assembly  20 . 
       FIG. 2  is a perspective view of a lower portion of the discharge assembly  10  with the interior visible to show the impeller  28  that is rotated by the shaft  24 . The embodiment shown in  FIG. 2  has a cap  25  on top of the shaft and the shaft. 
     The impeller  28  has radial vanes  30  that may be straight (as shown in  FIG. 2 ), swept or otherwise shaped to move biomass material radially outward to the inlet(s) to the nozzle(s)  14  and valve(s)  13 ,  43  at the periphery of the wall  36 . The impeller  28  is seated in an annular chamber  32  having a bottom surface  33  and an outer cylindrical wall  36  at the outer periphery of the chamber  32 . The vanes  30  are attached to a collar  34  on the shaft and rotate with the shaft. The bottom edges of the vanes  30  are complementary to the bottom surface  33  of the chamber such that the vanes sweep the bottom surface as they rotate in the chamber  32 . 
     The cylindrical outer wall  36  of the chamber  32  includes circular discharge openings  38  that extend from an inside surface of the wall facing the chamber to an outside surface of the wall. The openings  38  may by cylindrical, slightly conical or have some other shape. The openings  38  may be at the same elevation and each be symmetrically arranged at different radii of the axis of the assembly  20  of valves and nozzles. 
     The annular housing  40  for each pair of the valve  43  and nozzle  42  pairs may be mounted in a respective opening  38  in the wall  36 . An inner axial passage through each housing  38  may receive a conical or cylindrical nozzle liner  42  that slides into and fits in the housing. The inner axial end of the housing  40  is concave and flush with the inside surface of the wall  36  of the chamber. The outer axial end of the housings  40  mates with an inlet of a valve  13  or conduit  16 . The housing  40  and opening  38  may be arranged such that a lower edge of a biomass flow passage through nozzle liner  42  is adjacent the chamber bottom  33  to avoid creating a gap between the housing and bottom of the passage where abrasive or other debris can accumulate in the chamber. 
       FIG. 3  is a perspective view of a cross-section of the discharge assembly showing cut-away views of the assembly  20  of valves and nozzles. The radially outer ends of the vanes of the impeller  28  sweep across the inlets to the nozzles. Valves  43  are positioned in each inlet and beyond the periphery of the impeller. These inlets are the passages in the nozzle liners  42 . The sweeping movement of the impeller and the pressure in the vessel keep the biomass from becoming stagnant and plugging the nozzle. The internal pressure in the vessel forces the biomass material through the nozzle. 
     A nozzle flow passage extends from the inner wall  36  of the chamber, through the nozzle liner  42 , and to the valve  13  and blow line  16 . The flow passage allows biomass feed material from the chamber  32  to pass through the nozzle liner. As the feed material passes through the nozzle flow passage and is discharged from the passage or valve, the feed material undergoes a substantial pressure drop such that steam explosion pulping occurs. 
     The valve  13  is coupled to an outlet of the nozzle flow passage. The valve  13  may have a ball turret valve  15  and a stem handle  17  that is manually operated to open and close the nozzle flow passage. The inlet to the valve  13  is coupled, e.g. bolted, to the housing  40  or a flange associated with the housing  40 . The outlet of the valve may be uncoupled from the blow line  16  if the valve is closed. 
     The nozzle liner  42  may be concentric with the nozzle flow passage and the housing  40 . The nozzle liner  42  includes a throat  48  that defines a smallest area of the passage. The nozzle liner  42  may be cylindrical and include an end flange  44  that seats in an annular recess on the outer face of a housing  40 . The flange  44  for the nozzle liner is affixed to the housing by, for example, clips  49  attached to the rim of the flange. The nozzle liner  42  may be removed and replaced from the housing. For example, the nozzle liner may be removed by releasing the clips holding the flange  44  and sliding the liner out of the housing in an axial direction. 
     The nozzle liner  42  may have a tapered outer diameter. For example, the outer diameter of the inlet end of the liner  42  may be larger than at the outlet end or vice versa. A nozzle liner  42  with a tapered outer diameter fits into a complementary tapered opening  38  in the wall. The nozzle is easily removable from the opening  38  in the housing when the flange  49  is removed and after closing the valve  43  corresponding to the nozzle liner to be replaced. 
     Multiple on and off valves  43 ,  13  and nozzles  14  allow for the redirection of the biomass production to separate collection device, such as a start-up cyclone to separate the product stream during start-up which does not meet the required product specifications. 
     The nozzle liner  42  may be formed of ceramic or other durable material. The nozzle liner  42  has a hard surface at the inner flow passage that provides high resistance to wear as compared to the wear resistance of ball valves and segmented valves. Further, the nozzle liners are less expensive than ball and segmented ball valves. 
     The passage through the nozzle liner  42  may be cylindrical, conical or have converging and diverging sections separated by a throat. The throat  48  is the narrowest or smallest cross-sectional diameter portion of the passage in the liner  42 . The nozzle liner may be a laval type nozzle in which the passage is a venture having a converging and diverging sections with a throat  48  between the sections. 
     The internal throat  48  of one of the nozzle liners  42  may have a cross-sectional area that differs from the throat cross-sectional area of liners in the other nozzles. The differing cross-sectional areas, e.g. each throat  48  has a different diameter, provides nozzles with different flow capacities. The size and shape of the passage through the nozzle liner, e.g., the throat area, regulates the velocity and steam explosion of the biomass feed material flowing through the nozzle. 
     A desired flow rate, pressure drop or other condition of the biomass feed material can be achieved by selecting one of the nozzles  14  to be the discharge nozzle through which biomass feed material passes from the vessel. The valve  13  associated with the selected nozzle is turned on so that the biomass feed material flows through that nozzle. The other nozzles  14  are shut off by turning off the valves  13  associated with those nozzles. 
     The rapid pressure drop desired to achieve steam explosion pulping is achieved by selecting the one nozzle  14  of the plurality of nozzles that has appropriate flow capacity. Selecting the appropriate nozzle, opening the valve  13  associated with a selected nozzle  14  achieves the desired pressure drop for steam explosion pulping without the use of a conventional adjustable flow rate valve, such as a ball or segmented ball valve. 
     By substituting a simple on and off valve for an adjustable flow rate valve, the expensive maintenance and repair of adjustable flow rate valves is avoided. Further, steam explosion pulping may continue through one of the valve and nozzle assemblies while an unselected nozzle is repaired or replaced. The extra cost and labor associated with multiple blow lines (conduits  16 ) connected to the discharge assembly is favorably offset by the savings achieved by avoiding biomass feed material production losses due to repairs and avoiding the usage of ball and segmented ball valves. 
     The valve  43 ,  13  is not substantially subjected to damage and wear due to the biomass feed material and its associated pressure drop or because the valve is either fully open or fully closed. The valves  43 ,  13  require minimal replacement and repair because they are simple on and off valves. The valve  43  upstream of the nozzle liner  42  may be a simple on-off valve, such as a sliding door, knife gate valve, ball valve or butterfly valve. The valve  43  may be actuated manually by a control wheel or automatically by a solenoid that is remotely controlled. Closing the valve  43  shuts off flow through the nozzle and allows the nozzle liner to be repaired or replaced. 
     Adjustments to the discharge flow of biomass feed material from the vessel  12  is achieved by selection of the nozzle  14  used to discharge the material. If there are changes in the requirements for the pressure drop needed for steam explosion pulping or in the discharge flow of the biomass feed material, the nozzle  14  selected to be the discharge nozzle may be changed to stratify the changed requirements. Changing the selected nozzle may involve opening and closing the appropriate valves  13  and connecting and disconnecting blow lines  16 . Similarly, replacing a worn nozzle may involve redirecting the flow of biomass feed material to an unused nozzle, shutting the valve for the worn nozzle and replacing the worn nozzle, without interrupting the process flow of biomass feed material. 
     When the biomass production is either increased or decreased further, the production is switched to another nozzle and valve assembly. This switching allows to either completely open the valve at the active discharge opening and to completely close the other openings. A partial opening valve is not required. 
       FIG. 4  is a perspective view of a discharge assembly  10  connected to a pipe conduit  50  via a cylindrical coupling  52 . The conduit  50  is another example of a pressurized vessel to which the discharge assembly is connected. The cylindrical coupling includes an upper edge  53  that may be welded to an opening in the conduit  50 . The coupling  52  may include a flange  54  that connects to the upper flange  21  of the assembly  20  of the discharge assembly  10 . Nozzles  14  may include a first nozzle  14 -A and a second nozzle  14 -B having a different flow capacity different than first nozzle  14 -A. First nozzle  14 -A or second nozzle  14 -B may be selected based on a desired flow rate or pressure drop of the biomass feed material coming from pipe conduit  50  that subsequently flows through discharge assembly  10 . 
       FIG. 5  is a perspective view of the discharge assembly  10  wherein the pairs of nozzles  14  and valves are arranged on the underside of the assembly  20  of valves and nozzles. The housing  40  for each pair of nozzle and valve is positioned on an outer surface of the housing for the assembly  20  of nozzles and valves. The outer surface may be, for example, a bottom surface as shown in  FIG. 5  or a side surface as shown in  FIGS. 1 to 4 . 
     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.

Technology Category: 7