Abstract:
Apparatus ( 20 ) for injection of fluid into extrusion system components such as a preconditioner ( 24 ) or extruder ( 100 ) is provided, preferably as a composite assembly including a fluid injection valve ( 52 ) and an interconnected static mixer section ( 54 ). Alternately, use may be made of the fluid injection valve ( 52 ) or static mixer section ( 54 ) alone. The invention greatly simplifies the fluid injection apparatus used in extrusion systems, while giving more efficient absorption of thermal energy with a minimum of environmental contamination, and the ability to inject multiple streams into the extrusion systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a division of identically titled pending application Ser. No. 14/026,507, filed Sep. 13, 2013, which is a continuation of identically titled pending application Ser. No. 13/937,573 filed Jul. 9, 2013, both of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with improved apparatus for the injection of plural fluids into extrusion system processing components, such as preconditioners and extruders. More particularly, the invention is concerned with such apparatus, alone or in combination with extrusion system processing components, which include injector valves, preferably with interconnected static mixer sections, to efficiently inject steam/water mixtures (and other optional fluids, if desired) using greatly simplified equipment. 
     2. Description of the Prior Art 
     Extrusion cooking systems have long been used for the processing of various types of comestible products, such as human foods or animal feed. Such systems have a number of different components, but the principal processing components are an upstream product preconditioner coupled to a downstream extruder. In the preconditioner, initially dry ingredients are typically mixed with water and/or steam and oil in order to moisturize and partially pre-cook the ingredients. The preconditioned products are then fed into the extruder where the materials are subjected to increasing levels of temperature, pressure, and shear, and are extruded from restricted orifice die structure. In some instances, additional steam and/or water is injected into the extruder barrel during processing, as an extrusion aid and to facilitate complete cooking and forming of final products. 
     Conventional preconditioners generally include an elongated vessel or housing having one or two elongated, axially rotatable shafts therein having outwardly extending mixing elements or beaters thereon. As the ingredients are advanced toward the outlet of the housing, moisture in the form of steam or water is injected at separate locations along the housing length. Consequently, these preconditioners are equipped with corresponding manifolds with injectors leading to the interior of the housing. Moreover, delivery hoses are usually secured to the manifolds for delivery of moisture. This complicated apparatus can be difficult to service and clean, and requires sophisticated manual operator control to assure proper moisturization at the different injection locations. For example, U.S. Pat. No. 7,906,166 illustrates multiple-injector moisturization apparatus secured to a preconditioner housing. In other cases, additional such assemblies are used for injection along virtually the entire length of the preconditioner housing. 
     These conventional preconditioners tend to generate and vent a significant quantity of steam during use thereof. This is a serious problem for processors, owing to the fact that this escaping hot steam can readily mix with food particulates, creating a contamination problem as the materials coat the extrusion system components and the adjacent environment. This contamination is aesthetically unpleasant, and can create serious microbiological contamination problems as well. Moreover, the evolution of excess steam is a very inefficient waste of thermal energy. 
     The injectors used with typical preconditioners are of relatively small diameter, usually on the order of one-half-five-eighths inch, and can have relatively long lengths of over 6 inches. As such, it is quite common for the injectors to become partially or completely plugged during operation of the preconditioners, requiring down time and maintenance/cleanup. 
     Many of these problems are duplicated where extruders are equipped with conventional injectors, although not usually to the same extent as preconditioners. Nonetheless, it can be difficult to control and continuously operate an extruder where injection/contamination issues are faced. 
     There is accordingly a need in the art for improved injection apparatus which can be used with preconditioners and/or extruders in order to more efficiently inject plural fluids, while minimizing the plugging and contamination problems endemic with conventional extrusion systems, while optimizing the use of thermal energy. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems outlined above and provides improved apparatus for injection of fluids into extrusion system processing components, such as a preconditioner housing and/or an extruder barrel. The preferred apparatus comprises a fluid static mixer section including an elongated, tubular casing having a plurality of fluid inlets, a stationary mixing assembly within the casing and operable to mix plural fluids, and an outlet for delivering mixed fluids from the static mixer. The preferred apparatus further comprises an injector valve including a fluid inlet operably coupled with the static mixer outlet, a mixed fluid outlet, shiftable control valve structure, and an actuator operably coupled with the valve structure for selective shifting thereof. The overall apparatus has structure for permitting coupling of the valve fluid outlet to an extrusion system component selected from the group consisting of a preconditioner housing and an extruder barrel. 
     The composite static mixer/injector valve apparatus can be used with a preconditioner and/or an extruder for injection of fluids. In the case of a preconditioner, only a single composite apparatus is normally required, and in the case of an extruder, plural apparatus can be used adjacent the inlet end of the extruder barrel. 
     Although the composite apparatus is preferred, the invention is not so limited. That is, a preconditioner may be provided including fluid injection apparatus made up of an injector valve alone permitting selective injection of fluid into the preconditioner housing; the injector valve includes a fluid inlet, a fluid outlet, and shiftable valve structure for selective fluid flow control from the valve inlet to the valve outlet. 
     In order to minimize or eliminate plugging of the fluid injection apparatus, the axial distance between the valve outlet and the inner surface of the preconditioner housing should be less than about 3 inches, advantageously less than about 1 inch, and most preferably less than about one-half inch. Similarly, the diameter of the fluid-conveying structure of the injection apparatus should be relatively large, preferably at least about 1 inch. The combination of the large diameter fluid conveying-structure together with the short valve injection distance assures essentially plug-free operation of the preconditioner. 
     These same considerations apply in the context of fluid injection apparatus for extruders, i.e., the fluid-conveying components and the injection path lengths should be designed using the same diameter/length parameters recited above in the case of preconditioners. 
     While composite fluid injector valve/static mixer section injection apparatus is preferred, improvements can be realized using these components separately, i.e., a preconditioner or extruder may be equipped only with the injector valves of the invention, or conversely use can be made of static mixer sections without the need for injector valves. 
     The invention is primarily concerned with steam and/or water injection into extrusion components. However, other ingredients or additives can be injected separately or along with moisture, such as fats, colorants, emulsifiers, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a preconditioner in accordance with the invention, equipped with an improved fluid injection assembly including a fluid valve injector and a static mixing section; 
         FIG. 2  is a fragmentary top view of the preconditioner illustrated in  FIG. 1 ; 
         FIG. 3  is a vertical sectional view taken along the line  3 - 3  of  FIG. 2 ; 
         FIG. 4  is a perspective view of the access door of the preconditioner of  FIG. 1 , including a mounting bracket for the valve injector of the fluid injection assembly; 
         FIG. 4A  is an enlarged, fragmentary view illustrating a fluid injection valve assembly mounted on the door bracket of  FIG. 4 ; 
         FIG. 5  is a side view of a fluid injection assembly comprising an upright static mixing section, but without the use of a fluid valve injector; 
         FIG. 6  is a side elevational view of the internal mixing element forming a part of the static mixer section; 
         FIG. 7  is a perspective view of a twin screw extruder having four fluid injection assemblies mounted on the extruder barrel, with the assemblies comprising fluid valve injectors, without the use of static mixing sections; 
         FIG. 8  is a sectional view of a barrel section of the twin screw extruder, and illustrating four of the valve injectors of the invention mounted on a barrel section of the extruder; 
         FIG. 9  is an enlarged, fragmentary, sectional view of one of the valve injectors depicted in  FIG. 8 , and illustrating further details of the valve injector; and 
         FIG. 10  is a view similar to that of  FIG. 7 , but illustrating fluid injection assemblies including both fluid valve injectors and static mixing sections. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to  FIGS. 1-4 , a preconditioner  20  is illustrated, equipped with a composite fluid injection assembly  22  mounted thereon for delivery of mixed fluids, such as steam and water, to the interior of the preconditioner. The preconditioner is of the type described in U.S. Pat. No. 7,906,166, which is fully and completely incorporated by reference herein. 
     Broadly, the preconditioner  20  includes an elongated mixing housing  24  with a pair of parallel, elongated, axially-extending, rotatable mixing shafts  26  and  28  within and extending along the length thereof. The shafts  26 ,  28  are operably coupled with individual, digitally controlled, variable speed/direction drive devices (not shown). The preconditioner  20  is adapted for use with a downstream processing device such as an extruder or pellet mill, and is used to moisturize and partially cook comestible materials, such as human foods or animal feeds. 
     In more detail, the housing  24  has an elongated, transversely arcuate sidewall  30  presenting a pair of elongated, juxtaposed, intercommunicated chambers  32  and  34 , as well as a material inlet  36 , a lower material outlet (not shown), and a vapor vent  38 . The chamber  34  has a larger cross-sectional area than the adjacent chamber  32 , as will be readily apparent from a consideration of  FIG. 3 . The sidewall  30  has four, hingedly mounted access doors  40 , and the assembly  22  is secured to the rearmost access door  40  communicating with chamber  34 . This access door  40  is equipped with a mounting plate  42  having an injection aperture  43  which extends through the door and presents an innermost injection opening  43   a  ( FIG. 4A ). Of course, mounting plate  42  or other similar hardware can be affixed to other portions of the sidewall  30 , at the discretion of the designer. The opposed ends of housing  24  are equipped with end plates  44  and  46 , as shown. 
     Each of the shafts  26 ,  28  has a plurality of outwardly-extending mixing elements  48  and  50  thereon which are designed to agitate and mix material fed to the preconditioner, and to convey the material from inlet  36  towards and through the lower outlet. The elements  48  are axially offset relative to the elements  50 , and the elements  48 ,  50  are intercalated (i.e., the elements  50  extend into the cylindrical operational envelope presented by shaft  26  and elements  48 , and vice versa). Although the elements  48 ,  50  are illustrated as being substantially perpendicular to the shafts  26 ,  28 , the invention is not so limited; moreover, the elements  48 ,  50  are adjustable in both length and pitch, at the discretion of the user. It will be seen that the shaft  26  is located substantially along the centerline of chamber  32 , and that shaft  28  is likewise located substantially along the centerline of the chamber  34 . 
     The composite fluid injection assembly  22  of this embodiment broadly includes a fluid injection valve assembly  52  and a static mixing section  54 , and is designed to inject a plurality of mixed fluids into preconditioner  20 , such as steam/water or steam/water/additives. As explained in greater detail below, the assembly  22  simplifies the equipment required for fluid injection, is more sanitary, increases the energy efficiency of the preconditioner, and results in higher levels of moisture and/or cook in the preconditioned products, as compared with conventional fluid injection equipment. 
     The injection valve assembly  52  ( FIG. 4A ) includes a selectively actuatable valve body  56  having an internal mechanical drive (not shown) with an outwardly extending, axially rotatable stem  58 . The stem  58  is connected to a spherical valve ball  60  having a central passageway  62 . The ball  60  is located within a tubular segment  64 , which is received within an outer valve sleeve  66 . The inboard end of sleeve  66  is secured to mounting plate  42  by means of threaded fasteners. It will be observed that the central passageway  62  and the bore of segment  64  are of equal diameter, and that the opposed inboard and outboard faces  68 ,  69  of the segment  64  respectively define the fluid outlet  70  and fluid inlet  71  of the valve assembly  52 . In preferred practice, the valve assembly  52  is an automated valve, which can be controlled as a part of an overall digital control system for the preconditioner  20 . However, other types of valves may be used in this context. 
     The static mixing section  54  includes an upright tubular casing  72  with an uppermost tubular steam inlet  74  and an oblique water inlet  76 , preferably equipped with an atomizer  77 . A static mixer  78  is situated within casing  72  and includes an elongated, stationary central shaft  80  with a plurality of generally helical, outwardly extending plates  82  secured to the shaft  80 . The function of mixer  78  is to intensely mix incoming streams of steam and water, and any other desired additives, for delivery to injection valve assembly  52 . To this end, a pipe tee  84  is secured to the bottom end of casing  72 , and the transverse leg thereof is operatively coupled to the inlet  71  of valve assembly  52  by means of conventional piping  86 . 
     The lower end of tee  84  is equipped with a pipe section  88 , reducer  90 , and condensate outlet pipe  92 . The pipe  92  has an intermediate valve  94 , which is controlled by solenoid  96 . A resistance temperature probe  98  is operatively coupled with pipe  92  below valve  94 , and serves to measure the steam condensate temperature and monitor the presence of live steam prior to start-up of the system; once the temperature reaches 100 degrees C., the valve  94  closes and the system can start. Of course, the probe  98  and solenoid  96  are connected to the overall digital control system for the preconditioner  20  for automated control of valve  94 . 
     An important aspect of the invention is the geometry of the injection valve assembly  52  and the injection aperture  43 . In order to substantially reduce or even eliminate the possibility of plugging of the valve assembly  52 , the diameters of the injection aperture  43 , injection opening  43   a , valve ball passage  62 , the bore of segment  64 , the valve inlet  71 , and the valve outlet  70  should all be at least about 1 inch, and more preferably from about 1-2 inches, and are advantageously all the same diameter. Furthermore, the axial distance between the fluid outlet  70  and the injection outlet opening  43   a  should be held to a minimum. This distance should be no more than about 3 inches, preferably less than about 2 inches, still more preferably less than about 1 inch, and most preferably less than about one-half inch. 
     During the normal operation of preconditioner  20 , dry ingredients are fed to the inlet  36  during rotation of the shafts  26 ,  28 . Simultaneously, appropriate quantities of steam and/or water are directed through the inlets  74 ,  76  and are thoroughly blended during passage through static mixing section  54 . This blended mixture is passed into the injection valve assembly  52  through tee  84  and piping  86 , whereupon it is injected into the interior of housing  24  for mixing with the dry ingredients. During this sequence, the valve  94  is closed. When the temperature probe  98  detects the buildup of condensate above valve  94 , the latter is opened to allow collected condensate to drain from the system via pipe  92 . 
     Although the composite fluid injection assembly  22  has been illustrated and described in connection with a preconditioner, this assembly can also be used in the context of single or twin screw extruders. Furthermore, improved fluid injection results can be obtained when using the individual components of the assembly  22 . Hence, either preconditioners or extruders may be equipped with fluid injection valve assemblies  52  or the static mixing sections  54  to achieve improved results. It is preferred, however, to employ the composite injection assembly  22 . 
     For example,  FIG. 7  illustrates a twin screw extruder  100  equipped with four fluid injection valve assemblies  52  secured to the inlet head  102  of the extruder. The extruder  100  is itself of conventional design and includes an elongated, tubular, multiple head extruder barrel  104  made up of inlet head  102 , intermediate head  106 , and terminal head  108 . As illustrated, the inlet head  102  is equipped with a material inlet  110  adjacent the input end of the barrel  104 , whereas a restricted orifice die assembly  112  is provided at the outlet end of the barrel. Internally, the extruder  100  has a pair of elongated, axially rotatable, multiple-section extruder screws each having a central shaft with outwardly extended helical flighting thereon (see  FIG. 9 ). Material delivered to inlet  110  is subjected to increasing levels of temperature, pressure, and shear during passage through the extruder and such material is ultimately extruded through assembly  112   
     During the course of extrusion of many types of comestible materials, it is important that steam and/or water, with or without additional ingredients, be injected into the barrel where it is thoroughly mixed with the previously preconditioned ingredients during the extrusion cooking process. In the embodiment of  FIG. 7 , four of the injection valve assemblies  52  are secured to inlet head  102  at respective locations where injection bores  114  are formed through the sidewall of the head  102 , terminating in openings  114   a . A water and/or steam line  116  is secured to the input of each valve assembly  52 , in lieu of the piping  86 .  FIG. 10  illustrates the extruder  100 , but in this case equipped with the previously described complete fluid injection assemblies  22  mounted on the head  102 .  FIG. 9  further illustrates the internals of the twin screw extruder  100 , including the previously mentioned pair of extruder screw assemblies, labeled as  120 ,  122 , situated within an extruder barrel. Another option would be to have only a single static mixer section  54  plumbed for connection with the four injection valves  52  illustrated in  FIG. 10 . 
     In the foregoing extruder embodiments, the fluid injection assemblies have each included the fluid injection valve assemblies  52 . In these embodiments, the same geometrical considerations apply as in the case of the preconditioner embodiments. Specifically, in order to avoid plugging, the diameters of the passageway  62  and bore  117  should both be at least about ½ inch, and more preferably from about 1-2 inches, and are preferably of the same diameter. The axial distance between the fluid outlet  70  and the opening  114   a  should be no more than about 3 inches, preferably less than about 2 inches, still more preferably less than about 1 inch, and most preferably less than about one-half inch. 
     In other cases, use may be made of an injection assembly without an injector valve. As illustrated in  FIG. 5 , a fluid injection assembly may include the previously described static mixing section  54 , with tee  84  and related piping which is directly secured to a preconditioner and/or extruder barrel, as the case may be. 
     The use of composite fluid injection assembly  22  with preconditioner  20  results in a number of important advantages not obtainable with prior fluid injection apparatus, typically making use of a plurality of injectors and associated manifolds, piping, and hoses. For example, the preferred composite fluid injection apparatus gives at least the following improvements:
         Static Mixer—mixes/blends steam and water (and optional additional ingredients), delivering superheated water to the conditioning cylinder.
           No mechanical mixing.   No Venturi mixing.   
           Water Injector to Static Mixer—Atomizes water to provide more surface area to condense steam in the static mixer.   Automated Control Valve—Automated open/close valve that is closely mounted to the body of the conditioning cylinder allows for the efficient delivery of steam/water to the process, and is mounted in a manner to minimize the distance between the valve and the cylinder body to reduce injector plugging potential.   Condensate Resistance Temperature Detector—Determines the buildup of condensate.   Condensate Solenoid Valve—Upon detection of condensate, the solenoid valve opens to drain the condensate.   System Controls—Controls are tied into the overall extrusion system control software, such as the Wenger APM System, for the automated control of the valve and condensate temperature detector.       

     The principal advantages of the fluid injection assemblies include:
         Reduces the number of steam and water injection ports from typically 5-6 for steam and water injectors (10-12 total) to one.
           Simplifies control of system for operators and troubleshooting for maintenance
               Reduces operator influence on system, allowing better automated control.   Improves operation and product quality consistency.   
               Eliminates the need for multiple steam and water manifolds.
               Improves sanitary design of the conditioning cylinder by reducing the number of obstructions to clean around.   
               Reduces the number of valves, hoses, and injectors that have to be maintained and replaced.   
           Location of the fluid injector valve on the preconditioner housing or extruder barrel greatly reduces the potential for injector plugging:
           Increases equipment up time.   Improves process control.   Improves product consistency and quality.   
           Significant reduction in discharge steam vapor discharged from the system.
           Increase steam and water consumption on a per unit basis.   Reduces the food safety and sanitation risk from steam vapor and associated fine food particulate matter going into the atmosphere and potentially contaminating equipment and environment.   
           Utilizes a static mixer to combine the process team and water:
           Increases temperature of water to allow for better absorption into the product.   Reduces steam vapor that can blow through the produce and not be absorbed.   
           Higher product temperatures from the preconditioner
           Improved adsorption of the steam and water inputs result in higher product temperatures.   Achieves control point temperatures at lower steam and water inputs.   
           Higher starch gelatinization (cook) values
           The improved adsorption of the inputs increases cook potential and consistency   Higher cook values during preconditioning provide opportunity for higher final product cook values from extruder.   
               

     As indicated, use of the fluid injection apparatus is particularly important in the case of preconditioning of food or feed materials prior to extrusion thereof. In order to demonstrate the superiority of the present invention versus conventional fluid injection apparatus, a series of test runs were carried out using the improved preconditioner of the invention equipped with the composite assembly  22  of the invention, versus an otherwise identical preconditioner having the normal multiple steam/water injectors along the length of the preconditioner housing. In all cases, the individual comparative tests involved the same feed recipes (pet or aquatic feeds) with the same thermal energy inputs, retention times, and the like. 
     The test results confirm that the preferred apparatus of the invention consistently yields higher cook values (as measured by the extent of starch gelatinization) at a variety of preconditioner mixing intensities and feed rates. These improvements, coupled with the reduction in steam vapor venting from the apparatus of the invention and consequent better energy utilization, are salient features of the invention.