Patent Publication Number: US-2009238920-A1

Title: Process for making high grade protein product

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 61/038,688, filed on 21 Mar. 2008, the disclosure of which is incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention is directed to a process for making high grade protein product, such as a mammalian feed product, from a residual mixture of distilled grains, distilled dried grains, alcohol and other residual liquids formed during the conversion of starch and sugar to alcohol in a biomass distillation process. 
     BACKGROUND OF THE INVENTION 
     Typical cellulose plant fermentation processes use catalysts, enzymes and/or yeast to convert starch and/or cellulose into sugars for fermentation. The fermentation product typically includes a mixture of alcohol, yeast, enzymes, water, carbon dioxide, and grain and/or cellulose residues. The mixture is distilled to volatilize and remove much of the alcohol. The remaining residue is typically in the form of a biomass slurry (whole stillage) that also includes residual alcohol, yeast, enzymes, water and carbon dioxide. Known energy intensive water removal processes result in distilled grains (“DG”) called wet cake, and distilled dried grains with solubles (“DDGS”). 
     Wet distiller&#39;s residue spoils rapidly without drying or specialized and expensive preservation measures. The high cost of transporting heavy wet biomass residue generally prohibits its use more than 100 miles from the biorefinery. Various energy-intensive techniques have been employed to partially dry the residue, but generally do not achieve product moisture contents below about 10% by weight. Conventional heat drying technologies can damage the residue and its nutritional value, and do not convert the residue to a multi-use, very dry, storage-stable product. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a process and apparatus for making a high grade protein product, such as a mammalian feed product, by converting the protein-rich residue slurry following fermentation and distillation into a dry, crunchy, partially leavened protein-rich product with less energy expenditure than known art. The term “high grade protein product” refers generally to a product that is both rich in protein and storage-stable. The process includes the steps of providing a residual slurry, compressing the residual slurry (suitably under devolatilizing vacuum) to remove liquids without adding heat and form a compressed product, shaping the compressed product into one or more strands, further drying the compressed product to a low moisture content, and granulating the one or more strands to form the granulated high grade low moisture protein product. The high grade protein product can have many uses, such as a mammalian feed product, and can be formed from any fermentation and distillation residue. Residual alcohol may cause some leavening of the product during the shaping and subsequent heating steps. The leavening contributes to a lightweight, crunchy nature of the protein product. If the product is used for feed, then flavor enhancers, nutrients, texture modifiers and material to precipitate or chemically bind some unwanted nutrient components can be added during the process. The residual liquid removed during the compression step can be further distilled to separate the residual alcohol from the liquid. 
     The process of the invention permits processing of the residual biomass slurry at any location, including its point of collection, due to its energy efficiency and size compared to conventional processes. Because the resulting product has low moisture content, it can be stored for long periods without spoiling. 
     With the foregoing in mind, it is a feature and advantage of the invention to provide a process for making low moisture, high grade protein feed product from the residual biomass slurry of a fermentation and distillation process. It is also a feature and advantage of the invention to provide a process which converts the fermentation and distillation residue into a product having a profitable yield, which can be practiced at the site where the biomass slurry is generated. It is also a feature and advantage of the invention to provide the process at low energy cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a block diagram of the process of the invention. 
         FIG. 2  schematically illustrates an apparatus useful to practice the process of the invention in a continuous fashion. 
         FIG. 3  schematically illustrates an alternative apparatus useful to practice the process of the invention in a continuous fashion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a process  10  for making the high grade protein product is illustrated. Initially, hydrolysate formed from cellulose or starch conversion to sugars is directed via inlet  12  into a fermentation tank  14  where it is combined with yeast which converts sugars into alcohol useful for fuel and other purposes. The hydrolysate can be derived from various sources of starch or cellulose, including without limitation wood from trees, such as pine soft wood and other kinds of softwood and hardwood; food plants, such as corn, wheat, barley and soybeans; grasses; and other sources of starch and cellulose. 
     The fermentation product mixture exits the fermentation process via stream  16  and can include a mixture of alcohol, cellulose, grain residue, enzymes and/or yeast, water, carbon dioxide and possibly other by-products and ingredients. The fermentation product mixture is fed via stream  16  to a distillation process  18 , which may include one or more conventional distillation columns for distilling much of the alcohol. The distillation process  18  employs evaporative techniques, such as heat and vacuum, to volatilize and remove much of the alcohol product through exit stream  20 . The residue from the distillation process exits via stream  22 . The residue may include a combination of a plurality of ingredients selected from distiller&#39;s grains (“DG&#39;s”), dissolved sugars and proteins (“solubles”), residual alcohol, water, carbon dioxide, yeast, enzymes, and other by-products and ingredients. The DG&#39;s and solubles are often rich in protein and have potential nutritional value. 
     The following process steps, taken alone or in combination with the foregoing fermentation and distillation steps, are considered to define the invention. The residue from the distillation process is fed to suitable compression apparatus  24  which compresses the residue under vacuum to remove much of the residual alcohol, water and other liquid through exit  26 . A compressed residual product is formed, which contains much less liquid, which exits the compression apparatus via stream  28 . Whereas the residue entering the compression apparatus  24  via stream  22  may have a liquid content of greater than about 80 percent by weight, the compressed residual product that exits via stream  28  may have a much reduced liquid content of about 3 to about 8 percent by weight. 
     In one embodiment, flavor enhancers, nutrients, texture modifiers and other food product-enhancing ingredients can be added into the residue stream  22  before or during the compression step. In order to avoid having the food product-enhancing ingredients removed in large part via liquid stream  26 , it may be more advantageous to add them at later stages of the process  10 , for example, into compressed residue stream  28  via inlet stream  27 , or into shaping apparatus  30  via inlet stream  29 . Exemplary flavor enhancers include without limitation grain extracts, synthetic flavors, mineral salts, and combinations thereof. Exemplary nutrients include without limitation vitamins, minerals, proteins, and combinations thereof. Exemplary texture modifiers include without limitation grain extracts, proteins, synthetic additives, and combinations thereof. Other food product-enhancing ingredients include without limitation organic and inorganic precipitants, texture modifiers, and combinations thereof. 
     The compressed residue enters shaping apparatus  30  via stream  28 . The shaping apparatus shapes the compressed residue into one or more strands. The strands may have any elongated, relatively narrow shape that is suitable for subsequent drying and granulation. The strands may have a cross-section that is circular, ellipsoidal, square, rectangular, triangular, parabolic or otherwise, and may have an average diameter of about 1 to about 30 centimeters. 
     The strands may exit the shaping apparatus  30  via stream  32  and enter a drying apparatus  34  which typically employs heat, with or without vacuum, to dry the strands. The drying apparatus  34  may employ heated air or inert gas at a temperature of about 30° C. to about 180° C., for a time of about 1 to about 10 seconds, to accomplish sufficient drying of the elongated strands. Convection and/or vacuum may also be employed to facilitate drying of the strands. The strands should be dried to a moisture content of less than about 3% by weight, suitably less than about 2% by weight, or less than about 1% by weight, or less than about 0.5% by weight, or less than about 0.2% by weight. 
     Residual alcohol in the strands may facilitate leavening (expansion) of the elongated strands in the drying apparatus. The leavening helps the resulting high grade protein product develop a lightweight, texturized, crunchy constituency. 
     In an alternative embodiment, described further below, the compressed residue may be dried, such as by flash drying, and then shaped into strands before being cut. In other words, the order of steps may be varied to suit the specific processing techniques employed. 
     The dried elongated strands exit the drying apparatus  34  via stream  36  and are granulated into high grade protein product particles using a granulation device  38 , which can be a conventional mechanical shearing device or pelletizer. As explained below, the drying and pelletizing can also be accompanied using an apparatus that has been optimized for explosive drying and air cooling. The resulting particles travel via stream  40  into a package or other storage device  42 . The drying, processing and storage of the high grade protein product particles greatly extends their storage life for useful purposes. Carbon dioxide from the fermentation process can be used in the storage containers to further stabilize the product particles during storage. If desired, nitrogen and other inert or stabilizing gases can also be injected into the package or other storage device. 
       FIG. 2  illustrates an apparatus  100  for continuously making the high grade protein product particles from a residue that includes a plurality of ingredients selected from DG&#39;s, DDGS&#39;s, residual alcohol, water, carbon dioxide, yeast, enzymes, and other by-products and ingredients. The residue  122  that is processed by the apparatus  100  of  FIG. 2  may be the same residue that is supplied by stream  22  shown in  FIG. 1 . The residue  122 , typically a slurry, may be fed continuously from a hopper  110  into a compression extruder  124  which performs the compression step  24 , illustrated in  FIG. 1 . The compression extruder  124  includes a housing  102  having a diameter which becomes progressively narrower toward a distal end  103 , a drive shaft  104  driven by motor  106 , and a screw press  108  having plates  109  whose diameters become progressively narrower toward the distal end  103  of the housing  102 . The plates  109  may also become progressively smaller in pitch toward the distal end  103 . 
     The screw press  124  may also include internal mixing paddles and/or screw flights to convey the slurry residue forward. As the slurry residue  122  is conveyed forward in the compression extruder  124 , the changing geometry of plates  109  squeezes and compresses the slurry residue  102  causing residual liquid to exit through channel  126  into tank  112 . Vacuum may also be applied to the compression extruder  124  to remove further liquid. The liquid entering tank  112  can then be processed for further separation and distillation of alcohol from the liquid. 
     The compressed residue from the screw press  124  enters a narrower shaping module  130  where it is continuously extruded into shaped residue configured as a plurality of elongated narrow strands  132 . The pressure built up in the compression extruder  124  drives the extrusion through the shaping module  130 . In one embodiment, the plates  109  can be configured to define specific compartments in the screw press  124  such as one or more compartments mainly for removing liquids, one or more compartments for accepting food-enhancing ingredients, one or more compartments for compression and shaping, etc. One suitable extruder for screw press  124  which can employ plates to define compartments is a PAMA ROMA® extruder available from Parsi Macchine s.r.l. of San Cesario, Italy. The shaping module  30  may be in the form of an elongated extrusion barrel which is equipped with an extrusion die  131 , and which is adapted to engage the downstream end of screw press  124 . The shaping is performed by continuously extruding the compressed residue through extrusion die  131 . 
     The strands  132  from the shaping module  130  are continuously passed through a drying and leavening chamber  134  which can be a temperature-controlled block formed of steel or another metal. While in the chamber  134 , the strands  132  are exposed to heated gas at a sufficient temperature and for a sufficient time to dry the strands  132  to a desired low moisture content. One advantage of the chamber  134  is that the residence time under heat may be controlled to facilitate controlled leavening (expansion) of the strands  132  due to the action of residual alcohol, yeast and/or enzymes. 
     Upon exiting the drying and leavening chamber  134 , the strands  132  are continuously cut into granules or pellets  140  using a mechanical granulating device or pelletizer  138  having a cutting edge  139 . The granules  140  of animal feed product are deposited into a package or other storage device  142 . Because the granules  140  are substantially dry, they can be stored for extended periods without experiencing moisture-induced degradation. Residual carbon dioxide from the fermentation process may also aid storage stability. Carbon dioxide, nitrogen or other inert gas may also be added to the package for enhanced storage stability. 
       FIG. 3  illustrates an alternative apparatus  200  for carrying out the process of the invention. A mixer hopper  210  contains a residue  222  that includes a plurality of ingredients selected from DG&#39;s, DDGS&#39;s, residual alcohol, water, carbon dioxide, yeast, enzymes, and other by-products and ingredients. The residue  222  can be fed to the mixer hopper using inlet  212 , and can include the residue supplied by stream  22  shown in  FIG. 1 . The residue  222  can also include, or be combined with nutrients, precipitating agents and other additives fed to the mixer hopper via inlet  214 . 
     The residue mixture is fed from the mixer hopper via outlet  216  into a compression apparatus which, in this embodiment, can be a twin screw extruder  224  driven by a drive motor  206  and drive shaft  204 . Twin screw extruders are designed to accommodate a variety of screw configurations tailored for specific purposes. Twin screw extruder  224  is designed for mixing and compression of the ingredients, and includes a vacuum port at the location of arrow  226 . The vacuum port communicates with one or more vacuum pumps (not shown) to devolatalize and remove large amounts of water, in the form of water vapor, from the residue slurry. As the water vapor is removed, the residue mixture experiences decreasing viscosity and higher pressure as it is conveyed forward in the direction of arrow  227 . 
     The residue mixture passes from twin screw extruder  224  through channel  228  and pressure pump  230 , which raises the pressure in the mixture to between about 250 and about 3000 psi. The residue mixture then passes through channel  232  into a flash drying chamber  234  and enters a compression zone  233  in the chamber  234 . While in the compression zone  233 , or immediately prior thereto, the residue mixture is combined with compressed, heated gas such as air or carbon dioxide, at a pressure of about 250 to about 3000 psi and a temperature of about 65° C. to about 180° C. The subsequent release of pressure as the residue mixture leaves compression zone  233  results in rapid decompression and explosive “flash” drying in the chamber  234 . The residual water vapor leaves chamber  234  through outlet  237 . The resulting dried high grade protein product, which has a moisture content of less than about 3% by weight, passes through extrusion plate  235  in the form of one or more strands  236 , and can be granulated as described with respect to  FIG. 2 . 
     Notably, the embodiment of  FIG. 3  performs the drying step in flash drying chamber  234  before the shaping step, which is largely performed as the dried compressed residue passes through extrusion plate  235 . The explosive flash drying results in a high grade protein product having a low moisture content which can be less than about 2% by weight, suitably less than about 1% by weight, or less than about 0.5% by weight, or less than about 0.2% by weight, or less than about 0.1% by weight, or less than about 0.05% by weight, or less than about 0.02% by weight. The low moisture content enhances the storage stability of the high grade protein product by alleviating moisture-induced spoilation. 
     The embodiments of the invention described herein are exemplary. Various modifications and improvements can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that fall within the meaning and range of equivalents are intended to be embraced therein.