Abstract:
A processing method and an apparatus for producing ethanol that reduces the number of separation steps to the maximum extent possible and simplifies the production configuration while enabling the grits, pericarp and germ to be extracted with ease. The method includes a tempering step of wetting corn grains with a certain amount of water, a dehulling step of dehulling the corn grains while maintaining their shape without breaking the wetted grains, a pulverization step of pulverizing the dehulled corn grains into pieces, a separation step of separating grits and bran from the broken pieces, and a milling step of further milling the separated grits.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method and an apparatus for processing corn-grains for production of ethanol. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventionally, methods for processing corn grains for producing ethanol are well known. For example, the methods described in US 2006/0035354 A1 and described in WO 2006/081673 A1 are known. 
         [0005]    The invention described in US 2006/0035354 A1 comprises (1) a process of milling the corn grains with an impact miller; (2) a process of separating the milled corn into a first stream consisting of bran and a second stream that includes germ, grits (hereinafter, used as endosperm of corn) and residual bran; (3) a first refining process of refining the second stream consisting of germ, grits and bran; (4) a first separation process of separating and extracting the germ and the grits from the first-refined germ, grits and bran using a sifter; (5) a second refining process of refining an intermediate product consisting of the germ, grits and bran not extracted in the first separation process; and (6) a second separation process of separating and extracting the germ and the grits from the second-refined germ, grits and bran using a sifter. 
         [0006]    By this process, wet corn grains are impact-milled and broken into multiple pieces so as to retain the greatest average particle size of the milled fractions, as a result of which the milled germ is selected by particle size, such that, in a stage prior to movement of raw material to an ethanol extraction plant, at least 7% and preferably at least 10% milled germ is extracted from the corn grains, and at least 1%, and preferably at least 2.5% milled bran is extracted from the corn grains. In other words, the process improves the rate of recovery of grits from the corn grains and reduces the impurities/residue (pasty product) created during ethanol production at the ethanol extraction plant, enabling the degree of refinement of ethanol to be improved over conventional processing. 
         [0007]    However, in the method described above, in process (1) a single corn grain is broken into multiple small pieces and therefore germ and residual bran are mixed in with the crushed grits. Consequently, in order to supply only milled grits as fuel, the plurality of separation processes described in (2) through (6) are required in order to remove the germ and the residual bran from the grits. Adding this multiplicity of separation processes complicates the production configuration, increases production costs by increasing the cost of production equipment and facilities, and increases running costs by the cost of the electric power that is consumed in the plurality of separation processes. 
         [0008]    Moreover, the invention described in WO 2006/081673 A1 comprises (a) tempering a quantity of corn grains; (b) cracking the corn grains; (c) threshing the cracked corn grains; (d) separating the threshed corn grains into a first fraction that is above a threshold size and a second fraction that is below a threshold value size; (e) separating the second fraction into a large grit fraction and a medium grit fraction; (f) separating the large grit fraction by specific gravity into large grits and large germ/pericarp/small-grit mixtures; and (g) separating the medium grit fraction by specific gravity into medium grits, and medium germ/pericarp/small-grit mixtures. 
         [0009]    In step (b) described above, a single grain of corn is broken into a plurality of pieces larger than those described in US 2006/0035354 A1, for example, 3-10 pieces. In other words, the 3-10 pieces into which each corn grain is broken are aspirated and the large pericarps are removed, after which, in the step described in (c) above, the remaining pericarp, germ and bran are separated out, thus enabling the rate of recovery of the starch-rich grits to be improved. This process has the advantage of improving product yield in the ethanol production and dry milling processes. 
         [0010]    However, simply breaking a single grain of corn into 3-10 pieces means that the pericarp still remains on the plurality of pieces, thus necessitating the follow-on step described in (c) and separating out the pericarp, germ and bran, and further necessitating the plurality of separation processes described in (d) through (g) for separating the pericarp, germ and residual bran from the grits. 
         [0011]    Further, in the case of cracking the corn grains without removing the pericarp as described in step (b) above, there often arises a case where the pericarp remains as being adhered to the grits and the germ and the remaining pericarp affects vibration and air-blowing in the separation by the gravity separator to make it difficult to separate the grits and the germ. Thus, it has been necessary to provide a plurality of gravity separators to separate the grits and the germ with high precision. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a processing method and apparatus for producing ethanol that reduces the number of separation processes to the maximum extent possible and simplifies the production configuration while enabling the grits, pericarp and germ to be extracted with ease. 
         [0013]    A method of processing corn grains of the present invention comprises the steps of: tempering the corn grains by adding predetermined amount of moisture to the corn grains such that only pericarps of the corn grains are wetted by the moisture; dehulling the corn grains to remove the wetted pericarps such that the corn grains are not broken with shapes thereof maintained; pulverizing the dehulled corn grains into broken pieces; separating grits and germ from the broken pieces of the corn grains; and milling the separated grits to obtain flour of the corn grains. 
         [0014]    A beater-type impact dehuller or a friction-type dehuller is preferably used in the dehulling step. An impact-type miller is preferably used in the milling step. 
         [0015]    In the separating process, a specific-gravity separator or an optical separator is preferably used in the separating step. 
         [0016]    A primary refining step using an aspirator and a sifter may be provided between the dehulling step and the pulverization step, and a secondary refining step using an aspirator and a sifter may be provided between the pulverization step and the specific-gravity separation step. 
         [0017]    Further, there may be provided a step of wetting and tempering the dehulled corn grains between the refining step and the pulverization step. 
         [0018]    Furthermore, there may be provided a carbon-dioxide processing step of immersing the dehulled corn grains in a pressurized tank, between the primary refining step and the pulverization step, so as to allow carbon dioxide to soak into the dehulled corn grains, after which the dehulled corn grains are removed from the pressurized tank and briefly heat-treated. 
         [0019]    An apparatus for processing corn grains of the present invention comprises: a tempering device for tempering the corn grains by adding predetermined amount of moisture to the corn grains such that only pericarps of the corn grains are wetted by the moisture; a dehulling device for dehulling the corn grains to remove the wetted pericarps such that the corn grains are not broken with shapes thereof maintained; a pulverizer for pulverizing the dehulled corn grains into broken pieces; a separating device for separating grits and bran from the broken pieces; and a milling device for milling the separated grits, wherein the dehulling device includes a laterally disposed perforated cylinder, a grain supply tube provided at one end of the perforated cylinder, a grain discharge tube provided at another end of the perforated cylinder, a rotary shaft arranged rotatable within the perforated cylinder, and a peeler fixed on the rotary shaft. The dehulling device may further include a screw for feeding corn grains which is fixed on the rotary shaft at the one end of the perforated cylinder in the vicinity of the grain supply tube. 
         [0020]    The peeler of the dehulling device may comprise a plurality of support members arranged separately from one another along an axial direction of the rotary shaft, each having a proximal portion fixed to the rotary shaft and arm portions extending radially from the proximal portion toward the perforated cylinder, and beater blades arranged parallel to the rotary shaft and attached to distal ends of the arm portions of the plurality of support members. 
         [0021]    According to the present invention, after pre-sifted corn grains are tempered in the tempering step they are supplied to the dehulling step. In the dehulling step, the corn grains are not broken apart but are dehulled while retaining their shape. At this time, approximately 98% of the pericarp is peeled off and removed, and therefore, compared to the conventional process in which the corn is crushed after tempering, there is virtually no risk of pieces of the pericarp getting mixed in with the grits. After dehulling, the germ is attached to the grits, and in that state the corn grains are supplied to a succeeding pulverization step. In the pulverization step, the grits are broken into multiple pieces, for example 4-8, and at the same time any attached germ is removed. At this time the germ is in an elastic condition, and therefore can be separated easily from the grits without the germ itself being broken into small pieces. The pulverization of the corn grains with germs not broken is advantageous in that the germs can be collected with their original shapes maintained to improve efficiency of a subsequent refining process of the germs and prevent destroy of enzyme contained in the germs and oxidation and putridity of the germs so that the value-added germs can are provided with valuable elements remained. Next, the mixture of pulverized grits and germ is supplied to a specific-gravity separation step and separated by differences in density into the grits and the germ, with the separated grits then further milled in a milling step and recovered. In other words, according to the present invention, there is virtually no risk of pieces of pericarp getting mixed into the grits, and therefore specific-gravity separation can be completed in one step, thus reducing the separation step to the maximum extent possible and at the same time enabling the grits, the pericarp and the germ to be easily extracted. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a flow chart illustrating a method for processing corn to produce ethanol according to the present invention; 
           [0023]      FIG. 2  is a schematic vertical sectional view of a beater-type impact dehuller; and 
           [0024]      FIG. 3  is a sectional view along a line a-a′ shown in  FIG. 2 ; 
           [0025]      FIG. 4  is a perspective view of a long peeler; and 
           [0026]      FIG. 5  is a schematic vertical sectional view of a friction-type dehuller. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 1  is a flow chart illustrating a method for processing corn to produce ethanol according to the present invention. 
         [0028]    In  FIG. 1 , material corn grains are first supplied to a sifting process in which impurities and foreign matter are separated and removed. A separator called a milling separator indicated by reference numeral  1  is, for example, one that uses a two-stage sieve comprising an upper sieve consisting of a perforated metal plate with holes approximately 15 mm in diameter and a lower sieve consisting of a perforated metal plate with holes approximately 4 mm in diameter. The two-stage sieve at the upper sieve allows the corn grains to pass through the holes in the sieve but catches and separates overtailing large impurities from the raw material corn grains, whereas at the lower sieve it allows impurities smaller than the corn grains to pass through the sieve but catches and separates the overtailing raw material corn grains, thus enabling both large and small impurities to be separated and removed. Next, the corn grains are supplied to a stone sorter indicated by reference numeral  2 , where stones and dust are removed. For the stone sorter, a dry destoner that uses differences in density to separate stones and the like from the corn grains can be used. The sifted corn grains are then supplied to a wetting/tempering process indicated by reference numeral  3 . The wetting/tempering process  3  is for adjusting the moisture of the corn grains in order to improve the quality of the flour, and adds enough water to raise the moisture content of the raw material corn grains from approximately 12% to 15-16%, after which the wetted corn grains are tempered for 4-12 hours. 
         [0029]    Reference numeral  4  indicates a short tempering process to facilitate removal of the pericarp from the corn grains, in which the corn grains tempered in the wetting/tempering process  3  described above are wetted by moisture of 1%-6% by weight, and tempered for 5-30 minutes. By so doing, the moisture wets only pericarps of the corn grains without penetrating the fibers of the grits of the corn grains, which makes it easy to separate the pericarp from the grits. 
         [0030]    Reference numeral  5  indicates a dehulling process that is the essential part of the present invention, in which only the pericarp is removed from the corn grains tempered in the tempering process  4  without breaking up the corn grains tempered in the tempering process  4  while allowing the corn grains to maintain their shape. At this time, approximately 98% of the pericarp is peeled and removed, and the corn grains from which the pericarp has been removed are discharged from the dehulling process in a state in which the germ is attached to the grits. 
         [0031]    In the dehulling process  5 , the pericarp and small pieces of corn pass through the mesh of the dehuller and are supplied to a bran finisher  6  of a succeeding process. The overtailing corn grains in a state in which the germ is attached to the grits do not pass through the mesh if the dehuller but are caught and supplied to a succeeding process of an aspirator  7 . 
         [0032]    At the bran finisher  6 , the grits attached to the inside of the pericarp are removed and separated from the pericarp to produce flour. At the aspirator  7 , the pericarp and fine powder are separated and removed from the dehulled corn grains with a suction-type stream of air and refined. The refined corn grains are then supplied to a succeeding process of a sifter  8 , where the dehulled corn grains are separated according to their size into three types of pieces: Regular, medium, and small. 
         [0033]    The regular pieces separated by the sifter  8  are in a state in which the germ is attached to the grits, and therefore, after the grains are broken into 4-8 pieces, they are supplied to a pulverization process  10  to separate the grits and the germ. In addition, the medium pieces separated by the sifter  8  are supplied to a separation process  13  to separate the grits and the germ. 
         [0034]    In the separation process  13 , a specific-gravity separator may be used in which a punched porous steel plate is arranged inclined and moved to vibrate while air is flown from below so as to blow grains having relatively low specific-gravity. Further, an optical separator may be used in which colors and/or shapes of grains are optically discriminated in a continuous flow of the grains and grains to be separated are blown out of the continuous flow by an ejector using a jet of air so as to separate the grits and the germ. 
         [0035]    The small pieces separated by the sifter  8  are supplied to a milling process  14  to obtain flour. 
         [0036]    It is preferable to provide a wetting/tempering process  9  prior to the pulverization process  10  in order to give the germ attached to the grits elasticity. In the wetting/tempering process  9 , the corn grains are wetted and their moisture content increased 2% or less and tempered for 30 minutes or less. This process increases the elasticity of the germ, making it harder for the germ itself to be finely milled in the pulverization process  10  and making it easier to separate the grits and the germ. It should be noted that, as an alternative to the wetting/tempering process  9 , a carbon dioxide processing process of immersing the dehulled corn grains in a pressurized tank so as to allow carbon dioxide to soak into the dehulled corn grains, after which the dehulled corn grains are removed from the pressurized tank and briefly heat-treated. 
         [0037]    Carbon dioxide is an absorptive gas, and when this property is utilized the gas appears to be absorbed by the large amounts of fat and protein in the grits and the germ. Consequently, when the corn grains are immersed in a pressurized tank or the like and exposed to carbon dioxide under pressure, the cellular connections of the grits and the germ appear to loosen and break. As a result, the degerming of the cellular connection-weakened corn grains can be carried out with considerably ease once the corn grains are returned to atmospheric pressure. 
         [0038]    An impact mill or a pin mill, in which the corn grains are impacted and rubbed between a rotating pin and a fixed pin, may be used as the pulverizer used in the above-described pulverization process  10 , which removes the germ attached to the grits and at the same time breaks the grits into multiple pieces, for example, 4-8 pieces. 
         [0039]    Next, the corn grains, which now consist of a mixture of germ and grits pulverized into 4-8 pieces, are supplied to an aspirator  11 , where the pericarp and fine powder are separated and removed from the dehulled corn grains with a suction-type stream of air and the mixture refined, and further, the refined corn grains are supplied to a sifter  12  and separated by size into three types of pieces: Small pieces, medium/large pieces, and flour. The overtailing medium/large pieces are caught by the sifter  12  and supplied to a specific-gravity separation process  13  together with the medium pieces discharged from the sifter  8  described above, the grits and the germ are separated by specific gravity, and the small pieces that pass through the sifter  12  are supplied to a milling process  14  together with the small pieces discharged from the sifter  8  described above without going through the specific-gravity separation process  13  and are milled into flour. 
         [0040]    A roller mill is preferable for the milling machine in the milling process  14 . The milled product milled in the milling process  14  is supplied to a succeeding process of a sifter  15  and separated into three types: Large fractions, medium fractions and product flour (small fraction). The large fractions, which overtail the sifter  15 , are supplied to an aspirator  16  and the pericarp and the germ are separated by a suction-type stream of air, whereas the medium fractions, which pass through the sifter  15 , are supplied to an aspirator  17  and are separated into pericarp and small pieces by a suction-type stream of air. Then, the small pieces separated out by the aspirator  17  are returned to the milling process  14  and the milling/separation operation is repeated. The small fractions, i.e. particles of grits passed through the sifter  15  are taken out as product flour. 
         [0041]    Thus, as described above, because the tempered corn grains in the dehulling process  5  are dehulled while maintaining their shape without breaking apart the corn grains, approximately 98% of the pericarp is peeled off and removed, and therefore, compared to the conventional process in which the tempered corn grains are crushed, there is virtually no risk of the pericarp getting mixed in with the grits. Moreover, the dehulled corn grains are in a state in which the germ is attached to the grits, and in that state supplied to the succeeding pulverization process  10 . In the pulverization process  10  the grits are pulverized into 4-8 small pieces, and at the same time, the attached germ is removed. At this time, the germ is elastic, and therefore is removed from the grits without the germ itself being broken into smaller pieces. Then, the mixture of germ and grits, the latter having now been broken into 4-8 small pieces each, is supplied to the specific-gravity separation process  13 , where the grits and the germ are separated by their difference in density. The separated grits are then supplied to the milling process  14 , milled, and recovered. In other words, according to the present invention, there is virtually no risk of pieces of pericarp getting mixed into the grits, and therefore the specific-gravity separation process  13  can be completed in one process, thus reducing the separation process to the maximum extent possible and at the same time enabling the grits, the pericarp and the germ to be easily extracted. 
         [0042]    A description is now given of the dehuller used in the dehulling process of the present invention.  FIG. 2  is a schematic vertical sectional view of a beater-type impact dehuller.  FIG. 3  is a sectional view along a line a-a′ shown in  FIG. 2 . 
         [0043]    In  FIG. 2  and  FIG. 3 , the impact-type dehuller  20  is comprised mainly of a perforated cylinder  23  disposed laterally within a frame  22  mounted on a stand  21 , a grain supply tube  24  provided on one end side of the perforated cylinder  23 , a grain discharge tube  25  provided on the other end side of the perforated cylinder  23 , a rotary shaft  26  arranged to be rotatable within the perforated cylinder  23 , a grain transport screw  27  fixed to the rotary shaft  26  in the vicinity of the grain supply tube  25 , and a peeler  28  arranged within the perforated cylinder  23 . 
         [0044]    With the impact-type dehuller  20  shown in  FIG. 2  the grain transport screw  27  is mounted on the rotary shaft  26 . However, when using a long peeler  28  like that shown in  FIG. 4 , the grain transport screw  27  can be eliminated. 
         [0045]    Reference numeral  29  indicates a pericarp collection hopper provided beneath the perforated cylinder  23 . A pericarp discharge port  30  is provided at the bottom end of the pericarp collection hopper  29 . Reference numerals  31 ,  32  indicate shaft bearings provided exterior to the frame  22  that rotatably support the rotary shaft  26 . A V-pulley  33  is fixed to one end of the rotary shaft  26 , and is rotatably driven by a motor  36  mounted on the bottom of the stand  21  through a V-belt  34  and a motor pulley  35 . The rotary shaft  26  is set to rotate at a speed of 800-1000 rpm. 
         [0046]    The peeler  28  is comprised of a plurality of support members  37  provided in an axial direction of the rotary shaft  26  (in  FIG. 2  there are three support members  37 ) each having a proximal portion  37   a  fixed on the rotary shaft  26  and multiple arm portions  37   b  . . . that extend radially from the proximal portion  37   a  toward the perforated cylinder  23  (in  FIG. 3  there are four arm portions  37   b ), as well as long beater blades  38  . . . disposed parallel to the rotary shaft mounted on tip ends of the arm portions  37   b  of the plurality of support members  37 . 
         [0047]    In the embodiment shown in  FIG. 2  and  FIG. 3 , four long beater blades  38  . . . are shown, whereas in the embodiment shown in  FIG. 4 , eight long beater blades  38  . . . are shown. 
         [0048]    In the impact-type dehuller  20  of the present embodiment, when the tempered corn grains are supplied from the grain supply tube  24  they are moved into the perforated cylinder  23  by the action of the screw  27 . Inside the perforated cylinder  23 , as the volume of corn grains reaches 20-40% of capacity they are struck by the beater blades  38  . . . so that the pericarp on the surface of the corn grains is peeled off by the impact of the corn grains striking each other and by the friction of being pressed against the inner wall of the perforated cylinder  23 . At this point the corn grains are dehulled by the rotation of the long beater blades  38  . . . , and therefore, because they are dehulled while retaining their shape without being broken up, approximately 98% of the pericarp is peeled off and removed. The corn grains are then gradually moved toward the grain discharge tube  25  side and ultimately discharged to the exterior of the machine from the grain discharge tube  25 . 
         [0049]    The pericarp and milled fine powder created at this point are discharged to the exterior of the perforated cylinder  23  and discharged to the exterior of the machine through the pericarp collection hopper  29  and the pericarp discharge port  30 . 
         [0050]    It should be noted that although in the impact-type dehuller  20  of the present embodiment there is no stopper plate or lid provided on the discharge side of the perforated cylinder  23  or the rim of the grain discharge tube  25  opening, such may be provided when the amount of corn grains in the perforated cylinder  23  does not reach 20-40% of capacity. In addition, the amount of corn grains in the perforated cylinder  23  may be adjusted by adjusting the rotary shaft  26  rpm and the corn grains volume supply. 
         [0051]    Alternative to beater-type impact dehuller, a friction-type dehuller as shown in  FIG. 5  may be used in the dehulling process. The friction-type dehuller performs dehulling by utilizing a friction-type polisher having a blowing-friction polishing roller arranged rotatable in a porous polishing cylinder for removing bran. 
         [0052]    In  FIG. 5 , a friction-type dehuller  40  comprises a perforated cylinder  43  disposed laterally within a frame  42  mounted on a stand  41 , a grain supply tank  44  having a shutter  44   b  and a supply port  44   a  provided on one end side of the perforated cylinder  43 , a grain outlet  42   a  provided on the other end side of the perforated cylinder  43 , a hollow rotary shaft  45  arranged to be rotatable within the perforated cylinder  43 , a grain transport screw  46  fixed to the hollow rotary shaft  45  under the supply port  44   a  of the grain supply tank  44 , and a friction roller  47  arranged within the perforated cylinder  43 . 
         [0053]    A pericarp collection hopper  51  is provided beneath the perforated cylinder  43 . A pericarp discharge tube  52  is provided at the bottom end of the pericarp collection hopper  51 . A pulley  53  is fixed to one end of the hollow rotary shaft  45 , and is rotatably driven by a motor (not shown) mounted on the bottom of the stand  41  through a belt and a motor pulley. A resistant lid  49  is provided at the grain outlet  42   a  for adjusting the amount of corn grains in the perforated cylinder  43 . The other end of the hollow rotary shaft  45  is connected to an air supply  50  so that air is supplied into a peeling chamber  48  between the friction roller  47  and the perforated cylinder  43  through air holes  45   a  formed on the hollow shaft  45  and blow openings  47   a  formed in the friction roller  47 . 
         [0054]    In the friction-type dehuller  40 , when the tempered corn grains are supplied from the supply port  44   a  of the grain supply tank  44  the grains are moved into the perforated cylinder  43  by the action of the screw  46 . Inside the perforated cylinder  43 , the corn grains are scraped by the friction roller  47  so that the pericarp on the surface of the grains is peeled off by the friction of the corn grains and by the friction of being pressed against the inner wall of the perforated cylinder  43 . At this point the corn grains are dehulled while retaining their shape without being broken up. The corn grains are then gradually moved toward the grain outlet  42   a  and ultimately discharged to the exterior of the machine from the grain outlet  42   a.    
         [0055]    The pericarp and milled fine powder created in the peeling are discharged to the exterior of the perforated cylinder  43  and discharged to the exterior of the machine through the pericarp collection hopper  51  and the pericarp discharge tube  52  by the suction of a fan  54 . The air supplied into the peeling chamber  48  from the blow openings  47   a  facilitates discharge of the pericarp and milled fine powder to the exterior of the perforated cylinder  43 .