Method of and apparatus for processing corn grains for production of ethanol

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a method for processing corn to produce ethanol according to the present invention;

FIG. 2 is a schematic vertical sectional view of a beater-type impact dehuller; and

FIG. 3 is a sectional view along a line a-a′ shown in FIG. 2;

FIG. 4 is a perspective view of a long peeler; and

FIG. 5 is a schematic vertical sectional view of a friction-type dehuller.

DETAILED DESCRIPTION

FIG. 1 is a flow chart illustrating a method for processing corn to produce ethanol according to the present invention.

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.

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.

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.

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.

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.

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.

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.

The small pieces separated by the sifter 8 are supplied to a milling process 14 to obtain flour.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 37a fixed on the rotary shaft 26 and multiple arm portions 37b . . . that extend radially from the proximal portion 37a toward the perforated cylinder 23 (in FIG. 3 there are four arm portions 37b), as well as long beater blades 38 . . . disposed parallel to the rotary shaft mounted on tip ends of the arm portions 37b of the plurality of support members 37.

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.

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.

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.

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.

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.

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 44b and a supply port 44a provided on one end side of the perforated cylinder 43, a grain outlet 42a 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 44a of the grain supply tank 44, and a friction roller 47 arranged within the perforated cylinder 43.

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 42a 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 45a formed on the hollow shaft 45 and blow openings 47a formed in the friction roller 47.

In the friction-type dehuller 40, when the tempered corn grains are supplied from the supply port 44a 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 42a and ultimately discharged to the exterior of the machine from the grain outlet 42a.

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 47a facilitates discharge of the pericarp and milled fine powder to the exterior of the perforated cylinder 43.

Claims

1. A method of processing corn grains for production of ethanol, comprising 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; andmilling the separated grits to obtain flour of the corn grains.

2. A method according to claim 1, wherein a beater-type impact dehuller is used in said dehulling step.

3. A method according to claim 1, wherein a friction-type dehuller is used in said dehulling step.

4. A method according to claim 1, wherein an impact-type miller is used in said milling step.

5. A method according to claim 1, wherein a specific-gravity separator is used in said separating step.

6. A method according to claim 1, wherein an optical separator is used in said separating step.

7. A method according to claim 1, further comprising a primary refining step using an aspirator and a sifter between said dehulling step and said pulverization step.

8. A method according to claim 7, further comprising a secondary refining step using an aspirator and a sifter between said pulverization step and said specific-gravity separation step.

9. A method according to claim 7, further comprising a step of wetting and tempering the dehulled corn grains between said refining step and said pulverization step.

10. A method according to claim 7, further comprising a carbon-dioxide processing step of immersing the dehulled corn grains in a pressurized tank, between said primary refining step and said 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.

11. An apparatus for processing corn grains for production of ethanol, comprising: 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; anda milling device for milling the separated grits,wherein said dehulling device includes a laterally disposed perforated cylinder, a grain supply tube provided at one end of said perforated cylinder, a grain discharge tube provided at another end of said perforated cylinder, a rotary shaft arranged rotatable within said perforated cylinder, and a peeler fixed on said rotary shaft.

12. An apparatus according to claim 11, wherein said peeler of said dehulling device comprises a plurality of support members arranged separately from one another along an axial direction of said rotary shaft, each having a proximal portion fixed to said rotary shaft and arm portions extending radially from said proximal portion toward said perforated cylinder, and beater blades arranged parallel to said rotary shaft and attached to distal ends of said arm portions of said plurality of support members.