Abstract
A material bed roller mill for comminution of grain in a material bed. The material bed roller mill comprises rollers, at least one feed opening, a draw-in region between the rollers, a grinding gap between the rollers and at least one delivery opening. The material bed roller is configured, during operation, to produce a material bed in the draw-in region and to draw grain from a surplus thereof by a filled material duct or hopper. A specific grinding force of the material bed roller mill can be set in such a way that grain is heated, during the grinding operation, by less than 30° C., preferably by less than 15° C., to the temperature of the grain before the respective grinding.
Claims
1. A method for grinding cereal grain to produce flour and/or semolina from said cereal grain in a cereal grain material bed roller mill, the method comprising the steps of: setting a pressure exerted on rollers of said cereal grain material bed roller mill in a direction of a roller gap between said rollers of said cereal grain material bed roller mill, wherein a specific grinding force of less than 3 N/mm.sup.2 is set; configuring said cereal grain material bed roller mill such that said roller gap is variable during said grinding, whereby, during said grinding, said roller gap varies in such a way that an increase in a volume of said cereal grain in said roller gap leads to an increase in said roller gap; providing a surplus of said cereal grain via a filled material duct or hopper, thereby producing a material bed of said cereal grain in a draw-in region immediately upstream of said roller gap; rotating said rollers at different speeds; drawing said cereal grain into said roller gap by said rollers from said material bed to form a packed particle fill in said variable roller gap between said rollers; and grinding said cereal grain in said packed particle fill of said cereal grain in said variable roller gap to produce said flour and/or semolina; wherein said cereal grain material bed roller mill comprises said rollers, at least one feed opening, said draw-in region upstream of said rollers, said variable roller gap between said rollers and at least one delivery opening.
2. The method as claimed in claim 1, wherein said cereal grain is bread wheat, durum wheat, maize or buckwheat.
3. The method as claimed in claim 1, wherein said pressure set on said rollers in the direction of said roller gap is set so that said cereal grain is heated, during grinding, by less than 59° F. (15° C.).
4. The method as claimed in claim 1, wherein said variable grinding roller gap remains larger than a particle size of a majority of said cereal grain.
Description
(1) The invention is explained in more detail below with reference to exemplary embodiments for better understanding.
(2) FIG. 1: a schematic illustration of an apparatus according to the invention having a material bed roller mill and a separating apparatus;
(3) FIG. 2: a schematic illustration of an alternative grinding arrangement according to the invention having a roller mill and a separating apparatus;
(4) FIG. 3: a schematic illustration of a further alternative apparatus according to the invention having a material bed roller mill and an alternative separating apparatus;
(5) FIG. 4: a flow chart of a method according to the invention;
(6) FIG. 5: a schematic illustration of an additional alternative apparatus according to the invention having a material bed roller mill and a detacher;
(7) FIG. 6: a flow chart of an alternative method according to the invention;
(8) FIG. 7: a schematic illustration of a mill diagram with material bed roller mill, detacher, plan sifter, zigzag sifter and cyclone separator;
(9) FIG. 8: a schematic illustration of another alternative apparatus according to the invention having a roller mill with constant gap and computer control of the grain feed;
(10) FIG. 9: a schematic illustration of a material bed roller mill with grain in the roller gap;
(11) FIG. 10: a schematic illustration of a zigzag sifter;
(12) FIG. 11: a schematic illustration of an impact detacher;
(13) FIG. 12: a schematic illustration of a plan sifter.
(14) FIG. 1 shows a schematic illustration of a grinding arrangement 1 according to the invention.
(15) The grinding arrangement has, as grinder, a material bed roller mill 16, as shown, for example, in FIG. 9. The material bed roller mill 16 has a feed opening 3 and a delivery opening 4 for the grain 20. Furthermore, the grinding arrangement 1 has a separating apparatus 5 which has a zigzag sifter 13, for example according to FIG. 10, and a plan sifter 15, for example according to FIG. 12. Ground grain 20, which contains coarser ground product 21, finer ground product 22 and bran 23, is transported from the material bed roller mill 16 into the separating stage 5 by means of a conveying arrangement 9. Here, the rollers (not shown here) of the material bed roller mill 16 have a diameter of 250 mm. The conveying arrangement 9 is in this case designed as a gravity tube, such that the ground grain 20 is conveyed into the separating stage 5 by gravitational force. The separating stage 5 has an inlet opening 6 for receiving the coarser ground product 21, the finer ground product 22 and the bran 23. Furthermore, the separating stage 5 has three outlet openings 7, through which the coarser ground product 21, the finer ground product 22 and the bran 23 can be discharged separately in each case. The coarser ground product 21 is returned to the grinder 2 by means of the return arrangement 8. The return arrangement used here is a chain conveyor. Alternatively, however, the use of a bucket conveyor as return arrangement is also possible.
(16) Grain 20 is transported through the feed opening 3 into the material bed roller mill 16, the grain 20 being ground in the material bed roller mill 16 into coarser ground product 21, finer ground product 22 and bran 23. To this end, a maximum specific grinding force of 1 N/mm.sup.2 is set in the material bed roller mill 16, as a result of which a typical roller gap of between 1.25 mm and 5 mm forms as a function the quantity of grain 20 fed. The ground product is transported via the delivery opening 4 and the conveying arrangement 9 and through the inlet opening 6 into the separating stage 5. In the separating stage 5, the ground product is sorted in a first step according to size into coarser ground product 21 and a mixture of finer ground product 22 and bran 23. The plan sifter 15 is used for this purpose. The coarser ground product 21 is transported through one of the outlet openings 7 into the return arrangement 8 and is returned to the grinder 2 for grinding again. The mixture of finer ground product 22 and bran 23 located in the separating stage 5 is separated into bran 23 and finer ground product 22 by means of a zigzag sifter. The finer ground product 22 is discharged via the lateral outlet opening 7 and the bran 23 is discharged via the top outlet opening 7.
(17) Here, the material bed grinding mills have rollers having a roller diameter of 250 mm and a length of 44 mm. A force of 22 kN is exerted on the rollers. The grinding is effected at a specific grinding force of 2 N/mm.sup.2 with a roller gap of a thickness of 2 mm. Here, a flour yield in the ground product is 12.5%, approximately 5.3% of bran being separated with a zigzag sifter. The specific energy consumption at the mill is only 1.6 kWh/t; accordingly, about 12.8 kWh/t has to be consumed for the production of finished flour.
(18) Here, the grain fed to the circuit has an ash content of 0.52%, the ash content of the flour produced being 0.47%.
(19) FIG. 2 shows an alternative schematic illustration of a grinding arrangement 1 according to the invention. The same reference numerals in FIGS. 1 and 2 designate the same components here.
(20) In contrast to the grinding arrangement, the grinding arrangement 1 according to figure has a grinder 2 having two rollers 10 which are at a fixed distance s apart. The fixed distance s can be set and is adapted to the grain size and can be, for example, 1 mm.
(21) Here, in contrast to the method described with respect to FIG. 1, the coarser ground product 21 is not returned into the feed opening 3 of the grinder 2. For example, the coarser ground product 21 can be conveyed into a further grinder (not shown here).
(22) FIG. 3 shows a further alternative schematic illustration of a grinding plant 1 according to the invention. The same reference numerals in FIG. 2 and FIG. 3 designate the same components here.
(23) In contrast to the grinding plant 1 according to FIG. 2, the grinding plant 1 according to FIG. 3 has a separating apparatus 5 which comprises a zigzag sifter 13 and a semolina purifier 14. In the separating stage 5, the mixture of coarser ground product 21, finer ground product 22 and bran 23 is separated by means of the zigzag sifter 13 into coarser ground product 21 and a mixture of finer ground product 22 and bran 23. In a second step, the finer ground product 22 is separated from the bran 23 in the semolina purifier 14.
(24) The method for grinding the grain 20 and for separating the ground product of coarser ground product 21, finer ground product 22 and bran 23 is otherwise effected substantially as described in FIG. 1.
(25) FIG. 4 shows a flow chart of a method according to the invention. Grain 20 is transported into a conditioning apparatus 11, which contains a grist stage, and is pre-ground there into a mixture of bran 23 and semolina 21 or 22. In addition, the grain is regulated in the conditioning apparatus 11 to a temperature of 20° C. After this conditioning, the conditioned grain 20 is conveyed into a material bed roller mill 16 and is ground further here, wherein it is mixed, before the grinding, with coarser ground product 21 which is returned. In the process, the temperature increases during the grinding by less than 5° C. In other words, the temperature of the conditioned grain 20, which has a temperature of about 20° C. before the grinding, even after the mixing with the returned coarser ground product 21, is not heated above 25° C. during the grinding operation in the material bed roller mill 16. After the grinding in the material bed roller mill 16, the ground product is conveyed into a separating apparatus 5 which comprises a plan sifter 15 and a zigzag sifter 13. In this separating stage 5, the ground product is therefore separated into coarser ground product 21, finer ground product 22 and bran 23 and is discharged separately from the separating apparatus 5.
(26) It is also possible for the grain to be cooled between the grinding stages or else for the rollers themselves to also be cooled. The combination of both cooling means is also possible.
(27) FIG. 5 shows an additional alternative schematic illustration of a grinding arrangement 1 according to the invention. Grain 20 is conveyed into a material bed roller mill 16 and is ground therein. The grinding operation results in compaction of the ground product, and therefore in said ground product, before the separation in the plan sifter 15 into individual particle sizes, being conveyed into a detacher 12. Here, the detacher 12 is designed as an impact detacher, as shown in FIG. 11. The compacted ground product is substantially detached into the individual particles in this detacher 12 and is thereupon conveyed into a plan sifter 15 according to FIG. 12. This plan sifter 15 separates the ground product into coarser ground product 21 and finer ground product 22. The coarser ground product 21 is conveyed to the material bed roller mill by means of the return arrangement 8. Finer ground product 22 is discharged from the grinding arrangement 1. The return arrangement used here is a bucket conveyor. Alternatively, however, the use of a chain conveyor as return arrangement is also possible.
(28) FIG. 6 shows a flow chart of an alternative method according to the invention for producing flour 24. Grain 20 is conveyed into a material bed roller mill 16 according to FIG. 9 and is ground there. The ground grain 20 is then conveyed into a plan sifter 15 according to FIG. 12 and is separated there into coarser ground product 21 and a mixture of finer ground product 22 and bran 23. The coarser ground product 21 is returned into the material bed roller mill 16 for grinding again. The mixture of finer ground product 22 and bran 23 is ground again in another material bed roller mill 16. The ground product is thereupon conveyed into a semolina purifier 14 of Bühler AG (Article Number: MQRF-30/200) and is separated there into coarser ground product 21, bran 23 and flour 24. In the process, the coarser ground product 21, which has been separated as finer ground product 22 after the first grinding stage, is conveyed back into the material bed roller mill 16 for grinding again.
(29) FIG. 7 shows a mill diagram according to the invention in a schematic illustration. Grain 20 is conveyed into a material bed roller mill 16 according to FIG. 9 for grinding and, after the grinding, into a detacher 12, which is designed here as an impact detacher according to FIG. 11. The ground product is then conveyed into a further material bed roller mill 16 and is ground again there. The ground product is thereupon conveyed into a plan sifter 15 according to FIG. 12, which separates the ground product into four fractions which each have particles within a defined size range. Each of these four fractions is transported into a separate zigzag sifter 13 according to FIG. 10, in which the bran is removed from the ground product. The remaining ground product is thereupon ground in a further material bed roller mill 16, fed to a further detacher 12 and thereupon separated in a further plan sifter 15 into at least two, three, four or even five fractions. Said fractions can be ground again in material bed roller mills 16 or else can also be conveyed into zigzag sifters 13 for the separation of bran. In addition, the mill diagram has cyclone separators 18 for the further separation of bran from an air flow of a zigzag sifter 13.
(30) FIG. 8 shows an additional schematic illustration of a grinding plant 1 according to the invention. The same reference numerals in FIG. 1 and FIG. 8 designate the same components here.
(31) This grinding plant substantially corresponds to the grinding plant according to FIG. 1 and additionally has a sensor 31 for measuring the force exerted on the rollers 10 by the grain 20 in the roller gap W of thickness s and a compactor 19. The sensor 31 is connected to a closed-loop control device 30 for transmitting the measured forces to this closed-loop control device 30. Furthermore, the closed-loop control device 30 is connected to the drive of the rollers 10 for setting the rotary speed of the rollers. In order to avoid excessive heating of the grain 20 by the grinding operation, the force which is exerted on the rollers 10 by the quantity of grain 20 in the roller gap W is measured. If the measured force on the rollers 10 now increases due to, for example, a greater feed of grain 20 from the compactor 19, more heat is introduced into the grain 20 by the grinding operation in the grinder 2, a factor which can lead to changes in or damage to the proteins, in particular gluten, in the grain 20. By means of the force measured by the sensor 31, the rotary speed of the rollers can now be reduced by the closed-loop control device 30 in such a way that the measured force on the rollers 10 again reaches a desired value. This can ensure that an excessive amount of heat is not introduced into the grain 20 by the grinding operation and that the grinder 2 is also not damaged.
(32) The further method for producing flour corresponds to the method already described with respect to FIG. 1.
(33) FIG. 9 shows a schematic illustration of a material bed roller mill 16 having two rollers 10. In the material bed roller mill 16, grain 20 is drawn in by the opposed rotation r of the two rollers 10, such that a material bed situation arises in the roller gap W. A force F of 300 kN is exerted on the rollers 10 having a diameter D of 250 mm and a length of 1000 mm, such that a specific grinding force of 1.2 N/mm.sup.2 is achieved. The ground grain 20 contains coarser ground product 21, finer ground product 22 and bran 23. This ground product is compacted by the grinding in the material bed roller mill 16, such that said ground product, before separation in a separating stage (not shown here), has to be detached into individual particles in a detacher, as shown, for example, according to FIG. 11.
(34) FIG. 10 shows a zigzag sifter 13 having an inlet 41 for a mixture of finer ground product 22 and bran 23 to be separated. An air flow 40 is directed along the axis of the zigzag sifter and set in such a way that the bran 23, which has a lower density than the finer ground product 22, is blown out through the bran outlet 42. The heavier ground product 22 falls in the zigzag sifter 13 in such a way that said ground product 22 is conveyed out of the zigzag sifter 13 through the semolina outlet. Here, the “outflow velocity” of the air flow 40 is within the range of 0.7 m/s to 2.5 m/s, depending on the material to be separated.
(35) FIG. 11 shows an impact detacher 12 having an impact detacher inlet 50, rotors 51 and an impact detacher outlet 52. Compacted grain 53 is conveyed into the impact detacher 12 and strikes the rotors 51 there, which detach the compacted grain, inter alia, by the impact, such that grain 54 detached substantially into individual particles is formed. This detaching can be effected in a plurality of stages by rotors 51 connected one after the other, for example two to six rotors 51, wherein two rotors 51, which are attached to a shaft 55, are shown here. The rotors 51 have such a shape that the grain is conveyed to the impact detacher outlet 52.
(36) FIG. 12 shows a plan sifter 15 having a coarse sieve 61, a medium sieve 62 and a fine sieve 63. Ground grain 20, which contains coarser ground product, finer ground product 22 and bran 23, is conveyed into the plan sifter 15, such that the ground grain can be separated into a plurality of fractions of different size. The coarse sieve 61 has a mesh size of 1120 μm, the medium sieve 62 a mesh size of 560 μm and the fine sieve 63 a mesh size of 280 μm. The ground grain 20 is therefore separated into three fractions, wherein the first fraction has a size range of 1160 μm to 560 μm, the second fraction a size range of less than 560 μm to 280 μm, and the third fraction a size range of less than 280 μm. Here, the first fraction and the second fraction are classified as coarser ground product 21 and contain bran 23. These two fractions are thereupon conveyed according to FIG. 1, for example, into a material bed roller mill. The third fraction, which contains finer ground product 22 and bran 23, is conveyed according to FIG. 1, for example, into a zigzag sifter according to FIG. 10 for separating the bran.
