EQUIPMENT AND PROCESS FOR THE PRODUCTION OF SOYBEANFLOUR

Field of the invention The present invention refers to the field of soybean processing, and more particularly, to the production of soybean flour.

Description of the prior art

Soybeans are currently considered an important source of unsaturated fat and protein, being widely used for animal and human nutrition, since they contain in average 20% oil, 5% minerals, 34% carbohydrates and 40% protein, a value much higher than that of common beans, which have an average protein content of about 20%. Furthermore, soybeans contain isoflavone, a substance that provides countless benefits to health.

Soybean-based products are various and comprise, in addition to oil, textured soybean protein that replaces bovine meat, and soybean flour used in the preparation of soybean milk as well as of bakery and confectionery products, and so forth.

There are various known processes for obtaining soybean flour, the majority of these employing coarse and fine grinding using press rolls, such as described in US patent 4,076,851 bearing the title Method and apparatus for producing fine deodorized soybean powder. The process described in this document comprises an initial crushing step, whereby the

soybeans are flattened to a reduced thickness without extracting the oil and are dried to a moisture content of approximately 3%. There follows a first coarse grinding step, which produces fragments of a size corresponding to mesh size 10, and passage through an air blast curtain whereby the seed coats are separated from the fragments of seed leaves (cotyledons), the latter being subjected to the action of vapor at 110° - 120° C to neutralize the anti-trypsin factor. The treated fragments are then dried to reduce the moisture content to 2%, followed by the final steps of grinding (intermediate and fine), wherefrom results the soybean flour. In spite of preserving some of the nutritional components of the soybean (such as the oil) this process produces a degradation of the proteins due to the thermal treatment above 110°, and is also quite costly due to its complexity and the considerable energy consumption required to lower the moisture content of the soybeans (normally around 13%) to the level of 2% to 3% required by the process.

In point of fact, the grinding provided by press roll compression with no oil extraction results in the formation of a sticky and viscous residue when soybeans with the above mentioned moisture content of around 13% are used as raw material. Thus, the process described in the above quoted patent requires a substantial lowering of the moisture content in order to become feasible.

In addition to crushing by press rolls, other crushing techniques are known, such as impact pulverization, used in the processing of ore, mineral coal, recycling of materials (such as glass) and so forth. US patent 6,766,970 bearing the title Method and apparatus for a crusher

describes a pulverization process used for stone, ore and coal, where the material to be pulverized is placed in contact with a liquefied gas, such as liquid nitrogen, which reduces the temperature thereof to less than -100° C, rendering it fragile and brittle. The pieces of this material are then impacted by the blades of a centrifugal turbine that rotates at 2750 - 3000 rpm and throws them against the inner wall of the shell, thereby pulverizing the pieces. This process has the disadvantage of using a liquefied gas (nitrogen or equivalent), which raises the cost thereof.

Obj ects of the invention

In view of the preceding, a first object of the invention is to provide a process for the production of soybean flour with low cost and high yield.

Another object consists in avoiding the use of high-cost techniques such as excessive drying, intense cooling and so forth.

Yet another object of the invention consists on the production of a flour wherefrom may be preserved the nutritional qualities of the soybeans, particularly the original oil content of the beans.

Summary of the invention

The present invention achieves the above-mentioned and other objects by means of an equipment that comprises a high-speed hammer mill associated to a perforated screen and a device for aspirating the soybean flour.

According to another characteristic of the invention, the peripheral velocity in the hammer mill is above 60 meters per second (m/s), and preferentially in the order of 100 m/s.

According to another characteristic of the invention, the holes of said screen have a size of 15 microns or smaller.

According to another characteristic of the invention, the aspiration device is a centrifugal fan with a rotational speed above 4000 rpm.

According to another characteristic of the invention, said hammer mill and the fan rotor are mounted on the same axle.

Brief description of the figures

The additional features, advantages and characteristics of the invention will be more easily understood from the subsequent description of a preferred exemplary embodiment, taken in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic representation of the equipment used in the process according to the principles of the invention.

Figure 2 is a detailed view of the hammer mill used in the process according to the invention.

Figure 3 is a cross-section view depicting the arrangement of the apparatus used in the process, according to the principles of the invention.

Detailed description of a preferred embodiment of the invention Referring now to Fig. 1, the equipment comprises a hammer mill 10 provided with a loading port 11 for the soybeans 19 in its upper part, having a main housing 20 in which there is located the rotor provided with hammers (not illustrated in Fig. 1) and having its lower portion 12 tapered and coupled to the near end of a suction duct 13 whose far end is connected to the inlet of a centrifugal fan 14. The outlet 15 of said fan is connected, by means of a second duct 16, to a cyclone 17.

According to the process of the invention the soybeans 19, in the form of whole beans, cotyledons (halves) or fragments, are poured into the said loading port, and the powder produced by the action of the mill is suctioned by the high- vacuum centrifugal fan 14 through the duct 13. The air stream containing the soybean flour in suspension at the fan outlet is introduced into the cyclone 17 for separation of the powder (flour) which is unloaded through the outlet 18 at the lower end of the cyclone. The soybean flour may be directly conveyed to other equipment, such as an apparatus for the production of soybean milk (not illustrated), or may be packaged for later use.

Fig. 2 is a more detailed illustration of the hammer mill 10, with the main housing, shaded for better visualization, consisting of an upper half-cylindrical part 24 with a loading port 11 its top, for loading the raw

material, and a lower half-cylindrical portion 25 comprising a perforated screen. Inside said main housing there is located the mill rotor comprising a plurality of hammers - rigid bars 21 - hingedly coupled to the periphery of at least one disk 22 by means of pivot pins 27, said disk rotating at more than 4,000 rpm, preferably at about 6,000 rpm. The peripheral velocity of the tips of said hammers is proportional to the rotational speed of said rotor and to the diameter of the assembly, being at least over 60 meters per second, and preferably in the order of 100 m/s. The lower half 12 of the mill housing has a substantially tapering shape which converges to an outlet 26 that is coupled to suction means (not illustrated in the drawing). The openings of said screen have a maximum size of 15 μm, being preferably smaller than 10 μm and yet more preferably between 6 μm and 8 μm.

Fig. 3 illustrates the equipment in vertical cross-section, showing the mill 10 and the centrifugal fan 14 mounted on a common shaft 23 that is driven by the pulley 28 by means of drive belts and a motor (not illustrated). This figure depicts some details not shown in the preceding figures, such as the use of a plurality of bars 21 in the hammer mill and the sieve 25 occupying the whole width 29 of the mill housing, said width being equal to the height of the main cylindrical portion 20 of the mill 10 (see Fig.

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According to the invention, the soybeans to be processed - in the form of beans, cotyledons, fragments, and optionally, germ - is poured into the loading port 11, and is impacted by the hammers 21 of the mill. The high speed collision between said hammers - moving at a speed in the order

of 100 meters per second - and the soybeans causes the latter to be shattered into fine dust, which is hurled against the screen 25. The soybean flour particles pass through the openings thereof by the combined action of the centrifugal force with which the powder is flung against the inner face of said screen 25 and the strong suction (partial vacuum) applied to the outer face by means of the aspiration means coupled to said outlet 26, which in the present embodiment are provided by the centrifugal fan 14. Said suction contributes to avoid the obstruction of said openings by the soybean flour.

As mentioned before, said flour is pneumatically conveyed to the cyclone 15 (shown only in Fig. 1) wherein occurs the separation of the solid (powder) from the air stream, allowing the product to be packaged by means of an apparatus (nor shown) positioned under the discharge outlet 18.

Contrarily to the processes that employ crushing by means of press rollers, the equipment and the process of the present invention allow the pulverization of the soybeans irrespective of their moisture content. In fact, fully satisfactory results are achieved when the raw material is processed with the same moisture content - about 13% - used for soybean storage. As no preliminary drying of the raw material is needed, it follows that a substantial saving in thermal energy is brought about. Furthermore, the soybean flour obtained by means of the process of the invention preserves the full content of oil of the soybean in natura, and therefore has a higher nutritional value.

While the present invention has been described with respect to

what is believed to be the most practical embodiment thereof, it is particularly noted that this is by way of example only, and appropriate modifications and variations thereof are possible within the spirit and scope of the invention. Thus, for example, the outlet for the soybean flour may be placed in a position different from the one shown in the drawings, such as, for example, on the side of the housing. Furthermore, the screen 25 may be eliminated from the housing, the separation of the flour from the eventual coarser fractions of the ground soy being provided separately from the mill. Moreover, the equipment described previously may be supplemented by a bag filter placed at the cyclone air outlet, in order to retain the finer fractions of the powder resulting from the action of the mill, such addition remaining within the scope of the original inventive concept.

Therefore, the invention is to be described and limited only by the scope of the appended claims.