PROCESS FOR PROTEIN ENRICHMENT OF DRIED DISTILLERS GRAINS USING A TRIBO-ELECTROSTATIC SEPARATOR DEVICE

Abstract

A tribo-electrostatic separation process for fractionating a feed mixture derived from dried distiller's grains (DDG) or distiller's dried grains and mixed with solubles (DDGS) is disclosed.

Claims

1. A process for fractionating a feed mixture derived from dried distiller's grains (DDG) or distiller's dried grains and mixed with solubles (DDGS) using a single-step tribo-electrostatic separation process, comprising: a. milling the DDG or DDGS feed mixture to a specified particle size; b. supplying said milled DDG or DDGS feed mixture to a tribo-electrostatic separator; and c. simultaneously charging and separating said DDG or DDGS feed mixture into at least two subfractions, with one of the subfractions having a protein composition higher than the DDG or DDGS feed mixture and higher than that could be obtained otherwise.

2. The process of claim 1, further comprising optionally drying the milled DDG or DDGS feed mixture to a specified moisture level depending on the specified particle size.

3. The process of claim 2, wherein the milled DDG or DDGS feed mixture is dried if the specified median particle size is at least about, e.g. 225-250 micron or greater.

4. The process of claim 3, wherein the pre-drying moisture level for the feed mixture was greater than about 10.3% and the feed mixture moisture content after drying was less than about 7.9%.

5. The process of claim 1, wherein the DDG or DDGS feed mixture is characterized by a protein level of between about 30-45%, an oil content of less than about 20%, and/or a moisture content of less than about 30%.

6. The process of claim 5, wherein the feed protein level is in a range of from about 30% to about 35%.

7. The process of claim 6, wherein the protein level of one of the sub-fractions is enriched to be anywhere in a range of from about 35% to about 55%, e.g. from about 40% to about 55%.

8. The process of claim 1, wherein the protein level of one of the subfractions is enriched by at least an absolute protein increase of about 5%, e.g. an absolute protein increase of from about 10% to about 25%.

9. The process of claim 1, wherein the specified particle size is associated with a fine (e.g. about 50-75 micron or less), medium (e.g. about 100-125 micron) or coarse (e.g. about 225-250 micron or greater) particle size.

10. The process of claim 5, wherein the feed moisture content is from about 0% to about 12%.

11. The process of claim 5, wherein the feed oil content is from about 0.7% to about 12.0%.

12. The process of claim 1, wherein the feed mixture is processed at a rate of about 40 to about 17,000 kg per hour per meter of TBS electrode width.

13. The process of claim 1, wherein a belt speed of the tribo-electrostatic separation process is from about 10 to about 70 feet per second.

14. The process of claim 1, wherein an electric field strength of the tribo-electrostatic separation process is from about 120 to about 4,000 kV/m.

15. The process of claim 1, wherein the DDG or DDGS feed mixture is milled to a specified median particle size of about 225-250 micron or greater and then dried in order to achieve an absolute protein increase of at least about 10%.

16. The process of claim 15, wherein the milled DDG or DDGS feed mixture is dried in order to achieve a moisture content of about 6.4% or less.

17. The process of claim 1, wherein the DDG or DDGS feed mixture is milled to a specified median particle size of less than 125 microns.

18. The process of claim 17, wherein the feed mixture moisture content is less than about 5.8%.

19. The process of claim 17, wherein the milled DDG or DDGS feed mixture need not be dried in order to achieve an absolute protein increase of at least about 10%.

20. The process of claim 1, wherein the DDG or DDGS feed mixture is milled to a specified median particle size of about 50-75 micron or less.

21. The process of claim 20, wherein the milled DDG or DDGS feed mixture need not be dried in order to achieve an absolute protein increase of at least about 10%.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0030] Certain illustrative features and examples are described below with reference to the accompanying figures in which:

[0031] FIG. 1 is a schematic of a prior art tribo-electric belt separator system.

[0032] The advantages of the aspect and embodiments of this disclosure may be better understood by referring to the following description when taken in conjunction with the drawings. The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. It will be recognized by the person of ordinary skill in the art, given the benefit of this disclosure, that the dimensions, sizes, components, and views shown in the figures are for illustrative purposes. Other dimensions, representations, features, and components may also be included in the embodiments disclosed herein without departing from the scope of the description.

DETAILED DESCRIPTION

[0033] The disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects of the disclosure are capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing”, “involving”, and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. At least one aspect of the present disclosure is directed to a tribo-electric enrichment process and system for the enrichment of protein content from low value by-products such as, for example, those resulting from distillation industries i.e. dried distiller's grains with or without solubles (DDGS or DDG) and to the resulting products from the process, particularly the product that is enriched in protein. The higher protein content products can have increased value as an ingredient in animal feed formulations. In particular, at least one embodiment of the process includes supplying a DDGS/DDG feed mixture to a tribo-electric separator and charging and separating the feed mixture into at least two sub-fractions, with one of the subfractions enriched in protein and having a composition different than the feed mixture. In at least one embodiment, the protein concentration of one of the products of the separator apparatus and process is higher than would otherwise be achievable with the prior art processes or that is naturally occurring.

[0034] Corn DDGS/DDG feed produced by conventional methods may contain about 25% to about 35% protein. U.S. Pat. No. 8,227,015B2 discloses a process to extract minor amounts of residual oils from DDGS to raise the protein to a maximum of about 35%. U.S. Pat. Nos. 8,778,433 and 10,233,404 disclose a complicated wet process modification to the conventional alcohol production process where the whole stillage slurry after alcohol distillation is filtered, centrifuged, dewatered, and dried to produce a high protein meal product with greater than 40% protein. This wet process requires significant modification to the “back end” of the ethanol distillation process and complicates operation of the main process. It is an object of this disclosure to provide a process where the protein concentration of DDGS/DDG feed mixtures are increased using an entirely dry process that operates separately from the ethanol production process and does not require modification to the existing ethanol production process. According to at least one embodiment, it is an object to process such feed mixtures to provide subfractions having a protein composition of at least 40%. According to at least one embodiment, it is an object to process such feed mixtures to provide subfractions having a protein composition of at least 50% protein.

[0035] The present disclosure relates to a novel process for fractionating DDG/DDGS into their constitutive components using the tribo-electric belt separator (TBS) and process. The apparatus of FIG. 1 and the process are effective at processing dry, granular food and feed materials in a single-step separation process, as a continuously operating process, at commercially significant processing rates. By single step process, what is meant is that the constituents to be a separated are simultaneously tribo-electrically charged, conveyed and separated. The process has particular application in the enrichment of protein content of food and feed materials by separating the protein particles from fibers. Aspects and embodiments of the process have a particular benefit for the separation of dried distiller's grains resulting from the distillation industries mixed with solubles (DDGS) to enrich the protein content of at least one of the resulting products from the process.

[0036] The TBS operates as a single-step device where the food and feed particles are simultaneously tribo-charged by the frequent particle to particle collisions that occurs in the single device through the action of the special high-speed continuous-loop belt, conveyed and separated. Electrostatic separation processes based on tribo-charging are superior, and have wider application, than those based on charging by conductive induction or ion bombardment because separation can be achieved for a larger variety of particles with subtle differences in surface chemistry (or surface work function). Because the particle number density is so high within the electrode gap and the flow is vigorously agitated by the high speed belt, there are many collisions between particles in the device, and optimal tribo-charging occurs continuously throughout the separation zone. The counter-current flow induced by the motion of the continuous-loop belt creates counter-current multi-stage separation within the TBS device.

[0037] In contrast to the TBS apparatus and process according to this disclosure, vertical plate electrostatic separators all require a separate upstream processing step to tribo-charge the feed particles prior to separation by the vertical plate separator. For vertical plate separators, the tribo-charging step may require that each particle contacts a special solid surface with particular surface properties to enable differential charge to develop on the surface of particles. However, the need for each feed particle to contact a special solid surface creates a significant limitation on the maximum processing rate that can be achieved with a vertical plate separator for a compact device.

[0038] An issue with separating food and feed materials is that they tend to be cohesive powders that adhere especially well to the surface of the electrodes needed to create the electric field in an electro-static separator. An advantage of the motion of the high speed continuous loop belt in the TBS device and process of this disclosure is that it continuously scrapes the electrodes, which aids in removing the cohesive feed and feed materials from the electrodes and depositing them in the appropriate product hopper. The high speed continuous loop belt is the only moving part in the TBS device and process, and by its design and high speed motion it simultaneously conveys and tribo-charges the feed material, and the belt also provides a system to continuously clean electrodes of cohesive feed and feed materials that adhere to the electrodes. This feature enables the TBS apparatus and process of this disclosure to operate continuously without the need for complex electrode scraping mechanisms or electrode polarity switching systems that are required for vertical plate processes.

[0039] One advantage of the TBS apparatus and process of this disclosure, as illustrated by the test examples disclosed herein, is that the TBS apparatus and process can be used to separate feed materials, often in their naturally occurring state with their naturally occurring moisture and oil content (that little to no pre-processing is necessary) to achieve separation of the feed content into two enriched streams of at least one of protein, fiber or starch. It is also appreciated that the moisture content of feed material for the TBS apparatus and process can be adjusted to a range that optimizes the particle tribo-charging and therefore optimizes the resultant separation results. The optimal moisture level can depend on the nature of the feed material and will typically vary between 0% and 30%, and preferably between 0.2 and 12%. Adjustment of feed moisture is advantageous for some food and feed materials, but it is not a necessary requirement to adjust the moisture level of food and feed materials to achieve satisfactory separation results for some materials using the TBS device and process of this disclosure. This observation demonstrates a unique feature and advantage of the TBS apparatus and process of the disclosure, which is that the single step tribo-charging and separating that occurs in the TBS process is adequate to charge the individual components to be separated without the need for a separate tribo-charging step.

[0040] According to aspects and embodiments disclosed herein, the TBS device and process can be operated with belt speed between 10 and 70 feet per second, preferably between 15 and 65 feet per second; the voltage applied to the electrodes of the TBS apparatus and process electrodes can vary between 3 kV and 20 kV, preferably between 10 and 16 kV; and the gap between the electrodes may be continuously adjustable and can be varied between 0.5 to 2.5 cm, preferably between 0.9 to 1.7 cm.

[0041] Examples of separation results obtained from at least one feed material are detailed in the following example.

EXAMPLE 1

Enrichment of Protein from DDGS

[0042] A sample of corn-based distillers dried grains with solubles (DDGS) was prepared for testing using the TBS apparatus and process to demonstrate the capability of the TBS apparatus and process to simultaneously charge and separate distinct protein and starch particles using the TBS apparatus and process in a single step. Feed sample was prepared at three different particle sizes using an impact-type mill—coarse grind with a median (D50) particle size: 225-250 micron, medium grind (D50) with a median particle size: 100-125 micron, and fine grind with a median (D50) particle size: 50-75 micron. The results are described below:

Medium Grind

[0043] The sample was milled using an impact-type mill to a median particle size of approximately 100-125 micron, contained approx. 8% moisture after milling. The feed sample was fed as-received, with no adjustment to the moisture content, into the TBS separator at a rate of 17 tonne per hour per meter of TBS electrode width. The TBS belt speed was set at 15 feet per second, and 12 kV was applied across the TBS electrode gap to produce an electric field strength of 1390 kV/m. Two resulting products were collected from the two ends of the separator. There was no middling fraction that needed to be re-processed. Table 1 shows the mass yields of the two products, the composition of the feed and the products, achieved in a first pass. For purposes of this example, first pass refers to the feed material having been processed through the separator once.

TABLE-US-00001 TABLE 1 Results from testing corn-based DDGS (medium grind, first pass) Product 1 Product 2 Feed (Enriched Fiber) (Enriched Protein) Mass  100% .sup. 71% .sup. 29% Protein (dry basis) 34.8% 30.0% 46.8% Moisture  7.9% — — Crude Fiber  6.9%  9.0%  3.8% Fiber (ADF) 11.3% 11.8% 11.0% Fiber (NDF) 26.6% 34.8% 14.0% Oil  7.2%  7.1%  7.6% Protein Recovery .sup. 51% .sup. 49%

[0044] The high-protein product from the first pass was then processed through the separator again (second pass) and further protein increase was achieved. The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Results from testing corn-based DDGS (medium grind, second pass) Product 1 Product 2 Feed (Enriched Fiber) (Enriched Protein) Mass 100% .sup. 55% .sup. 45% Protein (dry basis) 46.8%  42.7% 51.8% Moisture  7.9% — — Fiber (ADF) 11.1%  8.9% Fiber (NDF) 19.3% 13.0% Oil  7.7%  7.8% Protein Recovery 50.3% 49.7%

[0045] The effect of moisture on medium grind feed by drying was tested, and no significant effect on protein separation was found.

Fine Grind

[0046] The sample was milled using an impact-type mill to a median particle size of approximately 50-75 micron, contained approx. 6% moisture after milling. The feed sample was fed as-received, with no adjustment to the moisture content, into the TBS separator at a rate of 17 tonne per hour per meter of TBS electrode width. The TBS belt speed was set at 15 feet per second, and 12 kV was applied across the TBS electrode gap to produce an electric field strength of 1390 kV/m. Table 3 shows the mass yields of the two products, the protein content of the feed and the products.

TABLE-US-00003 TABLE 3 Results from testing corn-based DDGS (fine grind) Product 1 Product 2 Feed (Enriched Fiber) (Enriched Protein) Mass 100% .sup. 70% .sup. 30% Protein (dry basis) 33.9%  28.8% 45.9% Moisture  5.8% — —

Coarse Grind

[0047] The sample was milled using an impact-type mill to a median particle size of approximately 225-250 micron, contained approx. 10% moisture after milling. The feed sample was fed as-received, with no adjustment to the moisture content, into the TBS separator at a rate of 17 tonne per hour per meter of TBS electrode width. The TBS belt speed was set at 65 feet per second, and 12 kV was applied across the TBS electrode gap to produce an electric field strength of 1390 kV/m. Table 4 shows the mass yields of the two products, the protein content of the feed and the products.

TABLE-US-00004 TABLE 4 Results from testing corn-based DDGS (coarse grind) Product 1 Product 2 Feed (Enriched Fiber) (Enriched Protein) Mass  100% .sup. 84% .sup. 16% Protein (dry basis) 34.1% 33.5% 39.0% Moisture 10.3% — —

[0048] Effect of moisture was investigated on coarse grind feed by drying. Table 5 shows the mass yields of the two products, and protein content of the feed and the products upon reduction of moisture content. In comparison to Table 4, results showed that the protein separation improved significantly at similar mass yields compared to the un-dried feed for coarse grind feed.

TABLE-US-00005 TABLE 5 Results from testing corn-based DDGS (coarse grind, dried) Product 1 Product 2 Feed (Enriched Fiber) (Enriched Protein) Mass 100% 85.1% 14.9% Protein (dry basis) 34.1%  32.5% 44.1% Moisture  6.4% — —

[0049] It was demonstrated that in order to achieve substantial protein increase (≥10% absolute) the feed material must be milled to a particle size with median (D50): 100-125 micron, or milled to finer particle size with median (D50): 50-75 micron, or milled to coarse particle size with median (D50): 225-250 micron and then dried, for example, to 6.4%. It is reasonable to conclude that drying is also useful for particle sizes of greater than 225-250 micron. For example, coarse milled feed material may need to be dried in order to achieve at least about a 10% absolute increase in protein content. Drying does not appear to be required for particle sizes of 100-125 micron or finer. In at least some embodiments, DDG or DDGS with a particle size equal to or less than about median (D50): 100-125 micron need not be dried in order to still achieve at least about a 10% absolute increase in protein content.

[0050] This example demonstrates the capability of TBS process to effectively tribo-charge and separate distinct protein and fiber particles in a single step from a DDGS feed sample in fine dry powder form, generating product streams enriched in each component.