Method for processing thin stillage and apparatus for producing a protein containing product

Abstract

A method for processing thin stillage (TS), characterized by the following steps: a) feeding of thin stillage (TS) into a working vessel (3); b) concentrating of thin stillage (TS) in a filtration unit (9); and c) returning of a first substream of concentrated thin stillage to the thin stillage (TSI) present in the working vessel (3) in order to adjust the solids content, and apparatus for producing a protein-containing product of value.

Claims

1. A method for processing thin stillage, comprising the steps of: a) feeding thin stillage into a working vessel; b) concentrating the thin stillage in a filtration unit; c) returning a first substream of concentrated thin stillage to the thin stillage contained in the working vessel to adjust the amount of dry matter content of the thin stillage in the working vessel; d) concentrating the thin stillage in the filtration unit, and e) splitting a flow of the concentrated thin stillage into the first substream and a second substream.

2. The method as claimed in claim 1, and further comprising the step of: clarifying at least the second substream of the concentrated thin stillage in a centrifuge to further concentrate the thin stillage.

3. The method as claimed in claim 2, wherein the further concentrated thin stillage has a dry matter amount of more than 12 percent by weight.

4. The method of claim 2, and further comprising the steps of: drying the concentrated thin stillage; and forming therefrom a protein containing product.

5. The method of claim 2, wherein the further concentrated thin stillage has a dry matter amount of more than 18 percent by weight.

6. The method of claim 1, wherein the first substream is at least three times greater than a second substream of concentrated thin stillage.

7. The method of claim 1, and further comprising the step of: processing grain stillage in a decanter to obtain the thin stillage.

8. The method of claim 1, and further comprising the steps of: discharging a permeate stream from the filtration unit; and routing the permeate stream to an anaerobic wastewater treatment facility.

9. The method of claim 1, wherein the step of concentrating the thin stillage in a filtration unit is controlled as a function of the dry matter content of the thin stillage located in the working vessel.

10. The method of claim 1, and further comprising the step of: controlling thin stillage flow based on a thin stillage flow rate after concentration of thin stillage in a filtration unit.

11. The method of claim 1, and further comprising the step of: clarifying at least the second substream of the concentrated thin stillage in a separator to further concentrate the thin stillage.

12. The method of claim 1, wherein the first substream is at least six times greater than a second substream of concentrated thin stillage.

13. The method of claim 1, and further comprising the steps of: discharging a permeate stream from the filtration unit, and reusing the permeate stream as process water.

14. A device for producing a product containing protein from thin stillage, the device comprising: a working vessel; a thin stillage concentrating filtration unit in fluid communication with the working vessel and the thin stillage concentrating filtration unit includes: a flow splitter in which concentrated stillage is split into a first substream and a second substream; a centrifuge in fluid communication with the thin stillage concentrating filtration unit; a dryer in fluid communication with the centrifuge; and a return line between the flow splitter and the working vessel for returning the first substream of concentrated thin stillage to the working vessel.

15. The device of claim 14, wherein the thin stillage concentrating filtration unit is an ultrafiltration unit.

16. The device of claim 14, and wherein the flow splitter in which the concentrated stillage is split into a first substream and a second substream, and is regulated as a function of the flow rate.

17. The device of claim 14, wherein the centrifuge is connected to the working vessel by way of a return line for returning a clarified centrifugate phase to the working vessel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 A schematic representation of a device for manufacturing a valuable product from thin stillage and

(2) FIG. 2 A schematic representation of a known process for preparing thin stillage.

DETAILED DESCRIPTION OF THE INVENTION

(3) FIG. 2 shows a known processing step for a grain stillage (whole stillage) WS, for example following an ethanol distillation process. This stillage WS has a dry matter content of about 10 wt.-%, with about 7 wt.-% being suspended solids and 3 wt.-% being dissolved solids, and is routed through a pump 1a to a decanter 1 where the stillage is processed into thick stillage (wet grains) WG and thin stillage TS.

(4) The fraction of dry matter in the thin stillage TS is about 4.15 wt.-% relative to the total mass of thin stillage TS, with about 1.15 wt.-% being suspended solids and about 3 wt.-% being dissolved solids. The fraction of dry matter in the wet grains WG is greater than 30 wt.-% relative to the total mass of the wet grains WG.

(5) The wet grains are routed from the decanter 1 to a dryer, such as a drum dryer 2, where the carrier fluid of the wet grains, usually water, is evaporated as much as possible resulting in a nutritious solid, called dry stillage (dried distillers grains with solubles) DDGS, which is used as a feed for livestock farming, among other things.

(6) The thin stillage has a volumetric flow of 6-7 m3/h and is then forwarded to a working vessel 3. (FIG. 2.)

(7) The recovery of proteins and fats from thin stillage TS is described in more detail using a concrete exemplary embodiment in the system of FIG. 1.

(8) The working vessel 3 holds 20 m.sup.3 in this concrete exemplary embodiment, and has a total of three inputs 4, 5 and 6. Input 4 of the working vessel 3 is an input for feeding thin stillage (TS) to the system, the input fed from the decanter 1 in FIG. 2, for example. The other inputs 5 and 6 to the working vessel 3 are provided for recycled thin stillage from the process and for the supernatant liquid phase.

(9) The working vessel 3 also comprises an outlet 7 that connects the working vessel 3 to an ultrafiltration unit 9 and allows the transfer of thin stillage from the working vessel 3 to the ultrafiltration unit 9. The thin stillage is transported from the working vessel 3 to the ultrafiltration unit 9 by way of a feed pump 8 at a pressure of 3-4 bar, wherein the feed pump power output is preferably 15 KW.

(10) The ultrafiltration unit 9 is only shown schematically in FIG. 1 and comprises at least one loop pump 10, a cooler 11 and one or more ultrafiltration modules 12.

(11) During the filtration, liquid is drawn out of the thin stillage and is discharged from the ultrafiltration unit 9 as permeate P at a volumetric flow of about 6 m.sup.3/h.

(12) A plurality of ceramic membrane filter rods (not shown), preferably alpha-aluminum oxide and zirconium oxide filter rods, are disposed in the ultrafiltration modules 12. These membrane filter rods are penetrated by parallel channels running in the longitudinal direction thereof, wherein the channels comprise a filter membrane, consisting of zirconium oxide deposited on an alpha-aluminum oxide carrier substance, along the channel wall and the entire perimeter thereof. In the process, the zirconium oxide layer comprises finely distributed pores, whereas the support material is constructed of aluminum oxide with coarse pores. The filter membrane has an average pore size of 50 nm.

(13) A total of 168 membrane filter rods are disposed in the six ultrafiltration modules shown in FIG. 2. These filter rods provide a filtering surface area of 72 m.sup.2 for separating liquid from the thin stillage. In the process, the permeate is forced through the ceramic filter membrane by the 3-4 bar of pressure produced by the feed pump. The retentate and the pre-concentrated thin stillage are discharged from the ultrafiltration unit by way of a control valve 13.

(14) Solids that are not able to pass through the 50 nm pores of the filter membrane build up on the surface of the membrane during filtration. In order to prevent plugging of the filter membrane, a turbulent flow of 5 m/s can be generated by the loop pump 10 with the valve 13 closed, at a volumetric flow of 810 m.sup.3/h. Such a flow can loosen or remove the accumulated solid particles from the filter membrane.

(15) After filtration, a concentrated thin stillage leaves the ultrafiltration unit as a retentate and is divided into two substreams TS1 and TS2.

(16) A second retentate substream or concentrated thin stillage substream TS2, which is preferably about 4-5 m.sup.3/h, is sent to a centrifuge, preferably a two-phase separator 16. The extent of the substream can be controlled by means for splitting flow, in this case a valve 15, for example as a function of the flow rate. This flow rate can be determined through a sensor 14 which then adjusts the flow to a pre-determined setpoint by way of the valve 15.

(17) In the centrifuge, the retentate produced in the ultrafiltration process is concentrated to a dry matter content of preferably greater than 12 wt.-%, wherein a clarified liquid is discharged at the overflow of the centrifuge as a supernatant liquid Z.

(18) The supernatant liquid Z has a solids fraction of less than one vol.-% and is returned from the centrifuge 16 to the working vessel through the return line 18 and the input 5 at a volumetric flow rate of 2.2-3.2 m.sup.3/h. The nozzle phase DP or centrifuged phase has a dry matter content of more than 12 wt.-%, preferably up to 18 wt.-% and an FC factor of 7-8, and is then processed into a transportable and storable product using a dryer, not shown here. This product can be converted to a more compact form, such as pellets, for example using a pelleting press 19. The pellets thus produced can be used as valuable feed additives, and have a fraction of dry matter of over 90 wt.-%, of which 40% is protein, 55% is fat and the rest is fiber and ash.

(19) A fractional second flow substream TS1 of 30 m/h is returned to the working vessel 3 through a return line 17 and the input 6 by way of flow control and mixed with the thin stillage from the decanter of the input 4 so that a dry matter content of about 7 wt.-% is adjusted for the thin stillage in the working vessel 3 and the FC factor, a concentration factor, is raised by a factor of 3 to 4 compared to the thin stillage from the decanter 1.

(20) The thin stillage TS leaving the decanter 1 is concentrated by the return line 17 for returning or recycling a second retentate substream TS2 to the working vessel 3. It was surprising to find that the optimum operating point for an ultrafiltration unit 9 in the processing of thin stillage is reached at a concentration of thin stillage TS to a dry matter content of about 7%.

(21) Solid particles in the size range of 5-100 nm were removed from the permeate P separated from the ultrafiltration unit 9, the permeate volume being preferably 6 m.sup.3/h and primarily water, so that this permeate can be fed to the community wastewater treatment facility or can be subjected to an anaerobic wastewater treatment. Moreover, the aqueous phase could be further used as process water, for example for creating a mash.