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.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
       [0001]    In the recovery of ethanol in a distillation process, recovered from grains such as corn, wheat and/or triticale, a large amount of stillage is left behind. 
         [0002]    This stillage can be used as a feed for livestock farming, among other things. 
         [0003]    In the conventional process up until now, the stillage is separated into thin stillage and thick stillage in a decanter. The thin stillage is fed to an evaporator for further reduction in water content and for further concentration. This process step leads to what is known as “stillage syrup”. Then, the thick stillage is mixed back in with the stillage syrup and fed to a dryer which takes the dry matter content to above 90 wt.-%. However, this recovered feed can only be fed to ruminants since the fraction of fibrous material is very high, the use of this nutritious feed additive therefore being limited to only a few areas of application. 
         [0004]    DE 20 2009 013 389.3 discloses a device for recovering a product in which the thin stillage is concentrated by way of ultrafiltration and then is sent to a dryer together with the thick stillage. This device has essentially proven its effectiveness, but in this case as well, the product produced can only be fed to ruminants. In addition, it has been shown that in the processing of the thin stillage, ultrafiltration can only be operated economically up to a certain concentration level. 
       SUMMARY OF THE INVENTION 
       [0005]    Hence, the object of the present invention on the one hand is to provide a method that ensures optimum operation of a filtration unit, and on the other hand provides a device for manufacturing a product of value that contains proteins and fats, and is essentially free of fiber. 
         [0006]    According to the invention, a method for processing thin stillage comprises the following steps:
       a) Feeding of thin stillage into a working vessel;   b) Filtering and pre-concentrating thin stillage in a filtration unit; and   c) Returning a first substream of pre-concentrated thin stillage to the thin stillage contained in the working vessel in order to adjust the amount of dry matter.       
 
         [0010]    By returning the first substream of pre-concentrated thin stillage to the thin stillage located in the working vessel, the dry matter content of the thin stillage can be raised, which facilitates a more optimal process and a higher efficiency of the filtration unit. 
         [0011]    After the pre-concentration of the thin stillage by way of the filtration unit, the flow can be split, wherein a first substream is returned to the working vessel and a second substream is further processed. 
         [0012]    After the filtration unit, this second substream can be routed to a mechanical solid-liquid separator in which the thin stillage is further concentrated to advantageously form a thin stillage with a dry matter content of preferably greater than 12 wt.-%. By combining a filtration unit with a centrifuge, the thin stillage can be advantageously concentrated in a particularly temperature-sensitive manner. 
         [0013]    After further concentration of the thin stillage by way of clarification and decanting of the clarified aqueous phase, the centrifuged thin stillage is transferred as a separator nozzle phase to a dryer, for example a spray dryer, where a product of value containing protein and that is essentially free of fiber is formed by way of drying the concentrated thin stillage, the product being suitable as a feed additive, for example. 
         [0014]    The drying can be done in a product-sensitive manner, in other words with no drying in furnaces, flames or the like such that the valuable contents are not damaged by the effect of heat. However, drying can also be done after processing in the centrifuge. 
         [0015]    It is advantageous that the thin stillage fed to the working vessel can be prepared by processing grain stillage in a decanter, for example following a distillation process. 
         [0016]    It is further advantageous if in addition to the concentrated thin stillage a permeate stream is discharged from the filtration unit, the permeate stream optionally being routable to an anaerobic wastewater treatment facility, for example, or being reusable as process water. This is advantageous since the wastewater can be easily processed as a result and a separate collection and storage system can be avoided, as is frequently needed in this case for process wastewater. 
         [0017]    According to the invention, a device for producing a valuable product containing protein from thin stillage comprises a working vessel, a filtration unit, a centrifuge, preferably a separator and a dryer, wherein the filtration unit is connected to the working vessel by way of a return line for a first substream of the concentrated thin stillage. This operating mode results in a nearly fiber-free valuable product, with the filtration unit operating efficiently. 
         [0018]    The invention is explained in more detail through the following exemplary embodiment and with the aid of the drawings in  FIGS. 1 and 2 . Shown are: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  A schematic representation of a device for manufacturing a valuable product from thin stillage and 
           [0020]      FIG. 2  A schematic representation of a known process for preparing thin stillage. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      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  1   a  to a decanter  1  where the stillage is processed into thick stillage (wet grains) WG and thin stillage TS. 
         [0022]    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. 
         [0023]    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. 
         [0024]    The thin stillage has a volumetric flow of 6-7 m3/h and is then forwarded to a working vessel  3 . ( FIG. 2 .) 
         [0025]    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 . 
         [0026]    The working vessel  3  holds 20 m 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. 
         [0027]    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. 
         [0028]    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 . 
         [0029]    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 3 /h. 
         [0030]    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. 
         [0031]    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 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 . 
         [0032]    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 3 /h. Such a flow can loosen or remove the accumulated solid particles from the filter membrane. 
         [0033]    After filtration, a concentrated thin stillage leaves the ultrafiltration unit as a retentate and is divided into two substreams TS 1  and TS 2 . 
         [0034]    A second retentate substream or concentrated thin stillage substream TS 2 , which is preferably about 4-5 m 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 . 
         [0035]    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. 
         [0036]    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 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. 
         [0037]    A fractional second flow substream TS 1  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 . 
         [0038]    The thin stillage TS leaving the decanter  1  is concentrated by the return line  17  for returning or recycling a second retentate substream TS 2  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%. 
         [0039]    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 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.