JPS6129963B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides wet milling (wet milling) of starch products.
milling). Although the present invention is described in connection with the wet milling of corn, the present invention also applies to other wet milling methods, such as corn chips, wheat, potatoes, etc.
It will be appreciated that it may also be applied for the collection of flea white matter. The conventional method of wet milling of corn may be divided into four steps: (i) Corn is soaked in water under conditions that soften the kernels and the resulting light steep
water) is separated from the softened grains. typically ground corn (corn groud)
Light soaking water of 0.3 m ³ to more than 1 m ³ is produced per ton. (ii) Mill the softened grain and remove the separated by-products, germ, fiber (husk) and gluten, to an average solids content of typically 30-50% by weight. Collect as wet material. (iii) The starch slurry obtained from wet milling is washed, usually in several stages with countercurrent water, to reduce the level of soluble and insoluble impurities below the desired value. For this cleaning process, typically 1
tons of ground corn
1.0m ³ to 2.0m ² or more of water is used per unit. (iv) The starch slurry obtained can optionally be dewatered depending on its intended use, in which case the water is recycled to the washing step (iii). usually,
The water for the process flows countercurrently to the starch. Fresh water enters the last washing stage of stage (iii) and passes continuously to proceed to the first stage. step
The water used in (iii) goes to the wet grinding stage (ii).
The water from the wet milling stage (ii) passes to the soaking stage (i) and finally exits the system as light soaking water. The solids content of the water increases with each of these stages and is typically between 60 and 110 g/l for light soak waters.
reach the level of Much or all of the light soak water is processed, typically by evaporation, to recover valuable solids for various uses, such as animal feed. One of the factors that determines the purity of starch products is the amount of water used in washing step (iii). For a given purity, it is possible to compensate to some extent for the reduction in the amount of wash water by increasing the number of wash stages. However, even with such improvements, it is not possible to obtain starch of high purity without washing it with large amounts of water - more water than required in the preceding (soaking and milling) steps. Alternatives have been proposed to recover starch and other products from corn or other starch products. For example, Chwalek and Olson US Pat. Nos. 4,171,384 and 4,181,748 disclose dry-wet milling processes for wheat and corn, respectively. There, the raw material is first dry-milled and most of the fiber and germ removed, after which the remaining portion of the grain is subjected to a wet process. Such systems use less water than wet milling, thus making starch washing more critical. If you add 1 kg of fresh water to the washing stage,
This results in an additional 1 kg of light soak water that must be evaporated or otherwise treated. The aim of the invention is to provide a method which makes it possible to use a higher amount of water in the washing step without concomitantly increasing the amount of light soaking water: or, on the contrary, without concomitantly reducing the amount of water for starch washing.
The objective is to provide a method for reducing the amount of light immersion water. Conventional wet processes applied to materials other than whole grains, such as potatoes or flour, do not employ such a soaking step. All wet processes thus employ a final starch washing step with water as well as preparatory treatments such as soaking, slurrying or conditioning with water. The present invention is a method for recovering a starch slurry from a starch product comprising: (i) forming an aqueous slurry of finely ground starch product; (ii) converting the starch-rich fraction to the majority of the remaining components of the slurry. and (iii) washing the starch-rich fraction in at least one stage and recovering a starch slurry product of the desired purity, with fresh water for the process being introduced into step (iii). is,
and in a process where the water for step (i) and step (ii) consists of the water used in step (iii), at least a portion of the water used in the process but not yet exiting the process. is divided into a first fraction and a second fraction,
The first fraction contains a lower content of both soluble and insoluble substances than the second fraction, and the first fraction is recycled to increase the purity of the starch in the washing step (iii). The method is characterized in that it is used with fresh water. When the starch product is corn, the first two steps of the above method are typically combined (i)
Includes soaking and (ii) wet milling. If the starch product is wheat, the first two steps together typically involve grinding, slurrying and gluten separation. When the starch product is potato, the first two steps together typically involve grinding and separating the fruit water and fiber. The following description is primarily directed to the processing of corn. The division that characterizes the invention leaves washing step (iii) and step (ii) when the treatment is applied to corn.
That is, it can be carried out in water proceeding to the wet grinding stage. Alternatively, it can be carried out in the water between stages (i) and (ii): or in the water between two stages of washing stage (iii) if multiple washing stages are used. The first fraction with low solids content is recycled to step (iii) or to its final stage if multiple washing steps are used; If carried out in the water used for washing step (iii), it is divided into a second fraction of relatively high solids content, which proceeds to wet grinding step (ii). In a particularly preferred embodiment of the invention, the characteristic splitting step can be carried out in water containing the gluten in suspension, which has left the point of preliminary separation of the gluten from the starch. As described in more detail below, examples of partitioning at this point result in preliminary separation of gluten from starch and washing of starch at higher dilutions;
and ultimately increase efficiency beyond what was previously economically possible. Partitioning requires concentrating both soluble and insoluble substances into one fraction, so conventional filtration or centrifugation is inadequate in itself. The desired separation can be carried out by critical filtration or by two-step methods such as centrifugation and activated adsorbents. However, the preferred splitting technique is reverse osmosis. Using this technique, the water from the starch washing step containing soluble protein equivalent to more than 1000 ppm nitrogen is divided into two fractions, the first of which contains protein equivalent to less than 10 ppm nitrogen, and the starch It is now possible to make it suitable for recirculation to the final stage of cleaning. It is understood that reverse osmosis involves contacting a solution to be purified with a pure solvent (e.g., water) through a semipermeable membrane, and that there is a pressure difference on either side of the membrane that is greater than the osmotic pressure of the solution. It will be. Typically pressure differentials of 20 to 100 atmospheres may be used. Since the solution in this case contains insoluble as well as soluble substances, it may be advantageous to maintain flow across the semipermeable membrane to slow or prevent pore blockage. A suitable arrangement is to maintain a continuous circulating flow of the liquid through the tube of semipermeable membrane material, to add the solution to be divided into fractions to the circulating liquid, and to remove the first fraction that has passed through the semipermeable membrane. and collecting a second fraction by bleeding from the circulating liquid. The technique of reverse osmosis performed on liquids containing insoluble as well as soluble substances is known in the art and does not require further description here. The desired purity of the starch slurry product depends on its intended end use. Typical quality specifications require a nitrogen content (as a measure of soluble protein) below a number in the range of 10 to 1000 ppm on a dry basis. For example, the first fraction of water separated by reverse osmosis needs to have a nitrogen content not significantly exceeding this figure, so that when such water is used for starch washing, it This will probably improve the purity of the product, rather than ruining it. This will be explained below with reference to the attached drawings. Figure 1 is a water balance diagram of an example of the conventional method, expressed in tons per day for a throughput of 1000 tons of corn per day; Figure 2 is a water balance diagram of an example of the method according to the invention; , expressed on the same basis: FIG. 3 is a water balance diagram of an example of an alternative process according to the invention, expressed in tons per day for a throughput of 1000 tons of corn per day: FIG. 2 is a diagram showing in more detail the mass balance during the preliminary separation and washing steps of the same system as that in the figure; FIG. Figures 5 and 6 relate to potatoes. FIG. 5 is a material balance diagram for an example of a conventional method, expressed in tons per day for a throughput of 1000 tons of potatoes per day. FIG. 6 is a material balance diagram on the same basis for an example of the method according to the invention. Figure 7 is a diagram of the method applied to wheat. Now, in FIG. 1, the three stages of the conventional method, namely soaking, grinding and washing, are shown as separate squares. Water is entered into the system at two points; as moisture normally present in the corn, into the steeping step (i);
150 tons/day; and 1572 to the final stage of cleaning stage (iii)
tons/day of fresh water. This water leaves the system as follows: 841 tons/day in the starch slurry product; 317 tons/day with the embryo, fiber and gluten separated from the starch and from each other in the milling stage (ii); and light soaking. 564 tons/day in water. If the amount of water transferred with starch, gluten, fiber and embryo is held constant, an increase in the amount of fresh wash water will result in an increase in the amount of light soak water produced. Referring now to Figure 2, the method of the invention is such that the water proceeding from the washing stage (iii) to the grinding stage (ii) is divided into two streams, one of which is a primary stream of 284 tons/day each by reverse osmosis. It is distinguished from the conventional method by the fact that it is divided into a second fraction and a second fraction. The first fraction is recycled and mixed with a fresh water supply for feeding to the final stage of washing step (iii). The second fraction is a stage
Proceed to the grinding stage with the remaining part of the water from (iii). With this method, the amount of fresh water supplied is reduced by 284 tons/day compared to the conventional method, which is 1288 tons/day, although the total amount of wash water used in step (iii) remains the same, 1572 tons/day. It becomes a day. Similarly, the amount of water leaving the system as light soak water is determined by the conventional method in Figure 1.
It will be reduced from 564 tons/day to 280 tons/day. In the method of the invention illustrated in FIG. 2, a relatively small proportion of soluble material is transferred into the light immersion water;
A relatively large proportion occurs with embryonic, fibrous and gluten fractions. If more water is used in the splitting stage (second
This change in the position of the soluble material would be more noticeable if it had passed through the soluble material (Fig.) and was recycled.
For various reasons, the essential proportion of soluble substances
It may be desirable to recover from the soak water rather than from the embryo, fibrous material and gluten fractions. This consideration may determine the proportion of water flow from washing stage (iii) to grinding stage (ii) that should be subjected to reverse osmosis. The division stage in Figure 2 shows that 568 tons/day of water is divided into equal amounts of first and second fractions. However, there is no reason why the weights of the two fractions should not be different: the proportions of the two fractions are best determined according to the reverse osmosis technique used and are not essential to the invention. . Partitioning is shown to be carried out on water between washing stage (iii) and grinding stage (ii). However, the splitting stage may include water between two stages of a multi-stage washing stage: or water passing from grinding stage (ii) to soaking stage (i): or any water flow within stage (i) or stage (ii). However, it can be implemented. As already mentioned, the method of the invention makes it possible to reduce the amount of light steeping water without reducing the quality of the starch product: however, it does this with a special operation, namely the two fractions of water. This can be done at the cost of dividing into Nevertheless, the energy savings obtained from the method of the invention can be quite substantial. A typical efficient evaporation process for light soak water requires 240 KWh per ton of water evaporated. On the other hand, the energy required to divide 2 m ³ of wash water into two fractions of 1 m ³ each by reverse osmosis is typically 8 KWh. Referring now to FIG. 3, the three stages of the conventional method, soaking, grinding and washing, are shown as separate squares. However, this diagram differs from Figures 1 and 2 in that the preliminary separation of gluten from starch is shown in the "Preliminary Separation/Washing" square rather than in the "Crushing" square. Different. Water enters the system at two points: 150 tons/day into soaking stage (i) as the water normally present in the corn.
day: and 1288 tons/day of fresh water to the final stage of washing stage (iii). This water leaves the system as follows: 841 tons/day in the starch slurry product: 317 tons/day of embryo (68 tons), fiber (179 tons) and gluten (70 tons).
with: and 280 tons/day in light immersion water. The numbers in the above clause are the same as those in the system in Figure 2. The major difference between the two systems is the amount of water recycled from reverse osmosis to the washing stage (iii). In Figure 3, 1712 tons/day of permeate is recycled, giving a total of 3000 tons/day of wash water. in the end,
Preliminary separation and washing step (iii) is carried out at high dilution. FIG. 4 shows a mass balance diagram of the preliminary separation and washing steps of the system shown in FIG. The system consists of two preliminary separation stages P ₁ and P ₂ (each a bank of hydroclones, which together effect the separation of the overflowing gluten slurry and the underflowing starch slurry). ); and seven starch washing stages W ₁ to _{W 7} (of which only W ₁ , W ₂ and W ₇ are shown for simplicity, each similarly consisting of a hydroclone bank).
includes. The ground starch enters the system at a flow rate of 172 m ³ /hr and at a concentration of 8°Be (160 g/) containing 7.6% protein by weight with 4.2 m ³ of water per ton of corn, and enters the first and second reserves. Proceed to physical separation steps P ₁ and P ₂ . Starch is made into a slurry with a concentration of 190g/(approximately 10°Be) along with ^9.8m3 of water per ton of corn.
411 m ³ /hr are recovered as underflow from the first preliminary separation stage P ₁ (underflow/feed ratio in stage P ₁ is 0.40) and proceed to the first washing stage W ₁ . The underflow from each cleaning stage W _o proceeds to the next higher order wash W _o+1 . Overflow from each wash stage W _o goes to the next lower wash stage W _o-1 . Starch product contains 485g/containing 0.3% insoluble protein and 0.010% soluble protein
56.5 m ³ /hr of slurry with a concentration of (23°Be) is recovered as the underflow of the seventh washing stage. Gluten is an insoluble substance of which 72% is protein, 12g/and ^5.95m3 /ton of corn.
of water is recovered as overflow from the second preliminary separation stage P ₂ as 246.5 m ³ /hr. 143 t/hr of this flow passes to the reverse osmosis stage RO where it is divided into equivolumic first and second fractions. The first fraction, which contains a relatively low content of soluble and insoluble substances, is recycled to the starch washing stage W ₇ . A second fraction containing a relatively high content of soluble and insoluble materials is combined with the remainder of the gluten slurry and passed to a gluten thickening device. Fresh water enters the system at a flow rate of 53.5 m ³ /hr (equivalent to 1.288 m ³ per ton of ground corn).
It consists of 71.5m ³ /h of water in the first fraction from the reverse soaking stage
The combined stream is mixed with
Mixed with starch in W ₇ . The first fraction from the reverse osmosis stage is transferred to the final washing stage W ₇
I was shown to enter. But it can be changed to enter an intermediate washing stage, for example W ₆ or W ₅ :
This may in fact be preferred if the nitrogen content of the first fraction is somewhat higher than the desired nitrogen content of the final starch slurry. The reverse osmosis stage can be designed to produce a first fraction (permeate) of suitable purity for introduction into the desired stage of starch washing. The amount of overflow and underflow and the direction in which they flow are indicated on the diagram. The embodiment of the invention described with reference to FIGS. 3 and 4 has a number of advantages over conventional wet corn milling operations. A. The present invention provides for preliminary separation and washing steps:
Enables the use of a hydroclone instead of a centrifuge. This allows for reduced equipment costs since hydroclones are cheaper than centrifuges. The use of hydroclons for preliminary separation and starch washing is not new. Our U.S. Pat. No. 4,144,087 relates to a method for separating ground starch into a starch-rich stream and a protein-rich stream under controlled conditions, including at least two protein separation stages and multiple starch washing stages. Characterized by the use of a special series of stages. The advantage of this method is that a hydroclone is used rather than a more expensive centrifuge. It is noted that this method makes it possible to simultaneously obtain gluten of acceptable protein content and starch of acceptable purity. The present invention takes advantage of this advantage, making it possible to obtain gluten of acceptable protein content together with starch of acceptable purity in a more flexible manner and using a wider range of operating conditions than previously possible. A direct comparison of the energy costs for operating conventional wet milling processes is difficult because the operations involved differ in many ways. However, even without taking into account the reduction in the amount of light soak water to be evaporated, the energy costs for operating the process of the present invention are approximately equal to or less than those of conventional wet grinding methods for the same product purity. Rather less. C Gluten can be used as animal feed, but
At purity levels greater than about 70%, industrial or food uses are also possible and can be sold at a premium. Conventional wet milling typically produces 68-70% gluten. The quality of a starch product depends to a large extent on its soluble and insoluble protein content. Based on its intended use, starch is typically 0.4%
It may be required to contain less insoluble protein and less than 0.02% soluble protein. It is known that if a given system is modified to improve gluten purity, a side effect is an increase in the insoluble protein content of the starch. The system illustrated in Figure 4 is notable for simultaneously achieving both high purity gluten of 72% and starch with low concentrations of soluble and insoluble proteins (0.01% and 0.3%, respectively). D At the same underflow density, the lower the density of the hydroclone feed, the more
It is known that at each stage, the proportion of insoluble proteins that go to overflow increases. In systems of the type shown in Figures 3 and 4, the density of the feed to the first preseparation stage P ₁ is typically 8
°Be', while typical densities in conventional operations using ground starch thickeners will be at least 8°Ee'. Similarly, in systems of the type shown in Figures 3 and 4, the density of the feed to the first wash stage _W1 will typically be less than the typical density in conventional wash operations. E It is known that the greater the amount of wash water to the final washing stage, the more the solubles in the underflow starch in each stage and thus in the final stage are reduced. In systems of the type shown in Figures 3 and 4, the amount of wash water introduced in the final stage will typically be greater than the amount of wash water used in conventional wet milling. It is known that the larger the overflow/feed volume ratio of a F hydroclone, the greater the proportion of solubles that goes with the overflow in each hydroclone stage.
In systems of the type shown in Figures 3 and 4, the overflow/feed volume ratio of the various hydroclones is typically greater than that used in conventional operations. G In conventional corn wet milling, the amount of wash water used is kept to a minimum in order to minimize the volume of light soak water that has to be evaporated.
In order to sufficiently wash the starch without using large amounts of water, it was necessary to increase the number of washing stages to about 10-13 or even 15 stages. This is expensive in terms of both equipment and space. Through the use of large volumes of wash water, the system of the present invention achieves high purity standards with as few wash stages as seven or fewer, depending on the desired protein content of the gluten. H. In conventional wet milling methods, a milled starch concentrator is placed upstream of the preliminary starch/gluten separation with the aim of reducing the passage of solubles to the starch washing process and thereby minimizing the number of starch washing stages required. It is normal to become In conventional corn wet milling, it is common to include middlings concentrators to treat the water that passes from the first starch washing stage to the preliminary starch/gluten separation station, with the aim of increasing the efficiency of the latter. be. The disadvantages of pulverized starch concentrator and coarse powder concentrator are:
They require separate controls. The system according to the invention does not require milled starch concentrators or coarse flour concentrators and is therefore cheap in equipment and easy to control and operate. I The efficiency of gluten recovery depends inversely on the density of the feed to the preliminary starch/gluten separation.
In conventional operation, it is possible to reduce the density of the feed and thus increase the efficiency of gluten recovery, but with the disadvantage that relatively large gluten concentration equipment is required. The system according to the invention, which places the reverse osmosis upstream of the gluten concentrator, achieves efficient gluten recovery without the disadvantage of requiring a relatively large gluten concentrator. J As mentioned above, one effect of the reverse osmosis and recirculation that characterizes the present invention is that the amount of light soak water is reduced. As a result, a relatively small proportion of soluble material is transferred into the soak water, and a relatively large proportion remains and is removed along with the embryo, fiber and gluten or contaminates the starch. In the system shown in Figure 2, this risk of starch contamination may place a limit on reducing the amount of light steeping water. Conversely, in the systems shown in Figures 3 and 4, the starch is well washed, ensuring that the risk of contamination is eliminated. In such a system, it is therefore possible to recirculate relatively little water to the soaking stage and thus bring the amount of light soak water close to zero;
It can also be advantageous. K The first fraction of water recycled from the reverse osmosis location to the starch washing stage can be considered to serve three functions: (a) reducing the volume of light soak water; (b) supplying the hydroclon. (c) increasing the total amount of wash water and thus improving the efficiency of the separation of starch from soluble substances; to do. The system of the present invention is extremely flexible, as the operator can enhance or reduce any one of the above-mentioned functions relative to the others by adjusting the flow rate. Now in FIG. 5, the steps of a conventional process for the recovery of starch from potatoes are shown as separate squares: juice separation, fiber separation/starch concentration, and starch washing steps. 1000
Tons/day of ground potatoes enter the system at the youth separation stage. Fresh water enters at two points: 800 tons/day at the fiber separation/starch concentration stage and 2700 tons/day at the end of the starch washing stage. These substances leave the system as follows: 803 tons/day as fruit water: 33.5 tons/day along with fiber:
3373.5 tons/day as wastewater: and 290 tons/day as washed starch slurry. If other conditions are held constant, an increase in the amount of fresh water for starch washing will result in an increase in the amount of waste water. 6, the method of the invention divides the water leaving the first stage of the starch washing stage by reverse osmosis into two fractions, of which the first fraction is recycled to the starch washing stage, and It is distinguished from conventional methods by passing the second fraction to a youth separation and fiber separation/starch concentration stage. By this means, the amount of washing water used remains the same, 2700 tons/day, but the amount of fresh water supplied is 1350 tons/day, half that of the conventional method. Similarly, the amount of wastewater removed will be reduced from 3373.5 tons/day to 2023.5 tons/day. 7, an operation comprising a method according to the invention for recovering starch from wheat flour is shown.
Shown as separate squares. The flour is slurried and separated into a starch-rich stream ("A" starch) and a gluten-rich stream that goes to a gluten recovery location. The effluent stream from this gluten recovery location is divided into two streams, one of which is subjected to reverse osmosis and a first fraction (permeate) with low soluble and insoluble content and a second fraction (“ B"
starch). The permeate is recycled and mixed with fresh water to enter the system in the final stage of the "A" starch wash. This arrangement reduces the need for fresh water by an amount equal to the permeate from the reverse osmosis location, and correspondingly reduces the amount of field flow that must be evaporated or otherwise treated. The size of the concentrator can also be reduced. Starch quality can be controlled by adjusting the amount of permeate produced and recycled. Wheat contains high concentrations of oxygen and salts, so cleaning starch from wheat requires careful control. The following experiments are performed to determine suitable conditions for reverse osmosis. In each case, the 50 feeds were divided into 25 permeate (first fraction) and concentrate (second fraction). All membranes used
Obtained from Wafilin NV, (Hardenberg. The Netherlands). Experiments The membrane used has a NaCl retention of 95% and a clean water flow through of 44/m ² hr at 40 atm and 14°C. The feed is grit water, the effluent from the grit concentrator, which is fed from stage (iii) of the corn wet milling process. The feed is circulated through the system at 17° C. and 40 atm at a speed of 2 m/sec. The results are presented in a table including a comparative experiment with city water.

【table】

[Table] (1) Nitrogen analysis performed on filtered samples.
Experiment Three different semipermeable membranes were used:

Table: The feed is the coarse effluent from stage (iii) which enters the coarse concentrator. The feed is at 17℃ and 42atm.
Circulated at 1.6m/sec. Summarize the results in a table.

【table】 [Brief explanation of the drawing]

Fig. 1 is a diagram showing the water balance of an example of the conventional method, Fig. 2 is a water balance diagram of an example of the method of the present invention, Fig. 3 is a water balance diagram of another example of the method of the present invention, and Fig. 4 is a diagram showing the water balance of an example of the method of the present invention. A diagram showing the detailed mass balance during preliminary separation and starch washing for the same system as in Figure 3, Figure 5 is a mass balance diagram for another example of the conventional method, and Figure 6 is a mass balance diagram for an example of the method of the present invention. FIG. 7 is a flow diagram of yet another example of the method of the present invention.

Claims (1)

[Claims] 1. A method for recovering a starch slurry from a starch product, comprising: (i) forming an aqueous slurry of finely ground starch product; (ii) dissolving a starch-rich fraction in the remainder of the slurry. (iii) washing the starch-enriched fraction in at least one stage and recovering a starch slurry product of desired purity; iii) and the water for stage (i) and stage (ii) is added to stage (iii).
In a process comprising water used in the process, at least a portion of the water used in the process but not yet leaving the process is divided into a first fraction and a second fraction, of which the first fraction contains a lower content of both soluble and insoluble substances than the second fraction, and the first fraction is recycled and used in a washing step (iii) with fresh water to increase the purity of the starch. A method characterized in that it is used. 2. The method of claim 1, wherein the starch product is corn and the first two steps include (i) soaking and (ii) wet milling. 3. A method according to claim 2, wherein the water leaving washing step (iii) and proceeding to step (ii) is divided into a first fraction and a second fraction. 4. Process according to claim 2, in which the water containing the gluten in suspension, which has left the point of preliminary separation of the gluten from the starch, is divided into a first fraction and a second fraction. 5. The method according to claim 1, wherein the starch product is potato. 6. The method of claim 5, wherein the water from the first stage of starch washing is divided into a first fraction and a second fraction. 7. The method according to claim 1, wherein the starch product is wheat or wheat flour. 8. The method of claim 7, wherein the water from the gluten recovery location is divided into a first fraction and a second fraction. 9. A method according to any one of claims 1 to 8, wherein the division of water into the first and second fractions is carried out by reverse osmosis. 10 Reverse osmosis partitioning involves maintaining a continuous circulating flow of liquid through a tube of semipermeable membrane material, adding the solution to be divided into fractions to the circulating liquid, and collecting a fraction;
and recovering a second fraction from the circulating liquid by breathing. 11. A process according to any one of claims 1 to 10, wherein the first fraction is recycled and introduced together with fresh water into the final stage of a multi-stage starch washing stage. 12. A process according to any one of claims 1 to 10, wherein the first fraction is recycled and introduced into an intermediate stage of a multistage starch washing stage.