Abstract:
The present invention relates to plant fiber processes (e.g., washing, drying, and/or grinding) that utilize recycle and/or make-up streams to use water resources efficiently and/or produce intermediate and/or final products with desired properties.

Description:
PRIORITY CLAIM 
       [0001]    The present non-provisional application claims the benefit of commonly owned provisional Application having Ser. No. 61/987,200, filed on May 1, 2014, which provisional application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Plants such as corn include a variety of constituents that can be used for many purposes. For example, starch obtained from corn plants can be used to make ethanol and plant fibers can be used as ingredients for a variety of products. Oftentimes it is desirable to separate the various plant constituents and purify them in an economical manner (e.g., energy efficient manner, environmentally friendly manner, and the like), while at the same time providing desired properties in the intermediate and/or final plant material products. 
         [0003]    Accordingly, there is a continuing need to improve processes for treating plant materials such as plant fibers in an economical manner while at the same time providing desirable properties in the intermediate and/or final products. 
       SUMMARY 
       [0004]    The present invention involves methods and systems that selectively adjust the amount of make-up aqueous stream(s) and recycled aqueous stream(s) that are used for washing plant fiber depending on the desired level of fiber purity so as to use water more efficiently. 
         [0005]    According to one aspect of the present invention, a method of cleaning plant fiber includes: a) providing a first plant fiber component including plant fiber and one or more additional plant constituents; b) combining the first plant fiber component with at least a first aqueous component comprising water and at least a portion of the one or more additional plant constituents to form a first mixture including: i) a second plant fiber component including plant fiber and one or more additional plant constituents; and ii) a second aqueous component including water and one or more additional plant constituents; c) separating at least a portion of the second aqueous component from the first mixture; d) after step (c), combining the first mixture with at least a third aqueous component including water to form a second mixture including: i) a third plant fiber component including plant fiber; and ii) the first aqueous component; e) separating the first aqueous component from the second mixture; and f) recycling at least a portion of the first aqueous component so that it can be combined with the first plant fiber component, wherein the concentration of plant fiber on a dry matter basis in the third plant fiber component is greater than the concentration of plant fiber on a dry matter basis in the first plant fiber component. 
         [0006]    According to another aspect of the present invention, a system for cleaning plant fiber includes: a) a first plant fiber component source including plant fiber and one or more additional plant constituents; b) a first aqueous component source including water and at least a portion of the one or more additional plant constituents; c) a first vessel in fluid communication with the first plant fiber component source and the first aqueous component source to combine the first plant fiber component with the first aqueous component to form a first mixture including: i) a second plant fiber component including plant fiber and one or more additional plant constituents; and ii) a second aqueous component including water and one or more additional plant constituents; d) a first separation apparatus in fluid communication with the first mixture to separate at least a portion of the second aqueous component from the first mixture; e) a second vessel in fluid communication with the first mixture from the first separation apparatus and a third aqueous component source including water to combine the first mixture with the third aqueous component to form a second mixture including: i) a third plant fiber component including plant fiber; and ii) the first aqueous component; f) a second separation apparatus in fluid communication with the second mixture to separate the first aqueous component from the second mixture; and g) a recycle line in fluid communication with the second separation apparatus and the first vessel to provide at least a portion of the first aqueous component to the first vessel, wherein the concentration of plant fiber on a dry matter basis in the third plant fiber component is greater than the concentration of plant fiber on a dry matter basis in the first plant fiber component. 
         [0007]    The present invention also involves methods and systems that can process a plant fiber to produce a fiber product (e.g., ground corn bran fiber) having a desired moisture level using recycle and make-up air streams. 
         [0008]    According to another aspect of the present invention, a method of processing a plant fiber includes: a) providing a plant fiber component including plant fiber, wherein the plant fiber component has an amount of moisture; b) processing the plant fiber component to provide a fiber product, wherein the plant fiber component is processed at a temperature that can reduce the amount of moisture in the plant fiber component; c) combining the plant fiber component with a first gas stream having a temperature and humidity value to control the moisture content of the fiber product; d) after said processing, separating at least a portion of gas from the fiber product to form a recycled gas stream; and e) using the recycled gas stream to form the first gas stream. 
         [0009]    According to yet another aspect of the present invention, a system for processing a plant fiber includes: a) a plant fiber component source including plant fiber, wherein the plant fiber component has an amount of moisture; b) a grinding apparatus in fluid communication with the plant fiber component source to grind the plant fiber and produce a fiber product, wherein the plant fiber component is exposed to a temperature in the grinding apparatus that can reduce the amount of moisture in the plant fiber component; c) a first gas stream in fluid communication with the grinding apparatus, wherein the first gas stream can be combined with the plant fiber component, and wherein the first gas stream has a temperature and humidity value to control the moisture content of the fiber product; and d) a separation apparatus in fluid communication with the grinding apparatus, wherein the separation apparatus is configured to separate at least a portion of the first gas stream from the fiber product to form a recycled gas stream, wherein the recycled gas stream is in fluid communication with the first gas stream so that the recycled gas stream can be used to form the first gas stream. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1A  is a process flow diagram illustrating an exemplary method and system for washing a corn bran fiber according to the present invention. 
           [0011]      FIG. 1B  is a process flow diagram illustrating an exemplary alternative of the method and system shown in  FIG. 1A  for washing a corn bran fiber according to the present invention. 
           [0012]      FIG. 2  is a process flow diagram illustrating an exemplary method and system for grinding a corn bran fiber to produce a corn bran fiber product according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Methods and systems are described in detail herein below for processing plant fiber according to the present invention. 
         [0014]    A wide variety of plant fibers can be processed according to the present invention. In some embodiments, plant fibers include grain fibers obtained from plants such as fibers from corn, sorghum, barley, oats, wheat, and the like. For example, a preferred plant fiber includes corn bran fiber obtained from one or more fractionation processes such as those used to make ethanol from corn grain. Fractionating corn grain to make ethanol is well-known and is described in, e.g., U.S. Pat. No. 8,454,802 (Redford); U.S. Pat. No. 8,449,728 (Redford); and U.S. Pat. No. 8,603,786 (Redford), wherein the entirety of each patent is incorporated herein by reference for all purposes. Corn bran fiber obtained from a fractionation process may include one or more additional materials such as additional plant constituents (e.g., starch). It may be desirable to remove such additional materials from corn bran fiber so as to purify and increase the content of the corn bran fiber. 
         [0015]    One aspect of the present invention involves washing a plant fiber to clean the plant fiber and increase the purity of the plant fiber. For example, as discussed above, plant fiber can have other materials such as plant constituents (e.g., starch) bound to the fiber. A method of removing a plant constituent such as starch from plant fiber according to the present invention can selectively adjust the amount of make-up water and recycled water that are used for cleaning the plant fiber depending on the desired level of fiber purity so as to use water more efficiently. 
         [0016]    An exemplary method and system  100  for washing a plant fiber according to the present invention will be described with respect to  FIG. 1  in the context of removing starch from corn bran fiber to increase the level of fiber while using water in an efficient manner. 
         [0017]    As shown in  FIG. 1A , a crude corn bran fiber stream (i.e., a “fiber component”)  101  is provided to a vessel such as tank  110 . Crude stream  101  can be obtained from a corn fractionation process used to make ethanol. The crude corn bran fiber stream  101  includes at least residual starch from the corn fractionation process. Much of the starch is still bound to the corn bran fiber. 
         [0018]    Aqueous steam  102  is also provided to tank  110  and combined with corn bran fiber stream  101  to form a mixture and help wet the corn bran fiber so that the starch can be more easily separated from the corn bran fiber. Aqueous stream  102  is preferably a recycle stream that includes water and one or more other materials separated from the corn bran fiber (e.g., soil, starch, and the like). 
         [0019]    Tank  110  is maintained at appropriate conditions to facilitate wetting of the corn bran fiber and to help separate at least some of the starch from the bran fiber. For example, in some embodiments, tank  110  can use agitation (e.g., stirring) to help wet and wash the starch from the bran fiber. Also, the contents of tank  110  can be heated (e.g., via heating tank  110  and/or heating stream  102 ) to help remove starch from the corn bran fiber. 
         [0020]    After processing the corn bran fiber in tank  110  for an appropriate amount of time, the mixture is pumped via line  103  so that at least a portion of the aqueous fraction of the mixture can be separated from the mixture. Because at least some washing occurs in tank  110 , the aqueous fraction of the mixture in line  103  tends to include relatively higher levels of washed materials (e.g., starch) as compared to aqueous stream  102  and the corn bran fiber tends to be relatively more clean as compared to the raw corn bran fiber in stream  101 . In some embodiments, an apparatus can be used to apply pressure to the mixture so as to separate at least a portion of the aqueous fraction from the mixture. Also, applying pressure can help abrade the corn bran fiber and separate material such as starch from the corn bran fiber. As shown, the mixture is pumped via pump  112  to screw press  114 . At least a portion of the aqueous fraction of the mixture that is separated via screw press  114  can be recycled to tank  110  via line  104  and another portion of the aqueous fraction of the mixture that is separated via screw press  114  can be removed from the washing process  100  via line  113 . 
         [0021]    The aqueous fraction of the mixture that removed from the washing process  100  via line  113  can be handled in a variety of ways. In some embodiments, it can be discharged to waste or delivered to another process. For example, because the aqueous stream in line  113  can include starch separated from corn bran fiber, the starch in line  113  can be delivered to a fermentation process and fermented into ethanol. 
         [0022]    After screw press  114 , the corn bran fiber is delivered to at least one additional vessel such as tank  120  so that an additional washing process can be performed with an aqueous stream that is different from stream  102 . As shown, aqueous stream  106  is delivered to tank  120  and is combined with the corn bran fiber from stream  105  to form a mixture and help wet the corn bran fiber so that at least some of the remaining starch can be more easily separated from the corn bran fiber. Preferably, aqueous stream  106  includes fresh clean water added to the system  100  (i.e., “make-up” water). 
         [0023]    Tank  120  is maintained at appropriate conditions to facilitate wetting of the corn bran fiber and to help separate at least some of the remaining starch from the bran fiber. For example, in some embodiments, tank  120  can use agitation (e.g., stirring) to help wet and wash starch from the bran fiber. Also, the contents of tank  120  can be heated (e.g., via heating tank  120  and/or heating line  106  and/or heating line  105 ) to help remove starch from the corn bran fiber. Preferably, tank  120  is substantially the same as tank  110 . 
         [0024]    After processing the corn bran fiber in tank  120  for an appropriate amount of time, the mixture is pumped via line  107  so that preferably as much of the aqueous fraction of the mixture can be separated from the mixture to create an aqueous stream  108  and a fiber stream  111 . Because at least some washing occurs in tank  120 , the aqueous fraction of the mixture in line  107  tends to include relatively higher levels of washed materials (e.g., starch) as compared to aqueous stream  106  and the corn bran fiber in line  111  tends to be relatively more clean as compared to the corn bran fiber in stream  105 . In some embodiments, an apparatus can be used to apply pressure to the mixture so as to help separate an aqueous fraction from the mixture. Also, applying pressure can help abrade the corn bran fiber and separate material such as starch from the corn bran fiber. As shown, the mixture is pumped via pump  122  to screw press  124  in a manner similar to screw press  114  (discussed above). At least a portion of the aqueous stream  108  that is separated via screw press  124  can be recycled to tank  120  via line  109  and another portion of the aqueous fraction of the mixture that is separated via screw press  124  can be recycled to tank  110  via line  102 . 
         [0025]    The flow rates of the recycle streams and fresh/discharge streams in process  100  can be adjusted to impact the fiber purity level as desired in stream  111 , while at the same time taking into account the amount of fresh (“make-up”) water used. In some embodiments, the concentration of fiber in tanks  110  and  120  can be kept constant so as to provide a desired residence time for the fiber to be exposed to washing action. In such embodiments, as the flow rate of fresh water  106  is increased, the purity of fiber in stream  111  is increased. For example, if a relatively higher level of fiber purity is desired in stream  111 , then the flow rate of fresh water introduced into process  100  via line  106  can be increased, which corresponds to an increase in flow rate of lines  102  and  113 . As a result, the flow rates of the recycle streams such as streams  104  and  109  can be reduced to maintain the appropriate concentrations in each of tanks  110  and  120 . As another example, if a relatively lower fiber purity can be tolerated, the flow rate of fresh water introduced into process  100  via line  106  can be reduced, thereby saving on the amount of fresh water used as well as reducing the amount of water discharged via line  113 . In such a scenario, the flow rate of line  102  can also be reduced (and be almost the same as the flow rate of line  106 ) while the flow rates of the recycle streams  104  and  109  can be increased to accommodate the reduced flow rate in line  106  and maintain the appropriate concentrations in each of tanks  110  and  120 . 
         [0026]    Fiber stream  111  can be further processed as desired. For example, fiber stream  111  can be ground as described below in connection with  FIG. 2 . The fiber cleaning process  100  cleans the corn bran fiber delivered in stream  101  such that the purity or concentration of fiber on a dry matter basis in stream  111  is higher as compared to the concentration of fiber on a dry matter basis in stream  101 . In some embodiments, the concentration of fiber in stream  111  is 80 percent or greater on a dry matter basis, preferably 85 percent or greater on a dry matter basis, even 90 percent or greater on dry matter basis. 
         [0027]    Optionally, the process  100  in  FIG. 1A  can be modified to include one or more additional washing vessels between tanks  110  and  120 . Such additional washing vessels could include recycle and/or fresh water streams to help wash the fiber in a manner as described above with respect to tanks  110  and  120 . Also optionally, such additional washing vessels could include one or more separating apparatuses (e.g., screw presses) between each washing vessel so as to separate an aqueous fraction from the fiber before delivering the fiber to the next washing vessel. In some embodiments, including additional washing vessels and maintaining similar concentrations as in the two tank system described in  FIG. 1A  (to provide appropriate residence times) can permit less fresh water to be used for a given fiber purity as compared to the two tank system in  FIG. 1A . For example, an alternative process  150  is shown in  FIG. 1B , where the same reference characters have been used for similar features as described in  FIG. 1A  (a discussion of those same reference characters is not repeated for  FIG. 1B ). Process  150  includes an additional wash tank  160 . Process  150  is set up with recycle streams and a fresh water stream  106  such that the fresh water is used to wash the cleanest fiber in process  150 , which is in the last tank  120 , and the relatively most unclean recycle water in stream  162  is used to wash the incoming fiber from stream  101 , which is typically the most unclean fiber in process  150 . As mentioned above, because a third wash tank  160  is introduced and the same concentration is used for tanks  110 ,  120 , and  160  as in  FIG. 1A , a lower flow rate for fresh water stream  106  can be used while at the same time producing the same level of fiber purity as compared to the system in  FIG. 1A , which would use a higher flow rate for fresh water line  106 . In a preferred embodiment, as shown in  FIG. 1B , a screw press is used at least for the first and last wash tanks (i.e., tanks  110  and  120 ). Using a screw press  114  for the first wash tank helps abrade and scrap starch that may be bound to the fiber so as to loosen such starch and permit it to be washed in a subsequent wash tank such as tank  160  and/or tank  120 . Using a screw press after the last tank such as screw press  124  after tank  120  helps permit a relatively high amount of wash water to be separated from the fiber. Separating a relatively high amount of wash water from fiber after the last wash tank can be advantageous as it can lower the amount of water that needs to be removed in a downstream drying apparatus, which can save on energy costs. After washing in tank  160 , the mixture of at least fiber, starch, and water is pumped from tank  160  to a separation apparatus  174  via pump  172  and line  163 . Separation apparatus  174  permits an aqueous stream to be recovered for use as recycled wash water in lines  162  and  164 . In some embodiments, separation apparatus  174  can include a screw press, especially if fiber abrasion is desired. The fiber stream  165  can be delivered to tank  120  and treated as discussed above with respect to  FIG. 1A . 
         [0028]    Optionally, the processes  100  and  150  shown in  FIGS. 1A and 1B  can include processing steps and equipment known in the fiber processing art to facilitate cleaning and/or maintaining appropriate cleaning conditions such as filters, cyclone separators, heat exchangers, pumps, and the like. 
         [0029]    Another aspect of the present invention involves processing a plant fiber to produce a fiber product (e.g., ground corn bran fiber) having a desired moisture level. For example, after washing corn bran fiber, it can be ground into a fiber product. Typically, the corn bran fiber is sufficiently dried before grinding so that the fiber can be handled in an efficient manner. If the corn bran fiber has too high of a moisture level, it can be difficult to handle and process. Oftentimes, the grinding process occurs at a temperature to inhibit bacterial growth in the grinding and related equipment as well as the final product. Such elevated temperatures can further dry the fiber to an undesirably low moisture level. A method of processing (e.g., grinding) a corn bran fiber according to the present invention can selectively adjust the flow rate of one or more recycled gas streams as well as the humidity, flow rate, and temperature of a fresh gas stream to create a combined gas stream that is exposed to the corn bran fiber during such processing so as to provide a desired moisture level in the final corn bran product. 
         [0030]    An exemplary method and system  200  for processing a plant fiber according to the present invention is described with respect to  FIG. 2  in the context of grinding corn bran fiber to produce a ground corn bran fiber product having a desired moisture level. 
         [0031]    As shown in  FIG. 2 , a stream of corn bran fiber  201  is delivered to a grinding apparatus  210  to reduce the size of the corn bran fiber to form a ground corn bran fiber stream  202 . After grinding the corn bran fiber in mill  210 , the ground corn bran fiber is transferred to separator  220  (e.g., a cyclone separator) to separate gas from the ground corn bran fiber. The gas is removed from the top of separator  220  via line  204  and the ground corn bran fiber leaves separator  220  through the bottom via line  203 . Gas stream  204  can be split into gas stream  205  (e.g., a gas exhaust) and recycled gas stream  206 , which are discussed in detail below. The ground corn bran fiber stream  203  can optionally be cooled via cooling apparatus  230  and packaged as a ground fiber product via line  209 . The process in  FIG. 2  is controlled to produce a ground corn bran fiber product in stream  209  to have a desired moisture content, which is typically below 12 percent so that the fiber product can be stored without being susceptible to mold growth. In some embodiments, the ground corn bran fiber product in stream  209  has a moisture content in the range of from 2 to 10 percent. 
         [0032]    The corn bran fiber in stream  201  typically has a moisture content before grinding. If the moisture level is too high, the fiber can become difficult to handle and process. In some embodiments, the stream of corn bran fiber  201  can be provided from a bran washing process, such as stream  111  discussed above with respect to  FIG. 1A . Optionally, as shown in  FIG. 2 , a corn bran fiber in stream  215  can be dried to the desired moisture content in dryer  240  prior to providing the stream  201  to grinding apparatus  210 . In some embodiments that include a dryer such as dryer  240  it can be desirable to dry the fiber so that it can at least be handled and processed. Removing more moisture than is necessary for the fiber to be handled and processed can add extra cost without necessarily providing a benefit. Accordingly, in some embodiments, the fiber in stream  201  can be as moist as possible as long as the fiber can be handled and is not prone to microbial growth. In some embodiments, the moisture content of the fiber in stream  201  is no more than 12 percent, preferably 10 percent or less. 
         [0033]    Grinding apparatuses are well-known and include, e.g., mills, etc. Grinding apparatus  210  can be maintained at conditions to facilitate reducing the size of the corn bran fiber in stream  201 . In addition, the grinding apparatus  210  can be operated at a temperature that inhibits the growth of bacteria in the process equipment (e.g., grinding apparatus  210  and separator  220 ) as well as the ground fiber. Exemplary temperatures include at least 130° F., preferably at least 135° F. (e.g., from 130° F. to 170° F.). Such temperatures can reduce the moisture level of the corn fiber product  202  as compared to the corn bran fiber  201  entering the grinding apparatus  210 . Higher temperatures can be tolerated as long as the quality of the ground fiber and/or process equipment is not impacted to an undue degree. In some embodiments, the grinding process can operate at a temperature of 250° F. or less. 
         [0034]    To help provide the ground fiber product in stream  209  with a desired moisture content (e.g., from 2-10 percent) the humidity and temperature of the incoming gas stream  208  are controlled. The humidity and temperature of gas stream  208  can be controlled using a combination of one or more of exhaust stream  205 , recycle gas stream  206 , and make-up (e.g., fresh) gas stream  207 . Controlling gas stream  208  in such a manner can advantageously produce a relatively quick response in moisture content of the ground fiber product in stream  209 . Also, controlling gas stream  208  in such a manner can provide desirable quality control of the moisture content in the ground fiber product. In embodiments that dry the fiber stream (e.g., via dryer  240 ) before it is provided to a grinding apparatus, the dryer can be used as a coarse adjustment for the moisture content of the fiber in stream  201  and gas stream  208  can be used as a fine adjustment to the moisture content of the fiber so as to provide the desired moisture content of the fiber in stream  209 . 
         [0035]    In some embodiments, the humidity and temperature of gas stream  208  are such that moisture is transferred out of the fiber coming in from stream  201  (i.e., the fiber in stream  201  is dried) so as to provide the desired moisture content in the ground fiber in stream  209 . In other embodiments, the humidity and temperature of gas stream  208  are such that moisture content of the fiber coming in from stream  201  is maintained through to stream  209  so as to provide the desired moisture content in the ground fiber in stream  209 . In still other embodiments, the humidity and temperature of gas stream  208  are such that moisture is transferred into the fiber coming in from stream  201  (i.e., the fiber in stream  201  is moistened) so as to provide the desired moisture content in the ground fiber in stream  209 . If moisture is transferred into the fiber that is provided in stream  201 , the humidity and temperature of gas stream  208  are preferably selected so as to avoid condensation on process equipment (e.g., apparatus  210  and separator  220 ) and thereby reduce the chance for microbial growth. 
         [0036]    The temperature and humidity of stream  208  can be controlled by selectively controlling at least the flow rates of gas streams  206  and  205 . Gas stream  206  is a recycled gas stream from the gas stream  204  leaving separator  220 . Gas stream  205  is an exhaust stream that can be used to throttle the flow of stream  206  as necessary to control the temperature and humidity of stream  208 . For example, if the moisture level of the fiber product in stream  209  is too high, then the flow rate of exhaust stream  205  can be increased. Optionally, make-up gas (e.g., air) stream  207  can be provided at a desired temperature and humidity and combined with recycled gas stream  206 . For example, if the fiber product in stream  209  is too dry and the temperature in grinding apparatus  210  is too high, then fresh humid air can be supplied via stream  207  and combined with recycled air stream  206  before being supplied to grinding apparatus  210 . As yet another example, if the moisture level of the fiber product in stream  209  is too high, then heated fresh air can be supplied via stream  207  and combined with recycled air stream  206  before being supplied to grinding apparatus  210 . 
         [0037]    As mentioned, the temperature of gas stream  208  is controlled to a temperature depending on the desired moisture content of the ground fiber in stream  209 . Exemplary temperatures for gas stream  208  include a temperature in the range of from 130 F to 170° F. As also mentioned, the humidity of gas stream  208  is controlled to a humidity level depending on the desired moisture content of the ground fiber in stream  209   
         [0038]    The temperature of make-up air stream  207  can be adjusted by techniques known in the art such using heating coils, cooling coils, combinations of these, and the like. The humidity of make-up air stream  207  can be adjusted using humidifying equipment and/or de-humidifying equipment, both of which are well known. Steam injection can also be used to adjust both temperature and humidity. 
         [0039]    Exemplary corn bran fiber products in stream  209  can include at least 80 percent fiber on a dry matter basis, preferably at least 85 percent fiber on a dry matter basis, and even more preferably at least 90 percent fiber on a dry matter basis.