Abstract:
A process for preparing a starch-containing biomass particle stream having a significant percentage of fiber for processing into ethanol comprises the first step of: mixing the particle stream with a liquid solvent to dissolve at least a portion of the starch in the carbohydrate particle stream to form a carbohydrate slurry stream containing starch dissolved in the liquid solvent. This first step removes a portion of the fiber from the carbohydrate slurry stream. In a second step, the carbohydrate slurry stream is held in a settling tank to remove a further portion of the fiber. An enhancement to the process is suitable for use with shell corn or other biomass having an oil-containing germ portion and a non-germ portion comprising mainly carbohydrates and fiber. This enhancement includes the step of grinding the corn to particles of a size suitable for separating the germ particles from the non-germ particles. The germ particles are processed first to remove the oil and then to remove the carbohydrates.

Description:
This is a regular application filed under 35 U.S.C. §111(a) claiming priority under 35 U.S.C. §119(e)(1), of provisional application Ser. No. 60/797,532, having a filing date of May 4, 2006. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the production of ethanol from grain and other biomass, in particular from corn. 
     BACKGROUND OF THE INVENTION 
     One solution to the problem of dependence on foreign sources for energy, particularly for fuel for motor vehicles, is converting biomass to ethanol. The presently available processes use corn (maize) or other starch-containing biomass. 
     For efficiency, the process must convert a large percentage of the biomass to ethanol. The process should proceed rapidly so that the plant can produce the maximum amount of ethanol per unit time. 
     Corn is one preferred substance used for ethanol production. As is well known, corn kernels comprise a germ portion and a carbohydrate portion. The germ portion comprises about 8% of the entire weight. The germ contains about 40% by weight of valuable corn oil as well as some carbohydrates and fiber. The carbohydrate portion comprises starch, sugar, and fiber, and contains almost no oil. On a weight basis, corn kernels are about 6-7% oil, 60-70% carbohydrates, 20-25% fiber, and 10-12% water. 
     An efficient ethanol process uses enzymes to convert starches in the biomass to sugar before the fermentation. The process ferments sugars of any kind to produce CO 2  and the ethanol, but cannot convert starch to ethanol. Since CO 2  is a greenhouse gas, the less CO 2  produced, the better. 
     In current corn ethanol processes, corn is ground and mixed with a solvent to form a ground corn slurry. This slurry comprises both the germ and the carbohydrate portions. Enzymes added to the slurry convert the starch to sugar. Fermenting the sugar in the slurry then produces ethanol. A distillation step separates the ethanol from the slurry. The ethanol is then further refined to a form useable as automobile fuel. 
     The common ethanol production process has a number of problems. One is lack of efficiency. It turns out that the sum of all of the energy inputs needed to produce a unit measure of corn is not much less than the energy content of the ethanol provided by that unit measure. Of course, the ethanol process does produce some useful by-products, such as animal feed and the corn oil usable in plastic manufacture. But overall, current ethanol production processes are not outstandingly efficient. 
     Secondly, the current ethanol processes produces more contaminating fusel oil in the distilled ethanol than desirable. Fusel oil is an aromatic alcohol that reduces speed and efficiency in the distillation step. The fusel oil is a byproduct of corn oil that reaches the fermenting tank. Accordingly, removing as much corn oil as possible from the ground corn slurry reduces the concentration of the fusel oil. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A process for preparing a starch-containing biomass particle stream having a significant percentage of fiber for processing into ethanol comprises a first step of: mixing the particle stream with a liquid solvent to dissolve at least a portion of the starch in the carbohydrate particle stream. This forms a carbohydrate slurry stream containing starch dissolved in the liquid solvent, and having a portion of the fiber removed. The solvent is typically an ethanol-water solution. 
     In a second step, holding the carbohydrate slurry stream in a settling tank for a time, allows a further portion of the fiber to settle to the bottom of the tank. Removing the upper portion of the material in the settling tank forms a liquid carbohydrate stream having only a small amount of fiber. 
     An enhancement to the process is suitable for use with shell corn or other biomass having an oil-containing germ portion and a non-germ portion comprising mainly carbohydrates and fiber. This enhancement includes the step of grinding the corn to particles of a size allowing separation of the germ particles from the non-germ particles. The germ particles are processed first to remove the oil and then to remove the carbohydrates. 
     In one embodiment, up-welling air lifts the lighter non-germ particles into a carbohydrate stream, and allows the germ particles to fall to form a germ stream. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  together form a block diagram of an ethanol production facility that incorporates the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show a facility that uses a continuous flow process efficiently for producing ethanol and corn oil. The particular facility shown has front end and parallel process steps designed specifically for shell corn. Where non-corn starch-containing biomass is used, portions of the facility are suitable for converting this non-corn biomass into ethanol with efficiency that may be higher than currently achieved. 
     When corn is the biomass, corn oil is a valuable byproduct of this process. If biomass other than corn is used, one may omit the steps that separate the germ and non-germ portions of individual kernels, and that process the germ portion. 
       FIG. 1  shows the facility components that perform initial processing for partially separating the corn germ from the non-germ or starch and sugar (carbohydrate) portion, and that process the starch and sugar components of the shell corn.  FIG. 2  shows the facility components that extract oil from the germ portion of the corn and process the remaining components of the germ portion for ethanol production. 
     Front End Corn Processing 
     In  FIG. 1 , loose kernel corn is stored in a bin  32 . The kernel corn flows in a continuous stream to a mill or grinder  36 . Ideally, mill  36  grinds the kernel corn to a fineness that creates individual particles that are either essentially all germ or are not germ. As mentioned, the germ is initially about 8% of the entire kernel. The particles comprising mainly germ material from the kernels have a slightly higher specific gravity than do non-germ particles. 
     Preferably individual particles exiting from mill  36  have a maximum dimension in the range of 0.3-0.6 mm. and a minimum dimensional range of perhaps half that range. This corresponds to a roller mill whose rollers are set to a 0.2-0.4 mm. spacing. For reasons to be explained, particles of this size are preferable. 
     The ground corn forms a stream of particles, hereafter “dry meal stream,” that is delivered to a mechanical separator  39 . In the version shown, separator  39  uses the different specific gravities of the particles in the dry meal stream to separate those with higher specific gravity containing the germ from those comprising only carbohydrate material. Preferably, separator  39  has an aspirator design that injects air at an air intake  38  near the bottom of separator  39 . The air flows upwardly through corn particles falling into the top of and through separator  39 . 
     Another version of mechanical separation relies on the characteristic of milled corn in which the germ portion particles are slightly larger than the non-germ portions. 
     For meal particles in the range mentioned, velocity of the upwelling air may be in the range of 50-150 fpm. A meal stream having particles in the upper end of the preferred size range will need slightly higher air velocity. Smaller particles will need lower air velocity. Experimentation suggests that too small particles will not allow the germ and non-germ particles to separate efficiently. 
     Separator  39  divides the corn meal stream into a carbohydrate stream and a germ stream. The carbohydrate stream exits the upper part of separator  39  and flows through a first duct or pipe  15  to a particle precipitator  13 . The corn germ falls downwards through separator  39 , flowing from the lower part of separator  39  as a germ stream into a second duct or pipe  37  and to an oil extractor  90 , see  FIG. 2 . Connector element B symbolizes the continuation of duct  37  from  FIG. 1  to  FIG. 2 . 
     The separation of the germ and the carbohydrate portions of the meal stream in the separator  39  is far from perfect. Typically, separator  39  approximately doubles the concentration of germ in the germ steam to around 15-20% from the approximately 8% by weight in the meal stream. Pure germ particles may comprise around 40% corn oil, so the concentration of corn oil in the germ stream may be approximately 6-8%. On the other hand, almost no germ particles flow into the carbohydrate stream. Hence little or no corn oil is present in the carbohydrate stream. 
     Carbohydrate Stream Processing 
     The velocity of the air flowing through duct  15  and carrying a higher proportion of slows as it enters precipitator  13 . Particles suspended in the moving air fall toward the bottom of the precipitator  13  as the air slows within precipitator  13 . In one version, a fan  17  connected at the top of precipitator  13  pulls air through a filter from precipitator  13 . The vacuum that fan  17  creates in precipitator  13  is propagated to separator  39  through duct  15  causing air inflow through the air intake  38 . 
     The carbohydrate stream falls into the intake  65  of a first auger-type carbohydrate extractor  60 . The processing of the carbohydrate stream as it enters extractor  60  is suitable for a wide range of fementable biomass. Thus, sugar cane, sugar beets, and other sources of starch or sugar may be ground to a proper size of particles and provided to intake  65 . 
     The intake  65  uses an auger to force the carbohydrate stream into a chamber  56  of extractor  60  maintained at relatively high pressure, perhaps 150-350 psi. The intake  65  includes an air seal or lock that retains pressure within chamber  56 . A motor slowly rotates the extractor  60  auger to move the carbohydrate stream toward the outlet at the right end of chamber  56 . 
     A pump  23  delivers a carbohydrate solvent, preferably an ethanol-water solution (also called a polar solvent), from a supply tank  26  maintained at a relatively high pressure, perhaps 3000-5000 psi., to the extractor chamber  56 . The solvent sprays into the carbohydrate stream in chamber  56 , and dissolves the carbohydrates in the carbohydrate stream to produce a liquid carbohydrate stream in the form of a thin slurry that flows through a throttling valve  68  to a settling tank  71 . Current the preferred weight ratio of solvent flow rate to carbohydrate stream flow rate into chamber  56  is approximately 2:1, but ratios in the range of approximately 3:2 to 3:1 may also serve adequately. 
     Throttling valve  68  reduces to approximately atmospheric, the pressure of the liquid carbohydrate stream flowing from extractor  60  to settling tank  71 . The liquid carbohydrate stream flowing to tank  71  has a substantial amount of particulate material comprising mainly fiber. 
     Settling tank  71  may be any of the drag link types that slowly stir and shift settling solids to an end of tank  71 . Tank  71  has a port near the top through which fluid drains or decants as a liquid carbohydrate stream that flows into an ethanol extractor  74 . 
     Solids that remain in chamber  56  of extractor  60  flow to a desolventizer unit  59  that vaporizes the ethanol-water solvent. The solvent vapors flow to a condenser  42  that condenses the solvent vapors. A throttling valve  57  forming a part of the condenser  42  reduces the pressure of the solvent vapors to approximately atmospheric in desolventizer  59 . Pump  53  transports the condensed solvent to a processor  29 . Pump  29  must produce pressure adequate to force the liquid solvent into the bottom of a tank  26  that may have solvent standing 30 m. or higher. Processor  29  represents components that rebalance the liquid water-ethanol solvent and supply it to tank  26  for reuse. 
     The solids flow from desolventizer  59  for further processing into animal feed. The processing to this point has removed most of the solvent from the solids. 
     In the settling tank  71 , much of the particulate material in the liquid carbohydrate stream settles to the bottom where it flows out through a port near the bottom of tank  71  as a slurry stream to desolventizer  72 . 
     Desolventizer unit  72  removes the ethanol from the slurry stream, which flows to condenser  48  and pump  51 . From pump  51 , the condensed ethanol flows to processor  29  for reuse. Where the composition of the slurry stream provided by the settling tank  71  is different from that provided by the desolventizer unit  59 , the processing for the settling slurry in desolventizer unit  72  differs from that for the solids from the desolventizer unit  59 . Where the composition of the solids exiting from tank  71  is similar to those that exit from extractor  60 , the output of tank  71  may flow to desolventizer  59 . 
     Extractor  74  vaporizes most of the ethanol remaining in the liquid carbohydrate stream. The solvent vapors flow through a pipe or duct as connector element A indicates, to a condenser  45  that condenses the ethanol vapors. Pump  53  brings the condensed ethanol vapors from condenser  45  to the input pressure of element  29 , and supplies the condensed ethanol vapors to element  29 . Extractor  74  may comprise several stages of ethanol removal employing distillation and other means as well. The industry well understands this ethanol extraction technology. 
     At this stage the liquid carbohydrate stream carries very little solid (fiber) material. The liquid carbohydrate stream flows to a digester  77  where enzymes mix with the liquid carbohydrate stream to convert starches in the liquid carbohydrate stream to sugar. Fermentation processes currently used cannot easily convert starch to ethanol. CO 2  is a normal byproduct of the fermentation process, and is provided by the piping indicated by connector element C to the oil removal portion of the process. 
     Digester  77 , fermenter  83  and ethanol extractor  80  are conventional devices. However, removing nearly all of the fiber from the liquid carbohydrate stream prior to entering digester  77  as extractor  60  and settling tank  71  do, improves efficiency of the process substantially. 
     Ethanol from extractor  80  is stored in a tank  86  for distribution to users. Some of the ethanol in tank  86  flows to processor  29  through a pump  88  to replace ethanol lost in the extraction process. A suitable feedback system may control the amount of replacement ethanol provided to processor  29 . 
     Oil Stream Processing 
     Mechanical separation of the germ and carbohydrate by separator  39  produces the germ stream carried in duct  37 . Connector element B symbolizes the germ stream flow to an extractor  90  operating in a dual solvent mode. 
     The oil content of the germ stream is dissolved by liquid CO 2  provided by CO 2  tank  96 . Preferably, the CO 2  in tank  96  is that fermenter  83  provides as a natural by-product of fermentation. Pump  93  receives the CO 2  from fermenter  83  through connector element C and compresses this CO 2  gas to liquefy the CO 2 . A heat exchanger may be integral with pump  93  or tank  96  to cool the liquid CO 2 , or even to allow the liquification to occur. 
     A pump  99  raises the pressure of the liquid CO 2  entering chamber  105  to a range of approximately 4000-8500 psi. The liquid CO 2  enters an oil extractor  90  at the upstream end of an extraction chamber  105 . 
     Structurally, extractor  90  may be quite similar to carbohydrate extractor  60 . However, extractor  90  operates in a dual mode that removes both oil and carbohydrates from the germ stream. 
     Extractor  90  has an intake  102  that receives the germ stream and forces this germ stream into an extraction chamber  105 . The intake  102  includes an air seal or lock such as the auger shown, that retains pressure within chambers  105  and  107 . Extractor  90  differs from extractor  60  because of the high pressure CO 2  intake at the upstream end of chamber  105 . 
     Liquid CO 2  entering chamber  105  dissolves the corn oil in the germ stream material within chamber  105 . Liquid CO 2  with dissolved oil flows from chamber  105  through a throttling valve  112  to conventional processing and storage elements. These elements remove the CO 2 , perhaps by flashing off the CO 2 , and refine the oil for use in food, plastics, and other industrial purposes. 
     The germ stream then flows to the downstream section of chamber  105  to remove much of the carbohydrate materials present in the germ stream. The downstream section of chamber  105  functions as an extractor in a manner very similar to that of extractor  60 . An ethanol-water solution enters chamber  105  at a midway point and mixes with the germ stream. 
     The output at the downstream end of chamber  105  is very similar to that from extractor  60 . Solids flow through throttling valve  108  to a desolventizer unit  148  similar to unit  59 . Ethanol in these solids is vaporized and flows to condenser  110  and pump  119 . Pump  119  pumps the condensed ethanol to a processor  128  and a storage tank  135  for reuse. Solids flow from unit  148  for further processing. It is easily possible that the ethanol vapors from extractor  90  have a compostion that allows desolventizer  59  to process them, in which case desolventizer  148 , condenser unit  110 , and pump  119  are unnecessary. 
     A liquid carbohydrate stream flows from chamber  105  through a throttling valve  144  to a second settling tank  141  similar to tank  71 . The liquid stream from chamber  105  has a substantial percentage of carbohydrates and solids. Settling tank  141  is very similar to settling tank  71 , and operates with very similar parameters. Tank  141  settles out much of the solid material in the liquid stream from extractor  90 . 
     The solids that settle out in tank  141  flow from the bottom of tank  141  to desolventizer unit  152 . The ethanol in the solids stream is vaporized and removed by desolventizer unit  152 , condensed by condenser  155 , and pumped up by pump  158  to the inlet pressure at processor  128 . 
     A liquid comprising mainly carbohydrates flows from the top of the material in settling tank  141  to an ethanol extractor  138 . Extractor  138  is similar to extractor  74  and removes most of the ethanol remaining in the liquid carbohydrate stream. The removed ethanol flows through connector element D to condenser  115  and pump  121  for reuse through processor  128 . 
     The carbohydrate stream flows from extractor  138  through connector element E to the digester  77  on  FIG. 1 . In this way, the carbohydrate content of the germ portion can by used to produce ethanol without the undesirable effects of fusel oil within the fermenter  83 . In addition, most of the fiber has been removed, which adds efficiency to the fermentation process.