Ethanol process using pre-fermentation solids removal

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.

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 CO2and the ethanol, but cannot convert starch to ethanol. Since CO2is a greenhouse gas, the less CO2produced, 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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2show 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. 1shows 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. 2shows 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

InFIG. 1, loose kernel corn is stored in a bin32. The kernel corn flows in a continuous stream to a mill or grinder36. Ideally, mill36grinds 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 mill36have 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 separator39. In the version shown, separator39uses 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, separator39has an aspirator design that injects air at an air intake38near the bottom of separator39. The air flows upwardly through corn particles falling into the top of and through separator39.

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.

Separator39divides the corn meal stream into a carbohydrate stream and a germ stream. The carbohydrate stream exits the upper part of separator39and flows through a first duct or pipe15to a particle precipitator13. The corn germ falls downwards through separator39, flowing from the lower part of separator39as a germ stream into a second duct or pipe37and to an oil extractor90, seeFIG. 2. Connector element B symbolizes the continuation of duct37fromFIG. 1toFIG. 2.

The separation of the germ and the carbohydrate portions of the meal stream in the separator39is far from perfect. Typically, separator39approximately 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 duct15and carrying a higher proportion of slows as it enters precipitator13. Particles suspended in the moving air fall toward the bottom of the precipitator13as the air slows within precipitator13. In one version, a fan17connected at the top of precipitator13pulls air through a filter from precipitator13. The vacuum that fan17creates in precipitator13is propagated to separator39through duct15causing air inflow through the air intake38.

The carbohydrate stream falls into the intake65of a first auger-type carbohydrate extractor60. The processing of the carbohydrate stream as it enters extractor60is 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 intake65.

The intake65uses an auger to force the carbohydrate stream into a chamber56of extractor60maintained at relatively high pressure, perhaps 150-350 psi. The intake65includes an air seal or lock that retains pressure within chamber56. A motor slowly rotates the extractor60auger to move the carbohydrate stream toward the outlet at the right end of chamber56.

A pump23delivers a carbohydrate solvent, preferably an ethanol-water solution (also called a polar solvent), from a supply tank26maintained at a relatively high pressure, perhaps 3000-5000 psi., to the extractor chamber56. The solvent sprays into the carbohydrate stream in chamber56, 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 valve68to a settling tank71. Current the preferred weight ratio of solvent flow rate to carbohydrate stream flow rate into chamber56is approximately 2:1, but ratios in the range of approximately 3:2 to 3:1 may also serve adequately.

Throttling valve68reduces to approximately atmospheric, the pressure of the liquid carbohydrate stream flowing from extractor60to settling tank71. The liquid carbohydrate stream flowing to tank71has a substantial amount of particulate material comprising mainly fiber.

Settling tank71may be any of the drag link types that slowly stir and shift settling solids to an end of tank71. Tank71has a port near the top through which fluid drains or decants as a liquid carbohydrate stream that flows into an ethanol extractor74.

Solids that remain in chamber56of extractor60flow to a desolventizer unit59that vaporizes the ethanol-water solvent. The solvent vapors flow to a condenser42that condenses the solvent vapors. A throttling valve57forming a part of the condenser42reduces the pressure of the solvent vapors to approximately atmospheric in desolventizer59. Pump53transports the condensed solvent to a processor29. Pump29must produce pressure adequate to force the liquid solvent into the bottom of a tank26that may have solvent standing 30 m. or higher. Processor29represents components that rebalance the liquid water-ethanol solvent and supply it to tank26for reuse.

The solids flow from desolventizer59for further processing into animal feed. The processing to this point has removed most of the solvent from the solids.

In the settling tank71, 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 tank71as a slurry stream to desolventizer72.

Desolventizer unit72removes the ethanol from the slurry stream, which flows to condenser48and pump51. From pump51, the condensed ethanol flows to processor29for reuse. Where the composition of the slurry stream provided by the settling tank71is different from that provided by the desolventizer unit59, the processing for the settling slurry in desolventizer unit72differs from that for the solids from the desolventizer unit59. Where the composition of the solids exiting from tank71is similar to those that exit from extractor60, the output of tank71may flow to desolventizer59.

Extractor74vaporizes 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 condenser45that condenses the ethanol vapors. Pump53brings the condensed ethanol vapors from condenser45to the input pressure of element29, and supplies the condensed ethanol vapors to element29. Extractor74may 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 digester77where 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. CO2is 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.

Digester77, fermenter83and ethanol extractor80are conventional devices. However, removing nearly all of the fiber from the liquid carbohydrate stream prior to entering digester77as extractor60and settling tank71do, improves efficiency of the process substantially.

Ethanol from extractor80is stored in a tank86for distribution to users. Some of the ethanol in tank86flows to processor29through a pump88to replace ethanol lost in the extraction process. A suitable feedback system may control the amount of replacement ethanol provided to processor29.

Oil Stream Processing

Mechanical separation of the germ and carbohydrate by separator39produces the germ stream carried in duct37. Connector element B symbolizes the germ stream flow to an extractor90operating in a dual solvent mode.

The oil content of the germ stream is dissolved by liquid CO2provided by CO2tank96. Preferably, the CO2in tank96is that fermenter83provides as a natural by-product of fermentation. Pump93receives the CO2from fermenter83through connector element C and compresses this CO2gas to liquefy the CO2. A heat exchanger may be integral with pump93or tank96to cool the liquid CO2, or even to allow the liquification to occur.

A pump99raises the pressure of the liquid CO2entering chamber105to a range of approximately 4000-8500 psi. The liquid CO2enters an oil extractor90at the upstream end of an extraction chamber105.

Structurally, extractor90may be quite similar to carbohydrate extractor60. However, extractor90operates in a dual mode that removes both oil and carbohydrates from the germ stream.

Extractor90has an intake102that receives the germ stream and forces this germ stream into an extraction chamber105. The intake102includes an air seal or lock such as the auger shown, that retains pressure within chambers105and107. Extractor90differs from extractor60because of the high pressure CO2intake at the upstream end of chamber105.

Liquid CO2entering chamber105dissolves the corn oil in the germ stream material within chamber105. Liquid CO2with dissolved oil flows from chamber105through a throttling valve112to conventional processing and storage elements. These elements remove the CO2, perhaps by flashing off the CO2, and refine the oil for use in food, plastics, and other industrial purposes.

The germ stream then flows to the downstream section of chamber105to remove much of the carbohydrate materials present in the germ stream. The downstream section of chamber105functions as an extractor in a manner very similar to that of extractor60. An ethanol-water solution enters chamber105at a midway point and mixes with the germ stream.

The output at the downstream end of chamber105is very similar to that from extractor60. Solids flow through throttling valve108to a desolventizer unit148similar to unit59. Ethanol in these solids is vaporized and flows to condenser110and pump119. Pump119pumps the condensed ethanol to a processor128and a storage tank135for reuse. Solids flow from unit148for further processing. It is easily possible that the ethanol vapors from extractor90have a compostion that allows desolventizer59to process them, in which case desolventizer148, condenser unit110, and pump119are unnecessary.

A liquid carbohydrate stream flows from chamber105through a throttling valve144to a second settling tank141similar to tank71. The liquid stream from chamber105has a substantial percentage of carbohydrates and solids. Settling tank141is very similar to settling tank71, and operates with very similar parameters. Tank141settles out much of the solid material in the liquid stream from extractor90.

The solids that settle out in tank141flow from the bottom of tank141to desolventizer unit152. The ethanol in the solids stream is vaporized and removed by desolventizer unit152, condensed by condenser155, and pumped up by pump158to the inlet pressure at processor128.

A liquid comprising mainly carbohydrates flows from the top of the material in settling tank141to an ethanol extractor138. Extractor138is similar to extractor74and removes most of the ethanol remaining in the liquid carbohydrate stream. The removed ethanol flows through connector element D to condenser115and pump121for reuse through processor128.

The carbohydrate stream flows from extractor138through connector element E to the digester77onFIG. 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 fermenter83. In addition, most of the fiber has been removed, which adds efficiency to the fermentation process.