Patent Application
20100129888
The present invention relates, inter alia, to a biomass treatment process suitable for use in manufacturing alcohol, such as, for example, ethanol for biofuel production. More specifically, the present invention relates to an improved process and apparatus for converting starch-based biomass into sugars. Subsequently, the sugars may undergo a series of processes (such as saccharification, fermentation and distillation) whose end product is an alcohol.
The process of converting starch-based biomass into sugars in biofuel production is a multi-step process involving hydration, activation (gelatinisation) and liquefaction (conversion). Hydration means the absorption of water via diffusion into the starch granule. Starch activation is the swelling of starch granules by the absorption of additional water in the presence of heat such that the hydrogen bonds between the starch polymers within the granule loosen and break allowing the polymeric structure to unfold in space in the presence of water. This is an irreversible breakdown of the crystalline structure of the starch, eventually the starch granule ruptures and the starch polymers are dispersed in solution forming a viscous colloidal state. The liquefaction process is the conversion of gelatinised starch into shorter chain polysaccharides (dextrins) (reduction of the dendrimer-like starch macromolecule into amylopectin chains which are then converted to dextrins). Subsequently, the dextrins may undergo saccharification (hydrolysis to small sugar units), fermentation and distillation into alcohol such as ethanol, for example.
Processes used in industry for the conversion of starch-based biomass into sugars typically involve an initial hydration step of mixing ground starch-based feedstock with water to form a slurry. The water may be pre-heated prior to being mixed with the feedstock. The slurry may additionally be heated in a vessel in order to activate the starch, and is then heated again and mixed with a liquefaction enzyme in order to convert the starch to shorter chain sugars.
At present, there are two main processes used in industry for the conversion of starch-based biomass to sugars. In the first process, the activation stage typically uses steam jacketed tanks or steam sparge heating to heat the slurry to the desired temperature typically above 70° C., preferably above 85° C., and hold it at that temperature for 30 to 45 minutes in order to hydrate and gelatinise the starch. A liquefaction enzyme may also be added at this stage to reduce the viscosity of the slurry. At the same time agitation mixers, slurry recirculation loops, or a combination of the two mix the slurry. The slurry is then pumped to a second heated vessel for the liquefaction stage where the gelatinised starch is converted to dextrins. One drawback of the above process is that the temperatures reached in the first vessel are not high enough to fully gelatinise the starch, leading to a reduction in yield.
However, despite the presence of the recirculation pumps these heating methods can result in regions being created in the slurry tank or vessel whose temperature is much greater than the remainder of the tank. In such hydration and gelatinisation processes, starch hydrated early in the process can be damaged if it comes into contact with these high temperature regions, resulting in a lower yield. These arrangements also do not provide particularly efficient mixing, as evidenced by the heat damage problem discussed above.
This first type of conventional process normally uses separate vessels for the activation and conversion stages of the process. Transfer of the slurry from the activation (and hydration) vessel to the conversion stage vessel is normally accomplished using centrifugal pumps, which impart a high shear force on the slurry and cause further damage to the hydrated gelatinised starch as a result.
The conversion (liquefaction) stage may also use steam- or water-jacketed tanks, or tanks heated by sparge heaters, to raise the temperature of the slurry to the appropriate level for the optimum performance of the enzyme.
In the second method, jet cookers are employed to heat the slurry to temperatures between 105° C. and 110° C. once it has left the activation vessel. The hot slurry is then flashed into a low pressure tank and water, vapour is removed. The slurry is then cooled and pumped into the conversion stage vessel. Not only can the slurry suffer the same heat damage as in the activation stage, but the high temperature regions also contribute to limiting the dextrin (sugar) yield from the process. The excessive heat of these regions promotes Maillard reactions, where the sugar molecules are destroyed due to interaction with proteins also present in the slurry. The combination of these Maillard losses with the shear losses from the transfer pumps limits the dextrin yield. A reduced yield of dextrins from the liquefaction process obviously reduces the yields of any subsequent processing stages, such as glucose yield from the saccharification stage, and hence alcohol yield from the fermentation stage. Additionally, the high temperatures caused by the jet cooker denature the liquefaction enzyme such that a second dose of enzyme needs to be added to enable the liquefaction process. This increases the cost of the process as does the energy required for the extra heating and cooling stages. Furthermore, existing liquefaction processes require a long residence time for the slurry in the conversion stage to ensure that as much starch is converted to sugars as possible. This can lead to a longer production process with increased costs.
Accordingly, one aim of the present invention to mitigate or obviate one or more of the foregoing disadvantages.
Thus, a first embodiment of the present invention is a process for the treatment of a starch-based feedstock. This process comprises mixing together a starch-based feedstock and a working fluid to form a slurry, hydrating the starch-based feedstock with the working fluid, adding an enzyme to the slurry, pumping the slurry into a substantially constant diameter passage of a fluid mover, and injecting a high velocity transport fluid into the slurry through a nozzle communicating with the passage, thereby further hydrating the starch-based feedstock and activating the starch content of the slurry.
According to a second embodiment of the present invention, there is provided an apparatus for treating a starch-based feedstock. The apparatus comprises a hydrator/mixer for mixing and hydrating the feedstock with a working fluid to form a slurry and a fluid mover in fluid communication with the first hydrator/mixer. In this embodiment, the fluid mover comprises a passage of substantially constant diameter having an inlet in fluid communication with the first hydrator/mixer and an outlet; and a transport fluid nozzle communicating with the passage and adapted to inject high velocity transport fluid into the passage.
According to a third embodiment of the present invention, there is provided a system for producing ethanol comprising an apparatus according to the present invention, which apparatus is integrated into an ethanol production plant.
According to a fourth embodiment of the present invention, there is provided a process for making ethanol comprising saccharifying and fermenting the activated starch content produced by carrying out a system according to the present invention on a starch-based feedstock.
According to a fifth embodiment of the present invention, there is provided a process for converting a starch contained within a starch-based feedstock into shorter chain polysaccharides by a process according to the present invention.
The present invention relates, inter alia, to improved processes and apparatuses for converting starch-based biomass into sugars. Accordingly, the processes and apparatuses of the present invention are suitable for use in industrial processes as a first step in the production of an alcohol such as ethanol. One such industrial process is the processing of starch-based biomass for biofuel production. Other applications are the production of ethanol for a wide variety of other uses. For example, ethanol is used as a solvent in the manufacture of varnishes and perfumes; as a preservative for biological specimens; in the preparation of essences and flavourings; in many medicines and drugs; and as a disinfectant and in tinctures (e.g. tincture of iodine). Ethanol is also used as a feedstock in the production of other chemicals, for instance in the manufacture of ethanal (i.e. acetaldehyde) and ethanoic acid (i.e. acetic acid). Because the processes and apparatuses of the present invention relate to an improved process for manufacturing sugars from starch-based biomass, they are also suitable for the production of sugar products, examples of which include dextrose, maltose, glucose and glucose syrup (e.g. corn syrup, widely used in processed foods, which is glucose syrup manufactured from maize). Such sugar products will be produced by processes (such as controlled saccharification steps) after the liquefaction step of the present invention.
There are two types of plant designs currently being built in the industry for making alcohol from starch-based biomass, namely “Dry Mill” and “Wet Mill” plants. Corn dry grind is the most common type of ethanol production in the United States. In the dry grind process, the entire corn kernel is first ground into flour and the starch in the flour is converted to ethanol via fermentation. The other products are carbon dioxide (used in the carbonated beverage industry) and an animal feed called dried distillers grain with solubles.
Corn wet milling is a process for separating the corn kernel into starch, protein, germ and fiber in an aqueous medium prior to fermentation. The primary products of wet milling include starch and starch-derived products (e.g. high fructose corn syrup and ethanol), corn oil, and corn gluten. The apparatuses and processes of the present invention, described in further detail below, may be integrated into any conventional bioethanol plant—either Dry Mill or Wet Mill—in order to improve the efficiency and lower the production costs of such a plant.
Accordingly, one embodiment of the present invention is a process for the treatment of a starch-based feedstock. This process comprises mixing together a starch-based feedstock and a working fluid to form a slurry, hydrating the starch-based feedstock with the working fluid, adding an enzyme to the slurry, moving by, e.g., pumping the slurry into a substantially constant diameter passage of a fluid mover, and injecting a high velocity transport fluid into the slurry through one or more nozzles communicating with the passage, thereby further hydrating the starch-based feedstock and activating the starch content of the slurry.
In this embodiment, the step of injecting a high velocity transport fluid into the slurry may include:
applying a shear force to the slurry;
atomising the liquid phase within the slurry to create a dispersed droplet flow regime;
forming a low pressure region downstream of the nozzle; and
generating a condensation shock wave within the passage downstream of the nozzle(s) by condensation of the transport fluid.
The first hydrating step may further include heating the slurry and/or maintaining it at a first predetermined temperature within a first vessel for a first predetermined period of time.
The process may further comprise the step of transferring the slurry to a second vessel from the fluid mover, and maintaining the temperature of the slurry in the second vessel for a second predetermined period of time.
The step of transferring the slurry to the second vessel may include passing the slurry through a temperature conditioning unit to raise the temperature of the slurry.
The process may also include the step of agitating the slurry in the first and/or second vessels for the respective first and second periods of time.
The transport fluid may be a hot, compressible gas, such as, e.g., steam, carbon dioxide, nitrogen, or other like gasses. Preferably, the transport fluid is steam. The transport fluid may be injected at a subsonic or supersonic velocity. The working fluid may be water as defined herein.
The step of injecting the transport fluid may comprise injecting the high velocity transport fluid into the slurry through a plurality of nozzles communicating with the passage. The step of injecting the transport fluid into the slurry may occur on a single pass of the slurry through the fluid mover. The step of injecting the transport fluid into the slurry may also include recirculating the slurry through the fluid mover.
The pumping of the slurry may be carried out using a pump, preferably a low shear pump.
In the process according to the present invention, the feedstock may be selected from any starch-based plant material suitable for conversion to, e.g., alcohol, such as ethanol. Preferably, the feedstock is dry milled maize, dry milled wheat, or dry milled sorghum.
According to another embodiment of the present invention, there is provided an apparatus for treating a starch-based feedstock. The apparatus comprises a hydrator/mixer for mixing and hydrating the feedstock with a working fluid to form a slurry and a fluid mover in fluid communication with the first hydrator/mixer. In this embodiment, the fluid mover comprises a passage of substantially constant diameter having an inlet in fluid communication with the first hydrator/mixer and an outlet; and a transport fluid nozzle communicating with the passage and adapted to inject high velocity transport fluid into the passage.
The hydrator/mixer may comprise a heater to heat the working fluid and/or the slurry. The hydrator/mixer may comprise a first vessel having an outlet in fluid communication with the inlet of the passage. The heater may comprise a heated water jacket surrounding the first vessel. Alternatively, the heater may be remote from the hydrator/mixer.
The apparatus may further comprise a second vessel having an inlet in fluid communication with the outlet of the passage. The second vessel may include an insulator to insulate the contents of the second vessel. The insulator may comprise a heated water jacket surrounding the second vessel. Alternatively, the insulator may comprise a layer of insulating material covering the exterior of the second vessel.
The apparatus may further comprise a residence tube section having an inlet in fluid communication with the outlet of the passage. The residence tube may include an insulator for insulating the contents of the residence tube as it passes through. Such an insulator may be a layer of insulating material covering the exterior of the residence tube section, or the residence tube may have a heated water jacket surrounding it.
The transport fluid nozzle may be annular and circumscribe the passage. The transport fluid nozzle may have an inlet, an outlet and a throat portion intermediate the inlet and the outlet, wherein the throat portion has a cross sectional area which is less than that of the inlet and the outlet. The passage may be of substantially constant diameter.
The apparatus may further comprise a transport fluid supply adapted to supply transport fluid to the transport fluid nozzle.
The apparatus may comprise a plurality of fluid movers in series and/or parallel with one another, wherein the transport fluid supply is adapted to supply transport fluid to the transport fluid nozzle of each device. The apparatus may comprise a plurality of transport fluid supply lines connecting the transport fluid supply with each nozzle, wherein each transport fluid supply line includes a transport fluid conditioner. The transport fluid conditioner may be adapted to vary the supply pressure of the transport fluid to each nozzle.
Alternatively, the apparatus may comprise a dedicated transport fluid supply for each transport fluid nozzle. Each transport fluid supply may include a transport fluid conditioner. Each conditioner may be adapted to vary the supply pressure of the transport fluid to each respective nozzle.
The apparatus may further comprise a temperature conditioning unit located between the fluid mover and the second vessel, the temperature conditioning unit adapted to increase the temperature of fluid passing from the device to the second vessel.
The apparatus may further comprise a recirculation pipe adapted to allow fluid recirculation between the outlet of the fluid mover and the first vessel, e.g., from downstream of the fluid mover to upstream of the fluid mover.
The apparatus may further comprise a pump, or other suitable device for moving the fluid. For example, the pump may be a low shear pump adapted to pump fluid from the hydrator/mixer to the fluid mover.
The apparatus may further comprise first and second agitators located in the first and second vessels, respectively. The first vessel may include a recirculator for recirculating slurry from the outlet to an inlet thereof.
The apparatus may be integrated into an ethanol production plant for producing ethanol from a feed stock, such as, e.g., a plant as disclosed in the Example or described herein.
In another embodiment, the invention is a system for producing alcohol, e.g., ethanol. The system includes an apparatus according to the present invention, which is integrated into an alcohol, e.g., ethanol, production plant.
In this embodiment, the ethanol production plant may be a dry mill or a wet mill plant. The plant may utilize either a dry grind based feedstock or a wet milling based feedstock. Preferably, the plant is a dry mill, which utilizes a dry grind based feedstock.
Another embodiment of the present invention is a process for making ethanol. This process includes carrying out a system according to the present invention and then saccharifying and fermenting the product to produce, an alcohol, e.g., ethanol. In the present invention, any conventional process for carrying out the saccharifying and fermenting steps, preferably commercial scale processes, are contemplated.
A further embodiment of the present invention is a process for converting a starch contained within a starch-based feedstock into shorter chain polysaccharides. This process involves carrying out a process according to the present invention, e.g., the process depicted in
The apparatuses and processes of the present invention will now be described in more detail with reference to the figures. Turning now to
The reactor 18 is formed from one or more fluid movers. A suitable device that may act as a fluid mover is shown in detail in
Referring once again to
Located downstream of the reactor 18 and fluidly connected thereto is a temperature conditioning unit (TCU) 52. The TCU 52 preferably comprises a fluid mover substantially identical to that illustrated in
Downstream of the TCU 52 is a second supply line 54, which fluidly connects the outlet of the TCU 52 with a second vessel 56. The second vessel 56 is similar to the first vessel 2, and therefore has a heater, such as, e.g., a heated water jacket 58 which surrounds the vessel 56 and receives heated water from a heated water supply (not shown). The vessel 56 also includes an agitator 60 that is powered by a motor 62. The agitator 60 is suspended from the motor 62 so that it lies inside the vessel 56. At the base of the vessel 56 are an outlet 64 and a valve 66 which controls fluid flow from the outlet 64.
A representative method of processing a starch-based feedstock using the apparatus illustrated in
As used in the present invention, an “enzyme” or a “liquefaction enzyme”, which are used interchangeably herein, is a naturally occurring or genetically engineered protein that functions as a biochemical catalyst either enabling and/or accelerating a given process, e.g., the breakdown/conversion of the feedstock. One skilled in the art will recognize that other types of catalysts, such as, e.g., non-natural catalysts, such as metal ions, graphitic carbon, etc., may also be used in the present invention. Preferably, the enzymes of the present invention are typically sourced from the fungus Aspergillis niger. An example of a suitable enzyme is α-amylase, for which a typical level of enzyme activity for the processes of the present invention is between 750 and 824AGU/g, where enzyme activity is given per unit mass of wet feedstock. The preferred enzyme concentration in the vessel 2 is about 0.09-0.18 ml/kg.
Preferably, the ratio of feedstock to liquid content in the slurry is 20%-40% by weight. Typical α-amylases used in the liquefaction stage have an activity optima when the pH is between about 6 and about 6.5. Optionally, one or more pH adjusters and/or surfactants may also be added to the slurry at this point. For instance, process condensate often has a low pH (2-3) and once it and the feedstock have been mixed to form a slurry ammonia may be added to adjust the pH to that required by the enzyme.
Heated water, such as, e.g., recycled hot water recovered from another part of a process plant, is fed into the water jacket 4 surrounding the vessel 2 and the heated water jacket then heats the slurry to a temperature of typically 30° C.-60° C., preferably 45° C.-55° C., and holds the slurry at this temperature for 30-120 minutes so as to hydrate the crystalline regions of the starch granules. The motor 8 drives the agitator 6, which stirs the slurry in the vessel 2 with gentle (i.e. low shear) agitation whilst the slurry is held in the vessel 2. Alternatively, the working fluid may be heated prior to being mixed with the feedstock and the heater 4 in the vessel 2 may then maintain the slurry at the desired temperature. The enzyme may be added into the vessel 2 separately from the working fluid. The enzyme may be added once the slurry has reached the desired temperature.
The slurry is held at the desired temperature in the vessel 2 for a sufficient period of time to allow the starch content to be prepared for full hydration and gelatinisation. “Sufficient” in this context means the time required for the crystalline, un-gelatinised starch grains in the slurry to absorb as much water as possible. The water being absorbed into the crystallised starch grains acts as a plasticiser, destabilising the hydrogen bonds that help to order the crystal structure. When the slurry has been steeped in the vessel 2 for sufficient time, the valve 12 is opened to allow the slurry to leave the vessel via the outlet 10. As used herein, “steeping,” “steeped,” and other like terms refer to the process of soaking the starch-based biomass as a slurry at a time and temperature in order to facilitate hydration of the un-gelatinised starch therein. The pump 14 pumps the slurry under low shear conditions from the vessel 2 through the first supply line 16 to the reactor 18.
Referring again to
The nozzle outlet 39 opens into a mixing chamber 25 defined within the passage 22. The angle at which the transport fluid exits the transport fluid nozzle 38 affects the degree of shear between it and the feedstock passing through the passage 22, the turbulence levels in the vapour-droplet flow regime and the further development of the fluid flow. The angle α most readily defines the angle of inclination of the transport nozzle 38 to the passage 22. This angle is that formed between the leading edge of the divergent portion of the transport nozzle 38 which is the relatively outer surface 36 of the distal end 34 of the protrusion 28 and the longitudinal axis L of the passage 22. The angle α is preferably between 0° and 70°, more preferably between 0° and 30°.
As the steam is injected into the slurry, a momentum and mass transfer occurs between the two which preferably results in the atomisation of the working fluid component of the slurry to form a dispersed droplet flow regime. This transfer is enhanced through turbulence. “Atomised” in this context should be understood to mean break down into very small particles or droplets. The steam preferably applies a shearing force to the slurry which not only atomises the working fluid component but also disrupts the cellular structure of the feedstock suspended in the slurry, such that the starch granules present are separated from the feedstock and dispersed into the slurry. Free surface area is critical in processing starch granules. For example, based on some simple finite element modelling based on rates of water diffusion and heat conduction into a generic polymer model, when free surface area is reduced from 100% to 70%, the time required for homogenous heating of the granules from 20° C. to 75° C. will be doubled. Similarly, the time required for achieving 80% of the saturated water absorption will at least be doubled when free surface area is reduced to 70%. Thus, atomising the starch granules will greatly speed the rate and completeness of the gelatinisation process.
The effects of the process on the temperature and pressure of the slurry can be seen in the graph of
The steam is injected into the slurry at the beginning of section B of the
As explained above, as the steam is injected into the slurry through nozzle 38 a pressure reduction may occur in the upstream section of the mixing chamber 25. This reduction in pressure forms an at least partial vacuum in this upstream section of the chamber 25 adjacent the nozzle outlet 39. Tests have revealed that an approximately 90% vacuum can be achieved in the chamber 25 as the steam is injected and subsequently condenses. This low pressure region may enhance the starch gelatinisation process.
As previously disclosed herein, the shear force applied to the slurry and the subsequent turbulent flow created by the injected steam disrupts the cellular structure of the feedstock suspended in the slurry, releasing the starch granules from the feedstock. As the slurry passes through the partial vacuum and condensation shock wave formed in the chamber 25, it is further disrupted by the changes in pressure occurring, as illustrated by the pressure profile in sections B and C of
As the starch granules in the feedstock pass into the reactor 18 (
The temperature at which the slurry leaves the reactor 18 is selected to avoid any heat damage to the slurry contents during the activation stage. However, this temperature may be below the temperature for optimal performance of the liquefaction enzyme, and so the temperature of the slurry may need to be raised without subjecting the slurry to excessively high temperatures or additional shear forces. This gentle heating is achieved using the optional TCU 52 downstream of the reactor 18.
As described above, the TCU 52 comprises one or more fluid movers of the type illustrated in
Once it has passed through the TCU 52, the slurry is preferably at a temperature of between 83° C.-86° C. The slurry then flows downstream through the second supply line 54 into the second vessel 56. The water jacket 58 of the second vessel receives heated water, which maintains the slurry at the aforementioned temperature. The slurry is held in the second vessel 56 for a sufficient residence time to allow the enzyme to convert or hydrolyse the starch content into shorter chain polysaccharides (e.g. dextrins). During that residence time, the motor 62 drives the agitator 60 to gently agitate the slurry. It has been found that approximately 30 minutes is a sufficient residence time in the present process, compared with a typical residence time of 120 minutes in existing liquefaction processes. The process of the present invention may also be used to reduce the amount of enzyme required whilst maintaining the slurry in the second vessel 56 for a residence time akin to existing liquefaction processes. The progress of the conversion is monitored during the residence time by measuring the dextrose equivalent (DE) of the slurry. As used herein, “DE’ indicates the degree of hydrolysis of starch into shorter chain polysaccharides. Calculating the DE is a simple method of estimating the efficiency of the liquefaction process. The higher the DE, the shorter the average length of the chains and the more efficient the liquefaction process. Typically, the DE value is in the range 1-10 prior to liquefaction and 6-22 after liquefaction. The required DE value depends on the application, those processes that do not require a subsequent fermentation step (such as commercial processes to manufacture sugars) can tolerate much higher DE values. For those processes that do involve a subsequent fermentation step, the required DE value depends substantially on the yeast that the process will use.
At the end of the residence time, the mash (after the liquefaction stage, the slurry is often referred to as a ‘mash’) may be transferred to a fermentation tank (not shown) via the outlet 64 and control valve 66 of the second vessel 56. pH adjustors may also be added at this point via a feed port (not shown) because the glucoamylases and yeasts used in the fermentation stage typically operate at a pH optima of 3.5-4.5. As an example, the pH may be adjusted using urea or phosphoric acid, materials which also act as nutrient sources for the yeast in the saccharification/fermentation step. It is also possible that an additional yeast food is added at this stage. Additionally, the mash may be cooled by a cooling device (not shown), such as a heat exchanger, prior to entry into the fermentation tank, because the fermentation stage typically requires much lower temperatures (e.g. 25° C.-35° C.) than the liquefaction stage. Furthermore, a mash dilute (e.g. water or Backset) may be added to thin the mash to maintain a consistent density.
Using a fluid mover of the type described herein allows the present invention to heat and activate the starch content of the slurry while avoiding the creation of regions of extreme heat, which can damage the starch content. Prevention of these regions also reduces or eliminates Maillard effects caused by the reaction of proteins with the extracted starch. These reactions can prevent conversion of the starch to sugar and therefore reduce yields. Furthermore, the gentle agitation, mixing, and low shear pumping at a lower temperature also ensures that there are no high shear forces which may damage the starch content of the slurry whilst held in a vessel or being transported between vessels. Such damage limits the ultimate glucose yield available from the feedstock.
The fluid mover(s) of the reactor also ensure that the slurry components are more thoroughly mixed than is possible using simple agitator paddles and/or recirculation loops alone. The atomisation of the liquid component of the slurry further ensures a more homogenous mixing of the slurry than previously possible. This improved mixing increases the efficiency of the enzyme in converting starch to shorter dextrins, reducing the time to achieve the desired DE values in the slurry when compared with existing processes. Another benefit of the processes of the present invention is that, in a continuous flow processing plant with a fixed liquefaction time, the amount of enzyme required to give the desired DE can be reduced. In addition, using the processes of the present invention, higher DE values than possible with existing processes may be achieved.
The shear action and condensation/pressure shock applied to the feedstock component of the slurry when in the reactor further improves the performance of the present invention as this exposes more of the cellular structure of the feedstock. This allows virtually all the starch granules in the feedstock to be separated, thereby providing improved starch activation rates compared to conventional processes as the enzymatic activation is supplemented by the mechanical activation in the reactor. This also allows the process to provide an accessible starch to sugar conversion ratio of substantially 100%. The processes of the present invention, therefore, may only require the slurry to pass once through the reactor before it is ready to pass to the second vessel for the conversion stage. Hence, yields are much improved as there is no time for loss build up during the process.
Exposing more starch also means that less of the enzyme is needed to achieve the desired DE value of 6-22 before the slurry is transferred to the saccharification and fermentation processes. In addition, the condensation/pressure shock kills bacteria at a relatively low temperature, thereby reducing losses in any subsequent fermentation process.
It has also been discovered that the processes and apparatuses of the present invention may also improve fermentation rates in the subsequent fermentation process. The improved hydration of the present invention also hydrates some proteins in the feedstock. These hydrated proteins act as additional feedstock to the fermenting yeast, thereby improving the fermenting performance of the yeast.
In summary, the processes and apparatuses of the present invention have been found to provide a number of advantages over existing arrangements. These advantages include an increase of up to 14% in starch to sugar yields, a reduction of up to 50% of the amount of liquefaction enzyme required, a reduction of up to 75% in the residence time for the conversion to take place, and a reduction of up to 30% in the time taken for the subsequent fermentation of the converted sugars into alcohol.
As described above, the reactor 18 may comprise a plurality of fluid movers 100 arranged in series and/or parallel as shown in
An alternative embodiment of a device according to the present invention that may act as a fluid mover is shown in detail in
Whilst the present invention need only utilise one fluid mover in the reactor, if the required process flow rate demands it the reactor may comprise a combination of fluid movers in series and/or parallel. This may also be the case with the temperature conditioning unit made up of one or more of such fluid movers.
The apparatus may also include one or more recirculation pipes which can selectively recirculate slurry from downstream of the fluid mover to upstream of the device, so that the slurry can pass through the device more than once, if necessary. Where included, the first vessel may also include such an arrangement so that slurry can pass through the first vessel more than once, if necessary.
Instead of having heaters such as heated water jackets, the first and/or second vessel may alternatively comprise an insulation layer on the exterior surface thereof. The insulation layer keeps the temperature of the slurry inside the vessel in the desired ranges stated above. The working fluid may be pre-heated by an external heater (not shown) prior to being mixed with the feedstock. The temperature of the slurry is maintained at the desired temperature in vessel 2 by either using the heated water jacket 4 or the insulation layer.
In addition to the agitator 60 and motor 62 in the second vessel 56, the second vessel may comprise a large number of internal baffles such that slurry is directed in a convoluted continuous flow path that slowly takes it through the vessel.
The low shear centrifugal pump which moves the slurry from the first vessel into the reactor may be replaced with any other suitable low shear pump, such as either a membrane pump or a peristaltic pump, for example.
Whilst the TCU described above comprises one or more fluid movers of the type shown in
The preferred concentration of the liquefaction enzyme in the slurry during development in the first vessel assumes an average of 10%-15% feedstock moisture content and an average starch content of 70%-75% dry weight.
Whilst the enzyme is preferably introduced to the slurry upstream of the fluid mover, the enzyme may also be introduced in the device or else, downstream of the device following activation of the starch content.
Whilst the illustrated embodiment of the invention includes both first and second vessels for handling the slurry, it should be appreciated that the invention need not include the vessels to provide the advantages highlighted above. Instead of a first vessel, the first hydrator may be a pipe or an in-line mixing device into which the feedstock, working fluid and enzyme are introduced upstream of the fluid mover. Similarly, the second vessel may be replaced by pipework in which the conversion of the activated starch to sugar takes place.
The example below describes the operation and performance of a typical plant (of the Dry Mill type) and compares this to the performance of the same plant after adding the apparatus and undertaking the process of the present invention.
Maize is supplied to the plant as grain and then ground to a flour. A conveyor feeds the flour to the slurry tank, where it is mixed with working fluid and continuously agitated (stirred). The plant working fluid is a combination of Backset (approx. 25%) and process condensate (approx. 75%). The process condensate is heated before it enters the slurry tank in order to maintain the temperature of the slurry at 85° C.-88° C. Aqueous ammonia is added to the slurry tank in order to maintain a pH of approximately 6.0. This temperature range and pH are the preferred conditions for the enzyme α-amylase, which is also added to the slurry tank.
The slurry is pumped from the slurry tank, passed through a strainer to remove large particles (which are returned to the slurry tank) and then split into two streams, the first is returned to the slurry tank via a recirculation loop, the second stream continues to the liquefaction tank. The temperature and pH in the liquefaction tank are the same as those in the slurry. The liquefaction tank is divided into compartments with baffles so that the slurry passes slowly through the tank over a period of 90-120 minutes.
The mash, which consists of a liquid portion (the ‘beer’) and a wet corn portion then leaves the liquefaction tank, a mash dilute may be added to maintain a consistent density. The mash is then cooled to about 32° C. in a mash cooler and then pumped to a fermenter. When the fermenter is about 5%-15% full of mash, a yeast prop is added. This is a pre-prepared mixture of 35% water and 65% mash to which is added yeast, gluco-amylase, urea (nitrogen to feed the yeast), zinc sulphate (speeds fermentation) and magnesium sulphate (aids yeast health), the proportions of each depend on the needs of the yeast. The yeast prop is held in a yeast mix tank with air bubbling through it for 10 hours prior to being added to the fermenter. During this time, a strong yeast mix forms containing a large number of colony forming units (approx. 500-600 million colony forming units per millilitre).
The plant uses a fermentation process known as Simultaneous Saccharification and Fermentation (SSF) whereby gluco-amylase is added to perform the saccharification step (breaking the dextrin and other short polysaccharide chains down to smaller sugar units such as glucose) the yeast then consumes the glucose to make ethanol. Too high a level of glucose stresses the yeast, and too low a level starves it, so gluco-amylase is added gradually (at the rates given in Table 2) throughout the fermenter fill time in order to maintain a constant glucose level in the mash. The total fermentation time (including 12 hours of fill time) is about 45-55 hours, after which the fermentation tank is drained and further treatment processes such as distillation occur.
The above plant was modified so that the apparatus of the present invention was installed after the slurry tank recirculation loop and before the liquefaction tank. The reactor 18 consisted of two parallel legs, each of which contained five in-series fluid movers of the type shown in
The conditions in the fermenter are given in Table 2. The gluco-amylase dosing level is initially higher for the process of the present invention (though both processes use the same total amount of the enzyme). This is because the altered proportions of solids and liquids and the balance of sugars in the mash suited the yeast, such that the rates of yeast growth and ethanol production at the start of the fermentation process were accelerated. The yeast, therefore, required a faster rate of glucose release to feed it, so the initial dosing levels of gluco-amylase compared to the typical process were increased.
A typical ethanol plant producing 40 million gallons of ethanol per year has to purchase 15.94 million bushels of corn. Table 2 shows that the process of the present invention gives a higher ethanol yield per bushel of corn, so less corn is required (15.33 million bushels) to produce the same amount of ethanol. At a purchase price of $4 per bushel of corn, this is a saving of $2.44 million per year. The process of the present invention also required less α-amylase for the liquefaction stage, providing a further cost saving. Energy savings due to the reduced heat requirements of the slurry tank are also possible.
Further improvements and modifications may be incorporated without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0416914.0 | Jul 2004 | GB | national |
| 0416915.7 | Jul 2004 | GB | national |
| 0417961.0 | Aug 2004 | GB | national |
| 0428343.8 | Dec 2004 | GB | national |
| 0708482.5 | May 2007 | GB | national |
| 0710659.4 | Jun 2007 | GB | national |
This application is a continuation-in-part of and claims benefit to international application no. PCT/GB2008/050210 filed Mar. 21, 2008, which international application claims benefit to Great Britain Application Nos. 0708482.5, which was filed on May 2, 2007, and 0710659.4, which was filed on Jun. 5, 2007. The present application also claims benefit, as a continuation-in-part, to U.S. application Ser. No. 11/658,265 filed Jan. 24, 2007, which is the national stage of international application No. PCT/GB2005/02999, which was filed on Jul. 29, 2005 and claims benefit to GB 0416914.0; GB 0416915.7; GB 0417961.0 and GB 0428343.8, dated 29 Jul. 2004; 29 Jul. 2004; 12 Aug. 2004 and 24 Dec. 2004, respectively. All of the foregoing applications are incorporated by reference in their entireties as if recited in full herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11658265 | Jan 2007 | US |
| Child | 12590129 | US | |
| Parent | PCT/GB2008/050210 | Mar 2008 | US |
| Child | 11658265 | US |
