阅读说明：本技术 用于对包括木质纤维素生物质和液体的浆料进行脱水的系统和方法
(System and method for dewatering a slurry comprising lignocellulosic biomass and a liquid
) 是由 大卫·查尔斯·卡尔森 于 2018-07-12 设计创作，主要内容包括：本发明涉及一种脱水系统和相关方法,其适于输送木质纤维素生物质以从木质纤维素生物质浆料中分离水的至少一部分并积累该脱水的木质纤维素生物质。脱水系统还包括被气体占据的顶部空间,该气体处于有助于将积累的生物质转移到具有加压的顶部空间的预处理反应器中的压力下。这种脱水系统可以防止来自预处理反应器的气体(例如蒸汽)的过度混合和过度回流。(The present invention relates to a dewatering system and associated method adapted to convey lignocellulosic biomass to separate at least a portion of water from a lignocellulosic biomass slurry and accumulate the dewatered lignocellulosic biomass. The dewatering system also includes a headspace occupied by a gas at a pressure that facilitates transfer of the accumulated biomass to a pretreatment reactor having a pressurized headspace. Such a dehydration system may prevent excessive mixing and excessive reflux of gases (e.g., steam) from the pretreatment reactor.)
1. A system for dewatering lignocellulosic biomass slurry, wherein the system comprises:
a) a source of lignocellulosic biomass slurry, wherein the lignocellulosic biomass slurry comprises:
i) a lignocellulosic biomass; and
ii) water;
b) a dewatering system in fluid communication with the source of the lignocellulosic biomass slurry and adapted to receive the lignocellulosic biomass slurry to separate at least a portion of the water from the lignocellulosic biomass slurry, wherein the dewatering system comprises at least a solids transfer device having a housing comprising an inlet and an outlet, wherein the solids transfer device is adapted to convey and accumulate dewatered lignocellulosic biomass proximate the outlet of the solids transfer device, wherein at least at the inlet of the solids transfer device there is a headspace occupied by a gas, wherein the headspace is at a first pressure; and
c) at least one vessel in fluid communication with the outlet of the solids transfer device, wherein the vessel is configured to receive the accumulated dehydrated lignocellulosic biomass and process the dehydrated lignocellulosic biomass, wherein the vessel has a head space occupied by a gas at a second pressure, wherein the first pressure has a value that inhibits backflow of the gas in the vessel through the solids transfer device.
2. The system of claim 1, wherein the first pressure is substantially equal to or greater than the second pressure.
3. The system of claim 1, wherein the source of the lignocellulosic biomass slurry comprises one or more pumps adapted to pump the lignocellulosic biomass slurry via one or more conduits in fluid communication with the dewatering system, wherein each pump is configured to pressurize the lignocellulosic biomass slurry above atmospheric pressure.
4. The system of claim 3, further comprising one or more containers in fluid communication with the one or more pumps, wherein each container is adapted to combine lignocellulosic biomass and an aqueous liquid to form the lignocellulosic biomass slurry.
5. The system of claim 4, wherein the one or more containers are adapted to expose their contents to atmospheric conditions.
6. The system of claim 1, wherein at least a portion of the gas present at the first pressure in the headspace at the inlet of the solids transfer device is capable of being supplied by gas entrained in the source of the lignocellulosic biomass slurry.
7. The system of claim 1, further comprising a source of gas in fluid communication with the dehydration system to provide the gas in the headspace at the first pressure, wherein the source of gas comprises one or more gas conduits connected to the dehydration system.
8. The system of claim 1, wherein the dewatering system further comprises an enclosed screen arrangement comprising a screen having a plurality of screen openings and a headspace above the screen; wherein the plurality of screen openings allow liquid to pass therethrough to separate at least a portion of the water from the lignocellulosic biomass slurry; wherein the screen has a first end and a second end and is positioned such that the first end is above the second end with respect to horizontal and such that the angle of the screen with respect to horizontal is greater than zero; wherein the enclosed screen apparatus is adapted to receive the lignocellulosic biomass slurry at the first end of the screen such that the slurry flows downwardly and through the screen to separate at least a portion of the water from the lignocellulosic biomass slurry and form a first dewatered lignocellulosic biomass comprising residual water and lignocellulosic biomass; wherein the solids transfer device is in fluid communication with the enclosed screen device; and wherein the headspace above the screen comprises the headspace at the first pressure at the inlet of the solids transfer device.
9. The system of claim 8, wherein the solids transfer device housing comprises a barrel member having the inlet at one end and the outlet at another end, wherein the inlet is adapted to receive the first dehydrated lignocellulosic biomass at the first pressure, wherein the solids transfer device is adapted to convey the first dehydrated lignocellulosic biomass through the barrel member to separate at least a portion of the residual water from the first dehydrated lignocellulosic biomass and accumulate a second dehydrated lignocellulosic biomass proximate the outlet of the solids transfer device.
10. The system of claim 8, further comprising a source of gas in fluid communication with the enclosed screen apparatus, wherein the enclosed screen apparatus is adapted to receive the gas such that the gas can occupy the headspace above the screen at the first pressure.
11. The system of claim 8, wherein the enclosed screen apparatus comprises a gravity screen having a screen opening size of about 0.25 inches or less.
12. The system of claim 9, wherein the cartridge member comprises:
a) a screw portion adjacent to the barrel inlet;
b) a rotatable screw disposed within the screw portion; and
c) an accumulator proximate the cartridge outlet.
13. The system of claim 12, further comprising a screen positioned in at least the screw section between the barrel member and the screw, wherein the screen is adapted to allow separation of at least a portion of the residual water from the first dewatered lignocellulosic biomass as the screw conveys the first dewatered lignocellulosic biomass through the barrel member.
14. A method of dewatering a lignocellulosic biomass slurry, wherein the method comprises:
a) providing a lignocellulosic biomass slurry to a dewatering system having an inlet and an outlet, wherein the lignocellulosic biomass slurry comprises lignocellulosic biomass and water;
b) separating at least a portion of the water from the lignocellulosic biomass slurry in the dewatering system to form a dewatered lignocellulosic biomass, wherein the dewatering system comprises a headspace occupied by a gas at a first pressure;
c) conveying the lignocellulosic biomass through the dewatering system to accumulate the dewatered lignocellulosic biomass near the outlet of the dewatering system; and
d) providing the accumulated dehydrated lignocellulosic biomass to at least one vessel in fluid communication with the dehydration system, wherein the vessel has a headspace occupied by a gas at a second pressure, wherein the first pressure has a value that inhibits the gas in the vessel from flowing into the dehydration system.
15. The method of claim 13, wherein the lignocellulosic biomass comprises ground corn stover.
16. The method of claim 14, wherein said ground corn stover has an average particle size such that at least 80% of said ground corn stover passes through a screen having a one inch mesh opening.
17. The method of claim 13, wherein the first pressure and the second pressure are in a range of 20psi to 200psi, wherein the first pressure is equal to or greater than the second pressure.
18. The method of claim 16, wherein the first pressure is greater than the second pressure, and wherein a difference between the first pressure and the second pressure is 5psi or less.
19. The method of claim 13, wherein the at least one vessel is a pretreatment reactor.
20. The method of claim 18, wherein the pretreatment reactor comprises a hydrolysis reactor operated under conditions to hydrolyze one or more polysaccharides in the lignocellulosic biomass.
21. The method of claim 19, wherein the conditions comprise exposing the lignocellulosic biomass to an aqueous liquid at a temperature in the range of 245 ° F to 350 ° F and a pH of 0.5 to 3.0 for a duration of 0.5 hours to 5 hours.
Background
The present invention relates to dewatering a slurry comprising lignocellulosic biomass and an aqueous liquid (e.g., water), and introducing the dewatered lignocellulosic biomass into a downstream process of a biorefinery having a gaseous headspace under pressure.
Disclosure of Invention
Embodiments of the present invention include a system for dewatering lignocellulosic biomass slurry, wherein the system comprises:
a) a source of lignocellulosic biomass slurry, wherein the lignocellulosic biomass slurry comprises:
i) a lignocellulosic biomass; and
ii) water;
b) a dewatering system in fluid communication with a source of lignocellulosic biomass slurry and adapted to receive the lignocellulosic biomass slurry to separate at least a portion of the water from the lignocellulosic biomass slurry, wherein the dewatering system comprises at least a solids transfer device having a housing comprising an inlet and an outlet, wherein the solids transfer device is adapted to convey and accumulate dewatered lignocellulosic biomass proximate the outlet of the solids transfer device, wherein at least at the inlet of the solids transfer device there is a headspace occupied by a gas, wherein the headspace is at a first pressure; and
c) at least one vessel in fluid communication with the outlet of the solids transfer device, wherein the vessel is configured to receive accumulated dehydrated lignocellulosic biomass and process the dehydrated lignocellulosic biomass, wherein the vessel has a head space occupied by a gas at a second pressure, wherein the first pressure has a value that inhibits backflow of the gas in the vessel through the solids transfer device.
Embodiments of the present invention also include a method of dewatering lignocellulosic biomass slurry, wherein the method comprises:
a) providing a lignocellulosic biomass slurry to a dewatering system having an inlet and an outlet, wherein the lignocellulosic biomass slurry comprises lignocellulosic biomass and water;
b) separating at least a portion of the water from the lignocellulosic biomass slurry in a dewatering system to form a dewatered lignocellulosic biomass, wherein the dewatering system comprises a headspace occupied by a gas at a first pressure;
c) conveying the lignocellulosic biomass through a dewatering system to accumulate dewatered lignocellulosic biomass near an outlet of the dewatering system; and
d) providing the accumulated dehydrated lignocellulosic biomass to at least one vessel in fluid communication with the dehydration system, wherein the vessel has a headspace occupied by a gas at a second pressure, wherein the first pressure has a value that inhibits the gas in the vessel from flowing into the dehydration system.
Drawings
FIG. 1 shows a schematic process flow diagram of an embodiment of the present invention;
FIG. 2A shows a schematic process flow diagram of another embodiment of the present invention;
FIG. 2B illustrates a portion of the embodiment of the solids transfer device of FIG. 2A; and
figure 3 shows a schematic process flow diagram of another embodiment of the present invention.
Detailed Description
Disclosed in the examples herein are systems and methods for dewatering lignocellulosic biomass slurry in biorefinery and transferring the dewatered lignocellulosic biomass to a pressurized environment for further processing of the lignocellulosic biomass. One or more advantages of systems and methods according to the present invention are described throughout the application. An illustrative embodiment is described below with reference to fig. 1 and 2.
Methods and systems according to illustrative embodiments of the invention may be used to dewater lignocellulosic biomass obtained from one or more sources of lignocellulosic biomass slurry. As used herein, a lignocellulosic biomass slurry is a composition comprising at least lignocellulosic biomass and water.
Lignocellulosic biomass includes residual agricultural material from harvesting, such as corn stover (e.g., corn cobs, stalks, and leaves), fiber in corn kernels, switchgrass, wood chips or other wood waste, and other plant matter (grown for processing into biological products or for other purposes). Lignocellulosic biomass includes hemicellulose, cellulose, and lignin.
The lignocellulosic biomass present in the slurry may be treated from the feedstock prior to or at the time of forming the slurry. Lignocellulosic feedstocks may be processed by various techniques, such as size reduction (size reduction), washing, cooking, combinations of these, and the like. For example, a biomass lignocellulosic feedstock may be produced by grinding the lignocellulosic biomass feedstock in one or more grinders to a ground solid to reduce the size of the feedstock and increase its surface area for subsequent processing (e.g., hydrolysis).
The lignocellulosic biomass may be combined with one or more sources of liquid including water to form a slurry. Non-limiting examples of water sources include recycled process water from one or more points in a biorefinery, fresh tap water, combinations of these, and the like. The recycled process water may or may not be treated prior to being combined with the lignocellulosic biomass.
In some embodiments, an amount of lignocellulosic biomass and a liquid (e.g., water) may be combined such that the total solids content of the lignocellulosic biomass slurry is 1% -10%, 2% -9%, or even 3% -8%. As used herein, "total solids content" means the total content of dissolved and suspended solids based on the total weight of the lignocellulosic biomass slurry.
An example of forming a lignocellulosic biomass slurry is described below in conjunction with fig. 2A and 2B.
In the illustrative embodiment of fig. 1, a source of lignocellulosic biomass slurry 105 is provided to (e.g., pumped to) a dewatering system 100 adapted to receive the lignocellulosic biomass slurry. For example, a source of lignocellulosic biomass slurry 105 may be provided to the system 100 via one or more pumps and associated piping and valves. The dewatering system 100 according to the present invention comprises at least a solids transfer device having an inlet and an outlet, which is adapted to convey and compress lignocellulosic biomass to separate at least a portion of the water from the lignocellulosic biomass slurry 105 and form an accumulated biomass 110 comprising dewatered lignocellulosic biomass. As shown in fig. 1, liquid (e.g., water) 115 removed from lignocellulosic biomass slurry 105 may be drained from dewatering system 100 via stream 115. In some embodiments, liquid stream 115 can be recycled to one or more points upstream and/or downstream in the biorefinery.
Biorefineries may include a number of unit operations configured to process lignocellulosic biomass for various purposes, particularly after dewatering the lignocellulosic biomass from a slurry. Many such unit operations include a head space occupied by a gas (e.g., air and steam) that is at an elevated pressure relative to the upstream process and/or ambient environment. Downstream of the dewatering system 100, as shown in fig. 1, is a system 190, the system 190 comprising at least one vessel in fluid communication with an outlet of a solids transfer device in the dewatering system 100. The vessel is configured to receive the accumulated dewatered biomass 110 and process the dewatered lignocellulosic biomass. The vessel has a head space occupied by a gas under pressure. Because the pressure in the vessels of the system 190 may be elevated relative to the upstream process and/or the ambient environment, there is an opportunity that gas from the system 190 may flow back to one or more upstream processes. Such backflow may be undesirable for a number of reasons. For example, such backflow may be considered a "leak" and pressurized gas may have to be replenished in the system 190, which may be inefficient. If the gas includes steam (e.g., for heating, processing, etc.), the heat is also "leaked" out, which may be inefficient. In addition, if steam leaks from system 190 into dewatering system 100, liquid 115 may be heated to its evaporation point. If the liquid 115 is recycled, it may have to be condensed before recycling, which may also be inefficient.
In some embodiments, systems and methods according to the present disclosure include combining gas and accumulated lignocellulosic biomass 110 in a dewatering system 100 under pressure to effectively prevent backflow of gas (e.g., steam) from the system 190. Dewatering system 100 may be configured such that gas under pressure is present in the headspace of dewatering system 100, combining the gas with the accumulated lignocellulosic biomass 110, prevents gas from flowing back from system 190 to an excessive degree. The pressure of the gas in the headspace of the dehydration system 100 is substantially equal to or greater than the pressure of the gas in the headspace of the system 190 to prevent backflow from the system 190. Nevertheless, the accumulated lignocellulosic biomass may help prevent excessive mixing of gases from the headspace of system 190 with gases in the headspace of system 100 at the interface of systems 100 and 190. The accumulated lignocellulosic biomass 110 acts as a physical barrier or pad to help isolate the headspace in the system 190 from the headspace in the dewatering system 100. It may be desirable to isolate the headspace in the system 190 from the headspace in the system 100 to prevent excessive mixing at the interface of the systems 100 and 190. For example, if the system 190 includes steam, it may be desirable to prevent mixing that may occur at the interface of the systems 100 and 190 and introduce excess steam into the system 100. It should be noted that the accumulated lignocellulosic biomass need not be compressed to the extent that a seal can be formed to seal the gases in the system 190 from back flowing to the dewatering system 100. The pressure of the gas in the headspace of the dehydration system 100 is substantially equal to or greater than the gas pressure of the headspace of the system 190 to help prevent backflow. The accumulated biomass helps to prevent excessive mixing at the interface. This is advantageous because some lignocellulosic biomass may have a variable particle size and/or low bulk density, which makes it difficult to compress it sufficiently to enable it to form a seal, while having a desired throughput on a continuous basis. It is due to the combination of the accumulated lignocellulosic biomass 110 and the gas pressure in the headspace of the dewatering system 100 that excessive backflow and excessive mixing of gases from the system 190 is prevented. Advantageously, this configuration can be operated at a desired throughput on a continuous basis, which is surprising for some lignocellulosic biomass that is difficult to process and process (e.g., corn stover, etc.).
In some embodiments, dewatering system 100 includes a head space occupied by a gas in fluid communication with at least an inlet of a solids transfer device. The gas pressure (first pressure) in the headspace of the dewatering system 100 may be selected such that, in combination with the accumulated lignocellulosic biomass 110, gas at the second pressure in the vessel of the system 190 is inhibited from flowing back through the solids transfer device to an excessive degree. In some embodiments, the first pressure and the second pressure may be substantially the same. For example, the difference between the first pressure and the second pressure may be 5psi or less, 1psi or less, or even 0.5psi or less. In some embodiments, the first pressure may be maintained at a pressure greater than the second pressure. For example, the first pressure may be maintained at a pressure of 0.5psi to 30psi greater than the second pressure, 0.5psi to 20psi greater than the second pressure, 0.5psi to 10psi greater than the second pressure, or even 0.5psi to 5psi greater than the second pressure.
The gases present in the headspace of the dehydration system 100 can be provided by a variety of sources. For example, at least a portion of the gas present at the first pressure in the headspace at the inlet of the solids transfer device in the dewatering system 100 may be supplied by the gas entrained in the lignocellulosic biomass slurry 105. Instead of or in addition to any entrained gas, a dedicated source of compressed gas 120 may be supplied to the headspace of the dehydration system 100. Examples of gas 120 include air, inert gases (e.g., nitrogen), carbon dioxide, combinations of these, and the like. In some embodiments, the pressure in the headspace of dewatering system 100 and the gas in the headspace of system 190 are greater than atmospheric pressure. For example, such pressure may be between 20psi and 200 psi.
Fig. 2A and 2B depict an illustrative embodiment of the present invention. As described below, the system in fig. 2A may advantageously dewater a slurry of ground lignocellulosic biomass on a continuous basis and at a desired throughput, for example, in the case of biorefineries that subsequently treat (e.g., hydrolyze) the dewatered lignocellulosic biomass.
In biorefinery, lignocellulosic biomass may be slurried using one or more tanks (with or without agitation, e.g., mixing). Lignocellulosic biomass slurry may be produced throughout the lignocellulosic biomass for one or more reasons, such as to allow the lignocellulosic biomass to be transported to one or more unit operations in a biorefinery and to facilitate the distribution of any treatment compositions (e.g., acid compositions, base compositions, enzyme compositions, combinations of these, etc.). As shown in fig. 2A, a ground lignocellulosic biomass feedstock 201 is supplied to a slurry system comprising one or more slurry tanks 270. In some embodiments, the ground lignocellulosic biomass 201 comprises ground corn stover having a particle size such that at least 80% of the ground corn stover passes through a screen having a six inch screen or even a screen having a one inch screen, and less than 20% of the ground corn stover passes through a screen having a 0.125 inch screen.
The ground lignocellulosic biomass feedstock 201 is mixed with an aqueous liquid 202 in a desired ratio. For example, the ground lignocellulosic biomass feedstock 201 may be combined with the aqueous liquid 202 in a ratio that facilitates formation of a slurry stream 205, the slurry stream 205 having a desired total solids content (as described above) and being pumpable (e.g., via pump 280). The lignocellulosic biomass slurry stream may be pumpable so that it may be conveyed to one or more downstream processes via a pipeline infrastructure comprising, for example, one or more pipelines, one or more valves, and the like. A variety of pumps may be used to pump the lignocellulosic biomass slurry according to the present invention. Non-limiting examples of such pumps include centrifugal pumps, such as those commercially available from Hayward Gordon under the tradename XCS screw centrifugal pump or under the tradename Hayward Gordon
Helico-centrifugal pumps are commercially available from Vaughan.
As shown in fig. 2A, an aqueous liquid 202 is obtained from at least stream 203, stream 250, and stream 260. Stream 203 can be fresh make-up water, recycled process water, or a combination of these. As shown, streams 250 and 260 are recycled from dewatering system 200, as will be discussed below.
Slurries according to the present invention can be formed under a variety of temperature and pressure conditions. In some embodiments, the slurry may be formed in slurry tank 270 at room temperature and atmospheric pressure.
As shown in fig. 2A, after formation of the lignocellulosic biomass slurry, the slurry stream 205 may be pumped to a downstream process, such as a pretreatment reactor 290, which pretreatment reactor 290 may have a gaseous headspace 291 at an elevated pressure (e.g., greater than atmospheric pressure). It may be desirable to dewater the lignocellulosic biomass present in the lignocellulosic biomass slurry stream 205 prior to introduction into the pretreatment reactor 290.
The method and system according to the embodiment of fig. 2A includes a dewatering system 200 for dewatering the lignocellulosic biomass slurry from stream 205 so that at least some liquid may be removed and the dewatered lignocellulosic biomass may be introduced into a system such as pretreatment reactor 290 without excessive mixing and excessive backflow of gases (e.g., steam) from pretreatment reactor 290 to dewatering system 200.
As shown in fig. 2A, dewatering system 200 includes an enclosed screen arrangement 240 that is directly connected to solids transfer arrangement 230.
Lignocellulosic biomass slurry 205 is conveyed to the inlet of a screen apparatus 240 where the slurry may undergo preliminary dewatering in the screen apparatus 240.
As shown in fig. 2A, the enclosed screen apparatus 240 includes a screen 241 located in a pressurizable housing 247.
The enclosed screen apparatus 240 is adapted to receive the lignocellulosic biomass slurry stream 205 at a first end 242 of the screen 241, to cause the slurry to flow downward (due at least in part to gravity) and through the screen 241 to separate at least a portion of the water from the lignocellulosic biomass slurry stream 205 and form a first dewatered lignocellulosic biomass, which may include residual water and lignocellulosic biomass from the lignocellulosic biomass slurry stream 205.
In some embodiments, at least 10%, at least 20%, at least 30%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or even at least 95% of the water present in the slurry stream 205 entering the closed screen apparatus 240 will pass through the screen 241. In some embodiments, the size of the mesh may be selected to be small enough so that substantially all of the lignocellulosic biomass does not pass through the mesh. In some embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, or even at least 99.9% of the lignocellulosic biomass will not pass through the screen 241 when flowing downward and through the screen 241.
The screen 241 has a plurality of screen holes 246. The plurality of mesh openings 246 allow liquid to pass through the screen 241 to separate at least a portion of the water from the lignocellulosic biomass slurry stream 205. The size of the mesh 246 used for the screen 241 may be selected to achieve a desired dewatering of the lignocellulosic biomass in the slurry 205 while achieving a desired throughput on a continuous basis. The screens 241 may have mesh openings 246 all of the same size or a variety of different sizes. In some embodiments, the screen 241 may have one or more mesh sizes of about 0.5 inches or less, about 0.125 inches or less, or even about 0.0625 inches or less. In some embodiments, the screen 241 may include a mesh 246 having a size of 0.03125 inches to 0.125 inches.
As shown, the screen 241 has a second end 243 in addition to the first end 242, and the screen 241 is positioned (angled) such that the first end 242 is above the second end 243 relative to the horizontal dashed line 245, and such that the angle 244 of the screen 241 relative to the horizontal line 245 is greater than zero. In some embodiments, the screen is positioned (angled) such that the angle 244 of the screen 241 relative to the horizontal 245 is greater than 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, or even 90 degrees.
As shown in fig. 2A, the screen 241 is straight from a first end 242 to a second end 243.
Alternatively, the screens in the enclosed screen apparatus may be curved and discussed below in connection with fig. 3.
A wide variety of widths and lengths may be selected for the screen 241 depending on a variety of factors, such as screen angle, desired throughput (gallons of slurry per minute), etc. In some embodiments, the length of the screen 241 from the first end 242 to the second end 243 may be 16 inches to 15 feet, 30 inches to 10 feet, or even 40 inches to 9 feet. In some embodiments, the width (perpendicular to the length) of the screen 241 may be 10 inches to 10 feet, or even 10 inches to 50 inches.
It has been found that by introducing the slurry stream 205 at the first end 242 (top) of the inclined screen 241 and flowing the slurry downwardly and through the screen 241, at least a portion of the liquid (e.g., water) can be separated from the lignocellulosic biomass without excessively plugging the screen 241. The dewatering techniques can accommodate changes in solids loading, biomass size, and/or biomass shape (e.g., due to grinding, different forms of lignocellulosic biomass (e.g., corn husks, comparative corn stover, comparative corn cobs), etc.). In some embodiments, such dehydration can be performed continuously (e.g., days, weeks, etc.) without excessive disruption. While not being bound by theory, it is believed that introducing the slurry 205 at the top of the inclined screen 241 causes the liquid near the top end 242 to have a relatively high volume and/or velocity, thereby helping to protect the screen 241 from becoming clogged to an excessive degree with lignocellulosic biomass, particularly flat biomass structures such as leaves and hulls, present in corn stover. In addition, because the lignocellulosic biomass is dewatered as it flows downward and through the screen 241, it may contact the screen 241 (e.g., due at least in part to gravity) and have a "scrubbing" effect that also helps to protect the screen 241 from becoming clogged to an excessive degree by the lignocellulosic biomass, particularly flat biomass structures such as leaves and shells.
Exemplary angled screens 241, such as "gravity screens," are commercially available. One example of a commercially available gravity screen is available from SWECO under the trade name STA-SIEVE fixed screening device having model SV10S Bb. Another example of a commercially available gravity screen may be referred to by the trade nameSolid-liquid separation equipment is available from Parkson Corporation. Another example of a commercially available gravity screen is available from Fluid-Quip, inc. To facilitate transfer of the dewatered lignocellulosic biomass from the enclosed screen apparatus 240 to the vessel 290 via the solids transfer apparatus 230, the enclosed screen apparatus 240 has a headspace 229 between the top of the screen 241 and the housing 247 that may have gas present at a pressure that combines with accumulated dewatered lignocellulosic biomass exiting the solids transfer apparatus 230, preventing the gas from the vessel 290 from mixing and flowing back through the solids transfer apparatus 230 to an excessive degree. As shown in fig. 2A, the headspace 229 is in fluid communication at least at an inlet 231 of the solids transfer device 230 (e.g., screw conveyor or feeder). The gas pressure in headspace 229 (the first pressure) may be selected so that, in combination with accumulated dehydrated lignocellulosic biomass from apparatus 230, the gas in headspace 229 inhibits backflow of gas (e.g., steam) at the second pressure in headspace 291 of vessel 290 through solids transfer apparatus 230 to an excessive degree, or inhibits mixing of the gas with any liquid or gas in system 200 to an excessive degree. In some embodiments, the first pressure and the second pressure may be substantially the same. For example, the difference between the first pressure and the second pressure may be 1psi or less, or even 0.5psi or less. In some embodiments, the first pressure may be maintained at a pressure greater than the second pressure. For example, the first pressure may be maintained at a pressure that is 5psi or greater than the second pressure, or even 10psi or greater than the second pressure.
The gas present in headspace 229 may be provided by a variety of sources. For example, at least a portion of the gas present at the first pressure in the headspace 229 at the inlet 231 of the solids transfer device 230 may be supplied by the gas entrained in the lignocellulosic biomass slurry stream 205. For example, while not being bound by theory, it is believed that the high velocity mixing in the slurry tank 270 may create turbulence that causes gases (e.g., air) to be entrained in the lignocellulosic biomass slurry. The entrained gas may be carried to the bottom of the slurry tank 270 where it may enter a pump 280 and be compressed and transported through one or more conduits in the slurry stream 205. As the slurry stream enters the blind screen apparatus 240, the gas expands and escapes from the slurry into the headspace 229, creating a pressurized headspace 229 near the inlet 231 of the solids transfer apparatus 230. Further, slurry stream 205 may form a physical seal between headspace 229 and slurry tank 270, such that headspace 229 is at an elevated pressure relative to the headspace in the slurry tank (which may be at atmospheric pressure). Additionally, the slurry stream 205 piping infrastructure may include one or more valves to create a seal between the headspace 229 and the slurry tank 270.
Instead of or in addition to any entrained gas, a dedicated source of compressed gas 220 may be supplied to the headspace 229. Examples of gas 220 include air, inert gases (e.g., nitrogen), carbon dioxide, combinations of these, and the like. In some embodiments, the pressure in the headspace 229 and the gas in the headspace 291 of the container 290 are greater than atmospheric pressure. For example, such pressure may be between 20psi and 200 psi.
As described above, dewatering system 200 also includes solids transfer apparatus 230, which solids transfer apparatus 230 is used to transfer dewatered lignocellulosic biomass (first dewatered lignocellulosic biomass) from enclosed screen apparatus 240 into vessel 290.
As shown in fig. 2A, solids transfer device 230 has an inlet 231 and an outlet 238, and is adapted to convey lignocellulosic biomass in the first dehydrated lignocellulosic biomass to separate at least a portion of residual water 250 from the first dehydrated lignocellulosic biomass and accumulate a second dehydrated lignocellulosic biomass proximate outlet 238 so that it can be fed into vessel 290. In some embodiments, the solids transfer device 230 removes 50% or more of the residual water present in the first dewatered lignocellulosic biomass. In some embodiments, the solids transfer device 230 may remove 30% or less, 20% or less, or even 10% or less of the water present in the first dewatered lignocellulosic biomass.
A variety of solids transfer devices may be used to convey and compress the lignocellulosic biomass according to the present invention. As shown in fig. 2A, the solids transfer device 230 includes a tubular trough or barrel member 232 having an inlet 231 at one end and an outlet 238 at the other end. Inlet 231 is adapted to receive a first dehydrated lignocellulosic biomass at a first pressure in headspace 229. As shown in fig. 2B, the barrel member 232 may include a screw section 237 for conveying the lignocellulosic material, the screw section 237 having a rotatable screw 236 in the screw section 237. The screw may be driven by a motor (not shown). Because the solids transfer device can be configured to transport and accumulate lignocellulosic biomass without highly compressing the biomass, engines with relatively low horsepower can be used for the desired throughput. For example, lignocellulosic biomass may be conveyed by the solids transfer device 230 at throughputs of up to 700 tons or even 800 tons per day using an engine having about 200 or less horsepower (e.g., 0.26 HP/(ton/day)). Because there is no need to compress the lignocellulosic biomass to form a gas seal between the head spaces 291 and 229, the solids transfer device 230 may be subjected to less abrasive wear.
As shown in fig. 2B, screw section 237 may also include a screen 235 mounted between barrel member 232 and screw 236 to assist in removing residual water from the first dewatered lignocellulosic biomass and forming recirculation stream 250.
As shown in fig. 2B, the barrel member 232 may also include an accumulator 234 near an outlet 238 of the barrel member 232.
The solids transfer device (such as solids transfer device 230) may include one or more mechanical features that facilitate the accumulation of lignocellulosic biomass near outlet 238 and between headspace 229 and headspace 291. Non-limiting examples of such mechanical features include flapper door 239 over discharge outlet 238; or a back-pressure cone (not shown) on the discharge outlet 238 of the solids transfer device 230.
As described above, biorefinery may include one or more unit operations (e.g., vessel 290) configured to treat lignocellulosic biomass for various purposes, particularly after dewatering the lignocellulosic biomass from a slurry. Such unit operations may include a headspace 291 and a quantity of lignocellulosic biomass 292, where the headspace 291 is occupied by a gas (e.g., air and/or steam) at an elevated pressure relative to an upstream process (e.g., slurry tank 270). Downstream of the slurry tank 270 is a vessel 290, as shown in fig. 2A, the vessel 290 being in fluid communication with the outlet 238 of the solids transfer device 230 in the dewatering system 200. As shown, vessel 290 is configured to continuously receive accumulated lignocellulosic biomass from solids transfer device 230 and process the dewatered lignocellulosic biomass. Since the pressure in the headspace 291 may be elevated relative to the slurry tank 270 and/or the ambient environment, there is an opportunity that gas from the vessel 290 may flow back to one or more upstream processes. Such backflow may be undesirable for a number of reasons. For example, such backflow may be considered a "leak" and pressurized gas may have to be replenished in the vessel 290, which may be inefficient. If the gas includes steam (e.g., for heating, etc.), the heat is also "leaked" out, which may be inefficient. In addition, if steam leaks from the vessel 290 into the dehydration system 200, the liquids in the streams 202, 250, and 260 can be heated to their vaporization points. Because the liquid in stream 202, stream 250, and stream 260 is recycled/recycled to slurry tank 275, it must be condensed before it is recycled/recycled, which can also be inefficient.
Dewatering system 200 includes combining the gas in headspace 229 and the dewatered lignocellulosic biomass accumulated in solids transfer device 230 to effectively prevent mixing and backflow of gas (e.g., steam) from vessel 290. Dewatering system 200 may be configured such that gas under pressure present in headspace 229 is combined with accumulated dewatered lignocellulosic biomass from feeder 230, preventing gas from vessel 290 from mixing and back-flowing through solids transfer device 230 to an excessive degree. The dewatered lignocellulosic biomass accumulated in the feeder 230 may act as a physical barrier or physical mat to isolate the headspace 229 from the headspace 291. It may be desirable to isolate headspace 291 from headspace 229 to prevent excessive mixing at the interface of system 200 and reactor 290. For example, if reactor 290 includes steam, it may be desirable to prevent mixing that may occur at the interface of system 200 and reactor 290 and introduce excess steam into system 200. It should be noted that the accumulated dehydrated lignocellulosic biomass need not be compressed to the extent that a seal can be formed to seal the gas in the vessel 290 from back flowing into the system 200. The gas in headspace 229 of dehydration system 200 is substantially the same as or greater than headspace 291 in reactor 290 to help prevent back flow. The accumulated biomass helps to prevent excessive mixing at the interface. It is the combination of accumulated biomass from the feeder 230 and the gas pressure in the headspace 229 that prevents excessive mixing and excessive back flow of gas from the vessel 290. Advantageously, this configuration can be operated at a desired throughput on a continuous basis, which is surprising for some lignocellulosic biomass that is difficult to process and process (e.g., ground corn stover, etc.). Another advantage is that the relatively small density and/or variable size lignocellulosic biomass that may be difficult to compress to form a "sealing" plug to seal headspace 229, can still be dewatered and transferred to a pressurized environment (such as vessel 290) by using a combination of pressurized headspace 229 and "less dense" accumulated biomass from feeder 229 in accordance with the present invention. Yet another advantage is that the solids transfer apparatus 230 can be operated at lower power consumption and lower equipment wear because there is no need to compress the lignocellulosic biomass to the extent that it forms a seal with the headspace 291.
A wide variety of reactors 290 may be used to treat lignocellulosic biomass 292. In biorefineries, one exemplary reactor is a pretreatment reactor. As shown, reactor 290 includes a pressurized headspace 291 above a stack of lignocellulosic biomass 292, the headspace 291 having a gas vent 293 to remove gas from the headspace 291 as needed. The contents of the pretreatment reactor (lignocellulosic biomass 292 and aqueous liquid (not shown)) may be exposed to temperature and pH for a period of time to hydrolyze one or more polysaccharides present in the lignocellulosic biomass to one or more monosaccharides (sugars) that may be converted into one or more biochemicals using one or more microorganisms. Exemplary hydrolysis conditions include exposing the lignocellulosic biomass to an aqueous liquid at a temperature in the range of 245 ° F to 350 ° F and a pH of 0.5 to 3.0 for a time period of 0.5 hours to 5 hours. Sugars may be made by processing lignocellulosic biomass using one or more techniques (e.g., acid hydrolysis, enzymatic hydrolysis, etc.).
Fig. 3 shows another embodiment of the present invention. The embodiment shown in fig. 3 is the same as the embodiment discussed above with respect to fig. 2A, except that the screen in the enclosed screen apparatus in fig. 3 is curved rather than straight. Dewatering system 300 includes an enclosed screen apparatus 340 that is directly connected to solids transfer apparatus 330. Lignocellulosic biomass slurry 305 is conveyed to the inlet of a screen apparatus 340 where the slurry may undergo preliminary dewatering.
As shown in fig. 3, the enclosed screen apparatus 340 includes a screen 341 in a pressurizable housing 347. The enclosed screen apparatus 340 is adapted to receive the lignocellulosic biomass slurry stream 305 at a first end 342 of the screen 341 such that the slurry flows downward (due at least in part to gravity) and through the screen 341 to separate at least a portion of the water from the lignocellulosic biomass slurry stream 305 and form a first dewatered lignocellulosic biomass, which may include residual water from the lignocellulosic biomass slurry stream 305 and lignocellulosic biomass.
The screen 341 has a plurality of mesh openings 346. The plurality of mesh openings 346 allow liquid to pass through the screen 341 to separate at least a portion of the water from the lignocellulosic biomass slurry stream 305. As shown, the screen 341 is a concavely curved surface from a first end 342 to a second end 343 with a radius of curvature of 20 inches to 150 inches, or even 40 inches to 120 inches. For a screen 341 having a concavely curved surface, such a screen may be positioned relative to horizontal to achieve a desired angle 349 at a first end 342 (inlet) and a desired angle 344 at a second end 343 (outlet). In some embodiments, the screen 341 may have an inlet angle 349 in a range of 55 to 99 degrees, or even 85 to 95 degrees, and an outlet angle 344 in a range of 25 to 60 degrees, or even 25 to 35 degrees. While not being bound by theory, it is believed that by having a relatively large angle 349 at the inlet 342, the liquid near the tip 342 has a relatively high velocity, thereby helping to protect the screen 341 from becoming clogged to an excessive degree by lignocellulosic biomass, particularly flat biomass structures such as leaves and hulls, present in corn stover.
As the lignocellulosic biomass exits the second end 343 of the screen 341, it enters the opening 331 of the solids transfer device 330. It can be seen that the opening 331 of the solids transfer device is exposed to the headspace 329 of the enclosed screen apparatus 340, such that the gas pressure at the inlet 331 can be controlled by controlling the pressure in the headspace 329, as discussed above with respect to fig. 2A.
