U.S. patent application number 12/493452 was filed with the patent office on 2010-12-30 for system and method for continuously treating biomass.
Invention is credited to Murray D. Bath, J. Todd Harvey.
Application Number | 20100326610 12/493452 |
Document ID | / |
Family ID | 43379446 |
Filed Date | 2010-12-30 |
![](/patent/app/20100326610/US20100326610A1-20101230-D00000.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00001.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00002.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00003.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00004.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00005.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00006.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00007.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00008.png)
![](/patent/app/20100326610/US20100326610A1-20101230-D00009.png)
United States Patent
Application |
20100326610 |
Kind Code |
A1 |
Harvey; J. Todd ; et
al. |
December 30, 2010 |
SYSTEM AND METHOD FOR CONTINUOUSLY TREATING BIOMASS
Abstract
A continuous biomass pretreatment system and method is provided.
The system comprises a pipe reactor having an input end, an output
end, an interior and an exterior. The pipe reactor does not have a
mixing component that passes from the interior to the exterior and
rotates with respect to the pipe. The system further comprises a
pump in communication with the input end of the pipe reactor, a
valve in communication with the output end of the pipe reactor, and
a flash vessel having an input opening in communication with the
output of the valve.
Inventors: |
Harvey; J. Todd; (Lakewood,
CO) ; Bath; Murray D.; (Centennial, CO) |
Correspondence
Address: |
JONES DAY
555 SOUTH FLOWER STREET FIFTIETH FLOOR
LOS ANGELES
CA
90071
US
|
Family ID: |
43379446 |
Appl. No.: |
12/493452 |
Filed: |
June 29, 2009 |
Current U.S.
Class: |
162/17 ;
162/237 |
Current CPC
Class: |
D21C 7/00 20130101; D21C
3/26 20130101 |
Class at
Publication: |
162/17 ;
162/237 |
International
Class: |
D21C 3/26 20060101
D21C003/26; D21C 7/00 20060101 D21C007/00 |
Claims
1. A system for continuously treating biomass, the system
comprising: a pipe reactor having an input end and an output end
and an interior and an exterior wherein the pipe reactor does not
have a mixing component that passes from the interior to the
exterior and rotates with respect to the pipe; a pump having an
input side and an output side wherein the output side of the pump
is in communication with the input end of the pipe reactor; a valve
having an input and an output wherein the output end of the pipe
reactor is in communication with the input of the a valve; and a
flash vessel having an input opening and an output opening wherein
the output of the valve is in communication with the input opening
of the at least one flash vessel.
2. The system of claim 1, wherein the valve is a choke valve.
3. The system of claim 1, further comprising a static mixer
disposed within the interior of the pipe reactor.
4. The system of claim 1, further comprising a static mixer
disposed within the interior of the pipe reactor and rigidly
affixed to the pipe reactor.
5. The system of claim 1, further comprising a counter current
splash vessel in communication with the input side of the pump.
6. The system of claim 5, wherein the counter current splash vessel
further comprises a steam input.
7. The system of claim 6, wherein the flash vessel further
comprises a steam output in communication with the counter current
splash vessel steam input and wherein steam is recycled from the
flash vessel to the counter current splash vessel.
8. The system of claim 1, wherein the pump is capable of handling
pressures between about 350 and 450 pounds per square inch,
temperatures between about 120 and 220.degree. C., and a biomass
slurry that is about 50% to 90% solids by mass.
9. A method of continuously treating biomass, the method comprising
the steps of: a. pumping a biomass slurry with a pump into a pipe
reactor at a reaction pressure wherein the pipe reactor does not
have a mixing component that passes from the interior to the
exterior and rotates with respect to the pipe; b. heating the
biomass within the pipe reactor to a reaction temperature; c.
ejecting the heated biomass from the pipe reactor through a valve
into a flash vessel to rapidly depressurize the biomass; and d.
maintaining a constant flow rate through the pipe reactor, wherein
the biomass reaches the reaction temperature before exiting the
pipe reactor.
10. The method according to claim 9, further comprising the step of
pre-heating the biomass in a counter current splash vessel before
the pumping step.
11. The method according to claim 10, further comprising the step
of recovering steam from the flash vessel and recycling the
recovered steam to the counter current splash vessel to pre treat
the biomass.
12. The method according to claim 9, wherein the valve is a choke
valve.
13. The method according to claim 9, further comprising the step of
injecting a reagent on an input side of the pump.
14. The method according to claim 9, wherein the pump is capable of
handling pressures between about 350 and 450 pounds per square
inch, temperatures between about 120 and 220.degree. C., and a
biomass slurry that is about 50% to 90% solids by mass.
15. The method according to claim 9, wherein the heating step is
performed by injecting steam into the pipe reactor.
16. A method of continuously treating biomass, the method
comprising the steps of: a. a high solids biomass slurry into a
pipe reactor at a reaction pressure wherein the pipe reactor has no
motor driven stirring method and wherein the pipe reactor has a
plurality of sealable openings for flowing biomass and steam; b.
injecting steam into the pipe reactor to heat the biomass; c.
ejecting the heated biomass from the pipe reactor through a valve
into a flash vessel to rapidly depressurize the biomass; and d.
maintaining a constant flow rate through the pipe reactor, wherein
the biomass reaches a reaction temperature before exiting the pipe
reactor by continuously performing the pumping, injecting, and
ejecting steps.
17. The method according to claim 16, further comprising the step
of pre-heating the biomass in a counter current splash vessel
before the pumping step.
18. The method according to claim 17, further comprising the step
of recovering steam from the flash vessel and recycling the
recovered steam to the counter current splash vessel in the
pre-heating step.
19. The method according to claim 17, wherein the valve is a choke
valve.
20. The method according to claim 17, further comprising the step
of injecting a reagent on an input side of the pump.
21. The method according to claim 17, wherein the pump is capable
of handling pressures between about 350 and 450 pounds per square
inch and temperatures between about 120 and 220.degree. C., and a
biomass slurry that is about 50% to 90% solids by mass.
Description
FIELD
[0001] The present patent document relates to systems and methods
for continuously treating biomass.
BACKGROUND
[0002] Recently, the conversion of lignocellulosic biomass
("biomass") into ethanol or other useful products as a replacement
for fossil fuels has garnished considerable attention. Biomass that
is suitable for conversion into fossil fuel substitutes can be
obtained from numerous different sources. For example, wood, paper,
agricultural residues, food waste, herbaceous crops, and municipal
and industrial solid wastes to name a few, can all be used as
sources of biomass. Before lignocellulosic biomass can be fermented
into ethanol, the biomass needs to undergo some kind of process to
disrupt the polymer network of cellulose, hemicellulose, and lignin
forming the biomass structure. This process is commonly referred to
as "pretreatment" and is designed to reduce the recalcitrance of
the biomass to enzymatic saccharification of the cellulose, and in
some instances the hemicellulose, therein.
[0003] For a number of reasons, biomass is an attractive feedstock
for producing fossil fuel substitutes. Biomass that is converted
and used as a fossil fuel substitute theoretically produces no net
carbon dioxide in the earth's atmosphere. Biomass is a
carbon-neutral fossil fuel substitute because the lignocellulosic
biomass found in plants is created by removing carbon dioxide from
the atmosphere through photosynthesis. Therefore, the carbon that
is released into the atmosphere during the combustion of fuels
created from biomass is reclaimed by the growth of the next crop.
Furthermore, the conversion of biomass provides an attractive way
to dispose of many readily available industrial and agricultural
waste products. In addition, biomass is a renewable resource
because crops that can be used as feedstock may be continuously
regrown.
[0004] While fermentation of lignocellulosic biomass has the
potential to provide an attractive fossil fuel alternative,
substantial difficulties still remain. Because the main product of
biomass conversion is a commodity, namely fuel, production costs
must be kept low to be competitive with other fuels sources. In
addition, one of the goals of using biomass as a fossil fuel
replacement is to reduce carbon pollution. Therefore, any processes
used during the conversion of biomass should be environmentally
friendly. Finally, because in the United States alone approximately
9 million barrels of gasoline are consumed each day, the process
used to create a fossil fuel replacement from biomass must be
scalable.
[0005] Lignocellulosic biomass is primarily comprised of cellulose,
hemicellulose, and lignin. The cellulose, hemicellulose, and lignin
within the biomass form an intermeshed polymer network, the
structure of which causes the biomass to be recalcitrant to
enzymatic saccharification of the cellulose and hemicellulose
therein. Consequently, in order to efficiently create a fossil fuel
substitute, such as ethanol or dimethyl ether, from biomass, the
structure of the organic polymer network must be altered. The
pretreatment of biomass can reduce the recalcitrance of the
lignocellulosic biomass to saccharification of the cellulose and
hemicellulose contained therein. By reducing the recalcitrance of
the biomass, microbial enzymes have increased access to the
carbohydrate polymers (cellulose and hemicellulose) within the
biomass. The successful commercial use of lignocellulosic biomass
as a feedstock for the production of fossil fuel substitutes
depends on the development of an efficient pretreatment
process.
[0006] Because of the potential benefits that will be derived from
using lignocellulosic biomass to create fossil fuels, the
development of suitable pretreatment processes for use with
lignocellulosic biomass has been the topic of significant
contemporary research. In addition, the paper making industry has
long used a process for creating paper pulp that involves
separation of cellulose from other constituents found in the
biomass.
[0007] The paper making industry uses conventional methods for
separating cellulose from other components of the biomass
feedstock. The Alkaline Kraft process is most commonly used in the
United States and the Sulphite Pulping process is most commonly
used in central Europe. These techniques are well established and
although relatively expensive, are viable solutions for the paper
making industry because of the high value of paper as an end
product.
[0008] The processes used in the paper making industry for pulping
have come under scrutiny as a potential method for treating biomass
to be used as a fossil fuel substitute for a number of reasons.
First, both the Alkaline Kraft process and the Sulphite Pulping
process create toxic byproducts. One of the goals of using biomass
as a fossil fuel substitute is to decrease the pollutant effects of
burning fossil fuels. The goal of reducing overall pollution is
defeated when the process used to create the fuel substitute
pollutes the environment or uses more energy than it produces.
Second, both processes used in the paper industry are too expensive
to allow the conversion of biomass to be competitive with naturally
occurring fossil fuels in the current market.
[0009] Recent work has been done to reduce the toxic byproducts of
conventional paper making processes by substituting organic
solvents for the more toxic traditional solvents. However, the
processes remain expensive and only fit for industries with high
value end products like paper.
[0010] Numerous pretreatments have been investigated which involve
exposing biomass to elevated pressures and temperatures without the
use of solvents to break hydrogen and covalent bonds found in the
intermeshed polymer network of cellulose, hemicellulose, and lignin
forming the structure of the biomass, thereby altering the
composition and/or structure of the biomass in a desired way. These
methods are often referred to as "steam cooking".
[0011] Initial work on steam cooking hardwoods was first done by
Mason and described in U.S. Pat. Nos. 1,578,609; 1,824,221;
2,645,633; 2,379,890; and 2,759,856. These patents disclose placing
small pieces of wood in a high pressure chamber or gun, subjecting
them to slow cooking at lower temperatures, and then following with
a rapid pressure rise and quick release.
[0012] The wood chips enter the pressure chamber or gun through a
gate valve from a hopper. While the wood chips are being loaded in
the chamber, both the chamber and the hopper are at atmospheric
pressure. The chamber or gun is then sealed with the wood chips
inside and the pressure in the chamber is increased to the desired
amount. After the wood chips remain in the chamber or gun for the
desired time, the wood chips leave the pressure chamber or gun
through a slot or relatively constricted opening while being
rapidly depressurized. The material is all forced out of the
chamber or gun by continuing to add pressurized gas to the chamber
as the material exits. When all of the material is discharged, the
gun or chamber is returned to atmospheric pressure, and the gun is
reloaded with the next batch of wood from the hopper.
[0013] The methods and apparatus disclosed in the Mason patents
have numerous drawbacks for use with the conversion of biomass for
a fossil fuel substitute. For example, the methods and apparatus
described by Mason are not conducive to scaling. The Mason patents
disclose a batch method for processing wood. A batch process
requires the pressure chamber to be decreased back to atmospheric
pressure for each batch of wood or biomass to enter. Continually
bringing the chamber or gun back to atmospheric pressure wastes
significant time and energy, and, therefore, the process can not be
economically scaled to make biomass conversion competitive with
naturally occurring fossil fuels.
[0014] The Mason patents further disclose an increase in pressure
of the chamber or gun after an initial cooking period. Similar to
continually bringing the chamber back to atmospheric pressure, the
increase in pressure of the entire chamber after initial cooking
forces the process into a batch mode which, as disclosed above, is
not conducive to scaling.
[0015] More recent work in the area of "steam cooking"
lignocellulosic biomass has been performed by Wingerson and is
described in U.S. Pat. No. 6,419,788 B1, U.S. Pat. No. 6,620,292 B2
and U.S. Patent Application 2006/0283995. The Wingerson patents
disclose a method for separating cellulose from lignocellulosic
biomass by forcing the biomass through a pressure chamber with a
motor driven rotating auger. The rotating auger may have more than
one screw pitch to further stress the biomass and create dynamic
plug segments in the biomass as it is forced through the pressure
chamber. These dynamic plug segments are used to create reaction
zones inside the pressure chamber.
[0016] Rotating augers that may be used in pressure chambers for
removing cellulose from biomass are readily available. The
Wingerson patents disclose that a rotating auger that may be used
for this purpose is commercially available from Stake Technology,
Ltd., and is commonly used in the paper pulping industry.
Furthermore, U.S. Pat. Nos. 4,119,025, 4,186,658, and 4,947,743
issued to Brown et. al. also disclose the use of a rotating auger
to convey material.
[0017] The use of a rotating auger as a means to move biomass along
the pressure chamber creates numerous problems. For example, the
use of a rotating auger as a means to facilitate biomass movement
along the pressure chamber requires a pressure reactor that is
extremely complex and capital intensive. The complexity and expense
are created because the rotating shaft must be sealed as it passes
into the pressure chamber. Both the Mason patents and the Wingerson
patents disclose pressures well in excess of 300 pounds per square
inch. Such high pressures will require, the rotating shaft to have
some type of bearing to enter the pressure chamber and this bearing
must be sealed against pressure leaks. While sealing against high
pressures may be done on a small bearing, as the scale increases,
sealing the bearing becomes increasingly difficult and increasingly
dangerous. Furthermore, the maintenance on high pressure bearing
seals is often frequent and expensive. In addition, as the scale of
the bearing increases so often do maintenance times and costs.
Finally, because of the inherent danger in having a high pressure
seal fail, many safety regulations and codes require redundant
safety seals or pressure locks. These added safety precautions
further increase both the initial cost of building such apparatus
and the cost of continued maintenance.
[0018] Custom shaped or designed reaction chambers such as those
disclosed in the Wingerson and Mason patents are extremely
difficult and expensive to make and not conducive to scaling. Batch
processing methods and apparatus, on the other hand, waste time and
energy in the conversion of biomass and therefore are not practical
for use in creating fossil fuel alternatives.
[0019] Because of the limitations and problems in conventional
biomass treatment systems, a need exists for an apparatus and
method for the pretreatment of biomass that is simple and may be
economically scaled to a sufficient size for use in the production
of viable fossil fuels alternatives.
SUMMARY OF THE INVENTION
[0020] In view of the foregoing, an object according to one aspect
of the present invention is to provide a system and method to
continuously treat biomass in a simple pressure chamber that is not
capital intensive to build.
[0021] To this end, the present specification discloses a system
and method for treating biomass. The system for treating biomass
comprises a pipe reactor having an input end and an output end and
an interior and an exterior wherein the pipe reactor does not have
a mixing component that passes from the interior to the exterior
and rotates with respect to the pipe. The system further comprises
a pump having an input side and an output side such that the output
side of the pump is in communication with the input end of the pipe
reactor. The system further comprises at least one valve having an
input and an output wherein the output end of the pipe reactor is
in communication with the input of the at least one valve, and at
least one flash vessel having an input opening and an output
opening wherein the output of the at least one valve is in
communication with the input opening of the at least one flash
vessel.
[0022] In one of the embodiments, the valve of the treatment system
is a choke valve. A choke valve may be preferable because choke
valves are more reliable, can maintain a pressure drop across their
interface, and can control the flow of biomass into the flash
vessel.
[0023] In yet another embodiment, the pipe reactor of the treatment
system may further comprise a static mixer. In one embodiment, the
static mixer comprises at least one mixer bar. In another
embodiment, it preferably comprises a helical static mixer. The
static mixer may be slideably inserted within the interior of the
pipe reactor or rigidly affixed to the pipe reactor.
[0024] According to a further embodiment, the system may further
comprise a second pipe reactor in series with the first pipe
reactor. This arrangement may be used to permit the removal of
hemicellulose from the lignocellulosic biomass between the first
and second pipe reactors.
[0025] According to a further embodiment, the treatment system may
further comprise at least one counter current splash vessel in
communication with the input side of the pump. The counter current
splash vessel may be used to stage the biomass before it is pumped
into the pipe reactor. The counter current splash vessel can also
add heat, steam, pressure, reagents, or other additives that may
increase the effectiveness of the treatment system. For example,
the counter current splash vessel may include a steam input to
allow steam to be added to the biomass.
[0026] In yet another embodiment, each flash vessel further
comprises a steam output in communication with a steam input of a
counter current splash vessel. In this manner, the steam from each
flash vessel may be recycled to a counter current splash vessel.
Recycling the steam allows the treatment system to be more
efficient and cost effective.
[0027] In a further embodiment, the pump in the treatment system is
capable of handling pressures between about 350 and 450 pounds per
square inch and temperatures between about 120 and 220 degrees
Celsius.
[0028] According to another aspect of the present patent document,
a method of continuously treating biomass is provided. The method
comprises: pumping a biomass with a pump into a pipe reactor at a
reaction pressure wherein the pipe reactor does not have a mixing
component that passes from the interior to the exterior and rotates
with respect to the pipe; injecting steam into the pipe reactor to
heat the biomass; ejecting the heated biomass from the pipe reactor
through a valve into at least one flash vessel to rapidly
depressurize the biomass; and maintaining a constant flow rate
through the pipe reactor wherein the biomass reaches a reaction
temperature before exiting the pipe reactor and wherein the
constant flow rate is achieved by continuously performing the
pumping, injecting, and ejecting steps.
[0029] In a further embodiment, a reagent may be injected on the
input side of the pump to increase the effectiveness or control of
the treatment system. The injected reagent may be, for example,
SO.sub.2, sulphite, or any other suitable reagent for the
pretreatment of lignocellulosic biomass to reduce its
recalcitrance.
[0030] According to another aspect of patent document, a method of
continuously pretreating biomass is provided. The method comprises:
pumping a biomass into a pipe reactor at a reaction pressure
wherein the pipe reactor has no motor driven stirring method and
wherein the pipe reactor has a plurality of sealable openings for
flowing biomass and steam; heating the biomass in the pipe reactor
to a reaction temperature; ejecting the heated biomass from the
pipe reactor through a valve into a flash vessel to rapidly
depressurize the biomass; and maintaining a constant flow rate
through the pipe reactor, wherein the biomass reaches the reaction
temperature before exiting the pipe reactor. In one implementation,
the biomass is heated within the pipe reactor by injecting steam
into the pipe reactor.
[0031] In a further embodiment, the flash vessel may be a pressure
let down cyclone. The flash vessel may also be equipped with an
auger to facilitate biomass removal from the bottom of the flash
vessel. If a pressure let down cyclone is used as the flash vessel,
it may similarly be equipped with an auger to facilitate material
removal.
[0032] In a further embodiment, the system involves two stages,
wherein each stage includes a pipe reactor and at least one flash
vessel as described above. In this embodiment, the method may
further comprise a step of removing hemicellulose after the
pumping, injecting, and ejecting steps of the first stage.
[0033] Other features and advantages that are inherent in the
systems and methods of the invention are described herein or will
become apparent to those skilled in the art from the following
detailed description and its accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 illustrates a view of a continuous biomass treatment
system;
[0035] FIG. 2 illustrates a view of the heat recovery system of a
continuous biomass treatment system with a plurality of flash
vessels and a plurality of counter current splash vessels;
[0036] FIG. 3 illustrates a cross sectional view of a choke
valve;
[0037] FIG. 4 illustrates a cross sectional view of an embodiment
of a counter current splash vessel;
[0038] FIG. 5A illustrates a view down the axis of an embodiment of
a pipe reactor containing a static mixer;
[0039] FIG. 5B illustrates a view down the axis of an embodiment of
a pipe reactor containing an alternative form of a static
mixer;
[0040] FIG. 5C illustrates an exterior view of an embodiment of a
pipe reactor containing a static mixer;
[0041] FIG. 5D illustrates a cross sectional view of an embodiment
of a pipe reactor with a static mixer slideably inserted in the
interior of the pipe reactor;
[0042] FIG. 6 illustrates a schematic of a continuous biomass
treatment method; and
[0043] FIG. 7 illustrates a schematic of a continuous biomass
treatment method.
[0044] FIG. 8 illustrates a helical static mixer.
[0045] FIG. 9 illustrates a grid-type static mixer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] In the following descriptions of the preferred embodiments,
reference is made to the accompanying drawings that form a part
hereof, and in which is shown by way of illustration specific
embodiments in which the invention may be practiced. It is to be
understood, however, that other embodiments may be utilized and
structural changes may be made without departing from the scope of
the present invention.
[0047] Consistent with its ordinary meaning as a renewable energy
source, the term "biomass" is used herein to refer to living and
recently dead biological material including carbohydrates, proteins
and/or lipids that can be converted to fuel for industrial
production. The biomass that may benefit from pretreatment in the
systems and methods described herein comprise lignocellulosic
biomass, which may include by way of non-limiting example, dead
trees and branches, yard clippings, wood chips, agricultural
residues (e.g., bagasse, rice straw, wheat straw, corn stover,
etc.), straw, and energy crops (e.g., switch grass, hybrid poplar,
willow, etc.).
[0048] As used herein, the term "pipe reactor" and "tubular
reactor" are interchangeable and refer to a section of pipe in a
system where chemical or other processes take place. For the
purposes of the present invention, a "pipe reactor" and "tubular
reactor" are devoid of any rotating parts that require connection
from the interior to the exterior of the reaction chamber. This
includes motor driven rotating augers used for stirring and any
other means requiring a seal which allows rotation but prevents
pressure leaks.
[0049] FIG. 1 illustrates a view of a continuous biomass treatment
system 10. Treatment system 10 of the illustrated embodiment
comprises counter current splash vessel 90, pump 50, pipe reactor
30, valve 110, flash vessel 70, and heat exchanger 120. While a
counter current splash vessel 90 and heat exchanger 120 are shown
in the FIG. 1 embodiment, other embodiments of treatment system 10
may be constructed in which a counter current splash vessel 90 and
heat exchanger 120 are omitted.
[0050] In use, treatment system 10 is preferably designed to
continuously flow biomass through the pipe reactor 30. The flow of
the biomass may be controlled by the combination of the pump 50 and
the valve 110. In the embodiment shown in FIG. 1, the biomass
enters the counter current splash vessel 90 and is then pumped into
the pipe reactor 30 by the pump 50. The valve 110 controls the flow
of the biomass out of the pipe reactor 30 and into the flash vessel
70. The biomass exits the flash vessel 70 and proceeds through a
heat exchanger 120.
[0051] The system 10 is designed to reduce the recalcitrance of
lignocellulosic biomass to enzymatic saccharification and
fermentation, and thereby render the biomass a more efficient
feedstock for producing fossil fuel alternatives. Unlike other
apparatus and systems used for the pretreatment of biomass that are
complex and not designed for scaling, the present embodiment of
treatment system 10 incorporates basic elements that may be easily
and cost effectively scaled for large industrial production.
Indeed, the system and methods described herein may be readily
scaled to handle hundreds of tonnes per hour of lignocellulosic
biomass.
[0052] As shown in FIG. 1, the biomass preferably enters treatment
system 10 in the counter current splash vessel where it may be
preconditioned with steam, heat or other additives. The biomass is
then pumped into the pipe reactor 30 with a large industrial pump
50 capable of handling high pressures, temperatures, and solids.
Once steady state is achieved within treatment system 10, when the
biomass leaves the pump 50 and enters the pipe reactor, the biomass
is already at the desired reaction pressure. The flow rate of the
biomass may be controlled to ensure the biomass reaches a reaction
temperature in the pipe reactor 30. The reaction pressure and
reaction temperature are preferably set to reduce sufficiently the
recalcitrance of the biomass to saccharification and/or
fermentation when it rapidly depressurizes into the flash vessel
70. The valve 110 controls the flow of the biomass into the flash
vessel 70. If desired, the biomass may be cooled by passing it
through a heat exchanger 120.
[0053] Depending on the biomass that is being used with treatment
system 10, it may be preferable to precondition the biomass before
it enters the pipe reactor 30. In such a case it may be preferable
to first have the biomass pass through a counter current splash
vessel 90 as shown in FIG. 1.
[0054] In one embodiment, counter current splash vessel 90 with a
biomass output 92 and a biomass input 94 is provided in
communication with the input side 52 of the pump 50. The biomass
may be preconditioned in the counter current splash vessel 90 in
any way desirable prior to entering the pump 50. For example, the
biomass may be heated or pressurized prior to entering the pump 50.
In addition, water or steam could be added to the biomass to
hydrate it. Furthermore, other additives, such as reagents or
enzymes, could be added to the biomass prior to the biomass
entering the pump 50. Such reagents or enzymes may be injected, for
example, through an injection port 56. While the counter current
splash vessel is one place where the biomass may be preconditioned,
the biomass may be preconditioned by any number of methods prior to
entering the pump 50. In addition, heat, steam, or additives can be
added anywhere along the biomass path through the treatment system
10. Alternatively, instead of adding steam into the system 10 to
heat the biomass, the biomass within system 10 may be heated using,
for example, a steam jacket or other suitable means, to avoid
dilution to the biomass.
[0055] In order to add steam to the biomass in the counter current
splash vessel 90, the counter current splash vessel 90 may have a
steam input 96. The steam input 96 injects steam near the bottom of
the counter current splash vessel 90 so the steam will flow
upwards. The upward flowing steam is used to pre-heat the biomass
flowing downward from the biomass input 94 before it enters the
pump 50.
[0056] Preferably, a counter current splash vessel 90 further
comprises a steam vent 98 to vent the steam injected through steam
input 96. The steam vent 98 prevents pressure from building up in
the counter current splash vessel 90 and thereby allows steam to be
continuously injected into the counter current splash vessel 90. In
addition, steam vent 98 is preferably located proximately near the
top of the counter current splash vessel 90 to enable the upward,
counter current flow of steam from the bottom to the top of the
vessel.
[0057] In a preferred embodiment, the steam that is injected into
the counter current splash vessel 90 may be recycled from the flash
vessel 70. When the biomass enters the flash vessel 70 a rapid
depressurization of the biomass occurs. Heated steam is a
by-product of the rapid depressurization. In order to make the
treatment system 10 more efficient, one embodiment of the flash
vessel 70 may have a steam output 76 to allow the steam that is a
by-product of the rapid depressurization to be recycled. The
recycled steam may be transferred from the steam output 76 of the
flash vessel 70 and injected into the steam input 96 of the counter
current splash vessel 90.
[0058] As shown in FIG. 1, a single counter current splash vessel
90 is depicted. While only a single counter current splash vessel
90 is shown, any number of counter current splash vessels can be
used. For example, more than one counter current splash vessel may
be used in series. In such an embodiment, the biomass output 92 of
each counter current splash vessel 90 may be in communication with
the biomass input 94 of the next counter current splash vessel 90.
The biomass output 92 of the final counter current splash vessel 90
in the series is connected to the input side 52 of the pump 50.
FIG. 2 illustrates one possible embodiment with multiple counter
current splash vessels 90.
[0059] The advantages of having additional counter current splash
vessels 90 includes allowing staged pre-heating of the biomass
before it enters the pump 50. For example, when more than one
counter current splash vessel 90 is used, it may also be preferable
to use more than one flash vessel 70 in conjunction. The more
stages over which the pressure within the pipe reactor 30 is
released to atmosphere, the less severe the let down and the less
wear that will occur on the interior of each of the flash vessels
70. The steam from each of the flash vessels 70 in series may be
recycled by connecting their respective steam output 76 with the
steam input 96 of one of the counter current splash vessels 90 in a
counter current manner as shown in FIG. 2. The treatment system 10
shown in FIG. 2 also permits the temperature of the biomass to be
increased in stages corresponding to each splash vessel 90, or
three stages in the illustrated embodiment. As a result, a more
controlled pre-heat may be performed to minimize likelihood that
the biomass will be over heated or that the hemicellulose contained
therein will be turned to inhibitory furfurals.
[0060] The counter current splash vessel 90, or series of vessels
90 or other biomass input reservoir, should be arranged to provide
a continuous supply of biomass ready to be pumped into the pipe
reactor 30. In order to pump the biomass into the pipe reactor 30
the treatment system preferably has a pump 50 with input side 52
and an output side 54.
[0061] A high solids content biomass slurry enters the input side
52 of the pump 50 and is pumped out of the output side 54 of the
pump 50 preferably at a reaction pressure. The output side 54 of
the pump 50 is in communication with the input end 32 of the pipe
reactor 30. The biomass is pumped from the input side 52 of the
pump 50, through the pump and into the input end 32 of the pipe
reactor 30.
[0062] The pump 50 is preferably designed to handle slurries with
high solids content, such as pastes or sludge, at high pressures,
and high temperatures. Preferably, pump 50 is capable of pumping
slurries with 50 to 90% solids by mass, more preferably 60 to 80%
by mass, at pressures in the range of about 350 to 450 pounds per
square inch, and at temperatures in the range of about 120 to
220.degree. C.
[0063] Using a pump 50 with the foregoing characteristics allows
the pump 50 to elevate the biomass to the desired reaction pressure
on the output side 54 of the pump 50. By incorporating a pump 50
that can elevate the biomass to the reaction pressure, batch
processing may be eliminated and the pump 50 may continuously feed
the biomass into the pipe reactor 30. Continuous processing is
advantageous because it saves time and is therefore more
economically viable for large scale, low cost processing of
biomass. In addition, continuous processing avoids pressure swings
as described previously.
[0064] The pump 50 is preferably a positive displacement pump;
however, the pump 50 may be any type of pump that can pump a slurry
of biomass with high solids content under high pressure and high
temperature. For example, the pump 50 may be a piston pump, a
piston diaphragm pump, a positive displacement rotary pump
including internal or external gears, or a screw pump. Preferably
pump 50 is a GEHO.RTM. pump by Weir Minerals, 2701 South Stoughton
Road Madison, Wis. 53716. Alternatively, pump 50 is preferably a
pump manufactured by Moyno, Inc 1895 W. Jefferson Springfield, Ohio
45506 suitable for slurries with high solids, such as the
MOYNO.RTM. 2000 HS System pump.
[0065] In operation, the pump 50 may serve to help control the flow
rate of biomass through the pipe reactor 30. By continuously
pumping biomass into the input end 32 of the pipe reactor 30,
biomass will be forced through the pipe reactor 30. The pump 50 may
increase the flow of biomass through the pipe reactor 30 by pumping
more biomass into the pipe reactor 30 and thereby increasing the
pressure in the pipe reactor 30.
[0066] Once the biomass leaves the pump 50, preferably at the
reaction pressure, the biomass must be raised to the desired
reaction temperature. The treatment system 10 elevates the biomass
to the reaction temperature by passing the biomass through pipe
reactor 30.
[0067] A pipe reactor is employed to raise the temperature of the
biomass to its reaction temperature because such reactors may be
easily and economically scaled. Existing reactor designs for
pretreating lignocellulosic biomass in advance of the
saccharification and fermentation steps of the conversion process
are complicated and incorporate rotating parts such as stirring
augers. The use of a pipe reactor 30 allows the treatment system 10
to employ a simple and straightforward design that is easy to scale
because, in part, it does not incorporate a complex seal. These
advantages allow a pipe reactor of substantial size to be
constructed with less capital than a more complex reactor design.
Furthermore, the safety concerns and down times associated with
maintenance of complicated pressure seals is eliminated when using
a pipe reactor.
[0068] While pipe reactor 30 is preferably a cylindrical pipe, pipe
reactor 30 may be any shape tube, conduit, or hollow body capable
of biomass transfer. Cylindrical pipe is preferable because a
majority of pipe is manufactured in a cylindrical shape and
therefore, cylindrical pipe is often cheap and readily
available.
[0069] The pipe reactor 30 has an interior 36 and an exterior 38.
As the biomass passes through the interior of the pipe reactor 30,
processing heat may be added to raise the biomass to the desired
reaction temperature. Additional process heat may be added to the
biomass through a number of methods, including heating the exterior
of the pipe reactor 30, injecting steam from a steam source 42 into
the interior of pipe reactor 30 through a steam injection port,
such as steam injection port 40, or by any other suitable method of
adding energy. In the embodiment shown in FIG. 1, pipe reactor 30
contains a single steam injection port 40. However, a plurality of
steam inputs may be used.
[0070] Once the biomass reaches the reaction temperature it may be
preferable to hold the biomass at that temperature for a period of
time. Because the biomass is continuously moving through the pipe
reactor 30, the volume of the pipe reactor 30 will need to be big
enough to accommodate the desired dwell time of the biomass at the
reaction temperature. The pipe length and diameter may be used as
design variables given a desired flow rate, reaction time, and
reaction temperature.
[0071] The pipe reactor 30 may be any length. However, preferably
the length of the pipe reactor is determined using the desired
retention time of the biomass in the pipe reactor 30. The desired
retention time can be divided by the constant flow rate of the
biomass through the pipe reactor 30 to estimate the preferable pipe
length. The retention time of the biomass in the pipe reactor 30 is
preferably short, in the range of about 1 to 30 minutes, and more
preferably in a range of between about 5 and 30 minutes.
Preferably, the retention time of the biomass in pipe reactor 30 is
as low as possible to achieve the desired pretreatment, but the
retention time should be at least sufficient to cause the biomass
to reach a desired reaction temperature. Reaction temperatures are
preferably between about 120-220 degrees Celsius. Short retention
times are preferred not only because they increase throughput and
improve the overall efficiency of the pretreatment process.
However, shorter retention times will also minimize the amount of
undesirable, and potentially inhibitory, side products, such as
furfurals, that are formed within the biomass.
[0072] Preheating the biomass in splash vessel 90 will also reduce
the necessary retention time in pipe reactor 30 and the amount of
energy required to be input into the pipe reactor 30.
[0073] Although as shown in FIG. 1, pipe reactor 30 is shown
disposed in a vertical orientation, and preferably in final form
the pipe reactor may be vertical, the pipe reactor can be in any
orientation or conceivable angle including horizontal. The vertical
orientation may be preferable because it allows for gravity to
assist in the flow of the biomass through the pipe reactor 30.
[0074] As the biomass leaves the pipe reactor at high pressure, it
enters a low pressure flash vessel 70. In order to control the flow
of the biomass from the pipe reactor 30 into the flash vessel 70,
and to separate the pressure regions, a valve 110 is incorporated
in the treatment system 10. The pipe reactor 30 has an output end
34 that is in communication with a valve 110 at the valve input
112. The valve 110 is preferably a choke valve, but other valves
that are suitable for handling slurries with high solids content
(such as a paste or sludge) at high temperatures and that may also
handle high pressure drops may also be used.
[0075] In operation, the valve 110, along with the pump 50, is used
to control the flow rate of the biomass through the pipe reactor
30. Preferably, the valve 110 is adjustable to control the rate of
biomass flow through the pipe reactor 30 and into the flash vessel
70 and to control the pressure in the pipe reactor 30. A choke
valve is preferably used because such valves can control the flow
rate of the biomass more linearly while maintaining the pressure
difference across the valve interface. In addition, choke valves
are less dependant on changes in fluid viscosity. These advantages
allow the choke valve to better control the flow of the biomass
through the pipe reactor 30.
[0076] As noted, choke valves are preferable because they are
designed to maintain a pressure drop across the valve interface.
The valve 110 is the interface between the higher pressure upstream
flow, as the biomass leaves the pipe reactor 30, and the lower
pressure down stream flow, as the biomass enters the flash vessel
70. Therefore, it is preferable to use a choke valve because it can
maintain the pressure difference across the valve interface.
[0077] In addition to a more linear flow and the ability to
maintain a pressure differential, choke valves are preferable
because they are less susceptible to damage than other valve
designs when limiting flow. For example, as a ball valve begins to
close, the area of the pipe is effectively narrowed and because of
the Bernoulli principle, the biomass will begin to flow faster
through the valve. As the high solids content slurry of biomass
rushes through the opening in the ball valve at a higher velocity,
the edges of the valve may be damaged, eventually ruining the ball
valve. Because of the design of the choke valve, it is not as
susceptible to the same type of damage during valve adjustment.
[0078] As the biomass flows out of the valve 110 through the valve
output 114 the biomass enters the flash vessel 70. The flash vessel
70 has an input 72 that is in communication with the valve output
114. As the biomass leaves the pipe reactor 30 and enters the flash
vessel 70 through the valve 110, a pressure drop occurs. When the
biomass has been maintained at the necessary reaction pressure and
reaction temperature for the required period in the pipe reactor
30, the structure of the organic polymer fibers in the biomass is
susceptible to being expanded or exploded as a result of the rapid
pressure drop. The rapid pressure drop thus causes the steam
trapped in the biomass to rapidly expand and disrupt the polymer
network of cellulose, hemicellulose, and lignin forming the biomass
structure, thereby reducing the recalcitrance of the biomass to
enzymatic saccharification of the cellulose and/or hemicellulose,
contained therein. In some implementations, it may be desirable to
carry out the process at a sufficiently high temperature to cause
the hydrolysis of at least some, if not all, of the hemicellulose
contained in the biomass feedstock. By contrast, in other
embodiments, it may desirable to use a reaction temperature,
pressure, and retention time that ensures the majority of the
hemicellulose, if not all of the hemicellulose, will be retained in
the pretreated biomass following discharge from pipe reactor
30.
[0079] In one embodiment, the flash vessel 70 may comprise a
pressure let down cyclone. The flash vessel 70 may also be equipped
with an auger to facilitate removal of the pretreated biomass from
the bottom of the flash vessel. If a pressure let down cyclone is
used as the flash vessel 70, it may similarly be equipped with an
auger to facilitate material removal.
[0080] According to a further embodiment, the treatment system 10
may further comprise a second pump 50, pipe reactor 30, valve 110,
and flash vessel 110 in series with the first pump 50, pipe reactor
30, valve 110, and flash vessel 110 to form a two-stage system.
This arrangement may be used to permit the removal of hemicellulose
from the lignocellulosic biomass between the first and second
stages. Further, the first stage of the process may be carried out
at generally lower temperatures and longer dwell times, to limit
the formation of side products such as furfurals.
[0081] As shown in FIG. 1 a single valve 110 and a single flash
vessel 70 are depicted. If only a single valve 110 and a single
flash vessel are used, the pressure drop between the pipe reactor
30 and the flash vessel 70 may be quite severe. For example, if
only a single flash vessel is used, the biomass may be going from
the reaction pressure within the pipe reactor 30, back to
atmospheric pressure all at once. If the pressure drop is too
severe, the expanding biomass may damage the interior of the flash
vessel 70. Therefore, in certain embodiments, it may be desirable
to use a plurality of pressure let down stages disposed in series,
wherein each pressure let down stage comprises a valve 110 and
flash vessel 70 so that each valve 110 and flash vessel 70 of a let
down stage is disposed in series with a valve 110 and flash vessel
70 of another let down stage. In this manner, the pressure drop
between each let down stage may be controlled to a desired level
while still exposing the biomass to a sufficient pressure drop
across each valve 110 to sufficiently alter the structure (and
possibly the composition) of the biomass and thereby reduce its
recalcitrance.
[0082] In an embodiment with multiple pressure let down stages, the
input 112 of each additional valve 110 used in the treatment system
10 may be in communication with the output opening 74 of the flash
vessel 70 of the previous let down stage. Further, the input
opening 72 of each additional flash vessel 70 may be connected to
the output 114 of the valve 110 in its let down stage. In this way,
any desired number of valves 110 and flash vessels 70 may be used
in series. In the embodiment shown in FIG. 2, three let down stages
in series are employed.
[0083] The more valves 110 and flash vessels 70 that are used, the
less severe the pressure drop becomes into any individual flash
vessel 70. However, if the pressure drop is not large enough the
crystalline structure of the biomass may not be sufficiently
disorganized to allow efficient post processing of the biomass into
fossil fuel alternatives. In other words, the recalcitrance of the
biomass to saccharification of the cellulose and/or hemicellulose
contained therein may not be sufficiently reduced.
[0084] As mentioned above with respect to the counter current
splash vessel 90, additives may be injected into the biomass to
increase the effectiveness of the treatment system 10 on the
biomass. In one embodiment of the invention, the pump 50 may
further comprise a port 56 to allow reagents to be injected into
the biomass on the suction side of the pump 50. The reagents may be
any substance that enhances the reaction, including alkalines,
acids, buffers or solvents. Alkaline reagents may be used, for
example, to prevent acids from forming during the treatment process
or to solubulize the lignin in the biomass. In general, any
alkaline reagent that reduces the pH but does not adversely react
with the biomass may be used. By way of non-limiting example,
specific reagents that may be used advantageously in the treatment
system 10 include sodium hydroxide, sodium sulphite, lime, ethanol,
sulfur dioxide, and carbon dioxide.
[0085] After the biomass has passed through the pipe reactor 30 and
into the flash vessel 70, the biomass is at an elevated
temperature. Therefore, it may be preferable to cool the biomass
after it leaves the flash vessel 70. In one embodiment, the
treatment system 10 may further comprise a heat exchanger 120. The
heat exchanger 120 is in communication with the biomass output 74
of the flash vessel 70. The heat exchanger may be of a shell or
tube type design but may also be any type of heat exchanger that
allows for proper cooling of the biomass.
[0086] FIG. 2 illustrates a counter current heat recovery system
for a continuous biomass treatment system 10 comprising a plurality
of flash vessels 70 and a plurality of counter current splash
vessels 90. In particular, as shown in FIG. 2, counter current
splash vessel 90C may be connected in series with a second counter
current splash vessel 90B which may be connected in series with a
third counter current splash vessel 90A. The biomass enters counter
current splash vessel 90C at a biomass input 94. The biomass flows
through counter current splash vessel 90C and into counter current
splash vessel 90B and continues into counter current splash vessel
90A where it eventually leaves through a biomass output 92 and into
the pump 50.
[0087] The use of more than one counter current splash vessel 90 as
shown in FIG. 2 allows for staged pre-heating with the temperature
in each stage increasing. This is advantageous, as it potentially
allows the dwell time of the biomass at higher temperatures to be
reduced, thereby potentially limiting undesirable side products
from being formed. Using a plurality of splash vessels 90 in series
will also permit the staged increase in the pressure of the biomass
in the treatment system 10 before it enters the pump 50. For
example, a two-stage pump (not shown) may be used between the
splash vessels to generate a pressure differential between counter
current splash vessel 90C and counter current splash vessel 90B.
The two stage pump may be used to maintain the pressure difference
and keep the flow of biomass moving. Similarly, if a pressure
difference is desired between counter current splash vessel 90B and
counter current splash vessel 90A, a two-stage pump (not shown) may
be installed between them for the same reasons.
[0088] More than one pressure let down stage, wherein each let down
stage comprises a valve 110 and flash vessel 70, may also be used
in treatment system 10. In the embodiment shown in FIG. 2, the
treatment system 10 includes three pressure let down stages. In
particular, pipe reactor 30 is in communication with a first valve
110A of the first stage at an input 112, which is in turn connected
in series to a first flash vessel 70A in the first stage. Flash
vessel 70A is connected to a second valve 110B in the second
pressure let down stage, which is in turn in communication with a
second flash vessel 70B in the second stage. Flash vessel 70B is
then in communication with a third valve 110C in the third let down
stage, which is in communication with a third flash vessel 70C in
the third stage. The biomass leaves the pipe reactor 30 and flows
through the first valve 110A and into the first flash vessel 70A.
The biomass continues on through the second valve 110B and into the
second flash vessel 70B. The biomass continues further through the
third valve 110C and into the third flash vessel 70C.
[0089] While three counter current splash vessels 90, three valves
110, and three flash vessels 70 are shown in series in FIG. 2, and
preferably two to three may be used, any number of counter current
splash vessels 90, valves 110, and flash vessels 70 may be
used.
[0090] It is advantageous, but not required, to match the number of
flash vessels 70 with the number of counter current splash vessels
90 for the purposes of steam recovery. As shown in FIG. 2, steam
may be recovered from flash vessel 70A through a steam output 76
and injected to pre-heat the biomass in the counter current splash
vessel 90A. Similarly, steam may be recovered from flash vessel 70B
to pre-heat the biomass in counter current splash vessel 90B and
steam may be recovered from flash vessel 70C to pre-heat the
biomass in counter current splash vessel 90C.
[0091] Steam recovered from the first flash vessel 70A, after the
pipe reactor 30, should preferably be used to pre-heat the biomass
in the first counter current splash vessel 90A, before the pipe
reactor 30. This is preferred because the pressure and temperature
is preferably increasing with each counter current splash vessel in
series as the biomass approaches the pipe reactor and the pressure
and temperature is decreasing with each flash vessel in series as
the biomass leaves the pipe reactor 30. By matching the steam
recovery of the flash vessels 70 in series, as they proceed
downstream from the pipe reactor 30, with the counter current
splash vessels 90, as they proceed upstream away from the pipe
reactor 30, the pressures of the connected vessels may be more
closely matched.
[0092] FIG. 3 illustrates a cross sectional view of a choke valve
of the present invention. As shown in FIG. 3, choke valve 200 may
comprise an input 212, an output 214 and a means to control the
rate of flow of the biomass 216. When used as an element of
treatment system 10, the choke valve input 212 may be in
communication with the pipe reactor 30 at the output end 34. The
choke valve output 214 may be in communication with the flash
vessel 70 input opening 72.
[0093] In operation, the high pressure, high solids content biomass
slurry enters the choke valve 200 through the input 212 and exits
to a lower pressure flash vessel 70. The choke valve 200 may have a
biomass flow control means 216 to control the flow rate of the
biomass through the choke valve 200. This allows the choke valve
200 to regulate pressure and flow rate in the upstream pipe reactor
30.
[0094] FIG. 4 illustrates a cross sectional view of an embodiment
of a counter current splash vessel. As shown in FIG. 4, counter
current splash vessel 90 may comprise a biomass input 94 and a
biomass output 92. Counter current splash vessel 90 may further
comprise a steam input 96, a steam vent 98, and baffles 102. In one
embodiment of a counter current splash vessel 90, heat in the form
of steam may flow in the opposite direction from the flow of the
biomass being heated. Biomass enters the counter current splash
vessel 90 through a biomass input 94 and flows downward towards the
biomass output 92. The steam is injected at the steam input 96 and
flows up towards the steam vent 98, in the opposite direction of
the downward flowing biomass.
[0095] In one embodiment, as shown in FIG. 4, baffles 102 may be
disposed on the inside of the counter current splash vessel 90 to
aid in the heat transfer process. Baffles increase the mixing of
the downward flowing biomass by directing biomass through the path
of the upwardly flowing steam. The use of baffles inside the
counter current splash vessel 90 may increases the efficiency of
the heat transfer between the steam and the biomass.
[0096] In order to better retain the heat within each counter
current splash vessel 90 and therefore within the biomass, each
counter current splash vessel 90 may be insulated with any suitable
material. Further, in order to protect the interior walls of each
splash vessel 90 from erosion due to the moving biomass and added
reagents, if any, the walls of each splash vessel 90 are preferably
lined with bricks to form a brick liner 104. Lining the walls of
splash vessel 90 with brick liner 104 made from refractory bricks
is also advantageous as it will permit each splash vessel 90 to be
constructed out of mild steel as opposed to an expensive alloy
material, which will lower the cost of the splash vessels
considerably. The brick lining 104 will protect the mild steel
construction and may be readily maintained using techniques known
in the art. Likewise, the interior surfaces of the pipe reactor 30
and each flash vessel 70 are preferably lined with brick to form a
brick liner 104, thereby allowing mild steel to be used as the
construction material for these components of the treatment system
10 as well.
[0097] FIG. 5A illustrates a view down the axis of an embodiment of
a pipe reactor containing a static mixer 31. The use of a static
mixer 31 is preferable because the mixer can provide mixing without
requiring complex seals between the interior 36 and exterior 38 of
the pipe reactor 30. A static mixer 31 can be used in combination
with the pipe reactor 30 to increase the efficiency of the heat
transfer to the biomass as it passes through the pipe reactor 30.
Mixing is accomplished by disturbing the flow of biomass in the
radial direction so that the biomass material near the interior
wall 36 of the pipe reactor 30 and the biomass material along the
center axis of the pipe reactor 30 reach equilibrium.
[0098] As shown in FIG. 5A, the static mixer 31 is disposed on the
interior 36 of the pipe reactor 30. Preferably the static mixer 31
may be welded to the in interior 36 of the pipe reactor 30;
however, the static mixer 31 can be brazed, tacked, press fitted or
affixed by any other manner that provides sufficient rigidity.
[0099] The static mixer 31 of the embodiment shown in FIG. 5A has a
circular member at its center with protruding members spaced at 120
degrees. However, the static mixer 31 can have any shape suitable
for facilitating the mixing of high solid content slurries. For
example, the static mixer 31 can comprise a single mixing bar
spanning the interior of pipe reactor 30 or it can comprise a more
complex mixing element as shown in FIG. 5A or some of the other
embodiments described below.
[0100] FIG. 5B illustrates a view down the axis of an embodiment of
a pipe reactor 30 that includes an alternative embodiment of a
static mixer 30. As shown in FIG. 5B, static mixer 31 comprises a
plurality of mixer bars 31A and 31B. While FIG. 5B illustrates only
two mixer bars, any number of mixer bars may be used.
[0101] FIG. 5C illustrates an exterior view of an embodiment of a
pipe reactor 30 containing a static mixer 31 comprising mixer bars
31A, 31B, and 31C. As shown in FIG. 5C, mixing bars 31A, 31B, and
31C are radially rotated with respect to each other. In the present
embodiment, each mixing bar is rotated by 90 degrees from the
previous mixing bar in the pipe reactor 30. However, other angles
may also be used.
[0102] The mixer bars 31A, 31B, and 31C of static mixer 31 may be
fixed to the pipe reactor 30 in a variety of ways, including by
extending through a hole in the pipe reactor 30 so that the mixing
bars 31 may be affixed from the exterior 38 of the pipe reactor 30.
An advantage to passing the bars through the pipe reactor 30 is
that the bars may be welded or affixed in place from the outside of
the pipe reactor.
[0103] FIG. 5D illustrates a cross sectional view of an embodiment
of a pipe reactor with a static mixer 31 that is slidably inserted
into the interior of the pipe reactor. Rather than being affixed to
the walls of the pipe reactor, the static mixer 31 may just be
contained within it. As shown in FIG. 5D, the static mixer 31
comprises a long bar that runs along the axis of the pipe reactor
30 with mixer bars extending out radially along the length of the
static mixer 31. While a particular static mixer 31 shape is shown
in FIG. 5D, the shape of the static mixer 31 can very greatly. For
example, the static mixer 31 could have less or more radial mixer
bars. The static mixer 31 could also have a more complex cross
sectional design. For example, the static mixer 31 could have the
cross-sectional design shown in FIG. 5A running along the length of
the axis of pipe reactor 30. Alternatively, the static mixer 31 may
comprise a helical static mixer such as illustrated in FIG. 8 or a
grid-type static mixer 31 such as illustrated in FIG. 9. Other
static mixers that are suitable for mixing high solids slurries may
also be used.
[0104] FIG. 6 illustrates a schematic of a continuous biomass
treatment method. In step 300, a biomass slurry is pumped with a
pump into a pipe reactor at a reaction pressure, wherein the pipe
reactor does not have a mixing component that passes from the
interior to the exterior and rotates with respect to the pipe. In
step 302, the biomass within the pipe reactor is heated to a
desired reaction temperature, preferably by the injection of steam
into the pipe reactor. In other embodiments, the biomass within the
pipe reactor may be heated by another means, such as by a steam
jacket. In step 304 the heated biomass is ejected from the pipe
reactor through a valve into a flash vessel to rapidly depressurize
the biomass. In step 306, a constant flow rate is maintained
through the pipe reactor, wherein the biomass reaches the reaction
temperature before exiting the pipe reactor. Preferably the biomass
reaches the reaction temperature by continuously performing the
pumping, heating, and ejecting steps.
[0105] FIG. 7 illustrates an alternative continuous biomass
treatment method. In step 400, a biomass slurry is pumped into a
pipe reactor at a reaction pressure wherein the pipe reactor has no
motor driven stirring method and wherein the pipe reactor has a
plurality of sealable openings for flowing biomass and steam. In
step 402, the biomass is heated within the pipe reactor to a
desired reaction temperature, preferably by injecting steam into
the pipe reactor. In step 404, the heated biomass is ejected from
the pipe reactor through a valve into at least one flash vessel to
rapidly depressurize the biomass. In step 406, a constant flow is
maintained through the pipe reactor, wherein the biomass reaches
the reaction temperature before exiting the pipe reactor.
Preferably the biomass reaches the reaction temperature by
continuously performing the pumping, heating, and ejecting
steps.
[0106] The foregoing description of the preferred embodiment of the
invention has been presented for the purpose of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many modifications and
variations are possible in light of the above teachings. It is
intended that the scope of the invention not be limited by this
detailed description, but by the claims and the equivalents to the
claims that are appended hereto.
* * * * *