U.S. patent application number 13/536572 was filed with the patent office on 2013-04-25 for method for the torrefaction of lignocellulosic material.
This patent application is currently assigned to ANDRITZ INC.. The applicant listed for this patent is Andrew EYER, Brian F. GREENWOOD, Joseph Monroe RAWLS, Bertil STROMBERG. Invention is credited to Andrew EYER, Brian F. GREENWOOD, Joseph Monroe RAWLS, Bertil STROMBERG.
Application Number | 20130098751 13/536572 |
Document ID | / |
Family ID | 48135071 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130098751 |
Kind Code |
A1 |
EYER; Andrew ; et
al. |
April 25, 2013 |
METHOD FOR THE TORREFACTION OF LIGNOCELLULOSIC MATERIAL
Abstract
A method for torrefaction of lignocellulosic biomass comprising:
continuously feeding the biomass to an upper inlet to the
torrefaction reactor vessel such that the biomass material is
deposited on an upper tray assembly of tray assemblies stacked
vertically within the reactor; as the biomass moves over each tray
assembly, heating and drying the biomass material with a
non-oxidizing gas under a pressure of at least 3 bar gauge and at a
temperature of at least 200.degree. C.; cascading the biomass down
through the trays by passing the biomass through an opening in each
of the trays to deposit the biomass on the tray of the next lower
tray assembly; discharging torrefied biomass from a lower outlet of
the torrefaction reactor, and circulating gas extracted from the
reactor vessel back to the reactor.
Inventors: |
EYER; Andrew; (Gansevoort,
NY) ; STROMBERG; Bertil; (Diamond Point, NY) ;
RAWLS; Joseph Monroe; (Alpharetta, GA) ; GREENWOOD;
Brian F.; (Cumming, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EYER; Andrew
STROMBERG; Bertil
RAWLS; Joseph Monroe
GREENWOOD; Brian F. |
Gansevoort
Diamond Point
Alpharetta
Cumming |
NY
NY
GA
GA |
US
US
US
US |
|
|
Assignee: |
ANDRITZ INC.
Glens Falls
NY
|
Family ID: |
48135071 |
Appl. No.: |
13/536572 |
Filed: |
June 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61501900 |
Jun 28, 2011 |
|
|
|
61502116 |
Jun 28, 2011 |
|
|
|
Current U.S.
Class: |
201/2 ; 201/27;
201/34; 201/4 |
Current CPC
Class: |
Y02E 50/10 20130101;
Y02E 50/15 20130101; C10B 49/06 20130101; Y02E 50/14 20130101; C10B
53/02 20130101; Y02P 20/145 20151101; C10L 9/083 20130101 |
Class at
Publication: |
201/2 ; 201/34;
201/4; 201/27 |
International
Class: |
C10B 49/06 20060101
C10B049/06 |
Claims
1. A method for torrefaction of lignocellulosic biomass using a
torrefaction reactor vessel having stacked tray assemblies, the
method comprising: feeding the biomass to an upper inlet to the
torrefaction reactor vessel such that the biomass material is
deposited on an upper tray assembly of a plurality of tray
assemblies stacked vertically within the reactor; as the biomass
moves across each tray of the tray assembly, heating and drying the
biomass material with a gas injected into the vessel, wherein the
gas is substantially non-oxidizing of the biomass and is under a
pressure of at least 3 bar gauge and at a temperature of at least
200.degree. C., and cascading the biomass down through the trays by
passing the biomass through an opening in each of the trays to
deposit the biomass on the tray of the next lower tray assembly;
discharging torrefied biomass from a lower outlet of the
torrefaction reactor, and circulating gas extracted from the
reactor vessel back to the reactor.
2. The method of claim 1 wherein the gas includes a substantial
portion of a least one of superheated steam or nitrogen.
3. The method of claim 1 further comprising pressurizing the
biomass before the feeding of the biomass into the vessel with a
pressure transfer device.
4. The method of claim 1 wherein the trays of each of the tray
assemblies have a mesh, screen or have perforations, and the
heating and drying of the biomass includes passing the gas through
the biomass and the trays.
5. The method of claim 4 wherein the gas entering at least one of
the tray assemblies enters through a pipe at substantially a
similar elevation as an extraction pipe which extracts gases from
an immediately above tray assembly.
6. The method of claim 1 wherein each tray assembly includes a
rotating scraper device above the tray.
7. The method of claim 1 wherein gas injected into the vessel at
the tray assemblies for torrefaction is hotter than gas injected at
the tray assemblies for drying.
8. The method of claim 1 wherein a cooling zone for the biomass is
below an elevation of the vessel having the tray assemblies and
adjacent the lower outlet.
9. The method of claim 1 wherein the circulated gas is processed to
remove at least a portion of gaseous byproducts of the torrefaction
reaction.
10. The method of claim 1 wherein the gas is substantially
nitrogen.
11. The method of claim 1 wherein gases byproduct from the
torrefaction reaction in the vessel are circulated back to the
vessel.
12. The method of claim 1 wherein a total number of tray assemblies
in the vessel is in a range of 4 to 20, and a lower most tray of
the tray assemblies discharges the biomass to a pile of biomass in
the vessel.
13. The method of claim 1 wherein the torrefaction of the biomass
begins in the tray assemblies and is completed in a pile of the
biomass below the tray assemblies.
14. The method of claim 13 further comprising cooling the biomass
in a lower portion of the pile of the biomass adjacent the lower
outlet.
15. The method of claim 1 wherein the gas flow through the biomass
on each tray assembly is in a range of 2 to 4 per kg of biomass on
the tray.
16. The method of claim 1 wherein a height of the biomass on each
tray is between 150 and 1000 millimeters or greater than 1000
millimeters.
17. The method of claim 1 wherein the extracted gas extracted by
suction of a blower or compressor, and the extracted gas is
reheated and injected into one or more of the tray assemblies of
the reactor.
18. The method of claim 1 further comprising moving gases extracted
from one or more of the tray assemblies through a cyclone or filter
to remove particles from the gasses and feed the gases to a blower
or compressor.
19. The method of claim 1 further comprising moving gases extracted
from one or more of the tray assemblies through a condenser,
removing condensable by-products from the extracted gases, and a
blower or compressor.
20. The method of claim 1 wherein the gases extracted from at least
one of the tray assemblies is at least partially directed to a
treatment process or combustion process separate from the
vessel.
21. The method of claim 1 wherein gases extracted from one or more
of the tray assemblies, which have a high concentration of
torrefaction reaction byproduct compounds, is at least partially
directed to a treatment process or combustion process separate from
the vessel.
22. The method of claims 1 wherein gases extracted from one or more
of the tray assemblies are at least partially directed to a
treatment process or combustion process separate from the
vessel.
23. The method of claim 1 further comprising cooling the torrefied
biomass material by injecting a cooling gas into the vessel,
wherein the cooling gas is cooler by 10 to 30 degrees Celsius that
the gas injected into the torrefaction tray assemblies.
24. The method of claim 1 further comprising cooling the torrefied
biomass material by injecting a cooling gas which suppresses the
torrefaction reaction in the biomass.
Description
CROSS RELATED APPLICATION
[0001] This applications claims priority to U.S. Provisional Patent
Application Ser. No. 61/501,900 filed Jun. 28, 2011 and is related
to U.S. Provisional Patent Application Ser. No. 61/502,116 filed
Jun. 28, 2011. The entirety of these applications are incorporated
by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to methods for
torrefaction of biomass material such as lignocellulosic material
including wood and other biomass, and more particularly relates to
a pressurized reactor vessel for the torrefaction of such
material.
[0003] Torrefaction can be used to convert biomass, e.g., wood, to
an efficient fuel having increased energy density relative to the
input biomass. For example, wood generally contains hemicellulose,
cellulose and lignin. Torrefaction removes organic volatile
components from wood. Torrefaction may also depolymerize the long
polysaccharide chains of the hemicellulose portion of biomass and
produce a hydrophobic solid combustible fuel product with an
increased energy density (on a mass basis) and improved
grindability. Because torrefaction changes the chemical structure
of the biomass, torrefied biomass may be burned in coal fired
facilities (torrefied wood or biomass has the characteristics that
resemble those of low rank coals) and can be compacted to high
grade fuel pellets.
[0004] Torrefaction refers to the thermal treatment of biomass,
usually in an oxygen deprived atmosphere at relatively low
temperatures of 200 degrees Celsius (.degree. C.) to 400.degree.
C., or 200.degree. C. to 350.degree. C., or temperatures outside
the range used for the process known as pyrolysis. An oxygen
deprived atmosphere may have a low percentage of oxygen as compared
to the percentage of oxygen in atmospheric air. A torrefaction
process is described in related U.S. Provisional Patent Application
Ser. No. 61/235,114.
[0005] Unpressurized reactor vessels with multiple trays have been
used for torrefaction, as is described in U.S. Patent Application
Publication 2010/0083530 (the '530 application). The '530
application states that torrefaction should be performed in a
reactor vessel operating at atmospheric pressure. By stating that
it is advantageous to operate the vessel at atmospheric pressure,
the '530 application teaches that vessels should not be operated at
above-atmospheric pressures. See '530 application, para. 0061.
[0006] Pressurized reactor vessels with multiple trays have been
used in pulp mills to delignify pulp by oxidation. Examples of a
pulping reactor vessel with multiple trays are disclosed in U.S.
Pat. Nos. 3,742,735 ('735 patent) and 3,660,225 ('225 patent).
Multiple tray vessels allow pulp to cascade through the vertical
arrangement trays in the reactor. The trays allow the pulp to
cascade in discrete batches down through the vessel. An oxygen rich
environment in the pulping reactor promotes delignification and
bleaching of the pulp. The '735 patent and '225 patent do not
suggest using a pulping reactor vessel having an oxygen deprived
environment for torrefaction of wood or other biomass material.
BRIEF DESCRIPTION OF THE INVENTION
[0007] A difficulty with unpressurized reaction vessels is their
large size needed to handle the large volume of gas required to
transfer a given amount of heat to the material to be torrefied.
The mass of a gas per unit volume at atmospheric pressure is
substantially less than the mass of gas per unit volume at a
substantial pressure, such as above 20 bar gauge (290 psig). The
volumetric flow rate of the gas impacts the pressure drop in the
bed of material, piping, heat exchangers, and thus requires larger
equipment and higher energy consumption to perform the same heating
duty.
[0008] Pressurizing the gas increases the mass of the gas for a
given volumetric flow rate. As compared to an unpressurized vessel,
a pressurized reaction vessel may have a smaller volume due to the
use of compressed gas. The ability of a gas to transfer heat to a
biomass is proportional to the mass of the gas. The greater its
mass, the faster a gas can heat the biomass.
[0009] As is well known in the art, pressurized reaction vessels
require seals and other devices to keep the gas and materials in
the vessel under pressure. Similarly, pressure transfer devices are
required at the input to or in the feed systems for a pressurized
vessel to pressurize the material being fed to the vessel. Further,
pressurized reaction vessels require pressurized gases and conduits
for the pressurized gases.
[0010] A novel reaction vessel has been conceived for torrefaction
of biomass material having vertically stacked trays for drying and
heating biomass using an oxygen deprived hot gas under substantial
pressure. The stacked trays provide what amounts to as a moving bed
for the biomass, in a relatively compact vertical reactor vessel.
In addition, the vessel may be substantially smaller than a
reaction vessel for torrefaction performed at atmospheric pressure.
The oxygen deprived pressurized gas may be circulated through the
vessel and through pressurized conduits that reheat the gas.
[0011] The vessel uniformly heats through each tray such that the
material being torrefied is uniformly heated at each elevation in
the vessel. To achieve uniform heating of the material on each tray
the flow of oxygen deprived gas through the bed of material on each
tray is regulated in a range of 1 to 6 kilograms (kg) of gas per
kilogram of dry material being treated on the tray. The ratio of
flowing oxygen deprived gas to dry material through the bed of
material on each tray may be in another range, such as a range of 1
to 3.
[0012] The flow of the oxygen deprived gas through each of the
trays may be continuous. The oxygen deprived gas is need not be
totally devoid of oxygen. The gas is a heat transfer media that may
add or remove heat from the material undergoing torrefaction. The
gas flows through the material and the trays. The continuous flow
of oxygen deprived gas through the material in the tray heats the
material, provided that the gas is at a higher temperature than the
material. The constant flow of gas may also cool the material where
the torrefaction reaction, which is exothermic, causes the material
to become hotter than the gas. If the material overheats, the
torrefaction reaction may over-react. Accordingly, the continuous
flow of gas regulates the temperature of the material in each tray
to be about the same temperature as the gas.
[0013] The biomass material may have a total retention period for
all of the trays in the reactor vessel of 15 to 60 minutes. This
retention period may include trays in which the material undergoes
torrefaction and lower trays in which the material is cooled after
the reaction. The retention period in the reaction vessel may be
selected based on the material processed in the vessel. For
example, the total retention period in the vessel may be to 25
minutes for lignocellulose material, such as wood.
[0014] Each tray may have a pie-segment shaped opening through
which biomass material falls to the tray at the next lower
elevation in the vessel. The biomass material falls through the
opening after traveling around the vessel and on the tray. A
scraper may slide the material over the tray toward the opening.
The rotational speed of the scraper is selected to provide the
desired retention period on each tray. The retention period may be
uniform for each of the trays in the vessel. The retention period
may be selected based on the number of trays performing each of
drying, torrefaction and cooling (optionally) of the biomass, and
the period required to perform each of these processes.
[0015] A method has been conceived for torrefaction of biomass
using a torrefaction reactor vessel having stacked trays including:
feeding the biomass to an upper inlet of the vessel such that the
biomass material is deposited on an upper tray of a vertical stack
of trays in the reactor; as the biomass moves around the vessel on
each of the stacked trays, heating and drying the biomass material
with an oxygen deprived gas injected into the vessel under a
pressure of 3 to 20 bar; cascading the biomass down through the
trays by passing the biomass through an opening in each of the
trays to deposit the biomass on a lower tray; discharging torrefied
biomass from a lower outlet of the torrefaction reactor vessel, and
circulating extracted gas from a lower elevation of the reactor and
feeding the gas to an upper region of the vessel.
[0016] The oxygen deprived gas may include superheated steam,
nitrogen and other non-oxygen gases, or oxygen lean gases suitable
for the purpose of this invention. The biomass may be pressurized
before being fed to the vessel with a pressure transfer device. The
trays may be a mesh, screen or have perforations or slots and the
heating and drying of the biomass includes passing the gas through
the biomass and the trays. A scraper device may rotate to move the
biomass material across the tray in an arch-shaped path.
Alternatively, the trays may rotate while the scraper device and
biomass do not rotate about the vessel. The opening in each tray
may be a triangular shaped section extending from the shaft in the
vessel to the wall of the vessel.
[0017] The gas may be injected into the vessel at multiple
elevations wherein the gas is hotter when injected at a lower
elevation than the gas injected at an upper elevation. At an
elevation of the vessel below from which the gas is extracted, the
biomass may continue to cascade down through the trays.
[0018] A method for torrefaction of lignocellulosic biomass using a
torrefaction reactor vessel having stacked tray assemblies has been
conceived comprising: continuously feeding the biomass to an upper
inlet to the torrefaction reactor vessel such that the biomass
material is deposited on an upper tray assembly of a plurality of
tray assemblies stacked vertically within the reactor; as the
biomass moves in the vessel while supported by a tray of each tray
assembly, heating and drying the biomass material with a gas
injected into the vessel, wherein the gas is substantially
non-oxidizing of the biomass and is under a pressure of at least 3
bar gauge and at least a temperature in a range of 200.degree. C.
to 250.degree. C., and cascading the biomass down through the trays
by passing the biomass through an opening in each of the trays to
deposit the biomass on the tray of the next lower tray assembly;
discharging torrefied biomass from a lower outlet of the
torrefaction reactor, and circulating gas extracted from the
reactor vessel back to the reactor.
[0019] The trays of each of the tray assemblies have a mesh, screen
or have perforations, and the heating and drying of the biomass
includes passing the gas through the biomass and the trays. Any
holes or openings in the tray assemblies may be cover by a finer
mesh or screen material than the material used to form the tray
assemblies. The gas entering each tray assembly may pass through a
pipe at substantially a similar elevation as an extraction pipe
which extracts gases from an immediately above tray assembly. In
addition, each tray assembly may include a rotating scraper device
above the tray and an extraction gas chamber below the tray.
[0020] The gas injected into tray assemblies for torrefaction may
be hotter, e.g., by 5 to 60.degree. C., than the gas injected to
the tray assemblies for drying or cooling. Further, a void space,
below all of the tray assemblies, in the bottom of the vessel may
be a zone in which the biomass forms a pile. The void space may be
used to complete the torrefaction of the biomass and cool the
torrefied biomass before it is discharged from the vessel. The
cooling gas injected into the cooling zone may be cooler than the
gas injected to the cooling tray assemblies, wherein the cooling
zone cools the torrefied biomass to below a temperature at which
the biomass auto-combusts when exposed to the atmosphere and the
cooling tray assemblies cool the torrefied biomass to stop or
suppress the torrefaction reaction. It is possible for gas flows in
the void to flow concurrent or countercurrent to the flow of the
biomass material.
[0021] Gases extracted from the tray assemblies and the cooing zone
may be circulated back to the vessel by blowers or compressors. The
gases to be circulated may pass through a cyclone, condenser or
filter to separate particles and condensable byproducts before the
gas flows to the compressor or blower. The gases circulated back to
the torrefaction tray assemblies may be heated before being
injected to the torrefaction tray assemblies. A portion of the
gases extracted from the tray assemblies may be directed to a
combustor to generate heat energy to be added to the gases
circulated back to the torrefaction tray assemblies, or for other
process steps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a perspective view of the front and top of a
pressurized reactor treatment vessel in which the front wall of the
vessel has been removed to allow for illustration of the interior
components of the vessel.
[0023] FIG. 2 is a perspective view of the front and bottom of a
pressurized reactor treatment vessel in which the front wall of the
vessel has been removed to allow for illustration of the interior
components of the vessel.
[0024] FIG. 3 is a perspective view of a lower region of the
pressurized reactor treatment vessel which illustrates the support
legs and bottom discharge outlet of the vessel, and shows the
convergence section in the interior of the vessel.
[0025] FIG. 4 is a bottom-up view of the pressurized reactor
treatment vessel.
[0026] FIG. 5 is a side view of the pressurized reactor treatment
vessel, with a quarter section of the vessel removed for purposes
of illustration.
[0027] FIG. 6 is a perspective view of the top and side of the
pressurized reactor treatment vessel with a quarter-section of the
vessel removed for purposes of illustration.
[0028] FIG. 7 is a close-up view of a cross-section of a portion of
the pressurized reactor treatment vessel that illustrates a portion
of tray assemblies.
[0029] FIG. 8 perspective view of an open top of the pressurized
treatment vessel wherein the outer wall of the vessel is removed to
illustrate the components of the tray assemblies.
[0030] FIG. 9 is a top down view of an open top of the pressurized
treatment vessel.
[0031] FIG. 10 is a cross-sectional view of a portion of the
pressurized treatment vessel which illustrates the vertical shaft
and the lower support for the shaft.
[0032] FIG. 11 is a perspective view of a spoke wheel scraper
component of a tray assembly.
[0033] FIG. 11A is a schematic diagram of an enlarged portion of
the lower edge of one of the spokes or blades 60 of the scraper
device.
[0034] FIG. 12 is a perspective view of a tray and bottom plate of
a tray assembly.
[0035] FIG. 13 is a perspective view of the convergence section of
the pressurized reactor vessel.
[0036] FIG. 14 is an enlarged view of the convergence section to
show the screen allowing gas to be extracted from the section.
[0037] FIG. 15 is a schematic diagram of a tray assembly to
illustrate the gas flowing in and gas flowing out of the biomass on
the tray.
[0038] FIG. 15A is an enlarged view of a cross-section of a tray to
illustrate an exemplary slot, hole or opening in the tray.
[0039] FIGS. 16 to 18 are process flow diagrams showing exemplary
torrefaction processes using the pressurized reactor treatment
vessel.
DETAILED DESCRIPTION OF THE INVENTION
[0040] FIGS. 1 and 2 illustrate a pressurized treatment vessel 10
for receiving, treating, drying and cooling biomass material from a
supply of biomass 12 through an upper inlet 14. The biomass may be
wood chips, wood pulp or other comminuted cellulosic material.
While moving over an upper series of drying tray assemblies 16 in
the vessel, the biomass is dried. In addition or alternatively, the
biomass may be dried prior to being introduced into the vessel
10.
[0041] The upper inlet 14 to the pressurized vessel may be coupled
to a continuous feed, pressure isolation device, such as a
conventional rotary valve or plug screw feeder, to feed the biomass
into the pressurized vessel from a source of biomass at atmospheric
pressure. The vessel 10 operates in a gas phase in which the dried
biomass remains dry in the vessel.
[0042] The biomass may be fed to the inlet 14 to the vessel at a
temperature of ambient temperature or, if a dryer 21 preheats the
biomass, at 80.degree. C. to 120.degree. C., or higher, before
entering the vessel. The biomass is heated in the vessel by a
pressurized, hot and oxygen starved or deprived gas. The gases
entering the vessel may be at a temperature in a range of
200.degree. C. to 600.degree. C. and may particularly be in any of
the ranges of 250.degree. C. to 400.degree. C., 250.degree. C. to
300.degree. C., and 300.degree. C. to 380.degree. C.
[0043] The biomass enters the pressure treatment vessel through the
upper inlet 14, which may be a single inlet orifice or an array of
inlet orifices in the top or upper portion of the vessel. The
biomass may have been previously dried before entering the vessel
or the biomass may be dried in an optional drying zone (trays) 15
in an upper region of the vessel. Below the drying zone, the
biomass enters a torrefaction zone 41 (trays and optionally a
chamber below the trays).
[0044] Immediately below the upper inlet in the vessel 10 may be a
chute that receives the biomass from the inlet and directs the
biomass to a trailing section portion of the upper tray of a drying
tray assembly 16. The trailing section is adjacent a discharge
opening 64 (FIG. 12) in the upper tray. The biomass falls on the
trailing section of the tray and is moved in an arc path across the
tray until the biomass passes over leading edge of the opening to
the tray and falls to the trailing section of the next lower tray.
The trailing section is a region of the tray furthermost from the
opening in the tray with respect to the path of the biomass on the
tray. Depositing the biomass on the trailing section of the tray
ensures that biomass entering the vessel is retained on the upper
tray for nearly a full rotational period of the tray.
[0045] The open sections 64 (also referred to as "openings") of
each tray preferably are not vertically aligned with the openings
64 in the trays immediately above and below the tray. If the
openings were vertically aligned, the biomass may fall from one
open section and immediately through the open section in the
underlying tray without resting on the support surface of the
underlying tray.
[0046] The opening sections 64 may be vertically staggered such
that each opening is over a trailing region of the upper section of
the tray immediately below the opening. The trailing region of a
tray is adjacent and behind the open section in the direction of
rotation of the scraper device 56. By aligning an open section 64
above a trailing region on a lower tray, the biomass falls through
the open section and onto the trailing region. As the scraper
turns, the biomass slides across the entire upper surface of the
tray in an arc-shaped path from the trailing region to the opening
section. Maintaining the biomass on the upper surface of each tray
maximizes the retention period of the biomass on tray and, thus,
allows the biomass to be heated and dried (in an upper tray and
undergo torrefaction (in a lower tray).
[0047] Immediately below the optional drying tray assembly(ies) 16
are arranged one or more torrefaction tray assemblies 18 on which
the dried biomass material is subjected to conditions which cause
the torrefaction reaction. Below the torrefaction tray assemblies
are arranged optional cooling tray assembly(ies) 20. The structure
of each of the tray assemblies 16, 18 and 20 may be substantially
similar. Each tray assembly is effectively a moving bed on which
the biomass is exposed to a flow of the oxygen deprived gas.
[0048] The flow of heated gas into, through and from the pressure
reaction vessel may be configured to promote the flow of hot,
pressurized gases through the tray assemblies in the upper
elevations of the vessel where the biomass is being heated to the
desired temperature for torrefaction. As shown in FIG. 1, the hot
oxygen deprived gas may be injected into the upper section of the
vessel 10 through a top input manifold 86 and gas injection nozzles
34 arranged at the various elevations of the tray assemblies 16, 18
and 20 in the upper portion of the vessel.
[0049] The oxygen deprived gases flowing to multiple elevations in
the vessel may be at temperatures and compositions that vary for
each of the tray assemblies. For example, the hot gas 86 introduced
to the uppermost elevation of the vessel may be at a temperature
slightly, e.g., 10.degree. C. to 40.degree. C., hotter than the
temperature, e.g., 100.degree. C., of the dried biomass 12 being
fed to the vessel. The hot gases introduced at succeeding lower
elevations of the vessel may be increasingly hotter to be slightly
above the temperature of the biomass in the vessel that is
proximate to the injected hot gas. By injecting the gas at
temperatures slightly above the biomass being heated by the gas,
the efficiency of heating can be increased as compared to injecting
gas at a single temperature which may be substantially hotter than
the incoming biomass to the vessel. Alternatively, the gases
injected for drying and torrefaction may be at substantially
similar temperatures and compositions, and the gases for cooling
the biomass may be recirculated gases extracted from other cooler
elevations in the vessel. For example the exhaust gas from the
drying trays will be cooler than that from the torrefaction levels
and will be below temperatures required for torrefaction.
[0050] The number of tray assemblies for drying, torrefaction and
cooling may depend on various factors, including whether an
optional drying device 21 is used to dry the biomass before the
material enters the vessel 10, and the extent to which the
torrefaction and cooling zones 22, 24 or cooling screw 68 (FIG. 16)
are able to cool the biomass from a temperature at which the
torrefaction reaction occurs to a lower temperature at which
torrefaction is quenched.
[0051] By way of example, the total number of tray assemblies may
be a number (N) and in a range of 5 to 15. The number of drying
tray assemblies 16 (DTA) may be zero, one (such as shown in FIG.
16) or determined based on the following algorithm:
DTA=N*L, where L is in a range of 0.2 to 0.3.
[0052] The number of cooling tray assemblies 20 (CTA), if any, may
be two, such as is shown in FIG. 16, or determined based on the
following algorithm:
CTA=N-(N*M), where M is in a range of 0.7 to 0.8.
[0053] The number of torrefaction tray assemblies 16 (TTA) may be
greater than each of DTA and CTA, such as the four TTAs shown in
FIG. 16, or determined based on the following algorithm:
TTA=((N*L)+1)-((N*M)-1)
[0054] The number of tray assemblies in a vessel and the
proportions of drying, torrefaction and cooling tray assemblies
will depend on the design requirements for the vessel. For example,
the total number of tray assemblies in the vessel 10 may be in any
of the ranges of 4 to 20 and 6 to 15. The proportion of drying tray
assemblies and of cooling tray assemblies may each be in a range of
15 to 30 percent (%) of the total number of tray assemblies. The
proportion of tray assemblies for torrefaction may be in a range of
70 to 40% of the total number of tray assemblies. These ranges are
exemplary and do not define limits on the numbers of tray
assemblies. For example, the vessel may have no drying tray
assemblies and no cooling tray assemblies, and have all tray
assemblies for torrefaction.
[0055] The torrefaction reaction may occur in the middle tray
assemblies. The ranges of the middle tray assemblies where
torrefaction occurs may be any of 15 to 85%, 30 to 60% and 15 to
100% of the total number of tray assemblies. Where torrefaction
occurs is most or all of the tray assemblies, the drying of the
biomass may occur fully or partially in a dryer external to and
upstream of the vessel, and the optional cooling may occur in the
pile of the torrefied biomass in a lower region of the vessel or in
a cooling screw near the discharge of the vessel.
[0056] The inlet nozzles and extraction nozzles are numbered in
FIG. 16 according to their corresponding tray assemblies. The top
tray assembly 16 receives hot oxygen deprived gas from the top
inlet 86 that receives gas from a heat exchanger 84 or from gases
extracted from the cooling tray assembly or zone of the vessel
10.
[0057] The supply of biomass 12 may provide, such as lignocellulose
material that has been chipped or cut to have chip dimensions of a
length between 10 to 50 millimeters (mm), a width of 10 to 50 mm,
and a thickness of 5 to 20 mm. The chip thickness may be in other
ranges, such as 20 to 30 mm, 15 to 25 mm, and 3 to 10 mm. These
chip dimensions may be most suitable for wood. Other chip
dimensions may be suitable depending on the type of wood or the
non-wood material being used for the biomass.
[0058] Below the stack of tray assemblies 16, 18 and 20, the vessel
10 may have a torrefaction zone 22 and an optional lower cooling
zone 24. The torrefaction zone 22 and lower cooling zone 24 may be
hollow regions of the pressure reactor vessel below the lowest tray
20 and may span the lower one-half or lower two-thirds of the
height of the pressure vessel. The pressure vessel may have
dimensions, such as diameter and height, based on the desired
operational conditions, such as the composition of the biomass
material and the volumetric rate of biomass to flow through the
vessel. In general, for industrial scale units, the pressure vessel
may have a height of over 100 feet (33 meters) and a diameter of
over 9 feet (3 meters).
[0059] The lower cooling zone 24 of the pressure reactor vessel may
include a convergence section, such as one-dimensional convergence,
to provide uniform movement of the biomass through the bottom of
the vessel and to a bottom discharge port 26. The convergence
section may be a DIAMONDBACK.RTM. convergence section sold by the
Andritz Group and described in U.S. Pat. Nos. 5,500,083; 5,617,975
and 5,628,873.
[0060] The lower zone 24 of the pressure reactor vessel may be
maintained at a cooler temperature than the tray assemblies used
for torrefaction. The lower zone 24 may contain a pile of torrefied
biomass material which has been treated in the tray assemblies and
drop down into the lower zone.
[0061] The temperature in the lower zone 24 may be below
265.degree. C., 240.degree. C. or 200.degree. C., in addition or
alternatively, the temperature in the lower zone 24 may be at least
15.degree. C. to 40.degree. C. lower than the maximum temperature
of the hot gases entering the torrefaction tray assemblies. To
control and maintain the temperature in the lower zone cooling gas
may be inject to the upper section of the lower zone such as into
the injection nozzle 92 (FIG. 16) to provide cooling gas the flows
concurrently with the downward flow of biomass through the reactor
vessel. It may also be desirable for these gases to flow
counter-currently to the flow of the biomass, displacing the hot
contaminated gas entering with the biomass toward the top of the
pile. Alternatively, cooling gas may be injected in to a bottom
portion of the lower region through nozzles 94, which nozzles may
be part of a center pipe extending upwardly and axially through the
vessel. The cooling gas entering through nozzles 94 flows
cross-currently to the biomass flow. Further, cooling gas nozzles
94 may be arranged to provide a cross-current gas flow through the
vessel such that gas is injected at one side of the vessel and
extracted at an opposite side of the vessel. The injection and
extraction of cooling gases may occur at several elevations of the
lower zone 24. The temperature of the cooling gases injected into
the cooling tray assemblies and cooling zone may be controlled such
that the cooler cooling gasses enter lower elevations of the
vessel. The torrefied biomass material should be at a temperature
below that which the material with auto-combusted at the bottom of
the vessel or at least when passed through a pressure transition
device after which the biomass is exposed to the atmosphere.
[0062] As shown in FIGS. 3 and 4, the pressure reactor vessel may
be supported by support legs 28 extending vertically between the
vessel and the ground. The support legs elevate the bottom of the
vessel to allow for discharge devices to be mounted to the
discharge port 26 and below the vessel. Alternative support
structures may include a skirt arrangement or use of a support ring
located at some mid-point on the vessel above the DIAMONDBACK.RTM.
convergence section. Such as support ring would then be attached to
the building structure in some appropriate fashion.
[0063] The pressure vessel 10 may have an access and observation
port 30 which, when open, provides access to the cooling and
convergence zones of the vessel. The access and observation port is
generally closed during operation of the vessel. The observation
port may include a clear window to provide for viewing of the
interior of the vessel. Other observation ports, with clear windows
or sight glasses, may be located in the vessel at locations other
than at the access and observation port 30.
[0064] FIG. 5 is a cross-sectional diagram of the pressurized
treatment vessel 10. A vertical shaft 32 is coaxial with the vessel
and extends at least up through the tray assemblies 16, 18 and 20
in the vessel. An upper portion of the shaft 32 extends from the
top of the vessel and is rotationally driven by a motor and gear
assembly 33, which is fixed to the top of the vessel for torsion
support. The lower end of the shaft 32 may be supported by a
bearing and bracket assembly 35 that is below the lowermost tray in
the vessel. Similarly the upper end of the shaft is supported by a
bearing at the top of the vessel and associated with the gear and
motor assembly. A spadone journal 37 may rotatably couple the shaft
32 to the bearing and bracket assembly 35.
[0065] FIG. 6 is a perspective view of the top and side of the
vessel 10 with a quarter-section of the vessel removed for purposes
of illustration. The shaft 32 extends up beyond the top of the
vessel. A spline on the top end of the shaft fits into the motor
and gear assembly. A top plate 38 (FIG. 5) seals the top of the
vessel and provides a support for the shaft bearing and the motor
and gear assembly 33.
[0066] FIGS. 6 to 12 illustrate the structure and operation of the
tray assemblies 16, 18 and 20. The tray assemblies 16, 18 and 20
each include a horizontal tray 40 which may be perforated,
screened, meshed or otherwise structured to allow gases to pass
through the tray and block the passage of the biomass materials,
such as fibers. The tray 40 may be annular and extend radially from
the shaft 32 to the inside surface of the cylindrical wall 42 of
the vessel 10. The tray may also be horizontal and generally level.
The tray may be fixed to the vessel and not rotate with the shaft.
For example, the tray may be a perforated steel mesh arranged
horizontally and substantially covering the open area in the vessel
between the shaft 32 and the wall 42 of the vessel. Other materials
that may be used to form the tray 40 included steel plates
perforated by drilled or laser cut openings, slots or holes.
[0067] FIG. 15A is an enlarged view of a cross-section of a tray to
illustrate an exemplary slot, hole or opening 100 in the tray. As
the biomass moves over the surface of the tray in the direction of
flow arrow 102, gas flows down through the biomass and through the
opening to the gas passage 52 below the tray. The slot, hole or
opening may have a generally uniform cross section through the
tray. Alternatively and as shown in FIG. 15A, it 100 may have an
upper portion 104 that is generally uniform in cross section and a
lower portion 106 that expands in cross-sectional area in a
downward direction. The upper portion of the slot, hole or opening
100 may be 30 to 50 percent the thickness of the tray. Further, the
upper rim of the slot, hole or opening may be beveled 108, such as
at the trailing edge as shown in FIG. 15A. The bevel 108 assists in
avoiding fibers from the biomass being caught on the upper rim of
the slot, hole or opening, and especially on the trailing edge of
the rim. The slot, hole or opening may be covered with finer mesh
or screen material.
[0068] Immediately below the tray 40 is a solid annular bottom
plate 44 that forms a bottom to a gas passage 52 between the tray
40 and the plate 44. The gas passage is for gases drawn through the
biomass and tray to be exhausted to the extraction nozzles 36 that
are mounted to the wall 42 of the vessel at elevations
corresponding to the gas passage between the tray and bottom plate
44. Baffle plates 46, 48 and 50 may be mounted on the bottom plate
44 and extend upward through the gas passage to the tray 40. The
baffle plates direct gases towards the inlets to the extraction
nozzles 36. The baffle plates may include short 46 and long 48
radially extending plates, and a circular wall plate 50 that forms
and end wall for the gas passage. The long 48 radial plates divide
the gas passage into triangular shaped screen segments. By way of
example, each tray may have four to eight screen segments. In
addition to the tray 40 being formed of pie-shaped segments, the
plate 44 may also be pie-shaped segments and the long radial plates
48 may form sidewalls to each of these segments.
[0069] The baffle plates also provide support for the screen or
grating of the tray 40. The circular wall plate may have open slots
to allow gases to flow to the inlet to the extraction nozzle 36 and
to allow the pipe for the injection nozzle 34 to pass from the wall
of the vessel through the bottom plate 44 and open to the next
lower tray assembly.
[0070] The trays 40 may be supported by the inner surface of the
wall 42 of the pressurized treatment vessel 10. The wall 42 may
include hangers, ridges or other support surfaces on which rest the
outer rim of each tray. The trays may be removed, replaced and
repositioned in the vessel by opening the vessel and sliding the
trays in and out of the vessel.
[0071] Alternatively, the trays, rotating scrapers and shaft may be
constructed as a cartridge assembly and primarily supported from
the top head plate of the vessel. A cartridge assembly could be
inserted and removed from the vessel as a whole. Anti-rotation
clips or pieces may be affixed to the vessel walls for the purpose
of preventing the cartridge assembly from rotating within the
vessel.
[0072] The biomass flowing through the chute 116 drops into an
optional lower portion 80 of the vessel. The biomass may form a
pile in the lower portion which temporarily retains the biomass in
the lower portion. While in the pile, the biomass continues to
undergo the torrefaction reaction. The torrefied biomass is
discharged from an outlet 116.
[0073] As an alternative to a rotating scraper device, the trays
may rotate with the shaft. A stationary scraper device may be in a
fixed position and may include radial arms extending over the
tray.
[0074] The injection nozzles 34 may extend through the gas passage
and have an outlet 53 that extends through the bottom plate 44. The
outlet 53 discharges gas into the biomass passage 54 formed between
a bottom plate 44 of one tray assembly and the tray 40 of tray
assembly immediately below the bottom plate. The biomass passage is
a volume in the vessel 10 which receives the biomass. The number of
injection nozzles 34 for each tray may be uniform and selected
based on operational requirements of the vessel. The selection of
the number of the nozzles may be sufficient to provide uniform gas
flow, at a uniform flow distribution and gas temperature, through
the biomass material on the tray. For example, six to eight
injection nozzles may be used to provide uniform gas flow to each
tray.
[0075] The injection nozzles 34 may be configured to supply 1 to 4
kilograms (kg) of gas per kilogram of biomass on the tray. The
volume of gas supplied by the injection nozzles may also be in
ranges of 1 to 6 kg, 1 to 12 kg or 1 to 24 kg of gas to kg of
biomass.
[0076] The injection nozzle may be fabricated with the tray 40,
bottom plate 44 and baffle plates 46, 48 and 50. For example, each
pie shaped segment of tray, bottom plate, baffle plates and
injection nozzle may be prefabricated and installed on a support
structure, e.g., radial spokes, in the vessel. Further, these
prefabricated tray assembly segments or prefabricated tray
assemblies may be installed in the vessel by removing the top plate
38 and lowering the prefabricated assemblies down into the vessel
to the appropriate elevations, wherein the assemblies are to be
positioned. Once positioned, the injection nozzle is coupled to a
nozzle opening in the sidewall 42 of the vessel 10. Similarly, once
the tray assembly has been positioned in the vessel, an opening in
the outer baffle plate 50 is aligned with an extraction nozzle 36
mounted to the sidewall 42 of the vessel.
[0077] Below each tray may one or more gas extraction nozzles 36
arranged at substantially the same elevation on the outer wall of
the vessel and separated by uniform angles around the vessel. The
number of gas extraction nozzles may be the same as or different
from the gas injection nozzles. For example, one, two or three gas
extraction nozzles may be below each tray or alternatively one for
each tray segment. The gas injection nozzles 34 may be of a smaller
diameter than the gas extraction nozzles, especially if the oxygen
deprived gas expands as it enters the vessel. The gas inlet
manifolds for the nozzles 34, 36 may be thick walled pipes or
fabricated from steel. With respect to each tray, gas enters the
vessel through the gas injection nozzles 34, passes through the
biomass material on the tray, the tray and is discharged from the
vessel through the extraction nozzles 36.
[0078] FIG. 11 shows a scraper device 56 that moves the biomass
through the biomass passage of each tray assembly. The scraper
device 56 may have radial scraper spokes or blades 60, a center
collar 58 and an outer annular ring 56. The ring 56 is proximate to
the wall 42 of the vessel 10, such as within 3 to 5 millimeters
(mm) of the wall 42. The lower edges of the blades 60 are proximate
to the upper surface of the tray, e.g., within 3 to 10 mm of the
tray. The upper edges of the blades may be proximate to, e.g.,
within 10 to 25 mm, the bottom plate 44 of the next higher tray
assembly. The spokes or blades 60 of the scraper device may
straight and aligned with radial lines extending between the collar
and ring. Alternatively, the spokes or blades 60 may be inclined
with respect to radial lines at angles of 15 to 20 degrees towards
the angle of rotation (as is shown in FIG. 11), and the blades may
be curved or swept towards the angle of rotation.
[0079] FIG. 11A is a schematic diagram of an enlarged portion of
the lower edge of one of the spokes or blades of the scraper
device. A slot, pipe or other gas passage 112 is provided on the
lower edge, and has openings or nozzles 114 arranged along the
radial length of the passage 112. A source of high pressure gas 114
is coupled to the passage 112 through the shaft 32 of the vessel.
The high pressure gas source 114 may be external to the vessel and
is shown in the shaft solely for illustrative purposes in FIG. 11A.
The high pressure gas flowing through the passage 112 and the
nozzles 114 is applied to clean the openings 100 in the tray to
ensure that gas is free to pass through the openings.
Alternatively, the high pressure gas source 114 may be a source of
suction such as an air pump or blower. The suction applied to the
passage 112 and nozzles 114 removes fibers and debris from the
openings. As the blade with the passage 112 rotates over the tray,
the openings 100 in the tray are cleaned. The cleaning of the
openings in the tray may be concurrent with the treatment of
biomass in the vessel 10.
[0080] The scraper device 56 may be prefabricated and installed by
sliding the device down into the vessel. The center collar may be
welded or otherwise affixed to the shaft. The diameter of the
scraper bar may conform to the inner diameter of the vessel with a
small clearance. The center collar may be fixed to the shaft 32,
such that the scraper device rotates with the shaft. The height of
the scraper device 56 may be nearly the same as the height of the
biomass space 54, or may be about the desired thickness of the
biomass 66 on the tray, as shown in FIG. 15.
[0081] The rotation of the shaft 32 rotates a scraper device 56
immediately above each of the trays 40. The biomass fills or
partially fills the volume between the spokes 60 of the scraper
device. The rotation of the scraper device over its respective the
tray moves the biomass material across the tray. As the biomass
material moves across the tray, the material is exposed to a
constant flow of the oxygen deprived gas at a uniform temperature.
The gas enters the vessel through gas injection nozzles 34 that has
an opening at the outer wall of the vessel or an opening 53 in the
bottom plate 44 above the tray and biomass space 54. The opening 53
in the bottom plate may be a single discharge port, or a gas
distribution manifold 55 with an array of gas discharge ports
arranged above the biomass on the tray. The opening may also be
flared to assist with disbursing the oxygen deprived gas over the
biomass on the tray. The gas distribution manifold 53 may be an
arrangement of pipes and pipe fittings with nozzles, and fabricated
with the tray assembly. The opening or gas distribution manifold
may be arranged to uniformly distribute gas over the biomass on the
entire tray. To achieve uniform gas distribution, multiple
injection nozzles may be arranged around the wall of the vessel,
such as at least one nozzle for each tray segment.
[0082] As the gas moves through the biomass and the tray, the
scraper device rotates to move the biomass in an arc shaped path
through the tray assembly. The biomass moves through the tray
assembly and is discharged through an opening 64, shown in FIG. 12.
The opening may include a chute, duct, pivoting door or other
discharge device in the tray. The biomass drops through the opening
64 to into the scraper device and onto the tray of the next lower
tray assembly. The opening 64 may be vertically aligned with the
opening 64 in the next lower tray assembly, such that the biomass
falls into the triangular shaped section of the scraper device that
has just rotated over the chute in the next lower tray assembly.
This alignment of the chutes ensures that the biomass moves in an
arc over the entire tray and provides maximum retention time of the
biomass in each of the tray assemblies. The lowermost tray may be
an inverted cone with a center discharge chute to allow biomass to
flow to a vertical center of the cooling zone.
[0083] FIGS. 13 and 14 show the convergence zone 24 in the bottom
section of the vessel 10. The convergence section may include
regions which converge in one-dimension only, such as having flat
sidewalls that converge and curved walls joining these sidewalls
that do not converge. One-dimensional convergence sections reduce
the tendency of biomass material to become stuck in the vessel
while flowing to the outlet 26. One-dimensional convergence
sections are marketed by the Andritz Group under the
Diamondback.TM.. One dimensional convergence sections generally
avoid the need to have a rotating scraper or other mechanical
device to prevent biomass blockages in the bottom of the vessel.
Although one dimensional convergence sections are disclosed here,
other means of bringing the material to a discharge point at the
bottom of the vessel such as motor driven moving bottom units,
e.g., scrapers, and outlet device assemblies may be used.
[0084] FIG. 15 is a schematic illustration of the gas flow through
a tray assembly. The gas flow through the injection nozzle 34 which
is aligned with and passes through the gas passage 52 of the
immediately above tray assembly. The injected oxygen deprived gas
flows through outlet 53 and into the biomass space 54 in the tray
assembly. There may be several injection nozzles 34 with outlets 53
arranged radially around the biomass space for each tray assembly.
The gas flow is distributed uniformly over the upper surface of the
bed of biomass 66 by entering a gas space in the biomass space 54
that is above the bed. The thickness of the bed may be, by way of
example, one meter (1 m) or some other thickness which achieves the
desired biomass throughput and allows heating gases to flow
uniformly through the bed. For example, the bed thickness may be in
ranges of 150 millimeters to one meter, or greater than one meter.
The bed sits on the tray 40.
[0085] Gases flow down through the bed and tray, and enter the gas
passage 52. The gases exhaust from the gas passage through the
extraction nozzles 36 arranged radially around the wall of the
vessel and at each segment of the tray. The gas extraction nozzles
36 may be arranged to promote the uniform flow of gases through the
biomass on the tray. The number of gas extraction nozzles may be
fewer than the number of gas injection nozzles 34.
[0086] FIG. 15A is an enlarged view of the cross-section of a tray
to illustrate n exemplary slot, hole or opening 100 in the tray
(not shown is a finer mesh or finer screen material that may be
used to cover the hole, slot or opening 100). As the biomass moves
over the surface of the tray in the direction of flow arrow 102,
gas flows down through the biomass and through the opening to the
gas passage 52 below the tray. The slot, hole or opening may have a
generally uniform cross section through the tray. Alternatively and
as shown in FIG. 15A, the hole, slot or opening 100 may have an
upper portion 104 that is generally uniform in cross section and a
lower portion 106 that expands in cross-sectional area in a
downward direction. The upper portion of the slot, hole or opening
100 may be 30 to 50 percent the thickness of the tray. Further, the
upper rim of the slot, hole or opening may be beveled 108, such as
at the trailing edge as shown in FIG. 15A. The bevel 108 assists in
avoiding the fibers from the biomass from being caught on the upper
rim of the slot, hole or opening, and especially on the trailing
edge of the rim.
[0087] FIGS. 16 to 18 are process flow charts showing exemplary
torrefaction processes that may be performed in the vessel 10. A
common feature of these processes is that the torrefied biomass
material is cooled prior to being depressurized and exposed to the
atmosphere. The cooling may occur in lower trays of the vessel, in
a cooling zone 24 or in a pressurized cooling chip tube 67 and
cooling screw 68 assembly, downstream of the discharge 26 of the
vessel. Alternatively, cooling could occur in a fluid bed (now
shown). It is also possible for zone 24 to be a combination
reaction zone followed by a cooling zone.
[0088] Cooling gases may be injected in the lower(s) trays, cooling
zone, chip tube or chip screw to cool the torrefied biomass prior
to discharge from the reactor. The cooling gases may be used to
stop or slow the torrefaction reaction and to make the torrefied
biomass safe and suitable for an oxygen atmosphere outside of the
vessel. For example, cooling to stop or slow the torrefaction
reaction may occur to make the biomass suitable for an oxygen
atmosphere may occur in the cooling zone 22 or in pressurized
cooling devices downstream of the vessel. The cooling to stop or
slow the torrefaction reaction may require cooling gases that are
10 to 30 degrees Celsius cooler than the gases injected in the
torrefaction tray assemblies to promote the torrefaction reaction.
The cooling gases to make the torrefied biomass safe for an oxygen
atmosphere may be cooler by an additional 10 to 30 degrees Celsius,
or 10 to 50 degrees Celsius, or 10 to 80 degrees Celsius, or 10 to
100 degrees Celsius, or 20 to 120 degrees Celsius from the cooling
gases added to the cooling tray assemblies.
[0089] Gases from the cooling zone 24, such as in the convergence
section, may be withdrawn through a screen 65 in a sidewall of the
vessel, as is shown in FIGS. 13 and 14. Similarly, cooling gases
may be withdrawn from a lower cooling tray or from the chip tube
and screw 68.
[0090] The cooled torrefied biomass passes through a pressure
transfer device 70, such as a rotary valve. The pressure of the
torrefied biomass downstream of the pressure transfer device may be
at atmospheric. From the pressure transfer device, the torrefied
biomass is moved to other processes such as using a screw conveyor
72.
[0091] Before the torrefaction reaction occurs in the vessel, such
as in the lower trays 18, the biomass may be dried and heated in an
oxygen deprived environment at a temperature of 200.degree. C. to
400.degree. C. The biomass may be dried and heated in a separated
dryer that acts on the biomass before it reaches the vessel 10. In
addition or alternatively, the biomass may be dried in an upper
drying zone of the vessel 10, which may include one or more of the
tray assemblies. The biomass may be directly heated with an oxygen
deprived gas, e.g., super-heated steam, nitrogen or a mixture of
both, injected into the top of the vessel or dryer.
[0092] The volume of hot oxygen deprived gas needed for the vessel
is dramatically reduced in a pressurized reaction vessel 10 as
compared to a vessel operating at atmospheric pressure.
Pressurizing the treatment vessel 10 the volume of hot gas needed
to heat the biomass is decreased by a factor of two (2) to
thirty-five (35) as compared to a vessel at atmospheric pressure.
The reduction factor for the vessel depends on the pressure in the
vessel.
[0093] Because of the reduced volume of hot gas needed in the
pressurized reactor, the volume and hence the size and cost of the
vessel 10 may be significantly reduced as compared to a vessel
operating at atmospheric pressure. A pressurized vessel in which a
hot gas is injected provides effective and economical heat transfer
from the gas to the biomass in the vessel.
[0094] The vessel 10 may be pressurized by injecting an oxygen
deprived gas, e.g., oxygen starved gas, at a pressure of up to 35
bar gauge (barg), such as in a range of 3 barg to 35 barg. The
pressurized vessel 10 operates in an oxygen deprived gas
environment in which a heated pressured gas circulates through the
vessel to directly heat the biomass and promote a torrefaction
reaction with the biomass.
[0095] The hot, oxygen deprived gas may be steam, e.g.,
super-heated steam, nitrogen or carbon dioxide and may contain in
lesser quantities gaseous byproducts from the torrefaction
reaction. Further, the hot gas may be injected into the biomass in
the feed system (not shown) such as in the inlet downstream of a
pressure isolation device or downstream of a high pressure transfer
device. If there is a high pressure transfer device, a pressure
isolation device may be unnecessary at the inlet to the vessel
10.
[0096] In the drying and torrefaction tray assemblies, the hot gas
flows through the biomass in the vessel 10 and directly heats the
biomass to a temperature that promotes a torrefaction reaction in
the material, such as a range of 240.degree. C. to 300.degree. C.
The hot gas and any gas generated in the reactor are exhausted from
the reactor at various elevations through extraction nozzles 36.
The gas may exhaust from the vessel at a temperature of about
250.degree. C. to 280.degree. C. The gases used for drying may be
cooler than the gases used for torrefaction. The gases for drying
may be gases extracted from the torrefaction tray assemblies, and
using a blower are circulated to the drying tray assemblies without
adding additional heat to the gases. Gases that are circulated back
to the torrefaction trays may be heated in a heat exchanger before
being returned to the torrefaction tray assemblies.
[0097] A portion of the exhausted gas is removed from the vessel
for use outside of the torrefaction system. Another portion of the
exhausted gas is indirectly heated in a heat exchanger 84 (or other
heat transfer device) and returned to the gas input manifold 24 at
the top of the vessel 10. The heat exchanger 34 may add heat energy
to heat the exhausted gas from about 250.degree. C. to 300.degree.
C. to 380.degree. C., for example. Reheating and recirculating the
exhausted gas reduces the amount for additional pressurized heated
oxygen deprived gas required to be supplied to the gas input
manifold of the vessel.
[0098] The exemplary process flow in FIG. 16 shows the pressurized
vessel 10 as having a drying tray assembly 16, four torrefaction
tray assemblies 18 and two cooling tray assemblies 20. Hot, oxygen
deprived gas circulates through the vessel, blowers 74, 79 and heat
exchanger 84 at an elevated pressure of 3 to 20 Barg (300 to 2,000
kiopascals, or in a range of 5 to 8 Barg. The hot gases for the
drying tray assembly 16 and torrefaction tray assemblies 18 are
provided from a heat exchanger 84. Heat energy is added to oxygen
deprived gases flowing through the heat exchanger by, for example,
hot gases 88 from a combustor. The warm combustion gases discharged
from the heat exchanger 84 may flow to warm air flowing to the
combustor.
[0099] FIGS. 17 and 18 show process flows in which the drying gas
flowing to a top inlet 90 is cooler, e.g., by 10.degree. C. to
30.degree. C., than the oxygen deprived gases flowing to the
torrefaction tray assemblies 18. In FIGS. 17 and 18, the gas
flowing to the top inlet 90 is also injected to the cooling tray
assembly 20.
[0100] The oxygen deprived gas shown in the process flows of FIGS.
16 to 18 are circulated through the pressurized treatment vessel 10
in a substantially closed gas loop system.
[0101] A portion of the gases may be removed from the system as
bleed off gases 90. The portion may be the just gases from the
lowest one or few torrefaction tray assemblies, all of the
torrefaction tray assemblies, a middle set of torrefaction tray
assemblies, or just gases removed from the drying tray
assembly(ies). The bleed off gases may be selected to have a high
concentration of torrefaction reaction byproducts to be removed and
later combusted or otherwise processed. Alternatively, bleed off
gases may be selected based on having a low concentration of
torrefaction reaction byproducts to be used in combustion or other
processes.
[0102] The oxygen deprived gases are circulated through the vessel
10 and heat exchanger 84. Blowers 74, 76 and 78 provide a motive
force to circulate the gases. The hot gases from the torrefaction
tray assemblies may flow through the high temperature blowers 76
and 74 and the heat exchanger 84, before being returned to the
torrefaction tray assemblies 18 and, optionally, to the top inlet
86 of the vessel. Multiple blowers 74, 76 may be used to provide
the needed flow rate to circulate gases through the many
torrefaction tray assemblies. Valves 80 between the blowers 74, 76
may remain open to allow high temperature gases to flow in parallel
through these blowers. Valves 82 may be closed to prevent the hot
gases flowing through the high temperature blowers 74, 76 from
mixing with the low temperature gases flowing through the low
temperature blower 78. The valves 80, 82 may be set as opened or
closed depending on the rate of hot gases extracted from the vessel
as compared to the rate of cooler gases extracted from the
vessel.
[0103] Relatively cooler oxygen deprived gases are extracted from
the cooling tray assemblies 20, the cooling zone 22 of the vessel
(such as through screen 65) and, optionally from the drying tray
assembly 16, and flow through piping separate from the piping used
for the hotter oxygen deprived gases extracted from the
torrefaction tray assemblies. The cooler gases are removed through
extraction nozzles 36 by a low temperature blower 78 which pushes
the gases back to the vessel where they enter through injection
nozzles 34 to the cooling tray assemblies 20, and optionally to the
top of the cooling zone 22 through a nozzle 92 aligned with the
bottom tray assembly.
[0104] The bleed off gases provide a means to remove primary
byproducts of the torrefaction reaction occurring in the vessel 10.
These primary byproducts may include acetic acid, carbon monoxide,
carbon dioxide, formaldehyde, formic acid, water, lignin fragments,
and other lesser components. The primary byproducts are generally
gaseous at the temperature and pressure at which the torrefaction
reaction occurs in the vessel. Some of the byproducts may be in
aerosol or fine char form carried by in the bleed off gases.
Similarly, fine particles of lignocellulose material from the
biomass may flow with the gas as it passes through the screens in
the trays and the vessel and be carried by the bleed off gases out
of the system.
[0105] The primary byproducts may combine and condense to form tar
like substances. If allowed to condense in the vessel and
downstream process components, the tar like substances can deposit
on the surfaces of the vessel and components, particularly on the
interior surfaces of piping and heat exchangers.
[0106] The gases being circulated through the reactor vessel 10 and
heat exchanger 84 may be treated to remove reaction byproducts from
the circulating gases. The system for circulating the gases through
the vessel 10 and heat exchanger 84 may include separation devices
96 for removing the reaction byproducts. Separation devices 96 may
be a condensation device which cools the gases to cause the
byproducts to be condensed to a liquid and removed, before the
gases are reheated in the heat exchanger. Other examples of
separation devices 96 include devices that oxidize the byproducts,
catalytically convert the byproducts, filter the byproducts from
the gas flow and flow separators, such as cyclones that use
centrifugal forces to separate particles from the gas stream. These
separation devices may be used singularly or in combination in the
system. The byproducts separated by these components may be further
processed by being separated, concentrated or purified into usable
products. The bleed off gases 90 remove the primary byproducts from
the vessel while these byproducts are in gaseous form. As shown in
FIGS. 16 and 17, the bleed off gases may be extracted from the
drying tray assembly and, particularly, from the extraction gas
stream flowing from the extraction nozzle 36 for the drying tray
assembly. The extracted gases from the drying tray assembly tends
to be rich in moisture and below the temperature required to
initiate torrefaction. As shown in FIG. 18, the bleed off gases may
be extracted from the torrefaction tray assemblies 18, and
particularly, from the middle to lower elevations of these tray
assemblies 18. The concentration of organic byproducts in the gases
extracted from the torrefaction tray assemblies may be at a maximum
level as compared to the gases extracted from the vessel 10.
[0107] The bleed off gases 90 may flow to the combustor where the
gases may be mixed with a natural gas, or other gaseous fuel, and
combusted. Combustion would release heat energy from the byproducts
which would be used to reheat the circulating gases in the heat
exchanger 84. The heat from combustion could also be used to dry
and heat the biomass in the optional dryer 21.
[0108] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *