U.S. patent application number 13/210980 was filed with the patent office on 2012-02-23 for method and system for the torrefaction of lignocellulosic material.
This patent application is currently assigned to Andritz Technology and Asset Management GmbH. Invention is credited to Tyson Hunt, Xiaoping Jiang, Joseph RAWLS, Bertil Stromberg, John Weston.
Application Number | 20120042567 13/210980 |
Document ID | / |
Family ID | 44534680 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120042567 |
Kind Code |
A1 |
RAWLS; Joseph ; et
al. |
February 23, 2012 |
METHOD AND SYSTEM FOR THE TORREFACTION OF LIGNOCELLULOSIC
MATERIAL
Abstract
A method for torrefaction of lignocellulosic biomass using a
torrefaction reactor vessel having stacked trays, the method
including: continuously feeding the biomass to an upper inlet of
the torrefaction reactor vessel such that the biomass material is
deposited on an upper tray of a plurality of trays stacked
vertically within the reactor; as the biomass moves across an upper
surface of each of the trays, heating and drying the biomass
material with a gas injected into the vessel, wherein the gas is
substantially non-oxidizing of the biomass, is under a pressure of
at least 20 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 a lower tray; discharging torrefied biomass from a lower
outlet of the torrefaction reactor vessel, and circulating gas
extracted from a lower elevation of the reactor vessel to an upper
region of the reactor vessel.
Inventors: |
RAWLS; Joseph; (Alpharetta,
GA) ; Stromberg; Bertil; (Diamond Point, NY) ;
Weston; John; (Queensbury, NY) ; Jiang; Xiaoping;
(Queensbury, NY) ; Hunt; Tyson; (Saratoga Springs,
NY) |
Assignee: |
Andritz Technology and Asset
Management GmbH
Graz
AT
|
Family ID: |
44534680 |
Appl. No.: |
13/210980 |
Filed: |
August 16, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61374412 |
Aug 17, 2010 |
|
|
|
Current U.S.
Class: |
44/606 ;
422/208 |
Current CPC
Class: |
Y02E 50/10 20130101;
C10L 5/44 20130101; Y02E 50/15 20130101; Y02E 50/30 20130101; C10L
9/083 20130101 |
Class at
Publication: |
44/606 ;
422/208 |
International
Class: |
C10L 5/44 20060101
C10L005/44; F28D 21/00 20060101 F28D021/00 |
Claims
1. A method for torrefaction of lignocellulosic biomass using a
torrefaction reactor vessel having stacked trays, the method
comprising: continuously feeding the biomass to an upper inlet of
the torrefaction reactor vessel such that the biomass material is
deposited on an upper tray of a plurality of trays stacked
vertically within the reactor; as the biomass moves across an upper
surface of each of the trays, heating and drying the biomass
material with a gas injected into the vessel, wherein the gas is
substantially non-oxidizing of the biomass, is under a pressure of
at least 20 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 a lower tray; discharging torrefied biomass from a lower
outlet of the torrefaction reactor vessel, and circulating gas
extracted from a lower elevation of the reactor vessel to an upper
region of the reactor vessel.
2. The method of claim 1 wherein the gas is at least one of
superheated steam, carbon dioxide and nitrogen.
3. The method of claim 1 further comprising a pressurizing the
biomass before the feeding of the biomass into the vessel with a
pressure transfer device.
4. The method of claim 1 wherein at least the upper trays are 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 trays below the upper trays
are solid such that the gas does not pass through the tray.
6. The method of claim 1 wherein the lower elevation of the vessel
where the gas is extracted is adjacent a lower tray of the
trays.
7. The method of claim 1 wherein gas is injected into the vessel at
two elevations wherein the gas is hotter when injected at a lower
elevation of the two elevations than the gas injected at an upper
elevation of the two elevations.
8. The method of claim 1 wherein below an elevation of the vessel
from which the gas is extracted, the biomass continues to cascade
down through at least one of the trays.
9. The method of claim 1 further comprising injecting the gas in
the biomass to purge oxygen from the biomass.
10. The method of claim 9 wherein the injection occurs before the
biomass enters the vessel or as the biomass enters the vessel.
11. A torrefaction pressurized reactor vessel assembly comprising:
a stack of trays housed within the vessel; a source of a
pressurized, reduced oxygen gas coupled to the vessel to allow the
gas to flow into at least an upper region of the vessel, wherein
the gas is at a pressure of at least 20 bar gauge and at a
temperature of at least 200.degree. C.; an upper inlet to the
vessel through which biomass enters the pressurized reactor vessel,
wherein a chute aligned with the upper inlet directs the biomass
from the inlet to an upper tray of the stack of trays; a scraper
device associated with an upper surface on each of the trays,
wherein at least one of the scraper device and tray rotates within
the vessel; a lower outlet in the vessel through which torrefied
biomass is discharged from the torrefaction reactor vessel, and a
gas circulation system through which gas extracted from a lower
elevation in the vessel flow to an upper elevation of the reactor
vessel.
12. The torrefaction pressurized reactor vessel assembly of claim
11 wherein the wherein the source of a pressurized, reduced oxygen
gas is a source of at least one of superheated steam, carbon
dioxide and nitrogen.
13. The torrefaction pressurized reactor vessel assembly of claim
11 further a pressure transfer device which pressurizes and feeds
the biomass to the reactor vessel.
14. The torrefaction pressurized reactor vessel assembly of claim
11 wherein at least one of the upper trays of the stack of trays is
a mesh, screen or has perforations.
15. The torrefaction pressurized reactor vessel assembly of claim
14 wherein trays below the upper trays are solid such that the gas
does not pass through the tray.
16. The torrefaction pressurized reactor vessel assembly of claim
11 wherein a lower elevation of the vessel at where the gas is
extracted for circulation is adjacent a lower tray.
17. The torrefaction pressurized reactor vessel assembly of claim
11 wherein the gas circulation system further comprises a heat
exchanger.
18. The torrefaction pressurized reactor vessel assembly of claim
11 further comprising a vertical rotating shaft extending through a
center axis of the reactor vessel and at least one of the scraper
device and trays are fixed to the shaft.
19. The torrefaction pressurized reactor vessel assembly of claim
11 wherein the reactor vessel includes a lower region devoid of
trays and receiving the biomass material.
20. The torrefaction pressurized reactor vessel assembly of claim
11 further comprising biomass supply bin a conduit conveying the
pressurized, reduced oxygen gas to the biomass supply bin.
Description
CROSS RELATED APPLICATION
[0001] The application claims priority to U.S. Ser. No. 61/374,412
filed on Aug. 17, 2010 which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to systems and
methods for torrefaction of lignocellulosic material, such as 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 moisture and low weight
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. Torrefaction changes the chemical structure
of the biomass to a form suitable for burning in coal fired
facilities. Torrefied wood or biomass has characteristics similar
to 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 (which is referred to
herein as an "inert atmosphere"), at relatively low temperatures of
200 degrees Celsius (.degree. C.) to 400.degree. C. A torrefaction
process is described in related U.S. Provisional Patent Application
Ser. No. 61/235,114, the entirety of which is incorporated by
reference.
[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 for torrefaction of wood or
other biomass material.
BRIEF DESCRIPTION OF THE INVENTION
[0007] A difficulty with unpressurized reaction vessels is the low
mass of gas at atmospheric pressure. 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. A
large reaction vessel is needed to heat biomass with a gas at
atmospheric pressure because a large volume of gas is necessary to
heat the biomass.
[0008] The mass of a gas at atmospheric pressure is substantially
less than the mass of gas at a substantial pressure, such as above
20 bar gauge (290 psig). The volume of gas under substantial
pressure needed to heat biomass to a certain temperature is much
less than the volume of atmospheric gas needed to heat the biomass.
A small pressurized vessel may be used to heat biomass, as compared
to a similar but unpressurized vessel.
[0009] 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 having vertically stacked trays for drying and heating
biomass using an inert hot gas under substantial pressure. The
vessel may be substantially smaller than a reaction vessel for
torrefaction performed at atmospheric pressure. The inert
pressurized gas may be circulated through the vessel and through
pressurized conduits that reheat the gas.
[0011] A method for torrefaction of lignocellulosic biomass using a
torrefaction reactor vessel (10, 70, 100) having stacked trays (42,
74, 102, 104), the method including: continuously feeding the
biomass to an upper inlet (14) of the torrefaction reactor vessel
such that the biomass material is deposited on an upper tray of a
plurality of trays stacked vertically within the reactor; as the
biomass moves across an upper surface of each of the trays, heating
and drying the biomass material with a gas (18) injected into the
vessel, wherein the gas is substantially non-oxidizing of the
biomass, is under a pressure of at least 20 bar gauge and at a
temperature of at least 200.degree. C.; cascading the biomass down
through the trays (42, 74, 102, 104) by passing the biomass through
an opening (46) in each of the trays to deposit the biomass on a
lower tray; discharging torrefied biomass from a lower outlet (16,
81, 116) of the torrefaction reactor vessel, and circulating gas
(30, 31, 24, 64, 76, 77, 78, 79) extracted from a lower elevation
of the reactor vessel to an upper region (15) of the reactor
vessel.
[0012] The gas may be superheated steam, nitrogen or carbon
dioxide. The biomass may be pressurized before being fed to the
vessel with a pressure transfer device. The upper trays may be a
mesh, screen or have perforations and the heating and drying of the
biomass includes passing the gas through the biomass and the trays.
The trays below the upper trays may be solid such that the gas does
not pass through the tray. The gas may be adjacent a lower tray of
the trays.
[0013] The gas may be injected into the vessel at two elevations
wherein the gas is hotter when injected at a lower elevation of the
two elevations than the gas injected at an upper elevation of the
two elevations. At an elevation of the vessel below from which the
gas is extracted, the biomass may continue to cascade down through
the trays. The gas may be injected in the biomass to purge oxygen
from the biomass, wherein the injection occurs before the biomass
enters the vessel.
[0014] A torrefaction pressurized reactor vessel assembly (10, 70,
100) has been conceived comprising: a stack of trays (42, 74, 102,
104) housed within the vessel; a source of a pressurized, reduced
oxygen gas (18) coupled to the vessel to allow the gas to flow into
at least an upper region of the vessel, wherein the gas is at a
pressure of at least 20 bar gauge and at a temperature of at least
200.degree. C.; an upper inlet (14) to the vessel through which
biomass enters the pressurized reactor vessel, wherein a chute (54)
aligned with the upper inlet directs the biomass from the inlet to
an upper tray of the stack of trays; a scraper device (52)
associated with an upper surface on each of the trays, wherein at
least one of the scraper device and tray rotates within the vessel;
a lower outlet (16, 81, 116) in the vessel through which torrefied
biomass is discharged from the torrefaction reactor vessel, and a
gas circulation system (30, 31, 24, 64, 76, 77, 78, 79) through
which gas extracted from a lower elevation in the vessel flow to an
upper elevation (15) of the reactor vessel.
[0015] In the torrefaction pressurized reactor vessel assembly, the
source of a pressurized, reduced oxygen gas (18) may be a source of
at least one of superheated steam, carbon dioxide and nitrogen. A
pressure transfer device (22) may pressurize and feed the biomass
to the reactor vessel. At least one of the upper trays of the stack
of trays (42, 74, 102) may be mesh, screen or have perforations.
The trays (104) below the upper trays may be solid such that the
gas does not pass through the tray. The lower elevation (72) of the
vessel at where the gas is extracted for circulation may be
adjacent a lower tray (104). The gas circulation system further
comprises a heat exchanger. A vertical rotating shaft (44) may
extend through a center axis of the reactor vessel and at least one
of the scraper device and trays are fixed to the shaft. Further, a
lower region of the vessel may be devoid of trays and receiving the
biomass material. In addition, a biomass supply bin (12) may
receive the pressurized, reduced oxygen gas to the biomass supply
bin from a conduit (90) leading from the source of the gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic diagram of a pressurized treatment
vessel receiving biomass from a feed system.
[0017] FIG. 2 is a schematic diagram of a second embodiment of a
pressurized treatment vessel receiving biomass from a feed
system.
[0018] FIG. 3 is a schematic diagram of a third embodiment of a
pressurized treatment vessel.
DETAILED DESCRIPTION OF THE INVENTION
[0019] FIG. 1 is schematic diagram of a pressurized treatment
vessel 10 for receiving, from a storage bin 12, biomass material,
such as wood chips, wood pulp and other comminuted cellulosic
material. The biomass enters the pressurized treatment vessel
through an upper inlet 14. The upper inlet may be a high pressure
transfer device that allows biomass at atmospheric pressure to be
transferred into the high pressure vessel. Alternatively, the
biomass may be pressurized by a high pressure feeder (HPF) or a
series of chip pumps 22 as the pressurized biomass flows through a
conduit 23 to the upper inlet which may be an open valve.
[0020] Within the vessel, the biomass is subjected to a
torrefaction reaction and is discharged as torrefied biomass 14
from a lower discharge outlet 16 of the vessel. Before the
torrefaction reaction occurs in the vessel, the biomass may be
dried and heated in an inert environment to a temperature of
200.degree. C. to 400.degree. C. The biomass may be dried and
heated in a separate dryer 11 or in an upper drying zone 15 of the
vessel 10. Within the pressurized treatment vessel 10, the biomass
may be heated in an upper drying zone 13 of the vessel. The biomass
may be indirectly heated by a heat exchanger 9 having surfaces in
contact with the biomass. The heat exchanger may be in the dryer or
vessel. Alternatively, the biomass may be directly heated with an
oxygen deprived gas 18, e.g., super-heated steam, injected into the
vessel or dryer.
[0021] The vessel may be operated at a relatively high
above-atmospheric pressure, such as above 20 bar gauge (290 psig).
Pressurizing the vessel 10 allows for higher gas temperatures in
the vessel and increases the amount of gas per unit volume
available to react with the biomass.
[0022] The volume of hot inert 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 reduces the volume of hot gas
needed to heat the biomass 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.
[0023] 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.
[0024] The vessel 10 may be pressurized by injecting an inert gas
18, e.g., oxygen starved gas, at a pressure of up to 35 bar gauge
(barg), such as in a range of 20 barg to 35 barg. The oxygen
starved gas (also referred to as the inert gas) may be
substantially nitrogen, a carbon oxide or steam. The pressurized
vessel 10 operates in an inert gas environment in which a heated
pressured gas 18 circulates through the vessel to directly heat the
biomass and promote a torrefaction reaction with the biomass.
[0025] The upper inlet 14 to the pressurized vessel may be coupled
to a continuous feed, pressure isolation device 20, 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.
[0026] The biomass may be fed to the inlet 14 to the vessel at a
temperature of 80.degree. C. to 120.degree. C., for example, or
higher if a dryer 11 heats the biomass before entering the vessel.
The biomass is heated in the vessel by a pressurized, hot and
oxygen starved gas 18. The gas entering the vessel may be at a
temperature in a range of 200.degree. C. to 600.degree. C. and may
particularly be in a range of 250.degree. C. to 400.degree. C. or a
range of 300.degree. C. to 380.degree. C. The hot gas 18 may be
injected to the vessel through a gas input manifold 24 including
nozzles arranged at an upper level of the vessel 10.
[0027] The hot inert gas 18 may be injected into the pulp in the
feed system 26 such as in the inlet downstream of the pressure
isolation device or downstream of a high pressure transfer device
28. If there is a high pressure transfer device 28, the pressure
isolation device may be unnecessary at the inlet to the vessel
10.
[0028] The hot gas 18 flows with the biomass in the vessel and
directly heats the biomass to a temperature that promotes a
torrefaction reaction in the pulp. The hot gas and any gas
generated in the reactor are exhausted from the reactor at a bottom
gas vent manifold 30. The gas may exhaust from the vessel at a
temperature of about 280.degree. C. A portion 32 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 34 (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 280.degree. C. to 300.degree. C. to 380.degree. C., for
example. Reheating and recalculating the exhausted gas reduces the
amount for additional pressurized heated gas 38 required to be
supplied to the gas input manifold of the vessel.
[0029] The biomass enters the pressure treatment vessel 10 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 15 in an
upper region of the vessel. Below the drying zone, the vessel
includes a torrefaction zone 40
[0030] The vessel 10, including the drying zone 15 (if any) and the
torrefaction zone 40, includes a stack of generally trays 42 each
of which are mounted on a center vertical shaft 44 extending
through the vessel. The trays may be circular discs having a
generally planar upper support surface. The trays 42 may each
include an opening 46, such as a pie-shaped open section of a
circular disc. The open section may be one or more openings in each
tray. The open section 46 allows biomass on the upper surface of
the tray to fall through to an underlying tray.
[0031] The open sections 46 (also referred to as "openings") of
each tray preferably are not vertically aligned with the openings
46 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.
[0032] The open sections 46 may be vertically staggered such that
each opening is over a trailing region 47 of the upper section of
the tray immediately below the opening. The trailing region 47 of a
tray is adjacent and behind the open section 46 in the direction of
rotation 56 of the tray. By aligning an open section 46 above a
trailing region 47 on a lower tray, the biomass falls through the
open section and onto the trailing region. As the tray turns, the
biomass slides across the entire upper surface of the tray in an
arc-shaped path from the trailing region to the open 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
[0033] The trays 42 may rotate with the shaft 44. Alternatively,
the trays may be stationary and mounted to the sidewall of the
vessel and a scraper device 52 may rotate with the shaft and across
the upper surface of each tray. The shaft 44 is rotatably driven by
a gear and motor assembly 50 which may be at the lower base of the
vessel 10. The rotational speed of the shaft may be adjusted to
control the flow rate of the biomass through the vessel. The
rotational speed of the shaft and tray governs the retention period
of the biomass on each tray. A fast rotational speed will cause the
biomass to flow faster through the vessel as compared to a slow
rotational speed.
[0034] The trays 42 may be perforated, wire frames with an open
network of support beams or otherwise open to allow hot gases to
pass through the trays and biomass on the trays. Allowing hot gas
to pass through the biomass and trays promotes the exposure of the
surfaces of the biomass particles to the hot gases.
[0035] The biomass is heated in the vessel by exposure to the hot
gases. The biomass may reach a temperature sufficient to promote
torrefaction within thirty (30) seconds to twenty (20) minutes
after entering the vessel.
[0036] The flow rate of inert gas needed to increase the
temperature of the biomass moving on the trays is greater than the
flow rate of inert gas needed to maintain the biomass as the
temperature desired for torrefaction. To provide an high flow rate
of the inert gas through an upper portion of the torrefaction zone
40, perforated trays may be use to enhance the exposure of hot gas
to the biomass and allow the gas to pass through the trays. The
solid trays 42 may be used below the elevation of the vessel at
which the biomass reaches the desired torrefaction temperature. The
use of solid trays in the middle and lower regions of the
torrefaction zone 40 assists in confining the hot gases in the
upper elevations of the vessel. By confining the high flow rate of
hot inert gasses to the upper elevations of the torrefaction zone
and the drying zone 15, the volume of gas needed in the vessel may
be optimized to that necessary to heat the biomass up to the
desired temperature for torrefaction.
[0037] The trays may be optionally heated, such as with electric
heating coils 48 to provide indirect heat to the biomass. The
heating coils 48 are arranged on the upper surface of the trays and
electrically connected through the shaft to a source of electric
power.
[0038] The biomass may be retained in the treatment vessel 10 for a
period of five (5) to one-hundred (100) minutes. The retention time
starts as the biomass enters the upper inlet 14 and ends as the
biomass is discharged through the outlet 16 at the bottom of the
vessel. Biomass continually flows through the vessel. As biomass
enters the upper inlet, biomass already in the vessel is on each
tray and biomass at the bottom of the vessel is being discharged
through the outlet 16.
[0039] Immediately below the inlet 14 and in the vessel 10 may be a
chute 54 that receives the biomass from the inlet and directs the
biomass to the trailing section 47 portion of the upper tray. The
chute ensures that biomass entering the vessel is retained on the
upper tray for nearly a full rotational period of the tray.
[0040] A scraper device 52, such as arms extending radially outward
from the shaft, may extend over the upper surface of each tray and
be fixed to the outer wall of the vessel. The scraper device may
not rotate with the shaft and trays. If the scraper device does not
rotate, it may be affixed to the shaft 44 by a collar 60 that is
rotatably mounted on the shaft and rests on the upper surface of
each tray. If the scraper device rotates, it may be affixed to the
shaft and the stationary trays may be fixed to the wall of the
vessel rather than the shaft.
[0041] The scraper device 52 forces biomass to slide across the
upper surface of the tray as the tray rotates. The biomass slides
across the tray until the biomass reaches the opening 46 in the
tray and falls to the next lower tray in the vessel.
[0042] A conventional bottom scraper device (not shown) may be
positioned in a bottom portion of the vessel 10. The bottom scraper
device directs biomass that has cascaded through each of the trays
into the discharge outlet 16. The bottom scraper device may be
fixed to and rotate with the shaft to move the biomass in the
bottom of the vessel into the outlet 16.
[0043] The discharge outlet 16 may be in or near the bottom of the
vessel. The shape of the discharge outlet may be conical,
hemispherical, elliptical or a chute formed of geometric panels
(such as disclosed in U.S. Pat. No. 5,000,083).
[0044] The flow of heated gas into, through and from the pressure
reaction vessel 10 may be configured to promote the flow of hot,
pressurized gases through the trays in the upper elevations of the
vessel 10 where the biomass is being heated to the desired
temperature for torrefaction. As shown in FIG. 1, the hot inert gas
may be injected into the upper section of the vessel 10 through an
input manifold 24 that has one or more gas injection nozzles 64
arranged at the same elevation on the vessel or at various
elevations such as the elevations of the upper trays used to
increase the temperature of the biomass. The introduced hot inert
gas may be supplied just to the top of the vessel as shown in FIG.
1, or also to multiple elevations of the vessel as shown in FIG.
2.
[0045] If gas flows to multiple elevations, the inert gas flowing
to each elevation may be a gas source at a temperature, pressure or
composition that is different from the gas sources supplying the
gas nozzles at other elevations of the vessel. For example, the hot
inert gas 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 biomass
being fed to the vessel. The hot inert gases introduced at
succeeding lower elevations of the vessel may be increasingly
hotter so as to be slightly above the temperature of the biomass in
the vessel that is proximate to the injected hot gas. By injecting
the inert gas at a temperature 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.
[0046] Hot gases in the pressure vessel may be extracted, e.g.,
purged, from various elevations in the vessel. The hot gases
include the inert gases injected into the vessel and gases, e.g.,
steam, generated by the heated biomass in the vessel. These gases
may be extracted through the bottom gas vent manifold 30. Rather
than or in addition to extracting the hot gases from a bottom gas
vent manifold 30, the gases may be extracted from one or more
outlets 31 between elevations at which there are trays 42. The
trays 42 proximate to the gas outlets 31 may be the trays on which
the biomass reaches the desired temperature for the torrefaction
reaction, e.g., 250.degree. C. to 300.degree. C. Extracting gases
through outlets 31 at elevations in the vessel at which the biomass
reaches the desired temperatures, allows the hot gas to be directed
to and circulated through the upper portion of the vessel 10 where
the temperature of the biomass is raised to the desired
temperature.
[0047] The portions of the vessel below the gas outlets 31 are
pressurized and maintain the biomass at the desired torrefaction
temperature. Hot inert gas from the upper regions of the vessel
will flow down to the lower portions of the vessel to maintain the
biomass at the desired temperature in the lower portions of the
vessel. In addition, a relatively small amount of hot inert gas may
be injected into the those lower portions of the vessel through one
or more inlet nozzles 77 arranged on the sidewall of the vessel, as
is shown in FIG. 2.
[0048] As shown in FIG. 2, a pressurized treatment vessel 70 may
have an upper portion 72 having perforated trays 74, gas inlets 76,
77 at upper and mid-elevations of the vessel to receive hot, inert
gas and gas outlets 78 at lower elevations of the vessel to purge
gases from biomass in the vessel. The upper portion 72 corresponds
to the volume in the vessel in which the temperature of the biomass
is raised to the temperature desired for the torrefaction reaction.
The uppermost portion of the vessel may include a drying section,
similar to the drying section 15 in the vessel 10 shown in FIG.
1.
[0049] In FIG. 2, the upper vessel portion 72 receives inert, hot
gas at gas inlets 76 and 77 that may be arranged at different
elevations of the upper vessel portion and at various positions on
the top of the vessel or around the circumference of the vessel.
The inert, hot gas for the gas inlets is provided by recovering
inert gas from exhaust vents 78 at lower elevations of the vessel
70 and from an external source 18 of inert gas.
[0050] Circulation conduits 79, e.g., pipes, external to the vessel
transport inert gas transport from the lower elevations of the
vessel to the upper elevation of the vessels and allow inert gas to
be added to the circulation from the gas source 18. Heat energy may
be added to the inert gas in the circulation conduits by heat
exchangers 34 and 85. The heat exchanger 34 increases the
temperature of the extracted inert gas extracted from the lower
elevations of the vessel so that the gas may be reintroduced into
the upper elevations of the vessel at higher temperatures to dry
and promote torrefaction of the biomass.
[0051] The heat exchanger 85 may be used to increase the
temperature of the inert gas fed via nozzles 77 to the lower trays
74 in the upper portion 72 of the vessel as compared to the upper
trays in the upper portion. The lower trays in the upper portion
may receive the hottest inert gas to heat the biomass on the lower
trays to the desired torrefaction temperature. The upper trays 74
in the upper portion 72 of the vessel receive a slightly cooler
inert gas from gas nozzles 76 because the biomass has not yet
reached the desired torrefaction temperature and is cooler than the
biomass on the lower trays. Heat energy is conserved by adding
inert gas at temperatures slightly, e.g., 10.degree. C. to
20.degree. C., above the biomass temperature adjacent the gas
inlets 76, 77.
[0052] The lower portion 80 of the vessel is maintained at a
pressure and temperature sufficient to promote the torrefaction
reaction of the biomass, but need not increase the temperature of
the biomass in the lower portion. The lower portion 80 may be a
generally open chamber without trays. The flow rate or volume of
hot gas needed to maintain the pressure and temperature in the
lower vessel portion 80 may be only that sufficient to allow the
biomass to flow downward in the portion 80 and stay at a desired
temperature.
[0053] in addition, hot inert gas 85 may be added to the lower
portion 80, such as at the discharge port 81. The hot inert gas 85
may be circulated gas directed from the conduits 79. A heat
exchanger 34 adds heat energy to the circulated gas by indirectly
transferring steam heat from a steam source 87 that flows through
the heat exchanger and to a recovery device 89.
[0054] The lower portion 80 of the vessel 70, below the gas
outlet(s) 78, may have trays 42 with solid surfaces which isolate
the lower portion from the upper portion of the vessel.
Alternatively, the lower portion 80 of the vessel may have no trays
and enclose a relatively open volume in which the hot biomass is
retained while the torrefaction reaction continues to occur and be
completed before the biomass is discharged from the vessel.
[0055] The lower portion 80 of the vessel may be shaped to
facilitate the flow of biomass down through the vessel. The
geometry, e.g., cross-sectional geometry, of the lower portion 80
of the vessel 70 may be a substantially circular cross-section open
top 82 and a substantially rectangular cross-section open bottom
discharge 84 for the biomass. The lower portion 80 may have
opposite side non-vertical gradually tapering planar side walls 86
that make an angle with respect to vertical of about 20 degrees to
30 degrees. These angles may be set depending upon the particular
biomass material handled by the chip bin 11, such as the particular
species of wood chips commonly fed to the bin. Between the opposite
planar side walls 86, are opposite curved side walls 86 connected
the planar side walls. The planar side walls may each be generally
triangular in plan view. These planar sidewalls may be arranged
vertically in diamond shape as shown in FIG. 2.
[0056] The discharge port 81 for the vessel 70 may be coupled to a
screw conveyor 83 that delivers the torrefied biomass 14 from the
vessel 70 to a vessel or other process. A screw conveyor 83 may
meter the flow of torrefied biomass 14 from the vessel to a
collection vessel or other process.
[0057] The shaft 44 may have a lower end within the vessel 70. The
lower end is driven by a gear box and motor 96 also within the
vessel. Brackets, e.g. radial ribs, within the vessel support the
lower end of the shaft and the gear box and motor within the
vessel. By mounting the end of the shaft and gearbox and motor in
the vessel, pressurized shaft seals become unnecessary between the
shaft and openings in the vessel.
[0058] A portion of the hot pressurized inert gas extracted from
the vessel 70 may flow through conduit 90 to the chip feed system
14. The hot gas flows through the chip feed system to purge air
from the chip feed system. For example, the hot gas may flow into a
lower gas manifold 92 into one or more locations in the chip bin
12. The gas from the manifold enters the chip bin and forces the
air in the bin out through an upper air vent 94 and to a
conventional non-condensable gas handling system. The hot gas
entering the chip bin adds heat to the biomass and thereby reduces
the heat energy needed to be added to the biomass in the vessel
70.
[0059] FIG. 3 is a schematic diagram of a pressurized treatment
vessel 100 for torrefaction of biomass. The vessel 100 is similar
to the vessels 10 and 70 shown in FIGS. 1 and 2, except that the
trays 102, 104 are stationary. The scraper bars 106 are fixed to
the shaft 108 that is rotated by a gear box and motor 96. The
scraper bars may be solid rods, frames with supporting ribs or
other radially extending rigid or semi-rigid arm. As the scraper
bars 106 rotate with the shaft, the bars sweep the biomass over the
surface of the stationary trays. As the biomass slides over the
trays, the biomass is dried and heated by hot inert gases
circulating through the vessel and fed to one or more upper gas
inlets 112 from an inert gas source 110.
[0060] There may be one or more scraper bars arranged in a radial
array on each tray 102, 104. The scraper bars may extend radially
outward or extend at an angle of zero to 90 degrees with respect to
a radial line. The bars may be straight, curved, concave, convex or
other shape that facilitates the movement of biomass over the
trays.
[0061] At least the upper trays 102 may be perforated, mesh,
screens or other open frames to promote the flow of hot inert gases
to flow through the biomass and the vessel. The lower trays 104 may
be solid to slow the flow of hot inert gases from the upper to the
lower regions of the vessel. Alternatively, the lower trays 104 may
be open frames as are the upper trays 102.
[0062] The trays may be supported by the inner surface of the wall
112 of the pressure vessel. The inner surface of the wall 112 may
include hangers, ridges or other support surfaces 114 on which rest
the outer rim of the trays. 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. The open section 46 of each tray
102, 104, allows the tray to slide past the shaft 108 from removal
and installation.
[0063] The lowermost tray may have a center chute 116 to direct
biomass to the lower portion 80 of the vessel. The lowermost tray
may be an inverted cone with the center discharge chute 116 to
allow biomass to flow directly to a center discharge outlet 116 of
the vessel.
[0064] 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.
[0065] 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.
* * * * *