U.S. patent application number 13/870564 was filed with the patent office on 2013-09-12 for method and system for the torrefaction of lignocellulosic material.
This patent application is currently assigned to ANDRITZ TECHNOLOGY AND ASSET MANAGEMENT GMBH. The applicant listed for this patent is Joseph Monroe RAWLS, Bertil STROMBERG. Invention is credited to Joseph Monroe RAWLS, Bertil STROMBERG.
Application Number | 20130232863 13/870564 |
Document ID | / |
Family ID | 43034618 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130232863 |
Kind Code |
A1 |
STROMBERG; Bertil ; et
al. |
September 12, 2013 |
METHOD AND SYSTEM FOR THE TORREFACTION OF LIGNOCELLULOSIC
MATERIAL
Abstract
Systems and methods for producing torrefied lignocellulosic
material in a commercially suitable process.
Inventors: |
STROMBERG; Bertil; (Diamond
Point, NY) ; RAWLS; Joseph Monroe; (Queensbury,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STROMBERG; Bertil
RAWLS; Joseph Monroe |
Diamond Point
Queensbury |
NY
NY |
US
US |
|
|
Assignee: |
ANDRITZ TECHNOLOGY AND ASSET
MANAGEMENT GMBH
Graz
AU
|
Family ID: |
43034618 |
Appl. No.: |
13/870564 |
Filed: |
April 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12832614 |
Jul 8, 2010 |
8449724 |
|
|
13870564 |
|
|
|
|
61235114 |
Aug 19, 2009 |
|
|
|
Current U.S.
Class: |
44/589 ;
44/605 |
Current CPC
Class: |
C10L 5/363 20130101;
Y02E 50/15 20130101; Y02E 50/30 20130101; C10L 5/44 20130101; C10L
9/083 20130101; C10L 5/447 20130101; Y02E 50/10 20130101; Y02E
50/14 20130101 |
Class at
Publication: |
44/589 ;
44/605 |
International
Class: |
C10L 5/44 20060101
C10L005/44 |
Claims
1. A method for the torrefaction of lignocellulosic material
comprising the steps of: drying lignocellulosic material to remove
at least a portion of moisture contained within the lignocellulosic
material; reacting the dried lignocellulosic material at a pressure
between 1 and 50 bar and at a temperature between 100 and
1000.degree. C. in a torrefaction reactor to generate torrefied
biomass and torrefaction gas; recycling at least a portion of the
torrefaction gas back to the torrefaction reactor; cooling the
torrefied biomass in a cooler operating in a substantially
oxygen-free environment; recycling inert gas to the cooler and
recycling inert gas to the torrefaction reactor; supplying make-up
inert gas to the cooler; wherein the method uses the inert gas as
at least a partial medium for transferring heat among the
torrefaction reactor and the cooler.
2. The method of claim 1, wherein the cooler is a fluidbed cooler,
and wherein the method further comprises a step of separating the
torrefied biomass and inert gas in a cyclone.
3. The method of claim 1, wherein the inert gas comprises
nitrogen.
4. The method of claim 1, wherein the step of drying removes
moisture present in the lignocellulosic material such that an
absolute moisture content of the lignocellulosic material is less
than 15% of the total weight of the lignocellulosic material.
5. The method of claim 1 further comprising the step of combusting
at least oxygen and a portion of the torrefaction gas produced in
the torrefaction reactor to produce a hot flue gas.
6. The method of claim 1 further comprising the step of providing
the hot flue gas to the dryer at a temperature of up to
1,000.degree. C.
7. The method of claim 1 further comprising the step of compacting
in a pelletizer the torrefied biomass solids obtained from the
cooler.
8. The method of claim 1 further comprising the steps of separating
air into at least a first stream comprising oxygen and a second
stream comprising nitrogen and using the nitrogen as the inert
gas.
9. The method of claim 1, wherein reacting the dried
lignocellulosic material occurs at a pressure between 5 and 20
bar.
10. The method of claim 1, wherein reacting the dried
lignocellulosic material occurs at a temperature of about
220-300.degree. C.
Description
RELATED APPLICATION
[0001] This application is a divisional of U.S. application Ser.
No. 12/832,614, filed on Jul. 8, 2010, and claims the benefit of
priority to U.S. Provisional App. No. 61/235,114, filed on Aug. 19,
2009, the entirety of each of which is incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to systems and
methods relating to the torrefaction of lignocellulosic
material.
[0003] Torrefaction refers to the thermal treatment of wood,
usually in an inert atmosphere, at relatively low temperatures of
225 to 300.degree. C. Torrefaction generally results in a fuel with
increased energy density relative to the mass, by the decomposition
of reactive hemicellulose content of the wood.
[0004] Wood generally contains hemicellulose, cellulose, and
lignin. In an aspect, the goal of torrefaction is to remove
moisture and low weight organic volatile components from the wood.
Torrefaction may also depolymerize the long polysaccharide chains
of the hemicellulose portion of the wood and produce a hydrophobic
solid product with an increased energy density (on a mass basis)
and improved grindability. Because of the change in the chemical
structure of the wood after torrefaction, it can be suitable for
use in coal fired facilities (torrefied wood or biomass has the
characteristics that resemble those of low rank coals) or can be
compacted into high grade pellets replacing standard wood
pellets.
[0005] Torrefaction has developed over the last few decades as a
possible method to turn wood based biomass into a viable addition
to the spectrum of energy products. Although there has been much
research into the compositional changes that occur in the biomass
(wood) while undergoing torrefaction, commercial processes are not
well developed. The torrefaction method and system put forth here
has been developed to meet the commercial need for a viable
torrefaction process. Other torrefaction processes are described
in: U.S. Patent Pub. No. 2008/0223269, in which conduction heat is
used to achieve torrefaction; U.S. Pat. No. 4,787,917, in which
torrefied wood is formed into sticks of unbarked wood; and PCT Pub.
No. WO 2005/056723, in which a continuous method and system
produces torrefied biomass from raw material (organic material and
originate from forestry or other agriculture and material of fossil
nature or mixture--lignocellulose).
BRIEF DESCRIPTION OF THE INVENTION
[0006] Torrefaction of the wood material typically produces three
products: a solid product of dark color which can be further
processed to pellets or used directly as biomass fuel; an acidic
phase comprised of condensable organics (including, but not limited
to acetic acid, formic acid, acetone, furfural); and gases such as
carbon monoxide or carbon dioxide. In an aspect the process may be
a low temperature, low oxygen pyrolysis process where the easy to
remove compounds having the lowest heat and energy values are
removed.
[0007] In an aspect of this process, approximately 30% of the mass
is burned off while losing only 10% of the energy value, that is to
say the remaining solid mass (approximately 70% of the original
material mass) contains 90% of the heat value originally present.
Torrefaction may occur in a pressurized reactor and a temperature
of 220-300.degree. C. where there is direct contact of the raw
material/biomass (lignocellulosic material), which has been
previously dried to remove up to approximately 95% of the moisture
initially present in the biomass, with hot gas (relatively oxygen
free gas). Heating of the dried biomass in the torrefaction reactor
may remove the remaining water from the biomass.
[0008] In an aspect, there is a system for the torrefaction of
lignocellulosic material. The system may include: a dryer for
drying lignocellulosic material adapted to remove at least of a
portion of moisture contained within the lignocellulosic material;
a torrefaction reactor adapted to operate at a pressure between 1
and 50 bar and at a temperature between 100 and 1000.degree. C.,
wherein the torrefaction reactor generates torrefied biomass and a
torrefaction gas from the lignocellulosic material; a first recycle
loop adapted to recycle torrefaction gas back to the torrefaction
reactor; a cooler adapted to cool torrefied biomass, wherein the
cooler is adapted to operate in a substantially oxygen-free
environment; a cyclone adapted to separate the cooled torrefied
biomass from an inert gas; a second recycle loop adapted to recycle
the inert gas from the cyclone to the cooler and to provide the
inert gas to the torrefaction reactor; and a supply line adapted to
supply inert gas for addition to the cooler. The system may be
adapted to use the inert gas as a medium for transferring heat
among the torrefaction reactor and the cooler.
[0009] In another aspect, there is a method for the torrefaction of
lignocellulosic material comprising the steps of: drying
lignocellulosic material to remove at least a portion of the
moisture contained within the lignocellulosic material; reacting
the dried lignocellulosic material at a pressure between 1 and 50
bar and at a temperature between 100 and 1000.degree. C. in a
torrefaction reactor to generate torrefied biomass and torrefaction
gas; recycling at least a portion of the torrefaction gas back to
the torrefaction reactor; cooling the torrefied biomass in the
cooler operating in a substantially oxygen-free environment;
separating the torrefied biomass and an inert gas in a cyclone;
recycling a portion of the inert gas separated in the cyclone to
the cooler and recycling a portion of the inert gas separated in
the cyclone to the torrefaction reactor; supplying make-up inert
gas to the cooler. The method may use the inert gas as a medium for
transferring heat among the torrefaction reactor and the
cooler.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic flowchart illustrating an embodiment
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] FIG. 1 schematically illustrates a commercial-scale facility
capable of torrefaction of biomass (lignocellulosic material). The
embodiment of FIG. 1 takes advantage of heat from the process while
maintaining an oxygen-free (i.e., substantially oxygen-free)
environment, which is beneficial for safe, efficient operation.
[0012] In the illustrated process, biomass material is fed via
conduit 1 to a drying device 2, which is any conventional or
nonconventional drying device capable of removing between 85 and
98% of the moisture present in the biomass. In the illustrated
drying device 2, the moisture present in the biomass is removed by
energy supplied via hot gas 23. The dryer may remove a sufficient
amount of moisture such that an absolute moisture content of the
dried lignocellulosic material is less than 15% of the total weight
of the lignocellulosic material. In the depicted embodiment, hot
gas in conduit is the result of flue gas in conduit 9 from the
combustion unit 8 after the flue gas has been cooled slightly by an
indirect heat exchanger 20. Heat exchanger 20 facilitates recycling
the energy in the hot flue gas 9 back to the torrefaction reactor 5
via conduit 19 for use in heating the reactor 5.
[0013] The drying gas fed to dryer 2 via conduit 23 may be at a
temperature of up to 1,000.degree. C. to allow for drying to the
desired residual moisture level. The dried biomass is then fed via
conduit 3 and rotary valve 4 to the inlet to a pressurized reactor
5 (also called torrefaction reactor). The torrefaction reactor 5
may operate at between 5 and 20 bar, and at an operating
temperature of about 220-300.degree. C. In other embodiments, the
pressure may range from 1 to 50 bar (and all subranges
therebetween), and the temperature may range between 100 and
1000.degree. C. (and all subranges therebetween).
[0014] To raise the temperature of the dried biomass material
(e.g., from 100 to 300.degree. C.), heat is provided from heated
reactor gas supplied via conduit 19. The heated reactor gas is
comprised of a portion of the torrefaction gas (gas produced in the
torrefaction reactor 5) which exits torrefaction reaction 5 via
conduit 6 and which is recycled to the torrefaction reactor 5 (as
recycled torrefaction gas via conduit 7) and a portion of the
cyclone nitrogen rich gas via conduit 18.
[0015] The portion of the recycled torrefaction gas which is
recycled to the torrefaction reactor 5 and any additional nitrogen
rich gas can be heated in an indirect heat exchanger 20 by flue gas
or other heating means in conduit 9 from the combustion unit 8
prior to use in the torrefaction reactor 5. A portion of the
torrefaction gas (e.g., the portion in conduit 21) produced in the
torrefaction reactor 5 can be sent to the combustion unit where the
torrefaction gas is mixed with oxygen containing gas fed via
conduit 12 from the Pressure Swing Adsorption (PSA) plant 11 and/or
combustion air and/or with utility fuel fed via conduit 22 (if
needed) to produce combustion flue gas exiting via conduit 9 from
combustion unit 8.
[0016] The combustion flue gas may be used as the heat source for
the indirect heat exchanger 20 to heat the reactor gas provided to
the torrefaction reactor 5 via conduit 19. The cooler combustion
flue gas of stream 23 may be used in the drying unit 2 to dry the
incoming biomass. The drying flue gas of conduit 24 produced from
the drying process may be sent to further processing prior to
disposal to the atmosphere or other acceptable disposal.
[0017] Torrefied biomass exiting via stream 25 from the
torrefaction reactor 5 at a temperature of about 220 to 300.degree.
C. may be fed to a rotary valve 26 at the inlet to the fluidbed
cooler 29 (or other direct contact cooler). The fluidbed cooler 29
may be a combination indirect cooler, using water as the cooling
medium, and direct cooler, using cooled nitrogen rich stream 17 or
any other inert gas from heat exchanger 16 and make-up nitrogen
from the PSA (or other gas separation type equipment) plant 11 or
any other inert gas to cool the torrefied biomass entering the
fluidbed cooler 29 via stream 25 to about 90.degree. C. in an
oxygen free or near oxygen free environment. The cooled torrefied
biomass may be discharged from the fluidbed cooler 29 via a rotary
valve 30 (or similar device to assure the fluidbed cooler 29
operates in an oxygen-free, or substantially oxygen-free,
environment). Cool torrefied biomass in stream 40 discharged from
the fluidbed cooler 29 may be mixed with torrefied biomass solids
stream 35 separated in the cyclone 32 (discharged through rotary
valve 33 or other such equipment to ensure an oxygen-free or near
oxygen-free environment is maintained in the cyclone 32) to produce
a stream 37 for further processing in a pelletizing unit 38 or
other product handling process for compacting or packaging the
torrefied biomass solids.
[0018] The fluidbed cooler 29 may operate at near atmospheric
pressure (e.g., the cooler may operate at a slight vacuum or
slightly above atmospheric pressure) and may use indirect cooling
from cooling water (noted as Cooling Water Supply (CWS) 27 and
Cooling Water Return (CWR) 28) as well as direct cooling from the
nitrogen rich gas in stream 17. The nitrogen rich gas in stream 17
may contain a portion of cyclone nitrogen rich gas in stream 36
combined with make-up nitrogen 13. Heat exchanger 16 can be
supplied with cooling water as the indirect cooling medium or other
available cooling material.
[0019] Fluidbed cooler gas in stream 31 from the fluidbed cooler 29
may be sent to cyclone 32 where cooled gas is separated from any
entrained solids. The cooled gas in stream 34 may then be split
into two or more portions. For example, cyclone nitrogen gas stream
34 may be split into two portions: (i) stream 18 which can be sent
to heat exchanger 20 in the heating loop around the torrefaction
reactor for mixing with stream 7 to feed the torrefaction reactor 5
and (ii) stream 36 which is fed to heat exchanger 16 to be
cooled.
[0020] Air in conduit 10 may be provided to PSA Plant 11 where two
gas streams are produced: make-up nitrogen stream 13 (a stream rich
in nitrogen with little or no oxygen) and an oxygen rich stream 12
which is used together with utility fuel in the combustion
unit.
[0021] While the description provided uses nitrogen as the gas in
the heating and cooling loops where oxygen-free, or substantially
oxygen-free, environments may be employed avoid explosive mixtures,
any inert gas (for example argon or carbon dioxide, but nitrogen is
preferred) can be used in place of nitrogen. The inert gas (e.g.,
nitrogen) is used in this process as a "carrier" gas, meaning the
inert gas carries the heat needed in the torrefaction reactor and
from the fluidbed cooler. Additionally, while the process may use a
PSA Plant to separate nitrogen from air, any other method of
separating nitrogen from air can also be used and is not a critical
feature of this invention. It is also within the scope of the
invention to use any source of nitrogen or other inert gas.
[0022] In the embodiment of FIG. 1, moreover, cooling water is
described as the cooling medium in the indirect cooling services.
In other embodiments, the cooling medium may be some medium other
than water without impacting the important technical features of
this process. That is, any fluid capable of effectively cooling may
be employed.
[0023] In an aspect, a notable feature of this process is the
ability to use nitrogen rich gas from the cyclone (which would
otherwise be purged from the system) as part of the reactor gas for
the torrefaction step. By using this nitrogen rich gas a balance
can be established in the both the cooling loop and the heating
loop with minimal addition of make-up nitrogen. This also means the
torrefaction gas composition is used to set the operating
conditions of the combustion unit by controlling the ratio of gas
(via conduit 21) from the reactor going to the combustion unit
versus gas (via conduit 6) produced by the reactor. This
ratio--which may be expressed in either volumetric or molar
terms--then influences the nitrogen needed for make-up as well as
the quantity of utility fuel required. It is also preferable that
the streams being recycled in both the heating and cooling loops
remain oxygen-free or substantially oxygen-free. In an aspect, the
described process of FIG. 1 may provide optimum equipment sizing,
thereby saving capital investment, as well as improves the impact
on the environment of the products from the process.
[0024] 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.
* * * * *