U.S. patent application number 14/414202 was filed with the patent office on 2015-07-23 for energy pellet.
The applicant listed for this patent is Michael A. Lake. Invention is credited to Michael A. Lake.
Application Number | 20150203774 14/414202 |
Document ID | / |
Family ID | 49949205 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150203774 |
Kind Code |
A1 |
Lake; Michael A. |
July 23, 2015 |
ENERGY PELLET
Abstract
A high-energy water-resistant pellet of at least 75% torrefied
wood and the remainder a binder comprising from about 2% to about
20% by total weight of the pellet. The binder is a two-component
system--a plasticizer, such as tall oil pitch, rosin, fatty acid,
vegetable oils, animal oils and corn protein--preferably from 3% to
about 20% of the binder, and lignin from about 80-97% of the
binder. A durable, low dust white wood energy pellet is also
provided using the same two-component binders.
Inventors: |
Lake; Michael A.; (Mt.
Pleasant, SC) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Lake; Michael A. |
|
|
US |
|
|
Family ID: |
49949205 |
Appl. No.: |
14/414202 |
Filed: |
July 16, 2013 |
PCT Filed: |
July 16, 2013 |
PCT NO: |
PCT/US2013/050679 |
371 Date: |
January 12, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61673573 |
Jul 19, 2012 |
|
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|
Current U.S.
Class: |
44/564 ; 44/578;
44/596 |
Current CPC
Class: |
C10L 5/447 20130101;
Y02E 50/10 20130101; Y02E 50/15 20130101; C10L 5/143 20130101; C10L
2200/0469 20130101; C10L 5/442 20130101; C10L 2290/06 20130101;
C10L 5/363 20130101; C10L 5/16 20130101; C10L 9/083 20130101; C10L
2290/24 20130101; Y02E 50/30 20130101; C10L 2230/22 20130101; C10L
5/24 20130101 |
International
Class: |
C10L 5/24 20060101
C10L005/24; C10L 5/36 20060101 C10L005/36; C10L 5/14 20060101
C10L005/14; C10L 5/44 20060101 C10L005/44; C10L 5/16 20060101
C10L005/16 |
Claims
1. A high-energy water-resistant pellet comprising: (a) at least
75% torrefied wood; and (b) the remainder of said pellet being a
two-component binder comprising from about 2% to about 20% by total
weight of the pellet wherein said binder is a two-component system
comprising a plasticizer selected from the group consisting of tall
oil pitch, fatty acids, rosin, vegetable oil, animal oils and corn
protein and the other component is lignin.
2. The high-energy water resistant pellet according to claim 1
wherein said high-energy water-resistant pellet comprises at least
85% torrefied wood and less than 10% by weight water.
3. (canceled)
4. (canceled)
5. The high-energy water resistant pellet according to claim 4
wherein said plasticizer is from about 3% to about 20% of said
binder.
6. The high-energy water resistant pellet according to claim 1
wherein said lignin is from about 80% to about 97% of said
binder.
7. The high-energy water resistant pellet according to claim 1
wherein high-energy water resistant pellets have a bulk density
40-45 lbs/ft,
8. A high-energy water-resistant pellet comprising: (a) at least
85% torrefied wood; and (b) the remainder of said pellet being a
two-component binder comprising from about 2% to about 20% by total
weight of the pellet, wherein one component of said binder is a
plasticizer selected from the group consisting of tall oil pitch,
fatty acids and rosin, vegetable oil, animal oils and corn protein
and the other component is lignin in an amount from about 80% to
about 97% of said binder.
9. A high-energy water-resistant pellet comprising: (a) at least
75% white wood; and (b) the remainder of said pellet being a
two-component binder comprising from about 2% to about 20% by total
weight of the pellet wherein said binder is a two-component system
comprising a plasticizer selected from the group consisting of tall
oil pitch, fatty acids, rosin., vegetable oil, animal oils and corn
protein and the other component is lignin.
10. (canceled)
11. (canceled)
12. The high-energy water resistant pellet according to claim 11
wherein said plasticizer is from about 5% to about 20% of said
binder.
13. The high-energy water resistant pellet according to claim 11
wherein said lignin is from about 80% to about 97% of said
binder.
14. The high-energy water resistant pellet according to claim 11
wherein high-energy water resistant pellets have a bulk density
40-45 lbs/ft.sup.3.
15. A high-energy water-resistant pellet comprising: (a) at least
85% white wood; and (b) the remainder of said pellet being to
two-component binder comprising from about 2% to about 20% by total
weight of the pellet, wherein one component of said binder is a
plasticizer selected from the group consisting of tall oil pitch,
fatty acids, rosin, vegetable oil, animal oils and corn protein and
the other component is lignin in an amount from about 80% to about
97% of said binder.
16. A process for making an energy pellet from torrefied wood or
white wood comprising: (a) mixing at least 75% of said wood; and
the remainder of said mixture being a two-component binder
comprising wherein one component of said binder is a plasticizer
selected from the group consisting of tall oil pitch, fatty acids,
rosin, vegetable oil, animal oils and corn protein and the other
component is lignin, said binder being from about 2% to about 20%
by total weight of said mixture; and (b) compressing said mixture
by extruding said mixture at a temperature at which said binder is
in a molten state to form a pellet.
17. The process for making an energy pellet from torrefied wood
according to claim 16 wherein said mixture is extruded at a
temperature from about 100.degree. C. to about 280.degree. C.
18. The process for making an energy pellet from torrefied wood
according to claim 16 wherein said mixture is extruded at a
temperature from about 100.degree. C. to about 165.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The contents of Provisional Application Ser. No. 61/673,573
filed Jul. 19, 2012, on which the present application is based and
benefit claimed under 35 U.S.C. .sctn. 119(e), is herein
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] (1) Field of the Invention
[0003] The present invention relates to energy pellets made from
torrefied wood and whole-tree (white) wood and methods of making
same. More particularly, this invention relates to energy pellets
made from torrefied wood or white wood combined with lignin and a
biomass-based plastizer to form a water-resistant and durable
high-energy-density pellet.
[0004] (2) Description of Related Art
[0005] In recent years renewal energy sources have become more
desirable and thus more important although the United States
continues to be heavily reliant on the combustion of non-renewable
fossil fuels to meet its energy needs. Additionally, energy from
biomass mandates in the European Union has led to a rapidly growing
export market for energy pellets. Exports of white-wood pellets to
the EU from North America was 4.4 million metric tons in 2012 and
is predicted to reach 25-70 million metric tons per year by 2020.
To meet the growing energy needs biomass based materials have been
pelletized to provide a dense, relatively high energy material.
[0006] One of the desirable biomass materials being developed is
torrefied wood. Torrefied wood is wood that has been partially
oxidized to drive off the water and the organic volatiles and a
fraction of the cellulose, so that a "blackened" wood chip is the
result. The torrefied wood chips are friable and can be easily
formed into a high-energy, high-density pellet. When a pellet is
made from southern yellow pine wood with its high resin content, it
will remain as a pellet for days when immersed in water--indicating
excellent water repellency. A pellet made from southern yellow pine
needs no binder, since the pellets from that wood is exposed to the
40,000+ psi of the extruder and temperatures exceeding 100.degree.
C., the natural components flow to form a water repellant binder
naturally. However, when a pellet is made from torrefied wood, most
of the natural binders are burned off so that the resulting pellet
has poor water repellency, and in a worst case, the pellets turn
into a black "mud" upon exposure to water.
[0007] Another problem with torrefied wood and even with white wood
pellets, especially those made from low-resin-containing biomass,
is durability. The pellets themselves tend to be friable and create
dust during mechanical processes needed to transport the pellets,
such as loading and unloading rail cars and ships. As much as 5-7%
loss of mass from dust has been reported for white-wood pellets. In
addition to product loss, the dust creates hazards, from inhalation
and the potential for dust explosions.
[0008] Torrefied wood has the strong advantage of being closer to
coal in its burning capabilities than white wood. And the energy
(bulk) density of torrefied wood is much greater than white wood so
its shipping costs are much lower.
[0009] The high-energy, high-density and coal-like mechanical
properties of torrefied wood pellets are desirable for large
biomass burning facilities--like the utilities but the coal is
normally transported in uncovered cars to and from ports and stored
in uncovered piles at the combustion site, so water repellency is a
key attribute. A single utility would have to spend $100 million or
more to cover these pellet piles and rail cars, and few if any will
make this capital expenditure, so water repellency is strongly
desirable.
[0010] Currently wood pellets are burned, but the lower energy
density and their pulverizing and burning characteristics limit
their use as a fuel since they are so different from coal. Energy
pellets made entirely of lignin has approximately the same energy
content as coal, about 12,000 Btu/lb, which is about 50% higher
energy per mass of low-moisture wood pellets having about 8,000
Btu/lb.
[0011] Within the wood matrix, lignin is a macromolecule is
chemically bound to cellulose and hemicellulose. In pulping
processes or enzymatic biorefineries, the lignin is separated from
the cellulose and hemicellulose and its molecular weight is reduced
(i.e., the lignin is "chopped up"). This isolated lignin at ambient
conditions is a solid, but it can be melted at elevated
temperature, with lower molecular weight lignin generally having a
lower melt point. The problem is that isolated solidified lignin is
very friable, and its melt point may not be ideal for the
pelletizing system so that the lignin melts and flows within the
pelletizer but solidifies upon exiting and cooling.
[0012] The lignin content in wood has recently been shown (Thomas
Wilson, PhD Thesis, Penn State University, 2010) to have no effect
on the durability of white wood pellets. In the Penn State study, a
wide variety of wood with varying lignin contents was used;
however, all that lignin was in the macromolecular form and
chemically bound to cellulose. Contrary to the Penn State study,
lignin with lower molecular weight that has been isolated from wood
has better binding capability. And the macromolecular lignin used
in the Penn State study may not have the required melt-point
profile.
[0013] For a binder to work well in forming energy pellets, the
binder must melt and flow under the extruder conditions of elevated
temperature and pressure. As the pellets emerge from the extruder
and cool, the binder must reform as a solid, coating and protecting
the smaller elements--loose fibers of white wood or particles of
torrefied wood.
[0014] Lignosulfonate is a byproduct of the sulfite pulping
process. Lignosulfonates have demonstrated commercial utility as
binders for animal foods. Lignosulfonates are a poor choice as
energy pellet binders because: (1) lignosulfonates have high levels
of organically-bound sulfur--as high as 10% by mass--that converts
to sulfur dioxide upon combustion; and (2) lignosulfonates contain
residual sugar from the pulping process. These sugars are
hydrophilic and deleteriously affect the water resistance of energy
pellets. The sulfonate groups on the lignin are also hydrophilic,
exacerbating the water resistance problem.
SUMMARY OF THE INVENTION
[0015] There is provided a high-energy water-resistant pellet
having at least 75% torrefied wood and the remainder being a
two-component binder comprising from about 2% to about 25% by total
weight of the pellet. The starting material is torrefied wood
having a moisture content of below 15% water, with the equilibria
water content being about 10-15% water. The binder is a
two-component system--with a plastizer to adjust the melt point,
such as tall oil pitch, rosin, fatty acids, animal oils, vegetable
oils, or corn-oil proteins, preferably from 3% to about 20% of the
binder, and lignin from about 80-97% of the binder.
[0016] There is also provided at method for making a high-energy
water-resistant pellet from torrefied wood and a two component
binder.
[0017] It is therefore the general object of the present invention
to provide a high-energy, high density fuel pellet made from
torrefied wood or white wood and a binder that is water
repellent.
[0018] Another object of the present invention is to provide a
high-energy, high-density water-repellant fuel pellet from
torrefied wood or white wood that includes a two-component
binder.
[0019] Yet another object of the present invention is to provide a
process for producing a high-energy pellet.
[0020] Other objects, features and advantages of the invention will
be apparent to those skilled in the art from the following detailed
description of the preferred embodiments of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0021] The present invention now will be described more fully
hereinafter in which preferred embodiments of the invention are
shown. This invention may, however, be embodied in many different
forms and should not be construed as limited to the embodiments set
forth herein; rather these embodiments are provided so that this
disclosure will be through and complete and will fully convey the
scope of the invention to those skilled in the art.
[0022] A preferred fuel pellet of the present invention is produced
from torrefied wood having a moisture content of below 15% water,
with the equilibria water content being about 10-15% water, that
has been mixed with a binder and compressed by passing through an
extruder, typically at a temperature at which the binder is in a
molten state while the torrefied wood is compressed. Forming the
pellets commonly involves hydraulic extrusion through a fuel pellet
die. Of course, other suitable compression equipment known to those
skilled in the art may be used. The temperature of the torrefied
wood and binder in the extruder is above 100.degree. C. but is not
allowed to exceed 280.degree. C. to avoid adverse exothermal
torrefication conditions. Preferably the temperature is maintained
between 100.degree. C. and 165.degree. C. Another embodiment of the
present invention uses whole-tree (white) wood in place of
torrefied wood. For use in this invention the white-wood is ground
to a size that allows free-flow into the throat of the
extruder.
[0023] The water-resistant high-energy pellet comprises at least
75% torrefied wood and preferably at least about 85% torrefied
wood, and the remainder a binder comprising from about 2% to about
25%, preferably about 3% to about 15%, by total weight of the
pellet. The binder comprises of a plasticizer, such as tall oil
pitch, preferably from 5% to about 20% by weight of the binder, and
lignin from about 80% to about 97% by weight of the binder. The
optimal ratio of the lignin to plasticizer will depend upon the
characteristics of the torrefied wood, the lignin, and the
plasticizer that are contained within the pellet. Those choices
typically are made with economics being the primary factor.
[0024] Lignin, a by-product of the pulp and paper industry, of
sufficiently low T.sub.g will flow and provide protective coverage
within the pellet that is needed for water repellency but may not
flow under the conditions of the pelletizer which operates at
105.degree. C. and .gtoreq.40,000 psi. The individual
characteristics of the lignin chosen may not be suitable without a
plasticizer since its T.sub.g may be too high which inhibits its
flow at the temperature of the pelletizer. Adding a plasticizer
that itself is water resistant can provide the requisite T.sub.g
allowing the binder to flow within the pelletizer yet solidify at
ambient temperature. Again this ratio will be driven by performance
and economics since lignin generally will be much less expensive
than tall oil pitch once the multiple large-volume lignin
production facilities come on-line from papermaking operations and
enzymatic conversion of biomass that will have lignin as a
byproduct stream.
[0025] The binders contemplated for use in this invention are
totally natural organics, preferably tall oil pitch, fatty acids,
rosin and the like. Tall oil pitch is the bottoms product from the
first distillation column of a refinery that has tall oil as a
feedstock and makes distilled rosins and fatty acids as products.
The tall oil pitch may be used, or the "spent" tall oil pitch from
which the valuable sterol fraction has been removed could be
used.
[0026] The binders of this invention may also include vegetable or
animal oils to plasticize the lignin while providing water
repellency. Corn oil and corn protein isolated from ethanol
processing provides a ready commercial source of natural
plasticizers. Corn protein has demonstrated binding capability, and
provides additional binding capability to the lignin.
[0027] Tall oil pitch is an excellent binder for fire logs, and TOP
is currently commercially used for this application. The cost of
TOP can be relatively high ($400-$600/ton). The "spent" tall oil
pitch, which has the valuable sterol fraction removed is less
expensive.
[0028] Torrefied wood pellets have a bulk density (40-45
lbs/ft.sup.3), about twice that of non-pelletized torrefied wood
(16-20 lbs/ft.sup.3), so making pellets dramatically reduces volume
and subsequent transportation costs. Torrefied wood pellets have an
energy density about the same as coal, 12,000 Btu/lb.
Size-reduction characteristics of wood pellets--how they break down
under mechanical forces--are much different than that of coal,
which is a problem when large fractions of wood pellets are fed
into existing pulverizing equipment used by all coal-burning
power-generation equipment. However, size-reduction characteristics
of torrefied wood pellets are very similar to those of coal. Thus
the mechanical handling characteristics and energy density of
torrefied wood pellets are very similar to coal, making those
pellets much more acceptable as a direct substitute for coal.
[0029] As noted, one of the critical characteristics of the
high-energy-content torrefied wood pellets of this invention is
that they are water repellant. Another important property is pellet
strength and attrition resistance, since dust creates not only
worker health and safety issues but also dust severely reduces the
bulk density of the pellets so that a ship loaded with pellets
crossing an ocean carries a lower mass loading causing the shipping
rates per ton to be higher. This densification effect is
counter-intuitive because the dust particles separate the
individual pellets thereby decreasing the bulk density instead of
partitioning entirely in the interstitial areas of the bulk
pellets.
[0030] Many modifications and other embodiments of the invention
set forth herein will come to mind to one skilled in the art to
which this invention pertains having the benefit of the teachings
presented in the foregoing descriptions. Therefore, it is to be
understood that the invention is not to be limited to the specific
embodiments disclosed and that modifications and other embodiments
are intended to be included within the scope of the appended
claims. Although specific terms are employed herein, they are used
in a generic and descriptive sense only and not for purposes of
limitation.
* * * * *