U.S. patent application number 14/211466 was filed with the patent office on 2014-09-18 for mobile pelletizing system.
The applicant listed for this patent is Bonfire Biomass Conversions, LLC. Invention is credited to Thomas K. Mason.
Application Number | 20140259895 14/211466 |
Document ID | / |
Family ID | 51520817 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140259895 |
Kind Code |
A1 |
Mason; Thomas K. |
September 18, 2014 |
Mobile Pelletizing System
Abstract
The present invention provides portable pelletizing systems for
in situ processing of biomass material to pellets. Systems
according to embodiments of the invention have a complete set of
processing components and an engine for powering the processing
components. The processing components are interconnected. Loading,
unloading, and coordination of each of the processing components is
automatically controlled through a controller. A heat exchange
network is integrated with the engine and the processing
components, wherein the heat exchange network transfers heat
between the engine and the processing components. The system is
self-contained and may be transported using a vehicle so that the
system may receive biomass material of varying composition and
moisture content at a point of origin. The complete set of
processing components may include an input, a means for reducing
the size of the biomass material, a blender, a dryer, a
conditioner, a pellet mill, a cooler, and an output.
Inventors: |
Mason; Thomas K.;
(Lynchburg, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bonfire Biomass Conversions, LLC |
Lynchburg |
VA |
US |
|
|
Family ID: |
51520817 |
Appl. No.: |
14/211466 |
Filed: |
March 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61783635 |
Mar 14, 2013 |
|
|
|
Current U.S.
Class: |
44/589 ;
44/636 |
Current CPC
Class: |
B30B 11/006 20130101;
B30B 15/281 20130101; B30B 15/26 20130101; B30B 15/0094 20130101;
B30B 11/28 20130101; Y02E 50/10 20130101; C10L 5/363 20130101; Y02E
50/30 20130101; C10L 5/44 20130101; B30B 11/201 20130101 |
Class at
Publication: |
44/589 ;
44/636 |
International
Class: |
C10L 5/44 20060101
C10L005/44 |
Claims
1. A mobile biomass pelletizing system comprising: modules for
reducing, blending, drying, conditioning, and pelletizing biomass;
one or more sensors for determining composition, moisture, and
temperature information about the biomass contained in the modules
during use; a control system in operable communication with the
modules and sensors for: receiving the composition, moisture, and
temperature information; adjusting operating parameters of one or
more module and automatically moving the biomass between modules in
response to the information received; wherein the modules are
disposed within a single, portable housing; and wherein during use
pellets having a density within a selected range are produced from
multiple batches of biomass feedstock varying in composition and
moisture content.
2. The system of claim 1, wherein during use the pellets produced
have a density varying no more than 10% and are produced from
biomass feedstock varying more than 2-5 times in moisture
content.
3. The system of claim 1, wherein during use total energy
consumption is less than 150 kWh/t for operating all modules.
4. A system for in situ processing of biomass material to pellets,
comprising: an input module for receiving biomass; a reducer module
for reducing particles size of the biomass; a blender module for
homogenizing the biomass; a dryer module for removing moisture from
the biomass; a conditioner module for adding moisture to the
biomass; a pellet mill module for converting the biomass into
pellets; a cooler module for optionally cooling the biomass or the
biomass pellets; an output module for exporting the biomass pellets
from the system; an engine in operable communication with and for
powering any one or more of the input, reducer, blender, dryer,
conditioner, pellet mill, cooler, or output modules; wherein each
module and the engine are disposed within a single housing.
5. The system of claim 4, further comprising a heat recycling
module for recycling heat from at least one of the engine or cooler
modules to at least one of the input, reducer, blender, dryer,
conditioner, or pellet mill modules.
6. The system of claim 4, further comprising a controller in
operable communication with any one or more of the input, reducer,
blender, dryer, conditioner, pellet mill, cooler, or output modules
for automatically operating each module.
7. The system of claim 6, wherein one or more modules are
interconnected by a means for transporting the biomass material
between modules, wherein loading, unloading, and coordination of
each module is automatically controlled through a controller.
8. The system of claim 1, wherein the system is capable of being
transported as a unit using a vehicle so that the system may
receive biomass material of varying composition and moisture
content at a point of origin.
9. The system of claim 1, wherein the reducer module is a grinder
comprising a grinder assembly with one or more pairs of opposed
cutting means operably connected to a grinding motor and wherein
spacing between the cutting means may be increased according the
load on the motor, so that spacing is increased with increased load
on the grinding motor, and wherein one of the pairs of opposed
cutting means is a pair of auger-style cutters or a pair of
shearing plates.
10. The system of claim 1, wherein the dryer module comprises
individual dryers comprised of a vertical tower wherein feed enters
through the top of the tower and exits at the bottom, and exhaust
enters from the bottom and exits from the top.
11. The system of claim 10, wherein the dryer module is
interconnected with a heat exchange network.
12. The system of claim 1, wherein the pellet mill module
comprises: a die assembly comprising two opposed cylindrical dies
that rotate in an inward direction from the die assembly; an input
for receiving biomass; and a motor; wherein each die is operably
connected to the motor; wherein the two opposed dies each comprise
a die head comprising a plurality of die holes extending radially
through its circumference; and wherein the two die heads having a
point of contact at their circumference wherein biomass is extruded
into pellets through compression of the biomass though the die
holes at the point of contact.
13. The system of claim 12, wherein spacing between the two opposed
die heads may be adjusted according to the load on the motor, so
that spacing is increased with increased load on the motor by:
adjusting one of the die head's center of rotation using a
cantilever operably connected to a cam actuator; or adjusting one
of the die head's center of rotation using a ring gear.
14. The system of claim 13, wherein each die head comprises a
plurality of vents for removal of water during extrusion.
15. The system of claim 8, wherein the vehicle is a truck or a
trailer.
16. The system of claim 7, wherein the controller is a
microprocessor operating under the control of a computer
program.
17. A process for in situ conversion of biomass to pellets,
comprising: a. Receiving biomass material; b. Reducing the size of
the biomass material after it has been received; c. Blending the
biomass material after it has been reduced in size; d. Drying the
biomass material after it has been blended; e. Conditioning the
biomass material after it has been dried; f. Pelletizing the
biomass material to pellets after it has been conditioned; g.
Cooling the pellets after they have been extruded; and h.
Offloading the pellets after they have been cooled.
18. The process of claim 17, wherein the biomass is screened
between drying and conditioning of the biomass.
19. The process of claim 17, wherein the process is carried out
within a transportable system.
20. The process of claim 17, wherein steps in the process are
powered by an engine and heat from the engine is transferred to one
or more of steps a-e.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of the
filing date of U.S. Provisional Application No. 61/783,635 filed
Mar. 14, 2013, the disclosure of which is hereby incorporated by
reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the conversion of biomass
material to pellets at a point of origin using a transportable
system. Such pellets are a useful energy source.
[0004] 2. Description of the Related Art
[0005] Pelletizing is the process of conversion of low density raw
materials into higher density cubes of uniform composition that
allow these materials to be more efficiently handled and utilized.
While pelletizing had been widely used to make feedstuffs for pets
and livestock, it is also used to compact biomass for use in the
energy industry. Feedstock used to make pellets for energy include
sawdust and scrap wood such as chips left over from hardwood
processing operation, as well as roundwood. The process of
converting this feedstock to pellets requires a number of
energy-intensive steps, including mechanical size reduction of the
raw materials, heated drying, steam conditioning, pressing the
conditioned materials at high pressure and temperature into
pellets, and cooling. According to conventional techniques, the
manufacture of one ton of pellets may use 300-3500 MJ for drying,
100-180 MJ for grinding or reducing, and 100-300 MJ for
densification (Netherlands Agency for Energy and Environment
(NOVEM), 1996). Pelletizing alone generally requires between 50 and
100 kilowatts of electricity for every ton hour of pellets
produced. Drying of the raw materials, an essential step of
conventional techniques, is typically the most energy-intensive
part of the process, typically representing 20% of the total cost
of the pellet. As current processes are not integrated, any
residual energy used in the individual processing steps is wasted.
For example, size reduction is typically carried out using a hammer
mill, a separate facility from the pellet mill, so that these
processes occur independently and often require transport of
biomass between them. Such lack of integration contributes to the
overall energy requirements of the pelletizing process.
[0006] Current pelletizing technology requires the use of a pellet
mill, which is essentially a hollow cylindrical die with press
rollers inside that extrude feedstock through holes in the die.
However, current pellet mills are extremely sensitive to the
quality of the input materials received. While the processing steps
prior to pelletizing are undertaken to ensure a consistent quality
and amount of feedstock are fed to the mill, these processes are
limited in efficacy, and often times improper drying, conditioning,
or size reduction occurs prior to extrusion of pellets. As a
result, the pellet mill may either become overloaded or receive
input of inconsistent composition, resulting in plugging of the
mill which requires costly downtime and must be cleared manually to
remedy. This downtime is a large contributor to the inefficiency of
these operations. The state of the art can be represented by
numerous disclosures, including U.S. Pat. Nos. 4,073,442,
4,354,817, 4,861,529, 4,979,887, 5,021,940, 5,152,215, 5,472,651,
5,509,610, 5,823,856, 6,045,070, 6,099,770, 6,102,310, 6,135,373,
and 7,241,127, and US Application Publication Nos. 2011/0041390,
2006/0193936, and 2006/0127510, for example. In embodiments,
features of these patents and patent applications can be
incorporated into the devices, systems and methods of the
invention, especially those listed in Appendix I, which forms a
part of this specification.
[0007] In addition to being energy intensive and inefficient,
current pelletizing technology is limited in its ability to handle
a variety of biomass, in part due to the potential for plugging,
but also due to the fact that the inefficiency of these systems
requires them to be stationary. As a result, a number of potential
sources of biomass end up going to waste due to the fact that there
is currently no means for conversion of biomass at a site of
origin. For example, wood waste from tree and yard service
companies currently are disposed rather than recycled. Further,
there are other potential sources of biomass that are not being
utilized effectively such as those produced from weather/natural
disasters, pest infestation, forest thinning operations, grasses
from cash crops, and random bioorganic waste. As a result, millions
of tons of potential energy sources end up going to waste each
year. Thus, there is a need for more efficient, integrated, and
transportable pelletizing systems capable of providing more
cost-effective sources of energy.
SUMMARY OF THE INVENTION
[0008] To address these concerns, embodiments of the invention
provide a system for in situ processing of biomass material to
pellets. Provided in embodiments is a mobile pelletizing system
(otherwise referred to as the MOPET pelletizing system) that is
novel due to the arrangement, compactness and efficiency and novel
adaptability of the component parts integrated together as a whole.
The combination of these attributes allows mobility of the unit.
There is nothing like this system in existence. Furthermore, the
pellet mill in and of itself is novel and can be used as a
stand-alone unit (i.e., as a stationary pellet plant) or it can be
used in a mobile system as well.
[0009] Systems according to the invention improve on current
stationary pelletizing operations in energy real-time adaptability,
efficiency, maintainability, ease of operation, and operating
costs. The system is mobile, energy efficient, and easy to set up
and, as a result, reduces the logistical barriers for conversion of
biomass to pellets in situ and allows conversion of a wide range of
biomass materials. The system includes automated process controls
for better product consistency and reorganizes the current process
steps to improve overall energy efficiency and reduce in-process
time requirements. The system improves upon the equipment that has
been conventionally used to carry out biomass processing and uses
process energy streams to reduce the overall cost of production. As
a result of these improvements, the system may be self-contained
and mobile for transport to sources of biomass at the point of
origin.
[0010] The system according to the invention has a complete set of
processing components and an engine for powering the processing
components. The processing components are interconnected by a means
for transporting the biomass material between processing
components, and loading, unloading, and coordination of each of the
processing components is automatically controlled through a
controller. A heat exchange network is integrated with the engine
and the processing components, wherein heat can be transferred
between the engine and the processing components. The system is
self-contained and may be transported using a vehicle or as a
self-propelled unit so that the system may receive biomass material
of varying composition and moisture content at a point of
origin.
[0011] The complete set of processing components may include an
input for receiving biomass material into the system, a means for
reducing the size of the biomass material preferably after it has
been received into the system (but before is also acceptable), a
blender for homogenizing the biomass material preferably after it
has been reduced in size (but before is also acceptable), a dryer
for drying the biomass material preferably after it has been
homogenized (but before is also acceptable), a conditioner for
conditioning the biomass material preferably after it has been
dried (but before is also acceptable), a pellet mill for extrusion
of biomass material to pellets preferably after it has been
conditioned (but before is also acceptable), a cooler for cooling
the pellets after they have been extruded, and an output for
transporting the pellets out of the system preferably after they
have been cooled (but before is also acceptable). The heat exchange
network is capable of transferring heat from the engine and the
cooler to components upstream in the process, ensuring more
efficient processing as well as conservation of heat within the
system. Due to this configuration, of having all modules disposed
in a single housing and by re-capturing heat from some parts of the
process and re-distributing the heat to other parts of the process,
the total energy consumption of the entire process is greatly
reduced.
[0012] The processing components are configured for the highest
degree of energy efficiency and quality production of the overall
system. For example, providing the drying components upstream of
the conditioning and pelletizing components ensures pelletizing
occurs at high temperatures, which has been shown to be correlated
with greater pellet quality. Further, some of the processing
components include adaptive feedback systems that prevent
interruption of steady-state operation of the system due to
blockages. Some of the components include sensors to ensure optimal
processing has occurred. The invention also provides for a novel
pellet mill and methods for operating a pellet mill, wherein the
pellet mill components are reconfigured and optimized for more
efficient processing as well as a feedback system for minimizing
blockages. The invention also includes a grinder with a similar
feedback system.
[0013] The integration, configuration, and optimization of the
components provides for the entire system to be self-contained and
mobile, so that the system can be transported for in situ
conversion of biomass to pellets at the point of origin. The system
allows for conversion of biomass that has not previously been able
to be utilized by conventional pelletizing systems, such as forest
slash, chips from tree trimming, grasses from cash crops, and
random bioorganic waste.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic diagram depicting a prior art
pelletizing operation.
[0015] FIG. 2 is a schematic diagram depicting an embodiment of a
mobile pelletizing system according to the invention.
[0016] FIG. 3 is a schematic diagram depicting another embodiment
of a mobile pelletizing system according to the invention.
[0017] FIG. 4 is a schematic diagram depicting energy streams that
a heat exchange system of a mobile pelletizing system according the
invention will manipulate.
[0018] FIG. 5 is a chart depicting energy usage data comparing
prior art pelletizing operations to that of the mobile pelletizing
systems of the invention.
[0019] FIG. 6A is a schematic diagram depicting an embodiment of a
grinder assembly of a mobile pelletizing system according to the
invention that is in low motor load mode.
[0020] FIG. 6B is a schematic diagram depicting an embodiment of a
grinder assembly of a mobile pelletizing system according to the
invention that is in high motor load mode.
[0021] FIG. 7A is a schematic diagram depicting a close-up
perspective of an embodiment of a grinder assembly of a mobile
pelletizing system according to the invention that is in low motor
load mode.
[0022] FIG. 7B is a schematic diagram depicting a close-up
perspective of an embodiment of a grinder assembly of a mobile
pelletizing system according to the invention that is in high motor
load mode.
[0023] FIG. 8 is a flow chart of a method for operation of a
grinder or a pellet mill.
[0024] FIG. 9A is a schematic diagram depicting an embodiment of a
blending auger of a mobile pelletizing system according to the
invention.
[0025] FIG. 9B is a schematic diagram depicting an embodiment of a
blending vessel of a mobile pelletizing system according to the
invention.
[0026] FIG. 10A is a schematic diagram depicting a cross-sectional
view of an embodiment of a drying module of a mobile pelletizing
system of the invention.
[0027] FIG. 10B is a schematic diagram depicting an outer view of
an embodiment of a drying module of a mobile pelletizing system
according to the invention.
[0028] FIG. 10C is a schematic diagram depicting a cross-sectional
view of the bottom portion of a drying module of a mobile
pelletizing system according to the invention.
[0029] FIG. 11 is a schematic diagram depicting an embodiment of a
dryer assembly of a mobile pelletizing system according to the
invention.
[0030] FIG. 12A is a schematic diagram of a prior art pellet mill
roller-and-die assembly.
[0031] FIG. 12B is a schematic diagram depicting an embodiment of a
die assembly according to the invention.
[0032] FIG. 13A is a schematic diagram depicting an embodiment of a
die assembly according to the invention that is in low motor load
mode.
[0033] FIG. 13B is a schematic diagram depicting an embodiment of a
die assembly according to the invention that is in high motor load
mode.
[0034] FIG. 14 is a schematic diagram of an embodiment of a die
assembly adjustment mechanism according to the invention.
[0035] FIG. 15 is a schematic diagram of an end-view of a pellet
mill of the invention.
[0036] FIG. 16 is a flow chart depicting a process for conversion
of biomass to pellets according to the invention.
[0037] FIGS. 17A and 17B are schematic diagrams depicting a
prototype die construction according to the invention.
[0038] FIGS. 18A and 18B are schematic diagrams of various views of
a grinder according to embodiments of the invention.
[0039] FIG. 19 is a schematic diagram of a pellet mill of the
invention.
[0040] FIG. 20 is a schematic diagram of a top view of a pellet
mill of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0041] Reference will now be made in detail to various exemplary
embodiments of the invention. The following detailed description is
presented for the purpose of describing certain embodiments in
detail. The present invention may be further illustrated in the
following figures, attention being called to the fact, however,
that the embodiments described in the description and shown in the
figures are illustrative only and are not intended to limit the
scope of the invention, and that changes may be made in the
specific constructions described in this specification and
accompanying drawings that a person of ordinary skill in the art
will recognize are within the scope and spirit of the
invention.
[0042] Referring now to FIG. 1, a conventional, prior art
pelletizing operation 1 is shown. The conventional pelletizing
operation begins with a rotary dryer 6, which has as its heat
source burner 2. The burner has an air intake 3 and a fuel intake
4. Feedstock is provided to the rotary dryer 6 through a feed
intake 5. As used in the context of this specification, the term
"feedstock" refers to biomass that is being processed for
pelletizing. The contents of the rotary dryer 6 are then fed to a
cyclone 7, then a hammer mill 8, where size reduction of the dried
feed occurs. The size-reduced feedstock is then transported to a
separate conditioner 9 where it is conditioned to a correct
moisture content and temperature through application of steam and
hot water, and fed to a pelletizing mill 10, the products of which
are fed to a cooler 11. The cooled pellets are then put through a
screener 12 to remove fines, and then are packaged 13. A blower 14
removes emissions from the cyclone 7 and conditioner 9. The large
arrows show the relative amounts of heat that are released as a
result of each step in the process. FIG. 1 also shows the amount of
energy required in each major step of the process, with drying
requiring the most energy at 84-970 kWh/t, followed by 50-83 kWh/t
grinding energy and 28-50 kWh/t pelletizing energy, with 160-1,106
kWh/t total energy required for the process. As the individual
processes are not integrated, heat radiated from each step in the
process is not recaptured. Further notable is that the drying step
occurs prior to size reduction as well as several steps prior to
pelletizing. In addition, the conventional pelletizing operation
shown in FIG. 1 is not mobile, and requires transport of biomass
from distal locations, thereby increasing the cost of production
due to transportation costs and increasing the overall energy
consumption of the process. Further, the individual processes are
not coordinated.
[0043] FIG. 2 shows an overview of embodiment of a mobile
pelletizing system 20A according to the invention. The entire
system 20A may be contained on a flat-bed truck, trailer, or
similar vehicle, as well as a self-propelled vehicle. The system
20A begins with an input device 21A for receiving raw biomass which
leads to a mechanism for size reduction 22A such as a crusher,
chopper, or grinder, where size reduction of the raw materials to a
consistent particle size occurs. Not depicted is an optional
blender that receives contents from the size reduction mechanism
and homogenizes them. The blended, size-reduced materials are fed
directly to a drier 23. The dried materials are then transported to
a conditioner (not shown), where the materials are prepared for
pelletizing by bringing them to a desired temperature and moisture
content. The conditioned materials are then fed to a pellet mill
24, preferably after which the hot pellets are fed to a cooler 25
(but cooling of the material can also be performed before
pelletizing if desired). The pellets are then conveyed to an output
container 28A, which may be a hopper, for offloading of the
pellets, which can be cooled before or after offloading. A diesel
generator 26A connected to a gas tank 27 is in operable
communication with the components of the system to provide
electricity to the motors powering each component.
[0044] A heat exchanger network 30 transfers heated exhaust from
the diesel generator 26A to provide heat to the dryer 23 and
conditioner. The heat exchange network also recovers heat from the
cooler 25, and sends heat upstream in the process to the mechanism
for size reduction 22A and the blender. Insulation 29 surrounds the
entire system 20A to prevent heat loss. The large arrows show the
flow of the biomass material as it is processed through the mobile
pelletizing system 20A. The smaller arrows show the flow of heat
within the heat exchanger network. The raw material is exposed to
progressively higher energy streams and acquires more heat as it
moves through the process, while the heat exchanger network 30
removes heat from heat-intensive processes upstream such as the
cooler 25 and diesel generator 26A and sends heat upstream to allow
warming of biomass at the beginning of the process for more
efficient processing.
[0045] FIG. 3 shows an overview of an embodiment of a single-pass
harvesting mobile pelletizing system 20B according to the
invention, for use in obtaining agricultural biomass. The
single-pass harvesting mobile pelletizing system 20B is similar to
the embodiment shown in FIG. 2, except that it has a combine head
21B at the input that feeds to a chopper 22B, and is powered by a
diesel hydraulic 26B. In a preferred embodiment, the single-pass
mobile pelletizing equipment has high-flotation tires to avoid
damage to cropland.
[0046] FIG. 4 is a schematic diagram depicting energy streams that
a heat exchanger of a mobile pelletizing system according the
invention will manipulate.
[0047] FIG. 5 depicts energy usage data comparing conventional
pelletizing mills to that of the mobile pelletizing system of the
invention, showing high and low estimates of conventional
pelletizing mills with that of the mobile pelletizing system
(MOPET) for total energy, drying energy, grinding energy,
pelletizing energy, and auxiliary energy. Notable is that standard
operations incur a heavy fuel cost for the drying process. In
contrast, the drying process in the present invention does not
include a fuel cost, because the drying energy is reclaimed from
the diesel engine and the heat exchange network, which recovers
thermal energy from the other heat sources in the system.
[0048] The mobile pelletizing system begins the process of biomass
conversion to pellets by receiving raw biomass in situ from forest
slash, chips from tree trimming, grasses from cash crops, random
organic biomass waste, and other suitable material through the
input 21A, as shown in FIG. 2. Preferably, the upper limit for the
size of the feedstock particles may be chips about 3 inches in
size, although the systems of the invention can be designed to
accommodate larger particle sizes, including feedstock with a
measurement in any one or more dimension of between 0 and 1 ft.
Especially preferred feedstock has a measurement in any one or more
dimension of from 1-6 inches, or from 2-5 inches, or from 3-4
inches. Batches of feedstock that can be used in the systems of the
invention can vary widely in moisture content from one batch to the
next. Any feedstock with a moisture content ranging between 0% up
to 100% can be used, such as from 10-90%, or from 20-80%, or from
30-70%, or from 40-60%. One advantage of systems of the invention
is that feedstock having varying moisture content can be input into
the system and processed into pellets having a desired target
density. For example, feedstock with a moisture content of 10% can
be introduced to the system through the input then feedstock with a
moisture content of 75% can be introduced to the system without
stopping the system from processing. The processing can be
continuous in that feedstocks with varying moisture content can be
continuously introduced and processed into pellets having a
consistent density. Preferably the target density of the pellets
varies no more than 10% from pellet to pellet even though the
feedstock input varies widely. In other embodiments, the target
density varies no more than 20%, or 25%, or 30%, or 40%, or 50%, or
60%, or 70%, or 100%, or 200%, or 300%, or 500% with varying
moisture level feedstock as input material. The temperature of the
feedstock particle will be ambient at intake. In chipped form, the
energy density is about 3000 BTU/lb.
[0049] Material may be loaded into the system using a large hopper.
In a preferred embodiment, the hopper is positioned in the rear of
the system (the back of the trailer). A grill or other suitable
conventional means may be positioned over the hopper to prevent
foreign objects and oversized biomass from entering the system. In
another embodiment, the chipped material is fed directly from an
on-site chipping machine into the debris separator, or directly
into the grinder/reduction unit. The material is moved into the
system using augers or other suitable means. Before, or preferably
after loading into the system, the biomass material may be cleaned
by separating the biomass from contaminants such as rocks and
metals based on the density differences between the materials. In
one embodiment, the biomass material is floated over an open space
by air forced upward which allows the lighter biomass material to
transit the space while denser contaminants fall into the space,
thereby separating the material from the contaminants. In another
embodiment, the material is separated by variations in surface area
to weight ratios as in a cyclone separator. However, similar means
based on density differential are known in the art and may be also
used. Before, during or after separation, any remaining
contaminants that may damage the equipment may be manually removed,
if desired.
[0050] The biomass material otherwise referred to as the feedstock,
whether cleaned or in a raw state, is advanced through the system
through a gravity-fed chute into the mechanism for size reduction
22A. In embodiments, size reduction mechanism 22A of the mobile
pelletizing system is a grinder comprising a grinding assembly. The
grinding assembly may receive raw biomass at a range of moisture
levels, including wet material. In a preferred embodiment, the
grinding assembly comprises multiple mechanisms for reducing the
wet biomass material to a consistent granular size.
[0051] For example, FIGS. 6A and 6B depict an embodiment of a
grinder assembly 40 of a mobile pelletizing system according to the
invention. FIGS. 18A and 18B provide additional views. The grinder
assembly 40 includes a pair of opposed inner 43 and outer 41
auger-style cutters and a pair of opposed shearing plates 42 and
44. The grinder assembly 40 is fed by an in-feed chute 45 that
brings feedstock to the auger 47, which advances the feedstock to
the pair of auger style cutters 41 and 43, and then to the shearing
plates 42 and 44. The pair of auger-style cutters 41 and 43 and
shearing plates 42 and 44 are separated by a gap that is adjustable
(independently from one another) according to the load on the
grinding motor. FIG. 6A shows the grinding assembly in a state when
the load on the grinding motor is relatively low, whereas FIG. 6B
shows the grinding assembly in a state when the load on the
grinding motor is higher.
[0052] As shown in FIG. 6B, the gap between the pair of auger
cutters 41 and 43 as well as the shearing plates 42 and 44
increases as a result of the increased load on the grinding motor.
The gap between the shearing plates may or may not be altered, as
it determines the granule size and hence affects the finished
product directly. This increase in the gap between the pairs of
cutters is shown in a magnified view in FIGS. 7A and 7B, where FIG.
7A shows the edges 41B and 43B of the pair of auger-style cutters
and the pair of shearing plates 42 and 44 together when there is a
relative small load on the grinding motor, and FIG. 7B shows the
separation of the two pairs of cutters as a result of increased
load on the grinding motor. The large arrows show the directional
movement of the components at low motor load and high motor load.
At low motor loads, the gap between the two pairs of cutters may be
varied only slightly depending on the material, and will retain a
slight pulsation in the gap, while at high motor loads, the
variable gap between the two pairs of cutters may increase
significantly to reduce the load on the grinding motor and prevent
jamming of the grinding assembly. As the motor slows down at high
loads, the two halves of the pairs of the cutters separate, and
when the separation is so large that the material is not correctly
sized, the outfeed chute 46 may deliver the material back to the
in-feed chute 45 for reprocessing. This self-clearing mechanism
obviates the need for human intervention and allows the grinder
assembly 40 to operate in a steady-state condition. Additional
mechanisms for clearing may be incorporated as needed, such as high
pressure steam or air or mechanical stripping plates or shredding
plates. The system, once cleared, re-engages to continue the
grinding process while still monitoring parameters such as load,
speed, and material in and material out.
[0053] Sensors can be used to monitor the load on the system, and
when the load reaches a specified threshold the auger style cutters
41 and/or 43 and/or the shearing plates 42 and/or 44 can be
automatically separated or drawn together a desired distance to
respectively reduce or increase the load on the system, thereby
maintaining the system within operating conditions below a maximum
load condition. In a preferred embodiment, a rapid adjustment
servo-driven feedback loop based on system load may be used to
maintain the system at or below a desired load condition during
operation. For example, control sensors such as an amperage monitor
and tachometer can be used to monitor changes in the grinder's amps
and rpms to detect an overload condition that may clog the
assembly, wherein a reduction in rpms and/or an increase in amps
indicates an anomaly. When an overload condition is detected, the
control sensors send a signal to an actuator to increase the
spacing between the auger style cutters 41 and/or 43 and/or the
shearing plates 42 and/or 44. The adjustment occurs within a second
or two to limit the load on the system and prevent clogging of the
grinder. Additionally, the feeding auger can be slowed down or
stopped or even reversed to reduce load on the grinding auger.
[0054] Thus, the invention also provides a grinder for
size-reduction of biomass in preparation for pelletizing,
comprising a grinding assembly comprising one or more pair of
opposed cutting means operably connected to a grinding motor,
wherein spacing between the cutting means may be increased in
response to increased load on the motor or decreased in response to
a decreased load on the motor.
[0055] In one embodiment, the grinder assembly 40 includes steam
and water jackets (not shown) from the heat exchanger network 30 to
heat the biomass for more efficient processing. In another
embodiment, the pairs of auger style cutters 41 and 43 and shearing
plates 42 and 44 have an automatic sharpening feature to improve
overall equipment efficiency of the grinder assembly 40. In another
embodiment, the auger may have a quick change mechanism to allow
the rapid replacement of new cutting tools.
[0056] In another embodiment, the invention provides a method for
operating a grinder for size-reduction of biomass in preparation
for pelletizing, wherein the grinder comprises a grinding assembly
comprising one or more pair of opposed cutting means operably
connected to a grinding motor, wherein the method comprises the
steps of: (a) receiving biomass into said grinder; (b) driving the
grinding motor to effect movement of the two opposed cutting means,
so that the movement provides for size reduction of biomass;(c)
monitoring the load on the motor for an overload condition; and (d)
increasing the distance between the cutting means and/or shearing
means when an overload condition has been reached, thereby reducing
the load on the grinding motor.
[0057] Such a method is represented schematically in FIG. 8,
wherein "INCREASE DISTANCE" refers to the distance between the two
opposed cutting and/or shearing means. The process may also include
the step of decreasing the distance between the cutting and/or
shearing means once the overload condition has been resolved. These
method steps can be performed automatically and/or manually by a
user.
[0058] The mobile pelletizing system further comprises a blender
that is placed directly under the grinder for receiving all ground
material. The blender of the mobile pelletizing system is used to
homogenize the feedstock, and is particularly advantageous for
allowing it to accept a variety of biomass concurrently for
pelletizing. The blender homogenizes the feedstock in preparation
for drying. The blender mixes the feedstock through the use of
blending augers. FIG. 9A shows an embodiment of a representative
blending auger 60 for use in systems of the invention with blades
62 on one side of the auger to mix the feedstock when turning
clockwise and to transport the feedstock when turning
counterclockwise. However, paddles or other conventional means may
be used. High pressure steam or air may also be utilized for the
purpose of agitation and blending. As shown in FIG. 9B, the
blending augers 60 can be contained in a blending vessel 70 with a
central auger 62 for transporting the feedstock out of the vessel.
The shell 65 of the blending vessel 70 contains a jacket for
circulation of engine coolant, for heating the biomass and cooling
the diesel generator 26A. The blending vessel 70 may use high
temperature thermocouplers to provide a continuous readout in
several locations inside the vessel 70. The capacity of the
blending vessel 70 may be more than 1.5 times that of a drying
tower, so that material is blended in overlapping batches. The
weight of the material may be monitored through the use of strain
gage load cells that provide a continuous readout.
[0059] Preferably after blending, the feedstock is further advanced
into a drier 23, however, blending can also take place during the
drying if preferred. The drier 23 component of the mobile
pelletizing system is particularly advantageous over conventional
drying systems, which are typically large rotating driers that run
continuously and operate on a steady-state. In these conventional
drying systems, the drying settings are set manually based on
variables such as moisture content, chip size, and type of biomass,
and these settings must be reset manually with a change in
materials. Thus, conventional drying systems are not suitable for
highly varying biomass.
[0060] In contrast, the drier 23 component of the mobile
pelletizing system of the present invention is highly suited to
varying biomass, as it relies on temperature and residence time to
adjust the moisture content of the biomass. In one embodiment, the
dryer uses moisture and temperature sensors to indicate whether the
correct moisture content and temperature has been reached, and
adjusts the residence time of a batch of biomass accordingly. The
drier may employ an algorithm to track the relationship between
time and temperature to determine the heat history for a batch
which is used in the downstream processes.
[0061] In one embodiment, the drier 23 is comprised of a series of
individual drying modules that are heated by exhaust from the
diesel generator 26A. FIG. 10A shows a cross-section of an
embodiment of a drying module 80 of a mobile pelletizing system
according to the invention. The direction of feedstock is shown by
82 while the direction of exhaust is shown by 81. FIG. 10B depicts
an outer view of an embodiment of a drying module 80 of a mobile
pelletizing system according to the invention. The feedstock input
chute 84 at the top of the drying module 80 allows biomass into the
drying module 80. After the drying module is filled to a desired
level, the feedstock input chute is closed. Once the moisture
sensors indicate that the correct moisture content has been
reached, the dried feedstock is advanced through a feedstock exit
chute 86 at the bottom of the drying module 80. Exhaust enters the
drying module 80 from an exhaust intake 83 on the bottom and exits
through an exhaust outlet pipe 85 at the top. The direct engine may
exhaust sequester CO.sub.2, CO, SO.sub.2, SO.sub.3, NO, and
NO.sub.2 into the biomass, resulting in reduced discharge of
pollutants.
[0062] FIG. 10C shows the bottom portion of the drying module 80 in
greater detail. The feedstock is fed through the drying module 80
by use of an agitation auger 91, and then ultimately exits the
drying module 80 through the feedstock exit chute 86. The process
gas first enters the drying module through the exhaust intake 83 on
the bottom, and flows inward from a dispersion cone 93.
[0063] FIG. 11 shows a drier assembly 23, which made up of a set of
individual drying modules 80. The use of multiple drier modules 80
ensures the throughput that is required by the mobile pelletizing
system, and allows the pellet mill 24 to operate in a steady state
even though incoming feedstock may vary widely.
[0064] Another configuration of the drier modules may be based on
the fluidized bed methodology wherein the material is spread on a
horizontal perforated grid which allows drying medium to circulate
up through the material being dried.
[0065] In another embodiment, the drier 23 may include a steam
drier. The use of superheated steam for drying the biomass is very
efficient from a heat transfer aspect, as steam from the drier may
be recovered and recompressed to 10-20 bar by use of a screw or
turbo steam compressor (Mechanical Vapor Recompression). The
recovered steam may then be reused as the heating media in the
drier.
[0066] Preferably after drying, batches of the biomass material
within the mobile pelletizing system may be advanced through a
screen to ensure consistent particle consistency. In embodiments,
drying can also be performed during the screening process. The
temperature of the biomass that was achieved in drying may be
maintained through the use of heating jackets on the screening
area, as well as insulated jacketed vessels. Preferably after
screening (but before or during screening is also acceptable), the
batch of biomass material is conditioned in a conditioning vessel
that may be similar to the blending vessel. In one embodiment, the
conditioning vessel contains high temperature and moisture sensors
to ensure that the biomass material has the correct moisture
content and temperature prior to pelletizing, and if additional
moisture is necessary the contents of the conditioning vessel may
be steamed. The conditioning vessel has multiple batch capacity
which allows mixing and averaging of batches in preparation for,
and as a buffer to, the pelletizing process to improve pellet
consistency.
[0067] Due to conservation of heat from the drying process, the
biomass material will already be at a high temperature prior to
conditioning, which is advantageous for allowing high temperatures
to be achieved during conditioning. For example, the biomass
material in the mobile pelletizing system may be increased to a
temperature of 400.degree. F. over a period of 5-10 minutes during
conditioning. Similar to the dryer, the mobile pelletizing system
uses heat from the diesel generator 26A in the form of exhaust and
coolant for the conditioning process. The higher temperatures
achieved during conditioning increases melting of the lignin,
reduces the amount of energy required for pelletizing, and improves
pellet hardness.
[0068] Preferably after conditioning (or during is also
acceptable), the biomass materials are transported to the pellet
mill of the mobile pelletizing system. For comparison, FIG. 12A
shows a schematic diagram of existing technology depicting a
sectional view of a conventional pelletizing die assembly 100
comprising two press rollers 106 disposed within an cylindrical die
104 containing die holes 105. For extrusion of pellets, press
rollers 106 press material radially outward away from press rollers
106 through circular die 104 by way of die holes 105.
[0069] High quality biomass pellets are themselves within the scope
of the invention. Preferably, biomass pellets are produced using
the system embodiments of the invention. High quality biomass
pellets of the invention can comprise an energy content ranging
between 0-20,000 btu/lb and a density ranging from between 0-2,000
kg/m.sup.3. Preferably, the energy content of the inventive pellets
ranges from 100-10,000 btu/lb, such as from 200-9,000 btu/lb, or
from 300-8,000 btu/lb, or from 400-7,000 btu/lb, or from 500-6,000
btu/lb, or from 600-5,000 btu/lb, such as from 1,000-4,000 btu/lb.
Especially preferred are inventive pellets having an energy content
ranging from 5,500-9,500 btu/lb, such as from 5,700-9,200 btu/lb,
or from 6,200-8,800 but/lb, such as from 6,500-7,500 btu/lb.
Alternatively or in addition, the preferred density of the
inventive pellets can range from 100-1,500 kg/m.sup.3, such as from
200-1,200 kg/m.sup.3, or from 300-1,000 kg/m.sup.3, or from 400-900
kg/m.sup.3, or from 500-800 kg/m.sup.3, such as from 600-700
kg/m.sup.3. In embodiments, the density and/or energy content of
pellets processed continuously from feedstock of varying
composition and/or moisture content can be consistent. For example,
the density and/or energy content of pellets produced in this
manner preferably varies no more than 2%, or 5%, or 10%, or 20%, or
30%, or 40%, or 50%, or 60%.
[0070] FIG. 12B is a schematic diagram showing an outer view of an
embodiment of a pelletizing die assembly 200 of the invention,
comprising two cylindrical dies 202 each comprising a die head 204
and a die support ring 203. The two dies 202 are arranged so that
the die heads 204 are opposed to each other and rotated inwardly.
Feedstock enters the pelletizing die assembly 200 at the interface
201 of the two die heads 204. Each die head 204 contains a
plurality of holes 205 extending radially through its circumference
so that pellets are compressed at the interface 201 between die
heads 204 and are extruded toward the interior of the die 202.
Using two die heads with holes in an opposed configuration creates
at least twice as many die holes per revolution than the prior art
configuration. Further, the use of two opposed die heads has the
further advantage of eliminating gyroscopic effects that are
present in systems that use a single die head. This aspect is
especially useful in a self-propelled single pass system that
remains in motion while processing the harvested feedstock.
[0071] Holes 205 of die heads 204 can be any shape or size.
Preferred embodiments comprise die heads where 20-90% of the
surface area of the die head has holes 205. For example, 30-80%, or
40-75%, or 50-60% of the die surface area can comprise holes 205.
Additionally, or alternatively, the holes 205 can have a diameter
ranging from 5-50 mm, such as from 10-30 mm, or from 15-25 mm, and
preferably about 20 mm. The size of holes 205 will correlate with
the diameter of the pellets, so virtually any diameter can be used.
The passageways through the die heads to which the holes 205 serve
as output and input can be cylindrical and of consistent diameter
throughout or can be tapered at one or both hole 205 ends. For
example, the holes 205 on the outer surface of one or more die
heads can be about 35 mm and the passageway through the die can
taper down to a diameter of about 12 mm at the inner surface of the
die head.
[0072] The die head 204 may be made of any suitable material
capable of withstanding pressure induced by feedstock disposed
between rotating die heads. In a preferred embodiment, the die head
204 is made of ceramic material such as silicon nitride or silicon
carbide. Other acceptable materials may include a sintered binary
solid solution of aluminum oxide and silicon nitride, with or
without a metal or metal alloy, such as molybdenum or tungsten,
dispersed and bonded therein. A ternary solid solution formed of
aluminum oxide, silicon nitride, and aluminum nitride, with or
without a metal or metal alloy dispersed in and bonded thereto is
also acceptable. The die heads may also be made of any metal, or
metal coated with ceramic. Acceptable metals include stainless
steel, steel, titanium, iron, cast iron, aluminum, or composites
such as tungsten carbide. Preferable materials for the die heads
have a hardness ranging from about 40 to 90 on the Rockwell C-scale
(HRC). Especially preferred are metals, alloys, or composites with
an HRC ranging from 45-70, such as from 55-65. Similarly, the die
heads can be made of metal or an alloy coated with ceramic, or a
ceramic coated with metal or an alloy. For example, a ceramic, such
as a zirconium ceramic, can be braised onto a stainless-steel die
body and coated/braised with a titanium carbide/stainless-steel
surface layer.
[0073] The opposed die head configuration keeps the die heads under
compression rather than tension as is the case for inner roller
style dies. Thus, the die material need not require extensive
tensile strength, allowing the use of high-wear ceramic materials
that exhibit excellent compression properties. Ceramic die heads
may be retained in a pelletizing die assembly using compression
mechanisms, such as clamps.
[0074] The invention also provides a pellet mill comprising a die
assembly comprising two opposed cylindrical dies that rotate in an
inward direction from the die assembly, an input for receiving
biomass, and a motor, wherein each die is operably connected to the
motor, wherein the two opposed dies each comprise a die head
comprising a plurality of die holes extending radially through its
circumference, the two die heads having a point of contact or
interface at their surface, wherein biomass is extruded into
pellets through compression of the feedstock though the die holes
at the interface.
[0075] FIG. 13A shows an embodiment of a pelletizing die assembly
200 of the invention, comprising two opposed die heads 204A and
204B. Die head 204A rotates around a stationary center, while die
head 204B is capable of changing its center of motion. Both dies
are in continuous rotation during the pelletizing process. However,
the center of rotation of die head 204B may be adjusted through
movement of actuator 213 the die head 204B away from die head 204A,
so that during heavy loads of material, the spacing between the die
heads 204A and 204B can be increased. As shown in FIG. 14, the
actuator can be manual and comprise a lever 208 in operable
communication with die head 204B for moving the center of rotation
of the die head. FIG. 13A depicts the positioning of the two die
heads 204A and 204B together at normal loads, while FIG. 13B
depicts an increase between the spacing of the die heads 204A and
204B as a result of the movement of the actuator 213, as indicated
by the heavy arrows.
[0076] FIG. 14 shows a diagrammatic view of the pellet die
adjustment, with pellet die head 204A in rotation around a
stationary center 210A and pellet die head 204B with an adjustable
center of motion 210B. In other embodiments, both die heads 204a
and 204B can be adjusted to relocate their center of rotation. The
pellet die head 204B is mounted on a lever arm 208 with high
mechanical advantage. A large clockwise motion on the lever arm 208
brings it to position 208', which moves the short arm 209 clockwise
to position 209', resulting in a movement of the center of motion
210B of the pellet die head 204B to 210B' as well as movement of
the die head 204B to position 204B'. This movement results in a
decrease in the distance of the two die heads 204A and 204B. A
counterclockwise motion of the lever arm 208 produces the opposite
effect, resulting in increased spacing between the two die heads
204A and 204B.
[0077] The pellet die adjustment may be a rapid adjustment
servo-driven feedback loop based on system load. Control sensors
such as an amperage monitor and tachometer can be used to monitor
changes in the pellet die assembly's amps and rpms for an overload
condition that may clog the assembly, wherein a reduction in rpms
and/or an increase in amps indicates an anomaly. When an overload
condition is detected, the control sensors send a signal to the
actuator 213 to increase the spacing between the two die heads 204A
and 204B. The adjustment occurs within a second or two to limit the
load on the system and prevent clogging of the die assembly.
[0078] Thus, another embodiment of the invention provides a method
for operating a pellet mill having a die assembly comprising two
opposed cylindrical dies that rotate in an inward direction from
the die assembly, an input for receiving biomass, and a motor,
wherein each die is operably connected to the motor, wherein the
two opposed dies each comprise a die head comprising a plurality of
die holes extending radially through its circumference, the two die
heads having a point of contact at their circumference wherein
biomass is extruded into pellets through compression of the biomass
though the die holes, wherein the method comprises the steps of:
(a) receiving biomass into said pellet mill;
[0079] (b) driving the motor to effect inward rotation of the two
opposed die heads; (c) monitoring the load on the motor for an
overload condition; and (d) increasing the distance between the two
dies' centers of rotation when an overload condition has been
reached, thereby increasing the distance between the two die heads
so that the point of contact is no longer maintained and the load
on the motor is reduced. In embodiments, the die heads need not
have a point of contact in order to extrude feedstock through the
die holes to produce pellets. There may be sufficient pressure for
extruding the material through the die holes by maintaining a
certain distance between the die heads and a certain amount of
feedstock between the die heads as the die heads rotate.
[0080] Additional rollers or pressing features may be used on the
exterior of the die to place the feedstock on the die heads in a
pre-determined thickness prior to reaching the interface of the
main dies with each other.
[0081] Another feature that may or may not be used is a variable
rate of material infeed through the use of augers or conveyors or
gates having limiting features to achieve the variable rates of
feed.
[0082] The method of operating the pellet mill may also be
represented schematically in FIG. 8, wherein "INCREASE DISTANCE"
refers to the distance between the two dies' centers of rotation.
The process may also include the step of decreasing the distance
between two dies' centers of rotation after the overload condition
has been resolved. These method steps can be performed
automatically and/or manually by a user.
[0083] FIG. 15 depicts an end-view of an embodiment of a pellet
mill 250 according to the invention. FIGS. 19 and 20 provide
additional views. The pellet mill 250 comprises a pelletizing die
assembly 200. The pelletizing die assembly comprises dual opposed
cantilevered die heads 204A and 204B, which assembly creates an
inward compressive force between die heads 204A and 204B due the
spacing between die heads and the amount of feedstock present
between the die heads during use. The die assembly 200 receives
feedstock at feedstock input 230. In preferred embodiments, the die
heads are in direct contact with one another during use and the
feedstock is forced through die holes disposed in the die heads at
the interface of the die heads during rotation. In the context of
this specification, the interface between die heads need not
involve direct contact between the die heads, but can also include
the situation where sufficient pressure is generated to extrude the
feedstock through the die heads by virtue of the amount of
feedstock disposed between the die heads during use. The pellet
mill includes a heavy duty short stroke eccentric cam 212 that is
connected to a lever 208. During use, lever 208 can be moved by a
linear stroke cam actuator 213 for cam adjustment and die spacing
control, wherein an upward movement of the actuator moves the
center of rotation of die head 204B away from that of die head
204A, thereby increasing the spacing between the die heads 204A and
204B. A horizontal bridge 214 connects and helps transfer movement
between the cam actuator 213 and the lever 208. A motor 215 powers
the rotation of the die heads 204A and 204B directly. Shrouds and
chutes for intake and output are not shown but can be incorporated
into the system. The chutes may serve the additional purpose of
returning bypassed feedstock to the feedstock input area of the
pelletizing system.
[0084] Direct drive of the dies eliminates belts and pulleys as
wear items. In another embodiment, a ring gear with a servo-driven
gearbox may be used for adjustment of the die head 204B instead of
the liner stroke cam actuator 213.
[0085] In another embodiment, the pelletizing die assembly 200 of
the mobile pelletizing system includes an automatic die hole
clean-out system (not shown) to automatically remove plugging that
does occur. The automatic die hole clean-out system may be a group
of boring tools to clean each die hole as the die is indexed using
a feedback system that indicates the radial location of the die
holes to allow clearing of any foreign material that may be become
impacted (e.g. small rocks).
[0086] In another embodiment, the die head 204 of the pelletizing
die assembly has a series of vents to allow the escape of water
from the die head during the extrusion process. In another
embodiment, the die holes 205 in the die head 204 are tapered to
mitigate friction at the interface 201 of the die heads 204 where
compression of the material begins. Thus, the invention provides a
die or die head assembly for use in a pellet mill wherein the die
is cylindrical and comprises a die head comprising a plurality of
die holes extending radially through its circumference, wherein the
die head comprises a plurality of vents for removal of water during
extrusion. Alternatively or in addition, the invention provides a
singular die or die assembly for use in a pellet mill wherein the
die is cylindrical and comprises a die head comprising a plurality
of die holes extending radially through its circumference, wherein
the die holes are tapered.
[0087] Preferably after pelletizing the hot pellets are transferred
to a cooler 25 that is connected to the heat exchange network 30.
The heat exchange network 30 removes and recovers heat from the hot
pellets and transfers it back upstream through the process where it
can be absorbed as an energy stream that increases or maintains the
temperature of the incoming material. For example, the heat
exchanger network may transfer heat back to the grinder or blending
vessels for more efficient processing.
[0088] Preferably after cooling (but before or during are also
acceptable), the pellets may be screened to remove small
particulates (fines) from the bulk pellets. The pellets then may be
stored in a small hopper aboard the mobile pelletizing system and
then transported to trucks or other containment through an offload
auger, conveyor, or other transport means.
[0089] The biomass material may be advanced between the different
components of the mobile pelletizing system through the use of
conveyor augers, belt conveyors, pneumatic conveyors, gravity, and
the like, wherein loading and unloading of the components is
automatically controlled through a controller that coordinates
operation of the various components. The controller may be a
conventional microprocessor operating under the control of a
computer program.
[0090] The mobile pelletizing system may be controlled by a human
operator through the use of a wireless HMI (Human-Machine
Interface) that may be positioned at input 21A of the mobile
pelletizing system. For example, the HMI may be mounted on a roll
cage of the input device 21A. The HMI allows the human operator to
interact with the controller and receive output about conditions
within the system at all times and give commands such as start-up
or shut down. However, as the system will automatically set up and
start up based on preprogrammed routines and will require minimal
maintenance, the human operator may be free to perform other duties
for system operation such as manual loading and unloading of the
system.
[0091] The diesel generator or other form of motive power 26A may
be sized to match the electrical and/or hydraulic and/or mechanical
loads from the grinding, pelletizing, and auxiliary equipment,
based on estimated energy usage. For example, at an estimated
energy usage of 80 kWh/ton (FIG. 5) and an output of five tons per
hour, the diesel generator 26A may have a size of 400-500 effective
kilowatt hour capacity to power the mobile pelletizing system. This
representative size generator would meet the needs for processing
biomass with a pellet output of about five (5) tons per hour at the
low energy usage rate disclosed herein. Diesel fuel usage is
estimated to be in the range of about 4-8 gallons per ton of
finished product. The capacity of the generator can be adjusted
according to desired operating needs.
[0092] Heat may be recovered from the diesel generator either
directly, as in the use of exhaust gas to heat the drier 23, or
through the use of a jacketed secondary circuit containing water,
ethylene glycol, or other heat transfer fluid for providing heat to
the heat exchange network 30.
[0093] The subcomponents of the mobile pelletizing system may be so
designed so that individual modules are hydraulically extended
clear of the main system for ease of maintenance, repair, and
replacement. This design allows the components to be adjacent to
each other, creating a compact system that may be made mobile.
[0094] In another embodiment, the present invention provides a
process for converting biomass material to pellets. The process
comprises the steps of: (a) receiving biomass material; (b)
reducing the size of the biomass material, preferably after it has
been received but before is also acceptable; (c) blending the
biomass material, preferably after it has been reduced in size, but
before is also acceptable; (d) drying the biomass material,
preferably after it has been blended, but before is also
acceptable; (e) conditioning the biomass material, preferably after
it has been dried, but before is also acceptable; (f) pelletizing
the biomass material to pellets, preferably after it has been
conditioned, but before is also acceptable; (g) cooling the
pellets, preferably after they have been extruded, but before is
also acceptable; and (h) offloading the pellets, preferably after
they have been cooled, but before is also acceptable.
[0095] A summary of a representative pellet fabrication process is
provided in FIG. 16. Processes of the invention may be carried out
using conventional pelletizing equipment and operations, or a
mobile pelletizing system as described herein. Notable in preferred
embodiments of the process is that size reduction occurs early in
the process before drying, and drying occurs prior to conditioning
and pelletizing. Providing the drying step immediately before the
conditioning and pelletizing steps ensures that the biomass is
provided at a high temperature prior to conditioning, enhancing the
energy efficiency of the overall process and facilitating
pelletizing at high temperatures, improving resultant pellet
quality.
[0096] In other embodiments of the process, biomass may be screened
between the drying and conditioning steps, and pellets may be
screened between cooling and offloading of the pellets. The process
may be carried out within a transportable system as described
herein, wherein steps in the process are powered by an engine or
other means, and heat from the engine or power supply and the
cooling step are transferred to one or more upstream steps in the
process, such as receiving, reducing, blending, drying,
conditioning, or pelletizing.
EXAMPLES
[0097] Die Design Extrusion Experiments
[0098] Since the die design's novel capabilities are key to
optimizing pelletizing efficiency in certain embodiments, a series
of experiments were done to study various changes to the die
chamber for pelletizing. It was determined by these experiments
that using other methods of construction for the die head of the
pellet mill allows very different geometry possibilities beyond the
standard reamed holes disclosed. For example, one experiment
examined whether gradual tapers may mitigate some of the friction
at the interface of the dies where the compression of the material
begins. A second concept was studied wherein vents were introduced
to the die chamber to release any unwanted matter, such as water.
These concepts are shown in FIG. 17A.
Example I
[0099] The extrusion mechanism was tested using the Nozzle Stack
Assembly 7410. The assembly (shown in FIG. 17B) has a series of
vents in the body of the die to allow the escape of moisture and
steam while the material is under pressure. Ambient temperature was
55 F. No heat was used for either the die or the feedstock
material. Feedstock was raw White Oak sawdust from using a
chainsaw. Hydraulic pressure was set at 1700 psi. Material was fed
into the chamber while the extrusion piston was cycled up and down
using limit switches at either end of the stroke and a delay timer
on the upper end of travel to allow feedstock to enter the chamber.
Some of the feedstock fell through the Nozzle Stack at the
beginning of cycling. This was blocked to allow the material to
build up inside the stack. After the material began to compress in
the stack, moisture in the form of water droplets came out of the
side holes as predicted. This moisture indicated that the venting
was functioning correctly and that water was migrating out to the
edge of the chamber and through the vents. The vents are in four
places equally spaced around the periphery and at intervals of 0.67
inch so as to have five equally spaced sets of vents down the sides
of the chamber within the Nozzle Stack. In other embodiments, any
number of vents may be used, such as 1-20 vents, or 2-15 vents, or
3-10 vents, such as 4-8 vents, or 5-7 vents, and the vents may be
disposed randomly.
[0100] The pressing cylinder was 23/4'' in diameter which
translates to about 10,000 lbf on the extrusion piston. The
extrusion piston area is about one square inch. The total pressure
was insufficient to force the wood through the end extrusion
orifice which is about 0.72'' diameter. The sawdust compacted into
a tight, flaky cone that retained considerable moisture even after
the pressing process.
[0101] The angle of the taper was determined to be too high. There
was too much internal friction to overcome within the feedstock
material to allow it to extrude or flow at the temperature used.
While higher temperatures might improve the flow, the moisture
level could cause the material to separate and blow forward rather
than to properly extrude as it should. The pressure behind the
extrusion piston (10,000 psi) was too low. It should be noted that
this experiment involved only one feedstock, that is White Oak.
Example II
[0102] The extrusion mechanism was tested using the Nozzle Stack
Assembly 7410. In this example, the piston diameter was reduced to
about 0.45 square inches and the cylinder was sleeved to the same
size. The nozzle stack was extended at the bottom and the top three
segments were removed. This change was made to reduce the overall
compression ratio at the throat. Ambient temperature was 45 F. No
heat was used for either the die or the feedstock material.
Hydraulic pressure was set at 1700 psi.
[0103] Material was fed into the chamber while the extrusion piston
was cycled up and down using limit switches at either end of the
stroke and a delay timer on the upper end of travel to allow
feedstock to enter the chamber. Feedstock was raw White Oak sawdust
from using a chainsaw and a variety of chopped dead leaves soaked
in water (mainly Oak and Maple). The leaves were fed through
without any sawdust. They exited the nozzle quite easily as there
was little compression. The leaves did not form into a tight mass.
They came out still wet but crushed together nonetheless. Sawdust
was added to make a 1:1 mixture of the two materials. This was
mixed until evenly distributed. The mixture was fed into the nozzle
in the same manner as before. This mixture offered more resistance
to compression and responded similarly to the sawdust mix in
Example I. More sawdust was added until the mixture was an even 2:1
(sawdust:leaves). The mixture again behaved more like sawdust,
offering increased resistance to compression. Water extraction
became more noticeable at this point. The pressing cylinder was
23/4'' in diameter which translates to about 10,000 lbf on the
extrusion piston. The extrusion piston area is about 0.45 square
inch. This translates into an available force of 22,000 psi. No
jamming occurred and all material was able to be processed without
increasing the force. This procedure was reiterated for 3:1, 4:1
and 5:1 with predictable results. With an increase in resistance
comes greater water extraction.
Example III
[0104] The material used for pelletizing (feedstock) was
sawdust/dry leaf mix with approximately 10% dry leaves (by weight).
This material was steamed in a closed container of approximately
five (5) cubic feet. Material was fed into the pressing chamber
directly from the steamer at about 160.degree. F. Pellet die
diameter was 0.400 inch. Heat set point was 310.degree. F. Ambient
temperature was 55.degree. F. Hydraulic pressure was 1500 psi.
Pressing cylinder diameter was 2.50 inch (4.9 sq in piston area).
Effective pressing force was 7360 lbf. Piston diameter was 0.50
inch (0.20 sq in pressing piston area). Pelletizing ram pressure
was 36,800 psi. Temperature controller mode was "on/off."
[0105] Material was fed into the throat of the chamber and pressed
at a controlled rate which was set using a hydraulic flow control.
Most effective rate for this experiment was about 0.3 inches per
second. The steamed, preheated material processed smoothly and
consistently. There was no tendency for the die to become clogged.
Material exited the pellet die with a surface temperature close to
that of the die temperature--about 280.degree. F. The experiment
was run for about 1/2 hr to validate the consistency of the
process. Sufficient pellets were collected for study and samples.
Pellet quality was inconsistent because the process was not a true
steady-state in this model.
[0106] Novel construction of the pellet die allows venting as well
as reshaping the die cavity. Venting of the chamber allows for
higher moisture content materials to be extruded to the same net
moisture content as standard pellet techniques. This allows for
material to be pelletized from the raw state. By shaping the
cross-section of the die chamber to minimize the maximum thickness
of the pellet, the moisture will be allowed to travel to the
surface of the pellet in the minimum time, allowing higher feed
rates.
[0107] It will be apparent to those skilled in the art that various
modifications and variations can be made in the practice of the
present invention without departing from the scope or spirit of the
invention. One skilled in the art will recognize that these
features may be used singularly or in any combination based on the
requirements and specifications of a given application or design.
Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention. The description of the invention
provided is merely exemplary in nature and, thus, variations that
do not depart from the essence of the invention are intended to be
within the scope of the invention. Additionally, the references
cited in this disclosure are each hereby incorporated by reference
herein in their entireties, especially for information that is well
known in the art for example with respect to pelletizing methods,
devices, systems and desired pellet composition. If there is any
conflict in the usages of a word or term in this specification and
another document that may be incorporated herein by reference,
definitions consistent with this specification should be
adopted.
[0108] Therefore, the present invention is well adapted to attain
the ends and advantages mentioned as well as those that are
inherent therein. While embodiments are described in terms of
"comprising," "containing," or "including" various components or
steps, the embodiments can also "consist essentially of" or
"consist of" the various components and steps. All numbers and
ranges disclosed above may vary by some amount and when terms such
as approximately or about are used the values can vary by up to
10%. Whenever a numerical range with a lower limit and an upper
limit is disclosed, any number and any included range falling
within the range is specifically disclosed. In particular, every
range of values (of the form, "from about a to about b," or "from
approximately a to b," or "from approximately a-b") disclosed
herein is to be understood to set forth every number and range
encompassed within the broader range of values. Also, the terms in
the claims have their plain, ordinary meaning unless otherwise
explicitly defined. Moreover, the indefinite articles "a" or "an,"
as used in the claims, are defined herein to mean one, at least
one, or more than one of the element that it introduces.
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