U.S. patent application number 13/994234 was filed with the patent office on 2013-12-12 for methods of drying biomass and carbonaceous materials.
This patent application is currently assigned to GTL ENERGY HOLDING PTY LIMITED. The applicant listed for this patent is Robert French, Robert A. Reeves. Invention is credited to Robert French, Robert A. Reeves.
Application Number | 20130326938 13/994234 |
Document ID | / |
Family ID | 46245375 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130326938 |
Kind Code |
A1 |
French; Robert ; et
al. |
December 12, 2013 |
METHODS OF DRYING BIOMASS AND CARBONACEOUS MATERIALS
Abstract
The invention provides methods of reducing the energy required
to remove moisture from biomass, carbonaceous materials and
mixtures of the same. The method significantly reduces the energy
requirements by removing moisture as a liquid and by transferring
the moisture to the surface of the material where it is more easily
and efficiently evaporated.
Inventors: |
French; Robert; (Wellington,
CO) ; Reeves; Robert A.; (Arvada, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
French; Robert
Reeves; Robert A. |
Wellington
Arvada |
CO
CO |
US
US |
|
|
Assignee: |
GTL ENERGY HOLDING PTY
LIMITED
Unley
SA
|
Family ID: |
46245375 |
Appl. No.: |
13/994234 |
Filed: |
December 15, 2011 |
PCT Filed: |
December 15, 2011 |
PCT NO: |
PCT/US11/65290 |
371 Date: |
August 28, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61423558 |
Dec 15, 2010 |
|
|
|
Current U.S.
Class: |
44/589 ; 44/550;
44/592 |
Current CPC
Class: |
Y02E 50/10 20130101;
Y02E 50/30 20130101; F26B 2200/24 20130101; C10L 5/361 20130101;
F26B 5/08 20130101; C10L 5/442 20130101; F26B 2200/02 20130101;
C10L 5/08 20130101; F26B 5/14 20130101 |
Class at
Publication: |
44/589 ; 44/592;
44/550 |
International
Class: |
C10L 5/08 20060101
C10L005/08 |
Claims
1. A method of reducing the energy consumed by drying biomass and
carbonaceous materials comprising: a. preparing feedstock to expose
its moisture-containing structure, b. compacting the prepared
material to form a compacted material, and, c. separating water
expressed during compaction from the compacted material to form a
dried compacted material.
2. The method of claim 1, wherein the feedstock is selected from
the group consisting of woody material, grasses, agricultural
plants, residues, bituminous coal, subbituminous coal, lignite,
brown coal, peat, and waste coal materials produced by screening or
gravity separation processes, and combinations thereof.
3. (canceled)
4. The method of claim 1 wherein the preparing comprises the use of
a device that reduces the size of the feed material to maximize the
exposure of porous structure(s) of the material that contains
surface or inherent or bonded water to an exterior surface.
5. The method of claim 1, wherein the compacting comprises the use
of a device that develops sufficient pressure to deform the
integrity of the material structure to release water contained
therein.
6. The method of claim 5, wherein the device is a double roll
press.
7. (canceled)
8. The method of claim 1, wherein the separating comprises at least
one of use of a vibrating screening machine to separate liquid
water as underflow from dewatered compacted material as overflow;
use of a belt filter press to separate liquid water as filtrate
from dewatered compacted material as filter cake; centrifuging the
compacted material to separate liquid water as effluent from
dewatered compacted material as product; vacuuming the compacted
material through a disk filter to separate liquid water as filtrate
from dewatered compacted material as filter cake; evaporating water
from an exterior surface of the compacted material; and, thermally
drying the compacted material at low temperature.
9-11. (canceled)
12. The method of claim 1, wherein the feedstock comprises a
mixture of biomass and carbonaceous material.
13. (canceled)
14. The method of claim 12, wherein the biomass and the
carbonaceous materials are prepared separately.
15. The method of claim 12, wherein the biomass and the
carbonaceous materials are compacted and separated from liquid
water separately.
16. The method of claim 12, wherein the biomass and the
carbonaceous materials are compacted and separated as a
mixture.
17. (canceled)
18. The method of claim 1, further comprising thermally drying the
dried compacted material at low temperature to form a low moisture
compacted material.
19. The method of claim 1, further comprising briquetting the low
moisture compacted material.
20. A biomass compacted material having a moisture content between
about 5 wt % and about 17 wt. %.
21-50. (canceled)
51. A method of forming a briquette comprising biomass and a
carbonaceous material, the method comprising: a. sizing a first
feed stream comprising biomass into a size that maximizes exposure
of the porous structure of the biomass; b. compacting the sized
first feed stream in a roll press to rupture and collapse the first
feed's porous structure and to express moisture held within the
pores of the first feed stream material; c. separating water
expressed during compaction of the first feed stream to form a
dried biomass; d. comminuting a second feed stream comprising mined
or reclaimed carbonaceous materials; e. compacting the second feed
stream in a roll press; f. separating water expressed during
compaction of the second feed stream to form a dried carbonaceous
material; g. combining the dried biomass and the dried carbonaceous
material to form a combined material stream; and h. briquetting the
combined material stream to form a briquette comprising processed
and dried biomass and carbonaceous materials.
52. The method of claim 14, wherein pressure applied in compacting
the first feed stream is between 5,000 lb/in.sup.2 and 80,000
lb/in.sup.2.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119(e) to U.S. Provisional Patent Application Ser. No.
61/423,558 filed Dec. 15, 2010, which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The invention relates to methods of reducing the moisture
content of materials including biomass, such as woody materials,
grasses, agricultural plants, and residues, and mixtures thereof
and carbonaceous materials such as bituminous coal, subbituminous
coal, lignite, brown coal, peat, waste coal and mixtures
thereof.
BACKGROUND OF INVENTION
[0003] Biomass and low-rank coals contain high levels of moisture,
which must be removed before they are commercially useful as a
source of fuel, or as a manufactured product. Low-rank coal is
typically used for power production in close proximity to where it
is found because its low energy density would likely be offset by
any energy expended to ship such low-rank coals any appreciable
distance. In some situations, it is desirable to use a mixture of
biomass and carbonaceous materials, such as low-rank coals, as fuel
to generate steam and power. When such mixtures are used, the
biomass component reduces carbon dioxide emissions compared to the
combustion of coal alone. But mixtures of biomass and coal often
contain too much moisture to be economically and technically useful
for power generation.
[0004] Industry has traditionally relied on heat to dry raw
materials to levels appropriate for their end use. Many types and
designs of thermal dryers have been used with a goal of reducing
the amount of energy required to evaporate water from the host
material. Even with improvements gained by more sophisticated
designs, the rising price of energy has outpaced the efficiency of
these drying processes, as applied to raw fuel materials.
Traditional drying of these fuel materials may also create large
volumes of flue gas and water vapor that must be handled in
accordance with environmental regulations. As such, operators of
thermal drying systems must plan for the added cost and adverse
environmental events associated with gas treatment systems. Such
costs and energy expended on environmental regulation compliance
can also offset the energy gained in the use of low rank coals and
biomass to generate energy.
[0005] Biomass has traditionally been dried using either directly
heated systems or indirectly heated systems. Direct heating occurs
when the wet material is brought into intimate contact with hot
gases produced by combustion. This type of drying system is usually
thermally efficient but can degrade the biomass material because of
the high temperatures involved. This system can also create
conditions that lead to fires and explosions. Direct drying systems
are seldom used for drying coal because of the dangers created in
bringing volatile coal into contact with high temperature gas.
[0006] Indirect drying systems bring wet material into contact with
surfaces heated with condensing steam or combustion gases. These
systems use smaller volumes of gas than direct drying systems and
can be maintained at relatively low temperature to avoid degrading
the dried material and minimizing conditions that can lead to fires
and explosions. However, indirect drying systems require larger
equipment to account for the lower drying rate created by
relatively temperate drying conditions.
[0007] Heat demand for a thermal drying system can account for
between 40 and 70% of the total energy required to manufacture wood
products such as fuel pellets and oriented strand board (OSB). The
associated costs of this energy as well as environmental controls
significantly add to overall manufacturing costs.
[0008] Low-rank coal and other carbonaceous materials are difficult
to dry because of the unfavorable physical and thermal properties
of coal. Low-rank coal in particular is a porous material that
holds most of its moisture in pores. Drying coal therefore requires
transferring sufficient heat into the material to vaporize the
water held in these pores. The process is inefficient because coal
is a good thermal insulator that resists heat transfer. Thus, large
amounts of energy are required to generate sufficient heat to dry a
low-rank coal that has a low energy density.
[0009] In order to use such low-rank coals and biomass for energy
production, there remains a need in the art for improved methods of
drying such materials that contain water within pores in the
material. These materials include biomass and carbonaceous
materials, and mixtures of the same. Ideally, drying methods would
reduce energy demand and mitigate environmental controls.
SUMMARY OF INVENTION
[0010] The invention provides methods of processing porous
materials, such as biomass and carbonaceous materials, to decrease
the thermal energy and cost required to dry the material to a
specified level. In addition, the invention treats mixtures of
particulate biomass and carbonaceous materials to form
low-moisture, compacted products that possess uniform chemical and
physical properties.
[0011] Thermal energy is traditionally used to heat and evaporate
water contained in carbonaceous and biomass materials. Thermal
drying equipment must use large volumes of hot air or combustion
flue gas to transfer the heat necessary to evaporate the water and
carry the resulting water vapor away from the dried product.
Considerable thermal energy and high temperature is required to
accomplish these tasks.
[0012] Biomass and carbonaceous materials have a porous structure
that can trap and hold moisture. The present invention uses
mechanical means to partially express the moisture contained in the
pores and partially remove the moisture by mechanical means such as
screens, filters, centrifuges and the like. Considerably less
energy and time is required to separate a portion of the moisture
by these devices than entirely by evaporation. The partially-dried
material may then be further dried by thermal methods to meet
product specifications.
[0013] The amount of heat demanded by a thermal dryer is greatly
reduced because the quantity of moisture in the thermal dryer feed
material is substantially reduced, thereby lowering the quantity of
moisture that is evaporated. This results in the benefits of a
smaller heat generation device, lower capacity thermal dryer, and
associated environmental control. In addition to a lower heat
requirement, less electrical energy is required to power the fans,
motors and controls associated with the dryer system. The result of
reducing heat and electrical power requirement further reduces
carbon dioxide emissions to the benefit of the environment.
[0014] Industry has experienced difficulty when firing combinations
of biomass and coal due to segregation of the two materials prior
to entering the boiler or furnace. The biomass burns with a
different characteristic than the coal, thus creating operational
difficulties. The present invention creates a better fuel that
contains an intimate mixture of biomass and coal that is bonded
together with sufficient integrity such that it does not segregate
prior to entering the boiler. Eliminating segregation of the two
components avoids many of the difficulties encountered by burning
combinations of fuels of traditional composition.
[0015] In one aspect, the invention includes preparing the material
to a particle size that is suitable for subsequent processing. The
prepared material is compacted by a roll press that exerts
sufficient pressure on the feed material to collapse its porous
structure and express moisture contained in the pores to the
exterior of the compacted material. The expressed moisture may be
removed by mechanical means such as screens, filters and
centrifuges. The partially dried material, free of the removed
moisture, may then be further dried by thermal methods to meet
product specifications. The amount of heat demanded by the thermal
dryer is greatly reduced because the moisture content of the feed
material is reduced, and the drying rate of the compacted feedstock
is greater than raw materials that have not been compacted.
[0016] In a specific embodiment of the present invention designed
to treat woody biomass, round wood is chipped into sizes and shapes
that maximize exposure of its porous structure. The prepared woody
material is fed into the nip of a roll press. The roll press is
operated with appropriate roll rotation speed, and roll closing
force to develop sufficient pressure to rupture and collapse the
feed's porous structure to express moisture held within pores in
the feed material. Moisture is separated from the compressed
material by mechanical means that are appropriate for the
application. One or a combination of screens, filters and
centrifuges mechanically removes moisture from the compacted
product. The moisture may be further treated if desired, for
example, if the moisture is collected water, it may report to a
water treatment system for use elsewhere, such as other
manufacturing processes.
[0017] In another embodiment of the invention designed to treat
harvested and gathered grasses, agricultural plants, and residues,
the feed material is ground into sizes and shapes that maximize
exposure of the porous structure to the compaction rolls. The
prepared material is fed into the nip of the roll press. The roll
press is operated with appropriate roll rotation speed, and roll
closing force to develop sufficient pressure to rupture and
collapse the feed's porous structure and to express moisture held
within the pores. Moisture is separated from the compressed
material by mechanical means that are appropriate for the
application. One or a combination of screens, filters and
centrifuges mechanically removes moisture from the compacted
product. The moisture may be further treated if desired, for
example, if the moisture is collected water, it may report to a
water treatment system for use elsewhere, such as other
manufacturing processes.
[0018] In another embodiment of the present invention, designed to
treat mined or reclaimed carbonaceous materials, the feed materials
are ground into sizes appropriate for compaction by a roll press.
The roll press is operated with appropriate roll rotation speed,
and roll closing force to develop sufficient pressure to rupture
and collapse the feed's porous structure and to express moisture
held within the pores. Moisture is separated from the compressed
material by mechanical means that are appropriate for the
application. One or combination of screens, filters and centrifuges
mechanically removes moisture from the compacted product. The
moisture may be further treated if desired, for example, if the
moisture is collected water, it may report to a water treatment
system for use elsewhere, such as other manufacturing
processes.
[0019] In embodiments of the invention in which a mixture of
biomass and coal are processed, the raw components are prepared
together or separately and compacted in a roll press. The roll
press is operated with appropriate roll rotation speed, and roll
closing force to develop sufficient pressure to rupture and
collapse the feed's porous structure and to express moisture held
within the pores. Moisture is separated from the compressed
material by mechanical means that are appropriate for the
application. One or a combination of screens, filters and
centrifuges mechanically removes moisture from the product. The
moisture may be further treated if desired, for example, if the
moisture is collected water, it may report to a water treatment
system for use elsewhere, such as other manufacturing
processes.
[0020] In one embodiment of the invention, a first feed stream
comprising biomass such as harvested and gathered grasses,
agricultural plants, wood and residues, is sized by grinding or
shredding into sizes and shapes that maximize exposure of the
porous structure of the biomass. The prepared material is fed into
the nip of the roll press. The roll press is operated with
appropriate roll rotation speed, and roll closing force to develop
sufficient pressure to rupture and collapse the first feed's porous
structure and to express moisture held within the pores. Moisture
is separated from the compressed material by mechanical means that
are appropriate for the application. One or a combination of
screens, filters and centrifuges mechanically removes moisture from
the compacted product. The moisture may be further treated if
desired, for example, if the moisture is collected water, it may
report to a water treatment system for use elsewhere, such as other
manufacturing processes. The first feed stream may then be dried
and/or stored before being combined with a second feed stream. If
the first feed stream is dried prior to being combined with a
second feed stream, the drying may be carried out by any useful
direct or indirect system. By way of non-limiting example, an
indirectly-fired drier may be used. In a preferred embodiment, the
first feed stream is dried at this point by direct drying.
[0021] In this embodiment, a second feed stream, comprising mined
or reclaimed carbonaceous materials such as low rank coals, is
prepared by sizing the carbonaceous materials such as by grinding.
The second feed stock may be compacted in a roll press. The roll
press is operated with appropriate roll rotation speed, and roll
closing force to develop sufficient pressure to rupture and
collapse the second feed's porous structure and to express moisture
held within the pores. Moisture is separated from the compressed
material by mechanical means that are appropriate for the
application. One, or a combination of screens, filters and
centrifuges mechanically removes moisture from the product. The
moisture may be further treated if desired, for example, if the
moisture is collected water, it may report to a water treatment
system for use elsewhere, such as other manufacturing processes.
The second feed stream may then be dried and/or stored before being
combined with the first feed stream. In a preferred embodiment, the
second feed stream is dried at this point by indirect drying. By
way of non-limiting example, an indirectly-fired drier may be
used.
[0022] In this embodiment, the first feed stream and the second
feed stream are combined after each of the first and second feed
stream have been compacted in a roll press. The first and second
feed stream are preferably combined and briquetted to form a
briquette comprising processed and dried biomass and carbonaceous
materials. In a preferred embodiment, the first feed stream of
processed and compacted biomass and the second feed stream of
compacted and processed carbonaceous material are combined in a
ratio of about 20:80 (first feedstream:second feedstream or
processed biomass:processed low rank coal).
[0023] Another aspect of the present invention improves the
efficiency of thermal drying methods by evaporating moisture that
was transferred to the surface of the particle from interior pores
during compaction by mechanical forces. Increased efficiencies
result because moisture residing on the surface that is in direct
contact with the working fluid can be evaporated with less time and
energy than moisture residing in the material's internal pores. The
present invention transforms biomass and carbonaceous feed
materials and combinations thereof to remove moisture, and in a
gasification application, improves the gasification characteristics
of raw feedstock.
[0024] In the present invention, high compaction forces are
continuously imparted at ambient temperature to the feed material.
Sufficient force is used to collapse the material's porous
structure and force the expelled moisture to the surface of the
compacted material. The wet compacted material is then fed to a
low-temperature or ambient temperature-drying device where a
substantial proportion of the moisture is evaporated from the
surface of the material. As an additional benefit, the present
invention, by being more efficient, can dry materials at ambient
temperatures that are too low to be economically practical with
conventional thermal drying systems that do not treat the feed
prior to drying. Operating the present invention at ambient
temperatures will provide additional desirable cost advantages to
the utility and gasification industries, among others, by allowing
production and use of low cost dried LRC and biomass products.
Benefits include, via increased drying efficiencies, reducing the
amount of carbon dioxide and other gaseous pollutants such as
sulfur dioxide and nitrous oxides released during production and
utilization. Providing the opportunity to economically use domestic
carbonaceous materials, such as LRC, and biomass resources to
produce motor fuels will substantially reduce the use of foreign
oil. Thus, the present invention proves beneficial in three ways:
economically reducing moisture content below about 15 wt %, forming
a briquette that has predictable reaction kinetics with steam and
oxygen, and providing a strong material that can support the weight
of burden held in the gasification reactor.
[0025] In all of these embodiments, the compacted and de-moistured
materials, depending on the intended application, are either used
directly without further processing or directed to a thermal drying
system for additional drying.
[0026] Additionally, the compacted and de-moistured materials may
be suitable for use as a fuel without additional processing, or if
transported to distant points of use, may be briquetted before
transport.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1 illustrates an embodiment of the invention,
integrated with a traditional thermal drying system.
[0028] FIG. 2 illustrates an embodiment of the present invention in
a stand-alone configuration.
[0029] FIG. 3 illustrates an embodiment of the present invention
including use of a roll press.
[0030] FIG. 4 illustrates a curve for compacted and un-compacted
pine at about 104.degree. F. Temperature.
[0031] FIG. 5 illustrates a drying curve for compacted and
un-compacted red oak at about 104.degree. F. Temperature.
[0032] FIG. 6 illustrates a drying curve for compacted and
un-compacted PRB coal at about 104.degree. F. Temperature.
[0033] FIG. 7 illustrates a drying curve for compacted and
un-compacted 1:1 mixture of pine and PRB coal at about 104.degree.
F. temperature.
[0034] FIG. 8 illustrates a drying curve for compacted and
un-compacted 1:1 mixture of pine and Brown Coal at about
104.degree. F. temperature.
[0035] FIG. 9 illustrates a drying curve for compacted and
un-compacted 1:1 Mixture of Red Oak and Brown Coal at about
104.degree. F. Temperature.
[0036] FIG. 10 illustrates brown coal briquettes containing about
15 wt % moisture produced by processes of the present
invention.
[0037] FIG. 11 illustrates a flow diagram of an embodiment of the
present invention where the biomass feedstock and the carbonaceous
material are processed in part in separate feeds.
[0038] FIG. 12 illustrates an embodiment of the invention wherein
the biomass feedstock and the carbonaceous feedstock are combined
following compaction.
[0039] FIG. 13 illustrates an embodiment of the present invention
wherein the biomass feedstock and the carbonaceous feedstock are
combined following preparation.
DESCRIPTION OF EMBODIMENTS
[0040] The present invention is drawn to a process of drying that
reduces the energy required to remove moisture from biomass such as
woody materials, grasses, agricultural plants and residues, and
carbonaceous materials such as low-rank coals, or mixtures of
biomass and carbonaceous materials.
[0041] Unless defined otherwise, technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs.
[0042] In this description, it should be understood that the
transitional term "comprising" is synonymous with "including,"
"containing," or "characterized by," is inclusive or open-ended and
does not exclude additional, unrecited elements or method steps.
The transitional phrase "consisting of excludes any element, step,
or ingredient not specified in the claim, but does not exclude
additional components or steps that are unrelated to the invention
such as impurities ordinarily associated therewith. The
transitional phrase "consisting essentially of limits the scope of
a claim to the specified materials or steps and those that do not
materially affect the basic and novel characteristic(s) of the
claimed invention.
[0043] For the descriptions herein and the appended claims, the
singular forms "a", "an" and "the" include plural referents unless
the context clearly indicates otherwise. Thus, for example,
reference to "a compound" refers to more than one compound.
[0044] As used within this specification, "moisture" includes
aqueous solutions (including liquid water), solid components
(including ice), solvents, and gaseous components, or combinations
thereof.
[0045] Examples of suitable biomass feedstocks for the processes of
the present invention include woody materials such as purpose-grown
trees, switch grass, corncobs, stover, oil plants, and residues
produced by harvesting and gathering activities. The initial
moisture content of these biomass feedstocks, prior to any
processing by the methods of the present invention may range as
high as about 75%. For example, the moisture content in a raw woody
biomass may be about 42%. Examples of carbonaceous feedstocks
include bituminous coal, subbituminous coal, lignite, brown coal,
and peat, or mixtures of these carbonaceous materials. Carbonaceous
feedstocks may also include waste coal materials produced by
screening or gravity separation processes.
[0046] Examples of preferred mixtures of biomass and carbonaceous
materials for use as feedstock in the processes of the invention
include woody materials combined with low-rank coals such as brown
coal, lignite and subbituminous coals. In preferred embodiments,
the feedstock is a mixture of biomass and a carbonaceous material
including combinations of pine wood, red oak wood, Powder River
Basin (PRB) coal, and brown coals. The mixture of biomass and a
carbonaceous material is prepared in varying ratios of
biomass:carbonaceous material, in a ratio between about 1:1 to
about 50:1. Most preferably, the mixture of biomass and
carbonaceous material is prepared in a ratio of
biomass:carbonaceous material of about 1:1.
[0047] In an embodiment, the biomass and/or carbonaceous materials,
individually or in combination, are comminuted prior to compaction.
Preferably, the comminution is sufficient to reduce the particle
size of the biomass and/or carbonaceous material. Any suitable
means of breaking up or crushing the biomass and/or carbonaceous
material to reduce the particle size may be used at this stage of
the transformation process. Comminution in its broadest sense is
the mechanical process of reducing the size of particles or
aggregates and embraces a wide variety of operations including
cutting, chopping, grinding, crushing, milling, micronizing and
trituration. For the purposes of the present disclosure,
comminution may be either a single or multistage process by which
material particles are reduced through mechanical means from random
sizes to a desired size required for the intended purpose.
Materials are often comminuted to improve flow properties and
compressibility as the flow properties and compressibility of
materials are influenced significantly by particle size or surface
area of the particle.
[0048] In one specific embodiment, the biomass and/or carbonaceous
material is not comminuted prior to compaction.
[0049] A feedstock for use in the methods of the invention is
prepared in a specified manner to maximize the release of liquid
water from the feedstock materials when compacted. The compaction
roll press applies mechanical forces on these materials to rupture
and collapse porous structures in the materials, releasing water
contained therein. The water expressed by the applied mechanical
forces moves from the collapsed porous structure to the surface of
the compacted material where it can be removed by mechanical
dewatering devices such as screens, filters and/or centrifuges.
[0050] It is well known to those skilled in the art that
significantly less energy is required to remove water by mechanical
means than to remove the same water by evaporation. By enhancing
the mechanical efficiency of water removal, the present invention
significantly reduces the energy required to remove water from
biomass and carbonaceous feedstocks compared with the energy
requirements required by thermal-evaporative processes.
[0051] The mechanical forces are applied by a roll press operated
at rotation speeds, and roll-closing forces that develop the
required pressure to compact the prepared feedstock, removing
porous structures in the materials and liberating liquid water held
in the porous structures. In addition to removing liquid water at a
lower energy demand than that imposed by thermal drying, the use of
the roll press to form the compacted product results in a faster
drying of the prepared materials compared with materials that have
not been prepared and compacted.
[0052] These processes are preferably performed at ambient
temperature as supplied heat is not required to express or remove
water as a liquid. Undesirable thermal degradation is thus avoided
to the benefit of temperature-sensitive materials such as woody
materials, grasses and low-rank coals and additional energy savings
are realized as temperature monitoring, adjustment and control are
not required.
[0053] The pressure applied to the prepared material by a double
roll press is at least about 5,000 lb/in.sup.2 and may be as great
as about 80,000 lb/in.sup.2. In one embodiment, the pressure
applied to the prepared material by a double roll press is between
about 10,000 lb/in.sup.2 and about 50,000 lb/in.sup.2. In another
embodiment, the pressure applied to the prepared material by a
double roll press is between about 20,000 lb/in.sup.2 and about
40,000 lb/in.sup.2.
[0054] Because electrical motors are used to drive the compaction
devices and dewatering equipment, compaction energy per ton of
material processed can be calculated. In the absence of any thermal
drying, the compaction energy is between about 8 kWh and about 15
kWh (27,300 Btu and 51,200 Btu) per short ton of feed material
processed. Mechanical dewatering requires less than about 3 kWh
(10,200 Btu) to treat a short ton of feed material. Total power
required by the invention not shared by thermal drying methods is
the sum of compaction power and dewatering power. The sum can range
between about 11 kWh and 18 kWh (37,500 Btu and 61,400 Btu) per
short ton of feed material. Performance data listed in Table 1 can
be used to estimate the total energy required by the present
invention to remove a specified amount of water.
[0055] The processes of the invention including feedstock
preparation and compaction in a double roll press typically remove
between about 10% and about 40% of the water contained in the
untreated material. The untreated material may have up to about 75
wt % moisture. The percent of moisture may vary depending upon the
location of the mines For example, coal from mines in Australia may
contain up to about 75 wt % moisture. The process of the invention
removes between about 2 wt % and about 20 wt % of the water
contained in the untreated material.
[0056] Upon treatment by the methods of the present invention
including product preparation and compaction in a double roll
press, the treated material may have a reduced moisture content
totaling as low as about 20% moisture. Upon treatment by the
methods of the present invention including product preparation and
compaction in a double roll press, followed by further drying by
evaporative heating, the treated material may have a reduced
moisture content totaling as low as about 5% moisture.
[0057] By comparing the time needed to treat a feedstock by the
methods of the present invention, including product preparation and
compaction in a double roll press, followed by thermal evaporation,
with the time needed to dry the same feedstock to the same level of
dryness using solely thermal evaporation, it is possible to
estimate the reduction in drying time. This savings in drying time
is between about 30 minutes and about 60 minutes. More typically,
this savings in drying time is approximately 45 minutes.
[0058] Products, including biomass, carbonaceous materials, and
mixtures thereof produced by the methods of the present invention
are amenable to additional processing into briquettes. Formed
products are typically used where the dried material is
transported, or used in stoker furnaces where a coarse particle
size distribution is required. In instances in which a shaped final
product is desired, the product is preferably a briquette of ovoid
shape with a minor dimension of at least about 6 mm, but less than
about 100 mm, and more preferably having a minor dimension of about
50 mm. Preferably, the shaped products have a total moisture
content between about 5 wt % and about 20 wt %, and more preferably
a total moisture content of about 15 wt %.
[0059] The separation of liquid water from the compacted material
may include the use of a vibrating screening machine to separate
liquid water as underflow from dewatered compacted material as
overflow. The separation may also include the use of a belt filter
press to separate liquid water as filtrate from dewatered compacted
material as filter cake. The separation may also include the
separation of a centrifuge to separate liquid water as effluent
from dewatered compacted material as product. The separation may
also include the use of a vacuum disk filter to separate liquid
water as filtrate from dewatered compacted material as filter
cake.
[0060] When additional thermal evaporation is used to further dry
the compacted and dewatered material, the increased drying rate
also allows for the use of smaller thermal drying equipment and
associated systems, with a corresponding reduction in capital and
operating costs.
[0061] The present invention reduces the thermal energy required to
dry the untreated feedstock by increasing the drying rate (the time
required to achieve a specified moisture content). Compaction
conditions the feed to a thermal dryer by transferring water held
in pores in the interior of the particle to the surface of the
particle. As a result, the water is more accessible to heat, so
less time is required for evaporation to take place. In addition, a
wet outer surface present on a compacted material can come into
intimate contact with a hot surface such as that present in an
indirectly heated system. The intimate contact allows the material
to accept a greater amount of thermal energy per unit area and
time. This concept has been demonstrated with industrial
experience. For example, certain compacted materials have required
1,300 Btu to evaporate a pound of water. The same un-compacted
materials are reported to require between 1,600 Btu to 2,500 Btu to
evaporate a pound of water. The amount of energy required to dry
the material depends on the physical characteristics of the dried
material, and the ability for heat to contact the moisture to
achieve evaporation.
[0062] A specific embodiment of the invention includes a
traditional thermal drying system, as shown in FIG. 1. The system
depicted in FIG. 1 is particularly well suited for applications in
which the product moisture content must be less than that
achievable by the application of the processes of the present
invention to a carbonaceous and/or biomass feedstock. In this
embodiment, the processes of the present invention benefit the
thermal drying system by reducing the evaporative load on the
thermal dryer.
[0063] Another embodiment is a stand-alone configuration shown in
FIG. 2. This embodiment is preferred for applications that require
product moisture content that can be achieved by the processes of
the present invention applied to a carbonaceous and/or biomass
feedstock.
[0064] Another embodiment of the invention is shown in FIG. 3. Feed
(1) enters a purpose-built size reduction device (2) designed to
prepare the feed in a manner that exposes the prepared product (3)
to maximize its porous structure to compaction forces exerted by
the roll press (4).
[0065] The prepared feed is engaged in the nip between the rolls to
collapse and destroy the porous structure that holds a substantial
amount of the moisture contained in the feed. Scrappers (5) remove
water that clings to the compaction rolls. The compacted product
(7) reports to a dewatering device (8) where water (9) is separated
from solids. Water collected by the scrappers (6) joins the water
(9) to produce a final water product (10) that reports to a process
that is suitable for the application. Dewatered product (11) is
collected and processed as required for the application. In some
embodiments, the dewatered product is sent to storage following
processing. In some embodiments of the invention, the dewatered
product (11) may be cooled prior to being placed into storage.
[0066] An embodiment of the present invention is shown on FIG. 11,
wherein the biomass feedstock and the carbonaceous feedstock are
separately prepared, compacted, mechanically dewatered, and dried
prior to mixing the biomass feedstock and carbonaceous feedstock
materials. The processed materials are stored, proportioned, mixed
to form a final product that may be available for further
processing.
[0067] As illustrated in FIG. 11, a source of biomass feedstock (1)
and source of carbonaceous feedstock (2) provide raw materials that
are processed separately, which may be concurrently, and eventually
mixed in the desired proportion to suit the application. The
as-received biomass material (3) is prepared by equipment (4) to
produce an appropriate feed (5) that is suitable for processing by
a roll press (6). The roll press (6) provides the necessary
configuration and operating conditions to compact the feed (5) to
express water held within the biomass internal structure so that
fluid may become present on the surfaces of the material. The
mechanically compacted biomass (7) may have excess free water that
can be removed by mechanical dewatering devices (8) such as
screens, belt filters, centrifuges and the like. The compacted and
mechanically dewatered biomass material (9) may be dried in a dryer
(10) to produce a dried biomass product (11). The dryer (10) can be
operated to optimally evaporate water from the compacted and
dewatered biomass (9). Vapors (12) including water and other gases
(14) produced during drying will be processed by a gas handling
system (13) to prepare the gases for discharge into the atmosphere
(15). The gas handling system (13), which may be several pieces of
equipment, prepares the vapors (12) for discharge into the
atmosphere (15). Separate gas handling systems may be used for the
biomass and carbonaceous feedstock streams. The dried biomass
product (11) may be stored in a vessel (16) such as a bin, silo, or
stockpile or other suitable device. Optionally, the dried biomass
material (11) is not stored, but instead is mixed directly with the
dried carbonaceous material (27). The withdrawal rate of the stored
biomass material (17) is controlled relative to the withdrawal rate
of dried carbonaceous material (30) to provide a feed for mixing in
a vessel (18) or place where the two dried materials come together.
The withdrawal rate may be automated and/or user operated. The
combined and mixed dried product (31) may report to downstream
processing (32) or stored in a suitable vessel.
[0068] Carbonaceous material (2) may be handed and processed in a
accordance with the following process, which may be similar to the
processing and handling procedure for the biomass material. The
as-received carbonaceous material (19) may prepared by the
appropriate equipment (20) to produce a prepared feed (21) that is
suitable for processing by a roll press (22). The roll press (22)
provides the necessary configuration and operating conditions to
compact the feed (21) and express water held within the
carbonaceous material internal structure so that fluid may become
present on the surfaces of the compacted carbonaceous material
(23). The compacted carbonaceous material (23) may have excess free
water that may be removed by mechanical dewatering devices (24)
such as screens, belt filters, centrifuges and the like. The
mechanically dewatered carbonaceous material (25) may be dried with
a dryer (26) to produce a dried carbonaceous product (27). The
dryer (26) may be operated to optimally evaporate water from the
compacted and dewatered carbonaceous material (25). Vapors (28)
including water and other gases produced during drying will be
processed by a gas handling system (13) to prepare the gases for
discharge into the atmosphere (15). The same gas handling system
(13) may be sized and designed to handle both biomass and
carbonaceous dryer emissions. The dried carbonaceous material (27)
may be stored in a vessel (29) such as a bin, silo, or stockpile or
other suitable device. The withdrawal rate of the stored
carbonaceous material (30) is controlled relative to the withdrawal
rate of dried biomass material (17) to provide a feed to the mixer
(18) that will be combined with the dried biomass material (30) or
place where the two dried materials come together, which may be
automated and/or manually operated.
[0069] In an embodiment, the two dryer products, (11) and (27) may
require cooling prior to being placed into storage vessels (16) and
(29). The cooling may be performed by any suitable method using any
suitable device.
[0070] It should be understood that the product from any of steps
may be stored for a suitable period of time then used for
subsequent steps at a later time.
[0071] An embodiment of the present invention is shown on FIG. 12.
FIG. 12 illustrates an embodiment of the invention wherein the
biomass feedstock and the carbonaceous feedstock are processed
separately until each feedstock is compacted. After compaction, the
feedstocks are combined. The processed materials are proportioned,
mixed, and dried together to form a final product that may be
available for further processing.
[0072] An embodiment of FIG. 12 is discussed in more detail herein.
A source of biomass feedstock (1) and source of carbonaceous
feedstock (2) provide raw materials that are processed separately,
and possibly concurrently, for a portion of the process. The
as-received biomass material (3) is prepared by equipment (4) to
produce an appropriate prepared feed (5) that is suitable for
processing by a roll press (6). The roll press provides the
necessary configuration and operating conditions to compact the
prepared feed (5) to express water held within the biomass material
internal structure so that fluid may become present on the surfaces
of the biomass compacted material (7). The compacted biomass
material (7) reports to mixing in a vessel (8) such as a bin, silo,
or stockpile or any suitable vessel with the mechanically compacted
carbonaceous material (13) to become a joint feed (14) that may be
dried by with a dryer (15) to produce a dried product (16) that is
available for downstream processing (17) or used directly to suit
the application. The dryer (15) can be operated to optimally
evaporate water from the joint feed (14) containing a mixture of
mechanically compacted biomass and compacted carbonaceous material.
Vapors (18) including water and other gases produced during drying
are processed by a gas handling system (19) to prepare the gases
(20) for discharge into the atmosphere (21).
[0073] Carbonaceous feedstock material (2) may be handed and
processed in a similar manner as the biomass material (1). The
as-received carbonaceous material (9) may be prepared by equipment
(10) to produce an appropriate feed (11) that is suitable for
processing by a roll press (12). The roll press (12) is provides
the necessary configuration and operating conditions to express
water held within the carbonaceous material internal structure so
that the fluid may become present on the surfaces of the compacted
carbonaceous material (13). The compacted carbonaceous material
(13) reports to the mixing vessel (8) or point where it joins the
compacted biomass material (7) to form the feed which may be sent
to the dryer (15). The withdrawal rate of the compacted biomass
material (7) may be controlled relative to the withdrawal rate of
the compacted carbonaceous material (13) to provide a feed for
mixing in a vessel (8) or place where the two dried materials come
together. The withdrawal rate may be automated and/or user
operated. The dryer product (16) may require cooling prior to
reporting to final product (17). The cooling may be performed by
any suitable method using any suitable device. The final dried
product (17) may be stored in any suitable storage vessel or used
directly to suit the application.
[0074] It should be understood that the product from any of steps
may be stored for a suitable period of time then used for
subsequent steps at a later time.
[0075] An embodiment of the present invention is shown on FIG. 13.
This embodiment illustrates a process whereby the biomass feedstock
and the carbonaceous feedstock are combined following the
preparation of the feedstock. The processed materials are dried to
form a final product that may be available for further
processing.
[0076] As illustrated in FIG. 13, a source of biomass feedstock (1)
and source of carbonaceous feedstock (2) provide raw materials that
are processed separately, which may be concurrently, in the desired
proportion to suit the application. The as-received biomass
material (3) may be prepared by equipment (4) to produce an
appropriate feed (5) that is suitable for processing by a roll
press (11). The as-received carbonaceous material (6) may be
prepared by equipment (7) to produce an appropriate prepared
carbonaceous feed (8) that is suitable for processing by the roll
press (11). The prepared biomass material and prepared carbonaceous
material report to a mixing vessel (9) or place where these two
materials come together to become a feed (10) for the roll press
(11).
[0077] The roll press (11) provides the necessary configuration and
operating conditions that will express water held within the
biomass material internal structure and water held in the
carbonaceous material internal structure so that fluid may become
present on the surfaces of the individually compacted material. The
compacted material (12) becomes the feed which may be sent to the
dryer (13).
[0078] In an embodiment, the prepared carbonaceous material (8) and
the prepared biomass material (5) may be fed directly into the roll
press (11) at an appropriate feeding rate.
[0079] The dryer (13) produces a dried product (14) that is
available for downstream processing (15) or used directly to suit
the application. The dryer (13) can be operated to optimally
evaporate water from the feed (12) containing a mixture of the
compacted biomass and compacted carbonaceous material. Vapors (16)
including water and other gases produced during drying are
processed by a gas handling system (17) to prepare the gases (18)
for discharge into the atmosphere (19). The dryer product (14) may
require cooling prior to reporting to final product (15). The
cooling may be performed by any suitable method using any suitable
device.
[0080] It should be understood that the product from any of steps
may be stored in a suitable manner then used for subsequent
steps.
[0081] The invention now being generally described will be more
readily understood by reference to the following examples, which
are included merely for the purposes of illustration of certain
aspects of the embodiments of the present invention. The examples
are not intended to limit the invention, as one of skill in the art
would recognize from the above teachings and the following examples
that other techniques and methods can satisfy the claims and can be
employed without departing from the scope of the claimed
invention.
EXAMPLES
Example 1
[0082] Samples of pine, red oak and PRB coal, and Brown Coal (coal
from LaTrobe Valley, Australia) were processed to confirm the
efficiency and performance of mechanical compaction to remove
liquid water. The samples were prepared to sizes and shapes
believed to be advantageous for compaction. Each material,
including a mixture of pine and PRB coal, were subjected to up to
40,000 lb/in.sup.2 pressure. Expressed water was collected. All
materials were weighed and assayed for moisture content. All
compaction tasks were conducted at ambient temperature.
[0083] Raw materials (unprocessed material) and compacted products
were dried at about 104.degree. F. on a laboratory moisture
determination device to ascertain the relative drying rates of each
sample. Results are summarized in Table 1, and plotted in FIGS.
4-9. Graphics were added to FIG. 4 that show the moisture removed
by compaction and the reduction in drying time required to achieve
an equal moisture content. In this case, compaction removed about
15 wt % moisture and reduced drying time to achieve about 20 wt %
moisture by about 46 minutes. The moisture reduction and reduced
drying time achieved by compaction are presented for red oak, PRB
coal, Brown Coal, and mixtures of woods and coals.
TABLE-US-00001 TABLE 1 Wood and Coal Compaction Test Results
Summary Water Total Moisture, Wt % Removed by Before After
Compaction, Sample Compaction Compaction Difference Wt % PRB Coal
25 22 3 12 Brown Coal 63 46 17 27 Pine 41 26 15 37 Red Oak 42 27 15
36 50/50 Pine-PRB 33 29 4 12 Coal Mixture 50/50 Red Oak- 52 37 15
29 Brown Coal Mixture
[0084] Brown Coal briquettes containing 15 wt % moisture were
produced by the system shown in FIG. 1. Brown Coal briquettes
produced using the system shown in FIG. 1 are shown in FIG. 10.
[0085] The energy savings accrued by removing water as a liquid
compared to removing water by evaporation can be estimated based on
first principles, dryer performance data supplied by vendors of
thermal dryers, and test data.
[0086] The energy required to evaporate water in a commercial
thermal dryer includes: [0087] 1. Vaporize liquid water to a gas.
[0088] 2. Raise the temperature of the air, feed and water in the
feed to drying conditions. [0089] 3. Replace heat loss due to
radiation and convection.
[0090] The energy required by an embodiment of the present
invention that removes water as a liquid at ambient temperatures is
less than 10%, and as little as 5% of that required to effect the
same amount of drying by thermal evaporative methods. The invention
uses mechanical energy to remove water thereby avoiding the three
energy-consuming factors listed above. Electrical motors drive the
compaction devices and dewatering equipment. Experiments have
demonstrated that compaction consumes between about 8 kWh and about
15 kWh (27,300 Btu and 51,200 Btu) to treat a short ton of feed
material. Mechanical dewatering requires less than about 3 kWh
(10,200 Btu) to treat a short ton of feed material. Total power
required by the invention not shared by thermal drying methods is
the sum of compaction power and dewatering power. The sum can range
between about 11 kWh and about 18 kWh (37,500 and 61,400 Btu) per
short ton of feed material. Performance data listed in Table 1 can
be used to estimate the total energy required by the present
invention to remove a specified amount of water.
[0091] In certain applications, the product must be dried below
that achievable solely by the mechanical means of the present
invention. In these cases, the raw material is initially processed
by the mechanical means of the present invention to remove a
portion of the water contained in the raw material. The
partially-dried product then reports to a conventional thermal
dryer to remove a specified amount of the remaining water by
evaporation. This combination of mechanical and thermal processing
is depicted in FIG. 1.
[0092] Table 2 presents an estimate of the energy required for
complete thermal drying compared with the mechanical processing of
the present invention combined with thermal drying, in the
processing of a raw woody biomass containing about 42 wt % moisture
to produce about 2000 pounds of dried woody product containing
about 5 wt % moisture. The mechanical processing removes liquid
water to provide a treated biomass containing about 26 wt %
moisture (reference Table 1). Thereafter, the mechanically treated
biomass is fed to a lower capacity thermal dryer that evaporates
water remaining on the surfaces of the treated material. The listed
values show that the present invention reduces overall net energy
consumption by about 60%. Additional benefits result if the feed or
final product moisture content increases.
TABLE-US-00002 TABLE 2 Energy Consumption Required to Produce 2,000
lb of Product by Thermal Methods and Mechanical Processing of the
Present Invention Mechanical Processing of the Thermal Present
Parameter Drying Invention Raw Feed Moisture, Wt % 42 42 Final
Product Moisture, Wt % 5 5 Feed Weight, lb 3,276 3,276 Product
Weight, lb 2,000 2,000 Water Removed by Compaction, lb n/a 673
Water Removed by Evaporation, lb 1,276 603 Total Energy Demand, Btu
2,040,000 820,000
Example 2
[0093] Industry requires briquettes to resist breakage during
handling and storage. Sometimes briquettes made exclusively from
low-rank coal are brittle or lack strength to satisfy industry's
requirements. In this example, a mixture consisting of low-rank
coal and pine wood was prepared and processed by the present
invention. Results confirm that the physical properties of
briquettes made from this mixture were superior to those made
exclusively from low-rank coal.
[0094] The first series of tests measured the compressive strength
of briquettes that contained various proportions of low-rank coal
and pine wood (biomass). Both materials were milled to pass about a
2.4 mm screen opening. Table 3 demonstrates that increasing the
proportion of biomass increases compressive strength, a measure of
the ability to bear weight without breaking. Observations have
concluded that biomass provides additional strength by making the
briquette slightly flexible, thus able to bend with the load
without breaking. Additional strength is imparted by the fibrous
structure of biomass. The fibers are intimately pressed into the
low-rank coal particles during compaction and thus bond the mixture
together. The great pressure imparted by the present invention is
critical to deform the low-rank coal particles sufficiently to
enclose and bond to the biomass fibers. Table 3 lists the
compressive strength of briquettes formed from various mixtures of
low-rank coal and biomass. The briquettes were compacted by a roll
press operated at a closing force of about 28,000 lbf/inch of roll
width.
TABLE-US-00003 TABLE 3 Compressive Strength of Briquettes Formed
from Various Proportions of Biomass and Low-Rank Coal Mixture
Composition, Compressive Strength Proportion of Biomass of
Briquette, psi 5 2,100 10 3,100 20 3,900
[0095] In commercial applications, briquettes are handled and
stored as part of the course of business. They are subjected to
forces that break a briquette into small pieces and generate dust.
It is desirable to minimize breakage and dust that increase costs.
Two tests recognized by industry, the drop shatter test (ASTM
D-440), and tumbler test (ASTM D-441), indicate the relative
tendency to break by impact and create dust be abrasion. Both tests
report results as the size stability factor. Higher values indicate
greater resistance to impact and abrasion.
[0096] Briquettes formed exclusively from low-rank coal and biomass
mixture were evaluated by the drop shatter test and tumbler test.
Results are presented in Table 4.
TABLE-US-00004 TABLE 4 Drop Shatter Test Results and Tumbler Test
Results for Briquettes Formed from Low-Rank Coal and a Mixture of
Low-Rank Coal and Biomass 80 wt % Low- 100 wt % Rank Coal Low- 20
wt % Biomass Parameter Rank Coal Mixture Drop Shatter Test Size
Stability Factor 90% 97% (ASTM D-440) Tumbler Test Size Stability
Factor 70% 82% (ASTM D-441)
These test results clearly demonstrate that briquettes formed from
a mixture of low-rank coal and biomass are more resistant to
breakage by impact and generating dust by abrasion.
Example 3
[0097] There is an incentive to reduce greenhouse gas (GHG)
emissions created by burning fossil fuels, especially low-rank
coal. Government agencies including the United States EPA,
publishes the carbon dioxide emission factor for low-rank coal
(lignite) is 4,600 lb/st lignite fired. The emission factor for
wood, the type of biomass used in the examples presented for the
present invention, is 3,400 lb/st wood fired. The carbon dioxide
produced by combusting wood, a renewable resource, is not
considered a GHG. Briquettes formed from a mixture of low-rank coal
and biomass therefore has the advantage of producing less GHG for
any given amount of energy produced by combustion. Carbon dioxide
emissions are reduced approximately in proportion to the amount of
biomass included in the briquette. For example, a briquette formed
as described in these Examples, containing about 20 wt % biomass,
will reduce GHG emissions by approximately 20%.
[0098] The foregoing examples of the present invention have been
presented for purposes of illustration and description.
Furthermore, these examples are not intended to limit the invention
to the form disclosed herein. Consequently, variations and
modifications commensurate with the teachings of the description of
the invention, and the skill or knowledge of the relevant art, are
within the scope of the present invention. The specific embodiments
described in the examples provided herein are intended to further
explain the best mode known for practicing the invention and to
enable others skilled in the art to utilize the invention in such,
or other, embodiments and with various modifications required by
the particular applications or uses of the present invention. It is
intended that the appended claims be construed to include
alternative embodiments to the extent permitted by the prior
art.
* * * * *