U.S. patent application number 12/967874 was filed with the patent office on 2011-04-14 for system and method for making low volatile carbonaceous matter with supercritical co2.
This patent application is currently assigned to Carbonxt Group Limited. Invention is credited to Randall J. Harris, Damian Wales.
Application Number | 20110085962 12/967874 |
Document ID | / |
Family ID | 40844729 |
Filed Date | 2011-04-14 |
United States Patent
Application |
20110085962 |
Kind Code |
A1 |
Harris; Randall J. ; et
al. |
April 14, 2011 |
SYSTEM AND METHOD FOR MAKING LOW VOLATILE CARBONACEOUS MATTER WITH
SUPERCRITICAL CO2
Abstract
A system for making low volatile carbonaceous material including
a digestion vessel in communication with a carbonaceous material
feedstock unit for producing a digested carbonaceous material; an
extraction vessel in communication with the digestion vessel, the
extraction vessel containing supercritical carbon dioxide fluid for
extracting hydrocarbons from the digested carbonaceous material to
produce an extract solvent and the low volatile carbonaceous
material; and at least one separation vessel in communication with
the extraction vessel for separating the extract solvent to a
carbon dioxide gas and a stream of extracted hydrocarbons.
Inventors: |
Harris; Randall J.; (Mount
Gay, WV) ; Wales; Damian; (Powellton, WV) |
Assignee: |
Carbonxt Group Limited
|
Family ID: |
40844729 |
Appl. No.: |
12/967874 |
Filed: |
December 14, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12008287 |
Jan 8, 2008 |
|
|
|
12967874 |
|
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|
Current U.S.
Class: |
423/448 ;
264/29.1; 423/449.1; 423/461 |
Current CPC
Class: |
Y02P 20/544 20151101;
C01B 32/342 20170801; C01B 32/378 20170801; Y02P 20/54
20151101 |
Class at
Publication: |
423/448 ;
264/29.1; 423/449.1; 423/461 |
International
Class: |
C01B 31/02 20060101
C01B031/02; C01B 31/00 20060101 C01B031/00; C01B 31/04 20060101
C01B031/04; C01B 31/08 20060101 C01B031/08 |
Claims
1. A method for making low volatile carbonaceous material
comprising: digesting contaminants in a carbonaceous material with
an acid mixture solution to produce a digested carbonaceous
material/acid mixture solution; separating said digested
carbonaceous material from said digested carbonaceous material/acid
mixture solution; contacting said digested carbonaceous material
with a supercritical carbon dioxide fluid for extracting
hydrocarbons from said digested carbonaceous material to produce an
extract solvent and a low volatile carbonaceous material; and
separating said low volatile carbonaceous material from said
extract solvent.
2. The method for making low volatile carbonaceous material of
claim 1 further comprising: separating carbon dioxide gas from said
extract solvent.
3. The method for making low volatile carbonaceous material of
claim 1 further comprising: condensing said carbon dioxide gas to a
carbon dioxide liquid.
4. The method for making low volatile carbonaceous material of
claim 1 further comprising: heating said carbon dioxide liquid to
produce a recycle stream of supercritical carbon dioxide fluid.
5. A method for making carbon fiber comprising: digesting
contaminants in a carbonaceous material with an acid mixture
solution to produce a digested carbonaceous material/acid mixture
solution; separating said digested carbonaceous material from said
digested carbonaceous material/acid mixture solution; producing a
carbon pitch from said digested carbonaceous material; drawing
ungraphitized carbon fiber from said carbon pitch to a desired
diameter; stabilizing said ungraphitized carbon fiber to produce a
stabilized carbon fiber; and graphitizing said stabilized carbon
fiber to make said carbon fiber.
6. The method for making carbon fiber of claim 5 wherein said
stabilizing ungraphitized carbon fiber comprises: transporting said
ungraphitized carbon fiber on a plurality of heated rollers through
a heater at a temperature of from about 200.degree. C. to about
300.degree. C.
7. The method for making carbon fiber of claim 5 wherein said
graphitizing said stabilized carbon fiber comprises: transporting
said stabilized carbon fiber through a heater in the absence of
oxygen at a temperature of from about 1,850.degree. C. to about
5,500.degree. C.
8. The method for making carbon fiber of claim 5 further
comprising: oxidizing the outer surface of said carbon fiber by
contacting said carbon fiber with an oxidizing agent.
9. The method for making carbon fiber of claim 5 further
comprising: coating said carbon fiber with an adhesive for to
improve subsequent bundling of said carbon fiber.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/008,287, filed Jan. 8, 2008, the contents of which are
incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The field of the invention is directed to devolatilizing
carbonaceous material and more specifically to devolatilizing
carbonaceous material while recovering volatile compounds from the
carbonaceous matter.
BACKGROUND OF THE INVENTION
[0003] Carbonaceous matter typically contains volatile compounds
that make the carbonaceous material less desirable or useful than
it otherwise would be for some purposes. Volatile compounds are
those compounds that are given off as a vapor or gas by heating the
carbonaceous material to a particular temperature. For example,
volatile compounds or matter are given off by heating coal up to
950.degree. C. under carefully controlled conditions and driving
off the volatile compounds; the mass of which is determined by
measuring the weight loss of the coal after the heating process. It
typically does not include the weight loss due to water content,
which is removed at 105.degree. C.
[0004] Volatility is usually critical to industries that commonly
use carbonaceous materials in their processes, for example coal for
furnaces for steel making, coke manufacturing, and also for power
generation. It is commonly known that volatility determines the
burn rate of a particular coal. High volatility coal ignites
easily, but it is not as desirable as moderately to low volatility
coals because it does not contain as much energy per unit volume
due to its high volatility. Many coals are "coked" prior to their
industrial use by removing the volatile compounds through heating
it to high temperatures in the absence of oxygen. Coking coal is
used in the steel manufacturing process, where carbon must be as
volatile-free and ash-free as possible. Calcining is another
thermal treatment process that removes the volatile fraction of the
carbonaceous material, such as coal. Typically, coking processes
occur at temperatures of approximately 500.degree. C. and calcining
processes occur at temperatures of approximately 1,300.degree. C.
Both of these processes typically occur in inert atmospheres in the
absence of oxygen. The problem with these types of processes is
that they require high energy requirements and do not typically
recover the volatile compounds as they are vented to the atmosphere
or a gas scrubber of some type.
[0005] It has become increasingly important to recover the volatile
compounds that are entrained in the carbonaceous material, such as
coal. For example, coal tar is a liquid having a high viscosity
that has many uses including: fuel, pharmaceutical bases, shampoos,
soaps, carbon fibers, waterproofing materials, and as a raw
material for dyes, drugs, and paints. Coal tar may be extracted
from coal by a variety of processes. For example, it is known to
use solvent extraction processes to remove the volatile coal tar
from coal.
[0006] In addition to calcining and coking coal, there exist
several solvent extraction methods for removing the volatile
compounds from carbonaceous material, such as coal. Typically,
organic solvents, such as chlorinated organic solvents, are used to
extract the volatile compounds from coal and then recovered during
a distillation process. Many of these type solvents are hazardous
materials and require substantial expenses related to implementing
safety devices and measures for handling, storing, and using such
solvents. In addition, efficient distillation of the volatile
compounds from the organic solvents may not always be
achievable.
[0007] U.S. Pat. Nos. 4,871,443 and 4,806,228 discloses a method
for removing salts from coal tar and coal pitches. The method
includes washing the coal tar/pitch in a pressure container with
water and carbon dioxide gas at a temperature and pressure near the
critical point of the gas. Recovery and removal of the solvent and
the tar or pitch phase occurs upon reduction of the pressure. The
methods are performed on an already extracted coal tar/pitch
specimen and not on untreated carbonaceous material, such as
coal.
[0008] U.S. Pub. Pat. App. No. 20070095753 discloses methods for
removing residues from substrates using environmentally friendly
solvents. Petroleum residue, including coal tar is removed from a
petroleum-based substrate by dissolution in carbon dioxide miscible
solvent, which dissolves a portion of the petroleum residue. The
solvent is then separated and contacted with carbon dioxide such
that the petroleum residue is precipitated. This reference
discloses the use of environmentally friendly solvents, known as
GRAS solvents.
[0009] U.S. Pat. No. 4,446,921 discloses a method for the
underground gasification of solid fuels in which volatile compounds
existing in the solid fuel can be recovered. Underground solid fuel
is opened up with a super critical gas phase that dissolves water
and the volatile organic compounds that would otherwise impede the
later gasification process. The volatile organic compounds and
water are later separated from the super critical gas phase above
ground. It discloses that the gas enters the underground solid fuel
at a temperature 10.degree. C. to 100.degree. C. above its
supercritical temperature and at a pressure 2 bar to 300 bar above
its critical pressure. This is performed on untreated solid fuel
deposits, such as underground coal deposits.
SUMMARY
[0010] In one embodiment, the present system and method for making
low volatile carbonaceous matter with supercritical CO.sub.2
("system for making low volatile carbonaceous matter") includes
removing coal tar from coal with supercritical CO.sub.2. Typically,
the coal is washed and sized at preparation plants located near
coal mines. Then, the coal may be further treated by processes that
remove inorganic impurities and/or contaminants, such as metal
oxides, and the like. After the coal has been treated to remove
these contaminants, then it is subjected to the present system for
making low volatile carbonaceous matter that contacts the treated
coal with supercritical CO.sub.2 that extracts volatile compounds
from the treated coal that are recovered in a subsequent separation
process.
[0011] The present system for making low volatile carbonaceous
matter provides a clean devolatilized coal and a supply of valuable
volatile compounds for later use as a base or intermediate raw
material in other manufacturing processes. Coal tar, one of the
extracts from the present system for making low volatile
carbonaceous matter, may be distilled to carbon pitch, which is a
primary component for making carbon fibers and related carbon fiber
composite materials. In another embodiment, the present system for
making low volatile carbonaceous matter produces a clean high
quality activated carbon product.
[0012] In one embodiment, the present system for making low
volatile carbonaceous material includes a digestion vessel in
communication with a carbonaceous material feedstock unit for
producing a digested carbonaceous material; an extraction vessel in
communication with the digestion vessel, the extraction vessel
containing supercritical carbon dioxide fluid for extracting
hydrocarbons from the digested carbonaceous material to produce an
extract solvent and the low volatile carbonaceous material; and at
least one separation vessel in communication with the extraction
vessel for separating the extract solvent to a carbon dioxide gas
and a stream of extracted hydrocarbons.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 illustrates a schematic diagram of a carbonaceous
material feedstock unit according to an embodiment of the present
invention;
[0014] FIG. 2 illustrates a schematic diagram of a microwave drying
unit according to an embodiment of the present invention;
[0015] FIG. 3 illustrates a schematic diagram of a digestion unit
according to an embodiment of the present invention;
[0016] FIG. 4 illustrates a schematic diagram of a fluidized bed
dryer unit according to an embodiment of the present invention;
[0017] FIG. 5 illustrates a schematic diagram of a packaging and
product unit according to an embodiment of the present
invention;
[0018] FIG. 6 illustrates a schematic diagram of a vapor recovery
unit according to an embodiment of the present invention;
[0019] FIG. 7 illustrates a schematic diagram of a feedstock
storage unit according to an embodiment of the present
invention
[0020] FIG. 8 illustrates a schematic diagram of an ultrasonic unit
according to an embodiment of the present invention;
[0021] FIG. 9 illustrates a schematic diagram of an ultrasonic unit
according to another embodiment of the present invention;
[0022] FIG. 10 illustrates a schematic diagram of a system for
making low volatile carbonaceous matter according to an embodiment
of the present invention;
[0023] FIG. 11 illustrates a schematic diagram of a solvent
extraction unit according to an embodiment of the present
invention;
[0024] FIG. 12 illustrates a schematic diagram of a carbon fiber
production unit according to an embodiment of the present
invention;
[0025] FIG. 13 is a pressure-temperature phase diagram of CO.sub.2
for determining a desired pressure and temperature of CO.sub.2
according to an embodiment of the present invention;
[0026] FIG. 14 illustrates a flow diagram for an exemplary process
for refining carbonaceous material according to an embodiment of
the present invention;
[0027] FIG. 15 illustrates a flow diagram for an exemplary process
for making low volatile carbonaceous matter; and
[0028] FIG. 16 illustrates a flow diagram for an exemplary process
for making carbon fiber.
DETAILED DESCRIPTION OF THE DRAWINGS
[0029] In the drawings, like or similar elements are designated
with identical reference numerals throughout the several views and
figures thereof, and various depicted elements may not be drawn
necessarily to scale.
[0030] The term "carbonaceous" means all materials that consist of
substantial amounts of carbon. Without limitation the term includes
coal, refined coal, activated carbon, carbon black, carbon
products, solid crude oil, coal tar pitch, carbon fibers, tar,
carbon, coke, graphite, and other carbon structures.
[0031] The term "digested carbonaceous material" means a
carbonaceous material that has been subject to a cleaning or
digesting process as herein described. In one aspect, the term
means chemically cleaning the carbonaceous material by digesting
the minerals embedded within the carbonaceous material. This term
may further mean a carbonaceous material that has been chemically
cleaned and may be noted as "chemically cleaned carbonaceous
material."
[0032] The term "macropore" typically means pores having a diameter
size of greater than 50 nm. The term "micropore" typically means
pores having a diameter size of smaller than 50 nm. The term
"product" means all materials that are made from refined
carbonaceous material, including without limitation: plastics,
fibers, solvents, pharmaceuticals, carbon black, inks, activated
carbon, carbon, tar, specialty minerals, boiler fuels, additives,
gas cleanup, and the like.
[0033] FIG. 1 illustrates an embodiment 100 of a carbonaceous
material feedstock unit according to the present invention. In one
embodiment, the carbonaceous material feedstock production unit 100
may be portable for relocating it at any location that produces a
waste stream and/or settling pond stream containing carbonaceous
material, such as preparation plants or washeries as is known to
those skilled in the arts. Typically, a preparation plant is a
plant that washes, sorts, sizes, cleans, and the like a source of
carbonaceous material usually in proximity to a carbonaceous
material mining operation, for example. Typically, these
preparation plants produce smaller-sized carbonaceous material that
are not processed further due to the cost of removing them from
their carrier fluid stream, such as water. These smaller-sized
carbonaceous particles required may be produced from washing the
clays, carbonaceous material, and rocks off of the larger sized
coal, which are generally separated out and discarded using various
density related processes at a preparation plant. They are
generally discarded because the size of the waste carbonaceous
material is too small or not worth the expense to recover it from
the preparation plant's process stream, thus this waste
carbonaceous material flows with the waste water out to settling
ponds where the waste carbonaceous material settles to the bottom
of the settling pond and the waste water is later treated. In some
instances, the percentage of carbonaceous material in these
settling pond streams and/or settling ponds may be between 25%-75%
of the entire settling pond depending on the age of the settling
pond. In one aspect, the system for refining carbonaceous material
may recover the carbonaceous material from a preparation plant's
process stream, such as a settling pond stream. In another aspect,
the system for refining carbonaceous material may recover the
carbonaceous material from an impoundment, such as a settling
pond.
[0034] The carbonaceous material feedstock production unit 100 may
be moved or located nearby a carbonaceous material washery,
carbonaceous material processing plant, coal preparation plant,
coal mining plant, settling impoundment, settling pond, and the
like where it is connected via pipe 102 to a waste stream of a
preparation plant or settling pond stream material with water added
that contains the smaller-sized carbonaceous material. The pipe 102
is connected to a vibratory screen unit 104 that separates the
larger-sized carbonaceous material pieces from the smaller-sized
carbonaceous material. In one aspect, the vibratory screen unit 104
includes a series of descending screens of decreasing screen size.
The vibratory screen units 104 may include gravity and/or density
separation apparatuses, such as teeter beds, waffle tables, jigs,
pulsing water beds, steady flow beds, and the like. Thus, the
larger-sized carbonaceous material pieces are screened out at the
upper screens while the smaller-sized carbonaceous material falls
through to the lower parts of the vibratory screen unit 104. In one
aspect, one of the intermediate screens may contain the desired
size of carbonaceous material. Offsite process water is supplied
through pipe 106 to the vibratory screen unit 104 for improved
washing and processing at the vibratory screen unit 104.
[0035] In one embodiment, the smaller-sized particles and
larger-sized particles that exceed a desirable predetermined size
of carbonaceous material are removed from the vibratory screen unit
104 via pipes 108 and 110 and may be returned to the preparation
plant, for example. Offsite process water may also accompany the
undesirable particles exiting the vibratory screen unit 104. For
ease of use, the pipes 102, 106, 108, and 110 may be flexible
hoses, tubes, pipes, and the like for ease of connecting the
carbonaceous material feedstock production unit 100 to the
preparation plant. The desirable sized particles exit the vibratory
screen unit 104 and flow via pipe 112 to a density differential
separator 114. In one embodiment, the density differential
separator 114 separates higher-density particles from lower-density
particles. Typically, the lower-density particles will contain the
desired carbonaceous material particles that will be processed as
further described. The higher-density particles typically contain
the material and particles that may not be used by the system for
refining carbonaceous material.
[0036] The desirable-sized particles exit the density differential
separator 114 and flow via pipe 122 to another vibratory screen
unit 120. In one aspect, the vibratory screen unit 120 may
additionally wash the particles and may further dry the
carbonaceous material particles that enter the vibratory screen
unit 120. Any sized particles that are not of a desired size may
exit the vibratory screen unit 120 via pipe 122 and be returned to
the preparation plant, for example. The washed and sized
carbonaceous material may further be dried by forced air from a
dryer 124. In one embodiment, the water content is preferably from
about 8% to about 40% w/w, and more preferably from about 12% to
about 18% w/w. As described more fully below, carbonaceous material
having such a water content may be ideal for the later digestion
processes and may eliminate the necessity and cost of re-wetting
dried carbonaceous material. This may further save energy that
would otherwise be expended to wet completely dry carbonaceous
material that is typically supplied to refining plants. In one
aspect, the water content may be further reduced at a preparation
plant by use of a microwave drying unit and/or centrifuge to lower
the expense of transporting the carbonaceous material to an
off-site refining plant. In this aspect, the water content of the
carbonaceous material may be approximately 7% w/w.
[0037] Once the carbonaceous material possesses water at a desired
level, it may be transported by a conveyor or other appropriate
device to an elevated height to be dropped into storage sacks,
vessels, tanks, trucks, containers, and the like (storage
containers 128). As described above, since the carbonaceous
material feedstock production unit 100 may be movable or portable,
the units described above may be mounted on a vehicle, such as a
trailer 130. This enables the carbonaceous material feedstock
production unit 100 to be moved from one site or preparation plant
to another for supplying the later processes described herein with
carbonaceous material of a desirable size and water or moisture
content, while reducing the waste stream going to settling ponds,
for example. In one embodiment, once the storage containers 128 are
filled they may be loaded or moved to another vehicle (not shown)
and may be transported to a microwave drying unit or digestion unit
further described below. In one embodiment, the carbonaceous
material feedstock production unit 100 may further include a
centrifuge unit 132 for accepting a feed of carbonaceous material
from the vibratory screen unit 120 for further reducing the
moisture and/or water content of the carbonaceous material.
[0038] FIG. 2 illustrates an embodiment 200 of a microwave drying
unit according to the present invention. In one embodiment, the
system for refining carbonaceous material includes a microwave
drying unit 200 and in another embodiment the system for refining
carbonaceous material does not include a microwave drying unit 200.
In this embodiment, storage containers 202 and 128 are emptied into
a hopper 204 that feeds a conveyor 206 that passes through the
microwave unit 208 for providing additional lowering of the water
content of the carbonaceous material should it be desired. After
exiting the microwave unit 208, the carbonaceous material may be
transported via conveyor 212 to a hopper 214 for feeding to the
next process unit. Hoppers 204 and 214 may be vibratory hoppers for
unsettling clumped together carbonaceous material. In one
embodiment, the microwave drying unit 200 may further include a
centrifuge unit 216 for accepting a feed of carbonaceous material
from the microwave unit 208 for further reducing the moisture
and/or water content of the carbonaceous material. In another
embodiment, additional centrifuge units may be used with the
microwave unit 208, such as just before the microwave unit 208, for
example.
[0039] FIG. 3 illustrates an embodiment 300 of a digestion unit
according to the present invention. Digestion unit 300 may include
a conveyor 302 for transporting the cleaned and sized carbonaceous
material to moisture balancing unit 346. The moisture balancing
unit 346 may include a source of water and steam that controllably
increases the moisture content of the cleaned and sized
carbonaceous material. In cases where the moisture content of the
carbonaceous material is reduced for transportation purposes, then
the moisture balancing unit 346 may add moisture to the
carbonaceous material. In one example, the moisture balancing unit
346 may produce carbonaceous material with a preferable moisture
content of from about 7% to about 40% w/w, and more preferably a
moisture content of from about 25% to about 35% w/w. After the
moisture content has been adjusted or balanced in the moisture
balancing unit 346, it may be fed to a conveyor 302, which
transports the carbonaceous material to one or more digestion
vessels 304, 308, and 310.
[0040] In one aspect, at the base of the conveyor 302 is a load
cell 316 for weighing the carbonaceous material that enters the
conveyor 302. Digestion unit 300 includes an acid mixture solution
that is transported from an H.sub.2SiF.sub.6 adjustment tank 712
(FIG. 7) via pipe 318. The acid mixture solution is fed into the
digestion vessel 304, which includes a mixer 312 and a heater 314.
The carbonaceous material is fed into the digestion vessel 304 and
the digestion of the carbonaceous material is started. A valve 306
may be used to switch the carbonaceous material/acid mixture
solution between the digestion vessels 304, 308, and 310. In one
aspect, the digestion vessels 304, 308, and 310 may be gravity fed
from one to another or pumped by pumps as described herein.
[0041] The carbonaceous material and acid mixture solution may then
be fed into one of the digestion vessels 308 and 310 where the
carbonaceous material is further digested. The digestion vessels
308 and 310 also include heaters 324 and 326, respectively, and
mixers 322 and 326, respectively. The heaters 314, 324, and 326 are
used to maintain the temperature of the digestion of the
carbonaceous material in the digestion vessels 304, 308, and 310.
The heaters may be steam fed heat exchangers as are commonly known
in the art.
[0042] By having downstream digestion vessels 308 and 310, the
carbonaceous material/acid solution mixture may be further digested
while a new batch is being loaded into digestion vessel 304.
Additionally, if a carbonaceous material/acid solution mixture is
not in specification, it may be dumped to one of the digestion
vessels 308 and 310 for further treating without holding up the
digestion in the digestion vessel 304. Further, the carbonaceous
material/acid mixture solution may be then moved or pumped to
digestion vessel 310, which may be used to further the digestion of
the carbonaceous material/acid mixture solution or may be used as a
hold, stage, or surge vessel for feeding a centrifuge 328 via pipe
330, which may have a capacity or volume that is less than the
digestion vessels 304, 308, and 310.
[0043] In one embodiment, the digestion vessels 304, 308, and 310
further include condensation loops or circuits 348 that may take
any acid mixture solution that is vaporized in the digestion
vessels 304, 308, and 310. The condensation circuits 348 may
include condensation units, such as coolers, for condensing the
vapor or gaseous acid mixture solution for storing in the present
system for refining carbonaceous material. Separators, commonly
known in the art, may further be used to separate the different
components or compounds of the acid mixture solution. In another
embodiment, catalyst beds may be used with the condensation
circuits 348. In one aspect, the acid mixture solution may contain
multiple acid compounds, such as HF and H.sub.2SiF.sub.6, that may
be separated from each other by use of temperature controlled
separators that separate the different compounds by temperature
specific distillation. This separation may be controlled by
controlling the temperature and ratio of the acid compounds within
the separators. In addition, the metals digested out of the
carbonaceous material may be precipitated at different pH levels
and then filtered from the carbonaceous material/acid mixture
solution.
[0044] In the above described embodiment, the present system for
refining carbonaceous material may include multiple digestion
vessels that are in series, one feeding the carbonaceous
material/acid mixture solution to another downstream digestion
vessel. In this embodiment, the carbonaceous material/acid mixture
solution may be batched in a way to have a continuous flow
downstream, which may be important for feeding a continuous
centrifuge 328 via pipe 330, for example.
[0045] In another embodiment, the present system for refining
carbonaceous material may include one digestion vessel by itself,
such as digestion vessel 304. In this embodiment, no further
downstream digestion vessels are fed the carbonaceous material/acid
mixture solution and it is fed directly to a centrifuge 328, for
example.
[0046] In yet another embodiment, the present system for refining
carbonaceous material may include multiple digestion vessels that
are in parallel that feed concurrently or simultaneously the
carbonaceous material/acid mixture solution to the centrifuge 328,
for example. In this embodiment, the digestion vessels 304, 308,
and 310 are each individually fed the carbonaceous material/acid
mixture solution from the conveyor 302.
[0047] Preferably, the acid mixture solution comprises HF and
H.sub.2SiF.sub.6 in a range of proportions. In one example, the HF
is present in a range preferably from about 2% to about 20% w/w,
and more preferably from about 5% to about 15% w/w. The
H.sub.2SiF.sub.6 is present in a range preferably from about 10% to
about 58% w/w. Preferably, the HF is present in a range of from
about 5% to about 12% w/w, and more preferably in the range of from
about 8% to about 10% w/w and the H.sub.2SiF.sub.6 is present in a
range preferably from about 30% to about 38% w/w, and more
preferably from about 22% to about 32% w/w. The balance of the
mixture is water. So for example, an acid mixture solution that
includes 10% HF and 35% H.sub.2SiF.sub.6 will have a H.sub.2O
content of 55% taking into account the moisture of the carbonaceous
material being fed into the digestion vessels, in one aspect.
Preferably, the acid mixture solution includes these mixed portions
of HF and H.sub.2SiF.sub.6 prior to mixing them with the
carbonaceous material.
[0048] In another embodiment, a fluorine acid solution can be
prepared from a solution of H.sub.2SiF.sub.6 plus H.sub.2O as the
base acid to which anhydrous HF acid is added so that both of these
reactive acids are in one solution. Some exemplary ranges of the
acids are from about 5%-34% w/w H.sub.2SiF.sub.6, 32%-90% w/w
H.sub.2O, and 5%-34% w/w HF acid. In one aspect, a fluorine acid
solution is prepared from a saturated solution of H.sub.2SiF.sub.6
in water and adding gaseous anhydrous HF acid. In another
embodiment, SiF.sub.4 may be reacted with H.sub.2O to form
H.sub.2SiF.sub.6.
[0049] In one embodiment, the digestion vessels 304, 308, and 310
may be operated at temperatures of from about 10.degree. C. to
about 125.degree. C. and at a pressure of from about 0 kPa to about
105 kPa. In another embodiment, the temperature of the digestion
vessels 304, 308, and 310 may be preferably in the range of from
about 55.degree. C. to about 85.degree. C., and more preferably in
the range of from about 70.degree. C. to about 85.degree. C.
[0050] In one embodiment, the carbonaceous material/acid mixture
solution is agitated or stirred in the digestion vessels 304, 308,
and 310 for preferably from about 20 to about 80 minutes, and more
preferably from about 40 to about 60 minutes.
[0051] The digestion vessels 304, 308, and 310 may be made of a
material that withstands the chemicals contained in them. For
example, the digestion vessel 304 may be made from a blend of
plastic and carbon fiber composites or any structural material
lined with any material that is impervious to the corrosive effects
of the acid used.
[0052] The treated carbonaceous material has a specific gravity
lower than the carbonaceous material/acid mixture solution, thus
the treated carbonaceous material may float to the top of the
carbonaceous material/acid mixture solution in the digestion
vessels 304, 308, and 310 when the mixers 312, 322, and 324 are
turned off. Unreacted iron sulfide and other un-dissolved heavy
metal salts whose specific gravities are greater than the acid
mixture solution may fall to the bottom of the digestion vessels
304, 308, and 310 if the agitation is stopped by turning off the
mixers 312, 322, and 324. In one embodiment, the specific gravity
of certain carbonaceous material, such as coal, is approximately
1.3 and the acid mixture solution is approximately 1.2 when
entering the digestion vessel. After digestion, the carbonaceous
material then typically has a specific gravity of 1.1 and the
specific gravity of acid solution is 1.2 entering the centrifuge
328. In addition, during the separation process, the treated
carbonaceous material acts as a filter to the metal fluorides
and/or metal fluorosilicates that are contained in the acid mixture
solution.
[0053] In one embodiment, the pipe 330 is connected to a pump 332
that pumps the carbonaceous material/acid mixture solution to the
centrifuge 328. Preferably, the pump 332 pumps the carbonaceous
material/acid mixture solution without degrading the particle size.
In one aspect, the pump 332 is a peristaltic pump.
[0054] In one aspect, the centrifuge 328 may include several
different stages. For example, it may spin at a speed sufficient to
remove the acid mixture solution from the carbonaceous material in
a first stage. In a second stage, water supplied from a de-ionized
water supply 336 and/or a rinse water supply 334 may be used in
washing the carbonaceous material. Preferably, this rinse water may
be applied to the carbonaceous material while it is being spun
inside of the centrifuge 328. The water used in this cycle may be
heated before it is input into the centrifuge 328. For example, the
water may be in a temperature preferably from about 30.degree. C.
to about 100.degree. C., and more preferably 75.degree. C. to about
85.degree. C. Then, the centrifuge 328 may remove this wash water
where it can be recycled after being filtered through a filtration
apparatus in this second stage. The rinse water that is removed
from the centrifuge 328 is sent for recycling via pipe 342 as
described below. In another embodiment, the wash water removed from
the centrifuge 328 may be sprayed on the carbonaceous material
prior to it entering the digestion vessels 304, 308, and 310 in the
moisture balancing unit 346 as the moisture content of the incoming
carbonaceous material is lower than desired prior to digestion as
described herein. The filtration apparatus removes some of the
metal fluorides and metal chlorides, which may be sold to other
markets, such as aluminum and steel plants.
[0055] Preferably, the third stage includes injecting steam into
the centrifuge 328 during a spinning process. In one embodiment,
the temperature within the centrifuge 328 is preferably from about
120.degree. C. to about 400.degree. C. and the quantity of steam
that is applied to the carbonaceous material in the centrifuge 328
may be determined by several factors, including the size or
carbonaceous material particles and the speed of drum inside the
centrifuge 328 to prevent slumping of the carbonaceous material
within the centrifuge 328. The steam helps in removing any residual
fluorides. For example, the amount of steam applied to the
carbonaceous material may be determined by the residual level of
fluorine required in the finished carbonaceous material. For
instance, an isotrope of HF, H.sub.2SiF.sub.6, and H.sub.2O may
vaporize preferably from about 105.degree. C. to about 120.degree.
C. depending on the concentrations of the individual compounds.
Thus, by providing steam into the centrifuge 328 the residual HF,
H.sub.2SiF.sub.6, and H.sub.2O are driven off of the carbonaceous
material as a vapor and recovered later via pipe 342, for example,
the steam process may also start the drying stage of the present
system for refining carbonaceous material.
[0056] The centrifuge 328 may further include scrapers that remove
the carbonaceous material from the centrifuge 328 by scraping the
carbonaceous material as it is spinning inside the centrifuge 328.
Thus, the carbonaceous material exits the centrifuge 328; the
carbonaceous material is then moved to a hopper 344 via a conveyor.
In one aspect, it may be important not to use any conveyance means
that will degredate the carbonaceous material to prevent the
creation of smaller undesirable fines. The moisture content of the
carbonaceous material at this point may be from about 4% to about
12% w/w.
[0057] FIG. 4 illustrates an embodiment 400 of a drying unit
according to the present invention. The drying unit 400 includes a
dryer 402 that may further dry the carbonaceous material produced
by the digestion unit 300. The carbonaceous material from the
hopper 344 is fed into the dryer 402 where the carbonaceous
material is subject to air flow of a desired velocity and
temperature. After a residence time the carbonaceous material then
exits the dryer 402 and is fed to a hopper 406 where it may be
elevated above a final packaging and product unit 500 that may
include a load cell or scale 504 for weighing the finished
carbonaceous material that is placed in a storage container 502 as
shown in FIG. 5, or sent to bulk storage, where the almost pure and
dried carbonaceous material is ready for the next stage, fuel,
activation and the like.
[0058] In one embodiment, dryer 402 may be a fluidized bed that is
generally a density dependent unit, like a teeter bed, that has air
flowing from the bottom to the top of the fluidized bed dryer that
pulls the lighter carbonaceous material out the top of the
fluidized bed dryer for transfer to drum 410 by a cyclone 408. The
carbonaceous material particles are suspended in the air flow based
on their density and are dried further by this process. The
medium-sized carbonaceous material particles that do not flow out
the top of the fluidized bed dryer are recovered at the bottom of
the fluidized bed dryer for transfer on conveyor 404. The fluidized
bed dryer includes a weir that controls the height of carbonaceous
material inside the fluidized bed dryer. Conveyor 404 may be a
vacuum conveyor as is known in the art. In one aspect, the
smaller-sized carbonaceous material particles that exit the top of
the fluidized bed dryer may be approximately 200 microns or
smaller. To control the separation of the particle sizes through
the fluidized bed dryer, the air flow may be adjusted. A higher air
flow through the fluidized bed dryer will produce larger-sized
carbonaceous material particles exiting the top of the fluidized
bed dryer, while a lower air flow will produce smaller-sized
carbonaceous material particles exiting the top of the fluidized
bed dryer. In addition, the smaller-sized carbonaceous material
particles may be fed into storage container, such as sacks and the
like.
[0059] In another embodiment, the dryer 402 may be a number of
designs so long as there is air flow and carbonaceous material
movement, the temperature of the dryer 402 may be preferably in the
range from about 100.degree. C. to about 160.degree. C., more
preferably from about 120.degree. C. to about 140.degree. C., the
temperature may be high enough to drive off most of the moisture
and some of the tars in order to liberate the residual fluorine to
a level close to the inherent value of the original carbonaceous
material.
[0060] FIG. 6 illustrates an embodiment 600 of a vapor recovery
unit 600 according to the present invention. The process water
produced by the system for refining carbonaceous material may be
fed to a scrubber 602 where air is pulled through the scrubber 602
to remove any additional light volatile vapors from the process
water. The air flow through the scrubber 602 is provided by blowers
608 which are fed to a stack 610. The stripped process water may be
returned to the top of the scrubber 602 via pump 612. Additionally,
the stripped process water may be fed to the moisture balancing
unit 346 to be used as a feedstock for increasing the moisture
content of the carbonaceous material within the moisture balancing
unit 346.
[0061] FIG. 7 illustrates an embodiment 700 of a feedstock storage
unit according to the present invention. The feedstock storage unit
700 includes a de-ionized water storage tank 702 for holding
de-ionized water that is used in the system for refining
carbonaceous material. For example, de-ionized water is fed from
de-ionized water storage tank 702 to centrifuge 328 via pipe 704.
Feedstock storage unit 700 further includes a HF storage tank 706
that feeds HF acid via pipe 708 to a HF adjustment tank 710 and a
H.sub.2SiF.sub.6 adjustment tank 712 may further include heaters to
heat their respective acid mixture solutions after blending the
acid mixture solution to a desirable strength. The H.sub.2SiF.sub.6
adjustment tank 712 may further be fed H.sub.2SiF.sub.6 in a more
concentrated form that is stored in a H.sub.2SiF.sub.6 storage tank
714. Once the desired strength of acid mixture solution is
achieved, then it is piped via pipe 716 to digestion vessel 304 for
mixing with carbonaceous material. In addition, HF adjustment tank
710 may feed a reduced strength of HF to the centrifuge 328 via
pipe 718. Also, feedstock storage unit 700 may further include a
rinse water collection tank 722 that contains rinse water collected
from the system for refining carbonaceous material. This rinse
water may be fed to centrifuge 328 via pipe 720. Additional vessels
724 and 728 may be used to contain caustic compounds, such as
bases, for neutralizing any acid spills or reducing the strengths
of the acids of the system for refining carbonaceous material. Such
bases may be fed to the digestion vessel 304 via pipe 726.
[0062] FIG. 8 illustrates an embodiment 800 of an ultrasonic unit
according to the present invention. In one embodiment, the
digestion vessels 304, 308, and 310 may include a pipe 802 that
takes a stream of the carbonaceous material/acid mixture solution
and pumps it through the pipe 802 through a source of ultrasonic
waves 804 for improved penetration of the acid mixture solution
into the micropores and macropores of the carbonaceous material. In
one aspect, the source of ultrasonic waves 804 may be a water bath
that is subject to a source of such ultrasonic waves, thus
imparting the ultrasonic waves through the pipe 802 for improved
penetration of the acid mixture solution. In one embodiment, the
wave signals are square to improve such penetrating and digesting
action.
[0063] FIG. 9 illustrates an embodiment 900 of an ultrasonic unit
according to the present invention. In this embodiment, a source of
ultrasonic waves 902 is placed upon the pipe 102 prior to entering
the vibratory screen unit 104.
[0064] In one embodiment, the frequency of the source of ultrasonic
waves 804 and 902 is from about 80 KHz to about 100 KHz. In one
example, an opening of a macropore of carbonaceous material may be
approximately 1 micron and it has been found that a frequency of
100 KHz source of ultrasonic waves 804 and 902 will cause the acid
mixture solution to penetrate the macropore opening. Additionally,
as the acid mixture solution is pumped into the macropores of the
carbonaceous material, pressure is created within the macropore
causing the acid mixture solution to be pumped out once the
pressure becomes greater within the macropore than outside the
macropore. This pumping action provides for improved penetration
and digestion of contaminants of the carbonaceous material. The
source of ultrasonic waves 804 and 902 may be generated by
ultrasonic transducers as well known in the art. In one aspect,
these transducers may be in contact or communication with a water
bath, which transfers the wave action to the water, which then
transfers the wave action to the pipe, and so on, to provide the
pumping action to the micropore and macropores of the carbonaceous
material. This reduces the need for mechanical agitation and
provides for improved digestion times. The frequency of the source
of ultrasonic waves 804 and 902 causes cavitations, cavitation
bubbles, and/or cavity bubbles within the acid mixture solution
such that they are the size or smaller than the typical openings of
the macropores of the carbonaceous material. In general, the higher
the frequency the smaller the cavitation bubbles. If the cavitation
bubbles are too large, they may tend to pulverize the carbonaceous
material to smaller sizes that may not be desirable to the process.
In one embodiment, source of ultrasonic waves 804 and 902 are
capable of producing power from about 250 watts to about 16,000
watts with a frequency of from about 10 KHz to about 50 KHz. The
ultrasonication may be performed at an increased pressure over
ambient pressure using a feed pump and adjustable back-pressure
valve next to the pipe where it is desired to operate.
[0065] In addition to the aforementioned aspects and embodiments of
the present system for refining carbonaceous material, the present
invention further includes a system for making low volatile
carbonaceous matter. The present system for making low volatile
carbonaceous matter devolatilizes the carbonaceous material and
recovers the volatile matter for subsequent use in a variety of
applications. FIG. 10 illustrates an embodiment 1000 of a system
for making low volatile carbonaceous matter according to the
present invention. In one embodiment, the system for making low
volatile carbonaceous matter 1000 preferably includes a source of
sized and digested carbonaceous material, such as the system for
refining carbonaceous material as described herein. In this
embodiment, the system for making low volatile carbonaceous matter
1000 produces digested carbonaceous material, such as coal, of a
desirable size that is fed into an extraction vessel 1002 via pipe
1030. The extraction vessel 1002 is a vessel made from a material
that is resistant to the coal and supercritical carbon dioxide
fluid ("SCCO.sub.2 fluid"). In this embodiment, the extraction
vessel 1002 is further capable to withstand the higher pressures
associated with SCCO.sub.2 extraction. Additionally, the system for
making low volatile carbonaceous matter 1000 preferably includes a
supply of digested carbonaceous material, such as produced by the
system for refining carbonaceous material described herein and
designated 1004 in FIG. 10.
[0066] A supply of SCCO.sub.2 fluid may be stored in a vessel 1020
that supplies the SCCO.sub.2 fluid to a pump 1022 via pipe 1028.
The SCCO.sub.2 fluid may be in a liquid state as in the vessel
1020. The pump 1022 compresses the SCCO.sub.2 fluid and may feed it
to a heater 1024. The SCCO.sub.2 fluid may then be fed into the
extraction vessel 1002 via pipe 1028 where it contacts the
carbonaceous material preferably processed by the system for
refining carbonaceous material. The carbonaceous material is
preferably fed to the extraction vessel 1002 via pipe 1030.
Preferably, a valve 1032 controls the amount of SCCO.sub.2 fluid
that is fed to the heater 1024 and extraction vessel 1002. The
extraction vessel 1002 may include a heater 1034 as well to control
the temperature and pressure of the SCCO.sub.2 fluid and
carbonaceous material within the extraction vessel 1002. The
extraction vessel 1002, heater 1034, and valve 1032 may maintain
the SCCO.sub.2 fluid at supercritical fluid temperatures and
pressures for proper extraction.
[0067] The extraction vessel 1002 is generally made of a strong
material, such as metal, and is shaped as a container with an inlet
connected to pipe 1028 for inputting the carbonaceous material and
SCCO.sub.2 fluid. Additionally, the extraction vessel 1002 may
contain a carbonaceous material outlet that is connected to pipe
1036 for feeding the carbonaceous material after is has been
extracted by the extraction vessel 1002 to a carbonaceous material
storage vessel 1014. The extraction vessel 1002 may further include
an outlet connected to pipe 1038 for feeding the SCCO.sub.2 fluid
with extracted soluble hydrocarbons ("extract solvent") to
separator 1006.
[0068] After the carbonaceous material has been contacted with the
SCCO.sub.2 fluid for a desired period of time, the SCCO.sub.2 fluid
extracts soluble hydrocarbons from the carbonaceous material to
produce the extract solvent, which may be fed to separator 1006. At
this point, the carbonaceous material, extracted of soluble
hydrocarbons, may be fed through extraction vessel 1002 to the
carbonaceous material storage vessel 1014. The system for making
low volatile carbonaceous matter 1000 may include a series of
separators for improved production of hydrocarbon cuts with
distinct or different densities and/or boiling points as known to
those skilled in the art. The separator 1006 may feed a portion of
its input to separator 1008, which may in turn feed a portion of
its input to separator 1010, which may in turn feed a portion of
its input to separator 1012. Flow restrictors may be used with
separators 1006, 1008, 1010, and 1012 to control the flow or
release of extract solvent.
[0069] The separators 1006, 1008, 1010, and 1012 may further
include heaters to control the temperature of the separators. Due
to the temperatures in the separators 1006, 1008, 1010, and 1012,
the extract solvent may become CO.sub.2 gas which may be fed to
condenser 1026. The CO.sub.2 gas may then be condensed back into a
liquid for feeding to the vessel 1020. As described above, the
extract solvent is a mixture of SCCO.sub.2 fluid and SCCO.sub.2
fluid soluble hydrocarbons. The SCCO.sub.2 fluid may be separated
from the extract solvent by having operating conditions within the
separators 1006, 1008, 1010, and 1012 such that the ratio of the
SCCO.sub.2 fluid vapor pressure to soluble hydrocarbons vapor
pressure is as high as possible. This ratio will typically increase
as the temperature decreases with the result that the optimum
temperature is very low and limited by the vapor
pressure-temperature characteristic of the SCCO.sub.2 fluid or
freezing point of the soluble hydrocarbons. In one aspect, the
liquid CO.sub.2 may be recycled back to the vessel 1020 by
compressing CO.sub.2 from a gas phase to a liquid phase.
[0070] In addition, the temperatures and pressures of the
separators 1006, 1008, 1010, and 1012 may be controlled such that
different cuts of the soluble hydrocarbons are produced. For
example, the operating conditions within the separators 1006 and
1008 may be controlled to provide a lighter cut of hydrocarbons,
such a thin carbon pitch, that may be stored in carbon pitch
storage vessel 1016. In another example, the operating conditions
within the separators 1006, 1008, 1010, and 1012 may be controlled
to provide a heavier cut of hydrocarbons, such as thick carbon
pitch, that may be stored in carbon pitch storage vessel 1018.
[0071] In one embodiment, the extraction process is carried out
under pressure and temperature conditions that lie above the
critical point of the SCCO.sub.2. For example, these pressures are
from about 73 atm to about 300 atm and at temperatures of from
about 32.degree. C. to about 300.degree. C.
[0072] In one embodiment, the system for making low volatile
carbonaceous matter 1000 further includes a secondary solvent that
may be mixed with the SCCO.sub.2 fluid prior to being fed into
extraction vessel 1002. For example, a hydrocarbon may be mixed
with the SCCO.sub.2 fluid prior to being fed into the extraction
vessel 1002. Some exemplary secondary solvents include ethane,
propane, trifluoro-chloromethane, difluoro-dichloromethane,
trifluoro-bromoethane, methyl fluoride, ethylene, propylene,
isobutene, n-pentane, isopentane, tetramethylmethane, n-heptane,
isoheptane, and the like. Preferably, the secondary solvent is in a
liquid state and miscible with the SCCO.sub.2. In one aspect, it is
important that the secondary solvent is miscible with the
SCCO.sub.2 fluid and has a gas phase temperature that is close to
that of the SCCO.sub.2 fluid. This assists in the recovery of the
dissolved compounds.
[0073] FIG. 11 illustrates an embodiment 1100 of a solvent
extraction unit of the present invention. The solvent extraction
unit 1100 includes a source of dipolar aprotic solvent, such as
N-Methyl-2-Pyrrolidone ("NMP") 1102, that may contain a supply NMP
that is fed through a pipe 1122 to an extraction vessel 1106 where
it contacts a supply of carbonaceous material. In one embodiment,
the supply of carbonaceous material is sized and digested, such as
by the system for refining carbonaceous material 1104 as described
herein. Preferably, the carbonaceous material is mixed with the NMP
in a ratio of from about 1:10 to about 1:1, carbonaceous material
to NMP. In one aspect, extraction vessel 1106 is a continuous
process vessel. A slurry of NMP/extract and carbonaceous material
is produced in the extraction vessel 1106 and is fed to a
separation unit 1108 via pipe 1122. Some other exemplary diprotic
aprotic solvents include dimethylformamide, dimethylacetamide, and
dimethyl sulfoxide. For example, typical extraction conditions may
include having an operating pressure of approximately 5,000 psi at
a temperature of approximately 80.degree. C. These conditions may
further include contacting approximately a ratio of 2:1 of the NMP
to solid carbonaceous material. The NMP may also include a
secondary solvent, such as toluene. The extraction may be a
combination of static and dynamic contact operations, such as 10
minutes of dynamic contact followed by 30 minutes of static
contact. Further, a hydrocarbon, such as ethanol in a ratio of
approximately 5:1 to the carbonaceous material may be used to as a
rinse.
[0074] The solvent extraction unit 1100 further includes a
separation unit 1108 that separates the NMP from the extract and
carbonaceous material. In one aspect, the separation unit 1108 may
be a centrifuge or filtration unit that is capable of separating
the extract and carbonaceous material, which may be in the form of
activated carbon at this stage. In one aspect, the extract is
filtered from the carbonaceous material; the extract filtrate is
fed to an extraction unit 1110 via pipe 1122. The extraction unit
1110 preferably separates a stream of NMP from an extract mixture.
The stream of NMP may be fed back to the extraction vessel 1106 as
recycled NMP via pipe 1134. The extract mixture may be fed to a
dryer unit 1112 via pipe 1124 for further removal of the NMP, which
may then be fed back to the pipe 1134. The dryer unit 1112 provides
temperatures that are sufficient to drive off the NMP from the
extract mixture in excess of approximately 202.degree. C. The NMP
vapors from this dryer may be condensed and reconstituted for
additional or subsequent use.
[0075] In one embodiment, the extract mixture from the dryer unit
1112 is fed via pipe 1128 to a secondary vacuum separation unit
1114. Secondary vacuum separation unit 1114 further separates the
extract mixture into NMP by providing a vacuum collection system
while the tars are cooled to a temperature above their free flow
point of approximately 100.degree. C., which is fed to the pipe
1134, and carbon pitch material that is collected in carbon pitch
storage vessel 1120.
[0076] In one embodiment, a coal waste stream from the separation
unit 1108 is fed via pipe 1126 to a secondary extraction unit 1116
where the NMP is separated from the coal waste stream and fed to
pipe 1134. The unit 1116 further provides a stream of activated
carbon that is stored in activated carbon storage vessel 1118.
Generally, the secondary extraction unit 1116 may provide
additional extraction functionality similar to that discussed above
relating to secondary vacuum separation unit 1114.
[0077] FIG. 12 illustrates an embodiment 1200 of a carbon fiber
production unit according of the present invention. The carbon
fiber production unit 1200 includes a source of carbon pitch fiber
1202 made from a carbon pitch, such as from the solvent extraction
unit 1100 or system for making low volatile carbonaceous matter
1000 described herein. In one embodiment, the carbon pitch from the
carbon pitch storage vessel 1120 may be drawn into long fibers or
strands and then spun into using any conventional method known to
those skilled in the art. In another aspect, individual strands or
fibers are subjected to the process herein described. The carbon
fiber production unit 1200 may further include additional vessels
for washing and cleaning the stretched carbon pitch fiber 1202.
Generally, the carbon pitch fiber 1202 is stretched to a desired
fiber diameter that helps align the molecules within the fiber
prior to additional processing as described herein. Many individual
fibers or strands are typically woven or bundled together to make a
carbon pitch fiber 1202 of a desirable thickness or diameter. The
supply of carbon pitch for the carbon pitch fiber 1202 may be
carbon pitch storage vessels 1120, 1016, and 1018.
[0078] The carbon fiber production unit 1200 further includes a
stabilizing unit 1204 that assists with chemically altering or
converting the linear atomic bonding of the carbon pitch fiber 202
to a more thermally stable ladder bonding. The stabilizing unit
1204 may include a plurality of rollers 1218 that are used to draw
the carbon pitch fiber 1202 through the stabilizing unit 1204. In
one aspect, the rollers 1218 may be heated rollers that are heated
by the heaters of the stabilizing unit 1204. The heaters of the
stabilizing unit 1204 generally operate at a temperature of from
about 200.degree. C. to about 300.degree. C. Air containing oxygen
molecules may be present in the stabilizing unit 1204 that are
picked up by the carbon pitch fiber 1202 that assists with
rearranging their atomic bonding pattern. In one aspect, the carbon
pitch fiber 1202 is heated for a duration of from about 10 minutes
to about 240 minutes, depending on the desired product. The
stabilizing unit 1204 may further include beds of loose materials
where the carbon pitch fiber 1202 is passed through by rollers
1218.
[0079] The carbon pitch fiber 1202 then exits the stabilizing unit
1204 and is then fed to a carbonizing unit 1206. The carbonizing
unit 1206 includes heaters that produce temperatures of from about
1,850.degree. C. to about 5,500.degree. C. The carbon pitch fiber
1202 is exposed to this temperature for a duration of about 2
minutes to about 20 minutes. Preferably, the carbonizing unit 1206
contains a gas mixture that does not contain oxygen. The lack of
oxygen prevents the carbon pitch fiber 1202 from burning in the
high temperatures of the carbonizing unit 1206. In one aspect, the
gas pressure within the carbonizing unit 1206 is greater than that
outside the carbonizing unit 1206 to prevent oxygen from entering
the interior of the carbonizing unit 1206. Further, seals may be
used at the entrance and exit of the carbonizing unit 1206 to
prevent oxygen from entering the interior of the carbonizing unit
1206. The temperature within the carbonizing unit 1206 provides
energy to strip non-carbon atoms and some carbon containing
compounds, such as carbon dioxide, from the carbon pitch fiber
1202. As the these elements and compounds are removed from the
carbon pitch fiber 1202, the remaining carbon atoms begin to pack
or bond more tightly providing for improved crystal alignment. In
one embodiment, the carbon fiber production unit 1200 further
includes an additional graphitizing unit 1208 for providing
additional heating to the carbon pitch fiber 1202 for better
temperature control of the carbonizing process. The graphitizing
unit 1208 may have similar operating parameters, but it may be
operated at slightly higher or lower temperatures than the
carbonizing unit 1206. After the carbon pitch fiber 1202 has been
carbonized and graphitized the carbon pitch fiber 1202 will be
generally referred to as carbon fiber 1216.
[0080] The carbon fiber production unit 1200 preferably also
includes a plurality of rollers 1220 located throughout the carbon
fiber production unit 1200 to transport the carbon fiber 1216
through the different units described herein. The carbon fiber
production unit 1200 may further include a surface treatment unit
1210 that treats the outside surface of the carbon fiber 1216 to
improve its bonding capacity to other materials, such as epoxies
and the like, used in composite material manufacture. The surface
treatment unit 1210 may slightly oxidize the outside of the carbon
fiber 1216 by adding oxygen atoms to the outside of the carbon
fiber 1216. The carbon fiber 1216 may be immersed in various gases
and/or liquids, such as air, carbon dioxide, ozone, sodium
hypochlorite, or nitric acid. The carbon fiber 1216 may be coated
electrolytically by applying a potential across the carbon fiber
1216, such as a positive potential, in a bath 1222 filled with
electrically conductive materials.
[0081] In one embodiment, the carbon fiber 1216 may be coated in a
sizing unit 1212 to protect them from damage during a subsequent
winding or weaving process. The coating materials are generally
selected to be compatible with a particular adhesive that will be
used to form a composite material. Some exemplary coating materials
include: epoxy, urethane, nylon, and the like. In one aspect, the
carbon fiber 1216 is then wound around a bobbin or spool 1214 prior
to being used in a composite manufacturing process as is commonly
known in the art.
[0082] FIG. 13 illustrates an embodiment 1300 of a phase diagram
for CO.sub.2 for determining a desired pressure and temperature for
the CO.sub.2. As shown, CO.sub.2 behaves as a gas at pressures and
temperatures below standard temperature and pressure ("STP"), which
is 273 K at 1 bar. A triple point 1302 for CO.sub.2 is shown where
CO.sub.2 may exists in a gas, liquid, or solid phase with slight
variations in temperature and/or pressure. When the temperature and
pressure are increased to beyond the critical point 1304, then the
CO.sub.2 behaves as a supercritical fluid, SCCO.sub.2, meaning it
adopts properties between a liquid and a gas. The critical point
1304 for CO.sub.2 has a critical temperature of 31.1.degree. C. and
a critical pressure of 74 bar. For the purposes of the present
invention, the SCCO.sub.2 may be at a temperature and pressure
above the critical point 1304 in the supercritical fluid area of
the phase diagram 1300 designated 1306.
[0083] In addition to the aforementioned aspects and embodiments of
the present system for refining carbonaceous material, the present
invention further includes methods for refining carbonaceous
material. FIG. 14 illustrates an embodiment 1400 of a method for
refining carbonaceous material. In step 1402, an acid mixture
solution is prepared by mixing HF, H.sub.2O, and H.sub.2SiF.sub.6
to a desired proportion. In this step, stored concentrated HF and
H.sub.2SiF.sub.6 may be individually pumped to individual vessels
where the concentration of each is reduced with water or a base.
Then, these reduced concentrations of the HF and H.sub.2SiF.sub.6
may be combined into a vessel that then mixes and heats the mixture
of HF, H.sub.2SiF.sub.6, and H.sub.2O. In this step the exact
amount of acid mixture solution is prepared for a specific amount
of carbonaceous material to be digested.
[0084] In step 1404, the carbonaceous material is prepared by
sizing a source of carbonaceous material, such as a preparation
plant settling pond stream. This step further includes wetting the
carbonaceous material with H.sub.2O to a desired content, such as
from about 8% to about 10% w/w. This step may further include the
application of ultrasonic waves to the carbonaceous material during
prior to or during the sizing operation.
[0085] In step 1406, the carbonaceous material and acid mixture
solution are combined in a digestion vessel which is temperature
and pressure controlled. This step may further include transferring
the carbonaceous material/acid mixture solution to a second
digestion vessel for additional digestion time. This step may
further include transferring the carbonaceous material/acid mixture
solution to a third digestion vessel for addition digestion time.
This step may further include the application of ultrasonic waves
to the digestion vessel or to a roundabout or circuit pipe that
takes a stream of the carbonaceous material/acid mixture solution
out of the digestion vessel and then later inputs it back into the
digestion vessel after the application of ultrasonic waves for
improved digestion.
[0086] In step 1408, the carbonaceous material/acid mixture
solution is transferred to a centrifuge for removal of the acid
mixture solution. This step may further include spraying rinse
water into the centrifuge for washing any residual acid mixture
solution from the carbonaceous material. This may be followed by
additional centrifuging until the carbonaceous material has a
desirable moisture content.
[0087] In step 1410, the carbonaceous material may be further dried
and separated based on densities to achieve the size of desirable
product for a particular application or order. This step may
include applying an air flow in a vertical vessel such that the
less dense carbonaceous material is removed from the top of the
dryer while the more dense carbonaceous material is retained in the
dryer for removal to a storage vessel, such as a sack. In step
1412, the carbonaceous material is finished and weighed into final
storage containers, such as sacks for their intended purpose. The
process described herein is scale independent and can be used on a
micro-scale, mesa-scale, and macro-scale.
[0088] In another embodiment, the present invention further
includes methods for making low volatile carbonaceous material.
FIG. 15 illustrates an embodiment 1500 of a method for making low
volatile carbonaceous material. In step 1502, a supply of
carbonaceous material is digested according to the description and
principles described herein. An acid mixture solution is contacted
with a supply of sized carbonaceous material to produce a digested
carbonaceous material/acid mixture solution. In step 1504, the
digested carbonaceous material is separated from the digested
carbonaceous material/acid mixture solution. In step 1506, the
digested carbonaceous material is contacted with supercritical
carbon dioxide fluid to extract hydrocarbons from the digested
carbonaceous material to produce an extract solvent and a low
volatile carbonaceous material. This step may include supplying the
digested carbonaceous material to an extraction vessel 1002.
[0089] In step 1508, the low volatile carbonaceous material is
separated from the extract solvent by use of an outlet in the
extraction vessel 1002, which may feed carbonaceous material
storage vessel 1014. In step 1510, a stream of carbon dioxide gas
is separated from the extract solvent. This step may include
feeding the extract solvent to one or more separators 1006, 1008,
1010, and 1012 that are pressure and temperature controlled to
increase the ratio of vapor pressure of the carbon dioxide gas to
soluble hydrocarbons contained in the extract solvent. In step
1512, the carbon dioxide gas is condensed to a liquid by means of a
condenser, such as condenser 1026. In step 1514, the carbon dioxide
liquid is heated to produce a recycle stream of supercritical
carbon dioxide fluid for re-use in the extraction vessel 1002.
[0090] FIG. 16 illustrates an embodiment 1600 of a method for
making carbon fiber. In step 1602, a supply of carbonaceous
material is digested according to the description and principles
described herein. In step 1604, the digested carbonaceous material
is separated from the digested carbonaceous material/acid mixture
solution as described herein. In step 1606, a carbon pitch is
produced from the digested carbonaceous material in accordance with
the description and principles described herein. In step 1608,
ungraphitized carbon fiber is drawn from the carbon pitch to a
desired diameter in accordance with principles commonly known to
those skilled in the art. In step 1610, the ungraphitized carbon
fiber is stabilized in a stabilizing unit 1204 to produce a
stabilized carbon fiber. In step 1612, the stabilized carbon fiber
is graphitized in a carbonizing unit 1206, graphitizing unit 1208,
or both, to make the carbon fiber.
[0091] There has been described a system for making low volatile
carbonaceous matter. It should be understood that the particular
embodiments described within this specification are for purposes of
example and should not be construed to limit the invention.
Further, it is evident that those skilled in the art may now make
numerous uses and modifications of the specific embodiment
described, without departing from the inventive concepts. For
example, different temperatures, pressures, acid mixture solution
compositions, solvent compositions, and the like may be changed or
altered to fit within the present system for making low volatile
carbonaceous matter described herein or other without departing
from the inventive concepts.
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