U.S. patent application number 14/048150 was filed with the patent office on 2014-04-17 for method for preparing a slurry of pulverized solid material in liquid or supercritical carbon dioxide.
This patent application is currently assigned to Massachusetts Institute Of Technology. The applicant listed for this patent is Cristina Botero, Randall Perkins Field, Ahmed F. Ghoniem, Howard J. Herzog. Invention is credited to Cristina Botero, Randall Perkins Field, Ahmed F. Ghoniem, Howard J. Herzog.
Application Number | 20140101986 14/048150 |
Document ID | / |
Family ID | 49447845 |
Filed Date | 2014-04-17 |
United States Patent
Application |
20140101986 |
Kind Code |
A1 |
Botero; Cristina ; et
al. |
April 17, 2014 |
Method for Preparing a Slurry of Pulverized Solid Material in
Liquid or Supercritical Carbon Dioxide
Abstract
Method for making a slurry of a pulverized solid in liquid or
supercritical carbon dioxide. The method includes making a
water-pulverized solid slurry at ambient pressure and pressurizing
the water-pulverized solid slurry to a high pressure. The
pressurized water-pulverized solid slurry is mixed in a pressurized
chamber with liquid or supercritical CO.sub.2 to form a
CO.sub.2.about.pulverized solid slurry.
Inventors: |
Botero; Cristina; (Boston,
MA) ; Field; Randall Perkins; (Andover, MA) ;
Herzog; Howard J.; (Belmont, MA) ; Ghoniem; Ahmed
F.; (Winchester, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Botero; Cristina
Field; Randall Perkins
Herzog; Howard J.
Ghoniem; Ahmed F. |
Boston
Andover
Belmont
Winchester |
MA
MA
MA
MA |
US
US
US
US |
|
|
Assignee: |
Massachusetts Institute Of
Technology
Cambridge
MA
|
Family ID: |
49447845 |
Appl. No.: |
14/048150 |
Filed: |
October 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61712954 |
Oct 12, 2012 |
|
|
|
61829321 |
May 31, 2013 |
|
|
|
Current U.S.
Class: |
44/280 |
Current CPC
Class: |
B01J 8/0005 20130101;
C10J 2300/0969 20130101; Y02P 20/54 20151101; Y02E 20/18 20130101;
B01J 13/00 20130101; C10J 2300/0936 20130101; Y02P 20/544 20151101;
C10L 1/326 20130101; B01J 2208/00787 20130101; Y02E 20/16 20130101;
B01J 8/0015 20130101; C10J 3/50 20130101 |
Class at
Publication: |
44/280 |
International
Class: |
C10L 1/32 20060101
C10L001/32 |
Claims
1. Method for making a slurry of a pulverized solid in liquid or
supercritical carbon dioxide comprising: making a water-pulverized
solid slurry at ambient pressure; press arising the
water-polverized solid slurry; and mixing the pressurized
water-pulverized solid slurry with liquid or supercritical CO.sub.2
in a pressurized chamber, to form a CO.sub.2-pulverized solid
slurry,
2. The method of claim 1 further including vaporizing excess
CO.sub.2 from the CO-pulverized solid slurry to concentrate the
CO.sub.2-pulverized solid slurry.
3. The method of claim 1 wherein the water-pulverized solid slurry
is pressurized in the range of 60-80 bar
4. The method of claim 2 wherein CO.sub.2 is vaporized to provide a
80% loading.
5. The method of claim 1 further including a slurry skimming to
remove substantially all of the CO.sub.2 from the
CO.sub.2-pulverized solid slurry.
6. The method of claim 5 wherein the slurry skimming step involves
low-grade heat addition.
7. The method of claim 5 wherein the slurry skimming step involves
a pressure reduction.
Description
[0001] The applications claims priority to provisional application
Ser. No. 61/712954 file on Oct. 12, 2012, and to provisional
application Ser. No. 61/831354 filed on May 31, 2013, the contents
of both of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to slurries and more particularly to
a method for producing a suspension or slurry of pulverized solid
material such as coal, in liquid or supercritical carbon dioxide.
The invention also relates to preparing a dense, high pressure
state via a phase inversion with carbon dioxide.
[0003] The continuous conveying of a solid feedstock such as
pulverized coal (PC) into a pressurized vessel is a challenging
step that is required in multiple processes such as gasification,
combustion, etc. Commercial technologies for continuous PC
conveying are classified as slurry or as dry feeding systems.
[0004] Dry feeding systems often use lock hoppers to feed coal in
its dense phase with the help of a transport gas. Such systems
operate on the principle of intermittent feeding across the
pressure boundary, typically by the staged opening and closing of
valves on the top and bottom of a charged pressure vessel called a
lock hopper. The top valve opens to receive material while the
bottom valve is closed. The top valve is then closed and the lock
hopper is brought to or above system pressure through injection of
a gas such as nitrogen. Once the hopper is pressurized, the bottom
valve is opened and the material discharged to the desire process.
Often dual or parallel lock hoppers are used [1].
[0005] Dry feeding systems are very efficient but are less reliable
mainly as a result of poor valve operation in a dusty environment.
Dry feeding systems also cost about three times as much as slurry
fed systems [2] and usually require feedstock drying to yield a
free flowing solid. Further, lock hopper-based dry feeding systems
have a range of application limited to below 30 bar, above which
the amount of transport gas required makes the process highly
inefficient [3].
[0006] In slurry feeding systems, the solid feedstock is first
suspended in a liquid medium such as water. The suspension, or
slurry, can then be pumped to a desired pressure. Commercial
systems for pulverized coal slurry feeding use water as the
slurrying medium. Other liquid slurrying media such as oil and
liquid carbon dioxide have also been suggested [4].
[0007] Slurry feeding systems are significantly cheaper and more
reliable and cam achieve higher pressures of 200 bar and beyond
[3]. However, injection of water into this process makes the system
very inefficient. The water must usually be brought to high process
temperatures which requires a large energy investment given its
high heat capacity and enthalpy of vaporization [5].
[0008] Other types of solid feeding systems such as rotary feeders,
plug-forming and non-plug-forming feeders are also known. However,
their range of applicability is limited both in terms of the
pressure and of the mass flows that they can handle [6].
Alternative feeding systems such as dry solids pumps are currently
under development [7, 8].
[0009] The use of liquid carbon dioxide as a coal slurrying medium
has been suggested in the past both in the context of pipeline
transportation of coal slurry and for feeding coal into pressurized
processes [10]. The low heat capacity, vaporization enthalpy, and
viscosity of liquid CO.sub.2 make it an attractive alternative to
water as a slurring meeting. In addition, liquid CO.sub.2 is
readily available from the CO.sub.2 compression unit of plants with
carbon capture.
[0010] Previous studies have estimated that the efficiency
advantage of a plant with coal-CO.sub.2 slurry is very significant.
For example, an integrated gasification combined cycle (IGCC) power
plant with coal-CO.sub.2 slurry is estimated to be up to 25% more
efficient than a plant based on a coal-water slurry [5]. This
increased efficiency is particularly true for abundant low-rank
coal whose utilization is otherwise very inefficient, making the
current feeding system very attractive.
[0011] Unlike coal-water slurry, however, coal-CO.sub.2 slurry
cannot be prepared at ambient pressure: the triple point pressure
or CO.sub.2 is five bar so CO.sub.2 will never exist in its liquid
slate at lower pressures including ambient pressure. The method for
mixing coal and liquid CO.sub.2 into a pressurized slurry is hence
a key aspect of the coal-CO.sub.2 slurry process since the coal
available for slurry preparation is at ambient conditions and must
be mixed with CO.sub.2 at high pressure.
[0012] The use of coal-CO.sub.2 slurry is known in the prior art.
U.S. Pat. No. 3,076,443 discloses the use of a coal-CO.sub.2 slurry
as a way to feed coal into a pressurized gasifier. U.S. Pat. Nos.
4,206,610 and 4,765,781 target the transport of coal through a
pipeline in the form of a slurry. All three of these patents
describe the method for preparing coal-CO.sub.2 slurry that
includes pressurization of coal in a lock hopper first, typically
with gaseous CO.sub.2, followed by mixing with pressurized liquid
carbon dioxide at temperatures above 90.degree. C. Preparation of a
coal-CO.sub.2 slurry at a lower temperature of 23.degree. C. is
discussed by Dooher et. al [11]. Dooher et. al implies the use of
lock hoppers to pressurized the coal first. Coal drying prior to
slurry preparation is often suggested in the proposed processes [2,
11,12].
[0013] U.S. Pat. No. 4,613,429 presents a method for removing
mineral matter from coal by employing liquid CO.sub.2. In the
disclosed process, coal-water slurry is thoroughly mixed with
CO.sub.2 in a pressurised, liquid contacting vessel. Two distinct
phases are formed and can be separated. Significantly, this patent
does not teach making a water-coal slurry at ambient pressure nor
does it teach or suggest pressurizing the coal/water feed slurry to
high pressure before introduction into a chamber for contact with
CO.sub.2. This patent likely requires a lock hopper to pressurized
the feed coal.
[0014] It is therefore an object of the present invention to
provide a method for preparing a slurry of pulverized solid
material in liquid or supercritical carbon dioxide using a coal
water slurry prepared at ambient pressure and then pumped to a high
pressure for contact with die carbon dioxide followed by
introduction into a desired process. A further object is a process
that requires neither coal drying nor the use of lock hoppers. The
present invention takes advantage of a physical phenomenon known as
phase-inversion, by which hydrophobic coal surfaces are
preferentially wetted by CO.sub.2, rather than by water. Coal is
used herein as an exemplary pulverized solid material. The process
disclosed herein is applicable to any other solid material such as
petcoke, biomass, etc.
SUMMARY OF THE INVENTION
[0015] The method according to the invention for making a slurry of
a pulverized solid in liquid or supercritical carbon dioxide
includes making a water-pulverized solid slurry at ambient pressure
and then pressurizing the water-pulverized solid slurry. The
pressurized water-pulverized solid slurry is then mixed in a
pressurized chamber with liquid or supercritical CO.sub.2 to form a
CO.sub.2 pulverized solid slurry. A preferred embodiment tender
includes vaporizing excess CO.sub.2 from the CO.sub.2-pulverized
solid slurry to concentrate the CO.sub.2pulverized solid slurry. In
a preferred embodiment, the water-pulverized solid slurry is
pressurized in the range of 60-80 bar. The carbon dioxide may be
vaporized to provide an 80% loading.
[0016] In yet another embodiment, the method includes slurry
skimming to remove substantially ail of the CO.sub.2 from the
CO.sub.2-pulverized solid slurry. The slurry skimming step may
involve low-grade heat addition and/or a pressure reduction.
BRIEF DESCRIPTION OF THE DRAWING
[0017] FIG. 1 is a schematic illustration of an embodiment of the
method disclosed herein.
[0018] FIG. 2 is a schematic illustration of production of CO.sub.2
slurry via phase inversion followed by full CO.sub.2 skimming to
produce a dense solid phase at high pressure.
[0019] FIG. 3a is a schematic of the slurry skimming step for a
preferred embodiment of the invention.
[0020] FIG. 3b is a graph of CO.sub.2 pressure versus enthalpy for
corresponding states.
[0021] FIG. 4 is a schematic illustration of slurry skimming
through indirect heat exchange with hot/warm fluid such as water
according to an embodiment of the invention.
[0022] FIG. 5 is a schematic illustration of slurry skimming
through direct heat exchange with hot CO.sub.2 according to an
embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Coal-water slurry (CWS) is prepared from pulverized coal and
water at ambient pressure and near ambient temperature in a slurry
mixing tank 10 as shown in FIG. 1. Coal drying can be carried out
prior to slurry preparation but is not required. The loading of
coal in the CWS is typically 20%, by weight, including coal
moisture. The CWS is pumped to a high pressure, typically 60-80
bar, by a pump 12 and mixed with liquid CO.sub.2 in a pressurized
vessel 14 at near ambient temperature. The residence time in the
mixing vessel 14 is about five minutes and dm mass flow rate of
CO.sub.2 is typically half that of the coal-water slurry. One or
more pre-mixing stages may be used as has been observed to be
beneficial to the process performance [7].
[0024] Two distinct phases form in the mixing vessel 14 under the
operating conditions of the present invention which can be
separated in the same or a separate vessel: a light CO.sub.2-rich
phase 16 is collected from the top of das vessel 14 and a heavy
aqueous phase 18 from the bottom of the vessel. Coal particles
preferentially accumulate in the CO.sub.2 phase, forming a
coal-CO.sub.2 slurry. Ash particles, on the other hand, tend to
accumulate in the heavier aqueous phase 18. Surface properties of
the coal being used and the process operating conditions determine
the coal and ash recovery in each phase.
[0025] The high-ash solids collected in the aqueous phase 18 are
dewatered at ambient pressure and disposed of. Any kind of
solid-liquid separation equipment such as a cyclone, moving
screens, filters, etc. can be used for this purpose. CO.sub.2
desorbed from the aqueous phase as a result of the pressure
reduction is flared or recompressed back to liquid CO.sub.2 and the
separated water is recirculated back to the CWS preparation tank
10. The coal-CO.sub.2 slurry collected from the top of the mixing
vessel 14 is at high pressure and ambient temperature. The coal's
moisture content is typically 5-10%, by weight, but can be low as
0% and as high as its as received moisture, depending on process
conditions.
[0026] The CO.sub.2-coal slurry can be directly fed to a high
pressure process such as a high-pressure gasified (not shown).
However, because the coal-CO.sub.2 step may be required. This stem
can be carried out by vaporizing excess CO.sub.2 through pressure
reduction and/or low-grade heat addition. A precise strategy
depends on the slurry overpressure and the loading required.
Loading of 80% is typical for adequate slurry flow properties;
however, a loading of close to 100%, I.e., a dry coal stream, can
also be produced by evaporating the entire CO.sub.2 content in the
slurry. The gaseous CO.sub.2 stream released in the concentration
step can be flared or recompressed back to liquid CO.sub.2. The
CO.sub.2 slurry can be pumped to a higher pressure before or after
the concentration step if required.
[0027] While not being held to any particular theory, the
accumulation of coal in the CO.sub.2 phase is believed to be a
physical, surface-property-driven phenomenon by which water is
displace from the coal as a result of the preferential wetting of
the hydrophobic coal surface by CO.sub.2. The exact mechanism of
this process, also known as phase-inversion, is not well understood
at the present time [15, 16]. Extensive experimental work conducted
in the past has demonstrated this phenomenon, whereas coal
recoveries of up to 90% in the CO.sub.2 slurry and the ash
separation efficiency of up to 95% have been observed. The low
moisture (5-10%) in the recovered coal has been identified to be
one of the largest appeals of the process disclosed herein.
[0028] Those of skill in this art will recognize that the coal, ash
and moisture content of the CO.sub.2 slurry obtained using the
present invention depends on the interaction among the interfacial,
sheer, and body forces present in the coal-CO.sub.2-H.sub.2O system
and hence on the characteristics of the feedstock and on the
operating conditions of the mixing process [14, 16].
[0029] In another aspect, the invention is a method for producing a
pressurized, dense stream of pulverized, solid material such as
coal that is achieved by flashing, or skimming, the CO.sub.2
content out of pressurized coal-CO.sub.2 slurry prepared as
discussed above.
[0030] Despite the thermodynamic appeal of liquid CO.sub.2 in the
feeding system, recent work has shown that the presence of CO.sub.2
in the feed could negatively impact the chemistry and thus the
performance of downstream units. For a high-pressure gasifier with
bituminous coal-CO.sub.2 slurry feed, for example, a significant
conversion reduction is predicted in a reactor when water is
substituted by CO.sub.2 as the slurrying medium. Once this is
accounted for, no performance advantage is predicted relative to
conventional coal-water slurry feed [6, 10]. To avoid potential
challenges associated with the presence of CO.sub.2 in the feed,
the flow of the latter can be reduced by flashing, or evaporating,
it from the pressurized coal-CO.sub.2 slurry prior to injection
into a reactor. If the entire content of the CO.sub.2 in the slurry
is evaporated, a dense solid stream at pressure results, which can
be used to feed any high pressure process.
[0031] A schematic illustration of this aspect of the invention is
shown in FIG. 2. A slurry skimming section 20 removes the entire
CO.sub.2 content of the slurry resulting in a dense solid phase
stream of material.
[0032] The removal of CO.sub.2 from coal-CO.sub.2 slurry can be
easily achieved thanks to the proximity of CO.sub.2 to its
saturation line. As shown in FIG. 3a, showing typical operating
conditions, slurry skimming can be carried out through a
combination of modest pressure reduction and low-grade heat
addition. Heat addition alone is sufficient if a pressure reduction
is not desired. The final slurry loading can be as high as 100% but
can be adjusted, as required, through the amount of heat added in
the skimming unit. FIG. 3b shows pressure against enthalpy for the
system.
[0033] The low-grade heat addition required for CO.sub.2 slurry
skimming can be added through direct or indirect neat exchange with
a heating medium. The process configuration and the type of
equipment that can be used in each case are illustrated
schematically in FIGS. 4 and 5, respectively.
[0034] Equipment such as a screw-type heat exchanger shown in FIG.
4 can be used for slurry skimming through indirect heat exchange
with a warm fluid such as, but not limited to, water. A cyclone may
be required to separate any entrained solids from the evaporated
CO.sub.2 stream. The dense solid stream can be fed to any
high-pressure process.
[0035] Alternatively, heat addition can be carried out through
direct heat exchange by using a similar piece of equipment but
putting the slurry in direct contact with the heating medium. Hot,
high-pressure CO.sub.2 from the CO.sub.2 compression unit can but
used for this purpose as shown in FIG. 5. Other kinds of equipment
such as a spray dryer can be used. The solid and gas phases are
separated in a cyclone, producing a dense, solid stream at high
pressure.
[0036] It is recognized that modifications and variations of the
present invention are included within the scope of the appended
claims.
[0037] The numbers in square brackets refer to the references
listed herewith, the contents of all of which are incorporated
herein by reference.
REFERENCES
[0038] 1. Swanson, M. et al., Feed System Innovation for
Gasification of Locally Economical Alternative Fuels (FIGLEAF).
Final Report, 2002
[0039] 2. National Energy Technology Laboratory (NETL), Cost and
Performance Baseline for Fossil Energy Plants, Volume 1: Bituminous
Coal and Natural Gas to Electricity, Revision 2;
DOE/NETL-2010/1397; 2010
[0040] 3. Higman, C.; van der Burgi M., Gasification, Second ed.;
Elsevier: 2008,
[0041] 4. Santhanam, C. J.; Dale, S. E.; Nadkarni, R. M. In
Non-water Slurry Pipelines--Potential Techniques, 5th International
Technical Conference on Slurry Transportation, Lake Tahoe, Nev.
(USA), Lake Tahoe, Nev. (USA), 1980.
[0042] 5. Botero, C.; Field, R. P.; Brasington, R. D.; Herzog, H.
J.; Ghoniem, A. F., Performance of an IGCC Plant with Carbon
Capture and Coal-C02.about.Slurry Feed: Impact of Coal Rank, Slurry
Loading, and Syngas Cooling Technology. Industrial &
Engineering Chemistry Research 2012, 51(36), 11778-11790.
[0043] 6. Swanson, M. L.; Musich, M. A.; Schmidt, D. D.; Schultz,
J. K. Feed System Innovation for Gasification of Locally Economic
Alternative Fuels (FIGLEAF): DE-FC26-00NT40904; National Energy
Technology Laboratory: 2003.
[0044] 7. National Energy Technology Laboratory, Development of a
High-Pressure Dry Feed Pump For Gasification Systems, Project Fact
Sheet, 2008-2012
[0045] 8, National Energy Technology Laboratory, Evaluation of the
Benefits of Advanced Dry Feed Systems for Low Rank Coal Project No.
DE-FE0007902, 2011-2012
[0046] 9. Paull, P. L.; Schlinger, W. G. Synthesis gas from solid
carbonaceous fuel. U.S. Pat. No. 3,976,443 1976.
[0047] 10. Santhanam, C. J., Method and Apparatus for Transporting
Coal as a Coal/Liquid Carbon Dioxide Slurry. U.S. Pat. No.
4,206,610, 1980.
[0048] 11. Dooher, J.; Marasigan, J.; Goldstein, H. N. In Liquid
C02 Slurry (LC02) for Feeding Low Rank Coal (LRC) to Gasifiers,
37th International Technical Conference on Clean Coal and Fuel
Systems, Clearwater, Fla. (USA). 2012.
[0049] 12. Wills, D. M. M., Steven L. Coal Slurry System. U.S. Pat.
No. 4,765,781 1988.
[0050] 13. Chiang, S.-H., Klinzing, G. E. Process for removing
mineral mater from coal. U.S. Pat. No. 4.613,419, 1986.
[0051] 14. Westinghouse Electric Corporation, Development of the
LICADO coal cleaning process; DOE/PC79873-Ti; 1990; p Medium; ED;
Size; Pages: (256 p)
[0052] 15. Kawatra, K., Coal Desulfurization: High Efficiency
Preparation Methods, Taylor & Francis: 2001.
[0053] 16. Chi, S. M., Interfacial properties and coal cleaning in
the LICADO process, PhD Thesis, University of Pittsburgh, 1986.
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