U.S. patent application number 12/538423 was filed with the patent office on 2011-02-10 for methods for removing impurities from coal including neutralization of a leaching solution.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Samuel D. Draper, Lawrence B. Kool, Chandrashekhar Sonwane.
Application Number | 20110030270 12/538423 |
Document ID | / |
Family ID | 43448472 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110030270 |
Kind Code |
A1 |
Sonwane; Chandrashekhar ; et
al. |
February 10, 2011 |
Methods for removing impurities from coal including neutralization
of a leaching solution
Abstract
A method for removing at least one impurity from coal is
provided. The method comprises providing coal having a plurality of
impurities and contacting the coal with a first leaching solution.
The first leaching solution reacts with at least one of the
impurities to produce one or more first products soluble in the
first leaching solution. The method further comprises adding a
neutralizing composition to the first leaching solution. The
neutralizing composition reacts with the first leaching solution to
form a precipitate. The method further comprises separating at
least a portion of the first leaching solution from the coal and
the precipitate and contacting the coal and the precipitate with a
second leaching solution. The second leaching solution reacts with
at least one of the impurities and the precipitate to form one or
more second products and one or more third products, respectively,
the second products and the third products being soluble in the
second leaching solution. The method further comprises separating
at least a portion of the second leaching solution from the
coal.
Inventors: |
Sonwane; Chandrashekhar;
(Philadelphia, PA) ; Draper; Samuel D.;
(Simpsonville, SC) ; Kool; Lawrence B.; (Clifton
Park, NY) |
Correspondence
Address: |
SUTHERLAND ASBILL & BRENNAN LLP
999 PEACHTREE STREET, N.E.
ATLANTA
GA
30309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
43448472 |
Appl. No.: |
12/538423 |
Filed: |
August 10, 2009 |
Current U.S.
Class: |
44/621 |
Current CPC
Class: |
C01B 37/02 20130101;
C01B 37/00 20130101 |
Class at
Publication: |
44/621 |
International
Class: |
C10L 5/00 20060101
C10L005/00 |
Claims
1. A method for removing at least one impurity from coal, the
method comprising: providing coal having a plurality of impurities;
contacting the coal with a first leaching solution, wherein the
first leaching solution reacts with at least one of the impurities
to produce one or more first products soluble in the first leaching
solution; adding a neutralizing composition to the first leaching
solution, wherein the neutralizing composition reacts with the
first leaching solution to form a precipitate; separating at least
a portion of the first leaching solution from the coal and the
precipitate; and contacting the coal and the precipitate with a
second leaching solution, wherein the second leaching solution
reacts with at least one of the impurities and the precipitate to
form one or more second products and one or more third products,
respectively, the second products and the third products being
soluble in the second leaching solution; and separating at least a
portion of the second leaching solution from the coal.
2. The method of claim 1, wherein the neutralizing composition
comprises calcium hydroxide, sodium hydroxide, or combinations
thereof.
3. The method of claim 1, wherein the neutralizing composition has
a neutralizing reactant concentration ranging from about 1 M to
about 10 M.
4. The method of claim 1, wherein the first leaching solution
comprises a hydrofluoric acid solution, the neutralizing
composition comprises calcium hydroxide, the precipitate comprises
a calcium fluoride, and the one or more third products comprise
calcium ions, nitrate ions, or combinations thereof.
5. The method of claim 1, wherein the first leaching solution
comprises a hydrofluoric acid solution, a nitric acid solution, a
hydrochloric acid solution, a hydrofluorosilicic acid solution, or
combinations thereof.
6. The method of claim 1, wherein the first leaching solution
comprises a hydrofluoric acid solution having a hydrofluoric acid
concentration ranging from about 3 M to about 10 M.
7. The method of claim 1, wherein the neutralizing composition
reacts with the first leaching solution to neutralize substantially
all of the first leaching solution.
8. The method of claim 1, wherein the second leaching solution
comprises nitric acid, aluminum nitrate, ferric nitrate,
fluoronitrate, hydroxide, hydroxyl fluoride, hydroxynitrate, ions
thereof, or combinations thereof.
9. The method of claim 1, wherein the second leaching solution
comprises a nitric acid solution having a nitric acid concentration
ranging from about 0.1 M to about 5 M.
10. The method of claim 1, wherein the method is carried out in a
batch reactor chamber.
11. A method for removing at least one impurity from coal, the
method comprising: providing coal having a plurality of impurities;
contacting the coal with a first leaching solution, wherein the
first leaching solution reacts with at least one of the impurities
to produce one or more first products soluble in the first leaching
solution; separating at least a portion of the first leaching
solution from the coal as an unreacted first leaching solution;
adding a neutralizing composition to the unreacted first leaching
solution, wherein the neutralizing composition reacts with the
unreacted first leaching solution to form a precipitate; separating
at least a portion of the unreacted first leaching solution from
the precipitate; contacting the coal and the precipitate with a
second leaching solution, wherein the second leaching solution
reacts with at least one of the impurities and the precipitate to
form one or more second products and one or more third products,
respectively, the second products and the third products being
soluble in the second leaching solution; and separating at least a
portion of the second leaching solution from the coal.
12. The method of claim 11, wherein the neutralizing composition
comprises calcium hydroxide, sodium hydroxide, or combinations
thereof.
13. The method of claim 11, wherein the neutralizing composition
has a neutralizing reactant concentration ranging from about 1 M to
about 10 M.
14. The method of claim 11, wherein the first leaching solution
comprise a hydrofluoric acid solution, the neutralizing composition
comprises calcium hydroxide, the precipitate comprises a calcium
fluoride, and the one or more third products comprise calcium ions,
nitrate ions, or combinations thereof.
15. The method of claim 11, wherein the first leaching solution
comprises a hydrofluoric acid solution, a nitric acid solution, a
hydrochloric acid solution, a hydrofluorosilicic acid solution, or
combinations thereof.
16. The method of claim 11, wherein the first leaching solution
comprises a hydrofluoric acid solution having a hydrofluoric acid
concentration ranging from about 3 M to about 10 M.
17. The method of claim 11, wherein the neutralizing composition
reacts with the unreacted first leaching solution to neutralize
substantially all of the unreacted first leaching solution.
18. The method of claim 11 wherein the second leaching solution
comprises nitric acid, aluminum nitrate, ferric nitrate,
fluoronitrate, hydroxide, hydroxyl fluoride, hydroxynitrate, ions
thereof, or combinations thereof.
19. The method of claim 11, wherein the second leaching solution
comprises a nitric acid solution having a nitric acid concentration
ranging from about 0.1 Mto about 5 M.
20. The method of claim 11, wherein the method is carried out in a
batch reactor chamber.
Description
TECHNICAL FIELD
[0001] This disclosure generally relates to methods for removing
impurities from coal, and more particularly relates to methods for
removing impurities from coal which include neutralization of a
leaching solution.
BACKGROUND OF THE INVENTION
[0002] Clean coal, such as ultra clean coal, may be provided by
treatment of coal including impurities to remove the impurities.
For instance, coal including impurities may be treated with a first
leaching solution such as hydrofluoric acid ("HF") in a first
reactor to produce a first reaction slurry. The first reaction
slurry may be transported to a filter (e.g., drum filter) to
produce filtered, wet coal. The filtered, wet coal may then be
transported to a second reactor for treatment with a second
leaching solution such as a nitrate solution to produce a second
reaction slurry. The second reaction slurry may then be transported
to a filter for filtering. The resulting ultra clean coal may then
be water washed and transported to a dryer for drying.
[0003] Typically, the moles of HF required for the first reaction
are significantly lower than the moles of HF used. Thus, the
unreacted HF remains in the liquid and may even remain in the coal
(e.g., in the areas of pre-existing moisture and in etched pores in
the coal created from the HF reacting with ash impurities) after
the coal is filtered.
[0004] HF is known to be extremely toxic and to corrode glass. HF
typically has an occupational exposure level of 2 ppm. The PPO's
needed include rubber gloves, face mask or safety glasses, apron,
and good ventilation. If HF is inhaled or ingested, the result may
be fatal. HF is readily absorbed through the skin and skin contact
may also be fatal. HF also acts as a systemic poison, causes severe
burns, and is a possible mutigen. In addition, the reaction with HF
may be delayed. Thus, any contact with HF, even if minor, requires
immediate medical attention.
SUMMARY OF THE INVENTION
[0005] This disclosure provides a method for removing at least one
impurity from coal. The method comprises providing coal having a
plurality of impurities and contacting the coal with a first
leaching solution. The first leaching solution reacts with at least
one of the impurities to produce one or more first products soluble
in the first leaching solution. The method further comprises adding
a neutralizing composition to the first leaching solution. The
neutralizing composition reacts with the first leaching solution to
form a precipitate. The method further comprises separating at
least a portion of the first leaching solution from the coal and
the precipitate and contacting the coal and the precipitate with a
second leaching solution. The second leaching solution reacts with
at least one of the impurities and the precipitate to form one or
more second products and one or more third products, respectively,
the second products and the third products being soluble in the
second leaching solution. The method further comprises separating
at least a portion of the second leaching solution from the
coal.
[0006] The present disclosure also provides another method for
removing at least one impurity from coal. The method comprises
providing coal having a plurality of impurities and contacting the
coal with a first leaching solution. The first leaching solution
reacts with at least one of the impurities to produce one or more
first products soluble in the first leaching solution. The method
further comprises separating at least a portion of the first
leaching solution from the coal as an unreacted first leaching
solution. The method further comprises adding a neutralizing
composition to the unreacted first leaching solution. The
neutralizing composition reacts with the unreacted first leaching
solution to form a precipitate. The method further comprises
separating at least a portion of the unreacted first leaching
solution from the precipitate and contacting the coal and the
precipitate with a second leaching solution. The second leaching
solution reacts with at least one of the impurities and the
precipitate to form one or more second products and one or more
third products, respectively, the second products and the third
products being soluble in the second leaching solution. The method
further comprises separating at least a portion of the second
leaching solution from the coal.
[0007] Other aspects, features, and advantages of this invention
will be apparent from the following detailed description, drawings,
and claims.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 illustrates a method 10 for removing at least one
impurity from coal in accordance with an embodiment of the present
invention.
[0009] FIG. 2 illustrates a method 50 for removing at least one
impurity from coal in accordance with another embodiment of the
present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0010] As summarized above, this disclosure encompasses methods for
removing at least one impurity from coal. Thus, the method of the
present disclosure may be used to produce ultra clean coal. As used
herein, the term "ultra clean coal" refers to coal having a reduced
ash content (e.g., below about 0.2%) and/or a substantially reduced
sulfur content such that the coal may be fed directly into
processes such as gas turbine processes and provide advantages such
as improved thermal efficiency, for example. As used herein, "ash"
refers to both the non-combustible components in the coal before
combustion and the non-combustible byproducts resulting from
combustion of the coal. Embodiments of the method for removing at
least one impurity from coal are described below and illustrated in
FIGS. 1 and 2. It should be understood that any system (e.g., gas
turbine systems such as coal fired gas turbine systems, pulverized
coal power plants, and integrated gasification combined cycle
systems) may use the coal (e.g., ultra clean coal) provided by
embodiments of the methods of the present disclosure.
[0011] FIG. 1 illustrates an embodiment of the method 10 for
removing impurities from coal of the present disclosure. The method
10 first provides coal 12 comprising a plurality of impurities.
Embodiments of method 10 may provide coal 12 in the form of
anthracite coal, bituminous coal, subbituminous coal, lignite coal,
or combinations thereof.
[0012] In some embodiments, the impurities include, but are not
limited to, oxides of aluminum, iron, potassium, calcium, sodium,
and other metals, minerals, inorganic and organic sulfur compounds,
alkalis, ash, or combinations thereof. In certain embodiments, the
impurities may be present in the coal 12 in an amount ranging from
about 2 wt. % to about 50 wt. %. In other embodiments, the
impurities may be present in the coal 12 in an amount ranging from
about 3 wt. % to about 8 wt. %. In still other embodiments, the
impurities may be present in the coal 12 in an amount ranging from
about 5 wt. % to about 7 wt. %.
TABLE-US-00001 TABLE 1 Examples of ranges of chemical composition
for fly ash produced from different coal types (expressed as
percent by weight). Component Bituminous Subbituminous Lignite
SiO.sub.2 20-60 40-60 15-45 Al.sub.2O.sub.3 5-35 20-30 10-25
Fe.sub.2O.sub.3 10-40 4-10 4-15 CaO 1-12 5-30 15-40 MgO 0-5 1-6
3-10 SO.sub.3 0-4 0-2 0-10 Na.sub.2O 0-4 0-2 0-6 K.sub.2O 0-3 0-4
0-4 LOI 0-15 0-3 0-5 Source: http://www.tfhrc.gov
[0013] The method 10 contacts the coal 12 with a first leaching
solution 14 in a first reactor 16. At least one of the impurities
reacts with the first leaching solution 14 to produce one or more
first products soluble in the first leaching solution. In certain
embodiments, the first leaching solution 14 may comprise an acid
solution. In some embodiments, the first leaching solution 14 may
include, but is not limited to, first reactants such as a
hydrofluoric acid, a nitric acid, a hydrochloric acid, a
hydrofluorosilicic acid, a combination thereof, or other strong
acids that dissolve oxides.
[0014] An example of a reaction of the first leaching solution 14
with at least one impurity is given below in Formula (I):
SiO.sub.2+4HF.fwdarw.SiF.sub.4+2H.sub.2O (I).
[0015] In certain embodiments, the first leaching solution 14 has a
first reactant concentration ranging from about 3 M to about 10 M.
In other embodiments, the first leaching solution 14 has a first
reactant concentration ranging from about 3 M to about 6 M. In
still other embodiments, the first leaching solution 14 has a first
reactant concentration ranging from about 4 M to about 6 M.
[0016] In particular embodiments, the weight ratio of first
leaching solution 14 to coal 12 added to the first reactor 16
ranges from about 10:1 to about 10:5. Unless otherwise indicated,
all ratios are weight to weight ratios. In other particular
embodiments, the weight ratio of first leaching solution 14 to coal
12 added to the first reactor 16 ranges from about 10:2 to about
10:4. In still other particular embodiments, the weight ratio of
first leaching solution 14 to coal 12 added to the first reactor 16
ranges from about 10:2.5 to about 10:3.5.
[0017] In certain embodiments, the first leaching solution 14
comprises a hydrofluoric acid solution having a hydrofluoric acid
concentration ranging from about 3 M to about 10 M. In other
embodiments, the first leaching solution 14 comprises a
hydrofluoric acid solution having a hydrofluoric acid concentration
ranging from about 3 M to about 6 M. In still other embodiments,
the first leaching solution 14 comprises a hydrofluoric acid
solution having a hydrofluoric acid concentration ranging from
about 4 M to about 6 M. In particular embodiments, the weight ratio
of hydrofluoric acid solution 14 to coal 12 added to the first
reactor 16 ranges from about 10:1 to about 10:5. In other
particular embodiments, the weight ratio of hydrofluoric acid
solution 14 to coal 12 added to the first reactor 16 ranges from
about 10:2 to about 10:4. In still other particular embodiments,
the weight ratio of hydrofluoric acid solution 14 to coal 12 added
to the first reactor 16 ranges from about 10:2.5 to about
10:3.5.
[0018] In particular embodiments, the coal 12 is in contact with
the first leaching solution 14 for about 1 hours to about 10 hours
in the first reactor 16. In other particular embodiments, the coal
12 is in contact with the first leaching solution 14 for about 3
hours to about 5 hours in the first reactor 16. In still other
particular embodiments, the coal 12 is in contact with the first
leaching solution 14 for about 4 hours to about 5 hours in the
first reactor 16.
[0019] In particular embodiments, the coal 12 is in contact with
the first leaching solution 14 at a temperature ranging from about
70.degree. F. to about 200.degree. F. in the first reactor 16. In
other particular embodiments, the coal 12 is in contact with the
first leaching solution 14 at a temperature ranging from about
110.degree. F. to about 170.degree. F. in the first reactor 16. In
still other particular embodiments, the coal 12 is in contact with
the first leaching solution 14 at a temperature ranging from about
140.degree. F. to about 160.degree. F. in the first reactor 16.
[0020] In particular embodiments, the coal 12 is in contact with
the first leaching solution 14 at a pressure ranging from about 14
psia to about 1000 psia in the first reactor 16. In other
particular embodiments, the coal 12 is in contact with the first
leaching solution 14 at a pressure ranging from about 14 psia to
about 42 psia in the first reactor 16. In still other particular
embodiments, the coal 12 is in contact with the first leaching
solution 14 at a pressure ranging from about 14 psia to about 20
psia in the first reactor 16.
[0021] In certain embodiments, the one or more first products
comprises one or more fluorides, hydroxyl fluorides, hydroxides, or
combinations thereof. In embodiments where the first products
comprise one or more fluorides, the fluorides may be selected from
silicon fluoride, aluminum fluoride, iron fluoride, calcium
fluoride, potassium fluoride, or combinations thereof.
[0022] The method 10 further comprises adding a neutralizing
composition 18 to the first leaching solution 14 such that
neutralizing composition reacts with the first leaching solution to
form a precipitate. By adding the neutralizing composition 18 to
the first leaching solution 14, any unreacted first reactant (i.e.
excess first reactant that has not reacted with at least one of the
impurities) in the first leaching solution is neutralized.
[0023] In some embodiments, the neutralizing composition 18
comprises a neutralizing reactant including a calcium hydroxide,
sodium hydroxide, any other alkali, or combinations thereof. In
certain embodiments, the first leaching solution comprises a
hydrofluoric acid solution, the neutralizing composition comprises
calcium hydroxide, the precipitate comprises a calcium fluoride,
and the one or more third products comprise calcium ions, nitrate
ions, or combinations thereof.
[0024] In certain embodiments, the neutralizing composition 18 is
added to the first leaching solution 14 after the coal 12 has been
in contact with the first leaching solution for about 1 hours to
about 10 hours in the first reactor 16. In other particular
embodiments, the neutralizing composition 18 is added to the first
leaching solution 14 after the coal 12 has been in contact with the
first leaching solution for about 3 hours to about 5 hours in the
first reactor 16. In still other particular embodiments, the
neutralizing composition 18 is added to the first leaching solution
14 after the coal 12 has been in contact with the first leaching
solution for about 4 hours to about 5 hours in the first reactor
16.
[0025] In certain embodiments, the neutralizing composition 18 has
a neutralizing reactant concentration ranging from about 1 M to
about 10 M. In other embodiments, the neutralizing composition 18
has a neutralizing reactant concentration ranging from about 1 M to
about 4 M. In still other embodiments, the neutralizing composition
18 has a neutralizing reactant concentration ranging from about 2 M
to about 3 M.
[0026] The method 10 further comprises separating at least a
portion of the first leaching solution 14 from the coal 12 and the
precipitate. By separating at least a portion of the first leaching
solution 14 from the coal 12, at least a portion of the first
products are also separated from the coal because they are soluble
in the first leaching solution. Thus, in particular embodiments,
substantially all of the first leaching solution 14 including
substantially all of the first products may be separated from the
coal 12 and the precipitate. In the method 10 illustrated in FIG.
1, the first leaching solution 14, the coal 12, and the
precipitate, are transported from the first reactor 16 as a slurry
20 to a drum filter 22. The drum filter 22 filters the slurry 20 to
separate the coal and the precipitate as wet coal 26 from the first
leaching solution 24.
[0027] The wet coal 26 is then fed to a second reactor 30 where the
coal 12 and the precipitate are contacted with a second leaching
solution 28. The second leaching solution 28 reacts with at least
one of the impurities and the precipitate to form one or more
second products and one or more third products, respectively. The
second products and the third products are soluble in the second
leaching solution 28. In certain embodiments, the second leaching
solution 28 may comprise a nitrate solution.
[0028] Examples of reactions of the second leaching solution 28
with at least one impurity are given below in Formulas (II) and
(III):
FeS.sub.2+14Fe(NO.sub.3).sub.3+8H.sub.2O.fwdarw.2SO.sub.4.sup.2-+16H.sup-
.++15Fe.sup.2++42NO.sup.3- (II)
SiF.sub.4+2(Al,Fe)(NO.sub.3).sub.3+2H.sub.2O.fwdarw.SiO.sub.2(s)+2(Al,Fe-
)F.sub.2.sup.++4H.sup.++6NO.sub.3.sup.- (III).
[0029] In certain embodiments, the second leaching solution 28
comprises a second reactant including, but not limited to nitric
acid, aluminum nitrate, ferric nitrate, fluoronitrate, other
nitrates, hydroxide, hydroxyl fluoride, hydroxynitrate ions
thereof, or combinations thereof. In some embodiments of the
method, the one or more second products comprises nitrate ions,
sulfate ions, iron ions, hydroxyfluorides, oxides, fluoronitrate,
or combinations thereof. In particular embodiments, the one or more
third products comprise calcium ions or combination thereof.
[0030] In particular embodiments, the second leaching solution 28
has a second reactant concentration ranging from about 0.1 M to
about 5 M. In other particular embodiments, the second leaching
solution 28 has a second reactant concentration ranging from about
0.1 M to about 0.4 M. In still other particular embodiments, the
second leaching solution 28 has a second reactant concentration
ranging from about 0.3 M to about 0.4 M.
[0031] In certain embodiments, the weight ratio of second leaching
solution 28 to wet coal 26 added to the second reactor 30 ranges
from about 10:1 to about 10:5. In other embodiments, the weight
ratio of second leaching solution 28 to wet coal 26 added to the
second reactor 30 ranges from about 10:2 to about 10:4. In still
other embodiments, the weight ratio of second leaching solution 28
to wet coal 26 added to the second reactant reactor 30 ranges from
about 10:2.5 to about 10:3.5.
[0032] In particular embodiments, the second leaching solution 28
comprises a nitric acid solution having a nitric acid concentration
ranging from about 0.1 M to about 5 M. In other particular
embodiments, the second leaching solution 28 comprises a nitric
acid solution having a nitric acid concentration ranging from about
0.1 M to about 0.4 M. In still other particular embodiments, the
second leaching solution 28 comprises a nitric acid solution having
a nitric acid concentration ranging from about 0.2 M to about 0.3
M. In certain embodiments, the weight ratio of nitric acid solution
28 to wet coal 26 added to the second reactor 30 ranges from about
10:1 to about 10:5. In other embodiments, the weight ratio of
nitric acid solution 28 to wet coal 26 added to the second reactor
30 ranges from about 10:2 to about 10:4. In still other
embodiments, the weight ratio of nitric acid solution to 28 to wet
coal 26 added to the second reactor 30 ranges from about 10:2.5 to
about 10:3.5.
[0033] According to certain embodiments of the present disclosure,
the second leaching solution 28 is in contact with the coal and the
precipitate for about 20 hours to about 30 hours in the second
reactor 30. In other particular embodiments, the second leaching
solution 28 is in contact with the coal and the precipitate for
about 22 hours to about 26 hours in the second reactor 30.
[0034] In particular embodiments, the second leaching solution 28
is in contact with the coal and precipitate at a temperature
ranging from about 70.degree. F. to about 190.degree. F. in the
second reactor 30. In other particular embodiments, the second
leaching solution 28 is in contact with the coal and precipitate at
a temperature ranging from about 150.degree. F. to about
1.90.degree. F. in the second reactor 30. In still other particular
embodiments, the second leaching solution 28 is in contact with the
coal and precipitate at a temperature ranging from about
140.degree. F. to about 160.degree. F. in the second reactor
30.
[0035] In particular embodiments, the second leaching solution 28
is in contact with the coal and precipitate at a pressure ranging
from about 14.4 psia to about 100 psia in the second reactor 30. In
other particular embodiments, the second leaching solution 28 is in
contact with the coal and precipitate at a pressure ranging from
about 14.4 psia to about 43 psia in the second reactor 30. In still
other particular embodiments, the second leaching solution 28 is in
contact with the coal and precipitate at a pressure ranging from
about 14.4 psia to about 28 psia in the second reactor 30.
[0036] The method 10 further comprises separating at least a
portion of the second leaching solution 28 from the coal. By
separating at least a portion of the second leaching solution 28
from the coal, at least a portion of the second products and at
least a portion of the third products are also separated from the
coal because they are soluble in the second leaching solution.
Thus, in particular embodiments, substantially all of the second
leaching solution 28 including substantially all of the second
products and substantially all of the third products may be
separated from the coal. In the method 10 illustrated in FIG. 1,
the second leaching solution 28 and the coal are transported from
the second reactor 30 as a slurry 32 to a drum filter 34. The drum
filter 34 filters the slurry 32 to separate wet coal 38 from the
second leaching solution 36.
[0037] The method 10 may further comprise washing the wet coal 38
with water in a water wash apparatus 40 to remove any residual
reactants or products from the coal. The water-washed coal 42 may
be transferred to a coal dryer (not shown) over a conveyer belt
(not shown), which will further act as a filter to remove water
from the coal.
[0038] Ash may be present in particular embodiments of the
water-washed coal 42 in an amount less than about 0.2% by weight.
In certain embodiments of the method 10, ash is present in the
water-washed coal 42 in an amount ranging from about 0.01% by
weight to about 0.5% by weight. In other embodiments of the method
10, ash is present in the water-washed coal 42 in an amount ranging
from about 0.01% by weight to about. 0.2% by weight.
[0039] In particular embodiments, the method further comprises
agitating the first leaching solution in the first reactor,
agitating the second leaching solution in the second reactor, or
both.
[0040] FIG. 2 illustrates an another embodiment of a method 50 for
removing impurities from coal. Like elements in FIGS. 1 and 2 are
numbered with like numerals.
[0041] As illustrated in FIG. 2, the neutralizing composition 18 is
added to an unreacted first leaching solution 54 rather than to the
first reactor 16 as in the method 10 illustrated in FIG. 1. Thus,
in this embodiment, the first leaching solution 12 and the coal 14
are transported from the first reactor 16 as a slurry 52 to the
drum filter 22. The drum filter 22 fillers the slurry 52 to
separate an unreacted first leaching solution 54 and from wet coal
56. The neutralizing composition 18 is added to the unreacted first
leaching solution 54 and the neutralizing composition reacts with
the unreacted first leaching solution to form a precipitate.
[0042] At least a portion of the unreacted first leaching solution
54 is separated by a filter apparatus 58 from the precipitate 60 as
a neutralized first leaching solution 62. The precipitate 60 is
then contacted with the second leaching solution 28 in the nitrate
reactor, along with the wet coal 56. The second leaching solution
28 reacts with at least one of the impurities and the precipitate
60 to form one or more second products and one or more third
products, respectively. The second products and the third products
are soluble in the second leaching solution 28.
[0043] In alternate embodiments (not shown), the methods may be
carried out in one reaction chamber in a batch process to avoid
using multiple reactors, multiple filters, and conveying equipment
(e.g., pumps and conveyer belts) an associated costs and space
requirements. In addition, exposure of coal outside of the reactor
is reduced, thus h
[0044] By adding a neutralizing composition to the first leaching
solution either in the first reactor or into an unreacted first
leaching solution separated from the coal and then contacting the
produced precipitate with the second leaching solution, excess
unreacted reactant, such as hydrofluoric acid, is reduced or
eliminated from the remainder of the process and the resulting
coal. Thus, the potential for exposure to hazardous chemicals, such
as hydrofluoric acid or other acids used, as it is neutralized
rather than transported to the second reactor along with the coal.
In addition, the reactors volumes may be lower and the process can
be carried out in a continuous manner instead of in a batch or
semi-batch process.
[0045] it should be apparent that the foregoing relates only to the
preferred embodiments of the present application and that numerous
changes and modifications may be made herein by one of ordinary
skill in the art without departing from the generally spirit and
scope of the invention as defined by the following claims and the
equivalents thereof.
* * * * *
References