U.S. patent application number 12/342715 was filed with the patent office on 2009-07-02 for catalytic gasification process with recovery of alkali metal from char.
This patent application is currently assigned to GreatPoint Energy, Inc.. Invention is credited to Alkis S. Rappas, Robert A. Spitz.
Application Number | 20090165382 12/342715 |
Document ID | / |
Family ID | 40565072 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090165382 |
Kind Code |
A1 |
Rappas; Alkis S. ; et
al. |
July 2, 2009 |
Catalytic Gasification Process with Recovery of Alkali Metal from
Char
Abstract
Processes for extracting and recycling alkali metal compounds
present in the char produced from the catalytic gasification of
carbonaceous materials are provided involving at least contacting
the char with and alkali metal hydroxide followed by carbon
dioxide. Both the alkali metal hydroxide and carbon dioxide
treatments serve to convert at least a portion of the insoluble
alkali metal compounds in the char into soluble species which can
be recovered and recycled.
Inventors: |
Rappas; Alkis S.; (Kingwood,
TX) ; Spitz; Robert A.; (Abington, MA) |
Correspondence
Address: |
MCDONNELL BOEHNEN HULBERT & BERGHOFF LLP
300 S. WACKER DRIVE, SUITE 3100
CHICAGO
IL
60606
US
|
Assignee: |
GreatPoint Energy, Inc.
Chicago
IL
|
Family ID: |
40565072 |
Appl. No.: |
12/342715 |
Filed: |
December 23, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61017312 |
Dec 28, 2007 |
|
|
|
Current U.S.
Class: |
48/127.7 ;
48/210; 75/419; 75/742 |
Current CPC
Class: |
C10J 2300/0973 20130101;
C10K 1/16 20130101; C10K 1/101 20130101; C10J 2300/0943 20130101;
C10J 2300/16 20130101; C10J 2300/1631 20130101; C10J 2300/0903
20130101; C10K 1/004 20130101; C10J 2300/169 20130101; C10K 1/143
20130101; C10K 1/165 20130101; C10J 2300/1853 20130101; C10K 1/146
20130101; C10J 3/463 20130101; C10J 2300/0986 20130101; C10J 3/00
20130101; C10J 2300/093 20130101; C10J 2300/1807 20130101; C10K
1/122 20130101 |
Class at
Publication: |
48/127.7 ;
75/419; 75/742; 48/210 |
International
Class: |
C10J 3/00 20060101
C10J003/00; C22B 26/10 20060101 C22B026/10 |
Claims
1. A process for extracting and recovering alkali metal from a
char, the char comprising (i) one or more soluble alkali metal
compounds and (ii) insoluble matter comprising one or more
insoluble alkali metal compounds, the process comprising the steps
of: (a) providing the char at an elevated temperature ranging from
50.degree. C. to about 600.degree. C.; (b) quenching the char in an
aqueous medium to fracture the char and form a quenched char
slurry; (c) contacting the quenched char slurry with an alkali
metal hydroxide under suitable pressure and temperature so as to
convert at least a portion of the insoluble alkali metal compounds
to one or more soluble alkali metal compounds, and produce a first
leached slurry comprising the soluble alkali metal compounds and a
partially extracted insoluble matter; (d) contacting the first
leached slurry with carbon dioxide under suitable pressure and
temperature so as to convert at least a portion of the insoluble
alkali metal compounds to one or more soluble alkali metal
compounds, and produce a second leached slurry comprising the
soluble alkali metal compounds and a residual insoluble matter; (e)
degassing the second leached slurry under suitable pressure and
temperature so as to remove a substantial portion of the excess
carbon dioxide and hydrogen sulfide, if present, and produce a
degassed second leached slurry; (f) separating the degassed second
leached slurry into a first liquid stream and a residual insoluble
matter stream, the first liquid stream comprising a predominant
portion of the soluble alkali metal compounds from the degassed
second leached slurry, and the residual insoluble matter stream
comprising residual soluble alkali metal compounds and residual
insoluble alkali metal compounds; (g) recovering the first liquid
stream; and (h) washing the residual insoluble matter stream with
an aqueous medium to produce a first wash stream comprising
substantially all of the residual soluble alkali metal compounds
from the residual insoluble matter stream, wherein the quenching
and contacting is performed in the substantial absence of gaseous
oxygen.
2. The process according to claim 1, wherein the char is a solid
residue derived from gasification of a carbonaceous material in the
presence of an alkali metal.
3. The process according to claim 2, wherein the carbonaceous
material comprises one or more of coal, petroleum coke, asphaltene,
liquid petroleum residue or biomass.
4. The process according to claim 1, wherein the aqueous medium to
fracture the char comprises the first wash stream.
5. The process according to claim 1, wherein the alkali metal
comprises sodium and/or potassium.
6. The process according to claim 2, wherein the alkali metal
comprises sodium and/or potassium.
7. The process according to claim 1, wherein the alkali metal is
potassium.
8. The process according to claim 1, wherein the source of alkali
metal is potassium carbonate.
9. The process according to claim 1, wherein contacting the
quenched char slurry with an alkali metal hydroxide is performed at
a temperature ranging from about 100.degree. C. up to about
300.degree. C., a steam pressure ranging from about 25 up to about
1000 psig, and time ranging from about 1 minute up to about 180
minutes.
10. A process for catalytically converting a carbonaceous
composition, in the presence of an alkali metal gasification
catalyst, into a plurality of gaseous products, the process
comprising the steps of: (a) supplying a carbonaceous composition
to a gasification reactor, the carbonaceous composition comprising
ash; (b) reacting the carbonaceous composition in the gasification
reactor in the presence of steam and an alkali metal gasification
catalyst under suitable temperature and pressure to form (i) a char
comprising alkali metal from the alkali metal gasification catalyst
in the form of one or more soluble alkali metal compounds and one
or more insoluble alkali metal compounds, and (ii) a plurality of
gaseous products comprising methane and one or more of hydrogen,
carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia, and
other higher hydrocarbons; (c) removing a portion of the char from
the gasification reactor; (d) extracting and recovering a
substantial portion of the alkali metal from the char according to
the process of claim 1; and (e) at least partially separating the
plurality of gaseous products to produce a stream comprising a
predominant amount of one of the gaseous products.
11. The process according to claim 10, wherein the carbonaceous
composition comprises one or more of coal, petroleum coke,
asphaltene, liquid petroleum residue or biomass.
12. The process according to claim 10, wherein the stream comprises
a predominant amount of methane.
13. The process according to claim 10, wherein the alkali metal
comprises sodium and/or potassium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.119
from U.S. Provisional Application Ser. No. 61/017,312 (filed Dec.
28, 2007), the disclosure of which is incorporated by reference
herein for all purposes as if fully set forth.
[0002] This application is related to commonly owned U.S.
application Ser. No. 11/421,511, filed Jun. 1, 2006, entitled
"CATALYTIC STEAM GASIFICATION PROCESS WITH RECOVERY AND RECYCLE OF
ALKALI METAL COMPOUNDS"; U.S. application Ser. No. ______, (filed
concurrently herewith), entitled "CATALYTIC GASIFICATION PROCESS
WITH RECOVERY OF ALKALI METAL FROM CHAR" (attorney docket no.
FN-0007 US NP1); U.S. application Ser. No. ______, (filed
concurrently herewith), entitled "CATALYTIC GASIFICATION PROCESS
WITH RECOVERY OF ALKALI METAL FROM CHAR" (attorney docket no.
FN-0015 US NP1); and U.S. application Ser. No. ______, (filed
concurrently herewith), entitled "CATALYTIC GASIFICATION PROCESS
WITH RECOVERY OF ALKALI METAL FROM CHAR" (attorney docket no.
FN-0016 US NP1).
FIELD OF THE INVENTION
[0003] The present invention relates to a catalytic gasification
process that involves the extraction and recovery of alkali metal
from char that remains following catalytic gasification of a
carbonaceous composition. Further, the invention relates to
processes for extracting and recovering alkali metal from char by
reacting a slurry of char particulate with carbon dioxide under
suitable temperature and pressure so as to convert insoluble alkali
metal compounds contained in the insoluble char particulate to
soluble alkali metal compounds.
BACKGROUND OF THE INVENTION
[0004] In view of numerous factors such as higher energy prices and
environmental concerns, the production of value-added gaseous
products from lower-fuel-value carbonaceous feedstocks, such as
petroleum coke and coal, is receiving renewed attention. The
catalytic gasification of such materials to produce methane and
other value-added gases is disclosed, for example, in U.S. Pat. No.
3,828,474, U.S. Pat. No. 3,998,607, U.S. Pat. No. 4,057,512, U.S.
Pat. No. 4,092,125, U.S. Pat. No. 4,094,650, U.S. Pat. No.
4,204,843, U.S. Pat. No. 4,468,231, U.S. Pat. No. 4,500,323, U.S.
Pat. No. 4,541,841, U.S. Pat. No. 4,551,155, U.S. Pat. No.
4,558,027, U.S. Pat. No. 4,606,105, U.S. Pat. No. 4,617,027, U.S.
Pat. No. 4,609,456, U.S. Pat. No. 5,017,282, U.S. Pat. No.
5,055,181, U.S. Pat. No. 6,187,465, U.S. Pat. No. 6,790,430, U.S.
Pat. No. 6,894,183, U.S. Pat. No. 6,955,695, US2003/0167961A1,
US2006/0265953A1, US2007/000177A1, US2007/083072A1,
US2007/0277437A1 and GB 1599932.
[0005] Gasification of a carbonaceous material, such as coal or
petroleum coke, can be catalyzed by loading the carbonaceous
material with a catalyst comprising an alkali metal source.
US2007/0000177A1 and US2007/0083072A1, both incorporated herein by
reference, disclose the alkali-metal-catalyzed gasification of
carbonaceous materials. Lower-fuel-value carbon sources, such as
coal, typically contain quantities of inorganic matter, including
compounds of silicon, aluminum, calcium, iron, vanadium, sulfur,
and the like. This inorganic content is referred to as ash. Silica
and alumina are especially common ash components. At temperatures
above 500-600.degree. C., alkali metal compounds can react with the
alumina and silica to form alkali metal aluminosilicates. As an
aluminosilicate, the alkali metal compound is substantially
insoluble in water and has little effectiveness as a gasification
catalyst.
[0006] At typical gasification temperatures, most components of ash
are not gasified, and thus build up with other compounds in the
gasification reactor as a solid residue referred to as char. For
catalytic gasification, char generally includes ash, unconverted
carbonaceous material, and alkali metal compounds (from the
catalyst). The char must be periodically withdrawn from the reactor
through a solid purge. The char may contain substantial quantities
of alkali metal compounds. The alkali metal compounds may exist in
the char as soluble species, such as potassium carbonate, but may
also exist as insoluble species, such as potassium aluminosilicate
(e.g., kaliophilite). It is desirable to recover the soluble and
the insoluble alkali metal compounds from the solid purge for
subsequent reuse as a gasification catalyst. A need remains for
efficient processes for recovering soluble and insoluble alkali
metal compounds from char. Such processes should effect substantial
recovery of alkali metal compounds from the char, minimize the
complexity of the processing steps, reduce the use of consumable
raw materials, and generate few waste products that require
disposal.
SUMMARY OF THE INVENTION
[0007] The present invention provides processes for converting a
carbonaceous composition into a plurality of gaseous products with
recovery of an alkali metal compounds that can be reused as a
gasification catalyst. The invention further provides processes for
extracting and recovering catalytically useful alkali metal
compounds from soluble and insoluble alkali metal compounds
contained in char, where the processes involve thermal quenching of
the char in an aqueous medium followed by treatment of the char
particulate with carbon dioxide gas under hydrothermal
conditions.
[0008] In a first aspect, the invention provides a process for
extracting and recovering alkali metal from a char, the char
comprising (i) one or more soluble alkali metal compounds and (ii)
insoluble matter comprising one or more insoluble alkali metal
compounds, the process comprising the steps of: (a) providing the
char at an elevated temperature ranging from 50.degree. C. to about
600.degree. C.; (b) quenching the char in an aqueous medium to
fracture the char and form a quenched char slurry; (c) contacting
the quenched char slurry with an alkali metal hydroxide under
suitable pressure and temperature so as to convert at least a
portion of the insoluble alkali metal compounds to one or more
soluble alkali metal compounds, and produce a first leached slurry
comprising the soluble alkali metal compounds and residual
insoluble matter; (d) contacting the first leached slurry with
carbon dioxide under suitable pressure and temperature so as to
convert at least a portion of the insoluble alkali metal compounds
to one or more soluble alkali metal compounds, and produce a second
leached slurry comprising the soluble alkali metal compounds and
residual insoluble matter; (e) degassing the second leached slurry
under suitable pressure and temperature so as to remove a
substantial portion of the excess carbon dioxide and hydrogen
sulfide, if present, and produce a degassed second leached slurry;
(f) separating the degassed second leached slurry into a first
liquid stream and a residual insoluble matter stream, the first
liquid stream comprising a predominant portion of the soluble
alkali metal compounds from the degassed second leached slurry, and
the residual insoluble matter stream comprising residual soluble
alkali metal compounds and residual insoluble alkali metal
compounds; (g) recovering the first liquid stream; and (h) washing
the residual insoluble matter stream with an aqueous medium to
produce a first wash stream comprising substantially all of the
residual soluble alkali metal compounds from the residual insoluble
matter stream, wherein the quenching and contacting is performed in
the substantial absence of gaseous oxygen.
[0009] In a second aspect, the invention provides a process for
catalytically converting a carbonaceous composition, in the
presence of an alkali metal gasification catalyst, into a plurality
of gaseous products, the process comprising the steps of: (a)
supplying a carbonaceous composition to a gasification reactor, the
carbonaceous composition comprising an ash; (b) reacting the
carbonaceous composition in the gasification reactor in the
presence of steam and an alkali metal gasification catalyst under
suitable temperature and pressure to form (i) a char comprising
alkali metal from the alkali metal gasification catalyst in the
form of one or more soluble alkali metal compounds and one or more
insoluble alkali metal compounds, and (ii) a plurality of gaseous
products comprising methane and one or more of hydrogen, carbon
monoxide, carbon dioxide, hydrogen sulfide, ammonia, and other
higher hydrocarbons; (c) removing a portion of the char from the
gasification reactor; (d) extracting and recovering a substantial
portion of the alkali metal from the char according to any process
of the first aspect of the invention; and (e) at least partially
separating the plurality of gaseous products to produce a stream
comprising a predominant amount of one of the gaseous products.
[0010] The process can be run continuously, and the recovered
alkali metal can be recycled back into the process to minimize the
amount of makeup catalyst required.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 provides a schematic diagram for one example of a
process for recovering alkali metal from char for reuse as a
catalyst in a catalytic gasification process.
DETAILED DESCRIPTION
[0012] The present invention relates to processes for the catalytic
conversion of a carbonaceous composition into a plurality of
gaseous products with substantial recovery of alkali metal used as
the gasification catalyst. The alkali metal is recovered from char
that develops as a result of the catalyzed gasification of a
carbonaceous material in a gasification reactor. The alkali metal
may exist in the char in either water-soluble or water-insoluble
forms. The present invention provides efficient processes for
extracting and recovering substantially all of the soluble and
insoluble alkali metal from char. Among other steps, these
processes include the quenching of the char in an aqueous solution
to fracture the char, dissolving substantially all of the
water-soluble alkali metal compounds, and forming a slurry of the
quenched char, and the reacting of a char slurry with an alkali
metal hydroxide followed by carbon dioxide at suitable pressures
and temperatures to solubilize and extract insoluble alkali metal
compounds. In this manner, soluble and insoluble alkali metal
compounds are substantially removed from char using simplified
processes that require few consumable raw materials.
[0013] The present invention can be practiced, for example, using
any of the developments to catalytic gasification technology
disclosed in commonly owned US2007/0000177A1, US2007/0083072A1 and
US2007/0277437A1; and U.S. patent application Ser. No. 12/178,380
(filed 23 Jul. 2008), Ser. No. 12/234,012 (filed 19 Sep. 2008) and
Ser. No. 12/234,018 (filed 19 Sep. 2008). Moreover, the present
invention can be practiced using developments described in the
following U.S. Patent Applications, each of which was filed on even
date herewith and is hereby incorporated herein by reference: Ser.
No. ______, entitled "PETROLEUM COKE COMPOSITIONS FOR CATALYTIC
GASIFICATION" (attorney docket no. FN-0008 US NP1); Ser. No.
______, entitled "STEAM GENERATING SLURRY GASIFIER FOR THE
CATALYTIC GASIFICATION OF A CARBONACEOUS FEEDSTOCK" (attorney
docket no. FN-0017 US NP1); Ser. No. ______, entitled "PETROLEUM
COKE COMPOSITIONS FOR CATALYTIC GASIFICATION" (attorney docket no.
FN-0011 US NP 1); Ser. No. ______, entitled "COAL COMPOSITIONS FOR
CATALYTIC GASIFICATION" (attorney docket no. FN-0009 US NP1); Ser.
No. ______, entitled "PROCESSES FOR MAKING SYNTHESIS GAS AND
SYNGAS-DERIVED PRODUCTS" (attorney docket no. FN-0010 US NP1); Ser.
No. ______, entitled "CARBONACEOUS FUELS AND PROCESSES FOR MAKING
AND USING THEM" (attorney docket no. FN-0013 US NP1); and Ser. No.
______, entitled "PROCESSES FOR MAKING SYNGAS-DERIVED PRODUCTS"
(attorney docket no. FN-0012 US NP1).
[0014] All publications, patent applications, patents and other
references mentioned herein, if not otherwise indicated, are
explicitly incorporated by reference herein in their entirety for
all purposes as if fully set forth.
[0015] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this disclosure belongs. In case
of conflict, the present specification, including definitions, will
control.
[0016] Except where expressly noted, trademarks are shown in upper
case.
[0017] Although methods and materials similar or equivalent to
those described herein can be used in the practice or testing of
the present disclosure, suitable methods and materials are
described herein.
[0018] Unless stated otherwise, all percentages, parts, ratios,
etc., are by weight.
[0019] When an amount, concentration, or other value or parameter
is given as a range, or a list of upper and lower values, this is
to be understood as specifically disclosing all ranges formed from
any pair of any upper and lower range limits, regardless of whether
ranges are separately disclosed. Where a range of numerical values
is recited herein, unless otherwise stated, the range is intended
to include the endpoints thereof, and all integers and fractions
within the range. It is not intended that the scope of the present
disclosure be limited to the specific values recited when defining
a range.
[0020] When the term "about" is used in describing a value or an
end-point of a range, the disclosure should be understood to
include the specific value or end-point referred to.
[0021] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article, or apparatus that comprises a
list of elements is not necessarily limited to only those elements
but can include other elements not expressly listed or inherent to
such process, method, article, or apparatus. Further, unless
expressly stated to the contrary, "or" refers to an inclusive or
and not to an exclusive or. For example, a condition A or B is
satisfied by any one of the following: A is true (or present) and B
is false (or not present), A is false (or not present) and B is
true (or present), and both A and B are true (or present).
[0022] The use of "a" or "an" to describe the various elements and
components herein is merely for convenience and to give a general
sense of the disclosure. This description should be read to include
one or at least one and the singular also includes the plural
unless it is obvious that it is meant otherwise.
[0023] The materials, methods, and examples herein are illustrative
only and, except as specifically stated, are not intended to be
limiting.
Carbonaceous Composition
[0024] The term "carbonaceous material" or "carbonaceous
composition" as used herein includes a carbon source, typically
coal, petroleum coke, asphaltene and/or liquid petroleum residue,
but may broadly include any source of carbon suitable for
gasification, including biomass. The carbonaceous composition will
generally include at least some ash, typically at least about 3 wt
% ash (based on the weight of the carbonaceous composition).
[0025] The term "petroleum coke" as used herein includes both (i)
the solid thermal decomposition product of high-boiling hydrocarbon
fractions obtained in petroleum processing (heavy residues--"resid
petcoke") and (ii) the solid thermal decomposition product of
processing tar sands (bituminous sands or oil sands--"tar sands
petcoke"). Such carbonization products include, for example, green,
calcined, needle and fluidized bed petroleum coke.
[0026] Resid petcoke can be derived from a crude oil, for example,
by coking processes used for upgrading heavy-gravity residual crude
oil, which petroleum coke contains ash as a minor component,
typically about 1.0 wt % or less, and more typically about 0.5 wt %
of less, based on the weight of the coke. Typically, the ash in
such lower-ash cokes predominantly comprises metals such as nickel
and vanadium.
[0027] Tar sands petcoke can be derived from an oil sand, for
example, by coking processes used for upgrading oil sand. Tar sands
petcoke contains ash as a minor component, typically in the range
of about 2 wt % to about 12 wt %, and more typically in the range
of about 4 wt % to about 12 wt %, based on the overall weight of
the tar sands petcoke. Typically, the ash in such higher-ash cokes
predominantly comprises materials such as compounds of silicon
and/or aluminum.
[0028] The petroleum coke can comprise at least about 70 wt %
carbon, at least about 80 wt % carbon, or at least about 90 wt %
carbon, based on the total weight of the petroleum coke. Typically,
the petroleum coke comprises less than about 20 wt % percent
inorganic compounds, based on the weight of the petroleum coke.
[0029] The term "asphaltene" as used herein is an aromatic
carbonaceous solid at room temperature, and can be derived, from
example, from the processing of crude oil and crude oil tar
sands.
[0030] The term "liquid petroleum residue" as used herein includes
both (i) the liquid thermal decomposition product of high-boiling
hydrocarbon fractions obtained in petroleum processing (heavy
residues--"resid liquid petroleum residue") and (ii) the liquid
thermal decomposition product of processing tar sands (bituminous
sands or oil sands--"tar sands liquid petroleum residue"). The
liquid petroleum residue is substantially non-solid; for example,
it can take the form of a thick fluid or a sludge.
[0031] Resid liquid petroleum residue can be derived from a crude
oil, for example, by processes used for upgrading heavy-gravity
crude oil distillation residue. Such liquid petroleum residue
contains ash as a minor component, typically about 1.0 wt % or
less, and more typically about 0.5 wt % of less, based on the
weight of the residue. Typically, the ash in such lower-ash
residues predominantly comprises metals such as nickel and
vanadium.
[0032] Tar sands liquid petroleum residue can be derived from an
oil sand, for example, by processes used for upgrading oil sand.
Tar sands liquid petroleum residue contains ash as a minor
component, typically in the range of about 2 wt % to about 12 wt %,
and more typically in the range of about 4 wt % to about 12 wt %,
based on the overall weight of the residue. Typically, the ash in
such higher-ash residues predominantly comprises materials such as
compounds of silicon and/or aluminum.
[0033] The term "coal" as used herein means peat, lignite,
sub-bituminous coal, bituminous coal, anthracite, or mixtures
thereof. In certain embodiments, the coal has a carbon content of
less than about 85%, or less than about 80%, or less than about
75%, or less than about 70%, or less than about 65%, or less than
about 60%, or less than about 55%, or less than about 50% by
weight, based on the total coal weight. In other embodiments, the
coal has a carbon content ranging up to about 85%, or up to about
80%, or up to about 75% by weight, based on total coal weight.
Examples of useful coals include, but are not limited to, Illinois
#6, Pittsburgh #8, Beulah (N.D.), Utah Blind Canyon, and Powder
River Basin (PRB) coals. Anthracite, bituminous coal,
sub-bituminous coal, and lignite coal may contain about 10 wt %,
from about 5 to about 7 wt %, from about 4 to about 8 wt %, and
from about 9 to about 11 wt %, ash by total weight of the coal on a
dry basis, respectively. However, the ash content of any particular
coal source will depend on the rank and source of the coal, as is
familiar to those skilled in the art. See, for example, "Coal Data:
A Reference", Energy Information Administration, Office of Coal,
Nuclear, Electric and Alternate Fuels, U.S. Department of Energy,
DOE/EIA-0064(93), February 1995.
[0034] The term "ash" as used herein includes inorganic compounds
that occur within the carbon source. The ash typically includes
compounds of silicon, aluminum, calcium, iron, vanadium, sulfur,
and the like. Such compounds include inorganic oxides, such as
silica, alumina, ferric oxide, etc., but may also include a variety
of minerals containing one or more of silicon, aluminum, calcium,
iron, and vanadium. The term "ash" may be used to refer to such
compounds present in the carbon source prior to gasification, and
may also be used to refer to such compounds present in the char
after gasification.
Alkali Metal Compounds
[0035] As used herein, the terms "alkali metal compound" refers to
a free alkali metal, as a neutral atom or ion, or to a molecular
entity, such as a salt, that contains an alkali metal.
Additionally, the term "alkali metal" may refer either to an
individual alkali metal compound, as heretofore defined, or may
also refer to a plurality of such alkali metal compounds. An alkali
metal compound capable of being substantially solubilized by water
is referred to as a "soluble alkali metal compound." Examples of a
soluble alkali metal compound include free alkali metal cations and
water-soluble alkali metal salts, such as potassium carbonate,
potassium hydroxide, and the like. An alkali metal compound
incapable of being substantially solubilized by water is referred
to as an "insoluble alkali metal compound." Examples of an
insoluble alkali metal compound include water-insoluble alkali
metal salts and/or molecular entities, such as potassium
aluminosilicate.
[0036] Alkali metal compounds suitable for use as a gasification
catalyst include compounds selected from the group consisting of
alkali metal carbonates, bicarbonates, formates, oxalates, amides,
hydroxides, acetates, halides, nitrates, sulfides, and
polysulfides. For example, the catalyst can comprise one or more of
Na.sub.2CO.sub.3, K.sub.2CO.sub.3, Rb.sub.2CO.sub.3,
Li.sub.2CO.sub.3, Cs.sub.2CO.sub.3, NaOh, KOH, RbOH, or CsOH, and
particularly, potassium carbonate and/or potassium hydroxide.
Catalyst-Loaded Carbonaceous Feedstock
[0037] The carbonaceous composition is generally loaded with an
amount of an alkali metal. Typically, the quantity of the alkali
metal in the composition is sufficient to provide a ratio of alkali
metal atoms to carbon atoms ranging from about 0.01, or from about
0.02, or from about 0.03, or from about 0.04, to about 0.06, or to
about 0.07, or to about 0.08. Further, the alkali metal is
typically loaded onto a carbon source to achieve an alkali metal
content of from about 3 to about 10 times more than the combined
ash content of the carbonaceous material (e.g., coal and/or
petroleum coke), on a mass basis.
[0038] Any methods known to those skilled in the art can be used to
associate one or more gasification catalysts with the carbonaceous
composition. Such methods include, but are not limited to, admixing
with a solid catalyst source and impregnating the catalyst onto the
carbonaceous solid. Several impregnation methods known to those
skilled in the art can be employed to incorporate the gasification
catalysts. These methods include, but are not limited to, incipient
wetness impregnation, evaporative impregnation, vacuum
impregnation, dip impregnation, and combinations of these methods.
Gasification catalysts can be impregnated into the carbonaceous
solids by slurrying with a solution (e.g., aqueous) of the
catalyst.
[0039] That portion of the carbonaceous feedstock of a particle
size suitable for use in the gasifying reactor can then be further
processed, for example, to impregnate one or more catalysts and/or
cocatalysts by methods known in the art, for example, as disclosed
in U.S. Pat. No. 4,069,304 and U.S. Pat. No. 5,435,940; previously
incorporated U.S. Pat. No. 4,092,125, U.S. Pat. No. 4,468,231 and
U.S. Pat. No. 4,551,155; previously incorporated U.S. patent
application Ser. Nos. 12/234,012 and 12/234,018; and previously
incorporated U.S. patent applications Ser. No. ______, entitled
"PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION" (attorney
docket no. FN-0008 US NP1), Ser. No. ______, entitled "PETROLEUM
COKE COMPOSITIONS FOR CATALYTIC GASIFICATION" (attorney docket no.
FN-0011 US NP1), Ser. No. ______, entitled "CONTINUOUS PROCESS FOR
CONVERTING CARBONACEOUS FEEDSTOCK INTO GASEOUS PRODUCTS" (attorney
docket no. FN-0018 US NP1), and Ser. No. ______, entitled "COAL
COMPOSITIONS FOR CATALYTIC GASIFICATION" (attorney docket no.
FN-0009 US NP1).
[0040] One particular method suitable for combining the coal
particulate with a gasification catalyst to provide a catalyzed
carbonaceous feedstock where the catalyst has been associated with
the coal particulate via ion exchange is described in previously
incorporated U.S. patent application Ser. No. 12/178,380 (filed 23
Jul. 2008). The catalyst loading by ion exchange mechanism is
maximized (based on adsorption isotherms specifically developed for
the coal), and the additional catalyst retained on the wet cake,
including inside the pores, is controlled so that the total
catalyst target value is obtained in a controlled manner. Such
loading provides a catalyzed coal particulate as a wet cake. The
catalyst loaded and dewatered wet coal cake typically contains, for
example, about 50% moisture. The total amount of catalyst loaded is
controlled by controlling the concentration of catalyst components
in the solution, as well as the contact time, temperature and
method, as can be readily determined by those of ordinary skill in
the relevant art based on the characteristics of the starting
coal.
[0041] The catalyzed feedstock can be stored for future use or
transferred to a feed operation for introduction into the
gasification reactor. The catalyzed feedstock can be conveyed to
storage or feed operations according to any methods known to those
skilled in the art, for example, a screw conveyer or pneumatic
transport.
Catalytic Gasification Methods
[0042] The extraction and recovery methods of the present invention
are particularly useful in integrated gasification processes for
converting carbonaceous feedstocks, such as petroleum coke, liquid
petroleum residue and/or coal, to combustible gases, such as
methane. The gasification reactors for such processes are typically
operated at moderately high pressures and temperature, requiring
introduction of a carbonaceous material (i.e. a feedstock) to the
reaction zone of the gasification reactor while maintaining the
required temperature, pressure, and flow rate of the feedstock.
Those skilled in the art are familiar with feed systems for
providing feedstocks to high pressure and/or temperature
environments, including, star feeders, screw feeders, rotary
pistons, and lock-hoppers. It should be understood that the feed
system can include two or more pressure-balanced elements, such as
lock hoppers, which would be used alternately.
[0043] Suitable gasification reactors include counter-current fixed
bed, co-current fixed bed, fluidized bed, entrained flow, and
moving bed reactors. The gasification reactor typically will be
operated at moderate temperatures of at least about 450.degree. C.,
or of at least about 600.degree. C. or above, to about 900.degree.
C., or to about 750.degree. C., or to about 700.degree. C.; and at
pressures of at least about 50 psig, or at least about 200 psig, or
at least about 400 psig, to about 1000 psig, or to about 700 psig,
or to about 600 psig.
[0044] The gas utilized in the gasification reactor for
pressurization and reactions of the particulate composition
typically comprises steam, and optionally, oxygen or air, and are
supplied to the reactor according to methods known to those skilled
in the art. For example, any of the steam boilers known to those
skilled in the art can supply steam to the reactor. Such boilers
can be powered, for example, through the use of any carbonaceous
material such as powdered coal, biomass etc., and including but not
limited to rejected carbonaceous materials from the particulate
composition preparation operation (e.g., fines, supra). Steam can
also be supplied from a second gasification reactor coupled to a
combustion turbine where the exhaust from the reactor is thermally
exchanged to a water source and produce steam.
[0045] Recycled steam from other process operations can also be
used for supplying steam to the reactor. For example, when the
slurried particulate composition is dried with a fluid bed slurry
drier, as discussed previously, the steam generated through
vaporization can be fed to the gasification reactor.
[0046] The small amount of required heat input for the catalytic
coal gasification reaction can be provided by superheating a gas
mixture of steam and recycle gas feeding the gasification reactor
by any method known to one skilled in the art. In one method,
compressed recycle gas of CO and H.sub.2 can be mixed with steam
and the resulting steam/recycle gas mixture can be further
superheated by heat exchange with the gasification reactor effluent
followed by superheating in a recycle gas furnace.
[0047] A methane reformer can be included in the process to
supplement the recycle CO and H.sub.2 fed to the reactor to ensure
that the reaction is run under thermally neutral (adiabatic)
conditions. In such instances, methane can be supplied for the
reformer from the methane product, as described below.
[0048] Reaction of the particulate composition under the described
conditions typically provides a crude product gas and a char. The
char produced in the gasification reactor during the present
processes typically is removed from the gasification reactor for
sampling, purging, and/or catalyst recovery. Methods for removing
char are well known to those skilled in the art. One such method
taught by EP-A-0102828, for example, can be employed. The char can
be periodically withdrawn from the gasification reactor through a
lock hopper system, although other methods are known to those
skilled in the art.
[0049] Crude product gas effluent leaving the gasification reactor
can pass through a portion of the gasification reactor which serves
as a disengagement zone where particles too heavy to be entrained
by the gas leaving the gasification reactor (i.e., fines) are
returned to the fluidized bed. The disengagement zone can include
one or more internal cyclone separators or similar devices for
removing fines and particulates from the gas. The gas effluent
passing through the disengagement zone and leaving the gasification
reactor generally contains CH.sub.4, CO.sub.2, H.sub.2 and CO,
H.sub.2S, NH.sub.3, unreacted steam, entrained fines, and other
contaminants such as COS.
[0050] The gas stream from which the fines have been removed can
then be passed through a heat exchanger to cool the gas and the
recovered heat can be used to preheat recycle gas and generate high
pressure steam. Residual entrained fines can also be removed by any
suitable means such as external cyclone separators followed by
Venturi scrubbers. The recovered fines can be processed to recover
alkali metal catalyst.
[0051] The gas stream exiting the Venturi scrubbers can be fed to
COS hydrolysis reactors for COS removal (sour process) and further
cooled in a heat exchanger to recover residual heat prior to
entering water scrubbers for ammonia recovery, yielding a scrubbed
gas comprising at least H.sub.2S, CO.sub.2, CO, H.sub.2 and
CH.sub.4. Methods for COS hydrolysis are known to those skilled in
the art, for example, see U.S. Pat. No. 4,100,256.
[0052] The residual heat from the scrubbed gas can be used to
generate low pressure steam. Scrubber water and sour process
condensate can be processed to strip and recover H.sub.2S, CO.sub.2
and NH.sub.3; such processes are well known to those skilled in the
art. NH.sub.3 can typically be recovered as an aqueous solution
(e.g., 20 wt %).
[0053] A subsequent acid gas removal process can be used to remove
H.sub.2S and CO.sub.2 from the scrubbed gas stream by a physical
absorption method involving solvent treatment of the gas to give a
cleaned gas stream. Such processes involve contacting the scrubbed
gas with a solvent such as monoethanolamine, diethanolamine,
methyldiethanolamine, diisopropylamine, diglycolamine, a solution
of sodium salts of amino acids, methanol, hot potassium carbonate
or the like. One method can involve the use of Selexol.RTM. (UOP
LLC, Des Plaines, Ill. USA) or Rectisol.RTM. (Lurgi AG, Frankfurt
am Main, Germany) solvent having two trains; each train consisting
of an H.sub.2S absorber and a CO.sub.2 absorber. The spent solvent
containing H.sub.2S, CO.sub.2 and other contaminants can be
regenerated by any method known to those skilled in the art,
including contacting the spent solvent with steam or other
stripping gas to remove the contaminants or by passing the spent
solvent through stripper columns. Recovered acid gases can be sent
for sulfur recovery processing. The resulting cleaned gas stream
contains mostly CH.sub.4, H.sub.2 and CO and, typically, small
amounts of CO.sub.2 and H.sub.2O. Any recovered H.sub.2S from the
acid gas removal and sour water stripping can be converted to
elemental sulfur by any method known to those skilled in the art,
including the Claus process. Sulfur can be recovered as a molten
liquid.
[0054] The cleaned gas stream can be further processed to separate
and recover CH.sub.4 by any suitable gas separation method known to
those skilled in the art including, but not limited to, cryogenic
distillation and the use of molecular sieves or ceramic membranes.
One method for recovering CH.sub.4 from the cleaned gas stream
involves the combined use of molecular sieve absorbers to remove
residual H.sub.2O and CO.sub.2 and cryogenic distillation to
fractionate and recover CH.sub.4. Typically, two gas streams can be
produced by the gas separation process, a methane product stream
and a syngas stream (H.sub.2 and CO). The syngas stream can be
compressed and recycled to the gasification reactor. If necessary,
a portion of the methane product can be directed to a reformer, as
discussed previously and/or a portion of the methane product can be
used as plant fuel.
Char
[0055] The term "char" as used herein includes mineral ash,
unconverted carbonaceous material, and water-soluble alkali metal
compounds and water-insoluble alkali metal compounds within the
other solids. The char produced in the gasification reactor
typically is removed from the gasification reactor for sampling,
purging, and/or catalyst recovery. Methods for removing char are
well known to those skilled in the art. One such method, described
in previously incorporated EP-A-0102828, for example, can be
employed. The char can be periodically withdrawn from the
gasification reactor through a lock hopper system, although other
methods are known to those skilled in the art.
Catalyst Recovery
[0056] Alkali metal salts, particularly sodium and potassium salts,
are useful as catalysts in catalytic coal gasification reactions.
Alkali metal catalyst-loaded carbonaceous mixtures are generally
prepared and then introduced into a gasification reactor, or can be
formed in situ by introducing alkali metal catalyst and
carbonaceous particles separately into the reactor.
[0057] After gasification, the alkali metal may exist in the char
as species that are either soluble or insoluble. In particular,
alkali metal can react with mineral ash at temperatures above about
500-600.degree. C. to form insoluble alkali metal aluminosilicates,
such as kaliophilite. As an aluminosilicate, or other insoluble
compounds, the alkali metal is ineffective as a catalyst.
[0058] As discussed, supra, char is periodically removed from the
gasification reactor through a solid purge. Because the char has a
substantial quantity of soluble and insoluble alkali metal, it is
desirable to recover the alkali metal from the char for reuse as a
gasification catalyst. Catalyst loss in the solid purge must
generally be compensated for by a reintroduction of additional
catalyst, i.e., a catalyst make-up stream. Processes have been
developed to recover alkali metal from the solid purge in order to
reduce raw material costs and to minimize environmental impact of a
catalytic gasification process. For example, a recovery and
recycling process is described in previously incorporated
US2007/0277437A1.
[0059] The present invention provides a novel process for
extracting and recovering soluble and insoluble alkali metal from
char.
1. Char Quenching (100)
[0060] Referring to FIG. 1, a char (10) removed from a gasification
reactor can be quenched in an aqueous medium (15) by any suitable
means known to those of skill in the art to fracture the char and
form a quenched char slurry (20) where the quenched char slurry
comprising soluble alkali metal compounds and insoluble matter
comprising insoluble alkali metal compounds. One particularly
useful quenching method is described in previously incorporated
US2007/0277437A1.
[0061] The invention places no particular limits on the ratio of
aqueous medium to char, or on the temperature of the aqueous
medium. In some embodiments, however, the wt/wt ratio of water in
the aqueous medium to the water-insoluble component of the char
ranges from about 3:1, or from about 5:1, up to about 7:1, or up to
about 15:1. Additionally, in some embodiments, the aqueous medium
has a temperature that ranges from about 95.degree. C. up to about
110.degree. C., or up to about 140.degree. C., or up to about
200.degree. C., or up to about 300.degree. C. The pressure need not
be elevated above atmospheric pressure. In some embodiments,
however, the quenching occurs at pressures higher than atmospheric
pressure. For example, the quenching may occur at pressures up to
about 25 psig, or up to about 40 psig, or up to about 60 psig, or
up to about 80 psig, or up to about 400 psig (including the partial
pressure of CO.sub.2). The quenching process preferably occurs
under a stream of gas that is substantially free of oxygen or other
oxidants and comprises carbon dioxide.
[0062] The quenching step fractures the heated char by dissolving
the rather large amount of water soluble alkali metal compounds
(e.g., carbonates) that holds it together such that a quenched char
slurry results. The char leaves the gasification reactor at high
temperature, and it is typically cooled down. For example, the
temperature of the char may range from about 35.degree. C., or from
about 50.degree. C., or from about 75.degree. C., up to about
200.degree. C., or up to about 300.degree. C., or up to about
400.degree. C. In some embodiments, the char has an elevated
temperature ranging from about 50.degree. C. to about 600.degree.
C. The quenched char slurry comprises both soluble alkali metal and
insoluble alkali metal. As the char fractures, soluble alkali metal
leaches into the aqueous solution.
[0063] The char quenching is preferably performed in the
substantial absence of gaseous oxygen. For example, the leaching
environment has less than about 1% gaseous oxygen, or less than
about 0.5% gaseous oxygen, less than about 0.1% gaseous oxygen,
less than about 0.01% gaseous oxygen, or less than about 0.005%
gaseous oxygen, based on the total volume.
[0064] In some embodiments, the aqueous medium used in the
quenching may comprise a wash stream that results from a washing
step of the present invention, described, infra.
2. Contacting of Quenched Char Slurry with an Alkali Metal
Hydroxide (200)
[0065] The quenched char slurry (20) can be contacted with an
alkali metal hydroxide (25) under suitable pressure and temperature
so as to convert at least a portion of the insoluble alkali metal
compounds in the insoluble matter to one or more soluble alkali
metal compounds and produce a first leached slurry (30) comprising
soluble alkali metal compounds and a partially extracted insoluble
matter comprising insoluble alkali metal compounds.
[0066] The contacting of the quenched char slurry (20) with the
alkali metal hydroxide (25) typically involves contacting the
slurry at an elevated temperature with an aqueous solution of the
alkali metal hydroxide such that at least a portion of the alkali
metal from the insoluble matter is extracted. Generally, the alkali
metal hydroxide is provided to the quenched char slurry (20) as an
aqueous solution having a concentration ranging form about 1 to
about 10 M alkali metal hydroxide. The alkali metal hydroxide can
comprise any of LiOH, NaOH, KOH, RbOH, and CsOH, as well as
mixtures thereof, preferably, the alkali metal comprises NaOH or
KOH. Most preferably the alkali metal hydroxide comprises KOH.
[0067] The quenched char slurry can be pressurized and heated by
the introduction of heated and pressurized steam. For example, the
temperature of the slurry can range from about 100.degree. C., or
from about 125.degree. C., or from about 150.degree. C., up to
about 240.degree. C., up to about 270.degree. C., or up to about
300.degree. C. In some embodiments, the slurry has an elevated
temperature ranging from about 150.degree. C. to about 240.degree.
C. In some embodiments, the slurry has an elevated temperature
ranging from about 100.degree. C. to about 150.degree. C.
[0068] In any combination with the preceding temperature ranges,
the slurry can be maintained at a pressure of from about 25 psig,
or from about 35 psig, or from about 50 psig, up to about 250 psig,
or up to 500 psig, or up to about 750 psig, or up to 1000 psig. In
some embodiments, the slurry may be maintained at a pressure of
from about 50 to 500 psig. In other embodiments, the slurry may be
maintained at a pressure of from about 50 to 250 psig.
[0069] The slurry can be maintained at an appropriate temperature
and pressure for a residence time ranging from about 1 minute, or
about 5 minutes, or about 15 minutes, or about 30 minutes, up to
about 60 minutes, or up to about 120 minutes, or up to about 150
minutes, or up to about 180 minutes. In some embodiments, the
slurry may be maintained at an appropriate temperature and pressure
for a residence time ranging from 30 minutes to 150 minutes.
[0070] In one embodiment, the contacting takes place in a
pressurized leaching operation using at least 2, and preferably 3,
continuous stirred-tank reactors (CSTRs), either in series (e.g.,
co-current), or a single horizontal pressure vessel with internal
weirs and stirrers to provide 3-6 internal stages for the slurry
(the gas phase may optionally be separated by stages).
3. Contacting of Quenched Char Slurry with Carbon Dioxide (300)
[0071] The contacting of the first leached slurry (30) with carbon
dioxide (35) occurs under pressure and temperature suitable to
convert at least a portion at least a portion, or even a
predominant portion, of the insoluble alkali metal compounds to one
or more soluble alkali metal compounds, and produce a second
leached slurry comprising the soluble alkali metal compounds and a
residual insoluble matter. In the alternative, this process step is
referred to as a first leaching or a first hydrothermal
leaching.
[0072] In some instances, as can be determined by one skilled in
the art, prior to contacting the first leached slurry with carbon
dioxide, the temperature and/or pressure of the first leached
slurry (30) can be reduced according to those methods known to
those skilled in the art. For example, the first leached slurry can
be flashed into a flash drum. Water can also be evaporated from the
first leached slurry (30) to increase the concentration of alkali
metals in the slurry solution. In one embodiment, the first leached
slurry may be cooled to a temperature ranging from about
120.degree. C. to 145.degree. C. and a pressure to 45 psig or less
prior to contacting the first leached slurry with carbon
dioxide.
[0073] The hydrothermal leaching process converts a portion of the
insoluble alkali metal compounds in the partially extracted
insoluble matter to one or more soluble alkali metal compounds, as
well as neutralizes excess alkalinity, hydrolyzes carbonates,
precipitates silica and/or alumina, and strips sulfidic sulfur as
hydrogen sulfide to yield a second leached slurry (40) comprising
soluble alkali metal compounds and a residual insoluble matter. The
alkali metal in the second leached slurry (40) comprises at least
potassium carbonate and the pH of the solution generally ranges
from about 7, or about 8, or about 9, up to about 10, or up to
about 11, or up to about 12.
[0074] The hydrothermal leaching may be performed by any suitable
means known to those of skill in the art for performing
hydrothermal leaching. For example, in some embodiments, the first
hydrothermal leaching step is carried out in three pressurized
continuous flow stirred tank reactors (CSTRs) in series (in three
co-current stages). In other embodiments, for example, the first
hydrothermal leaching step is carried out in a single horizontal
pressure leaching vessel with internal weirs and stirrers to
provide between 3-6 internal stages for the slurry.
[0075] The contacting of the carbon dioxide (35) with the first
leached slurry (30) may occur by any means known to those of skill
in the art suitable for introducing a gas into a slurry. Suitable
methods include, but are not limited to, solubilizing the gas under
pressure with gas-phase entrainment stirring or bubbling the gas
through the slurry.
[0076] For the first hydrothermal leaching step, suitable
temperatures and pressure (including partial pressures of various
gases), and the duration of the leaching may be selected based on
the knowledge of one skilled in the art. This choice may depend on,
among other factors, the composition of the carbonaceous feedstock:
Higher temperatures and/or pressures may be more suitable for
carbonaceous feedstock having higher mineral ash content (e.g.,
Powder River Basin coal with 7-10% ash). Suitable temperatures may,
for example, range from about 90.degree. C., or from about
100.degree. C., or from about 110.degree. C., up to about
120.degree. C., or up to about 130.degree. C., or up to about
140.degree. C., or up to about 160.degree. C. The leaching is
typically carried out in the presence of steam. Suitable partial
pressures of steam, for example, range from about 3 psig, or from
about 6 psig, up to about 14 psig, up to about 20 psig. Suitable
total pressures, for example, range from about 30 psig, or from
about 40 psig, or from about 50 psig, up to about 75 psig, or up to
about 90 psig, or up to about 110 psig. Suitable partial pressures
of carbon dioxide may, for example, range from about 25 psig, from
about 40 psig, or from about 60 psig, to about 100 psig, to about
120 psig, to about 140 psig, or to about 170 psig. Suitable
durations, for example, range from about 15 minutes, or from about
30 minutes, or from about 45 minutes, up to about 60 minutes, or up
to about 90 minutes, or up to about 120 minutes.
[0077] The hydrothermal leaching is performed in the substantial
absence of gaseous oxygen or other oxidants. For example, the
leaching environment has less than about 1% gaseous oxygen, or less
than about 0.5% gaseous oxygen, less than about 0.1% gaseous
oxygen, less than about 0.01% gaseous oxygen, or less than about
0.005% gaseous oxygen, based on the total volume.
[0078] The first leaching process converts at least a portion, or
even a predominant portion, of the insoluble alkali metal compounds
to one or more soluble alkali metal compounds. As used in this
first leaching process, the conversion of insoluble alkali metal
compounds to soluble alkali metal compounds generally involves the
chemical conversion of a water-insoluble alkali metal compound
(such as potassium aluminosilicate) into a water-soluble alkali
metal compound (such as potassium carbonate).
[0079] The amount of insoluble alkali metal compounds converted to
soluble alkali metal compounds in this leaching step will depend on
a variety of factors, including the composition of the char, the
temperature, the pressure (including the partial pressures of steam
and carbon dioxide), and the duration of the leaching operation.
The amount of insoluble alkali metal compound converted will also
depend on the composition of the insoluble alkali metal compounds
present in the char. Some insoluble alkali metal compounds, such as
kaliophilite, are more difficult to convert into soluble alkali
metal compounds than others. For example, the first leaching step
may convert at least about 5%, or at least about 10%, or at least
about 20%, or at least about 40%, or at least about 50%, or at
least about 60%, or at least about 70%, or at least about 80% of
the insoluble alkali metal compounds from the insoluble matter,
based on the total moles of insoluble alkali metal compounds in the
quenched char.
[0080] In some embodiments of the invention, the alkali metal
hydroxide contacting and/or the first hydrothermal leaching step is
combined with the char quenching step into a single step. In these
embodiments, the char quenching is performed at a pressure and
temperature more typical for the first hydrothermal leaching step.
Suitable temperatures may, for example, range from about 90.degree.
C., or from about 100.degree. C., or from about 110.degree. C., up
to about 120.degree. C., or up to about 130.degree. C., or up to
about 140.degree. C., or up to about 160.degree. C. Suitable total
pressures, for example, range from about 30 psig, or from about 40
psig, or from about 50 psig, up to about 75 psig, or up to about 90
psig, or up to about 110 psig. At these elevated temperatures and
pressures, the partial pressures of carbon dioxide and steam are
similar to those for the first leaching step. By performing the
char quenching under the temperature and pressure conditions
typical of the first leaching step, the two steps are effectively
combined. In these embodiments, the combined quenching/leaching
step substantially leaches the water-soluble alkali metal compounds
from the insoluble matter and converts at least a portion of the
insoluble alkali metal compounds in the char to one or more soluble
alkali metal compounds, and thereby produces a second leached
slurry comprising soluble alkali metal compounds and residual
insoluble matter.
[0081] By performing the alkali metal hydroxide hydrolysis and
carbonation prior to before filtration of the slurry, the bulk of
the slurry solids will act as a filtering aid for any fine (e.g.,
colloidal) silica and alumina precipitate.
4. Degassing (400)
[0082] The second leached slurry (40) is degassed under suitable
pressures and temperatures so as to remove a substantial portion of
the excess carbon dioxide and hydrogen sulfide, if present, and
produce a degassed second leached slurry (50).
[0083] Any suitable degassing methods known to those of skill in
the art may be used to perform the degassing step. The degassing
may be performed by pumping and heating the leached slurry and
flashing it into a flash drum. For these embodiments, a suitable
temperature may be, for example, about 130.degree. C. or higher, or
about 140.degree. C. or higher, or about 145.degree. C. or higher,
or about 150.degree. C. or higher. For these embodiments, after
flashing into the flash drum, the slurry temperature may drop to
120.degree. C. or less, or 110.degree. C. or less, or 100.degree.
C. or less, or 95.degree. C. or less. For these embodiments,
suitable pressures range from about 10 to about 20 psig, or at
about atmospheric pressure.
[0084] As necessary, depending on the pressure and temperature at
which any preceding steps are performed, the degassing may be
performed by feeding a heated pressurized solution into a series of
staged pressure let-down vessels equipped with stirring or other
recirculation mechanisms. In some embodiments, the slurry may be
cooled prior to being fed into a first pressure let-down vessel,
for example to a suitable temperature of about 170.degree. C. or
below, or to about 150.degree. C. or below, or to about 130.degree.
C. or below. Suitable pressures will depend on the pressure under
which the first hydrothermal leaching was performed. Suitable
pressures for degassing are, for example, about 300 psig or less,
or about 100 psig or less, or about 50 psig or less, or about 25
psig or less.
[0085] The off-stream gas may be handled by any means known to
those of skill in the art. For example, the off gases from a
let-down vessel may be fed, as needed, through gas/water breakdown
drums and the separated water recycled into the degassed slurry. In
some embodiments, the degassing apparatus is equipped with safety
features for handling hydrogen sulfide as an off gas.
[0086] The degassing step results in the substantial removal of
excess carbon dioxide. For example, the partial pressure of carbon
dioxide is reduced to less than about 10 psig, or less than about 5
psig, or less than about 2 psig. The degassing also results in the
substantial removal of excess hydrogen sulfide, if present. For
example, the partial pressure of hydrogen sulfide is reduced to
less than about 1 psig, or less than about 0.1 psig, less than
about 0.05 psig, or less than about 0.01 psig.
5. Separation and Recovery of Liquid from Partially Extracted
Insoluble Matter (500)
[0087] The degassed second leached slurry (50) is separated into a
first liquid stream (60) and a residual insoluble matter stream
(65). The first liquid stream comprises recovered soluble alkali
metal, including soluble alkali metal compounds that were converted
from insoluble alkali metal compounds in the char.
[0088] The residual insoluble matter steam comprises at least a
portion of the alkali metal contained in the insoluble matter of
the char. For example, the residual insoluble matter steam
comprises less than about 95 molar percent, or less than about 90
molar percent, or less than about 80 molar percent, or less than
about 60 molar percent, or less than about 50 molar percent, or
less than about 40 molar percent, or less than about 30 molar
percent, of the alkali metal contained in the insoluble matter of
the char. The residual insoluble matter stream may also comprise a
residual amount of soluble alkali metal compounds in addition to
residual insoluble alkali metal compounds.
[0089] The separation and recovery of the first liquid stream from
the residual insoluble matter stream (65) may be carried out by
typical methods of separating a liquid from a solid particulate.
Illustrative methods include, but are not limited to, filtration
(gravity or vacuum), centrifugation, use of a fluid press,
decantation, and use of hydrocyclones.
[0090] Separation and recovery steps are generally performed
following contacting of the insoluble matter with carbon dioxide
and degassing to remove excess carbon dioxide and hydrogen
sulfide.
[0091] The recovered first liquid stream will contain soluble
alkali metal compounds that may be captured for reuse as a
gasification catalyst. Methods for recovery of soluble alkali metal
from an aqueous solvent for reuse as a gasification catalyst are
known in the art. See, for example, previously incorporated
US2007/0277437A1.
[0092] The recovered first liquid stream comprises a predominant
portion of the soluble alkali metal compounds from the degassed
second leached slurry. For example, the first liquid stream
comprises at least about 50 molar percent, or at least about 55
molar percent, or at least about 60 molar percent, or at least
about 65 molar percent, or at least about 70 molar percent, of the
soluble alkali metal compounds from the degassed second leached
slurry.
6. Washing (600)
[0093] Following separation from the first liquid stream, the
residual insoluble matter stream (65) is produced comprising a
residual amount of soluble alkali metal compounds in addition to
residual insoluble alkali metal compounds. The residual insoluble
matter stream (65) can be washed with an aqueous medium (70) to
substantially recover the residual soluble alkali metal compounds
present in the residual insoluble matter as a first wash stream
(75). The residual soluble alkali metal compounds consists of
soluble alkali metal compounds that failed to separate into the
first liquid stream during separation (e.g., entrained aqueous
solution). The amount of entrained solution in the residual
insoluble matter stream will depend on the particle size of the
residual insoluble matter as well as the concentration of the
soluble alkali metal compounds in the entrained solution, as are
familiar to those skilled in the art.
[0094] In some embodiments of the invention, the residual insoluble
matter stream is washed with an aqueous medium to produce a first
wash stream comprising at least a portion, or even a predominant
portion, or substantially all of the residual soluble alkali metal
compounds in the residual insoluble matter stream. The first wash
stream may, for example, comprise more than about 60%, or more than
about 75%, or more than about 90%, or more than about 95%, of the
residual alkali metal in the residual insoluble matter stream,
based on the total weight of residual alkali metal.
[0095] As used herein, the term "washing" is not limited to a
single flush of the insoluble matter with an aqueous medium, such
as water. Rather, each washing step may include multiple staged
counter-washings of the insoluble matter. In some embodiments of
the invention, the washing of the residual insoluble matter stream
comprises at least two staged counter-washings. In some
embodiments, the washing of the residual insoluble matter stream
comprises at least five staged counter-washings. The washing may be
performed according to any suitable method known to those of skill
in the art. For example, the washing step may be performed using a
continuous multi-stage counter-current system whereby solids and
liquids travel in opposite directions. As known to those of skill
in the art, the multi-stage counter current wash system may include
mixers/settlers (CCD or decantation), mixers/filters,
mixers/hydrocyclones, mixers/centrifuges, belt filters, and the
like.
[0096] The first wash stream (75) is recovered by typical means of
separating a solid particulate from a liquid. Illustrative methods
include, but are not limited to, filtration (gravity or vacuum),
centrifugation, and use of a fluid press.
[0097] In some embodiments, the recovered first wash stream may be
used as at least part of the aqueous medium used for quenching the
char.
EXAMPLES
Example 1
Extraction of Soluble Potassium from High-KAlSiO.sub.4 Ash
Sample
[0098] An agglomerate char material was provided having a
composition especially concentrated in kaliophilite. By weight, the
sample was approximately 90% ash (including soluble and insoluble
potassium) and about 10% carbon. The material was ground to a
particle size (Dp80) of 68.5 microns. The sample was subjected to
water at 95.degree. C. in a nitrogen atmosphere. The sample was
filtered and dried. Analysis of the resulting sample indicated that
the amount of water-soluble potassium removed from the sample
amounted to 40.08 wt % (dry basis) of the original sample.
Example 2
Extraction of Insoluble Potassium from High-KAlSiO.sub.4 Ash
Sample
[0099] he post-treatment sample from Example 1 was used. The
hot-water-washed sample consisted of 78.20 wt % of ash and 8.99 wt
% fixed carbon. Analysis of the ash portion determined that the ash
contained 36.42 wt % of silica, 15.72 wt % of alumina, 18.48 wt %
of insoluble potassium oxide, 12.56 wt % of calcium oxide, 9.13 wt
% of ferric oxide, and trace quantities of other inorganic oxides.
SEM data confirmed that most of the insoluble potassium oxide in
the ash is tied up in KAlSiO.sub.4, primarily as kaliophilite and
kalsilite.
[0100] The post-treatment sample from Example 1 was provided to a
450 ml autoclave. KOH was added and supplemented with an amount of
potassium carbonate to simulate a recycle stream from washing, the
autoclave pressurized by the addition of CO.sub.2, and the system
was heated to 200.degree. C. for 3 hours. The leached slurries were
filtered, the solids washed, and the solutions and solids analyzed
to provide a material balance on potassium. The experimental
conditions yielded an incremental extraction of the insoluble
potassium species of 40%, based on the total weight of the starting
char.
Example 3
Extraction of Insoluble Potassium from Typical Char Sample
[0101] A char sample was provided from the gasification (87-89%
carbon conversion) of Class B catalyzed Powder River Basin coal.
The dry sample was determined to contain 34.4 wt % potassium. The
char sample was crushed and added to water to form a slurry in a
nitrogen atmosphere. The slurry sample was added to an autoclave
with KOH and additional water. The system was pressurized with
CO.sub.2 and heated for 90 minutes at 160.degree. C. The autoclave
was cooled to ambient temperature. The solid was filtered and
washed three times with water. Thus, the soluble potassium was
largely removed from the sample. The total potassium extraction was
92.0%.
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