U.S. patent application number 11/421507 was filed with the patent office on 2007-01-04 for mild catalytic steam gasification process.
Invention is credited to Edwin J. Hippo, Atul C. Sheth.
Application Number | 20070000177 11/421507 |
Document ID | / |
Family ID | 37587889 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070000177 |
Kind Code |
A1 |
Hippo; Edwin J. ; et
al. |
January 4, 2007 |
MILD CATALYTIC STEAM GASIFICATION PROCESS
Abstract
The present invention provides an improved alkali metal
catalyzed steam gasification process that utilizes a CO.sub.2 trap
material and/or a mineral binder material within the gasifier. The
process optimally achieves over 90% carbon conversion with over 80%
yield of methane. The raw gas product can be used directly as fuel.
The catalyst can be recovered from the solid purge and recycled to
the gasifier and/or the CO.sub.2 trap can be regenerated and
recycled to the gasifier.
Inventors: |
Hippo; Edwin J.; (Makanda,
IL) ; Sheth; Atul C.; (Fairfield, CA) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 WORLD FINANCIAL CENTER
NEW YORK
NY
10281-2101
US
|
Family ID: |
37587889 |
Appl. No.: |
11/421507 |
Filed: |
June 1, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60695994 |
Jul 1, 2005 |
|
|
|
Current U.S.
Class: |
48/210 |
Current CPC
Class: |
Y02E 20/18 20130101;
C10J 2300/0903 20130101; C10J 2300/0969 20130101; C10J 2300/093
20130101; C10J 3/06 20130101; C10J 2300/0983 20130101; C10J 3/463
20130101; C10J 2200/158 20130101; C10J 2300/1807 20130101 |
Class at
Publication: |
048/210 |
International
Class: |
C10J 3/00 20060101
C10J003/00 |
Claims
1. A method for catalytic gasification of carbonaceous material to
combustible gases, the method comprising: reacting carbonaceous
material and steam in the presence of an alkali catalyst at a
temperature in the range of from about 300.degree. C. to about
700.degree. C. to form a gas comprising CO.sub.2, CH.sub.4,
H.sub.2O and H.sub.2; combining said CO.sub.2 in said gas with a
CO.sub.2 trap material; removing H.sub.2O from said gas to form a
dry raw gaseous product; wherein said CO.sub.2 trap material is
present in an amount sufficient to combine with sufficient
quantities of CO.sub.2 to form a dry raw gaseous product comprising
at least about 40% methane by volume.
2. A method for catalytic gasification of carbonaceous material to
combustible gases, the method comprising: reacting carbonaceous
material and steam in the presence of an alkali catalyst at a
temperature in the range of from about 300.degree. C. to about
700.degree. C. to form a gas comprising CO.sub.2, CH.sub.4 and
H.sub.2, wherein said carbonaceous material includes silica,
alumina, and other mineral constituents; and providing a mineral
binder material to combine with at least a portion of said mineral
constituents to inhibit said mineral constituents from combining
with said alkali catalyst.
3. A method for catalytic gasification of carbonaceous material to
combustible gases, the method comprising: reacting carbonaceous
material and steam in the presence of an alkali catalyst at a
temperature in the range of from about 300.degree. C. to about
700.degree. C. to form a gas comprising CO.sub.2, CH.sub.4,
H.sub.2O and H.sub.2, wherein said carbonaceous material includes
silica, alumina, and other mineral constituents; providing a
mineral binder material to combine with at least a portion of said
mineral constituents to inhibit said mineral constituents from
combining with said alkali catalyst. combining said CO.sub.2 in
said gas with a CO.sub.2 trap material; removing H.sub.2O from said
gas to form a dry raw gaseous product; wherein said CO.sub.2 trap
material is present in an amount sufficient to combine with
sufficient quantities of CO.sub.2 to form a dry raw gaseous product
comprising at least about 40% methane by volume.
4. A method according to claim 1, 2, or 3, wherein the temperature
is in the range from about 300.degree. C. to about 550.degree.
C.
5. A method according to claim 1, 2, or 3, wherein substantial
quantities of H.sub.2 and/or CO are not recycled or added to the
reactor.
6. A method according to claim 1, 2, or 3, wherein the alkali
catalyst comprises one or more compounds selected from the group
consisting 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, KNO.sub.3, K.sub.2SO.sub.4,
LiOH, NaOH, KOH and naturally occuring minerals containing alkali
metal salts.
7. A method according to claim 1 or 3, wherein said CO.sub.2 trap
material comprises one or more compounds selected from the group
consisting of CaO, Ca(OH).sub.2, dolomite, limestone, Trona, and
other compounds effective for regeneratively combining with
CO.sub.2 to form solid carbonates and bicarbonates.
8. A method according to claim 7 wherein said CO.sub.2 trap
material comprises CaO.
9. A method according to claim 8 wherein the weight ratio of CaO to
carbon in the reactor is in the range of about 0.5:1 to about
4:1.
10. A method according to claim 9 wherein the weight ratio of CaO
to carbon in the reactor is about 2:1.
11. A method for catalytic gasification of carbonaceous material to
combustible gases, the method comprising: reacting carbonaceous
material and steam in an environment in the presence of an alkali
catalyst and a quantity of CO.sub.2 trap material at a temperature
in the range from about 300.degree. C. to about 700.degree. C. to
form a gas comprising CH.sub.4 and H.sub.2O and solid particles
comprising carbonated CO.sub.2 trap material; removing H.sub.2O
from said gas to form a dry raw gaseous product comprising at least
about 30% methane; removing said solid particles from the
environment, regenerating CO.sub.2 trap material therefrom, and
returning said regenerated CO.sub.2 trap material to said
environment.
12. A method according to claim 11 wherein said regenerated
CO.sub.2 trap material comprises at least 50% of said quantity of
CO.sub.2 trap material.
13. A method according to claim 12 wherein said regenerated
CO.sub.2 trap material comprises at least 90% of said quantity of
CO.sub.2 trap material.
14. A method according to claim 2 or 3, wherein said mineral binder
material comprises one or more compounds selected from the group
consisting of CaO, Ca(OH).sub.2, CaCO.sub.3, and other alkaline
earth metal salts.
15. A method according to claim 2 or 3 further comprising
dispersing said mineral binder material into said carbonaceous
material prior to said reacting.
16. A method according to claim 14 wherein the stoichiometric ratio
of said mineral binder material relative to said mineral
constituents of said carbonaceous material is in the range of about
0.5 to about 1.5.
17. A method according to claim 14 wherein the stoichiometric ratio
of said mineral binder material relative to said mineral
constituents of said carbonaceous material is about 1:1.
18. A method according to claim 1, 2 or 3 wherein the carbon
conversion of the carbonaceous material is at least about 50%.
19. A method according to claim 18 wherein the carbon conversion of
the carbonaceous material is at least about 65%.
20. A method according to claim 19, wherein the carbon conversion
of the carbonaceous material is at least 80%.
21. A method according to claim 1 or 3 wherein the dry raw gaseous
product includes at least about 50% methane by volume.
22. A method according to claim 21 wherein the dry raw gaseous
product includes at least about 60% methane by volume.
23. A method according to claim 21 wherein the dry raw gaseous
product includes at least about 70% methane by volume.
24. A method according to claim 21 wherein the dry raw gaseous
product includes at least about 80% methane by volume.
25. A method according to claim 1, 2, or 3, further comprising
maintaining the molar ratio of steam to carbon in the reactor
within the range of about 1.5:1 to 3:1.
26. A method according to claim 1, 2, or 3, further comprising
controlling the partial pressure of the steam by addition of a
non-reactive gas to the reactor.
27. The method according to claim 1, 2, or 3 wherein the reactor
comprises a fluid bed or a moving bed.
28. A method according to claim 6 wherein the alkali catalyst
comprises a eutectic salt mixture.
29. A method according to claim 28, wherein the eutectic salt
mixture is a binary salt mixture.
30. A method according to claim 29 wherein the binary salt mixture
is 29% Na.sub.2CO.sub.3 and 71% K.sub.2CO.sub.3 by mole
percent.
31. A method according to claim 28, wherein the eutectic salt
mixture is a ternary salt mixture.
32. A method according to claim 31 wherein the ternary salt mixture
is 43.5% Li.sub.2CO.sub.3, 31.5% Na.sub.2CO.sub.3 and 25%
K.sub.2CO.sub.3 by mole percent.
33. A method according to claim 31 wherein the ternary salt mixture
is 39% Li.sub.2CO.sub.3, 38.5% Na.sub.2CO.sub.3 and 22.5%
Rb.sub.2CO.sub.3 by mole percent.
34. A method according to claim 4 wherein the alkali catalyst
comprises NaOH, Na.sub.2CO.sub.3, or Trona.
35. A method for catalytic gasification of carbonaceous material to
combustible gases, the method comprising: reacting carbonaceous
material and steam in the presence of an alkali catalyst at a
temperature in the range of from about 300.degree. C. to about
700.degree. C. to form a gas comprising CO.sub.2, CH.sub.4,
H.sub.2O and H.sub.2; combining said CO.sub.2 in said gas with a
CO.sub.2 trap material; removing H.sub.2O from said gas to form a
dry raw gaseous product; wherein said CO.sub.2 trap material is
present in an amount sufficient to combine with sufficient
quantities of CO.sub.2 so said dry raw gaseous product comprises
less than about 2% CO.sub.2 by volume.
Description
[0001] This application claims priority under 35 U.S.C. 119(e) to
provisional application 60/695,994 which is hereby incorporated by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to low temperature catalytic
gasification of carbonaceous material. More particularly, the
present invention relates to an improved process for gasifying
carbonaceous material that achieves high carbon conversion to
methane at mild temperatures.
BACKGROUND--DESCRIPTION OF RELATED ART
[0003] The world-wide availability of petroleum is predicted to
peak and then decline rapidly. Rapid economic, technological and
industrial growth of populous countries such as China and India
serves to increase this demand, making the need for alternative
sources of energy even more severe. To meet this growing demand it
has been suggested to convert coal into more useful and
transportable forms. One such technique is to gasify coal into
combustible gases. A coal gasification process for producing
pipeline grade fuel, such as methane, would be especially desirable
because of the existing infrastructure adapted to transport methane
as natural gas.
[0004] In typical coal gasification systems, coal or other
carbonaceous materials and steam are reacted with oxygen (or air)
to produce a syngas, comprised primarily of hydrogen and carbon
monoxide. Commercial, non-catalyzed, coal gasification systems and
designs face a number of economic and technical challenges. These
processes are expensive to operate since, in order to drive the
endothermic non-catalytic gasification of carbonaceous materials,
they utilize severe temperatures (2400 to 2600.degree. F.) and can
consume high levels of oxygen. Slagging and corrosion also can
present operating and maintenance issues which reduce economic
viability and increase product cost.
[0005] A current concept of an Integrated Gasification Combined
Cycle (IGCC) system incorporates a non-catalyzed coal gasification
system to produce syngas as an intermediate and burns the syngas to
produce electricity. The capital cost of an IGCC system is
estimated to range from about $1,250 to $1,400 per KW, depending
upon the design and process integration. One way to reduce the cost
significantly would be to develop a process that enables one to
gasify coal at lower temperature and without added oxygen. Toward
this end, it is useful to consider the thermodynamics of gasifying
coal.
[0006] The gasification of coal and similar materials generally
involves the following reactions: C+H.sub.2O.fwdarw.CO+H.sub.2
(Endothermic) (1) C+2H.sub.2.fwdarw.CH.sub.4 (Exothermic) (2)
C+CO.sub.2.fwdarw.2CO (Endothermic) (3)
CO+H.sub.2O.ident.CO.sub.2+H.sub.2 (Exothermic) (4) The reaction
kinetics during conventional (i.e. thermal) gasification generally
produce only small amounts of methane. Direct
hydrogenation/gasification of carbon such as depicted by equation
(2) above is very slow compared to the endothermic reactions of
steam and carbon dioxide with carbon, as depicted in equations (1)
and (3). The gasification of coal and similar materials thus
normally produces a synthesis gas composed primarily of hydrogen
and carbon monoxide.
[0007] Addition of alkali metal catalysts enables steam
gasification to proceed at lower temperatures and can enhance the
production of methane through the following exothermic reactions:
2CO+2H.sub.2.fwdarw.CO.sub.2+CH.sub.4 (Exothermic) (5)
CO+3H.sub.2.fwdarw.H.sub.2O+CH.sub.4 (Exothermic) (6)
CO.sub.2+4H.sub.2.fwdarw.2H.sub.2O+CH.sub.4 (Exothermic) (7)
[0008] One such catalytic steam gasification process is disclosed
in U.S. Pat. No. 4,094,650 to Koh et al. ("the '650 process"). The
preferred temperature and pressure ranges disclosed therein are
around 1300.degree. F. (700.degree. C.) and 500 psia (34 atm).
Potassium carbonate is disclosed as a preferred catalyst. Though
the temperature is lower than in non-catalyzed gasification, the
main raw products are still H.sub.2 and CO. In order to suppress
the formation of H.sub.2 and CO, and drive the carbon conversion to
methane, the '650 process teaches recycling the H.sub.2 and CO from
the raw product. A catalyst makeup stream is also required in the
'650 process because, at the temperatures therein, the alkali metal
catalyst can volatilize and/or react with ash constituents of the
coal causing a substantial decrease in catalyst activity.
[0009] Various combinations of compounds have been investigated to
find less expensive coal gasification catalysts. For example, U.S.
Pat. No. 4,336,034 to Lang et al. discloses that at catalyst
loadings up to 12% by weight, the relatively inexpensive
combination of K.sub.2SO.sub.4 and calcium compounds such as CaO,
Ca(OH).sub.2, or CaCO.sub.3 can provide gasification rates
comparable to relatively expensive K.sub.2CO.sub.3. The '034 patent
reports better performance for mixtures having a K/Ca ratio of 2.0
(i.e., 1/3 calcium) than for mixtures with more calcium. Lang
reports the use of small amounts of calcium to enhance the activity
of a relatively poor catalyst such as K.sub.2SO.sub.4. There is no
suggestion in Lang that higher quantities of calcium can influence
the catalytic activity of potassium hydroxide or potassium
carbonate, or that calcium salts can be used to enhance product
yield, change the reaction kinetics, or enable gasification to
proceed at lower operating temperatures. There is also no
suggestion that the presence of calcium can improve catalyst
recovery.
[0010] Other modifications have been proposed to attain more
complete carbon conversion in a catalytic coal gasification
process, examples being U.S. Pat. No. 4,558,027 to McKee et al.
which discloses using eutectic alkali catalyst mixtures, and U.S.
Pat. Nos. 4,077,778 and 6,955,695 to Nahas which disclose,
respectively, using two reactors, or a two-stage reactor. These
processes, like that of the '650 patent, report recycling
substantial quantities of H.sub.2 and CO from the raw product gases
to the gasifier to maximize the production of methane.
[0011] Thermodynamically, methane generation is favored at mild
temperatures below about 540.degree. C. and high pressures, but
catalytic coal gasification processes typically operate hotter,
i.e., at temperatures between about 700.degree. C. to about
820.degree. C., because the gasification rate, and yield, are low
in conventional catalytic coal gasification processes at lower
temperatures.
[0012] Mild temperature coal gasification can achieve higher direct
conversion of carbon to methane and can reduce or avoid catalyst
losses which can occur at higher temperatures due to binding with
mineral matter in the carbonaceous feed or volatilization. Mild
temperature coal gasification can also minimize the conversion of
coal to significantly less reactive char. However, catalysts have
not heretofore been identified that can catalyze mild temperature
gasification at acceptably high reaction rates.
[0013] Several metals (other than alkali metals) have been
identified that can catalyze steam/coal gasification, but have not
shown promise for mild temperature gasification. Transition metals
such as iron or nickel can catalyze coal gasification, but are
subject to being deactivated rapidly, after only about 10 or 15%
carbon conversion. (D. Tandon, Low Temperature and Elevated
Pressure Steam Gasification of Illinois Coal (1996) (Ph.D.
dissertation, Southern Illinois University at Carbondale)).
Research has found that unsupported Raney Ni can be severely
deactivated by H.sub.2S, possibly due to the formation of
NiAl.sub.2S.sub.4 on the surface of the catalyst, but can be less
affected when supported by ZrO.sub.2 and Al.sub.2O.sub.3.
[0014] Catalytic metals, in combination, can be less vulnerable to
deactivation than single-metal catalysts. For example, eutectic
catalyst mixtures can maintain catalytic activity longer than one
constituent of the mixture. Similarly, Tandon reported that
potassium combined with nickel or iron as a steam/graphite
gasification catalyst can remain active longer than iron or nickel
alone. It is possible that highly dispersed alkali metal salts can
provide a reducing atmosphere for transition metal salts and thus
sustain their catalytic activity.
[0015] A catalytic effect from highly dispersed calcium has also
been observed. For example, the article by Yasuo Ohtsuka and Kenji
Asami, "Highly active catalysts from inexpensive raw materials for
coal gasification", Catalysis Today 39:111 (1997) reports that
calcium salts, such as CaCO.sub.3 or Ca(OH).sub.2, that have been
"kneaded" with coal particles, can promote steam gasification of
lignite at about 550.degree. C., but are reportedly not effective
with low-oxygen containing higher rank coals.
[0016] CaO or lime can also be used with coal conversion processes
to absorb CO.sub.2. For example, U.S. Pat. No. 4,747,938 to Khan,
which is directed to coal pyrolysis at about 550.degree. C.,
discloses that using particulate CaO at up to 25 wt % loading can
yield a product stream with less H.sub.2S and CO.sub.2. Neither the
Khan nor the Ohtsuka and Asami processes utilize alkali
catalysts.
[0017] Though coal gasification catalysis has been extensively
researched, it is still not completely understood. Without
intending to limit this invention to any particular theory, it is
believed that transition metals that can catalyze coal gasification
are those which can oscillate between two oxidation states and
participate in oxidation-reduction cycles on the carbon surface,
and that gasification with alkali metal catalysts involves the
alkali metals donating electrons to the carbon lattice, or forming
alkali/carbon complexes, thereby increasing the number of active CO
complexes on the carbon surface. It is also believed that
combinations of such catalysts exhibit sustained activity because
different types of active sites on the carbon surface can be
activated by different catalytic moieties, making more reaction
sites available and reducing the impact of the deactivation of any
particular type of reaction site or reaction mechanism.
[0018] It is further believed that transition metals and alkali
metals are catalytically inactive when they are oxidized, and that
they can be oxidized by components of the gasification environment
such as H.sub.2O, CO.sub.2, CO and H.sub.2S. The alkali metal
catalysts can also become inactive or ineffective by volatilizing
and/or binding with mineral constituents of coal.
[0019] It would be highly desirable to develop a catalytic coal
gasification process that could sustain high reactivity with high
carbon conversion, and even more desirable to develop a catalytic
process capable of high carbon conversion to methane without
recycling from the raw product (or feeding) a substantial H.sub.2
and CO stream. It would be further desirable if such a process
could operate at mild temperatures where catalyst losses by
vaporization or deactivation by interaction with mineral
constituents of the carbonaceous feed could be minimized. These and
other objects are the subject of the process disclosed herein.
SUMMARY OF THE INVENTION
[0020] It has been found that using calcium salts to remove or
"trap" carbon dioxide and other oxidizing agents from a catalytic
coal gasification environment can shift the kinetics towards
greater carbon conversion to methane, and can also drive the
conversion of CO to CO.sub.2 such that the process can yield a dry
raw gaseous product comprised mainly of H.sub.2 and CH.sub.4 and
substantially free of carbon oxides. The overall coal/carbon
conversion can be at least 50% but conversions greater than 95% are
also obtainable. The process disclosed herein can directly produce
a dry raw gaseous product comprised of about 40% methane or more,
by volume, without the need for substantial recycling or feeding
H.sub.2 and CO to the environment. Advantageously, the dry raw
gaseous product can be used as a fuel without further enrichment,
and can provide pipeline quality methane with little additional
treatment.
[0021] Calcium salts and other compounds can react with CO.sub.2
and H.sub.2S and form solids which can be withdrawn in a solid
purge, thereby eliminating or greatly reducing the need to treat
the raw gaseous product for acid gas removal. According to the
present invention, calcium salts can also bind with, and render
inert or relatively inert, mineral constituents of the carbonaceous
feed so the alkali metal salt catalysts can remain active longer.
By preventing such minerals from reacting with and deactivating the
alkali metal catalysts, greater catalyst recovery from the solid
purge can be achieved and catalyst losses can be reduced. The
process can allow for up to .about.90% catalyst recovery.
[0022] While the invention is not limited to any theory, it is
believed that CO.sub.2 in the gasifier causes the catalyst to
deactivate, so that by eliminating the CO.sub.2, high catalytic
activity can be sustained and more complete conversion can be
achieved. In addition, removal of CO.sub.2 from the gas phase can
substantially alter the ratio of hydroxide to carbonate forms of
the catalyst. Eliminating CO.sub.2 effectively increases the
activity of the catalyst and enables a high rate of gasification to
occur at mild operating temperatures. At mild temperatures, the
kinetics favor greater direct conversion of coal (or other
carbonaceous materials) to methane, and the coal, which can convert
to less reactive char at conventional catalytic coal gasification
temperatures, can remain more reactive. Mild temperature operation
can also reduce catalyst losses and corrosion of system components
caused by volatilization of the catalyst and hazardous trace
elements in the carbonaceous feed.
[0023] The catalytic gasification processes of the present
invention can also be simpler and less costly to build and operate
than known prior processes, and can be less prone to overheating,
corrosion, char build-up and other problems long associated with
other gasification processes and systems. The estimated Btu in,
versus Btu out, efficiency can be on the order of 80 to 85%
overall.
[0024] In one embodiment of the invention there is provided a
method for direct catalytic gasification of carbonaceous material
to methane comprising causing a reaction of the carbonaceous
material in an environment including steam and an alkali metal salt
catalyst at mild temperatures in the range from about 300 to about
700.degree. C. and a pressure from about 15 to about 100
atmospheres, and removing CO.sub.2 (and H.sub.2O) from the products
of the reaction in the environment so as to produce a dry raw
gaseous product consisting of from about 30% to about 90% methane.
Thus, the dry raw gaseous product can include at least about 40%
methane, or at least about 50%, or at least about 60%, or even at
least about 70% methane by volume. This embodiment can be carried
out in the absence of or without extensive added or recycled
H.sub.2 or CO.
[0025] Another embodiment provides an improved method for direct
catalytic gasification of carbonaceous material to combustible
gases, which can be carried out in the absence of added or recycled
H.sub.2 or CO, wherein the gasification reaction occurs at a
temperature range from about 300 to about 700.degree. C. and a
pressure from about 15 to about 100 atmospheres in an environment
including steam, an alkali catalyst, and a mineral binder material,
and wherein said carbonaceous material includes silica and/or
alumina, and other mineral constituents. The mineral binder
material can combine with at least a portion of these mineral
constituents to inhibit the silica and/or alumina, and other
mineral constituents from combining with the alkali catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The foregoing features of the invention will be more readily
understood by reference to the following detailed description. FIG.
1 is a general Flow Diagram of a Mild Catalytic Coal Gasification
(MCCG) Process in accordance with an embodiment of the present
invention.
DETAILED DESCRIPTION
[0027] As used in this description and the accompanying claims, the
following terms shall have the meanings indicated, unless the
context otherwise requires:
[0028] The term "catalyst" refers to compositions that are
introduced to the process to facilitate the gasification reactions.
The term is not meant to be limited to the specific chemical moiety
or moieties that activate the carbon surface or otherwise actually
participate in the gasification reactions.
[0029] "Mild temperature gasification" as used herein, means steam
gasification of carbonaceous material at about 550.degree. C. or
lower.
[0030] "Syngas " as used herein, means synthetically produced fuel
gas, typically produced from standard coal gasification processes,
comprising mostly CO and H.sub.2 by volume.
[0031] "Dry raw gaseous product" as used herein means non-steam or
substantially non-steam products of direct catalytic steam
gasification. Although steam can be a component of the raw gaseous
reaction products from direct catalytic steam gasification of
carbonaceous materials, reference to `dry raw gaseous product`
herein means the gaseous products, other than steam, that flow from
the gasification reactor and have not been further purified.
[0032] "CO.sub.2 trap material" as used herein can be CaO,
Ca(OH).sub.2, dolomite, limestone, Trona, or other compounds
effective for regeneratively combining with CO.sub.2 to form solid
carbonates or bicarbonates, and combinations thereof.
[0033] "Mineral binder material" as used herein can be a calcium
salt, such as CaO, Ca(OH).sub.2, CaCO.sub.3, or any other alkaline
earth metal salts which can react with and tie up silica, alumina,
and other mineral constituents of the carbonaceous feed so as to
inhibit such constituents from reacting with and deactivating the
catalyst.
[0034] The present invention provides a catalytic steam
gasification process for converting carbonaceous materials to gases
substantially comprising methane or other combustible gases. The
process can operate at mild temperatures and produce a dry raw
gaseous product that can be used either directly as fuel or
purified to pipeline quality methane without the need to remove
therefrom substantial quantities of carbon monoxide or acid gases.
The process can include a feed preparation zone, a gasification
reactor, a catalyst recovery system, and a CO.sub.2 trap
regeneration zone.
[0035] In the gasification reactor operating at between about
300.degree. C. to about 700.degree. C. and with pressure in the
range from about 10 atm to about 100 atm, carbonaceous material can
be reacted with oxidizing agents such as steam and/or oxygen in the
presence of CO.sub.2 trap material, and one or more alkali metal
salt catalysts, to produce predominantly methane as the raw product
gas. In preferred embodiments, the operating temperature in the
reactor is below about 550.degree. C., and the pressure is in the
range from about 12 to about 40 atm. The gasification reactor can
have a moving bed or a fluidized bed. Mineral binder material can
also be present in the reactor, and can bind with silica, alumina,
and other mineral constituents of the carbonaceous feed and thereby
prevent or inhibit such constituents from reacting with and
deactivating the catalyst.
[0036] The feed preparation zone can include one or more mixers for
combining the carbonaceous material, the alkali metal catalyst, the
mineral binder material, and the CO.sub.2 trap material, and a feed
system for introducing the catalyst/carbon/CO.sub.2 trap mixture to
the gasification reactor as dry solids or as a liquid slurry. The
feed system can be a star feeder, screw feeder, or other mechanism
effective in maintaining required temperature, pressure and flow
rate of the materials to be introduced to the gasification
reactor.
[0037] The carbonaceous material can be coal, heavy oils, petroleum
coke, other petroleum products, residua, or byproducts, biomass,
garbage, animal, agricultural, or biological wastes and other
carbonaceous waste materials, etc., or mixtures thereof. The coal
or other carbonaceous material can be ground or pulverized to an
average particle size of about 30 to 100 mesh before its delivery
for use in the gasification process. Such particles can be
impregnated with alkali catalyst in aqueous solution and dried by
known methods. The impregnated and dried particles can be mixed
with the CO.sub.2 trap material and/or mineral binder material and
introduced to the gasifier as a single stream, or such streams can
be fed separately, or in combination, as convenient.
[0038] In a preferred embodiment, however, the carbonaceous
materials for use in the process can be more coarse, with an
average particle size of about 1-2 mm. Such coarse particles can be
combined and ground with an aqueous slurry of finely divided
mineral binder material. The resulting paste can be ground with
alkali catalyst, dried at about 100.degree. C. with superheated
steam to recover a fine powder of carbonaceous material with highly
dispersed mineral binder and alkali catalyst having an average
particle size of less than roughly 0.02 mm, pelletized to a
particle size of about 30-100 mesh, and fed to the gasification
reactor. The CO.sub.2 trap material can be combined and fed with
the prepared carbonaceous material, or can be fed separately.
[0039] The CO.sub.2 trap material can be CaO or Ca(OH).sub.2, or
any other compound that can react with CO.sub.2 to form solid
carbonates or bicarbonates, so as to shift the kinetics in the
direction of increased methane concentration in the raw gas
product. In particular embodiments the CO.sub.2 trap material is
CaO. Sufficient CO.sub.2 trap material can be used so as to remove
substantially all the CO.sub.2 from the products of the reaction to
yield a dry raw gaseous product containing less than about 2%
CO.sub.2 by volume. The molar ratio of CO.sub.2 trap material to
carbon in the reactor can be in the range of about 0.1:1 to about
1:1, or more particularly in the range of about 0.3:1 to about
0.7:1, and more particularly about 0.5:1. On a weight basis, if CaO
is used as the CO.sub.2 trap material, the CaO to carbon ratio fed
to the reactor can be in the range of about 0.5:1 to about 4:1, or
more particularly in the range of about 1:1 to about 3:1, and more
particularly about 2:1. The CO.sub.2 trap material can be effective
without being highly dispersed on the carbon surface. Thus
operating convenience can dictate whether the CO.sub.2 trap
material and the carbonaceous feed are mixed and then fed or
introduced separately to the gasifier.
[0040] The alkali catalyst can comprise any 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, KNO.sub.3, K.sub.2SO.sub.4, LiOH, NaOH, KOH, or
any suitable alkali metal salts, or naturally occuring minerals
containing alkali metal salts such as Trona, or mixtures thereof.
The catalyst can be a single compound or a combination of alkali
metal salts, which can be binary or ternary salt mixtures. The
alkali catalyst loading can be from 1 to 50 weight percent based on
the carbonaceous feed on a dry, ash-free basis. Preferably, the
alkali loading is in the range of about 1 to 30 wt %. The alkali
catalyst can be effective without the presence of any fluorinated
compounds.
[0041] The alkali metal salt catalyst can comprise a eutectic salt
mixture of Li.sub.2CO.sub.3, Na.sub.2CO.sub.3, K.sub.2CO.sub.3,
Rb.sub.2CO.sub.3, and Cs.sub.2CO.sub.3 or mixtures thereof. In one
embodiment, the eutectic salt mixture can be a binary salt mixture
of about 29% Na.sub.2CO.sub.3 and about 71% K.sub.2CO.sub.3, mole
percent. In other embodiments the eutectic salt mixture can be a
ternary composition of about 43.5% Li.sub.2CO.sub.3, 31.5%
Na.sub.2CO.sub.3 and 25% K.sub.2CO.sub.3, mole percent, or a
ternary salt mixture of about 39% Li.sub.2CO.sub.3, 38.5%
Na.sub.2CO.sub.3 and 22.5% Rb.sub.2CO.sub.3, mole percent.
[0042] The mineral binder material can be a compound or a mixture
of compounds selected from the group consisting of CaO,
Ca(OH).sub.2, CaCO.sub.3, and other alkaline earth metal salts. The
mineral binder can be kneaded or otherwise dispersed on the
carbonaceous feed particles in a feed pretreatment step before the
alkali catalyst is contacted with the carbonaceous feed. In the
present invention, kneading calcium salts with the carbonaceous
feed particles can be used to help prevent mineral interactions
with the alkali metal catalyst. In other embodiments, the
carbonaceous feed, the mineral binder, and alkali catalyst can be
mixed together simultaneously by conventional methods. In still
further embodiments, the mineral binder material can be fed
separately to the gasifier and/or mineral binder material can form
in the gasifier, wherein such mineral binder material (e.g.,
CaCO.sub.3) can react with silica, alumina, and other mineral
constituents present in the carbonaceous feed and prevent or
inhibit some alkali catalyst loss and deactivation.
[0043] The mineral binder can combine with at least a portion of
any reactive mineral constituents in the carbonaceous feed such as
aluminum and silicon constituents, and thereby prevent or inhibit
such reactive mineral constituents from reacting with the alkali
catalysts. The mineral binder material can thus be effective at
stoichiometric quantities about equal to that of the reactive
mineral constituents in the carbonaceous feed. Thus, for example,
if the carbonaceous feed material is Illinois #6 coal which
contains on a dry basis about 10 to 11 wt % ash of which silica
comprises about 51 wt % and alumina comprises about 18 wt %, then
7.1 tons of CaCO.sub.3 or the equivalent amount of another mineral
(e.g., about 4.0 tons of CaO) would be enough to react with all the
silica and alumina in 100 tons of Illinois #6 coal. It may be
preferable to use a higher or lower than stoichiometric amount,
e.g. in the range of about 0.5 to about 1.5. Higher amounts of
mineral binder can promote more complete material binding,
particularly at higher operating temperatures. Lower amounts can be
sufficient at milder operating temperatures.
[0044] It may be desired to process carbonaceous feeds according to
this invention promoting mineral binding or CO.sub.2 trapping or
both. Thus, for the example of using CaO for either purpose with
Illinois #6 coal, to promote only mineral binding, the amount of
CaO utilized can be in the range of about 2 to 6 wt % and is
preferably highly dispersed with the feed; whereas to promote
CO.sub.2 trapping, higher amounts in the range of 50 to 200 wt %,
which need not be highly dispersed with the feed can be utilized.
It is expected that substantial amounts in the range of at least
60% to about 90% of the CO.sub.2 trap material can be recovered in
the CO.sub.2 trap regenerator and recycled within the process, such
that the amount of fresh CO.sub.2 trap material can be about 5 to
80 wt % CaO. To promote both mineral binding and CO.sub.2 trapping,
the feed can include about 5% CaO highly dispersed within the feed
and the balance as a separate stream.
[0045] The reactor is designed so that a solid purge can be
periodically or continuously withdrawn. The CO.sub.2 trap material
reacts with CO.sub.2 in the reactor and is withdrawn in the
"carbonated" form with the solid purge. If the CO.sub.2 trap
material is CaO or Ca(OH).sub.2, the solid purge can include
particles of CaCO.sub.3, as well as particles of unreacted carbon,
the ash or mineral constituents of the carbonaceous feed, and some
alkali catalyst in various forms.
[0046] The process of the invention can include a regeneration
process of conventional design to recover and recycle active
CO.sub.2 trap material, if desired or necessary. If the CO.sub.2
trap material is CaO, for example, the CO.sub.2 trap material
regenerator can be a calciner. In such case, CaCO.sub.3 particles
can be separated from said withdrawn solids by passing through a
coarse sieve, or by elutriation of fine particles or other
techniques, and can be directed to the calciner to recover the CaO.
If necessary, the recovered CaO can be activated or its surface
area increased by steam treatment or similar treatment, during or
after calcination and prior to recycling. The regenerated CaO
recycled to the gasifier can constitute as much as about 90% of the
calcium value withdrawn in the solid purge. The calcined off-gas,
mostly CO.sub.2 and possibly some CaCO.sub.3, CaS and CaSO.sub.4,
as well as H.sub.2S and possibly SO.sub.2 and O.sub.2, can be
sequestered or otherwise properly disposed.
[0047] The solid purge fraction that passes through the sieve can
include soluble alkali metal salts, and can also include insoluble
alkali and/or calcium aluminosilicates. These can be treated in a
catalyst recovery system for recovery and recycle of the catalyst.
The catalyst recovery system can comprise a water wash system and
optionally can comprise a lime digestion system. In one embodiment,
the hot carbon/ash particles can be contacted with water and
soluble catalyst constituents of the particles can dissolve into
solution. If the particles contain small amounts of alkali
aluminosilicates, then the water contacting step can be sufficient
to accomplish essentially complete catalyst recovery. If the washed
solids contain appreciable amounts of insoluble alkali components,
the washed solids can be digested in an alkaline solution or slurry
to recover insoluble alkali moieties. The washed solids can contain
sufficient calcium or other alkaline compounds such that little or
no additional lime or other alkaline solution is necessary for
digestion.
[0048] The partial pressure and/or concentration of steam can be
monitored and controlled to maximize conversion rates and maximize
overall conversion to methane or other desired gaseous product such
as syngas. In some embodiments, causing the reaction includes
maintaining a molar ratio of steam to carbon in the range of about
1.5 to 3 and/or controlling partial pressure of the steam by
addition of a non-reactive gas to the gasification environment.
[0049] The catalytic steam gasification process can produce a dry
raw gaseous product that includes at least about 40% methane and
can include at least about 50%, or at least about 60%, or even at
least about 70% or higher, methane by volume, without the need for
H.sub.2 and CO recycling, or extensive recycling, and without the
need for separate stage water-gas shift reactions. Other
embodiments produce a dry raw gaseous product that can include
about 80% methane or higher.
[0050] The overall direct carbon conversion of carbonaceous
material to methane can be at least about 50%, more particularly at
least about 65%, still more particularly at least about 80%, and
still more particularly at least about 90%. In still more
particular embodiments, the carbon conversion of the carbonaceous
material can be at least about 50% or at least about 65% at less
than about 550.degree. C.
[0051] The invention and specific embodiments are described more
fully in the following examples:
EXAMPLE 1
Low Temperature Steam Gasification Results
[0052] Steam gasification of Illinois #6 coal was studied at
elevated pressures and low temperatures. In the absence of a
catalyst at 500.degree. C. and elevated pressure (500-1000
psig--i.e. .about.34 to 68 atm), no coal conversion was observed.
When the temperature was increased to 700.degree. C., a significant
amount of conversion was observed. Apparently the lower temperature
is insufficient to overcome the activation energy barrier. Gas
analyses at 700.degree. C. showed no or substantially no methane
formation for de-mineralized coal samples. A small amount of
methane was detected for the raw coal gasification. These
observations are in agreement with the findings that significant
amounts of methane cannot be generated in the absence of catalysts,
and that minerals in coal can contribute to catalysis.
[0053] The catalytic effects of iron, nickel and potassium in steam
gasification were also studied. In the presence of these catalysts
a substantial amount of Illinois #6 coal was gasified at
500.degree. C. With single catalysts at about 10 wt % loading,
almost 30-35 wt % coal was gasified and most was gasified in the
first 5 minutes. Methane and carbon dioxide were the main product
gases, with little to no carbon monoxide produced. Thus, at low
temperatures and elevated pressures the equilibrium is shifted to
methane formation and syngas formation is minimized. Higher coal
conversion and methane formation were observed at 1000 psig
(.about.68 atm) as expected. Iron- and nickel-catalyzed reactions
were reactive for about 15 minutes, after which a sharp drop in
reactivity was observed. Overall, higher conversions were obtained
for de-mineralized coal samples but the methane concentrations were
slightly higher for the raw coal gasification.
[0054] When a potassium salt was used with either iron or nickel
salts as a catalyst for raw coal gasification, synergistic effects
were observed. At 500.degree. C. and 500 psig (.about.34 atm) a
potassium/iron salt catalyst system (5 wt % each) resulted in 42 wt
% carbon conversion. The conversion went up to 53 wt % when the
catalyst loading was increased to 10 wt % each. The gas analyses
showed that with this catalyst, a combination of methane and
hydrogen production was favored. A nickel/potassium mixture 5 wt %
each did not show significant synergistic effects (39% conversion),
which may be attributed to mineral interactions with these salts.
At 10 wt % each, however, a conversion of 55 wt % was achieved.
When the pressure was increased from 500 (.about.34 atm) to 1000
psig (.about.68 atm) the conversion increased to 58 wt %. The gas
analyses for the potassium/nickel catalyst were comparable to the
potassium/iron system under similar conditions.
[0055] These conversions indicate that alkali metal salts
compliment transition metal salts in that they keep them active for
longer reaction times. The active catalyst state may actually
contain three metals (two outside catalysts and one from the
mineral in coal). Studies also indicated that at 500.degree. C. and
in the pressure range of 500 to 1000 psig, sodium salts were more
effective than potassium salts or any transition metal--potassium
salt mixture. Conversions as high as 70% were obtained with
Illinois coal. Transition metal--sodium salt mixtures were not
investigated.
[0056] The results indicate that coal can be gasified at low
temperatures and elevated pressures to produce methane, and that
lower temperatures help to minimize syngas formation.
EXAMPLE 2
MCCG in Accordance with an Embodiment of the Invention
[0057] A process flow diagram for the envisioned low temperature
steam gasification process, mild catalytic coal gasification
(MCCG), is shown in FIG. 1. Among the advantages for this process
is, as discussed above, that it is a simple process. Particulate
coal or other carbonaceous material, particles of CO.sub.2 trap
material and/or mineral binder material, and an alkali metal
catalyst solution, can be combined and mixed in mixer 100 to form a
feed stream and fed to one or more lock hoppers shown generally as
lock hopper 200. Said particulate streams can be fed separately to
mixer 100 or combined (not shown) before being fed to mixer 100.
From lock hopper 200, the feed stream can be fed to gasifier 300 by
a screw feeder 250, which alternatively can be a star feeder, or a
mechanism that feeds the carbonaceous material as a liquid slurry,
or any other feed mechanism known in the art which allows
carbonaceous material to be fed to a gasifier at a rate,
temperature and pressure necessary to achieve the desired
gasification result.
[0058] Gasifier 300 can be operated in a fluid bed 400A or a moving
bed 400B mode. Advantages of fluid bed mode 400A include ease of
design and easy tar control. One disadvantage of the fluid bed is
that fresh feed particles of coal and the CO.sub.2 trap material
may be removed with converted residue (solid purge). Also the steam
concentration in the outlet gas will be higher than in the moving
bed. In contrast, the moving bed mode is more complex because solid
recycle is needed to move partially gasified coal to the top of the
bed to prevent tar from leaving the reactor with the product gas.
Still, an advantage of the moving bed is that the steam
concentration in the outlet gas will be substantially reduced and
attrition of the CO.sub.2 trap material is minimized. This mode
also maximizes coal conversion.
[0059] When CaO, Ca(OH).sub.2, CaCO.sub.3, or another alkaline
earth metal salt is present in gasifier 300, such compounds can
react with and tie up minerals in the coal or other carbonaceous
material, preventing or inhibiting the minerals from reacting with
the alkali metal salt catalysts so the alkali metal salt catalysts
will remain active longer, increasing the carbon conversion
efficiency and carbon conversion rate and improving catalytic
recovery. For example, such compounds can react with alumina,
silica, or other mineral constituents of the coal. The coal or
other carbonaceous feed can also be pretreated with CaO,
Ca(OH).sub.2, CaCO.sub.3, or other alkaline earth metal salts to
tie up the minerals/ash in the coal.
[0060] Gasifier 300 is operated at about 550.degree. C. or less and
at an operating pressure of less than about 1000 psig (68 atm).
CaO, Ca(OH).sub.2, or other compounds effective for regeneratively
combining with CO.sub.2 can be used as a trap for CO.sub.2 and
sulfur gases. This will enhance catalytic activity by driving the
reaction forward and will also enhance production of methane by
shifting the reaction kinetics toward increased production of
methane.
[0061] Steam is fed to the bottom of gasifier 300. It can be
beneficial to add a small quantity of O.sub.2/air to the steam to
activate the catalyst. In such embodiments, between about 0.1% to
3% oxygen or air is added to the steam to provide oxidized sites on
the coal surface and provide complexes where catalyst can interact
with the coal to produce higher gasification rates and carbon
conversion. Product gases will leave the top of gasifier 300 and
pass through a condenser 500 to remove steam. The condensed water
can be used within the catalyst recovery system 600. The product
gases, mostly CH.sub.4, with lesser amounts of H.sub.2 and NH.sub.3
can be diverted for separation (not shown) using traditional
methods, as needed. Gas separation will be dependent on target
product end use. If desired, syngas is produced by lowering
pressure and reducing CaO feed (or other CO.sub.2 trap) to control
the H.sub.2/CO ratio.
[0062] Spent residue leaves the bottom of reactor/gasifier 300 and
is separated (700) by a screen or other device to separate the
larger sized CaCO.sub.3 particles, which form when CaO or
Ca(OH).sub.2 is used as the CO.sub.2 trap material. The smaller
sized residue is fed to extractor/catalyst recovery system, shown
generally as 600, where the catalyst is dissolved, concentrated (if
necessary) and recycled. Residue from extractor 600 then goes to
waste, perhaps landfill, or for by-product utilization after
determination of hazard waste potential. The calcium carbonate is
calcined in calciner 800 and recycled to mixer 100. The calcined
off gas, (mostly CO.sub.2 and possibly some particulate CaCO.sub.3,
CaS and CaSO.sub.4 as well as H.sub.2S and possibly SO.sub.2 and
O.sub.2) is ready for sequestration if the system is operated under
pressure.
EXAMPLE 3
MCCG in Accordance with Another Embodiment
[0063] In other particular embodiments, coal or other carbonaceous
material; a CO.sub.2 trap material such as CaO or Ca(OH).sub.2
particles; and an alkali metal catalyst solution, are mixed in
mixer 100, fed to lock hopper 200, and fed to gasifier 300 as
described above. Mixer 100 can comprise an impeller and means to
heat the contents such that the carbonaceous particles can become
impregnated with alkali catalyst therein.
[0064] Gasifier 300 can be operated in a fluid bed 400A or a moving
bed 400B mode, as described, and is operated at a temperature
between about 300.degree. C. about 700.degree. C. and a pressure
from about 12 to about 40 atm. As described in Example 2, CaO or
Ca(OH).sub.2 can be used as a trap for CO.sub.2 and sulfur gases,
and CaO, Ca(OH).sub.2, CaCO.sub.3, or other alkaline earth metal
salts can react with alumina, silica, or other mineral constituents
of the coal.
[0065] The remainder of the process follows that described for
Example 2.
EXAMPLE 4
Test Results of Steam Gasification using KOH and CaO
[0066] Carbon conversion rate for steam gasification of Powder
River Basin coal (PRB) was studied in the temperature range of
500.degree. C. and 700.degree. C. Carbon conversion without
catalyst was about 60% after 15 minutes at 700.degree. C. and
increased to about 75% after 30 minutes. With KOH catalyst, the
conversion increased to about 65% and 85% respectively.
Interestingly, with KOH catalyst and CaO/C loading of 1:2 molar
(about 2:1 weight ratio), conversion increased to about 95%
irrespective of the reaction time. Thus, with the CaO trap
material, the coal conversion is essentially complete in just about
15 minutes, showing that a gasification reactor for these
conditions can be designed for a short residence time and achieve
good conversion.
[0067] The effect of temperature can be shown by comparing the
conversion after 30 minutes at 650.degree. C., 600.degree. C., and
550.degree. C. The uncatalyzed conversion was about 70% at
650.degree. C., and decreased to about 50% at lower temperatures.
With KOH catalyst, the conversion was about 80% at 650.degree. C.
and decreased to about 65% and about 60% at 600.degree. C. and
550.degree. C. respectively. With KOH and CaO (loaded at CaO/C of
1:2 molar as above), the conversion at 650.degree. C. was nearly
100% and decreased only slightly at the lower temperatures to about
90%. (The conversion at 650.degree. C. was better than that
observed at 700.degree. C., which was about 95%.)
[0068] The conversion at 500.degree. C. after just 20 minutes,
using the same KOH and CaO loading, was at least 90%, and increased
slightly after 50 or 60 minutes. This demonstrates that the
CO.sub.2 trap enables the use of lower gasification temperatures
(where methane formation is favored) and small residence times
without unduly sacrificing conversion.
[0069] Carbon conversion rate for steam gasification of petroleum
coke was studied at 700.degree. C. and 650.degree. C. Carbon
conversion without catalyst at 700.degree. C. was about 35% after
15 minutes and only increased to about 45% after 60 minutes and
about 55% after 90 minutes. With KOH catalyst, the conversion
increased to about 45% after 15 minutes, and to about 55%, 60%, and
80% after 30, 60, and 90 minutes respectively. With KOH catalyst
and CaO (again loaded at 1:2 molar CaO/C), conversion increased to
about 85% after 15 or 30 minutes and to about 95% after 60 or 90
minutes. The corresponding conversions at 650.degree. C. and 60
minutes, were 15% for uncatalyzed petroleum coke, about 50% with
KOH, and about 80% with the CO.sub.2 trap. The increase in
conversion with the CO.sub.2 trap at 650.degree. C. indicates that
steam gasification of petroleum coke at 650.degree. C. can be
economically feasible.
EXAMPLE 5
Test Results of Steam Gasification using KOH, LiOH, NaOH, and
Ca(OH).sub.2
[0070] Carbon conversion for catalytic steam gasification in the
temperature range of 500.degree. C. and 700.degree. C. of Powder
River Basin coal (PRB) in the presence of KOH, LiOH, NaOH, and
Ca(OH).sub.2 was measured. The conversion with KOH was about 90%
and 85% respectively at 700.degree. C. and 650.degree. C., and
decreased to about 70% at 600.degree. C. and to about 60% at
550.degree. C. and 500.degree. C. Surprisingly, NaOH showed
significantly better performance of about 80% conversion at
600.degree. C. and 70% at 550.degree. C., and performed about the
same as KOH at 700.degree. C., 650.degree. C. and 500.degree. C.
This suggests NaOH as a preferred low cost catalyst for low
temperature steam gasification.
[0071] The conversion with LiOH was 5 to 10% lower than with NaOH,
except at 500.degree. C. where LiOH gave about 65% conversion
compared to about 60% conversion with NaOH, KOH, or Ca(OH).sub.2.
The conversion with Ca(OH).sub.2 was about 70% at temperatures from
700.degree. C. to 550.degree. C., and dropped below 60% at
500.degree. C.
EXAMPLE 6
Steam Gasification of Coal and Residua in Accordance with the
Invention
[0072] In other particular embodiments, coal is mixed with an
alkali metal catalyst, and calcium salts selected from CaO,
Ca(OH).sub.2, CaCO.sub.3 and other alkaline earth metal salts as
described above, and then mixed with petroleum residua. The
coal/residua mixture is heated to about 400 to 500.degree. C. for
about 3 to 30 minutes to disperse the catalyst, and then is
gasified and further processed as described above.
[0073] Dispersing the catalyst allows for better catalyst contact,
allowing temperatures to be dropped to about 300.degree. C. to
about 550.degree. C. Such dispersal also provides better contact
and reaction between reactive mineral components of the
carbonaceous feed and such alkaline earth salts, thereby avoiding
mineral/catalyst interactions and enhancing catalyst recovery.
Dispersal also allows for more efficient sulfur removal, reduced
catalyst quantities, and enables extensive gasification to result
in only unreactive solids and minerals remaining after gasification
is complete. In particular embodiments, the coal to residua weight
ratio is in the range of about 1:1 to about 1:10.
[0074] The four feed components can be combined first into two
streams, one comprising coal and calcium salts, and the other
comprising alkali catalyst and residua; and such combined streams
can then be mixed together and heated, as above, to about 400 to
500.degree. C. for about 3 to 30 minutes to disperse the alkali
catalyst onto the coal. This advantageously allows catalyst to be
removed from potential poisons more quickly and leaves the coal
mixture exposed to the catalyst only in a dilute phase. Again, such
dispersal allows more complete gasification of the carbon/residue
mixture to gaseous product.
[0075] Alternatively, a small amount of residua can be combined
with the coal, blended with the catalyst, and then blended with the
balance of the residua. The coal/residua/catalyst mixture is then
introduced into a reactor at the dispersing temperature described
above (400 to 500.degree. C.) for about 3 to 30 minutes as
described, and the dispersed mixture is introduced into another
reactor where steam is added. Gasification is then done with steam
to produce gases (methane, ethane, propane and butane) and light
distillate C5 to C10 fraction (gasoline fraction). In this
embodiment, catalyst remains dispersed in the liquid phase and only
a small amount is removed with unreacted material, allowing for
better catalyst recovery and recycling, enhancing economics.
[0076] While the invention has been described in conjunction with a
particular flow diagram, operating conditions and examples, various
modifications and substitutions can be made thereto without
departing from the spirit and scope of the present invention. No
limitation should be imposed other than those indicated by the
following claims.
* * * * *