U.S. patent application number 13/586577 was filed with the patent office on 2013-02-21 for hydromethanation of a carbonaceous feedstock.
This patent application is currently assigned to GREATPOINT ENERGY, INC.. The applicant listed for this patent is Avinash Sirdeshpande. Invention is credited to Avinash Sirdeshpande.
Application Number | 20130042824 13/586577 |
Document ID | / |
Family ID | 46785795 |
Filed Date | 2013-02-21 |
United States Patent
Application |
20130042824 |
Kind Code |
A1 |
Sirdeshpande; Avinash |
February 21, 2013 |
HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK
Abstract
The present invention relates to processes for hydromethanating
a carbonaceous feedstock to a methane product stream and electrical
power, in which heat energy from the hot methane-enriched synthesis
gas is used to generate a dry saturated steam stream, the dry
saturated steam stream is converted into a superheated steam stream
via pressure drop for feeding into the hydromethanation reactor to
satisfy the steam demand of the hydromethanation reaction, and heat
generated from a downstream gas methanation processing is recovered
to produce a superheated process steam stream which is used to
generate the electric power.
Inventors: |
Sirdeshpande; Avinash;
(Chicago, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sirdeshpande; Avinash |
Chicago |
IL |
US |
|
|
Assignee: |
GREATPOINT ENERGY, INC.
Cambridge
MA
|
Family ID: |
46785795 |
Appl. No.: |
13/586577 |
Filed: |
August 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61524536 |
Aug 17, 2011 |
|
|
|
Current U.S.
Class: |
122/1R |
Current CPC
Class: |
C10L 3/08 20130101 |
Class at
Publication: |
122/1.R |
International
Class: |
F22B 33/00 20060101
F22B033/00 |
Claims
1. A process for generating a cooled methane product stream and
electrical power from a non-gaseous carbonaceous material, the
process comprising the steps of: (a) preparing a carbonaceous
feedstock from the non-gaseous carbonaceous material; (b)
introducing the carbonaceous feedstock, a hydromethanation
catalyst, a steam stream and an amount of oxygen into a
hydromethanation reactor, wherein the hydromethanation reactor is
operating at a first pressure condition; (c) reacting a portion of
the carbonaceous feedstock in the hydromethanation reactor with
oxygen to generate carbon monoxide, hydrogen and heat energy; (d)
reacting a portion of the carbonaceous feedstock in the
hydromethanation reactor in the presence of carbon monoxide,
hydrogen, steam and hydromethanation catalyst to produce a
methane-enriched raw product gas; (e) withdrawing a
methane-enriched raw product gas stream of the methane-enriched raw
product gas from the hydromethanation reactor, wherein the
methane-enriched raw product gas stream comprises methane, carbon
monoxide, hydrogen, carbon dioxide, hydrogen sulfide, steam and
heat energy; (f) introducing the methane-enriched raw product
stream into a first heat exchanger unit to recover heat energy and
generate a cooled methane-enriched raw product stream and a dry
saturated steam stream, wherein the dry saturated steam stream is
at a second pressure condition that is higher than the first
pressure condition; (g) providing at least a portion of the dry
saturated steam stream to the hydromethanation reactor under a
reduced pressure condition such that the portion of dry saturated
steam stream provided to the hydromethanation reactor is converted
to a first superheated steam stream at or prior to introduction
into the hydromethanation reactor, wherein the reduced pressure
condition is higher than the first pressure condition but lower
than the second pressure condition; (h) steam shifting a portion of
the carbon monoxide in the cooled methane-enriched raw product
stream to generate a hydrogen-enriched raw product stream; (i)
removing a substantial portion of the carbon dioxide and a
substantial portion of the hydrogen sulfide from the
hydrogen-enriched raw product stream to produce a sweetened gas
stream, wherein the sweetened gas stream comprises a substantial
portion of the hydrogen, carbon monoxide and methane from the
hydrogen-enriched raw product stream; (j) methanating a substantial
portion of the carbon monoxide in the sweetened gas stream with
hydrogen in the sweetened gas stream to generate a methane-enriched
treated product stream and heat energy; (k) recovering a portion of
the heat energy from step (j) to generate the cooled methane
product stream; (l) generating a second superheated steam stream
from at least a portion of the heat energy recovered in step (k);
and (m) generating electrical power from at least a portion of the
second superheated steam stream generated in step (l), wherein (1)
the reaction of step (d) has a steam demand and a heat demand, (2)
the steam demand is substantially satisfied by the steam stream,
(3) the steam stream substantially comprises steam from the dry
saturated steam stream, and (4) the amount of oxygen introduced
into the hydromethanation reactor is sufficient so that the heat
demand of the reaction of step (d) is substantially satisfied by
the reaction of step (c).
2. The process of claim 1, wherein the steam demand is at least
satisfied by the steam stream.
3. The process of claim 1, wherein the steam stream comprises only
steam from the dry saturated steam stream.
4. The process of claim 2, wherein the steam stream comprises only
steam from the dry saturated steam stream.
5. The process of claim 1, wherein the second pressure condition is
at least about 25 psi (about 172 kPa) greater than the first
pressure condition.
6. The process of claim 5, wherein the second pressure condition is
at least about 50 psi (about 345 kPa) greater than the first
pressure condition.
7. The process of claim 6, wherein the second pressure condition is
at least about 100 psi (about 690 kPa) greater than the first
pressure condition.
8. The process of claim 7, wherein the second pressure condition is
about 200 psi (about 1379 kPa) or less greater than the first
pressure condition.
9. The process of claim 1, wherein the second pressure condition is
at least about 5% greater than the first pressure condition.
10. The process of claim 9, wherein the second pressure condition
is at least about 10% greater than the first pressure
condition.
11. The process of claim 10, wherein the second pressure condition
is about 20% or less greater than the first pressure condition.
12. The process of claim 1, wherein the first pressure condition is
about 400 psig (about 2860 kPa) or greater.
13. The process of claim 12, wherein the first pressure condition
is about 450 psig (about 3204 kPa) or greater.
14. The process of claim 1, wherein the first pressure condition is
about 1000 psig or less (about 6996 kPa).
15. The process of claim 14, wherein the first pressure condition
is about 900 psig (about 6307 kPa) or less.
16. The process of claim 15, wherein the first pressure condition
is about 600 psig (about 4238 kPa) or less.
17. The process of claim 12, wherein the first pressure condition
is about 1000 psig or less (about 6996 kPa).
18. The process of claim 17 wherein the second pressure condition
is at least about 25 psi (about 172 kPa) greater than the first
pressure condition.
19. The process of claim 17, wherein the second pressure condition
is at least about 5% greater than the first pressure condition.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn.119
from U.S. Provisional Application Ser. No. 61/524,536 (filed 17
Aug. 2011), 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. patent
application Ser. No. ______, (attorney docket no. FN-0070 US NP1,
entitled HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK, concurrently
filed herewith), the disclosure of which is incorporated by
reference herein for all purposes as if fully set forth.
FIELD OF THE INVENTION
[0003] The present invention relates to processes for
hydromethanating a carbonaceous feedstock to a methane product
stream and electrical power, in which heat energy from the hot
methane-enriched synthesis gas is used to generate a dry saturated
steam stream, and the dry saturated steam stream is converted into
a superheated steam stream via pressure drop for feeding into the
hydromethanation reactor to satisfy the steam demand of the
hydromethanation reaction, and heat generated from a downstream gas
methanation processing is recovered to produce a superheated
process steam stream which is used to generate the electric
power.
BACKGROUND OF THE INVENTION
[0004] In view of numerous factors such as higher energy prices and
environmental concerns, the production of value-added products
(such as pipeline-quality substitute natural gas, hydrogen,
methanol, higher hydrocarbons, ammonia and electrical power) from
lower-fuel-value carbonaceous feedstocks (such as petroleum coke,
resids, asphaltenes, coal and biomass) is receiving renewed
attention.
[0005] Such lower-fuel-value carbonaceous feedstocks can be
gasified at elevated temperatures and pressures to produce a
synthesis gas stream that can subsequently be converted to such
value-added products.
[0006] One advantageous gasification process is hydromethanation,
in which the carbonaceous feedstock is converted in a fluidized-bed
hydromethanation reactor in the presence of a catalyst source and
steam at moderately-elevated temperatures and pressures to directly
produce a methane-enriched synthesis gas stream (medium BTU
synthesis gas stream) raw product. This is distinct from
conventional gasification processes, such as those based on partial
combustion/oxidation of a carbon source at highly-elevated
temperatures and pressures (thermal gasification, typically
non-catalytic), where a syngas (carbon monoxide +hydrogen) is the
primary product (little or no methane is directly produced), which
can then be further processed to produce methane (via catalytic
methanation, see reaction (III) below) or any number of other
higher hydrocarbon products.
[0007] Hydromethanation processes and the conversion/utilization of
the resulting methane-rich synthesis gas stream to produce
value-added products are disclosed, for example, in U.S. Pat. No.
3828474, U.S. Pat. No. 3,958,957, 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. 4,243,639, 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. 4,604,105, 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, US2003/0167691A1,
US2006/0265953A1, US2007/000177A1, US2007/083072A1,
US2007/0277437A1, US2009/0048476A1, US2009/0090056A1,
US2009/0090055A1, US2009/0165383A1, US2009/0166588A1,
US2009/0165379A1, US2009/0170968A1, US2009/0165380A1,
US2009/0165381A1, US2009/0165361A1, US2009/0165382A1,
US2009/0169449A1, US2009/0169448A1, US2009/0165376A1,
US2009/0165384A1, US2009/0217582A1, US2009/0220406A1,
US2009/0217590A1, US2009/0217586A1, US2009/0217588A1,
US2009/0218424A1, US2009/0217589A1, US2009/0217575A1,
US2009/0229182A1, US2009/0217587A1, US2009/0246120A1,
US2009/0259080A1, US2009/0260287A1, US2009/0324458A1,
US2009/0324459A1, US2009/0324460A1, US2009/0324461A1,
US2009/0324462A1, US2010/0071235A1, US2010/0071262A1,
US2010/0120926A1, US2010/0121125A1, US2010/0168494A1,
US2010/0168495A1, US2010/0179232A1, US2010/0287835A1,
US2010/0287836A1, US2010/0292350A1, US2011/0031439A1,
US2011/0062012A1, US2011/0062721A1, US2011/0062722A1,
US2011/0064648A1, US2011/0088896A1, US2011/0088897A1,
US20110146978A1, US20110146979A1, US2012/0046510A1,
US2012/0060417A1, US2012/0102836A1, US2012/0102837A1,
WO2011/029278A1, WO2011/029282A1, WO2011/029283A1, WO2011/029284A1,
WO2011/029285A1, WO2011/063608A1 and GB1599932. See also
Chiaramonte et al, "Upgrade Coke by Gasification", Hydrocarbon
Processing, September 1982, pp. 255-257; and Kalina et al, "Exxon
Catalytic Coal Gasification Process Predevelopment Program, Final
Report", Exxon Research and Engineering Co., Baytown, Tex.,
FE236924, December 1978.
[0008] The hydromethanation of a carbon source typically involves
four theoretically separate reactions:
Steam carbon: C+HO.fwdarw.CO+H.sub.2 (I)
Water-gas shift: CO+H.sub.2O.fwdarw.H.sub.2'CO.sub.2 (II)
CO Methanation: CO+3H.sub.2.fwdarw.CH.sub.4+H.sub.2O (III)
Hydro-gasification: 2H.sub.2+C.fwdarw.CH.sub.4 (IV)
[0009] In the hydromethanation reaction, the first three reactions
(I-III) predominate to result in the following overall
reaction:
2C+2H.sub.2O.fwdarw.CH.sub.4+CO.sub.2 (V).
[0010] The overall hydromethanation reaction is essentially
thermally balanced; however, due to process heat losses and other
energy requirements (such as required for evaporation of moisture
entering the reactor with the feedstock), some heat must be added
to maintain the thermal balance.
[0011] The reactions are also essentially syngas (hydrogen and
carbon monoxide) balanced (syngas is produced and consumed);
therefore, as carbon monoxide and hydrogen are withdrawn with the
product gases, carbon monoxide and hydrogen need to be added to the
reaction as required to avoid a deficiency.
[0012] In order to maintain the net heat of reaction as close to
neutral as possible (only slightly exothermic or endothermic), and
maintain the syngas balance, a superheated gas stream of steam,
carbon monoxide and hydrogen is often fed to the hydromethanation
reactor. Frequently, the carbon monoxide and hydrogen streams are
recycle streams separated from the product gas, and/or are provided
by reforming/partially oxidating a portion of the product methane.
See, for example, previously incorporated U.S. Pat. No. 4,094,650,
U.S. Pat. No. 6,955,595, US2007/083072A1, US2010/0120926A1,
US2010/0287836A1, US2011/0031439A1, US2011/0062722A1 and
US2011/0064648A1.
[0013] In one variation of the hydromethanation process, required
carbon monoxide, hydrogen and heat energy can also at least in part
be generated in situ by feeding oxygen into the hydromethanation
reactor. See, for example, previously incorporated
US2010/0076235A1, US2010/0287835A1, US2011/0062721A1
US2012/0046510A1, US2012/0060417A1, US2012/0102836A1 and
US2012/0102837A1.
[0014] The result is a "direct" methane-enriched raw product gas
stream also containing substantial amounts of hydrogen, carbon
monoxide and carbon dioxide which can, for example, be directly
utilized as a medium BTU energy source, or can be processed to
result in a variety of higher-value product streams such as
pipeline-quality substitute natural gas, high-purity hydrogen,
methanol, ammonia, higher hydrocarbons, carbon dioxide (for
enhanced oil recovery and industrial uses) and electrical
energy.
[0015] In addition to the heat and syngas demands of the
hydromethanation reaction, steam is also a reactant in the process
and the process thus also has a steam demand. A portion of the
steam demand for the reaction can be satisfied by evaporation of
moisture entering the reactor with the feedstock; however, the
majority of the steam demand is satisfied by feeding superheated
steam into the hydromethanation reactor. Desirably, the required
superheated steam is generated substantially entirely from process
heat recovery so that little or no imported steam is needed.
[0016] Generating the required amount and type
(temperature/pressure) of superheated steam solely from process
heat recovery, however, is challenging, especially at or near the
operating temperature of the hydromethanation reactor. While the
superheated steam may in some cases desirably be fed at a
temperature less than the operating temperature of the
hydromethanation reactor (such as disclosed in previously
incorporated US2012/0046510A1), more oxygen may be required for the
hydromethanation reactor in order to maintain the heat balance,
which could have an effect on the overall efficiency of the
process.
[0017] It would, therefore, be desirable to find a way to utilize
lower temperature steam in order the satisfy the steam demand of
the hydromethanation reaction without degrading the overall process
efficiency in a material way.
SUMMARY OF THE INVENTION
[0018] In one aspect, the invention provides a process for
generating a cooled methane product stream and electrical power
from a non-gaseous carbonaceous material, the process comprising
the steps of:
[0019] (a) preparing a carbonaceous feedstock from the non-gaseous
carbonaceous material;
[0020] (b) introducing the carbonaceous feedstock, a
hydromethanation catalyst, a steam stream and an amount of oxygen
into a hydromethanation reactor, wherein the hydromethanation
reactor is operating at a first pressure condition;
[0021] (c) reacting a portion of the carbonaceous feedstock in the
hydromethanation reactor with oxygen to generate carbon monoxide,
hydrogen and heat energy;
[0022] (d) reacting a portion of the carbonaceous feedstock in the
hydromethanation reactor in the presence of carbon monoxide,
hydrogen, steam and hydromethanation catalyst to produce a
methane-enriched raw product gas;
[0023] (e) withdrawing a methane-enriched raw product gas stream of
the methane-enriched raw product gas from the hydromethanation
reactor, wherein the methane-enriched raw product gas stream
comprises methane, carbon monoxide, hydrogen, carbon dioxide,
hydrogen sulfide, steam and heat energy;
[0024] (f) introducing the methane-enriched raw product stream into
a first heat exchanger unit to recover heat energy and generate a
cooled methane-enriched raw product stream and a dry saturated
steam stream, wherein the dry saturated steam stream is at a second
pressure condition that is higher than the first pressure
condition;
[0025] (g) providing at least a portion of the dry saturated steam
stream to the hydromethanation reactor under a reduced pressure
condition such that the portion of dry saturated steam stream
provided to the hydromethanation reactor is converted to a first
superheated steam stream at or prior to introduction into the
hydromethanation reactor, wherein the reduced pressure condition is
higher than the first pressure condition but lower than the second
pressure condition;
[0026] (h) steam shifting a portion of the carbon monoxide in the
cooled methane-enriched raw product stream to generate a
hydrogen-enriched raw product stream;
[0027] (i) removing a substantial portion of the carbon dioxide and
a substantial portion of the hydrogen sulfide from the
hydrogen-enriched raw product stream to produce a sweetened gas
stream, wherein the sweetened gas stream comprises a substantial
portion of the hydrogen, carbon monoxide and methane from the
hydrogen-enriched raw product stream;
[0028] (j) methanating a substantial portion of the carbon monoxide
in the sweetened gas stream with hydrogen in the sweetened gas
stream to generate a methane-enriched treated product stream and
heat energy;
[0029] (k) recovering a portion of the heat energy from step (j) to
generate the cooled methane product stream;
[0030] (l) generating a second superheated steam stream from at
least a portion of the heat energy recovered in step (k); and
[0031] (m) generating electrical power from at least a portion of
the second superheated steam stream generated in step (l),
[0032] wherein
[0033] (1) the reaction of step (d) has a steam demand and a heat
demand,
[0034] (2) the steam demand is substantially satisfied by the steam
stream,
[0035] (3) the steam stream substantially comprises steam from the
dry saturated steam stream, and
[0036] (4) the amount of oxygen introduced into the
hydromethanation reactor is sufficient so that the heat demand of
the reaction of step (d) is substantially satisfied by the reaction
of step (c).
[0037] The process in accordance with the present invention is
useful, for example, for more efficiently producing higher-value
products and by-products from various carbonaceous materials at a
reduced capital and operating intensity.
[0038] These and other embodiments, features and advantages of the
present invention will be more readily understood by those of
ordinary skill in the art from a reading of the following detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a diagram of an embodiment of the process for
generating a cooled methane-enriched raw product gas stream and dry
saturated steam stream in accordance with the present
invention.
[0040] FIG. 2 is a diagram of an embodiment for the further
processing of the cooled methane-enriched raw product stream to
generate the cooled methane product stream and electrical power in
accordance with the present invention.
DETAILED DESCRIPTION
[0041] The present invention relates to processes for converting a
non-gaseous carbonaceous material ultimately into one or more
value-added gaseous products. Further details are provided
below.
[0042] In the context of the present description, 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.
[0043] 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.
[0044] Except where expressly noted, trademarks are shown in upper
case.
[0045] Unless stated otherwise, all percentages, parts, ratios,
etc., are by weight.
[0046] Unless stated otherwise, pressures expressed in psi units
are gauge, and pressures expressed in kPa units are absolute.
Pressure differences, however, are expressed as absolute (for
example, pressure 1 is 25 psi higher than pressure 2).
[0047] 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.
[0048] 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.
[0049] 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.
[0050] Further, unless expressly stated to the contrary, "or" and
"and/or" refers to an inclusive and not to an exclusive. For
example, a condition A or B, or A and/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).
[0051] 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.
[0052] The term "substantial", as used herein, unless otherwise
defined herein, means that greater than about 90% of the referenced
material, preferably greater than about 95% of the referenced
material, and more preferably greater than about 97% of the
referenced material. If not specified, the percent is on a molar
basis when reference is made to a molecule (such as methane, carbon
dioxide, carbon monoxide and hydrogen sulfide), and otherwise is on
a weight basis (such as for entrained fines).
[0053] The term "predominant portion", as used herein, unless
otherwise defined herein, means that greater than 50% of the
referenced material. If not specified, the percent is on a molar
basis when reference is made to a molecule (such as hydrogen,
methane, carbon dioxide, carbon monoxide and hydrogen sulfide), and
otherwise is on a weight basis (such as for entrained fines).
[0054] The term "depleted" is synonymous with reduced from
originally present. For example, removing a substantial portion of
a material from a stream would produce a material-depleted stream
that is substantially depleted of that material. Conversely, the
term "enriched" is synonymous with greater than originally
present.
[0055] The term "carbonaceous" as used herein is synonymous with
hydrocarbon.
[0056] The term "carbonaceous material" as used herein is a
material containing organic hydrocarbon content. Carbonaceous
materials can be classified as biomass or non-biomass materials as
defined herein.
[0057] The term "biomass" as used herein refers to carbonaceous
materials derived from recently (for example, within the past 100
years) living organisms, including plant-based biomass and
animal-based biomass. For clarification, biomass does not include
fossil-based carbonaceous materials, such as coal. For example, see
previously incorporated US2009/0217575A1, US2009/0229182A1 and
US2009/0217587A1.
[0058] The term "plant-based biomass" as used herein means
materials derived from green plants, crops, algae, and trees, such
as, but not limited to, sweet sorghum, bagasse, sugarcane, bamboo,
hybrid poplar, hybrid willow, albizia trees, eucalyptus, alfalfa,
clover, oil palm, switchgrass, sudangrass, millet, jatropha, and
miscanthus (e.g., Miscanthus.times.giganteus). Biomass further
include wastes from agricultural cultivation, processing, and/or
degradation such as corn cobs and husks, corn stover, straw, nut
shells, vegetable oils, canola oil, rapeseed oil, biodiesels, tree
bark, wood chips, sawdust, and yard wastes.
[0059] The term "animal-based biomass" as used herein means wastes
generated from animal cultivation and/or utilization. For example,
biomass includes, but is not limited to, wastes from livestock
cultivation and processing such as animal manure, guano, poultry
litter, animal fats, and municipal solid wastes (e.g., sewage).
[0060] The term "non-biomass", as used herein, means those
carbonaceous materials which are not encompassed by the term
"biomass" as defined herein. For example, non-biomass include, but
is not limited to, anthracite, bituminous coal, sub-bituminous
coal, lignite, petroleum coke, asphaltenes, liquid petroleum
residues or mixtures thereof. For example, see US2009/0166588A1,
US2009/0165379A1, US2009/0165380A1, US2009/0165361A1,
US2009/0217590A1 and US2009/0217586A1.
[0061] "Liquid heavy hydrocarbon materials" are viscous liquid or
semi-solid materials that are flowable at ambient conditions or can
be made flowable at elevated temperature conditions. These
materials are typically the residue from the processing of
hydrocarbon materials such as crude oil. For example, the first
step in the refining of crude oil is normally a distillation to
separate the complex mixture of hydrocarbons into fractions of
differing volatility. A typical first-step distillation requires
heating at atmospheric pressure to vaporize as much of the
hydrocarbon content as possible without exceeding an actual
temperature of about 650.degree. F., since higher temperatures may
lead to thermal decomposition. The fraction which is not distilled
at atmospheric pressure is commonly referred to as "atmospheric
petroleum residue". The fraction may be further distilled under
vacuum, such that an actual temperature of up to about 650.degree.
F. can vaporize even more material. The remaining undistillable
liquid is referred to as "vacuum petroleum residue". Both
atmospheric petroleum residue and vacuum petroleum residue are
considered liquid heavy hydrocarbon materials for the purposes of
the present invention.
[0062] Non-limiting examples of liquid heavy hydrocarbon materials
include vacuum resids; atmospheric resids; heavy and reduced
petroleum crude oils; pitch, asphalt and bitumen (naturally
occurring as well as resulting from petroleum refining processes);
tar sand oil; shale oil; bottoms from catalytic cracking processes;
coal liquefaction bottoms; and other hydrocarbon feedstreams
containing significant amounts of heavy or viscous materials such
as petroleum wax fractions.
[0063] The term "asphaltene" as used herein is an aromatic
carbonaceous solid at room temperature, and can be derived, for
example, from the processing of crude oil and crude oil tar sands.
Asphaltenes may also be considered liquid heavy hydrocarbon
feedstocks.
[0064] The liquid heavy hydrocarbon materials may inherently
contain minor amounts of solid carbonaceous materials, such as
petroleum coke and/or solid asphaltenes, that are generally
dispersed within the liquid heavy hydrocarbon matrix, and that
remain solid at the elevated temperature conditions utilized as the
feed conditions for the present process.
[0065] The terms "petroleum coke" and "petcoke" as used herein
include 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
petcoke.
[0066] Resid petcoke can also be derived from a crude oil, for
example, by coking processes used for upgrading heavy-gravity
residual crude oil (such as a liquid petroleum residue), which
petcoke 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.
[0067] 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 silica and/or
alumina.
[0068] 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.
[0069] Typically, the petroleum coke comprises less than about 20
wt % inorganic compounds, based on the weight of the petroleum
coke.
[0070] 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 the total coal weight.
Examples of useful coal include, but are not limited to, Illinois
#6, Pittsburgh #8, Beulah (ND), 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.
[0071] The ash produced from combustion of a coal typically
comprises both a fly ash and a bottom ash, as is familiar to those
skilled in the art. The fly ash from a bituminous coal can comprise
from about 20 to about 60 wt % silica and from about 5 to about 35
wt % alumina, based on the total weight of the fly ash. The fly ash
from a sub-bituminous coal can comprise from about 40 to about 60
wt % silica and from about 20 to about 30 wt % alumina, based on
the total weight of the fly ash. The fly ash from a lignite coal
can comprise from about 15 to about 45 wt % silica and from about
20 to about 25 wt % alumina, based on the total weight of the fly
ash. See, for example, Meyers, et al. "Fly Ash. A Highway
Construction Material," Federal Highway Administration, Report No.
FHWA-IP-76-16, Washington, D.C., 1976.
[0072] The bottom ash from a bituminous coal can comprise from
about 40 to about 60 wt % silica and from about 20 to about 30 wt %
alumina, based on the total weight of the bottom ash. The bottom
ash from a sub-bituminous coal can comprise from about 40 to about
50 wt % silica and from about 15 to about 25 wt % alumina, based on
the total weight of the bottom ash. The bottom ash from a lignite
coal can comprise from about 30 to about 80 wt % silica and from
about 10 to about 20 wt % alumina, based on the total weight of the
bottom ash. See, for example, Moulton, Lyle K. "Bottom Ash and
Boiler Slag," Proceedings of the Third International Ash
Utilization Symposium, U.S. Bureau of Mines, Information Circular
No. 8640, Washington, D.C., 1973.
[0073] A material such as methane can be biomass or non-biomass
under the above definitions depending on its source of origin.
[0074] A "non-gaseous" material is substantially a liquid,
semi-solid, solid or mixture at ambient conditions. For example,
coal, petcoke, asphaltene and liquid petroleum residue are
non-gaseous materials, while methane and natural gas are gaseous
materials.
[0075] The term "unit" refers to a unit operation. When more than
one "unit" is described as being present, those units are operated
in a parallel fashion unless otherwise stated. A single "unit",
however, may comprise more than one of the units in series, or in
parallel, depending on the context. For example, an acid gas
removal unit may comprise a hydrogen sulfide removal unit followed
in series by a carbon dioxide removal unit. As another example, a
contaminant removal unit may comprise a first removal unit for a
first contaminant followed in series by a second removal unit for a
second contaminant. As yet another example, a compressor may
comprise a first compressor to compress a stream to a first
pressure, followed in series by a second compressor to further
compress the stream to a second (higher) pressure.
[0076] The term "a portion of the carbonaceous feedstock" refers to
carbon content of unreacted feedstock as well as partially reacted
feedstock, as well as other components that may be derived in whole
or part from the carbonaceous feedstock (such as carbon monoxide,
hydrogen and methane). For example, "a portion of the carbonaceous
feedstock" includes carbon content that may be present in
by-product char and recycled fines, which char is ultimately
derived from the original carbonaceous feedstock.
[0077] The term "superheated steam" in the context of the present
invention refers to a steam stream that is non-condensing under the
conditions utilized, as is commonly understood by persons of
ordinary skill in the relevant art.
[0078] The term "dry saturated steam" or "dry steam" in the context
of the present invention refers to slightly superheated saturated
steam that is non-condensing, as is commonly understood by persons
of ordinary skill in the relevant art.
[0079] The term "syngas demand" refers to the maintenance of syngas
balance in the hydromethanation reactor for the hydromethanation
reaction of step (d). As indicated above, in the overall desirable
steady-state hydromethanation reaction (see equations (I), (II) and
(III) above), hydrogen and carbon monoxide are generated and
consumed in relative balance. Because both hydrogen and carbon
monoxide are withdrawn as part of the gaseous products, hydrogen
and carbon monoxide must be added to (via a superheated syngas feed
stream as discussed below) and/or generated in situ in (via a
combustion/oxidation reaction with supplied oxygen as discussed
below) the hydromethanation reactor in an amount at least required
to substantially maintain this reaction balance. For the purposes
of the present invention, the amount of hydrogen and carbon
monoxide that must be added to and/or generated in situ for the
hydromethanation reaction (step (d)) is the "syngas demand".
[0080] The term "steam demand" refers to the amount of steam that
must be added to the hydromethanation reactor via the steam stream
(step (b), see also (12) in FIG. 1). Steam is consumed in the
hydromethanation reaction and some steam must be added to the
hydromethanation reactor. The theoretical consumption of steam is
two moles for every two moles of carbon in the feed to produce one
mole of methane and one mole of carbon dioxide (see equation (V)).
In actual practice, the steam consumption is not perfectly
efficient and steam is withdrawn with the product gases; therefore,
a greater than theoretical amount of steam needs to be added to the
hydromethanation reactor, which added amount is the "steam demand".
Steam can be added, for example, via the steam stream and the
oxygen-rich gas stream (which are typically combined prior to
introduction into the hydromethanation reactor as discussed below).
The amount of steam to be added (and the source) is discussed in
further detail below. Steam generated in situ from the carbonaceous
feedstock (e.g., from vaporization of any moisture content of the
carbonaceous feedstock, or from an oxidation reaction with
hydrogen, methane and/or other hydrocarbons present in or generated
from the carbonaceous feedstock) can assist in providing steam;
however, it should be noted that any steam generated in situ or fed
into the hydromethanation reactor at a temperature lower than the
hydromethanation reaction temperature will have an impact on the
"heat demand" for the hydromethanation reaction.
[0081] The term "heat demand" refers to the amount of heat energy
that must be added to the hydromethanation reactor and/or generated
in situ (for example, via a combustion/oxidation reaction with
supplied oxygen as discussed below) to keep the reaction of step
(d) in substantial thermal balance, as discussed above and as
further detailed below. In the context of the present invention, as
discussed below, in steady-state operation of the process, all
streams are typically fed into the hydromethanation reactor at a
temperature below the operating temperature of the hydromethanation
reaction (step (d)). In that case the "heat demand" will be
satisfied by the in situ combustion/oxidation reaction (step
(c)).
[0082] 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. The materials, methods, and examples herein are
thus illustrative only and, except as specifically stated, are not
intended to be limiting.
General Process Information
[0083] In one embodiment of the invention, a cooled methane product
(99) and electrical power (92) are ultimately generated from a
non-gaseous carbonaceous material (10) as illustrated in FIGS. 1
and 2.
[0084] Referring to FIG. 1, in accordance with an embodiment of the
invention, the non-gaseous carbonaceous material (10) is processed
in a feedstock preparation unit (100) to generate a carbonaceous
feedstock (32) which is fed to a catalyst application unit (350)
where hydromethanation catalyst is applied to generate a catalyzed
carbonaceous feedstock (31+32).
[0085] In certain optional embodiments as discussed below, all or a
portion of a recycle carbon-enriched and inorganic ash-depleted
char stream (65) and/or all or a portion of a recovered fines
stream (362) may be (i) fed to feedstock preparation unit (100) and
co-processed with the non-gaseous carbonaceous material (10), (ii)
combined with carbonaceous feedstock (32) for feeding to catalyst
application unit (350), (iii) combined with catalyzed carbonaceous
feedstock (31+32); or (iv) some combination of the above may be
utilized.
[0086] The hydromethanation catalyst will typically comprise a
recycle catalyst from recycle catalyst stream (57) and a makeup
catalyst from make-up catalyst stream (56). Further details are
provided below.
[0087] The catalyzed carbonaceous feedstock (31+32) is fed into a
hydromethanation reactor (200) along with a steam stream (12) and
an oxygen-rich gas stream (14), and optionally a superheated syngas
feed stream (16).
[0088] As discussed in further detail below, steam stream (12) is
derived from a dry saturated steam stream (40) generated from
process heat recovery (from heat energy recovery from the hot raw
product gas), and is converted to superheated steam via pressure
drop prior to or at introduction into hydromethanation reactor
(200).
[0089] The steam stream (12), oxygen-rich gas stream (14) and
optional superheated syngas feed stream (16) may be a single feed
stream which comprises, or multiple feed streams which comprise, in
combination with the in situ generation of heat energy and syngas,
steam and heat energy, and optionally hydrogen and carbon monoxide,
as required to at least substantially satisfy, or at least satisfy,
the syngas, steam and heat demands of the hydromethanation reaction
that takes place in hydromethanation reactor (200).
[0090] In the hydromethanation reactor (200), (i) a portion of the
carbonaceous feedstock reacts with oxygen to generate heat energy
and typically carbon monoxide, hydrogen and carbon dioxide
(combustion/oxidation reaction), and (ii) a portion of the
carbonaceous feedstock, steam, hydrogen and carbon monoxide react
in the presence of the hydromethanation catalyst to generate a
methane-enriched raw product gas (the hydromethanation reaction).
The generated methane-enriched raw product gas is withdrawn as a
methane-enriched raw product gas stream (50) from the
hydromethanation reactor (200). The withdrawn methane-enriched raw
product gas stream (50) typically comprises at least methane,
carbon monoxide, carbon dioxide, hydrogen, hydrogen sulfide, steam,
entrained solids fines and heat energy.
[0091] The hydromethanation reactor (200) comprises a fluidized bed
(202) with an upper portion (202b) and a lower portion (202a).
Without being bound by any particular theory, the hydromethanation
reaction predominates in upper portion (202b), and an oxidation
reaction with the oxygen from oxygen-rich gas stream (14)
predominates in lower portion (202a). It is believed that there is
no specific defined boundary between the two portions, but rather
there is a transition as oxygen is consumed (and heat energy and
syngas are generated) in lower portion (202a). It is also believed
that oxygen consumption is rapid under the conditions present in
hydromethanation reactor (200); therefore, the predominant portion
of fluidized bed (202) will be upper portion (202b).
[0092] The steam stream (12) and oxygen-rich gas stream (14) may be
fed separately into the hydromethanation reactor (200), but are
typically combined prior to feeding into lower portion (202a) of
fluidized bed (202). In one embodiment, as disclosed in previously
incorporated US2012/0046510A1, optional superheated syngas feed
stream (16) is not present, and the catalyzed carbonaceous
feedstock (31+32), steam stream (12) and oxygen-rich gas stream
(14) are all fed to hydromethanation reactor (200) at a temperature
below the target operating temperature of the hydromethanation
reaction.
[0093] At least a portion of the carbonaceous feedstock in lower
portion (202a) of fluidized bed (202) will react with oxygen from
oxygen-rich gas stream (14) to generate heat energy, and also
hydrogen and carbon monoxide (syngas). In one embodiment, this
occurs in sufficient amounts to satisfy the heat and syngas demands
of the hydromethanation reaction (no separate superheated syngas
feed stream (16) is utilized in steady-state operation of the
process). This includes the reaction of solid carbon from unreacted
(fresh) feedstock, partially reacted feedstock (such as char and
recycled fines), as well gases (carbon monoxide, hydrogen, methane
and higher hydrocarbons) that may be generated from or carried with
the feedstock and recycle fines in lower portion (202a). Generally
some water (steam) may be produced, as well as other by-products
such as carbon dioxide depending on the extent of
combustion/oxidation.
[0094] As indicated above, in hydromethanation reactor (200)
(predominantly in upper portion (202b) of fluidized bed (202)) the
carbonaceous feedstock, steam, hydrogen and carbon monoxide react
in the presence of the hydromethanation catalyst to generate a
methane-enriched raw product, which is ultimately withdrawn as a
methane-enriched raw product stream (50) from the hydromethanation
reactor (200).
[0095] The reactions of the carbonaceous feedstock in fluidized bed
(202) also result in a by-product char comprising unreacted carbon
as well as non-carbon content from the carbonaceous feedstock
(including entrained hydromethanation catalyst) as described in
further detail below. To prevent buildup of the residue in the
hydromethanation reactor (200), a solid purge of by-product char is
routinely withdrawn (periodically or continuously) via char
withdrawal line (58).
[0096] The withdrawn by-product char can be processed in a catalyst
recovery unit (300) to recover entrained catalyst, and optionally
other value-added by-products such as vanadium and nickel
(depending on the content of the non-gaseous carbonaceous material
(10)), to generate a depleted char (59). Depleted char (59) may
optionally processed in a carbon recovery unit (325) to generate
the recycle carbon-enriched and inorganic ash-depleted char stream
(65) and a carbon-depleted and inorganic ash-enriched stream (66),
as disclosed in U.S. patent application Ser. No. 13/450,995
(incorporated below). In an alternative embodiment as discussed
below, all or a portion of the recovered fines stream (362) may be
co-processed with the withdrawn by-product char in catalyst
recovery unit (300).
[0097] In one embodiment of the present invention, as disclosed in
previously incorporated US2012/0102836A1, carbonaceous feedstock
(32) (or catalyzed carbonaceous feedstock (31+32)) is fed into
lower portion (202a) of fluidized bed (202). Because catalyzed
carbonaceous feedstock (31+32) is introduced into lower portion
(202a) of fluidized bed (202), char withdrawal line (58) will be
located at a point such that by-product char is withdrawn from
fluidized bed (202) at one or more points above the feed location
of catalyzed carbonaceous feedstock (31+32), typically from upper
portion (202b) of fluidized bed (202).
[0098] In this embodiment, due to the lower feed point of catalyzed
carbonaceous feedstock (31+32) into hydromethanation reactor (200),
and higher withdrawal point of by-product char from
hydromethanation reactor (200), hydromethanation reactor (200) with
be a flow-up configuration as discussed below.
[0099] Hydromethanation reactor (200) also typically comprises a
zone (206) below fluidized-bed (202), with the two sections
typically being separated by a grid plate (208) or similar divider.
Particles too large to be fluidized in fluidized-bed section (202),
for example large-particle by-product char and non-fluidizable
agglomerates, are generally collected in lower portion (202a) of
fluidized bed (202), as well as zone (206). Such particles will
typically comprise a carbon content (as well as an ash and catalyst
content), and may be removed periodically from hydromethanation
reactor (200) via char withdrawal lines (58) and (58a) for catalyst
recovery and further processing as discussed below.
[0100] Typically, the methane-enriched raw product passes through
an initial disengagement zone (204) above the fluidized-bed section
(202) prior to withdrawal from hydromethanation reactor (200). The
disengagement zone (204) may optionally contain, for example, one
or more internal cyclones and/or other entrained particle
disengagement mechanisms. The "withdrawn" (see discussion below)
methane-enriched raw product gas stream (50) typically comprises at
least methane, carbon monoxide, carbon dioxide, hydrogen, hydrogen
sulfide, steam, heat energy and entrained fines.
[0101] The methane-enriched raw product gas stream (50) is
initially treated to remove a substantial portion of the entrained
fines, typically via a cyclone assembly (360) (for example, one or
more internal and/or external cyclones), which may be followed if
necessary by optional additional treatments such as Venturi
scrubbers, as discussed in more detail below. The "withdrawn"
methane-enriched raw product gas stream (50), therefore, is to be
considered the raw product prior to fines separation, regardless of
whether the fines separation takes place internal to and/or
external of hydromethanation reactor (200).
[0102] As specifically depicted in FIG. 1, the methane-enriched raw
product stream (50) is passed from hydromethanation reactor (200)
to a cyclone assembly (360) for entrained particle separation.
While cyclone assembly (360) is shown in FIG. 1 as a single
external cyclone for simplicity, as indicated above cyclone
assembly (360) may be an internal and/or external cyclone, and may
also be a series of multiple internal and/or external cyclones.
[0103] The methane-enriched raw product gas stream (50) is treated
in cyclone assembly (360) to generate the fines-depleted
methane-enriched raw product gas stream (52) and a recovered fines
stream (362).
[0104] Recovered fines stream (362) may be fed back into
hydromethanation reactor (202), for example, into upper portion
(202b) of fluidized bed (202) via fines recycle line (364), and/or
into lower portion (202a) of fluidized bed (202) via fines recycle
line (366) (as disclosed in previously incorporated
US2012/0060417A1). To the extent not fed back into fluidized bed
(202), recovered fines stream (362) may, for example, be recycled
back to feedstock preparation unit (100) and/or catalyst recovery
unit (300), and/or combined with catalyzed carbonaceous feedstock
(31+32).
[0105] The fines-depleted methane-enriched raw product gas stream
(52) typically comprises at least methane, carbon monoxide, carbon
dioxide, hydrogen, hydrogen sulfide, steam, ammonia and heat
energy, as well as small amounts of contaminants such as remaining
residual entrained fines, and other volatilized and/or carried
material (for example, mercury) that may be present in the
carbonaceous feedstock. There are typically virtually no (total
typically less than about 50 ppm) condensable (at ambient
conditions) hydrocarbons present in fines-depleted methane-enriched
raw product gas stream (52).
[0106] The fines-depleted methane-enriched raw product gas stream
(52) is then provided to a heat recovery unit, e.g., first heat
exchanger unit (400), which removes at least a portion of the heat
energy from the fines-depleted methane-enriched raw product stream
(52) and reduces the temperature of the fines-depleted
methane-enriched raw product stream (52) to generate a cooled
methane-enriched raw product stream (70) having a temperature less
than the fines-depleted methane-enriched raw product stream
(52).
[0107] The heat energy recovered by first heat exchanger unit (400)
is used to generate a first process steam stream (40) from a boiler
feed water stream (39a), with the resulting first process steam
stream (40) being a dry saturated steam at a pressure (second
pressure condition) higher than the operating pressure (first
pressure condition) of hydromethanation reactor (200). At least a
portion of the first process steam stream (40) is fed back to the
hydromethanation reactor (200) as steam stream (12). Another
portion of first process steam stream (40) (for example, that is
excess to the steam demand of the hydromethanation reaction) can be
withdrawn as steam stream (12a) and used, for example, in other
process operations (such as catalyst application and recovery).
[0108] As indicated above, steam stream (12) as fed into
hydromethanation reactor (200) is superheated steam. As first
process steam stream (40) is at a pressure higher than in the
hydromethanation reactor (200), the conversion from dry saturated
steam to superheated steam can occur due to the pressure drop
across the feed point into hydromethanation reactor (200), or first
process steam stream (40) can be passed through an expander or
other similar pressure reduction device (405) to convert the dry
saturated steam into superheated steam, as discussed in further
detail below.
[0109] The cooled fines-depleted methane-enriched raw product gas
stream (70) is treated in one or more downstream processing steps
to further recover heat energy, decontaminate and convert, to
produce a cooled methane product stream, electrical power and,
optionally, one or more value-added products such as, for example,
substitute natural gas (pipeline quality), hydrogen, carbon
monoxide, syngas, ammonia, methanol and other syngas-derived
products, as disclosed in many of the documents referenced in the
"Hydromethanation" section below and as further discussed
below.
[0110] Additional details and embodiments are provided below.
Hydromethanation
[0111] Catalytic gasification/hydromethanation and/or raw product
conversion processes and conditions are generally 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. 4,604,105, U.S.
Pat. No. 4,617,027, U.S. Pat. No. 4609456, 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,
US2003/0167691A1 and US2006/0265953A1, as well as in previously
incorporated US2007/0000177A1, US2007/0083072A1, US2007/0277437A1,
US2009/0048476A1, US2009/0090056A1, US2009/0090055A1,
US2009/0165383A1, US2009/0166588A1, US2009/0165379A1,
US2009/0170968A1, US2009/0165380A1, US2009/0165381A1,
US2009/0165361A1, US2009/0165382A1, US2009/0169449A1,
US2009/0169448A1, US2009/0165376A1, US2009/0165384A1,
US2009/0217582A1, US2009/0220406A1, US2009/0217590A1,
US2009/0217586A1, US2009/0217588A1, US2009/0218424A1,
US2009/0217589A1, US2009/0217575A1, US2009/0229182A1,
US2009/0217587A1, US2009/0246120A1, US2009/0259080A1,
US2009/0260287A1, US2009/0324458A1, US2009/0324459A1,
US2009/0324460A1, US2009/0324461A1, US2009/0324462A1,
US2010/0076235A1, US2010/0071262A1, US2010/0121125A1,
US2010/0120926A1, US2010/0179232A1, US2010/0168495A1,
US2010/0168494A1, US2010/0292350A1, US2010/0287836A1,
US2010/0287835A1, US2011/0031439A1, US2011/0062012A1,
US2011/0062722A1, US2011/0062721A1, US2011/0064648A1,
US2011/0088896A1, US2011/0088897A1, US20110146978A1,
US20110146979A1, US2011/0207002A1, US2011/0217602A1,
US2011/0262323A1, US2012/0046510A1, US2012/0060417A1,
US2012/0102836A1 and US2012/0102837A1. See also commonly-owned U.S.
patent applications Ser. No. 13/402,022 (attorney docket no.
FN-0067 US NP1, entitled HYDROMETHANATION OF A CARBONACEOUS
FEEDSTOCK WITH NICKEL RECOVERY, which was filed 22 Feb. 2012), Ser.
No. 13/450,995 (attorney docket no. FN-0068 US NP1, entitled
HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK, which was filed 19
Apr. 2012) and Ser. No. 13/484,918 (attorney docket no. FN-0069 US
NP1, entitled HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK, which
was filed 31 May 2012).
[0112] In an embodiment in accordance with the present invention as
illustrated in FIG. 1, catalyzed carbonaceous feedstock (31+32),
steam stream (12) and, optionally, superheated syngas feed stream
(16) are introduced into hydromethanation reactor (200). In
addition, an amount of an oxygen-rich gas stream (14) is also
introduced into hydromethanation reactor (200) for in situ
generation of heat energy and syngas, as generally discussed above
and disclosed in many of the previously incorporated references
(see, for example, previously incorporated US2010/0076235A1,
US2010/0287835A1, US2011/0062721A1, US2012/0046510A1,
US2012/0060417A1, US2012/0102836A1 and US2012/0102837A1).
[0113] Steam stream (12), oxygen-rich gas stream (14) and
superheated syngas feed stream (16) (if present) are introduced
into hydromethanation reactor at a temperature below the target
operating temperature of the hydromethanation reaction, as
disclosed in previously incorporated US2012/0046510A1. Although
under those conditions this has a negative impact on the heat
demand of the hydromethanation reaction, this advantageously allows
full steam/heat integration of the hydromethanation portion of the
process, without the use of fuel-fired superheaters (in
steady-state operation of the process) that are typically fueled
with a portion of the product from the process.
[0114] Typically, superheated syngas feed stream (16) will not be
present in steady-state operation of the process.
[0115] Hydromethanation reactor (200) is a fluidized-bed reactor.
Hydromethanation reactor (200) can, for example, be a "flow down"
countercurrent configuration, where the catalyzed carbonaceous
feedstock (31+32) is introduced at a higher point so that the
particles flow down the fluidized bed (202) toward lower portion
(202a) of fluidized bed (202), and the gases flow in an upward
direction and are removed at a point above the fluidized bed
(202).
[0116] Alternatively, hydromethanation reactor (200) has a "flow
up" co-current configuration, where the catalyzed carbonaceous
feedstock (31+32) is fed at a lower point (bottom portion (202a) of
fluidized bed (202)) so that the particles flow up the fluidized
bed (202), along with the gases, to a char by-product removal zone,
for example, near or at the top of upper portion (202b) of
fluidized bed (202), to the top of fluidized bed (202). In one
embodiment, the feed point of the carbonaceous feedstock (such as
catalyzed carbonaceous feedstock (31+32)) should result in
introduction into fluidized bed (200) as close to the point of
introduction of oxygen (from oxygen-rich gas stream (14)) as
reasonably possible. See, for example, previously incorporated
US2012/0102836A1.
[0117] Hydromethanation reactor (200) is typically operated at
moderately high pressures and temperatures, requiring introduction
of solid streams (e.g., catalyzed carbonaceous feedstock (31+32)
and if present recycle fines) to the reaction chamber of the
reactor while maintaining the required temperature, pressure and
flow rate of the streams. Those skilled in the art are familiar
with feed inlets to supply solids into the reaction chambers having
high pressure and/or temperature environments, including star
feeders, screw feeders, rotary pistons and lock-hoppers. It should
be understood that the feed inlets can include two or more
pressure-balanced elements, such as lock hoppers, which would be
used alternately. In some instances, the carbonaceous feedstock can
be prepared at pressure conditions above the operating pressure of
the reactor and, hence, the particulate composition can be directly
passed into the reactor without further pressurization. Gas for
pressurization can be an inert gas such as nitrogen, or more
typically a stream of carbon dioxide that can, for example be
recycled from a carbon dioxide stream generated by an acid gas
removal unit.
[0118] Hydromethanation reactor (200) is desirably operated at a
moderate temperature (as compared to "conventional" oxidation-based
gasification processes), with a target operating temperature of at
least about 1000.degree. F. (about 538.degree. C.), or at least
about 1100.degree. F. (about 593.degree. C.), to about 1500.degree.
F. (about 816.degree. C.), or to about 1400.degree. F. (about
760.degree. C.), or to about 1300.degree. F. (704.degree. C.); and
a pressure (first operating pressure of step (c)) of about 250 psig
(about 1825 kPa, absolute), or about 400 psig (about 2860 kPa), or
about 450 psig (about 3204 kPa), to about 1000 psig (about 6996
kPa), or to about 800 psig (about 5617 kPa), or to about 700 psig
(about 4928 kPa), or to about 600 psig (about 4238 kPa), or to
about 500 psig (about 3549 kPa). In one embodiment,
hydromethanation reactor (200) is operated at a pressure (first
operating pressure) of up to about 600 psig (about 4238 kPa), or up
to about 550 psig (about 3894 kPa).
[0119] Typical gas flow velocities in hydromethanation reactor
(200) are from about 0.5 ft/sec (about 0.15 m/sec), or from about 1
ft/sec (about 0.3 m/sec), to about 2.0 ft/sec (about 0.6 m/sec), or
to about 1.5 ft/sec (about 0.45 m/sec).
[0120] As oxygen-rich gas stream (14) is fed into hydromethanation
reactor (200), a portion of the carbonaceous feedstock (desirably
carbon from the partially reacted feedstock, by-product char and
recycled fines) will be consumed in an oxidation/combustion
reaction, generating heat energy as well as typically some amounts
carbon monoxide and hydrogen (and typically other gases such as
carbon dioxide and steam). The variation of the amount of oxygen
supplied to hydromethanation reactor (200) provides an advantageous
process control to ultimately maintain the syngas and heat balance.
Increasing the amount of oxygen will increase the
oxidation/combustion, and therefore increase in situ heat
generation. Decreasing the amount of oxygen will conversely
decrease the in situ heat generation. The amount of syngas
generated will ultimately depend on the amount of oxygen utilized,
and higher amounts of oxygen may result in a more complete
combustion/oxidation to carbon dioxide and water, as opposed to a
more partial combustion to carbon monoxide and hydrogen.
[0121] The amount of oxygen supplied to hydromethanation reactor
(200) must be sufficient to combust/oxidize enough of the
carbonaceous feedstock to generate enough heat energy and syngas to
meet the heat and syngas demands of the steady-state
hydromethanation reaction.
[0122] In one embodiment, the amount of molecular oxygen (as
contained in the oxygen-rich gas stream (14)) that is provided to
the hydromethanation reactor (200) can range from about 0.10, or
from about 0.20, or from about 0.25, to about 0.6, or to about 0.5,
or to about 0.4, or to about 0.35 pounds of O.sub.2 per pound of
carbonaceous feedstock (32).
[0123] The hydromethanation and oxidation/combustion reactions
within hydromethanation reactor (200) will occur contemporaneously.
Depending on the configuration of hydromethanation reactor (200),
the two steps will typically predominate in separate zones--the
hydromethanation in upper portion (202b) of fluidized bed (202),
and the oxidation/combustion in lower portion (202a) of fluidized
bed (202). The oxygen-rich gas stream (14) is typically mixed with
steam stream (12) and the mixture introduced at or near the bottom
of fluidized bed (202) in lower portion (202a) to avoid formation
of hot spots in the reactor, and to avoid (minimize) combustion of
the desired gaseous products. Feeding the catalyzed carbonaceous
feedstock (31+32) with an elevated moisture content, and
particularly into lower portion (202a) of fluidized bed (202), also
assists in heat dissipation and the avoidance if formation of hot
spots in reactor (200), as disclosed in previously incorporated
US2012/0102837A1.
[0124] If superheated syngas feed stream (16) is present, that
stream will typically be introduced as a mixture with steam stream
(12), with oxygen-rich gas stream (14) introduced separately into
lower portion (202a) of fluidized bed (202) so as to not
preferentially consume the syngas components.
[0125] The oxygen-rich gas stream (14) can be fed into
hydromethanation reactor (200) by any suitable means such as direct
injection of purified oxygen, oxygen-air mixtures, oxygen-steam
mixtures, or oxygen-inert gas mixtures into the reactor. See, for
instance, U.S. Pat. No. 4,315,753 and Chiaramonte et al.,
Hydrocarbon Processing, September 1982, pp. 255-257.
[0126] The oxygen-rich gas stream (14) is typically generated via
standard air-separation technologies, and will be fed mixed with
steam, and introduced at a temperature above about 250.degree. F.
(about 121.degree. C.), to about 400.degree. F. (about 204.degree.
C.), or to about 350.degree. F. (about 177.degree. C.), or to about
300.degree. F. (about 149.degree. C.), and at a pressure at least
slightly higher than present in hydromethanation reactor (200). The
steam in oxygen-rich gas stream (14) should be non-condensable
during transport of oxygen-rich stream (14) to hydromethanation
reactor (200), so oxygen-rich stream (14) may need to be
transported at a lower pressure then pressurized (compressed) just
prior to introduction into hydromethanation reactor (200).
[0127] As indicated above, the hydromethanation reaction has a
steam demand, a heat demand and a syngas demand. These conditions
in combination are important factors in determining the operating
conditions for the hydromethanation reaction as well as the
remainder of the process.
[0128] For example, the hydromethanation reaction requires a
theoretical molar ratio of steam to carbon (in the feedstock) of at
least about 1. Typically, however, the molar ratio is greater than
about 1, or from about 1.5 (or greater), to about 6 (or less), or
to about 5 (or less), or to about 4 (or less), or to about 3 (or
less), or to about 2 (or less). The moisture content of the
catalyzed carbonaceous feedstock (31+32), moisture generated from
the carbonaceous feedstock in the hydromethanation reactor (200),
and steam included in the steam stream (12), oxygen-rich gas stream
(14) and recycle fines stream(s) (and optional superheated syngas
feed stream (16)), all contribute steam for the hydromethanation
reaction. The steam in steam stream (12) should be sufficient to at
least substantially satisfy (or at least satisfy) the "steam
demand" of the hydromethanation reaction.
[0129] As also indicated above, the hydromethanation reaction (step
(d)) is essentially thermally balanced but, due to process heat
losses and other energy requirements (for example, vaporization of
moisture on the feedstock), some heat must be generated in the
hydromethanation reaction to maintain the thermal balance (the heat
demand). The partial combustion/oxidation of carbon in the presence
of the oxygen introduced into hydromethanation reactor (200) from
oxygen-rich gas stream (14) should be sufficient to at least
substantially satisfy (or at least satisfy) both the heat and
syngas demand of the hydromethanation reaction.
[0130] The gas utilized in hydromethanation reactor (200) for
pressurization and reaction of the catalyzed carbonaceous feedstock
(31+32) comprises the steam stream (12) and oxygen-rich gas stream
(14) (and optional superheated syngas feed stream (16)) and,
optionally, additional nitrogen, air, or inert gases such as argon,
which can be supplied to hydromethanation reactor (200) according
to methods known to those skilled in the art. As a consequence,
steam stream (12) and oxygen-rich gas stream (14) must be provided
at a higher pressure which allows them to enter hydromethanation
reactor (200).
[0131] All streams should be fed into hydromethanation reactor
(200) at a temperature less than the target operating temperature
of the hydromethanation reactor, such as disclosed in previously
incorporated US2012/0046510A1.
[0132] Steam stream (12) will be at a temperature above the
saturation point at the feed pressure. When fed into
hydromethanation reactor (200), steam stream (12) will be a
superheated steam stream to avoid the possibility of any
condensation occurring. Typical feed temperatures of steam stream
(12) are from about 400.degree. F. (about 204.degree. C.), or from
about 450.degree. F. (about 232.degree. C.), to about 650.degree.
F. (about 343.degree. C.), or to about 600.degree. F. (about
316.degree. C.). Typical feed pressures of steam stream (12) are
about 25 psi (about 172 kPa) or greater than the pressure within
hydromethanation reactor (200).
[0133] The actual temperature and pressure of steam stream (12)
will ultimately depend on the level of heat recovery from the
process and the operating pressure within hydromethanation reactor
(200), as discussed below. In any event, desirably no fuel-fired
superheater should be used in the superheating of steam stream (12)
in steady-state operation of the process.
[0134] When steam stream (12) and oxygen-rich stream (14) are
combined for feeding into lower section (202a) of fluidized bed
(202), the temperature of the combined stream will be controlled by
the temperature of steam stream (12), and will typically range from
about from about from about 400.degree. F. (about 204.degree. C.),
or from about 450.degree. F. (about 232.degree. C.), to about
650.degree. F. (about 343.degree. C.), or to about 600.degree. F.
(about 316.degree. C.).
[0135] The temperature in hydromethanation reactor (200) can be
controlled, for example, by controlling the amount and temperature
of steam stream (12), as well as the amount of oxygen supplied to
hydromethanation reactor (200).
[0136] In steady-state operation, steam for the hydromethanation
reaction is solely generated from other process operations through
process heat capture (such as generated in a waste heat boiler,
generally referred to as "process steam" or "process-generated
steam"), specifically from the cooling of the raw product gas in
heat first heat exchanger unit (400). Additional steam can be
generated for other portions of the overall process, such as
disclosed, for example, in previously incorporated US2010/0287835A1
and US2012/0046510A1.
[0137] The overall process described herein is desirably steam
positive, such that steam demand (pressure and amount) for the
hydromethanation reaction can be satisfied via heat exchange in
first heat exchange unit (400), with process heat recovery at the
different stages allowing for production of excess steam that can
be used for power generation and other purposes. Desirably,
process-generated steam from first heat exchange unit (400)
accounts for 100 wt % or greater of the steam demand of the
hydromethanation reaction.
[0138] The result of the hydromethanation reaction is a
methane-enriched raw product, which is withdrawn from
hydromethanation reactor (200) as methane-enriched raw product
stream (50) typically comprising CH.sub.4, CO.sub.2, H.sub.2, CO,
H.sub.2S, unreacted steam and, optionally, other contaminants such
as entrained fines, NH.sub.3, COS, HCN and/or elemental mercury
vapor, depending on the nature of the carbonaceous material
utilized for hydromethanation.
[0139] If the hydromethanation reaction is run in syngas balance,
the methane-enriched raw product stream (50), upon exiting the
hydromethanation reactor (200), will typically comprise at least
about 15 mol %, or at least about 18 mol %, or at least about 20
mol %, methane based on the moles of methane, carbon dioxide,
carbon monoxide and hydrogen in the methane-enriched raw product
stream (50). In addition, the methane-enriched raw product stream
(50) will typically comprise at least about 50 mol % methane plus
carbon dioxide, based on the moles of methane, carbon dioxide,
carbon monoxide and hydrogen in the methane-enriched raw product
stream (50).
[0140] If the hydromethanation reaction is run in syngas excess,
e.g., contains an excess of carbon monoxide and/or hydrogen above
and beyond the syngas demand (for example, excess carbon monoxide
and/or hydrogen are generated due to the amount of oxygen-rich gas
stream (14) fed to hydromethanation reactor (200)), then there may
be some dilution effect on the molar percent of methane and carbon
dioxide in methane-enriched raw product stream (50).
[0141] The non-gaseous carbonaceous materials (10) useful in these
processes include, for example, a wide variety of biomass and
non-biomass materials. The carbonaceous feedstock (32) is derived
from one or more non-gaseous carbonaceous materials (10), which are
processed in a feedstock preparation section (100) as discussed
below.
[0142] The hydromethanation catalyst (31) can comprise one or more
catalyst species, as discussed below.
[0143] The carbonaceous feedstock (32) and the hydromethanation
catalyst (31) are typically intimately mixed (i.e., to provide a
catalyzed carbonaceous feedstock (31+32)) before provision to the
hydromethanation reactor (200), but they can be fed separately as
well.
Gas Processing
Fines Removal
[0144] The hot gas effluent leaving the reaction chamber of the
hydromethanation reactor (200) can pass through a fines remover
unit (such as cyclone assembly (360)), incorporated into and/or
external of the hydromethanation reactor (200), which serves as a
disengagement zone. Particles too heavy to be entrained by the gas
leaving the hydromethanation reactor (200) (i.e., fines) are
returned to the hydromethanation reactor (200), for example, to the
reaction chamber (e.g., fluidized bed (202)).
[0145] Residual entrained fines are substantially removed by any
suitable device such as internal and/or external cyclone separators
optionally followed by Venturi scrubbers. As discussed above, at
least a portion of these fines can be returned to lower section
(202a) of fluidized bed (202) via recycle line (366). A portion may
also be returned to upper portion (202b) of fluidized bed (202) via
recycle line (364). Any remaining recovered fines can be processed
to recover alkali metal catalyst, and/or combined at some stage
with carbonaceous feedstock (32), and/or directly recycled back to
feedstock preparation as described in previously incorporated
US2009/0217589A1.
[0146] Removal of a "substantial portion" of fines means that an
amount of fines is removed from the resulting gas stream such that
downstream processing is not adversely affected; thus, at least a
substantial portion of fines should be removed. Some minor level of
ultrafine material may remain in the resulting gas stream to the
extent that downstream processing is not significantly adversely
affected. Typically, at least about 90 wt %, or at least about 95
wt %, or at least about 98 wt %, of the fines of a particle size
greater than about 20 .mu.m, or greater than about 10 .mu.m, or
greater than about 5 .mu.m, are removed.
Heat Exchange and First Process Steam Stream
[0147] Depending on the hydromethanation conditions, the
fines-depleted methane-enriched raw product stream (52) can be
generated having at a temperature ranging from about 1000.degree.
F. (about 538.degree. C.) to about 1500.degree. F. (about
816.degree. C.), and more typically from about 1100.degree. F.
(about 593.degree. C.) to about 1400.degree. F. (about 760.degree.
C.); a pressure of from about 250 psig (about 1825 kPa) to about
1000 psig (about 6996 kPa), more typically from about 400 psig
(about 2860 kPa), or from about 450 psig (about 3204 kPa), to about
800 psig (about 5617 kPa), or to about 600 psig (about 4238 kPa);
and a velocity of from about 0.5 ft/sec (about 0.15 m/sec) to about
2.0 ft/sec (about 0.61 m/sec), more typically from about 1.0 ft/sec
(0.30 m/sec) to about 1.5 ft/sec (about 0.46 m/sec).
[0148] The fines-depleted methane-enriched raw product stream (52)
is provided to a heat recovery unit, e.g., first heat exchanger
unit (400) as shown in FIG. 1. First heat exchanger unit (400)
removes a portion of the heat energy from the fines-depleted
methane-enriched raw product stream (52) and reduces the
temperature of the fines-depleted methane-enriched raw product
stream (52) to generate a cooled methane-enriched raw product
stream (70) having a temperature less than the fines-depleted
methane-enriched raw product stream (52). The heat energy recovered
by first heat exchanger unit (400) is used at least in part to
generate a first process steam stream (40) which is a dry saturated
steam stream. At least a portion of the first process steam stream
(40) is fed back to the hydromethanation reactor (200) as steam
stream (12).
[0149] In one embodiment, first heat exchanger unit (400) is a
steam boiler, for example, a shell and tube heat exchanger of a
type well-known to those of ordinary skill in the relevant art. A
stream of boiler feed water (39a) is passed through first heat
exchanger unit (400) to generate first process steam stream (40),
which is a dry saturated steam stream of a pressure higher than the
pressure in hydromethanation reactor (200).
[0150] The resulting cooled methane-enriched raw product stream
(70) will typically exit first heat exchanger unit (400) at a
temperature ranging from about 450.degree. F. (about 232.degree.
C.) to about 1100.degree. F. (about 593.degree. C.), more typically
from about 550.degree. F. (about 288.degree. C.) to about
950.degree. F. (about 510.degree. C.); a pressure of from about 250
psig (about 1825 kPa) to about 1000 psig (about 6996 kPa), more
typically from about 400 psig (about 2860 kPa), or from about 450
psig (about 3204 kPa), to about 800 psig (about 5617 kPa), or to
about 600 psig (about 4238 kPa); and a velocity of from about 0.5
ft/sec (about 0.15 m/sec) to about 2.0 ft/sec (about 0.61 m/sec),
more typically from about 1.0 ft/sec (0.30 m/sec) to about 1.5
ft/sec (about 0.46 m/sec).
[0151] The resulting first process steam stream (40) is a dry
saturated steam stream that will exit first heat exchanger unit
(400) at a pressure that is ultimately dependent on the operating
pressure within hydromethanation reactor (200). The temperature of
first process steam stream (40) will typically be slightly above
the saturation temperature, for example, about 20% or less, or
about 10% or less, or about 5% or less, above such saturation
temperature.
[0152] In one embodiment, the pressure of first process steam
stream (40) at the exit of first heat exchanger unit (400) (second
pressure condition) is at least about 25 psi (about 172 kPa), or at
least about 50 psi (about 345 kPa), or at least about 100 psi
(about 690 kPa), greater than the operating pressure of the
hydromethanation reactor (200) (first pressure condition). In
another embodiment, the pressure of first process steam stream (40)
at the exit of first heat exchanger unit (400) (second pressure
condition) is at least about 5%, or at least about 10%, greater
than the operating pressure of the hydromethanation reactor (200)
(first pressure condition).
[0153] In another embodiment, the pressure of first process steam
stream (40) at the exit of first heat exchanger unit (400) (second
pressure condition) is about 200 psi (about 1379 kPa) or less
greater than the operating pressure of the hydromethanation reactor
(200) (first pressure condition). In another embodiment, the
pressure of first process steam stream (40) at the exit of first
heat exchanger unit (400) (second pressure condition) is at least
about 20% or less greater than the operating pressure of the
hydromethanation reactor (200) (first pressure condition).
[0154] As indicated above, steam stream (12) substantially
comprises, or fully comprises, steam from first process steam
stream (40). To the extent not utilized as part of steam stream
(12), an excess steam stream (12a) can be withdrawn for use
elsewhere in the process.
[0155] At or before feeding into hydromethanation reactor (200),
steam stream is converted from a dry saturated steam stream to a
superheated steam stream by pressure drop. For example, because
steam stream (12) is at a pressure higher than the operating
pressure of hydromethanation reactor (200), simply feeding steam
stream (12) into hydromethanation reactor (200) will result in such
conversion. To the extent necessary, steam stream (12) can also be
processed through an expander or other pressure drop device (405)
to reduce the pressure in steam stream (12) as appropriate for
feeding into hydromethanation reactor (200).
Gas Purification/Conversion
[0156] Referring to FIG. 2, raw product purification/conversion
will typically comprise, for example, water-gas shift processes
(700), dehydration (450), acid gas removal (800) and methanation
(950), and other optional processes such as, for example, trace
contaminant removal (500) and ammonia removal and recovery
(600).
[0157] Trace Contaminant Removal (500)
[0158] As is familiar to those skilled in the art, the
contamination levels of the gas stream, e.g., cooled
methane-enriched raw product stream (70), will depend on the nature
of the carbonaceous material used for preparing the carbonaceous
feedstocks. For example, certain coals, such as Illinois #6, can
have high sulfur contents, leading to higher COS contamination; and
other coals, such as Powder River Basin coals, can contain
significant levels of mercury which can be volatilized in
hydromethanation reactor (200).
[0159] COS can be removed from a gas stream, e.g. the cooled
methane-enriched raw product stream (70), by COS hydrolysis (see,
U.S. Pat. No. 3,966,875, U.S. Pat. No. 4,011,066, U.S. Pat. No.
4,100,256, U.S. Pat. No. 4,482,529 and U.S. Pat. No. 4,524,050),
passing the gas stream through particulate limestone (see, U.S.
Pat. No. 4,173,465), an acidic buffered CuSO.sub.4 solution (see,
U.S. Pat. No. 4,298,584), an alkanolamine absorbent such as
methyldiethanolamine, triethanolamine, dipropanolamine or
diisopropanolamine, containing tetramethylene sulfone (sulfolane,
see, U.S. Pat. No. 3,989,811); or counter-current washing of the
cooled second gas stream with refrigerated liquid CO.sub.2 (see,
U.S. Pat. No. 4,270,937 and U.S. Pat. No. 4,609,388).
[0160] HCN can be removed from a gas stream, e.g., the cooled
methane-enriched raw product stream (70), by reaction with ammonium
sulfide or polysulfide to generate CO.sub.2, H.sub.2S and NH.sub.3
(see, U.S. Pat. No. 4,497,784, U.S. Pat. No. 4,505,881 and U.S.
Pat. No. 4,508,693), or a two stage wash with formaldehyde followed
by ammonium or sodium polysulfide (see, U.S. Pat. No. 4,572,826),
absorbed by water (see, U.S. Pat. No. 4,189,307), and/or decomposed
by passing through alumina supported hydrolysis catalysts such as
MoO.sub.3, TiO.sub.2 and/or ZrO.sub.2 (see, U.S. Pat. No.
4,810,475, U.S. Pat. No. 5,660,807 and U.S. Pat. No.
5,968,465).
[0161] Elemental mercury can be removed from a gas stream, e.g.,
the cooled methane-enriched raw product stream (70), for example,
by absorption by carbon activated with sulfuric acid (see, U.S.
Pat. No. 3,876,393), absorption by carbon impregnated with sulfur
(see, U.S. Pat. No. 4,491,609), absorption by a H.sub.2S-containing
amine solvent (see, U.S. Pat. No. 4,044,098), absorption by silver
or gold impregnated zeolites (see, U.S. Pat. No. 4,892,567),
oxidation to HgO with hydrogen peroxide and methanol (see, U.S.
Pat. No. 5,670,122), oxidation with bromine or iodine containing
compounds in the presence of SO.sub.2 (see, U.S. Pat. No.
6,878,358), oxidation with a H, Cl and O-containing plasma (see,
U.S. Pat. No. 6,969,494), and/or oxidation by a chlorine-containing
oxidizing gas (e.g., ClO, see, U.S. Pat. No. 7,118,720).
[0162] When aqueous solutions are utilized for removal of any or
all of COS, HCN and/or Hg, the waste water generated in the trace
contaminants removal units can be directed to a waste water
treatment unit (not depicted).
[0163] When present, a trace contaminant removal of a particular
trace contaminant should remove at least a substantial portion (or
substantially all) of that trace contaminant from the so-treated
gas stream (e.g., cooled methane-enriched raw product stream (70)),
typically to levels at or lower than the specification limits of
the desired product stream. Typically, a trace contaminant removal
should remove at least 90%, or at least 95%, or at least 98%, of
COS, HCN and/or mercury from a cooled first gas stream, based on
the weight of the contaminant in the prior to treatment.
[0164] Ammonia Removal and Recovery (600)
[0165] As is familiar to those skilled in the art, gasification of
biomass, certain coals, certain petroleum cokes and/or utilizing
air as an oxygen source for hydromethanation reactor (200) can
produce significant quantities of ammonia in the product stream.
Optionally, a gas stream, e.g. the cooled methane-enriched raw
product stream (70), can be scrubbed by water in one or more
ammonia removal and recovery units (600) to remove and recover
ammonia.
[0166] The ammonia recovery treatment may be performed, for
example, on the cooled methane-enriched raw product stream (70),
directly from heat exchanger (400) or after treatment in one or
both of (i) one or more of the trace contaminants removal units
(500), and (ii) one or more sour shift units (700).
[0167] After scrubbing, the gas stream, e.g., the cooled
methane-enriched raw product stream (70), will typically comprise
at least H.sub.2S, CO.sub.2, CO, H.sub.2 and CH.sub.4. When the
cooled methane-enriched raw product stream (70) has previously
passed through a sour shift unit (700), then, after scrubbing, the
gas stream will typically comprise at least H.sub.2S, CO.sub.2,
H.sub.2 and CH.sub.4.
[0168] Ammonia can be recovered from the scrubber water according
to methods known to those skilled in the art, can typically be
recovered as an aqueous solution (61) (e.g., 20 wt %). The waste
scrubber water can be forwarded to a waste water treatment unit
(not depicted).
[0169] When present, an ammonia removal process should remove at
least a substantial portion (and substantially all) of the ammonia
from the scrubbed stream, e.g., the cooled methane-enriched raw
product stream (70). "Substantial" removal in the context of
ammonia removal means removal of a high enough percentage of the
component such that a desired end product can be generated.
Typically, an ammonia removal process will remove at least about
95%, or at least about 97%, of the ammonia content of a scrubbed
first gas stream, based on the weight of ammonia in the stream
prior to treatment.
[0170] Any recovered ammonia can be used as such or, for example,
can be converted with other by-products from the process. For
example, sulfur recovered from the acid gas removal unit can be
used in conjunction with the ammonia to generate products such as
ammonium sulfate.
[0171] Water-Gas Shift (700)
[0172] A portion or all of the methane-enriched raw product stream
(e.g., cooled methane-enriched raw product stream (70)) is
typically supplied to a water-gas shift reactor, such as sour shift
reactor (700).
[0173] In sour shift reactor (700), the gases undergo a sour shift
reaction (also known as a water-gas shift reaction) in the presence
of an aqueous medium (such as steam) to convert at least a
predominant portion (or a substantial portion, or substantially
all) of the CO to CO.sub.2 and to increase the fraction of H.sub.2.
The generation of increased hydrogen content is utilized, for
example, to optimize hydrogen production, or to otherwise optimize
H.sub.2/CO ratios for downstream methanation.
[0174] The water-gas shift treatment may be performed on the cooled
methane-enriched raw product stream (70) passed directly from heat
exchanger (400), or on the cooled methane-enriched raw product
stream (70) that has passed through a trace contaminants removal
unit (500) and/or an ammonia removal unit (600).
[0175] A sour shift process is described in detail, for example, in
U.S. Pat. No. 7,074,373. The process involves adding water, or
using water contained in the gas, and reacting the resulting
water-gas mixture adiabatically over a steam reforming catalyst.
Typical steam reforming catalysts include one or more Group VIII
metals on a heat-resistant support.
[0176] Methods and reactors for performing the sour gas shift
reaction on a CO-containing gas stream are well known to those of
skill in the art. Suitable reaction conditions and suitable
reactors can vary depending on the amount of CO that must be
depleted from the gas stream. In some embodiments, the sour gas
shift can be performed in a single stage within a temperature range
from about 100.degree. C., or from about 150.degree. C., or from
about 200.degree. C., to about 250.degree. C., or to about
300.degree. C., or to about 350.degree. C. In these embodiments,
the shift reaction can be catalyzed by any suitable catalyst known
to those of skill in the art. Such catalysts include, but are not
limited to, Fe.sub.2O.sub.3-based catalysts, such as
Fe.sub.2O.sub.3--Cr.sub.2O.sub.3 catalysts, and other transition
metal-based and transition metal oxide-based catalysts. In other
embodiments, the sour gas shift can be performed in multiple
stages. In one particular embodiment, the sour gas shift is
performed in two stages. This two-stage process uses a
high-temperature sequence followed by a low-temperature sequence.
The gas temperature for the high-temperature shift reaction ranges
from about 350.degree. C. to about 1050.degree. C. Typical
high-temperature catalysts include, but are not limited to, iron
oxide optionally combined with lesser amounts of chromium oxide.
The gas temperature for the low-temperature shift ranges from about
150.degree. C. to about 300.degree. C., or from about 200.degree.
C. to about 250.degree. C. Low-temperature shift catalysts include,
but are not limited to, copper oxides that may be supported on zinc
oxide or alumina. Suitable methods for the sour shift process are
described in previously incorporated US2009/0246120A1.
[0177] The sour shift reaction is exothermic so it is often carried
out with a heat exchanger, such as second heat exchanger unit
(401), to permit the efficient use of heat energy. Shift reactors
employing these features are well known to those of skill in the
art. An example of a suitable shift reactor is illustrated in
previously incorporated U.S. Pat. No. 7,074,373, although other
designs known to those of skill in the art are also effective.
[0178] Following the sour gas shift procedure, the resulting
hydrogen-enriched raw product stream (72) generally contains
CH.sub.4, CO.sub.2, H.sub.2, H.sub.2S, steam, optionally CO and
optionally minor amounts of other contaminants.
[0179] As indicated above, the hydrogen-enriched raw product stream
(72) can be provided to a heat recovery unit, e.g., second heat
exchanger unit (401). While second heat exchanger unit (401) is
depicted in FIG. 2 as a separate unit, it can exist as such and/or
be integrated into the sour shift reactor (700), thus being capable
of cooling the sour shift reactor (700) and removing at least a
portion of the heat energy from the hydrogen-enriched raw product
stream (72) to reduce the temperature and generate a cooled
stream.
[0180] At least a portion of the recovered heat energy can be used
to generate a second process steam stream from a water/steam
source.
[0181] In a specific embodiment as depicted in FIG. 2, the
hydrogen-enriched raw product stream (72), upon exiting sour shift
reactor (700), is introduced into a superheater (401a) followed by
a boiler feed water preheater (401b). Superheater (401a) can be
used, for example, to superheat a stream (42a) which can be a
portion of cooled methane-enriched raw product stream (70), to
generate a superheated stream (42b) which is then recombined into
cooled methane-enriched raw product stream (70). Alternatively, all
of cooled methane-enriched product stream can be preheated in
superheater (401a) and subsequently fed into sour shift reactor
(700) as superheated stream (42b). Boiler feed water preheater
(401b) can be used, for example, to preheat boiler feed water (46)
to generate a preheated boiler water feed stream (39) for one or
more of first heat exchanger unit (400) and third heat exchanger
unit (403), as well as other steam generation operations.
[0182] If it is desired to retain some of the carbon monoxide
content of the methane-enriched raw product stream (50), a gas
bypass loop (71) in communication with the first heat recovery unit
(400) can be provided to allow some of the cooled methane-enriched
raw product stream (70) exiting the first heat exchanger unit (400)
to bypass the sour shift reactor (700) and second heat exchanger
unit (401) altogether, and be combined with hydrogen-enriched raw
product stream (72) at some point prior to dehydration unit (450)
and/or acid gas removal unit (800). This is particularly useful
when it is desired to recover a separate methane product, as the
retained carbon monoxide can be subsequently methanated as
discussed below.
[0183] Dehydration (450)
[0184] Subsequent to sour shift reactor (700) and second heat
exchanger unit (401), and prior to acid gas removal unit (800), the
hydrogen-enriched raw product stream (72) will typically be treated
in a dehydration unit (450) to reduce water content. Dehydration
unit (450) can, for example, be a knock-out drum or similar water
separation device, and/or water absorption processes such as glycol
treatment. Such dehydration units and processes are in a general
sense well known to those of ordinary skill in the relevant
art.
[0185] A resulting waste water stream (47) (which will be a sour
water stream) can be sent to a wastewater treatment unit (not
depicted) for further processing. The resulting dehydrated
hydrogen-enriched raw product stream (72a) is sent acid gas removal
unit (800) as discussed below.
[0186] Compressor Unit (452)
[0187] The dehydrated raw sour gas stream, such as dehydrated
hydrogen-enriched raw product stream (72a) may optionally be
compressed prior to treatment in acid gas removal unit (800) to
generate a compressed raw sour gas stream (72b), as disclosed in
previously incorporated U.S. patent application Ser. No.
13/484,918. A compressor unit (452) compresses dehydrated raw sour
gas stream (72a) to a third pressure condition which is higher than
dehydrated raw sour gas stream (72a), and typically higher than the
first pressure condition (the operating pressure of
hydromethanation reactor (200)).
[0188] Compressor unit (452) can be a single or series of gas
compressors depending on the required extent of compression, as
will be understood by a person of ordinary skill in the art.
Suitable types of compressors are also generally well known to
those of ordinary skill in the art, for example, compressors known
suitable for use with syngas streams (carbon monoxide plus
hydrogen) would also be suitable for use in connection with the
present invention.
[0189] As indicated above, compressed raw sour gas stream (72b) is
at a pressure higher than dehydrated raw sour gas stream (72a). In
one embodiment, the pressure of compressed raw sour gas stream
(72b) (the third pressure condition) is about 20% higher or
greater, or about 35% higher or greater, or about 50% higher or
greater, to about 100% higher or less, than the pressure of
dehydrated raw sour gas stream (72a).
[0190] In another embodiment, the pressure of compressed raw sour
gas stream (72b) (the third pressure condition) is about 720 psig
(about 5066 kPa) or greater, or about 750 psig (about 5273 kPa) or
greater, and about 1000 psig (about 6996 kPa) or less, or about 900
psig (about 6307 kPa) or less, or about 850 psig (about 5962 kPa)
or less.
[0191] In another embodiment, the pressure of dehydrated raw gas
stream (72a) is about 600 psig (about 4238 kPa) or less, or about
550 psig (about 3894 kPa) or less, or about 500 psig (3549 kPa) or
less, and about 400 psig (about 2860 kPa) or greater, or about 450
psig (about 3204 kPa) or greater.
[0192] Acid Gas Removal (800)
[0193] A subsequent acid gas removal unit (800) is used to remove a
substantial portion of H.sub.2S and a substantial portion of
CO.sub.2 from the hydrogen-enriched raw product stream (72), or the
dehydrated raw sour gas stream (72a) if present, or the compressed
raw product stream (72b) if present, and generate a sweetened gas
stream (80).
[0194] Acid gas removal processes typically involve contacting a
gas stream 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 to generate CO.sub.2 and/or H.sub.2S laden absorbers.
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 containing an
H.sub.2S absorber and a CO.sub.2 absorber.
[0195] One method for removing acid gases is described in
previously incorporated US2009/0220406A1.
[0196] At least a substantial portion (e.g., substantially all) of
the CO.sub.2 and/or H.sub.2S (and other remaining trace
contaminants) should be removed via the acid gas removal processes.
"Substantial" removal in the context of acid gas removal means
removal of a high enough percentage of the component such that a
desired end product can be generated. The actual amounts of removal
may thus vary from component to component. For "pipeline-quality
natural gas", only trace amounts (at most) of H.sub.2S can be
present, although higher (but still small) amounts of CO.sub.2 may
be tolerable.
[0197] Typically, at least about 85%, or at least about 90%, or at
least about 92%, of the CO.sub.2 should be removed from the stream
fed into acid gas removal unit (800). Typically, at least about
95%, or at least about 98%, or at least about 99.5%, of such
H.sub.2S, should be removed.
[0198] Losses of desired product (hydrogen and/or methane) in the
acid gas removal step should be minimized such that the sweetened
gas stream (80) comprises at least a substantial portion (and
substantially all) of the methane and hydrogen from the stream fed
into acid gas removal unit (800). Typically, such losses should be
about 2 mol % or less, or about 1.5 mol % or less, or about 1 mol %
of less, respectively, of the methane and hydrogen from the
compressed raw product stream (72b).
[0199] The resulting sweetened gas stream (80) will generally
comprise CH.sub.4, H.sub.2 and optionally CO (for the downstream
methanation), and typically small amounts of CO.sub.2 and
H.sub.2O.
[0200] Any recovered H.sub.2S (78) from the acid gas removal (and
other processes such as 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.
[0201] Any recovered CO.sub.2 (79) from the acid gas removal can be
compressed for transport in CO.sub.2 pipelines, industrial use,
and/or sequestration for storage or other processes such as
enhanced oil recovery, and can also be used for other process
operations (such as in certain aspects catalyst recovery and feed
preparation).
[0202] The resulting sweetened gas stream (80) is further processed
as described below.
[0203] Hydrogen Separation Unit (850)
[0204] Hydrogen may be separated from the sweetened gas stream (80)
according to methods known to those skilled in the art, such as
cryogenic distillation, the use of molecular sieves, gas separation
(e.g., ceramic) membranes, and/or pressure swing adsorption (PSA)
techniques. See, for example, previously incorporated
US2009/0259080A1.
[0205] In one embodiment, a PSA device is utilized for hydrogen
separation. PSA technology for separation of hydrogen from gas
mixtures containing methane (and optionally carbon monoxide) is in
general well-known to those of ordinary skill in the relevant art
as disclosed, for example, in U.S. Pat. No. 6,379,645 (and other
citations referenced therein). PSA devices are generally
commercially available, for example, based on technologies
available from Air Products and Chemicals Inc. (Allentown, Pa.),
UOP LLC (Des Plaines, Ill.) and others.
[0206] In another embodiment, a hydrogen membrane separator can be
used followed by a PSA device.
[0207] Such separation provides a high-purity hydrogen product
stream (85) and a hydrogen-depleted sweetened gas stream (82).
[0208] The recovered hydrogen product stream (85) preferably has a
purity of at least about 99 mole %, or at least 99.5 mole %, or at
least about 99.9 mole %.
[0209] The hydrogen product stream (85) can be used, for example,
as an energy source and/or as a reactant. For example, the hydrogen
can be used as an energy source for hydrogen-based fuel cells, for
power and/or steam generation and/or for a subsequent
hydromethanation process. The hydrogen can also be used as a
reactant in various hydrogenation processes, such as found in the
chemical and petroleum refining industries.
[0210] The hydrogen-depleted sweetened gas stream (82) will
comprise substantially methane, with optional minor amounts of
carbon monoxide (depending primarily on the extent of the sour
shift reaction and bypass), carbon dioxide (depending primarily on
the effectiveness of the acid gas removal process) and hydrogen
(depending primarily on the extent and effectiveness of the
hydrogen separation technology). The hydrogen-depleted sweetened
gas stream (82) can be utilized can be further processed/utilized
as described below.
[0211] Methanation (950)
[0212] All or a portion of sweetened gas stream (80), or
hydrogen-depleted sweetened gas stream (82) if present, is fed to a
trim methanator (950) to generate additional methane from the
carbon monoxide and hydrogen that may be present in those streams,
resulting in a methane-enriched product stream (97).
[0213] If a hydrogen separation unit (850) is present, a portion of
sweetened gas stream (80) may bypass hydrogen separation unit (850)
via bypass line (86) to adjust the hydrogen content of
hydrogen-depleted sweetened gas stream (82) to optimize the
H.sub.2/CO ratio for methanation.
[0214] The methanation reaction can be carried out in any suitable
reactor, e.g., a single-stage methanation reactor, a series of
single-stage methanation reactors or a multistage reactor.
Methanation reactors include, without limitation, fixed bed, moving
bed or fluidized bed reactors. See, for instance, U.S. Pat. No.
3,958,957, U.S. Pat. No. 4,252,771, U.S. Pat. No. 3,996,014 and
U.S. Pat. No. 4,235,044. Methanation reactors and catalysts are
generally commercially available. The catalyst used in the
methanation, and methanation conditions, are generally known to
those of ordinary skill in the relevant art, and will depend, for
example, on the temperature, pressure, flow rate and composition of
the incoming gas stream.
[0215] As the methanation reaction is highly exothermic, the
methane-enriched product gas stream (97) is provided to a heat
recovery unit, e.g., third heat exchanger unit (403) to remove a
portion of the heat energy and generate the cooled methane product
stream (99). While third heat exchanger unit (403) is depicted as a
separate unit, it can exist as such and/or be integrated into
methanator (950), thus being capable of cooling the methanator unit
and removing at least a portion of the heat energy from the
methane-enriched gas stream to reduce the temperature of the
methane-enriched gas stream. The recovered heat energy can be
utilized to generate a third process steam stream (43) from a water
and/or steam source (39b). Although not depicted as such in FIG. 2,
third heat exchanger unit (403) may comprise a superheating section
followed by a boiler section such as previously described for
second heat exchanger unit (401). Because of the highly exothermic
nature of the methanation reaction, second process stream (43) can
be generated as a highly-superheated steam suitable, for example,
for driving a steam turbine.
[0216] Cooled methane product stream (99) can be utilized as the
final methane product stream, or it can be further processed, when
necessary, 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 gas separation (e.g., ceramic) membranes. Additional gas
purification methods include, for example, the generation of
methane hydrate as disclosed in previously incorporated
US2009/0260287A1, US2009/0259080A1 and US2009/0246120A1.
[0217] Pipeline-Quality Natural Gas
[0218] The invention provides processes and systems that, in
certain embodiments, are capable of generating "pipeline-quality
natural gas" (or "pipeline-quality substitute natural gas") from
the hydromethanation of non-gaseous carbonaceous materials. A
"pipeline-quality natural gas" typically refers to a
methane-containing stream that is (1) within .+-.5% of the heating
value of pure methane (whose heating value is 1010 btu/ft.sup.3
under standard atmospheric conditions), (2) substantially free of
water (typically a dew point of about -40.degree. C. or less), and
(3) substantially free of toxic or corrosive contaminants. In some
embodiments of the invention, the cooled methane product stream
(99) described in the above processes satisfies such
requirements.
Waste Water Treatment
[0219] Residual contaminants in waste water resulting from any one
or more of the trace contaminant removal, sour shift, ammonia
removal, acid gas removal and/or catalyst recovery processes can be
removed in a waste water treatment unit to allow recycling of the
recovered water within the plant and/or disposal of the water from
the plant process according to any methods known to those skilled
in the art. Depending on the feedstock and reaction conditions,
such residual contaminants can comprise, for example, aromatics,
CO, CO.sub.2, H.sub.2S, COS, HCN, ammonia, and mercury. For
example, H.sub.2S and HCN can be removed by acidification of the
waste water to a pH of about 3, treating the acidic waste water
with an inert gas in a stripping column, and increasing the pH to
about 10 and treating the waste water a second time with an inert
gas to remove ammonia (see U.S. Pat. No. 5,236,557). H.sub.2S can
be removed by treating the waste water with an oxidant in the
presence of residual coke particles to convert the H.sub.2S to
insoluble sulfates which may be removed by flotation or filtration
(see U.S. Pat. No. 4,478,425). Aromatics can be removed by
contacting the waste water with a carbonaceous char optionally
containing mono- and divalent basic inorganic compounds (e.g., the
solid char product or the depleted char after catalyst recovery,
supra) and adjusting the pH (see U.S. Pat. No. 4,113,615).
Aromatics can also be removed by extraction with an organic solvent
followed by treatment of the waste water in a stripping column (see
U.S. Pat. No. 3,972,693, U.S. Pat. No. 4,025,423 and U.S. Pat. No.
4,162,902).
Process Steam
[0220] The process steam streams (e.g., 40 and 43) resulting from
heat energy recovery can be generated by contacting a water/steam
source (such as (39a) and (39b)) with the heat energy recovered
from the various process operations using one or more heat recovery
units, such as first and third heat exchanger units (400) and
(403).
[0221] Any suitable heat recovery unit known in the art may be
used. For example, a steam boiler or any other suitable steam
generator (such as a shell/tube heat exchanger) that can utilize
the recovered heat energy to generate steam can be used. The heat
exchangers may also function as superheaters for steam streams,
such as (401a) in FIG. 2, so that heat recovery through one of more
stages of the process can be used to superheat the steam to a
desired temperature and pressure, thus eliminating the need for
separate fuel fired superheaters.
[0222] While any water source can be used to generate steam, the
water commonly used in known boiler systems is purified and
deionized (about 0.3-1.0 .mu.S/cm) so that corrosive processes are
slowed.
[0223] If needed, a suitable steam boiler or steam generator can be
used to provide any make-up steam stream. 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 feedstock preparation
operations (e.g., fines, supra). In one embodiment, such an
additional steam boiler/generator may be present, but is not used
in steady state operation of the process.
[0224] In one embodiment, the process steam streams supply at least
all of the total steam demand for the entire process, in which
during steady state operation there is substantially no make-up
steam stream.
[0225] In another embodiment, an excess of process steam is
generated. The excess steam can be used, for example, for power
generation via a steam turbine, for driving an air separation unit
via a steam turbine, and/or drying the carbonaceous feedstock in a
fluid bed drier to a desired moisture content (as discussed
below).
[0226] Power Generation
[0227] In accordance with the present invention, at least a portion
of third process steam stream (43) is provided to a steam turbine
(986) to generate electrical power (92). The steam stream (43a)
exiting steam turbine (986) may be utilized elsewhere in the
process, for example, may be recycled to third heat exchanger unit
(403) as part of an integrated combined cycle operation.
[0228] In addition, a portion of the cooled methane product stream
(99) can be utilized for combustion and steam generation, as can a
portion of any recovered hydrogen (85). As indicated above, excess
recycle steam may be provided to one or more power generators, such
as a combustion or steam turbine.
[0229] Any produced electrical power can, for example, be utilized
within the plant or can be sold onto the power grid.
Preparation of Carbonaceous Feedstocks
[0230] Carbonaceous Materials Processing (100)
[0231] Particulate carbonaceous materials, such as biomass and
non-biomass, can be prepared via crushing and/or grinding, either
separately or together, according to any methods known in the art,
such as impact crushing and wet or dry grinding to yield one or
more carbonaceous particulates. Depending on the method utilized
for crushing and/or grinding of the carbonaceous material sources,
the resulting carbonaceous particulates may be sized (i.e.,
separated according to size) to provide the carbonaceous feedstock
(32) for use in catalyst loading processes (350) to form a
catalyzed carbonaceous feedstock (31+32) for the hydromethanation
reactor (200).
[0232] Any method known to those skilled in the art can be used to
size the particulates. For example, sizing can be performed by
screening or passing the particulates through a screen or number of
screens. Screening equipment can include grizzlies, bar screens,
and wire mesh screens. Screens can be static or incorporate
mechanisms to shake or vibrate the screen. Alternatively,
classification can be used to separate the carbonaceous
particulates. Classification equipment can include ore sorters, gas
cyclones, hydrocyclones, rake classifiers, rotating trommels or
fluidized classifiers. The carbonaceous materials can be also sized
or classified prior to grinding and/or crushing.
[0233] The carbonaceous particulate can be supplied as a fine
particulate having an average particle size of from about 25
microns, or from about 45 microns, up to about 2500 microns, or up
to about 500 microns. One skilled in the art can readily determine
the appropriate particle size for the carbonaceous particulates.
For example, when a fluidized bed reactor is used, such
carbonaceous particulates can have an average particle size which
enables incipient fluidization of the carbonaceous materials at the
gas velocity used in the fluidized bed reactor. Desirable particle
size ranges for the hydromethanation reactor (200) are in the
Geldart A and Geldart B ranges (including overlap between the two),
depending on fluidization conditions, typically with limited
amounts of fine (below about 25 microns) and coarse (greater than
about 250 microns) material.
[0234] Additionally, certain carbonaceous materials, for example,
corn stover and switchgrass, and industrial wastes, such as saw
dust, either may not be amenable to crushing or grinding
operations, or may not be suitable for use as such, for example due
to ultra fine particle sizes. Such materials may be formed into
pellets or briquettes of a suitable size for crushing or for direct
use in, for example, a fluidized bed reactor. Generally, pellets
can be prepared by compaction of one or more carbonaceous material;
see for example, previously incorporated US2009/0218424A1. In other
examples, a biomass material and a coal can be formed into
briquettes as described in U.S. Pat. No. 4,249,471, U.S. Pat. No.
4,152,119 and U.S. Pat. No. 4,225,457. Such pellets or briquettes
can be used interchangeably with the preceding carbonaceous
particulates in the following discussions.
[0235] Additional feedstock processing steps may be necessary
depending on the qualities of carbonaceous material sources.
Biomass may contain high moisture contents, such as green plants
and grasses, and may require drying prior to crushing. Municipal
wastes and sewages also may contain high moisture contents which
may be reduced, for example, by use of a press or roll mill (e.g.,
U.S. Pat. No. 4,436,028). Likewise, non-biomass, such as
high-moisture coal, can require drying prior to crushing. Some
caking coals can require partial oxidation to simplify operation.
Non-biomass feedstocks deficient in ion-exchange sites, such as
anthracites or petroleum cokes, can be pre-treated to create
additional ion-exchange sites to facilitate catalyst loading and/or
association. Such pre-treatments can be accomplished by any method
known to the art that creates ion-exchange capable sites and/or
enhances the porosity of the feedstock (see, for example,
previously incorporated U.S. Pat. No. 4,468,231 and GB1599932).
Oxidative pre-treatment can be accomplished using any oxidant known
to the art.
[0236] The ratio and types of the carbonaceous materials in the
carbonaceous particulates can be selected based on technical
considerations, processing economics, availability, and proximity
of the non-biomass and biomass sources. The availability and
proximity of the sources for the carbonaceous materials can affect
the price of the feeds, and thus the overall production costs of
the catalytic gasification process. For example, the biomass and
the non-biomass materials can be blended in at about 5:95, about
10:90, about 15:85, about 20:80, about 25:75, about 30:70, about
35:65, about 40:60, about 45:55, about 50:50, about 55:45, about
60:40, about 65:35, about 70:20, about 75:25, about 80:20, about
85:15, about 90:10, or about 95:5 by weight on a wet or dry basis,
depending on the processing conditions.
[0237] Significantly, the carbonaceous material sources, as well as
the ratio of the individual components of the carbonaceous
particulates, for example, a biomass particulate and a non-biomass
particulate, can be used to control other material characteristics
of the carbonaceous particulates. Non-biomass materials, such as
coals, and certain biomass materials, such as rice hulls, typically
include significant quantities of inorganic matter including
calcium, alumina and silica which form inorganic oxides (i.e., ash)
in the catalytic gasifier. At temperatures above about 500.degree.
C. to about 600.degree. C., potassium and other alkali metals can
react with the alumina and silica in ash to form insoluble alkali
aluminosilicates. In this form, the alkali metal is substantially
water-insoluble and inactive as a catalyst. To prevent buildup of
the residue in the hydromethanation reactor (200), a solid purge of
by-product char (58) (and (58a)) comprising ash, unreacted
carbonaceous material, and various other compounds (such as alkali
metal compounds, both water soluble and water insoluble) is
withdrawn and processed as discussed below.
[0238] In preparing the carbonaceous particulates, the ash content
of the various carbonaceous materials can be selected to be, for
example, about 20 wt % or less, or about 15 wt % or less, or about
10 wt % or less, or about 5 wt % or less, depending on, for
example, the ratio of the various carbonaceous materials and/or the
starting ash in the various carbonaceous materials. In other
embodiments, the resulting the carbonaceous particulates can
comprise an ash content ranging from about 5 wt %, or from about 10
wt %, to about 20 wt %, or to about 15 wt %, based on the weight of
the carbonaceous particulate. In other embodiments, the ash content
of the carbonaceous particulate can comprise less than about 20 wt
%, or less than about 15 wt %, or less than about 10 wt %, or less
than about 8 wt %, or less than about 6 wt % alumina, based on the
weight of the ash. In certain embodiments, the carbonaceous
particulates can comprise an ash content of less than about 20 wt
%, based on the weight of processed feedstock where the ash content
of the carbonaceous particulate comprises less than about 20 wt %
alumina, or less than about 15 wt % alumina, based on the weight of
the ash.
[0239] Such lower alumina values in the carbonaceous particulates
allow for, ultimately, decreased losses of catalysts, and
particularly alkali metal catalysts, in the hydromethanation
portion of the process. As indicated above, alumina can react with
alkali source to yield an insoluble char comprising, for example,
an alkali aluminate or aluminosilicate. Such insoluble char can
lead to decreased catalyst recovery (i.e., increased catalyst
loss), and thus, require additional costs of make-up catalyst in
the overall process.
[0240] Additionally, the resulting carbonaceous particulates can
have a significantly higher % carbon, and thus btu/lb value and
methane product per unit weight of the carbonaceous particulate. In
certain embodiments, the resulting carbonaceous particulates can
have a carbon content ranging from about 75 wt %, or from about 80
wt %, or from about 85 wt %, or from about 90 wt %, up to about 95
wt %, based on the combined weight of the non-biomass and
biomass.
[0241] In one example, a non-biomass and/or biomass is wet ground
and sized (e.g., to a particle size distribution of from about 25
to about 2500 .mu.m) and then drained of its free water (i.e.,
dewatered) to a wet cake consistency. Examples of suitable methods
for the wet grinding, sizing, and dewatering are known to those
skilled in the art; for example, see previously incorporated U.S.
Pat. No. 2009/0048476A1. The filter cakes of the non-biomass and/or
biomass particulates formed by the wet grinding in accordance with
one embodiment of the present disclosure can have a moisture
content ranging from about 40% to about 60%, or from about 40% to
about 55%, or below 50%. It will be appreciated by one of ordinary
skill in the art that the moisture content of dewatered wet ground
carbonaceous materials depends on the particular type of
carbonaceous materials, the particle size distribution, and the
particular dewatering equipment used. Such filter cakes can be
thermally treated, as described herein, to produce one or more
reduced moisture carbonaceous particulates.
[0242] Each of the one or more carbonaceous particulates can have a
unique composition, as described above. For example, two
carbonaceous particulates can be utilized, where a first
carbonaceous particulate comprises one or more biomass materials
and the second carbonaceous particulate comprises one or more
non-biomass materials. Alternatively, a single carbonaceous
particulate comprising one or more carbonaceous materials
utilized.
[0243] Catalyst Loading for Hydromethanation (350)
[0244] The hydromethanation catalyst is potentially active for
catalyzing at least reactions (I), (II) and (III) described above.
Such catalysts are in a general sense well known to those of
ordinary skill in the relevant art and may include, for example,
alkali metals, alkaline earth metals and transition metals, and
compounds and complexes thereof. Typically, the hydromethanation
catalyst comprises at least an alkali metal, such as disclosed in
many of the previously incorporated references.
[0245] For the hydromethanation reaction, the one or more
carbonaceous particulates are typically further processed to
associate at least one hydromethanation catalyst, typically
comprising a source of at least one alkali metal, to generate a
catalyzed carbonaceous feedstock (31+32). If a liquid carbonaceous
material is used, the hydromethanation catalyst may for example be
intimately mixed into the liquid carbonaceous material.
[0246] The carbonaceous particulate provided for catalyst loading
can be either treated to form a catalyzed carbonaceous feedstock
(31+32) which is passed to the hydromethanation reactor (200), or
split into one or more processing streams, where at least one of
the processing streams is associated with a hydromethanation
catalyst to form at least one catalyst-treated feedstock stream.
The remaining processing streams can be, for example, treated to
associate a second component therewith. Additionally, the
catalyst-treated feedstock stream can be treated a second time to
associate a second component therewith. The second component can
be, for example, a second hydromethanation catalyst, a co-catalyst,
or other additive.
[0247] In one example, the primary hydromethanation catalyst
(alkali metal compound) can be provided to the single carbonaceous
particulate (e.g., a potassium and/or sodium source), followed by a
separate treatment to provide one or more co-catalysts and
additives (e.g., a calcium source) to the same single carbonaceous
particulate to yield the catalyzed carbonaceous feedstock (31+32).
For example, see previously incorporated US2009/0217590A1 and
US2009/0217586A1.
[0248] The hydromethanation catalyst and second component can also
be provided as a mixture in a single treatment to the single second
carbonaceous particulate to yield the catalyzed carbonaceous
feedstock (31+32).
[0249] When one or more carbonaceous particulates are provided for
catalyst loading, then at least one of the carbonaceous
particulates is associated with a hydromethanation catalyst to form
at least one catalyst-treated feedstock stream. Further, any of the
carbonaceous particulates can be split into one or more processing
streams as detailed above for association of a second or further
component therewith. The resulting streams can be blended in any
combination to provide the catalyzed carbonaceous feedstock
(31+32), provided at least one catalyst-treated feedstock stream is
utilized to form the catalyzed feedstock stream.
[0250] In one embodiment, at least one carbonaceous particulate is
associated with a hydromethanation catalyst and optionally, a
second component. In another embodiment, each carbonaceous
particulate is associated with a hydromethanation catalyst and
optionally, a second component.
[0251] Any methods known to those skilled in the art can be used to
associate one or more hydromethanation catalysts with any of the
carbonaceous particulates and/or processing streams. Such methods
include but are not limited to, admixing with a solid catalyst
source and impregnating the catalyst onto the processed
carbonaceous material. Several impregnation methods known to those
skilled in the art can be employed to incorporate the
hydromethanation catalysts. These methods include but are not
limited to, incipient wetness impregnation, evaporative
impregnation, vacuum impregnation, dip impregnation, ion
exchanging, and combinations of these methods.
[0252] In one embodiment, an alkali metal hydromethanation catalyst
can be impregnated into one or more of the carbonaceous
particulates and/or processing streams by slurrying with a solution
(e.g., aqueous) of the catalyst in a loading tank. When slurried
with a solution of the catalyst and/or co-catalyst, the resulting
slurry can be dewatered to provide a catalyst-treated feedstock
stream, again typically, as a wet cake. The catalyst solution can
be prepared from any catalyst source in the present processes,
including fresh or make-up catalyst and recycled catalyst or
catalyst solution. Methods for dewatering the slurry to provide a
wet cake of the catalyst-treated feedstock stream include
filtration (gravity or vacuum), centrifugation, and a fluid
press.
[0253] In another embodiment, as disclosed in previously
incorporated US2010/0168495A1, the carbonaceous particulates are
combined with an aqueous catalyst solution to generate a
substantially non-draining wet cake, then mixed under elevated
temperature conditions and finally dried to an appropriate moisture
level.
[0254] One particular method suitable for combining a coal
particulate and/or a processing stream comprising coal with a
hydromethanation catalyst to provide a catalyst-treated feedstock
stream is via ion exchange as described in previously incorporated
US2009/0048476A1 and US2010/0168494A1. Catalyst loading by ion
exchange mechanism can be maximized based on adsorption isotherms
specifically developed for the coal, as discussed in the
incorporated reference. Such loading provides a catalyst-treated
feedstock stream as a wet cake. Additional catalyst retained on the
ion-exchanged particulate wet cake, including inside the pores, can
be controlled so that the total catalyst target value can be
obtained in a controlled manner. The total amount of catalyst
loaded can be controlled by controlling the concentration of
catalyst components in the solution, as well as the contact time,
temperature and method, as disclosed in the aforementioned
incorporated references, and as can otherwise be readily determined
by those of ordinary skill in the relevant art based on the
characteristics of the starting coal.
[0255] In another example, one of the carbonaceous particulates
and/or processing streams can be treated with the hydromethanation
catalyst and a second processing stream can be treated with a
second component (see previously incorporated
US2007/0000177A1).
[0256] The carbonaceous particulates, processing streams, and/or
catalyst-treated feedstock streams resulting from the preceding can
be blended in any combination to provide the catalyzed second
carbonaceous feedstock, provided at least one catalyst-treated
feedstock stream is utilized to form the catalyzed carbonaceous
feedstock (31+32). Ultimately, the catalyzed carbonaceous feedstock
(31+32) is passed onto the hydromethanation reactor(s) (200).
[0257] Generally, each catalyst loading unit comprises at least one
loading tank to contact one or more of the carbonaceous
particulates and/or processing streams with a solution comprising
at least one hydromethanation catalyst, to form one or more
catalyst-treated feedstock streams. Alternatively, the catalytic
component may be blended as a solid particulate into one or more
carbonaceous particulates and/or processing streams to form one or
more catalyst-treated feedstock streams.
[0258] Typically, when the hydromethanation catalyst is solely or
substantially an alkali metal, it is present in the catalyzed
carbonaceous feedstock in an amount sufficient to provide a ratio
of alkali metal atoms to carbon atoms in the catalyzed carbonaceous
feedstock ranging from about 0.01, or from about 0.02, or from
about 0.03, or from about 0.04, to about 0.10, or to about 0.08, or
to about 0.07, or to about 0.06.
[0259] With some feedstocks, the alkali metal component may also be
provided within the catalyzed carbonaceous feedstock to achieve an
alkali metal content of from about 3 to about 10 times more than
the combined ash content of the carbonaceous material in the
catalyzed carbonaceous feedstock, on a mass basis.
[0260] Suitable alkali metals are lithium, sodium, potassium,
rubidium, cesium, and mixtures thereof. Particularly useful are
potassium sources. Suitable alkali metal compounds include alkali
metal carbonates, bicarbonates, formates, oxalates, amides,
hydroxides, acetates, or similar compounds. For example, the
catalyst can comprise one or more of sodium carbonate, potassium
carbonate, rubidium carbonate, lithium carbonate, cesium carbonate,
sodium hydroxide, potassium hydroxide, rubidium hydroxide or cesium
hydroxide, and particularly, potassium carbonate and/or potassium
hydroxide.
[0261] Optional co-catalysts or other catalyst additives may be
utilized, such as those disclosed in the previously incorporated
references.
[0262] The one or more catalyst-treated feedstock streams that are
combined to form the catalyzed carbonaceous feedstock typically
comprise greater than about 50%, greater than about 70%, or greater
than about 85%, or greater than about 90% of the total amount of
the loaded catalyst associated with the catalyzed carbonaceous
feedstock (31+32). The percentage of total loaded catalyst that is
associated with the various catalyst-treated feedstock streams can
be determined according to methods known to those skilled in the
art.
[0263] Separate carbonaceous particulates, catalyst-treated
feedstock streams, and processing streams can be blended
appropriately to control, for example, the total catalyst loading
or other qualities of the catalyzed carbonaceous feedstock (31+32),
as discussed previously. The appropriate ratios of the various
stream that are combined will depend on the qualities of the
carbonaceous materials comprising each as well as the desired
properties of the catalyzed carbonaceous feedstock (31+32). For
example, a biomass particulate stream and a catalyzed non-biomass
particulate stream can be combined in such a ratio to yield a
catalyzed carbonaceous feedstock (31+32) having a predetermined ash
content, as discussed previously.
[0264] Any of the preceding catalyst-treated feedstock streams,
processing streams, and processed feedstock streams, as one or more
dry particulates and/or one or more wet cakes, can be combined by
any methods known to those skilled in the art including, but not
limited to, kneading, and vertical or horizontal mixers, for
example, single or twin screw, ribbon, or drum mixers. The
resulting catalyzed carbonaceous feedstock (31+32) can be stored
for future use or transferred to one or more feed operations for
introduction into the hydromethanation reactor(s). The catalyzed
carbonaceous 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.
[0265] In one embodiment, the carbonaceous feedstock as fed to the
hydromethanation reactor contains an elevated moisture content of
from greater than 10 wt %, or about 12 wt % or greater, or about 15
wt % or greater, to about 25 wt % or less, or to about 20 wt % or
less (based on the total weight of the carbonaceous feedstock), to
the extent that the carbonaceous feedstock is substantially
free-flowing (see previously incorporated US2012/0102837A1).
[0266] The term "substantially free-flowing" as used herein means
the carbonaceous feedstock particulates do not agglomerate under
feed conditions due to moisture content. Desirably, the moisture
content of the carbonaceous feedstock particulates is substantially
internally contained so that there is minimal (or no) surface
moisture.
[0267] A suitable substantially free-flowing catalyzed carbonaceous
feedstock (31+32) can be produced in accordance with the
disclosures of previously incorporated US2010/0168494A1 and
US2010/0168495A1, where the thermal treatment step (after catalyst
application) referred to in those disclosures can be minimized (or
even potentially eliminated).
[0268] To the extent necessary, excess moisture can be removed from
the catalyzed carbonaceous feedstock (31+32). For example, the
catalyzed carbonaceous feedstock (31+32) may be dried with a fluid
bed slurry drier (i.e., treatment with superheated steam to
vaporize the liquid), or the solution thermally evaporated or
removed under a vacuum, or under a flow of an inert gas, to provide
a catalyzed carbonaceous feedstock having a the required residual
moisture content.
[0269] Catalyst Recovery (300)
[0270] Reaction of the catalyzed carbonaceous feedstock (31+32)
under the described conditions generally provides the
fines-depleted methane-enriched raw product stream (52) and a solid
char by-product (58) (and (58a)) from the hydromethanation reactor
(200). Unless otherwise indicated, reference to solid char
by-product (58) also includes reference to solid char by-product
(58a) as well.
[0271] The solid char by-product (58) typically comprises
quantities of unreacted carbon, inorganic ash and entrained
catalyst. The solid char by-product (58) is removed from the
hydromethanation reactor (200) for sampling, purging, and/or
catalyst recovery via a char outlet.
[0272] The term "entrained catalyst" as used herein means chemical
compounds comprising the catalytically active portion of the
hydromethanation catalyst, e.g., alkali metal compounds present in
the char by-product. For example, "entrained catalyst" can include,
but is not limited to, soluble alkali metal compounds (such as
alkali metal carbonates, alkali metal hydroxides and alkali metal
oxides) and/or insoluble alkali compounds (such as alkali metal
aluminosilicates). The nature of catalyst components associated
with the char extracted are discussed, for example, in previously
incorporated US2007/0277437A1, US2009/0165383A1, US2009/0165382A1,
US2009/0169449A1 and US2009/0169448A1.
[0273] The solid char by-product is continuously or periodically
withdrawn from the hydromethanation reactor (200) through a char
outlet which can, for example, be a lock hopper system, although
other methods are known to those skilled in the art. Methods for
removing solid char product are well known to those skilled in the
art. One such method taught by EP-A-0102828, for example, can be
employed.
[0274] The char by-product (58) from the hydromethanation reactor
(200) may be passed to a catalytic recovery unit (300), as
described below. Such char by-product (58) may also be split into
multiple streams, one of which may be passed to a catalyst recovery
unit (300), and another stream which may be used, for example, as a
methanation catalyst (as described in previously incorporated
US2010/0121125A1) and not treated for catalyst recovery.
[0275] In certain embodiments, when the hydromethanation catalyst
is an alkali metal, the alkali metal in the solid char by-product
(58) can be recovered to produce a catalyst recycle stream (57),
and any unrecovered catalyst can be compensated by a catalyst
make-up stream (57) (see, for example, previously incorporated
US2009/0165384A1). The more alumina plus silica that is in the
feedstock, the more costly it is to obtain a higher alkali metal
recovery.
[0276] In one embodiment, the solid char by-product (58) from the
hydromethanation reactor (200) can be quenched with a recycle gas
and water to extract a portion of the entrained catalyst. The
recovered catalyst (57) can be directed to the catalyst loading
unit (350) for reuse of the alkali metal catalyst.
[0277] Other particularly useful recovery and recycling processes
are described in U.S. Pat. No. 4,459,138, as well as previously
incorporated US2007/0277437A1 US2009/0165383A1, US2009/0165382A1,
US2009/0169449A1 and US2009/0169448A1. Reference can be had to
those documents for further process details.
[0278] The recycle of catalyst can be to one or a combination of
catalyst loading processes. For example, all of the recycled
catalyst can be supplied to one catalyst loading process, while
another process utilizes only makeup catalyst. The levels of
recycled versus makeup catalyst can also be controlled on an
individual basis among catalyst loading processes.
[0279] The by-product char (58) can also be treated for recovery of
other by-products, such as vanadium and/or nickel, in addition to
catalyst recovery, as disclosed in previously incorporated
US2011/0262323A1 and U.S. patent application Ser. No.
13/402,022.
[0280] As indicated above, all or a portion of recovered fines
stream (362) can be co-treated in catalyst recovery unit (300)
along with by-product char (58).
[0281] The result of treatment for catalyst and other by-product
recovery is a "cleaned" depleted char (59), at least a portion of
which can be provided to a carbon recovery unit (325) as discussed
below.
[0282] Carbon Recovery Unit (325)
[0283] In one embodiment, at least a portion, or at least a
predominant portion, or at least a substantial portion, or
substantially all, of the depleted char (59) can be treated in a
carbon recovery unit (325) to generate a carbon-enriched and
inorganic ash-depleted stream (65) and a carbon-depleted and
inorganic ash-enriched stream (66), as disclosed in previously
incorporated U.S. patent application Ser. No. 13/450,995. At least
a portion, or at least a predominant portion, or at least a
substantial portion, or substantially all, of the carbon-enriched
and inorganic ash-depleted stream (65) can be recycled back to
feedstock preparation unit (100) for processing and ultimately
feeding back to hydromethanation reactor (200) as part of
carbonaceous feedstock (32).
[0284] Because of the carbon content of depleted char (59), it can
be treated by known coal beneficiation techniques to separate a
higher carbon (lower ash) fraction from a lower carbon (higher ash)
fraction. The particle size of the depleted char (59) will
typically be similar to or smaller than the carbonaceous feedstock
(32) as provided to hydromethanation reactor (200) (below 6 mm),
and thus most suited for wet beneficiation and/or magnetic
separation techniques. Such techniques and equipment suitable for
use in connection therewith are generally known those of ordinary
skill in the relevant art, and are readily available from many
commercial sources. For example, techniques and equipment such as
dense-medium cyclones, hydrocyclones, wet concentration tables,
cone concentrators, spiral concentrators, centrifuges and froth
flotation may be utilized.
[0285] The resulting carbon-depleted and inorganic ash-enriched
stream (66) will still retain some residual carbon content and can,
for example, be combusted to power one or more steam generators
(such as disclosed in previously incorporated US2009/0165376A1)),
or used as such in a variety of applications, for example, as an
absorbent (such as disclosed in previously incorporated
US2009/0217582A1), or disposed of in an environmentally acceptable
manner.
Multi-Train Processes
[0286] In the processes of the invention, each process may be
performed in one or more processing units. For example, one or more
hydromethanation reactors may be supplied with the carbonaceous
feedstock from one or more catalyst loading and/or feedstock
preparation unit operations. Similarly, the methane-enriched raw
product streams generated by one or more hydromethanation reactors
may be processed or purified separately or via their combination at
various downstream points depending on the particular system
configuration, as discussed, for example, in previously
incorporated US2009/0324458A1, US2009/0324459A1, US2009/0324460A1,
US2009/0324461A1 and US2009/0324462A1.
[0287] In certain embodiments, the processes utilize two or more
hydromethanation reactors (e.g., 2-4 hydromethanation reactors). In
such embodiments, the processes may contain divergent processing
units (i.e., less than the total number of hydromethanation
reactors) prior to the hydromethanation reactors for ultimately
providing the catalyzed carbonaceous feedstock to the plurality of
hydromethanation reactors, and/or convergent processing units
(i.e., less than the total number of hydromethanation reactors)
following the hydromethanation reactors for processing the
plurality of methane-enriched raw product streams generated by the
plurality of hydromethanation reactors.
[0288] When the systems contain convergent processing units, each
of the convergent processing units can be selected to have a
capacity to accept greater than a 1/n portion of the total feed
stream to the convergent processing units, where n is the number of
convergent processing units. Similarly, when the systems contain
divergent processing units, each of the divergent processing units
can be selected to have a capacity to accept greater than a 1/m
portion of the total feed stream supplying the convergent
processing units, where m is the number of divergent processing
units.
EXAMPLES OF SPECIFIC EMBODIMENTS
[0289] A specific embodiment of the process is one in which the
second pressure condition is at least about 25 psi (about 172 kPa),
or at least 50 psi (about 345 kPa), or at least about 100 psi
(about 690 kPa), and/or about 200 psi (about 1379 kPa) or less,
greater than the first pressure condition.
[0290] Another specific embodiment is one in which the pressure of
first process steam stream (40) is at least about 5% or greater, or
at least about 10% or greater, than the operating pressure of the
hydromethanation reactor (200) (first pressure condition). In
another specific embodiment, the pressure of first process steam
stream (40) at the exit of first heat exchanger unit (400) (second
pressure condition) is at least about 20% or less greater than the
operating pressure of the hydromethanation reactor (200) (first
pressure condition).
[0291] Another specific embodiment is one in which the first
pressure condition is about 400 psig (about 2860 kPa) or greater,
or about 450 psig (about 3204 kPa) or greater; and/or about 1000
psig or less (about 6996 kPa), or about 900 psig (about 6307 kPa)
or less, or about 600 psig (about 4238 kPa) or less.
[0292] Another specific embodiment is one in which at least a
portion of the superheated steam generated as a result of step (k)
is, for example, used to drive an air separation unit (for example,
for generating an oxygen-rich stream to be provided to the
hydromethanation reactor). For example, the superheated steam can
be supplied to a turbine (one or more) that mechanically drives a
generator and an air separation unit.
[0293] Another specific embodiment is on in which the steam demand
of the hydromethanation reaction is at least satisfied by the steam
stream.
[0294] Another specific embodiment is one in which the steam stream
comprises only steam from the dry saturated steam stream.
* * * * *