U.S. patent application number 12/860520 was filed with the patent office on 2011-02-24 for recuperative combustion system.
Invention is credited to Timothy J. REILLY.
Application Number | 20110041740 12/860520 |
Document ID | / |
Family ID | 43604254 |
Filed Date | 2011-02-24 |
United States Patent
Application |
20110041740 |
Kind Code |
A1 |
REILLY; Timothy J. |
February 24, 2011 |
RECUPERATIVE COMBUSTION SYSTEM
Abstract
The methods and systems described herein relate to a
recuperative combustion system that recuperates energy from fuel
combustion that would otherwise be lost. The recuperative
combustion system minimizes or eliminates the need for an air
separator unit through the use of a clean water splitter section,
consisting of a thermochemical cycle or high-temperature
electrolysis. Water is split into its component hydrogen and
oxygen, primarily with process heat from the combustion process.
The oxygen produced by the water splitter provides oxygen necessary
for oxy-fuel combustion, thereby reducing or eliminating the need
for the power intensive air separator unit and/or external oxygen
source, significantly increasing the efficiency of the oxy-fuel
combustion cycle. Hydrogen produced by the water splitter may be
used for a variety of industrial uses, or combined with carbon
dioxide (captured from the flue gases produced by said combustion
process) to produce methanol. Methanol can further be refined in a
methanol to gasoline reactor to produce dimethyl ether, olefins or
high grade gasoline. Described herein are methods and systems that
1) increase oxy-fuel combustion efficiency, 2) produce hydrogen for
a suite of industrial/energy uses, and 3) capture carbon dioxide
and convert it to high value hydrocarbons.
Inventors: |
REILLY; Timothy J.;
(Rockport, MA) |
Correspondence
Address: |
NELSON MULLINS RILEY & SCARBOROUGH LLP;FLOOR 30, SUITE 3000
ONE POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Family ID: |
43604254 |
Appl. No.: |
12/860520 |
Filed: |
August 20, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61274745 |
Aug 20, 2009 |
|
|
|
61345541 |
May 17, 2010 |
|
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|
Current U.S.
Class: |
110/341 ;
110/214 |
Current CPC
Class: |
F23C 9/00 20130101; F23L
7/007 20130101; Y02E 20/34 20130101; Y02E 20/344 20130101; Y02E
20/14 20130101 |
Class at
Publication: |
110/341 ;
110/214 |
International
Class: |
F23L 7/00 20060101
F23L007/00; F23C 9/00 20060101 F23C009/00 |
Claims
1. A method for oxy-fuel combustion, comprising: providing a system
comprising a combustion chamber arranged and disposed to receive
fuel, oxygen and recycled flue gas and combust said fuel, oxygen
and recycled flue gas to produce heat and heated flue gas;
capturing heat produced by the oxy-fuel combustion; using a portion
of the heat to power a water splitter, thereby generating hydrogen
gas and oxygen gas; and transferring the oxygen gas from the water
splitter to the combustion chamber for use in said oxy-fuel
combustion.
2. The method of claim 1, further comprising providing an air
separator unit, or another external oxygen supply, wherein the
combustion chamber is arranged and disposed to receive oxygen from
the air separator unit and/or external oxygen supply and/or the
water splitter.
3. The method of claim 1, further comprising one or more heat
exchangers for the capture and transfer of heat from the heated
flue gas to the water splitter.
4-5. (canceled)
6. The method of claim 1, wherein the amount of oxygen required
from the air separator unit and/or external oxygen supply, is
reduced or eliminated in proportion to the amount of oxygen
provided by the water splitter.
7. (canceled)
8. The method of claim 1, wherein the oxy-fuel comprises any
hydrocarbon-based fuel.
9. The method of claim 8, wherein the oxy-fuel comprises a
coal/water slurry.
10. (canceled)
11. The method of claim 1, wherein the water splitter produces
hydrogen gas and oxygen gas by means of high-temperature
electrolysis.
12. The method of claim 1, wherein the water splitter produces
hydrogen gas and oxygen gas by means of a thermochemical cycle.
13. The method of claim 12, wherein the thermochemical cycle is
selected from: a hybrid copper-chlorine cycle; a sulfur-iodine
cycle; and a hybrid sulfur cycle.
14-15. (canceled)
16. The method of claim 13, wherein the thermochemical cycle is a
hybrid copper-chlorine cycle.
17. The method of claim 16, wherein the hybrid copper-chlorine
cycle is selected from: a 3-step cycle, a 4-step cycle, and a
5-step cycle.
18. The method of claim 17, wherein the hybrid copper-chlorine
cycle is the 4-step cycle.
19. The method of claim 18, wherein the 4-step cycle of the hybrid
copper chlorine cycle may be represented by the following steps:
Step I: Cu(s)+2HCl(g).fwdarw.2CuCl(molten)+H.sub.2(g) Step II:
4CuCl(s).fwdarw.2Cu(s)+2CuCl.sub.2(aq)+HCl(aq) Step III:
CuCl.sub.2(aq)+n.sub.fH.sub.2O(l).fwdarw.CuOCuCl.sub.2(s)+2HCl(g)+(n.sub.-
f-1)H.sub.2O(g) Step IV:
CuOCuCl.sub.2(s).fwdarw.2CuCl(molten)+0.50.sub.2(g)
20. (canceled)
21. The method of claim 19, wherein n.sub.f is 5-30.
22. (canceled)
23. The method of claim 1, wherein the hydrogen from the water
splitter is used directly or indirectly in a subsequent
process.
24. (canceled)
25. The method of claim 1, wherein the hydrogen from the water
splitter and the carbon dioxide from the combustion flue gas are
reacted to form methanol and water.
26-29. (canceled)
30. The method of claim 1, wherein the amount of oxygen that the
combustion chamber requires from an air separator unit and/or
external oxygen supply, is reduced or eliminated in proportion to
the amount of oxygen received from the water splitter, resulting in
increased efficiency.
31. The method of claim 30, wherein the increased efficiency is
measured in terms of increased gross power output of the combustion
process.
32. The method of claim 31, wherein the gross power output of the
combustion process is increased by 1-20%.
33-35. (canceled)
36. An oxy-fuel combustion system, comprising: a combustion chamber
arranged and disposed to receive fuel, oxygen and recycled flue gas
and combust said fuel, oxygen and recycled flue gas to produce heat
and heated flue gas containing carbon dioxide; one or more heat
exchangers arranged and disposed to capture heat produced by the
oxy-fuel combustion and transfer said heat to a water splitter; and
a water splitter, for the conversion of heat and electricity into
hydrogen gas and oxygen gas.
37. The system of claim 36, further comprising an air separator
unit, or another external oxygen supply, wherein the combustion
chamber is arranged and disposed to receive oxygen from the air
separator unit, or external oxygen supply, and/or the water
splitter.
38. The system of claim 36, wherein one or more heat exchangers
serve as the means to capture the heat produced by the oxy-fuel
combustion and to transfer said heat to the water splitter.
39-62. (canceled)
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 61/274,745, filed Aug. 20, 2009, and U.S.
Provisional Application No. 61/345,541, filed May 17, 2010. The
entire contents of these patent applications are hereby
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The methods and systems described herein relate to a
recuperative combustion system that recuperates energy from fuel
combustion that would otherwise be lost. The recuperative
combustion system minimizes or eliminates the need for an air
separator unit through the use of a clean water splitter section,
consisting of a thermochemical cycle or high-temperature
electrolysis. Water is split into its component hydrogen and
oxygen, primarily with process heat from the combustion process.
The oxygen produced by the water splitter provides oxygen necessary
for oxy-fuel combustion, thereby reducing or eliminating the need
for the power intensive air separator unit and/or external oxygen
source, significantly increasing the efficiency of the oxy-fuel
combustion cycle. Hydrogen produced by the water splitter may be
used for a variety of industrial uses, or combined with carbon
dioxide (captured from the flue gases produced by said combustion
process) to produce methanol. Methanol can further be refined in a
methanol to gasoline reactor to produce dimethyl ether, olefins or
high grade gasoline. Described herein are methods and systems that
1) increase oxy-fuel combustion efficiency, 2) produce hydrogen for
a suite of industrial/energy uses, and 3) capture carbon dioxide
and convert it to high value hydrocarbons.
BACKGROUND
[0003] Energy supply and concerns over unmitigated greenhouse gas
emissions are two critical issues of the 21.sup.st century. The use
of fossil fuels (coal, oil and natural gas) shall continue to play
a central role in electricity production for decades to come, and
is projected to significantly increase before they are phased out.
Hydrogen, a clean energy carrier, is anticipated to play a
significant role in energy production in the future.
[0004] While carbon capture and sequestration results in a
reduction in atmospheric inputs of carbon from industrial sources,
it will require large-scale construction of a pipeline distribution
and storage system, which will be extremely costly to build.
Additionally, the effectiveness of long-term subterranean CO.sub.2
storage on a scale of hundreds to thousands of years (required for
carbon dioxide mineralization) is presently unproven. Rather than
simply disposing of purified, captured and pressurized CO.sub.2
from oxy-fuel combustion and purification systems at great expense,
consideration for use of carbon dioxide as an industrial feedstock
for developing reconstituted high-value carbon-based compounds
(e.g., hydrocarbons and oxygenated hydrocarbons) may be seen as an
economically and environmentally attractive alternative.
Reconstituting waste carbon dioxide into useful materials turns a
significant liability into an asset which may 1) reduce carbon
emissions and 2) yield fuels, fuel precursors and other beneficial
industrial compounds and products.
SUMMARY OF THE INVENTION
[0005] In one aspect, provided herein is a method for oxy-fuel
combustion, comprising:
[0006] providing a system comprising a combustion chamber arranged
and disposed to receive fuel, oxygen and recycled flue gas and
combust said fuel, oxygen and recycled flue gas to produce
heat;
[0007] capturing heat produced by the oxy-fuel combustion;
[0008] using a portion of the heat to power a water splitter,
thereby generating hydrogen gas and oxygen gas; and
[0009] transferring the oxygen gas from the water splitter to the
combustion chamber for use in said oxy-fuel combustion.
[0010] In another aspect, provided herein is a method for oxy-fuel
combustion, comprising:
[0011] providing a system comprising a combustion chamber arranged
and disposed to receive coal/water slurry, oxygen and recycled flue
gas, wherein the chamber is arranged and disposed to receive said
oxygen from an air separator unit and/or external oxygen source,
and/or a water splitter, and combust said coal/water slurry, oxygen
and recycled flue gas to produce heat and heated flue gas
containing carbon dioxide; one or more heat exchangers arranged and
disposed to capture heat from said heated flue gas and transfer a
portion of the captured heat to a water splitter; a water splitter
using a 4-step hybrid copper-chlorine thermochemical cycle for the
conversion of heat and/or electricity into hydrogen gas and oxygen
gas, arranged and disposed to transfer the oxygen gas to the
combustion chamber for use in said oxy-fuel combustion;
[0012] combusting the coal/water slurry and oxygen to produce heat
and heated flue gas containing carbon dioxide;
[0013] capturing heat from heated flue gas and transferring
captured said heat to the water splitter;
[0014] using a portion of the heat to power the water splitter
using a 4-step hybrid copper-chlorine thermochemical cycle, thereby
producing hydrogen gas and oxygen gas;
[0015] transferring the oxygen gas to the combustion chamber for
use in said oxy-fuel combustion; and
[0016] reducing or eliminating the amount of oxygen that the
combustion chamber requires from an air separator unit and/or
external oxygen supply, in proportion to the amount of oxygen
received from the water splitter.
[0017] In yet another aspect, provided herein is a method for the
reaction of hydrogen produced by a water splitter and carbon
dioxide obtained from combustion flue gas to form methanol and
water.
[0018] In still aspect, provided herein is an oxy-fuel combustion
system, comprising:
[0019] a combustion chamber arranged and disposed to receive fuel,
oxygen and recycled flue gas and combust said fuel, oxygen and
recycled flue gas to produce heat and heated flue gas containing
carbon dioxide;
[0020] one or more heat exchangers arranged and disposed to capture
heat produced by the oxy-fuel combustion and transfer said heat to
a water splitter; and
[0021] a water splitter, for the conversion of heat and electricity
into hydrogen gas and oxygen gas.
[0022] In another aspect, provided herein is an oxy-fuel combustion
system, comprising:
[0023] a combustion chamber arranged and disposed to receive
coal/water slurry, oxygen and recycled flue gas, wherein the
chamber is arranged and disposed to receive said oxygen from an air
separator unit and/or external oxygen source, and/or a water
splitter, and combust said coal/water slurry, oxygen and recycled
flue gas to produce heat and heated flue gas containing carbon
dioxide;
[0024] one or more heat exchangers arranged and disposed to capture
heat from said heated flue gas and transfer a portion of the
captured heat to a water splitter; and
[0025] a water splitter using a 4-step hybrid copper-chlorine
thermochemical cycle for the conversion of heat and electricity
into hydrogen gas and oxygen gas, arranged and disposed to transfer
the oxygen gas to the combustion chamber for use in said oxy-fuel
combustion.
[0026] As described herein, these methods and systems of oxy-fuel
combustion are recuperative.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 depicts the recuperative combustion process described
herein, further comprising a methanol reactor, means for separating
methanol and water, and means for conversion of methanol to
downstream products.
[0028] FIG. 2 depicts a recuperative combustion system Integrated
with an 875 MWTH (HHV) ISOTHERM PWR System (modified from Hong et
al. 2008).
[0029] FIG. 3 depicts a flow diagram of a methanol synthesis plant
(modified from Ushikoshi et al. 2000).
[0030] FIG. 4 depicts a recuperative combustion system compared to
an archetypal combustion system.
[0031] FIG. 5 depicts the steps of the four-step copper chlorine
thermochemical cycle (Wang et al. 2009).
[0032] FIG. 6 depicts an overview of the sulfur-iodine
thermochemical cycle (Brown et al. 2003).
[0033] FIG. 7 depicts an archetypal convective recuperator (Bureau
of Energy Efficiency 2004).
[0034] FIG. 8 depicts an archetypal radiation/convective
recuperator (Bureau of Energy Efficiency 2004).
[0035] FIG. 9 depicts an archetypal regenerator (Bureau of Energy
Efficiency 2004).
DETAILED DESCRIPTION OF THE INVENTION
[0036] In one aspect, provided herein is a method for oxy-fuel
combustion, comprising: providing a system comprising a combustion
chamber arranged and disposed to receive fuel, oxygen and recycled
flue gas and combust said fuel, oxygen and recycled flue gas to
produce heat; capturing heat produced by the oxy-fuel combustion;
using a portion of the heat to power a water splitter, thereby
generating hydrogen gas and oxygen gas; and transferring the oxygen
gas from the water splitter to the combustion chamber for use in
said oxy-fuel combustion.
Combustion Chamber and Fuel
[0037] Oxy-fuel combustion for the production of electricity (FIG.
1-1) can occur in a variety of combustion systems. Non-limiting
examples of combustion systems include: circulating fluidized bed
boiler, pulverized coal boiler, and combustors. Combustible
materials, including, but not limited to coal, coal/water slurry,
petroleum products including oil, methane and natural gas, biomass,
and plasma fuels (FIG. 1-3), may undergo oxy-fuel combustion. The
primary products of oxy-fuel combustion include heat and flue gas
rich in carbon dioxide (FIG. 1-23). A portion of the flue gas is
recycled, as described herein (FIG. 1-13).
[0038] In one embodiment of the method, the oxy-fuel comprises any
combustible material. In another embodiment, the oxy-fuel comprises
any hydrocarbon-based fuel. In yet another embodiment, the oxy-fuel
comprises coal/water slurry. In still another embodiment, the
oxy-fuel comprises oil.
[0039] Pressurized oxy-fuel combustion systems have the potential
for better performance when compared to conventional atmospheric
oxy-fuel combustion power cycles such as the ITEA ISOTHERM.RTM.
pressurized oxy-fuel system (Hong et al, 2008). For example,
oxy-fuel combustion at high pressures may increase the burning rate
of char and the heat transfer rates in the convective sections of
the heat transfer equipment. Further, because of the raised dew
point and the corresponding available latent enthalpy in the raw
flue gases, the pressurized oxy-fuel system can recover more
thermal energy from the flue gases and eliminate the bleeding from
the high-pressure and the low-pressure steam turbines.
Consequently, the cycle efficiency for the pressurized oxy-fuel
system may be superior to the atmospheric system. To operate this
high combustion pressure system, a high pressure deaerator and a
flue gas acid condenser can be used. The acid condenser may be
modified to work at a high pressure level with flue gas composition
seen in oxy-combustion. (Hong et al. 2008).
Air Separator Unit and Water Splitter
[0040] In one embodiment of the method, the system comprises a
water splitter arranged and disposed to provide oxygen to the
combustion chamber for use in oxy-fuel combustion.
[0041] In one embodiment of the method, the system further
comprises an air separator unit arranged and disposed to provide
oxygen to the combustion chamber for use in oxy-fuel
combustion.
[0042] The normal source of oxygen for oxy-fuel combustion is an
air separator unit (ASU) (FIG. 1-5). The selection and
implementation of air separator units will be well known to those
skilled in the art. Commonly, oxygen is produced in the ASU through
a cryogenic distillation process. However, the production of oxygen
from an ASU requires 15-20% of the gross power output of an
industrial facility. The need for an ASU for oxygen generation may
be reduced or eliminated through the use of a water splitter.
Candidate water splitters include a hybrid copper-chlorine
thermochemical Cycle (CuCl Cycle), sulfur-iodine thermochemical
cycle, hybrid sulfur thermochemical cycle (HyS Cycle) and/or high
temperature electrolysis (HTE). Other candidate water splitters
include volatile metal oxide thermochemical cycles (e.g.,zinc/zinc
oxide, hybrid calcium), and non-volatile metal oxide cycles (e.g.,
iron oxide, cerium oxide) thermochemical cycles. Other
water-splitting thermochemical cycles are available, and known to
those skilled in the art. Water splitters use thermal or electrical
energy in order to convert water (FIG. 1-17) to hydrogen gas (FIG.
1-15) and oxygen gas (FIG. 1-11). In the recuperative combustion
process described herein, the water splitter is powered by excess
process heat provided by oxy-fuel combustion (FIG. 1-7), and by
electricity (FIG. 1-17). Oxygen produced by a thermochemical cycle
or HTE offsets, reduces or eliminates the need for an ASU, or
external oxygen source, for oxy-fuel combustion, thereby increasing
combustion efficiency. The thermochemical cycle or HTE unit
employed in the system also produces hydrogen as a product of water
splitting. The hydrogen may be used for a variety of purposes,
including reaction with the carbon dioxide produced by oxy-fuel
combustion to yield methanol and water (FIG. 1-25).
[0043] In another embodiment of the method, the system further
comprises an air separator unit, wherein the combustion chamber is
arranged and disposed to receive oxygen from the air separator unit
and/or the water splitter.
[0044] Use of a water splitter to produce oxygen results in a
reduction, or elimination, of the need for an air separation unit
(ASU), or other oxygen source, to supply oxygen for oxy-fuel
combustion. The scaling of the water splitter determines if an ASU
output is either reduced or eliminated. The employment of a water
splitter may significantly reduce, or eliminate, the cost of an ASU
unit and, correspondingly, reduce the power penalty resulting from
the operation of an ASU. Captured process/waste heat, some of which
may be upgraded by chemical heat pumps, may be used to supply
additional power needs by the water splitter as well.
[0045] In one embodiment of the method, the combustion chamber is
arranged and disposed to receive oxygen from the air separator unit
and/or external oxygen supply, and/or the water splitter.
[0046] The selection and implementation of suitable water
splitters, apparatus and procedures for use in the methods and
systems described herein will be well known to those skilled in the
art.
[0047] In a pressurized combustor (Hong et al. 2008), the oxygen
purity delivered from the water splitter and/or ASU may be 95% (mol
%) and delivered at 200.degree. C.; oxygen content in the recycled
flue gas may be about 3% (mol %). The oxygen delivery temperature
to the combustor is controlled to prevent the acid condensation
when mixed with the recycled flue gases. The flue gases contain
acid gases, such as SO.sub.3, SO.sub.2, nitrogen oxides, and HCl
produced during combustion. As shown in FIG. 2, the recycled flue
gases, state 2-19, are mixed with the oxygen stream from the water
splitter, state 2-13, which may be colder, depending on the ASU or
water splitter technology employed. To avoid corrosion due to the
condensation of these acid gases when mixed with the oxygen stream,
the oxygen delivery temperature needs to be carefully controlled to
nearly 200.degree. C. The 200.degree. C. delivery temperature
target is achieved by using a two-stage oxygen compressor with an
intercooler. The mass flow rate of the oxygen stream is determined
such that the raw flue gases exiting the combustor have 3% oxygen
on a molar basis (Hong et al. 2008)
[0048] In one embodiment of the method, the amount of oxygen
required from the air separator unit and/or external oxygen supply
is reduced or eliminated in proportion to the amount of oxygen
provided by the water splitter. The amount of oxygen that is
required from the air separator unit, and/or another oxygen source,
and/or the water splitter, may be determined by methods taught
herein (see, for example, the section of Algorithms and Formulae),
or by methods known to those of skill in the art.
Thermochemical Cycles
[0049] In another embodiment of the method, the water splitter
produces hydrogen gas and oxygen gas by means of a thermochemical
cycle. In still another embodiment, the water splitter produces
hydrogen and oxygen gas by means of a hybrid
thermochemical/electrochemical cycle.
[0050] The selection and implementation of suitable thermochemical
or hybrid thermochemical/electrochemical cycles, apparatus and
procedures for use in the methods and systems described herein will
be well known to those skilled in the art.
[0051] Non-limiting examples of thermochemical cycles and hybrid
thermochemical/electrochemical cycles include sulfur cycles (e.g.,
hybrid sulfur and sulfur-iodine thermochemical cycles), low
temperature cycles (e.g., hybrid copper-chlorine thermochemical
cycle), volatile metal oxide cycles (e.g.,zinc/zinc oxide, hybrid
calcium), and non-volatile metal oxide cycles (e.g., iron oxide,
cerium oxide) thermochemical cycles. Other suitable thermochemical
water-splitting cycles are available, and known to those skilled in
the art.
[0052] In one embodiment, the thermochemical cycle is selected
from: a hybrid copper-chlorine cycle; a sulfur-iodine cycle; and a
hybrid sulfur cycle.
[0053] In one embodiment, the thermochemical cycle is a hybrid
copper-chlorine cycle. In another embodiment, the copper-chlorine
cycle is selected from: a 3-step cycle, a 4-step cycle, and a
5-step cycle. In yet another embodiment, the hybrid copper-chlorine
cycle is the 4-step cycle. In still another embodiment, the 4-step
cycle of the hybrid copper chlorine cycle may be represented by the
following steps: [0054] Step I:
Cu(s)+2HCl(g).fwdarw.2CuCl(molten)+H.sub.2(g) [0055] Step II:
4CuCl(s).fwdarw.2Cu(s)+2CuCl.sub.2(aq)+HCl(aq) [0056] Step III:
CuCl.sub.2(aq)+n.sub.fH.sub.2O(l).fwdarw.CuOCuCl.sub.2(s)+2HCl(g)+(n.sub.-
f-1)H.sub.2O(g) [0057] Step IV:
CuOCuCl.sub.2(s).fwdarw.2CuCl(molten)+0.5O.sub.2(g)
[0058] In certain embodiments, n.sub.f is 5-30.
[0059] Three-step, four-step and five-step versions of the
copper-chlorine (Cu--Cl) hybrid electrochemical-thermochemical
cycle are described in Wang et al. (2009). While the five-step
version requires less heat than the three-step version of the
hybrid Cu--Cl cycle, it is more complex from equipment and process
engineering standpoints. A hybrid Cu--Cl Cycle using the four-step
process is described by Chukwu et al. (2008). Step III of the
four-step process is an electrochemical step, requiring the input
of electricity. Chukwu et al. provides reaction-specific
thermodynamic data and Aspen Plus heat/mass balance modeling of the
four-step hybrid Cu--Cl cycle.
[0060] The four-step process (FIG. 5) consists of three thermal
reactions in which H.sub.2, O.sub.2 and HCl are generated, and an
electrochemical step in which CuCl is disproportionated to yield
copper metal and CuCl.sub.2. The oxygen is released from the copper
oxychloride between 450.degree. C. and 530.degree. C., which is the
highest temperature limit for this cycle (Sattler 2010).
[0061] In one embodiment of the method, the water splitter operates
at a temperature 450.degree. C. for Step I; 30-80.degree. C. for
Step II; 375.degree. C. for Step III; and 530.degree. C. for Step
IV. another embodiment, the heat required to produce 1 mole of O
and 1 mole of H.sub.2 is about 554.7 kJ/mol.
[0062] The hybrid Cu--Cl four-step cycle receives process heat in
adequate supply from oxy-fuel combustion through a heat exchanger
system. The hybrid Cu--Cl four-step cycle is sized to accommodate
oxygen requirements for oxy-fuel combustion within the fossil fuel
combustor or boiler. This sizing is based on either a partial or
complete replacement of the air separator unit (ASU), depending on
a number of pre-existing, technical and economic factors unique to
an industrial/power plant, or other site of combustion. Hydrogen
production rates for various downstream hydrogen uses are also an
important aspect of sizing the four-step hybrid Cu--Cl
thermochemical cycle reactor.
[0063] In one embodiment of the method, the thermochemical cycle is
a sulfur-iodine (S--I) cycle. In another embodiment, the
sulfur-iodine cycle may be represented by the following steps:
[0064] Step I:
2H.sub.2O+SO.sub.2+I.sub.2.fwdarw.H.sub.2SO.sub.4+2HI [0065] Step
II: H.sub.2SO4.fwdarw.H.sub.2O+SO.sub.2+1/2O.sub.2 [0066] Step III:
2HI.fwdarw.H.sub.2+I.sub.2
[0067] Heat and mass balances associated with the S--I Cycle can be
found in Brown et al. (2003). The gross heat needed per mole
H.sub.2 (and 0.5 mole O.sub.2) is 674.9 kJ/mole H.sub.2 with net
heat requirements is 391.3 kJ/mol H.sub.2 (full HI gasification),
432.9 kJ/mol H.sub.2 (no HI gasification), as compared with 554.7
kJ/H.sub.2 gross heat and 322.7 kJ/H.sub.2 net heat required for
the Cu--Cl cycle (Wang et al. 2009). A major difference between the
Cu--Cl and S--I thermochemical cycles is the substantially lower
temperatures that the Cu--Cl cycle operates at relative to the S--I
cycle, allowing almost 30% of the heat needed for the Cu--Cl
process to come from low grade heat (i.e., heat at temperatures
lower than 343 K).
[0068] The hybrid sulfur (HyS) cycle is a hybrid
electrochemical--thermochemical cycle (Bilgen 1988). It consists of
splitting sulfuric acid into water and sulfur trixode
(endothermic), followed by further decomposition of sulfur trioxide
to sulfur dioxide (highly endothermic). As a final step, sulfur
dioxide is electrochemically oxidized to sulfuric acid with
concomitant production of hydrogen. The steps of the HyS cycle are
as follows: [0069] Step I: H.sub.2SO.sub.4.fwdarw.H.sub.2O+SO.sub.3
(>450.degree. C.) [0070] Step II:
SO.sub.3.fwdarw.SO.sub.2+1/2O.sub.2 (>850.degree. C. with
catalyst; 1150.degree. C. without catalyst) [0071] Step III:
2H.sub.2O+SO.sub.2.fwdarw.H.sub.2SO.sub.4+H.sub.2 (electrolysis,
80.degree. C.)
[0072] Electrical power is required for the electrolysis, but the
electrochemical oxidation of SO.sub.2 is far more efficient than
the electrolytic splitting of water. The overall efficiency of the
process is calculated to be about 40%. Carbon-supported platinum
electrodes are used for the SO.sub.2 oxidation. Cells made from
ceramics such as silicon carbide, silicon nitrite, and cermets
possess excellent resistance to corrosion by sulfuric acid at
ambient temperature and at low acid concentration. Catalysts mainly
based on iron oxide are available for accelerating the reaction
rate of the SO.sub.3 reduction at "low" temperature (850.degree.
C.). The kinetics of the reaction are much faster if higher
temperatures are available as in solar tower installations.
Therefore, the use of catalysts might be reduced or even
unnecessary if the sulfuric acid splitting is coupled to
concentrated solar radiation. It has to be evaluated whether the
higher temperatures are more efficient than the catalyzed reaction
on an annual basis. Reactors used in laboratory tests have been
made of glass or fused silica; solar reactors are mostly
constructed from ceramics such as silicon carbide, but gold-coated
steel has also been used (Noglik et al. 2009; Sattler 2010). Like
the S--I Cycle, the HyS cycle may be integrated with the
recuperative combustion process described herein. However, the high
grade heat (>850 C with catalyst, or 1150 C without catalyst)
limits the application for combustion facilities to those
applications with very high heat output (i.e., oxy-fuel combustion
with high oxygen content/lower recirculated flue gases, or high
temperature industrial processes such as, for example, steel
milling or glass production).
High Temperature Electrolysis
[0073] In one embodiment of the method, the water splitter produces
hydrogen gas and oxygen gas by means of high-temperature
electrolysis.
[0074] The selection and implementation of suitable high
temperature electrolysis apparatus and procedures for use in the
methods and systems described herein will be well known to those
skilled in the art.
[0075] Hydrogen and Oxygen can be produced via the classical
electrolysis of water at low temperature or, alternatively, by
using the different fuel cell technologies. These technologies are
based on (i) proton-exchange membrane fuel cells (PEMFCs)
(referring to the solid polymeric electrolyte membrane), (ii) fuel
cells using solid oxide proton conductors, and (iii) fuel cells
with a solid oxide ion (O.sup.2-) conductor (SOFCs). In a fuel
cell, electrical energy is generated by the exothermic oxidation of
hydrogen. In the reverse electrolysis operation of such a cell,
steam is reduced in an endothermic reaction using electrical
energy.
[0076] The operating temperatures of fuels cells vary widely, from
around 80-120.degree. C. for PEMFCs to 700-1000.degree. C. for
SOFCs. The free energy required for the reaction (.DELTA.G)
decreases with increasing temperature whereas the free enthalpy
(.DELTA.H) remains almost constant. This thermodynamic relation, in
principle unfavorable for the fuel cell mode at high temperatures,
explains the particular interest in performing electrolysis at high
temperatures. Since the SOFCs achieve competitive
(chemical-to-electrical) energy conversion efficiencies despite the
less favorable thermodynamic conditions, one can a priori expect
that high-temperature electrolysis (HTE) cells achieve much higher
(electrical to-chemical) energy conversion efficiencies (the term
energy conversion efficiency for the HTE refers to the
electrical-to-chemical energy conversion). Because ionic transfer
numbers are close to one for both cell types, the difference in
cell voltage translates linearly to the energy consumption for the
reaction.
[0077] The primary motivation for HTE is the above-mentioned
potential of a reduced demand for electrical energy compared with
electrolysis at low temperature. This may allow
electrical-to-chemical energy conversion efficiencies even
exceeding 100%, as already recognized in early work (Isenberg
1981). The free energy of the reaction .DELTA.G decreases from
.about.1.23 eV (237 kj mol.sup.-1) at ambient temperature to -0.95
eV (183 kj mol.sup.-1) at 900.degree. C., while the free enthalpy
term remains essentially unchanged (.DELTA.H.apprxeq.1.3 eV or 249
kj mol.sup.-1 at 900.degree. C.). Part of the energy required for
an ideal (loss-free) HTE can thus be provided by heat. Increasing
ohmic and/or reaction losses in a real HTE system increase the
demand for electrical energy and decrease the demand for an
external heat supply until, finally, the reaction becomes
exothermic. Hence three modes of operation are distinguishable in
HTE: thermoneutral, endothermic, and exothermic. HTE operates at
thermal equilibrium (the thermoneutral mode) when the electrical
energy input equals the enthalpy of the reaction. In that case, the
entropy necessary for water splitting equals the heat generated by
the loss reactions, and the energy conversion efficiency is 100%.
In the exothermic mode, on the other hand, the electric energy
input exceeds the .DELTA.H term, which corresponds to efficiency
below 100%. Finally, in the endothermic mode, the electric energy
input remains below the enthalpy term. Therefore, heat must be
supplied to maintain the cell temperature. This mode means that
energy conversion efficiencies of the cell or the stacks are above
100%.
[0078] An HTE system can be operated with and without an external
heat supply. This is different to low-temperature electrolyzers,
which run in the exothermic mode, because the energy losses, which
arise mainly from the electrochemical reactions, exceed the small
difference between .DELTA.H and .DELTA.G at low temperature. The
availability of an external heat source influences the design of an
HTE system.
[0079] Without a heat source, the goal is to approach the
thermoneutral mode, that is, to limit the thermal losses to a value
required to compensate for the endothermic reaction. This leaves a
wide margin for cell overvoltages and, therefore, for an increase
in the current density or a lowering of the temperature. Operating
temperatures in the range 600-700.degree. C., known from the SOFC
development, may therefore also be accessible for electrolysis.
[0080] With an external heat source of high temperature, on the
other hand, the goal is to reduce the overvoltages as far as
possible to allow for a significant uptake of heat. This implies,
at least with present cell technology, operation under higher
temperatures (800.degree. C. or above) and lower electrode
overvoltages (i.e., current densities somewhat lower than those
achieved in thermoneutral operation).
[0081] The operation of SOFCs in electrolysis mode has been
demonstrated in several research projects since 2004 (EIFER 2010).
Cells of both commercial and research types and including the
common designs were tested (electrolyte, hydrogen electrode, and
metal substrate-supported). As for fuel cell operation, the
hydrogen electrode-supported cells showed the highest performance
owing to the low resistance of the thin electrolyte layer. A high
current density of -3.6 A cm.sup.-2 at a cell voltage of 1.48 V and
a cell temperature of 950.degree. C., for example, was reached with
such a cell at DTU-Risoe (Denmark) (Mogensen et al. 2006; Zahid et
al. 2010).
Heat Exchangers
[0082] In one embodiment of the method, the system further
comprises one or more heat exchangers for the capture and transfer
of heat from the oxy-fuel combustion to the water splitter.
[0083] Heat exchangers are required for transferring process heat
from the heated flue gas to endothermic reactions within the water
splitter section. For example, in the Cu--Cl Cycle, sufficient heat
must be transferred from the flue gas coming from the
boiler/combustor to the chlorination step (Step I), oxychlorination
step (Step (III) and decomposition step (Step IV) (FIG. 5).
[0084] Numerous types of heat exchangers are available for the
adequate transfer of heat to the water splitter. Specific choice of
heat exchanger is dependent on a number of factors, including, but
not limited to: the nature or quality of the flue gases, the
temperature of primary process flue gases, matching heat demand of
the secondary (i.e., water splitting) process with the heat supply
from the primary process, matching timing of the heat supply for
the primary process and the heat demand in the secondary process,
and placement of primary and secondary heating equipment.
[0085] The selection and implementation of suitable heat exchanger
apparatus and procedures for use in the methods and systems
described herein will be well known to those skilled in the
art.
[0086] In one embodiment of the method, the system further
comprises one or more heat exchangers for the capture and transfer
of heat from the heated flue gas to the water splitter. In another
embodiment, said one or more heat exchangers are selected from: a
convective recuperator, a radiation/convective recuperator, a
ceramic recuperator and a regenerator. In yet another embodiment,
said one or more heat exchangers are selected from appropriately
scaled heat exchangers which function within specified heat ranges
(i.e., heat ranges specified herein or known to those of skill in
the art). Other suitable heat exchangers are available, and known
to those of skill in the art.
[0087] Convective Recuperator. In a recuperator, heat exchange
takes place between the flue gases and the air through metallic or
ceramic walls. Ducts or tubes carry the air or other gas to be
heated; the other side contains the waste heat stream. A common
configuration for recuperators is called the tube type or
convective recuperator. As seen in the FIG. 7, the hot gases are
carried through a number of parallel small diameter tubes, while
the incoming air/gas to be heated enters a shell surrounding the
tubes and passes over the hot tubes one or more times in a
direction normal to their axes. If the tubes are baffled to allow
the gas to pass over them twice, the heat exchanger is termed a
two-pass recuperator; if two baffles are used, a three-pass
recuperator, etc. Although baffling increases both the cost of the
exchanger and the pressure drop in the combustion air path, it
increases the effectiveness of heat exchange. Shell and tube type
recuperators are generally more compact and have a higher
effectiveness than radiation recuperators, because of the larger
heat transfer area made possible through the use of multiple tubes
and multiple passes of the gases.
[0088] Radiation/convective Recuperator. For maximum effectiveness
of heat transfer, combinations of radiation and convective designs
are used, with the high-temperature radiation recuperator being
first followed by convection type. These are more expensive than
simple metallic radiation recuperators, but are less bulky. A
Convective/radiative Hybrid recuperator is shown in FIG. 8.
[0089] Ceramic Recuperator. The principal limitation on the heat
recovery of metal recuperators is the reduced life of the liner at
inlet temperatures exceeding 1100.degree. C. In order to overcome
the temperature limitations of metal recuperators, ceramic tube
recuperators have been developed whose materials allow operation on
the gas side to 1550.degree. C. and on the preheated air side to
815.degree. C. on a more or less practical basis. Early ceramic
recuperators were built of tile and joined with furnace cement, and
thermal cycling caused cracking of joints and rapid deterioration
of the tubes. Later developments introduced various kinds of short
silicon carbide tubes which can be joined by flexible seals located
in the air headers. Earlier designs had experienced leakage rates
from 8 to 60 percent. The new designs are reported to last two
years with air preheat temperatures as high as 700.degree. C., with
much lower leakage rates.
[0090] Regenerator. Regenerators are rechargeable storage batteries
for heat. A regenerator (FIG. 9) is an insulated container filled
with metal or ceramic shapes that can absorb and store relatively
large amounts of thermal energy. During the operating cycle,
process exhaust gases flow through the regenerator, heating the
storage medium. After a while, the medium becomes fully heated
(charged). The exhaust flow is shut off and cold combustion air
enters the unit. As it passes through, the air extracts heat from
the storage medium, increasing in temperature before it enters the
burners. Eventually, the heat stored in the medium is drawn down to
the point where the regenerator requires recharging. At that point,
the combustion air flow is shut off and the exhaust gases return to
the unit. This cycle repeats as long as the process continues to
operate. For a continuous operation, at least two regenerators and
their associated burners are required. One regenerator provides
energy to the combustion air, while the other recharges. An
alternate design of regenerator uses a continuously rotating wheel
containing metal or ceramic matrix. The flue gases and combustion
air pass through different parts of the wheel during its rotation
to receive heat from flue gases and release heat to the combustion
air. Regenerators may be preferable for large capacities and have
been very widely used in glass and steel melting furnaces.
Important relations exist between the size of the regenerator, time
between reversals, thickness of brick, conductivity of brick and
heat storage ratio of the brick. In a regenerator, the time between
the reversals is an important aspect. Long periods would mean
higher thermal storage and hence higher cost. Also long periods of
reversal result in lower average temperature of preheat and
consequently reduce fuel economy.
[0091] In one aspect, provided herein is a method for oxy-fuel
combustion, comprising:
[0092] providing a system comprising a combustion chamber arranged
and disposed to receive coal/water slurry, oxygen and recycle flue
gas, wherein the chamber is arranged and disposed to receive said
oxygen from an air separator unit and/or a water splitter, and
combust said coal/water slurry, oxygen and recycled flue gas to
produce heat and heated flue gas containing carbon dioxide; one or
more heat exchangers arranged and disposed to capture heat from
said heated flue gas and transfer a portion of the captured heat to
a water splitter; a water splitter using a 4-step hybrid
copper-chlorine thermochemical cycle for the conversion of heat
and/or electricity into hydrogen gas and oxygen gas, arranged and
disposed to transfer the oxygen gas to the combustion chamber for
use in said oxy-fuel combustion;
[0093] combusting coal/water slurry, oxygen and recycled flue gas
to produce heat and heated flue gas containing carbon dioxide;
capturing heat from heated flue gas and transferring captured heat
to the water splitter; Using a portion of the heat to power the
water splitter using a 4-step hybrid copper-chlorine thermochemical
cycle, thereby producing hydrogen gas and oxygen gas; transferring
the oxygen gas to the combustion chamber for use in said oxy-fuel
combustion; reducing or eliminating the amount of oxygen that the
combustion chamber requires from an air separator unit and/or
external oxygen supply, in proportion to the amount of oxygen
received from the water splitter.
Efficiency
[0094] In one embodiment of the method, the amount of oxygen that
the combustion chamber requires from an air separator unit and/or
external oxygen supply, is reduced or eliminated in proportion to
the amount of oxygen received from the water splitter results in
increased efficiency.
[0095] In one embodiment of the method, the increased efficiency is
measured in terms of increased gross power output of the combustion
process. In one embodiment, the gross power output of the
combustion process is increased by 1-20%. In another embodiment,
the gross power output of the combustion process is increased by
1-10%. In yet another embodiment, the gross power output of the
combustion process is increased by 10-20%. In still another
embodiment, the gross power output of the combustion process is
increased by 15-20%.
Primary and Secondary Products
[0096] In one embodiment of the method, the oxy-fuel combustion
products further comprise heated flue gas containing carbon
dioxide.
[0097] Oxy-fuel combustion yields flue gases consisting of
predominantly carbon dioxide (FIG. 1-23) and condensable water,
whereas conventional air-fired combustion flue gases are
nitrogen-rich with only about 15% (by volume) of carbon dioxide (Hu
et al. 2008; IEA, 2008). The high carbon dioxide concentration (up
to 95%) and the significantly lower nitrogen concentration in the
oxy-fuel raw flue gases is a unique feature that lowers the energy
and capital costs of oxy-fuel carbon dioxide capture when compared
to alternatives (Buhre et al 2005). Further, decreasing relative
recycled flue gas input increases combustion, and flue gas,
temperatures, and may be a mode for increasing heat grade for
secondary water splitting processes. For example, oxy-fuel
combustion, using a pressurized coal combustor, occurs at 1400 to
1600.degree. C.; however, stoichiometric combustion of coal in pure
oxygen reaches up to 3500.degree. C. Optimization of
oxygen/recycled gas content with respect to high grade heat
production and oxygen/hydrogen yields requires additional
research.
[0098] Oxy-fuel combustion involves the burning of fuel in an
oxygen-rich, nitrogen-lean and carbon dioxide-rich environment,
which is achieved by feeding the combustor or boiler with an
oxygen-rich stream and recycled flue gases. Oxy-fuel combustion
produces a flue gas stream containing mostly CO.sub.2, which can be
directly purified and compressed for conversion to useful materials
or for carbon sequestration purposes. In the process shown in FIG.
1, the CO.sub.2 concentration in the flue gas is greatly increased
by using a mixture of recirculated flue gas and pure oxygen instead
of air for firing coal. Recirculation of flue gas is necessary to
provide sufficient mass flow of flue gas for cooling the flame and
also heat capacity and flue gas velocity for convective heat
transfer in the boiler. In the oxy-fuel process, CO.sub.2 purity is
mainly influenced by (a) where the flue gas is recycled in the
process (the cleaning that has been done up to this point), (b) the
sealing of boiler and other components to prevent air ingress, (c)
the purity of the oxygen from the Air Separation Unit (ASU) (or
alternative oxygen source), (d) the performance of all air quality
control system equipment (e.g., SCR, FGD, and ESP), and (e)
additional CO.sub.2 purification during/after compression (Wu et
al. 2009). Oxy-fuel combustion involves using a mixture of
recirculated flue gas and pure oxygen, instead of air, for firing
the fuel. Oxy-fuel combustion may take place at 1400 to
1600.degree. C. The stoichiometric combustion of coal in pure
oxygen may reach up to 3500.degree. C. While oxy-fuel combustion is
close to stoichiometric, lower combustion temperature are achieved
by using the appropriate amount of the recycled flue gases (Hong et
al 2008). Further, certain additional efficiencies are realized
when oxy-fuel combustion takes place under pressurized conditions
(Hong et al. 2008).
[0099] The primary outputs of the recuperative combustion process
include the following:
[0100] CO.sub.2 (and small amounts of CO) in the flue gas,
following post combustion treatment; [0101] H.sub.2 and O.sub.2
from the water splitter (i.e., Cu--Cl, S--I, or HyS thermochemical
cycles) or HTE. The secondary outputs from the downstream portions
of the process include: methanol from the methanol reactor (FIG.
1-25), dimethyl ether (DME), olefins, and gasoline (mainly C5-C9)
from methanol to gasoline conversion (FIG. 1-35), and water, as a
by-product of methanol and other hydrocarbon production. This water
may be treated, as necessary, and recycled to the water splitter
(FIGS. 1-31 and 1-41). The secondary outputs of the recuperative
combustion process described herein are valuable products on the
global market (FIG. 1-39).
[0102] In one embodiment of the method, the hydrogen from the water
splitter is used directly or indirectly in a subsequent process. In
another embodiment of the method, the hydrogen from the water
splitter is used directly in a subsequent process.
[0103] In another embodiment of the method, the hydrogen from the
water splitter and the carbon dioxide from the combustion flue gas
are reacted to form methanol and water.
[0104] In one aspect, provided herein is a method for the reaction
of hydrogen produced by a water splitter and carbon dioxide
obtained from combustion flue gas to form methanol and water. In
one embodiment, the carbon dioxide is purified and compressed prior
to reacting with hydrogen. In another embodiment, the hydrogen and
carbon dioxide are both produced by the recuperative combustion
system. In yet another embodiment of the method, the products of
the reaction further comprise waste heat.
[0105] Using carbon dioxide or carbon monoxide for downstream
conversion to hydrocarbons requires carbon dioxide separation and
removal of the impurities in the high-concentration carbon dioxide
flue gases resulting from oxy-fuel combustion. Carbon dioxide
purification involves the removal of contaminants from the flue
gas, including nitrogen oxides, sulfur oxides, and mercury,
generally under pressurized conditions. While numerous strategies
for removal of these contaminants already exist at modern fossil
fuel power plants, including flue gas desulfurization (FGD) for
sulfur oxides, selective catalytic reduction (SCR) for nitrogen
oxides compounds and activated carbon or sorbents for mercury,
these are capital-intensive technologies that do not result in a
comprehensive removal of impurities from, and separation of, carbon
dioxide from flue gas. A host of developing technologies for
increasing carbon dioxide purity are currently under development
(e.g., see White and Fogash 2009; Hong et al., 2008; and Shah
2006). Specific technologies employed for contaminant removal in
the carbon dioxide stream depends on the end use of carbon dioxide
(i.e., for methanol production, enhanced oil recovery (EOR) or
sequestration).
[0106] The high-concentration carbon dioxide flue gas that is
produced by the oxy-fuel combustion process may be hydrogenated in
a fluidized bed reactor with hydrogen gas at 200-300.degree. C. at
a pressure of 50-100 bar in a catalytically-mediated reaction
(heterogeneous catalyst includes, but is not limited to:
Cu/ZnO/ZrO.sub.2/Al.sub.2O.sub.3/SiO.sub.2), yielding methanol,
water and substantial heat (FIGS. 1-25, 1-21 and 1-31). The
following three reactions are controlled in the methanol reactor to
maximize methanol synthesis (Hirotani et al. 1998):
CO+2H.sub.2.fwdarw.CH.sub.3OH (.DELTA.H=-90.6 kJ/mol),
CO.sub.2+3H.sub.2.fwdarw.CH.sub.3OH+H.sub.2O (.DELTA.H=-49.4
kJ/mol), and
CO.sub.2+H.sub.2.fwdarw.CO+H.sub.2O (.DELTA.H=+41.2 kJ/mol).
[0107] The selection and implementation of suitable apparatus and
procedures for the production of methanol for use in the methods
and systems described herein will be well known to those skilled in
the art.
[0108] The methanol reactor may be of several types, including a
modified test methanol synthesis reactor from Ushikoshi et al.
(2000). FIG. 3 shows a flow diagram of the test plant, which is
designed with facilities for recycling unreacted gases. The gases
(mixture of CO.sub.2, CO and H.sub.2) supplied from the CO.sub.2
purification and compression unit (mainly CO.sub.2) and the water
splitter (H.sub.2) (FIGS. 3-1, 3-2, 3-3, 3-4) are compressed (FIGS.
3-5, 3-6, 3-7) along with recycled gases (FIG. 3-23), and then fed
into the reaction tube (FIGS. 3-8, 3-13) through a pre-heater (FIG.
3-9). The reactor (FIG. 3-14) is surrounded by a heat exchanger
divided into four parts to facilitate isothermal operation, and
capture of waste heat. The temperature profile along the bed is
measured by means of eight thermocouples situated at the central
axis of the reactor. The temperature difference along the reactor
is less than 2.degree. K. The pressure is controlled within 0.1 MPa
by changing the total flow rate of the make-up gas, in which the
H.sub.2/CO/CO.sub.2 ratio is adjusted with the flow
controllers.
[0109] The flow rate of the inlet gas to the reactor is controlled
by the flow controller placed just after the recycle gas
compressor. Reaction products are cooled down (FIGS. 3-18, 3-19),
and then the mixture of methanol and water is separated at the
gas-liquid separator (FIGS. 3-20, 3-21) from unreacted gases.
Unreacted gases and gaseous products, such as CO, methane and so
on, excluding small amounts of purge gas, are recycled back to the
reactor (FIGS. 3-22, 3-23)). The mixture of methanol and water is
subjected to separation (see below) then stored in a container
(FIGS. 3-25, 3-26, 3-27). Control of temperature in the methanol
reactor for pre-reaction reduction of the catalyst (in the presence
of heat and hydrogen and nitrogen gases) as well as during methanol
synthesis is controlled by a preheater, oil heater and oil cooler
system with (FIGS. 3-9, 3-10, 3-11, 3-12, 3-13, 3-14, 3-15, 3-16
and 3-17).
[0110] The make-up gas, the inlet and outlet gases of the reactor
and the recycle gas are analyzed with an on-line gas chromatograph.
Gas chromatography is employed for analysis of the reaction
products; H.sub.2, CO and CO.sub.2 are analyzed by
thermal-conductivity detector; methanol, dimethyl ether, methyl
formate and hydrocarbons are analyzed by the flame ionization
detector. Excess heat produced by exothermic methanol reaction
(FIG. 3-30) may be recuperated and recirculated for use in the
water splitter (FIG. 3-32) (through heat upgrading using chemical
heat pumps) (FIG. 3-31).
[0111] The methanol and water are separated through a solvent
dehydration process (e.g., by energetically attractive
pervaporation using a hydrophilic ZeoSep A membrane or equivalent
hydrophobic membrane for concentration of organics, or a
distillation column). Final selection of appropriate pervaporation
membrane or distillation column design shall depend on optimized
methanol and water concentrations in the methanol/water
mixture.
[0112] The methanol may be used as is, or used as an industrial
feedstock (e.g., for conversion to dimethyl ether, olefins,
gasoline and a spectrum of other industrial applications) using a
variety of industrial processes such as the Mobil Methanol to
Gasoline process. The byproduct water is filtered and re-used in
the in the water splitter.
Chemical Heat Pumps
[0113] Chemical Heat Pumps (CHPs) are systems that use coupled
exothermic and endothermic reactors to store thermal energy and
transform it to another temperature, including waste heat whose
thermal energy at low temperatures can be upgraded to higher
temperatures (Naterer 2008). CHPs may be useful in the conversion
of waste heat captured from exothermic portions of the Water
Splitter Section or downstream Methanol Reactor for Methanol to
Gasoline Sections and upgraded for use in heat-intensive,
endothermic portions of the Water Splitter Section. Gainful use of
CHPs result in significant increase in hydrogen and oxygen
production efficiency, and overall oxy-fuel combustion system
efficiencies.
[0114] The selection and implementation of suitable chemical heat
pump apparatus and procedures for use in the methods and systems
described herein will be well known to those skilled in the
art.
[0115] Two specific solid-gas CHPs, namely salt/ammonia and
MgO/water systems, are particularly useful in application to waste
heat upgrading for thermochemical hydrogen production, especially
when configured in series (Naterer 2008). These are described
below.
[0116] A salt/ammonia chemical heat pump consists of salts that are
able to absorb/desorb ammonia vapor at different operating
temperatures. The ammonia vapor pressure is a function of
temperature for two different salts, designated by LTS
(low-temperature salt) and HTS (high-temperature salt). The
desorption reaction is endothermic. Heat must be supplied to the
gas/solid reactor to release ammonia vapor from the LTS. When this
ammonia vapor flows to the HTS, it is absorbed and heat is released
in an exothermic reaction. The pair of salts is MnSO.sub.4/NH.sub.3
(LTS) and NiCl.sub.2/NH.sub.3 (HTS). The operation of the chemical
heat pump is described below:
MnSO.sub.4.6NH.sub.3+Q.sub.waste4MnSO.sub.4.2NH.sub.3+4NH.sub.3;
.DELTA.H=+57.6 kJ/mol (NH.sub.3)
NiCl.sub.2.2NH.sub.3+4NH.sub.3NiCl.sub.2.6NH.sub.3+Q.sub.out;
.DELTA.H=-55.3 kJ/mol (NH.sub.3)
[0117] An integrated closed cycle of a salt/ammonia chemical heat
pump was presented and analyzed by Spoelstra et al. (2002). In
their analysis, 5000 kW of low-temperature heat at 140.degree. C.
was upgraded to 2051 kW of high-temperature heat at 240.degree. C.
Shell-and-tube reactors were used with finned tubes to achieve this
operating capacity. Each reactor vessel was about 6 m in height,
with a diameter of 2-3 m. The total weight of one vessel was about
50 tons, including the salt and heat exchanger tubes. A very high
coefficient of performance for this CHP was reported by the authors
(COP=97), since electrical power is only required to pump around
liquid streams. This chemical heat pump could be used as a
"bottoming cycle" to upgrade waste heat to an intermediate stage,
before another CHP upgrades further to higher temperatures. It is
anticipated that equipment performance and reaction kinetics would
become unfavorable if a single CHP attempts to operate over an
excessively large temperature range. Therefore, a magnesium oxide
(MgO)/vapor chemical heat pump, which operates at temperatures
above the salt/ammonia CHP may be useful in increasing the grade of
heat further.
[0118] The MgO/Vapor CHP is described by the following chemical
reaction:
MgO(s)+H.sub.2O(g)4Mg(OH)2; .DELTA.H=.sub.---81.02 kJ/mol
[0119] The rightward reaction is exothermic MgO hydration. The
kinetics of the reaction have been reported by Kato et al. (1996).
The operation consists of heat storage and heat supply modes, with
solid products from each reactor supplied as solid feed to the
other. Magnesium hydroxide (Mg(OH).sub.2) is initially charged into
a gas/solid reactor. Heat is added, after which solid MgO and water
vapor are formed. The heat of condensation is recovered from the
steam and the resulting water is stored as a liquid. In the heat
supply mode, the stored water is then vaporized by another separate
heat input. The vapor is supplied to an exothermic solid/gas
reactor for hydration of MgO. Scientific feasibility of the
MgO/vapor chemical heat pump has been demonstrated by Kato et al.
(1996). A lab-scale demonstration was performed by the authors,
with an average heat output rate of 349 W per kg of Mg(OH).sub.2
solid feed. The experimental apparatus consisted of an evaporator,
gas/solid reactor, heating supply with an electric furnace,
condenser, water trap and vacuum pump. Future research and
development are still needed to scale up this system to larger
heating capacities (Naterer 2008).
[0120] Using a sequence of chemical heat pumps in series, a
conceptual framework of coupled CHPs and a Cu--Cl thermochemical
cycle may be advantageous. Specifically, an exothermic step within
the Cu--Cl cycle (or Methanol Reactor Section) could supply heat
into the MgO/vapor CHP, to be subsequently upgraded to a higher
temperature that is then used by the endothermic hydrolysis step in
the Cu--Cl cycle. The lower temperature endothermic step of copper
oxychloride decomposition could then be supplied separately from
the salt/ammonia CHP. Input power is needed to drive compressors in
the CHPs. With existing heat recovery technology available in
commercial systems, electricity generated from waste heat could be
supplied directly to the CHPs, thereby potentially making the CHPs
and Cu--Cl cycle solely driven by process/waste heat from
industrial or power plants (Naterer 2008).
[0121] Naterer (2008) presents a thermodynamic analysis of combined
chemical heat pumps for a thermochemical cycle of hydrogen
production, demonstrating that low-grade waste heat can be upgraded
to higher temperatures via salt/ammonia and MgO/vapor chemical heat
pumps, which release heat at successively higher temperatures
through exothermic reactions. Using this new approach, waste heat
industrial sources can be transformed to a useful energy supply for
thermochemical hydrogen and oxygen production. Naterer (2008)
further provides an example the application of salt/ammonia and
MgO/vapor chemical heat pumps to the Cu--Cl thermochemical cycle
production of oxygen and hydrogen.
[0122] In one embodiment, thermal energy from exothermic processes
of the method is captured by one or more chemical heat pumps. In
another embodiment, said thermal energy is transformed to another
temperature. In yet another embodiment, said thermal energy is used
in endothermic processes of the method. In certain embodiments,
thermal energy from the water splitter cycle and/or the methanol
reactor is captured, transformed to another temperature, and used
in endothermic processes of the method.
System
[0123] In one aspect, provided herein is an oxy-fuel combustion
system, comprising:
[0124] a combustion chamber arranged and disposed to receive fuel,
oxygen and recycled flue gas and combust said fuel, oxygen and
recycled flue gas to produce heat and heated flue gas containing
carbon dioxide; one or more heat exchangers for capturing heat
produced by the oxy-fuel combustion and transferring said heat to a
water splitter; and a water splitter, for the conversion of heat
and electricity into hydrogen gas and oxygen gas.
[0125] In one embodiment of the system, the water splitter is
arranged and disposed to provide oxygen to the combustion chamber
for use in oxy-fuel combustion.
[0126] In one embodiment, the system further comprises an air
separator unit arranged and disposed to provide oxygen to the
combustion chamber for use in oxy-fuel combustion. In another
embodiment, the system further comprises an external oxygen
supply.
[0127] In one embodiment, the system further comprises an air
separator unit, wherein the combustion chamber is arranged and
disposed to receive oxygen from the air separator unit and/or
external oxygen supply and/or the water splitter.
[0128] In one embodiment of the system, one or more heat exchangers
serve as the means to capture the heat produced by the oxy-fuel
combustion and to transfer said heat to the water splitter. In
another embodiment, said one or more heat exchangers captures heat
from the heated flue gas. In yet another embodiment, said one or
more heat exchangers are selected from: a convective recuperator, a
radiation/convective recuperator, a ceramic recuperator and a
regenerator. In still another embodiment, said one or more heat
exchangers are selected from appropriately scaled heat exchangers
which function within specified heat ranges (i.e., heat ranges
specified herein or known to those of skill in the art).
[0129] In one embodiment of the system, the amount of oxygen
required from the air separator unit and/or external oxygen supply
is reduced or eliminated in proportion to the amount of oxygen
provided by the water splitter. The amount of oxygen that is
required from the air separator unit, and/or another oxygen source,
and/or the water splitter, may be determined by methods taught
herein (see, for example, the section of Algorithms and Formulae),
or by methods known to those of skill in the art.
[0130] In one embodiment of the system, the oxy-fuel combustion
products further comprise heated flue gas containing carbon
dioxide.
[0131] In one embodiment of the system, the oxy-fuel comprises any
combustible material. In another embodiment, the oxy-fuel comprises
any hydrocarbon-based fuel. In yet another embodiment, the oxy-fuel
comprises coal/water slurry. In still another embodiment, the
oxy-fuel comprises oil.
[0132] In one embodiment of the system, the water splitter produces
hydrogen gas and oxygen gas by means of high-temperature
electrolysis.
[0133] In one embodiment of the system, the water splitter produces
hydrogen gas and oxygen gas by means of a thermochemical cycle. In
another embodiment, the thermochemical cycle is selected from: a
hybrid copper-chlorine cycle; a sulfur-iodine cycle; and a hybrid
sulfur cycle. In yet another embodiment, the thermochemical cycle
is a sulfur-iodine cycle. In still another embodiment, the
sulfur-iodine cycle may be represented by the following steps:
[0134] Step I:
2H.sub.2O+SO.sub.2+I.sub.2.fwdarw.H.sub.2SO.sub.4+2HI [0135] Step
II: H.sub.2SO4.fwdarw.H.sub.2O+SO.sub.2+1/2O.sub.2 [0136] Step III:
2HI.fwdarw.H.sub.2.fwdarw.I.sub.2
[0137] In one embodiment of the system, the thermochemical cycle is
a hybrid copper-chlorine cycle. In another embodiment, the hybrid
copper-chlorine cycle is selected from: a 3-step cycle, a 4-step
cycle, and a 5-step cycle. In yet another embodiment, the hybrid
copper-chlorine cycle is the 4-step cycle. In still another
embodiment, the 4-step hybrid copper chlorine cycle may be
represented by the following steps: [0138] Step I:
Cu(s)+2HCl(g).fwdarw.2CuCl(molten)+H.sub.2(g) [0139] Step II:
4CuCl(s).fwdarw.2Cu(s)+2CuCl.sub.2(aq)+HCl(aq) [0140] Step III:
CuCl.sub.2(aq)+n.sub.fH.sub.2O(l).fwdarw.CuOCuCl.sub.2(s)+2HCl(g)+(n.sub.-
f-1)H.sub.2O(g) [0141] Step IV:
CuOCuCl.sub.2(s).fwdarw.2CuCl(molten)+0.5O.sub.2(g)
[0142] In certain embodiments, n.sub.f is 5-30.
[0143] In one embodiment of the system, the water splitter operates
at a temperature 450.degree. C. for Step I; 30-80.degree. C. for
Step II; 375.degree. C. for Step III; and 530.degree. C. for Step
IV. In another embodiment, the heat required to produce 1 mole of O
and 1 mole of H.sub.2 is about 554.7 kJ/mol.
[0144] In one embodiment of the system, the hydrogen from the water
splitter is used directly or indirectly in a subsequent process. In
another embodiment of the system, the hydrogen from the water
splitter is used directly in a subsequent process.
[0145] In one embodiment of the system, the hydrogen from the water
splitter and the carbon dioxide from the combustion flue gas are
reacted to form methanol and water.
[0146] In one aspect, provided herein is an oxy-fuel combustion
system, comprising:
[0147] a combustion chamber arranged and disposed to receive
coal/water slurry, oxygen and recycled flue gas, wherein the
chamber is arranged and disposed to receive said oxygen from an air
separator unit and/or external oxygen source, and/or a water
splitter, and combust said coal/water slurry, oxygen and recycled
flue gas to produce heat and heated flue gas containing carbon
dioxide; one or more heat exchangers arranged and disposed to
capture heat from said heated flue gas and transfer a portion of
the captured heat to a water splitter; a water splitter using a
4-step hybrid copper-chlorine thermochemical cycle for the
conversion of heat and electricity into hydrogen gas and oxygen
gas, arranged and disposed to transfer the oxygen gas to the
combustion chamber for use in said oxy-fuel combustion.
[0148] Integration of the unit processes of the system described
herein will be well known to those of skill in the art. An example
of an integrated system is depicted in FIG. 2 and described in
Table 1.
Module
[0149] In one aspect, provided herein is a method for converting a
non-oxy-fuel combustion system into a recuperative oxy-fuel
combustion system, said method comprising:
[0150] Providing a system comprising an air separator unit and/or
external oxygen source; one or more heat exchangers; a
thermochemical and/or electrochemical water splitter; and a flue
gas converter; and converting a non-oxy-fuel combustion system into
a recuperative oxy-fuel combustion system.
[0151] In one embodiment of the method, the non-oxy-fuel combustion
system comprises a combustion chamber.
[0152] In one embodiment of the method, the water splitter is
arranged and disposed to provide oxygen to the combustion chamber
for use in oxy-fuel combustion.
Algorithms and Formulae
[0153] The following algorithms and formulae pertain to system
scaling. Underlying chemical formulae pertaining to water splitters
may be found in the Thermochemical Cycles section. System scaling
is based on the maximum mass flow rate of the fuel (e.g., coal)
used in the boiler or combustor, which in turn is based on the
gross cumulative power produced by the entire power plant (MWg),
not considering the power penalty incurred by equipment at the
plant. The following are specific scaling considerations for the
combustion system described herein. Specifically, system scaling is
based on the following method (modified from Rubin et al. 2007):
[0154] i. Calculate maximum fuel flow rate; [0155] ii. Calculate
oxygen requirement to meet this fuel flow rate; [0156] iii.
Considerations for sizing the water splitter to meet the oxygen
flow rate [0157] iv. Calculate CO.sub.2 flow rate from combustion
[0158] v. Calculate hydrogen flow rate for converting carbon
dioxide to methanol; and [0159] vi. Considerations for sizing the
methanol to gasoline section. These considerations are described
below. i. Calculate Maximum Fuel Flow Rate
[0160] Fuel flow rate is calculated based on a plant's gross
cumulative power (MWg), heat rate and fuel properties (heating
value). The relationship in the equation below can be used to
determine the fuel flow rate required to generate the desired (or
actual) gross power, given the fuel properties and gross heat
rate.
M coal = MW g .times. HR steam 2 .times. .eta. boiler .times. HHV
coal ##EQU00001##
wherein, [0161] M.sub.coal=mass flow rate of fuel (ton/hr) [0162]
MW.sub.g=gross cumulative power produced by the entire power plant;
this does not consider power used by equipment in the power plant
(MW) [0163] HR.sub.steam=heat rate of the steam cycle, which
excludes the effects of the boiler efficiency (Btu/kWh) [0164]
.eta..sub.boiler=boiler efficiency (fraction) [0165]
HHV.sub.Coal=higher heating value of the coal on a wet basis
(Btu/lb) ii. Calculate Oxygen Requirement to Meet this Fuel Flow
Rate
[0166] The maximum rate of oxygen produced by the water splitter is
determined as follows: [0167] a) Calculate the stoichiometric
O.sub.2 requirement based on the fuel flow rate, fuel composition,
and emission factors for incomplete combustion reactants; [0168] b)
Calculate the total O.sub.2 requirement based on the excess oxygen
specified (approximately 3-5% excess); and [0169] c) Calculate the
total oxygen product (i.e., oxidant) flow rate based on the oxygen
purity (.gtoreq.95%) and total O.sub.2 requirement.
[0170] This oxygen flow should replace the oxygen that would have
been produced by the Air Separation Unit (ASU) in a normal oxy-fuel
system.
iii. Considerations for Sizing the Water Splitter to Meet the
Oxygen Flow Rate
[0171] The water splitter (i.e., Cu--Cl or S--I or HyS
thermochemical cycles; or HTE) is sized to produce the maximum
oxygen flow rate, thereby replacing the ASU. Sizing the water
splitter such that oxygen flow rate is lower than the maximum flow
rate for the facility may result in the need to supplement oxygen
production with another source (e.g., an ASU).
[0172] The water splitter is sized based on stoichiometric oxygen
output from particular water splitter reactions to meet the O.sub.2
flow rate determined above.
iv. Calculate CO.sub.2 Flow Rate from Combustion
[0173] The carbon dioxide mass flow rate, m.sub.FG, can be derived
based on the following equation:
m.sub.CO2=[m.sub.COAL(1-%
ash)+m.sub.RFG+m.sub.O2-m.sub.IMPURITIES](CO2.sub.CAPTURE)(CO2.sub.PURITY-
)
Wherein:
[0174] m.sub.FG=flue gas mass flow rate [0175] % ash=fuel ash
content, mass fraction [0176] m.sub.RFG=recycle flue gas mass flow
rate [0177] m.sub.Impurities=mass of impurities removed during CO2
purification (i.e., NOx, SOx and Hg) [0178] CO.sub.2Capture=capture
efficiency of CO2 in the flue gas [0179] CO.sub.2pUrity=carbon
dioxide purity requirement (generally.gtoreq.95%)
[0180] Zhou et al. (2010) found that oxy-fuel combustion in a
conventional utility boiler had an ideal flue gas recycle (FGR)
ratio generally around 0.7-0.75; whereas Hong et al. (2008) found a
flue gas recycle ratio in a pressurized coal combustor to be about
0.78. Flue gas ratios depends on boiler exit O.sub.2 and fuel
properties such that flue gas recycle ratio is a linear function of
the boiler exit O.sub.2 and increases slightly with air-to-fuel
ratio.
v. Calculate Hydrogen Flow Rate for Converting Carbon Dioxide to
Methanol
[0181] The hydrogen flow rate is determined stoichiometrically
based on the following equation:
CO.sub.2+3H.sub.2.fwdarw.CH.sub.3OH+2H.sub.2O
[0182] Thus, the flow rate of hydrogen is three times the flow rate
of carbon dioxide on a molar basis. This likely will be offset
somewhat by the overall efficiency of carbon dioxide to methanol
conversion, which is dependent on specific methanol reactor
employed. The methanol reactor shall be sized to accommodate
maximum carbon dioxide flow, based on maximum fuel flow rates.
vi. Considerations for Sizing the Methanol to Gasoline Section
[0183] The methanol to gasoline reactor system shall be sized to
accommodate maximum methanol flow, based, in turn, on maximum fuel
and carbon dioxide flow rates, respectively. Methanol to gasoline
reactor sizing is based on stoichiometric considerations of the
following overall reactions:
##STR00001##
[0184] The dimethyl ether product is then further dehydrated over a
zeolite catalyst (preferred zeolites may include ZSM-5, ZSM-11,
ZSM-12, ZSM-35, and ZSM-48) to give a gasoline with 80% C5+
hydrocarbon products. Conversion efficiencies for methanol to
gasoline conversion shall also be considered when sizing the
reaction system.
[0185] Like the Methanol Section, the Methanol to Gasoline Section
produces substantial amounts of heat which may be recuperated and
transferred through chemical heat pumps and/or other heat
exchangers to the Water Splitter Section to power endothermic
reactions. Therefore, these Sections should be sized and positioned
in a manner which facilitates waste heat recuperation and
transfer.
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EXEMPLIFICATION
[0230] An example of how the recuperative combustion system
integrates with the ISOTHERM.RTM. pressurized coal combustion
follows. The ISOTHERM.RTM. system, as designed, makes use of an
ASU, which requires nearly 20% of gross facility power output to
operate. The recuperative combustion system described herein is
integrated with this system, replacing the ASU with a water
splitter, and resulting in significant reductions in power penalty
for the plant. FIG. 2 provides a system schematic of the
integration of the recuperative combustion system with the
ISOTHERM.RTM. oxy-fuel (coal) combustion process. Table 1 provides
the temperature and mass data from each process, and includes a
description of each step numerically keyed to the process step
numbers in FIG. 2. System efficiencies, heat requirements and
electrical requirements may vary with the choice of water splitter
employed (i.e., Cu--Cl Cycle, S--I Cycle, HyS Cycle,
high-temperature electrolysis or other suitable water splitter
known to those in the art). In all cases ASU (and corresponding
power requirements) are significantly reduced, or eliminated, due
to the production of oxygen from the water splitter, hence
increasing system efficiency. Additional heat and mass balance
tests are required to further quantify power penalty reductions and
corresponding increases in system efficiencies with the
recuperative combustion system relative to the ISOTHERM.RTM. base
case (i.e., where oxygen is supplied for combustion from an
ASU).
TABLE-US-00001 TABLE 1 Recuperative Combustion System Integration
with ISOTHERM PWR System for a 875 MW.sub.TH Pressurized Coal Fired
Power Plant Mass Flow Pressure Temperature Rate State # Process
Stream State/Description (bar) (C..degree.) (kg/s) 2-1 Condensate
leaves the condenser and is compressed 0.41 32.6 198.1 by the first
feedwater pump. 2-2 The pressurized condensate leaves the first
feedwater 11.2 32.9 198.1 pump and enters the Acid Condenser Unit
where most of the latent enthalpy in the flue gases is recovered.
2-3 Condensate leaves the Acid Condenser Unit and picks 11.2 158.7
198.1 up more thermal energy from the Coal Combustor Unit walls.
2-4 Condensate leaves the Coal Combustor Unit walls and 11.2 177.2
198.1 enters the Deaerator Unit. 2-5 According to the saturation
condition of the deaerator, 11.2 179.9 210 the design point
pressure level fixes the exit temperature of the water leaving the
deaerator. After the deaerator, the feedwater stream at state 2-5
is pumped to the supercritical state, by the second feedwater pump.
2-6 After leaving the second feedwater pump, the 250 215 210
supercritical steam feedwater is heated regeneratively and enters
the Heat Recovery Steam Generator (HRSG). 2-7, The supercritical
steam feedwater leaves the Heat 250 600 210 2-9 to 2-12 Recovery
Steam Generator (HRSG) where it was (process heated to 600.degree.
C. at 250 bars. It then enters the High stream/ Pressure Turbine
(HPT) to generate electricity. state Resultant subcritical steam
leaves the HPT and is description circulated for 1) steam injection
into the Coal only) Combustor Unit (State 2-8); 2) reheat to
HRSG/Intermediate-Pressure Turbine (IPT; States 2-9 and 2-10), and
reheat to HRSG/Low-Pressure Turbine (LPT; States 2-11 and 2-12);
and 3) regeneratively reheated to supercritical steam as in State
2-6 for entry to HRSG followed by the HPT. 2-8 Steam is bled from
the high pressure steam turbine to 70 316 3 be injected into the
pressurized combustor in order to atomize the slurry particles.
2-13 An oxygen stream is produced from the Water 10 201.2 73.52
Splitter Section. Produced oxygen is mixed with the recycled flue
gases, state 2-19. 2-14 The recycled flue gas/oxygen mixture is
injected 10 256.5 335.8 into the pressurized Coal Combustor. 2-15
The Coal Combustor Unit yields flue gases at about 10 1549.7 382.8
1550.degree. C. Some of the thermal energy in the flue gas is
transferred through one or more heat exchangers to the Water
Spltter Section. The flue gas temperature downstream of the heat
exchangers is at least 800.degree. C. 2-16 The flue gas stream
leaves the Water Splitter 10 800 1004.7 Section and enters the HRSG
and transfers thermal energy to the steam while being cooled down
to state 2-17. 2-17 The flue gas stream leaves the HRSG and is
either 1) 9.351 259.7 1004.7 recycled, or 2) passed through the
Acid Condenser Unit. 2-18 The flue gas stream is cooled down to
800.degree. C. - as 10 268.7 621.9 necessary - by recycled flue
gases. 2-19 Recycled gases leaving the HRSG are either used 10
268.7 262.2 for 1) mixing with the oxygen stream for injection into
the Coal Combustor Unit, or 2) cooling flue gas stream downstream
from the Water Splitter Section to 800.degree. C. 2-20 A portion of
the flue gas exhaust stream goes to acid 9.351 259.7 120.6
condenser for cooling/heat recovery 2-21 Cooled flue gas leaves
acid condenser and enters 9.351 60.51 87.7 Carbon Dioxide
Purification/Compression Unit. 2-22 CO.sub.2 is pumped to the
Methanol Reactor Section. 110 30 72.5 2-23 Exhaust gases are
monitored and vented. 1.2 30 16.9 2-24 Hydrogen gas (H.sub.2) is
produced in the Water 50 25 9.96 Splitter Section and pumped to the
Methanol Reactor. 2-25 A methanol/water mixture is produced in the
75 250 82.46 (Methanol Methanol Reactor and separated in the and
Water); Methanol/Water Separation Unit through either 52.78
pervaporation or distillation. (Methanol); 29.68 Water) 2-26 Water
is separated from methanol through 1.38 26.7 29.68 (water
distillation in the Methanol/Water Separation Unit, from Methanol
and is treated, as necessary, and recirculated to the Reactor);
Water Splitter Section). Additional water is 29.56 (water provided
from State 2-29 (water separated from from MTG petrochemical
distillates in MTG Unit) and Unit); 82.78 external water sources,
as necessary. (total water needed to run Water Splitter Section to
produce adequate H.sub.2 and O.sub.2 for Combustor System) 2-27
Methanol resulting from the Methanol/Water 1 25 52.78 Separation
Unit is pumped to bulk storage tanks for temporary storage prior to
transport and sale, or pumped to the Methanol to Gasoline Reactor
Unit. 2-28 Hydrocarbon distillate products of the Methanol to
.ltoreq.55 (MTG 200-540 (MTG 23.22 Gasoline Reactor/Distillation
System are pumped to Reactor Unit); Reactor Unit); bulk storage
tanks for temporary storage prior to 1 (storage) 25 (storage)
transport and sale. 2-29 Water resulting from the Methanol to
Gasoline 1 25 29.56 Reactor/Distillation System is treated and
recirculated to the Water-Splitting Section via State 2-26. 2-30
Coal/Water Slurry injection to Coal Combuster. Coal 30 - Coal Only
is supplied in the form of a coal-water slurry stream which
contains 0.35 kg water per 1 kg of its total weight.
* * * * *
References