U.S. patent application number 12/631302 was filed with the patent office on 2011-04-28 for process and apparatus for high energy efficiency chemical looping combustion.
Invention is credited to Lawrence F. McHugh, Leonid N. Shekhter.
Application Number | 20110094226 12/631302 |
Document ID | / |
Family ID | 43897207 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110094226 |
Kind Code |
A1 |
McHugh; Lawrence F. ; et
al. |
April 28, 2011 |
PROCESS AND APPARATUS FOR HIGH ENERGY EFFICIENCY CHEMICAL LOOPING
COMBUSTION
Abstract
Process and apparatus are provided for a high energy efficiency
chemical combustion process. The process provides two reaction
steps, both of which are exothermic. First, a reduced oxygen
carrier is contacted with oxygen in a reactor to form an oxidized
oxygen carrier, such as metal oxide or metal suboxide, and then the
oxidized oxygen carrier is fed to a second reactor and combusted
with a fuel. The reaction produces the reduced oxygen carrier and
carbon dioxide. The reduced oxygen carrier from the second reactor
is recycled back to said first reactor. Carbon monoxide can also be
produced during the process depending on stoichiometric amounts of
the reactants. Though the process can be performed in various types
of reactor systems, one preferred embodiment is the flash furnace
with the production of fly ash during combustion. The process is
highly efficient and produces a large amount of usable work.
Inventors: |
McHugh; Lawrence F.; (North
Andover, MA) ; Shekhter; Leonid N.; (Ashland,
MA) |
Family ID: |
43897207 |
Appl. No.: |
12/631302 |
Filed: |
December 4, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61255716 |
Oct 28, 2009 |
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Current U.S.
Class: |
60/645 ; 110/204;
431/2; 431/4; 431/5 |
Current CPC
Class: |
Y02E 20/18 20130101;
F23C 2900/99008 20130101; Y02E 20/346 20130101; F01K 23/064
20130101; Y02E 20/34 20130101; F23C 99/00 20130101; Y02E 20/324
20130101; Y02E 20/32 20130101 |
Class at
Publication: |
60/645 ; 431/2;
431/4; 431/5; 110/204 |
International
Class: |
F01K 13/00 20060101
F01K013/00; F23L 7/00 20060101 F23L007/00; F23C 6/04 20060101
F23C006/04; F23C 9/06 20060101 F23C009/06; F23J 7/00 20060101
F23J007/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The present invention was not developed with the use of any
Federal Funds, but was developed independently by the inventors.
Claims
1. A process for chemical looping combustion comprising: (a)
contacting a reduced oxygen carrier with oxygen to form an oxidized
oxygen carrier, and (b) contacting said oxidized oxygen carrier and
a fuel to produce said reduced oxygen carrier and carbon dioxide,
wherein both steps are exothermic.
2. A process for chemical looping combustion in a furnace
comprising: (a) a first step wherein a reduced oxygen carrier is
contacted with oxygen to form an oxidized oxygen carrier, and (b) a
second step wherein an ash-containing fuel is contacted with said
oxidized oxygen carrier to produce a reaction product comprising
said reduced oxygen carrier, carbon dioxide and fly ash, wherein
both the first step and the second step are exothermic.
3. A process for chemical looping combustion comprising the steps
of: (c) contacting at least one reduced oxygen carrier with oxygen
in a first reactor to form at least one oxidized oxygen carrier,
(d) passing the at least one oxidized oxygen carrier from said
first reactor to a second reactor receivably connected to said
first reactor, (e) contacting said at least one oxidized oxygen
carrier with at least one fuel in said second reactor to produce
said at least one reduced oxygen carrier and carbon dioxide, and
(f) passing said at least one reduced oxygen carrier from said
second reactor to said first reactor, wherein both reaction steps
are exothermic.
4. A process for chemical looping combustion in a flash furnace,
said flash furnace comprising a first reactor and a second reactor
receivably connected to said first reactor, said process comprising
the steps of: (a) feeding oxygen and a reduced oxygen carrier into
the first reactor having a first reactor temperature at a location
that is not a reaction zone, said oxygen and said reduced oxygen
carrier each having a temperature that is lower than said first
reactor temperature, and said first reactor temperature being
sufficient to ignite the oxygen and the reduced oxygen carrier as
they pass through the first reactor and create a reaction that is
sufficiently exothermic to form a self-sustaining reaction zone
having a first flash temperature, said reaction producing an
oxidized oxygen carrier; (b) feeding said oxidized oxygen carrier
and a fuel into said second reactor at a location that is not a
reaction zone having a second reactor temperature, said oxidized
oxygen carrier and said fuel each having a temperature that is
lower than said second reactor temperature, and said reactor
temperature being sufficient to ignite the oxidized oxygen carrier
and the fuel as they pass through the second reactor and create a
reaction that is sufficiently exothermic to form a self-sustaining
reaction zone having a second flash temperature, said reaction
producing the reduced oxygen carrier and carbon dioxide; and (c)
optionally, feeding said reduced oxygen carrier from said second
reactor to said first reactor.
5. A process for chemical looping combustion comprising the steps
of: (g) feeding a reduced oxygen carrier and oxygen into a first
reactor; (h) contacting the reduced oxygen carrier with the oxygen
source in said first reactor to form an oxidized oxygen carrier;
(i) passing the oxidized oxygen carrier from said first reactor to
a second reactor receivably connected to said first reactor; (j)
feeding a fuel into said second reactor for contact with said
oxidized oxygen carrier within said second reactor to produce a
reaction product comprising said reduced oxygen carrier, carbon
dioxide and carbon monoxide; and (k) passing said reduced oxygen
carrier from said second reactor to said first reactor; wherein the
reaction in the first reactor and the reaction in the second
reactor are both exothermic.
6. The process of claim 4 wherein the fuel is an ash-containing
fuel and wherein the reaction in the second reactor further
produces fly ash.
7. The process of claim 4 wherein the reduced oxygen carrier and
the oxygen are preheated before being fed into the first reactor of
the furnace.
8. The process of claim 4 wherein the fuel and the oxidized oxygen
carrier are preheated before being fed into the second reactor of
the furnace.
9. The process of claim 3 wherein the oxygen and the reduced oxygen
carrier are fed into the first reactor at a rate that is
substantially constant and the first reactor temperature and the
second reactor temperature remain substantially constant.
10. The process of claim 4, wherein after step (b), the fuel and
the oxidized oxygen carrier are blended prior to being passed into
the second reactor.
11. The process of claim 1 or claim 2 wherein said process is
performed in a flash furnace.
12. The process of claim 1 wherein said process is performed in a
rotary kiln, a multiple hearth furnace, a vertical tube furnace or
a fluidized bed reactor.
13. The process of claim 1 wherein said process is continuous.
14. The process of claim 1 further comprising recycling the reduced
oxygen carrier produced during said second step into said first
step of the process.
15. The process of claim 1 further comprising the step of
separating and sequestering the carbon dioxide produced during the
second step.
16. The process of claim 2 wherein at least a portion of the
reduced oxygen carrier together with at least a portion of the fly
ash are removed from the furnace.
17. The process of claim 16 wherein the amount of reduced oxygen
carrier is fed into the furnace in an amount that is substantially
the same as the amount of reduced oxygen carrier being removed from
the furnace.
18. The process of claim 2 wherein at least a portion of the
reduced oxygen carrier together with at least a portion of the fly
ash are removed from the furnace and subsequently utilized as a
ferroalloy addition in a process to produce an alloy material
containing iron and slag.
19. The process of claim 5 further comprising the step of
separating the carbon monoxide produced during the second step.
20. The process of claim 1 or claim 2 wherein the reduced oxygen
carrier is a metal or a metal suboxide.
21. The process of claim 1 wherein the reduced oxygen carrier is a
metal selected from the group consisting of rhenium, platinum,
rhodium, palladium, copper, barium, manganese, molybdenum,
vanadium, bismuth, lead, mercury, sodium, potassium, rubidium, and
cesium.
22. The process of claim 2 wherein the oxygen carrier is
substantially free-flowing.
23. The process of claim 1 wherein the fuel is selected from
carbon, coal, hydrogen, hydrocarbon, biofuel, methane, natural gas,
petroleum, crude oil, tar sands, oil shale, biomass, algae,
fuel-rich waste gases from fuel cells, other fossil fuel or
synthetic fuel.
24. The process of claim 2 wherein the ash-containing fuel is
coal.
25. The process of claim 1 wherein the fuel is a carbon, a
hydrocarbon, or hydrogen in the form of a solid, a liquid or a
gas.
26. The process of claim 1 wherein the oxygen carrier is in the
form of a powder.
27. The process of claim 26 wherein the oxygen carrier powder has a
particle size of from 100 nanometers to 1 mm as determined by laser
light scattering.
28. The process of claim 1 wherein the oxygen carrier is in the
form of a powder having a particle size of from 20 microns to 250
microns as determined by laser light scattering.
29. The process of claim 1 wherein the fuel is a coal in the form
of a powder.
30. The process of claim 29 wherein the coal powder has a particle
size of from 100 nanometers to 10 mm as determined by laser light
scattering.
31. The process of claim 1 wherein the fuel is a coal in the form
of a powder having a particle size of from 20 microns to 250
microns as determined by laser light scattering.
32. The process of claim 1 wherein the fuel is coal having a
particle size that is substantially similar to the particle size of
the oxygen carrier.
33. The process of claim 1 wherein said oxidized oxygen carrier is
at least partially vaporized during said second step of the
process.
34. The process of claim 4 wherein the difference between said
first reactor temperature and said first flash temperature in the
first reactor is at least 300.degree. C.
35. The process of claim 4 wherein the difference between said
second reactor temperature and said second flash temperature in the
second reactor is at least 300.degree. C.
36. The process of claim 4 wherein the difference between said
first reactor temperature and said first flash temperature in the
first reactor is at least 800.degree. C.
37. The process of claim 4 wherein the difference between said
second reactor temperature and said second flash temperature in the
second reactor is at least 800.degree. C.
38. The process of claim 4 wherein the reduced oxygen carrier and
the oxygen are fed into the first reactor at a rate sufficient to
substantially off-set the heat loss of the first reactor and create
a stable self-sustaining reaction zone within the first
reactor.
39. The process of claim 4 wherein the oxidized oxygen carrier and
the fuel are fed into the second reactor at a rate sufficient to
substantially off-set the heat loss from the second reactor and
create a stable self-sustaining reaction zone within the second
reactor.
40. The process of claim 2 wherein the temperature within the first
reactor is above the solid/liquid phase transition temperature of
the reduced oxygen carrier.
41. The process of claim 2 wherein the temperature within the first
reactor is above the solid/gas phase transition temperature of the
reduced oxygen carrier.
42. The process of claim 2 wherein the temperature within the first
reactor is above the liquid/gas phase transition temperature of the
reduced oxygen carrier.
43. The process of claim 2 wherein the temperature within the
second reactor is above the solid/liquid phase transition
temperature of the oxidized oxygen carrier.
44. The process of claim 2 wherein the temperature within the
second reactor is above the solid/gas phase transition temperature
of the oxidized oxygen carrier.
45. The process of claim 2 wherein the temperature within the
second reactor is above the liquid/gas phase transition temperature
of the oxidized oxygen carrier.
46. The process of claim 3 wherein the residence time of the oxygen
and the reduced oxygen carrier in the first reactor is from 0.01 to
1.0 minute.
47. The process of claim 3 wherein the residence time of the oxygen
and the reduced oxygen carrier in the first reactor is from 0.01 to
10 seconds.
48. The process of claim 3 wherein the process is performed in a
flash furnace and the residence time of the fuel and the oxidized
oxygen carrier in the second reactor is from 0.01 seconds to 1.0
minute.
49. The process of claim 3 wherein the process is performed in a
flash furnace and the residence time of the fuel and the oxidized
oxygen carrier in the second reactor is from 0.01 seconds to 10
seconds.
50. The process of claim 4 wherein the reduced oxygen carrier flows
concurrently in the same direction with the flow of the oxygen in
the first reactor.
51. The process of claim 4 wherein the oxidized oxygen carrier
flows concurrently in the same direction with the flow of the fuel
in the second reactor.
52. The process of claim 5 wherein the fuel and the oxidized oxygen
carrier are fed into the second reactor in substantially
stoichiometric amounts.
53. The process of claim 5 wherein the fuel and the oxidized oxygen
carrier are fed into the second reactor in less than stoichiometric
amounts in order to produce carbon monoxide.
54. A process for generating useful work comprising the process of
claim 1.
55. A process for generating useful work comprising the first step
of the process of claim 1.
56. A process for generating useful work comprising the second step
of the process of claim 1.
57. The process of claim 1 further comprising utilizing the energy
produced during the exothermic process in a generator for
generating electricity.
58. The process of claim 1 further comprising converting the energy
produced during the exothermic process into steam that is used to
rotate a turbine engine.
59. The process of claim 1 wherein the steps can be performed in
either order.
60. The process of claim 4 further comprising (d) feeding carbon
dioxide into said second reactor.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of prior-filed U.S.
Provisional Patent Application Ser. No. 61/255,716, filed on Oct.
28, 2009, the subject matter of which is hereby incorporated by
reference in its entirety.
FIELD OF THE INVENTION
[0003] The present invention relates to apparatus and methods of
high efficiency generation of useful work via combustion, more
specifically, in combustion looping systems, for high efficiency
energy production and more particularly, the chemical looping
combustion in furnaces of fuel sources using metal oxides. The
invention relates to clean coal technology with carbon dioxide
capture and sequestration. The invention also relates to the
removal of fly ash produced during the combustion process that can
be further utilized in ferroalloy processes.
BACKGROUND OF THE INVENTION
[0004] The burning of fuels is currently the main mechanism that
the world utilizes in order to meet its energy needs. Global
warming is the increase in the average temperature of the Earth's
near-surface air and oceans. Global warming was first noticed in
the mid-20th century and scientists have projected its
continuation. The Intergovernmental Panel on Climate Change (IPCC)
has noted that the global surface temperature has increased
0.74.+-.0.18.degree. C. (1.33.+-.0.32.degree. F.) during the last
century. The IPCC also concludes that although variations in
natural phenomena such as solar radiation and volcanoes produced
most of the warming from pre-industrial times to 1950 and had a
small cooling effect afterward, most of the observed temperature
increase since the middle of the 20th century was caused by
increasing concentrations of greenhouse gases resulting from human
activity such as fossil fuel burning and deforestation. Although
not unanimous, these basic conclusions have been endorsed by more
than 40 scientific societies and academies of science, including
all of the national academies of science of the major
industrialized countries. The basic argument that greenhouse gases
keep the Earth comfortably warm has never been challenged and it
follows that an increase in carbon dioxide in the atmosphere
undoubtedly produces a rise in temperature at ground level.
[0005] It is known that naturally occurring greenhouse gases have a
warming effect by trapping heat radiated from the sun. The major
greenhouse gases are water vapor, carbon dioxide (CO.sub.2),
methane (CH.sub.4), sulfur dioxide (SO.sub.2) and ozone (O.sub.3).
Clouds also affect the radiation balance, but they are composed of
liquid water or ice and so are considered separately from water
vapor and other gases. CO.sub.2 concentrations in the atmosphere
are continuing to rise due to the continual burning of fossil fuels
and land-use change.
[0006] Currently, the amount of carbon dioxide in the atmosphere is
increasing at the rate of about one part per million per year. If
this continues, some meteorologists expect that the average
temperature of the earth will increase by about 2.5 degrees
Celsius. Such changes could be enough to cause glaciers to melt,
which would cause coastal flooding. Today the amount of carbon
dumped globally into the atmosphere corresponds, on average, to one
ton per person on the planet, each year. Because carbon-based
energy is especially important in the United States, the average
American per capita emission is 5 tons of carbon annually.
[0007] Among the fossil fuels, coal is the most carbon intensive so
energy generated by coal produces the highest carbon dioxide
emissions. Coal is the second largest domestic contributor to
carbon dioxide emissions in the United States. Currently about
fifty percent of the energy in the United States is generated from
coal, with more than 500 coal-fired power plants in the United
States. U.S. coal burning power plants contribute 1.5 billion tons
per year of carbon dioxide. Coal is found in abundance in various
countries, including the Unites States, India and China. The supply
of coal in the United States is projected to last for up to 250
years. It is currently thought that coal will continue to be used
to meet the world's energy needs in significant quantities
throughout the world because coal is plentiful and relatively less
expensive than other energy producing technologies. Globally, coal
is responsible for 40% of carbon dioxide emissions. The
International Energy Agency predicts that China will surpass the
United States in carbon dioxide emissions by the end of 2009 and
China continues to build new coal-fired power plants for its energy
needs.
[0008] In 2006, environmental groups pushed for legislation that
would reinstate CO.sub.2 as a pollutant. In August of 2006, EPA
General Counsel Robert Fabricant concluded that since the Clean Air
Act does not specifically authorize regulation to address climate
change, CO.sub.2 is not a pollutant. Nonetheless, the public has
become more concerned about global warming which has led to new
legislation. US power plants face pressure to reduce CO.sub.2
emissions. The coal industry has responded by running advertising
campaigns touting clean coal in an effort to counter negative
perceptions, as well as by putting more than $50 billion towards
the development and deployment of clean coal technologies,
including carbon capture and storage. The expenditure has been
unsuccessful to date in that there is not a single commercial scale
coal fired power station in the United States that captures and
stores more than token amounts of carbon dioxide.
[0009] European power plants are also faced with reducing their
CO.sub.2 emissions significantly by 2012 as required by the Kyoto
Protocol. Energy producers have embarked upon a unique way to
reduce the CO.sub.2 emitted into the atmosphere via a technique
known as carbon capture and storage which involves siphoning off
and burying the CO.sub.2 underground. While the CO.sub.2 is not
eliminated, it is contained. The Department for Environment Food
and Rural Affairs is working out plans to give industries credit
for carbon capturing and storing in the second phase, from 2008-12,
of the European carbon trading scheme. Such technologies, however,
also have potential negative effects on the environment, such as
underground leaking, contamination of waters, and potential health
effects on plants and animals. Geological structures used to store
carbon dioxide need to be able to remain stable and retain their
capacity for hundreds or even thousands of years. Thus, these
technologies are in development and testing and are not yet
considered to be a final solution for carbon dioxide reduction in
the atmosphere.
[0010] Carbon capture and sequestration can reduce carbon dioxide
emissions significantly, while allowing the use of coal as a fuel
source. First, coal is collected in a gasifier with oxygen and
steam where heat and pressure are used to form a synthetic gas,
known as "syngas". The carbon dioxide can then be captured. The
syngas is composed of carbon monoxide and hydrogen. Potential uses
of syngas include power generation and fertilizers.
[0011] After being captured as a gas from the separation stage, the
carbon dioxide can be compressed to supercritical fluid and/or
cooled to decrease its volume. Tankers, trucks and ships are used
for bulk transport over short distances and in small to moderate
scales. For larger plants, a pipeline is usually the practical
alternative for transportation of carbon dioxide.
[0012] The CO.sub.2 can be sent to food production, such as
incorporation into soft drinks or to the agricultural industry as a
viable ingredient in feedstock, or it can be contained for
geological storage.
[0013] Typical carbon dioxide sequestration technologies include
coal beds, depleted oil and gas reservoirs, and saline aquafiers.
Carbon dioxide can also be dissolved in the ocean deeper than half
a mile, or deposited on the sea floor more than two miles down in
liquefied form. Unfortunately, some sequestration technologies are
still subject to potential leaks into the environment with harmful
consequences. Geological structures used to store carbon dioxide
need to be able to remain stable and retain their capacity for
hundreds or even thousands of years. Thus, the optimal solution to
the carbon dioxide problem is to minimize its emission.
[0014] In addition to CO.sub.2. various other emissions are
produced during fuel combustion processes, including sulfur
dioxide, nitrogen oxides and mercury. It has been found that these
pollutants also promote the greenhouse effect as well as the
reduction of the ozone layer in the stratosphere. Extensive
research of these emissions has been carried out in recent
years.
[0015] Of course, the best alternative to avoid greenhouse effects
and other negative environmental consequences would be to find a
way to eliminate or minimize the production of CO.sub.2 and other
pollutants during the process of power generation. Thus, a focus
has developed on methods of high efficiency energy production.
[0016] Clean coal technology is an umbrella term used to describe
technologies being developed that aim to reduce the environmental
impact of coal energy generation. These technologies include
chemically washing minerals and impurities from the coal,
gasification, treating the flue gases with steam to remove sulfur
dioxide, carbon capture and storage technologies to capture the
carbon dioxide from the flue gas and dewatering lower rank coals
(brown coals) to improve the calorific quality, and thus the
efficiency of the conversion into electricity.
[0017] Clean coal technology usually addresses atmospheric problems
resulting from burning coal. Historically, the primary focus was on
sulfur dioxide and particulates, since it is the most important gas
in the causation of acid rain. More recent focus has been on carbon
dioxide. Concerns exist regarding the economic viability of these
technologies and the timeframe of delivery, potentially high hidden
economic costs in terms of social and environmental damage, and the
costs and viability of disposing of removed carbon and other toxic
matter.
[0018] The world's first "clean coal" power plant went on-line in
September 2008 in Spremberg, Germany. The plant is state-owned and
has been built by the Swedish firm Vattenfall. The plant is state
owned because of the high costs of this technology. Private
investors often invest in other sources of power such as nuclear,
solar and wind power generation technologies. The facility captures
carbon dioxide and acid rain producing sulfides, separates them,
and compresses the carbon dioxide into a liquid state. It has been
planned to inject the carbon dioxide into depleted natural gas
fields or other geological formations.
[0019] In conventional pulverized coal-fired power plants and Super
Critical Pulverized coal technologies (SCPC) that produce flue
gases, the carbon dioxide is separated out of the flue gases.
Typical CO.sub.2 capture is in the range of 80 to 95%. The flue gas
is passed through an absorber where a solvent removes most of the
carbon dioxide. In Integrated Gasification Combined-Cycle
technology (IGCC), which is utilized in newer power plants and well
suited for high grade bituminous coal, about 90% of the CO.sub.2 is
removed. Syngas is cooled and cleaned to remove particulates and
other emissions. It is then combusted with air or oxygen to drive
turbine engines. Exhaust gases undergo heat exchange with water and
steam to drive steam turbines and power generators.
[0020] A major disadvantage to IGCC technology and SCPC
technologies are the major technical modifications required for
retrofitting existing power plants, involving massive costs. In
fact, engineering estimates show it may prove that it would be less
expensive to destroy existing power plants and build new ones
rather than to retrofit the existing facilities. Such costs may
thus prove prohibitive for implementing clean air technology.
[0021] Another technology option for reducing carbon dioxide
emissions is Underground Coal Gasification (UCG). This technology
however, presents other environmental concerns associated with coal
mining. Oxygen fired pulverized coal combustion appears to be more
promising for lower quality coals. The process involves burning
coal in an oxygen-rich atmosphere to produce a pure stream of
carbon dioxide.
[0022] Chemical Looping Combustion (CLC) has presented itself as a
viable technology for improved fuel combustion and power
generation. First introduced in 1954, in 1983 chemical looping
combustion was presented as a way of increasing the thermal
efficiency of power plants, and in the 1990's, it was recognized as
a possibility to capture carbon dioxide from fossil fuels in order
to reduce climate impact. CLC is a combustion technology where no
direct contact occurs between air and fuel. It is an emerging
technology that enables carbon dioxide capture without the high
efficiency loss of current carbon capture technologies.
[0023] The chemical looping combustion process for hydrocarbons or
hydrogen based fuels that has been developed to date is a process
in which metal-based oxygen carriers undergo repeated
reduction/oxidation cycles to allow for combustion without the fuel
coming into contact with air. In the simplest form of CLC, an
oxygen carrying species, normally a metal or metal suboxide is
first oxidized in air forming a metallic oxide. This oxide is then
utilized as the oxygen source for the oxidation of the fuel
material. In this step, the metal oxide is reduced back to the pure
metal or suboxide using the hydrocarbon as reducer in the second
step of the reaction.
[0024] The two step reaction process provides two product streams,
the first of which contains carbon dioxide and water, wherein the
carbon dioxide and minor impurities can be collected and
sequestered for storage. Thereby, CLC enables the generation of
power. The CLC system is composed of two reactors, an air reactor
and a fuel reactor. The fuel is introduced into the fuel reactor,
which contains a metal oxide. In the most common process where
methane is utilized, the exit gas stream from the fuel reactor
contains CO.sub.2 and H.sub.2O. A stream of substantially pure
CO.sub.2 is obtained when H.sub.2O is condensed. The reduced metal
oxide is transferred to the air reactor where it is oxidized.
[0025] In one example of the prior art, a nickel-based system
burning pure carbon would involve the two following redox
reactions:
2Ni+O.sub.2.fwdarw.2NiO (1)
C+2NiO.fwdarw.CO.sub.2+2Ni (2)
When reactions (1) and (2) are combined, the reaction set reduces
to straight carbon oxidation with the nickel acting as a catalyst
or oxygen carrier only:
C+O.sub.2.fwdarw.CO.sub.2 (3)
[0026] In chemical looping combustion of the prior art, the
CO.sub.2 is inherently separated from other flue gas components,
such as N.sub.2 and O.sub.2 and thus no energy is expended for the
gas separation and no gas separation equipment is needed. Depending
on the metal oxide and fuel used, reaction (I) is often exothermic,
while reaction (2) is endothermic. The total amount of heat evolved
from reactions (1) and (2) is the same as for common combustion
processes where the oxygen is in contact with the fuel.
[0027] In 2001, a design based on the circulating fluidized bed
principle was presented by Lyngfelt, Leckner and Mattison. Most of
the work so far in chemical looping combustion has been directed to
applications that employ a dual fluidized bed system where the
fluidized beds are interconnected. The metal oxide is in the form
of particles employed as an oxygen carrier and bed material
providing the oxygen for combustion in the fuel reactor. The
reduced metal is then transferred to the second fluidized bed (air
reactor) and re-oxidized before being reintroduced back to the fuel
reactor completing the loop.
[0028] In the processes of the prior art, the metal oxide or metal
suboxide is typically placed on a ceramic support material, for
example NiAl.sub.2O.sub.4, and this material is processed in dual
fluid bed type reactor systems in a pelletized form. Besides nickel
oxide, iron, manganese and copper oxides have been evaluated. For
example, the National Energy Technology Laboratory carried out an
evaluation of these metal oxides using a high-pressure flow reactor
at 150 psi with synthesis gas and found that they showed a stable
reactivity over three high-pressure cycles. The team concluded that
though direct coal combustion is feasible with metal oxides, it
would be necessary to develop an efficient solid circulation
process and ash/metal-oxide separation process.
[0029] The prior art focuses on the development of suitable oxygen
carrier supports or binders for the process. The ability of the
oxygen carrier supports to convert a fuel gas fully to CO.sub.2 and
H.sub.2O has been investigated thermodynamically. For example, U.S.
patent application Ser. No. 11/010,648 to Thomas et al. discloses a
method for producing hydrogen gas which comprises reducing a metal
oxide in a reduction reaction between a carbon-based fuel and a
metal oxide to provide a reduced metal or metal oxide having a
lower oxidation state, and oxidizing the reduced metal or metal
oxide to produce hydrogen and a metal oxide having a higher
oxidation state. The metal or metal oxide is provided in the form
of a porous composite of a ceramic material containing the metal or
metal oxide.
[0030] Many types of oxygen carrier supports or binders have been
studies, including zirconia, alumina, metal aluminate spinels,
titanium dioxide, silica, and kaolin clay. Yttriated zirconia
remains the support considered to be the most efficient because it
acts as an ion conductor for the O.sup.2- ions at the working
temperatures and thereby increases the reactivity of the redox
system. A number of patents disclose cerine-zirconia type oxides in
the field of the process using a redox active mass in a circulating
bed process, including in chemical looping combustion.
[0031] A common problem with all transitional metal oxygen carriers
is the formation of carbon deposits (i.e. coke) on the surfaces of
carrier particles during the reduction phase. M. Ishida and H. Jin
have reported that carbon deposits cause degradation of the
physical strength of the particles and their chemical
stability.
[0032] In conventional CLC, the bulk of the power is generated by
the hot flue gas from the air reactor entering a gas turbine. Thus,
a power plant's overall thermal efficiency is highly dependent on
the maximum temperature that can be tolerated by the carrier during
oxidation for extended periods. Sensitivity analysis shows that
thermal efficiency varies with an increase in temperature of the
reaction. It is currently thought that to achieve greater
efficiencies, appropriate metal oxygen carrier supports are
required.
[0033] The arrangement of a reversible CLC engine is based on
receiving heat at high temperature from the exothermic oxidation
reaction. Part of this energy can be converted into work; the rest
is utilized as heat. Almost all of that heat can be absorbed by the
endothermic reduction reaction. Therefore, this arrangement
requires the redox reactions to be exothermic and endothermic
respectively.
[0034] U.S. Pat. No. 5,447,024 to Ishida et al. discloses a
chemical looping combustion system utilizing the following formulae
(1) and (2).
RH+MO.fwdarw.mCO.sub.2+nH.sub.2O+M (1)
M+0.5O.sub.2.fwdarw.MO (2)
The reduction product (M) of metallic oxide (MO) obtained according
to formula (1) is utilized in the oxidation reaction of formula
(2). Therefore, a chemical looping reaction occurs with MO as an
oxygen carrier. The reaction of the formula (1) is an endothermic
reaction of the metallic oxide (MO) and a fuel (RH) with low-energy
absorption in a low-temperature region (about 600-1,000 K). The
reaction of the second formula (2) is an exothermic oxidation
reaction of the product (M) of the first step in a high-temperature
region (about 800-1,700 K). A high-temperature exhaust gas is
produced by the heat of the reaction and is utilized for driving a
gas turbine. The product (M) is exemplified by metals such as iron,
nickel, copper and manganese. The patented process uses circulating
bed technology to allow continuous change of the active mass from
the oxidized state to the reduced state.
[0035] The patent claims as the active mass the use of the redox
pair NiO/Ni, alone or associated with binder YSZ (defined by
zirconia stabilized by yttrium). The advantage of the binder in the
process is the increase of the mechanical strength of the
particles. The particles would be too weak to be used in a
circulating bed when NiO/Ni is used alone.
[0036] FIGS. 1 and 2, demonstrate the CLC process of the prior art
utilizing NiO, Mn.sub.3O.sub.4, Fe.sub.2O.sub.3 and other oxides.
The figures demonstrate that reaction (2) is highly exothermic with
adiabatic temperatures exceeding 3000.degree. C. Such high
temperatures make it difficult to control and maintain the
temperature in the fluidized bed reactor below the melting point of
either the metal oxide or the metal. In addition, in order to avoid
forming sintered build-ups, good temperature control and cooling is
required, lack of which in the prior art processes results in
increased heat losses from the process. The endothermic step of
these two reactions consumes substantial energy from the exothermic
reaction step and this heat transfer cannot be realized with zero
heat loss. As a result, the thermal efficiency of the chemical
looping combustion processes of the prior art is poor and a process
for improved thermal efficiency is needed.
[0037] Heat transfer and endothermicity of reaction are also
substantial problems in various other industrial processes. In the
industrial process known as steam reforming, hydrogen is produced
by passing steam and a hydrocarbon through a nickel catalyst. Other
processes include the gasification of biomass, the catalytic
reforming of petroleum hydrocarbons, the decomposition of methanol.
G. P. Curran, C. E. Fink, and E. Gorin in an article entitled
CO.sub.2 Acceptor Gasification Process, in Fuel Gasification,
suggest the reaction: CO.sub.2+CaO.dbd.CaCO.sub.3. The reaction is
highly exothermic, thereby supplying the heat consumed by the
endothermic gasification reaction. Furthermore, CO.sub.2 and CO are
in equilibrium via the water shift reaction:
H.sub.2O+CO.dbd.CO.sub.2+H.sub.2. Consequently, removing the
CO.sub.2 has the effect of also removing the CO, allowing the
production of a gas containing a large mole fraction of hydrogen.
The authors conclude, however, that for this process to be
practical, it is necessary to reconvert the CaCO.sub.3 back to CaO.
The heat necessary to do this can be readily generated by burning
some fuel; however, transferring the heat to where it is needed
within the reactor system is a difficult and expensive problem.
Thus, these processes of the prior art leave a need for a new
method of burning fuel which allows for more effective energy
generation, better heat transfer and reduced heat losses.
[0038] The majority of the work performed to date on chemical
looping combustion has been performed using methane and coal as the
fuels of choice. Current CLC processes operate most effectively
with a gaseous fuel material such as methane. Solid fuel material
CLC processing of coal is desirable but is less effective due to
the restrictions of the solid to solid reactant mass transfer
limitations of the process. In addition, when processing coal as
the fuel material, the oxygen carrier becomes "poisoned" over time
by the non-combustible mineral components contained in the coal,
known as fly ash. This contamination affects the reactivity and
porosity of the heterogeneous oxygen carrier system rendering the
metal oxide and support ceramic unusable. When the oxygen carrier
is depleted, the pelletized oxygen carrier material must be removed
from the fluid bed reactor for reprocessing. At that point, the
valuable metal oxide must be separated from the substrate or
support ceramic. Rejuvenation of the metal oxide and separation and
recovery of the substrate ceramic waste components is a costly
process which has an adverse impact on the overall cost of the CLC
processes of the prior art.
[0039] Limited studies have been performed with oxygen carriers
used to combust liquid fuels. The application for CLC for power
production for liquid fuels such as heavy hydrocarbons is gaining
wide interest in the oil and refining industry. The use of liquid
fuels raises specific problems of implementation that are different
than for gas or solids.
[0040] The largest, a 50 kW, chemical looping combustion system in
operation as of 2008 was been built in Korea and operated
continuously for 25 hours. In Europe, current experience is from a
10 kW CLC facility located in Chalmers University of Technology in
Sweden. The Technical University of Vienna in Austria is working on
scaling-up its CLC process. These various CLC facilities implement
the known developed variables and each process implements various
trade-offs between efficiency, carbon dioxide capture and oxygen
carrier properties.
[0041] Therefore, despite the progress in CLC technology, the world
still desires an energy generation process that is highly efficient
and can reduce the emission of unwanted side products while being
economically practical to operate. The process and apparatus of the
present invention take us one step closer to the desired
solution.
[0042] The above and other features of the invention, including
various novel details of construction and combination of parts,
will now be more particularly described with reference to the
accompanying drawings and pointed out in the claims. It will be
understood that the particular reactions and apparatus embodying
the invention are shown by way of illustration only and not as a
limitation of the invention. The principles and features of the
invention may be employed in various and numerous embodiments
without departing from the scope of the invention.
SUMMARY OF THE INVENTION
[0043] An object of the present invention is the generation of
useful work. The improvement over the prior art is that both
reaction steps of the process are exothermic and useful work is
generated during exothermic chemical looping combustion conditions
in both reactions steps of the process. Embodiments of the present
invention address the need for a high efficiency energy generation
process by providing a process for chemical looping combustion
comprising contacting a reduced oxygen carrier with oxygen to form
an oxidized oxygen carrier, and contacting said oxidized oxygen
carrier and a fuel to produce said reduced oxygen carrier and
carbon dioxide, wherein both steps of the process are exothermic.
During the process, the steps can be performed in either order
within the furnace.
[0044] In accordance with one embodiment of the present invention,
the process for chemical looping combustion is performed in a
furnace and comprises a first step wherein a reduced oxygen carrier
is contacted with oxygen to form an oxidized oxygen carrier, and a
second step wherein an ash-containing fuel is contacted with said
oxidized oxygen carrier to produce a reaction product comprising
said reduced oxygen carrier, carbon dioxide and fly ash. Both the
first step and the second step are exothermic.
[0045] One preferred embodiment of the present invention provides a
process for chemical looping combustion in a flash furnace. The
flash furnace comprises a first reactor and a second reactor
receivably connected to the first reactor. The process comprises
the steps of: (a) feeding oxygen and a reduced oxygen carrier into
the first reactor having a first reactor temperature at a location
that is not a reaction zone, the oxygen and the reduced oxygen
carrier each having a temperature that is lower than the first
reactor temperature, and the first reactor temperature being
sufficient to ignite the oxygen and the reduced oxygen carrier as
they pass through the first reactor and create a reaction that is
sufficiently exothermic to form a self-sustaining reaction zone
having a first flash temperature, said reaction producing an
oxidized oxygen carrier; (b) feeding the oxidized oxygen carrier
and a fuel into the second reactor at a location that is not a
reaction zone having a second reactor temperature, the oxidized
oxygen carrier and fuel each having a temperature that is lower
than the second reactor temperature, and the reactor temperature
being sufficient to ignite the oxidized oxygen carrier and the fuel
as they pass through the second reactor and create a reaction that
is sufficiently exothermic to form a self-sustaining reaction zone
having a second flash temperature, the reaction producing the
reduced oxygen carrier and carbon dioxide; and (c) optionally,
feeding the reduced oxygen carrier from the second reactor to the
first reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] In order that the manner in which the above-recited and
other advantages and objects of the invention are obtained, a more
particular description of the invention will be rendered by
reference to specific embodiments thereof which are illustrated in
the appended figures.
[0047] FIG. 1 is a graph showing the enthalpy change for reduction
reactions with carbon.
[0048] FIG. 2 is a graph showing the enthalpy change for reduction
reactions with methane.
[0049] FIG. 3 is a diagram flowsheet of the high thermal efficiency
chemical looping combustion process of the present invention.
[0050] FIG. 4 is a graph showing the enthalpy change for reduction
reactions with hydrogen.
[0051] FIG. 5 is a graph showing of the thermal decomposition of
MoO.sub.3 according to the process of the present invention.
[0052] FIG. 6 is a graph showing the equilibrium composition for
the reduction of MoO.sub.3 with a stoichiometric amount of carbon
according to the process of the invention.
[0053] FIG. 7 is a graph showing the thermal decomposition of
Na.sub.2O.sub.2.
[0054] FIG. 8 is a graph showing the thermal decomposition of
MnO.sub.2.
[0055] FIG. 9 is a graph showing the thermal decomposition of
Rh.sub.2O.sub.3.
[0056] FIG. 10 is a graph showing the thermal decomposition of
PdO.
[0057] FIG. 11 is a graph showing the thermal decomposition of
PtO.
[0058] FIG. 12 is a graph showing the thermal decomposition of
NiO.
[0059] FIG. 13 is a graph showing the thermal decomposition of
V.sub.2O.sub.5.
[0060] FIG. 14 is a graph showing the thermal decomposition of
TlO.sub.3.
[0061] FIG. 15 is a graph showing the thermal decomposition of
OsO.sub.4.
[0062] FIG. 16 is a graph showing the thermal decomposition of
Re.sub.2O.sub.7.
[0063] FIG. 17 is a graph showing the thermal decomposition of
Tc.sub.2O.sub.7.
[0064] FIG. 18 is a graph showing the thermal decomposition of
CuO.
[0065] FIG. 19 is a graph showing the thermal decomposition of
BaO.sub.2.
[0066] FIG. 20 is a graph showing the equilibrium composition for
the reduction of carbon dioxide with carbon.
DETAILED DESCRIPTION OF THE INVENTION
Furnaces
[0067] The process of the invention is particularly suited in the
environment of chemical looping combustion systems. Without
limiting the applicability of the invention, the invention will be
specifically described in the environment of chemical looping
combustion. The process of the current invention may be carried out
in various types of combustion systems, including rotary kilns,
multiple hearth furnaces, vertical tube furnaces or fluidized bed
reactors.
[0068] With reference to FIG. 3, in a preferred embodiment, the
process is carried out in a flash furnace. The flash furnace
utilized for the process of the invention will contain at least two
separate reaction vessels, herein referred to as "reactors", though
more reactors may be appended.
[0069] The temperature of one reactor may vary from the temperature
of the second reactor. The term "reactor temperature" as used
herein refers to the temperature of a reactor at any particular
time at the location within the reactor where the reactants are
being fed into the reactor. It is preferred that the reactants be
fed into the reactor at the top of the furnace, such that the
reactants fall gravitationally through the furnace and react with
one another as they are falling. As the reagents begin and continue
to react within the reactor, the temperature within the reactor
will increase. The reactants will then enter the flash zone where
the reaction will proceed to its completion.
[0070] Therefore, in a preferred embodiment of the process of the
invention, the reduced oxygen carrier flows concurrently in the
same direction with the flow of the oxygen in the first reactor.
Similarly, in the second reactor of the furnace, the oxidized
oxygen carrier flows concurrently in the same direction with the
flow of the fuel. The concurrent flow of the process increases the
contact time between the reactants, thereby increasing the kinetics
of the reaction and ensuring completion of the reaction. Concurrent
flow also enables control of the oxygen carrier to fuel ratio
within the process thereby increasing the accuracy of the reagent
ratio in the process of the invention.
Flash
[0071] Embodiments of the invention provide a high thermal
efficiency CLC process wherein substantial energy is generated
during both reaction steps of the process. Each reaction creates a
sufficiently exothermic reaction having a stable flash reaction
zone in which these reactions proceed to their completion. The term
"flash" or "flash zone" will be used herein to refer to a reaction
zone that is self-sustaining and has a high temperature as a result
of the reactants coming into contact with one another in the
reactor. As used herein, the term "flash temperature", as
distinguished from "reactor temperature", refers to the highest
temperature of the reaction in the flash zone of the reactor.
[0072] For practical purposes of operation of the flash furnace, it
is preferred that the length of the reactor be sufficiently long to
allow some differential between the reactor temperature and the
flash temperature so that the reactants can have at least a few
seconds to fall through the reactor before the flash is created
within the reactor. In one embodiment of the process, the fuel and
the oxidized oxygen carrier are blended prior to being passed into
the second reactor. The blending can be carried out by various
mixing or blending processes commonly known and commercially
available for such industrial processes.
Continuous Process
[0073] The preferred process is continuous in that the reduced
metal oxide or metal suboxide is recycled back in a loop into the
system, hence the term "looping". The oxygen carrier can be
recycled in its' heated state from the second reactor, which will
further facilitate the formation of a stable flash in the reactor.
In order to optimize the continuity of reaction, in a preferred
embodiment, the oxygen and the reduced oxygen carrier are fed into
the first reactor at a rate that is substantially constant while
the first and the second reactor are, respectively, maintained at
substantially constant temperatures.
Oxygen Carriers
[0074] The exothermic conditions of the process of the invention
can be achieved by carefully choosing the appropriate oxygen
carrier and unique operating conditions in a way that both
reactions (1) and (2) become highly exothermic. By the term
"reduced oxygen carrier" as used herein is meant a metal or a metal
suboxide. The term "oxidized oxygen carrier" as used herein refers
to an oxygen carrier that has been oxidized such that it has a
higher oxidation state than the reduced oxygen carrier. The term
"oxygen carrier" is used herein to refer to either reduced oxygen
carrier or oxidized oxygen carrier.
[0075] The preferred reduced oxygen carriers of the invention are
rhenium, platinum, rhodium, palladium, copper, barium, manganese,
molybdenum, vanadium, bismuth, lead, mercury, sodium, potassium,
rubidium, and cesium.
[0076] One embodiment of the invention is a process wherein more
than one oxygen carrier is utilized at the same time within the
furnace. A preferred embodiment of such a process is the
combination of MoO.sub.3 and Re.sub.2O.sub.7.
[0077] In contrast to the prior art, the oxygen carrier within the
process of the invention is substantially free-flowing. By
"free-flowing", it is meant that the oxygen carrier is not
supported on a binder material of any sort, such as the ceramic
supports of the prior art. When coal is reacted with a
heterogeneous system, where the oxygen carrier is bound to a
substrate, it becomes challenging to completely burn the fuel due
to the difficulty in providing direct physical contact between the
reagent particles.
[0078] In addition, virtually no vapor pressure is created over the
oxygen carrier systems of the prior art, as can be seen for example
in FIG. 12 for NiO in the temperature range of 100-1500.degree. C.
The oxidation reaction proceeds solely in a solid state. In the
improved process of the invention, the free-flowing reactants flow
co-currently while the oxygen carrier acting as oxidizing agent
develops a tangible vapor pressure. The vapor greatly facilitates
the mass transfer and kinetics and ultimately leads to complete
fuel combustion. Creating such unique kinetic conditions for the
CLC process of the invention also leads to the removal of the
volatile impurities, such as mercury, sulfur and others. Thus the
CO.sub.2, SO.sub.2. and Hg are removed in highly concentrated form
for capture and sequestration. It is also important to note that
production and emission of nitrogen oxides are dramatically reduced
during the fuel combustion process of the invention.
[0079] It is relevant to note that the nickel oxide used in the CLC
processes of the prior art presents well-known serious health and
environmental problems. Among the oxides that can be used in the
improved CLC process of the present invention, lead, mercury and
some other compounds present a clear hazard. Therefore, preferred
are oxides and/or metals that do not present serious health
problems. These are molybdenum, vanadium, bismuth, platinum,
rhodium, and palladium oxides, though due to their high cost,
platinum, rhodium and palladium are less preferred.
[0080] Preferably, the oxygen carrier particles used in the process
of the invention are in powder form. By "powder" is meant a solid
substance that is in a state of fine, loose particles. The powder
form of the oxygen particles can be obtained by crushing, grinding,
disintegration, or other mechanisms. Preferably, the oxygen carrier
has a particle size of from 100 nanometers to 1 mm as determined by
laser light scattering. More preferably, the oxygen carrier is in
the form of a powder having a particle size of from 20 microns to
250 microns as determined by laser light scattering.
[0081] In order for the materials to be accepted for use in the CLC
process of the invention, it is desirable that the oxide/suboxide
or oxide/metal pairs meet the following criteria: (1) both
reactions must be exothermic; (2) the reduced oxygen carrier must
generate enough gaseous species to promote the oxidation of a solid
fuel such as coal; and (3) the re-oxidation of the suboxide/metal
with air at atmospheric pressure must be thermodynamically
feasible.
[0082] Tables 11-13 of the Examples and FIGS. 7-19 reflect the
correspondence of various oxide/suboxide and oxide/metal pairs that
meet the outlined criteria of the invention. Various oxygen
carriers can be chosen for reaction with fuel in the chemical
looping combustion process of the invention. For example, rhenium
(VII) oxide is a volatile compound and its reaction with fuel is
exothermic (see Table 11).
[0083] It can be seen from FIGS. 14, 15 and 17 that the oxides of
Tl, Os, and Tc become volatile at low temperatures which make them
practically impossible for processing. On the contrary, the
vanadium pentoxide (FIG. 15) is thermally quite stable and may be
difficult to use for the oxidation of a solid fuel such as coal.
For comparison, the nickel oxide (FIG. 13) normally used in the
traditional CLC processes of the prior art exhibits the same
thermal pattern.
Vaporization
[0084] In another embodiment of the invention, the oxygen carrier
is at least partially vaporized in the furnace. In a process where
coal is utilized as the fuel in the reaction, a substantial vapor
phase in the reactor is important to create the exothermic reaction
of the solid coal particulate in order to maintain the
high-temperature flash conditions and the stability of the flash.
The reactions can therefore be driven to their completion using
near stoichiometric amounts of the reagents. On the contrary,
carrying out the reduction of the metal oxides in either a rotary
kiln or a fluidized bed reactor requires a large excess of one
reagent and/or long retention time due to mass transfer limitations
that make it difficult to achieve complete reaction.
[0085] Other embodiments of the invention include processes wherein
the temperature within the first reactor is above the solid/liquid
phase transition temperature of the reduced oxygen carrier; the
temperature within the first reactor is above the solid/gas phase
transition temperature of the reduced oxygen carrier; the
temperature within the first reactor is above the liquid/gas phase
transition temperature of the reduced oxygen carrier; the
temperature within the second reactor is above the solid/liquid
phase transition temperature of the oxidized oxygen carrier; the
temperature within the second reactor is above the solid/gas phase
transition temperature of the oxidized oxygen carrier; or the
temperature within the second reactor is above the liquid/gas phase
transition temperature of the oxidized oxygen carrier.
Volatilization of the oxygen carrier reagents will create superior
mass transfer of the oxygen carriers and promote the reaction
kinetics. This advantage will promote the completion of the
reactions while allowing for a reduction in the need for a large
excess availability of the oxygen carrier materials. These phase
changes can be identified by the change in enthalpy values, such as
those set forth in the tables within the Examples of the invention
hereinbelow.
[0086] In chemical looping combustion, isolation of the fuel from
air simplifies the number of chemical reactions in combustion.
According to a preferred embodiment of the process of the
invention, employing oxygen in the oxygen carrier without nitrogen
and the trace gases found in air will eliminate the primary source
for the formation of nitrogen oxide (NO.sub.x), producing an off
gas composed primarily of carbon dioxide and water vapor. Such a
rich gas stream high in CO.sub.2 is a great advantage for carbon
capture technologies.
Temperature Conditions
[0087] Using as an example a nickel-based system, burning pure
carbon involves the following reactions, with .DELTA.G signifying a
change of Gibbs free energy:
2Ni+O.sub.2.fwdarw.2NiO (-.DELTA.G.sub.1)
C+2NiO.fwdarw.CO.sub.2+2Ni (-.DELTA.G.sub.2)
C+O.sub.2.fwdarw.CO2 (-.DELTA.G.sub.3)
[0088] According to the 1.sup.st and 2.sup.nd laws of
thermodynamics, the maximum amount of work that a system can
produce is equal to the change of free Gibbs energy for reaction
(3)--(-.DELTA.G.sub.3). This statement is true provided
thermodynamically reversible conditions exist for reactions (1) and
(2). It is practically impossible to carry out the process at
thermodynamic equilibrium at each given time/intermediate
composition. Therefore, according to the 2.sup.nd law of
thermodynamics, the actual amount of useful work will be always
less than -.DELTA.G.sub.3. As only one exothermic reaction is used
to produce useful work in the chemical looping combustion processes
of the prior art, the useful work of the prior art CLC processes
cannot exceed -.DELTA.G.sub.2. In order to get closer to
thermodynamically reversible conditions and maximum useful work,
the heat losses for reactions (1) and (2) should be minimized. In a
preferred embodiment, the creation of adiabatic conditions (zero
heat losses) within the reaction process would bring the
theoretical temperature conditions of the reaction closer to
thermodynamic reversibility.
[0089] In order to minimize heat losses, retention of temperature
through "looping" of the oxygen carrier or preheating of the
reagents will further promote stability of the flash in each
reactor. Therefore, "looping" steps 1 and 2 will create an
opportunity to charge heated metal oxides and suboxides or metals
into the furnace further increasing the thermal efficiency of the
system. Therefore, in a preferred embodiment of the process, the
reactants can be preheated before being fed into the reactor,
though preferably to a temperature that is lower than the flash
temperature. Thus, the reduced oxygen carrier and the oxygen can be
preheated before being fed into the first reactor of the furnace
and the fuel and the oxidized oxygen carrier can be preheated
before being fed into the second reactor of the furnace.
[0090] Carrying out the process at higher temperatures will greatly
increase the rate and the completion of the reactions. This
opportunity simply does not exist for the processing of NiO,
Fe.sub.2O.sub.3 and Mn.sub.3O.sub.4 oxygen carriers utilized in the
processes of the prior art as these first reactions are endothermic
(see FIGS. 1 and 2).
[0091] Another means for controlling the temperature conditions
within the furnace is by controlling the amount of reagent fed into
the system. In a preferred embodiment, the reduced oxygen carrier
and the oxygen are fed into the first reactor at a rate sufficient
to substantially off-set the heat loss of the first reactor and
create a flash; and the oxidized oxygen carrier and the fuel are
fed into the second reactor at a rate sufficient to substantially
off-set the heat loss from the second reactor and create a
flash.
Residence Time
[0092] Due to the short residence time in the flash furnace, the
oxygen carriers in either the first or the second step will have
little or no time to agglomerate, and therefore, will have high
surface area. Since the oxygen carriers will be free flowing and
their bulk densities will be lower than those of agglomerated
oxygen carriers. As a result, the residence time in the flash will
increase and will work to drive the chemical reactions to their
completion. In the preferred embodiment of the process under
desired reaction conditions within a flash furnace, the process of
the residence time of the oxygen and the reduced oxygen carrier in
the first reactor being from 0.01 to 1.0 minute, and more
preferably, from 0.01 to 10 seconds. Similarly, the residence time
of the fuel and the oxidized oxygen carrier in the second reactor
is from 0.01 seconds to 1.0 minute and preferably from 0.01 seconds
to 10 seconds.
[0093] According to the invention, drastic reduction of the
residence time and the oxygen carrier gas volume in the first step
of the process will facilitate a dramatic reduction of the heat
losses of the process in a flash furnace thereby allowing more
energy to be converted into useful work.
Fuel
[0094] Many types of fuel can be utilized in the process of the
invention, such as carbon, coal, hydrogen, hydrocarbon, biofuel,
methane, natural gas, petroleum, crude oil, tar sands, oil shale,
biomass, algae, fuel-rich waste gases from fuel cells and other
fossil fuels and synthetic fuels. Various types of fuels may be
combined during the process. Furthermore, the invention is not
limited by the physical characteristics of the fuel being in a
solid, liquid or gas phase, although embodiments having smaller
particle sizes are preferred. It has been found that where the fuel
is a carbon, a hydrocarbon, or hydrogen, it can be fed into the
process and apparatus of the invention in the form of a solid, a
liquid or a gas.
[0095] For solid fuels, the process will be optimized if the fuel
is fed into the reactor in a powder form. By "powder" as used
herein is meant that a solid fuel source is first pulverized such
that it creates free-flowing particles. In a preferred embodiment,
the coal powder has a particle size of from 100 nanometers to 10 mm
as determined by laser light scattering, and more preferably the
coal powder has a particle size of from 20 microns to 250 microns
as determined by laser light scattering. In one preferred
embodiment of the process, particle size of the coal powder is
substantially similar to the particle size of the oxygen carrier in
order to optimize reaction kinetics.
Fly Ash
[0096] When a fuel that contains ash is utilized in the process,
fly ash is produced during the process. As used herein, the term
"fly ash" refers to non-combustible mineral components in the
off-gas stream of the process. The fly ash produced from the
burning of pulverized coal in a typical coal-fired boiler is a
fine-grained, powdery particulate material that is carried off in
the flue gas and usually collected from the flue gas by means of
electrostatic precipitators, bag-houses, or mechanical collection
devices such as cyclones. The chemical properties of fly ash are
influenced to a great extent by those of the coal burned and the
techniques used for handling and storage. There are four main
types, or ranks, of coal, each of which varies in terms of its
heating value, its chemical composition, ash content, and
geological origin. In addition to coal, ash-containing fuels
include crude oil, tar sands, oil shale and natural gas.
[0097] Dealing with fly ash is a major obstacle to overcome when
burning coal. The fly ash accumulates over time on the surface of
the oxygen carrier causing the oxygen carrier to lose its
effectiveness. Eventually, the oxygen carrier becomes unusable for
further processing because it becomes practically impossible to
either oxidize or reduce the compound.
[0098] Therefore, the oxygen carrier should be constantly or
periodically removed from the reaction and the reaction compensated
with pure oxygen carrier at the same time to avoid deleterious
level of contamination. In one embodiment of the process of the
invention, the reduced oxygen carrier and the fly ash are
continuously removed from the furnace. Continuous removal of fly
ash keeps the furnace free of build up and maintains the integrity
of the process. In order to keep the process in continuous looping,
substantially the same amount of reduced oxygen carrier that is
removed from the furnace is fed back into the furnace, thereby
maintaining the same reaction rates and flash temperatures within
the reactors.
[0099] In traditional CLC processes, the material contaminated with
fly ash is either considered a loss or requires costly
re-processing to separate the metal or metal oxide from the support
material and recover the valuable metal components. In the process
of the invention, especially when processing oxides of molybdenum
and vanadium, the material removed from the furnace is a mixture of
fly ash together with the reduced oxygen carrier. The removed
material can be utilized as an alloy additive in steel or
ferroalloy production, particularly in a process to produce an
alloy material containing iron and slag, including ferroalloys such
as ferrovanadium, ferromolybdenum and ferromanganese. Since the
oxygen carrier is a homogeneous free-flowing material without any
binder or substrate support, no separation step is required. Taking
out the homogeneous free-flowing oxygen carrier in a suboxide form
for direct sale will also result in a reduced reagent usage in the
alloy production field. As a result, coal combustion via the
improved CLC process of the invention will become even more
economically attractive as compared to prior art processes having
supported oxygen carrier systems.
Carbon Dioxide and Carbon Monoxide
[0100] The gaseous products of the combustion process of the
invention will be comprised of CO.sub.2, CO and H.sub.2O. Carbon
monoxide is a chemically reactive gas that can be used for the
production of a variety of chemicals, like metal carbonyls,
phosgene and array of organic compounds such as methanol and other
alcohols, formic and other organic acids, and their derivatives.
According to an embodiment of the invention, the carbon monoxide
can be separated and carbon dioxide can be substantially separated,
captured and sequestered.
[0101] The prior art fluidized bed technology is well known for
generating large amounts of dust during the combustion process. The
off-stream of the endothermic reaction is comprised not only of
CO.sub.2 but also of tangible amounts of carbon. Excess amounts of
carbon are required by the processes of the prior art at least in
part due to their use of supported oxygen carriers of undetermined
particle sizes. As shown in FIG. 20, as the temperature of the
off-gas of the reaction changes, the CO.sub.2 and carbon do not
remain chemically inert to each other, and consequently a small
amount react to generate an appreciable amount of CO. The amount of
CO cannot be controlled nor calculated because the temperature of
the off-stream gas is unstable. As a result, the presence of CO
within the CO.sub.2 stream, especially in unknown ratios, presents
a challenge for the separation and sequestration of carbon dioxide.
High CO levels may be desired for production of carbon containing
chemicals. CO can be desired over CO.sub.2 due to its significantly
higher chemical reactivity.
[0102] In one embodiment of the invention, in order to produce a
substantially pure stream of CO.sub.2 during the process of the
invention, the fuel and the oxidized oxygen carrier are fed into
the second reactor in substantially stoichiometric amounts in order
to produce an excess of carbon dioxide over carbon monoxide. In a
process where the fuel and the oxidized oxygen carrier are fed into
the second reactor in less than stoichiometric amounts, larger
quantities of carbon monoxide will be produced.
[0103] It has also been discovered herein that another means of
controlling the production of CO.sub.2 and CO involves the use of
the following chemical reaction:
CO.sub.2(g)+C=2CO(g)
K.dbd.(P.sub.CO).sup.2/(P.sub.CO2)
wherein K is the equilibrium constant at a given temperature and K
is a function of temperature solely and P is the partial pressure
of the corresponding gaseous species (CO and CO.sub.2
respectively). Adding CO.sub.2 gas to the system at a given
temperature will cause an increase in the partial pressure of CO
according to the above equation for the equilibrium constant. In
the event that the CO.sub.2 gas is injected into the furnace at the
location of the flash, wherein the CO.sub.2 gas has a temperature
significantly lower than the flash temperature, the temperature of
the flash will be decreased. This will cause a change in the
equilibrium constant. As a result, the partial pressure of CO may
decrease (depending on the decrease of temperature.) Therefore, the
amount of CO produced can be controlled not only by the partial
pressure of the CO.sub.2 gas in the flash zone but also by the
flash temperature which can be changed by the amount of the
CO.sub.2 gas added to the flash zone. In this manner, it is hereby
possible to control the CO.sub.2/CO ratio and production of the
CO.sub.2 and CO.
EXAMPLES
[0104] The following examples illustrate the process and are
intended to be purely exemplary of the use of the invention and
should not be viewed as limiting its scope. In the tables below, T
(in degrees Celsius) indicates the reaction or reactor temperature
within the furnace. .DELTA.H indicates the enthalpy change of the
reaction, .DELTA.S is the entropy change of the reaction and
.DELTA.G is the change in Gibbs free energy. K is the equilibrium
constant of the reaction at the given temperature. The values of
the examples were calculated using HSC CHEMISTRY.RTM. for Windows
Thermodynamic Software by Outokumpu Research Oy of Finland.
[0105] Negative .DELTA.G values in the tables below signify that
the equilibrium of the reaction is shifted toward the right, i.e.
toward formation of the products. The greater the value of the
negative .DELTA.G, the more complete the reaction, such that there
would be an insignificant amount of reactants left in the product
of the reaction, which is also indicated by the extremely high K
values. The negative .DELTA.H values in the tables indicate that
the reactions are exothermic.
Example 1
[0106] Molybdenum was used as the metal and reacted with oxygen to
form molybdenum trioxide as the oxidized oxygen carrier. Table 1
demonstrates the thermodynamic analyses of the chemical looping
combustion process of the invention using molybdenum trioxide with
the following combustion reaction:
2MoO.sub.3+C=2MoO.sub.2+CO.sub.2(g)
TABLE-US-00001 TABLE 1 T .DELTA.H .DELTA.S .DELTA.G C kcal cal/K
kcal K 100.000 -19.277 34.432 -32.126 6.565E+018 200.000 -19.412
34.113 -35.552 2.649E+016 300.000 -19.577 33.797 -38.948 7.124E+014
400.000 -19.802 33.437 -42.310 5.469E+013 500.000 -20.095 33.033
-45.634 7.956E+012 600.000 -20.453 32.597 -48.916 1.757E+012
700.000 -20.877 32.139 -52.153 5.169E+011 800.000 -21.360 31.667
-55.343 1.870E+011 900.000 -45.876 8.910 -56.329 3.122E+010
1000.000 -47.006 7.984 -57.172 6.531E+009 1100.000 -48.010 7.225
-57.931 1.663E+009 1200.000 -48.880 6.613 -58.622 4.984E+008
1300.000 -49.609 6.134 -59.258 1.710E+008 1400.000 -50.190 5.775
-59.852 6.587E+007 I500.000 -50.616 5.527 -60.417 2.801E+007
Example 2
[0107] Vanadium pentoxide was used as the reduced oxygen carrier
and reacted with oxygen as follows:
V.sub.2O.sub.5+C.dbd.V.sub.2O.sub.3+CO.sub.2(g). Table 2
demonstrates the thermodynamic analyses of the CLC process of the
invention using vanadium pentoxide.
TABLE-US-00002 TABLE 2 T .DELTA.H .DELTA.S .DELTA.G C kcal cal/K
kcal K 100.000 -14.618 42.080 -30.320 5.746E+017 200.000 -14.573
42.187 -34.533 8.963E+015 300.000 -14.553 42.227 -38.755 6.011E+014
400.000 -14.587 42.172 -42.976 8.994E+013 500.000 -14.710 42.005
-47.186 2.184E+013 600.000 -14.957 41.706 -51.372 7.237E+012
700.000 -30.684 25.207 -55.215 2.518E+012 800.000 -31.253 24.651
-57.707 5.664E+011 900.000 -31.786 24.175 -60.147 1.607E+011
1000.000 -32.284 23.768 -62.544 5.461E+010 1100.000 -32.744 23.420
-64.903 2.142E+010 1200.000 -33.165 23.124 -67.230 9.435E+009
1300.000 -33.543 22.875 -69.529 4.573E+009 1400.000 -33.874 22.671
-71.806 2.400E+009 1500.000 -34.156 22.507 -74.065 1.348E+009
Example 3
[0108] Table 3 sets forth the thermodynamic analyses of methane gas
using molybdenum trioxide as the reduced oxygen carrier with the
following reaction formula:
4MoO.sub.3+CH.sub.4(g)=4MoO.sub.2+CO.sub.2(g)+2H.sub.2O(g)
TABLE-US-00003 TABLE 3 T .DELTA.H .DELTA.S .DELTA.G C kJ J/K kJ K
100.000 -176.034 279.607 -280.370 1.780E+039 200.000 -176.182
279.264 -308.316 1.097E+034 300.000 -176.765 278.165 -336.196
4.387E+030 400.000 -178.059 276.101 -363.917 1.743E+028 500.000
-180.146 273.224 -391.389 2.785E+026 600.000 -183.023 269.734
-418.541 1.098E+025 700.000 -186.645 265.814 -445.321 8.035E+023
800.000 -190.942 261.616 -471.695 9.147E+022 900.000 -396.477
70.843 -479.586 2.267E+021 1000.000 -406.413 62.709 -486.251
8.944E+019 1100.000 -415.364 55.936 -492.173 5.295E+018 1200.000
-423.266 50.377 -497.479 4.375E+017 1300.000 -430.045 45.920
-502.285 4.778E+016 1400.000 -435.631 42.474 -506.697 6.608E+015
1500.000 -439.948 39.964 -510.811 1.120E+015
Example 4
[0109] Table 4 sets forth the thermodynamic analyses of methane
using vanadium pentoxide having the following reaction:
2V.sub.2O.sub.5+CH.sub.4(g)=2V.sub.2O.sub.3+CO.sub.2(g)+2H.sub.2O(g)
TABLE-US-00004 TABLE 4 T .DELTA.H .DELTA.S .DELTA.G C kJ J/K kJ K
100.000 -137.042 343.602 -265.257 1.363E+037 200.000 -135.690
346.825 -299.790 1.256E+033 300.000 -134.720 348.700 -334.577
3.123E+030 400.000 -134.418 349.203 -369.484 4.714E+028 500.000
-135.085 348.297 -404.371 2.099E+027 600.000 -137.027 345.953
-439.095 1.863E+026 700.000 -268.714 207.807 -470.942 1.907E+025
800.000 -273.724 202.905 -491.472 8.394E+023 900.000 -278.571
198.586 -511.542 6.003E+022 1000.000 -283.213 194.788 -531.207
6.253E+021 1100.000 -287.622 191.452 -550.515 8.777E+020 1200.000
-291.765 188.539 -569.511 1.568E+020 1300.000 -295.604 186.016
-588.236 3.415E+019 1400.000 -299.099 183.861 -606.727 8.774E+018
1500.000 -302.207 182.056 -625.020 2.593E+018
Example 5
[0110] Table 5 sets forth the thermodynamic analyses of hydrogen
utilizing molybdenum trioxide in the following combustion reaction:
MoO.sub.3+H.sub.2(g)=MoO.sub.2+H.sub.2O(g)
TABLE-US-00005 TABLE 5 T .DELTA.H .DELTA.S .DELTA.G C kJ J/K kJ K
100.000 -86.121 24.017 -95.083 2.047E+013 200.000 -87.311 21.189
-97.336 5.580E+010 300.000 -88.498 18.914 -99.339 1.133E+009
400.000 -89.745 16.910 -101.128 7.046E+007 500.000 -91.073 15.072
-102.726 8.726E+006 600.000 -92.482 13.359 -104.147 1.702E+006
700.000 -93.966 11.751 -105.401 4.550E+005 800.000 -95.510 10.241
-106.500 1.528E+005 900.000 -147.260 -37.779 -102.939 3.835E+004
1000.000 -150.014 -40.034 -99.045 1.159E+004 1100.000 -152.436
-41.867 -94.946 4.093E+003 1200.000 -154.520 -43.333 -90.684
1.643E+003 1300.000 -156.254 -44.474 -86.291 7.335E+002 1400.000
-157.630 -45.322 -81.799 3.580E+002 1500.000 -158.633 -45.906
-77.235 1.886E+002
Example 6
[0111] Table 6 sets forth the thermodynamic analyses of hydrogen
utilizing and vanadium pentoxide in the following reaction:
V.sub.2O.sub.5+2H.sub.2(g)=V.sub.2O.sub.3+2H.sub.2O(g)
TABLE-US-00006 TABLE 6 T .DELTA.H .DELTA.S .DELTA.G C kJ J/K kJ K
100.000 -152.746 80.031 -182.609 3.667E+025 200.000 -154.375 76.159
-190.410 1.053E+021 300.000 -155.973 73.096 -197.868 1.082E+018
400.000 -157.670 70.370 -205.040 8.164E+015 500.000 -159.616 67.680
-211.943 2.090E+014 600.000 -161.967 64.827 -218.570 1.193E+013
700.000 -228.966 -5.501 -223.613 1.008E+012 800.000 -232.412 -8.874
-222.889 7.077E+010 900.000 -235.567 -11.687 -221.856 7.569E+009
1000.000 -238.427 -14.028 -220.567 1.122E+009 1100.000 -241.001
-15.976 -219.064 2.157E+008 1200.000 -243.289 -17.585 -217.383
5.112E+007 1300.000 -245.288 -18.899 -215.557 1.439E+007 1400.000
-246.993 -19.951 -213.612 4.671E+006 1500.000 -248.395 -20.765
-211.574 1.711E+006
[0112] Tables 1 through 6 demonstrate that the reactions of the
process of the invention are thermodynamically favorable over a
wide range of temperatures as indicated by the negative .DELTA.G
values. The negative .DELTA.H values show that the reactions are
exothermic.
[0113] Reactions taking place during the first step of the process
are complex and sometimes cannot be described with one reaction in
such a wide temperature range (Tables 1-4). For example, at high
temperatures, carbon monoxide will evolve as one of the products
when reducing molybdenum trioxide. Equilibrium composition for the
reduction of MoO.sub.3 with carbon as a function of temperature is
shown in FIG. 6. It can be seen from FIG. 6 that only up to
800.degree. C. of the equilibrium composition is described by the
reaction shown in Table 1. Above that temperature, the CO content
becomes tangible. It reaches almost 20% at 1500.degree. C.
Example 7
[0114] Re-oxidation of the metal suboxides/metals is as critical as
the oxidation of the fuel. The re-oxidation will be carried out in
air, so the oxygen potential in air (2.1 E-01 atm) must be greater
than the equilibrium partial pressure of oxygen for the
corresponding re-oxidation reaction. The temperature ranges in
which the oxygen potential in air is greater than that of the
re-oxidation reaction can be calculated.
[0115] The equilibrium partial pressure of oxygen as a function of
temperature for the re-oxidation reaction of bismuth is given in
Table 7. The K column represents the oxygen pressure. It can be
seen from Table 7 that the temperature range in which bismuth can
be re-oxidized with air is approximately 100.degree.
C.-1500.degree. C. in the reaction
0.667Bi.sub.2O.sub.3=1.333Bi+O.sub.2(g).
TABLE-US-00007 TABLE 7 T .DELTA.H .DELTA.S .DELTA.G C kJ J/K kJ K
100.000 384.602 178.070 318.155 2.884E-045 200.000 383.379 175.165
300.500 6.648E-034 300.000 397.339 200.706 282.304 1.861E-026
400.000 396.042 198.628 262.336 4.383E-021 500.000 394.440 196.413
242.583 4.069E-017 600.000 392.541 194.107 223.056 4.518E-014
700.000 390.344 191.729 203.764 1.153E-011 800.000 367.765 169.272
186.111 8.719E-010 900.000 352.523 155.524 170.070 2.673E-008
1000.000 346.251 150.393 154.778 4.459E-007 1100.000 340.010
145.674 139.977 4.729E-006 1200.000 333.797 141.307 125.631
3.508E-005 1300.000 327.612 137.244 111.706 1.953E-004 1400.000
321.452 133.448 98.173 8.607E-004 1500.000 315.316 129.886 85.009
3.130E-003
Example 8
[0116] Table 8 sets forth the temperature ranges calculated for the
re-oxidation reactions listed in column 1 of the table according to
the same analysis carried out for bismuth in Example 7.
TABLE-US-00008 TABLE 8 Temperature Range Reaction (.degree. C.)
2Na.sub.2O + O.sub.2 = 2Na.sub.2O.sub.2 100-1000 2K.sub.2O +
O.sub.2 = 2K.sub.2O.sub.2 100-1200 2Rb.sub.2O + O.sub.2 =
2Rb.sub.2O.sub.2 100-700 2Cs.sub.2O + O.sub.2 = 2Cs.sub.2O.sub.2
100-900 2BaO + O.sub.2 = 2BaO.sub.2 100-700 2MnO + O.sub.2 =
2MnO.sub.2 100-900 4TcO.sub.2 + 3O.sub.2 = 2Tc.sub.2O.sub.7
100-1500 4ReO.sub.2 + 3O.sub.2 = 2Re.sub.2O.sub.7 100-1500
OsO.sub.2 + O.sub.2 = OsO.sub.4 100-1500 Rh.sub.2O + O.sub.2 =
Rh.sub.2O.sub.3 100-800 2Pt + O.sub.2 = 2PtO 100-500 2Pd + O.sub.2
= 2PdO 100-700 2Cu + O.sub.2 = 2CuO 100-1400 2Hg + O.sub.2 = 2HgO
100-500 Tl.sub.2O + O.sub.2 = Tl.sub.2O.sub.3 100-700 MoO.sub.2 +
O.sub.2 = MoO.sub.3 100-1500 V.sub.2O.sub.3 + O.sub.2 =
V.sub.2O.sub.5 100-1500 Pb + O.sub.2 = PbO.sub.2 100-1100 4Bi +
3O.sub.2 = 2Bi.sub.2O.sub.3 100-1500
Example 9
[0117] In reference to the example systems, metal sub-oxides and/or
metals produced in the first step of the process, will be
re-oxidized in the second step according to the reactions shown in
Tables 9 and 10. Table 8 is a combustion reaction utilizing
molybdenum trioxide with the formula
2MoO.sub.2+O.sub.2(g)=2MoO.sub.3.
TABLE-US-00009 TABLE 9 T .DELTA.H .DELTA.S .DELTA.G C kJ J/K kJ K
100.000 -312.890 -141.309 -260.160 2.637E+036 200.000 -312.395
-140.133 -246.091 1.480E+027 300.000 -311.826 -139.046 -232.132
1.437E+021 400.000 -311.057 -137.814 -218.287 8.708E+016 500.000
-310.037 -136.407 -204.575 6.643E+013 600.000 -308.749 -134.843
-191.011 2.678E+011 700.000 -307.193 -133.158 -177.610 3.421E+009
800.000 -305.381 -131.388 -164.382 1.004E+008 900.000 -203.013
-36.357 -160.361 1.383E+007 1000.000 -198.490 -32.654 -156.917
2.745E+006 1100.000 -194.498 -29.633 -153.808 7.101E+005 1200.000
-191.067 -27.219 -150.970 2.257E+005
Example 10
[0118] Table 9 is a combustion reaction utilizing vanadium
pentoxide with the formula:
V.sub.2O.sub.3+O.sub.2(g)=V.sub.2O.sub.5.
TABLE-US-00010 TABLE 10 T .DELTA.H .DELTA.S .DELTA.G C kJ J/K kJ K
100.000 -332.386 -173.307 -267.717 3.013E+037 200.000 -332.641
-173.913 -250.354 4.374E+027 300.000 -332.849 -174.314 -232.941
1.703E+021 400.000 -332.877 -174.365 -215.503 5.295E+016 500.000
-332.568 -173.943 -198.084 2.420E+013 600.000 -331.747 -172.953
-180.734 6.501E+010 700.000 -266.158 -104.155 -164.800 7.023E+008
800.000 -263.989 -102.032 -154.494 3.315E+007 900.000 -261.966
-100.228 -144.383 2.687E+006 1000.000 -260.090 -98.693 -134.439
3.283E+005 1100.000 -258.370 -97.391 -124.637 5.515E+004 1200.000
-256.817 -96.299 -114.954 1.192E+004 1300.000 -255.447 -95.399
-105.370 3.155E+003 1400.000 -254.277 -94.677 -95.868 9.844E+002
1500.000 -253.323 -94.123 -86.429 3.518E+002
[0119] The data shown in Tables 8-10 demonstrate that oxidation of
the metal suboxides/metals with oxygen according to the process of
the invention can be carried out in a flash furnace. The flash
furnace will allow operation of the process at temperatures higher
than those of fluidized bed or rotary kiln furnaces. Running the
process at high temperature will significantly increase the rate of
the chemical reaction and, therefore, the process throughput. The
flash temperatures can be controlled by modifying the reactor
temperatures.
Examples 11 and 12
[0120] Examples 11 and 12 demonstrate that that the oxygen carriers
in the process of the invention do not have to be completely cooled
down to room temperature after the reduction or oxidation.
According to the invention, they can be fed preheated into the next
step of the reaction. This will facilitate the formation of a
stronger sustainable flash and increase the overall thermal
efficiency of the process as a result of reduced heat losses. The
initial temperature of the oxygen carriers for steps 1 and 2 was
assumed to be 400.degree. C. This temperature was used to calculate
the flash temperatures for the oxygen carriers, which are set forth
in Tables 10 and 11. Tables 11 and 12 demonstrate that both
reactions of the process are exothermic and the heat energy
released is sufficient to create a stable flash.
TABLE-US-00011 TABLE 11 Reactor Flash Temperature Temperature
Reaction (.degree. C.) (.degree. C.) CH.sub.4 + 4Na.sub.2O.sub.2 =
CO.sub.2 + 4Na.sub.2O + 2H.sub.2O 400 1071 CH.sub.4 +
4K.sub.2O.sub.2 = CO.sub.2 + 4K.sub.2O + 2H.sub.2O 400 740 CH.sub.4
+ 4Rb.sub.2O.sub.2 = CO.sub.2 + 4Rb.sub.2O + 2H.sub.2O 400 1163
CH.sub.4 + 4Cs.sub.2O.sub.2 = CO.sub.2 + 4Cs.sub.2O + 2H.sub.2O 400
1032 H.sub.2 + BaO.sub.2 = BaO + H.sub.2O 400 1834 CH.sub.4 +
4MnO.sub.2 = 4MnO + CO.sub.2 + 2H.sub.2O 400 1073 1.5C +
Tc.sub.2O.sub.7 = 2TcO.sub.2 + 1.5CO.sub.2 400 2134 1.5C +
Re.sub.2O.sub.7 = 2ReO.sub.2 + 1.5CO.sub.2 400 1521 C + OsO.sub.4 =
OsO.sub.2 + CO.sub.2 400 2499 C + Rh.sub.2O.sub.3 = Rh.sub.2O +
CO.sub.2 400 1266 C + 2PtO = 2Pt + CO.sub.2 400 2093 4PdO +
CH.sub.4 = 4Pd + CO.sub.2 + 2H.sub.2O 400 1555 C + 2CuO = 2Cu +
CO.sub.2 400 1085 C + 2HgO = 2Hg + CO.sub.2 400 2199 C +
Tl.sub.2O.sub.3 = Tl.sub.2O + CO.sub.2 400 1282 C + PbO.sub.2 = Pb
+ CO.sub.2 400 1632 C + 2MoO.sub.3 = CO.sub.2(g) + 2MoO.sub.2 400
771 C + V.sub.2O.sub.5 = CO.sub.2(g) + V.sub.2O.sub.3 400 705 1.5C
+ Bi.sub.2O.sub.3 = 2Bi + 1.5CO.sub.2 400 318
TABLE-US-00012 TABLE 12 Reactor Flash Temperature Temperature
Reaction (.degree. C.) (.degree. C.) 2Na.sub.2O + O.sub.2 =
2Na.sub.2O.sub.2 400 917 2K.sub.2O + O.sub.2 = 2K.sub.2O.sub.2 400
1254 2Rb.sub.2O + O.sub.2 = 2Rb.sub.2O.sub.2 400 767 2Cs.sub.2O +
O.sub.2 = 2Cs.sub.2O.sub.2 400 909 2BaO + O.sub.2 = 2BaO.sub.2 400
1225 2MnO + O.sub.2 = 2MnO.sub.2 400 1994 4TcO.sub.2 + 3O.sub.2 =
2Tc.sub.2O.sub.7 400 876 4ReO.sub.2 + 3O.sub.2 = 2Re.sub.2O.sub.7
400 1439 OsO.sub.2 + O.sub.2 = OsO.sub.4 400 721 Rh.sub.2O +
O.sub.2 = Rh.sub.2O.sub.3 400 1870 2Pt + O.sub.2 = 2PtO 400 1316
2Pd + O.sub.2 = 2PdO 400 1944 2Cu + O.sub.2 = 2CuO 400 2008 2Hg +
O.sub.2 = 2HgO 400 1675 Tl.sub.2O + O.sub.2 = Tl.sub.2O.sub.3 400
1413 2MoO.sub.2 + O.sub.2 = 2MoO.sub.3 400 1272 V.sub.2O.sub.3 +
O.sub.2 = V.sub.2O.sub.5 400 1779 Pb + O.sub.2 = PbO.sub.2 400
>3000 4Bi + 3O.sub.2 = 2Bi.sub.2O.sub.3 400 3166
Example 13
[0121] It was calculated that when carbon is heated with molybdenum
oxide to 850.degree. C., the flash temperature of the products will
reach 1628.degree. C. At temperatures above 700.degree. C.,
molybdenum trioxide exhibits a tangible vapor pressure of various
gaseous species (see FIG. 5). The existence of a gaseous metal
oxide oxygen carrier species radically improves the mass transfer
capability of this system improving the reaction rate kinetics and
reaction completion. It can be seen from FIG. 5 that molybdenum
trioxide creates tangible amounts of gaseous species during its
decomposition at high temperatures; therefore, the fuel combustion
reaction with MoO.sub.3 at those temperatures will proceed mostly
in the gaseous state.
Example 14
[0122] It was calculated that when methane is heated with
molybdenum oxide to 850.degree. C., the flash temperature of the
products will reach 1600.degree. C. When the reducing agent is also
in the vapor phase, such as methane, the reaction will proceed very
quickly to its full completion.
Examples 15 and 16
[0123] For the combustion of carbon and methane with vanadium
pentoxide as the oxygen carrier, heating of the reagents to
700.degree. C. leads to flash temperatures of 1371.degree. C. and
1361.degree. C., respectively. The release of energy during the
process of the examples can be used to bring the fuel combustion
processes to higher temperatures to form a stable flash. The
enthalpy change steeply increases (.about.100%) at 900.degree. C.
for the combustion of fuel with molybdenum trioxide and at
700.degree. C. for the combustion of fuel with vanadium pentoxide.
These steep enthalpy changes are demonstrated in FIGS. 1, 2 and
4.
[0124] It will be apparent to those skilled in the art that various
changes may be made without departing from the scope of the
invention which is not considered limited to the specific
embodiments described in the specification and drawings, but is
only limited by the scope of the appended claims.
* * * * *