U.S. patent application number 14/294621 was filed with the patent office on 2015-12-03 for activation of waste metal oxide as an oxygen carrier for chemical looping combustion applications.
This patent application is currently assigned to Saudi Arabian Oil Company. The applicant listed for this patent is Saudi Arabian Oil Company. Invention is credited to Bandar A. Fadhel, Ahmad D. Hammad, Ali Hoteit, Per Tobias Mattisson, Zaki Yusuf.
Application Number | 20150343416 14/294621 |
Document ID | / |
Family ID | 53525247 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150343416 |
Kind Code |
A1 |
Fadhel; Bandar A. ; et
al. |
December 3, 2015 |
Activation of Waste Metal Oxide as an Oxygen Carrier for Chemical
Looping Combustion Applications
Abstract
A process for producing black powder oxygen carriers for use in
a chemical looping combustion unit includes the steps of: (a)
removing and collecting the black powder waste material that was
formed in a gas pipeline; (b) pre-treating the collected black
powder to adjust its spherical shape to avoid attrition and fines
production; and (c) activating the black powder to increase its
reactivity rate and produce the black powder oxygen carrier that is
suitable for use in the chemical looping combustion process as an
oxygen carrier.
Inventors: |
Fadhel; Bandar A.; (Dammam,
SA) ; Yusuf; Zaki; (DHAHRAN, SA) ; Hammad;
Ahmad D.; (DHAHRAN, SA) ; Hoteit; Ali;
(Abqaiq, SA) ; Mattisson; Per Tobias; (Torslanda,
SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saudi Arabian Oil Company |
Dhahran |
|
SA |
|
|
Assignee: |
Saudi Arabian Oil Company
Dhahran
SA
|
Family ID: |
53525247 |
Appl. No.: |
14/294621 |
Filed: |
June 3, 2014 |
Current U.S.
Class: |
252/186.1 ;
252/372; 431/7 |
Current CPC
Class: |
B01J 8/0055 20130101;
C10J 2300/0959 20130101; C10J 2300/0943 20130101; C01B 32/50
20170801; C10J 2300/1631 20130101; B01J 8/0065 20130101; C10J 3/463
20130101; C10J 2300/093 20130101; C10J 2300/1807 20130101; Y02E
20/346 20130101; Y02P 20/10 20151101; B01J 20/28016 20130101; C10J
2300/0993 20130101; F23C 10/10 20130101; B01J 20/3433 20130101;
C01P 2006/21 20130101; F23C 2900/99008 20130101; B01J 8/388
20130101; C01B 5/00 20130101; F23C 10/24 20130101; B01J 8/12
20130101; C10J 3/523 20130101; C01P 2006/80 20130101; B01J 20/0229
20130101; Y02E 20/34 20130101; C10J 3/84 20130101; B01J 20/06
20130101; B01J 20/3085 20130101; C01G 45/02 20130101; C01G 49/02
20130101; B01J 8/08 20130101; B01J 20/3078 20130101; F23C 13/08
20130101 |
International
Class: |
B01J 20/06 20060101
B01J020/06; F23C 13/08 20060101 F23C013/08; C01B 5/00 20060101
C01B005/00; F23C 10/01 20060101 F23C010/01; C01B 31/20 20060101
C01B031/20; B01J 20/02 20060101 B01J020/02 |
Claims
1. A process for producing an oxygen carrier that is suitable for
use in a chemical looping combustion unit, comprising the steps of;
removing and collecting black powder that is formed within a gas
pipeline; pre-treating the collected black powder; and activating
the collected black powder to increase the reactivity of the black
powder to form a black powder oxygen carrier for use in the
chemical looping combustion unit.
2. The process of claim 1, wherein the black powder comprises iron
hydroxides, iron oxides, and iron carbonates.
3. The process of claim 1, wherein the black powder is removed from
a natural gas pipeline and collected using at least one of a
separator and cyclone device such that gas laden with black powder
passes through the separator or cyclone, and black powder particles
are knocked out of the gas stream to walls of the separator or
cyclone, where they fall and are collected internally within the
separator or cyclone in a collection media.
4. The process of claim 1, wherein the collected black powder is
pre-treated via a synthesis method.
5. The process of claim 4, wherein the synthesis method consists
one of a spray drying process and a freeze granulation process.
6. The process of claim 4, wherein the synthesis method comprises
the steps of: forming a powder mixture that comprises about 60.1%
black powder and about 39.9% manganese ore; dispersing the powder
mixture in deionized water along with organic additives to form an
aqueous suspension; homogenizing the aqueous suspension; spray
drying the aqueous suspension to form a solid black powder based
composition that has a range of particle sizes; sieving the solid
black powder based composition to collect particles within a
predetermined particle range; and sintering the collected
particles.
7. The process of claim 1, wherein the activation of the black
powder comprises the step of: using a flue gas to reduce the black
powder and activate the black powder by increasing porosity and
surface area of the black powder for improved gas-solid contact,
thereby improving the reactivity of the black powder towards other
gas, liquid or solid fuels.
8. The process of claim 7, wherein the flue gas contains at least
10-50% of H.sub.2 and at least 10-50% of CO.
9. The process of claim 1, wherein the activation of the black
powder comprises the step of increasing the reactivity of the black
powder by mixing the black powder with one or more other metal
oxides to form a black powder based composition that has increased
reactivity.
10. The process of claim 9, wherein the other metal oxide comprises
a copper oxide, manganese oxide or a combination thereof.
11. The process of claim 9, wherein the black powder based
composition comprises about 60.1% black powder and about 39.9
Mn.sub.3O.sub.4.
12. A process for combustion using a chemical looping combustion
while producing a product stream comprising the steps of;
delivering fuel into a fuel reactor that contains an oxygen carrier
which comprises black powder; reducing the oxygen carrier in the
presence of the fuel to provide gas-phase oxygen in the fuel
reactor; combusting the fuel under oxycombustion conditions within
the fuel reactor to produce a product stream; oxidizing the reduced
oxygen carrier with air in the air reactor to produce the oxygen
carrier; and delivering the oxidized oxygen carrier back to the
fuel reactor.
13. The process of claim 12, wherein the black powder oxygen
carrier comprises a fixed bed that is disposed in the fuel reactor
and the fixed bed is fluidized by a stream of gas.
14. The process of claim 12, wherein the fuel is a fuel selected
from the group consisting of a gas feed; a liquid feed, and a solid
feed.
15. The process of claim 14, wherein the fuel is a solid fuel
selected from the group consisting of coal and petcoke.
16. The process of claim 12, wherein the black powder comprises
iron hydroxides, iron oxides, and iron carbonates recovered from
gas pipelines.
17. The process of claim 12, further including the steps of:
removing and collecting the black powder that is formed in a gas
pipeline; pre-treating the collected black powder; and activating
the collected black powder to increase the reactivity and form the
black powder oxygen carrier.
18. The process of claim 12, wherein the black powder is removed
from a gas pipeline and collected using at least one of a separator
and cyclone device such that gas laden with black powder passes
through the separator or cyclone, and black powder particles are
knocked out of the gas stream to walls of the separator or cyclone,
where they fall and are collected internally within the separator
or cyclone in a collection media.
19. The process of claim 17, wherein the collected black powder is
pre-treated via a synthesis method.
20. The process of claim 19, wherein the synthesis method consists
one of a spray drying process and a freeze granulation process.
21. The process of claim 17, wherein the activation of the black
powder comprises the step of: using a flue gas to reduce the black
powder and activate the black powder by increasing porosity and
surface area of the black powder for improved gas-solid contact,
thereby improving the reactivity of the black powder towards other
gas, liquid or solid fuels.
22. The process of claim 21, wherein the flue gas contains at least
10-50% of H.sub.2 and at least 10-50% of CO.
23. The process of claim 17, wherein the activation of the black
powder comprises the step of mixing the black powder with one or
more other metal oxides to increase the reactivity of the black
powder.
24. The process of claim 23, wherein the other metal oxide
comprises a copper oxide, manganese oxide or a combination
thereof.
25. An oxygen carrier for use in a CLC process prepared in
accordance with the process of claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a process to produce
energy, syngas, hydrogen, and heat, etc. by means of a chemical
looping combustion scheme. More specifically, the present invention
relates to the utilization of a gas pipeline waste material (which
was previously discarded) as the oxygen carrier in a chemical
looping combustion scheme.
BACKGROUND
[0002] The increased attention paid to global warming in recent
decades has led to increased research in the field of power
generation. Different measures for fighting against the undesirable
effects of global warming have been proposed. One such measure is
carbon capture and storage (CCS), which has widely been considered
a mid-to-long term mitigating measure against the emission of
CO.sub.2. CCS has the potential to be both valuable and
environmental, and this can be achieved if CO.sub.2 can be utilized
in industrial applications after it has been captured. For example,
CO.sub.2-EOR (Enhanced Oil Recovery by injecting CO.sub.2 into oil
reservoirs) is a potential industrial usage of CO.sub.2 that
increases petroleum production. This process has been commercially
used for approximately 40 years, typically utilizing CO.sub.2 from
natural resources, and its feasibility has been well recognized in
terms of transportation and injection of CO.sub.2. Nevertheless,
the biggest problem with CCS lies not with the potential industrial
uses of the captured CO.sub.2, but rather with the costliness of
current CCS processes.
[0003] Combustion is a commonly used reaction in the field of power
generation. Several carbon capturing techniques exist for capturing
CO.sub.2 from a combustion unit, including post-treatment,
O.sub.2/CO.sub.2 firing (oxyfuel), and CO-shift. These CO.sub.2
capture techniques all suffer from the fact that very significant
gas separation steps are needed. Moreover, these gas separation
steps involve very significant operational costs as well as large
energy penalties, estimated in the order of about 10 percentage
points of plant efficiency, leading to a substantial increase-25 to
30%--in fuel consumption and plant size. Gas separation technology
is generally a mature technology, and no major technology
breakthroughs in this area are foreseen.
[0004] This is in great contrast to chemical looping combustion
(CLC) where no gas separation is needed. CLC is a specific type of
combustion reaction that was originally created in the 1950s to
produce CO.sub.2, but recently it has received increased attention
as a potential CO.sub.2 capturing process. In a CLC process, an
oxygen carrier acts as an intermediate transporter of oxygen
between air and fuel, and thus the air and the fuel are prevented
from directly contacting one another. As a result, the exhaust gas
stream ideally consists of CO.sub.2 and H.sub.2O only, and the
CO.sub.2 is readily available after condensation of H.sub.2O. Thus
the energy requirement of gas-gas-separation is avoided.
[0005] In general, the overall heat of a CLC process will be the
sum of the two heat states, exothermic during oxidation and
endothermic during reduction, which is equivalent to the heat
released in a convention combustion reaction. Accordingly, one
advantage of the CLC process is that minimal extra energy is
required to capture CO.sub.2 while still maintaining a combustion
efficiency similar to direct combustion processes. More precisely,
there is minimal energy penalty for CO.sub.2 capturing in a CLC
process, estimated at only 2-3% efficiency lost. Additionally, NO
formation is reduced in the CLC process compared with direct
combustion processes as the oxidation reaction occurs in the air
reactor in the absence of fuel and at a temperature of less than
1200.degree. C.--above which NO formation increases considerably.
Thus, the lack of NO.sub.x formation makes CO.sub.2 capturing in
CLC processes less costly compared with other combustion methods
because CO.sub.2 does not need to be separated from the NOx gas
prior to capture. Overall, CLC is one of the few technologies today
where a significant breakthrough could be envisaged for avoiding
the large costs and energy penalty of gas separation in CO.sub.2
capture.
[0006] A key factor for the CLC technology development is the
selection of an oxygen carrier. Suitable oxygen-carriers must show
high reaction rates and oxygen transport capacity, complete fuel
conversion to CO.sub.2 and H.sub.2O, negligible carbon deposition,
avoidance of agglomeration, sufficient durability, and good
chemical performance. These properties must be maintained during
several reduction and oxidation cycles. In addition, the cost of
the oxygen-carrier is also important.
[0007] In a typical chemical looping combustion process, a solid
metal oxide oxygen carrier is used to oxidize the fuel stream in a
fuel reactor. Transition metal oxides such as nickel, copper,
cobalt, iron, and manganese are good oxygen carrier candidates
because of their favorable reductive and oxidative thermodynamic
properties. Still, the effective use of metal oxides as oxygen
carriers can make CLC processes costly. For instance, U.S. Pat. No.
5,447,024 claims as the active mass the use of redox pair NiO/Ni
combined with the binder type yttriated zirconia in order to
improve the mechanical strength and the reactivity of the
particles. Using binder's type yttrium-zirconia increases the cost
of the metal oxide and consequently the cost of a CLC process.
[0008] Black powder is regenerative and is formed inside natural
gas pipelines as a result of corrosion of the internal walls of the
pipeline. Black powder forms through chemical reactions of iron
(Fe) in ferrous pipeline steel with condensed water containing
oxygen, CO.sub.2, and other gases. FIG. 1 shows an exemplary pipe
10 that has an outer surface and an opposing inner surface 12.
Black powder 20 is shown collecting along the inner surface 12 of
the pipe 10.
[0009] Black powder is mainly composed of iron hydroxides, iron
oxides, and iron carbonates. As used herein including in the
present claims, black powder refers to the residue (material) that
is formed along inner surface of pipelines as a natural waste
product as a result of corrosion and comprises a metal oxide. Black
powder can also be collected from upstream filters employed in gas
refineries.
[0010] For many years, pipeline companies have observed the
presence of black powder and its effects, but have viewed it only
as a nuisance and therefore have done little to understand it and
use it. Instead, pipeline companies have primarily sought ways of
removing the black powder from the pipelines. There are several
methods to remove the black powder, such as separators and
cyclones, where the black powder-laden gas passes through these
devices and the black powder particles are physically knocked out
of the gas stream. Specifically, the black powder particles are
removed from the gas stream and attach to the walls of the device
(e.g., separator, cyclone) where they fall and are collected at the
bottom in a collection media.
[0011] Pipeline companies have yet to find a beneficial use for the
black powder. Throughout the world, black powder from gas pipeline
exists in large amounts, and is thus readily available at a very
low cost due to its perceived lack of value. Today, black powder is
generally discarded as waste.
[0012] Overall, there is a need for efficient CO.sub.2 capture in
the field of power generation in light of growing concerns
regarding global warming. Further, there is a need to reduce the
cost of current CLC processes, and in particular, reduce the cost
of oxygen carriers utilized in CLC processes. Lastly, there is a
need to utilize the black powder waste formed in gas pipelines.
SUMMARY
[0013] The present invention is directed to a cost-effective method
for operating a chemical looping combustion (CLC) unit. More
specifically, the present invention relates to a CLC process in
which black powder which originates from gas pipelines is collected
and is used as a low-cost, effective oxygen carrier in the CLC
unit.
[0014] In one embodiment, the black powder is removed and collected
from a gas pipeline using a separator or a cyclone device. Once the
black powder is collected, it is then treated via a synthesis
method, such as spray drying or freeze granulation, in order to
adjust the spherical shape of the black powder to avoid attrition
and fines production. Next, the black powder undergoes an
activation treatment to increase its reactivity and produce the
black powder oxygen carrier. In another embodiment, the black
powder can also be mixed with other metal oxides to increase the
reactivity of the black powder oxygen carrier.
[0015] In one embodiment, the activated black powder oxygen carrier
is located in a bed (fluidized bed) within the fuel reactor of the
CLC unit. In the fuel reactor, the black powder acts as an oxygen
carrier for the combustion reaction with the fuel. The black powder
oxygen carrier releases gas phase oxygen in the fuel reactor of the
CLC unit, and has properties such that high amounts of gas phase
oxygen are released. The release of gas phase oxygen in the fuel
reactor can increase the reactivity towards the fuels and reduce
the bed emission. The combustion reaction in the fuel reactor
results in the reduction of the black powder oxygen carrier.
Following the combustion reaction, the reduced black powder is then
transported to the air reactor where it is oxidized by an injection
of air. The resulting re-oxidized black powder is then recycled
from the air reactor to the bed in the fuel reactor to again act as
an oxygen carrier.
[0016] The black powder oxygen carrier can be used in a CLC method
to react with different types of fuel, such as gaseous fuel, liquid
fuel, and solid fuel. The CLC method of the present invention can
also be used to produce energy, heat, syngas, and hydrogen,
etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] A more complete understanding of the invention and its many
features and advantages will be attained by reference to the
following detailed description and the accompanying drawings. It is
important to note that the drawings illustrates only a few
embodiments of the present invention and therefore should not be
considered to limit its scope.
[0018] FIG. 1 is a perspective view of an end portion of a pipe
that includes black powder formation along an inner surface
thereof;
[0019] FIG. 2 is a schematic of a CLC process in accordance with an
embodiment of the present invention;
[0020] FIG. 3 is a schematic of the process of producing a black
powder oxygen carrier in accordance with one embodiment;
[0021] FIG. 4 is a schematic showing the oxygen release from black
powder particles; and
[0022] FIG. 5 is a schematic showing the reactivity of various
black powder containing compositions toward CH.sub.4.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0023] As previously mentioned and with reference to FIG. 2,
chemical looping combustion (CLC) typically employs a system in
which an oxygen carrier is employed as a bed material providing the
oxygen for combustion in a fuel reactor. The reduced oxygen carrier
is then transferred to the air reactor and re-oxidized before being
reintroduced back to the fuel reactor completing the loop. CLC thus
uses two or more reactions to perform the oxidation of hydrocarbon
based fuels. In its simplest form, an oxygen-carrying species
(normally a metal) is first oxidized in air forming an oxide (e.g.,
a metal oxide). This oxide is then reduced using a hydrocarbon as a
reducer in a second reaction.
[0024] The CLC system 100 shown in FIG. 2 consists of the
traditional components of a CLC process. More specifically, the
system 100 includes a fuel reactor 110 which receives a fuel
(indicated at 120) which is combusted within the fuel reactor 110
under combustion conditions. As mentioned herein, the CLC system
involves fluidization of the fuel by causing the fuel 120 to flow
through an oxygen carrier 130 that is associated with the fuel
reactor 110. For example, the oxygen carrier 130 can be in the form
of a bed of material that is in fluid communication with the fuel
reactor 110.
[0025] The product(s) of the combustion reaction that takes place
in the fuel reactor 110 are generally shown at 140. The reaction
products can include CO2, H2O, etc. The reaction products are
removed from the fuel reactor for further processing and/or
storage.
[0026] The oxygen carrier 130 produces oxygen and over time, this
material is chemically reduced and must be oxidized to permit the
material to continue to function as an oxygen provider. The looping
of the CLC system 100 thus includes a loop for oxidizing the oxygen
carrier 130. More specifically, an air reactor 200 is in selective
fluid communication with the fuel reactor 110. A conduit 220
carries the reduced oxygen carrier 130 from the fuel reactor 110 to
the air reactor 200. With the air reactor 200, an oxidizing agent
220, for example air, is introduced into the air reactor 200 and
contacts the reduced oxygen carrier that resides in the air reactor
200 under conditions that result in oxidization of the oxygen
carrier material. Once the oxygen carrier material is oxidized, the
material is transported through a conduit 230 from the air reactor
200 to the fuel reactor 110 where it serves as an oxygen carrier
and the looping process continues. The product(s) (e.g., N2, O2) of
the oxidation reaction in the air reactor 200 are shown at 240 and
are discharged from the air reactor 200.
[0027] The CLC process of the present invention is designed to use
black powder--the waste material formed in natural gas pipelines
(and other gas containing lines)--as an oxygen carrier (e.g.,
oxygen carrier 130 in FIG. 2). Because black powder is very rich in
iron oxides, the present Applicant unexpectedly discovered that
black powder can be used as an oxygen carrier in CLC processes.
Specifically, black powder typically contains about 62% wt of
magnetite (Iron (II,III) oxide [Fe.sub.3O.sub.4]); about 11.1% wt.
of goethite (.alpha.-FeO(OH)); about 18.8% wt. of akaganeite,
(.beta.-FeO(OH)), and about 5.4% wt. of siderite (FeCO.sub.3). In
terms of elementary measurement, black powder contains almost 65.5%
wt. of iron, 26% wt. of oxygen, and the remaining weight is from
other metals such as manganese, calcium, and silicon. Unless
otherwise indicated, the percentages recited herein are weight
percentages.
[0028] FIG. 3 is a schematic of an exemplary flow process for using
black powder as an oxygen carrier. FIG. 3 thus shows a series of
steps (some optional). More specifically, FIG. 3 shows a step 300
which involves removal/recovery of the black powder from a source
(e.g., pipeline); step 310 is a pre-treatment step; step 320 is an
activation step; and step 330 is use of the treated/activated black
powder in a CLC unit. Each of these steps is described in detail
below.
[0029] One method according to the invention utilizes the black
powder after it is removed (recovered) from a gas pipeline (step
300). The black powder 110 (FIG. 1) can be collected from a
pipeline (pipeline 100 in FIG. 1) (the origin location) or received
from equipment downstream of the pipeline for use in a CLC process
in a variety of ways. For instance, in one embodiment, black
powder-laden gas passes through a separator where the black powder
is "knocked off" onto the walls of the separator. The black powder
then falls off the wall of the separator and collects at the bottom
of the separator on a collection media. In another embodiment, a
cyclone is used to remove the black powder from the pipeline.
[0030] It will therefore be appreciated that black powder material
can be collected and recovered from its pipeline origin using any
number of suitable techniques.
[0031] Once the black powder has been collected from the pipeline
(step 300), it is then treated in a step 310 via a synthesis method
(which can include spray drying or freeze granulation processes) in
order to adjust its spherical shape to avoid attrition and fines
production--both of which could limit the use of black powder in
the CLC process. In other words, this step changes the physical
characteristics of the black powder to optimize its use as an
oxygen carrier in a CLC process.
[0032] In one embodiment of the treatment of black powder, oxygen
via a synthesis method, a water-based slurry of a mixture,
consisting of 60% black powder and 40% manganese oxide is prepared
via a ball mill--a type of grinder in which the powder mixture and
the ball are located inside a cylindrical container and the ball
rotates around the cylinder thereby grinding the mixture into a
fine powder. Prior to mixing with the manganese oxide, the black
powder is heat treated at about 500.degree. C. in order to remove
possible organic contaminants. A small amount of dispersant is also
added to this mixture in order to improve the slurry
characteristics. After milling, an organic binder is added to the
slurry to keep the particles intact during later stages in the
production process (i.e., freeze-drying and sintering). Spherical
particles are then produced by freeze-granulation. Specifically,
the slurry is pumped to a spray nozzle where passing atomizing-air
produces drops, which are sprayed into liquid nitrogen where they
freeze instantaneously. The frozen water in the resulting particles
is then removed by sublimation in a freeze-drier operating at a
pressure that corresponds to the vapor pressure over ice at about
-10.degree. C. After freeze drying, the particles are sintered at a
temperature of about 950.degree. C. for 6 hours using a heating
rate of about 50 degree C./min. Finally the particles are sieved to
obtain particles of well-defined sizes.
[0033] In another embodiment of the synthesis method, a powder
mixture of about 60.1% of black powder and about 39.9% manganese
ore is dispersed in deionized water with organic additives that
ensure proper dispersion and binding characteristics. For example
and according to one embodiment, polyethyleneoxide (PEO, type PEO-1
Sumitomo Seika, Japan) and/or polyvinylalcohol (PVA 1500 Fluka,
Switzerland) and/or polyethyleneglycol (PEG 6000, Merck-Schuchardt,
Germany) were used as organic binder and Darvan (type C, RT
Vanderbilt, USA) and/or Dolapix (types A88, PC75 and PC80,
Zschimmer & Schwarz, Germany) and/or Targon 1128 (BK Giulini
Chemie, Germany) were used as dispersants as part of the synthesis
method. Appropriate (effective) amounts of the above materials are
weighed before suspending in deionized water. The suspension is
homogenized by milling in a planetary ball mill. The water-based
suspension is continuously stirred with a propeller blade mixer
while being pumped to a 2-fluid spray dry nozzle, positioned in the
lower cone part of the spray drier. After spray drying, the
fraction within the required particle size range is separated from
the rest of the spray dried product by sieving the chamber
fraction. In order to obtain an oxygen carrier with sufficient
mechanical strength, sintering is performed for the samples at
temperatures between about 950.degree. C. and 1100.degree. C. In
one embodiment, a desired particle range is between about 0.08 mm
to about 2 mm; however, other ranges are possible depending upon
different parameters and different applications.
[0034] In preferred embodiments of the present invention and as
shown in step 320, the black powder then preferably undergoes an
activation process to increase the reactivity of the black powder
as an oxygen carrier. In general, the activation method is a
treatment in which a flue gas containing about 10 to 50% of CO and
about 10 to 50% of H.sub.2 is used to reduce the black powder. The
use of this CO/H.sub.2 gas activates the black powder particles by
increasing their porosity and surface area for better gas-solid
contact, thereby improving their reactivity towards other gas,
liquid, or solid fuels. In one embodiment, the activation method
consists of increasing the temperature to 500.degree. C. for 12 to
48 hours, preferentially between 18 and 32 hours, under a flue gas
media containing at least 21% of O.sub.2. The flue gas as described
above (i.e., containing at least 10-50% of H.sub.2 and 10-50% of
CO) is injected during 5 successive cycles where syngas is used as
a fuel prior to the other gas, liquid, or solid fuel cycles. The
syngas cycles are performed at 950.degree. C., and can be followed
by gas, liquid, or solid fuel cycles at the same temperature.
Thereafter, the temperature can be increased to 1000.degree. C. and
1050.degree. C.
[0035] Thus, the activation step involves contacting and passing
syngas through the black powder material to "activate" the black
powder by making it more reactive towards other gas, liquid, or
solid fuels. The result of this activation step is the formation of
black powder oxygen carrier that is suitable for use in the CLC
unit (looping process). Once this activation step is completed,
fuel to be combusted is then run through the system (CLC unit),
with the black powder serving as the oxygen carrier for the
process.
[0036] In another embodiment, the black powder can be mixed with
one or more other active masses in order to increase its
reactivity. More specifically, black powder can be mixed with one
or more other metal oxide, including copper oxides and manganese
oxides or a combination of both with different proportions (between
about 10% and 80%, and preferentially between about 30% and 50%) to
create an oxygen carrier with increased reactivity. Specifically,
in one embodiment, the mixture is 60.1% black powder and 39.9%
Mn.sub.3O.sub.4 (hereinafter referred to as SA7T1100). FIG. 4,
stemming from an example using the mixture SA7T1100, shows the
oxygen release from the particles in an inert atmosphere of oxygen.
Time 0 indicates transition from an inert flow containing oxygen in
N.sub.2 to an inlet flow of 100% N.sub.2. The solid lines represent
oxygen release at a constant temperature of 900.degree. C. and the
dashed lines represent the oxygen release when the temperature is
increased from 900.degree. C. to 1000.degree. C. The phenomena set
forth in FIG. 4 is known as the CLOU effect, which is the ability
of certain oxygen carriers to evolve gaseous oxygen at high
temperature in the fuel reactor to avoid the direct contact between
the fuel and the oxygen carrier. This will help in utilizing solid
or liquid fuels with the need to gasify them.
[0037] In accordance with step 330, the black powder oxygen carrier
produced in accordance with the present invention releases gas
phase oxygen in the fuel reactor of the CLC unit. Further, the
black powder oxygen carrier has properties such that high amounts
of gas phase oxygen are released. Other advantageous properties of
black powder oxygen carriers other than the activated CLOU effect
include good mechanical strength after modification and treatment,
no agglomeration even at 1000.degree. C. The release of gas phase
oxygen in the fuel reactor can increase the reactivity towards the
fuels and reduce the bed emission, both of which increase the
efficiency of the oxygen carrier.
[0038] As previously mentioned, in one preferred embodiment, the
black powder oxygen carrier is located in a bed (fluidized bed)
within the fuel reactor. The black powder oxygen carrier bed can be
fluidized by a suitable fluid, such as a stream of CO.sub.2 or by
another suitable fluid stream (gas stream). In one embodiment, a
stream consisting of both CO.sub.2 and steam is used to fluidize
the oxygen carrier bed. In the fuel reactor, the black powder acts
as an oxygen carrier for the combustion reaction with the fuel. The
black powder according to the present invention can be used in a
CLC method to react with different types of fuel, such as gaseous
fuel, liquid fuel, and solid fuel.
[0039] The combustion reaction in the fuel reactor results in the
reduction of the black powder oxygen carrier. Following the
combustion reaction, the reduced black powder is then transported
to the air reactor where it is oxidized by an injection of air. The
resulting re-oxidized black powder is then recycled from the air
reactor to the bed in the fuel reactor to again act as an oxygen
carrier.
[0040] In many embodiments, the CLC method of the present invention
produces CO.sub.2 and H.sub.2O. The CLC method of the present
invention can also be used to produce syngas, hydrogen, heat, or
energy.
[0041] In an embodiment in which syngas is produced, the syngas can
be used to produce liquid fuel such as dimethyl ether (DME)--a
potentially renewable fuel. In order to produce the syngas, a
high-pressure fixed bed technology must be utilized in accordance
with a Fischer-Tropsch application.
[0042] In an embodiment in which hydrogen is produced, the hydrogen
can be used in a number of ways, including: 1) in refining, 2) to
produce energy, and 3) for hydrotreatment.
EXAMPLES
[0043] The following examples are provided to better illustrate
embodiments of the present invention, but they should not be
construed as limiting the scope of the present invention.
[0044] In the first example, the reactivity rates of different
variations of black powder oxygen carriers (described above) are
compared. Specifically, this example compares the reactivity rates
of activated black powder, unactivated black powder, activated
SA7T1100, and unactivated SA7T1100. The black powder, mainly
consisting of Fe.sub.3O.sub.4, was collected from gas pipelines and
was found in the upstream filters of gas refineries. The SA7T1100,
as mentioned previously, is a mixture of 60.1% black powder and
39.9% Mn.sub.3O.sub.4. The reactivity of the activated material
treated at 500.degree. C. is investigated in a batch fluidized bed
reactor using CH.sub.4 as fuel under the following conditions: a)
the mass of the particles for each group of oxygen carriers was 15
g; b) the flow during reduction of the oxygen carrier (combustion
of CH.sub.4) was 450 mLn/min; c) the flow during oxidation of the
oxygen carrier (5% O.sub.2) was 900 mLn/min; and d) the temperature
of the cycles was maintained at about 950.degree. C. Prior to the
cycles with CH.sub.4 used as fuel, 5 activation cycles with syngas
as the fuel were conducted. The syngas activation cycles were
performed at 950.degree. C. and they were followed by the
aforementioned CH.sub.4 cycles at the same temperature. Thereafter,
the temperature was increased to 1000.degree. C. At both
950.degree. C. and 1000.degree. C., 3 cycles with CH.sub.4 were
conducted. The experiment was started at 950.degree. C. because
this temperature gave the highest gas yield for all tested
particles.
[0045] The reactivity of black powder was very high towards syngas,
for both the "as is" black powder and the SA7T1100, with almost
complete conversion of syngas to CO.sub.2 after the second cycle
with syngas. After the syngas reactivity test cycles, the
particles' reactivity toward CH.sub.4 was initially measured at
950.degree. C. and then at 1000.degree. C. The results (solid line)
from these tests are presented in FIG. 5, where they were also
compared to the conversion results (no line) prior to syngas
activation at 950.degree. C. In this figure, the results at
950.degree. C. and the results at 1000.degree. C. are
distinguishable from one another using the legend key set forth in
FIG. 5. As shown, the two uppermost curves represent the results at
1000.degree. C., while the four bottommost curves represent the
results 950.degree. C.
[0046] As shown by FIG. 5, the activation of the "as is" black
powder resulted in more than double the yield of CH.sub.4 compared
with unactivated "as is" black powder. This conversion reached a
maximum of 50% at 950.degree. C. for activated "as is" black powder
compared with about 20% at the same condition for unactivated "as
is" black powder. Activated SA7T1100, reaching a maximum of about
75% at 950.degree. C., had an even more significant improvement
compared with unactivated SA7T1100 at the same condition (about 10%
at 950.degree. C.). At 1000.degree. C. both activated particles
displayed a similar behavior with a maximum CH.sub.4 conversion of
above 95%. This example demonstrates that the activation of black
powder substantially improves its reactivity and results in the
formation of black powder oxygen carrier in that after the virgin
black powder material undergoes the treatment and activation steps,
it yields an oxygen carrier.
[0047] The second example thus illustrates an embodiment of black
powder suitable for use as an oxygen carrier in accordance with the
present invention. The non-treated black powder in this example has
the composition as described by Table 1.
TABLE-US-00001 TABLE 1 Elemental Composition of Non-treated Black
Powder Element Weight (%) C 20.85 O 29.29 Mg 1.07 Si 0.41 S 1.88 Cl
2.10 Ca 1.23 Fe 43.06 Total 100.00
[0048] The non-treated black powder is then heated at 500.degree.
C. for 24 hours. The composition of the heated black powder
material is given in Table 2.
TABLE-US-00002 TABLE 2 Elemental Composition of Black Powder (After
Heating at 500.degree. C.) Element wt % C 0 O 25.39 Mg 1.08 Si 0.48
S 2.63 Cl 1.53 Ca 1.88 Mn 1.32 Fe 65.70 Total 100.00
[0049] The crushing strength of the non-treated black powder
material is 2.25 N prior to heating and 2.68 N for the material
heat treated at 500.degree. C. in terms of elementary measurement,
the black powder of this example, after heating at 500.degree. C.,
contains almost 66% wt. of iron (Fe) and almost 26% wt. of oxygen
(Table 2). The rest of the heated black powder consists of metals
such as Mn, Ca, Si, and others.
[0050] Although the present invention has been described above
using specific embodiments and examples, there are many variations
and modifications that will be apparent to those having ordinary
skill in the art. As such, the described embodiments are to be
considered in all respects as illustrative, and not restrictive.
Therefore, the scope of the invention is indicated by the appended
claims, rather than by the foregoing description. All changes that
come within the meaning and range of equivalency of the claims are
to be embraced within their scope.
* * * * *