U.S. patent application number 12/952676 was filed with the patent office on 2011-03-17 for plasma reactor.
This patent application is currently assigned to DREXEL UNIVERSITY. Invention is credited to YOUNG I. CHO, VIJAY A. DESHPANDE, ALEXANDER FRIDMAN, ALEXANDER GUTSOL, LAWRENCE KENNEDY, TECLE S. RUFAEL, ALEXEI SAVELIEV.
Application Number | 20110062014 12/952676 |
Document ID | / |
Family ID | 33539261 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110062014 |
Kind Code |
A1 |
GUTSOL; ALEXANDER ; et
al. |
March 17, 2011 |
PLASMA REACTOR
Abstract
A plasma reactor (10) is provided. The plasma reactor (10)
includes a reaction chamber (12) formed by a wall (13). Proximate
to the first end of the reaction chamber, the plasma reactor
includes a feed gas inlet (14) for creating a reverse vortex gas
flow (16) in the reaction chamber. The plasma reactor (10) also
includes an anode and a cathode connected to a power source for
generation of an electric arc for plasma generation in said
reaction chamber. The plasma reactor (10) may optionally include a
movable electrode adapted for movement from a first, ignition
position to a second, operational position in the reaction chamber.
Also provided is a method of converting light hydrocarbons to
hydrogen-rich gas, using the plasma reactor of the invention.
Inventors: |
GUTSOL; ALEXANDER; (San
Remo, CA) ; FRIDMAN; ALEXANDER; (MARLTON, NJ)
; CHO; YOUNG I.; (CHERRY HILL, NJ) ; KENNEDY;
LAWRENCE; (NAPERVILLE, IL) ; SAVELIEV; ALEXEI;
(CARY, NC) ; RUFAEL; TECLE S.; (STAFFORD, TX)
; DESHPANDE; VIJAY A.; (HOUSTON, TX) |
Assignee: |
DREXEL UNIVERSITY
PHILADELPHIA
PA
BOARD OF TRUSTEES OF THE UNIVERSITY OF ILLINOIS
URBANA
IL
CHEVRON U.S.A., INC.
SAN RAMON
CA
|
Family ID: |
33539261 |
Appl. No.: |
12/952676 |
Filed: |
November 23, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10560439 |
Jul 24, 2006 |
7867457 |
|
|
12952676 |
|
|
|
|
Current U.S.
Class: |
204/164 ;
422/186.04; 422/186.21 |
Current CPC
Class: |
B01J 2219/0832 20130101;
B01J 2219/0816 20130101; Y02P 20/132 20151101; B01J 2219/0871
20130101; C01B 3/342 20130101; B01J 2219/0835 20130101; B01J
2219/083 20130101; B01J 2219/0833 20130101; B01J 2219/0898
20130101; B01J 2219/0883 20130101; Y02P 20/129 20151101; B01J
2219/082 20130101; B01J 2219/0828 20130101; C01B 2203/1241
20130101; B01J 2219/0875 20130101; H05H 2245/121 20130101; B01J
2219/0826 20130101; C01B 2203/0861 20130101; B01J 2219/0869
20130101; B01J 19/088 20130101; B01J 2219/0809 20130101; H05H 1/48
20130101 |
Class at
Publication: |
204/164 ;
422/186.04; 422/186.21 |
International
Class: |
C01B 3/36 20060101
C01B003/36; B01J 19/08 20060101 B01J019/08 |
Claims
1. A plasma reactor, comprising: a wall defining a reaction
chamber; an outlet; a reagent inlet fluidly connected to the
reaction chamber for creating a reverse vortex flow in said
reaction chamber; a first electrode; and a second electrode
connected to a power source for generation of an electric discharge
in the reaction chamber.
2. The plasma reactor of claim 1, wherein the reaction chamber is
substantially cylindrical.
3. The plasma reactor of claim 1, wherein said reagent inlet for
creating said reverse vortex flow comprises a gas supply and one or
more gas inlet nozzles oriented tangentially relative to the wall
of the plasma reactor.
4. The plasma reactor of claim 3, wherein said reactor comprises
first and second ends, the reagent inlet is located proximate to
the first end and the outlet is also located proximate to the first
end.
5. The plasma reactor of claim 4, wherein said reactor further
comprises a second inlet fluidly connected to the second end of
said reactor.
6. The plasma reactor of claim 4, wherein the first electrode is
located proximate to the first end of the reactor.
7. The plasma reactor of claim 6, wherein the second electrode is
positioned at substantially constant distance from the first
electrode during operation of the reactor.
8. The plasma reactor of claim 7, wherein at least a portion of the
second electrode is positioned in the reaction chamber to create a
gap between the first electrode and the second electrode for
initiation of a plasma generating electrical discharge at said
gap.
9. A plasma reactor as claimed in claim 6, wherein the first
electrode also functions as a flow restrictor to assist in the
generation of a reverse vortex flow.
10. A plasma reactor as claimed in claim 9, wherein the second
electrode is a spiral shaped electrode.
11. A plasma reactor as claimed in claim 10, wherein a distal end
of the spiral shaped electrode, relative to the position of the
first electrode, terminates in a circular ring shape.
12. A plasma reactor as claimed in claim 9, wherein the second
electrode is a combination of a spiral shaped electrode and a
circular ring electrode.
13. A plasma reactor as claimed in claim 7, wherein the second
electrode is a movable electrode which can be positioned in a first
position to create a gap between the second electrode and the first
electrode for electric discharge ignition, and in a second
position, after electric discharge ignition, at a greater distance
from said first electrode to provide a stable plasma in said
reaction chamber.
14. A plasma reactor as claimed in claim 1, further comprising at
least one heat exchanger for preheating at least one reagent for
feeding to said plasma reactor by heat exchange with at least one
product from said plasma reactor.
15. The plasma reactor of claim 1, wherein the discharge closes the
distance between the electrodes (is attached to both
electrodes).
16. The plasma reactor of claim 15, wherein at least one discharge
attachment spot moves over the electrode surface and therefore the
discharge is a gliding discharge.
17. The plasma reactor of claim 16, wherein the gliding discharge
is direct current (DC) or alternative current (AC) gliding arc.
18. The plasma reactor of claim 16, wherein the gliding discharge
is direct current (DC) or alternative current (AC) gliding normal
glow discharge.
19. The plasma reactor of claim 1, wherein the electric discharge
is non-equilibrium plasma discharge.
20. The plasma reactor of claim 1, wherein the plasma reactor
serves for converting of light hydrocarbons to a hydrogen-rich
gas.
21. A method for converting light hydrocarbons to a hydrogen-rich
gas comprising the steps of: providing a plasma reactor, said
plasma reactor comprising: a wall defining a reaction chamber; an
outlet; a reagent inlet fluidly connected to the reaction chamber
for creating a reverse_vortex flow in said reaction chamber; a
first electrode; and a second electrode connected to a power source
for generation of electric discharge in the reaction chamber;
introducing a gas selected from the group consisting of one or more
light hydrocarbons, oxygen, an oxygen containing gas, and mixtures
thereof, into said reaction chamber in a manner which creates a
reverse vortex flow in the reaction chamber; processing said light
hydrocarbons using a plasma assisted flame; and recovering
hydrogen-rich gas from said reactor.
22. The method of claim 21, wherein said reverse vortex flow is
created by feeding a gas containing light hydrocarbons into said
reaction chamber in a direction tangential to the wall of said
reaction chamber.
23. The method of claim 21, wherein said reverse vortex flow is
created by feeding an oxygen-rich gas into said reaction chamber in
a direction tangential to the wall of said reaction chamber.
24. The method of claim 21, wherein said plasma reactor comprises
first and second ends, the reagent inlet is located proximate to
the first end, the reactor further comprises a second inlet fluidly
connected to the second end of said reactor, and wherein at least
some of said gas selected from the group consisting of one or more
light hydrocarbons, oxygen, an oxygen containing gas, and mixtures
thereof, is provided to the reaction chamber via the second
inlet.
25. The method of claim 24, wherein the plasma reactor comprises a
movable second electrode and said method further comprises the
steps of igniting an electrical arc with said movable second
electrode in a first position, and moving the movable second
electrode to a second position farther from said first electrode
than said first position for operation of said reactor.
26. The method of claim 21, wherein said gas is preheated before
entering the plasma reactor.
27. The method of claim 26, wherein the plasma reactor further
comprising at least one heat exchanger for preheating at least one
reagent for feeding to said plasma reactor by heat exchange with at
least one product from said plasma reactor.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation of U.S. patent
application Ser. No. 10/560,439 filed Jul. 4, 2006, which was the
National Stage Entry of and claims priority to PCT/U.S. 04/19589,
filed Jun. 18, 2004, which further claims the benefit of U.S.
Provisional Patent Application Ser. No. 60/480,132 filed Jun. 20,
2003, each of which is incorporated by reference in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates to a plasma reactor and
process for the production of hydrogen-rich gas from light
hydrocarbons.
BACKGROUND
[0003] Improving the efficiency of energy production remains an
important technological goal, owing to the significant economic
benefits that result in almost every sector of the economy. One
potential method for improving the efficiency of energy production
is to provide an energy efficient method of converting light
hydrocarbons to hydrogen-rich gas, to thereby increase energy
production from natural gas.
[0004] Plasma fuel converters such as plasmatrons are known to
reform hydrocarbons to produce hydrogen-rich gas. DC arc
plasmatrons, for example, are disclosed in U.S. Pat. Nos. 5,425,332
and 5,437,250. DC arc plasmatrons generally operate at low voltage
and high current. As a result, these plasmatrons are particularly
susceptible to electrode erosion and/or melting. DC arc plasmatrons
also require relatively high power inputs of 1 kW or more and
relatively high flow rates of coolant to keep the temperature in
check.
[0005] Other conventional methods for the conversion of light
hydrocarbons to hydrogen-rich gas are generally energy inefficient
and, as a result, in many small-scale applications, such as the
production of hydrogen for fuel cells, the cost of hydrogen gas
made by these methods is not competitive. Thus, there is a need in
the art for a more energy efficient process for the conversion of
light hydrocarbons to hydrogen-rich gas.
[0006] U.S. Pat. Nos. 5,993,761 and 6,007,742 (Czernichowski et
al.) describe processes for the conversion of light hydrocarbons to
hydrogen-rich gas using gliding arc electric discharges in the
presence of oxygen and, optionally, water. In the process, two
electrodes having flat sheet geometry are arranged for arc ignition
and subsequent gliding of the arc. The distance between the cathode
and anode gradually increases to a point that no longer supports
the gliding arc. As a result, the gliding arc disappears at one end
of the electrodes, creating pulsed plasma wherein the properties of
the plasma change with time. Due to the use of pulsed plasma, the
process is relatively unstable over time. Reagents and oxygen are
preheated using an external heat source. As a result of the
preheating of the reagents and oxygen using an external heat
source, the process suffers from poor energy efficiency. A premixed
feed gas including hydrocarbons and oxygen is introduced to the
reactor located at the central axis of the reactor.
[0007] U.S. Pat. No. 5,887,554 (Cohn et al.) also discloses a
system for the production of hydrogen-rich gas from light
hydrocarbons. The system includes a plasma fuel converter for
receiving hydrocarbon fuel and reforming it into hydrogen-rich gas.
The plasma fuel converter can be operated using either pulsed or
non-pulsed plasma and can utilize arc or high frequency discharges
for plasma generation. Products from the plasma fuel converter are
employed to preheat air input to the fuel converter. In one
embodiment shown in FIG. 6, residence time in the reactor is
increased by providing a centralized anode and a plurality of
radial cathodes to thereby cause the arc to glide towards the
center of the reactor under the influence of gas flowing in the
same direction as the gliding arc.
[0008] U.S. Pat. No. 6,322,757 (Cohn et al.) discloses a plasma
fuel converter which employs a centralized electrode and a
conductive reactor structure which acts as the second electrode for
creation of a plasma discharge. Reagents are fed to the reactor
just below the smallest gap between the electrodes and flow in the
same direction as the gliding arc to thereby produce hydrogen-rich
gas. In alternative embodiments, air and/or fuel are preheated by
counter-flow heat exchange with the products of the reforming
reaction and fed to the reactor either above or just below the
smallest gap between the electrodes.
[0009] Although some improvements in the energy efficiency of
plasma fuel converters have been achieved, there remains a need for
higher energy efficiencies for use of non-equilibrium low
temperature plasma.
SUMMARY
[0010] Accordingly, it is an object of certain embodiments of the
invention to provide a plasma fuel converter and a process for the
conversion of light hydrocarbons to hydrogen-rich gas using a low
temperature, non-equilibrium plasma.
[0011] It is another object of certain embodiments of the invention
to provide a plasma fuel converter and a process for the conversion
of light hydrocarbons to hydrogen-rich gas using a low temperature,
non-equilibrium plasma that has a relatively high energy
efficiency.
[0012] In order to achieve the above and other objects of the
invention, a plasma reactor for conversion of light hydrocarbons to
hydrogen-rich gas is disclosed. In a first aspect, the plasma
reactor has a wall defining a reaction chamber. The plasma reactor
also has an outlet. The plasma reactor has a reagent inlet fluidly
connected to the reaction chamber for creating a vortex flow in the
reaction chamber. The plasma reactor also has a first electrode and
a second electrode connected to a power source for generating a
sliding arc discharge in the reaction chamber.
[0013] In another aspect of the invention, a method for plasma
conversion of light hydrocarbons to hydrogen-rich gas is provided.
In the method, a plasma reactor is provided. The plasma reactor has
a wall defining a reaction chamber, an outlet, and a reagent inlet
fluidly connected to the reaction chamber for creating a vortex
flow in the reaction chamber. The plasma reactor also has a first
electrode and a second electrode connected to a power source for
generating a sliding arc discharge in the reaction chamber. The
method includes introducing a gas selected from the group
consisting of one or more light hydrocarbons, oxygen, an oxygen
containing gas, and mixtures thereof, into the reaction chamber in
a manner that creates a vortex flow in the reaction chamber. The
method also includes processing the light hydrocarbons using a
plasma assisted flame; and recovering hydrogen-rich gas from the
reactor.
[0014] These and various other advantages and features of novelty
that characterize the invention are pointed out with particularity
in the claims annexed hereto and forming a part hereof. However,
for a better understanding of the invention, its advantages, and
the objects obtained by its use, reference should be made to the
drawings which form a further part hereof, and to the accompanying
descriptive matter, in which there is illustrated and described a
preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic representation of a vortex reactor in
accordance with the present invention showing the circumferential
flow component of the first gas.
[0016] FIG. 2 is a schematic representation of a vortex reactor in
accordance with the present invention showing the axial flow
component of the gases in the reaction chamber.
[0017] FIG. 2b is a schematic representation of a vortex reactor
showing a second swirl generator.
[0018] FIG. 3 is a schematic representation of a vortex reactor in
accordance with the present invention and having a third gas
inlet.
[0019] FIG. 4 is a schematic representation of a vortex reactor in
accordance with the present invention provided with a
counter-current heat exchanger.
[0020] FIG. 4b is a schematic representation of a vortex reactor
with two heat exchangers employed.
[0021] FIG. 5 is a schematic representation of an alternative
embodiment of a heat exchanger which may be used in accordance with
the present invention.
[0022] FIG. 6 is a schematic representation of a vortex reactor in
accordance with the present invention showing the movable circular
ring electrode in the ignition position.
[0023] FIG. 7a is a schematic representation of a vortex reactor in
accordance with the present invention showing the movable circular
ring electrode in the reactor operating position.
[0024] FIG. 7b is schematic representation of a vortex reactor
showing a circular ring electrode supported by supporting
wires.
[0025] FIG. 8 is a schematic representation of a vortex reactor in
accordance with the present invention provided with a spiral
electrode.
[0026] FIG. 9 is a schematic representation of a vortex reactor in
accordance with the present invention provided with both a spiral
electrode and a circular ring electrode.
[0027] FIG. 10 is a schematic representation of a vortex reactor in
accordance with the present invention provided with a circular ring
electrode which forms part of the bottom of the reactor.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0028] The present invention relates to a device and process for
conversion of light hydrocarbons to hydrogen-rich gas using a low
temperature, non-equilibrium plasma. The term "light hydrocarbons"
as used herein refers to C.sub.1 to C.sub.4 hydrocarbons, which may
be saturated or unsaturated, branched or unbranched, and
substituted or unsubstituted with one or more oxygen, nitrogen, or
sulfur atoms.
[0029] In general, dimensions, sizes, tolerances, parameters,
shapes and other quantities and characteristics are not and need
not be exact, but may be approximate and/or larger or smaller, as
desired, reflecting tolerances, conversion factors, rounding off,
measurement error and the like, and other factors known to those of
skill in the art. In general, a dimension, size, parameter, shape
or other quantity or characteristic is "about" or "approximate" as
used herein, whether or not expressly stated to be such.
[0030] Gaseous hydrocarbons and oxygen (pure oxygen or oxygen in
air, or oxygen in enriched air) are the reagents in the process of
the present invention. The conversion process consists of two steps
as illustrated below using methane as the light hydrocarbon
reagent:
CH.sub.4+2O.sub.2..fwdarw.2H.sub.2O+CO.sub.2 (I)
2CH.sub.4+CO.sub.2+2H.sub.2O.fwdarw.6H.sub.2+3CO (II)
[0031] Step (I) is exothermic, whereas step (II) is endothermic and
tends to be the rate-determining step.
[0032] Referring now to the drawings, wherein like reference
numerals designate corresponding structure throughout the views,
and referring in particular to FIG. 1, a schematic view of a vortex
reactor 10 of the present invention is depicted. Vortex reactor 10
includes a reaction chamber 12. At or near the top of vortex
reactor 10, there are one or more nozzles 14 for feeding a first
gas to vortex reactor 10. Nozzles 14 may be located about the
circumference of vortex reactor 10 and are preferably spaced evenly
about the circumference. Preferably, at least four nozzles 14 are
employed. The first gas is introduced to reaction chamber 12 via
nozzles 14 which are oriented tangential relative to wall 13 of
reaction chamber 12. The tangential orientation of nozzles 14
imparts a circumferential velocity component 16 to the first gas as
it is introduced to reaction chamber 12. The set of nozzles 14 for
the first gas feeding will be referred to as the first swirl
generator. Optionally, a second swirl generator comprising nozzles
15, shown in FIG. 2b can be installed along the length of the
chamber. Multiple swirl generators, i.e. more than two, can be
installed for introduction of multiple gases as desired. Preferably
all swirl generators rotate gas in the chamber in the same
direction. Products leave reaction chamber 12 via outlet 20 located
at or near the top of reaction chamber 12.
[0033] One embodiment of the present invention employs a flange 30
with a circular opening 32 located substantially at the center of
flange 30 to form a reverse vortex flow. Flange 30 is located
proximate to the first swirl generator with nozzles 14. The opening
32 in the flange 30 is preferably circular, but may be other shapes
such as pentagonal or octagonal. The size of circular opening 32 is
important to determining the flow pattern in reaction chamber 12.
The diameter of opening 32 in flange 30 should be from about 70% up
to 95% of the diameter of reaction chamber 12 to form the reverse
vortex flow similar to that shown in the FIG. 2 without a
considerable recirculation zone. To form the reverse vortex flow
with a considerable recirculation zone 110 (FIG. 2b), the diameter
of opening 32 in flange 30 should be from about 10% up to 75% of
the diameter of reaction chamber 12.
[0034] The reverse vortex flow in reaction chamber 12 causes the
reagents to swirl around a region of plasma and flame 80, shown,
for example, in FIG. 7a, in reaction chamber 12. This provides
heating of the reagents as they move downwardly around central core
region 24. Also, the reverse vortex flow increases the residence
time of reactants inside reaction chamber 12. Increased residence
time helps to complete the second step (II) of the conversion
reaction. Large recirculation zone 110 also promotes completion of
the conversion process especially by decreasing ignition time
(initiation of the first step (I) of the conversion reaction).
[0035] Reverse vortex flow in this invention means that the vortex
flow has axial motion initially from the swirl generator to the
"closed" end of reaction chamber 12 (along wall 13 of the chamber),
and then the flow turns back and moves along the axis to the "open"
end of the chamber, where a swirl generator may be placed. This
flow is similar to the flow inside a dust separation cyclone, or
inside a natural tornado. This flow has very interesting and useful
properties. For example, gas dynamic insulation of the central
(axial) zone: walls of the chamber do not "feel" what is going on
in the center. It can be cold or extremely hot (flame or plasma) in
the center of reaction chamber 12. Primarily the temperature of
incoming gas defines the temperature of wall 13. For the process pf
hydrocarbon conversion it means that the zone of combustion is
separated from wall 13.
[0036] Without the reverse vortex flow, the reagents would enter
reaction chamber 12 through inlet 18 and pass between the
electrodes forming the plasma and leave reaction chamber 12 at a
relatively high velocity, and, at least in a small reactor,
incomplete conversion of the reagents of the conversion reaction
would likely occur. The present invention provides an increased
residence time in reaction chamber 12, by causing the reactants to
travel a greater distance in the reactor by imparting a
circumferential velocity component to the reagents. Residence times
can be increased by an order of magnitude using a preferred form of
the reverse vortex flow. This helps to ensure complete conversion
of the reactants to products of the conversion reaction.
[0037] In the embodiment of FIG. 1, the reagents are premixed and
introduced to reaction chamber 12 via nozzles 14. This creates a
full volume of flame in reaction chamber 12 causing reactor wall 13
to become very hot, indicating a significant energy loss to the
environment from reactor 10. As a result of this condition, care
must be taken to provide safe conditions for ignition of the flame
and to prevent combustion of the reagents prior to their entry into
reaction chamber 12. These factors indicate that the embodiment of
FIG. 1, wherein the reagents are premixed and fed to reaction
chamber 12 via nozzles 14, is a less preferred embodiment of the
invention. Typical inlet velocities for feeding gas into reaction
chamber 12 via nozzles 14 is from about 10 m/s to about 50 m/s.
[0038] In order to reduce heat loss to the environment and minimize
the risk of unwanted combustion outside the reactor, two separate
gases or gaseous mixtures that both are non-flammable and that form
together a flammable gas mixture, can be fed to reaction chamber 12
via different inlets as depicted in FIG. 2. In the present
invention, non-flammable means non-combustible under the conditions
existing at the specified location (in this embodiment, outside the
reactor). In this embodiment, a second gas is fed from the bottom
of reaction chamber 12 via gas inlet 18 co-directionally with an
upward axial flow component of the first gas in reaction chamber 12
accelerating this axial flow component. In this manner, the present
invention ensures a sufficiently high axial velocity in reaction
chamber 12 to move a gliding arc axially upwardly for plasma
creation. The reverse vortex flow also helps to mix the first and
second gases in the reaction chamber 12.
[0039] In order to minimize the risk of unwanted combustion outside
the reactor, two separate gases or gaseous mixtures that both are
non-flammable and that form together flammable gas mixture, can
also be fed to the reaction chamber via different swirl generators
(made of nozzles 14 and nozzles 15 as depicted in FIG. 2b).
[0040] A preferred ratio of the tangential flow velocity to the
axial flow velocity is about 4.0. This ratio of flow velocities
causes the reverse vortex flow to follow approximately a 15 degree
slope in reaction chamber 12. Preferably, in this embodiment, the
hydrocarbon-rich feed gas is introduced to reaction chamber 12 via
nozzles 14 and an oxygen-rich gas is introduced to reaction chamber
12 through inlet 18. In this manner, the flame in reaction chamber
12 can be maintained at a distance from wall 13 of reactor 10,
thereby keeping the wall of reactor 10 relatively cool. This is
achieved as a result of the downward flow of the hydrocarbon-rich
gas from nozzles 14 along wall 13 of reaction chamber 12, which
provides insulation between the plasma and flame and reactor wall
13. In this manner, heat loss to the environment can be reduced
thereby further improving the efficiency of reactor 10. However, it
is also possible to achieve acceptable results by feeding the
hydrocarbon-rich feed gas to reaction chamber 12 via inlet 18 and
the oxygen-rich gas via nozzles 14.
[0041] Referring to FIG. 3, there is shown another embodiment of
reactor 10 of the present invention which further includes a third
inlet 26 at the top of reaction chamber 12 for introduction of a
third gas to reaction chamber 12. The third gas may be employed, as
necessary, to assist the flame in t reaction chamber 12.
Preferably, the third gas is oxygen-rich gas.
[0042] In another embodiment of the invention shown in FIG. 4, a
heat exchanger 40 is employed to preheat the at least one feed gas
for reactor 10. Preferably, when employing two or more inlets to
feed gas to reactor 10, at least two of the feed gases are
preheated in heat exchanger 40. More preferably, both the
hydrocarbon-rich gas fed via nozzles 14 and the oxygen-rich gas fed
via inlet 18 are preheated in heat exchanger 40. Also, it is
preferred to preheat the feed gases by counter-current heat
exchange with the product stream from reactor 10 as shown in FIG.
4. This reduces the amount of energy input to the system for
preheating the feed gases, and cools the product stream, which is
also desirable in the process of the invention.
[0043] FIG. 4 shows reactor 10, provided with a wall 13, nozzles
14, inlet 18 and a product outlet 20. Product stream 50 is fed from
product outlet 20 to inlet 42 at a first end of heat exchanger 40,
through heat exchanger 40 to product outlet 43 of heat exchanger
40. Product stream 50 leaves heat exchanger 40 as a hydrogen-rich
cooled gas. At least one feed gas is fed to inlets 44, 46 located
at a second end of the heat exchanger 40 for counter-current heat
exchange with product stream 50. In the embodiment of FIG. 4, first
feed gas stream 52 is fed to inlet 44 of heat exchanger 40 and
leaves heat exchanger 40 via first gas outlet 45, whereupon first
feed gas stream 52 is fed to nozzles 14 of reactor 10. Second feed
gas stream 54 is fed to inlet 46 of heat exchanger 40, and leaves
heat exchanger 40 via second gas outlet 47, whereupon second feed
gas stream 54 is fed to inlet 18 of reactor 10.
[0044] In order to increase the heat exchange capacity of heat
exchanger 40, heat exchanger 40 may be filled with a heat
conducting material, such as nickel pellets 48. Other suitable heat
conducting materials may be employed, though it is preferable to
use nickel-based metals as the heat conducting material. In a more
preferred embodiment, heat exchanger 40 is partially filled with a
heat conducting material, such as nickel pellets 48, as shown in
FIG. 5. The remaining, unfilled portion 49 of heat exchanger 40 may
be left as empty space. In a preferred embodiment, about half of
the volume of heat exchanger 40 is filled with heat-conducting
material. This serves to increase the residence time of
intermediate products of product stream 50 in heat exchanger 40 to
thereby improve conversion of the intermediate products to the
final products via step (II) of the reaction given above. In this
manner, significant conversion of intermediate products to final
products can be realized in heat exchanger 40.
[0045] In another embodiment of the invention shown in FIG. 4b, two
or more heat exchangers, 40a and 40b, are employed to preheat the
feed gases separately to desirable temperatures. Preferably, when
employing one or more inlets to feed pure hydrocarbon gas to
reactor 10, this pure hydrocarbon gas should not be preheated to
the temperature higher than the decomposition temperature (gaseous
hydrocarbons decompose under the high temperature conditions to
soot and hydrogen, for example for methane this decomposition start
temperature is about 450.degree. C.). It is preferred to preheat
the feed gases by counter-current heat exchange with the product
stream from reactor 10, and also to preheat oxygen-rich gas to
higher temperature as shown in FIG. 4b.
[0046] In FIG. 4b, reactor 10 is provided with a wall 13, nozzles
14, inlet 18 and a product outlet 20. Product stream 50 is fed from
product outlet 20 to inlet 42a at a first end of heat exchanger
40a, through heat exchanger 40a to product outlet 43a of heat
exchanger 40a. Product stream 50 then enters inlet 42b at a first
end of heat exchanger 40b, passes through heat exchanger 40b to
product outlet 43b of heat exchanger 40b. Product stream 50 leaves
heat exchanger 40b as a hydrogen-rich, cooled gas. At least one
feed gas is fed to inlets 44, 46 located at the second ends of heat
exchangers 40b and 40a, respectively, for counter-current heat
exchange with product stream 50. In the embodiment of FIG. 4b,
first feed gas stream 52 is fed to inlet 44 of heat exchanger 40b
and leaves heat exchanger 40b via first gas outlet 45, whereupon
first feed gas stream 52 is fed to nozzles 14 of reactor 10. Second
feed gas stream 54 is fed to inlet 46 of heat exchanger 40a, and
leaves heat exchanger 40a via second gas outlet 47, whereupon
second feed gas stream 54 is fed to inlet 18 of reactor 10.
[0047] If it is necessary to preheat the hydrocarbon-rich feed gas
to the temperature higher than decomposition temperature, it is
necessary to dilute the hydrocarbon gas with oxygen-rich gas, but
this dilution should not result in formation of flammable mixture
in feed gas stream.
[0048] The reactor of the present invention employs a
plasma-assisted flame (PAF) in reaction chamber 12. The PAF is
produced by preheating reaction chamber 12 and the heat
exchanger(s) with an inert gas such as nitrogen, or with a lean
(leaner than the mixture of reagents for conversion) combustion
mixture, and replacing the preheating gas with the feed gases which
provide the reagents for the reactions (I) and (II). As the
reagents mix in reaction chamber 12, a flammable state is produced
thereby resulting in the appearance of a flame in reaction chamber
12. Finally, the oxygen concentration in reaction chamber 12 is
reduced to a low level, which is at least sufficient to maintain a
stable flame and to avoid soot formation. The oxygen concentration
in reaction chamber 12 can alternatively be maintained at a level
which provides a stoichiometric amount of oxygen for the reactions
(I) and (II), as long as the flame is stable at this concentration.
Thus, in a preferred embodiment, the number of oxygen atoms [O] in
the sum of all feed gases that come to reaction chamber 12 is at
least as large as the number of carbon atoms [C] in the same sum of
all feed gases coming to reaction chamber 12, as long as the flame
is stable at this oxygen-rich gas feed. If the flame is stable
using a stoichiometric concentration of oxygen ([O]/[C]=1), part of
oxygen atoms can be fed to the reactor in the form of water vapor
to produce more hydrogen via the reaction:
CH.sub.4+H.sub.2O.fwdarw.CO+3H.sub.2
[0049] Using sliding arc plasma, as in the present invention, the
soot-less flame can be maintained even with combinations of
reactants which would normally be outside the limit of flammability
or which can burn only with soot production, hence the term "plasma
assisted flame" (PAF) appears. The PAF provides fast conversion of
reagents to intermediate products, while keeping the energy input
to the reactor at an efficient level (preferably less than 2% of
the total chemical energy of the hydrocarbon gas), since the PAF
consumes less electrical energy than sliding arc plasma alone. The
PAF also permits the use of lower concentrations of oxygen in
reaction chamber 12 to maintain the soot-less flame. This is
desirable since lower oxygen concentrations tend to result in
greater hydrogen production by minimizing the amount of water
generated in reaction chamber 12 by reaction of oxygen with light
hydrocarbons.
[0050] In one embodiment of the invention, the present invention
utilizes a constant distance between electrodes to maintain a
stable sliding arc in order to avoid the production of pulsed
plasma, wherein the properties of the plasma constantly change with
time. By maintaining the sliding arc with a constant distance
between the electrodes, stable plasma is obtained and the
properties of the plasma do not change significantly with time.
[0051] The stable sliding arc can be obtained, for example, using
electrodes as shown in FIG. 6. In FIG. 6, a first electrode is
provided in reaction chamber 12 in the form of a circular ring
electrode 60, supported by supporting wires 62 and connected to a
power supply 64 via an electrical connection 66. A second electrode
70 is preferably located in an upper portion of reaction chamber
12.
[0052] Circular ring electrode 60 is mounted, via supporting wires
62 on a movable mount 68 for substantially vertical movement in
reaction chamber 12. Movable mount 68 is actuatable from outside
reactor 10 to permit adjustment of the distance between circular
ring electrode 60 and second electrode 70. This arrangement permits
circular ring electrode 60 to be positioned a first, minimum
distance 69 from second electrode 70 for ignition of the sliding
arc. Once the sliding arc is ignited, circular ring electrode 60 is
moved vertically downwardly using movable mount 68 to position
circular ring electrode 60 at a second, greater distance from
second electrode 70, as shown in FIG. 7. In this manner, a short
distance between circular ring electrode 60 and second electrode 70
can be provided for ignition, and a longer distance between
circular ring electrode 60 and second electrode 70 can be provided
for operation of reactor 10. The ability to adjust the distance
between the electrodes also allows the optimization of the sliding
arc plasma generation in t reaction chamber 12 by selection of the
optimal distance between the electrodes for reactor operation.
[0053] Power consumption per unit length of the sliding arc for a
fixed current is constant, and electrode spot energy is constant.
Thus, by increasing the distance between circular ring electrode 60
and second electrode 70, the power consumption in reaction chamber
12 can be substantially increased without increasing the current
strength provided to the reactor. As a result, the sliding arc can
be operated without overheating, melting, evaporation and droplet
erosion of the electrode surface at the arc point. This provides a
significantly improved life expectancy for the electrodes.
[0054] Circular ring electrode 60, which forms the first electrode,
can be interchanged with electrodes having other geometries. A
circular geometry, for example, is desirable for a cylindrical
reaction chamber 12, such as that illustrated in the drawings since
this geometry will maintain the sliding arc at a relatively
constant distance from wall 13 of reactor 10. Thus, for a
cylindrical reaction chamber 12, circular ring electrode 60 can be
interchanged with, for example a flat circular disc, not shown.
Second electrode 70 can also be in the form of a circular ring
electrode or flat circular disc. In a more preferred embodiment,
second electrode 70 also acts as a flow restrictor and thus may
take the place of flange 30, discussed above.
[0055] Referring to FIG. 7, there is shown reactor 10 of FIG. 6
with circular ring electrode 60 in position to maintain a stable
sliding arc for plasma generation. As shown in FIG. 7, the
combination of the gas flows, electrode geometry and reagent
mixture provide a PAF 80. Reagents flow around PAF 80 in a reverse
vortex flow pattern 82, as shown. The stable sliding arc can be
obtained, for example, using electrodes as shown in FIG. 7b. In
FIG. 7b, a first electrode is provided in reaction chamber 12 in
the form of a circular ring electrode 60, connected to a power
supply 64. Second electrode 70 may be in the form of a circular
ring electrode or flat circular disc. In a more preferred
embodiment, second electrode 70 also acts as a flow restrictor and
thus may take the place of flange 30. Also shown in FIG. 7b are
swirl generators comprised of nozzles 15 and 14.
[0056] The distance between the circular ring electrode and
grounded cylindrical wall of the reactor is small enough to ensure
electrical breakdown in cold gas. Once the breakdown takes place,
the sliding arc is elongated and rotated by the gas flow and
reaches the constant length, which is the largest possible
length.
[0057] In another embodiment shown in FIG. 8, the present invention
employs a spiral electrode 90 as the cathode for providing the
sliding arc. The anode may again be a flat disc 70 or circular ring
as in the previous embodiments. Spiral electrode 90 may be anchored
to the reactor 10 at one end thereof by any suitable attachment
mechanism 92, such as a screw. Preferably spiral electrode 90 is of
sufficient structural rigidity to support itself within reaction
chamber 12, as shown. Spiral electrode 90 produces an arc, which
slides from free end 94 of spiral electrode 92 toward anchored end
93 of spiral electrode 90.
[0058] The movement of the sliding arc is the result of reverse
vortex flow 82 in reaction chamber 12. Since the sliding arc moves
around, the arc spot on the surface of spiral electrode 90
continuously moves to a new location, thus protecting the electrode
material from excessive wear in a single location. This helps
provide a longer life for spiral electrode 90, and to prevent
overheating, melting, evaporation and/or droplet erosion of the
electrode surface at the arc point. Since the length of the sliding
arc elongates by the reverse vortex flow, the arc reaches the
maximal possible length, extinguishes and starts again once reactor
10 is running. Moreover, reverse vortex flow 82 of reagents in
reaction chamber 12 helps provide easy breakdown conditions for the
sliding arc in reactor 10.
[0059] The shape of spiral electrode 90 can be optimized based on
the flow conditions within reaction chamber 12, and the type of
power supply employed. For example, experimental flow
visualization, numerical modeling and/or computerized flow
simulation can be employed to help design the optimal shape for
spiral electrode 90. For the preferred shape for spiral electrode
90 the diameter of each successive spiral decreases relative to the
previous spiral, as the distance from anode 70 increases. Also, it
may be preferable for the bottom of the spiral to form a circular
ring to provide a similar geometry to that shown below in FIG.
9.
[0060] When a high potential, e.g. 3 kV/mm is applied across the
electrodes, electrical breakdown ignites the gliding arc. The
strong reverse vortex flow 82 in reaction chamber 12 forces the
gliding arc to move around the longitudinal axis 100 of the reactor
10. The arc thus elongates itself along spiral electrode 90 until
it eventually reaches the end of spiral electrode 90 furthest away
from anode 70. Since the gliding arc is maintained in a central
zone of t reaction chamber 12 by spiral electrode 90 as shown in
FIG. 8, it is subjected to significantly less flow disturbances
than it would be subjected to if the gliding arc extended closer to
wall 13 of reactor 10. Also, the area of the gliding arc is
subjected to intensive convective cooling as a result of reverse
vortex flow 82 and the gliding arc is thermally insulated from wall
13 of reactor 10 by this same reverse vortex flow 82. These factors
allow the provision of high plasma density, high power and high
operating pressures, high electron temperatures, and relatively low
gas temperatures. This combination of properties allows the
selective stimulation of certain chemical processes within reactor
10, if desired.
[0061] In another embodiment of the present invention, shown in
FIG. 9, a combination of a spiral electrode 90 and a circular ring
electrode 60 is employed. This embodiment combines the advantage of
having the arc between circular ring electrode 60 and anode 70
during normal operation of reactor 10 with the ability to reignite
the sliding arc without moving circular ring electrode 60, if, for
any reason, the arc should extinguish itself. Thus, in operation,
the sliding arc is ignited at free end 94 of spiral electrode 90
and moves down spiral electrode 90 as described above. Once the
sliding arc reaches circular ring electrode 60, it is maintained
between circular ring electrode 90 and anode 70. Should the arc be
extinguished, it will immediately reignite at free end 94 of spiral
electrode 90 and the process will repeat itself. This arrangement
adds additional stability to the plasma generation by minimizing
the time that the arc is extinguished.
[0062] The arrangement shown in FIG. 9 is for the case of DC or
two-phase AC power. For three-phase AC power, multiple arrangements
of electrodes as shown in FIG. 9, can be employed.
[0063] In yet another embodiment, shown in FIG. 10, a circular ring
electrode 60 forms part of the bottom end of reactor 10.
[0064] In yet another embodiment (not shown), spiral electrode 90
forms part of cylindrical wall 13 of reactor 10.
[0065] It is to be understood that various features of the
different embodiments shown in the drawings may be combined with
one another in a vortex reactor in accordance with the present
invention. For example, the various embodiments of heat exchanger
40 can be employed in any of the embodiments of the vortex reactor
shown in the figures.
[0066] In a second aspect, the present invention relates to a
method for the conversion of light hydrocarbons to hydrogen-rich
gas in a vortex reactor. The method includes the steps of
introducing at least one light hydrocarbon and oxygen into a
reaction chamber, subjecting at least the light hydrocarbon feed
gas to a reverse vortex flow, and converting said light
hydrocarbons to hydrogen-rich gas with a plasma assisted flame
(PAF).
[0067] In the method, the axial gas flow may be created by the
steps of feeding gas in an axial direction into said reaction
chamber and, optionally, accelerating said axial gas flow through a
flow restriction. The circumferential gas flow may be created by
the step of feeding gas into said reaction chamber in a direction
tangential to a sidewall of said reaction chamber. In order to
assist in the maintenance of the PAF, a third, oxygen-rich gas
stream can optionally be introduced at the top of the reaction
chamber.
[0068] The method includes generating plasma in said reaction
chamber. Plasma generation may include the step of providing a
sliding electrical arc in said reaction chamber, as discussed
above.
[0069] The methods of the present invention may employ any of the
reactors shown in the figures. In addition, each method of the
present invention may optionally include the step of preheating one
or more feed gases by counter-current heat exchange with the
product stream from the vortex reactor.
[0070] If a vortex reactor with a movable electrode is employed,
the method may further include the step of moving the electrode
from a first, ignition position, to a second, operation position
after ignition of the sliding arc in the reactor. In this method,
operating conditions can be optimized, for example, by varying the
distance between the movable electrode and the fixed electrode.
[0071] It is to be understood that even though numerous
characteristics and advantages of the present invention have been
set forth in the foregoing description, together with details of
the structure and function of the invention, the disclosure is
illustrative only, and changes may be made in detail, especially in
matters of shape, size and arrangement of parts within the
principles of the invention to the full extent indicated by the
broad general meaning of the terms in which the appended claims are
expressed.
* * * * *