U.S. patent application number 13/002435 was filed with the patent office on 2011-05-05 for process and a reactor for oxidation of a hydrocarbon.
This patent application is currently assigned to Ammonia Casale S.A.. Invention is credited to Luca Zanichelli.
Application Number | 20110104623 13/002435 |
Document ID | / |
Family ID | 40091806 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110104623 |
Kind Code |
A1 |
Zanichelli; Luca |
May 5, 2011 |
Process and a Reactor for Oxidation of a Hydrocarbon
Abstract
A process and related reactor (1) for oxidation of a hydrocarbon
feedstock are disclosed, the reactor (1) comprising a vessel (3)
and a neck (5) with an axial burner (6) and a tangential gas inlet
(2), wherein the neck (5) has a swirling chamber (10) located below
said burner (6) and connected to said gas inlet (2), to produce a
gas vortex (V) which optimizes the mixing between the gas stream
(G) and the oxidizer in said neck (5). Preferably the swirling
chamber (10) has an internal surface (12) with a log-spiral
profile.
Inventors: |
Zanichelli; Luca; (Grandola
Ed Uniti, IT) |
Assignee: |
Ammonia Casale S.A.
Lugano-Besso
CH
|
Family ID: |
40091806 |
Appl. No.: |
13/002435 |
Filed: |
June 16, 2009 |
PCT Filed: |
June 16, 2009 |
PCT NO: |
PCT/EP2009/057472 |
371 Date: |
January 24, 2011 |
Current U.S.
Class: |
431/9 ;
431/159 |
Current CPC
Class: |
C01B 2203/1211 20130101;
B01J 8/0285 20130101; C01B 3/363 20130101; C01B 3/382 20130101;
C01B 2203/1241 20130101; C01B 2203/1282 20130101; B01J 2208/00504
20130101; B01J 8/0278 20130101; C01B 3/36 20130101; C01B 2203/0255
20130101; F23D 14/20 20130101; B01J 8/025 20130101; C01B 2203/0244
20130101 |
Class at
Publication: |
431/9 ;
431/159 |
International
Class: |
F23M 3/00 20060101
F23M003/00; F23D 11/00 20060101 F23D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 4, 2008 |
EP |
08012085.0 |
Claims
1. A reactor for reacting a hydrocarbon-containing feedstock with
an oxidizer stream, the reactor comprising: a vessel defining a
combustion chamber, at least an axial burner for delivering said
oxidizer stream to said combustion chamber, an inlet for said
hydrocarbon-containing feedstock, and a swirling chamber connected
to said inlet, wherein said swirling chamber is located downstream
of said burner and upstream of said combustion chamber, and is in
fluid communication with said burner and combustion chamber,
wherein said inlet and swirling chamber are arranged to impart a
swirling motion around an axis of the reformer to the
hydrocarbon-containing feedstock.
2. The reactor according to claim 1, wherein said vessel has a neck
delimiting at least part of said combustion chamber, the neck
having a portion with enlarged cross section, and wherein said
portion delimits the swirling chamber and is connected with the
hydrocarbon-containing feedstock inlet.
3. The reactor according to claim 2, wherein said swirling chamber
is located at the top of the neck.
4. The reactor according to claim 1, wherein there is a gap between
said swirling chamber and the tip of said burner, so that a
pre-chamber is formed downstream the burner and above said swirling
chamber.
5. The reactor according to claim 1, wherein said swirling chamber
is delimited laterally by a side wall with a spiral-like internal
surface so that the distance of said internal surface from the axis
of the reformer progressively decreases from the inlet section of
said hydrocarbon-containing feedstock inlet.
6. The reactor according to claim 5, wherein said spiral-like
internal surface of the swirling chamber covers an angle of about
360 degrees.
7. The reactor according to claim 6, wherein said spiral-like
internal surface has one end matching an internal wall of the
hydrocarbon-containing feedstock inlet, at the inlet section, and
an opposite end matching an opposite internal side of said
inlet.
8. The reactor according to claim 6, wherein said spiral-like
internal surface is a log-spiral surface, having a cross-section
profile following a logarithmic spiral.
9. The reactor according to claim 1, wherein said swirling chamber
is delimited laterally by a side wall with a cylindrical internal
surface.
10. The reactor according to claim 1, wherein the vessel contains a
catalytic bed and the combustion chamber is above said catalytic
bed.
11. The reactor according to claim 1, said reactor being an
autothermal reformer, a secondary reformer of a
hydrocarbon-reforming equipment, or a partial oxidation gas
generator.
12. A process for reacting a hydrocarbon-containing feedstock with
an oxidizer stream inside a combustion chamber, wherein said
oxidizer stream is fed to said combustion chamber in direction of
an axis of said chamber, the process being characterized in that a
swirling motion around said axis is imparted to said gas stream
entering the combustion chamber.
13. The process according to claim 12, wherein a substantially
axial-symmetric velocity field is imparted to said
hydrocarbon-containing feedstock inside the combustion chamber, by
feeding said stream to said combustion chamber via a spiral-like
path.
14. The process according to claim 13, wherein said spiral-like
path follows a logarithmic spiral around said axis of the
combustion chamber.
15. The process according to claim 12, wherein said
hydrocarbon-containing feedstock is a gas stream containing gaseous
hydrocarbon(s) such as natural gas or methane, or a gaseous flow
containing suspended solid combustible such as coal dust or carbon
soot, or a gaseous flow comprising dispersed liquid hydrocarbons,
and the oxidizer stream contains air, enriched air or pure oxygen.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a process for oxidation of a
hydrocarbon-containing feedstock, and a related reactor. The
invention can be applied for example to autothermal reforming,
secondary reforming and partial oxidation for production of a
syngas or fuel.
PRIOR ART
[0002] Partial or total oxidation of a hydrocarbon-containing
feedstock (HCF) is carried out in processes such as: the
autothermal reforming of coke oven gas or natural gas; the
secondary reforming of the process gas coming from a primary
reformer, for example for the production of a synthesis gas; the
partial oxidation (POX) of a HCF for conversion into a synthesis
gas, a fuel or a reducing gas. The oxidizer stream, depending on
the application, may be air, O.sub.2-enriched air or pure oxygen
(usually 95% molar or more), in a reaction chamber of a suitable
vessel.
[0003] FIG. 13 shows an example of a prior-art air secondary
reformer. The reformer has a vessel 100 with a neck 101 where a
burner 102 is installed and connected to an air pipe 110. A
hydrocarbon-containing feedstock or HCF enters the reformer via
refractory-lined transfer line 103, connected to the side of the
neck 101. A process gas distributor 104 is installed above the tip
105 of the burner 102, to provide uniform distribution of process
gas across the cross section of the vessel neck, and achieve a good
mixing with the oxidizer. The burner 102 is installed at the bottom
end of the neck 101, so that the combustion takes place in the
chamber located at the bottom end of the vessel neck and on top of
the catalytic bed (not shown) contained in vessel 100.
[0004] FIG. 14 shows a typical arrangement of oxygen secondary
reformers. The reformer comprises a vessel 200, a neck 201, a
burner 202, process gas transfer line 203 and gas distributor 204.
The burner tip is about at the center of the neck 201, so that the
neck itself is used as a combustion chamber.
[0005] An autothermal reformer or ATR essentially consist of a
reactor where the HCF is subject to partial combustion followed by
methane steam reforming and shift conversion over a catalytic bed.
The HCF and oxidizer inlets are usually arranged in accordance to
FIG. 14, where HCF and steam enter at 203 and oxygen or enriched
air enters via the burner 202.
[0006] Partial oxidation of a HCF, in the known art, is carried out
in a so-called POX gas generator usually comprising a
refractory-lined shell defining a suitable combustion chamber and
having an axial air (or oxygen) inlet and a lateral HCF inlet.
[0007] A drawback of the above-cited prior art is that the HCF
inlet stream is subject to a 90.degree.-degree change of direction
to enter the combustion chamber. Moreover, due to the asymmetrical
inlet, the gas distributor is indispensable is the conventional
reformers, to obtain an acceptable mixing between the HCF and the
oxidizer stream inside the chamber. The gas distributor however
involves a relevant pressure drop. POX gas generator may be
realized without the gas distributor, but nevertheless they suffer
a relevant pressure drop of the HCF stream since the HCF is forced
to flow through the burner itself.
[0008] More in detail, the kinetic energy of the HCF is almost
completely lost in said change of direction and pressure drop
through the gas distributor; hence, the prior art provides that the
energy required for the mixing of gas and oxidizer streams is
furnished by feeding the oxidizer stream at a pressure well above
the operating pressure inside the reformer. The extra pressure
energy of the oxidizer stream is converted into kinetic energy,
obtaining a high-speed oxidizer stream which promote the mixing
with the process gas. This solution however involves relevant
pressure drop of oxidizer and, hence, costs and energy consumption
for compression
[0009] A further drawback is that the gas distributor being
installed downstream of the HCF inlet, a significant portion of the
burner is directly exposed to the hot (around 800.degree. C.) HCF
gas, e.g. coming from a primary reformer or pre-heater.
[0010] With reference to FIG. 13, it can be seen that the air pipe
is directly exposed to the HCF gas stream, usually pre-reformed or
pre-heated at a high temperature; an expensive high-alloy pipe is
therefore necessary. In oxygen reformers or ATRs (FIG. 14), the
body of the burner itself is exposed to the HCF. The gas
distributor is also exposed to the hot gas and hence need to be
realized with an expensive material, such as an alloy adapted to
extreme environment.
[0011] Furthermore, the need to maintain the burner tip downstream
the gas distributor increases the length of the burner or of the
air pipe thereof, which is then exposed to vibrations, especially
induced by the gas flow.
[0012] As apparent from the above discussion the technical problem
and drawback of the prior-art can be summarized as follows: [0013]
relevant pressure drop of the HCF; [0014] need of a gas
distributor, with the related drawbacks of cost and pressure drop;
[0015] need to compress the oxidizer stream, to provide the kinetic
energy required for mixing in the combustion chamber; [0016] burner
directly exposed to the hot gas flow; [0017] need of an elongated
design of the burner, especially in oxygen reformers, exposed to
flow-induced vibrations.
[0018] The above drawbacks have not yet been solved in the prior
art, despite the need of efficient and cost-effective equipment for
hydrocarbon reforming, autothermal reforming or partial oxidation,
for example for the production of substitute natural gas or
production of hydrogen/nitrogen syngas for ammonia synthesis, or
other purposes.
SUMMARY OF THE INVENTION
[0019] The problem underlying the invention is to provide a new
design for reactors herein considered, such as air or oxygen
reformers, autothermal reformers and POX gas generators, in order
to solve the above listed drawbacks.
[0020] The basic idea is to use the inlet kinetic energy of the
hydrocarbon-containing feedstock, to generate a suitable swirling
motion inside the combustion chamber.
[0021] Hence, the above problems are solved with a process for
reacting a hydrocarbon-containing feedstock with an oxidizer stream
inside a combustion chamber, wherein said oxidizer stream is fed to
said combustion chamber in direction of an axis of said chamber,
the process being characterized in that a swirling motion around
said axis is imparted to said gas stream entering the combustion
chamber.
[0022] Preferably, the hydrocarbon-containing feedstock is fed to
the combustion chamber with a spiral path, more preferably
according to a logarithmic spiral, so that a gas vortex with a
substantially axial-symmetry of the velocity field is formed inside
the combustion chamber.
[0023] The hydrocarbon-containing feedstock or HCF, according to
the invention, is a gas stream containing gaseous hydrocarbon(s)
such as natural gas or methane, or a gaseous flow containing
suspended solid combustible such as coal dust or carbon soot, or a
gaseous flow comprising dispersed liquid hydrocarbons. The oxidizer
stream can be any stream containing oxygen or having oxidizing
property, including air, enriched air, pure oxygen, steam or
mixtures containing O.sub.2, steam and CO.sub.2.
[0024] As non-limitative examples, the process can be used for:
stand-alone autothermal reforming of a raw HCF; secondary reforming
of a pre-reformed stream, e.g. coming from a primary reforming
step; partial oxidation of a HCF for the production of a
syngas.
[0025] In accordance, the invention provides a reactor for reacting
a hydrocarbon-containing feedstock with an oxidizer stream, the
reactor comprising a vessel defining a combustion chamber, at least
an axial burner for delivering said oxidizer stream to said
combustion chamber, and an inlet for said hydrocarbon-containing
feedstock, characterized in that it comprises a swirling chamber
connected to said inlet, said chamber being located downstream said
burner and upstream said combustion chamber, and being in fluid
communication with said burner and combustion chamber, said inlet
and swirling chamber being arranged to impart a swirling motion
around the axis of the reformer to the hydrocarbon-containing
feedstock.
[0026] According to a preferred embodiment of the invention, the
vessel has a neck delimiting at least part of said combustion
chamber; said neck has a portion with enlarged cross section,
defining said swirling chamber and connected to the gas inlet.
[0027] In one embodiment of the invention, said swirling chamber is
located at one end of the neck of the reactor, where the burner is
installed; in a further embodiment, there is a gap between
combustion chamber and the tip of said burner, so that a
pre-chamber is formed downstream the burner and above the swirling
chamber. This pre-chamber may serve for the formation of the
diffusion flame, in a relatively quite, reduced-swirl
environment.
[0028] In preferred embodiments, the HCF inlet is tangential,
namely the direction of the HCF stream at the inlet of the swirling
chamber is tangential to a circumference lying in a plane
perpendicular to the axis of the reactor.
[0029] According to further aspects of the invention, the swirling
chamber is delimited laterally by a side wall having a suitable
profile to obtain a vortex around the axis of the neck of the
reformer, with no or negligible component of the vector of velocity
in the plane normal to said axis. More in detail, according to one
aspect of the invention said swirling chamber is delimited
laterally by a side wall with a spiral-like internal surface, and
the distance of said internal surface from the axis of the reactor
progressively decreases from the process gas inlet section of said
gas inlet.
[0030] In a preferred embodiment said spiral-like surface covers an
angle of 360 degrees.
[0031] According to a further and preferred aspect of the
invention, said spiral-like surface is in accordance with a
logarithmic spiral, having the same axis of the reformer. The
swirling chamber, in other words, has a log-spiral cross
section.
[0032] In another and simplified embodiment, the swirling chamber
has a circular cross section, in a plane perpendicular to the axis
of the neck, i.e. the internal profile of the lateral wall of said
chamber is cylindrical rather than following a spiral
arrangement.
[0033] The invention is applicable to HCF inlets having any cross
section, for example rectangular or circular. The gas inlet is
connected to a flow line feeding the HCF to said reactor, which is
also called transfer line. Preferably, in a reactor connected to a
transfer line with a circular cross section, the internal side wall
of the swirling chamber has a semi-circular cross section, as will
be explained below.
[0034] A reactor according to the invention can be, as
non-limitative examples, an autothermal reformer, a secondary
reformer of a hydrocarbon-reforming equipment, or a partial
oxidation gas generator. In the following description, references
to a reformer should equally be intended to a POX gas generator or,
more generally, to a reactor for oxidizing a HCF.
[0035] The reaction can be a catalytic reaction, particularly if
the reactor is a secondary reformer or an autothermal reformer. In
this case, the vessel contains a catalytic bed and said combustion
chamber is defined above said catalytic bed. ATR and secondary
reformer are usually catalytic reactors; a POX gas generator can be
non-catalytic, if operated at a suitable high temperature.
[0036] The advantages of the invention are now discussed.
[0037] The HCF stream receives a controlled swirling motion while
entering the combustion chamber, due to passage through said
swirling chamber, rather than being subject to a highly dissipative
change of direction from the (usually horizontal) axis of the
transfer line to the (usually vertical) axis of the reactor. This
swirling motion allows an efficient mixing between the HCF and the
flame formed in the burner, and the oxidizer stream, thus
eliminating the need of the gas distributor.
[0038] It can be stated that the energy of the process gas is used
in an efficient way to improve the mixing with the oxidizer,
instead of being wasted through the dissipation and pressure drop
across the gas distributor, as in the prior art. A fraction of the
energy for the mixing process is found in the gas stream itself,
rather than being provided by the oxidizer stream, as in the prior
art. Hence, the oxidizer stream can be fed at a lower pressure,
reducing the costs related to size and energy consumption of the
oxygen or air compressor. On the other hand, for a given velocity
of the oxidizer the reformer can be realized with a shorter
neck.
[0039] Having no gas distributor, it is no longer necessary that
the burner tip is below the HCF inlet and, hence, to expose the
burner to the process gas. The burner can be shorter and totally
removed from the path of the hot gas, for example flushed in the
cap of the vessel. The burner is less exposed to flow-induced
vibrations and does no longer need expensive materials for extreme
environment.
[0040] The swirling chamber with a log-spiral cross section is
particularly preferred for the following reason. The axis of vortex
created in the combustion chamber is coincident with the axis of
the reformer and the velocity profiles (axial, radial and
tangential) are axis-symmetric. The momentum of the process gas in
the direction of the transfer line axis is balanced by the pressure
distribution on the wall, resulting in negligible components of the
velocity vector (momentum vector) in direction normal to the
reactor axis. The oxidizer is injected on the axis of the reactor
and from the top of the swirling chamber, forming a diffusion flame
in the swirling and combustion chambers, for example in the vessel
neck. The oxidizer jet has a momentum vector directed along the
axis of the reformer, with radial components being substantially
null. The only source of momentum in direction normal to the axis
of the reactor, for the diffusion flame, is the entrained process
gas. Given the negligible component of momentum normal to the axis,
obtained with the shape of the swirling chamber, the flame is not
deflected by the lateral injection of the HCF stream. In these
conditions, the best mixing between the HCF and the oxidizer is
achieved.
[0041] In the circular cross-section embodiment, the distribution
of pressure is no longer able to balance completely the lateral
momentum of the HCF stream from the transfer line, and the axis of
the vortex is not coincident with the vertical axis of the vessel.
The flame is then slightly deflected by the residual lateral
momentum and rotates with the gas, assuming a corkscrew shape. The
deflection as well as the rotation increases from the burner nozzle
to the tip of the flame, due to the increase in entrained gaseous
mass. However the flame deflection can be reduced with a proper
design of the reactor, especially the top chamber elements and
vessel neck. This embodiment then maintains the main advantages of
the invention, with a simplified construction and low cost.
[0042] Summarizing, the advantages of the invention are: gas
distributor no longer needed; a burner shorter than in the prior
art and protected from the gas flow, thus less exposed to
flow-induced vibration; increased mixing rate in the neck of the
reactor, which means a shorter neck and/or a lower pressure drop
for a given mixing length. These and other advantages and features
of the invention will be more evident with the following detailed
description of a preferred embodiment.
FIGURES
[0043] FIG. 1 is a simplified scheme of a reactor according to a
first embodiment of the invention.
[0044] FIG. 2 is a simplified cross section of the swirling chamber
of reactor of FIG. 1.
[0045] FIG. 3 is a scheme of a reactor according to another
embodiment of the invention.
[0046] FIG. 4 is a simplified cross section of the swirling chamber
of reactor of FIG. 3.
[0047] FIG. 5 is a scheme of a reactor according to another
embodiment of the invention.
[0048] FIG. 6 is a cross section of the swirling chamber of reactor
of FIG. 5.
[0049] FIG. 7 is a scheme of a further embodiment of the
invention.
[0050] FIG. 8 is a cross section of the swirling chamber of reactor
of FIG. 7.
[0051] FIG. 9 shows a further variant of the invention, applicable
to embodiments of FIGS. 1 to 8.
[0052] FIGS. 10 and 11 show further examples of the form of the
neck of the reactor or the transition connecting the neck to the
catalytic zone below.
[0053] FIG. 12 shows the flow paths and the flame inside the
combustion chamber of the reactor of FIG. 1, in operation.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0054] Referring to FIGS. 1-2, a reformer 1 is connected to a gas
inlet 2, carrying a hydrocarbon-containing feedstock or HCF stream
G. Said HCF stream G can be obtained from primary reforming of a
hydrocarbon; an offgas of a coke production plant (coke oven gas)
can also form the HCF stream G.
[0055] The gas inlet 2 is tangential, as shown, so that the stream
G enters the reformer 1 with a direction lying in a plane
perpendicular to the vertical axis A-A of the reformer.
[0056] The reformer 1 comprises a vessel 3 containing a catalytic
bed 4, and having a neck 5 where an oxidizer nozzle or burner 6 is
installed. The burner 6, in the shown embodiment, is flushed in a
top cover 7 of the neck 5. The oxidizer fed to the burner 6 can be
air, oxygen-enriched air, pure oxygen, steam and/or a mixture
containing steam, oxygen and carbon dioxide. The neck 5 and vessel
3 are connected by a transition conical wall 8.
[0057] The neck 5 comprises a portion 5a with enlarged cross
section, defining a swirling chamber 10 connected to the HCF inlet
2. The swirling chamber 10 is located below and in communication
with the burner tip 6a, in order to receive the diffusion flame
during operation, and has an open bottom 10b in fluid communication
with the inside of vessel 3 through the remaining portion of neck
5. It should be noted that there is no gas distributor downstream
the gas inlet, so that the open bottom 10b is in direct
communication also with the downstream catalytic zone inside vessel
3. The neck portion under the swirling chamber 10 defines a
combustion chamber B.
[0058] In embodiment of FIGS. 1-2, the swirling chamber 10 is
delimited substantially by a side wall 11 with an internal surface
12 following a log-spiral around the same axis A-A. In other words,
the cross-section of chamber 10 (FIG. 2) appears as a logarithmic
spiral with axis coincident with the axis A-A of the neck 5 and
whole reformer 1.
[0059] One end 12a of the surface 12 matches a wall 2a of the HCF
inlet 2, at the process gas inlet surface S (FIG. 2), while the
opposite end 12b of the same surface 12 is tangential to the
opposite wall 2b of said inlet 2, in correspondence of the same gas
inlet surface S. The log-spiral surface 12, hence, covers an angle
of about 360 degrees. Distance of the surface 12 from axis A-A, due
to the log-spiral profile, decreases progressively from the end 12a
at the gas inlet, towards the end 12b.
[0060] Indicating as r the distance from axis A-A, and .theta.
(theta) the angle from the surface S, the cross-section line of
surface 12 (FIG. 2) follows an equation of the type:
r=ae.sup.b.theta.
where a and b are preferably chosen to match the walls 2a and 2b of
the inlet line 2 at the inlet section S.
[0061] In the simplified embodiment of FIGS. 3 and 4, the surface
12 is cylindrical with the distance from axis A-A remaining
constant. Cross-section of surface 12, in this embodiment, is a
circular arc; as seen in FIG. 4, the angle covered by the surface
12, starting from the gas inlet surface S, is less than 360
degrees. Preferably said angle is more than 270 degrees and more
preferably around 300 degrees.
[0062] Embodiments of FIGS. 5 to 8 have a HCF inlet 2 with a
circular cross section. In this case, the surface 12 has preferably
a semi-circular cross section in the plane perpendicular to the
inlet direction of gas stream G, as shown in FIG. 5.
[0063] The embodiment of the invention where the surface 12 has a
semi-circular cross section and a log-spiral path is best for
avoiding lateral component of the momentum of the process gas flow,
and achieve a substantially axis-symmetric velocity vector field of
the gas entering the combustion chamber B.
[0064] A plane surface 12, however, can also be adopted with the
inlet 2 having a circular cross section (FIG. 7). The simplified
embodiment of FIGS. 3 and 4 can also be used. In this cases, slight
deviation from the axis-symmetric velocity vector field will
occur.
[0065] FIG. 9 shows a further embodiment of the invention, where
the swirling chamber 10 is distanced from top of the neck 5, so
that there is a gap forming a pre-chamber 20 between the tip of the
burner 6, and the chamber 10. Said pre-chamber 20 may be preferred
to provide a low-swirling environment for formation of the
diffusion flame under burner tip 6a.
[0066] FIGS. 10 shows non-limitative examples of the transition
connecting the neck 5 with the vessel 3, wherein the transition
portion 8 is realized as hemispherical dome (left) or cone (right).
FIG. 11 shows a further embodiment of the invention wherein the
neck 5 is conical with increasing cross section from top to bottom.
The forms of the transition portion 8 of FIG. 10, as well as the
conical neck of FIG. 11, are applicable to all embodiments of FIGS.
1 to 9.
[0067] According to one of the applications of the invention, the
reformer 1 is a secondary reformer of a hydrocarbon reforming
equipment. In a further preferred application of the invention,
said hydrocarbon reforming equipment is the front-end of an ammonia
plant, where the reformed gas produced in the secondary reformer 1
is then subject to known treatments such as shift, carbon dioxide
separation and methanation, obtaining a syngas containing nitrogen
and hydrogen in a suitable HN ratio for ammonia synthesis.
[0068] It should be noted that the above detailed description is
referred to a reformer, but the invention is applicable as well to
different kinds of reactors, including autothermal reformers,
secondary reformers, POX gas generators.
[0069] In operation (FIG. 12), the HCF gas stream G enters the
swirling chamber 10 where, due to profile of surface 12, a swirling
motion is imparted to said gas stream G around axis A-A, thus
forming a vortex V with axis coincident with said axis A-A. The
vortex V, through the open bottom 10b, extends in the combustion
chamber B formed by the neck 5 downstream the gas inlet 2. A
diffusion flame F is produced by the oxidizer stream from burner 6
and extends into the combustion chamber B through the swirling
chamber 10.
[0070] Interaction between the flame F, and oxidizer stream, and
the gas vortex V in accordance with the invention, provides a
surprisingly effective mixing between the oxidizer and the process
gas G. Moreover, the flame F is stable and not deflected from axis
A-A, despite the tangential inlet 2 of the gas stream.
[0071] In fact, the vortex V produced in the log-spiral swirling
chamber has an axis-symmetric velocity vector field with a
substantially null component in direction perpendicular to axis
A-A. The momentum of the process gas in the direction of the
transfer line axis is balanced by the pressure distribution on the
surface 12. The vortex V, hence, is unable to transmit any relevant
momentum to the flame F, in any direction other than axis A-A.
Flame F then maintains the axial direction.
[0072] It should be appreciated that the kinetic energy of the HCF
stream is not wasted in an uncontrolled deflection from the
tangential inlet direction of line 2 to the axis of reformer 1, nor
it is dissipated in the passage through a gas distributor. The
energy of the HCF stream is actively used to produce the vortex V
inside the combustion chamber, where the combination of the
oxidizer jet velocity, directed according to axis A-A, and of the
swirled velocity field imparted to the HCF stream by chamber 10,
increase the strength of the mixing layer between the two streams
(gas/oxidizer). Using the same kinetic energy of the entering
stream G allows to feed the oxidizer at a lower pressure or to
shorten the neck 5 for a given velocity of the oxidizer.
[0073] In simplified embodiments of the invention, such as the one
of FIGS. 3 and 4, the distribution of pressure on the surface 12 is
no longer able to completely balance the lateral momentum of the
HCF stream. The axis of vortex V, due to lateral and tangential
inlet of line 2, is not coincident with the axis A-A and the there
is a slight deflection of flame F, which may assume a corkscrew
shape. Said effect of flame deflection can be minimized with a
proper design of the chamber 10 and neck 5. The same apply to the
embodiment of FIG. 7, due to circular transfer line 2 and plane
surface 12. These embodiments, however, are still able to improve
the gas/oxidizer mixing compared to the prior art, they do not
require the gas distributor as well, and may be chosen for reasons
of cost and simplicity.
* * * * *