U.S. patent application number 12/176202 was filed with the patent office on 2009-05-28 for flameless combustion heater.
Invention is credited to Karl Gregory ANDERSON, Abdul Wahid Munshi, Peter Veenstra.
Application Number | 20090136879 12/176202 |
Document ID | / |
Family ID | 39865135 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090136879 |
Kind Code |
A1 |
ANDERSON; Karl Gregory ; et
al. |
May 28, 2009 |
FLAMELESS COMBUSTION HEATER
Abstract
A flameless combustion heater is described, that comprises an
oxidation conduit and a fuel conduit positioned within the
oxidation conduit to form an oxidation zone having an inlet and an
outlet, said fuel conduit having a plurality of openings that
provide fluid communication from within the fuel conduit to the
oxidation conduit wherein the longitudinal axis of at least one
opening forms an oblique angle with the inner surface of the
oxidation conduit. A method for providing heat to a process conduit
is described, that comprises providing an oxidation conduit;
providing a fuel conduit having a plurality of openings that
provide fluid communication from within the fuel conduit to the
oxidation conduit wherein the longitudinal axis of at least one
opening forms an oblique angle with the inner surface of the
oxidation conduit; providing a process conduit in a heat exchange
relationship with the oxidation conduit; introducing fuel into the
fuel conduit; introducing an oxidant into the oxidation conduit;
and introducing the fuel into the oxidation conduit through the
plurality of openings such that flameless combustion occurs in the
oxidation conduit.
Inventors: |
ANDERSON; Karl Gregory;
(Missouri City, TX) ; Munshi; Abdul Wahid;
(Houston, TX) ; Veenstra; Peter; (Amsterdam,
NL) |
Correspondence
Address: |
SHELL OIL COMPANY
P O BOX 2463
HOUSTON
TX
772522463
US
|
Family ID: |
39865135 |
Appl. No.: |
12/176202 |
Filed: |
July 18, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60950938 |
Jul 20, 2007 |
|
|
|
Current U.S.
Class: |
431/2 ; 431/268;
431/326 |
Current CPC
Class: |
F23C 99/00 20130101;
F23C 2900/99001 20130101; Y02E 20/342 20130101; Y02E 20/348
20130101; Y02E 20/34 20130101; F23D 14/66 20130101; F23C 13/00
20130101 |
Class at
Publication: |
431/2 ; 431/268;
431/326 |
International
Class: |
F23Q 11/04 20060101
F23Q011/04; F23K 5/00 20060101 F23K005/00; F23L 15/00 20060101
F23L015/00 |
Claims
1. A flameless combustion heater comprising an oxidation conduit
and a fuel conduit having a plurality of openings that provide
fluid communication from within the fuel conduit to the oxidation
conduit wherein the longitudinal axis of at least one opening forms
an oblique angle with the inner surface of the oxidation
conduit.
2. A heater as claimed in claim 1 wherein the longitudinal axis of
the at least one opening forms an acute angle with the inner
surface of the oxidation conduit, as measured from the inlet end of
the fuel conduit.
3. A heater as claimed in claim 2 wherein the angle is less than
about 80 degrees.
4. A heater as claimed in claim 2 wherein the angle is greater than
about 20 degrees.
5. A heater as claimed in claim 2 wherein the angle is from about
35 to about 75 degrees.
6. A heater as claimed in claim 2 wherein the angle is from about
50 to about 70 degrees.
7. A heater as claimed in claim 1 wherein the longitudinal axis of
the at least one opening forms an obtuse angle with the inner
surface of the oxidation conduit, as measured from the inlet end of
the fuel conduit.
8. A heater as claimed in claim 7 wherein the angle is greater than
about 100 degrees.
9. A heater as claimed in claim 7 wherein the angle is less than
about 160 degrees.
10. A heater as claimed in claim 7 wherein the angle is from about
105 to about 145 degrees.
11. A heater as claimed in claim 7 wherein the angle is from about
110 to about 130 degrees.
12. A heater as claimed in claim 1 wherein a majority of the
openings form oblique angles with the inner surface of the
oxidation conduit.
13. A heater as claimed in claim 1 wherein all of the openings form
oblique angles with the inner surface of the oxidation conduit.
14. A heater as claimed in claim 1 wherein the longitudinal axis of
the at least one opening does not intersect the longitudinal axis
of the fuel conduit.
15. A heater as claimed in claim 14 wherein the distance between
the longitudinal axis of the opening and the longitudinal axis of
the fuel conduit is greater than one-fourth of the internal radius
of the fuel conduit.
16. A heater as claimed in claim 14 wherein the distance between
the longitudinal axis of the opening and the longitudinal axis of
the fuel conduit is greater than one-half of the internal radius of
the fuel conduit.
17. A heater as claimed in claim 1 wherein the longitudinal axis of
one opening forms a first angle with the inner surface of the
oxidation conduit and the longitudinal axis of another opening
forms a second angle with the inner surface of the oxidation
conduit that is not equal to the first angle.
18. A heater as claimed in claim 1 wherein at least one opening has
a circular cross-section.
19. A heater as claimed in claim 1 wherein one opening has a
cross-sectional area that is greater than the cross-sectional area
of another opening.
20. A heater as claimed in claim 1 further comprising an oxidant
conduit, the oxidant conduit having an inlet for oxidant and an
outlet for preheated oxidant that is in fluid communication with
the inlet of the oxidation conduit.
21. A heater as claimed in claim 1 further comprising a process
conduit in a heat exchange relationship with the oxidation
conduit.
22. A heater as claimed in claim 21 wherein the process conduit is
adapted for carrying out an endothermic chemical reaction.
23. A heater as claimed in claim 1 further comprising a preheater
in fluid communication with the flameless combustion heater,
wherein the preheater is capable of preheating the oxidant to a
temperature at which when the oxidant and fuel are mixed in the
oxidation conduit, the temperature of the mixture exceeds the
auto-ignition temperature of the mixture.
24. A heater as claimed in claim 21 wherein the oxidant conduit is
in heat exchange relationship with the process conduit.
25. A heater as claimed in claim 1 wherein the heater further
comprises an oxidation catalyst.
26. A heater as claimed in claim 25 wherein the oxidation catalyst
is selected from the group consisting of palladium, platinum and
mixtures thereof.
27. A method for providing heat to a process conduit comprising:
providing an oxidation conduit; providing a fuel conduit having a
plurality of openings that provide fluid communication from within
the fuel conduit to the oxidation conduit wherein the longitudinal
axis of at least one opening forms an oblique angle with the inner
surface of the oxidation conduit; providing a process conduit in a
heat exchange relationship with the oxidation conduit; introducing
fuel into the fuel conduit; introducing an oxidant into the
oxidation conduit; and introducing the fuel into the oxidation
conduit through the plurality of openings such that flameless
combustion occurs in the oxidation conduit.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/950,938, filed Jul. 20, 2007 which is hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a flameless combustion heater and
a method for providing heat to a process.
BACKGROUND OF THE INVENTION
[0003] Flameless combustion heaters are described in U.S. Pat. No.
7,025,940. The patent describes a process heater utilizing
flameless combustion, which is accomplished by preheating a fuel
and combustion air to a temperature above the auto-ignition
temperature of the mixture. The fuel is introduced in relatively
small increments over time through a plurality of orifices in a
fuel gas conduit, which provide communication between the fuel gas
conduit and an oxidation reaction chamber. As described in the
patent, a process chamber is in heat exchange relationship with the
oxidation reaction chamber.
[0004] Flameless combustion heaters can encounter problems related
to the fuel conduit and the openings that provide for communication
from within the fuel gas conduit to the oxidation reaction chamber.
Conventional flameless combustion heaters have openings that have a
longitudinal axis perpendicular to the inner surface of the
oxidation conduit.
[0005] The fuel passing through these perpendicular openings has a
tendency to impinge directly on the inner surface of the oxidation
conduit. Thus, a minimum distance is typically maintained between
the outside of the fuel conduit and the inside of the oxidation
conduit to reduce hot spots on the oxidation conduit wall. The
oxidant flow may be increased to address this tendency to impinge,
but that results in disadvantages such as excessive pressure drop.
Further, the fuel exiting the perpendicular openings may not mix
well with the oxidant. This incomplete mixing may occur immediately
downstream of the opening.
[0006] The heat provided by the flameless combustion is to a
certain extent typically concentrated in the same radial
orientation and directly downstream of the opening. This can result
in uneven heating of the heater materials of construction that
leads to thermal expansion that tends to bend the fuel and
oxidation conduits. Additionally, this results in uneven heating of
the material to be heated by the heater.
SUMMARY OF THE INVENTION
[0007] The invention provides a flameless combustion heater
comprising an oxidation conduit and a fuel conduit having a
plurality of openings that provide fluid communication from within
the fuel conduit to the oxidation conduit wherein the longitudinal
axis of at least one opening forms an oblique angle with the inner
surface of the oxidation conduit.
[0008] The invention further provides a method for providing heat
to a process conduit comprising: providing an oxidation conduit;
providing a fuel conduit having a plurality of openings that
provide fluid communication from within the fuel conduit to the
oxidation conduit wherein the longitudinal axis of at least one
opening forms an oblique angle with the inner surface of the
oxidation conduit; providing a process conduit in a heat exchange
relationship with the oxidation conduit; introducing fuel into the
fuel conduit; introducing an oxidant into the oxidation conduit;
and introducing the fuel into the oxidation conduit through the
plurality of openings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 depicts a two-tube flameless combustion heater with
acute angled openings.
[0010] FIG. 1a depicts a cross-sectional view of the heater of FIG.
1.
[0011] FIG. 1b depicts a cross-sectional view of the heater of FIG.
1.
[0012] FIG. 2 depicts a three-tube flameless combustion heater with
acute angled openings.
[0013] FIG. 2a depicts a cross-sectional view of the heater of FIG.
2.
[0014] FIG. 3 depicts a four-tube flameless combustion heater with
acute angled openings.
[0015] FIG. 3a depicts a cross-sectional view of the heater of FIG.
3.
[0016] FIG. 4 depicts a two-tube flameless combustion heater with
obtuse angled openings.
[0017] FIG. 4a depicts a cross-sectional view of the heater of FIG.
4.
[0018] FIG. 4b depicts a cross-sectional view of the heater of FIG.
4.
[0019] FIG. 5 depicts a three-tube flameless combustion heater with
obtuse angled openings.
[0020] FIG. 5a depicts a cross-sectional view of the heater of FIG.
5.
[0021] FIG. 6 depicts a four-tube flameless combustion heater with
obtuse angled openings.
[0022] FIG. 6a depicts a cross-sectional view of the heater of FIG.
6.
[0023] FIG. 7 depicts a two-tube flameless combustion heater with
tangential openings.
[0024] FIG. 7a depicts a cross-sectional view of the heater of FIG.
7.
[0025] FIG. 8 depicts a three-tube flameless combustion heater with
tangential openings.
[0026] FIG. 8a depicts a cross-sectional view of the heater of FIG.
8.
[0027] FIG. 9 depicts a four-tube flameless combustion heater with
tangential openings.
[0028] FIG. 9a depicts a cross-sectional view of the heater of FIG.
9.
[0029] FIG. 10 depicts an embodiment that uses a flameless
combustion heater in an ethylbenzene dehydrogenation process.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The invention provides a flameless combustion heater that is
used in the direct transfer of heat energy released by the
flameless combustion of fuel. The heater has many possible uses and
applications including heating underground formations and heating
process streams. The flameless combustion heater is especially
useful in conjunction with processes that carry out endothermic
reactions, for example, dehydrogenation of alkylaromatic compounds
and steam methane reforming. The invention provides a flameless
combustion heater with at least one opening in the fuel conduit
that forms an oblique angle with the inner surface of the oxidation
conduit. Angled openings reduce the problems associated with fuel
impingement on the inner surface of the oxidation conduit and
improve the mixing of fuel and oxidant in the oxidation
conduit.
[0031] Flameless combustion in a heater can be accomplished by
preheating an oxidant stream and a fuel stream sufficiently that
when the two streams are combined the temperature of the mixture
exceeds the auto-ignition temperature of the mixture, but the
temperature of the mixture is less than a temperature that would
result in the oxidation upon mixing being limited by the rate of
mixing as described in U.S. Pat. No. 7,025,940 which is herein
incorporated by reference. The auto ignition temperature of the
mixture depends on the types of fuel and oxidant and the
fuel/oxidant ratio. The auto ignition temperature of mixtures used
in a flameless combustion heater may be in a range of from
850.degree. C. to 1400.degree. C. The auto ignition temperature may
be reduced if an oxidation catalyst is employed in the heater
because this type of catalyst effectively lowers the auto-ignition
temperature of the mixture.
[0032] The fuel conduit provides for the controlled rate of fuel
introduction into an oxidation conduit in a manner so as to provide
for a desired heat release. The heat release is determined in part
by the location and number of openings, which can be tailored to
each heater application. The heat release may be constant over the
length of the heater, or it may be decreasing or increasing over
the length of the heater.
[0033] Because there is no visible flame associated with flameless
combustion of a fuel, the flameless combustion reaction occurs at a
lower temperature than that observed in conventional fired heaters.
Due to the lower temperatures observed, and the efficiency of
direct heating, the heater may be designed using lower cost
materials resulting in reduced capital expenditure.
[0034] The flameless combustion heater has two main elements: an
oxidation conduit and a fuel conduit. The oxidation conduit may be
a tube or pipe that has an inlet for oxidant, an outlet for
oxidation products and a flow path between the inlet and outlet.
Suitable oxidants include air, oxygen, and nitrous oxide. The
oxidant that is introduced into the oxidation conduit may be
preheated such that when mixed with fuel, the mixture is at a
temperature above the auto-ignition temperature of the mixture. The
oxidant may be heated externally to the flameless combustion
heater.
Alternatively, the oxidant may be heated inside the heater by heat
exchange with any of the streams inside the heater. The oxidation
conduit may have an internal diameter of from about 2 cm to about
20 cm. The oxidant conduit may however be larger or smaller than
this range depending on the heater requirements.
[0035] The fuel conduit transports fuel into the heater and
introduces it into the oxidation conduit. The fuel conduit may be a
tube or pipe that has an inlet for fuel and a plurality of openings
that provide fluid communication from within the fuel conduit to
the oxidation conduit. The fuel conduit may be located within and
surrounded by the oxidation conduit. The fuel passes through the
openings and into the oxidation conduit where it mixes with the
oxidant and results in flameless combustion. The fuel conduit may
have an internal diameter of from about 1 cm to about 10 cm,
preferably from about 1.5 cm to 5 cm. Depending on the design,
however, the fuel conduit may have a diameter greater than 10 cm or
less than 1 cm.
[0036] The geometry, orientation and location of the openings in
the fuel conduit may be designed to overcome problems that arise
due to the fluid and mixing dynamics of the heater system. The
openings can be drilled or cut into the wall of the fuel conduit.
The wall of the fuel conduit typically has a thickness of from
about 0.25 cm to about 2.5 cm. The openings may have cross sections
that are circular, elliptical, rectangular, of another shape, or
even irregularly shaped. The openings preferably have a circular
cross-section.
[0037] The openings may have a cross-sectional area of from about
0.001 cm.sup.2 to about 2 cm.sup.2, preferably from about 0.03
cm.sup.2 to about 0.2 cm.sup.2. The size of the openings is
determined by the desired rate of fuel introduction into the
oxidation conduit, but openings that are too small may result in
plugging. The openings may be located along the fuel conduit at a
distance of from 1 cm to 100 cm in the axial direction from any
other opening. The openings are preferably spaced from 15 cm to 50
cm apart in the axial direction. The openings may be positioned in
their respective radial planes at different orientations along the
length of the fuel conduit. For example, the position of the
openings may alternate 180 degrees in the radial plane along the
length of the fuel conduit, or they may alternate 120 degrees or 90
degrees. Therefore the position of the openings in the fuel conduit
may be such that their orientation in the radial plane alternates
along the length of the fuel conduit with their orientations
separated by 30 degrees to 180 degrees. It is preferred for the
radial orientation of the openings to alternate at from 60 degrees
to 120 degrees along the length of the fuel conduit.
[0038] In one embodiment, a sintered plate may be used in addition
to openings to provide fluid communication from the fuel conduit to
the oxidation zone, and the openings in a sintered plate may have a
diameter on the order of 10-100 microns.
[0039] Different openings along the length of the heater typically
have the same cross-sectional area. In the alternative, the
cross-sectional area of the openings may be different to provide a
desired heat release. Additionally the spacing between openings
along the fuel conduit may be different to provide a desired heat
release. The openings are typically the same shape. In the
alternative, the openings may be different shapes.
[0040] The openings each have a longitudinal axis defined by the
line that connects the centers of the cross-sections at each end of
the opening. The fuel conduit also has a longitudinal axis defined
by the line connecting the centers of the cross sections of the
conduit.
[0041] The term acute angle as used herein is defined as an angle
between 0 and 90 degrees. The term obtuse angle as used herein is
defined as an angle between 90 and 180 degrees. The term oblique
angle as used herein is defined as an angle that is either acute or
obtuse.
[0042] The flameless combustion heater may additionally comprise a
process conduit that carries a process fluid where the process
conduit is in heat exchange relationship with the oxidation
conduit. The inclusion of a process conduit in the heater allows
for direct heating of a process stream. The process conduit may
optionally be used to carry out a chemical reaction. The process
conduit may contain catalyst to facilitate the chemical reaction.
This heater is especially useful for carrying out endothermic
reactions because heat is added directly to the process during the
reaction. For example, this heater may be incorporated into the
dehydrogenation reactor to directly heat the dehydrogenation
reaction of ethylbenzene to styrene.
[0043] The flameless combustion heater may optionally comprise an
oxidant conduit. The oxidant conduit has an inlet for oxidant and
an outlet for preheated oxidant that is in fluid communication with
the inlet of the oxidation conduit. The oxidant conduit is in a
heat exchange relationship with the oxidation conduit and/or the
process conduit, which provide direct heat to preheat the oxidant
to a temperature sufficient that when mixed with fuel in the
oxidation conduit the mixture is at or above the auto ignition
temperature.
[0044] A preheater may be used to preheat the oxidant before it
enters the heater. A preheater may be any apparatus or method that
provides heat. The preheater may for example be a conventional heat
exchanger or a flameless combustion heater.
[0045] Preferred embodiments of the flameless combustion heater
will be described further in relation to the Figures presented in
this application.
[0046] FIGS. 1-3 depict embodiments of flameless combustion heaters
with what is hereinafter referred to as acute angled openings. FIG.
1 depicts a flameless combustion heater (10) that has a fuel zone
(11) formed by fuel conduit (12) and an oxidation zone (13) formed
by oxidation conduit (14). This type of heater is referred to as a
two-tube heater. In this embodiment, the fuel conduit (12) is a
cylindrical pipe that has an inlet (24) for fuel and a plurality of
openings (20). The longitudinal axes (22) of the openings form
acute angles (34) with the inner surface of the oxidation conduit
(14). Oxidation conduit (14) is a cylindrical pipe concentrically
positioned around fuel conduit (12) that has an inlet (26) for
preheated oxidant and an outlet (30) for combustion products. In
the alternative the oxidant may be introduced at (30) and the
combustion products may exit the heater at (26), which provides for
a countercurrent flow of the fuel and oxidant. Countercurrent flows
of fuel and oxidant can provide better mixing of the fuel and
oxidant than co-current flows. The direction of the flows may be
changed to suit the desired mixing and heat release of the specific
heater application. During operation, the fuel enters fuel zone
(11) via inlet (24) and then is mixed with preheated oxidant in
oxidation zone (13) after it passes through the angled openings
(20). The openings (20) are angled in the direction opposite fuel
inlet (24).
[0047] The openings are such that the longitudinal axis of an
opening forms an angle of less than ninety degrees with the inner
surface of the oxidation conduit as measured from the fuel inlet
(24) of the fuel conduit (12). These openings are hereinafter
referred to as acute angled openings. The longitudinal axis of an
opening preferably forms an angle of from twenty to eighty degrees
with the inner surface of the oxidation conduit, more preferably
from thirty to seventy-five degrees and most preferably from fifty
to seventy degrees.
[0048] FIG. 1a is a cross-sectional view of FIG. 1 taken along line
A-A. This figure depicts one embodiment where the longitudinal axis
of an opening intersects the longitudinal axis of the fuel
conduit.
[0049] FIG. 1b is a cross-sectional view of FIG. 1 taken along line
B-B. This figure depicts another embodiment where the longitudinal
axis of an opening is at a distance (40) from the longitudinal axis
of the fuel conduit such that the axes do not intersect. These
openings are hereinafter referred to as acute angled tangential
openings.
[0050] A heater may have a cross-sectional view as depicted in FIG.
1a (acute angled openings) or a cross-sectional view as depicted in
FIG. 1b (acute angled tangential openings). In the alternative, a
heater may have a combination of acute angled openings and acute
angled tangential openings and the cross-sectional views of FIG. 1a
and FIG. 1b would represent the cross-sectional view of the same
heater at different points in the heater.
[0051] An acute angled opening is angled such that the fuel exiting
the opening is directed in the direction opposite the fuel conduit
inlet. Acute angled openings result in lower peak temperatures,
which reduces the risk to heater materials and allows less
expensive materials to be used in heater construction. Further,
acute angled openings allow the distance between the fuel conduit
and the oxidation conduit to be reduced resulting in a smaller
heater and reduced capital expenditure.
[0052] Acute angled tangential openings provide for more even heat
release in the radial direction. The use of acute angled tangential
openings also provides a more even heating profile and improved
mixing of the fuel and oxidant. The use of acute angled tangential
openings also allows the flameless combustion heater to be operated
at a higher fuel/air ratio than a flameless combustion heater with
typical perpendicular openings. When less air is needed, the
oxidation conduit can be smaller, thus reducing the capital
expenditure.
[0053] FIG. 2 depicts a flameless combustion heater (10) that has a
fuel conduit (12), an oxidation conduit (14), and a process conduit
(16). This type of heater is referred to as a three-tube heater and
may be used for direct heating of a process fluid. The three-tube
heater depicted in FIG. 2 is similar to FIG. 1, and the fuel
conduit and oxidation conduit are the same. In FIG. 2, however, a
process zone (15) is formed by process conduit (16). Process
conduit (16), is a cylindrical pipe that has an inlet (32) for a
process stream and an outlet (28) for a heated process stream.
Alternately, the process stream may enter at (28) and exit the
process conduit at (32) to provide a process flow co-current with
the oxidation conduit flow.
[0054] FIG. 2a is a cross-sectional view of FIG. 2 taken along line
A-A. FIG. 2a depicts an embodiment where the longitudinal axis of
the opening intersects the longitudinal axis of the fuel conduit.
Another embodiment, not shown, comprises an opening where the
longitudinal axis of an opening is at a distance from the
longitudinal axis of the fuel conduit such that the axes do not
intersect.
[0055] FIG. 3 depicts a flameless combustion heater (100) that has
a fuel conduit (102), an oxidation conduit (104), a process conduit
(108), and an oxidant conduit (106). The fuel zone (111) is formed
by fuel conduit (102) that is a cylindrical pipe or tube with
angled openings (126) along the pipe. The oxidation zone (113) is
formed by oxidation conduit (104) that is cylindrical and
concentric to the fuel conduit. The process zone (117) is formed by
process conduit (108), and it may be a cylindrical pipe or the
shell side of a shell and tube heat exchanger. The oxidant zone
(115) is formed by oxidant conduit (106) that is cylindrical and
concentric to the oxidation conduit. During operation, the fuel
enters the fuel conduit at inlet (110) and exits the fuel conduit
at the angled openings (126). The angled openings (126) are angled
in the direction away from the fuel inlet (110). The oxidant enters
the oxidant conduit at oxidant inlet (114) and exits the oxidant
conduit at oxidation conduit inlet (120). The oxidant is preheated
in oxidant zone (115). The preheated oxidant is mixed with the fuel
from openings (126) and the combustion products exit the heater at
oxidation conduit outlet (112). A process stream may enter at (116)
and exit at (118) or it may enter at (118) and exit at (116).
[0056] This embodiment is different from that shown in FIGS. 1 and
2 in some respects. The oxidant is preheated inside the heater
because it is introduced into the oxidant conduit that is in a heat
exchange relationship with the oxidation conduit and the process
conduit. The oxidant may also be preheated before being introduced
into the oxidant conduit. The process conduit is in heat exchange
relationship with a portion of the oxidant and oxidation conduit.
These different embodiments provide for more freedom to design the
heater application to meet the requirements of the process and
incorporate design features to recover additional heat from the
combustion products of the flameless combustion.
[0057] FIG. 3a is a cross-sectional view of FIG. 3 taken along line
A-A. This figure depicts one embodiment where the longitudinal axis
of an opening intersects the longitudinal axis of the fuel conduit.
Another embodiment, not shown, comprises an opening where the
longitudinal axis of an opening is at a distance from the
longitudinal axis of the fuel conduit such that the axes do not
intersect.
[0058] FIGS. 4-6 depict embodiments of flameless combustion heaters
with what is hereinafter referred to as obtuse angled openings.
FIG. 4 depicts a flameless combustion heater (10) that is similar
to the two-tube flameless combustion heater depicted in FIG. 1,
although the openings are angled in a different direction. The
angled openings (20) are angled in the direction towards the fuel
conduit inlet.
[0059] The openings are such that the longitudinal axis of an
opening forms an angle of greater than ninety degrees with the
inner surface of the oxidation conduit as measured from the inlet
end of the fuel conduit. These openings are hereinafter referred to
as obtuse angled openings. The longitudinal axis of an opening
preferably forms an angle of from 100.degree. to 160.degree. with
the inner surface of the oxidation conduit, more preferably from
105.degree. to 145.degree. and most preferably from 110.degree. to
130.degree..
[0060] The longitudinal axis of an opening may intersect the
longitudinal axis of the fuel conduit as depicted in FIG. 4a. In
the alternative, the longitudinal axis of an opening may be at a
distance (40) from the longitudinal axis of the fuel conduit such
that the axes do not intersect, as depicted in FIG. 4b, and such
openings are hereinafter referred to as obtuse angled tangential
openings. Obtuse angled tangential openings provide for similar
benefits as acute angled tangential openings.
[0061] Obtuse angled openings typically result in increased
turbulence of the fuel flow and mixing with the oxidant in the
oxidation conduit that improves the flameless combustion reaction.
In addition, obtuse angled openings provide many of the same
benefits that acute angled openings provide, for example, allowing
the distance between the fuel conduit and the oxidation conduit to
be reduced resulting in a smaller heater and reduced capital
expenditure.
[0062] FIG. 5 depicts a flameless combustion heater (10) that is
similar to the three-tube flameless combustion heater depicted in
FIG. 2. FIG. 5 however depicts obtuse angled openings in the heater
as described above. FIG. 5a is a cross-sectional view of FIG. 5
taken along line A-A.
[0063] FIG. 6 depicts a flameless combustion heater (100) that is
similar to the four-tube flameless combustion heater depicted in
FIG. 3. FIG. 6 however depicts obtuse angled openings in the
heater. FIG. 6a is a cross-sectional view of FIG. 6 taken along
line A-A.
[0064] FIGS. 7-9 depict embodiments of flameless combustion heaters
with what is hereinafter referred to as tangential openings. FIG. 7
depicts a flameless combustion heater (10) that is similar to the
two-tube flameless combustion heater depicted in FIG. 1, although
the openings are angled differently. The tangential openings 20 are
not angled in the direction of the fuel conduit inlet or outlet.
FIG. 7a is a cross-sectional view of FIG. 7 taken along line
A-A.
[0065] The tangential openings are such that the longitudinal axis
of an opening is at a distance (40) from the longitudinal axis of
the fuel conduit such that the axes do not intersect. The distance
between the longitudinal axis of the opening and the longitudinal
axis of the fuel conduit may be greater than one-fourth of the
internal radius of the fuel conduit, preferably greater than
one-half of the internal radius of the fuel conduit and more
preferably greater than three-fourths of the internal radius of the
fuel conduit.
[0066] Tangential openings provide for more even heat release in
the radial direction, similarly to acute and obtuse angled
tangential openings.
[0067] FIG. 8 depicts a flameless combustion heater (10) that is
similar to the three-tube flameless combustion heater depicted in
FIG. 2. FIG. 8 however depicts tangential openings in the heater as
described above. FIG. 8a is a cross-sectional view of FIG. 8 taken
along line A-A.
[0068] FIG. 9 depicts a flameless combustion heater (100) that is
similar to the four-tube flameless combustion heater depicted in
FIG. 3. FIG. 9 however depicts tangential openings in the heater.
FIG. 9a is a cross-sectional view of FIG. 9 taken along line
A-A.
[0069] The flameless combustion heater may be operated at a variety
of conditions depending on the particular configuration of heater
and the heater application. Various examples and conditions are
described in U.S. Pat. No. 5,255,742 and U.S. Pat. No. 7,025,940,
which are herein incorporated by reference.
[0070] FIG. 10 depicts the use of a flameless combustion heater in
an ethylbenzene dehydrogenation unit. A process feedstock
containing steam and ethylbenzene is fed to the dehydrogenation
reactor (204) via conduit (202). The dehydrogenation reactor (204)
contains a suitable dehydrogenation catalyst, which may be an iron
oxide based catalyst, and provides means for contacting the process
feedstock with the dehydrogenation catalyst. A dehydrogenation
reactor effluent is discharged from dehydrogenation reactor (204)
through conduit (206) and introduced into the flameless combustion
heater (208) through its process fluid inlet (210).
[0071] Because the dehydrogenation reaction is an endothermic
reaction, the dehydrogenation reactor effluent will have a lower
temperature than that of the process feedstock to the
dehydrogenation reactor (204). The flameless combustion heater
(208) is used to heat the dehydrogenation reactor effluent before
it is introduced into the second stage dehydrogenation reactor
(212). The heated process fluid passes from the flameless
combustion heater (208) through its discharge outlet (214) and
conduit (216) to be introduced as a feed into the second stage
dehydrogenation reactor (212). A dehydrogenation reactor effluent
is discharged from the second stage reactor (212) through conduit
(218). The dehydrogenation process may be carried out with more
than two reactors in which case a flameless combustion heater may
be placed in front of each additional reactor.
[0072] Fuel is introduced to the flameless combustion heater (208)
through conduit (220) and through fuel inlet (222). Oxidant is
introduced into the heater (208) through conduit (224) and through
oxidant inlet (226). The combustion products are discharged from
the flameless combustion heater (208) through conduit (228).
[0073] A preheater (230) is shown in this embodiment to preheat the
oxidant before it is passed into the heater (208). This is an
optional part of the heater system.
[0074] The flameless combustion heater described herein can be used
in any application with any variation of the described details of
opening location and geometry.
* * * * *