U.S. patent application number 13/473239 was filed with the patent office on 2013-01-03 for combustion of volatile organic compounds to co2 and h2o with low nox formation.
This patent application is currently assigned to CONOCOPHILLIPS COMPANY. Invention is credited to Joe D. Allison, Devadas Panjala.
Application Number | 20130004903 13/473239 |
Document ID | / |
Family ID | 47391021 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130004903 |
Kind Code |
A1 |
Allison; Joe D. ; et
al. |
January 3, 2013 |
Combustion of Volatile Organic Compounds to CO2 and H2O with Low
NOx Formation
Abstract
A process of combusting a gaseous volatile organic compound over
a modified alumina catalyst at a temperature below 5.degree. C.
while exothermically producing CO.sub.2 and H.sub.2O at a
temperature from about 5.degree. C. to about 1100.degree. C.
Inventors: |
Allison; Joe D.;
(Bartlesville, OK) ; Panjala; Devadas; (Pearland,
TX) |
Assignee: |
CONOCOPHILLIPS COMPANY
Houston
TX
|
Family ID: |
47391021 |
Appl. No.: |
13/473239 |
Filed: |
May 16, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61502142 |
Jun 28, 2011 |
|
|
|
Current U.S.
Class: |
431/2 ;
431/11 |
Current CPC
Class: |
F23C 13/08 20130101;
F28D 21/001 20130101 |
Class at
Publication: |
431/2 ;
431/11 |
International
Class: |
F23C 13/08 20060101
F23C013/08; F23C 10/22 20060101 F23C010/22 |
Claims
1) A process comprising: a) combusting a gaseous volatile organic
compound over a modified alumina catalyst at a temperature below
5.degree. C.; b) exothermically producing CO.sub.2 and H.sub.2O at
a temperature from about below 5.degree. C. to about 1100.degree.
C.; and c) adding a fuel gas to supplement the heat generated from
the combustion of the volatile organic compound.
2) The process of claim 1, wherein the modified alumina catalyst
comprises from about 0.005 wt % to about 5 wt % Pt.
3) The process of claim 1, wherein the modified alumina catalyst
comprises a modified alpha-alumina cloth support.
4) The process of claim 1, wherein the modified alumina catalyst
comprises a MgO modified alpha-alumina cloth support or a gamma
alumina support.
5) The process of claim 1, wherein NOx is not substantially formed
during the production of CO.sub.2 and H.sub.2O.
6) The process of claim 1, wherein the gaseous volatile organic
compounds are selected from a group consisting of: methanol,
ethanol, propanol, n-heptane, gasoline, crude oil,
n-C.sub.1-C.sub.6 paraffins, i-butanol, n-hexane, toluene, acetone,
hydrogen and combinations thereof.
7) The process of claim 1, wherein the fuel gas is methane, natural
gas or a refinery fuel gas.
8) The process of claim 1, wherein the oxygen containing gas are
selected from a group consisting of: oxygen air, oxygen enriched
air, nitrogen enriched air or combinations thereof.
9) The process of claim 1, wherein the oxygen content can range
from 1% to 100%.
10) A process comprising: a) combusting a gaseous volatile organic
compound selected from a group consisting of: methanol, ethanol,
propanol, n-heptane, gasoline, crude oil, n-C.sub.1-C.sub.6
paraffins, i-butanol, n-hexane, toluene, acetone, hydrogen and
combinations thereof in an oxygen containing gas, over a modified
alumina catalyst at a temperature below 5.degree. C. wherein the
oxygen containing gas consists of a group selected from: oxygen,
air, nitrogen and combinations thereof; b) exothermically producing
CO.sub.2 and H.sub.2O at a temperature from about 5.degree. C. to
about 1100.degree. C. while not substantially forming NOx; wherein
the modified alumina catalyst is comprises from about 0.005 wt % to
about 5 wt % Pt and a MgO modified alpha-alumina cloth support or a
gamma alumina support; and c) adding a fuel gas to supplement the
heat from the combustion of the volatile organic compound.
11) A process comprising: a) using a heat exchanger comprising: i.
a heat exchanger; and ii. a thin layer of a modified alumina
catalyst bed in contact with the heat exchanger, b) combusting a
gaseous volatile organic compound with an oxygen containing gas
over the modified alumina catalyst at a temperature below 5.degree.
C.; and c) exothermically producing CO.sub.2 and H.sub.2O while
simultaneously raising the temperature of the heat exchanger from
about 5.degree. C. to about 1100.degree. C.
12) The process of claim 10, wherein the modified alumina catalyst
comprises from about 0.005 wt % to about 5 wt % Pt.
13) The process of claim 10, wherein the modified alumina catalyst
comprises a modified alpha-alumina cloth support or a gamma alumina
support.
14) The process of claim 10, wherein the modified alumina catalyst
comprises a MgO modified alpha-alumina cloth support or a gamma
alumina support.
15) The process of claim 10, wherein NOx is not substantially
formed during the production of CO.sub.2 and H.sub.2O.
16) The process of claim 10, wherein the gaseous volatile organic
compounds are selected from a group consisting of: methanol,
ethanol, propanol, n-heptane, gasoline, crude oil,
n-C.sub.1-C.sub.6 paraffins, i-butanol, n-hexane, toluene, acetone,
hydrogen and combinations thereof.
17) The process of claim 10, wherein the oxygen containing gas are
selected from a group consisting of: oxygen air, oxygen enriched
air, nitrogen enriched air or combinations thereof.
18) The process of claim 10, wherein the oxygen content can range
from 1% to 100%.
19) The process of claim 10, wherein the heat exchanger is
connected to a preheater or a steam generator.
20) A process comprising: a) using a heat exchanger comprising: i.
a heat exchanger; and ii. a thin layer of a modified alumina
catalyst bed in contact with the heat exchanger, b) combusting a
gaseous volatile organic compound selected from a group consisting
of: methanol, ethanol, propanol, n-heptane, gasoline, crude oil,
n-C.sub.1-C.sub.6 paraffins, i-butanol, n-hexane, toluene, acetone,
hydrogen and combinations thereof in an oxygen containing gas, over
the modified alumina catalyst at a temperature below 5.degree. C.
wherein the oxygen containing gas are selected from a group
consisting of: oxygen, air, nitrogen and combinations thereof; c)
adding a fuel gas to supplement the heat from the combustion of the
volatile organic compound; d) exothermically producing CO.sub.2 and
H.sub.2O at a temperature from about 5.degree. C. to about
1100.degree. C. while not substantially forming NOx; and wherein
the modified alumina catalyst is comprises from about 0.005 wt % to
about 5 wt % Pt and a MgO modified alpha-alumina cloth support.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a non-provisional application which
claims the benefit of and priority to U.S. Provisional Application
Ser. No. 61/502,142 filed Jun. 28, 2011, entitled "Combustion of
Volatile Organic Compounds to CO2 and H2O with Low NOx Formation,"
which is hereby incorporated by reference in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None.
FIELD OF THE INVENTION
[0003] A process of combusting gaseous volatile organic compounds
with low NOx formation.
BACKGROUND OF THE INVENTION
[0004] The preheating of gases and/or feedstocks in a refinery (or
other plant) is an important step in overall plant operations. Most
plant processes operate at an elevated temperature that requires
preheating the gases and/or feedstocks. The gases and/or feedstocks
are generally preheated combusting a fuel gas in a furnace and
passing the gases and/or feedstocks through heat exchanger tubes in
the heated portion of the furnace. Conventional flame combustion
methods have the disadvantages of NO.sub.x formation at typical
flame temperatures and inefficient heat transfer between the flame
and the heat exchanger tubes.
[0005] Accordingly, a preheating method is needed to reduce the
formation of NO.sub.x and to improve the heat transfer between the
flame and the heat exchanger tubes.
SUMMARY OF THE INVENTION
[0006] A process of combusting a gaseous volatile organic compound
over a modified alumina catalyst at a temperature below 5.degree.
C. while exothermically producing CO.sub.2 and H.sub.2O at a
temperature from about 5.degree. C. to about 1100.degree. C.
[0007] In an alternate embodiment a process of combusting a gaseous
volatile organic compound selected from a group consisting of:
methanol, ethanol, propanol, n-heptane, gasoline, crude oil,
n-C.sub.1-C.sub.6 paraffins, i-butanol, n-hexane, toluene, acetone,
hydrogen and combinations thereof in an oxygen containing gas such
as air, over a modified alumina catalyst at a temperature below
5.degree. C. This is followed by exothermically producing CO.sub.2
and H.sub.2O at a temperature from about 5.degree. C. to about
1100.degree. C. while not substantially forming NOx. In this
embodiment the modified alumina catalyst comprises from about 0.005
wt % to about 5 wt % Pt and a MgO modified alpha-alumina cloth
support and/or a gamma alumina powder support.
[0008] In yet another embodiment a process discloses using a heat
exchanger with a thin layer of a modified alumina catalyst bed in
contact with the heat exchanger and sprayed or coated catalyst
alumina slurry on heat exchanger. A gaseous volatile organic
compound is combusted over the modified alumina catalyst at a
temperature below 5.degree. C. This is followed by exothermically
producing CO.sub.2 and H.sub.2O while simultaneously raising the
temperature of the heat exchanger from about 5.degree. C. to about
1100.degree. C.
[0009] In an alternate embodiment a process discloses using a heat
exchanger with a thin layer of a modified alumina catalyst bed in
contact with the heat exchanger and sprayed or coated catalyst
containing alumina slurry on heat exchanger. A gaseous volatile
organic compound selected from a group consisting of: methanol,
ethanol, propanol, n-heptane, gasoline, crude oil,
n-C.sub.1-C.sub.6 paraffins, i-butanol, n-hexane, toluene, acetone,
hydrogen and combinations thereof in oxygen containing gas such as
air, is then combusted over a modified alumina catalyst at a
temperature below 5.degree. C. This is followed by exothermically
producing CO.sub.2 and H.sub.2O at a temperature from about
5.degree. C. to about 1100.degree. C. while not substantially
forming NOx. In this embodiment the modified alumina catalyst
comprises from about 0.005 wt % to about 5 wt % Pt and a MgO
modified alpha-alumina cloth support and/or a gamma alumina
support.
[0010] These and other objects, features, and advantages will
become apparent as reference is made to the following detailed
description, preferred embodiments, and examples, given for the
purpose of disclosure, and taken in conjunction with the
accompanying drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a further understanding of the nature and objects of the
present inventions, reference should be made to the following
detailed disclosure, taken in conjunction with the accompanying
drawings, in which like parts are given like reference numerals,
and wherein:
[0012] FIG. 1a is a schematic of a heat exchanger;
[0013] FIG. 1b is a schematic of a catalyst on a single heat
exchanger-style tube-catalyst-shell heater from FIG. 1a;
[0014] FIG. 2 is a schematic of an apparatus for evaluation of a
single heat exchanger-style catalyst tube-shell heater;
[0015] FIG. 3 is a chart of data for combustion of methane in air
over a methanol combustion catalyst in a heat exchanger; and
[0016] FIG. 4 is a chart of data for combustion of methane in air
over a diluted methanol combustion catalyst in a heat
exchanger.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTIONS
[0017] The following detailed description of various embodiments of
the present embodiment references the accompanying drawings, which
illustrate specific embodiments in which the embodiment can be
practiced. While the illustrative embodiments of the invention have
been described with particularity, it will be understood that
various other modifications will be apparent to and can be readily
made by those skilled in the art without departing from the spirit
and scope of the embodiment. Accordingly, it is not intended that
the scope of the claims appended hereto to be limited to the
examples and descriptions set forth herein but rather that the
claims be construed as encompassing all the features of patentable
novelty which reside in the present embodiment, including all
features which would be treated as equivalents thereof by those
skilled in the art to which the embodiment pertains. Therefore, the
scope of the present embodiment is defined only by the appended
claims, along with the full scope of equivalents to which such
claims are entitled.
[0018] A process of combusting a gaseous volatile organic compound
over a modified alumina catalyst at a temperature below 5.degree.
C. while exothermically producing CO.sub.2 and H.sub.2O at a
temperature from about 5.degree. C. to about 1100.degree. C.
[0019] In one embodiment gaseous volatile organic compounds can
contain methanol, ethanol, propanol, n-heptane, gasoline, crude
oil, n-C.sub.1-C.sub.6 paraffins, i-butanol, n-hexane, toluene,
acetone, hydrogen or any combinations of the above in an oxygen
containing gas such as air. One skilled in the art would be able to
determine the appropriate flow rate of the different gaseous
volatile organic compounds by balancing the rate of total
combustion versus the rate of undesirable products produced. In one
embodiment there is a complete combustion of the volatile organic
compounds to produce CO.sub.2 and H.sub.2O.
[0020] As an example, the chemical reaction for complete combustion
of methane in oxygen is
CH.sub.4+2O.sub.2.fwdarw.CO.sub.2+2H.sub.2O+heat,
and the reaction for complete combustion of methane in air is
CH.sub.4+2O.sub.2+7.52N.sub.2.fwdarw.CO.sub.2+2H.sub.2O+7.52N.sub.2+heat-
.
[0021] The modified alumina catalyst can be modified by any group
8, 9, 10, 11 or 12 metal. An example of a metal that has been shown
to be compatible is platinum. The modified alumina catalysts were
prepared using a conventional impregnation methods followed by
calcinations. The amount of metal impregnated onto the modified
alumina catalyst can from about 0.005 wt % to about 5 wt %, 0.01 wt
% to about 5 wt % or even 0.01 wt % to about 4 wt %. The modified
alumina catalyst can also be modified by incorporating a modified
alpha-alumina cloth or a gamma alumina support. An example of an
alpha-alumina cloth or a gamma alumina support that is capable of
being incorporated onto the modified alumina catalyst is a MgO
modified alpha-alumina cloth and/or a gamma alumina support. In one
embodiment the modified alumina catalyst is modified by both
platinum and a MgO modified alpha-alumina cloth support or a gamma
alumina support.
[0022] Unlike conventional volatile organic compound combustion
methods the temperature of the gaseous volatile organic compound
does not need to be extensively heated in our current process. The
catalytic reaction is capable of reacting at temperatures below
150.degree. C., 100.degree. C., or even below 5.degree. C. under
certain conditions. When the gaseous volatile organic compound
reacts on the modified alumina catalyst bed it produces an
exothermic reaction to produce CO.sub.2 and H.sub.2O.
[0023] Under conventional volatile organic compound combustion
methods, excessive amounts of NOx are produced. This is partially
due to the high temperatures in which their conventional reactions
occur at. In our current embodiments, due to the selective nature
of our modified alumina catalyst bed, the exothermic reaction does
not achieve a temperature sufficient to generate significant
quantities of NOx gases. In one embodiment the exothermic reactions
occurs from below 5.degree. C. to about 1100.degree. C.,
100.degree. C. to about 1100.degree. C. 500.degree. C. to about
1100.degree. C., 700.degree. C. to about 1100.degree. C. or even
800.degree. C. to about 1100.degree. C.
[0024] In one embodiment the exothermic reaction of the gaseous
volatile organic compounds are able to transfer heat to a heat
exchanger. In such an embodiment a thin layer of a modified alumina
catalyst bed is in contact with the heat exchanger. When the
gaseous volatile organic compound flows over the modified alumina
catalyst the exothermic reaction transfers the heat to the heat
exchanger. There are a variety of commercial uses for such a
reaction to occur, such as a pre-heater for high temperature
reactors or for generating steam.
[0025] An improved heater-exchanger style preheater with a
plurality of catalyst beds is shown in FIGS. 1a and 1b. As shown in
FIG. 1a, the heat exchanger 100 comprises an inlet 110 for a fuel
gas mixture with volatile organic compounds and oxygen containing
gas such as air and an outlet 115 for flue gas (e.g., CO.sub.2,
H.sub.2, CO, N.sub.2). A plurality of heat exchanger tubes 105 pass
through a heated portion of the heat exchanger 120. Each of the
heat exchanger tubes 105 has an inlet 110 for cool gas and/or
feedstock, and an outlet 115 for hot gas and/or feedstock.
[0026] As shown in FIG. 1b a thin layer of a modified alumina
catalyst 135 is in contact with a heat exchanger tube 105. The
modified alumina catalyst wraps or sprayed around the heat
exchanger tube 105 to form a catalyst bed 135 in the annulus
between the heat exchanger tube 105 (i.e., inner tube) and a shell
140 (i.e., outer tube). The catalyst 135 formed greatly improves
the heat exchanger capabilities.
[0027] In an embodiment, a fuel gas/volatile organic compound and
oxygen containing gas mixture is initially passed over the
catalyst-covered heat exchanger tubes in the heat exchanger-style
furnace. The volatile organic compounds combust over the catalyst,
and raises the catalyst temperature to a combustion temperature
that supports combustion of the coexisting fuel gas. Experimental
evidence has shown that this combustion temperature is generally
about 800.degree. C., and that, at this temperature, NO.sub.x does
not form from the nitrogen in the air. Once the catalyst bed
temperature reaches the combustion temperature for the fuel gas and
the combustion reaction sustains itself, the volatile organic
compound supply may be shut off from the feed.
[0028] In an alternate embodiment the catalyst does not cover the
outside of the heat exchanger but instead coat the inside of the
heat exchanger.
[0029] An experimental apparatus for evaluation of a single heat
exchanger-style catalyst tube-shell heater is shown in FIG. 2. As
shown in FIG. 2, the heat exchanger-style preheater 200 comprises
an inlet 240 for a fuel gas mixture (e.g., fuel gas and volatile
organic compounds) and an outlet 265 for flue gas (e.g., CO.sub.2,
H.sub.2O, CO, N.sub.2). A single heat exchanger tube 205 (i.e.,
inner tube) passed through a heated portion of the heat
exchanger-style, catalyst tube-shell heater 255 (i.e., outer tube).
Both inner 205 and outer 255 tubes were made of stainless steel. A
catalytic combustion catalyst was packed in the inner tube 205 to
form a catalyst bed 250.
[0030] Air was used as a cooling medium for the inner tube 205 (and
catalyst bed 250), and was controlled using a flow meter. The
cooling air entered the outer tube at one end 245, passed through
the annulus between the inner 205 and outer 255 tubes to remove
some of the heat generated by the combustion reaction, and exited
the other end 260.
[0031] A fuel gas mixture was blended in-situ by flowing fuel gas
210, air 215 and nitrogen 220 into one end of the inner tube 205.
The mass flow rate of the fuel gas was controlled by a mass flow
controller 225, the mass flow rate of the air was controlled by a
mass flow controller 230, and the mass flow rate of the nitrogen
was controlled by a mass flow controller 235. The fuel gas mixture
(i.e., methane and air) entered the inner tube 205 at one end,
combusted over the catalyst bed 250, and the flue gas (e.g.,
CO.sub.2, H.sub.2O, CO, N.sub.2) exited the other end.
[0032] A portion 270 of the flue gas was diverted to a NO.sub.x
Analyzer for analysis of NO.sub.x, and a portion 275 of the flue
gas was diverted to a gas chromatograph for a compositional
analysis including CO. A backpressure element (not shown) was used
to create a back pressure so that the portion of the flue gas would
be diverted to the analyzers. The NO.sub.x analyzer was used to
detect NO.sub.x, and to determine the NO.sub.x concentration in the
flue gas. The gas chromatograph was used to detect CO and other
components, and to determine their concentrations in the flue
gas.
[0033] Three methods may be used to initiate a combustion reaction.
One method is to add methanol or ethanol vapor to the fuel gas
mixture. The methanol combusts (i.e., reacts with oxygen) on the
catalyst bed 135, 250, and raises the catalyst bed 135, 250
temperature to a combustion temperature that supports combustion of
the coexisting fuel gas. Once the catalyst bed 135, 250 temperature
reaches the combustion temperature for the fuel gas and the
combustion reaction sustains itself, the methanol supply may be
shut off from the feed if desired.
[0034] A second method is to add hydrogen gas to the fuel gas
mixture. The hydrogen combusts (i.e., reacts with oxygen) on the
catalyst bed 135, 250, and raises the catalyst bed 135, 250
temperature to a combustion temperature that supports combustion of
the coexisting fuel gas mixture. The hydrogen combustion on the
catalyst bed 135, 250 may be spontaneous. Once the catalyst bed
135, 250 temperatures reach the combustion temperature for the fuel
gas and the combustion reaction sustains itself, the hydrogen
supply may be shut off from the feed if desired.
[0035] A third method is to preheat the fuel gas mixture to the
temperature that supports combustion of the fuel gas mixture.
[0036] Catalysts used for the experiments were platinum (Pt)
supported on magnesium modified aluminum oxide (Al.sub.2O.sub.3).
The catalysts were prepared using a conventional impregnation
method followed by calcinations. The catalyst compositions are
shown in Table 1.
TABLE-US-00001 TABLE 1 Catalyst Compositions Catalyst Pt (wt %) Mg
(wt %) Support Size (mesh) 1 4 3 Al.sub.2O.sub.3 20 to 30 2.sup.1 4
3 Al.sub.2O.sub.3 20 to 30 3 1 3 Al.sub.2O.sub.3 20 to 30 .sup.1The
4 wt % Pt catalyst was diluted with an inert catalyst carrier
material (e.g., silicon carbide (SiC) support).
Example 1
4 wt % Pt/3 wt % Mg/Al.sub.2O.sub.3
[0037] In Example 1, 4 wt % platinum (Pt) catalyst was evaluated
for combustion of methane in air. The length of the catalyst bed
250 was 1.375 inches. The fuel gas mixture feed was 3.3 standard
liters per minute (SLPM), the fuel gas was methane, and the ratio
of air to methane was 10:1, at which the oxygen content in the air
is slightly greater than the amount that is required for complete
combustion of methane.
[0038] Air 245 was used as a cooling medium for the inner tube 205
(and catalyst bed 250). The flow rate of the cooling air was
between 25 to 100 standard cubic feet per hour (SCFH). The cooling
air was used to cool the inner tube 205 (and catalyst bed 250) so
that the effects of combustion temperature on NO.sub.x formation
could be quantitatively determined.
[0039] The experimental data for combustion of methane in air over
combustion catalyst 1 in a heat exchanger-style catalyst tube-shell
heater is shown in FIG. 3. As shown in FIG. 3, the data indicates
that the temperatures (i.e., inlet temperature of the catalyst bed
250, outside surface temperature of the inner tube 205, outlet
temperature of the cooling air 260) decreased with increasing
cooling air flow except the outlet temperature of the catalyst bed
250. The outlet temperature of the catalyst bed 250 decreased with
increasing cooling air flow up to 80 SCFH, and then, above this
flow rate, the outlet temperature increased. This increase may be
attributed to a reaction zone shifting or extending closer to the
end of the catalyst bed 250 than the prior position.
[0040] NO.sub.x formation varies with reactor temperature, and
generally NO.sub.x formation tends to decrease with decreasing
temperature. NO.sub.x concentration in the flue gas was about 38
ppm at an outside surface temperature of the inner tube 205 of
about 655.degree. C., and about 1 ppm at an outside surface
temperature of about 254.degree. C. For a NO.sub.x concentration of
about 1 ppm, outlet temperature of the catalyst bed was about
640.degree. C. An upper limit for the outlet temperature of the
catalyst bed was about 716.degree. C.
[0041] During the experiment, no carbon monoxide was detected in
the flue gas, and, therefore, all of the methane was combusted.
Example 2
4 wt % Pt/3 wt % Mg/Al.sub.2O.sub.3 Diluted with Inert Catalyst
Carrier Material
[0042] In Example 2, 4 wt % Pt catalyst was diluted with an inert
catalyst carrier material (e.g., SiC support). The diluted catalyst
was evaluated for combustion of methane in air. The length of the
diluted catalyst bed 250 was 1.375 inches. Similar to Example 1,
the fuel gas mixture (i.e., methane and air) feed was 3.3 SLPM, the
fuel gas was methane, and the ratio of air to methane was 10:1.
[0043] Air 245 was used as a cooling medium for the inner tube 205
(and catalyst bed 250). The flow rate of the cooling air was
between 50 to 65 SCFH. The cooling air was used to cool the inner
tube 205 (and catalyst bed 250) so that the effects of combustion
temperature on NO.sub.x formation could be quantitatively
determined.
[0044] A chart of experimental data for combustion of methane in
air over a diluted combustion catalyst in a heat exchanger-style
catalyst tube-shell heater is shown in FIG. 4. As shown in FIG. 4,
the highest observed NO.sub.x concentration was about 6 ppm. At
this NO.sub.x concentration, the outlet temperature of the catalyst
bed 250 was about 678.degree. C. and the outside surface
temperature of the inner tube 205 was about 523.degree. C. During
the experiment, the NO.sub.x concentration ranged from about 0 to 6
ppm, the outlet temperature of the catalyst bed 250 ranged from
about 647 to 678.degree. C., and the outside surface temperature of
the inner tube 205 ranged from about 342 to 523.degree. C.
[0045] No carbon monoxide was detected in the flue gas, and,
therefore, all of the methane was combusted.
Example 3
1 wt % Pt/3 wt % Mg/Al.sub.2O.sub.3
[0046] In Example 3, the catalyst loading was reduced from 4 to 1
wt % Pt to spread the combustion reaction across the catalyst bed.
The combustion reaction on the 4 wt % Pt catalyst occurred on the
front of the bed. The 1 wt % Pt catalyst was evaluated for
combustion of methane in air. Reducing the catalyst loading
requires a longer residence time on the catalyst for reaction thus
extending the hot zone of the catalyst bed. This provide for a
larger surface of tube 205 that is heated. Accordingly, the 1 wt %
Pt catalyst bed 250 was 1.5 inches, which is slightly longer than
the 1.375 inch bed used in Examples 1 and 2. Similar to Examples 1
and 2, the fuel gas mixture (i.e., methane and air) feed was 3.3
SLPM, the fuel gas was methane, and the ratio of air to methane was
10:1.
[0047] The experiment was carried out without air cooling. Less
than 1 ppm of NO.sub.x was detected in the flue gas. The inlet and
outlet temperatures of the catalyst bed 250 were about 854.degree.
C. and 993.degree. C., respectively. The outside surface
temperature of the inner tube 205 was about 662.degree. C.
[0048] Two experiments were carried out with the same 1 wt % Pt
catalyst under the same operating conditions. Less 9 ppm of CO was
detected in the flue gas during both of these experiments, and,
therefore, nearly all of the methane was combusted. The CO
concentration could be reduced to less than 1 ppm by increasing the
length of the catalyst bed to increase residence time.
TABLE-US-00002 TABLE 2 Experimental Results for Combustion of
Methane in Air Over Combustion Catalysts in a Heat Exchanger-Style
Catalyst Tube-Shell Heater Temperature Outlet of Outside Length of
Temperature Surface of Air Catalyst of Catalyst Inner Tube Cooling
NO.sub.x Example Catalyst Bed (in.) Bed (.degree. C.) (.degree. C.)
(SCFH) (ppm) 1 4 wt % Pt/3 wt % 1.375 555 to 716 254 to 655 25 to
100 1 to 38 Mg/Al.sub.2O.sub.3 2 4 wt % Pt/3 wt % 1.375 647 to 678
342 to 523 50 to 65 0 to 6 Mg/Al.sub.2O.sub.3 diluted with inert
catalyst carrier material 3 1 wt % Pt/3 wt % 1.5 ~1000 ~662 0 0 to
1 Mg/Al.sub.2O.sub.3
[0049] The experimental data indicates that the process for
catalytic combustion in a heat exchanger-style catalyst tube-shell
heater has an advantage over conventional flame combustion methods
in the reduction of NO.sub.x formation. The improved catalyst
tube-shell heater reduced the NO.sub.x concentration in the flue
gas to less than about 7 ppm, which is a significant reduction from
about the 15 ppm NO.sub.x formed for most conventional burners.
[0050] Similarly, the improved heat exchanger tube-catalyst-shell
heater should reduce NO.sub.x concentration in flue gas to less
than the NO.sub.x formed for most conventional burners.
DEFINITIONS
[0051] As used herein, the terms "a," "an," "the," and "said" means
one or more.
[0052] As used herein, the term "and/or," when used in a list of
two or more items, means that any one of the listed items can be
employed by itself, or any combination of two or more of the listed
items can be employed. For example, if a composition is described
as containing components A, B, and/or C, the composition can
contain A alone; B alone; C alone: A and B in combination; A and C
in combination; B and C in combination; or A, B, and C in
combination.
[0053] As used herein, the terms "comprising," "comprises," and
"comprise" are open-ended transition terms used to transition from
a subject recited before the term to one or elements recited after
the term, where the element or elements listed after the transition
term are not necessarily the only elements that make up of the
subject.
[0054] As used herein, the terms "containing," "contains," and
"contain" have the same open-ended meaning as "comprising,"
"comprises," and "comprise," provided above.
[0055] As used herein, the terms "having," "has," and "have" have
the same open-ended meaning as "comprising," "comprises," and
"comprise," provided above.
[0056] As used herein, the terms "including," "includes," and
"include" have the same open-ended meaning as "comprising,"
"comprises," and "comprise," provided above.
[0057] As used herein, the term "simultaneously" means occurring at
the same time or about the same time, including concurrently.
INCORPORATION BY REFERENCE
[0058] All patents and patent applications, articles, reports, and
other documents cited herein are fully incorporated by reference to
the extent they are not inconsistent with this invention.
* * * * *