U.S. patent application number 11/266926 was filed with the patent office on 2007-05-10 for industrial radiant heater.
This patent application is currently assigned to NOVA Chemicals (International) S.A.. Invention is credited to Leslie Wilfred Benum, Haiyong Cai, Andrzej Krzywicki, Hong Ma.
Application Number | 20070105060 11/266926 |
Document ID | / |
Family ID | 38004156 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070105060 |
Kind Code |
A1 |
Cai; Haiyong ; et
al. |
May 10, 2007 |
Industrial radiant heater
Abstract
High temperature industrial radiant heaters may be improved by
coating a refractory or lining in and adjacent to the flame
impingement zone which refractory or lining does not transmit fuel
to the burner with a metal oxide catalyst or metal oxide catalyst
precursor other than iron, iron oxides or mixtures thereof, to
promote the burning of one or more of the fuel, and combustion
products thereof.
Inventors: |
Cai; Haiyong; (Calgary,
CA) ; Krzywicki; Andrzej; (Calgary, CA) ;
Benum; Leslie Wilfred; (Red Deer, CA) ; Ma; Hong;
(Sarnia, CA) |
Correspondence
Address: |
Kenneth H. Johnson;Patent Attorney
P.O. Box 630708
Houston
TX
77263
US
|
Assignee: |
NOVA Chemicals (International)
S.A.
|
Family ID: |
38004156 |
Appl. No.: |
11/266926 |
Filed: |
November 4, 2005 |
Current U.S.
Class: |
431/202 |
Current CPC
Class: |
F23D 14/18 20130101;
F23D 14/125 20130101; F23C 13/08 20130101 |
Class at
Publication: |
431/202 |
International
Class: |
F23G 7/08 20060101
F23G007/08 |
Claims
1. In a fluid fueled heater, comprising a mechanical burner, a
flame impingement zone adjacent said burner, and a refractory or
lining in and adjacent to the flame impingement zone which
refractory or lining does not transmit fuel to the burner the
improvement of substantially coating the refractory or lining with
a metal oxide catalyst or metal oxide catalyst precursor other than
iron, iron oxides, and mixtures thereof, to promote the burning of
one or more of the fuel, and combustion products from the fuel.
2. The heater according to claim1, wherein the fuel is fluid
hydrocarbon.
3. The heater according to claim 2, wherein the refractory is
selected from the group consisting of dolomites, silicon carbide,
aluminates, aluminum silicates, chromites, silica, alumina,
zirconia, magnesia, Al.sub.2O.sub.3, and ZrO.sub.2 and mixtures
thereof.
4. The heater according to claim 3, wherein during operation the
refractory is at a temperature from 600.degree. C. to 1300.degree.
C.
5. The heater according to claim 4, wherein the refractory has a
porosity of not less than 0.1 cc/g.
6. The heater according to claim 5, wherein the refractory or
lining is in the form of bricks, a metal lining on refractory
bricks or refractory metals.
7. The heater according to claim 6, wherein the fuel is a gaseous
hydrocarbon.
8. The heater according to claim 7, wherein the metal oxide is
selected from the group consisting of oxides of perovskites,
hexaaluminate, spinels, PtO, PdO, MgO, Ce.sub.2O.sub.3, CoO,
Cr.sub.2O.sub.3, CuO, MnO, NiO, and their precursors and mixtures
thereof.
9. The heater according to claim 8, wherein the thickness of the
metal oxide coating on the refractory from 0.0001 to 5 mm
thick.
10. The heater according to claim 9, wherein the refractory is
selected from the group consisting of silica, Al.sub.2O.sub.3,
aluminium silicates, ZrO.sub.2, magnesia and mixtures thereof
11. The heater according to claim 10, wherein the metal oxide is
selected from the group consisting of oxides of PtO, PdO, MgO,
Ce.sub.2O.sub.3, CoO, CuO, Cr.sub.2O.sub.3, MnO, NiO, and a mixture
thereof
12. The heater according to claim 11, where in a refractory is
exposed to the flame in the flame impingement zone.
13. The heater according to claim 11, wherein a metal liner is
exposed to the flame in the flame impingement zone.
14. The heater according to claim 12 which is in the radiant heater
of a steam cracker.
15. The heater according to claim 14, wherein the fuel is natural
gas or a natural gas rich fuel.
16. The heater according to claim 13 which is in the radiant heater
of a steam cracker.
17. The heater according to claim 16, wherein the fuel is natural
gas.
18. A process for preparing a refractory or lining having a metal
oxide or metal oxide precursor component which catalyses the
burning of a fluid fuel or combustion products from a fluid fuel
when subject to flame impingement selected from the group
consisting of: a) direct application of a coating composition
comprising said metal oxide or metal oxide precursor to the
refractory or lining surface; and b) incorporating said metal oxide
or metal oxide precursor into the refractory or lining composition
during manufacture of said refractory.
19. The process according to claim 18, wherein said metal oxide or
metal oxide precursor is applied to the surface of said refractory
or lining in the form of a paint or paste.
20. The process according to clam 19, wherein said paint is applied
to the surface of said refractory or lining by an applicator
selected from the group consisting of brush, roller and spray
device.
21. The process according to claim 20 which is carried out prior to
installation of said refractory or lining in said burner.
22. The process according to claim 20, which is carried out during
scheduled maintenance of said burner.
23. A method to increase burner stability by substantially coating
the refractory or lining in the flame impingement zone with a metal
oxide catalyst or precursor for a metal oxide catalyst to promote
the burning of one or more of the fuel and the combustion products.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to burners for fluid fuels and
in particular burners for volatile organic fuels such as natural
gas or a fuel rich in natural gas. More particularly the present
invention relates to heaters having improved radiant efficiency and
which burn cleaner.
BACKGROUND OF THE INVENTION
[0002] There is a significant field of art relating to non-flame
catalytic combustion. In this type of process a fuel to be burned
passes over a supported catalyst at an elevated temperature and the
fuel is consumed. The most common of this type of catalytic burner
is the catalytic converter in cars. The support is typically in the
shape of an open honeycomb and the exhaust gasses pass through the
honeycomb where combustion gasses are consumed or converted to more
environmentally acceptable products. The converter technology does
not use flame impingement of the present technology.
[0003] German Patent DE 195 32 152 B4 discloses the use of a
coating of metal oxide based catalysts such as FeO,
Fe.sub.2O.sub.3, and Fe.sub.3O.sub.4 on fireproof (refractory)
materials placed on the walls of a residential fireplace and/or
chimney. The catalyst help burn the "off gas" from the solid fuel
burning in fire. The reference does not teach or suggest a flame
impingement process as required by the present invention. Further
the reference teaches iron oxide catalysts which are not included
in the scope of the present invention. U.S. Pat. No. 3,565,830
issued Feb. 23, 1971 to Keith et al., assigned to Englehard
Minerals and Chemicals Corporation discloses a catalytic converter
comprising a honeycomb support having a porosity of at least 0.1 to
0.3 cc/g upon which is deposited a platinum group metal. The
converter differs from the heater of the present invention in that
it does not require a direct flame impingement.
[0004] U.S. Pat. No. 6,431,856 issued Aug. 13, 2002, to Maenishi et
al. teaches a refractory supporting one or more combustion
catalysts in a combustion chamber. However, the refractory is
shaped in such a manner that the fuel gas or combustions products
thereof pass through the refractory. The present invention requires
a refractory or lining through which neither the fuel nor the
combustion products pass.
[0005] The present invention seeks to provide a simple method to
improve the heating and particularly the radiant heating of a
heater. More particularly the present invention seeks to provide a
heater, and particularly a high temperature heater, having a higher
wall temperature in or adjacent a flame impingement zone and a
higher emisvity (radiation) under equivalent fuel and combustion
air input.
SUMMARY OF THE INVENTION
[0006] The present invention provides in a fluid fueled heater,
comprising a mechanical burner, a flame impingement zone adjacent
said burner, and a refractory or lining in and adjacent to the
flame impingement zone which refractory or lining does not transmit
fuel to the burner the improvement of substantially coating the
refractory or lining with a metal oxide catalyst or metal oxide
catalyst precursor other than iron, iron oxides and mixtures
thereof (e.g. the catalyst or precursor can not be Fe, FeO,
Fe.sub.2O.sub.3, Fe.sub.3O.sub.4 or mixtures thereof) to promote
the burning of one or more of the fuel, and combustion products
from the fuel.
[0007] The present invention further provides a process for
preparing a refractory or lining having a metal oxide or metal
oxide precursor component other than iron oxides, and mixtures
thereof, which catalyses the burning of a fluid fuel or combustion
products from a fluid fuel when subject to flame impingement
selected from the group consisting of:
[0008] a) direct application of a coating composition comprising
said metal oxide or metal oxide precursor to the refractory or
lining surface; and
[0009] b) incorporating said metal oxide or metal oxide precursor
into the refractory or lining composition during manufacture of
said refractory.
[0010] The present invention further provides a method to increase
burner stability by substantially coating the refractory or lining
in the flame impingement zone with a metal oxide catalyst or
precursor for a metal oxide catalyst other than iron, iron oxides
and mixtures thereof, to promote the burning of one or more of the
fuel and the combustion products.
BRIEF DESCRIPTON OF THE DRAWINGS
[0011] FIG. 1 is a schematic drawing of a combustion testing
apparatus (CTA) used in the Examples.
DETAILED DESCRIPTION
[0012] As used in this specification "substantially coating" means
coating the refractory or lining in the flame impingement zone.
[0013] The heaters of the present invention may be used in a number
of applications typically industrial applications where process
streams are heated while passing through metallic tubes in an oven,
furnace or radiant heater including the hot box of a steam cracker.
Generally, the present invention is useful in high temperature
burner applications having a flame impingement zone. Additionally
the present invention provides improved flame/burner stability.
[0014] The refractory material may be any type of refractory
materials that are commonly used in the construction of a furnace
refractory wall. Examples of such refractory materials include
dolomites, silicon carbide, aluminates (Al.sub.2O.sub.3), aluminum
silicates, chromites, silica, alumina, zirconia (ZrO.sub.2), and
mixtures thereof, preferably silica, alumina (Al.sub.2O.sub.3),
aluminum silicates, zirconia, (ZrO.sub.2), and mixtures thereof.
Such a refractory may optionally be non-porous in nature, even
though the mentioned refractory materials are typically porous.
Typically the refractory will be porous and have a porosity of not
less than 0.1 cc/g. Typically the porosity may be from 0.1 to 0.5
cc/g, preferably from 0.1 to 0.3 cc/g. The intended coating is to
cover a two dimensional refractory wall surface, rather than to
impregnate a significant depth of refractory material with the
intended combustion catalysts. More specifically, it is irrelevant
how deep the coated catalysts may penetrate into the refractory
wall. Generally the coating may have a thickness from 0.0001 to 5
mm thick, typically 0.0001 to 1 mm thick. The refractory could take
any convenient form such as bricks, plates and slabs.
[0015] The present invention also contemplates a lining rather than
or in addition to the refractory. The lining needs to be suitable
for the temperature at which the burner is operated from
600.degree. C. to 1300.degree. C., typically from 850.degree. C. to
1300.degree. C., preferably from 900.degree. C. to 1300.degree. C.
The lining may be a suitable metal applied to or over the
refractory. The metal could be cast or wrought iron or more
typically steel such as stainless or high temperature steel. For
lining on the blades of natural gas turbines, the metal is
typically nickel based alloys. The metal surface may be attached to
or encompass (e.g. folded over) a refractory substrate. The metal
would protect the refractory from ablative losses.
[0016] The catalyst may be selected from the group oxides of
perovskites, hexaaluminate, spinels, PtO, PdO, MgO,
Ce.sub.2O.sub.3, CoO, Cr.sub.2O.sub.3, CuO, MnO, NiO, and their
precursors and mixtures thereof. The catalyst does not include
iron, iron oxides, and mixtures thereof or their precursors.
Preferably the catalyst is selected from the group consisting of
PtO, PdO, MgO, Ce.sub.2O.sub.3, CoO, Cr.sub.2O.sub.3, CuO, MnO, NiO
and mixtures thereof. Most preferably the catalyst is selected from
the group consisting of PtO, PdO, Ce.sub.2O.sub.3, CoO,
Cr.sub.2O.sub.3, CuO, MnO, NiO and mixtures thereof.
[0017] The catalyst may be prepared as an emulsion, solution or a
paste ("mud") and applied to the refractory or lining in any
convenient manner such as painting, spraying or roller. The coating
could be applied to the refractory prior to incorporation into the
heater or after incorporation into the heater for example during
routine maintenance or during a turn around. The catalyst may be,
incorporated into the refractory or the liner during manufacture.
Although, as noted above, the affect is primarily a surface affect
and the catalyst need not be incorporated into the interior of the
refractory or liner.
[0018] The fuel should be fluid. Preferably the fuel is a gaseous
hydrocarbon such as natural gas or a natural gas rich (e.g. greater
than 30% (volume) of natural gas) fuel. However, the fuel could
also be liquid such as naphtha stream, a gas oil or a vacuum gas
oil, and the like.
[0019] As noted above the refractor or liner is preferably exposed
to the burner flame or at least a portion of the burner flame in
the flame impingement zone. There are several improvements which
may be achieved by the present invention. There is a more complete
combustion of the fuel and in particular a more complete combustion
of the initial combustion products from the fuel. There is also a
reduction in carbon monoxide and NO.sub.x in the exhaust gases
[0020] In the experiments a combustion testing apparatus (CTA) was
used. FIG. 1 is a schematic sectional drawing showing the apparatus
in which like parts are designated with like numbers. Forced air 1
and natural gas 2, pass valves 3, enter the mass flow controller 5
under controlled pressures shown on the gauges 4 and then flow into
a laboratory type of gas burner 6. In addition to the forced air 1,
there is a fixed amount of draft air flowing through the opening 16
at the bottom of the combustion chamber in which the burner 6 is
inserted. A flame 7 is fired against the surface of a refractory
brick 8 which is backed by an electric block heater 9 in order to
prevent severe heat loss from the brick and to better control the
brick surface temperature. During the experiments, five spots on
the surface of a test refractory brick (with or without catalyst
coating) are selected for temperature measurement by a laser
pyrometer 10, during which the insolated window cover 11 is opened.
Additionally, the temperature of the combustion chamber 12 and
temperature of the exhaust gas 13 are also monitored through type-K
thermocouples. The combustion chamber was insulated with ceramic
fibre insulation materials 14. The exhaust gas leaving the
combustion chamber 15 enters into a centre ventilation system.
[0021] Table 1 lists two sets of parameters for both fuel rich
flame (FRF) and normal flame (NF) conditions. TABLE-US-00001 TABLE
1 Typical Conditions Employed by CTA for Combustion Tests Parameter
Value Fuel Rich Flame Normal Flame Test Parameter (FRF) (NF)
Natural gas flow rate (slpm) 20 12 Flow rate of a forced air 55 55
(slpm) Flow rate of draft air (slpm) .about.82.4 .about.82.4 Block
heater temperature 700 700 (.degree. C.) Size of the fire brick 6''
.times. 9'' .times. 1.5'' 6'' .times. 9'' .times. 1.5'' Firebrick
material Al.sub.2O.sub.3: 67 wt %, SiO.sub.2, 30.5 wt %, + other
metal oxides in trace amount
EXAMPLE 1
[0022] Two commercially available combustion catalysts, made of
non-noble metals and intended for use at temperature up to
1200.degree. C., were obtained from catalyst providers. Each
catalyst was provided in an undisclosed slurry form and
brush-coated on the surface of a firebrick. The coated catalysts
were then left to dry under ambient conditions for 24 hours before
the coated bricks were heat-treated in a muffle oven to calcine the
catalyst. These two coated bricks, plus an un-coated firebrick as
reference, were tested using the CTA and under the test conditions
specified in Table 1. The test results are given in Table 2.
TABLE-US-00002 TABLE 2 Comparative Results of Catalyst Coated
Bricks and an Un-Coated Brick NF Testing Condition FRF Testing
Condition Un- Un- Coated Coated Catalyst A Catalyst B Firebrick
Catalyst A Catalyst B Firebrick Average Brick 940.3 942.9 930.8
847.1 809.0 788.5 Temperature (.degree. C.) Average 0.62 0.60 0.57
0.60 0.59 0.58 Brick Emissivity Combustion 437.7 421.6 412.2 678.5
656.6 641.9 Chamber Temperature (.degree. C.) Exhaust Gas 332.7
334.8 302.7 554.4 567.1 524.9 Temperature (.degree. C.)
Example 2
[0023] Five nitrates salts (Mg(NO.sub.3).sub.2, Ce(NO.sub.3),
Co(NO.sub.3).sub.2, Cu(NO.sub.3).sub.2, and Mn(NO.sub.3).sub.2)
were dissolved in 200 ml of de-ionized water each to prepare five
nitrate solutions of a nominal 5 weight % in concentration. A spray
bottle was used to contain one of these solutions at a time and to
spray coat the nitrate solution on a fresh refractory brick
surface. Each brick surface, albeit not controlled exactly, was
sprayed with one solution for 30 times. The wet bricks were then
left in a laboratory fume hood at ambient conditions to dry for
about 15 hours. After the drying, each of these five coated bricks
was put in a muffle oven at room temperature, which was heated at
about 10.degree. C./min from ambient temperature to 600.degree. C.
and held at 600.degree. C. for 30 minutes before cooling down.
After a complete cooling to ambient temperature, these bricks were
tested under the same testing conditions as used for Example 2. The
heat treatment procedure was developed based on a set of separate
experiments using a thermal balance, which confirmed that this heat
treatment procedure will convert the nitrates into their
corresponding oxides. More precisely, these oxides are primarily
MgO, Ce.sub.2O.sub.3, CoO, CuO and MnO, respectively.
[0024] Using again the CTA, these five coated bricks were tested
under both NF and FRF conditions as given in Example 2. However, it
is worth mentioning that due to some modifications made to the CTA
(the spacing between the burner and the firebrick) before this
batch of tests, these results should not be compared with the
results given in Example 2. Nevertheless, the results in Table 3
were obtained under the identical conditions and therefore can be
compared. TABLE-US-00003 TABLE 3 Comparative Results of Metal
Oxides Coated Bricks and an Un-Coated Brick Average Brick Chamber
Exhaust Gas Average Temperature Temperature Temperature Brick
(.degree. C.) (.degree. C.) (.degree. C.) Emissivity NF Testing
Condition Un-Coated 921.4 440.0 362.9 0.58 Firebrick MgO 933.5
450.1 369.6 0.64 Ce.sub.2O.sub.3 924.4 438.9 373.7 0.68 CoO 924.8
455.3 370.0 0.70 CuO 908.5 434.0 371.0 0.75 MnO, 912.3 448.3 381.3
0.69 FRF Testing Condition Un-Coated 820.5 674.1 541.1 0.59
Firebrick MgO 835.8 723.9 572.6 0.62 Ce.sub.2O.sub.3 835.3 657.5
560 0.66 CoO 849.8 680.6 561.4 0.68 CuO 850.3 648.2 566.3 0.70 MnO,
828.3 650.7 568.4 0.66
[0025] These results confirm that there are noticeable improvements
in the measured temperatures for all five oxides under the FRF
condition. For example, the maximum increase in brick surface
temperature is about 30.degree. C. with CuO while the maximum rise
in chamber temperature was observed from MgO for about 50.degree.
C., which shows also a maximum increase in exhaust temperature for
about 32.degree. C. In contrast, these observed improvements become
less significant under NF test condition. For example, the highest
increase in surface temperature is about 12.degree. C. from the MgO
coated brick, whilst decreases in surface temperature were also
observed with the CuO and MnO coated bricks. However, from both
test conditions, the emissivity with the coated bricks are seen to
improve, possibly due to the changed surface compositions.
Example 4
[0026] In order to evaluate the potential benefits from using the
above mentioned catalysts as refractory coating, an ethylene
furnace simulator (SPYRO from TECHNIP PYROTEC) was used to simulate
the radiant box operation of a SRT butane cracker which is heated
by natural gas at a NOVA Chemicals' production plant. Using the
real operating parameters (about 4,000 kg/hr butane feed), two
cases were considered for simulation: a base case and a modified
case which assumes about 14.degree. F. temperature rise on
refractory wall. Considering the same butane conversion in both
cases, the simulation results (Table 4) show clearly that with
about 14.4.degree. F. (8.degree. C.) temperature rise on refractory
temperature, the overall efficiency in radiant box increases by
0.98%. As a result, a slightly less firing is required, suggesting
a possible saving in fuel gas. Furthermore, with the refractory
wall temperature increasing, a slight increase in coil outlet
temperature could also be realized. Considering together that the
maximum tube skin temperature is lowered by 7.5.degree. F. (about
4.degree. C.) than in the base case, these results do suggest that
the radiant box become more homogenous in terms of temperature.
TABLE-US-00004 TABLE 4 Spyro Simulation Results of a SRT Butane
Cracker Base Modified Case Case Change Feed Flow Per Coil (Lb/H)
8666.8 8666.8 0.0 Coil Inlet Temperature (.degree. F.) 1040 1040
0.0 Average Radiant Refractory 2106 2120.4 +14.4 Temperature
(.degree. F.) Radiant Box Efficiency On Fired 39.029 40.008 +0.98
Heat (%) Fired Heat Based On LHV 186.7 182.8 -3.9 (MBTU/H) Coil
Outlet Temperature (.degree. F.) 1580 1583.4 +3.4 Maximum Tube Skin
Temperature 1894.4 1886.9 -7.5 (.degree. F.)
* * * * *