U.S. patent application number 11/831381 was filed with the patent office on 2008-01-24 for staged combustion system with ignition-assisted fuel lances.
This patent application is currently assigned to Air Products and Chemicals, Inc.. Invention is credited to Mahendra Ladharam Joshi, Xianming Jimmy Li, Aleksandar Georgi Slavejkov.
Application Number | 20080020334 11/831381 |
Document ID | / |
Family ID | 34981388 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080020334 |
Kind Code |
A1 |
Joshi; Mahendra Ladharam ;
et al. |
January 24, 2008 |
Staged Combustion System With Ignition-Assisted Fuel Lances
Abstract
Combustion system comprising a furnace having a thermal load and
a combustion atmosphere, wherein the thermal load and combustion
atmosphere are disposed within the furnace; one or more fuel lances
adapted to inject fuel into the combustion atmosphere; and one or
more igniters associated with the one or more fuel lances and
adapted to ignite the fuel injected by the one or more fuel
lances.
Inventors: |
Joshi; Mahendra Ladharam;
(Allentown, PA) ; Slavejkov; Aleksandar Georgi;
(Allentown, PA) ; Li; Xianming Jimmy; (Orefield,
PA) |
Correspondence
Address: |
AIR PRODUCTS AND CHEMICALS, INC.;PATENT DEPARTMENT
7201 HAMILTON BOULEVARD
ALLENTOWN
PA
181951501
US
|
Assignee: |
Air Products and Chemicals,
Inc.
7201 Hamilton Boulevard
Allentown
PA
18195-1501
|
Family ID: |
34981388 |
Appl. No.: |
11/831381 |
Filed: |
July 31, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10883349 |
Jul 1, 2004 |
7303388 |
|
|
11831381 |
Jul 31, 2007 |
|
|
|
Current U.S.
Class: |
431/2 ;
431/264 |
Current CPC
Class: |
F23D 14/22 20130101;
F23D 14/583 20130101; F23C 2201/30 20130101; F23D 2203/1026
20130101; F23D 14/32 20130101 |
Class at
Publication: |
431/002 ;
431/264 |
International
Class: |
F23Q 3/00 20060101
F23Q003/00 |
Claims
1. A combustion system comprising (a) a furnace having a thermal
load and a combustion atmosphere disposed therein; (b) one or more
fuel lances adapted to inject fuel into the combustion atmosphere;
and (c) one or more igniters associated with the one or more fuel
lances and adapted to ignite the fuel injected by the one or more
fuel lances into the combustion atmosphere.
2. The system of claim 1 wherein the one or more igniters are
selected from the group consisting of intermittent spark igniters,
continuous spark igniters, DC arc plasmas, microwave plasmas, RF
plasmas, high energy laser beams, and oxidant-fuel pilot
burners.
3. The system of claim 1 wherein at least one of the igniters is
disposed adjacent to a fuel lance and is adapted to ignite fuel
discharged therefrom.
4. The system of claim 1 wherein at least one of the igniters is
integrated into a fuel lance and is adapted to ignite fuel
discharged therefrom.
5. The system of claim 1 wherein the number of fuel lances is equal
to or less than the number of igniters.
6. A combustion system comprising (a) a furnace comprising an
enclosure and a thermal load disposed within the enclosure; (b) one
or more oxidant gas injectors mounted in the enclosure and adapted
to introduce an oxidant gas into the furnace; (c) one or more fuel
lances mounted in the enclosure and spaced apart from the one or
more oxidant gas injectors, wherein the one or more fuel lances are
adapted to inject fuel into the furnace; and (d) one or more
igniters associated with the one or more fuel lances and adapted to
ignite the fuel injected by the fuel lances.
7. The system of claim 6 wherein the one or more igniters are
selected from the group consisting of intermittent spark igniters,
continuous spark igniters, DC arc plasmas, microwave plasmas, RF
plasmas, high energy laser beams, and oxidant-fuel pilot
burners.
8. The system of claim 6 wherein at least one of the igniters is
adjacent to a fuel lance and is adapted to ignite fuel discharged
therefrom.
9. The system of claim 6 wherein at least one of the igniters is
integrated into a fuel lance and is adapted to ignite fuel
discharged therefrom.
10. The system of claim 6 wherein the number of fuel lances is
equal to or less than the number of igniters.
11. The system of claim 6 wherein the distance between the
periphery of one of the one or more oxidant gas injectors and the
periphery of an adjacent fuel lance is in the range of 2 to 50
inches.
12. A combustion system comprising (a) a furnace having a thermal
load and a combustion atmosphere disposed therein; (b) a central
burner having an axis, a primary fuel inlet, an oxidant gas inlet,
and a combustion gas outlet adapted to introduce the combustion gas
into the furnace; (c) one or more staging fuel lances disposed
radially from the axis of the central burner and adapted to inject
a staging fuel into the combustion atmosphere in the furnace; and
(d) one or more igniters associated with the one or more staging
fuel lances and adapted to ignite the staging fuel injected
therefrom.
13. The system of claim 12 wherein the one or more igniters are
selected from the group consisting of intermittent spark igniters,
continuous spark igniters, DC arc plasmas, microwave plasmas, RF
plasmas, high energy laser beams, and oxidant-fuel pilot
burners.
14. The system of claim 12 wherein at least one of the igniters is
adjacent to a staging fuel lance and is adapted to ignite fuel
discharged therefrom.
15. The system of claim 12 wherein at least one of the igniters is
integrated into a staging fuel lance and is adapted to ignite fuel
discharged therefrom.
16. The system of claim 12 wherein the number of staging fuel
lances is equal to or less than the number of igniters.
17. The system of claim 12 which further comprises main fuel piping
adapted to provide the primary fuel to the central burner and
staging fuel piping adapted to provide the staging fuel to the one
or more staging fuel lances.
18. The system of claim 17 wherein the primary fuel to the central
burner and the staging fuel to the one or more staging fuel lances
are identical in composition.
19. The system of claim 17 wherein the primary fuel to the central
burner and the staging fuel to the one or more staging fuel lances
are different in composition.
20. The system of claim 12 wherein the one or more staging fuel
lances are disposed outside of the central burner and are disposed
radially from the axis of the central burner.
21. A combustion process comprising (a) providing a combustion
system comprising (1) a furnace having a thermal load and a
combustion atmosphere disposed therein; (2) a central burner having
an axis, a primary fuel inlet, an oxidant gas inlet, and a
combustion gas outlet adapted to introduce the combustion gas into
the furnace; (3) one or more staging fuel lances disposed radially
from the axis of the central burner and adapted to inject a staging
fuel into the combustion atmosphere in the furnace; and (4) one or
more igniters associated with the one or more staging fuel lances
and adapted to ignite the staging fuel discharged therefrom. (b)
introducing the oxidant gas through the oxidant gas inlet and
injecting fuel through the one or more fuel lances into the
combustion atmosphere in the furnace; and (c) operating the one or
more igniters and igniting the fuel from the fuel lances to cause
combustion of the fuel with oxygen in the combustion
atmosphere.
22. The process of claim 21 wherein the fuel is selected from
natural gas, refinery offgas, associated gas from crude oil
production, and combustible process waste gas
23. The process of claim 21 wherein a plurality of fuel lances are
used and fuels of different compositions are used in the plurality
of fuel lances.
24. A combustion process comprising (a) providing a combustion
system including (1) a furnace having an enclosure with a thermal
load and a combustion atmosphere disposed within the enclosure; (2)
one or more oxidant gas injectors mounted in the enclosure and
adapted to introduce oxygen-containing gas into the furnace; (3)
one or more fuel lances mounted in the enclosure and spaced apart
from the one or more oxidant gas injectors, wherein the one or more
fuel lances are adapted to inject fuel into the furnace; and (4)
one or more igniters associated with the one or more fuel lances
and adapted to ignite the fuel injected by the fuel lances; (b)
injecting the oxygen-containing gas through the one or more oxidant
gas injectors into the combustion atmosphere in the furnace; (c)
injecting the fuel through the one or more fuel lances into the
combustion atmosphere in the furnace; and (d) operating the one or
more igniters and igniting the fuel from the fuel lances to cause
combustion of the fuel with oxygen in the combustion atmosphere.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application and claims the
benefit of priority under 35 USC 120 of U.S. application Ser. No.
10/883,349, filed Jul. 1, 2004, the specification and claims which
are incorporated by reference and made a part of this
application.
BACKGROUND OF THE INVENTION
[0002] Staged combustion systems are used to improve combustion by
introducing successive portions of fuel into the combustion process
to allow the oxidant and fuel to react in multiple zones or stages.
This produces lower peak flame temperatures and other favorable
combustion conditions that reduce the generation of nitrogen oxides
(NO.sub.x). A wide variety of staged combustion methods are known
and used in combustion applications including process heaters,
furnaces, steam boilers, gas turbine combustors, coal-fired power
generation units, and many other combustion systems in the
metallurgical and chemical process industries.
[0003] The combustion of a gaseous fuel with oxygen in an
oxygen-containing gas such as air occurs when a fuel-oxygen-inert
gas mixture having a composition in the combustible region reaches
its autoignition temperature or is ignited by a separate ignition
source. When the combustion occurs in a three-dimensional process
space such as a furnace, the degree of mixing is another important
variable in the combustion process. The degree of mixing in the
furnace, especially in the regions near the burners, affects
localized gas compositions and temperatures, and therefore is an
important factor in operating stability.
[0004] In combustion processes, particularly in staged combustion
processes for NO.sub.x reduction, it is important to have good
flame stability and proper location of the flame front relative to
the points at which staging fuel is introduced into the combustion
space. In conventional combustion systems, flame stability may be
maintained by the use of fuel injection devices and internal
recirculation patterns to improve the contact of the fuel stream
with the combustion atmosphere and to provide the ignition energy
required to sustain flame stability. Improper control of flame
stability and flame location in staged combustion systems,
particularly during cold startup, process upsets, or turndown
conditions, may result in undesirable combustion performance,
higher NO.sub.x emissions, and/or unburned fuel. This latter
condition could lead to substantial pockets of fuel in the furnace
and the possibility of an uncontrolled energy release.
[0005] There is a need in staged combustion processes for improved
flame stability and complete fuel combustion, particularly during
unsteady-state operating periods such as cold startup, process
upsets, or process turndown conditions. Improved staged combustion
systems to meet these needs are disclosed by embodiments of the
present invention described below and defined by the claims that
follow.
BRIEF SUMMARY OF THE INVENTION
[0006] An embodiment of the invention relates to a combustion
system comprising a furnace having a thermal load and a combustion
atmosphere disposed therein; one or more fuel lances adapted to
inject fuel into the combustion atmosphere; and one or more
igniters associated with the one or more fuel lances and adapted to
ignite the fuel injected by the one or more fuel lances into the
combustion atmosphere. The one or more igniters may be selected
from the group consisting of intermittent spark igniters,
continuous spark igniters, DC arc plasmas, microwave plasmas, RF
plasmas, high energy laser beams, and oxidant-fuel pilot burners.
In this embodiment, at least one of the igniters may be disposed
adjacent to a fuel lance and may be adapted to ignite fuel
discharged therefrom. Alternatively, at least one of the igniters
may be integrated into a fuel lance and adapted to ignite fuel
discharged therefrom. The number of fuel lances may be equal to or
less than the number of igniters.
[0007] Another embodiment relates to a fuel lance comprising a
nozzle body having an inlet face, an outlet face, and an inlet flow
axis passing through the inlet and outlet faces, and two or more
slots extending through the nozzle body from the inlet face to the
outlet face, each slot having a slot axis, wherein the slot axis of
at least one of the slots is not parallel to the inlet flow axis of
the nozzle body, and wherein the slots are adapted to discharge a
fuel at the outlet face of the nozzle body; and an igniter
associated with the nozzle body and adapted to ignite the fuel
discharged at the outlet face of the nozzle body. The igniter may
be disposed adjacent the outlet face of the nozzle body;
alternatively, the igniter may be integrated into the nozzle body
and passes through the outlet face of the nozzle body.
[0008] An alternative embodiment pertains to a fuel lance
comprising a nozzle body having an inlet face, an outlet face, and
an inlet flow axis passing through the inlet and outlet faces, two
or more slots extending through the nozzle body from the inlet face
to the outlet face, each slot having a slot axis and a slot center
plane, wherein none of the slots intersect other slots and all of
the slots are in fluid flow communication with a common fuel supply
conduit; and an igniter associated with the nozzle body and adapted
to ignite the fuel discharged at the outlet face of the nozzle
body. The igniter may be disposed adjacent the outlet face of the
nozzle body; alternatively, the igniter may be integrated into the
nozzle body and passes through the outlet face of the nozzle
body.
[0009] In another alternative embodiment, the fuel lance may
comprise a nozzle body having an inlet face, an outlet face, and an
inlet flow axis passing through the inlet and outlet faces and two
or more slots extending through the nozzle body from the inlet face
to the outlet face, each slot having a slot axis and a slot center
plane, wherein a first slot of the two or more slots is intersected
by each of the other slots and the slot center plane of at least
one of the slots intersects the inlet flow axis of the nozzle body;
and an igniter associated with the nozzle body and adapted to
ignite the fuel discharged at the outlet face of the nozzle body.
The igniter may be disposed adjacent the outlet face of the nozzle
body; alternatively, the igniter may be integrated into the nozzle
body and passes through the outlet face of the nozzle body.
[0010] A related embodiment of the invention includes a combustion
system comprising a furnace comprising an enclosure and a thermal
load disposed within the enclosure; one or more oxidant gas
injectors mounted in the enclosure and adapted to introduce an
oxidant gas into the furnace; one or more fuel lances mounted in
the enclosure and spaced apart from the one or more oxidant gas
injectors, wherein the one or more fuel lances are adapted to
inject fuel into the furnace; and one or more igniters associated
with the one or more fuel lances and adapted to ignite the fuel
injected by the fuel lances.
[0011] In this embodiment, the one or more igniters may be selected
from the group consisting of intermittent spark igniters,
continuous spark igniters, DC arc plasmas, microwave plasmas, RF
plasmas, high energy laser beams, and oxidant-fuel pilot burners.
At least one of the igniters may be adjacent to a fuel lance and
adapted to ignite fuel discharged therefrom. Alternatively, at
least one of the igniters may be integrated into a fuel lance and
adapted to ignite fuel discharged therefrom. The number of fuel
lances may be equal to or less than the number of igniters. The
distance between the periphery of one of the one or more oxidant
gas injectors and the periphery of an adjacent fuel lance may be in
the range of 2 to 50 inches.
[0012] Another related embodiment of the invention pertains to a
combustion system comprising a furnace having a thermal load and a
combustion atmosphere disposed therein; a central burner having an
axis, a primary fuel inlet, an oxidant gas inlet, and a combustion
gas outlet adapted to introduce the combustion gas into the
furnace; one or more staging fuel lances disposed radially from the
axis of the central burner and adapted to inject a staging fuel
into the combustion atmosphere in the furnace; and one or more
igniters associated with the one or more staging fuel lances and
adapted to ignite the staging fuel injected therefrom.
[0013] In this embodiment, the one or more igniters may be selected
from the group consisting of intermittent spark igniters,
continuous spark igniters, DC arc plasmas, microwave plasmas, RF
plasmas, high energy laser beams, and oxidant-fuel pilot burners.
At least one of the igniters may be adjacent to a fuel lance and
adapted to ignite fuel discharged therefrom. Alternatively, at
least one of the igniters may be integrated into a fuel lance and
adapted to ignite fuel discharged therefrom. The number of fuel
lances may be equal to or less than the number of igniters.
[0014] The system of this embodiment may further comprise main fuel
piping adapted to provide the primary fuel to the central burner
and staging fuel piping adapted to provide the staging fuel to the
one or more staging fuel lances. The primary fuel to the central
burner and the staging fuel to the one or more staging fuel lances
are identical in composition; alternatively, the primary fuel to
the central burner and the staging fuel to the one or more staging
fuel lances are different in composition. The one or more staging
fuel lances may be disposed outside of the central burner and may
be disposed radially from the axis of the central burner.
[0015] An alternative related embodiment of the invention includes
a combustion process comprising [0016] (a) providing a combustion
system comprising [0017] (1) a furnace having a thermal load and a
combustion atmosphere disposed therein; [0018] (2) a central burner
having an axis, a primary fuel inlet, an oxidant gas inlet, and a
combustion gas outlet adapted to introduce the combustion gas into
the furnace; [0019] (3) one or more staging fuel lances disposed
radially from the axis of the central burner and adapted to inject
a staging fuel into the combustion atmosphere in the furnace; and
[0020] (4) one or more igniters associated with the one or more
staging fuel lances and adapted to ignite the staging fuel
discharged therefrom. [0021] (b) introducing the oxidant gas
through the oxidant gas inlet and injecting fuel through the one or
more fuel lances into the combustion atmosphere in the furnace; and
[0022] (c) operating the one or more igniters and igniting the fuel
from the fuel lances to cause combustion of the fuel with oxygen in
the combustion atmosphere.
[0023] In this embodiment, the fuel may be selected from natural
gas, refinery offgas, associated gas from crude oil production, and
combustible process waste gas. A plurality of fuel lances may be
used and fuels of different compositions may be used in the
plurality of fuel lances.
[0024] Another alternative related embodiment of the invention
pertains to a combustion process comprising: [0025] (a) providing
burner assembly including: [0026] (1) a central flame holder having
inlet means for an oxidant gas, inlet means for a primary fuel, a
combustion region for combusting the oxidant gas and the primary
fuel, and an outlet for discharging a primary effluent from the
flame holder; and [0027] (2) a plurality of secondary fuel injector
nozzles surrounding the outlet of the central flame holder, wherein
each secondary fuel injector nozzle comprises [0028] (2a) a nozzle
body having an inlet face, an outlet face, and an inlet flow axis
passing through the inlet and outlet faces; and [0029] (2b) one or
more slots extending through the nozzle body from the inlet face to
the outlet face, each slot having a slot axis and a slot center
plane; [0030] (3) one or more igniters associated with the
plurality of secondary fuel injector nozzles; [0031] (b)
introducing the primary fuel and the oxidant gas into the central
flame holder, combusting the primary fuel with a portion of the
oxidant gas in the combustion region of the flame holder, and
discharging a primary effluent containing combustion products and
excess oxidant gas from the outlet of the flame holder; and [0032]
(c) injecting the secondary fuel through the secondary fuel
injector nozzles into the primary effluent from the outlet of the
flame holder; and [0033] (d) operating the one or more igniters and
igniting the fuel from the secondary fuel injector nozzles to cause
combustion of the fuel with the excess oxidant in the combustion
products.
[0034] In this embodiment, the primary fuel and the secondary fuel
may be gases having different compositions. The primary fuel may be
natural gas or refinery offgas and the secondary fuel may comprise
hydrogen, methane, carbon monoxide, and carbon dioxide obtained
from a pressure swing adsorption system. Alternatively, the primary
fuel and the secondary fuel may be gases having the same
compositions.
[0035] A different embodiment of the invention relates to a
combustion process comprising [0036] (a) providing a combustion
system including [0037] (1) a furnace having an enclosure with a
thermal load and a combustion atmosphere disposed within the
enclosure; [0038] (2) one or more oxidant gas injectors mounted in
the enclosure and adapted to introduce oxygen-containing gas into
the furnace; [0039] (3) one or more fuel lances mounted in the
enclosure and spaced apart from the one or more oxidant gas
injectors, wherein the one or more fuel lances are adapted to
inject fuel into the furnace; and [0040] (4) one or more igniters
associated with the one or more fuel lances and adapted to ignite
the fuel injected by the fuel lances; [0041] (b) injecting the
oxygen-containing gas through the one or more oxidant gas injectors
into the combustion atmosphere in the furnace; [0042] (c) injecting
the fuel through the one or more fuel lances into the combustion
atmosphere in the furnace; and [0043] (d) operating the one or more
igniters and igniting the fuel from the fuel lances to cause
combustion of the fuel with oxygen in the combustion
atmosphere.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0044] FIG. 1 is a schematic sectional view of a burner assembly
utilizing secondary fuel injection nozzles.
[0045] FIG. 2 is an isometric view of a nozzle assembly and nozzle
body that may be used in an embodiment of the present
invention.
[0046] FIG. 3 an axial section drawing of the nozzle body of FIG.
2.
[0047] FIG. 4 is a schematic front view of the burner assembly of
FIG. 1.
[0048] FIG. 5 is a schematic sectional view of a burner assembly
utilizing secondary fuel injection nozzles and exemplary igniters
relating to embodiments of the invention.
[0049] FIG. 6 is a schematic front view of the burner assembly of
FIG. 5.
[0050] FIG. 7A is a schematic sectional view of an exemplary
igniter used in an embodiment of the invention.
[0051] FIG. 7B is a front view of FIG. 7A.
[0052] FIG. 8A is a schematic sectional view of an alternative
exemplary igniter pilot used in an embodiment of the invention.
[0053] FIG. 8B is a front view of FIG. 8A.
[0054] FIG. 9 is an isometric view of an integrated fuel injector
nozzle and igniter according to an embodiment of the invention.
[0055] FIG. 10 is a schematic sectional view of another embodiment
of the invention in which the integrated fuel injector nozzle and
igniter of FIG. 9 and an oxidant gas injector are installed in the
wall or enclosure of a furnace.
[0056] FIG. 11 is a schematic view of a matrix furnace combustion
system in an embodiment using multiple integrated fuel injector
nozzles and igniters of FIG. 10 and multiple oxidant gas injectors
of FIG. 10.
DETAILED DESCRIPTION OF THE INVENTION
[0057] Combustion-based processes utilize the combustion of fuel
streams with oxygen to generate process heat and, in some cases, to
consume combustible off-gas streams from other process systems. In
the establishment of a combustion reaction with these various
fuels, autoignition will occur if the temperature of the
fuel-oxidant mixture is above the autoignition temperature of the
mixture. In air/natural gas mixtures, for example, the autoignition
temperature is about 1,000.degree. F. An ignition source is
required to initiate the combustion reaction if the temperature of
the fuel-oxidant mixture is below its autoignition temperature.
[0058] An additional variable, the extent of mixing in the
combustion atmosphere or combustion region, can affect the
stability of the combustion process with a gaseous or vaporized
fuel. Stabilization of the combustion process becomes complicated
when fuel staging is used to limit formation of NO.sub.x. In fuel
staging, raw fuel (without air or oxygen) is introduced into the
combustion atmosphere containing excess oxygen remaining from an
earlier step of combustion. Although the fuel for each stage of
combustion typically is identical, different fuel sources may be
used, and the use of different staging fuels may affect the
operating stability of the combustion process. In order to minimize
formation of NO.sub.x, it is desirable to introduce the staging
fuel into the combustion atmosphere at or near a location having a
minimum concentration of oxygen.
[0059] The maintenance of flame stability and flame location in
staged fuel combustion systems may be difficult during
unsteady-state process conditions that occur in a furnace during
cold startup, process upsets, or turndown conditions. During such
conditions, localized temperatures may fall below the autoignition
temperature of the fuel-oxidant mixture and may result in unstable
flames and/or regions containing unburned fuel. This is undesirable
and may lead to the possibility of an uncontrolled energy release
in the furnace.
[0060] Flame stability, which is the proper location of the flame
front relative to the point of introduction of the fuel stream in
the combustion atmosphere, is a key aspect of the successful
application of fuel staging. In conventional staged combustion
systems, flame stability is maintained by the use of combinations
of fuel injection devices and mixing patterns to improve the
contact between the fuel-rich jet and the source of oxygen, which
could be the inlet combustion air stream or unreacted oxygen
contained in the gaseous atmosphere in the furnace. The proper
location and amount of ignition energy also is important. Designs
for fuel injection devices typically attempt to anchor the flame at
the flame holder tip, which can be the fuel injector itself, a
separate bluff body device (such as an external surface of
refractory tile), or a swirl stabilizer nozzle. The drawback of
conventional bluff body type flame stabilizers is that they have a
limited turndown ratio, which limits their stability performance
during cold start-up and process upset conditions. Any substantial
distance or lift-off height between the staged fuel jet flame front
and the flame holder surface will cause oscillation in the flame
and result in undesirable combustion performance, including
NO.sub.x emissions and/or the presence of unburned fuel.
[0061] When non-steady state conditions such as start-up or process
upsets occur while flow through the conventional fuel staging
system is maintained, the volume of fuel that exists at high
concentrations can increase substantially within the combustion
system. The regions near the fuel-rich jets from the injection
devices may be outside of the flammability limits (e.g., between 5
and 15 vol % for natural gas) and there may be insufficient
ignition energy available in the cold furnace. When multiple
elements of these fuel staging systems are included in one piece of
equipment or when the flame is re-established from a single burner,
additional sources of ignition may be present in the furnace. These
ignition sources may be, for example, radicals formed in the
combustion reactions at the burner and/or the staged fuel injection
devices. An uncontrolled energy release promoted by the reaction of
these radicals with the volume of unburned fuel in a process
heater, boiler, reformer, or other similar unit operation is a
safety and operability concern.
[0062] Conventional burner technology cannot provide flame
stability for individual fuel staging lances during cold start-up,
at low furnace temperatures, and during upset or turndown
conditions. Lack of stability during these periods could lead to
flame lift-off and subsequent uncontrolled energy release as
discussed above. A robust solution is needed to address these
potentially unsafe conditions. The preferred solution should
utilize changes and enhancements to the combustion equipment itself
rather than require the execution of specific operating and control
steps by process operating personnel. Such a solution is disclosed
in embodiments of the present invention wherein one or more
ignition sources are used in conjunction with the fuel injection
lances that introduce staging fuel into a combustion region or
zone.
[0063] Ignition-assisted fuel lances are used in various
embodiments of the invention in order to ensure ignition of the
fuel injected into oxygen-containing gases in a combustion
atmosphere in a process heater, furnace, steam boiler, gas turbine
combustor, or other gas-fired combustion system. A fuel lance is
defined herein as a device for injecting fuel at an elevated
velocity into a combustion atmosphere. The combustion atmosphere
contains an oxidant gas, and the staging fuel injected into the
oxidant gas is combusted with oxygen in the oxidant gas. The
oxidant gas may be air, oxygen-enriched air, or a combustion gas
containing combustion products and excess unreacted oxygen. For
example, ignition-assisted fuel lances may be installed in a
furnace boundary, wall, or enclosure adjacent to but separate from
a burner wherein the fuel lances inject fuel into the combustion
atmosphere generated by the burner to effect staged combustion.
Alternatively, ignition-assisted fuel lances may be installed
adjacent to but separate from a source of oxidant gas such as air,
wherein the fuel lances inject portions of the fuel into the
oxidant gas or the combustion atmosphere to effect parallel staged
combustion.
[0064] The term "combustion atmosphere" as used herein means the
atmosphere within the enclosure or boundaries of a furnace. The
overall combustion atmosphere within the boundaries of the furnace
comprises oxygen, fuel, combustion gas containing combustion
reaction products (e.g., carbon oxides, nitrogen oxides, and
water), and inert gases (e.g., nitrogen and argon). The source of
the oxygen and inert gases typically is air; an alternative or
additional source of oxygen may be an oxygen injection system which
introduces oxygen-enriched air and/or high purity oxygen to enhance
the combustion process. The combustion atmosphere is heterogenous
because the concentration of the components varies throughout the
furnace. For example, the concentration of oxygen may be higher
near oxidant injection points and the concentration of fuel may be
higher near the fuel injection points. In other regions of the
combustion atmosphere, there may be no fuel present. The
concentration of oxygen and combustion reaction products will vary
depending on the extent of combustion at various locations within
the combustion atmosphere. At certain locations, injected fuel may
react directly with oxygen in the oxidant gas injected into the
combustion atmosphere; at other locations, injected fuel may react
with unreacted oxygen from combustion occurring elsewhere in the
combustion atmosphere.
[0065] A thermal load is disposed in the combustion atmosphere
within the interior of the furnace, wherein a thermal load is
defined as (1) the heat absorbed by material transported through
the furnace combustion atmosphere wherein the heat is transferred
from the combustion atmosphere to the material as it is transported
through the furnace or (2) the heat exchange apparatus adapted to
transfer heat from the combustion atmosphere to the material being
heated.
[0066] An exemplary concentrically-staged combustion burner system
is illustrated in sectional view in FIG. 1, which shows a central
burner or flame holder surrounded by multiple injection lances for
injecting staging fuel. A burner is defined as an integrated
combustion assembly for the combustion of oxidant and fuel, wherein
the burner is adapted for mounting in the wall or enclosure of a
furnace. Central burner or flame holder 1 comprises outer pipe 3,
concentric intermediate pipe 5, and inner concentric pipe 7. The
interior of inner pipe 7 and annular space 9 between outer pipe 3
and intermediate pipe 5 are in flow communication with the interior
of outer pipe 3. Annular space 11 between inner pipe 7 and
intermediate pipe 5 is connected to and in flow communication with
fuel inlet pipe 13. The central burner is installed in furnace wall
14.
[0067] In the operation of this central burner, oxidant gas
(typically air or oxygen-enriched air) 15 flows into the interior
of outer pipe 3, a portion of this air flows through the interior
of inner pipe 7, and the remaining portion of this air flows
through annular space 9. Primary fuel 15 flows through pipe 13 and
through annular space 11, and is combusted initially in combustion
zone 17 with air from inner pipe 7. Combustion gas from combustion
zone 17 mixes with additional air in combustion zone 19. Combustion
in this zone is typically extremely fuel-lean. A visible flame
typically is formed in combustion zone 19 and in combustion zone 21
as combustion gas 23 enters furnace interior 25. The term
"combustion zone" as used here means a region within the burner in
which combustion occurs.
[0068] A staging fuel system comprises inlet pipe 27, manifold 29,
and a plurality of staging fuel lances 31. The ends of the staging
fuel lances may be fitted with injection nozzles 33 of any desired
type. Staging fuel 35 flows through inlet pipe 27, manifold 29, and
staging fuel injection lances 31. Staging fuel streams 37 from
nozzles 33 mix rapidly and combust with the oxidant-containing
combustion gas 23. The cooler combustion atmosphere in furnace
interior 25 is rapidly entrained by staging fuel streams 37 by the
intense mixing action promoted by nozzles 33, and the
concentrically-injected staging fuel is combusted with the
oxidant-containing combustion atmosphere downstream of the exit of
central burner 1. The primary fuel may be 5 to 30% of the total
fuel flow rate (primary plus staging) and the staging fuel may be
70 to 95% of the total fuel flow rate.
[0069] The primary and staging fuels may have the same composition
or may have different compositions and either fuel may be any
gaseous, vaporized, or atomized hydrocarbon-containing material.
For example, the fuel may be selected from the group consisting of
natural gas, refinery offgas, associated gas from crude oil
production, and combustible process waste gas. An exemplary process
waste gas is the tail gas or waste gas from a pressure swing
adsorption system in a process for generating hydrogen from natural
gas.
[0070] An exemplary type of nozzle 33 is illustrated in FIG. 2.
Nozzle assembly 201 comprises nozzle body 203 joined to nozzle
inlet pipe 205. Slot 207, illustrated here as vertically-oriented,
is intersected by slots 209, 211, 213, and 215. The slots are
disposed between outlet face 217 and an inlet face (not seen) at
the connection between nozzle body 203 and nozzle inlet pipe 205.
Fluid 219 flows through nozzle inlet pipe 205 and through slots
207, 209, 211, 213, and 215, and then mixes with another fluid
surrounding the slot outlets. In addition to the slot pattern shown
in FIG. 2, other slot patterns are possible; the nozzle assembly
can be used in any orientation and is not limited to the generally
horizontal orientation shown. When viewed in a direction
perpendicular to outlet face 217, exemplary slots 209, 211, 213,
and 215 intersect slot 207 at right angles. Other angles of
intersection are possible between exemplary slots 209, 211, 213,
and 215 and slot 207. When viewed in a direction perpendicular to
outlet face 217, exemplary slots 209, 211, 213, and 215 are
parallel to one another; however, other embodiments are possible in
which one or more of these slots are not parallel to the remaining
slots.
[0071] The term "slot" as used herein is defined as an opening
through a nozzle body or other solid material wherein any slot
cross-section (i.e., a section perpendicular to the inlet flow axis
defined below) is non-circular and is characterized by a major axis
and a minor axis. The major axis is longer than the minor axis and
the two axes are generally perpendicular. For example, the major
cross-section axis of any slot in FIG. 2 extends between the two
ends of the slot cross-section; the minor cross-section axis is
perpendicular to the major axis and extends between the sides of
the slot cross-section. The slot may have a cross-section of any
non-circular shape and each cross-section may be characterized by a
center point or centroid, where centroid has the usual geometric
definition.
[0072] A slot may be further characterized by a slot axis defined
as a straight line connecting the centroids of all slot
cross-sections. In addition, a slot may be characterized or defined
by a center plane which intersects the major cross-section axes of
all slot cross-sections. Each slot cross-section may have
perpendicular symmetry on either side of this center plane. The
center plane extends beyond either end of the slot and may be used
to define the slot orientation relative to the nozzle body inlet
flow axis as described below.
[0073] Axial section I-I of the nozzle of FIG. 2 is given in FIG.
3. Inlet flow axis 301 passes through the center of nozzle inlet
pipe 302, inlet face 303, and outlet face 217. In this embodiment,
the center planes of slots 209, 211, 213, and 215 lie at angles to
inlet flow axis 301 (i.e., are not parallel to inlet flow axis 301)
such that fluid flows from the slots at outlet face 217 in
diverging directions from inlet flow axis 301. The center plane of
slot 207 (only a portion of this slot is seen in FIG. 3) also lies
at an angle to inlet flow axis 301. This exemplary feature directs
fluid from the nozzle outlet face in another diverging direction
from inlet flow axis 301. In this exemplary embodiment, when viewed
in a direction perpendicular to the axial section of FIG. 3, slots
209 and 211 intersect at inlet face 303 to form sharp edge 305,
slots 211 and 213 intersect to form sharp edge 307, and slots 213
and 215 intersect to from sharp edge 309. These sharp edges provide
aerodynamic flow separation to the slots and reduce pressure drop
associated with bluff bodies. Alternatively, these slots may
intersect at an axial location between inlet face 303 and outlet
face 217, and the sharp edges would be formed within nozzle body
203. Alternatively, these slots may not intersect when viewed in a
direction perpendicular to the axial section of FIG. 2, and no
sharp edges would be formed.
[0074] The term "inlet flow axis" as used herein is an axis defined
by the flow direction of fluid entering the nozzle at the inlet
face, wherein this axis passes through the inlet and outlet faces.
Typically, but not in all cases, the inlet flow axis is
perpendicular to the center of nozzle inlet face 303 and/or outlet
nozzle face 217, and meets the faces perpendicularly. When nozzle
inlet pipe 302 is a typical cylindrical conduit as shown, the inlet
flow axis may be parallel to or coincident with the conduit
axis.
[0075] The axial slot length is defined as the length of a slot
between the nozzle inlet face and outlet face, for example, between
inlet face 303 and outlet face 217 of FIG. 3. The slot height is
defined as the perpendicular distance between the slot walls at the
minor cross-section axis. The ratio of the axial slot length to the
slot height may be between about 1 and about 20.
[0076] The multiple slots in a nozzle body may intersect in a plane
perpendicular to the inlet flow axis. As shown in FIG. 2, for
example, slots 209, 211, 213, and 215 intersect slot 207 at right
angles. If desired, these slots may intersect in a plane
perpendicular to the inlet flow axis at angles other than right
angles. Adjacent slots also may intersect when viewed in a plane
parallel to the inlet flow axis, i.e., the section plane of FIG. 3.
As shown in FIG. 3, for example, slots 209 and 211 intersect at
inlet face 303 to form sharp edge 305 as earlier described. The
angular relationships among the center planes of the slots, and
also between the center plane of each slot and the inlet flow axis,
may be varied as desired. This allows fluid to be discharged from
the nozzle in any selected direction relative to the nozzle
axis.
[0077] Alternative, a nozzle body may be envisioned in which none
of the slots intersect each other in any plane perpendicular to
axis 301. In this alternative embodiment, for example, all slots
viewed perpendicular to the nozzle body face are separate and do
not intersect other slots. Such a nozzle could, for example, be
similar to the nozzle of FIG. 2 without slot 207, wherein the
nozzle would have only slots 209, 211, 213, and 215. These slots
may intersect axially as shown in FIG. 2.
[0078] FIG. 4 is a plan view showing the discharge end of the
exemplary apparatus of FIG. 1 utilizing the staging fuel lance
nozzles of FIGS. 2 and 3. Concentric pipes 403, 405, and 407
enclose annular spaces 409 and 411 which are fitted with radial
members or fins. Slotted staging fuel injection nozzles 433
(earlier described) may be disposed concentrically around the
central burner as shown. In this embodiment, the slot angles of the
slotted injection nozzles are oriented to direct injected staging
fuel in diverging directions relative to the axis of central burner
1.
[0079] Other types of nozzle configurations may be used for nozzle
body 203 (FIG. 2) at the injection ends of staging fuel nozzles 433
(FIG. 4). For example, the openings in outlet face 217 of nozzle
body 203 may be formed in the shape of one or more cross-shaped
openings formed by two intersecting slots. Alternatively, any other
types of openings may be used in the nozzle body face which have
shapes different from the slots described above.
[0080] The exemplary concentrically-staged combustion burner system
of FIG. 1 may be modified according to an embodiment of the
invention as illustrated in FIG. 5. Igniters 501, shown here
schematically, are associated with staging fuel lances 31 and are
adapted to ignite staging fuel 37 discharged from nozzles 33. The
igniters may be adjacent the staging fuel lances as shown, wherein
the ignition ends 503 of the igniters are adjacent the tips of
nozzles 33. Alternatively, the igniters may be integrated into the
staging fuel lances as described later. The generic meaning of the
term "igniter" as used herein is a device to generate a localized
temperature above the autoignition temperature of the fuel-oxidant
mixture. For example, igniters 501 adjacent to nozzles 33, thereby
ensuring ignition of the staging fuel stream. Igniters 501 are
shown schematically in FIG. 5 and may be any type of igniter
capable of generating temperatures sufficiently high to ignite the
mixture of staging fuel and oxidant. For example, these igniters
may generate pilot flames at ignition ends 503 wherein the pilot
flames are formed by combusting a fuel-oxidant mixture separate
from the fuel-oxidant mixture of the central burner. Alternatively,
igniters 501 may be intermittent spark igniters, continuous spark
igniters, DC arc plasmas, microwave plasmas, RF plasmas, high
energy laser beams, or any other type of igniter at ignition ends
503.
[0081] The location of the igniters in FIG. 5 may be seen in the
plan view of FIG. 6 showing the discharge end of the central burner
and schematic ignition ends 503 associated with concentric
injection nozzles 33. In this embodiment, each ignition end is
adjacent a staging injection nozzle. Alternatively, the igniters
may be integrated into staging fuel lances 31 as described later.
In the embodiment of FIG. 6, each injection nozzle and fuel lance
has an adjacent igniter, and the number of igniters and the number
of staging fuel lances are equal. Alternatively, the number of
staging fuel lances may be less than the number of igniters,
wherein each igniter effects the ignition of a plurality of fuel
lances. In one example, igniters may be associated with alternating
staging fuel lances wherein the number of igniters is half the
number of fuel lances. Any number and configuration of igniters may
be used to effect proper ignition of the staging fuel-oxidant
mixture. In the present disclosure, the term "associated with"
means that an igniter associated with a staging fuel lance is
adapted for and is capable of igniting the fuel-oxidant mixture
formed by the staging fuel from the staging fuel lance and the
oxidant present in the region adjacent the discharge of the lance.
As mentioned above, an igniter associated with a lance may be
adjacent the lance or may be an integral part of the lance.
[0082] Igniter 501 (FIG. 5) may utilize a pilot flame formed at
ignition end 503 by a pilot fuel and a pilot oxidant. The pilot
fuel may be the same fuel as that provided to the staging fuel
lance, or may be a different fuel such as, for example, the primary
fuel 15 of central burner 1. The pilot oxidant may be air,
oxygen-enriched air, or other oxygen-containing gas. The direction
of the pilot flame discharge may be generally parallel to the
direction of the staging fuel discharge, or alternatively may be at
any angle to the direction of the staging fuel discharge. In one
embodiment, the pilot flame may be directed radially outward from
the axis of the central burner and in another embodiment may be
directed generally parallel to the axis of the central burner. The
pilot fuel and pilot oxidant may be premixed upstream of the end of
the igniter or alternatively the fuel and oxidant may be delivered
to and combusted near the ignition end of the pilot-type igniter.
The igniter itself may be equipped with spark ignition means to
ignite the pilot fuel and pilot oxidant as described below.
[0083] An exemplary igniter is a pilot device shown in FIGS. 7A
(side sectional view) and 7B (end view). This pilot comprises outer
pipe 701, inner pipe 703, flow turbulence generator or bluff body
705, and annulus 707. An oxidant gas such as air or oxygen-enriched
air flows through annulus 707 and over flow turbulence generator or
bluff body 705, and fuel gas flows through inner pipe 703. The fuel
and oxidant combust to form a pilot flame at the outlet of the
pilot. If desired, an electrical ignition device may be used for
initial ignition of the pilot fuel and oxidant. An exemplary
ignition device is shown in FIGS. 8A and 8B, wherein electrode 801
is installed in the interior of inner pipe 703. The end of the
electrode typically extends beyond the end of inner pipe 703 and is
disposed in the region between the ends of inner pipe 703 and outer
pipe 701. A spark is generated between the end of the electrode and
the inner wall of outer pipe 701 when the electrode is electrically
energized. Oxidant and fuel flow through inner pipe 703 and annulus
707, respectively, mix in the region between the ends of inner pipe
703 and outer pipe 701, and are ignited by a spark generated
between the end of the electrode and the inner wall of outer pipe
701.
[0084] An alternative type of igniter pilot may be used as an
alternative to FIGS. 8A and 8B. In this alternative, inner pipe 703
is not used, and a pre-mixed fuel-oxidant mixture is provided
through pipe 701 and ignited by a spark from the end of electrode
801.
[0085] The pilot igniters described above may be operated
continuously, for example, during operation of a furnace fired by a
plurality of burners, for example, as in burner 1 of FIG. 5).
Alternatively, the pilot igniters may be operated only during cold
startup of the furnace and would be inactive during normal
operation of the furnace.
[0086] A pilot igniter of FIGS. 7A and 7B or FIGS. 8A and 8B may be
installed adjacent each staging fuel lance as shown in FIGS. 5 and
6. Alternatively, the pilot igniter may be designed as an integral
part of a staging fuel lance as illustrated in FIG. 9. In this
exemplary embodiment, the electrode-assisted pilot igniter of FIGS.
8A and 8B is integrated into the fuel lance and nozzle of FIGS. 2
and 3. In the integrated fuel lance and igniter assembly 901 of
FIG. 9, slots 909, 911, 913, and 915 intersect slot 907 as shown,
and all slots pass through fuel lance nozzle face 917 and lie at
angles to the inlet flow axis of the lance such that fluid flows
from the slots at outlet face 917 in diverging directions from
inlet flow axis. The igniter comprises outer pipe 903, inner pipe
904, and electrode 905, and these components are installed in a
bore through the lance parallel to the axis of the lance. The
igniter operates as described above with reference to FIGS. 8A and
8B.
[0087] Fuel 919 enters the lance inlet end, flows through an
interior fuel passage (not seen), and exits slots 907, 909, 911,
913, and 915 at nozzle face 917. Pilot fuel 921, which may be the
same or different than lance fuel 919, flows into and through inner
pipe 904. Pilot oxidant gas 923, (for example, air or
oxygen-enriched air) flows into and through the annulus between
outer pipe 903 and inner pipe 904. Ignition electrode 905 is used
to ignite the mixture of pilot fuel and oxidant gas as described
above.
[0088] Instead of the pilot flame igniter discussed above as part
of the ignition-assisted lance of FIG. 9, any other type of igniter
may be used. The igniter may be selected from. for example,
intermittent spark igniters, continuous spark igniters, DC arc
plasmas, microwave plasmas, RF plasmas, and high energy laser
beams.
[0089] An alternative embodiment of the invention relates to a
combustion system having oxidant injectors for injecting oxidant
gas into a furnace and separate ignition-assisted fuel lances for
injecting fuel into the furnace. No individual burners are used in
this embodiment, which may be considered a matrix combustion
system. The system comprises a furnace having an enclosure and a
thermal load disposed within the enclosure; one or more oxidant gas
injectors mounted in the enclosure and adapted to introduce an
oxygen-containing gas into the furnace; one or more fuel lances
mounted in the enclosure and spaced apart from the one or more
oxidant gas injectors, wherein the one or more fuel lances are
adapted to inject fuel into the furnace; and one or more igniters
associated with the one or more fuel lances and adapted to ignite
the fuel injected by the fuel lances. When one or more oxidant gas
injectors and a plurality of fuel lances are used, the combustion
system may be defined as a matrix-staged combustion system.
[0090] This embodiment is illustrated schematically in FIG. 10
wherein oxidant gas 1001 is injected through oxidant gas injector
1003 mounted in furnace wall or enclosure 1005. The furnace wall or
enclosure may be lined with high-temperature refractory 1007 as
shown. Oxidant gas 1001 may be air, oxygen-enriched air, or any
other oxygen-containing gas. Injected oxidant gas forms distributed
jet 1009 within the combustion atmosphere in the interior 1011 of
the furnace.
[0091] Ignition-assisted fuel lance 1013 is disposed in furnace
wall 1005 apart from oxidant gas injector 1003 and operates to
inject fuel gas 1015 into furnace interior 1011 and form
distributed fuel gas jet 1017. Ignition-assisted fuel lance 1013 is
shown here as a sectional view of the lance described above with
reference to FIG. 10, although any type of ignition-assisted lance
may be used. The distance D between the periphery of oxidant gas
injector 1003 and the periphery of adjacent ignition-assisted fuel
lance 1013 may be in the range of 2 to 50 inches. Pilot flame 1019
is formed by the combustion of an oxidant-fuel mixture provided by
pilot fuel 1021 and pilot oxidant 1023 ignited by the electrode
disposed within the lance as earlier described.
[0092] Pilot flame 1019 ignites the fuel-oxidant mixture formed by
fuel 1017 and oxidant 1009 in combustion atmosphere 1011 in the
furnace interior if the temperature of the fuel-oxidant mixture is
below its autoignition temperature. Typically a flame (not shown)
is formed immediately downstream of distributed fuel gas jet 1017.
If the temperature of the fuel-oxidant mixture is above its
autoignition temperature, operation of the pilot flame igniter may
not be needed; however, operation of the pilot flame may be
continued to provide ignition of the fuel-oxidant mixture if needed
in the event of an operating upset in the furnace operation.
[0093] Additional ignition-assisted fuel lances may be disposed at
other spaced-apart locations in furnace wall 1005; for example, a
lance identical to lance 1013 may be installed in opening 1025
shown on the opposite side of oxidant gas injector 1003. In the
embodiment of FIG. 10, oxidant gas injector 1003 and
ignition-assisted fuel lance 1013 (and any other ignition-assisted
fuel lances not shown) typically are separate elements installed in
furnace wall 1005. One or more oxidant gas injectors and a
plurality of fuel lances may be used to provide a matrix-staged
combustion system.
[0094] An exemplary matrix-staged installation utilizing multiple
oxidant gas injectors and ignition-assisted fuel lances is
illustrated in the embodiment of FIG. 11. An exemplary furnace 1101
is defined by walls or enclosure 1103 to form a right
parallelepiped combustion space or volume enclosing a combustion
atmosphere, although in other embodiments the combustion atmosphere
may be enclosed by any furnace shape. A plurality of oxidant gas
injectors 1105, 1107, and 1109 and a plurality of ignition-assisted
fuel lances 1111, 1113, and 1115 are installed in the upper
boundary or ceiling of the furnace. Each of the oxidant gas
injectors introduce jets or streams of oxidant gas into the furnace
and each of ignition-assisted fuel lances introduces jets or
streams of fuel gas, as illustrated by the downward arrows from
each of the injectors and lances. The oxidant gas injectors may be
identical to oxidant gas injector 1003 of FIG. 10 and the
ignition-assisted fuel lances may be identical to ignition assisted
fuel lance 1013 of FIG. 10. Other types of oxidant gas injectors
and ignition-assisted fuel lances may be used as desired, and any
geometrical arrangement of oxidant gas injectors and
ignition-assisted fuel lances may be used.
[0095] The injected fuel gas is combusted with the oxidant gas, and
combustion may be initiated by the pilot flames in the
ignition-assisted lances as earlier described with reference to
FIG. 10. Flames typically are formed below the downward-directed
fuel jets, and these flames may or may not be visible. The hot
combustion atmosphere including carbon oxides, nitrogen oxides,
water, unconsumed oxygen, and inert gases exit furnace 1101 as flue
gas 1117. Matrix-staged combustion occurs in the furnace as
portions of the fuel are injected in fuel lances along the flow
axis of the furnace in the direction of the outlet of flue gas
1117.
[0096] A thermal load typically will exist in furnace 1101 to
absorb a portion of the combustion heat generated therein. In this
illustration, schematic heat exchanger 1119 is shown in the bottom
of the furnace to heat process feed stream 1121 and convert it to
process effluent stream 1123 exiting the furnace. Process feed
stream 1121 may be heated in the furnace with or without
accompanying chemical reaction. Phase change in the process stream
may or may not occur, depending on the particular application.
Instead of a process stream comprising the thermal load, articles
may be conveyed through the furnace and absorb heat therein, for
example, in a metallurgical heat treating process. Regardless of
the type of material passing through the furnace, the system and
process are characterized by a thermal load which absorbs heat from
the hot combustion atmosphere in the furnace. In all embodiments of
the invention, the generic meaning of "thermal load" as earlier
described is (1) the heat absorbed by material transported through
the furnace combustion atmosphere wherein the heat is transferred
from the combustion atmosphere to the material as it is transported
through the furnace or (2) the heat exchange apparatus adapted to
transfer heat from the combustion atmosphere to the material being
heated. The combustion atmosphere is contained within the furnace,
wherein the furnace is defined as an enclosure within which
combustion of injected oxidant and fuel occurs.
[0097] While the embodiment of FIG. 11 illustrates a parallelepiped
furnace enclosure with top-mounted downward directed injectors, any
other desired geometry may be used. For example, the furnace of
FIG. 11 may be wall-fired with horizontal oxidant and fuel
injection or may be floor-fired with upward oxidant and fuel
injection. Alternatively, a cylindrical furnace may be used in
which the process tubes are installed in a circular geometry
parallel to the cylindrical walls. Fuel and oxidant may be injected
at the bottom of the furnace in an upward direction and combustion
products may exit at the top of the furnace through a stack. A
concentrically-staged combustion system (FIGS. 5 and 6) or a
matrix-staged combustion system (FIGS. 10 and 11) may be used in
any furnace geometry to yield a uniform heat distribution, better
flame stability, and lower NO.sub.x emissions.
* * * * *