U.S. patent application number 11/542439 was filed with the patent office on 2008-04-03 for low nox combustion.
Invention is credited to Mark C. Hannum, Thomas B. Neville, John J. Nowakowski, Thomas F. Robertson.
Application Number | 20080081301 11/542439 |
Document ID | / |
Family ID | 39271292 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080081301 |
Kind Code |
A1 |
Hannum; Mark C. ; et
al. |
April 3, 2008 |
Low NOx combustion
Abstract
A furnace has a process chamber and a burner that is operative
to fire a flame into the process chamber with the influence of a
flame stabilizer. A bypass apparatus is configured to inject an
unignited stream of premix into the process chamber without the
influence of a flame stabilizer.
Inventors: |
Hannum; Mark C.; (Aurora,
OH) ; Robertson; Thomas F.; (Medina Township, OH)
; Neville; Thomas B.; (Incline Village, NV) ;
Nowakowski; John J.; (Valley View, OH) |
Correspondence
Address: |
Stephen D. Scanlon, Esq.;JONES DAY
North Point, 901 Lakeside Avenue
Cleveland
OH
44114
US
|
Family ID: |
39271292 |
Appl. No.: |
11/542439 |
Filed: |
October 3, 2006 |
Current U.S.
Class: |
431/12 ;
431/75 |
Current CPC
Class: |
F23N 2237/02 20200101;
F23N 2237/20 20200101; Y02E 20/342 20130101; Y02E 20/34 20130101;
F23N 2227/02 20200101; F23N 5/00 20130101; F23C 2900/99001
20130101; F23N 2225/08 20200101; F23N 1/022 20130101 |
Class at
Publication: |
431/12 ;
431/75 |
International
Class: |
F23N 1/02 20060101
F23N001/02; F23N 5/00 20060101 F23N005/00 |
Claims
1. An apparatus configured for use with a furnace process chamber
and a burner that is operative to fire into the process chamber
with flame stabilization, said apparatus comprising: a premix
injection apparatus that is configured to inject unignited premix
into the process chamber without flame stabilization.
2. An apparatus as defined in claim 1 wherein the premix injection
apparatus includes a mixer chamber configured to form premix as
fuel and oxidant streams mix together upon flowing into the mixer
chamber, and includes a premix injector tube configured to extend
from the mixer chamber to the process chamber to transmit the
premix to the process chamber.
3. An apparatus as defined in claim 1 wherein the premix injection
apparatus includes a premix injector tube configured to receive
separate fuel and oxidant streams in an inner end of the tube, to
form premix as the fuel and oxidant streams mix upon flowing
through the tube, and to inject the premix into the process chamber
from an open outer end of the tube.
4. An apparatus as defined in claim 1 further configured for use
with a reactant supply system that controls the transmission of
fuel and oxidant to the process chamber, and a temperature sensor
in the process chamber, said apparatus further comprising a
controller configured a) to operate the reactant supply system in a
flame stabilization mode in which the reactant supply system
transmits fuel and oxidant to the process chamber through the
burner but prevents transmission of unignited premix to the process
chamber through the premix injection apparatus, b) to operate the
reactant supply system in a non-stabilization mode in which the
reactant supply system blocks transmission of fuel and oxidant to
the process chamber through the burner but transmits unignited
premix to the process chamber through the premix injection
apparatus, and c) to respond to the temperature sensor by shifting
from the flame stabilization mode to the non-stabilization mode at
a time when the temperature of the process chamber is not less than
the autoignition temperature of the premix.
5. An apparatus as defined in claim 4 wherein the flame
stabilization mode is a startup mode.
6. An apparatus as defined in claim 1 further configured for use
with a reactant supply system that controls the transmission of
fuel and oxidant to the process chamber, said apparatus further
comprising a controller configured to operate the reactant supply
system in a mode in which the reactant supply system transmits fuel
and oxidant to the process chamber through the burner and
simultaneously transmits unignited premix to the process chamber
through the premix injection apparatus.
7. An apparatus comprising: a furnace structure defining a process
chamber; a burner, which includes a flame stabilizer, that is
operative to fire a flame into the process chamber; and a bypass
apparatus that is configured to inject unignited premix into the
process chamber along a flow path that bypasses the burner and is
free of a flame stabilizer.
8. An apparatus as defined in claim 7 wherein the bypass apparatus
includes a mixer chamber configured to form premix as fuel and
oxidant streams mix together upon flowing into the mixer chamber,
and includes a premix injector tube extending from the mixer
chamber to the process chamber to transmit the premix to the
process chamber.
9. An apparatus as defined in claim 7 wherein the bypass apparatus
includes a premix injector tube configured to receive separate fuel
and oxidant streams in an inner end of the tube, to form premix as
the fuel and oxidant streams mix upon flowing through the tube, and
to inject the premix into the process chamber from an open outer
end of the tube.
10. An apparatus as defined in claim 7 wherein the burner is a
premix burner with a mixer tube and a burner tile that defines a
reaction zone between the mixer tube and the process chamber, and
the flame stabilizer is configured to obstruct the flow of
unignited premix from the mixer tube into the reaction zone.
11. An apparatus as defined in claim 7 further comprising a
reactant supply system configured to control the transmission of
fuel and oxidant to the process chamber, a temperature sensor in
the process chamber, and a controller configured a) to operate the
reactant supply system in a burner mode in which the reactant
supply system transmits fuel and oxidant to the process chamber
through the burner but prevents transmission of unignited premix to
the process chamber through the bypass apparatus, b) to operate the
reactant supply system in a bypass mode in which the reactant
supply system blocks transmission of fuel and oxidant to the
process chamber through the burner but transmits unignited premix
to the process chamber through the bypass apparatus, and c) to
respond to the temperature sensor by shifting from the burner mode
to the bypass mode at the time when the temperature of the process
chamber is not less than the autoignition temperature of the
premix.
12. An apparatus as defined in claim 11 wherein the burner mode is
a startup mode.
13. An apparatus as defined in claim 7 further comprising a
reactant supply system that controls the transmission of fuel and
oxidant to the process chamber, and a controller configured to
operate the reactant supply system in a mode in which the reactant
supply system transmits fuel and oxidant to the process chamber
through the burner and simultaneously transmits unignited premix to
the process chamber through the bypass apparatus.
14. A method of operating a furnace having a process chamber, a
burner that is operative to fire into the process chamber with
flame stabilization, and a reactant supply system configured to
control the transmission of fuel and oxidant to the process
chamber, said method comprising: forming unignited premix from the
fuel and oxidant and injecting the unignited premix into the
process chamber to induce autoignition and combustion of the premix
in the process chamber without flame stabilization.
15. A method as defined in claim 14 wherein the unignited premix is
injected into the process chamber in a non-stabilization mode of
operation in which fuel and oxidant are not transmitted to the
process chamber through the burner, and the non-stabilization mode
is preceded by a flame stabilization mode in which fuel and oxidant
are transmitted to the process chamber through the burner but the
unignited premix is not injected into the process chamber, with the
intervening step of shifting from the flame stabilization mode to
the non-stabilization mode at a time when the temperature of the
process chamber is not less than the auto ignition temperature of
the premix.
16. A method as defined in claim 15 wherein the flame stabilization
mode is a startup mode.
17. A method as defined in claim 14 wherein the unignited premix is
injected into the process chamber to induce autoignition and
combustion of the premix in the process chamber without flame
stabilization in an operational mode in which the burner is
simultaneously fired into the process chamber with flame
stabilization.
18. A method of operating a furnace having a process chamber, a
burner that is operative to fire into the process chamber with the
influence of a flame stabilizer, and a reactant supply system
configured to control the transmission of fuel and oxidant to the
process chamber, said method comprising: forming unignited premix
from the fuel and oxidant and injecting the unignited premix into
the process chamber along a flow path that bypasses the flame
stabilizer to induce autoignition and combustion of the premix in
the process chamber without flame stabilization.
19. A method as defined in claim 18 wherein the premix is injected
into the process chamber in a bypass mode of operation in which
fuel and oxidant are not transmitted to the process chamber through
the burner, and the bypass mode is preceded by a burner mode in
which fuel and oxidant are transmitted to the process chamber
through the burner but the premix is not injected into the process
chamber, with the intervening step of shifting from the burner mode
to the bypass mode at a time when the temperature of the process
chamber is not less than the autoignition temperature of the
premix.
20. A method as defined in claim 19 wherein the burner mode is a
startup mode.
21. A method as defined in claim 18 wherein the unignited premix is
injected into the process chamber to induce autoignition and
combustion of the premix in the process chamber without flame
stabilization in an operational mode in which the burner is
simultaneously fired into the process chamber with flame
stabilization.
22. A method of retrofitting a furnace having a process chamber and
a burner that is operative to fire into the process chamber with
flame stabilization, said method comprising: installing a premix
injection apparatus that is configured to inject unignited premix
into the process chamber without flame stabilization.
23. A method as defined in claim 22 wherein the apparatus further
includes a reactant supply system configured to control the
transmission of fuel and oxidant to the process chamber, and a
temperature sensor in the process chamber, and said method further
comprises installing a controller configured a) to operate the
reactant supply system in a flame stabilization mode in which the
reactant supply system transmits fuel and oxidant to the process
chamber through the burner but prevents transmission of unignited
premix to the process chamber through the premix injection
apparatus, b) to operate the reactant supply system in a
non-stabilization mode in which the reactant supply system blocks
transmission of fuel and oxidant to the process chamber through the
burner but transmits unignited premix to the process chamber
through the premix injection apparatus, and c) to respond to the
temperature sensor by shifting from the flame stabilization mode to
the non-stabilization mode at a time when the temperature of the
process chamber is not less than the auto-ignition temperature of
the premix.
24. A method as defined in claim 23 wherein the flame stabilization
mode is a startup mode.
25. A method as defined in claim 22 wherein the apparatus further
includes a reactant supply system configured to control the
transmission of fuel and oxidant to the process chamber, and said
method further comprises installing a controller that is configured
to operate the reactant supply system in a mode in which the
reactant supply system transmits fuel and oxidant to the process
chamber through the burner and simultaneously transmits unignited
premix to the process chamber through the premix injection
apparatus.
Description
TECHNICAL FIELD
[0001] This technology relates to a method and apparatus for
operating a furnace.
BACKGROUND
[0002] As shown partially in the schematic view of FIG. 1, a prior
art furnace 10 has a wall structure 12 defining a process chamber
15. The process chamber 15 is sized to contain a load to be heated.
A burner 16 fires into the process chamber 15. The burner 16
includes a mixer tube 18 and a burner tile 20. The burner tile 20
defines a reaction zone 21 between the mixer tube 18 and the
process chamber 15.
[0003] In operation of the burner 16, streams of fuel and oxidant
form a combustible mixture known as premix as they flow together
through the mixer tube 18 toward and into the reaction zone 21
through the open outer end 22 of the mixer tube 18. An igniter 24
ignites the premix in the reaction zone 21 so that combustion
proceeds with a flame that extends across the reaction zone 21 and
through a port 25 that communicates with the process chamber
15.
[0004] A burner, by definition, includes a flame stabilizer which
functions to hold the flame in the desired location by inhibiting
flashback and blow off. The premix flows from left to right as
viewed in FIG. 1, while the flame propagates in the opposite
direction toward the source of premix. Flashback occurs when the
flame advances too far into the mixer tube 18. This can be
inhibited by controlling the premix speed relative to the flame
speed. Blow off occurs when the flame is driven too far from the
mixer tube 18. This can be inhibited by a flame stabilizer which,
as known in the art, may comprise an obstruction that is placed in
the premix flow path to slow the premix and thereby help to ensure
that the premix speed does not overly exceed the flame speed. A
flame stabilizer can further inhibit blow off by inducing
turbulence that includes recirculation toward the stabilizer. The
recirculating products of combustion help to anchor the flame by
maintaining ignition of the premix near the stabilizer.
[0005] In the example shown in FIG. 1, the burner 16 includes a
flame stabilizer 30 in the form of a circular metal plate. The
plate 30 is preferably located coaxially within the mixer tube 18
at a location spaced a short distance inward from open outer end
22, but could be located farther back inward from the end 22 or a
short distance outward from the end 22, as known in the art. The
plate 30 extends fully across the inside of the mixer tube 18, as
shown in enlarged detail in FIG. 2, but an alternative arrangement
could provide an annular flow area radially between the plate 30
and the surrounding tube 18. In either case, small ports 31 extend
through the plate 20 to direct jets of premix into the reaction
zone 21. The jets of premix together induce recirculation toward
the outer side surface 32 of the plate 30, and also define zones of
lower premix flow velocity in the spaces between the jets. The
plate 30 thus functions to inhibit blow off by anchoring the flame
at or near the surface 32. The plate 30 also functions to inhibit
flashback upstream of the plate 30, which is to the left as viewed
in FIGS. 1 and 2, by enabling the upstream premix speed to exceed
the flame speed as needed.
[0006] The furnace 10 can be operated in a mode in which diffuse
combustion occurs in the process chamber 15 in the absence of a
flame in the reaction zone 21. This can occur without the use of
the igniter 24 if the premix is injected through the reaction zone
21 and into the process chamber 15 when the process chamber 15 is
at or above the autoignition temperature of the premix. The diffuse
combustion mode produces less NOx because the furnace gases
circulating throughout the volume of the process chamber 15 absorb
heat from the burning reactants. This results in a lower flame
temperature which, in turn, results in less NOx formation.
[0007] Another prior art furnace 40 with a process chamber 43 and a
burner 44 is shown partially in the schematic view of FIG. 3. The
burner 44 of FIG. 3 raises the process chamber 43 to the auto
ignition temperature of the premix, and is then shut off. Diffuse
combustion follows as separate streams of fuel and air are injected
into the process chamber 43 through fuel and air injectors 46 and
48, respectively. Combustion in the diffuse mode of FIG. 3 produces
less NOx than combustion in the diffuse mode of FIG. 1. This is
because the reactants of FIG. 3 are injected directly into the
process chamber 43, whereas the reactants of FIG. 1 must first move
through the reaction zone 21 before reaching the process chamber
15. Direct injection into the process chamber 43 enables the
reactants of FIG. 3 to become more extensively diluted by furnace
gases as they mix together to form a combustible mixture prior to
reaching the autoignition temperature. When the diluted reactants
ignite, the greater amount of diluant absorbs more heat to suppress
the flame temperature and thereby to suppress the formation of
NOx.
SUMMARY
[0008] The claimed invention provides an apparatus for use with a
furnace process chamber and a burner. The burner, which includes a
flame stabilizer, is operative to fire into the process chamber
with flame stabilization. The claimed invention comprises a premix
injection apparatus configured to inject unignited premix into the
process chamber without flame stabilization. In the absence of a
stabilized flame at the premix injection apparatus, the furnace can
operate with diffuse combustion more uniformly throughout the
process chamber with correspondingly less NOx formation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic view of parts of a prior art
furnace.
[0010] FIG. 2 is an enlarged partial view of parts of the furnace
of FIG. 1.
[0011] FIG. 3 is a schematic view of parts of another prior art
furnace.
[0012] FIG. 4 is a schematic view of parts of a furnace configured
according to the claimed invention.
[0013] FIG. 5 is a schematic view of parts of another furnace
configured according to the claimed invention.
[0014] FIG. 6 is a schematic view of parts of yet another furnace
configured according to the claimed invention.
DETAILED DESCRIPTION
[0015] The furnaces illustrated schematically in FIGS. 4, 5 and 6
have parts that are examples of the elements recited in the
apparatus claims, and can be operated in steps that are examples of
the elements recited in the method claims. The following
description thus includes examples of how a person of ordinary
skill in the art can make and use the claimed invention. It is
presented here to provide enablement and best mode without imposing
limitations that are not recited in the claims. The various parts
as shown, described, and claimed, may be of either original or
retrofitted installation as required to accomplish any particular
implementation of the claimed invention.
[0016] The furnace 100 of FIG. 4 includes a wall structure 110. The
wall structure 110 defines a process chamber 115 that is sized to
contain a load to be heated. A burner 116 is mounted on the wall
structure 110 and is operative to fire into the process chamber
115. A reactant supply system 120 includes lines and valves that
provide the burner 116 with fuel from a fuel source 122, which is
preferably a supply of natural gas, and with oxidant from an
oxidant source 124, which is preferably an air blower. The reactant
supply system 120 also transmits fuel and oxidant from the sources
122 and 124 to a bypass apparatus 126 that delivers those reactants
to the process chamber 115 separately from the burner 116. A
controller 130 operates the reactant supply system 120 to control
combustion in the process chamber 115.
[0017] Although a nozzle mix burner could be used, this burner 116
is a premix burner with a mixer tube 140 and a burner tile 142. The
burner tile 142 defines a reaction zone 145 between the mixer tube
140 and a port 147 leading to the process chamber 115. The burner
116 also includes a flame stabilizer 148. The flame stabilizer 148
could be configured in any suitable manner known in the art, but is
preferably the same as the flame stabilizer 30 described above with
reference to FIGS. 1 and 2.
[0018] As further shown schematically in FIG. 4, the burner 116
includes a mixer body 160 that is coupled to the reactant supply
system 120. The mixer body 160 includes an oxidant coupling 162, a
fuel coupling 164, and an internal fuel line 166. The internal fuel
line 166 extends from the fuel coupling 164 into the inner end of
the mixer tube 140. The oxidant coupling 162 communicates with the
inner end of the mixer tube 140 through an oxidant plenum 165
within the mixer body 160.
[0019] The reactant supply system 120 has fuel and oxidant supply
lines 170 and 172. It also has a plurality of branch lines with
flow control valves. A first branch line 174 extends from the fuel
supply line 170 to the fuel coupling 164 at the burner 116. A first
valve 176 controls the flow of fuel through the first branch line
174. A second branch line 178 extends from the oxidant supply line
172 to the oxidant coupling 162 at the burner 116. A second valve
180 controls the flow of oxidant through the second branch line
178. Third and fourth branch lines 184 and 186 likewise have third
and fourth valves 188 and 190. Those branch lines 184 and 186
extend from the fuel and oxidant supply lines 170 and 172 to the
bypass apparatus 126.
[0020] Unlike the burner 116, the bypass apparatus 126 does not
include a flame stabilizer. It is instead configured to inject
unignited premix into the process chamber 115 without the influence
of a flame stabilizer, whereby the resulting ignition and
combustion of the premix proceeds without flame stabilization. In
this particular example, the bypass apparatus 126 includes a mixer
body 200 and a premix injector tube 204. A mixing chamber 205 is
defined within the mixer body 200. The mixing chamber 205
communicates with the third branch line 184 through a fuel coupling
206, and communicates with the fourth branch line 186 through an
oxidant coupling 208. The premix injector tube 204 has an open
inner end 210 at the mixing chamber 205 and an open outer end 212
at the process chamber 115. There is no structure in the bypass
apparatus 126 for slowing the flow of premix at a location between
the inner end 210 of the injector tube 204 and the region of the
process chamber 115 where the premix emerges from the open outer
end 112 of the injector tube 204. Nor is there any structure for
inducing upstream recirculation toward or within the injector tube
204. Instead, the bypass apparatus 126 is free of any structure
configured for the purpose of inhibiting flashback or blow off of a
flame propagating in a direction inwardly of the premix injector
tube 204.
[0021] The controller 130 has hardware and/or software configured
to control combustion in the process chamber 115 by selective use
of the burner 116 and the bypass apparatus 126. The controller 130
may thus comprise any suitable programmable logic controller or
other control device, or combination of control devices, that is
programmed or otherwise configured to perform as recited in the
claims. As the controller 130 carries out those instructions it
actuates the valves 176, 180, 188 and 190 to initiate, regulate and
terminate flows of reactant streams through the reactant supply
system 120.
[0022] In a startup mode of operation, the controller 130 actuates
an igniter 220 in the reaction zone 145, and opens the first and
second valves 176 and 180 while maintaining the third and fourth
valves 188 and 190 in closed conditions. This transmits streams of
fuel and oxidant to the mixer body 160 at the burner 116 while
blocking transmission of fuel and oxidant to the process chamber
115 through the bypass apparatus 126. The reactant streams
transmitted to the burner 116 form premix as they mix and flow
together through the mixer tube 140 toward the reaction zone 145.
The premix is ignited upon emerging form the mixer tube 140 to form
a flame that projects through the reaction zone 145 and into the
process chamber 115 through the port 147 under the influence of the
flame stabilizing structure 148. As a safety precaution the flame
is monitored by the controller 130 and a flame sensor 222. The
flame sensor 222 may comprise any suitable device that is operative
to detect the presence of a flame stabilized at a burner. Such
devices that are known in the art include, for example, a flame
rod, a UV (ultraviolet) flame detector, an IR (infrared) flame
detector, a thermopile, and an acoustic flame sensor.
[0023] When a temperature sensor 224 indicates that the temperature
in the process chamber 115 has risen to a level at or above the
autoignition temperature of the premix, the controller 130 responds
by shifting from the startup mode of operation to a diffuse
combustion mode of operation. The controller 130 shifts to the
diffuse combustion mode by closing the first and second valves 176
and 178 to block the transmission of fuel and oxidant to the burner
116, and by opening the third and fourth valves 188 and 190 to
transmit fuel and oxidant to the bypass apparatus 126. The fuel and
oxidant then mix together in the chamber 205 to form unignited
premix that is transmitted through the injector tube 204 for
injection into the process chamber 115. Importantly, the premix
emerging from the open outer end 212 of the injector tube 204 flows
into the process chamber 115 without the influence of a flame
stabilizer. This enables autoignition of the premix to result in
diffuse combustion more uniformly throughout the process chamber
115. Since the bypass apparatus 126 does not produce a stabilized
flame, the furnace 100 does not have a flame sensor in operative
association with the bypass apparatus 126, but instead employs the
temperature sensor 224 as a safety device to monitor diffuse
combustion in the process chamber 115.
[0024] The furnace 300 of FIG. 5 also is configured according to
the claimed invention. A wall portion 302 of the furnace 300
defines a process chamber 305. A premix burner 306 with an igniter
308 is operative to fire through a reaction zone 315 and into the
process chamber 305 under the direction of a controller 320. This
is accomplished by actuating a reactant supply system 330 to
transmit streams of fuel and oxidant from their sources 332 and 334
to a mixer tube 336 in the burner 306 in the manner described above
with reference to the furnace 100 of FIG. 4.
[0025] As shown in the drawing, the furnace 300 differs from the
furnace 100 by including a bypass apparatus 340 that is
structurally combined with the burner 306 rather than structurally
separate from the burner 306. Specifically, the bypass apparatus
340 includes a premix injector tube 342 that extends through the
burner tile 344. The outer end 346 of the injector tube 342 is open
to the process chamber 305. The inner end 348 of the injector tube
342 is open to an oxidant plenum 349 within a bypass mixer body 350
that is joined with the mixer body 352 at the burner 306.
[0026] An oxidant branch line 360 with a flow control valve 362
extends from an oxidant supply line 364 to an oxidant coupling 366
at the bypass mixer body 350. A fuel branch line 370 with a flow
control valve 372 extends from a fuel supply line 374 to a fuel
coupling 376 at the bypass mixer body 350. The flow path of fuel
from the source 332 to the injector tube 342 is completed by an
internal fuel line 380 that extends from the fuel coupling 376 into
the inner end 348 of the injector tube 342.
[0027] The controller 320 initiates a startup mode of operation by
actuating the igniter 308 and opening the fuel and oxidant flow
control valves 390 and 392 that serve the burner 306. The resulting
flame is stabilized by a flame stabilizer 394 and monitored by a
flame sensor 396 throughout the startup mode. The flow control
valves 362 and 372 that serve the bypass apparatus 340 are
maintained in closed conditions throughout the startup mode.
[0028] When the temperature in the process chamber 305 reaches a
level at or above the autoignition temperature of the premix, as
indicated by a temperature sensor 398 in the process chamber 305,
the controller 320 responds by shifting from the startup mode of
operation to a diffuse combustion mode of operation. This is
accomplished by closing the valves 390 and 392 that serve the
burner 306, and by opening the valves 362 and 372 that serve the
burner bypass apparatus 340. Streams of fuel and oxidant then flow
into the open inner end 346 of the injector tube 342 and form
premix as they flow together along the length of the tube 342
toward the process chamber 305.
[0029] As shown in the drawing, there is no flame stabilizer in the
premix flow path that extends through the injector tube 342 and
into the process chamber 305 from the open outer end 348 of the
injector tube 342. There is no flame sensor operatively associated
with the bypass apparatus 340. Therefore, in operation of the
bypass apparatus 340, an unignited stream of premix flows through
the open outer end 348 of the injector tube 342 and into the
process chamber 305 without the influence of a flame stabilizer.
Diffuse combustion in the process chamber 305 proceeds accordingly,
and is monitored for safety by the temperature sensor 398.
[0030] The claimed invention further provides other operational
modes in addition to the startup and diffuse combustion modes
described above. For example, furnace startup is not the only time
at which the burner can be on while the bypass apparatus is off.
That flame stabilization mode can be continued after startup, and
can be alternated with the non-stabilization mode in which the
burner is off and the bypass apparatus is on. It may also be
appropriate to operate in a mode in which the burner and the bypass
apparatus are on simultaneously. Overall target rates of fuel and
oxidant injection could then be provided in partial rates at the
burner and the bypass apparatus. In this regard, FIG. 6 shows a
modification of the furnace 300 in which fuel and oxidant valves
are arranged to distribute the overall rates of fuel and oxidant
injection between the burner mixer body 352 and the bypass mixer
body 350. In this arrangement a directional control valve 400 for
fuel is shiftable to initiate, regulate, and terminate flows of
fuel to only the burner mixer body 352, to only the bypass mixer
body 350, or to both throughout a range of proportional conditions.
A directional control valve 402 for oxidant is shiftable in the
same manner.
[0031] This written description sets forth the best mode of
carrying out the invention, and describes the invention to enable a
person of ordinary skill in the art to make and use the invention,
by presenting examples of the elements recited in the claims. The
patentable scope of the invention is defined by the claims and may
include other examples that occur to those skilled in the art. Such
other examples, which may be available either before or after the
application filing date, are intended to be within the scope of the
claims if they have structural or method elements that do not
differ from the literal language of the claims, or if they have
equivalent structural or method elements with insubstantial
differences from the literal language of the claims.
* * * * *