U.S. patent application number 11/936284 was filed with the patent office on 2009-05-07 for burner control.
Invention is credited to Bruce E. Cain.
Application Number | 20090117503 11/936284 |
Document ID | / |
Family ID | 40588421 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090117503 |
Kind Code |
A1 |
Cain; Bruce E. |
May 7, 2009 |
Burner Control
Abstract
A reactant supply and control system supplies a regenerative
burner assembly with streams of pilot fuel and pilot air. The
system can maintain a pilot flame throughout regenerative cycles in
which a main flame is turned on and off, and supplies either or
both of the pilot streams with an increased flow rate for shifting
from a regenerative exhaust condition to a regenerative firing
condition.
Inventors: |
Cain; Bruce E.; (Akron,
OH) |
Correspondence
Address: |
PATENT GROUP 2N;JONES DAY
NORTH POINT, 901 LAKESIDE AVENUE
CLEVELAND
OH
44114
US
|
Family ID: |
40588421 |
Appl. No.: |
11/936284 |
Filed: |
November 7, 2007 |
Current U.S.
Class: |
431/12 ; 431/18;
431/42 |
Current CPC
Class: |
F23N 2227/10 20200101;
F23N 2229/14 20200101; F23N 2229/02 20200101; F23N 2227/22
20200101; F23N 1/022 20130101; F23G 7/068 20130101 |
Class at
Publication: |
431/12 ; 431/18;
431/42 |
International
Class: |
F23N 1/02 20060101
F23N001/02 |
Claims
1. An apparatus comprising: a regenerative bed; a burner assembly
in air flow communication with the regenerative bed; and a reactant
supply and control system configured a) to shift from a
regenerative exhaust condition in which the system does not supply
the burner assembly with a main fuel stream to a regenerative
firing condition in which the system supplies the burner assembly
with a main fuel stream, b) to supply the burner assembly with a
flow rate of pilot fuel and a flow rate of pilot air in the
regenerative exhaust condition, and c) to supply the burner
assembly with a different flow rate of pilot fuels or a different
flow rate of pilot air, or different flow rates of both pilot fuel
and pilot air, in the regenerative firing condition.
2. An apparatus as defined in claim 1 wherein each of the different
flow rates in the regenerative firing condition is greater than the
corresponding flow rate in the regenerative exhaust condition.
3. An apparatus as defined in claim 1 wherein the reactant supply
and control system is configured to shift back and forth between
the flow rates throughout consecutive cycles of shifting back and
forth between the regenerative exhaust condition and the
regenerative firing condition.
4. An apparatus as defined in claim 3 wherein the reactant supply
and control system is configured to supply the pilot burner with
pilot fuel and pilot air to form a pilot flame continuously
throughout the consecutive cycles of shifting back and forth
between the regenerative exhaust condition and the regenerative
firing condition.
5. An apparatus comprising: a regenerative bed; a pilot burner
configured receive streams of pilot fuel and pilot air to form a
pilot flame; a main burner configured to receive streams of main
fuel and primary air to be ignited by the pilot flame and thereby
to form a main flame; a first supervisory device configured to
sense the pilot flame; a second supervisory device configured to
sense the main flame but not to sense the pilot flame; and a
reactant supply and control system configured a) to alternate
between a regenerative exhaust condition and a regenerative firing
condition, b) to identify a first condition in which the first
supervisory device senses the pilot flame and the second
supervisory device does not sense a main flame, c) to identify a
second condition in which the second supervisory device senses a
main flame, d) to supply the pilot burner with a flow rate of pilot
fuel and a flow rate of pilot air in the first condition, and e) to
supply the pilot burner with a different flow rate of pilot fuel,
or a different flow rate of pilot air, or different flow rates of
both pilot fuel and pilot air, in the second condition.
6. An apparatus as defined in claim 5 wherein each of the different
flow rates is an increased flow rate.
7. An apparatus as defined in claim 5 wherein the first condition
is a regenerative exhaust condition and the second condition is a
regenerative firing condition.
8. An apparatus as defined in claim 7 wherein the reactant supply
and control system is configured to shift back and forth between
the flow rates throughout consecutive cycles of shifting back and
forth between the regenerative exhaust condition and the
regenerative firing condition.
9. An apparatus as defined in claim 8 wherein the reactant supply
and control system is configured to supply the pilot burner with
pilot fuel and pilot air to form a pilot flame continuously
throughout the consecutive cycles of shifting back and forth
between the regenerative exhaust condition and the regenerative
firing condition.
10. An apparatus comprising: a pilot burner configured to receive
fuel and air flows to form a pilot flame; a reactant supply and
control system configured to supply the pilot burner with a first
combination of fuel and air flows, and a second combination of fuel
and air flows distinct from the first combination by virtue of
differing amounts of either or both of fuel flow and air flow, and
capable of switching between the two combinations; a main burner
configured to receive streams of main fuel and primary air to be
ignited by the pilot flame and thereby to form a main flame; a
first supervisory device configured to sense the pilot flame under
either combination of fuel and air flows, regardless of whether or
not the main fuel stream is being delivered to the main burner; and
a secondary supervisory device configured to sense the main flame
when the main fuel stream is present, but which will not sense the
pilot flame when the main fuel stream is absent and the pilot
burner is being supplied with the first combination of fuel and air
flows; wherein the reactant supply and control system is further
configured a) to identify a first condition in which the first
supervisory device senses the pilot flame, the second supervisory
device does not sense the main flame, and there is no main fuel
stream supplied to the main burner, b) to identify a second
condition in which the second supervisory device senses the main
flame, c) to supply the pilot burner with the first combination of
fuel and air flows in the first condition, and d) to supply the
pilot burner with the second combination of fuel and air flows in
the second condition.
11. An apparatus as defined in claim 10 wherein the reactant supply
and control system is configured to shift back and forth between
the first and second combinations throughout consecutive cycles of
shifting back and forth between the first and second
conditions.
12. An apparatus as defined in claim 11 wherein the reactant supply
and control system is configured to supply the pilot burner with
fuel and air flows to form a pilot flame continuously throughout
the consecutive cycles of shifting back and forth between the first
and second conditions.
13. An apparatus as defined in claim 10 further comprising a
regenerative bed in air flow communication with the reactant supply
and control system, and wherein the first condition is a
regenerative exhaust condition and the second condition is a
regenerative firing condition.
14. A method comprising: shifting a reactant supply and control
system from a regenerative exhaust condition in which the system
does not supply a burner assembly with a main fuel stream to a
regenerative firing condition in which the system supplies the
burner assembly with a main fuel stream and with preheated air from
a regenerative bed; operating the reactant supply and control
system to supply the burner assembly with a flow rate of pilot fuel
and a flow rate of pilot air in the regenerative exhaust condition;
and operating the reactant supply and control system to supply the
burner assembly with a different flow rate of pilot fuel, or a
different flow rate of pilot air, or different flow rates of both
pilot fuel and pilot air, in the regenerative firing condition.
15. A method as defined in claim 14 wherein each of the different
flow rates in the regenerative firing condition is greater than the
corresponding flow rate in the regenerative exhaust condition.
16. A method as defined in claim 14 wherein the reactant supply and
control system is shifted back and forth between the flow rates
throughout consecutive cycles of shifting back and forth between
the regenerative exhaust condition and the regenerative firing
condition.
17. A method as defined in claim 16 wherein the reactant supply and
control system is operated to supply the burner assembly with pilot
fuel and pilot air continuously throughout the consecutive cycles
of shifting back and forth between the regenerative exhaust
condition and the regenerative firing condition.
18. A method of operating an apparatus comprising a pilot burner
configured to receive streams of pilot fuel and pilot air to form a
pilot flame, and a main burner configured to receive streams of
main fuel and primary air to be ignited by the pilot flame and
thereby to form a main flame, the method comprising: operating a
first flame sensor that is configured to sense the pilot flame;
operating a second flame sensor that is configured to sense the
main flame but not to sense the pilot flame; identifying a first
condition in which the first flame sensor senses the pilot flame
but the second flame sensor does not sense the main flame;
identifying a second condition in which the second flame sensor
senses the main flame; supplying the pilot burner with a flow rate
of pilot fuel and a flow rate of pilot air in the first condition;
and supplying the pilot burner with a different flow rate of pilot
fuel, or a different flow rate of pilot air, or different flow
rates of both pilot fuel and pilot air, in the second
condition.
19. A method as defined in claim 18 wherein each of the different
flow rates is an increased flow rate.
20. A method as defined in claim 18 wherein the flow rates are
shifted back and forth throughout consecutive cycles of shifting
back and forth between the first condition and the second
condition.
21. A method as defined in claim 18 wherein the pilot flame is
formed at the pilot burner continuously throughout the consecutive
cycles of shifting back and forth between the first condition and
the second condition.
22. A method as defined in claim 18 wherein the first condition is
a regenerative exhaust condition and the second condition is a
regenerative firing condition.
Description
TECHNICAL FIELD
[0001] This technology relates to the operation of a burner for a
furnace.
BACKGROUND
[0002] Regenerative burners may be used to heat a process chamber
in a furnace. Each regenerative burner has a bed of
heat-regenerative material, and is arranged in a pair with another
regenerative burner. The two burners are cycled alternately such
that one burner is actuated while the other is not. When a burner
is actuated, it discharges fuel and combustion air into the process
chamber for combustion to proceed in the process chamber. Much of
the combustion air is pre-heated by driving it through the
regenerative bed. Alternately, when a burner is not actuated,
exhaust gases from the process chamber are drawn outward through
the regenerative bed at that burner. The exhaust gases heat the
regenerative bed to provide the thermal energy that pre-heats the
combustion air when the burner is again actuated to fire into the
process chamber.
SUMMARY
[0003] A reactant supply and control system supplies a regenerative
burner assembly with streams of pilot fuel and pilot air. The
system can maintain a pilot flame continuously throughout
consecutive regenerative cycles in which a main flame is turned on
and off, and can supply either or both of the pilot streams with
flow rates that differ between a regenerative exhaust condition and
a regenerative firing condition. This can help to ensure that the
pilot flame ignites a main flame for each regenerative firing
condition. Lower flow rates of pilot reactants in the regenerative
exhaust conditions can reduce fuel consumption and exhaust
emissions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a schematic view showing parts of a furnace with
regenerative burners.
[0005] FIG. 2 is a perspective view of a regenerative burner
assembly shown in FIG. 1.
[0006] FIG. 3 is a sectional view of the burner assembly of FIG.
2.
[0007] FIG. 4 is a sectional view of a part shown in FIG. 3.
[0008] FIG. 5 is a side view of another part shown in FIG. 3.
[0009] FIG. 6 is a sectional view taken on line 6-6 of FIG. 5.
[0010] FIG. 7 is a rear view taken on line 7-7 of FIG. 5.
[0011] FIG. 8 is a front view taken on line 8-8 of FIG. 5.
[0012] FIG. 9 is a schematic view illustrating an operational
feature of the furnace of FIG. 1.
[0013] FIG. 10 also is a schematic view illustrating an operational
feature of the furnace of FIG. 1.
DETAILED DESCRIPTION
[0014] The furnace 10 shown in the drawings has parts that are
examples of the elements recited in the 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 meet the statutory requirements of written
description, enablement, and best mode without imposing limitations
that are not recited in the claims.
[0015] As shown partially in the schematic view of FIG. 1, the
furnace 10 has a wall structure 12 defining a process chamber 15.
Burner assemblies 16, one of which is shown in FIG. 1, are arranged
in pairs in which one burner assembly 16 fires into the process
chamber 15 while the other exhausts from the process chamber 15.
Each burner assembly 16 is mounted over a respective regenerative
bed 18. When a burner assembly 16 fires into the process chamber
15, it receives preheated combustion air from the regenerative bed
18. Alternately, when a burner assembly 16 exhausts from the
process chamber 15, it directs exhaust gases into the regenerative
bed 18. This heats the regenerative bed 18 which, in turn, heats
the combustion air when the burner assembly 16 once again fires
into the process chamber 15.
[0016] As shown in FIG. 2, this example of a burner assembly 16 has
a generally cylindrical body 20 with a central axis 21. A primary
port 25 is centered on the axis 21 at the front of the body 20. A
reactant delivery structure 26 extends along the axis 21 from the
rear of the body 20 toward the primary port 25. Secondary ports 27
also are located at the front of the body 20. Air flow passages
within the body 20 communicate the secondary ports 27 with a base
28 at the bottom of the body 20. The base 28 is configured to
communicate with the regenerative bed 18 (FIG. 1).
[0017] As shown in FIG. 3, the reactant delivery structure 26
includes an array of concentric conduits centered on the axis 21.
These include a pilot fuel conduit 30 at the center of the array.
The pilot fuel conduit 30 has an inlet 32 at its rear end and an
outlet 34 at its front end. A flame stabilizer 36 projects from the
outlet 34. Surrounding the pilot fuel conduit 30 is a pilot air
conduit 40 with an inlet 42 at its rear end and an outlet 44 at its
front end. A section 46 of the pilot air conduit 40 is located
forward of the pilot fuel conduit 30. That section 46 is tapered
radially inward to promote the mixing of fuel and air axially
between the stabilizer 36 and the outlet 44. In this arrangement,
these two conduits 30 and 40 together define a pilot burner that is
configured to provide a pilot flame that projects axially forward
from the outlet 44.
[0018] A main fuel conduit 50 surrounds the pilot air conduit 40. A
primary air conduit 52 surrounds the main fuel conduit 50. These
conduits 50 and 52 have inlets 54 and 56 at their rear ends and
outlets 58 and 60 at their front ends, respectively. This provides
a main burner that is configured to provide a main flame that
projects axially forward from the outlets 58 and 60. In the
illustrated example, the concentric outlets 44, 58 and 60 are
coplanar and radially adjacent. More specifically, the pilot burner
outlet 44 is the circular space bounded by the surrounding edge of
the pilot air conduit 40. It is spaced radially inward from the
main fuel outlet 58 by only the thickness of the conduit 40 that is
interposed radially between those two outlets 44 and 58. The main
fuel outlet 58 is the annular space bounded by the concentric edges
of the pilot air conduit 40 and the main fuel conduit 50. That
outlet 58 is spaced radially inward from the surrounding outlet 60
by only the thickness of the main fuel conduit 50. The primary air
outlet 60 likewise has an annular configuration defined by and
between the concentric edges of the main fuel conduit 50 and the
primary air conduit 52.
[0019] The cylindrical body 20 in the illustrated example has three
major portions. These include a rear portion 70, a central portion
72, and a front portion 74. The rear portion 70 includes a
refractory structure 80 within a steel shell 82. Lower portions of
those parts 80 and 82 define the base 28 at which the burner
assembly 16 is mounted over a regenerative bed. The refractory
structure 80 within the steel shell 82 defines a plenum 85
extending upward from a port 87 at the lower end of the base 28.
The refractory structure 80 further defines a generally conical
pocket 89 (FIG. 4) that is centered on the axis 21.
[0020] As shown separately in FIGS. 5-8, the central portion 72 of
the body 20 includes a refractory structure configured as a baffle
90. The baffle 90 in this particular example has a generally
conical configuration centered on an axis 93. The primary port 25
is located on a circular front surface 98 of the baffle 90. A
cylindrical bore 100 (FIG. 6) extends into the baffle 90 along the
axis 93. A tapered bore 101 extends forward from the cylindrical
bore 100, and has a front end at the primary port 25. The tapered
bore 101 constricts radially inward from the cylindrical bore 100,
and then flares radially back outward to the primary port 25.
[0021] The secondary ports 27 also are located on the circular
front surface 98 of the baffle 90. Two pairs 104 and 106 of air
flow passages extend from the rear of the baffle 90 to the
secondary ports 27 at the front surface 98. As shown in FIG. 8, the
secondary ports 27 are arranged in an array that is asymmetrical
with respect to a plane 109 containing the central axis 93. In this
arrangement of the secondary ports 27, at least a major portion of
their combined flow area is located at one side of the circular
area of the front surface 98.
[0022] As shown in FIG. 3, the baffle 90 is fitted coaxially within
the pocket 89 at the rear portion 70 of the body 20. The front
portion 74 of the body 20 includes a ring-shaped refractory
structure 122 that surrounds and projects axially forward from the
baffle 90. The reactant delivery structure 26 extends fully into
the cylindrical bore 100 in the baffle 90, with the coplanar
outlets 44, 58 and 60 facing outward through the tapered bore 101
toward the primary port 25. The air flow passages 104 and 106
extending through the baffle 90 communicate the secondary ports 27
with the plenum 85 and the port 87 at the lower end of the base
28.
[0023] Referring again to FIG. 1, the furnace 10 has a reactant
supply and control system 140. This system 140 connects the furnace
10 with a source of fuel 142, which is preferably the plant supply
of natural gas, and a source of combustion air 144, which may
include one or more blowers. The reactant supply and control system
140 includes a controller 146 and a valve assembly 148. It further
includes fuel lines and air lines that connect each burner assembly
16 with the valve assembly 148 in the manner shown schematically in
FIG. 1. The burner assemblies 16 and regenerative beds 18 are thus
connected with the sources of fuel and air 142 and 144 for
combustion to proceed in the process chamber 15, and are also
connected with a flue 150 for discharging exhaust gases from the
process chamber 15. Specifically, a pilot fuel line 160 delivers
pilot fuel to the inlet 32 of the pilot fuel conduit 30. A pilot
air line 162 delivers pilot air to the inlet 42 of the pilot air
conduit 40. A main fuel line 164 delivers main fuel to the inlet 54
of the main fuel conduit 50. A primary air line 166 delivers
primary combustion air to the inlet 56 of the primary air conduit
52. Moreover, a secondary air line 170 carries secondary combustion
air to the regenerative bed 18, and an exhaust line 172 carries
exhaust gases away from the regenerative bed 18 for transmission to
the flue 150.
[0024] The controller 146 has hardware, software, or a combination
of hardware and software that is configured to control the valve
assembly 148. The controller 146 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
146 carries out those instructions, it actuates the valve assembly
148 to initiate, modulate, and terminate independent flows of
reactant streams through the burner assembly 16.
[0025] In one particular example of a start-up sequence, the
controller 146 first directs the valve assembly 148 to supply the
reactant delivery structure 26 with streams of pilot fuel, pilot
air, and primary air, and also actuates an igniter (not shown).
This causes a pilot flame to project axially forward toward the
primary port 25 (FIG. 3). The controller 146 then monitors a pilot
flame supervisory device 180 for a period of time, such a five
seconds, to confirm the presence of the pilot flame. If the pilot
flame is not confirmed, the controller 146 directs the valve
assembly 148 to terminate the stream of pilot fuel. If the pilot
frame is confirmed, the controller 146 next directs the valve
assembly 148 to supply the reactant delivery structure 26 with a
stream of main fuel. The main fuel stream flows through the main
fuel conduit 50 to emerge from the annular outlet 58 over the pilot
flame. The primary air stream flowing through the primary air
conduit 52 emerges from the annular outlet 60 over the main fuel
stream.
[0026] The streams of main fuel and primary air begin to mix as
they flow together through the tapered bore 101 toward the primary
port 25, and continue to mix as they flow outward from the port 25
into the process chamber 15. The mixture surrounds, ignites and
begins to combust over the pilot flame. As shown schematically in
FIG. 9, this stage of combustion occurs in a primary reaction zone
185 defined by the main fuel and primary air streams as they form a
main flame projecting axially and radially outward from the primary
port 25.
[0027] Secondary combustion air flows through the secondary air
line 170 to the regenerative bed 18. The plenum 85 (FIG. 3)
receives the secondary combustion air as it flows from the
regenerative bed 18 upward through the port 87 in the base 28. The
air flow passages 104 and 106 in the baffle 90 (FIG. 5-7) convey
the secondary combustion air from the plenum 85 to the secondary
ports 27. The air streams emerging from the secondary ports 27
enable secondary combustion to occur in the process chamber 15 at
locations spaced axially downstream ftom the baffle 90. This occurs
as the secondary air streams project axially and radially outward
from the secondary ports 27 to form secondary reaction zones 187
(one of which is shown schematically in FIG. 10) where they
intersect the primary reaction zone 185. With the combined flow
area of the secondary ports 27 located on one side of the plane 109
(FIG. 8), the secondary reaction zones 185 are likewise located
predominantly on that side of the plane 109. This enables a
recirculation zone 189 to form beside the front surface 98 of the
baffle 90 on the opposite side of the plane 109.
[0028] A main flame supervisory device 186 monitors combustion in
the primary reaction zone 185. If the main flame supervisory device
186 fails to confirm combustion of the main fuel and primary air,
the controller 146 directs the valve assembly 148 to terminate the
main fuel stream. If combustion of the main fuel and primary air is
confirmed, the controller 146 directs the valve assembly 148 to
continue supplying those reactant streams to maintain a
regenerative firing condition until the burner assembly 16 is
switched to a regenerative exhaust condition.
[0029] The flame supervisory devices 180 and 186, which may be UV
or other sensors for detecting a flame, are configured in a known
manner for the pilot sensor 180 to sense the pilot flame, or
optionally to sense both the pilot flame and the main flame, and
for the main sensor 186 to sense the main flame but not the pilot
flame. This prevents the pilot frame from being mistaken for a main
flame, which permits the pilot flame to be maintained continuously
throughout consecutive cycles in which the main flame is turned on
and off for regenerative operation of the burner assembly 16. The
reactant supply and control system 140 is configured accordingly.
Specifically, when the burner assembly 16 is in the regenerative
exhaust condition, the pilot sensor 180 senses the pilot flame but
the main sensor 186 does not sense a main flame. The controller 146
directs the valve assembly 148 to supply the reactant delivery
structure 26 with first streams of pilot fuel and pilot air in that
condition. Since there is no stream of main fuel and no need for a
main flame, either or both of the first streams of pilot fuel and
pilot air can have a flow rate that is lower than the flow rate
ordinarily provided for the pilot flame to ignite a main flame.
[0030] The system 140 is further configured to continue supplying
pilot fuel and pilot air to the reactant delivery structure 26 to
maintain the pilot flame, but to shift from the first streams to
second streams that differ from the first streams when the burner
assembly 16 is being shifted from a regenerative exhaust condition
to a regenerative firing condition. The controller 146 then directs
the valve assembly 148 to supply a main fuel stream, and also to
provide either or both of the second streams of pilot fuel and
pilot air with a flow rate that exceeds the corresponding first
stream flow rate sufficiently to ensure that the pilot flame
ignites a main flame. The increased pilot flow rate or rates can be
shifted back to a lower level during the regenerative firing
condition, when shifting to the next subsequent regenerative
exhaust condition, or during the next subsequent regenerative
exhaust condition. In each case lower pilot flow rates can reduce
both fuel consumption and exhaust emissions as the pilot streams
are continued without interruption but are shifted back and forth
between the first and second flow rates throughout multiple cycles
of shifting back and forth between the regenerative exhaust
condition and the regenerative firing condition.
[0031] The patentable scope of the invention is defined by the
claims, and may include other examples of how the invention can be
made and used. 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 elements that do not
differ from the literal language of the claims, or if they have
equivalent elements with insubstantial differences from the literal
language of the claims.
* * * * *