U.S. patent application number 12/264066 was filed with the patent office on 2010-05-06 for apparatus and method for a modulating burner controller.
Invention is credited to Bradford L. Blankenship, Dennis S. Gambiana, Dennis R. Maiello.
Application Number | 20100112500 12/264066 |
Document ID | / |
Family ID | 42131852 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100112500 |
Kind Code |
A1 |
Maiello; Dennis R. ; et
al. |
May 6, 2010 |
APPARATUS AND METHOD FOR A MODULATING BURNER CONTROLLER
Abstract
This invention describes a modulating burner controller device
for varying burner combustion over a wide range and has an output
that integrates the control of all functions required to operate
the burner. Specifically, the controller uses measured feedback
from a fuel flow sensor to attain the proper mixture of fuel and
air for optimum combustion performance for both individual and
multiple the burner applications.
Inventors: |
Maiello; Dennis R.;
(Bloomington, MN) ; Gambiana; Dennis S.;
(Bloomington, MN) ; Blankenship; Bradford L.;
(Orono, MN) |
Correspondence
Address: |
PAULEY PETERSEN & ERICKSON
2800 WEST HIGGINS ROAD, SUITE 365
HOFFMAN ESTATES
IL
60169
US
|
Family ID: |
42131852 |
Appl. No.: |
12/264066 |
Filed: |
November 3, 2008 |
Current U.S.
Class: |
431/76 |
Current CPC
Class: |
F23N 3/082 20130101;
F23N 5/00 20130101; F23N 1/022 20130101; F23N 3/042 20130101 |
Class at
Publication: |
431/76 |
International
Class: |
F23N 5/00 20060101
F23N005/00 |
Claims
1. A combustion apparatus for use in fired variable demand
applications, the apparatus comprising: a fuel valve modulating a
fuel flow; a fuel sensor with a range measuring the fuel flow and
sending a fuel output; a combustion air device modulating an air
flow; an air sensor measuring the air flow and sending an air
output; and a controller connected to the fuel valve, the fuel
sensor, the combustion air device, and the air sensor, the
controller modulating the fuel valve based on the fuel output using
an extrapolation algorithm when the fuel output extends outside of
the range of the fuel sensor, the controller modulating the
combustion air device based on the air output; wherein the
controller simultaneously or sequentially modulates the fuel flow
and the air flow over an extended fuel/air ratio and provides
continuous modulation during a single burn cycle.
2. The apparatus according to claim 1, wherein the extrapolation
algorithm comprises fuzzy logic derived from a fuel sensor curve
over the range.
3. The apparatus according to claim 1, wherein the extrapolation
algorithm comprises linear extension derived from a fuel sensor
curve over the range.
4. The apparatus according to claim 1, wherein the extrapolation
algorithm comprises a mathematical function derived from selected
points on a fuel sensor curve over the range.
5. The apparatus according to claim 1, wherein the controller
utilizes the extrapolation algorithm to provide a predetermined
rate leaner or with excess air than a stoichiometric ratio of air
to fuel.
6. The apparatus according to claim 1, wherein the controller
utilizes the extrapolation algorithm to provide a predetermined
rate richer or with excess fuel than a stoichiometric ratio of air
to fuel.
7. The apparatus according to claim 1, wherein the fuel sensor
comprises a pressure sensor.
8. The apparatus according to claim 1, wherein the fuel sensor
comprises a mass flow sensor, a volumetric flow sensor, or
combinations thereof.
9. The apparatus according to claim 1, wherein the fuel sensor
comprises an anemometer, a turbine, an orifice, a venturi, a
nozzle, or combinations thereof.
10. The apparatus according to claim 1, wherein the combustion air
device comprises full modulation operation between a minimum of the
extrapolation algorithm and a full system capacity.
11. The apparatus according to claim 1, wherein controller
maximizes burner efficiency.
12. The apparatus according to claim 1, wherein the controller
maintains a target efficiency over an entire operating range.
13. The apparatus according to claim 1, wherein the controller
maximizes turn down.
14. The apparatus according to claim 1, wherein the controller
minimizes carbon monoxide, excess oxygen, nitrogen oxides, or
combinations thereof.
15. The apparatus according to claim 1, wherein the controller
learns from a flame-out due to low combustion fuel and modifies the
extrapolation algorithm for future use upward to prevent additional
flame-outs.
16. The apparatus according to claim 1, further comprising: a first
burner with a capacity; and one or more additional burners each
with a capacity and with the first burner forming a sequentially
staged burner system; wherein the controller communicates with the
first burner and the one or more additional burners when a heating
demand exceeds the capacity of the first burner the controller
activates the one or more additional burners.
17. The apparatus according to claim 16, wherein the controller
uses a sequential algorithm modulating the first burner to provide
continuous modulation operation over a system range.
18. The apparatus according to claim 16, wherein the controller
uses a sequential algorithm modulating the first burner and the one
or more additional burners to provide continuous modulation
operation over a system range.
19. The apparatus according to claim 16, further comprising a
second sequentially staged burner system to provide a broader
system range.
20. The apparatus according to claim 1, further comprising a flue
gas sensor indicating a flue gas characteristic.
21. The apparatus according to claim 20, wherein the flue gas
sensor comprises a temperature sensor, a carbon monoxide sensor, an
oxygen sensor, nitrogen oxide sensor, or combinations thereof.
22. A combustion apparatus for use in fired variable demand
applications, the apparatus comprising: a fuel valve modulating a
fuel flow; a fuel sensor with a range measuring the fuel flow and
sending a fuel output; a variable speed driver modulating an air
flow of a combustion air device; a damper modulating the air flow
of the combustion air device; an air sensor measuring the air flow
and sending an air output; and a controller connected to the fuel
valve, the fuel sensor, the variable speed driver, the damper, and
the air sensor, the controller modulating the fuel valve based on
the fuel output, the controller modulating the variable speed
driver and the damper based on the air output; wherein the
controller simultaneously or sequentially modulates the fuel flow
and the air flow over an extended fuel/air ratio and provides
continuous modulation during a single burn cycle.
23. The apparatus according to claim 22, wherein the fuel sensor
comprises a pressure sensor.
24. The apparatus according to claim 22, wherein the fuel sensor
comprises a mass flow sensor, a volumetric flow sensor, or
combinations thereof.
25. The apparatus according to claim 22, wherein the fuel sensor
comprises an anemometer, a turbine, an orifice, a venturi, a
nozzle, or combinations thereof.
26. The apparatus according to claim 22, wherein the combustion air
device comprises full modulation operation.
27. The apparatus according to claim 22, wherein controller
maximizes burner efficiency.
28. The apparatus according to claim 22, wherein the controller
maintains a target efficiency over an entire operating range.
29. The apparatus according to claim 22, wherein the controller
maximizes turn down.
30. The apparatus according to claim 22, wherein the controller
minimizes carbon monoxide, excess oxygen, nitrogen oxides, or
combinations thereof.
31. A method of operating a combustion apparatus for use in fired
variable demand applications, the method comprising: measuring a
fuel flow with a fuel sensor having a range and a fuel output;
measuring an air flow with an air sensor having an air output;
modulating the fuel flow with a fuel valve and a controller based
on the fuel output; modulating the air flow with a combustion air
device and the controller based on the air output; calculating the
air flow or the fuel flow when the fuel output extends outside of
the range of the fuel sensor with an extrapolation algorithm; and
maintaining simultaneously or sequentially the fuel flow and the
air flow over an extended fuel/air ratio and to provide continuous
modulation during a single burn cycle with the controller.
32. The method according to claim 31, wherein the extrapolation
algorithm comprises fuzzy logic, linear extension, a mathematical
function, or combinations thereof.
33. The method according to claim 31, wherein the maintaining
comprises a stoichiometric ratio, a lean ratio, or a rich
ratio.
34. The method according to claim 31, wherein the modulating the
air flow and modulating the fuel flow comprise maximum burner
efficiency, target efficiency over an entire operating range, or
maximum turndown.
35. The method according to claim 31, wherein the maintaining
further comprises minimizing carbon monoxide, excess oxygen,
nitrogen oxides, or combinations thereof.
36. A method of operating a combustion apparatus for use in fired
variable demand applications, the method comprising: measuring a
fuel flow with a fuel sensor having a range and a fuel output;
measuring an air flow with an air sensor having an air output;
modulating the fuel flow with a fuel valve and a controller based
on the fuel output; modulating the air flow with a damper and a
variable speed driver of a combustion air device and the controller
based on the air output; and maintaining simultaneously or
sequentially the fuel flow and the air flow over an extended
fuel/air ratio and to provide continuous modulation during a single
burn cycle with the controller.
37. The method according to claim 36, wherein the modulating the
air flow and modulating the fuel flow comprise maximum burner
efficiency, target efficiency over an entire operating range, or
maximum turndown.
38. The method according to claim 36, wherein the maintaining
further comprises minimizing carbon monoxide, excess oxygen,
nitrogen oxides, or combinations thereof.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The present invention describes a control system to modulate
fired combustion burners based on a fuel flow feedback loop with
corresponding modulating combustion air flow to provide precise
control of the fuel/air ratio. In particular, the present invention
relates specifically to the control of burners and includes
provisions for systems and techniques for a wide variety of
applications.
[0003] 2. Discussion of the Related Art
[0004] West, U.S. Pat. No. 4,645,450, discloses a system and a
process for controlling the flow of air and fuel to a burner. West
discloses a pair of differential pressure sensors connected across
1) the air conduit and the burner, and 2) the fuel conduit and the
burner. West discloses a butterfly valve in the blower conduit
after the blower.
[0005] Tesar et al., U.S. Pat. No. 6,213,758, discloses a burner
air/fuel ratio regulation method and apparatus for a web dryer.
Tesar et al. discloses monitoring the differential air pressure
between the air chamber and the burner enclosure. Tesar et al.
discloses regulation of the air flow of a combustion blower with a
variable speed drive controlled motor rather than with a damper to
achieve faster and more accurate burner modulation with less
electrical energy.
[0006] Yoshihiko, Japanese Patent Application Publication 11-12419,
discloses a combustor and its control method during ignition.
Yoshihiko discloses keeping the gas proportional valve at a
predetermined value from the time gas is fed until burner ignition
to address a temporal reduction of the gas flow rate at the
ignition. Yoshihiko does not address modulation over a broad range
of operating parameters.
[0007] Kazou et al., Japanese Patent Application Publication
06-174381, discloses equipment for controlling an atmosphere in a
furnace. Kazou et al. discloses a proportional valve on both the
air and the gas supply pipelines to make the air/gas ratio fixed
over the output range. Kazou et a. disclosures a gas pressure
setting proportional valve upstream of the first gas proportional
valve that changes gas pressure in accordance with an output.
[0008] The art has long recognized the benefits of modulation and
turndown for combustion devices. Although the foregoing disclosures
provide advances in the art, there is a need and a desire for a
modulating combustion apparatus and method having low cost and high
turndown capabilities. There is also a need and a desire for a
modulating combustion apparatus and method able to operate outside
of the range of a low cost sensor. There is also a need and a
desire for a modulating combustion apparatus and method able to
stably turndown a combustion air device.
SUMMARY OF THE INVENTION
[0009] The present invention provides a cost effective control
methodology for variable output burner applications through the use
of a series of controllable variable output components and
utilizing feedback sensors for precision closed loop control. In
some embodiments, the invention includes a modulating combustion
apparatus and method having low cost and high turndown
capabilities. In some embodiments, the invention also includes a
modulating combustion apparatus and method able to operate outside
of the range of a low cost sensor. In some embodiments, the
invention also includes a modulating combustion apparatus and
method able to stably turndown a combustion air device.
[0010] In a first embodiment, the invention includes a combustion
apparatus for use in fired variable demand applications. The
apparatus includes a fuel valve modulating a fuel flow, and a fuel
sensor with a range measuring the fuel flow and sending a fuel
output. The apparatus also includes a combustion air device
modulating an air flow, and an air sensor measuring the air flow
and sending an air output. The apparatus also includes a controller
connected to the fuel valve, the fuel sensor, the combustion air
device, and the air sensor. The controller modulates the fuel valve
based on the fuel output using an extrapolation algorithm when the
fuel output extends outside of the range of the fuel sensor, and
the controller modulates the combustion air device based on the air
output. The controller simultaneously and/or sequentially modulates
the fuel flow and the air flow over an extended fuel/air ratio and
provides continuous modulation during a single burn cycle.
[0011] In a second embodiment, the invention includes a combustion
apparatus for use in fired variable demand applications. The
apparatus includes a fuel valve modulating a fuel flow, and a fuel
sensor with a range measuring the fuel flow and sending a fuel
output. The apparatus also includes a variable speed driver
modulating an air flow of a combustion air device, and a damper
modulating the air flow of the combustion air device. The apparatus
also includes an air sensor measuring the air flow and sending an
air output, and a controller connected to the fuel valve, the fuel
sensor, the variable speed driver, the damper, and the air sensor.
The controller modulates the fuel valve based on the fuel output,
and the controller modulates the variable speed driver and the
damper based on the air output. The controller simultaneously
and/or sequentially modulates the fuel flow and the air flow over
an extended fuel/air ratio and provides continuous modulation
during a single burn cycle.
[0012] In a third embodiment, the invention relates to a method of
operating a combustion apparatus for use in fired variable demand
applications. The method includes the step of measuring a fuel flow
with a fuel sensor having a range and a fuel output, and the step
of measuring an air flow with an air sensor having an air output.
The method also includes the step of modulating the fuel flow with
a fuel valve and a controller based on the fuel output, and the
step of modulating the air flow with a combustion air device and
the controller based on the air output. The method also includes
the step of calculating the air flow or the fuel flow when the fuel
output extends outside of the range of the fuel sensor with an
extrapolation algorithm, and the step of maintaining simultaneously
and/or sequentially the fuel flow and the air flow over an extended
fuel/air ratio and to provide continuous modulation during a single
burn cycle with the controller.
[0013] In a fourth embodiment, the invention relates to a method of
operating a combustion apparatus for use in fired variable demand
applications. The method includes the step of measuring a fuel flow
with a fuel sensor having a range and a fuel output, and the step
of measuring an air flow with an air sensor having an air output.
The method also includes the step of modulating the fuel flow with
a fuel valve and a controller based on the fuel output, and the
step of modulating the air flow with a damper and a variable speed
driver of a combustion air device and the controller based on the
air output. The method also includes the step of maintaining
simultaneously and/or sequentially the fuel flow and the air flow
over an extended fuel/air ratio and to provide continuous
modulation during a single burn cycle with the controller.
BRIEF DISCUSSION OF THE DRAWINGS
[0014] These and other objects and features of this invention will
be better understood from the following detailed description taken
in conjunction with the drawings, wherein:
[0015] FIG. 1 shows a diagram of a modulating burner controller, in
some embodiments;
[0016] FIG. 2 shows a diagram of burner controller components for
modulating fuel and air feedback loops, in some embodiments;
[0017] FIG. 3 show a diagram of a fuel/air mixture curve with a
fuel/air ratio having operating end points for a range of a fuel
flow sensor and an extrapolation for an extended fuel flow sensor
range, in some embodiments;
[0018] FIG. 4 shows a diagram of an air/fuel mixture curve with the
air/fuel ratio having operating end points for a range of a fuel
flow sensor and an extrapolation for an extended fuel flow sensor
range, in some embodiments;
[0019] FIG. 5 shows a diagram of a burner controller using an
extrapolation to extend a modulating fuel valve range and with fuel
and air feedback loops, in some embodiments;
[0020] FIG. 6 shows a diagram of a burner controller using
modulating combustion air inlet vane control, in some
embodiments;
[0021] FIG. 7 shows a diagram of a burner controller using a
communication port to stage sequential burners, in some
embodiments;
[0022] FIG. 8 shows a diagram of a burner controller using a flue
emission sensor, in some embodiments; and
[0023] FIG. 9 shows a schematic of a modulating combustion
apparatus, in some embodiments.
DETAILED DESCRIPTION
[0024] In some embodiments, the invention relates to burners or
combustion devices, such as furnaces, heaters, forced warm air
applications, water heaters, boilers, power burners, kilns, ovens,
process furnaces, gas turbines, internal combustion engines, and/or
the like. The apparatus and the method can provide control of a
burner beyond merely supplying fuel and providing air for
combustion at a fixed flow rate while igniting the mixture.
Desirably, the apparatus and the method allow for efficient
operation over a wide or broad range of operation or firing.
[0025] Furnaces may include any suitable size and/or configuration.
Residential furnaces may include any suitable capacity, such as
less than about 41 kilowatts (about 140,000 british thermal units
per hour). Commercial furnaces may include any suitable capacity,
such as greater than about 58 kilowatts (about 200,000 british
thermal units per hour). Additional furnaces or units may be
staged, such as to add or supply additional capacity.
[0026] Power burners may include any suitable combustion chamber.
Power burner applications may include process applications, cooking
ovens, glass melting, glass blowing, industrial processes, and/or
the like.
[0027] Burners may include fixed (single) operation, two-stage
(levels) operation, three-stage (levels), and/or more. Fuel valves
can modulate or vary by three positions or more to supply fuel to a
burner, for example. Modulating fuel valves and two stage
combustion air blowers offer limited turndown capacities. However,
cost effective modulation and control over a wide range of
capacities or outputs is not presently available in the industry.
Desirably, it may be appropriate to operate a burner in a very rich
(excess fuel) condition for a short time to facilitate a smooth and
consistent light-off (ignition), but operate the burner at a leaner
(lower fuel/air ratio) there after.
[0028] Modulating or controllable burners can be used in
conjunction with a combustion air blower or device. The combustion
air blower may be before the burner in a forced draft configuration
or after the burner in an induced draft configuration. Balanced
devices or combination devices may include both a forced draft and
induced draft configuration. The combustion air device may include
any suitable motive force apparatus, such as a fan, an axial fan, a
radial fan, a variable pitch fan, a blower, an axial blower, a
radial blower, a squirrel cage blower, a compressor, an ejector,
and/or the like.
[0029] The combustion air device may include a damper or suitable
flow control device, such as an inlet vane damper, an inlet damper,
an inlet suction valve, a butterfly valve, a discharge damper, a
discharge valve, and/or the like. Combinations of inlet and
discharge dampers are within the scope of this invention, as well
as combinations of dampers and variable speed drivers.
[0030] In some embodiments, the combustion air blower includes an
inducer blower to create or make a negative pressure in a
combustion chamber, such as to bring or draw air into the
combustion chamber and create or make a draft to remove products of
combustion. In other embodiments, the blower forms part of a power
burner to create or make a positive pressure in a combustion
chamber.
[0031] In some embodiments, the method may include a technique to
control the flow of combustion air into a power burner application.
The technique may allow accurate stable control of the flow for
moderate to high turn-down applications, for example.
[0032] Known control of the combustion air flow in power burner
applications has traditionally been accomplished in one of two
ways. The first known method is to employ a damper assembly in the
combustion air flow path to decrease the flow during reduced rate
operation. This known damper method is commonly used because of low
implementation costs and straight-forward mechanical design methods
(mechanical linkages), such as without complicated electronic
controls. However, the stability of these known systems at higher
turn-down ratios is sacrificed for the simplicity of design,
causing significant commissioning time at start-up and frequent
scheduled maintenance.
[0033] The second known method for controlling combustion air flow
has been with variable speed blower motors utilizing three phase
variable frequency drive systems having elaborate feed-back
circuits to directly monitor the combustion process through the use
of oxygen sensors and the like. These systems may achieve stable
control at higher turn-down ratios, but are prohibitively expensive
and used only on very large burner systems with high maintenance
costs.
[0034] In some embodiments, this invention may include a
less-expensive (reduced capital costs, and/or reduced operating
costs) method for controlling a power burner or other combustion
device. The apparatus may include a variable speed combustion air
blower using a flow-indicating feed-back, such as pressure drop
across the blower. The apparatus may include turndown ratios of
about 3 to 1 with a relatively high control pressures, such as with
the use of affordable (low cost) sensors for the control feedback.
For higher turn-down systems of 10:1, 20:1, 30:1, or more, a
combination of control may improve operation.
[0035] Given a burner system with a relatively large turn-down
range of 30:1, a combination of mechanical dampers and variable
speed motor technologies can be optimized for affordable, stable
control of the combustion air flow over the modulated range.
Utilizing air flow measurement sensors, such as a pressure
transducer sensing the pressure drop across the combustion air
blower, the mechanism of controlling the combustion air flow to the
desired level to optimize combustion efficiency, flame stability,
combustion emissions or other required parameters, can be divided
between restricting the air flow with a damper in the flow stream
and/or reducing the blower motor speed. These methods can be
optimized to the blower system characteristics and/or fan curves,
for example.
[0036] During modulation of the burner in the upper portion of the
modulated range or envelope, the combustion process can be much
more forgiving of variations of the combustion air flow and
stability of the air flow, for example. This portion of the
modulation process may be suited for control by the restricting
damper in the combustion air flow stream. The combustion blower
motor can be efficiently maintained at full speed while the damper
can be adjusted to maintain the desired combustion air flow.
[0037] As the requirement for additional turn-down increases, the
damper cannot be closed further towards the completely closed
position without encountering decreased stability due to the flow
resolution at these operating conditions. With the damper closed,
the blower may experience internal recirculation, starved flow,
and/or other less stable operation. Desirably, air flow modulation
switches from the damper at some point and continues with the
reduction of combustion air flow to the burner using the variable
speed capabilities of the combustion air device drive. With the
restriction the damper has already placed on the system, modulation
of the blower motor may result in the deep turn-down operation to
support the high turn-down capabilities of the burner. In the
alternative, the blower may slow down and the damper may open, such
as for a net reduction in air flow.
[0038] Other methods or apparatus may include holes or apertures in
the damper at or around the damper sealing surface, such as to
allow complete closure of the damper actuator while allowing a
designed air flow to by-pass the damper blade, such as at least
about 0.1 percent flow, at least about 0.5 percent flow, at least
about 1 percent flow, and/or the like.
[0039] Efficient burner operation may include operating with a
close to stoichiometric amount of fuel and oxygen. Stoichiometric
broadly refers to the amount of an element or compound needed to
complete a balanced chemical reaction or equation. Stoichiometric
combustion broadly refers to the proper ratio of fuel to oxygen for
complete combustion with out excess oxygen, such as 1 mole of
methane (CH.sub.4) with 2 moles of oxygen (O.sub.2) yield 1 mole of
carbon dioxide (CO.sub.2) and 2 moles of water (H.sub.2O).
Stoichiometric combustion can efficiently use all of the available
fuel without warming up excess oxygen or air. Desirably,
stoichiometric combustion includes combustion of the fuel, such as
generally without particulate matter or soot.
[0040] Complete combustion broadly refers to carbon in the fuel
being oxidized to substantially carbon dioxide, such as with
reduced, minimal, or no carbon monoxide. If the amounts of fuel and
combustion air are known, the actual combustion conditions,
relative to stoichiometric, maybe defined. Some applications
operate in conditions more appropriately within a lean setting
while others may operate more appropriately at a rich setting when
compared to stoichiometric. The use of catalytic combustion
processes is within the scope of this invention.
[0041] There are several factors that may affect efficient
combustion. Low or fluctuating fuel line pressure can cause
unwanted variation of the fuel flow rates. Also altitude can have
an effect on burner performance, such as at higher altitudes
burners receive air that is less dense with less oxygen. Known
controllers without adjustment are derated (lower thermal output)
when used at higher elevations than base or nominal altitude, such
as sea level. Other factors affecting combustion efficiency may
include ambient air temperature, humidity, barometric pressure,
and/or the like. Factors affecting combustion efficiency can very
from time of day, change in season, and/or the like.
[0042] Known technology can physically vary the supplies of fuel
and combustion air in finite increments, such as through the use of
complex mechanical systems or mechanical jackshafts. Mechanical
jackshafts are difficult to maintain calibration and need frequent
maintenance. Other known applications may modulate or vary fuel
flow over a wide supply range for a wide range of burner capacity
(firing rates) through a single burner assembly, but prohibitively
use high fuel pressures and/or very expensive sensors. Known
sensors for modulating fuel flows can be more than about 7 times as
costly or more compared to the sensors in some embodiments.
[0043] In some embodiments, modulating the fuel/air mixture may
greatly increase a system overall efficiency. Known two-stage
systems capable of operating at a high and a low firing rate
provide limited scope and range of operation due to their inability
to precisely control the fuel and air mixture at two levels only.
The known two-stage systems have a wide excess-air safety margin
which reduces efficiency.
[0044] A continuously modulating appliance or apparatus can use
close control of the fuel/air ratio at all output levels, in some
embodiments. Modulating broadly refers to changing, regulating,
proportioning, and/or the like, such as in response to a change or
a need. Continuously modulating broadly refers to adjusting or
changing a value in increments or steps of less than about 5
percent of a range or span, less than about 2 percent of a range or
a span, less than about 1 percent of a range or a span, less than
about 0.5 percent of a range or a span, less than about 0.1 percent
of a range or a span, and/or the like. In some embodiments,
modulating may exclude discrete or stepwise changes, such as going
from pilot light about 2 percent capacity to a minimum burner
firing of 30 percent capacity with no stable firing regime in
between. Full modulation broadly refers to covering a complete span
or range, such as from pilot to full firing.
[0045] Various known techniques to directly measure the fuel flow
and air flow rates may independently determine a fuel air mixture,
but such measurement systems use expensive and complex sensors
which are prohibitive for many burner applications. Another known
technique to increase the efficiency includes variable speed blower
motors for tempered air movement, but variable speed blower motors
alone do not allow the burner to vary its output since other
components must also be driven to safely modulate the combustion
application. Many variable speed motors are expensive.
[0046] Generally, for more modulation and control capability placed
into a burner controller, the greater the cost to supply and
maintain control and sensing to achieve the desired burner
efficiencies. In some embodiments, the invention provides a control
system for a modulating burner system at a reasonable cost and
performance level. In additional embodiments may include
inexpensive variable speed motor technology as described in U.S.
Pat. No. 6,864,659 for a control of a shaded pole or standard
permanent split capacitor (PSC) AC induction motor. The entire
teachings of U.S. Pat. No. 6,864,659, U.S. Pat. No. 5,590,642, and
U.S. Pat. No. 7,293,718 are of common ownership with this
specification, and are incorporated herein by reference in their
entirety.
[0047] In some embodiments, a variable burner output application
includes a system with a controller to vary or modulate controlled
elements of an appliance and corresponding sensors to assure safe
and efficient operation at all firing rates of a modulating output
fuel valve or fuel valves and a combustion air blower or device.
Controllers broadly refer to devices having comparative or logic
capabilities, such as single loop controllers, programmable logic
controllers (PLCs), distributed control systems (DCS), personal
computers, work stations, microprocessors, central processing
units, digital computers, analog computers, hardwired relay boards,
hardwired circuits, and/or the like. Controllers may include
suitable software or programming, such as machine code, compiled
executable programs, ladder logic, and/or the like.
[0048] In additional embodiments, the system may include a fully
modulating fuel valve and a variable speed combustion air blower
with corresponding sensors to produce a modulating combustion
fuel/air mixture. Additional variable components and feedback
sensors are within the scope of this invention.
[0049] Modulating broadly refers to adjusting to or keeping in
proper measure or proportion. Modulating may be over or within a
certain span or range, such as 0 percent to 100 percent, about 20
percent to 100 percent, any other suitable range, and/or the like,
for example. Modulating may include discrete, finite, or stepwise
increments, such as one burner at full firing or two burners at
full firing. Any suitable number of modulating steps may be used,
such as at least about 2, at least about 3, at least about 5, at
least about 10, at least about 20, and/or the like. The steps may
be generally equally spaced and/or may be varied, such as smaller
increments at or near a lower operating regime and larger
increments at or near higher operating regime.
[0050] In addition, modulating may include continuous or infinite
spans, such as any spot or location within a span or range. Fully
modulating broadly refers to provide continuous modulation.
[0051] In some embodiments, a controller may respond to an input
command signal to initiate or adjust burner operation. The input
command may originate from a suitable input/output sensor or
control unit, such as from an On/Off thermostat, a temperature
sensor, a thermocouple, a boiler pressure sensor a pressure switch,
an analog control input, an intelligent proportional control
device, and/or the like.
[0052] A firing demand or heat call can determine a fuel/air
mixture, herein sometimes collectively referred to as a "firing
rate", from a variable, or modulating, element controlling such
conditions. For example, the controller may set a variable, or
modulating, fuel valve to the desired setting and deliver an
assumed amount of fuel flow. Then, based on an algorithm defined
firing rate for the burner, the controller adjusts the airflow from
the combustion air device to match the assumed fuel flow.
[0053] A set of variable operating conditions can be derived by
calculation of the required air flow for the assumed fuel flow or
by accessing a lookup table so as to achieve a desired
stoichiometry or ratio. A speed of the combustion air device may be
economically and reliably monitored by an air flow sensor. The
variable speed driver or motor of the combustion air device may be
adjusted until obtaining or reaching the correct air flow, for
example.
[0054] In some embodiments, the system trims or fine tunes the
fuel/air mixture based on the measured fuel flow from the fuel flow
sensor. Desirably, the measured fuel flow from the fuel flow sensor
feedback allows or provides accurate position of the fuel valve
corresponding to the fuel flow. The combustion air can then adjust
to meet the defined fuel/air ratio for the intended firing rate.
When a different burner output is commanded, the modulated fuel
valve as well as the speed of the combustion air device driver may
be altered and then re-trimmed to achieve the correct fuel/air
ratio at the new firing rate, for example.
[0055] The fuel valves may include any suitable device, such as
electronic combination valves, pneumatic valves, valve trains,
globe valves, plug valves, ball valves, diaphragm valves, pinch
valves, butterfly valves, shut off valves, stop cocks, solenoids,
and/or the like. Actuators, positioners, and/or other suitable
linkages may be included with the fuel valve. Valves may be used
with gas phase fuels, vapor phase fuels, or liquid phase fuels
including slurries, suspensions and pneumatically conveyed streams,
for example. For solid fuels, an equivalent to modulating fuel
valves include a variable rate feeders or delivery devices, such as
rotary feeders, screw augers, vibratory feeders, pellet dispensers,
conveyors, chutes, hoppers, and/or the like.
[0056] A variable input signal from a separate controller or
control system may connect to the burner controller through the
communication port to modulate the fuel/air supply. In some
embodiments, the apparatus may include a suitable burner, such as
powered burners, induced draft in-shot burners, partially mixed
burners, fully pre-mixed burners, and/or the like. In-shot burners
may be used in residential furnace applications or commercial
furnace applications, for example. Pre-mixed burners may provide
improved emission characteristics, for example.
[0057] Referencing FIGS. 1, 3, 4 a controller 1, a fuel valve 10
and a combustion air blower 11, such as may be employed in a
control burner application, is shown in some embodiments. FIG. 1
shows the components of the modulating burner control platform.
FIGS. 3 and 4 show the combustion mixture ratios for the fuel/air
mixture curve and the air/fuel mixture curve as they correspond to
various burner applications, in some embodiments and as further
described below.
[0058] FIG. 2 illustrates a block diagram of a controller 1 for the
primary application of modulation of fuel flow and air flow based
on both fuel and air flow feedback, in some embodiments. Components
of the burner control application may include a controller 1 with
modulating outputs 4 to a fuel valve 10 and a modulating output 5
to a combustion air blower 11, a modulating fuel valve 10, a
combustion air blower 11, a fuel flow feedback sensor 3, and an air
flow feedback sensor 6.
[0059] The controller 1 may receive a command for operation of an
appliance or a furnace from a sensing element, such as a simple
On/Off thermostat, or a separate command controller. A command
algorithm or program residing in the controller 1 may then be used
by the controller 1 to determine the firing rate of the variable,
or modulating, fuel valve 10 and the corresponding airflow from the
variable speed combustion air device 11, to efficiently operate the
burner, as further discussed below.
[0060] The input signal to the modulating fuel valve 10 (FIG. 2)
may be set in accordance with an appropriate value calculated by
memory, from a lookup table value, or it may be an arithmetic
component of the controller central processing unit 2 (CPU). The
modulating fuel valve 10 can be initially positioned at the percent
of the operating range to produce the desired burner capacity. The
speed of the combustion air blower motor 11 can then be adjusted
until attaining or reaching the correct air flow so as to achieve
the correct fuel/air stoichiometry operating point. The controller
1 may then further trim the fuel/air ratio by adjusting the fuel
flow, the air flow, or a combination of both, through the output to
the fuel valve 10 and the combustion air blower 11, respectively,
as further explained below.
[0061] The controller 1, in addition, may perform the following
standard functions of the exemplary fuel burner control including
safety start-up checks, the burner ignition sequencing, the safety
routines, the monitoring of control limits, the monitoring of the
fuel flow sensor 3 for controlling the firing rate, providing and
monitoring the air flow sensor 6 in order to maintain optimum
burner performance, and/or the like.
[0062] In some embodiments, the invention may include
simultaneously modulating, or varying, both fuel flow and
combustion air flow based on a commanded operating point and
continuously adjusting the flow based on fuel flow sensor feedback.
The fuel valve 10 can be initially driven to the calculated
position to achieve the desired burner capacity. The separate fuel
flow sensor 3 and the air flow sensor 6 inputs to the controller 1
to provide the basis for developing incremental adjustments to the
precise position of the fuel valve 10. The burner output can be
further adjusted to the desired operating point on the fuel/air
mixture curve by modulation of the variable speed combustion air
blower 11 to match the fuel/air mixture curve of FIG. 3, for
example. Similarly, the invention includes a process for initially
setting the air flow and then adjusting the fuel flow to achieve
the corresponding operating point on the air/fuel mixture curve in
FIG. 4.
[0063] A modulating fuel valve 10 or valves may respond to either
an analog or digital input signal where it can be desirable to
apply a variable input signal to the fuel valve 10. The fuel valves
10 may be modulated through a wide operating range. Variable
fuel/air burner systems may allow operation of a fully modulated
burner using any suitable method of modulation. The controlled
operating range of the modulating devices can be defined as 0
percent to 100 percent and can be controllable in minimal 1 percent
increments. Turn down ratios or rangeability may include any
suitable amount, such as at least about 2:1, about 3:1, about 4:1,
about 5:1, about 10:1, about 12:1, about 15:1, about 18:1, about
20:1, about 25:1, about 30:1, about 40:1, about 50:1, and/or the
like. In some embodiments, modulation may exclude periodic turning
on and off, such as providing continuous circulation of air through
a furnace.
[0064] The modulating fuel valve of FIG. 2 can be less expensive
and permits finer tuning when used in conjunction with a
self-calibrating controller using fuel sensor feedback. The
relationship between desired air and fuel flow to assure proper
stoichiometry can be performed with a lookup table or algorithm
equation, such as within the controller.
[0065] Fuel for burners or combustors broadly may include hydrogen,
natural gas, methane, ethane, propane, butane, liquefied petroleum
gas, carbon monoxide, gasoline, diesel fuel, jet fuel, fuel oil,
bunker fuel, methanol, ethanol, butanol, biodiesel, wood, wood
pellets, coal, municipal solid waste, sanitary sewage, and/or any
other suitable combustible material from renewable or nonrenewable
sources.
[0066] Fuel supply pressures may include any suitable range, such
as about 13 centimeters of water column gauge (about 5 inches of
water column gauge), to several bar of pressure or more depending
upon the application. Supply pressure may influence turndown
capabilities, such as dividing about 13 centimeters into 30
increments for a 30:1 turndown uses a sensor that detects at low as
about 4.33 millimeters of water column, for example. In the
alternative, about 13 centimeters of water column in 100 increments
includes sensors and/or techniques for measuring about 1.3
millimeters of water column.
[0067] FIG. 2 can be defined for the performance of the modulating
fuel valve with a fuel pressure sensor and an air flow pressure
sensor as the prescribe flow feedback sensors in an actual
application, in some embodiments.
[0068] A fuel pressure sensor 3 (FIG. 2) located in the fuel burner
manifold can be used as a mechanism of providing a feedback loop
control for the modulating fuel valve. The fuel pressure
corresponding to fuel flow may be automatically sensed by the
controller to adjust the position of the fuel valve to the desired
flow position. The fuel valve may be a ball valve and a compatible
actuator to achieve the desired valve positing accuracy and
commanded by the controller output signal.
[0069] An air pressure sensor 6 in FIG. 2 can be also used as a
mechanism of providing feedback loop control of the air flow
through the combustion air blower 11. The motor speed can be
automatically increased or decreased until achieving the desired
air pressure. The air pressure sensor 6, when used in this manner,
may be able to measure the combustion mass airflow and compensate
for air side variations, such as varying vent lengths, flow
blockages, plugged inlet filters, altitude, and/or the like.
[0070] FIG. 2 can be further defined for the performance of the
modulating fuel valve with another fuel flow sensor as the
prescribe feedback sensors in other actual applications. Sensors
broadly refer to devices for measuring or monitoring at least one
attribute, characteristic, or quality. Desirably, sensors include
an output in some manner proportional (directly, indirectly, or
otherwise) corresponding to the measured attribute. Sensors may
include a useful or rated span, such as a linear output range.
Output broadly refers to a signal or impulse, such as corresponding
to a measured attribute of a sensor. Outputs or signals may include
pneumatic, hydraulic, electronic, analog, digital, and/or the
like.
[0071] In some embodiments, these alternate fuel flow sensors may
include pressure sensors, mass flow sensors, volumetric flow
sensors, positive displacement sensors, and/or the like. In some
embodiments, the fuel flow sensor includes pressure switches,
pressure sensors, differential pressure sensors, anemometers,
turbine meters, vortex shedding meters, orifice plates, venturi,
nozzles, pitot tubes, coriolis meters, and/or the like. Sensors may
include suitable mounting equipment and signal equipment, such as
pipes, tubing, wiring, fiber optics, radio frequency transmitters,
and/or the like.
[0072] In some embodiments, the variable driver of the combustion
air device may be controlled inexpensively and efficiently through
a wide speed range in order to provide the correct airflow for the
combustion process. Additionally, the more expensive brushless DC
motors can be used to provide variable speed control for combustion
air. The variable speed drive may include any suitable device, such
as an inerter driven (variable frequency drive) AC motor, brushless
DC motor, PSC motor, steam turbine, hydraulic turbine, steam
engine, combustion engine, gas turbine, microtubine, mechanically
regulated constant speed devices (transmissions, gearboxes, belts,
continuous variable transmission, and/or the like), and/or the
like.
[0073] These modulating and feedback control concepts can be
applied to 2-stage combustion and 3-stage combustion air as well as
full modulation operation, for example.
[0074] In some embodiments, to avoid using a more costly modulating
thermostat as an input to describe the desired control point,
aspects of the present invention may provide a software based
command thermostat algorithm, or routine, which translates the
incoming command signal from a simple low cost thermostat into an
output signal proportional to the system demand. The thermostat may
include a bimetallic device and/or the like. The controller 1 can
use this command algorithm to increase or decrease the firing
rates, such as the amount of fuel supplied directly for the
modulating valve and indirectly for the fuel pressure feedback.
Duty cycle, or on time, of the fuel supply and speed of the
combustion air movement, desired from the combustion air blower 11
may also be determined by the thermostat algorithm.
[0075] The controller may respond to a call for heat by requesting
a predetermined firing rate, such as a fuel output from the
appliance. Based on the desired output, the controller may also
determine the airflow required from the inducer blower. The input
signals to the modulated fuel valve 10 (FIG. 2) may be set in
accordance with the appropriate firing rate value so as to achieve
the correct stoichiometry (rich, lean, and/or stoichiometric). Fuel
flow accuracy can be achieved with a ball valve and a compatible
actuator. The speed of the inducer blower fan may be adjusted until
the correct pressure may be attained or satisfied. When a different
burner output may be commanded, the speed of the combustion air
blower motor as well as the modulated fuel valve setting may be
altered to achieve the correct stoichiometry or ratio at the new
firing rate
[0076] The burner control algorithm can be configured to provide
over all maximum burner efficiency, to maintain target efficiency
over the entire operating range, and/or to maximize turn down.
Maximum burner efficiency may include any suitable number or
percent oxidized fuel, such as combusting at least about 90 percent
of the fuel, at least about 95 percent of the fuel, at least about
98 percent of the fuel, at least about 99 percent of the fuel, at
least about 99.9 percent of the fuel, and/or the like. Maintaining
target efficiency over the entire operating range may include any
suitable efficiency of combusting the fuel, such as at least about
30 percent of the fuel, at least about 50 percent of the fuel, at
least about 75 percent of the fuel, at least about 85 percent of
the fuel, at least about 90 percent of the fuel, at least about 95
percent of the fuel, and/or the like. Maximizing turn down may
include any suitable amount or percent of the firing span or range,
such as at least about 50 percent of the span, at least about 75
percent of the span, at least about 85 percent of the span, at
least about 90 percent of the span, at least about 95 percent of
the span, at least about 98 percent of the span, at least about 99
percent of the span, at least about 99.5 percent of the span,
and/or the like.
[0077] Other applications of the burner controller may be to
optimize the burner combustion setting to minimize carbon monoxide
(less than a few parts per million, molar basis), excess oxygen
(less than a few percent, molar basis), nitrogen oxides (less than
a few parts per million, molar basis), or some other combustion
characteristic. Stack temperature may also be a feedback
variable.
[0078] The controller of this invention can be configured as in
FIG. 5 to provide extended efficient operation of the burner system
with a fuel valve operating control point above and/or below the
manufactures published accuracy point on the fuel flow sensor
detection range as shown in FIGS. 3 and 4, such as outside the
range of the sensor. The controller may use a fuzzy logic
algorithm, a linear extension of the fuel/air curve, a math formula
using selected points on the fuel flow curve, and/or the like to
extrapolate or extend the low end of the fuel sensor operating
point below the point of minimum accuracy of the sensor.
[0079] Possible math formulas may include where the extrapolation
algorithm has a mathematical function derived from selected
non-linear points near an extreme end of the measured fuel--sensor
curve which provide a better extension of the desired stoichiometry
characteristics. The formula may include any suitable curve fitting
technique including linear functions, power functions,
trigonometric functions, exponential functions, geometric
functions, hypergeometric functions, and/or the like. The
relationships for the extrapolation techniques of this invention
may be applied to below and/or above the range of the sensor.
[0080] With the extrapolation of the fuel sensor curve beyond the
range, the fuel ball valve can be driven to the extended position
for the required fuel flow, for example. Desirably, the modulating
range of the combustion air blower may be compatible with the fuel
valve extended positioning. The extrapolation can be extended to
the point of fuel valve and burner operation until the flame goes
out or is "snuffed" out. Optionally, the controller can recognize
the snuff out condition and shift the fuel valve operating point
upward until continuous burn can be maintained. The new minimum
fuel operating points for the given fuel valve and burner
configuration will be redefined or spanned as the 0 percent to 100
percent modulating range and may be controlled in 1 percent
increments, for example.
[0081] In some embodiments, the increments of this invention over
the range may include at least about 50 percent, at least about 33
percent, at least about 25 percent, at least about 20 percent, at
least about 15 percent, at least about 10 percent, at least about 5
percent, at least about 2 percent, at least about 1 percent, at
least about 0.5 percent, at least about 0.1 percent, and/or the
like.
[0082] The fuel/air mixture curves of FIGS. 3 and 4 can also
include extrapolation to provide either an air rich combustion
curve or a fuel rich combustion curve. The excess air for a lean
combustion curve may include any suitable amount above
stoichiometric, such as at least about 0.05 percent, at least about
0.1 percent, at least about 0.5 percent, at least about 1.0
percent, at least about 1.5 percent, at least about 2 percent, at
least about 3 percent, at least about 5 percent, and/or the like.
The excess fuel for a rich combustion curve may include any
suitable amount above stoichiometric, such as at least about 0.05
percent, at least about 0.1 percent, at least about 0.5 percent, at
least about 1.0 percent, at least about 1.5 percent, at least about
2 percent, at least about 3 percent, at least about 5 percent,
and/or the like.
[0083] In some embodiments, the burner controller can also be
configured according to FIG. 6 to provide burner operation of very
large burner assemblies with correspondingly large combustion air
blower assemblies. These large blowers may be difficult to
accurately control air flow near the ends of their operating range
or envelope, such as either open or closed. The burner controller
can optimize the burner capacity at these extended operating end
points using the same extrapolation techniques for the air flow
sensor as described above for the fuel flow sensor and provide an
auxiliary output 7 to modulate a combustion air blower inlet vane
15 to fine tune the air flow to match the fuel/air curve in FIG. 3
or 4.
[0084] The controller may also be applicable to very large burner
assemblies consisting of a modulating burner in combination with
multiple fixed capacity sequentially staged burners. Control of the
staged burners can be configured in the controller and sequenced
into to the continuous modulation of the total burner assembly
through a communication method as shown in FIG. 7. Various
communication serial or parallel methods may be used, such as
RS485, RS232, and/or the like.
[0085] Desirably, the controller provides modulation of the primary
variable capacity burner unit. The control algorithm can be
expanded to modulate the primary burner up to full capacity in
response to the command from the media sensing unit. If the heat or
firing call exceeds the capacity of the primary unit to satisfy the
request, the controller can turn on the next burner stage by the
communication link, such as to run or operate the next burner at
full burner capacity. The controller in FIG. 7 can then reduce the
modulation rate on the primary modulating burner back to a burner
output that can satisfy the call. This process may be repeated with
each burner stage as necessary to satisfy the call (adding or
reducing a number of fixed capacity burners). The staging sequence
can work with one or more additional burner units, such as a
sequentially staged burner configuration. The use of multiple
burners may also include two or more modulating burners
communicating with each other and in communication to one or more
staged burners to provide continuous modulation over the entire
operating range of the system. Multiple burner applications can
also include systems using several simple on/off burners and one or
two modulating burners to achieve wide modulation ranges.
[0086] Due to environmental restrictions on burner emissions or to
operate the burner at specific emission level (regulatory
compliance), the controller in FIG. 8 can be configured with a flue
emission sensor. The controller algorithm can be programmed to
monitor the flue fuel emission to further adjust the burner
operating point to meet fuel emission requirements or to set
operating limits for the discharge. The flue emission sensors may
include a temperature sensor, a carbon monoxide sensor, an oxygen
sensor, a nitrogen oxides sensor, gas chromatograph, mass
spectrometer, and/or the like.
[0087] The sensed or measured emission value can be incorporated
into the burner control loop to adjust the burner capacity to the
required operating performance of the burner. For example the
firing call may result in adjusting the fuel valve to a position
and the air device driver at a speed, but a carbon monoxide sensor
may read too high. The controller may increase the speed of the air
device drive to supply additional oxygen to reduce the carbon
monoxide. If needed the fuel valve may adjust or increase to
compensate for the additional air in a feedback loop. Feedback and
feed-forward loops are within the scope of this invention.
[0088] As schematically shown in FIG. 9 and in some embodiments,
the invention includes a modulating combustion apparatus 20, such
as a gas forced warm air furnace. The apparatus 20 includes a
burner 21, a housing 24, an on/off fuel valve 23, a modulating fuel
valve 10, and a fuel sensor 4. The apparatus 20 also includes an
air sensor 22 and a combustion air device 11. Desirably, in furnace
applications, the modulating controller provides increased comfort,
such as for persons within the room or building. The temperature
within a room may vary less than about 5 degrees Celsius, less than
about 4 degrees Celsius, less than about 3 degrees Celsius, less
than about 2 degrees Celsius, less than about 1 degree Celsius,
less than about 0.5 degrees Celsius, less than about 0.1 degrees
Celsius, and/or the like.
[0089] In some embodiments, the invention may include a combustion
apparatus for use in fired variable demand applications. The
apparatus may include a fuel valve modulating a fuel flow, and a
fuel sensor with a range measuring the fuel flow and sending a fuel
output. The apparatus may also include a combustion air device
modulating an air flow, and an air sensor measuring the air flow
and sending an air output. The apparatus may also include a
controller connected to the fuel valve, the fuel sensor, the
combustion air device, and the air sensor. The controller may
modulate the fuel valve based on the fuel output using an
extrapolation algorithm when the fuel output extends outside of the
range of the fuel sensor, and the controller may modulate the
combustion air device based on the air output. The controller
simultaneously and/or sequentially may modulate the fuel flow and
the air flow over an extended fuel/air ratio and may provide
continuous modulation during a single burn cycle.
[0090] Simultaneously broadly refers to two or more items at the
same time or substantially the same time, such as both the fuel and
the air moving in five percent increments in response to a change
in heat load (increase or decrease). Sequentially broadly refers to
one item first and then the other item or substantially a first
item and substantially a second item, such as moving the fuel first
followed by the air each in five percent increments in response to
a change in heat load (increase or decrease), the air first
followed by the fuel each in five percent increments in response to
a change in heat load (increase or decrease), and/or the like.
[0091] Single burn cycle broadly refers to one stage combustion
where at least a substantial amount of the fuel burns or oxidizes.
A dual burn cycle or multiple burn cycle may include partial
oxidization of the fuel in a first stage lacking enough oxygen for
complete combustion and then a second stage with additional oxygen
and complete combustion, for example. In some embodiments, this
invention may include multiple stage burn cycles, such as with over
fire air.
[0092] As discussed above, the extrapolation algorithm may include
fuzzy logic derived from a fuel sensor curve over the range, linear
extension derived from a fuel sensor curve over the range, a
mathematical function derived from selected points on a fuel sensor
curve over the range, and/or the like. In some embodiments, the
controller utilizes the extrapolation algorithm to provide a
predetermined rate leaner or with excess air than a stoichiometric
ratio of air to fuel. In the alternative, the controller utilizes
the extrapolation algorithm to provide a predetermined rate richer
or with excess fuel than a stoichiometric ratio of air to fuel.
[0093] In some embodiments, the fuel sensor includes a pressure
sensor, a mass flow sensor, and/or a volumetric flow sensor, such
as an anemometer, a turbine, an orifice, a venturi, and/or a
nozzle. Desirably, but not necessarily, the combustion air device
includes full modulation operation full modulation operation
between a minimum of the extrapolation algorithm and a full system
capacity, such as between about 2 percent and 100 percent, between
about 5 percent and about 100 percent, between about 10 percent and
about 100 percent, between about 12 percent and 100 percent,
between about 15 percent and about 100 percent, and/or the
like.
[0094] The controller may maximize burner efficiency, maintain a
target efficiency over an entire operating range, maximize turn
down, and/or the like, as discussed above. Optionally, the
controller minimizes carbon monoxide, excess oxygen, and/or
nitrogen oxides.
[0095] Desirably, the controller learns from a flame-out due to low
combustion fuel (unstable regime for the burner) and modifies the
extrapolation algorithm for future use upward, to the right, and/or
the like to prevent additional flame-outs, such as resetting the
zero flow of the span.
[0096] In some embodiments, the apparatus may include a first
burner with a capacity, and one or more additional burners each
with a capacity and with the first burner forming a sequentially
staged burner system. The controller may communicate with the first
burner and the one or more additional burners. When a heating
demand or call exceeds the capacity of the first burner, the
controller may activate the one or more additional burners, as
described above. Desirably, but not necessarily, the controller
uses a sequential algorithm modulating the first burner to provide
continuous modulation operation over a system range, such as over a
broader range but still with fine adjustment by the modulating
burner.
[0097] In the alternative, the controller may use a sequential
algorithm modulating the first burner and the one or more
additional burners to provide continuous modulation operation over
a system range. Optionally, the apparatus may include a second
sequentially staged burner system to provide a broader system
range, such as a greater range than with a single sequentially
staged burner system. The sequentially staged burners may be in
different furnace units or banks of furnace units, for example.
[0098] In some embodiments, the apparatus may include a flue gas
sensor indicating a flue gas characteristic, such as a temperature
sensor, a carbon monoxide sensor, an oxygen sensor, nitrogen oxide
sensor, and/or the like, as discussed above.
[0099] In some embodiments, the invention may include a combustion
apparatus for use in fired variable demand applications. The
apparatus may include a fuel valve modulating a fuel flow, and a
fuel sensor with a range measuring the fuel flow and sending a fuel
output. The apparatus may also include a variable speed driver
modulating an air flow of a combustion air device, and a damper
modulating the air flow of the combustion air device. The apparatus
may also include an air sensor measuring the air flow and sending
an air output, and a controller connected to the fuel valve, the
fuel sensor, the variable speed driver, the damper, and the air
sensor. The controller may modulate the fuel valve based on the
fuel output, and the controller may modulate the variable speed
driver and the damper based on the air output. The controller may
simultaneously and/or sequentially modulate the fuel flow and the
air flow over an extended fuel/air ratio and may provide continuous
modulation during a single burn cycle.
[0100] The combined damper and variable speed driver may provide
greater turn down, finer control, and/or a more stable flame
pattern, as discussed above. Desirably, but not necessarily, the
combined damper and the variable speed driver may be combined with
the extrapolation algorithm, such as to provide or extend the
operating envelope even further for the apparatus.
[0101] The fuel sensor may include any of the characteristics and
qualities discussed above with respect to any other embodiments.
The modulation of the apparatus and the controller may include any
of the characteristics and qualities discussed above with respect
to any other embodiments.
[0102] In some embodiments, the invention may include a method of
operating a combustion apparatus for use in fired variable demand
applications. The method may include the step of measuring a fuel
flow with a fuel sensor having a range and a fuel output, and the
step of measuring an air flow with an air sensor having an air
output. The method may also include the step of modulating the fuel
flow with a fuel valve and a controller based on the fuel output,
and the step of modulating the air flow with a combustion air
device and the controller based on the air output. The method may
also include the step of calculating the air flow or the fuel flow
when the fuel output extends outside of the range of the fuel
sensor with an extrapolation algorithm, and the step of maintaining
simultaneously and/or sequentially the fuel flow and the air flow
over an extended fuel/air ratio and to provide continuous
modulation during a single burn cycle with the controller.
[0103] Calculating broadly refers to any suitable logic based
operation to derive, estimate, and/or arrive at the desired output,
such as discussed above. Maintaining broadly refers to executing a
control loop structures such as a feedback loop. The feedback loop
may include a set point and a measured output. The set point may be
adjusted based on the measured output, for example.
[0104] The extrapolation algorithm of the method may include any of
the characteristics and qualities discussed above with respect to
any other embodiments.
[0105] In some embodiments, the maintaining comprises a
stoichiometric ratio, a lean ratio, and/or a rich ratio, as
discussed above. Optionally, the controller may operate different
fuel/air ratios in different operating modes, such as start up,
stand by, minimum firing, mid-level firing, maximum firing, and/or
the like.
[0106] The modulating of the method may include any of the
characteristics and qualities discussed above with respect to any
other embodiments. The method may also include minimizing or
reducing carbon monoxide, excess oxygen, nitrogen oxides, and/or
the like, as discussed above.
[0107] In some embodiments, the invention may include a method of
operating a combustion apparatus for use in fired variable demand
applications. The method may include the step of measuring a fuel
flow with a fuel sensor having a range and a fuel output, and the
step of measuring an air flow with an air sensor having an air
output. The method may also include the step of modulating the fuel
flow with a fuel valve and a controller based on the fuel output,
and the step of modulating the air flow with a damper and a
variable speed driver of a combustion air device and the controller
based on the air output. The method may also include the step of
maintaining simultaneously and/or sequentially the fuel flow and
the air flow over an extended fuel/air ratio and to provide
continuous modulation during a single burn cycle with the
controller.
[0108] The modulating the damper and the variable speed driver may
be done in any suitable manner including simultaneously and/or
sequentially, such as to avoid unstable operations or excessive
"hunting" as the system moves between points or settings. The
controller of the method may include any of the characteristics and
qualities discussed above with respect to any other embodiments.
Similarly, the fuel/air ratio of the method may include any of the
characteristics and qualities discussed above with respect to any
other embodiments. The modulating and the reduced emission control
of the method may include any of the characteristics and qualities
discussed above with respect to any other embodiments.
[0109] A system has been shown whereby a controller and an
economical sensing and control systems provides an inexpensive
means for operating a modulating burner assembly through the use of
a variable output components. It will be appreciated that details
of the foregoing embodiments, given for purposes of illustration,
are not to be construed as limiting the scope of this invention.
Although only a few exemplary embodiments of this invention have
been described in detail above, those skilled in the art will
readily appreciate that many modifications and/or combinations are
possible in the exemplary embodiments without materially departing
from the novel teachings and advantages of this invention.
Accordingly, all such modifications and/or combinations are
intended to be included within the scope of this invention, which
is defined in the following claims and all equivalents thereto.
Further, it is recognized that many embodiments may be conceived
that do not achieve all of the advantages of some embodiments,
particularly of the preferred embodiments, yet the absence of a
particular advantage shall not be construed to necessarily mean
that such an embodiment is outside the scope of the present
invention.
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