U.S. patent application number 09/761424 was filed with the patent office on 2001-10-25 for pressure feedback signal to optimise combustion air control.
Invention is credited to Crowle, William E., Howlett, Michael, Murray, Gordon Alexander.
Application Number | 20010032571 09/761424 |
Document ID | / |
Family ID | 26871690 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010032571 |
Kind Code |
A1 |
Howlett, Michael ; et
al. |
October 25, 2001 |
Pressure feedback signal to optimise combustion air control
Abstract
A novel method of combustion air control for multiple burner
furnaces, whereas a pressure transducer is located in the air
piping downstream of each zone air flow control device. The
pressure transducer sends a feedback signal to a pressure control
loop that is in a logical cascade from the furnace temperature
control loop. The pressure control loop repositions the air flow
control device to compensate for changes in both downstream and
upstream conditions. Output from the temperature control loop is
interpreted by the pressure control loop as a changing remote
set-point value. In one embodiment, the system is ideally suited to
compensate for the pressure drop changes that occur across a zone
air flow control valve, when flow rate changes occur as burners are
started or stopped, thus providing a substantially higher turndown
ratio and better control at low fire settings.
Inventors: |
Howlett, Michael; (ST.
Lambert, CA) ; Murray, Gordon Alexander; (Baie
D'Urfe, CA) ; Crowle, William E.; (Rigaud,
CA) |
Correspondence
Address: |
M. Howlett
755 Boissy Street
ST. Lambert
QC
J4R IKI
CA
|
Family ID: |
26871690 |
Appl. No.: |
09/761424 |
Filed: |
January 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60175927 |
Jan 13, 2000 |
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Current U.S.
Class: |
110/185 |
Current CPC
Class: |
F23N 2225/08 20200101;
F23N 2225/06 20200101; F23N 1/10 20130101; F23N 2225/04 20200101;
F23N 2235/06 20200101; F23N 2005/181 20130101; F23N 1/027 20130101;
F23N 2235/16 20200101; F23N 2235/20 20200101; F23N 5/022
20130101 |
Class at
Publication: |
110/185 |
International
Class: |
F23N 005/00 |
Claims
What we claim is:
1. A combustion control system comprising; a) a means for
controlling air flow; b) a means for controlling fuel flow
substantially in proportion to said air flow; c) a pressure
transducer for sensing pressure downstream of said means for
controlling air flow and producing electrical output signals
indicative thereof, d) an electronic pressure controller for
controlling said means for controlling air flow in response to
inputs from the pressure transducer electrical output signals and a
remote set-point value; e) a temperature transducer for sensing
process temperature and producing electrical output signals
indicative thereof; f) an electronic temperature controller for
generating electrical output signals in response to inputs from the
temperature transducer output signals and an internal programmable
set-point; g) a means for connecting the electronic temperature
controller output signals with the electronic pressure controller
remote set-point value input; whereby the air pressure downstream
of said means for controlling air flow is controlled in direct
proportion to said electronic temperature controller output
signals.
2. A combustion control system according to claim 1 wherein said
electronic pressure controller and said electronic temperature
controller are functionally combined in an electronic control
device capable of a plurality of control functions.
3. A combustion control system according to claim 1 wherein said
means for controlling air flow is a motor speed control device
controlling the rotational speed of an electric motor powering a
means for compressing air.
4. A furnace assembly comprising; a) a plurality of burners; b) a
means for controlling air flow; c) a means for controlling fuel
flow substantially in proportion to said air flow; d) a pressure
transducer for sensing pressure downstream of said means for
controlling air flow and producing electrical output signals
indicative thereof; e) an electronic pressure controller for
controlling said means for controlling air flow in response to
inputs from the pressure transducer electrical output signals and a
remote set-point value; f) a temperature transducer for sensing
furnace temperature and producing electrical output signals
indicative thereof; g) an electronic temperature controller for
generating electrical output signals in response to inputs from the
temperature transducer output signals and an internal programmable
set-point; h) a means for connecting the electronic temperature
controller output signals with the electronic pressure controller
remote set-point value input; whereby the air pressure downstream
of said means for controlling air flow is controlled in direct
proportion to said electronic temperature controller output
signals.
5. A furnace assembly comprising a plurality of zones each
according to claim 1.
Description
BACKGROUND
[0001] Discussion of Prior Art
[0002] At the present time, there are four basic types of
combustion control systems used in multiple burner furnaces. They
are; pressure balance control, linked valve control, flow balance
control and mass flow control.
[0003] In the first three cases, a single flow control valve is
normally used to control the combustion air flow to a group (zone)
of burners. This valve is usually actuated by a valve actuator
(electric control motor) through mechanical linkages. Control of
the valve actuator is by an output signal from the furnace zone
temperature controller. The controller sends an output signal to
the valve actuator that proportionally positions the air flow
control valve. Thus a 10% output signal will position the valve in
the 10% open position and the 70% output signal positions the valve
in a 70% open position, etc.
[0004] Since the result of a temperature control output is a
specific valve position, these systems do not respond directly to
system pressure changes. In the typical event of a burner being
shut-off in a multiple burner zone, there is a decrease in airflow
through the control valve and, as a result, there is a decreased
pressure drop across the control valve. With the lower pressure
drop, the net pressure downstream of the control valve will
increase, thus increasing the flow to the remaining burners.
Therefore, as more burners are shut-off, increasing amounts of air
(and gas) will go to the remaining burners, partially defeating the
purpose (less heat input) of shutting off the burners.
[0005] The mass flow control system measures the air mass flow and
fuel mass flow and controls each according to a calculated ratio.
Differential pressure transmitters or other accurate flow measuring
devices are needed to achieve optimum ratio control. Air and fuel
temperature and pressure measurements are made to correct for minor
variations. A microprocessor based control unit calculates and
controls the actual mass flow of both streams to suit the process
requirements. North American Combustion Company's MARC.RTM. IIIE
Combustion Controller is an example of this type of system. These
systems are generally complex and thus expensive and are not
suitably designed for a simple air valve repositioning.
SUMMARY
[0006] This invention concerns a novel method of air control where
there is more that one burner or item per control zone on a
furnace, heating system, cooling system or other apparatus
requiring a controlled air flow to multiple devices. A pressure
transducer in the air piping, located downstream of the flow
control device, sends a feedback signal to a pressure control loop
that is a logical cascade from the temperature control loop. The
pressure control loop repositions the air flow control device to
compensate for changes in both downstream and upstream
conditions.
OBJECTS AND ADVANTAGES
[0007] Accordingly, several objects and advantages of our invention
are:
[0008] 1. The system is designed to readjust the air flow control
device to correct for variations of the upstream and downstream air
pressure.
[0009] 2. The system is ideally suited to compensate for the
pressure drop changes that occur across the zone air flow control
valve when burners are started or stopped in a multiple burner
zone. This provides a much higher "turndown ratio" and better
control at "low fire" settings.
[0010] 3. The system can be easily retrofitted to most existing
burner system at reasonable cost.
[0011] 4. The pressure feedback signal system can optimise air flow
control valve positioning on; pressure balance, linked valve and
flow balance combustion systems.
[0012] 5. Our invention provides greater fuel efficiency in
multiple burner systems by providing better control at low fire and
an increased operating range.
[0013] 6. The system provides a fast response time
[0014] Further objects and advantages of our invention will become
apparent from a consideration of the drawings and ensuing
description.
DRAWING FIGURES
[0015] FIG. 1 is a Process and Instrumentation Diagram of the
Invention as shown in a pressure balance combustion system with the
feedback signal to a valve actuator driving an air flow control
butterfly valve.
[0016] FIG. 2 is a Process and Instrumentation Diagram of the
Invention as shown in a linked valve combustion system with the
feedback signal to a valve actuator driving linked butterfly air
and gas valves. The temperature and pressure control functions are
combined in a dual loop controller.
[0017] FIG. 3 is a Process and Instrumentation Diagram of the
Invention as shown in a flow balance combustion system with the
feedback signal to a motor speed drive controlling a combustion air
blower.
LIST OF REFERENCE NUMERALS
[0018] 1. Pressure Transducer
[0019] 2. Pressure Controller
[0020] 3. Valve Actuator
[0021] 4. Air Flow Control Valve
[0022] 5. Fuel Flow Control Valve
[0023] 6. Temperature Transducer
[0024] 7. Temperature Controller
[0025] 8. Motor Speed Drive
[0026] 9. Combustion Air Blower
[0027] 10. Burner
[0028] 11. Furnace
[0029] 12. Dual Loop Controller
[0030] 13. Orifice Plate
[0031] 14. Differential Pressure Regulator
[0032] 15. Air Manifold
DESCRIPTION OF INVENTION
[0033] Physical Description
[0034] A pressure transducer (Item 1, FIG. 1) measures the pressure
in an air manifold (Item 15, FIG. 1), at a point that is both;
upstream of multiple burners (or other devices), and downstream of
an air flow control device such as an air flow control valve (Item
4, FIG. 1). The pressure transducer is generally a differential
pressure transmitter (with one side open to atmospheric pressure)
of about 0-1.5 PSIG (pounds per square inch gage) pressure range
with a proportional output signal (generally 4-20 mA (milliamps) or
0-10 volts). A pressure controller (Item 2, FIG. 1) can be any
microprocessor based electronic instrument capable of; receiving a
remote set-point input (generally 4-20 mA), calculating a PID
(proportional, integral and derivative) control loop, and sending a
proportional output signal (generally 4-20 mA). The air flow
control valve can be a butterfly, ball, adjustable port, gate,
globe or other type that is suitably sized for the air flow range
and that can be driven by a valve actuator (Item 3, FIG. 1). The
valve actuator must be able to accurately position the air flow
control valve proportionally to the output signal of the pressure
controller.
[0035] Fuel flow is varied in proportion to air flow by a fuel flow
control valve (Item 5, FIG. 1) that can be of types actuated by
either pneumatic signal, mechanical linkage, or differential
pressure signal as shown in FIG. 1, FIG. 2 and FIG. 3 respectively.
The flow balance combustion system uses an orifice plate (Item 13,
FIG. 3) in the zone air line to produce the differential pressure
signal that actuates the differential pressure regulator (Item 14,
FIG. 3) governing fuel flow. The air and fuel flows both supply a
plurality of burners (Item 10, FIG. 1) located in a furnace (Item
11, FIG. 1). A temperature transducer (Item 6, FIG. 1), that can be
any appropriate temperature measuring element such as a
thermocouple, produces an output signal that is transmitted to a
temperature controller (Item 7, FIG. 1). The temperature can be any
microprocessor based electronic instrument capable of, receiving a
temperature signal, calculating a PID (proportional, integral and
derivative) control loop, and sending a proportional output signal
(generally 4-20 mA).
[0036] Process Description
[0037] This invention uses the pressure transducer to sense the air
pressure at a location downstream of an air flow control device
such as the air flow control valve. The pressure transducer sends
an electric signal (called PV1), that is proportional to the air
pressure, to the pressure controller. The pressure controller
compares this signal to a set-point input signal (called SP1) and
computes an output value that is proportional to the difference.
This output value is transmitted as an output signal (called
Output1) to the valve actuator that operates the air flow control
valve. Alternately, said Output1 signal can be transmitted to a
motor speed drive (Item 8, FIG. 3) that controls the rotational
speed of a combustion air blower (Item 9, FIG. 3) and thus vary the
air flow rate.
[0038] This pressure control loop is a cascaded from the main
temperature control loop. In the temperature control loop, the
temperature transducer sends a temperature signal (called PV2),
that is proportional to the process temperature of the furnace, to
the temperature controller. The temperature controller compares
said temperature signal to an internal programmed set-point value
(called SP2) and computes an output value (called Output2) that is
proportional to the difference. Said Output2 value is transmitted
to the pressure controller where it is interpreted as a set-point
input (SP1).
[0039] The function of the pressure controller and the temperature
controller can be combined into a signal unit such as a dual loop
controller (Item 12, FIG. 2) or a programmable logic controller
(PLC).
[0040] The pressure control loop maintains a desired pressure in
the air manifold. Any pressure upsets, such as when burners are
first started or stopped, are quickly corrected by the opening or
closing of the air flow control valve. The desired (set-point)
pressure is a function of the demand for heat of the temperature
controller. A high manifold pressure results in a high air flow
rate and thus high gas flow rate to the burners.
[0041] Conclusion, Ramification, and Scope of Invention
[0042] Thus the reader will see that the Pressure Feedback Signal
to Optimise Combustion Air Control invention represents a
significant improvement in the state of the art of combustion air
control for multiple burner furnaces. The invention's pressure
feedback signal is used to reposition the zone air flow control
device so that a desired pressure is maintained in the zone's air
manifold. This counters unwanted pressure changes that normally
would have occurred due to changes in air flow through the control
valve.
[0043] While the above description contains many specificities,
these should not be construed as limitations on the scope of the
invention, but rather as an exemplification of one preferred
embodiment thereof. Many other variations are possible. For
example; The principal could be used for air curtains, cooling
jets, air knives, Coanda air jets, paper support high speed jets,
ribbon burners (with sections that are closed off to decrease heat
input), water agitation, fish tank aeration, water removal air
jets, vacuum systems, chip scale removal, and furnace pressure
control.
[0044] Accordingly, the scope of the invention should be determined
not by the embodiments illustrated, but by the appended claims and
their legal equivalents.
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