U.S. patent application number 12/365511 was filed with the patent office on 2009-08-06 for premix burner control system and method.
This patent application is currently assigned to Maxitrol Company. Invention is credited to Mark Masen.
Application Number | 20090197212 12/365511 |
Document ID | / |
Family ID | 40932034 |
Filed Date | 2009-08-06 |
United States Patent
Application |
20090197212 |
Kind Code |
A1 |
Masen; Mark |
August 6, 2009 |
Premix Burner Control System and Method
Abstract
A fan modulated premix burner control system includes a
regulating control valve for regulating the pressure of gas fed to
a premix chamber. The pressure of the gas is based on the pressure
of air also fed into the chamber to produce a constant air/fuel
ratio. The system also includes an air restrictor for reducing the
pressure of the air to permit operation of the burner at low fan
speeds.
Inventors: |
Masen; Mark; (Leonard,
MI) |
Correspondence
Address: |
HOWARD & HOWARD ATTORNEYS PLLC
450 West Fourth Street
Royal Oak
MI
48067
US
|
Assignee: |
Maxitrol Company
Southfield
MI
|
Family ID: |
40932034 |
Appl. No.: |
12/365511 |
Filed: |
February 4, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61026041 |
Feb 4, 2008 |
|
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|
Current U.S.
Class: |
431/12 ;
431/18 |
Current CPC
Class: |
F23N 1/022 20130101;
F23N 2225/04 20200101; F23N 2233/08 20200101 |
Class at
Publication: |
431/12 ;
431/18 |
International
Class: |
F23N 1/02 20060101
F23N001/02 |
Claims
1. A method of maintaining flow of an air/fuel mixture to a burner,
the burner fed from a premix chamber enclosing a variable speed fan
and defining an air inlet, a fuel inlet, and an outlet in fluidic
communication with the burner, said method comprising the steps of:
sensing a pressure of air at the air inlet; regulating a pressure
and flow of gaseous fuel though the fuel inlet with a regulating
control valve; drawing the gaseous fuel and air into the premix
chamber by operation of the fan; affecting mixture of the gaseous
fuel and the air in the premix chamber by operation of the fan to
produce an air/fuel mixture; forcing the air/fuel mixture to the
outlet by operation of the fan; and lowering an inlet air pressure
of air drawn through the air inlet by reducing the area of an air
duct ahead of the air inlet to decrease the flow rate of the
air/fuel mixture.
2. A method as set forth in claim 1 further comprising the step of
monitoring the speed of the fan.
3. A method as set forth in claim 2 wherein said step of lowering
an inlet air pressure is done in response to the speed of the fan
falling below a certain speed.
4. A method as set forth in claim 1 further comprising the step of
maintaining a constant ratio of gaseous fuel and air in producing
the air/fuel mixture.
5. A method as set forth in claim 1 further comprising the step of
sensing the pressure of air at the air inlet;
6. A method as set forth in claim 5 wherein said step of regulating
a pressure and flow of gaseous fuel though the fuel inlet with a
regulating control valve is done in accordance with the sensed
pressure of the air at the air inlet.
7. A premix burner control system comprising: a housing defining a
gas inlet for receiving a gaseous fuel, an air inlet for receiving
air, and at least one outlet for connection to a burner; a fan
disposed in said housing for drawing the gaseous fuel and the air
into said housing, affecting mixture of the gaseous fuel and the
air to produce an air/fuel mixture, and forcing the air/fuel
mixture to the outlet; a motor operatively connected to said fan
for turning said fan; a variable speed drive operatively connected
to said motor for turning said fan at a plurality of speeds to
control a flow rate of the air/fuel mixture into the outlet; a
regulating control valve in fluid communication with said gas inlet
for regulating the flow and pressure of the gaseous fuel; and a
restrictor device in fluid communication with said air inlet for
controlling an air inlet pressure of air drawing through said air
inlet and into said housing; said restrictor device operable to
lower the air inlet pressure of the air drawn through said air
inlet by reducing the area of an air duct ahead of said air inlet
to decrease the flow rate of the air/fuel mixture.
8. A system as set forth in claim 7 wherein said regulating control
valve regulates the pressure of the gaseous fuel based on the
pressure of air drawing through said air inlet.
9. A system as set forth in claim 8 further comprising a pneumatic
sensing tube connected between said air inlet and said regulating
control valve such that said regulating control valve can sense the
pressure of the air at said air inlet.
10. A system as set forth in claim 7 further comprising a gas
orifice plate disposed between said gas regulator and said gas
inlet and defining a gas orifice through which the gaseous fuel
passes.
11. A system as set forth in claim 7 further comprising an air
orifice plate disposed between said restrictor device and said air
inlet and defining an air orifice through which the air passes.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of provisional patent
application No. 61/026,041, filed Feb. 4, 2008, which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to gas burners. More
specifically, the present invention relates to a control system for
premix gas burners and a method for maintaining flow of an air/fuel
mixture to the premix gas burner.
[0004] 2. Description of the Related Art
[0005] Premix gas burners operate by mixing gaseous fuel and air
prior to produce an air/fuel mixture. The air/fuel mixture then
enters the burner and is ignited and burned. A fan is often used to
induce mixing of the air and fuel.
[0006] However, typical methods of controlling the air/fuel mixture
limit minimum firing rates of the burner due to their inability to
maintain the desired air/fuel mixtures at very low fan pressures.
That is, the controls are not sensitive enough to react to minute
changes in pressure that occur at reduced flow rates. Eventually,
the firing rate, i.e., the rate at which the air/fuel mixture is
burned, is limited with these typical control systems. For example,
the fan motor may actually stall or the air pressure changes may be
so minute that the control valve is no longer able to adequately
sense the changes and react accordingly.
[0007] Accordingly, there exists a need for new and improved
systems and methods for regulating air and/or fuel flow in fan
modulated premix gas burners that overcome at least one of the
aforementioned problems.
SUMMARY OF THE INVENTION AND ADVANTAGES
[0008] The present invention discloses a method of maintaining flow
of an air/fuel mixture to a burner. The burner is fed from a premix
chamber enclosing a variable speed fan. The premix chamber also
defines an air inlet, a fuel inlet, and an outlet in fluidic
communication with the burner. The method includes the step of
regulating a flow of gaseous fuel though the fuel inlet with a
regulating control valve to maintain a specified pressure. The
gaseous fuel and air are drawn into the premix chamber by operation
of the fan. Mixture of the gaseous fuel and the air in the premix
chamber are affected by operation of the fan to produce an air/fuel
mixture. The air/fuel mixture is forced to the outlet by operation
of the fan. The method continues with the step of lowering an inlet
air pressure of air drawn through the air inlet by reducing the
area of an air duct ahead of the air inlet to decrease the flow
rate of the air/fuel mixture.
[0009] The present invention also discloses a premix burner control
system. The system includes a housing defining a gas inlet for
receiving a gaseous fuel, an air inlet for receiving air, and at
least one outlet for connection to a burner. A fan is disposed in
the housing for drawing the gaseous fuel and the air into the
housing, affecting mixture of the gaseous fuel and the air to
produce an air/fuel mixture, and forcing the air/fuel mixture to
the outlet. A motor is operatively connected to the fan for turning
the fan. A variable speed drive is operatively connected to the
motor for turning the fan at a plurality of speeds to control a
flow rate of the air/fuel mixture into the outlet. A regulating
control valve in fluid communication with the gas inlet regulates
the flow and pressure of the gaseous fuel. A restrictor device is
in fluid communication with the air inlet for controlling an air
inlet pressure of air drawing through the air inlet and into the
housing. The restrictor device is operable to lower the air inlet
pressure of the air drawn through said air inlet by reducing the
area of an air duct ahead of said air inlet to decrease the flow
rate of the air/fuel mixture.
[0010] By lowering the inlet air pressure ahead of the air inlet
with the restrictor device, a constant air/fuel ratio can be
obtained even at very low fan speeds. As such, the control system
and method of the present invention permits operation of the burner
at a wider range of fan speeds, thus improving efficiency and
economy of the burner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Other advantages of the present invention will be readily
appreciated, as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings wherein:
[0012] FIG. 1 is a schematic diagram of an embodiment of a system
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Referring to the Figures, wherein like numerals indicate
like parts throughout the several views, a premix burner control
system 10 and method of maintaining flow of an air/fuel mixture to
a burner 12 is described herein.
[0014] Referring to FIG. 1, the premix burner control system 10
(hereafter referred to simply as the system 10) includes a housing
14 for mixing a gaseous fuel and air to produce an air/fuel
mixture. Accordingly, the housing 14 defines a gas inlet 16 for
receiving the gaseous fuel and an air inlet 18 for receiving air.
The gaseous fuel may be natural gas; however, other suitable
gaseous fuels may alternatively be utilized. The housing 14 may
also be referred to as a pre-mix chamber by those skilled in the
art.
[0015] The housing 14 also defines at least one outlet 20 for
connection to the burner 12. The burner 12 preferably defines a
plurality of burner ports (not shown) as is well known those
skilled in the art. The air/fuel mixture is ignited and burned via
these burner ports. Other than the inlets 16, 18 and the outlet 20,
the housing 14 is generally sealed from the environment.
[0016] A fan 22 is disposed in the housing 14 for drawing the
gaseous fuel and the air into the housing 14. More specifically,
the fan 22 generates a negative pressure within the housing 14
which precipitates the flow of the gaseous fuel and the air. The
fan 22 also affects the mixture of the gaseous fuel and the air to
produce the air/fuel mixture. Furthermore, the fan 22 forces the
air/fuel mixture to the outlet 20, and accordingly, into the burner
12.
[0017] A motor 24 is operatively connected to the fan 22 for
turning the fan 22. The motor 24 may be one of the many types
(e.g., AC, DC, brushless, synchronous, asynchronous, etc.) that are
known to those skilled in the art. Furthermore, the coupling
between the motor 24 and the fan 22 may be accomplished using
techniques that are also well known to those skilled in the
art.
[0018] A variable speed drive 26 is operatively connected to the
motor 24. The variable speed drive 26 preferably facilitates
movement of the motor 24 at a plurality of speeds which may range
from stopped (i.e., zero speed) to full speed (i.e., the fastest
speed capable by the motor 24). As the motor 24 is operatively
connected to the fan 22, the variable speed drive 26 also
facilitates rotation of the fan 22 at a plurality of speeds.
Accordingly, the variable speed drive 26 and the fan 22 are
utilized to control and vary a flow rate of the air/fuel mixture
into the outlet 20, and accordingly, into the burner 12. The
variation of the flow rate corresponds to a firing rate of the
air/fuel mixture in the burner 12.
[0019] A ratio of gaseous fuel and air in the air/fuel mixture,
i.e., an air/fuel ratio, is preferably kept constant over the
various flow rates of the air/fuel mixture into the burner.
Maintaining a constant or near constant air/fuel mixture is
critical for proper performance of the burner 12. The techniques
for accomplishing this constant air/fuel ratio is described in
further detail below.
[0020] In the illustrated embodiment, a gas pipe 26, supplying the
gaseous fuel, is connected to the gas inlet 16. A gas orifice plate
28 is disposed inline with the gas pipe 26 and immediately upstream
from the gas inlet 16. The gas orifice plate 28 defines a gas
orifice 30 through which the gaseous fuel passes.
[0021] A regulating control valve 32 is also disposed inline with
the gas pipe 26. As such, the regulating control valve 32 is in
fluid communication with the gas inlet 16. In the illustrated
embodiment, the regulating control valve 32 is disposed immediately
upstream from the gas orifice plate 28. The regulating control
valve 28 regulates the gaseous fuel at a specified pressure to the
gas orifice 30. During normal conditions at a high flow rate of the
air/fuel mixture, this specified pressure of the gaseous fuel is
preferably kept constant.
[0022] The regulating control valve 32 preferably includes a servo
regulator (not shown) for controlling the pressure and flow of the
gaseous fuel. A pneumatic sensing tube 34 is connected between the
air inlet 18 and the servo regulator of the regulating control
valve 32. The connection of the tube 34 allows the servo regulator
to sense the pressure of the air in the air inlet 34. By sensing
the pressure of the air in the air inlet 34, the servo regulator of
the regulating control valve 32 adjusts the pressure of the gaseous
fuel at the gas inlet 16 in accordance with the pressure of the air
at the air inlet 34. As such, a generally constant air/fuel ratio
may be maintained.
[0023] The gas line 26 of the illustrated embodiment also includes
a safety shutoff valve 36 and a main gas regulator 38. The safety
shutoff valve 36 and main gas regulator 38 are disposed inline with
the gas line 26 and upstream of the regulating control valve 32.
The main gas regulator 38 produces a first, coarse pressure drop
for the gaseous fuel 38. The safety shutoff valve 36 is operable to
completely shut off the flow of the gaseous fuel for system
maintenance or other conditions as realized by those skilled in the
art.
[0024] In the illustrated embodiment, an air duct 40 is connected
to the air inlet 18. As such, the air duct 40 supplies the air to
the housing 14 to be mixed with the gaseous fuel. An air orifice
plate 42 is disposed inline with the air duct 40 and immediately
upstream from the air inlet 18. The air orifice plate 42 defines an
air orifice 44 though which air passes.
[0025] A restrictor device 46 is also disposed inline with the air
duct 40 26. As such, the restrictor device 46 is in fluid
communication with the air inlet 18. In the illustrated embodiment,
the restrictor device 46 is disposed immediately upstream from the
air orifice plate 44. The restrictor device 46 controls an air
inlet pressure of air drawing through the air inlet 18 and into the
housing 14.
[0026] The restrictor device 46 is operable to lower the air inlet
pressure of the air drawn through the air inlet 18 by reducing an
area of the air duct 40 ahead of the air inlet 18. Reducing this
area creates a pressure drop ahead of the air inlet 18, thus
lowering the pressure of the air at the air inlet 18. This pressure
drop is sensed by the regulating control valve 32, which reduce
gaseous fuel pressure accordingly, to maintain a constant air/fuel
ratio.
[0027] Preferably, the restrictor device 46 operates at low firing
rates of the burner 12. These low firing rates are characterized by
low speeds of the fan 22. By reducing the pressure at the air inlet
18, the system 10 decreases the flow rate to a point where the
regulating control valve 32 can properly react to pressure changes
in the air at the air inlet 18. Without the restrictor device 46,
the fan 22 would stall at lower speeds. As such, operation of the
restrictor device 46 increases the range at which the fan 22 can
operate, thus allowing the burner 12 to function at a wider range
of air/fuel mixture flow rates.
[0028] In one embodiment, operation of the restrictor device 46 is
based on the speed of the fan 22. That is, the restrictor device 46
only restrict when the speed of the fan 22 falls below a
predetermined level. Furthermore, the amount of restriction of air
flow caused by the restrictor device 46 is based on the speed of
the fan 22. The speed of the fan 22 may be determined by a fan
speed sensor (not shown) or the variable speed drive 26. Of course,
other techniques for predicating operation of the restrictor device
46 may be implemented.
[0029] Although the system 10 is described above with references to
a method of operation, for convenience and clarity, a recitation of
the method of the subject invention is recited below.
[0030] Preferably, the method of maintaining flow of the air/fuel
mixture to 1 burner 12 requires that the burner 12 is fed from a
premix chamber 14 enclosing a variable speed fan 22. The premix
chamber 14 defines an air inlet 18, a fuel inlet 16, and an outlet
20 in fluidic communication with the burner 12.
[0031] The method includes the step of regulating a flow of gaseous
fuel though the fuel inlet 16 with a regulating control valve 32 to
maintain a specified pressure. The specified pressure is based on
the pressure at the air inlet 18 to maintain a constant air/fuel
ratio.
[0032] The method also includes the step of drawing the gaseous
fuel and air into the premix chamber 14 with the fan 22. Mixture of
the gaseous fuel and the air is affected in the premix chamber 14
with the fan 22 to produce an air/fuel mixture. Furthermore, the
air/fuel mixture is forced to the outlet 20 with the fan 22. The
method preferably includes the step of maintaining a constant ratio
of gaseous fuel and air in producing the air/fuel mixture.
[0033] The method further includes the step of lowering an inlet
air pressure of air drawn through the air inlet 18 by reducing the
area of an air duct 40 ahead of the air inlet 18 to decrease the
flow rate of the air/fuel mixture. In one embodiment, this is
accomplished by first monitoring the speed of the fan 22 and then
lowering the inlet air pressure in response to the speed of the fan
22 falling below a certain speed.
[0034] The present invention has been described herein in an
illustrative manner, and it is to be understood that the
terminology that has been used is intended to be in the nature of
words of description rather than of limitation. Obviously, many
modifications and variations of the invention are possible in light
of the above teachings. The invention may be practiced otherwise
than as specifically described within the scope of the appended
claims.
* * * * *