U.S. patent application number 12/932161 was filed with the patent office on 2011-08-25 for boiler system stabilizing damper and flue control method.
Invention is credited to John Robert Weimer.
Application Number | 20110203569 12/932161 |
Document ID | / |
Family ID | 44475419 |
Filed Date | 2011-08-25 |
United States Patent
Application |
20110203569 |
Kind Code |
A1 |
Weimer; John Robert |
August 25, 2011 |
Boiler system stabilizing damper and flue control method
Abstract
One embodiment of a boiler system stabilizing damper for boiler
flue systems comprising a cylindrical main housing (418), a
pressure sensing means composed of sensor cap (414) and sensor hole
(416), a pressure loss generating means composed of a single blade
damper (410), a shaft (406) and motor (404), and a controller (402)
comprising a pressure transducer and electronic control. Other
embodiments are described.
Inventors: |
Weimer; John Robert; (Stacy,
MN) |
Family ID: |
44475419 |
Appl. No.: |
12/932161 |
Filed: |
February 18, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61338727 |
Feb 23, 2010 |
|
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Current U.S.
Class: |
126/285B |
Current CPC
Class: |
F23J 11/12 20130101;
F23L 13/02 20130101; F23N 3/045 20130101; F23J 11/02 20130101 |
Class at
Publication: |
126/285.B |
International
Class: |
F23L 13/00 20060101
F23L013/00 |
Claims
1. A stabilizing damper for flue control and boiler system
stability, comprising: a.) a fluid conduit enabling the
transmission of a gaseous fluid, b.) a means near the inlet of said
fluid conduit for sensing the static pressure of said gaseous
fluid, c.) a means near the outlet of said fluid conduit for
generating a variable pressure loss in said gaseous fluid, and d.)
a controller in communication with said static pressure sensing
means, and in communication with said means for generating a
variable pressure loss, the controller comprising electronic
circuitry capable of controlling said variable pressure loss.
2. The stabilizing damper of claim 1 wherein said conduit is of
cylindrical geometry.
3. The stabilizing damper of claim 1 wherein said conduit is of
oval geometry.
4. The stabilizing damper of claim 1 wherein said conduit is of
rectangular geometry.
5. The stabilizing damper of claim 1 wherein said sensing means is
a hole through said conduit and covered by a rectangular is of
cylindrical geometry.
6. The stabilizing damper of claim 1 wherein said pressure loss
means is a single blade damper.
7. The stabilizing damper of claim 1 wherein said pressure loss
means is a butterfly damper.
8. The stabilizing damper of claim 1 wherein said pressure loss
means is an iris damper.
9. The stabilizing damper of claim 1 wherein said controlling means
comprises a stepper motor, a pressure transducer and an electronic
control.
10. The stabilizing damper of claim 1 wherein said controlling
means comprises a brushless DC motor, a pressure transducer and an
electronic control.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of provisional patent
application Ser. No. 61/338,727, filed 2010 Feb. 23 by the present
inventor.
FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable
SEQUENCE LISTING OR PROGRAM
[0003] Not Applicable
BACKGROUND
[0004] 1. Field of Invention
[0005] This invention, the stabilizing damper and boiler flue
control method, applies to flue gas venting systems, and is used to
control and stabilize both the flue venting system and the
boiler/heater operations.
[0006] 2. Prior Art
[0007] For purposes of discussion in the remainder of this
document, unless otherwise stated, we will refer to all combustion
heating equipment that incorporates a flue system, as a boiler. The
particular type of heating equipment does not affect the operation
of this invention.
[0008] This section explores boiler flue venting systems that
incorporate one or more boilers. Current control functions for flue
venting systems, and methods for stabilizing boiler operations via
a venting system will be examined. To illustrate the prior art and
its limitations, we begin with a discussion of the overall
structure of a boiler system as illustrated in FIG. 1, and the
functions of a boiler system as depicted in the schematic
representation in FIG. 7. FIG. 1 illustrates a typical example of a
boiler system comprising three boilers 102 connected in a common
flue architecture that includes a common breach section 108. This
example includes barometric dampers 104 on each boiler which is one
method used with current boiler designs for stabilizing boiler and
flue operations. These barometric dampers are connected between the
flue outlet of the boilers 103 and the riser inlets 105 to the
breach section. The breach section acts as a manifold connecting
the multiple boilers to the common chimney 110. This example shows
a mechanical venting system which includes a flue exhaust fan 112,
and a breach pressure sensor 106. The part of this entire boiler
system originating from the flue outlet of the boilers and ending
at either the chimney outlet, or the exhaust fan in a mechanical
venting system, is the boiler flue system.
[0009] The ultimate purpose of a boiler system is to provide
building heat, domestic hot water (DHW), or process heat. Except
for certain minor cases, there is always a variable demand rather
than a constant demand for the quantity of building heat, DHW heat,
and process heat. As example, the heat demand in a building will
vary depending on the outdoor temperature. An increase or decrease
in the outdoor temperature will require a corresponding change in
the building heat demand and the heat output of the boiler system.
A typical boiler provides heat at a constant output rate. Because
of this, a boiler cannot generate heat that continuously matches
the process or building heat demand. A constant output will result
in either too little or too much heat. In order to match the heat
being generated by the boiler system to the required heat demand of
the building or process, a boiler is operated cyclically as an
ON/OFF device over a certain period of time. One exception to
ON/OFF cycling is the use of a modulating output boiler. The
average heat generated over the full cyclic operating period when
the boiler is ON will equal the total required heat demand over
that period. As example, this is a common method employed in a home
using a thermostatically controlled forced air furnace. When
designing a boiler system, the smallest size boiler is selected
that will meet the minimum heat demand without running the boiler
in a damaging short cycle. Short cycling is the excessive switching
of a boiler between the ON and OFF state over relatively short
periods of time in an attempt to equal heat demand. In order to
meet the maximum heat demand for the building or process, multiple
boilers are added until enough heat generating capacity is reached
to meet that maximum demand. This required continuous boiler
cycling in a multi-boiler system with a common flue is the root
cause of boiler stability problems. Although modulating boilers
circumvent the ON/OFF cycling problem, they still have this
stability problem associated with flue venting. It is this
stability problem that needs to be solved.
[0010] There are only two possible ways to connect boilers to a
boiler flue system. One way is for a single boiler to be connected
into its own individual boiler flue system. The other way is for
multiple boilers to be connected into a single boiler flue system,
referred to as a common flue configuration. This common flue
configuration in combination with boiler cycling is the source of
boiler stability problems arising from multi-boiler systems.
Because this is the only way to connect multiple boilers into a
single boiler flue system, the stability issue is always inherent
to the design. This creates a problem difficult to correct using
current methods. In addition to the stability problem, this
configuration tends to reduce boiler efficiency. Although less
complicated, stability issues also exist with single boilers
incorporating a single flue. In this case, the efficiency problem
is the overriding, one.
[0011] The stability and efficiency issues can be understood from
the key functional aspects of how a boiler system operates which
are illustrated in FIG. 7. FIG. 7 is a schematic representation of
the processes inherent to a complete boiler system. These boiler
system processes can be divided into three sub-processes. They are
the combustion sub-process CC, the heat transfer sub-process HE,
and the draft sub-process FM. Everything begins with the combustion
of the fuel/air mixture, which produces the hot flue gases that are
the ultimate source of heat for the boiler system. This is the
first sub-process CC. The hot flue gases then move into the heat
exchanger, which transfers the heat from the flue gases to a heat
transfer medium such as water. A heating system that uses water as
a heat transfer medium is referred to as an hydronic heating
system. This heat transfer process constitutes the second
sub-process HE. The extracted heat has many uses such as heating a
building or providing heat to a manufacturing process. Finally, the
flue gases are removed from the boiler(s) and moved into the flue
piping, which can include a chimney and/or exhauster fan(s). We
call this third sub-process the flue mover FM. The flue mover is
commonly referred to in this industry as a flue gas venting system,
but for our purposes "flue mover" is more descriptive of its actual
function. The flue gases are transported through the flue mover and
are subsequently disposed. This is usually into the outside air or
atmosphere, but could also be into some post processing application
such as a gas scrubber to remove contaminants or CO.sub.2. The key
to making this entire boiler system process operate correctly and
efficiently is the proper control of the volumetric flow rate of
the fuel/air mixture (combustion gases) and flue gases through the
boiler itself. The volumetric flow rate of the combustion and flue
gases is ultimately controlled by the flue mover sub-process FM.
This is why we prefer calling the flue gas venting system a "flue
mover", because that is its exact function. This flue mover is the
key to the proper, efficient operation of the entire boiler system.
This flow rate establishes the residence time and pressures of the
combustion gases in the combustion chamber and the flue gases in
the heat exchanger. The residence time and the pressures in the
combustion chamber determine the reaction mechanisms and efficiency
of the combustion process. The residence time in the heat exchanger
determines the efficiency of the heat transfer process from the
combustion (flue) gases to the heat transfer medium.
[0012] The discharge static pressure at the flue outlet of the
boiler is a measure of the flow rate of the fuel/air mixture and
flue gases through the boiler equipment (the combustion chamber,
and heat exchanger). Measuring this pressure with a magnehelic gage
is one technique used to set up a boiler during boiler
commissioning, or to diagnose problems during operation. In order
to move the flue gases from the discharge point of the boiler
through the flue section (flue mover) and maintain the correct
discharge static pressure, the static pressure throughout the flue
section must be continuously more negative in the direction of flow
from the discharge of the boiler to the discharge of the flue
section (the chimney outlet). The problem with the current design
of flue sections which causes the instability problems lies with
the inability to maintain the correct static pressures at all times
in every location throughout the flue system. This occurs as a
result of boiler cycling.
[0013] As previously mentioned, two basic types of flue systems
currently exist: a single boiler incorporating a single flue, and
multiple boilers incorporating a single flue. The flue system may
or may not include a chimney. There are four possible ways that
flue gases can be forced through the flue system. The first is with
a chimney and is called a natural draft system. In this case, the
required negative pressures relative to the discharge point of the
boiler are generated by the stack effect in the flue system. This
creates the necessary forces within the flue mover to move the flue
gasses and the combustion gases. The second and third methods
involve two types of mechanical draft or mechanical venting
systems. One type of mechanical venting system uses an exhaust
fan(s) alone. In this case, the negative flue pressures with
respect to the boiler flue outlet are created by the venting or
exhaust fan(s). The third type uses an exhaust fan(s) in
combination with a chimney. This approach uses a combination of
both a fan and the stack effect to create the negative flue
pressure in relation to the boiler discharge point. The fourth
method involves the use of a fan assist within the boiler itself to
force the combustion and flue gases through the boiler. This method
is commonly used with category III and IV (positive pressure) flue
movers. This fourth method creates a new problem in multi-boiler
systems in maintaining the correct, required, negative pressure
gradient within the flue mover. All flue movers must use a negative
relative pressure gradient through the flue system to provide the
correct driving force for moving the flue gases.
[0014] There are several methods currently used to control flue gas
flow rates in the flue mover as operating conditions change within
the system. For natural draft systems this is normally done with a
barometric damper. This works by pulling in cooler room air and
mixing it with the hot flue gases, thus cooling those flue gases
and increasing their density, which in turn reduces the stack
effect. The result is a reduction in the flue gas flow rate. The
assumption for this method to work is that an excess stack effect
always exists within the flue system. The barometric damper works
in a Category I, or non-condensing negative pressure, flue system
only. This technique will not work with high efficiency boilers and
low NOX positive pressure boilers. The excess heat in the flue
gases, plus the use of indoor air to cool the flue gases is a
source of inefficiency for this type of system. Natural draft
systems can also incorporate a draft hood to initiate the flow of
flue gases when the boiler first turns on. If a chimney does not
contain hot, low density, flue gases, there will be no stack effect
to create flue gas movement. A draft hood works by starting the
process of filling the chimney with hot flue gases thus creating
the stack effect. As with the barometric damper, this creates
boiler inefficiency. Another method for initiating the stack effect
is to use a two stage or multistage boiler firing system. The first
stage, or low fire stage, provides a means for slowly filling a
chimney with hot flue gases in order to start the natural draft
process. Another method currently used to control boiler flue gas
flow rates, which applies to mechanical draft systems, uses a
variable speed fan to move the flue gases. A single pressure sensor
in the main breach is used for controlling fan speed in an attempt
to regulate breach pressures. This works by varying the fan speed
in order to hold at least one section of the main breach at a
pressure set point. The problem with this approach is that it does
not control the required pressure gradient throughout the flue
system. This in turn fails to control the all important pressures
in the boiler branch sections of the flue system during boiler
cycling. The net effect is boiler system instability. Another
method used in an attempt to control boiler instability is to
increase the breach diameter. This tends to reduce the effects of
boiler instability to a tolerable level, but does not eliminate it.
In addition to failing to eliminate instability, there are
restrictions imposed on boiler layouts using this method. This
limits boiler system design options and results in increased
building costs.
[0015] An improper flow rate, or a flow rate of flue gases that is
not within specifications, is referred to as an uncontrolled draft.
An uncontrolled draft results in flue gas flow rates being higher
or lower than specifications. An uncontrolled draft can be in
either a fixed or constantly fluctuating state between too high and
too low. An uncontrolled draft that is too high is an overdraft
case. An uncontrolled draft that is too low is an under draft case.
A controlled draft is often referred to as a balanced draft, and
this is the flue state that is desired for the proper operation of
the boilers.
[0016] The following are some of the consequences of uncontrolled
draft: [0017] 1. Poor combustion efficiency. [0018] 2. Unstable
pilot. [0019] 3. Pilot and main flame ignition problems. [0020] 4.
Flame retention and flame failure problems. [0021] 5. Unstable
flame pulsations. [0022] 6. Incorrect fuel/air ratios that result
in problems such as sooting, CO and NOx. [0023] 7. Heat transfer
problems within the heat exchanger. [0024] 8. Incomplete combustion
carried into the breach piping. [0025] 9. Damage to the
boiler/heating unit, and/or the flue piping.
[0026] An actual case history illustrates the substantial problems
that exist using the current flue control methods. FIG. 2 shows a
boiler layout employed in a boiler heating system. It consists of
four boilers in a common flue architecture with a chimney and
employing mechanical draft exhausters. By definition, a boiler
system firing state is one of the possible combinations of ON OFF
conditions for each and every boiler making up a boiler system at
some point in time. For example, considering the boiler system in
FIG. 2, one firing state would be boiler #1 ON and all others OFF
at a point in time. Another state would be Boiler #2 ON and all
others OFF at a point in time. The full gamut of firing states
would be all possible combinations of ON OFF states for the boilers
in the system.
[0027] FIG. 3 is a table showing operating data for some of the
boiler operating states for the example boiler system illustrated
in FIG. 2. Each column in this table gives the operating data for
one of the four boilers, labeled 1 through 4 in a particular boiler
system firing state. The table shows four columns, one for each
boiler. Each row, labeled 1 through 7, is the full operating data
for the boilers during a firing state at a point in time. This data
consists of the ON/OFF state of the boiler with the boiler
discharge pressure below measured in inches of water column (InWC).
The required boiler discharge pressure, as established by the
manufacturer of the boilers in this system, was in the range from
-0.05 InWC to 0.0 InWC.
[0028] For a stable system, the boiler discharge pressure must be
within the recommended operating range as established by the boiler
manufacturer for all possible boiler firing states of the boiler
system. As shown by the data in this table, the magnitudes of the
boiler discharge pressures in this system range widely from 0.0
InWC to -0.6290 InWC depending on the firing state of the boilers.
The extremely high negative pressures are well out of the
acceptable operating limits, in some cases by over a factor of ten.
Furthermore, as the boiler system changes from one boiler firing
state to another, the boiler discharge pressures fluctuate wildly
outside the recommended operating pressures as established by the
manufacturer. This is a classic example of a seriously unstable
boiler system, and is not uncommon in the industry. The remedies
for such a problem are typically very expensive. This expense is
compounded by the fact that these types of instability problems do
not normally show up until the system has been fully installed and
is in the process of being commissioned. Often, the end result is
to completely replace the system using a trial and error approach
to find some workable solution. Many times, if the system
instability does not create a situation that is too far out of
tolerance, the system is left as is. This often results in
premature failure of equipment, and operating inefficiency.
[0029] Current attempts to solve the balance and instability
problems consist of using fixed position dampers, barometric
dampers, redesigning the boiler system and building to employ
multiple single boiler/single flue systems, and increasing the
diameter of the breach piping. The best one can do with these
techniques is minimize the problem, but at additional costs. Fixed
position dampers usually don't work. A barometric doesn't work with
high efficiency heating units and decreases the efficiency of less
efficient units. Increasing the breach pipe diameter adds costs and
has size limitations without actually eliminating the stability
problem. This is the most common approach. An increase in the
breach diameter necessitates an increase in the chimney diameter. A
common method used today for a mechanical drafting system employs a
pressure sensor to control draft. Some boilers incorporate a
non-modulating damper that is used to retain the residual heat of
the boiler in its OFF state. When the boiler is ON, the damper is
fully open. When the boiler is OFF, it is closed to prevent heat
from being naturally drafted out the chimney and thus wasted to the
outside. This does nothing to eliminate the stability problem. In a
nutshell, the way this is currently handled is to simply find an
acceptable way to live with the problem.
SUMMARY
[0030] In accordance with one embodiment a stabilizing damper
comprises a main tube for housing the unit and providing a means
for conducting flue gases through the damper, and incorporating a
means located on the damper inlet end for connecting to the boiler
flue output point, and another means located on the damper outlet
end for connecting to the riser inlet to the breach section of the
flue system, also incorporating a pressure sensing cap with a
sensor hole in the main tube on the stabilizing damper inlet side
for determining the boiler discharge pressure, and incorporating on
the outlet side a damper mechanism capable of varying a damper
blade angle resulting in a continuous change in static pressure
loss in the flue gas flow of the main tube, a motor for varying the
blade angle or position, and a main controller for interfacing to
the boilers, and controlling the operation of the stabilizing
damper.
DRAWINGS
Figures
[0031] FIG. 1 shows a standard layout for a three boiler flue
system with barometric dampers.
[0032] FIG. 2 shows a layout for the example boiler heating system
including the boilers, the breach and a partial chimney
section.
[0033] FIG. 3 shows boiler operating state data for the boiler
system illustrated in FIG. 2.
[0034] FIG. 4A shows a side view of the stabilizing damper.
[0035] FIG. 4B shows an inlet view of the stabilizing damper.
[0036] FIG. 4C shows an outlet view of the stabilizing damper.
[0037] FIG. 5 shows a perspective 3D view of the stabilizing
damper.
[0038] FIG. 6 shows a flow chart for the control operation of the
stabilizing damper.
[0039] FIG. 7 shows a functional diagram for a boiler flue
system.
[0040] FIG. 8 shows a layout for a three boiler flue system with
the stabilizing dampers.
DRAWINGS
Reference Numerals
[0041] 102 Boiler [0042] 103 Boiler flue outlet or discharge point
[0043] 104 Barometric damper [0044] 105 Riser inlet to breach
section [0045] 106 Breach pressure sensor [0046] 108 Breach section
of boiler flue system [0047] 110 Chimney section of boiler flue
system [0048] 112 Flue exhauster fan [0049] 402 Controller for the
stabilizing damper [0050] 404 Damper blade motor for stabilizing
damper [0051] 406 Blade shaft [0052] 408 Standoff support [0053]
410 Damper blade [0054] 412 Pressure sensor tubing [0055] 414
Pressure sensor cap on main housing [0056] 416 Pressure sensor hole
in main housing [0057] 418 Main housing [0058] 420 Stabilizing
damper inlet [0059] 422 Stabilizing damper outlet [0060] 424 Damper
shaft seal bushing [0061] 426 Sensor cap tube fitting [0062] 428
Mounting plate [0063] CC Combustion sub-process of boiler system
[0064] HE Heat transfer sub-process of boiler system [0065] FM
Draft sub-process of boiler system (flue mover) [0066] 802 Boiler
[0067] 803 Boiler flue outlet or discharge point [0068] 804
Stabilizing damper [0069] 806 Breach pressure sensor [0070] 808
Breach section [0071] 810 Chimney section [0072] 812 Flue exhauster
fan
DETAILED DESCRIPTION
FIGS. 4A, 4B, 4C, and 5--Preferred Embodiment
[0073] One embodiment of the stabilizing damper is illustrated in
FIG. 4A (side view), FIG. 4B (bottom view), FIG. 4C (top view), and
the isometric view in FIG. 5. FIG. 5 illustrates the mechanical
mechanism of this embodiment, while FIG. 4A and FIG. 4C also
include the control components. The stabilizing damper has a
tubular main housing 418 made from uniform sheet material. In this
embodiment the main housing is a rolled cylinder of constant
diameter along the main length of the cylinder. This sheet material
can be a metal such as galvanized steel, stainless steel, etc., the
choice of which depends on the environment in which the stabilizing
damper will be employed. A stainless steel such as AL29-4c is
preferable in hot, acidic environments to avoid corrosion problems.
Other types of stainless steel or galvanized steel can be used in
more tolerable environments. In a cool, condensing, acidic
environment a plastic material could be employed provided it was
resistant to attack by the acidic environment, and had sufficient
structural strength for the application. It is preferred that the
stabilizing damper inlet 420 be shaped as a standard female opening
to facilitate connection to the boiler discharge piping. It is
preferred that the stabilizing damper outlet 422 be shaped as a
standard male opening to facilitate connection to the riser inlet
of the flue piping.
[0074] One embodiment of the damper mechanism is a damper blade
410, as a flat circular plate, attached to a round shaft 406. Other
damper mechanisms could be a multi-blade butterfly or an iris. The
material choices for construction of the damper blade and the shaft
would follow the same reasoning as that applied to materials for
the main housing. Damper shaft bushings 424 on each end of the
damper blade are used for providing a seal between the shaft and
the housing, and to provide a smooth rotation of the shaft and
blade. The shaft is connected to a motor 404 which acts as a means
for rotating the damper blade. One embodiment uses a stepper motor
to provide an accurate positioning control of the damper blade. A
brushless DC motor is an example of another type of motor that can
provide positioning control. A mounting plate 428 provides a means
of support for the motor mechanism and the controller 402, and
provides shielding from the potentially hot surface of the main
tubular section. Standoff supports 408 are attached to the main
housing and the mounting plate 428, and provides a means of support
for the mounting plate. In this embodiment the standoff supports
were constructed from as thin a piece of sheet metal as
mechanically and structurally possible. Since the outlet flue gases
can reach high temperatures, sometimes on the order of 650 degrees
Fahrenheit, a means is required to protect the electronic controls
and motor from excessive heating. The thin material and cutaway
sections for the standoff supports eliminate overheating from heat
transfer by minimizing the cross sectional area needed for
significant heat transfer to take place. The small cross sectional
area of the standoff support limits heat transfer to the mounting
plate, and a large surface area provides a dissipative heat
transfer path to the surroundings rather than transmission to the
mounting plate. In this embodiment all of the longitudinal edges
were folded to increase the structural strength of the standoff
support while minimizing the thickness of the construction
material.
[0075] A pressure sensing cap 414 is located at the inlet side of
the stabilizing damper. For this embodiment, the pressure sensing
cap is placed above the damper inlet approximately a length equal
to one radius of the main housing diameter. The cap and its
position provide a stable static pressure reading from which the
damper operates. In order to keep a stable flue gas flow field, and
thus a stable static pressure reading, the pressure sensing cap is
kept a length of at least 2 main tube diameters away from the fully
open inside edge position of the damper blade. The sensing cap for
this embodiment is approximately 2 inches by 2 inches in the base
dimensions, and approximately 1.5 inches in height. A pressure
sensor hole 416 of approximately 3/4 inch in diameter for this
embodiment is centered under the pressure sensing cap, and into and
through the main housing. A sensor cap tube fitting 426 is placed
in the side of the pressure sensing cap centered at approximately
1/2 inch from the top of the cap. A pressure sensor tubing 412 is
attached to the sensor cap tube fitting and runs to a pressure
sensing means which is part of the controller 402 for the
stabilizing damper. This pressure sensor tubing can be made of a
flexible material such as rubber tubing, or a rigid material such
as stainless steel metal tubing. The appropriate sensor cap tube
fitting is used depending on the type of pressure sensor tubing
used. A controller for the stabilizing damper would include a means
for sensing the pressure at the pressure sensing cap and then
activating the motor to move the damper mechanism.
Operation--FIGS. 4A, 4B, 4C, 6, and 8
[0076] FIG. 8 shows the system in FIG. 1 with the barometric
dampers 104 replaced by the stabilizing dampers 804 of this
invention. Each of the stabilizing dampers controls the discharge
pressure at each of the boiler discharge points 803 in order to
hold these pressures at their required operating points.
[0077] To stabilize the boiler system and provide flue control, the
volumetric flow rate of the flue gases from the boiler needs to be
controlled within specifications established by the boiler
manufacturer. This can be accomplished by adjusting or controlling
three variables at the boiler discharge point: the flue gas
velocity pressure, the static pressure, and the flue gas
density.
[0078] The main housing acts as a pipe for the transport of the
flue gases, as well as the support for components of the
stabilizing damper. The diameter of the flue outlet of the boiler
at the boiler discharge point is set by the boiler manufacturer
from the boiler design specifications. These specifications would
include the flue gas density and volumetric flow rate. The
volumetric flow rate at any point is determined by the flue gas
density, the flue gas velocity pressure and the static pressure at
that discharge point. The flue gas density within the stabilizing
damper is the same as that set by boiler specifications. If the
diameter of the stabilizing damper is the same as the diameter of
the boiler discharge, the velocity pressure at the pressure sensor
hole 416 will be the same as that set by the boiler specifications.
In this case, the static pressure measured at the pressure sensor
hole is the only remaining variable needed to control the
volumetric flow rate of the flue gases. The set point static
pressure is used for controlling the volumetric flow rate and is
measured at the pressure sensor hole. It is also the same static
pressure as that at the boiler discharge point and set by the
boiler specifications. The stabilizing damper controls this static
pressure by varying the position of the damper mechanism as the
flow conditions vary in the flue system. This in turn controls the
flue and stabilizes the boiler system irrespective of the
fluctuations in flow properties within the flue system itself.
[0079] If the diameter of the balancing damper is different from
that of the boiler discharge point, it will be necessary to
calculate or measure a new static pressure set point and velocity
pressure in order to maintain the correct volumetric flow rate for
the flue gases. Calculating the new static pressure and velocity
pressure is within the ability of persons skilled in the discipline
of fluid mechanics. Instead of calculating the pressure set point,
a method for measuring this pressure, after the damper system has
been installed, is presented here. When a stabilizing damper with a
diameter different from the diameter at the boiler discharge point
is installed, it will be necessary to attach a short section of
straight pipe, typically one pipe diameter in length, at the
discharge point of the boiler followed by either a pipe reducer or
diffuser finally followed by the stabilizing damper. A small hole
is placed into the short section of pipe at the discharge of the
boiler, and a magnehilic is used to measure the static pressure at
this point. This is a standard technique currently practiced by
boiler installers. A second magnehelic would be attached to the
pressure sensing tube from the pressure sensing cap of the
stabilizing damper. With the stabilizing damper maintained open, in
the full unrestricted flow position, the boilers are fired and
adjusted to the correct operating point using the magnehelic
pressure at the discharge of the boiler as a reference. The
magnehelic pressure measured at the stabilizing damper would then
give the correct set point operating pressure for the stabilizing
damper.
[0080] The damper mechanism creates a varying resistance, and thus
a varying pressure loss in the flow of flue gases, as the damper
mechanism changes position. In this embodiment the damper mechanism
is a simple single blade damper, and a change in the blade angle
would constitute a change in position of the damper mechanism. The
pressure loss created by the damper mechanism is equal to the
static pressure at the outlet of the stabilizing damper less the
static pressure at the pressure sensor hole. Thus, the static
pressure at the pressure sensor hole can be held constant by a
simple adjustment of the damper mechanism as the static pressure at
the outlet of the stabilizing damper fluctuates. These fluctuations
are a result of variations in the operating conditions in the flue
system, which manifest as instability.
[0081] Any flue system will require a means for moving the flue
gases though the system. This means has been previously described
as the stack effect and/or mechanical venting. All flue systems,
whether with the stabilizing damper or not, require a sufficiently
more negative static pressure through the flue system, which is
provided by the flue moving means. This normally required flue
moving means also provides the more negative pressure at the outlet
of the stabilizing damper that enables the damper to work
correctly.
[0082] The controller requires a control signal used to adjust the
damper mechanism that controls the discharge pressure of the
boiler. The control signal is supplied through a pressure sensing
port made up of the sensor hole in the main housing plus the sensor
cap, which is attached to a pressure transducer that provides the
pressure signal used by a controller to adjust the damper
mechanism. The pressure signal is constantly monitored by the
controller. If the pressure is too low or too high, the damper
mechanism is adjusted to a more closed or more open position,
creating more or less static pressure losses from the damper
mechanism until the boiler discharge pressure is within the proper
operating range for the boiler. Electronic control means and
controllers are readily available for this control purpose. A
wireless controller is ideal for this purpose. An example of a
control strategy for this invention that can be incorporated within
an electronic controller is shown in the flow chart in FIG. 6.
[0083] As the pressures within the flue section fluctuate from
variations in boiler firing cycles and atmospheric changes,
creating conditions for instability and inefficiency in the boiler
system, the stabilizing damper holds the boiler discharge pressure
within its proper, optimal operating range.
Advantages
[0084] From the description above, a number of advantages of some
embodiments of the stabilizing damper become evident: [0085] (a)
First and foremost, this damper provides a means to eliminate the
system instability problems currently associated with boiler room
flue system. [0086] (b) The stabilizing damper affords a
significant reduction in design, material and installation costs
for boiler systems. [0087] (c) The stabilizing damper provides a
means for improving the efficiency of boiler operations. [0088] (d)
The stabilizing damper simplifies boiler system design methods and
is more forgiving of boiler system design errors. [0089] (e) The
stabilizing damper will permit Category I II III and IV boilers to
be installed in a Category I breach flue system. This is impossible
by current methods. [0090] (f) The stabilizing damper will permit
the mixing of Category I II III and IV boilers in a common flue
system. This is impossible by current methods.
Conclusion, Ramifications, and Scope
[0091] Accordingly, the reader will see that the stabilizing damper
of the various embodiments solves the current boiler instability
problems that plague this industry. Furthermore, along with the
stabilization of boiler operations comes an improvement in the
efficiency of boiler operations. Another unexpected result of the
stabilizing damper is the potential for reduced design and
installation costs for the boiler system, and also potential
reduced costs for the building itself. The use of the stabilizing
damper provides for a boiler design that is far more forgiving of
design errors.
[0092] Although the description above contains many specificities,
these should not be construed as limiting the scope of the
embodiment but as merely providing illustrations of some of the
presently preferred embodiments. For example, the main housing
although presented as a cylindrical device, could be of another
shape such as a square, oval, etc.; the controller can be a
wireless electronic device rather than the usual wired
controller.
[0093] Thus, the scope of the embodiment should be determined by
the appended claims and their legal equivalents, rather than by the
examples given.
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