U.S. patent application number 15/914217 was filed with the patent office on 2018-09-13 for method of improving fire tube burner efficiency by controlling combustion air flow and an air damper for a fire tube.
The applicant listed for this patent is Millstream Energy Products Ltd.. Invention is credited to Frank FAN, Willie FISHER, Rob LUNDSTROM, Greg NUK.
Application Number | 20180259184 15/914217 |
Document ID | / |
Family ID | 63444496 |
Filed Date | 2018-09-13 |
United States Patent
Application |
20180259184 |
Kind Code |
A1 |
NUK; Greg ; et al. |
September 13, 2018 |
METHOD OF IMPROVING FIRE TUBE BURNER EFFICIENCY BY CONTROLLING
COMBUSTION AIR FLOW AND AN AIR DAMPER FOR A FIRE TUBE
Abstract
A method of improving natural draft fire tube burner efficiency
by controlling combustion air flow. The method involves positioning
in a fire tube an air damper body comprising a fixed plate having a
plurality of air flow openings and a rotatable plate having a
plurality of air flow openings. Air flow through the air damper
body is controlled by adjusting the relative rotational position of
the fixed plate and the rotatable plate. The air damper body has an
air inlet face, an air outlet face, and an outer circumference. The
method involves establishing and maintaining a relationship between
an air damper open area, firing rate and excess air to maintain
stack oxygen below 3% in accordance with a formula
A2+A3<DR.times.FR.times.A1.
Inventors: |
NUK; Greg; (Victoria,
CA) ; LUNDSTROM; Rob; (Edberg, CA) ; FISHER;
Willie; (Surrey, CA) ; FAN; Frank; (Nanaimo,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Millstream Energy Products Ltd. |
Surrey |
|
CA |
|
|
Family ID: |
63444496 |
Appl. No.: |
15/914217 |
Filed: |
March 7, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F23L 13/04 20130101;
F23N 3/005 20130101; F23D 14/22 20130101 |
International
Class: |
F23N 3/00 20060101
F23N003/00; F23D 14/22 20060101 F23D014/22 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 2017 |
CA |
2960508 |
Claims
1. An air damper for a natural draft fire tube, comprising: an air
damper body comprising a fixed plate having a plurality of air flow
openings and a rotatable plate having a plurality of air flow
openings, with air flow through the air damper body being
controlled by adjusting the relative rotational position of the
fixed plate and the rotatable plate, the air damper body having an
air inlet face, an air outlet face, and an outer circumference; and
a relationship is maintained between an air damper open area,
firing rate and excess air in accordance with a formula
A2+A3<DF.times.FR.times.A1, in which: A1=total area of air flow
openings in the air damper body created by a relative positioning
of the air flow openings of the fixed plate and the air flow
openings of the rotatable plate at a given closing position for a
given firing rate; A2=total area of other openings in the air
damper body through which air can bypass the air flow openings;
A3=total area between an outer diameter (OD) of the air damper body
and an inner diameter (ID) of the fire tube through which air can
bypass the air flow openings, and FR=firing rate in % of maximum
rate for a particular firetube-burner combination; DF=diameter
factor, where D=fire tube inner diameter and the factor is a
relationship of 0.12D 2-6.29D+92.
2. The air damper of claim 1, wherein a central burner passage
through the air damper body, the central burner passage being
adapted to receive a burner body.
3. The air damper of claim 1, wherein a deformable circumferential
seal around the outer circumference of the air damper body, the
circumferential seal being adapted to engage an inner circumference
of a fire tube solely by friction.
4. The air damper of claim 1, wherein the rotatable plate is
positioned at the inlet face of the air damper body and the fixed
plate is positioned at the outlet face of the air damper body.
5. The air damper of claim 4, wherein the outlet face of the air
damper body has outwardly projecting air deflectors overlying the
air flow openings of the fixed plate.
6. The air damper of claim 4, wherein a handle is provided on the
rotatable plate, whereby a manual force is exerted via the handle
to rotate the rotatable plate thereby adjusting the position of the
air flow openings of the rotatable plate relative to the air flow
openings of the fixed plate.
7. The air damper of claim 2, wherein an ignitor passage extends
through the air damper body in parallel spaced relation to the
central burner passage, wherein an ignitor can be inserted and
removed, a seal being provided to prevent airflow through the
ignitor passage bypassing the air damper.
8. The air damper of claim 2, in combination with a burner body,
the burner body being positioned within the central burner passage
of the air damper body, the burner body having a nozzle end
protruding passed the air outlet face of the air damper body and a
fuel gas source attachment end protruding passed the air inlet face
of the air damper body.
9. The air damper of claim 8, in combination with a fire tube.
10. An air damper for a natural draft fire tube having an inner
circumference and a burner body disposed therein, the air damper
comprising: an air damper body comprising: a burner passage adapted
to receive the burner body; a peripheral seal adapted to engage the
inner circumference of the fire tube; and a plurality of air flow
openings disposed about the central burner passage with the size of
the air flow openings adjustable; wherein, in use, air flow between
the central burner passage and the burner body is impeded, air flow
between the peripheral seal and the inner circumference of the fire
tube is impeded, and air flow through the air flow openings is user
adjustable with a relationship maintained between an air damper
open area, firing rate and excess air in accordance with a formula
A2+A3<DF.times.FR.times.A1, in which: A1=total area of air flow
openings in the air damper body created by a relative positioning
of the air flow openings of the fixed plate and the air flow
openings of the rotatable plate at a given closing position for a
given firing rate; A2=total area of other openings in the air
damper body through which air can bypass the air flow openings;
A3=total area between an outer diameter (OD) of the air damper body
and an inner diameter (ID) of the fire tube through which air can
bypass the air flow openings, and FR=firing rate in % of maximum
rate for a particular firetube-burner combination; DF=diameter
factor, where D=fire tube inner diameter and the factor is a
relationship of 0.12D 2-6.29D+92.
11. A method of improving natural draft fire tube burner efficiency
by controlling combustion air flow, comprising: positioning in a
fire tube an air damper body comprising a fixed plate having a
plurality of air flow openings and a rotatable plate having a
plurality of air flow openings, with air flow through the air
damper body being controlled by adjusting the relative rotational
position of the fixed plate and the rotatable plate, the air damper
body having an air inlet face, an air outlet face, and an outer
circumference; and establishing and maintaining a relationship
between an air damper open area, firing rate and excess air to
maintain excess air below 3% in accordance with a formula
A2+A3<DF.times.FR.times.A1, in which: A1=total area of air flow
openings in the air damper body created by a relative positioning
of the air flow openings of the fixed plate and the air flow
openings of the rotatable plate at a given closing position for a
given firing rate; A2=total area of other openings in the air
damper body through which air can bypass the air flow openings;
A3=total area between an outer diameter (OD) of the air damper body
and an inner diameter (ID) of the fire tube through which air can
bypass the air flow openings, and FR=firing rate in % of maximum
rate for a particular firetube-burner combination; DF=diameter
factor, where D=fire tube inner diameter and the factor is a
relationship of 0.12D 2-6.29D+92.
12. An air damper for a natural draft fire tube, comprising: an air
damper body comprising a fixed plate having a plurality of air flow
openings and a rotatable plate having a plurality of air flow
openings, with air flow through the air damper body being
controlled by adjusting the relative rotational position of the
fixed plate and the rotatable plate, the air damper body having an
air inlet face, an air outlet face, and an outer circumference; and
a deformable circumferential seal around the outer circumference of
the air damper body, the circumferential seal being adapted to
engage an inner circumference of a fire tube solely by
friction.
13. The air damper of claim 12, wherein an ignitor passage extends
through the air damper body, wherein an ignitor can be inserted and
removed, a seal being provided to prevent airflow through the
ignitor passage bypassing the air damper.
Description
[0001] Method of improving fire tube burner efficiency by
controlling combustion air flow and an air damper for a fire
tube.
FIELD
[0002] There is described a method of improving natural draft fire
tube burner efficiency by controlling combustion air flow and an
air damper in accordance with the teachings of the method.
BACKGROUND
[0003] British Patent GB 1,603,618 contains a good summary of the
theory behind combustion air control for burners. Fuel supply and
air supply for a burner are controlled separately in stoichiometric
proportions. It is necessary to have some excess air to ensure that
combustion is complete, if the air and fuel are not perfectly
mixed. However, it has been determined that burner efficiency drops
if too much excess air is provided, as it takes energy to heat the
excess air without producing any useful effect. For example, if the
ambient air temperature is 40 degrees Fahrenheit and the burner
tube stack temperature is 700 degrees Fahrenheit, excess air is
heated by 660 degrees Fahrenheit. It is, therefore, best to have
the smallest possible amount of excess air, while still ensuring
that there is complete combustion. Air supply control is
implemented by means of an air damper.
[0004] U.S. Pat. No. 4,702,692 (Burns et al) titled "Air Reduction
Controls for Oil-Treating Vessels", describes an air damper for a
natural draft fire tube for use in the oil industry. This air
damper consists of a fixed plate having a plurality of air flow
openings and a rotatable plate having a plurality of air flow
openings. By rotating the rotatable plate, the air flow openings in
the rotatable plate can either be brought into register with the
air flow openings in the fixed plate or the air flow openings in
the fixed plate can be at least partially blocked by the rotatable
plate. The air damper of Burns et al was welded in a duct that
extended radially from a fire tube.
[0005] U.S. Pat. No. 4,383,820 (Camacho) titled "Fuel Gas Burner
and Method of Producing a Short Flame", describes placing blades in
an annulus of a burner to create a turbulent swirling action.
SUMMARY
[0006] According to one aspect there is provided a method of
improving natural draft fire tube burner efficiency by controlling
combustion air flow. The method involves positioning in a fire tube
an air damper body comprising a fixed plate having a plurality of
air flow openings and a rotatable plate having a plurality of air
flow openings. Air flow through the air damper body is controlled
by adjusting the relative rotational position of the fixed plate
and the rotatable plate. The air damper body has an air inlet face,
an air outlet face, and an outer circumference. The method involves
establishing and maintaining a relationship between an air damper
open area, firing rate and excess air to maintain stack oxygen
below 3% in accordance with a formula
A2+A3<DF.times.FR.times.A1, in which:
[0007] A1=total area of air flow openings in the air damper body
created by a relative positioning of the air flow openings of the
fixed plate and the air flow openings of the rotatable plate at a
given closing position for a given firing rate;
[0008] A2=total area of other openings in the air damper body
through which air can bypass the air flow openings;
[0009] A3=total area between an outer diameter (OD) of the air
damper body and an inner diameter (ID) of the fire tube through
which air can bypass the air flow openings, and
[0010] FR=firing rate in % of maximum for a particular
firetube-burner combination;
[0011] DF=diameter factor, where D=fire tube inner diameter and the
factor is a relationship of 0.12D 2-6.29D+92.
[0012] According to another aspect, there is provided an air damper
for a natural draft fire tube which includes an air damper body
comprising a fixed plate having a plurality of air flow openings
and a rotatable plate having a plurality of air flow openings. Air
flow through the air damper body is controlled by adjusting the
relative rotational position of the fixed plate and the rotatable
plate. The air damper body having an air inlet face, an air outlet
face, and an outer circumference; and
[0013] a relationship is maintained between an air damper open
area, firing rate and excess air in accordance with a formula
A2+A3<DF.times.FR.times.A1, in which:
[0014] A1=total area of air flow openings in the air damper body
created by a relative positioning of the air flow openings of the
fixed plate and the air flow openings of the rotatable plate at a
given closing position for a given firing rate;
[0015] A2=total area of other openings in the air damper body
through which air can bypass the air flow openings;
[0016] A3=total area between an outer diameter (OD) of the air
damper body and an inner diameter (ID) of the fire tube through
which air can bypass the air flow openings, and
[0017] FR=firing rate in % of maximum rate for a particular
firetube-burner combination;
[0018] DF=diameter factor, where D=fire tube inner diameter and the
factor is a relationship of 0.12D 2-6.29D+92.
[0019] As will hereinafter be further described, the use of
circumferential seal has a dramatic beneficial effect on
performance, when compared to the same assembly without a
circumferential seal. It is, therefore, preferred that there is a
deformable circumferential seal around the outer circumference of
the air damper body. Making the circumferential seal deformable
accommodates "out of round" shape imperfections and surface
imperfections, such as weld deposits, of the inner circumference of
the fire tube. It is also preferred that the circumferential seal
engage an inner circumference of a fire tube solely by friction.
This facilitates ease of servicing and replacement.
[0020] A common industry approach was to leave a 1/4 inch gap
around the circumference of the air damper body. As will be
apparent from the test data set forth below, it is now realized
that this and other gaps rendered the air damper body ineffectual,
as air would bypass the air damper body dictated solely by fire
tube draft. As a result, at less than 100% maximum combustion rate,
stack oxygen was always greater than 3%. Greater than 3% stack
oxygen reduces fire tube burner efficiency and results in
unnecessary carbon dioxide emissions.
[0021] There will hereinafter be described further beneficial
features of the air damper. For example, an ignitor passage extends
through the air damper body in parallel spaced relation to the
central burner passage. This allows an ignitor to be inserted and
removed. This is a useful feature as ignitors frequently need
replacing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] These and other features will become more apparent from the
following description in which reference is made to the appended
drawings, the drawings are for the purpose of illustration only and
are not intended to be in any way limiting, wherein:
[0023] FIG. 1 is a front elevation view of an air damper for a fire
tube.
[0024] FIG. 2 is a front perspective view of the air damper
illustrated in FIG. 1.
[0025] FIG. 3 is a rear elevation view of the air damper
illustrated in FIG. 1.
[0026] FIG. 4 is a rear perspective view of the air damper
illustrated in FIG. 1.
[0027] FIG. 5 is a top plan view of the air damper illustrated in
FIG. 1.
[0028] FIG. 6 is a rear perspective view of the air damper
illustrated in FIG. 1, positioned in a fire tube.
[0029] FIG. 7 is a front perspective view of the air damper
illustrated in FIG. 1, positioned in a fire tube.
[0030] FIG. 8 is a side elevation view, in section, of the air
damper illustrated in FIG. 1, positioned in a fire tube.
[0031] FIG. 9 is a detailed side elevation view, in section, of the
air damper illustrated in FIG. 1 positioned in a fire tube.
DETAILED DESCRIPTION
[0032] An air damper, generally identified by reference numeral 10,
will now be described with reference to FIG. 1 through FIG. 9.
Structure and Relationship of Parts:
[0033] Referring to FIG. 5, air damper 10 includes an air damper
body 12 with a fixed plate 14 and a rotatable plate 16. Referring
to FIG. 1 and FIG. 2 fixed plate 14 has a plurality of air flow
openings 18. Referring to FIG. 3 and FIG. 4, rotatable plate 16
also has a plurality of air flow openings 20. Referring to FIG. 5,
air damper body 12 has an air inlet face 22, an air outlet face 24,
and an outer circumference 26. Air, indicated by arrows 28, enters
air damper body 12 through air inlet face 22 and exits air damper
body 12 through air outlet face 24. Referring to FIG. 2, FIG. 4 and
FIG. 5, a central burner passage 30 is provided through air damper
body 12. Referring to FIG. 7, central burner passage 30 is adapted
to receive a burner body 100, as will hereinafter be further
described. Referring to FIG. 1 through FIG. 4, a circumferential
seal 32 is provided around outer circumference 26 of air damper
body 12 to prevent natural draft air bypassing the air flow
openings 18 and 20. Referring to FIG. 8 and FIG. 9, circumferential
seal 32 is adapted to engage an inner circumference 102 of a fire
tube 104 solely by friction. Referring to FIG. 1 through FIG. 4, a
seal 31 is also provided to prevent natural draft air bypassing the
air flow openings 18 and 20 through central burner passage 30.
[0034] Referring to FIG. 2, FIG. 4 and FIG. 5, it is preferred that
rotatable plate 16 is positioned at inlet face 22 of air damper
body 12 and that fixed plate 14 is positioned at outlet face 24 of
air damper body 12. With this configuration, the rotatable plate is
more readily accessed for the purpose of making adjustments.
[0035] Referring to FIG. 2 and FIG. 5, it is preferred that outlet
face 24 of air damper body 12 has outwardly projecting air
deflectors 34 overlying air flow openings 18 of fixed plate 14.
This configuration imparts a helical flow to air flowing through
air damper body 12.
[0036] Referring to FIG. 4 and FIG. 5, it is preferred that a
handle 36 is provided on rotatable plate 16. This enables a manual
force to be exerted via handle 36 to rotate rotatable plate 16
thereby adjusting the position of air flow openings 20 of rotatable
plate 16 relative to air flow openings 18 of fixed plate 14.
[0037] Referring to FIG. 4 and FIG. 5, in order to prevent air flow
from circumventing air damper body 12, fixed plate 14 and rotatable
plate 16 are loosely clamped together. The term "loosely is used,
as the mode of clamping must not impede rotation of rotatable plate
16. The mode of clamping illustrated are nuts 40 and bolts 42.
Bolts 42 extend through fixed plate 14. However, to facilitate
rotation of rotatable plate 16, bolts 42 extend through slots 44 in
rotatable plate 16.
[0038] Referring to FIG. 2, FIG. 4 and FIG. 5, It is preferred that
an ignitor passage 46 extend through air damper body 12 in parallel
spaced relation to central burner passage 30. This configuration
enables an ignitor 106 to be positioned to ignite combustion gas
flowing through burner body 100. Referring to FIG. 1 through FIG.
4, a seal 47 is provided to prevent natural draft air bypassing the
air flow openings 18 and 20 through ignitor passage 46.
Operation:
[0039] Referring to FIG. 6 through FIG. 8, burner body 100 has a
nozzle end 108 and a fuel gas source attachment end 110. In
preparation for installation, burner body 100 is inserted into
central burner passage 30 of air damper body 12 with nozzle end 108
protruding past air outlet face 24 of air damper body 12 and fuel
gas source attachment end 110 protruding past air inlet face 22 of
air damper body 12. Air damper 12 is then inserted into fire tube
104. When air damper 12 is inserted into fire tube 104,
circumferential seal 32 engages inner circumference 102 of fire
tube 104 solely by friction. Referring to FIG. 9, it can be seen
that circumferential seal 32 deforms to create an air seal.
Beneficial results have been obtained when circumferential seal 32
is made of a flexible, high temperature rated material. Referring
to FIG. 8, either before or after insertion of air damper body 12
into fire tube 104 ignitor 106 extended through ignitor passage 46
and positioned relative to nozzle end 108 to ignite combustion gas
flowing through burner body 100 to nozzle end 108.
[0040] Tests were conducted to determine the relative efficiency of
air damper 10, with and without circumferential seal 32. It was
determined that air damper 10 with circumferential seal 32
outperformed air damper 10 without circumferential seal 32. The
increase in total efficiency (BTUs into the process for BTUs
created from gas combustion) depended upon the turn down rate of
the combustion system. For example, when the combustion system
firing rate was reduced to 40% of the maximum possible firing rate
(60% turn down) and rotatable plate 14 was rotated relative to
fixed plate 14 to reduce the air flow through air damper body 12
appropriately, air damper 10 with circumferential seal 32
transferred up to 43% more heat into the process for the same
quantity of gas consumed, as compared to combustion assemblies
having air dampers without circumferential seal 32.
[0041] The gap about the periphery of the damper had never
previously been considered a problem because the relationship
between air damper uncontrolled open area, controllable secondary
air flow area, excess air and firing rate was not well understood.
A peripheral seal was added, forcing all the air flow to pass
through the damper. The effect on efficiency was then measured.
Marginal increases in efficiency were measured at lower turn down
rates. However, as the turn down rates became higher, unexpected
increases in efficiency were measured. As set forth above, with a
60% turn down rate, up to 43% more heat is transferred. It was then
realized that the other openings through the damper were also
having an effect upon burner efficiency.
[0042] It is known that stack oxygen in a 2-3% range is sufficient
to promote combustion without adversely affecting burner
efficiency. It has been determined that a relationship exists
between air damper open area, firing rate (turndown) and excess
air. A secondary air control plate (damper) should be designed in
accordance with a formula A2+A3<DF.times.FR.times.A1, in
which:
[0043] A1=total area of air flow openings in the air damper body
created by a relative positioning of the air flow openings of the
fixed plate and the air flow openings of the rotatable plate at a
given closing position for a given firing rate;
[0044] A2=total area of other openings in the air damper body
through which air can bypass the air flow openings;
[0045] A3=total area between an outer diameter (OD) of the air
damper body and an inner diameter (ID) of the fire tube through
which air can bypass the air flow openings, and
[0046] FR=firing rate in % of maximum rate for a particular
firetube-burner combination;
[0047] DF=diameter factor, where D=fire tube inner diameter and the
factor is a relationship of 0.12D 2-6.29D+92. (The symbol
reflecting a raising to the power of 2)
[0048] This formula is applicable for all firing rates below 100%
and natural draft greater than -0.05 mm h20. Stated another way, if
A2+A3>DF.times.FR.times.A1, then there will no longer be excess
air control and stack oxygen levels will be dictated by fire tube
draft alone and will always exceed 3%. There follows a series of
graphs and a summary of results showing a test comparison of five
different models operating at 100% of Maximum Combustion Rate
(MCR), 80% MCR, 60% MCR and 40% MCR. As will become apparent from a
review of the test data set forth below, the differences in
efficiency become more pronounced as the MCR is lowered. At 40%
MCR, a burner controlled in accordance with the formula
A2+A3<DF.times.FR.times.A1 uses 43% less fuel gas to provide the
same heat input to the process vessel than other burners having
dampers where A2+A3>DF.times.FR.times.A1. It is believed that
the reason for this is that, notwithstanding the presence of a
damper, too much excess air is drawn through various openings as
dictated by fire tube draft. This formula is believed to be
applicable to all natural draft tubes with a nominal outer diameter
of 10 inches to 30 inches.
[0049] In this patent document, the word "comprising" is used in
its non-limiting sense to mean that items following the word are
included, but items not specifically mentioned are not excluded. A
reference to an element by the indefinite article "a" does not
exclude the possibility that more than one of the element is
present, unless the context clearly requires that there be one and
only one of the elements.
[0050] The scope of the claims should not be limited by the
illustrated embodiments set forth as examples, but should be given
the broadest interpretation consistent with a purposive
construction of the claims in view of the description as a
whole.
* * * * *