U.S. patent number 3,819,319 [Application Number 05/390,785] was granted by the patent office on 1974-06-25 for industrial pollution control systems and components thereof.
This patent grant is currently assigned to Hauck Manufacturing Company. Invention is credited to Robert E. Schreter.
United States Patent |
3,819,319 |
Schreter |
June 25, 1974 |
INDUSTRIAL POLLUTION CONTROL SYSTEMS AND COMPONENTS THEREOF
Abstract
There is disclosed a closed combustion system designed to reduce
the level of noise generated by its operation. The system includes
an enclosed combustion chamber with ducts for supplying combustion
air to the chamber and for supplying atomizing air to the fuel
burner. The system is designed to be connected to an industrial
furnace or kiln or rotary drier in a substantially sealed manner. A
noise attenuator is connected to the combustion chamber air inlet.
The combination of the attenuator and the closed construction of
the system provides a reduction of the operational noise down to a
tolerable level over a wide frequency band. The combustion system
includes apparatus for burning gaseous pollutants. A heater is
provided between the gaseous pollutant source and the attenuator to
preclude condensation of pollutants in the attenuator. The
pollutants pass from the pollutant source, through the heater and
attenuator into the combustion chamber where they are burned.
Attenuator by-pass means also are provided to permit combustion of
the pollutants in the heater and direct exhaust to the
atmosphere.
Inventors: |
Schreter; Robert E. (Lebanon,
PA) |
Assignee: |
Hauck Manufacturing Company
(Lebanon, PA)
|
Family
ID: |
26979527 |
Appl.
No.: |
05/390,785 |
Filed: |
August 23, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
314741 |
Dec 13, 1972 |
|
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|
Current U.S.
Class: |
431/5; 431/114;
431/202 |
Current CPC
Class: |
F23G
7/065 (20130101); F23D 11/00 (20130101); G10K
11/161 (20130101) |
Current International
Class: |
F23G
7/06 (20060101); F23D 11/00 (20060101); G10K
11/00 (20060101); G10K 11/16 (20060101); F23j
015/00 () |
Field of
Search: |
;431/114,5,202
;122/7C,7D |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Favors; Edward G.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow &
Garrett
Parent Case Text
This is a continuation-in-part of patent application Ser. No.
314,741, filed Dec. 13, 1972 and entitled "Industrial Pollution
Control Systems and Components Thereof."
Claims
What is claimed is:
1. A combustion system for use with furnaces, driers and like
equipment, said system being designed to combust gaseous
pollutants, the system comprising:
A. a combustion chamber having an output end adapted to be coupled
to the aforesaid equipment and an air inlet for receiving
combustion air;
B. a fuel burner mounted adjacent to said combustion chamber to
direct its flame thereinto;
C. an acoustic attenuator in air flow communication with said
combustion chamber air inlet and through which at least a
substantial portion of said combustion air flows before entering
said combustion chamber;
D. a source of gaseous pollutants;
E. a heater for heating said gaseous pollutants above the
condensation temperature of said pollutants;
F. first ducting means for conveying said gaseous pollutants to
said heater;
G. second ducting means for conveying the gaseous pollutants heated
in said heater to said attenuator; and
H. means for causing said gaseous pollutants to flow sequentially
from said source of gaseous pollutants through said first ducting
means, said heater, said second ducting means, said attenuator and
into said combustion chamber.
2. A combustion system as claimed in claim 1 wherein said first
ducting means includes an adjustable air inlet to enable controlled
admission of combustion air into said first ducting means.
3. A combustion system as claimed in claim 1 wherein the means for
causing the pollutants to flow through said system is a first
fan.
4. A combustion system as claimed in claim 3 including a booster
fan for assisting said first fan to cause said pollutants to flow
through said system.
5. A combustion system as claimed in claim 1 wherein said gaseous
pollutant source is the aforesaid equipment, said equipment
including a gas collector and wherein said first ducting means is
connected at one end to said collector and at its other end to said
heater.
6. A combustion system as claimed in claim 5 wherein said first
ducting means includes an adjustable air inlet to enable controlled
admission of combustion air into said first ducting means.
7. A combustion system as claimed in claim 1 wherein said gaseous
pollutant source is a reservoir in which the products of the
aforesaid equipment are stored, said reservoir including an outlet
through which the products pass and wherein said first ducting
means is connected at one end to said reservoir adjacent to said
outlet and at its other end to said heater whereby dust and vapors
formed when said products pass through the reservoir outlet are
caused to flow into said first ducting means and to said
heater.
8. A combustion system as claimed in claim 7 wherein said first
ducting means includes an adjustable air inlet to enable controlled
admission of combustion air into said first ducting means.
9. A combustion system as claimed in claim 7 including a hood
having one end surrounding said reservoir outlet, said hood being
adapted to receive means for receiving said products at its other
end to prevent the escape of said dust and vapors into the
atmosphere outside said system and wherein said one end of said
first ducting means is in flow communication with said hood.
10. A combustion system as claimed in claim 9 wherein said hood is
size adjustable.
11. A combustion system as claimed in claim 1 wherein said heater
has sufficient capacity to heat said gaseous pollutants above their
combustion temperature and including attenuator by-pass ducting
means in flow communication with the outlet of said heater and gas
flow control means which enables the gas passing through the heater
outlet to flow selectively through either said second ducting means
or said attenuator by-pass ducting means and including means for
causing the gas passing through the heater outlet to flow through
said attenuator by-pass ducting means.
12. A combustion system as claimed in claim 11 wherein the means
for causing the gas passing through the heater to flow through said
attenuator by-pass ducting means is said first mentioned means for
causing said gaseous pollutants to flow.
13. A method for buring gaseous pollutants including the sequential
steps of:
A. causing the gaseous pollutants to flow from a source of said
pollutants to a heater;
B. heating said gaseous pollutants above the condensation
temperature of said pollutants;
C. causing the heated gaseous pollutant to flow through an acoustic
attenautor and into a combustion chamber; and
D. heating said gaseous pollutants above their combustion
temperature.
14. A method as defined in claim 13 including the step of mixing
combustion air with the gaseous pollutants prior to heating the
pollutants and then heating the pollutants and air above the
condensation temperature of said pollutants.
15. A method for buring gaseous pollutants in a combustion system
having a combustion chamber and an acoustic attenuator through
which air flows before entering the combustion chamber including
the steps of:
A. causing the gaseous pollutants to flow from a source of said
pollutants to a heater;
B. heating said pollutants
i. between the condensation temperature and combustion temperature
of said pollutants when said combustion system is in a first state
or
ii. above said combustion temperature when said combustion system
is in a second state,
said first state existing when said combustion chamber is operating
and said second state existing when said combustion chamber is not
operating
C. causing the heated gaseous pollutants to flow through said
attenuator and into the combustion chamber when said combustion
system is in said first state and
D. causing the heated gaseous pollutants to by-pass said attenuator
and be exhausted to the atmosphere when said combustion system is
in said second state.
16. A method as defined in claim 15 including the step of mixing
combustion air with the gaseous pollutants prior to heating the
pollutants.
Description
BACKGROUND OF THE INVENTION
The present invention is directed to industrial pollution control
systems, and more particularly to systems which abate or lessen
noise pollution created by the operation of industrial equipment,
as well as novel subsystems and components used in such
systems.
Historically, it has been the generally accepted practice to use
open-fired burners and combustion systems on rotary driers and
kilns and on most low temperature kilns as well. The primary reason
has been an economical one because air can be induced, such as by
the use of a suction fan, at lower cost than by the use of a
pressurized air supply for the entire combustion system. Because of
the generally large size of this type of equipment and the
attendant heat loss, it has been necessary to use combustion
systems which operate at high combustion levels and large air
flows.
During operation of such large-scale equipment, high noise levels
are generated. For example, it is common to find noise levels of
125 dBA to 130 dBA within 3 or 4 feet of the burner unit. While the
effect of this noise on exposed personnel has always been a
concern, the recent advent of noise abatement legislation has
brought the matter into even closer study. The responsibility for
reducing excessive noise levels has been placed directly on the
employer in most cases.
The primary purpose of this legislation is to protect employees
from unhealthy sound levels under working conditions. For example,
an employee might be safely exposed to a sound level of 90 dBA
during an 8 hour workday; however, exposure to a sound level of 115
dBA should occur for no longer than about 1/4 hour during the same
time period. In order to reduce or abate the level of industrial
noise and thus safeguard the employee against the hazards of noise
at the level which is considered dangerous to his health and
safety, the noise abatement system of the present invention has
been devised. By this novel system the noise can be reduced to a
tolerable or allowable level.
The actual noise which is generated in the use of the
afore-mentioned industrial equipment varies in frequency over a
wide acoustical range. The very low frequency noise is generally a
result of the response of the drum-shaped kiln or drier and
associated ducts and appurtenances, which drum may be as large as
20 feet in diameter and varying in length from 20-400 feet. This
low frequency noise generally ranges in frequency from a few cycles
up to about 100 or 200 Hz. Medium frequency noise mostly stems from
the burner flame and flame front and is generally referred to as
combustion roar. This noise will vary in range from approximately
70 Hz up to about 1,000 Hz. High frequency noise can result from
such causes as air flow, turboblower operation, equipment
vibration, and resonance, and the frequency thereof can range
anywhere from approximately 500 Hz up to 7 or 8 KHz, and even
higher.
SUMMARY OF THE INVENTION
The problem of excessive noise levels caused by the operation of
state-of-the-art industrial equipment of the general aforedescribed
type is overcome in the present invention by a combustion system
designed to abate the amount of noise which escapes into the
atmosphere during operation and which enables combustion of gaseous
pollutants. In accordance with the purpose of the invention, as
embodied and broadly described herein, the combustion system of
this invention includes a combustion chamber having an output end
adapted to be coupled to a furnace, drier or the like and an air
inlet for receiving combustion air. A fuel burner is mounted
adjacent to the combustion chamber and an acoustic attenuator is
placed in air flow communication with the combustion chamber air
inlet. At least a substantial portion of the combustion air flows
through the attenuator before entering the combustion chamber. The
system also includes a source of gaseous pollutants, a heater for
heating the pollutants above their condensation point, first
ducting means for conveying the pollutants to the heater and second
ducting means for conveying the pollutants heated in the heater to
the attenuator. Means are provided for causing the gaseous
pollutants to flow sequentially from the source of gaseous
pollutants through the first ducting means, the heater, the second
ducting means, the attenuator and into the combustion chamber.
Preferably, the first ducting means includes an adjustable air
inlet to enable controlled admission of combustion air into the
first ducting means.
In a second form of this invention, the heater is sized to
selectively permit it to heat the gaseous pollutants above their
combustion temperature and acoustic attenuator by-pass ducting
means in communication with the outlet of the heater is provided
along with gas flow control means which enables the gas passing
through the heater outlet to flow selectively through either the
second ducting means to the attenuator or through the attenuator
by-pass ducting means.
The invention consists in the novel parts, constructions,
arrangements, combinations and improvements shown and described.
The unique features and advantages of the invention will become
apparent by a reading of the following description which, taken in
conjunction with the accompanying drawings, which are incorporated
in and constitute a part of this specification, disclose preferred
embodiments thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 show, respectively, the plan and side elevation views
of a noise attenuated combustion system of one particular design
which can be used with the system of the present invention;
FIG. 3 shows, in perspective, a partial view of the aforesaid
combustion system in which portions are presented in cutaway form
and having an alternative arrangement of the duct;
FIG. 4 shows, in cross section, a front elevation view of a damper
used in the aforesaid system, taken along line 4--4 of FIG. 1;
FIGS. 5 and 6 show, in cross section, elevation views of an
improved combustion chamber taken along lines 5--5 and 6--6 of FIG.
1;
FIG. 7 is a rear elevation view of an improved attenuator which can
be used in the aforesaid system;
FIG. 8 is a plan view of the aforesaid attenuator with the top
surface removed therefrom to show its interior construction;
FIG. 9 is a side elevation view, in cross section, of an
alternative embodiment of the deflector used in the aforesaid
system;
FIG. 10 is a partial elevation view, in section, showing the grill
used in the combustion chamber, taken along line 10--10 of FIG.
1;
FIG. 11 is a top plan view of an alternative construction of a
grill section;
FIG. 12 is an enlarged partial elevation view of the cutaway
combustion chamber shown in FIG. 3;
FIG. 13 is a schematic illustration of a gaseous pollutant burning,
acoustic attenuated combustion system formed in accordance with a
first embodiment of this invention; and
FIG. 14 is a schematic illustration of a modification of the
combustion system illustrated in FIG. 13.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIGS. 1 and 2, there is shown, respectively, the
plan and side elevation views of a preferred embodiment of a noise
attenuated combustion system indicated generally by arrow 10 which
is suitable for use with the system of this invention. The system
10 includes an enclosed combustion chamber 12 having an open output
end designed to be coupled with a front opening formed in an
industrial drier or furnace which is represented in phantom outline
and identified by the numeral 14. As embodied herein, the chamber
12 is preferably provided at its forward end with an extension 16
of reduced diameter which protrudes into the drier or furnace a
fixed distance to protect the front end of such structure from the
high temperature flame generated in the combustion chamber 12. As
can be seen in FIG. 1, the extension 16 is shown as being offset
horizontally, and the reason for this will be explained
hereinafter.
An annular flange 18 is attached to the combustion chamber 12 near
its forward end and is used to bolt this chamber to the front face
of the drier or furnace 14. In this manner, the opening into the
drier or furnace is closed off and thus prevents the escape of
noise, dust, and other potential pollutants at that point. If
needed, gaskets, adhesive sealants, or other conventional sealing
materials can be used to obtain a seal between the combustion
chamber 12 and the drier or furnace 14. Although the present
invention is designed to be used with both rotary and stationary
driers and furnaces, the front end or furnace portion of the rotary
structures is generally designed to be stationary. However, if it
is desired to have the portion 14 of the structure shown rotate,
the flange 18 will not be bolted but instead a conventional seal of
the same type which is commonly employed to seal a rotating drier
or kiln cylinder to the breeching or end box can be used. Examples
of such seals are the wet and dry friction type, the flexible
rubbing seal, and also the labyrinth seal if rubbing contact is to
be avoided. Should the drier or furnace opening be found to be
oversized, it can be reduced in size by conventional construction
techniques to where it can be closed against the combustion chamber
12 in any of the ways set forth above. Regardless of whether the
connection is between stationary or rotating structures, it is
important that an effective seal be obtained to avoid escape of
noise and thereby a reduction in the effectiveness of the
system.
The particular type of drier or furnace to which the combustion
system can be adapted forms no part of the present invention, and
thus is not intended to limit the wide applicability of this
invention. By way of example, this combustion system can be used
with either direct driers or indirect driers, such driers being
either stationary or rotary. A particularly suitable type is the
rotary drier or rotary kiln which has a wide range of uses,
including but not limited to those of drying, roasting, heating,
and calcining. Similarly, with regard to furnaces, the combustion
systems of this invention find wide utility with processing
furnaces, as well as industrial furnaces, and of the direct as well
as the indirect type. One of the more important types of process
furnace is the rotary kiln because of its wide use in many
different industries, encompassing such things as the burning of
cement and lime, the dehydrating, roasting or sintering of bauxite
and alumina, as well as the calcining and decomposition of
materials, and the processing of stone, aggregate, and sand to be
used in the manufacture of asphalt paving materials, all by way of
example.
With reference again to the embodiment of FIGS. 1 and 2, the
combustion chamber 12 is preferably of cylindrical shape and has at
its aft end a cylindrical extension 20 of reduced diameter which
will hereafter be called the sealed chamber for purposes of
convenience. In accordance with the invention, a fuel burner is
mounted adjacent to the combustion chamber 12 to direct its flame
thereinto. As here embodied, a burner unit 22 is attached to and
extends into the sealed chamber 20 at its aft endface. The burner
unit 22 is of a conventional construction and houses the burner
apparatus (not shown). Fuel, such as oil and/or gas, is supplied
from any convenient source through fuel lines (not shown) to this
burner. Chamber 20 and burner unit 22 are offset horizontally to be
in line with extension 18.
As here embodied, the combustion chamber 12 further includes at
least one and preferably two externally mounted, movable rods 24
which are connected internally to an air adjusting damper, later
described, to provide manual control of the flow of air within the
combustion chamber to neutralize the suction pressure of the burner
flame jet. Another adjustable rod 26 is mounted external of the
endface of sealed chamber 20 and serves as an adjusting screw which
permits lateral adjustment of an ignition tile, later described,
within the combustion chamber.
In accordance with the invention, enclosed first means are provided
for ducting air to the combustion chamber 12. The air ducting means
has an upstream end for admitting air, and a downstream end which
terminates at an opening in the combustion chamber for receiving
combustion air. As embodied herein, and with reference additionally
to FIG. 3, the air ducting means includes a duct system, the shape,
length, and placement of which is not critical because this will be
determined by the placement of the equipment, available space,
design factors, and like considerations. This is readily apparent
by a comparison of FIG. 1 with FIG. 3, which shows two different
duct embodiment. However, in order to prevent the escape of noise,
it is preferred that there be a single opening or entrance 28 at
the upstream end for admitting air to the combustion system.
In the particular embodiment shown, the entrance 28 is formed as a
horizontal opening in an intake hood or deflector 32 which is
connected to the front of an attenuator 30, later described.
Deflector 32 is formed with flat side and bottom surface and has a
front which is formed of two plane surfaces 34 and 36. Plane 36 is
positioned obliquely between vertical plane 34 and the bottom
surface of deflector 32 to deflect upwardly any noise which escapes
past the attenuator 30 so that it will have a reduced effect upon
workers or other people nearby. Surface 34 also assists in noise
abatement by acting as a reflector which reflects a portion of the
noise, particularly in the lower frequencies, that escapes from
attenuator 30 back through this attenuator, where it is further
attenuated, and into the interior of the combustion system. A small
strip 38 is formed across the back of opening 28 to help support a
conventional flange 40 formed around the rear periphery of the
deflector 32 for attaching it to the attenuator 30. The deflector
32 can be constructed in a conventional manner, such as for example
by cutting sheet metal to size and assembling it in the desired
shape.
The acoustic attenuator or silencer 30 is connected at the upstream
end of the air ducting means to be in airflow communication
therewith. The purpose of attenuator 30 is to prevent or minimize
the escape of noise from the combustion system 10, yet freely pass
in counter flow to noise flow the air necessary for combustion of
fuel and whatever additional air might be needed for the process
carried out in unit 14. Should it be necessary by reason of
engineering design or the like that the duct system be provided
with several entrances or openings, it would then be necessary to
place an attenuator, such as depicted by numeral 30, at each
entrance.
The rear of attenuator 30 is connected by the duct system to the
remainder of the combustion system 10. To this end, a main duct
assembly 42 is connected between the rear of attenuator 30 and the
combustion chamber 12 to supply secondary combustion air thereto.
Downstream of said attenuator 30, a second enclosed air ducting
means is connected to said first air ducting means. As embodied
herein, this second air ducting means comprises duct 44 of smaller
cross section which branches off of duct 42 and is sealed to the
intake of an air compressing means, here embodied as a
turbocompressor 46. The turbocompressor 46 is a conventional device
and is illustrative of many available means which can be used to
supply pressurized air for a burner such as that housed in burner
unit 22. In the particular embodiment shown, the compressed air is
used to atomize the fuel prior to ignition. This compressed air is
supplied from turbocompressor 46 to burner unit 22 through the duct
48 which is included as part of the second air ducting means.
The ducts 42, 44, and 48 can be made in a conventional manner out
of material such as sheet metal and includes the necessary reducing
and expanding sections, elbows, flanges, etc., all of the necessary
size and shape to provide an enclosed air supply system. As shown
in FIG. 3, the duct 42 has been provided with an elbow 50 merely to
demonstrate the alternatives to the arrangement of the ducts
depending on the needs of the installation. Similarly, the duct 44
has been provided with two elbows 52 for coupling this duct to the
turbocompressor 46, the latter having been omitted from FIG. 3 for
ease of illustration. Where the ducting system for the
turbocompressor 46 becomes lengthy, it may be advantageous to
eliminate duct 44 and connect a separate attenuator 30 at the
intake of this turbocompressor.
In accordance with the invention, a damper is positioned in the
first air ducting means downstream of the point of intersection of
said second ducting means. As embodied herein, damper 54 is
inserted in duct 42 between branch 44 and combustion chamber 12.
The purpose of damper 54 is to modulate or control the flow of
secondary combustion air into combustion chamber 12. Damper 54 is
preferably an opposed vane damper and consists essentially of a
small length of duct having mounted therein a plurality of louvers
56 which are disposed across the flowpath and are adjustable to
control the cross-sectional flow area through the duct. With
reference also to FIG. 4, taken along line 4--4 of FIG. 1, the
louvers 56 are preferably movable from a position in which they are
parallel to the flow of air, at which time the cross-sectional flow
area is approximately 100 percent of the inside area of the duct,
to a position where they are perpendicular to the flow of the air,
at which time the duct is closed. This, therefore, gives control
from zero to 100 percent of capacity over the amount of air which
can flow through duct 42 into combustion chamber 12.
As embodied herein, each louver 56 is formed of a longitudinal rod
58 onto which thin blades 60 and 62 are attached, as by welding.
The louvers 56 are mounted in damper 54 by positioning rods 58 in
spaced aligned holes 64 and 66 formed, respectively, in the bottom
and top surfaces of the damper. At the top of this damper, the rods
58 extend sufficiently far to permit them to be grasped and rotated
manually either by hand or an appropriate tool. The top surface of
each rod 58 can be notched or otherwise marked in alignment with
its louver 56 to indicate the latter's position within the damper.
Preferably, the rods are connected to some form of control means
(not shown) so that they can be moved in unison to predetermined
positions to obtain the desired quantity of air flow. By the use of
such a control means, the air flow through damper 54 can be
controlled to be in proportion to the fuel/air requirements for the
burner 22. Each edge of the damper 54 has a flange 68 formed about
its entire periphery for mounting the damper 54 within the duct
42.
Before proceeding to a detailed discussion of combustion chamber
22, it should now become clear that the present system to the
extent it has been discussed in FIGS. 1, 2, and the portion of FIG.
3 relating to the air ducting means, is an enclosed system to abate
the escape of noise therefrom, in marked contrast to the open
combustion systems in common use. In systems of the latter type, it
is generally the practice to have the aft end of the combustion
chamber open in order to induce or entrain air past the burner unit
22, rather than receiving combustion air through a duct system as
taught herein. The intake to a compressed air source, such as
turbocompressor 46, is also open to the air rather than being
connected to a duct such as duct 44. There is generally no concern
over closing off the opening between the drier or furnace 14 and
the combustion chamber 12. Obviously, there is no way to modulate
the air flow as by damper 54 and no way to attenuate noise as by
attenuator 30.
With reference again to FIG. 3, the construction of the preferred
embodiment of the combustion chamber 12 can be described. The
purpose of this chamber is to burn the fuel supplied by burner unit
22. Combustion chamber 12 is designed to be of the recuperative
type where some of the heat which is generated internally preheats
the secondary combustion air, and where some of this heat is also
radiated internally back into the combustion zone. Both steps
increase the rate of reaction between the air and fuel, and thus
the completeness and thereby the efficiency of combustion.
In accordance with the invention, the combustion chamber 12
comprises an outer shell 70 and a second acoustic attenuator within
the outer shell to exhibit sound absorptive properties for the
noise generated within the combustion system. As herein embodied,
shell 70 is a metal cylinder having a large rectangular opening 72
on the side where it attaches to duct 42. As shown, the inner
surface of shell 70 is lined with a layer of insulation 76. Under
certain conditions, the use of a recuperative combustion chamber
can permit shell 70 to remain unlined because the temperature level
at the inside surface of shell 70 is normally in the region of
300.degree.-400.degree.F. This is in marked contrast to
temperatures in excess of 2,000.degree.F to which conventional
ignition or combustion chambers are normally exposed. This latter
temperature level requires that the combustion chamber have a
refractory lining. The refractories which are used cannot generally
withstand the thermal shock caused by sudden changes in temperature
resulting from intermittent operation of the combustion system.
Often such chambers will fail because the sudden expansion of the
refractory surface ultimately results in thermal spalling.
Therefore, by designing a combustion chamber free of refractory
lining, the thermal spalling problem is averted.
In some cases, however, it may be found desirable to attach a layer
of insulation 76 along the inner cylindrical surface of shell 70,
as shown. The opening 72 will, of course, extend through this
insulation. Insulation 76 aids in the reduction of heat loss and
better recuperation of heat between the interior of the combustion
chamber 12 and the incoming secondary air stream. It should be
realized, however, that the insulation 76 is a low temperature
insulation in contrast to the high temperature insulation or
refractory material presently used in combustion chambers. As such,
insulation 76 can be selected so that it is free of such problems
as thermal spalling.
As embodied herein, extension 16 of combustion chamber 12 is formed
as a cylindrical metal shell 74 of reduced diameter attached to the
forward end of shell 70. Insulation 76, which is also applied to
the inner surface of shell 74 is made thicker because of its
exposure to the combustion flame. Preferably, here, the insulation
is a high temperature insulation and thus a different material from
that used to line shell 70. The forward end of shell 74 is open and
serves as the output end of the combustion chamber 12.
With reference also to the cross-sectional view of FIG. 5, at the
front end of combustion chamber 12 there is mounted a circular
metal band 78 aligned substantially flush with the opening in shell
74. Band 78 is preferably not continuous but is formed of a
plurality of curved sectors 79 to allow for thermal expansion. Each
sector is mounted on one or more struts 81 which extend upward from
shell 70 through insulation 76. This metal band serves as a support
for the forward end of a combustion chamber grill 80 which rests
loosely within this band and is retained there by a plurality of
L-shaped clips 83 formed on sectors 82.
With additional reference to the cross-sectional view of FIG. 6,
grill 80 is, in accordance with the invention, of a substantially
tubular shape and is supported within but spaced from the interior
of the combustion chamber shell 70. As herein embodied, grill 80 is
made of a high-temperature material, such as a metal which resists
the high temperature of combustion, and is articulated in
construction in that it is made from a number of arcuate,
longitudinal overlapping sections 82. Each section 82 has two
lengthwise edges and the grill is formed such that an edge of each
section overlaps the edge of an adjacent section as shown to
provide for thermal expansion.
Grill 80 extends substantially the entire length of cylindrical
shell 70 and the spacing between grill 80 and insulation 76 permits
the free flow of secondary combustion air over its external
cylindrical surface. There are means provided for mounting the
grill 80 within shell 70 and these means are herein embodied as a
plurality of bolts 84 which are circularly arranged and attached to
the interior of shell 70 toward its aft end. Each bolt 84 extends
through the overlapped edges of two grill sections 82 and is
retained there by a nut. The holes in the sections 82 which receive
the bolts are oversized to permit thermal expansion.
The bolts 84 are made longer on the side of shell 70 where duct 42
attaches and progressively decrease in length toward the opposite
side. The result of this arrangement is that the grill 80 is offset
or eccentrically mounted with respect to the longitudinal axis of
the cylindrical shell 70 and thus provides greater space at opening
72, as compared with the space around the remainder of the grill,
for the intake and distribution of the large volume of secondary
combustion air which must be handled under maximum operational
conditions. The secondary air, it should be noted, is prevented
from escaping forwardly past the exterior surface of grill 80
because the insulation 76 is thickened annularly where metal band
78 is mounted and thus blocks forward air flow. The secondary air
therefore either flows into grill 80 or back toward burner unit 22,
as hereafter described.
Between band 78 and bolts 84, the grill 80 is preferably
unsupported, but the sections 82 are maintained in a substantially
cylindrical shape by spaced retention means. As embodied herein and
shown in FIG. 10, which is a partial elevation view, in section, of
the grill 80, these means include a clip 86 attached to one edge of
each grill section 82. Preferably, each clip 86 is attached to the
inside of the overlapping edge of each section 82 to form a space
therebetween for receiving the lapped edge of the adjacent section.
This space has a sufficient depth to accommodate thermal expansion
of the grill sections 82. Clips 86 are preferably made of stainless
steel or a like metal and are spaced at one or more points along
the length of the grill, as desired.
In accordance with the invention, a plurality of small diameter
holes, identified by numeral 90, are formed throughout the grill
80. As herein embodied, holes 90 are formed in each of the sections
82 comprising cylindrical grill 80. One purpose of these holes is
to admit the secondary combustion air supplied by duct 42 into the
interior of the grill where combustion occurs. This combustion air
flows over the cylindrical surface of grill 80 and into its
interior through holes 90. The holes 90 are preferably uniformly
placed over the cylindrical surface of the grill, and are of
uniform size. It is also preferred that the rate of air flow
through the holes 90 in the grill be substantially uniform. As here
embodied, the aforedescribed eccentric mounting of the grill 80
assists in attaining this end. The progressive reduction in the
annular spacing between the grill 80 and shell results in a
constant velocity pressure and thereby the maintenance of a
constant and uniform air flow rate through the grill holes 90.
In FIG. 11, an alternative preferred embodiment of the hole sizing
and placement in grill 80 is shown. Here, a top plan view of a
grill section 82 is depicted whose holes consist of three distinct
sizes. Holes of the same size are grouped in three bands across the
width of the section 82, resulting in three cylindrical bands
disposed along the length of the grill, when assembled. The sizes
of holes 90a, 90b, and 90c have been purposely exaggerated to
emphasize their difference in size.
The grill temperature is greatest at its forward end during
combustion and with certain grill materials, additional cooling
becomes necessary in order to protect the grill. The largest holes
90a are placed in the front of section 82, the medium-sized holes
90b in the middle band and the smallest holes 90c in the rear. A
greater flow of secondary combustion air flows through holes 90a, a
lesser amount through holes 90b, and the least of all through holes
90c. During operation, the larger air flow at the front of the
grill improves temperature reduction. The numerals 86 point to the
clips, previously discussed, formed on the inner face of the
section 82 for receiving the edge of an adjacent section during
assembly of the grill. Holes 88 are for receiving bolts 84 during
placement of the grill in the combustion chamber and are oversized
to permit thermal expansion of the section 82.
The combustion chamber 12 has an annular plate 92 which is attached
to the aft end of cylindrical shell 70 by a weld or other suitable
means. The opening of plate 92 is eccentric and sized to mate with
the sealed chamber 20 so that this chamber is aligned with grill
80. Chamber 20, as shown, is formed as a cylindrical metal shell 94
having an annular flange 96 which is connected to plate 92 by
bolts, welding, or the like, to seal the combustion chamber at this
junction.
The grill 80 terminates short of plate 92 so that a path is
provided for the flow of secondary combustion air around the aft
end of grill 80 into the interior of chamber 20, thus bypassing
grill 80. In accordance with the invention, the combustion chamber
comprises a damper positioned therein to control the flow of
combustion air. As best illustrated in FIG. 12, a metal band 98 is
positioned adjacent to the aft end of grill 80 but is not rigidly
attached thereto. Band 98, which serves as an annular damper, is
adjustable longitudinally over the aft end of the grill 80 and
thereby controls the size of the annular opening at the rear of
chamber 12 leading to chamber 20. Adjustment of the damper and
thereby control of air flow is made possible by the provision of
two movable rods 24, previously described, which are attached to
band 98 and which extend outside of the combustion chamber through
holes appropriately formed in plate 92. The positioning of these
rods 24 will determine the percentage breakdown of air flow between
these chambers. This damper affords an adjustment of the pressure
relationship between the interior of grill 80 and the sealed
chamber 20 to eliminate suction within this latter chamber which
results in pressure oscillations during combustion, as more fully
described hereinafter. The rear of grill 80 is closed by an annular
air retaining plate 97. This plate 97 is preferably not attached to
grill 80 but is mounted inside of the combustion chamber by a
plurality of struts 99 welded to the inside of plate 92.
The aft end face of chamber 20 is closed by plate 100 which is
attached to annular flange 102 by welding, bolting, or other
convenient means. A hole 104 is formed in plate 100 and is sized to
receive the forward portion of burner unit 22. The positioning of
burner unit 22 is accomplished by an annular flange 106 formed on
its periphery which permits the burner unit to be attached to plate
100 by bolts or other convenient means.
Because burner 22 is an enclosed unit, it can be seen from the
foregoing description that the combustion chamber 12 including its
sealed chamber extension 20 are a fully enclosed or sealed unit
which minimizes or abates the escape of noise therefrom. The only
openings are those that are designed, namely, opening 72 which is
connected to duct 42, and the discharge opening at extension 16,
although there is provision for sealing the combustion chamber to
the front end of the drier or furnace unit 14, as earlier
described.
The front end 108 of burner 22 is positioned adjacent the rear of a
conventional ignition tile 110 which assists in the ignition and
burning of the fuel in a well-known manner. Ignition tile 110 is of
a sufficient length to extend forwardly into cylindrical shell 70
where it opens into the interior of grill 80. Tile 110 is of a
generally cup-shaped design formed of an outer cylindrical metal
shell 112 and bottom metal plate 114, both of which can be
constructed from stainless steel or other suitable material. It is
to be understood, however, that the tile 110 can be formed in other
shapes. The interior of this metal cup is lined with a thick layer
of tile 116 made from any suitable high-temperature refractory
material. The bottom of tile 110 has a large hole or opening 118
aligned with the forward end 108 of burner unit 22. Ignition tile
110 rests on support or saddle 120 attached to the bottom of
chamber 20.
Ignition tile 110 is movable along its longitudinal axis so that
its position with respect to the burner nozzle (not shown) at end
108 of the burner unit 22 can be adjusted. The reason for this
adjustment is to permit control over the stability and shape of the
flame. Adjustment is effected through the provision of an L-shaped
bracket 122 attached to plate 114 and tile adjusting screw 26. A
threaded member, such as nut 124, is positioned in the base of the
L-shaped bracket to receive the threaded shank of screw 26. By
clockwise or counterclockwise rotation of the screw 26, tile 110
can be caused to move rearwardly or forwardly, as desired.
To simplify the drawings, no attempt has been made to portray the
conventional apparatus associated with a burner unit, such as
depicted at 22. This would include, without limitation, such
apparatus as a pilot, fuel input ports, throttles, gages, valves,
and all associated plumbing. It is to be understood, of course,
that any access required into the interior of the burner unit 22 or
chamber 20 would be made through an opening properly sealed to
avoid the escape of noise.
In operation of the combustion system 10, it is to be assumed that
the drier or furnace 14 to which the system is attached includes a
suction fan (not shown) at its discharge end to draw in, via the
air ducting means, the secondary air required for combustion. If
such fan is not available, than an impeller, compressor or similar
device (not shown) can be installed in the air ducting means to
create a pressurized, forced-air system and thereby meet the air
flow requirements of combustion. By whatever means are employed,
air is drawn in through entrance 28, passes through attenuator 30,
main duct 42, damper 54, and into combustion chamber 12 via opening
72. The louvers 56 of damper 54 are positioned to control the
secondary air flow in proportion to the fuel/air requirements of
the burner 22. At this time the turbocompressor 46 is started, and
air is drawn out of duct 42 through duct 44 and into the
turbocompressor 46 intake where it is compressed. A supply of
compressed air is provided to burner unit 22 by duct 48. Fuel is
also supplied to the burner 22 at this time by conventional means
(not shown) where it is atomized by the compressed air and sprayed
as a fuel/air mixture out of the burner unit 22.
The spray of atomized fuel is ignited by conventional ignition
means (not shown), such as a high energy electrical discharge or
spark or gas pilot, and a flame issues forth out of the burner unit
22 into ignition tile 110. If adjustment of the tile 110 is
necessary, this can be accomplished by the proper rotation of tile
adjusting screw 26 so that the desired flame stability and shape
are attained.
The secondary air which enters the combustion chamber via opening
72 follows essentially two paths. The first path is about the outer
surface of grill 80 and into its interior via the plurality of
holes 90. The other path is past the annular opening controlled by
damper 98, along the outer shell 112 of ignition tile 110 and into
hole 118 where it is diffused with the atomized fuel jet. A flame
front progresses out of the interior of ignition tile 110 into
grill 80 of combustion chamber 12 where combustion principally
occurs and is essentially completed. Heat is now transferred from
the chamber 12 into the unit 14 by flow of the hot combustion gases
generated in chamber 12 as well as by radiation from the flame
itself and the heated exposed components of the combustion chamber
12 and its extension 18.
As explained earlier, the combustion chamber is recuperative in its
operation. Grill 80 is elevated to a relatively high temperature
within the temperature limits of the material used, and transfers
heat to the inflow of secondary combustion air by radiation and
conduction. This air by such preheating causes an increase in the
rate of combustion reaction between the air and fuel. Also, the
high temperature of grill 80 radiates heat back into the combustion
zone in front of ignition tile 110 and further increases the
air/fuel reaction rate. The result is that a more complete
combustion of fuel occurs in chamber 12 and this increase in fuel
combustion efficiency results in a more economical operation.
Where insulation, such as shown at 76, is used to line the inside
of shell 70, it aids in reducing the loss of heat through the wall
of combustion chamber 12 and will also result in better
recuperation of heat in relation to the incoming secondary air
flow.
It is important during operation to maintain a reasonably constant
pressure between the combustion zone (interior of grill 80) and the
generally annular zone 126 surrounding and adjacent to the front
end 108 of burner unit 22. This balance can be attained by means of
the earlier-discussed adjustable damper 98 (FIGS. 3 and 12) which
controls the flow of secondary combustion air into chamber 20 and
to zone 126. If this control is not provided, the entrainment of
secondary combustion air by the high velocity burner jet can create
a suction effect which lowers the pressure in zone 126 until a
sufficient pressure differential is reached where air flows from
the combustion zone back toward zone 126. The pressure within the
zones equalizes and the flow is again forward. However, an
imbalance soon recurs accompanied by another backflow. Thus, the
pressure oscillations cause flow oscillations which result in fuel
being brought back into zone 126 where it will burn and damage or
destroy the equipment. In the case where a liquid fuel is used,
fuel droplets would be sprayed in all directions and some would
impinge on the exposed surfaces of the equipment. Because of the
high temperature, low boiling components of the fuel would
volatize, leaving sticky hydrocarbon deposits adhering to these
surfaces, and the operation of the system would be seriously
impaired. Where possible, it is preferred that the components be
positioned within the combustion chamber 12 and the chamber 20 so
that no pressure differential occurs; however, the addition of the
adjustable damper 98 affords a means to vent the desired amount of
air to zone 126 and thus neutralize any suction pressure imbalance.
It is preferable, although not essential, that the total air flow
into grill 80 and to zone 126 combined remain constant regardless
of the position of band 98. One way to accomplish this is to have
the band arranged progressively to close off holes 90 as it is
moved forward from plate 92. Thus, as less air flows into grill 80,
more flows through the annular space between band 98 and plate 92,
but the total flow remains constant.
As discussed earlier, there is a tremendous amount of noise
generated by the operation of these combustion systems and the
equipment which utilizes the generated heat. It is quite common to
find noise levels of 125 dBA or higher. As pointed out,
overexposure to these noise levels can be severely harmful to the
personnel who must work near this equipment and can lead to hearing
loss, heart problems, and be the cause of high blood pressure and
eardrum damage, just to name a few examples.
When the combustion system 10 is enclosed and the connection
between the system 10 and the unit 14 is sealed, as has just been
described, essentially all of the noise which is generated is
confined within the combustion system. For practical purposes, it
can be assumed that the noise which is so confined does not
diminish and absent some way to attenuate or absorb it, it will
escape from the system. For example, the noise within chamber 12
attempts to escape by propagation into duct 42 from the chamber, as
well as by the path through burner unit 22, turbocompressor 46, and
duct 44, and this collected noise, including the noise generated by
the turbocompressor itself, will attempt to pass out entrance
28.
As previously described, the noise emanating from the combustion
system 10 can be broken down into three general frequency ranges:
low, medium, and high. It has been found that low frequency noise
is the most difficult to attenuate. In accordance with the
invention, a Helmholtz chamber has been incorporated into the
combustion chamber 12 to absorb or selectively attenuate the noise
in the low frequency range and up into the medium frequency range
also.
A Helmholtz chamber is an acoustic resonator which is generally
tuned over a narrow range of frequencies about a resonant frequency
and can be used as an absorber of acoustical energy. As herein
embodied, and with reference again to FIGS. 3, 5, and 6, the grill
80 generally defines the Helmholtz chamber, and the holes 90 are
the openings which admit acoustical energy into the interior of the
chamber. The range of hole sizes available for selection is
restricted somewhat by the need to insure sufficient secondary air
flow into grill 80. Preferably, the area or size of the holes 90 is
selected so that energy is absorbed in the low frequency range.
Because, in this embodiment, the holes are also made a uniform size
for the aforedescribed purpose of having a uniform flow rate,
energy is absorbed in a narrow range of low frequencies about the
resonant frequency of the Helmholtz chamber.
It has been found that the level of low frequency noise can be
reduced from between 5 to 15 dB. This reduction tends to bring the
low frequency component of the overall noise down to a more
tolerable level so that the adverse effect of longterm exposure is
reduced. Furthermore, should any low frequency noise which is not
absorbed escape from the combustion system through attenuator 30,
the use of a reflector, such as shown at 32, will reflect a portion
of the noise back into the system and will direct the remainder of
this noise upwardly or in the direction most favorable for the
particular installation involved.
In the alternative grill embodiment of FIG. 11, three distinct hole
sizes are shown as holes 90a, 90b, and 90c. The range of
frequencies which are attenuated by having holes varied in size is
widened over that of the previous embodiment where all holes are of
the same size. It is also within the scope of this invention to
vary the size of the grill holes across the entire surface of the
grill 80. In such case, the holes 90 shown in the FIG. 3 embodiment
would not be made of uniform size throughout, but instead would
vary in size in accordance with the range of frequencies which it
is desired to attenuate. It has been found that the system can
readily accommodate hole sizes in grill 80 which vary an order of
magnitude between the smallest and largest holes and still satisfy
uniform flow rate requirements. Within such design constraints of
uniform flow, where the size of the holes 90 is reduced, the holes
must be increased in number, and where the hole size is enlarged,
the number of holes must be decreased. In this manner the total
cross-sectional hole area remains substantially the same as in the
uniform-hole-size embodiment. In view of the above teaching, it
should be realized that in the FIG. 11 embodiment, the holes in
each band of sections 82 can also be varied in size yet still
satisfy the uniform flow rate requirement for each of the bands of
the completed grill. A wider range of frequencies is thus
attenuated by each band of the completed grill as compared to where
each band contains holes of a uniform size.
The other acoustic attenuator embodied herein is attenuator 30,
which was described earlier. In FIG. 2, the deflector 32 has been
partially cut away to show the front of this attenuator. In
accordance with the invention, there is at least one passageway
formed in the attenuator for the flow of combustion air
therethrough. As herein embodied, a plurality of partitions 130 are
mounted within the acoustic attenuator housing 30 to define a
plurality of passageways for the flow of combustion air
therethrough. Preferably, the partitions 130 are spaced vertically
between the top and bottom opposed surfaces of attenuator housing
30 to form a plurality of open passageways 132 for admitting air
into the interior of combustion system 10. By additional reference
to FIG. 7, which is a rear view of attenuator 30, and FIG. 8, which
is a plan view of the attenuator with the top surface removed, a
better understanding of the construction and operation can be
obtained. Each of the interior partitions 130 is hollow and is made
from a pair of spaced metal sheets 134 forming opposed sidewalls
which are substantially parallel throughout their length but which
are bent and joined at the rear by riveting, welding, or the like,
to form a tapered trailing edge. The front of each of these
partitions 130 has a nose fairing 136 which also extends between
the top and bottom surfaces of the attenuator housing 30. Fairing
136 is formed of a metal sheet curved through 180.degree..Each nose
fairing 136 is joined to its two sheets 134 by riveting, welding,
or the like.
The two end partitions 130 are also hollow and are essentially half
the size of the interior partitions and are connected at the nose
fairings and trailing edges to an opposite one of opposed surfaces
forming sidewalls of the attenuator housing. Each consists of a
single sheet of metal 134 which serves as the partition sidewall
and a nose fairing 136 of approximately 90.degree. curvature in
contrast with the 180.degree. curvature of the nose fairings of the
interior partitions. Each nose fairing 136 of an end partition has
a flange to aid in attaching it to the sidewall of attenuator 30.
The rear of these end partitions are also tapered by bending metal
sheets 134. All partitions 130 are conveniently formed with top and
bottom flanges to assist in the mounting of these partitions to the
top and bottom surfaces of the attenuator 30.
Preferably, the passageways 132, as formed, are streamlined to
assist in the flow of air therethrough. The nose fairings 136 act
to reduce the pressure drop of air drawn through the inlet, and the
nozzle-like discharge created by the tapered trailing edges of
partitions 134 provide a smooth expansion of the flowing air to
reduce turbulence and pressure drop.
It should be clear from the foregoing description that the
combustion system 10 is from an airflow standpoint in open
communication with the exterior air by virtue of the passageways
132 of attenuator 30. Furthermore, these passageways 132 must be of
sufficient size to accommodate the air flow demands of the
combustion system; yet at the same time, there must be means for
absorbing sound positioned adjacent these passageways to attenuate
or impede the flow of sound, i.e., noise energy, therethrough in a
direction opposite to that of the airflow so that any noise which
does pass through is reduced in level.
As herein embodied, each partition has at least one surface
adjacent one of the passageways and the sound absorbing means
includes a plurality of holes formed in each of the surfaces.
Preferably, each vertical sheet 134 is constructed with a plurality
of holes 138, as depicted in FIGS. 3 and 7, throughout its length
and height. Each of the partitions 130, therefore, acts as a
multihole Helmholtz resonator, similar to that described previously
in regard to combustion grill 80, and the holes 138 admit noise
energy into the interior of their associated partitions. The holes
138 are preferably varied in size resulting in each Helmholtz
resonator being tuned to absorb noise through a reasonably wide
frequency range in the medium frequencies of about 200 Hz up to
approximately 800 or 1,000 Hz. The exact tuning of the resonators
will depend upon the hole diameters, thickness of the sheet 134,
and the volume within the enclosed partitions 130. The selection of
hole size is not constrained by air flow requirements as in grill
80, and the range of frequencies which can be attenuated is
accordingly greater.
As embodied herein, the sound absorbing means further comprises a
sound absorbing material 140 substantially filling each of the
enclosed partitions 130. Preferably, each is filled with an
acoustic absorption material 140 which is designed to absorb sound
above the 800 to 1,000 Hz level. Examples of the materials which
can be used are fiber glass, mineral wool, or other fibrous
substances, without limitation, all of which are of a well-known
construction and commonly used as sound absorbing materials.
Attenuator 30 is therefore preferably sized and constructed to
provide effective attenuation of noise in the medium and high
frequencies. In operation, as the noise propagates through ducts 42
and 44 and attempts to pass through attenuator 30, it reverberates
in passageways 132 and a portion of the noise energy passes through
holes 138 in the adjacent sheets or sidewalls 134. The
characteristics of the Helmholtz resonators absorb energy in the
medium frequencies and the acoustic absorption material 140 absorbs
noise energy in the high frequencies beginning at about 800 Hz.
While the attenuator 30 does not eliminate all medium and high
frequency noise, it has been found that a substantial reduction in
noise level by about 20 to 30 dB can be attained, which is
sufficient to bring the medium and high frequency noise down to a
tolerable level.
FIG. 9 is a cross-sectional view in elevation of an alternative
embodiment of the intake hood deflector 32 shown in FIG. 1.
Deflector 42 has a curved front surface 144 and opposed flat sides
146, one of which is shown in this sectional view. The top of
deflector 142 is open to form the entrance 28 for admitting air
into the combustion system. A conventional flange 148 is formed on
the rear periphery of deflector 142 for attaching it to the flange
of attenuator 30.
Positioned horizontally across the deflector 142 adjacent its rear
portion is a plurality of curved vanes 150. The ends of these vanes
are connected to the sides 146 of the deflector so that they span
the width of the deflector. The vanes 150 are positioned such that
their concave inner surfaces 152 face the downstream end of the air
ducting means from a flow standpoint, and thereby the inlet of
attenuator 30.
In operation, combustion air is admitted through entrance 28 and
flows around vanes 150 into attenuator 30 and then on to the rest
of the combustion system, in the manner previously described.
Noise, particularly in the low frequency range, which passes in
counter flow through attenuator 30 without being absorbed, will
attempt to escape via deflector 142. However, the vanes 150, by
virtue of covering the major part of the inlet flow path of
attenuator 30, act as relectors to reflect a substantial portion of
this long wavelength energy from their inner surfaces 152 back into
the system where its level is further reduced. This arrangement has
been found to have considerable effect in reduction of noise in the
low frequency range. Noise which does escape past the vanes 152 is
preferably deflected away from the operating personnel, here shown
as being in the upward direction by deflection by front surface
144.
The combustion system has been described as being sealed to reduce
the level of noise generated during operation. This construction
also serves to minimize and preferably eliminate the escape of
other potential pollutants such as dust, smoke, combustion gases,
and the like, to the atmosphere via the combustion system. This
concerns over the reduction of pollution is not solely associated
with combustion systems but carries over to other parts of
industrial driers and furnaces with which combustion systems are
used. Most designs being used to reduce or eliminate the escape of
pollutants include sealing off the remainder of these driers or
furnaces, except for exhaust stacks and chimneys where other
techniques for reducing pollution are employed. One adverse result
of virtually sealing off these driers and furnaces is that the
likelihood of explosions is enhanced. If an explosive atmosphere is
created within the drier or furnace, a spark or flame can cause
ignition and a resulting explosion, destroying or severly damaging
the equipment.
In accordance with the present invention, there is provided means
for relieving the pressure generated by an explosion. As embodied
herein, said relieving means includes a movable wall in duct 42
which is opened in response to the build-up of such pressure in the
drier or furnace in order to vent the explosion gases and thereby
reduce the pressure. Preferably, duct 42 has one panel 154 hinged
at 156, as shown in FIG. 3, so that it will swing open under such
excess pressures. Normally, panel 154 is kept in the closed
position shown by a magnetic closure comprising several magnets 158
mounted at spaced intervals along the edge of panel 154 and
corresponding metal holding plates 160 mounted at the top edge of
side panel 162. If necessary, a gasket (not shown) or similar
sealing material can be placed around the entire edge of panel 154
to insure a seal between this panel and the adjacent duct panels.
While only one section of duct 42 has been shown here with an
explosive venting construction, it should be understood that other
sections of duct 42 and the other ducts in the system can be
similarly constructed.
As mentioned previously, the recuperative operation of combustion
chamber 12 leads to an increase in efficiency and thereby a
substantial savings in fuel consumption. Additional savings by
virtue of a reduced operating cost is realizable by the provision
of damper 54 which serves to modulate the secondary combustion air.
During turndown operation, absent the damper, the exhaust fan in
the drier or furnace 14 will draw the same volume of air through
the system. Being able to modulate the flow of secondary combustion
air, the volume of air which is moved by the exhaust fan can be
reduced. This results in a lower operational cost from two
standpoints. First, the reduction of secondary air flow means that
there will be a considerably lower amount of air passing through
the drier or furnace and carrying off valuable heat. Secondly, the
horsepower at the fan required to draw this reduced volume of air
is obviously less than the horsepower required to draw the full
volume of air absent modulation and significant savings can
therefore be recognized by the reduction in electrical power
consumption. Although damper 54 is not essential to the combustion
system or its noise abatement properties, its incorporation can
lead to increased operating efficiency.
There are many applications of the aforedescribed apparatus where,
instead of feeding air into the air entrance 28 of the combustion
system 10, it is desirable to feed in a mixture of air and
combustible gaseous pollutants from a combustion process or other
source. Such an application may be suitable wherein a combustion
process is incomplete leaving combustible products in the exhaust
gas and wherein, for efficiency purposes as well as air
purification purposes, it is desired to recycle these combustion
products to burn off the unburned combustible products. Another
example of a suitable application is where dust or impure vapors
containing combustible materials are generated and where it is
desirable to preclude expulsion of this dust or combustible vapors
into the atmosphere. Rather than passing the dust or vapors through
a filtering system which removes and discards the pollutants, these
materials can be removed more economically. However, in both of the
above applications, care must be taken to prevent these gaseous
pollutants from adversely affecting the efficient operation of the
combustion system 10 and, particularly, the noise attenuator
30.
Turning now to FIG. 13, there is schematically illustrated a
combustion system 198 formed in accordance with one embodiment of
this invention. Gaseous pollutants are fed through an acoustic
attenuator, such as attenuator 30 described above, into a
combustion chamber such as chamber 12 (FIG. 3). While there are
many possible applications for a system of this type, one
application is in the production of asphalt road material. Since
the actual asphalt production process does not form a part of the
invention itself, there is no need to discuss the process in
detail. Let it suffice to say that in an asphalt plant operation
graded stone, sand and gravel are dried and heated to a temperature
in the range of 300.degree.-400.degree.F. in a rotary drier such as
drier 14 which is attached to the combustion chamber 12. The heated
aggregate is stored in the top section of a reservoir such as a
tower 200. When asphalt road material is required, selective
weights of the various types of grades of aggregate are discharged
from the top section of the tower 200 into a lower section 201
called a pug mill. At the same time preheated liquid asphalt is
sprayed onto stone, sand and gravel mixture and the asphalt and
aggregate are blended together in the pug mill 201 into a uniform
mixture. The blended mixture is discharged into a truck 202 to be
transported to its place of use.
When the asphalt mixture is discharged into the truck 202 a cloud
of blue smoke and other vapors are emitted from the asphalt mixture
as it leaves the tower outlet or discharge chute. In order to
prevent the escape of the blue smoke and vapors into the
atmosphere, one embodiment of this invention contemplates removing
the blue smoke and vapors and using them to advantage. In
accordance with the invention, gaseous pollutants are caused to
flow from a pollutant source to a combustion chamber to be burned.
As herein embodied, a gas collector is provided to serve as a gas
pollutant source. One specific type of collector can be seen in
FIG. 13, wherein an adjustable hood, such as a flexible bellows
enclosure 204 surrounds the discharge chute of the tower 200 and
storage unit of the truck 202 to prevent the blue smoke and vapors
from escaping to the atmosphere. The gaseous pollutants are
conveyed away from the mixing tower 200 through any suitable
ducting means 206 toward the combustion chamber.
Since the blue smoke will cool to some extent as it passes through
the ducts 206, it is possible that condensation will take place and
that a liquid asphalt mixture, or some substance of asphalt, will
be condensed on the ducts and in the acoustic attenuator 30. Such
condensation will contaminate the attenuator making it less
efficient and ineffective in certain frequency ranges.
In accordance with the invention, to prevent such an occurrence,
the gaseous pollutants are caused to pass through a heater before
entering the attenuator. While many types of heaters can be used,
as embodied herein, the heater shown is a conventional gas or
oil-fired burner 208 which has sufficient capacity to maintain the
temperature of the pollutants above their condensation point and
sufficiently high so that as they pass through the acoustic
attenuator 30, they do not condense. In the example described
herein where the gaseous pollutants are asphalt blue smoke and
vapor, the temperature of the gas preferably should be maintained
above the condensation point of the blue smoke air mixture which
depends upon the type of asphalt involved and other factors.
Normally, the gaseous pollutants would not have to have a
temperature greater than approximately 100.degree.-150.degree.F.
After being heated, the gaseous pollutants are conveyed to the
attenuator through a second ducting means, such as duct 209.
Further in accordance with the invention, means are provided for
causing the gaseous pollutants to flow from the gas collector
sequentially through the ducting means, heater, second ducting
means, attenuator and into the combustion chamber. As embodied
herein, one such suitable gas flow causing means is a combustion
system exhaust fan 210 which is conventionally employed with a
furnace or kiln. If it is found that the fan 210 is inadequate to
efficiently remove the pollutants from the gas collector, a booster
fan 211 can be added to the system at any appropriate location, for
example immediately upstream of the heater 208.
Because of the variable quantities of air passing through the duct
206 as a result of the variable characteristics of the seals of the
bellows enclosure 204 and other variable characteristics within the
system 198, an adjustable air inlet is provided to permit
controlled admission of combustion air into system in order to
provide a sufficient quantity of air to burn efficiently the
quantity of fuel that it is desired to burn in the combustion
chamber 12. As herein embodied, an atmospheric damper 212 is
provided in the ducting means 206 upstream from the heater 208 in
order to permit the admission of air into the system at a position
where the air can be heated so that the air does not cool the
gaseous pollutants to the condensation level in the acoustic
attenuator. The damper 212 preferably is provided with suitable
conventional controls 214 which can be automatically or manually
operated to permit the damper to be appropriately adjusted for
efficient buring in the combustion chamber 12.
While the gas collector is shown in FIG. 13 as a flexible bellows
204, it should be noted that if the furnace exhaust fan 210 alone
or together with the booster fan 211 provides adequate suction at
the outlet of the mixing tower 200 to pull all of the vapors and
blue smoke into the duct 206, the bellows or other suitable hood
may be eliminated.
In accordance with another form of the first embodiment of this
invention, another application of the use of a heater in
combination with a noise attenuated combustion system is in a
system which removes from further combustion all or some of the
gaseous products, resulting from a heating process. It is desirable
to reduce the amount of nitrous oxide produced in a fuel burning
system. It has been found that nitrous oxide production can be
reduced if the exhaust gases are mixed with incoming air in order
to introduce carbon dioxide nitrogen mixtures into the combustion
air. This embodiment contemplates providing a hood 216 or other gas
collector on the top of a kiln or furnace 14 which is connected
through suitable ducting means 218 and 206 to the heater 208 as
shown in FIG. 13. An adjustable damper 220 may be used to control
the quantity of exhaust gas recycled by this system.
While FIG. 13 illustratively shows both an asphalt mixing 200 and a
drier 14, which can be used for producing asphalt road material,
being connected to the heater 208 through suitable ducting means,
it is clear that either one alone could be so connected. If more
than one gas pollutant source is connected to the heater 208,
appropriate conventional gas flow control means, such as dampers,
may be used to selectively control the source and quantity of gas
pollutants admitted to the heater.
A second embodiment of this invention contemplates the use of the
heater as a burner for heating the gaseous pollutants above their
combustion temperature. For example, if the primary burner and
combustion chamber are not in operation, gaseous pollutants might
still be generated, such as when asphalt in a reservoir is being
dispensed to a truck resulting in the emission of blue smoke and
other vapors. In such a case, the heater 208 can serve as the
pollutant combustion chamber by raising the temperature of the
gaseous pollutants above their combustion temperature. To avoid
damaging the acoustic attenuator, the high temperature combustion
products leaving the heater flow through an attenuator by-pass
duct.
Turning now to FIG. 14, there is illustrated one specific
combustion system 250 incorporating this embodiment. As embodied
herein, the system 250 includes a heater or burner, such as a gas
or oil-fuel burner 252, having sufficient capacity to be able to
raise the temperature of gaseous pollutants above their combustion
temperature. Acoustic attenuator by-pass ducting means, for example
duct 254, provides gas flow communication between the downstream or
exhaust end of the burner 252 and an exhaust system which may
include the exhaust fan 256 of a furnace 14. Gas flow control means
is provided to permit the products of combustion from the burner
252 to flow selectively either to an acoustic attenuator, such as
attenuator 30, and combustion chamber, such as chamber 12, or to
by-pass the attenuator and flow directly to the exhaust fan 256 and
out to the atmosphere through a flue 258. A suitable flow control
means is a manual or motor controlled damper 260 shown in position
to close off the duct leading to the attenuator 30. The phantom
lines indicate the position of the damper 260 which closes off the
duct 254 allowing gases leaving the burner 252 to flow to the
attenuator 30.
When the combustion chamber 12 is fired and in operation, the gas
pollutants are heated by the burner 252 to a temperature above
their condensation point. The damper 260 is positioned to close the
attenuator by-pass duct 254 and the exhaust fan 256 causes the
heated gaseous pollutants to pass through the duct 262 leading to
the acoustic attenuator 30 and into the combustion chamber 12 where
the temperature is above the combustion temperature of the gaseous
pollutants. The pollutants are oxidized in the combustion chamber
and enter the furnace 14 and then exist through the flue 258.
When the combustion chamber 12 is not operating, the damper 260 is
positioned to close the duct 262 leading to the attenuator 30
thereby opening the attenuator by-pass duct 254. This is to prevent
the hot gases from entering the attenuator which would be adversely
effected by such temperatures. The burner 252 is operated at a
temperature level above the combustion temperature of the gaseous
pollutants (approximately 1,400.degree. to 1,600.degree.F) thus
effecting burning of the pollutants. The exhaust fan 256 then
causes the products of combustion to exit from the system, such as
through the furnace flue 258.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit or
scope of the invention.
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