U.S. patent application number 11/471861 was filed with the patent office on 2007-12-27 for exhaust gas stack.
Invention is credited to Dipti Datta.
Application Number | 20070298700 11/471861 |
Document ID | / |
Family ID | 38874098 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070298700 |
Kind Code |
A1 |
Datta; Dipti |
December 27, 2007 |
Exhaust gas stack
Abstract
An exhaust gas stack includes an elongate, tubular stack member
having inlet and outlet ends and a central longitudinal axis. An
end section is mounted on the outlet end and has open first and
second ends, the first end connected to the outlet end of the stack
member and a frustoconical passage extending between these ends. An
inner duct section has a central axis co-axial with the axis of the
stack member and is mounted centrally in the end section. An
annular gas passage is formed between the duct section and the end
section. An air plug is movable between an open position at which
exhaust gases can flow through the inner duct section and another
position at which the plug restricts or prevents passage of exhaust
gases through this duct section. An actuator is connected to the
plug in order to move it between an open and other positions.
Inventors: |
Datta; Dipti; (Mississauga,
CA) |
Correspondence
Address: |
GIFFORD, KRASS, SPRINKLE,ANDERSON & CITKOWSKI, P.C
PO BOX 7021
TROY
MI
48007-7021
US
|
Family ID: |
38874098 |
Appl. No.: |
11/471861 |
Filed: |
June 21, 2006 |
Current U.S.
Class: |
454/1 ;
110/184 |
Current CPC
Class: |
F23J 2900/13003
20130101; F23J 13/08 20130101; E04F 17/02 20130101; F23L 17/02
20130101 |
Class at
Publication: |
454/1 ;
110/184 |
International
Class: |
E04F 17/02 20060101
E04F017/02; F23J 11/00 20060101 F23J011/00 |
Claims
1. An exhaust gas stack comprising: an elongate, tubular stack
member having an inlet end, an outlet end, a central longitudinal
first axis, and an exhaust gas passage extending between said inlet
and outlet ends, said stack member adapted to extend vertically
with said inlet end being a bottom end when said exhaust gas stack
is installed for use; an end section mounted on said outlet end and
having open first and second ends and a frustoconical passage
extending between the first and second ends, said first end being
connected to the outlet end of said stack member; an inner duct
section, which is substantially circular in transverse
cross-section, has a first duct end, an open second duct end, and a
central, longitudinal axis coaxial with said first axis, said duct
section being mounted centrally in said passage in the end section
whereby a gas flow passage is formed around the duct section and
between the duct section and the end section, said duct section
having a first axial portion adjacent said first duct end and a
second axial portion adjacent said second duct end with the two
axial portions meeting at an annular junction of reduced diameter
relative to the diameter of said first axial portion at said first
duct end; an air plug member movable between an open position at
which exhaust gases can flow past said plug member and through said
inner duct section and another position at which said plug member
restricts or prevents flow of exhaust gases through said inner duct
section; and an actuator connected to said plug member and capable
of moving said plug member between said open position and said
closed position.
2. An exhaust gas stack according to claim 1 wherein an annular
duct wall forming said first axial portion of the inner duct
section curves radially inwardly and upwardly as seen in
cross-section through said central, longitudinal axis of the duct
section and said second axial portion has a frustoconical shape
which diverges upwardly from said annular junction.
3. An exhaust gas stack according to claim 2 wherein said plug
member has a hemispherical top portion with a convex exterior
surface directed upwardly during use of said stack and a
substantially cylindrical skirt extending from said top portion
towards the inlet end of the stack member.
4. An exhaust gas stack according to claim 3 wherein a section of
said convex exterior surface of the plug member extends parallel to
and is spaced apart from said annular duct wall when said plug
member is in the open position.
5. An exhaust gas stack according to claim 1 wherein an elongate
central airflow-defining member is mounted in said stack member,
extends along at least a substantial major portion of said
longitudinal first axis, and has a top end arranged adjacent said
air plug member.
6. An exhaust gas stack according to claim 5 wherein said airflow
defining member has a substantially cylindrical exterior shell made
of sheet metal perforated with numerous small holes distributed
over at least a substantial major portion of the exterior shell and
containing sound attenuating material arranged within said exterior
shell in the region of said numerous small holes.
7. An exhaust gas stack according to claim 1 wherein said actuator
includes a linear actuator unit mounted in said stack member along
the longitudinal first axis and an elongate connecting member
extending from said actuator unit to said plug member and
operatively connected to said actuator unit so as to be axially
movable thereby in order to move said plug member between said open
position and said closed position.
8. An exhaust gas stack according to claim 5 wherein said actuator
includes a linear actuator unit mounted in said airflow-defining
member, and said exhaust gas stack includes an electronic
controller for controlling operation of said linear actuator and a
sensor located at said end section for measuring velocity pressure
of exhaust gases flowing from said end section and generating an
electrical signal indicative thereof, said sensor being
electrically connected to said controller and wherein said
controller is programmed to operate said actuator unit from
electrical input that includes said electrical signal so as to move
said plug member to a controller calculated position amongst a
range of positions between said open and closed positions in order
to seek or maintain desired airflow velocity for the exhaust gases
flowing from said end section of the stack.
9. An exhaust stack according to claim 8 wherein said airflow
defining member has a substantially cylindrical exterior shell made
of sheet metal perforated with numerous small holes distributed
over at least a substantial major portion of the exterior shell and
containing sound attenuating material arranged within said exterior
shell in the region of said numerous small holes.
10. An exhaust stack according to claim 1 including an air
induction collar extending around and mounted on said end section,
said collar during use of said exhaust stack providing induction of
outside air into the flow of exhaust gases from said second end of
the end section.
11. A velocity control apparatus for use at a top end of an exhaust
stack, said apparatus comprising: a hollow member adapted for
mounting on said top end of the exhaust stack and having open first
end, an open second end of smaller diameter than the first end, and
a frustoconical passage extending between the first and second
ends, said first end being connected to said top end during use of
said apparatus; an inner duct section having a first duct end, an
open second duct end, and a central longitudinal axis which is
aligned with a central longitudinal axis of said exhaust stack when
said apparatus is mounted on the exhaust stack, said duct section
being mounted centrally in said hollow member whereby a gas flow
passage is formed around the duct section and between the duct
section and the hollow member; an air plug member movable between
an open position at which exhaust gases can flow past said plug
member and through said inner duct section and another position at
which said plug member restricts or prevents flow of exhaust gases
through said inner duct section and thereby at least reduces the
amount of exhaust gases flowing through said inner duct section
during use of said apparatus; and an actuator connected to said
plug member and adapted to move said plug member between said open
and said another position.
12. A velocity control apparatus according to claim 11 wherein said
inner duct section has a first axial portion adjacent said first
duct end and a second axial portion adjacent said second duct end,
the two axial portions meet at an annular junction of reduced
diameter relative to the diameter of said first axial portion at
said first duct end, and said second axial portion has a
frustoconical shape which diverges in an axial direction away from
said junction.
13. A velocity control apparatus according to claim 11 wherein said
plug member has a hemispherical top portion with a convex exterior
surface directed upwardly during use of said apparatus and a
substantially cylindrical skirt extending from said top portion
towards an inlet end of the exhaust stack during use of said
apparatus.
14. A velocity control apparatus according to claim 11 wherein said
actuator includes a linear actuator unit adapted for mounting in
said exhaust stack and an elongate connecting member capable of
extending from said actuator unit to said plug member and of being
connected to said actuator unit so as to be movable lengthwise
thereby in order to move said plug member between said open
position and said another position.
15. A velocity control apparatus according to claim 11 wherein said
actuator includes a linear actuator unit adapted for mounting in
said exhaust stack and said apparatus further includes an
electronic controller for controlling operation of said linear
actuator and a sensor for measuring velocity pressure of exhaust
gases flowing from said hollow member and generating electrical
input signals indicative thereof, said sensor being electrically
connected to said controller, and wherein said controller is
programmed to operate said actuator unit upon receiving said
electrical signals so as to move said plug member to a controller
calculated position amongst a range of possible positions between
said open position and said another position in order to seek or
maintain a desired airflow velocity for the exhaust gases flowing
from said hollow member.
16. An exhaust gas stack comprising: an elongate, tubular stack
member having an inlet end, an outlet end, and an exhaust gas
passage extending between said inlet and outlet ends, said stack
member adapted to extend vertically upwardly from said inlet end
when said stack is installed for use, said stack member including
an exterior wall, an interior wall made of perforated sheet metal
having numerous small holes distributed over its surface and spaced
inwardly from said exterior wall, and sound attenuating material
sandwiched between said exterior wall and said interior wall; an
elongate central airflow defining member mounted in said stack
member and having a central, longitudinal axis which is coaxial
with a central, longitudinal axis of said stack member, said
exhaust gas passage being an annular passage along the length of
the airflow defining member, said airflow defining member having a
sheet metal exterior shell perforated with numerous small holes
distributed over at least a substantial portion of the exterior
shell and containing sound attenuating material arranged within
said exterior shell; an end section mounted on said outlet end of
the stack member and having an open first end, an open second end,
and a frustoconical passage that tapers upwardly from the first end
to the second end, said first end being connected to the outlet end
of the stack member; and an exhaust gas velocity control mechanism
having an inner duct section which is coaxial with and mounted in
said end section and an air plug member movable between an open
position at which exhaust gases can flow through said inner duct
section and another position at which said plug member restricts or
prevents passage of exhaust gases through said inner duct section,
a further passage being formed around said inner duct section
between this duct section and the end section.
17. An exhaust gas stack according to claim 16 wherein said control
mechanism includes a linear actuator connected by an elongate
connecting member to said plug member and capable of moving said
plug member between said open position and said another position,
said linear actuator is mounted in a lower portion of said airflow
defining member, and said connecting member extends along said
longitudinal axis of the airflow defining member.
18. An exhaust gas stack according to claim 16 wherein said air
plug member has a rounded top portion adapted to engage an interior
surface of said inner duct section in said another position and a
substantially cylindrical skirt portion extending from said top
portion towards said inlet end of the stack member and wherein said
exterior shell of said airflow defining member is substantially
cylindrical and has a substantially hollow upper portion, said
skirt portion being mounted for telescoping, sliding movement in
said hollow upper portion.
19. An exhaust gas stack according to claim 16 including a drain
system for draining off water that enters an upper portion of the
airflow defining member via the second end of said end section,
wherein an inlet of said drain system is arranged above the
substantial portion of the exterior shell containing sound
attenuating material.
Description
BACKGROUND OF THE INVENTION
[0001] The present disclosure is directed to exhaust gas stacks and
to apparatus and devices for controlling the velocity of exhaust
gases exiting from exhaust stacks.
[0002] A variety of exhaust gas stacks and exhaust ducts are known
in industry for the purpose of exhausting gases from sources such
as furnaces. Vertical exhaust stacks can vary in height and in some
cases can be of substantial height. Existing conventional exhaust
gas stacks are generally constant geometry (fixed discharge area)
devices. In many cases, such stacks are sized so as to maintain
approximately 4,000 fpm velocity at the stack discharge at the
maximum flow rate for the particular exhaust application in order
to diffuse the exhaust gases into the atmosphere as required by
local building codes.
[0003] With a conventional stack design, the velocity of the gases
at the stack discharge will drop when the airflow volume changes to
lower than maximum since the discharge area of the stack remains
constant. To explain further, in the case of an exhaust stack for
the removal of air from a number of laboratories, the airflow rate
for the exhaust will be reduced when fewer laboratories are being
used since fewer laboratories will generate a lower amount of
exhaust air flow. One known method of overcoming this difficulty is
the introduction of outside air into the exhaust air system in
order to bring the total flow rate to the maximum design value for
the system, thereby maintaining the required discharge velocity at
the top end of the stack. This is accomplished by using outside air
dampers with the air intake plenum. As the exhaust air quantity
drops, these dampers are opened to introduce outside air into the
fan inlet chamber so that the fan delivers constant airflow at all
times. However, the operation of this exhaust system is not energy
efficient.
[0004] Another concern with a standard exhaust stack design is the
amount of noise that eminates from the exhaust stack. This is
becoming a more significant problem for industry and for
laboratories because the allowable noise levels that can be
radiated to the environment is becoming more restricted by local
by-laws and other legislation.
[0005] Various systems for throttling or controlling the flow of
exhaust gases from a chimney or stack are provided in the patent
literature. For example, U.S. Pat. No. 3,978,776 to R. Kausche
describes an exhaust gas chimney which, at its top end, is fitted
with a first upwardly converging funnel having an outlet for the
flow of exhaust gases and a second upwardly converging funnel
co-axial with the first funnel but of smaller size. There is a
mechanism for moving the funnels relative to each other for
throttling the flow of exhaust gases between the funnels. In a
closed position, the funnels adjoin each other to form an outlet of
a size smaller than the outlet of the first funnel.
[0006] U.S. Pat. No. 3,537,411 to J. R. Roy describes a double
shelled chimney stack made with a metal load-bearing outer shell
and a nonload-bearing, gas conveying metal inner shell. A
hermetically sealed annular air space between the shells provides
insulation. This air space comprises a plurality of axially spaced
annular spaces located between the shells and the top of the stack
has a frustoconical cap for increasing the velocity of the
gases.
SUMMARY OF THE PRESENT DISCLOSURE
[0007] The present disclosure provides an advantageous exhaust gas
stack for emitting exhaust gases into the atmosphere and an
advantageous velocity control apparatus for use at the top end of
an exhaust stack which is able to adjust or control the exit
velocity of exhaust gases. As will be apparent from the following
detailed description and appended figures that follow, the present
disclosure provides, inter alia, the following advantageous
advances to the field of stacks or chimneys for exhaust gases:
[0008] (a) An exhaust gas stack or a velocity control apparatus for
use with such a stack wherein the net opening area of the stack can
be varied in order to maintain a predetermined exhaust airflow
velocity at the outlet of the stack; [0009] (b) An exhaust gas
stack with sound attenuating features that enable quiet operation;
and [0010] (c) An exhaust gas stack that provides energy efficiency
as it can permit the use of an exhaust fan powered by a smaller
motor, i.e. lower horsepower motor than the fan/motor combination
required by a conventional exhaust gas stack designed for similar
exhaust airflow rates.
[0011] According to an exemplary embodiment of the present
disclosure, an exhaust gas stack comprises an elongate, tubular
stack member having an inlet end, an outlet end, a central
longitudinal first axis and an exhaust gas passage extending
between the inlet and outlet ends. The stack member is adapted to
extend vertically with the inlet end being a bottom end when the
exhaust gas stack is installed for use. An end section is mounted
on the outlet end and has an open first end, an open second end of
small diameter than the first end, and a frustoconical passage
extending between the first and second ends. The first end is
connected to the outlet end of the stack member. An inner duct
section, which is substantially circular in transverse
cross-section, has a first duct end, an open second duct end, and a
central longitudinal axis co-axial with the first axis. The duct
section is mounted centrally in the passage of the end section
whereby an annular gas flow passage is formed between the duct
section and the end section. The duct section has a first axial
portion adjacent the first duct end and a second axial portion
adjacent the second duct end with the two axial portions meeting at
an annular junction of reduced diameter relative to the diameter of
the first axial portion at the first duct end. An air plug member
is movable between an open position at which exhaust gases can flow
past the plug member and through the inner duct section and another
position at which the plug member restricts or prevents flow of
exhaust gases through the inner duct section. An actuator is
connected to the plug member and is capable of moving the plug
member between the open position and the closed position.
[0012] In one embodiment of this exhaust gas stack, an annular duct
wall forming the first axial portion of the inner duct section
curves radially inwardly and upwardly as seen in cross-section
through the central, longitudinal axis of the duct section and the
second axial portion has a frustoconical shape which diverges
upwardly from the annular junction.
[0013] According to another exemplary embodiment of the present
disclosure, a velocity control apparatus for use at a top end of an
exhaust fan includes a hollow member adapted for mounting on the
top end of the exhaust stack and having an open first end, an open
second end of smaller diameter than the first end, and a
frustoconical passage extending between the first and second ends.
The first end of this member is connected to the top end of the
stack during use of the apparatus. An inner duct section is also
provided and this section has a first duct end, an open second duct
end, and a central longitudinal axis which is aligned with the
central longitudinal axis of the exhaust stack when the apparatus
is mounted on the exhaust stack. The duct section is mounted
centrally in the hollow member whereby an annular gas flow passage
is formed between the duct section and the hollow member. An air
plug member is movable between an open position at which the
exhaust gases can flow past the plug member and through the inner
duct section and another position at which the plug member
restricts or prevents flow of the exhaust gases through the inner
duct section and thereby at least reduces the amount of exhaust
gases flowing through the inner duct section during use of this
apparatus. The apparatus includes an actuator connected to the plug
member and adapted to move the plug member between the open and
another position.
[0014] According to one version of this embodiment, the actuator
includes a linear actuator unit adapted for mounting in the exhaust
stack and an elongate connecting member capable of extending from
the actuator unit to the plug member and being connected to the
actuator unit so as to be movable lengthwise thereby in order to
move the plug member between the open position and the another
position.
[0015] According to yet another exemplary embodiment of the present
disclosure, an exhaust gas stack includes an elongate, tubular
stack member having an inlet end, an outlet end, and an exhaust gas
passage extending between the inlet and outlet ends. The stack
member is adapted to extend upwardly from the inlet end when the
stack is installed for use. The stack member includes a tubular
exterior wall, an interior wall made of perforated sheet metal
having numerous small holes distributed over its surface and spaced
inwardly from the exterior wall, and sound attenuating material
sandwiched between the exterior wall and the interior wall. An
elongate, airflow defining member is mounted in the stack member
and has a central longitudinal axis which is co-axial with a
central longitudinal axis of the stack member. The exhaust gas
passage is an annular passage along the length of the airflow
defining member. The airflow defining member has a sheet metal
exterior shell perforated with numerous small holes distributed
over at least a substantial portion of the exterior shell and
containing sound attenuating material arranged within the exterior
shell. There is also an end section mounted on the outlet end of
the stack member and having an open first end, an open second end
of smaller diameter than the first end, and a frustoconical passage
extending between the first and second ends. The first end is
connected to the outlet end of the stack member. There is also
provided an exhaust gas velocity control mechanism having an inner
duct section which is co-axial with and mounted in the passage of
the end section. An air plug member is movable between an open
position at which exhaust gases can flow through the inner duct
section and another position at which the plug member restricts or
prevents passage of exhaust gases through the inner duct section. A
further passage is formed around the inner duct section between
this duct section and the end section.
[0016] These and other aspects of the disclosed exhaust gas stacks
and velocity control apparatus for use on an exhaust stack will
become more readily apparent to those having ordinary skill in the
art from the following detail description taken in conjunction with
the accompanying-drawings.
BRIEF DESCRIPTON OF THE DRAWINGS
[0017] So that those having ordinary skill in the art to which the
present disclosure pertains will more readily understanding how to
make and use the subject invention, exemplary embodiments thereof
will be described in detail herein below with reference to the
drawings, wherein:
[0018] FIG. 1 is an elevational view along an axial cross-section
of an exemplary exhaust gas stack according to the present
disclosure, this view showing an air plug member in a fully closed
position;
[0019] FIG. 2 is an elevational view along an axial cross-section
similar to FIG. 1, this view showing the plug member in a fully
open position;
[0020] FIG. 3 is a top view of the top end of the exhaust gas stack
of FIG. 1;
[0021] FIG. 4 is a horizontal cross-section along the line IV-IV of
FIG. 1;
[0022] FIG. 5 is a horizontal cross-section taken along the line
V-V of FIG. 1;
[0023] FIG. 6 is a side view of an upper section of an exhaust gas
stack which has been fitted with an induction collar mounted at the
top end of the stack;
[0024] FIG. 7 is an elevational view of two exemplary exhaust gas
stacks mounted one beside the other with the stacks being shown in
axial cross-section and mounted on top of a housing and respective
vane-axial fans; and
[0025] FIG. 8 is a schematic elevational view of the exhaust gas
stack showing booster relay and control connections.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0026] FIGS. 1 and 2 illustrate one exemplary embodiment of an
exhaust gas stack constructed in accordance with the present
disclosure. This exhaust gas stack includes an elongate, tubular
stack member 12 having an inlet end 14, an outlet end 16, a central
longitudinal first axis indicated at A and exhaust gas passage 18
extending between the inlet and outlet ends. The stack member is
adapted to extend vertically with the inlet end being a bottom end
when the stack is installed for use. The illustrated embodiment of
the stack member has an exterior wall 20 which can be made of
imperforate sheet metal such as sheet steel having sufficient
thickness and strength to support the weight of the stack and
external forces acting thereon such as wind. The illustrated stack
member 12 has a square, horizontal cross-section defined by this
exterior wall but it will be appreciated that the exterior
horizontal cross-section can also be circular along the entire
length of the stack member. Spaced inwardly from each side of the
exterior wall is an interior wall 22 which can be made of
perforated sheet metal having numerous small holes distributed over
its surface. The interior wall can also be made of sheet steel. The
interior wall can be connected to the exterior wall by means of
suitable connecting brackets (not shown). The space 24 between each
interior wall and the exterior wall can be filled with sound
attenuating material in order to reduce the level of sound that
eminates from the stack. Common forms of sound attenuating material
that can be used include fiberglass batting and mineral wool. This
material is protected from rainwater or other moisture in the stack
by a moisture proof plastic barrier layer that extends between this
material and the interior wall 22. Suitable plastic materials for
this purpose are those sold under the trademarks TEDLAR.TM. AND
MYLAR.TM.. These materials do not interfere significantly with the
sound attenuation. Horizontal bars or tubes 26 mounted in the space
between the interior and exterior walls can help support the sound
attenuating material in each side wall of the stack. Arranged at
the top end or outlet end of the stack member is an end section 28,
this end section having an open first end 30, an open second end 32
of smaller diameter than the first end, and a central axis which is
co-axial with the axis A. The first end is connected to the outlet
end 16 of the stack member. Preferably the end section 28 is
tapered from its first end 30 to its second end as shown. More
preferably the end section 28 has a frustoconical exterior. Like
the stack member, the end section 28 can also be of double-walled
construction. Thus, in the illustrated embodiment, the end section
has an imperforate exterior wall 36 which forms a small acute angle
with the vertical plane on each of the four sides of the stack and
a perforated interior wall 38, the latter forming a frustoconical
gas passage. Again, sound attenuating material can be stuffed or
placed in the space 40 formed between the interior and exterior
walls. The interior and exterior walls can be connected to each
other by means of horizontally extending metal tubes 42 located at
the top and bottom ends of these walls.
[0027] As part of a velocity control apparatus for the stack 10,
there is provided an inner duct section indicted generally at 44.
This duct section can be substantially circular in transverse
cross-section and has a first duct end 46, an open second duct end
48 and a central longitudinal axis co-axial with the first axis A.
This duct section 44 is mounted centrally in the passage of the end
section 28 whereby an annular gas flow passage is formed between
the duct section and the end section, this passage indicated at 50.
The duct section 44 has a first axial portion 52 adjacent the first
duct end and a second axial portion 54 adjacent the second duct
end, with the two axial portions meeting at an annular junction 56
of reduced diameter relative to the diameter of the first axial
portion at the first duct end 46. The first axial portion 52 of the
inner duct section curves radially inwardly and upwardly as shown
in FIGS. 1 and 2, that is, in cross-section through the central
longitudinal axis of the duct section. A lower section of the first
axial portion can extend vertically from the first duct end before
the wall of the duct section curves inwardly. Also, in the
embodiment of FIG. 1, the second axial portion 54 has a
frustoconical shape which diverges upwardly from the annular
junction 56. The annular junction can form a rounded interior
surface as shown. The top end 48 of the duct section can be aligned
with the top or second end 32 of the end section 28. The first or
lower duct end 46 of the duct section can project a short distance
into the stack member 12.
[0028] The stack is fitted with an air plug member 60 which is
movable between an open position at which exhaust gases can flow
past the plug member and through the inner duct section 44 and a
closed position at which the plug member engages an interior
surface of the inner duct section at the annular junction and
thereby prevents exhaust gases from flowing through the inner duct
section. The open position of the air plug member is shown in FIG.
2 while the closed position is shown in FIG. 1. An actuator 62 is
connected to the plug member 60 and is capable of moving the plug
member between the open position and the closed position. In the
illustrated embodiment, the plug member has a hemispherical top
portion 64 with a convex exterior surface directed upwardly during
use of the stack. This plug member also has a substantially
cylindrical skirt 66 extending from the top portion towards the
inlet end of the stack member. A flat, horizontal plate 68 can
extend across the bottom of the top portion 64 and provide
structural rigidity to the plug member, as well as an attachment
point for the actuator 62. The plug member can also be made of a
sheet metal such as sheet steel. In an exemplary embodiment of the
stack, the convex exterior surface of the plug member extends
parallel to but is spaced apart from the annular duct wall of the
duct section 44 where the duct wall curves inwardly when the plug
member is in the open position. This relationship can be seen
clearly in FIG. 2. Thus, in the open position, exhaust gases can
flow smoothly through the annular gap 70 which is of substantially
uniform width and smoothly curved.
[0029] The actuator 62 can be a linear actuator unit and can be
mounted in the stack member along the longitudinal first axis A. In
an exemplary embodiment, the actuator is a pneumatic actuator but
it is also possible to use an electric operator or a hydraulic
actuator. It will be understood that the pneumatic actuator is
provided with pressurized air from a source of pressurized air by
pressurized air line 170 (see FIG. 8). Although the illustrated
actuator 62 is shown mounted near the inlet end 14 of the stack, it
will be appreciated that it is also possible to mount the actuator
further up the stack and closer to the plug member if desired. By
mounting the actuator in the position shown, it can be easier to
access the actuator for repair or replacement and to make the
necessary connections for its support and operation. The movable
rod of the actuator which extends from its top end is connected to
an elongate connecting member 72 which can be a solid metal rod of
one inch diameter. The member 72 is operatively connected to the
actuator unit so as to be axially movable thereby in order to move
the plug member between its open and closed positions. The rod
member 72 can be slidably supported along its length by several
bushings 73 which are rigidly mounted in a central airflow defining
member 100 (described below) by means of braces 75. The exhaust
stack can include an electronic controller 80 for controlling
operation of the linear actuator and a flow sensor 76 located in
the end section 28 for measuring the velocity of exhaust gases
flowing from this end section and generating an electrical signal
indicative thereof. The controller in one embodiment is a model
CSC-3000 series volume reset controller sold by KMC Controls.
[0030] The flow sensor 76 can be a pitot tube such as Dwyer Model
160-8. The purpose of the sensor 76 is to provide a means to
measure the velocity pressure, which can then be converted to
velocity. This known type of sensor has two parts, one for
measuring the total pressure and the other for measuring the static
pressure. The difference between these two measurements is the
velocity pressure. In one version, the flow sensor is mounted 5
inches radially in from the edge of the stack, flush with the top
end 32 of the end section 28. Wires 78 and 79 shown in FIG. 8 can
connect the sensor 76 to the electronic controller 80 which can be
suitably housed at the bottom end of the stack. The controller can
be a microprocessor or a programmable computer, which can be of
standard construction. The controller 80 is programmed to operate
the actuator unit 62 from electrical inputs that include the
electrical signals from the sensor 76 so as to move the plug member
to a controller calculated position amongst a range of positions
between the open and closed positions in order to seek or maintain
a desired airflow velocity for the exhaust gases flowing from the
end section 28. In one version of the sensor 76, it has a total
pressure connection which is connected by line 78 to the "H"
terminal on the controller and has a static pressure connection
which is connected by line 79 to the "L" terminal on the controller
80. The pitot tube line and head for measuring total pressure are
represented by line 190 in FIG. 8. It will be seen that this line
terminates outside the end section 28 of the stack. In an exemplary
embodiment of the present exhaust stack and its controller, the
position of the plug member 60 is adjusted so as to vary the net
open area at the top end of the exhaust stack in order to maintain
a selected constant velocity at all exhaust air flow rates. Thus,
for example, in one exemplary embodiment, the exhaust airflow rate
can vary from 9,000 fpm to 26,400 fpm while the velocity control
apparatus, including the aforementioned controller, is able to
maintain a velocity discharge of about 4,000 fpm at all of the
operating levels in this range.
[0031] With reference now to the detail drawings of FIGS. 3 to 5,
FIG. 3 illustrates features at the top end of the frustoconical end
section 28. The round second duct end 48 of the inner duct section
is supported on four sides by four braces 84 which can be made of
1/4 inch flat bar. In one embodiment, the diameter of the end 48 is
22.5 inches while the diameter of the round top of end section 28
is at least 32.5 inches. The outer end of each brace 84 can be
welded or bolted (by means of a connecting flange) to the
perforated interior wall 38 which has a frustroconical shape and a
round, horizontal top. As illustrated, the exterior wall 36 has a
frustroconical shape with this wall extending parallel to the
interior wall 38. Alternatively, the exterior wall 36 can be
constructed so as to have four sides with opposite sides converging
in the upwards direction.
[0032] The cross-section of FIG. 4 shows the cross-section of the
stack member about midway along its height. As illustrated, the
stack member has a square, exterior horizontal cross-section formed
by four sides of exterior wall 20 made of sheet metal. However, the
perforated interior wall 22 has a circular horizontal
cross-section. Extending inwardly from the interior wall 22 are
four metal braces 86 which again can be welded or bolted to the
interior wall and can be made of 1/4 inch flat bar. The inner ends
of these braces can be rigidly connected to a reinforcement ring 88
which provides support for an elongate, central, cylindrical tube
90. The tube 90 has a central longitudinal axis which is co-axial
with the central axis A. The tube 90 forms a hollow passage through
which passes the connecting member or rod 72.
[0033] FIG. 5 shows a horizontal cross-section similar to that of
FIG. 4, with this cross-section being further down on the stack
member. Shown in this view is a further set of four braces 92 which
are connected at their outer ends to the interior wall 22. The
inner ends of these braces are connected to a reinforcement ring 94
which also is used to support the tube 90. There can also be
mounted on the exterior wall in the vicinity of the braces 92,
horizontal, tubular frame members 96 which are connected to one
another at the corners of the stack.
[0034] The illustrated embodiment of the gas stack also has the
aforementioned elongate, central airflow defining member 100 which
has a substantially cylindrical exterior shell 102 made of sheet
metal perforated with numerous small holes distributed over at
least a major portion of this shell. The member 100 can extend from
a bottom end 104 located in the region of the inlet end 14 of the
stack to a top end 106 located in the region of the top of stack
member 12 and adjacent to the plug member. In order to reduce sound
emitted from the stack, sound attenuating material 108 can be
arranged within the exterior shell in the region where the numerous
small holes of the shell are located. In order to protect the
material 108 from moisture or rain entering the stack, a moisture
proof plastic barrier layer (not shown) is arranged between the
material 108 and the exterior shell 102. One suitable known plastic
layer is sold under the trademark TEDLAR.TM. and another suitable
material is sold under the trademark MYLAR.TM.. These plastic
layers still allow sound attenuation to take place. It will be
understood that if quiet operation of the stack is not required,
then the sound attenuating material, which can be fiberglass
batting or mineral wool, can be omitted and the shell 102 entirely
can be made of imperforate sheet metal. As illustrated, the top of
the portion of member 100 containing the material 108 can be closed
by horizontal metal plate 110 while the bottom of this portion can
be closed by a round, horizontal plate 112. Each of these plates is
fitted with a central hole for passage of the elongate rod 72. A
bottom portion of the member 100 forms a cylindrical hollow chamber
114 which accommodates the actuator 62. Also, located in this
chamber is an actuator support 116. An upper portion 118 of the
member 100 is also hollow and is open at the top. The
aforementioned skirt 66 of the plug member extends into this upper
portion and is able to move upwardly or downwardly therein. The
cylindrical exterior surface of the skirt 66 is preferably sized
and arranged to be close to the interior surface of the upper
portion of member 100 and, in the lowermost position of the plug
member shown in FIG. 2, the skirt 66 can be immediately adjacent
the interior surface of the shell which is slightly tapered in the
downward direction.
[0035] It will be seen that the airflow defining member 100 has a
central, longitudinal axis which is coaxial with the central,
longitudinal axis A of the stack member. Furthermore, the exhaust
gas passage 18 is an annular passage along the length of this
airflow defining member. As shown in FIGS. 1 and 2, in an exemplary
embodiment of the stack, the transverse width or the diameter D of
the airflow defining member increases gradually in the axial
direction towards the outlet end of the stack member. By
restricting the effective width of the exhaust gas passage 18 in
this manner, the velocity of the exhaust gases in the exhaust stack
can be maintained and even increased, thereby assisting in
maintaining the required exit velocity of the exhaust gases at the
top end of the stack. Also, at the bottom end of the stack, the
effective width W of the annular passage around the airflow
defining member should be sufficiently large to receive the airflow
coming from the fan outlet when a fan unit is mounted below the
stack (such as shown in FIG. 7 and described below). However, it
can be desirable to have the airflow defining member wider at its
top end in order to accommodate the skirt 66 and a reasonably wide
plug member. As indicated, the narrowing of the effective width of
the annular passageway at the top end of the stack member causes
the airflow velocity to increase at the top end which is desirable
to expel the exhaust gases upwards into the atmosphere as much as
possible.
[0036] FIG. 7 illustrates the possible use of twin exhaust gas
stacks arranged one beside the other, these stacks being indicated
by references 120 and 122. FIG. 7 also illustrates the manner in
which an exhaust stack of the present disclosure can be mounted
according to a typical installation and how an exhaust stack of
this type can be mounted in conjunction with air handling and air
treatment components. Shown in FIG. 7 is a portion of a roof slab
124 which is a portion of the roof of a building which has not been
illustrated. This building can be an industrial building, factory
or laboratory. Located in the building is an air handling housing
126 which can have access doors 128 as shown. There can be located
in the housing 126 heat recovery coils and air filters (not shown)
which can be of standard construction. Mounted on a suitably strong
roof 130 of the housing are two vane-axial fan units 132 and 136.
In a system employing only a single exhaust stack, there would
normally only be a single fan unit. Although a vane-axial fan unit
is illustrated, it is also possible for the fan unit to be a
centrifugal fan in which case the fan outlet is generally
rectangular and a transition section is provided then in the
exhaust stack to change from a rectangular internal cross-section
to a circular internal cross-section. In a known manner, each fan
unit can be mounted by means of a coil spring system indicated at
138 which reduces vibration from the operation of the fan. Mounted
on top of each fan unit (which is the outlet side) is a respective
one of the exhaust gas stacks 120, 122.
[0037] Mounted on the outside of each exterior wall 20 of each
stack is a mounting flange 140 which can be a four sided flange
with a square periphery, this flange extending along the sides of
its respective stack which can have a square, horizontal
cross-section along at least a lower section extending from the
bottom end of the stack member to the flange. Suitable stack
supporting sleeves 142, 144 can be mounted on the roof 124 and each
extends around an opening 146 in the roof. Each mounting flange can
be connected by means of nuts and bolts to a connecting flange
provided on the top end of each sleeve 142, 144. The portion of the
stack member above the mounting flange 140 can either have a
circular exterior cross-section or a square exterior cross-section.
It is also possible for the exterior of the stack to have a
circular cross-section throughout the entire length of the stack
member 12.
[0038] FIG. 6 illustrates an optional feature that can be fitted on
the present exhaust gas stack 10. In particular, there can be
provided an air induction collar 150 extending around and mounted
on the tapered end section 28. This collar, during use of the
exhaust stack, can provide induction of outside air into the flow
of exhaust gases from the second end 32 of the end section 28. By
providing an induction collar in this manner, outside air, which
enters through the bottom end 152 of the collar, effectively
dilutes the exhaust gas concentration. As a result, the overall
stack height can be reduced from the stack height that would
otherwise be required to meet local standards. For example, in one
embodiment of an exhaust gas stack with an induction collar mounted
thereon, the overall height of the stack is reduced from thirty
feet to twenty feet.
[0039] The use of an induction collar or windband is taught in U.S.
Pat. No. 4,806,076 which issued Feb. 21, 1989 to 1. S. Andrews and
the description and drawings of this prior patent are incorporated
herein by reference. As indicated in this existing patent, the
induction collar can be secured to the exterior of the tapered end
section 28 adjacent its upper outlet and in spaced relation to its
exterior surface by means of suitable connecting brackets (not
shown) which do not interfere with the air flow through the collar.
The illustrated induction collar is in the form of a frustoconical
collar which tapers upwardly and which can be made of a suitable
sheet metal. The collar has an open top at 154 which can be located
well above the top end 32 of the end section 28. If desired, the
collar can also have an annular interior wall 156 which can also be
made of imperforate sheet metal. The interior wall can have a lower
portion 158 that tapers upwardly from the bottom end of the
induction collar to a narrow throat at 160. Above this throat, the
interior wall diverges.
[0040] An additional optional feature of a stack constructed with a
central airflow defining member 100 is the provision of a drain
system 170 shown in FIGS. 1 and 2. This system is used to drain off
any water that enters the hollow upper portion 118 of the member
100. An inlet 172 of this drain system is arranged above the
substantial portion of the exterior shell of member 100 that
contains sound attenuating material. The system 170 can include a
one inch diameter pipe that extends through and projects from the
wall of the stack.
[0041] The schematic illustration of the stack 10 shown in FIG. 8
illustrates an exemplary version of a control system for
controlling operation of the linear actuator 62. This control
system includes the aforementioned electronic controller 80 which
can be connected to a booster relay 172. The booster relay is used
to get faster response from the actuator 62 when a signal is sent
from the controller. It amplifies the volume of the control air in
the circuit. Both the relay and the controller are connected by
respective air lines 174 and 176 to a source 178 of pressurized
air. This source can provide pressurized air in the range of 20 to
30 psig. The two electrical lines 78 and 79 that connect the sensor
76 to the controller can extend through stainless steel tubes
arranged on the interior of the stack. These steel tubes extend to
two fittings 180. Extending between each fitting 180 and the
controller can be relatively short flexible vinyl tubes through
which the electrical lines extend. Both the controller 80 and the
booster relay 172 can be preset in the factory. The controller and
relay 172 can be mounted on the side of the stack or inside the
building (and not necessarily on the stack). If they are mounted on
the stack in a manner that would otherwise expose them to the
elements, then a protective weather guard (not shown) is
provided.
[0042] One embodiment of an exhaust gas stack constructed according
to the present disclosure (without the optional induction collar)
was constructed on the basis of the following design parameters for
the flow of the exhaust gases:
[0043] Maximum Flow: 26,400 cfm (Emergency mode)
[0044] Maximum Flow: 20,000 cfm (Normal mode)
[0045] Minimum Flow: 9,000 cfm (Normal mode)
[0046] Average Flow: 17,500 cfm (Assumed)
In the case of a conventional exhaust gas stack operating at 20,000
cfm continuously, the required BHP of the axial vane fan is
approximately 6.3 horsepower. On the other hand, with an exhaust
gas stack according to the present disclosure which is able to
operate at an average flow of 17,500 cfm continuously, the fan
power required is only 11.1 horsepower. On the basis of this
comparison and assuming twenty-four hours per day operation and
electricity costs of ten cents per kW, the energy savings per year
are approximately $3,600.00 per fan. It should be noted that this
comparison between the power requirements for the fan when an
exhaust gas stack according to the present disclosure is used as
compared to when a conventional exhaust gas stack is used, is based
on the assumed need to maintain 4,000 fpm velocity discharge at all
operating levels. The energy efficiency of the disclosed exhaust
gas stack is primarily due to its variable air volume (VAV)
operation capability. The airflow volume handled by an exhaust fan
used with this gas stack is reduced as the exhaust gas volume is
reduced when compared to prior exhaust systems that introduce
outside air in order to maintain flow velocity. As a result, the
disclosed exhaust gas system requires less power than prior exhaust
gas systems. The present exhaust gas system can be a VAV apparatus
since the outlet velocity is maintained over at least a range of
exhaust airflow rates by adjusting the opening area at the stack
discharge.
[0047] While the present invention has been illustrated and
described as embodied in certain exemplary embodiments, it is to be
understood that the present invention is not limited to the details
shown herein, since it will be understood that various omissions,
modifications, substitutions and changes in the forms and details
of the disclosed exhaust gas stacks and velocity control apparatus
for use with such stacks may be made by those skilled in the art
without departing in any way from the spirit and scope of the
present invention. For example, those with ordinary skill in the
art will readily adapt the present disclosure for various other
applications without departing from the spirit and scope of the
present invention.
* * * * *