Exhaust gas stack
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.
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.
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.
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.
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.
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.
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 DISCLOSUREThe 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:
-
- (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;
- (b) An exhaust gas stack with sound attenuating features that enable quiet operation; and
- (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.
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.
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.
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.
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.
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.
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.
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:
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
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
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
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
With reference now to the detail drawings of
The cross-section of
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™ and another suitable material is sold under the trademark MYLAR™. 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
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
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.
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.
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
The schematic illustration of the stack 10 shown in
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:
Maximum Flow: 26,400 cfm (Emergency mode)
Maximum Flow: 20,000 cfm (Normal mode)
Minimum Flow: 9,000 cfm (Normal mode)
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.
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.
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.
Type: Application
Filed: Jun 21, 2006
Publication Date: Dec 27, 2007
Inventor: Dipti Datta (Mississauga)
Application Number: 11/471,861
International Classification: E04F 17/02 (20060101); F23J 11/00 (20060101);