Boiler Flue Gas and Oven Exhaust Economizer Systems
A representative mechanical draft system includes an in-line draft inducer that comprises a motor and a backward-inclined impeller. The mechanical draft system also includes an economizer coupled to the in-line draft inducer, where the economizer comprises a housing and a horizontally mounted heat recovery unit.
There are many types of boilers, ovens, and other heat generating appliances on the market that vent or exhaust differently. An atmospheric boiler with a draft hood or draft diverter relies on the natural draft, which typically range from 0.0 to 0.03 inch water column (inWC) draft. Even a small restriction in the chimney flue can cause the boiler to fail or prevent proper discharge of products of combustion.
A forced draft boiler used for steam or hot water has a built-in fan to push products of combustion through the venting system and the forced draft typically range from 0.0 to 0.5 inWC. Other boiler types fall in between these two extremes. As a result, it is generally a challenge to use flue gas economizers and they are rarely used with atmospheric boilers. Economizers used with forced draft boilers must generally be designed so that the resistance never exceeds 0.3-0.4 inWC, thereby causing such economizers to be voluminous and space consuming. This restriction also limits the number of boilers a single economizer can serve. Thus, in most applications, a dedicated economizer is needed for each boiler even when exhausted through a single common chimney.
Baking ovens and process ovens experience the same challenges as boilers. Often, there is no driving force in the exhaust stream, so it is very difficult to integrate a heat recovery unit in the exhaust stream to recapture the heat in the exhaust gases. In addition to the applications described above, other processing equipment such as cooling systems, smokehouses, drying equipment, brewing equipment, pasteurizers, etc. generate hot exhaust. Most of these applications face serious challenges when heat recovery is attempted, where such attempts often lead to oven failures, unintended processing results, and so on. There is therefore a need in the industry for devices capable of saving and recovering energy.
SUMMARYVarious embodiments of a mechanical draft system are disclosed. Briefly described, one embodiment of a mechanical draft system includes an in-line draft inducer that comprises a motor and a backward-inclined impeller. The mechanical draft system also includes an economizer coupled to the in-line draft inducer, where the economizer comprises a housing and a horizontally mounted heat recovery unit.
Another embodiment of a mechanical draft system includes an in-line draft inducer comprising a motor and a backward-inclined impeller. The mechanical draft system also includes an economizer detachably coupled to the in-line draft inducer, the economizer comprising a cylindrical housing for horizontally mounting a heat recovery unit that partitions the housing into an upper chamber and a lower chamber.
Another embodiment is a method implemented in a draft controller in a mechanical draft system comprising an in-line draft inducer and an economizer, the economizer comprising a heat recovery unit and a damper assembly. In response to a heat recovery request, a fan speed of the in-line draft inducer is increased based on a predetermined draft set point value. Upon reaching the draft set point value, a valve of the economizer is opened to allow fluid to flow through the heat recovery unit. The damper assembly is placed in a closed position to channel exhaust flow through the heat recovery unit, and in response to the damper assembly being placed in a closed position, the fan speed of the in-line draft inducer is increased to maintain the predetermined draft set point value.
Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.
Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Embodiments of a mechanical draft system are disclosed that comprise an economizer that may be either fan-powered with an integrated draft fan or configured as a stand-alone unit. Reference is made to
In the embodiment of
As shown, the heat recovery unit 106 is horizontally mounted such that the main body portion of the heat recovery unit 106 is perpendicular to the flue gas flow. The economizer 104 is further equipped with a bypass damper assembly 108, where the bypass damper assembly 108 may comprise a butterfly damper or a multi-blade damper, as shown in
In a second exhaust flow configuration, the flue gases flow over and bypass the heat recovery unit 106, as shown in
Referring back to
Reference is made to
The backward inclined configuration of the centrifugal impeller 112 places the motor on the outside of the air stream with the centrifugal impeller 112 inside the housing 119, which is made possible by installing the variable speed motor and centrifugal impeller 112 at an angle. The variable speed motor and the centrifugal impeller 112 form an integrated drive unit assembly that can be removed from the housing 119 without removing the entire in-line draft inducer 110 from the stack system. While
It should be emphasized that while the heat recovery unit 106 is shown horizontally mounted in the economizer 104, the heat recovery unit 106 may alternatively be vertically mounted in the economizer 104. The heat recovery unit 106 includes a top face 310 and a bottom face (not shown) formed by a series of copper tubing and fins. Referring briefly to
The heat recovery unit 106 comprises rectangular plate fins with a matrix of die-extruded tube collars. A sheet metal casing provides rigidity to the fin-tube assembly prior to tube expansion. After assembly, the tubes are expanded into the fin collars, which allows for a gap-free connection maximizing heat recovery unit performance and structural integrity. It should be appreciated that the design is extremely compact and efficient, and the pressure drop through the heat recovery unit may exceed 0.5 inWC.
Referring back to
Reference is made to
In a second exhaust flow configuration, the flue gases flow over and bypass the heat recovery unit 106. This configuration prevents over-heating of the coils in case the liquid inside the coils is not flowing or if the exhaust heat exceeds the performance of the heat recovery unit 106. The combination of the variable position actuator and the bypass damper assembly 108 allow modulation of the exhaust air flow over the heat recovery unit 106 so that a variable percentage of the exhaust air can pass through the heat recovery unit 106 and the remainder bypass the heat recovery unit 106.
Reference is made to
In block 1010, in response to a call for heat, the inline draft inducer 110 begins operation and speeds up until a predetermined draft set point in an external draft controller has been reached. For some embodiments, the draft set point is specified by the boiler manufacture. Specifically, the boiler manufacturer publishes a draft range for the specific boiler, which should be satisfied by the chimney/venting system. This set point is then used as the draft set point.
In block 1020, once the draft set point has been reached, the external draft controller releases the mechanical draft system 102 and allows the system to operate. In block 1030, an external valve opens, and fluid will begin to flow through the heat recovery unit 106. In block 1040, the actuator 301 will begin closing the damper assembly 108 so that the hot products of combustion will increasingly pass through the heat recovery unit 106. In block 1050, as the damper assembly 108 is closing and the products of combustion is channeled through the heat recovery unit 106, the inline draft inducer 110 will increase the fan speed in order to overcome the additional pressure loss created by the air flow through the heat recovery unit in order to maintain the predetermined draft point.
In block 1060, with the hot products of combustion flowing through the airside of the heat recovery unit 106, heat is transferred through the finned tubes of the heat recovery unit 106 and eventually to the fluids flowing inside the tubes. In block 1070, if the fluid temperature increases to a predetermined temperature (e.g., 200° F.), the actuator 301 gradually begins to open the damper assembly 108 to keep the temperature at or below the predetermined temperature by allowing flue gases to gradually bypass the heat recovery unit 106. Specifically, the damper assembly 108 will go from a fully closed position to a half open position and then to a fully open position.
In block 1080, if the fluid temperature reaches a second predetermined temperature (e.g., 210° F.), the actuator 301 completely opens the damper assembly 108 to allow the hot products of combustion to completely by-pass the heat recovery unit 106 (as shown in
In block 1090, when the mechanical draft system 102 begins the process of turning off, the inline draft inducer 110 continues to operate in a post-purge mode and the damper assembly 108 will stay closed for a predetermined amount of time (e.g., 3 minutes), thereby allowing the products of combustion to be cleared from the heat recovery unit 106. In block 1100, after the post-purge period passes, the actuator 301 will completely open the damper assembly 108.
Reference is made to
In
It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.
Claims
1. A mechanical draft system, comprising:
- an in-line draft inducer comprising a motor and a backward-inclined impeller; and
- an economizer coupled to the in-line draft inducer, the economizer comprising a housing and a horizontally mounted heat recovery unit.
2. The system of claim 1, wherein the motor is a variable speed motor and is mounted externally to a housing of the in-line draft inducer.
3. The system of claim 1, wherein the economizer comprises at least one bypass damper controlled by an actuator, wherein the actuator is configured to control a position of the least one bypass damper to control a flow of gases through the economizer.
4. The system of claim 3, wherein the at least one bypass damper comprises a fin having a semi-circular cross section.
5. The system of claim 3, wherein the at least one bypass damper comprises one of a butterfly damper and a multi-blade damper.
6. The system of claim 3, wherein the actuator is configured to configure the at least one bypass damper in one of a neutral position and a blocking position, wherein the neutral position allows free flow of gases through the economizer, and wherein the blocking position inhibits the flow of gases.
7. The system of claim 1, wherein the heat recovery unit comprises a water-based radiator.
8. The system of claim 1, wherein the heat recovery unit is mounted on a guide rail assembly within the economizer.
9. The system of claim 1, wherein the guide rail assembly is horizontally disposed along a centerline of the economizer.
10. The system of claim 1, wherein the economizer further comprises a tapered inlet for channeling exhaust flow.
11. The system of claim 1, wherein the tapered inlet is coupled to a boiler unit and is configured to receive hot exhaust from the boiler.
12. The system of claim 1, wherein the heat recovery unit comprises rectangular plate fins and a plurality of die-extruded tube collars.
13. A mechanical draft system, comprising:
- an in-line draft inducer comprising a motor and a backward-inclined impeller; and
- an economizer detachably coupled to the in-line draft inducer, the economizer comprising a cylindrical housing for horizontally mounting a heat recovery unit that partitions the housing into an upper chamber and a lower chamber.
14. The system of claim 13, wherein the economizer further comprises a dual-damper configuration controlled by separate actuators, wherein each actuator is configured to control a position of the corresponding damper to control exhaust flow through the economizer.
15. The system of claim 14, wherein the actuator controls a position of each damper to allow flue gases entering the economizer to flow in one of two exhaust flow configurations,
- wherein the first exhaust flow configuration comprises exhaust flow through only one of the upper chamber and the lower chamber to bypass the heat recovery unit, and
- wherein the second exhaust flow configuration comprises turbulent exhaust flow through one of the lower chamber and upper chamber, through the heat recovery unit, and into the other chamber.
16. The system of claim 14, wherein the actuator is configured to place each damper in one of a neutral position, a first blocking position, and a second blocking position;
- wherein the neutral position allows free exhaust flow, and wherein each of the first and second blocking positions inhibits exhaust flow.
17. The system of claim 13, wherein the economizer further comprises:
- a single damper disposed on one end of the economizer; and
- a fixed end plate disposed on another end of the economizer;
- wherein the damper is controlled by an actuator, wherein the actuator is configured to control a position of the damper to control exhaust flow through the economizer.
18. The system of claim 13, wherein the economizer comprises a circular inlet and a circular outlet, wherein the circular inlet and circular outlet each include mounting flange fittings.
19. A method implemented in a draft controller in a mechanical draft system comprising an in-line draft inducer and an economizer, the economizer comprising a heat recovery unit and a damper assembly, the method comprising:
- in response to a heat recovery request, increasing a fan speed of the in-line draft inducer based on a predetermined draft set point value;
- upon reaching the draft set point value, opening a valve of the economizer to allow fluid to flow through the heat recovery unit;
- placing the damper assembly in a closed position to channel exhaust flow through the heat recovery unit; and
- in response to the damper assembly being placed in a closed position, increasing the fan speed of the in-line draft inducer to maintain the predetermined draft set point value.
20. The method of claim 19, further comprising:
- in response to a temperature of the fluid flowing through the heat recovery unit reaching a first predetermined temperature, placing the damper assembly in a partially open position; and
- in response to a temperature of the fluid flowing through the heat recovery unit reaching a second predetermined temperature, placing the damper assembly in a fully open position.
Type: Application
Filed: Jul 17, 2014
Publication Date: Jan 21, 2016
Inventors: Steen Hagensen (Atlanta, GA), Bruce Works (Atlanta, GA)
Application Number: 14/333,637