Direct gas-fired process air heater assembly utilizing a premix burner applied to a shrink wrap conveyer oven

Abstract

A direct gas-fired process air heater assembly that utilizes a premix burner applied to a shrink wrap conveyor oven for uniform dissemination of heated air into the a recirculating air stream of a circulating blower, said air circulating blower directing the heated air into the shrink wrap chamber or tunnel for shrinking polymer film around packaged goods for shipment and/or storage. According to various aspects, exemplary embodiments are disclosed of the direct gas-fired packaged process air heater assembly construction features including the application of premix burner technology.

Claims

1. A direct gas-fired air heater assembly utilizing a premix burner for use for application to a shrink wrap conveyor oven to provide uniform dissemination of heated air in a recirculating air stream during its application, for shrink wrapping of polymer film, comprising: a heater assembly, having a premix gas and combustion air blower with a burner assembly at its entrance end, and a refractory block provided at its opposite end, an insulated bulkhead provided at the entrance end of the heater assembly and provided for mounting of the said premix burner, blower, and other heater accessories at the entrance end of the heater assembly, a ventilating tube extending between the insulated bulkhead at one end, and securing with the refractory block at its other end, a burner firing tube extending into the ventilating tube, said burner firing tube provided for conveying the gas-fired processed air from the entrance end to the opposite end of said burner firing tube, whereat the refractory block directs the direction of flow of said heated air to the space between said burner firing tube and the ventilating tube, said ventilating tube having a series of perforations provided therethrough, and discharging heated air through the ventilating tube and into the region of the shrink wrap conveyor oven to provide for the uniform dissemination of the heated air into a recirculating air stream to provide for shrink wrapping of the polymer film surrounding any packaged goods being conveyed through the conveyor oven assembly; and wherein the refractory block enclosure has holes provided above and below the refractory block to disseminate a portion of the heat absorbed by the refractory block to the circulating airflow.

2. The direct gas-fired air heater assembly of claim 1, wherein at least one of said burner firing tube and ventilating tube is of round configuration.

3. The direct gas-fired air heater assembly of claim 1, wherein at least one of said burner firing tube and ventilating tube is of polygonal shape along its length.

4. The direct gas-fired air heater assembly of claim 3 wherein said at least one burner firing tube and ventilating tube is of octagonal shape.

5. The direct gas-fired air heater assembly of claim 1, wherein said air heater assembly is applied within a shrink wrap chamber for shrinking polymer film around packaged goods during their processing.

6. The direct gas-fired air heater assembly of claim 1 wherein at least one temperature balancing channel provided upon the exterior surface of the ventilating tube along its length to further control the dissemination of the heated air into the shrink wrap chamber during processing of the packaged goods conveyed through the shrink wrap oven.

7. The direct gas-fired air heater assembly of claim 1 wherein said heater assembly is perpendicularly arranged through the shrink wrap conveyor in its assembly.

8. The direct gas-fired air heater assembly of claim 1, wherein said burner produces no visible external flame during its operation and the air stream that flows into and around the heater assembly to provide uniform dissemination of heated air, thereby minimizing clearances requirements between the heater assembly and downstream components.

9. The direct gas fired heater assembly of claim 6 wherein said ventilation tube has holes provided under the temperature balancing channel for delivering a portion of the combustion heat to a localized section of the heater assembly.

10. The direct gas-fired air heater assembly of claim 6, wherein air restrictor baffles are provided between the insulated bulkhead and rail mounting supports, between rail mounting supports, and/or between the rail mounting supports and the refractory block enclosure to reduce the temperature leaving the ventilated tube for the section of the heater with the air restrictor baffles or to increase the airflow volume in heater sections without the air restrictor baffles as a means to uniformly disseminate the thermal rise across the length of the heater assembly.

11. A direct gas-fired air heater assembly utilizing a premix burner for use for application to a shrink wrap conveyor oven to provide uniform dissemination of heated air in a recirculating air stream during its application, for shrink wrapping of polymer film, comprising: a heater assembly, having a premix gas and combustion air blower with a burner assembly at its entrance end, and a refractory block provided at its opposite end, an insulated bulkhead provided at the entrance end of the heater assembly and provided for mounting of the said premix burner, blower, and other heater accessories at the entrance end of the heater assembly, a ventilating tube extending between the insulated bulkhead at one end, and securing with the refractory block at its other end, a burner firing tube extending into the ventilating tube, said burner firing tube provided for conveying the gas-fired processed air from the entrance end to the opposite end of said burner firing tube, said refractory block directs a portion of said heated air to the space between said burner firing tube and the ventilating tube, said ventilating tube having block-off sections attached to the interior surface top and bottom ends of the ventilated tube and extending to the burner firing tube external surface so as to ensure the refractory block directs the remaining portion of the heated air into the cavity of said temperature balancing channels mounted to the top and bottom exterior surface of said ventilated tube, said ventilating tube and temperature balancing channels having a series of perforations provided therethrough, and discharging heated air through the ventilating tube and temperative balancing channels and into the region of the shrink wrap conveyor oven to provide for the uniform dissemination of the heated air into a recirculating air stream to provide for shrink wrapping of the polymer film surrounding any packaged goods being conveyed through the conveyor oven assembly; and wherein the refractory block enclosure has holes provided above and below the refractory block to disseminate a portion of the heat absorbed by the refractory block to the circulating airflow.

12. The direct gas-fired air heater assembly of claim 11, wherein air restrictor baffles are provided between the insulated bulkhead and rail mounting supports, between rail mounting supports, and/or between the rail mounting supports and the refractory block enclosure to reduce the temperature leaving the ventilated tube for the section of the heater with the air restrictor baffles or to increase the airflow volume in heater sections without the air restrictor baffles as a means to uniformly disseminate the thermal rise across the length of the heater assembly.

13. The direct gas-fired air heater assembly of claim 11, wherein said burner produces no visible external flame during its operation and the air stream that flows into and around the heater assembly to provide uniform dissemination of heated air, thereby minimizing clearances requirements between the heater assembly and downstream components.

14. A direct-gas fired air process air duct heater assembly utilizing a premixed burner for use for application in drying ovens, curing ovens, and the like, and which heater assembly provides for a uniformed dissemination of heated air as a recirculating air stream during its application, comprising; a heater assembly, having a premix gas and combustion air blower with a burner assembly at its entrance end, and a refractory block provided at its opposite end, an insulated bulkhead provided at the entrance end of the heater assembly and provided for mounting of the said premix burner, blower, and other heater accessories at the entrance end of the heater assembly, a ventilating tube extending between the insulated bulkhead at one end, and securing with the refractory block at its other end, a burner firing tube extending into the ventilating tube, said burner firing tube provided for conveying the gas-fired processed air from the entrance end to the opposite end of said burner firing tube, whereat the refractory block directs the direction of flow of said heated air to the space between said burner firing tube and the ventilating tube, said ventilating tube having a series of perforations provided there through, and discharging heated air through the ventilating tube and into the region of the said assembly to provide for the uniform dissemination of the heated air into a recirculating air stream to provide for its usage in drying and curing of the materials contained within the oven assembly.

15. The direct gas-fired air heater assembly of claim 14 wherein at least one temperature balancing channel provided upon the exterior surface of the ventilating tube along its length to further control the dissemination of the heated air into the circulating airflow of the application in drying ovens, curing ovens, and the like.

16. The direct gas fired heater assembly of claim 14 wherein said ventilation tube has holes provided under the temperature balancing channel for delivering a portion of the combustion heat to a localized section of the heater assembly.

17. The direct gas-fired air heater assembly of claim 14, wherein air restrictor baffles are provided between the insulated bulkhead and rail mounting supports, between rail mounting supports, and/or between the rail mounting supports and the refractory block enclosure to reduce the temperature leaving the ventilated tube for the section of the heater with the air restrictor baffles or to increase the airflow volume in heater sections without the air restrictor baffles as a means to uniformly disseminate the thermal rise across the length of the heater assembly.

18. The direct gas-fired air heater assembly of claim 14, wherein said burner produces no visible external flame during its operation and the air stream that flows into and around the heater assembly to provide uniform dissemination of heated air, thereby minimizing clearances requirements between the heater assembly and downstream components.

19. A direct gas-fired process air duct heater assembly utilizing a premixed burner for use for applications in drying ovens, curing ovens, and the like, and which heater provides for a uniformed dissemination of heated air as a recirculating air stream during its application, comprising; a heater assembly, having a premix gas and combustion air blower with a burner assembly at its entrance end, and a refractory block provided at its opposite end, an insulated bulkhead provided at the entrance end of the heater assembly and provided for mounting of said premix burner, blower, and other heater accessories at the entrance end of the heater assembly, a ventilated tube extending between the insulated bulkhead at one end, and securing with the refractory block at its other end, said burner firing tube extending into the ventilating tube, a burner firing tube provided for conveying the gas-fired processed air from the entrance end to the opposite end of said burner firing tube, whereat the refractory block directs a portion of said heated air to the space between said burner firing tube and the ventilating tube, said ventilating tube having block-off sections attached to the interior surface top and bottom ends of the ventilated tube and extending to the burner firing tube external surface so as to ensure the refractory block directs the remaining portion of the heated air into the cavity of said temperature balancing channels mounted to the top and bottom exterior surface of said ventilated tube, said ventilating tube and temperature balancing channels having a series of perforations provided therethrough, and discharging heated air through the ventilating tube and the temperature balancing channels and into the region of the said assembly to provide for the uniform dissemination of the heated air into a recirculating air stream to provide for its usage in drying and curing of the material contained within the oven assembly; and wherein the refractory block enclosure has holes provided above and below the refractory block to disseminate a portion of the heat absorbed by the refractory block to the circulating airflow.

20. The direct gas-fired air heater assembly of claim 19, wherein air restrictor baffles are provided between the insulated bulkhead and rail mounting supports, between rail mounting supports, and/or between the rail mounting supports and the refractory block enclosure to reduce the temperature leaving the ventilated tube for the section of the heater with the air restrictor baffles or to increase the airflow volume in heater sections without the air restrictor baffles as a means to uniformly disseminate the thermal rise across the length of the heater assembly.

21. The direct gas-fired air heater assembly of claim 19, wherein said burner produces no visible external flame during its operation and the air stream that flows into and around the heater assembly to provide uniform dissemination of heated air, thereby minimizing clearances requirements between the heater assembly and downstream components.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In referring to the drawings:

(2) FIG. 1 provides an isometric view of a generic electric heater bank with an electrical junction box to illustrate the prior art;

(3) FIG. 2 shows an isometric view of the prior art of a direct gas-fired power burner assembly with its attached heat box with an integral linear slot that is located within a hot air envelop;

(4) FIGS. 3 and 3a depict section views of a generic shrink wrap conveyor oven with the heater assembly of the current invention installed in its' intended location with an enlarged depiction of the air circulating flow through the heater assembly;

(5) FIG. 4 is an isometric representation of the current invention;

(6) FIG. 5 provides an exploded and isometric view of the current invention;

(7) FIGS. 6a and 6b provide the right and left side views of the heater assembly of the current invention;

(8) FIGS. 7a, 7b, 7c and 7d provide section views of the octagon version of the heater assembly near the the center of the horizontal and vertical cut through the heater assembly of the current invention;

(9) FIG. 8 provides an exploded and isometric view of the round version of the burner firing tube, ventilated tube, tube block-offs, temperature balancing channel and refractory block;

(10) FIG. 9 presents an exploded view of the octagonal version of the heater assembly of the current invention;

(11) FIGS. 10a, 10b, and 10c provide views of the insulated bulkhead along with the section views along the vertical and horizontal cuts shown as Section A-A or Section B-B, and also showing the ground rods in FIGS. 10 a and 10b;

(12) FIGS. 11a, 11b, and 11c present the section views similar to FIG. 7 near the center of the horizontal and vertical cut through the heater assembly of the current invention that utilizes an alternative design premix tube burner;

(13) FIGS. 12 and 12a is an isometric and section view of a generic drying oven and/or curing oven that utilizes a direct gas-fired duct heater;

(14) FIGS. 13 and 13a is an isometric and section view of a generic paint booth that is shown as being equipped with a direct gas-fired packaged process air heater or direct gas-fired process air duct heater that utilizes the heater assembly of the current invention;

(15) FIG. 13b provides a partial view of the bypass damper and the exhaust blower receiving air from the exhaust pletta of the heated chamber of the invention;

(16) FIGS. 14 and 14a is an isometric and section view of a blow-through heater design that included the heater assembly of the current invention mounted downstream of the blower; and

(17) FIGS. 15 and 15a is an isometric and section view of a draw-through heater design that included the heater assembly of the current invention mounted upstream of the blower.

(18) The attached Appendix discloses a listing of the identification of the heater assembly parts, and their reference characters or item part numbers.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(19) In referring to the drawings, FIG. 1, the current version and prior art of an electric heater assembly is shown that includes the insulated bulkhead with an external electrical junction box. This design has electric heating elements that traverse the full width and height of the assembly that is inside the conveyor oven chamber. It is easily understood that the heat generated by electric elements is uniformly released to the circulating air stream being drawn through the heater element and into the blower inlet.

(20) FIG. 2 shows the current version and prior art of a gas-fired heater assembly which includes a power burner design that is mounted in the insulated bulkhead that contains an embedded combustion air blower that supplies the air to the burner section necessary for attaining complete combustion. The burner outlet is connected to a rectangular shaped fire box that includes a formed linear slot (not shown) through the top surface where the heated air is discharged into the circulating air stream as it passes through the cavity formed above the fire box and below the top of the hot air envelope.

(21) FIG. 3 depicts a section view of a generic shrink wrap conveyor oven that shows a section view of the premix gas-fired heater assembly 1 of the current invention in the same location provided for either of the prior art electric or gas-fired heater assembly design as shown in FIG. 1 and FIG. 2, respectively. The circulating airflow is shown as it passes through the heater assembly and is circulated through the rest of the shrink oven conveyor system.

(22) FIG. 3a demonstrates the air that enters the octagon shaped ventilated tube 7 is routed around the octagon shaped burner firing tube 1 to discharge out the opposite side of the ventilated tube 7. The cavity formed between the ventilated tube 7 and the burner firing tube 13 is where the majority of the heat from the heat of combustion interacts and mixes with the circulating air steam by way of one of the following heat transfer methods: a. the circulating airflow absorbs the conducted heat of the burner firing tube 13 from the heat from combustion within the burner firing tube 13; b. The heat radiated from the surface of the burner firing tube 13 to the internal surface of the ventilated tube 7 which is subsequently absorbed by the circulating air flow; c. The circulating airflow absorbs the conducted heat from the surface of the ventilated tube 7 directly under the temperature balancing channel 11 which is transporting the heat of combustion directed through it from the refractory block 8; and d. The heat of combustion that is directed into the said cavity between the burner firing tube 13 and the ventilated tube 7 from the refractory block 8.

(23) Continuing with FIG. 3a, the circulating airflow that enters the temperature balancing channel 11 absorbs the heat from the heat of combustion air that is directed into the cavity formed between the temperature balancing channel 11 and the exterior top and bottom surface of ventilating tube 7 from the refractory block 8 and out the opposite side of the temperature balancing channel.

(24) The circulating airflow that passes between temperature balancing channel and the airflow restrictor baffles 10 absorbs the conducted heat of the temperature balancing channel 11 exterior surfaces as a result of the heat of combustion air directed from the refractory block 8 through the passageway of the temperature balancing channel 11.

(25) The circulating air that passes between the air restrictor baffles 10, FIG. 3a, and the mounting rail 6 does not absorb any heat and is therefore considered bypass air which serves to blend the temperature gain across the heater assembly prior to the mixing action of the circulating air blower.

(26) The isometric view of the heater assembly 1 of FIG. 4 begins with the optional filter housing 3 that directly connects to the inlet venturi of the premix gas and combustion air blower 2 (partially hidden by the filter housing 3). The zero governor gas valve, 4 is connected to the gas port on the side of the inlet venturi (hidden, but mounted on the combustion air blower). The combustion air envelope 26 carries the fuel-air mixture from the premix gas and combustion air blower 2 to the premix burner 12 (not shown in this figure) which is mounted inside the insulated bulkhead 5. The spark igniter 14 and the flame rod 15 are mounted on the insulated bulkhead face plate 29 along with the sight glass 19. The static pressure ports 17 and the emissions sampling tube 9 all pass through the insulated bulkhead 5.

(27) Beyond the insulated bulkhead 5, are the heater assembly 1 components that are positioned in the circulating airflow of the shrink wrap conveyor oven of FIG. 3. The four mounting rails 6 are provided to accommodate both right and left hand conveyor installations. These mounting rails are bolted to the back of the insulated bulkhead 5 on the near end and secured to the refractory block enclosure 20 on the far end.

(28) The burner firing tube 13 is bolted to the insulated bulkhead 5 (not shown in this Figure) and extends to the refractory block 8 and centered inside the ventilated tube 7. The ventilated tube 7 is also bolted to the insulated bulkhead 5 on the near end and is embedded into the refractory block 8 on the far end of the heater assembly 1. The heat of combustion air produced by the premix burner 12 (not shown in this Figure) and flows inside the burner firing tube 13 (not shown as indicated above) where it is delivered to the refractory block 8 and where it is directed back by the refractory block 8 into the inside cavity between the burner firing tube 13 and the ventilated tube 7. The heat of combustion air within the said cavity is diluted by the circulating airflow that enters the ventilation holes in the ventilated tube 7 and exit that portion of the ventilated tube 7 on the opposite side.

(29) The temperature balancing channel 11 is attached to ventilated tube 7 and is also embedded into the refractory block 8 as well as being secured to the refractory block enclosure 20. There is a temperature balancing channel 11 located above and below the ventilated tube 7. The heat of combustion air that is directed back by the refractory block 8 into the top and bottom cavity between the temperature balancing channel 11 and the ventilated tube 7 is pushed down the said cavity with dilution air being added along its length from the circulating air stream entering the upstream holes in the vertical sides of the temperature balancing channels 11. After the circulating air flow has mixed with the heat of combustion air it exits the holes provided on the downstream in the vertical sides of the temperature balancing channels 11 and the four ventilation holes in the center section are provided on both sides of the ventilation tube 7 and directly under the temperature balancing channel 11 (not shown in this figure).

(30) As previously mentioned, the burner flame generates a higher temperature rise on the surface of the burner firing tube 13 on the near end of the heater assembly 1 than on the far end of the heater assembly 1 since the flame length at the maximum firing rate is only half the length of the burner firing tube 13. However, the heat of combustion air that exits the burner firing tube 13 carries a higher percentage of the total heat produced by the gas burner, therefore, the arrangement of the ventilation holes that are provided in the ventilation tube 7 and the temperature balancing channels 11 of current invention are spaced to permit the heat of combustion air to move further along the cavities provided to equalize the thermal gain along the length of the heater assembly 1.

(31) There are three spaces provided for mounting air restrictor baffles 10 above and below the temperature balancing channels 11 to the rail mounting supports 21 and the insulated bulkhead 5 on the near end and the refractory block enclosure 20 on the far end. The objective of the air restrictor baffles 10, when installed, is to add resistance to the heater assembly 1 which forces more circulating air flow through the ventilated tube 7 and temperature balancing channel 11 as the height of air restrictor baffle 10 is increased as well as reducing the volume of bypass air within that section. The more air that flows through the ventilation holes for that section on the upstream side of the heater assembly 1, the lower the temperature rise leaving the ventilation holes on the downstream side of that section the heater assembly 1. Furthermore, more airflow is pushed through the other sections that are without air restrictor baffles 10.

(32) Increasing the height of only the air restrictor baffles 10 for the center section between the rail mounting supports 21 may be a solution to balance the temperature across the length of a heater assembly 1 that was experiencing slightly warmer temperatures on the heater ends compared to the middle section.

(33) The configuration provided in FIG. 4 only utilizes air restrictor baffles 10 in the section between the bulkhead 5 and the rail mounting supports 21 in order to force more circulating airflow into the ventilating tube 7 for the first section while the other two sections were designed to have more circulating airflow bypass the heating sections for more mixing downstream. This configuration was found to produce even temperatures in a specific conveyor oven system at an oven temperature of 425° F.

(34) Two ventilation holes have been provided in the top and bottom side panels of the refractory block enclosure 20 for the circulating airflow to absorb the conducted heat from the refractory block 8 and the external surfaces of the refractory block enclosure 20. It was found that the refractory block 8 retained a significant amount of heat during operation and the extremely hot refractory block resembled an afterburner in a burn-off oven. This characteristic consumed carbon emissions such that the downstream emissions actually measured zero carbon monoxide (CO) for all firing ranges,

(35) FIG. 5 presents an exploded view of the components that comprises the heater assembly 1. The exploded view improves the visibility of some of the components of the heater assembly 1 from that shown in the isometric view shown in FIG. 4. The premix gas and combustion air blower 2 presents the interface information regarding the inlet venturi for the mounting surface of the filter housing 3, the connection point for the zero governor gas valve 4 and associated piping components to the embossments on the side of the inlet venturi casting and the gas and combustion air blower 2 outlet's connection to the combustion air envelope 26.

(36) The combustion air envelope 26 is a fully welded assembly that transports the fuel/air mixture to the premix burner 12. The metal mesh cylinder of the premix burner 12 is visible with the combustion air envelope 26 removed. The capped cylinder provides the barrier between the fuel/air mixture and the burner flame that takes place on the inside of the perforated metal cylinder.

(37) The octagon shaped burner firing tube 13 with its flanged joint is attached to the insulated bulkhead 5 and is positioned in the center of the octagon shaped ventilated tube 7 by the tube block-offs 22. Besides securing and centering the burner firing tube 13 in the ventilated tube, the tube block-offs 22 serve to block the heat of combustion air from entering the top and bottom sections of the ventilated tube 7 leaving only the side cavities between the burner firing tube 13 and the ventilated tube 7 and the open ends of the temperature balancing channels 11.

(38) The refractory block 8 and the refractory block enclosure 20a, b and c are shown along with the emission sampling tube 9. The emission sampling tube 9 is embedded into the extruded slot in the refractory block 8 prior to the assembly of the refractory block enclosure 20. The interior cutout of the refractory block 8 forms the curved surface that turns the heat of combustion air to direct it to the open cavities of the ventilated tube 7 and temperature balancing channel 11. In the center of the refractory block 8 is a raised shape that includes a hole that permits the emissions tube 9 to capture the combustion emissions generated by the premix burner 12 prior to any interaction of the emission, such as, carbon monoxide, to the hot surface of the refractory block 8.

(39) FIG. 6a and FIG. 6b present the left and right hand side views of the heater assembly 1 to demonstrate the ventilation holes provided in the ventilated tube 7, the temperature balancing channel 11 and the refractory block enclosure 20 are identical on both sides of the heater assembly 1.

(40) FIG. 7 provides sectional views of the heater assembly 1. FIG. 7a presents an enlarged view, FIG. 7d, of the end of the 4 inch burner firing tube 13 with arrows representing the heat of combustion air flow direction around the curved surface machined into the refractory block 8 and into the open cavity between the burner firing tube 13 and the ventilated tube 7. FIG. 7b presents an enlarged view, FIG. 7c, of the end of the 4 inch burner firing tube 13 with arrows representing the heat of combustion air flow direction around the curved surface machined into the refractory block 8 and into the open cavity between the ventilated tube 7 and the temperature balancing tube 11.

(41) Also shown in FIG. 7b is the positioning of the emissions tube 9 in the refractory block 8.

(42) FIG. 8 provides the components of the heater assembly 1 that would be impacted if the round version of the burner firing tube 25 and the round version of the ventilated tube 24 were utilized. There would be a round version of the temperature balancing channel 28 as well as round versions of the tube block-offs 30. The refractory block 27 and the front of the refractory block enclosure 20c would need to be machined to match the round ventilated tube 24.

(43) FIG. 9 provides a side by side comparison of the octagon design affected components.

(44) FIG. 10a addresses the insulated bulkhead 5 and provides section views in FIG. 10b and FIG. 10c in order to add design details. FIG. 10a shows the positioning of the spark igniter 14, ground rod 16 and flame rod 15 in relationship to the premix burner 12 outlet. FIG. 10b shows a section view of the premix burner 12 and the sight glass 19 with its associated sight glass viewing channel 18. FIG. 10c adds clarity of the flame rod 15 and spark igniter 14 positioning with respect to the premix burner 12 outlet.

(45) FIG. 11a and FIG. 11b provide sectional views of the heater assembly 1 that is similar to those provided in FIG. 7a and FIG. 7b except the preferred premix burner 12 is replaced with an alternate burner design that is known as the premix tube burner 23.

(46) FIG. 12 presents an isometric and section view of a generic drying oven and/or curing oven that shows the direct fired-gas process air duct heater assembly 49 that contain heater assembly 1 located in the ductwork 31 that moves air from the heated chamber 32 shown in FIG. 12a to the direct fired-gas process air duct heater assembly 49 and on to the circulating fan 33 that discharge the circulating airstream into a porous ceiling plenum 34. A fresh air intake 35 provides dilution air to the circulating air stream upstream of the heater assembly and an exhaust stack 36 removes the contaminated air from the heated chamber 32.

(47) FIG. 13 presents an isometric and section view of a generic paint booth that is equipped with a direct gas-fired packaged process air heater assembly 37 or direct gas-fired process air duct heater assembly 49 that contain the heater assembly 1. In the ventilation mode while painting is occurring, the recirculating damper 38 shown in FIG. 13a is closed and the outside air damper 39 is open allowing fresh air to enter the intake hood 40 and through the direct gas-fired packaged process air heater assembly 37 or direct gas-fired process air duct heater assembly 49. The air discharged from the direct gas-fired packaged process air heater 37 or direct gas-fired process air duct heater assembly 49 circulating fan-is passed through the ductwork 31 to the filtered discharged plenum 41 which is located inside the entrance of the heated chamber 32. As the air moves through the heated chamber 32, it enters the exhaust plenum 42 and through the bypass damper 43 as shown in the section view titled Bypass Damper and Exhaust Blower on FIG. 13b and out the exhaust fan 44. In the paint drying mode, the direct gas-fired packaged process air heater 37 or direct gas-fired process air duct heater assembly 49 circulating fan-operates in the recirculation mode with the outside air damper 39 and the bypass damper 43 partially open and the recirculating damper 38 fully open. The direct gas-fired process air heater 37 or direct gas-fired process air duct heater assembly 49-circulating fan-draws most of its air from the exhaust plenum 42 and a smaller portion (5 to 20%) from the intake hood 40. This circulated airflow passes through the direct gas-fired packaged process air heater assembly 37 or direct gas-fired process air duct heater assembly 49—where heat is added to this airstream until it reaches the desired oven temperature of the heated chamber 32. Any excess air in the system will vent through the partially open bypass damper 43 to the outdoors.

(48) FIG. 14 is an isometric and section view of a blow-through heater design 45 that incorporates the heater assembly 1 shown in FIG. 14a mounted downstream of the blower.

(49) FIG. 15 is an isometric and section view of a draw-through heater design 46 that incorporates the heater assembly 1 mounted shown in FIG. 15a upstream of the blower.

(50) Variations or modifications to the subject matter of this invention may occur to those skilled in the art upon review of the development as described herein. Such variations, if within the spirit of this invention, are intended to be encompassed within the scope any claims to patent protection issuing hereon. The summary of the invention herein, its depiction in the drawings, and description in the preferred embodiment, are intended for illustrative purposes only.

(51) TABLE-US-00001 APPENDIX Item Number Patent Nomenclature 1 Heater Assembly 2 Premix Gas and Combustion Air Blower 3 Filter Housing 4 Zero Governor Gas Valve 5 Insulated Bulkhead Enclosure 6 Mounting Rail 7 Ventilated Tube-(octagon design) 8 Refractory Block 9 Emissions Sampling Tube 10 Airflow Restrictor Baffles 11 Temperature Balancing Channel-(octagon design) 12 Premix Burner 13 Burner Firing Tube-(octagon design) 14 Spark Igniter 15 Flame Rod 16 Ground Rod 17 Static Pressure Ports 18 Sight Glass Viewing Channel 19 Sight Glass 20 Refractory Block Enclosure 21 Rail Mounting Support 22 Tube Block-Off-(octagon design) 23 Tube Burner-Premix 24 Ventilated Tube-(round design) 25 Burner Fire Tube-(round design)c 26 Combustion Air Envelope 27 Refractory Block-(round design) 28 Temperature Balancing Channel-(round design) 29 Bulkhead Face Plate-(insulated) 30 Tube Block-Off-(round design) 31 Ductwork 32 Heated Chamber 33 Circulating Fan 34 Porous Ceiling Plenum 35 Fresh Air Intake 36 Exhaust Stack 37 Direct Gas-Fired Process Air Duct Heater 38 Recirculating Damper 39 Outside Air Damper 40 Intake Hood 41 Filtered Discharge Plenum 42 Exhaust Plenum 43 Bypass Damper 44 Exhaust Fan 45 Blow-Through Heater Design 46 Draw-Through Heater Design 47 Control Panel 48 Refractory Block Retainer 49 Direct Gas-Fired Process Air Duct Heater