HIGH EFFICIENCY RADIANT HEATER

Abstract

A radiant tube heater with a burner assembly, a radiant tube assembly and a combustion air pre-heater, wherein the burner assembly comprises: a burner fuel nozzle; a plenum chamber and a pre-mixer chamber; the plenum chamber having a combustion air inlet; wherein in use: combustion air flows from said plenum chamber through an orifice to said pre-mixer where said air is mixed with burner fuel entering said pre-mixer through said nozzle prior to being combusted at a burner head; said pre-mixer being at least partly located within said radiant tube assembly; and where in use at least part of the combustion air supplied to said plenum is preheated in said air pre-heater using residual sensible heat of the hot combustion gas products of the heater.

Claims

1. (canceled)

2. A radiant tube heater comprising: a burner assembly including a combustion inlet, the burner to produce combustion air using pre-combustion air; a radiant tube assembly connected to the burner assembly, the radiant tube assembly to deliver combustion air to a radiant tube discharge; a combustion pre-heater comprising: a housing coupled to the radiant tube discharge and the combustion inlet; a pre-heater block located in the housing, the pre-heater block comprising: a first pre-combustion duct and a second pre-combustion duct parallel to the first pre-combustion duct; a member connected the first and second pre-combustion ducts to direct the pre-combustion air from the first pre-combustion duct to the second pre-combustion duct; and a plurality of combustion channels connected to the first pre-combustion duct and the second pre-combustion duct.

3. The radiant tube heater of claim 2, wherein the radiant tube assembly comprises a u-shaped heater connected to the burner assembly.

4. The radiant tube heater of claim 2, further comprising: an outlet duct connecting the pre-heater block to an inlet of the burner assembly, the outlet duct to deliver the heated pre-combustion air to the burner assembly inlet.

5. The radiant tube heater of claim 2, wherein the plurality of combustion channels are located in a single enclosure located between first and second end plate members.

6. The radiant heater of claim 5, wherein the combustion air is cooled by pre-combustion air in a cross-flow arrangement through the single enclosure.

7. The radiant tube heater of claim 5, the first and second pre-combustion ducts comprising: a plurality of internal flow channels in thermal communication with the plurality of combustion channels.

8. The radiant heater of claim 7, further comprising: a separation assembly coupled to the first plate member, the separation assembly configured to direct pre-combustion air to the plurality of internal flow channels to limit bypass air.

9. The radiant tube heater of claim 2, wherein the plurality of combustion channels connected to the first pre-combustion duct in a cross-flow arrangement and the second pre-combustion duct in a cross-flow orientation parallel to the first pre-combustion duct, to deliver hot combustion air to the first pre-combustion duct and the second pre-combustion duct to cool the combustion air and to heat pre-combustion air in both the first and second-pre-combustion ducts.

10. A radiant tube heater comprising: a burner assembly including to produce combustion air using pre-combustion air; a radiant tube assembly to deliver combustion air from the burner; a combustion pre-heater comprising: a housing coupled to the radiant tube assembly; a pre-heater block located in the housing, the pre-heater block comprising: a first pre-combustion duct and a second pre-combustion duct parallel to the first pre-combustion duct; and a plurality of combustion channels in thermal communication with the first pre-combustion duct and the second pre-combustion duct to cool the hot combustion air and to heat pre-combustion air in both the first and second-pre-combustion ducts in parallel.

11. The radiant tube heater of claim 10, the first pre-combustion duct and second pre-combustion duct comprising: a plurality of internal flow channels in thermal communication with the plurality of combustion channels.

12. The radiant heater of claim 11, wherein the plurality of internal flow channels and the plurality of combustion channels are arranged in a cross-flow orientation.

13. The radiant heater of claim 11, further comprising: a separation assembly coupled to the first plate member, the separation assembly configured to direct pre-combustion air to the plurality of internal flow channels to limit bypass air.

14. The radiant heater of claim 13, the separation assembly further comprising: a central member to direct air flow between the first pre-combustion duct and the second pre-combustion duct.

15. The radiant tube heater of claim 10, wherein the first and second pre-combustion ducts are held in place by end plate members and are connected by a member to create a single pre-combustion heat exchanger

16. The radiant tube heater of claim 10, wherein the radiant tube assembly comprises a u-shaped heater connected to the burner assembly.

17. The radiant tube heater of claim 10, further comprising: an outlet duct connecting the pre-heater block to an inlet of the burner assembly, the outlet duct to deliver the heated pre-combustion air to the burner assembly inlet.

18. A method of heating air using a radiant tube heater comprising a burner assembly including a combustion inlet, the method comprising: producing combustion air using pre-combustion air with a burner assembly; delivering combustion air to a radiant tube assembly connected to the burner assembly; delivering combustion air to a pre-heater block of a combustion pre-heater from a radiant tube discharge; delivering pre-combustion air to the pre-heater block; and exchanging heat in a cross-flow orientation, using the pre-heater block, between the pre-combustion air and the combustion air.

19. The method of claim 18, further comprising: delivering the pre-combustion air to the burner assembly from the pre-heater block using an outlet duct.

20. The method of claim 18, wherein delivering the combustion air includes delivering the combustion air to a plurality of combustion channels in thermal communication with the first pre-combustion air.

21. The method of claim 20, wherein delivering the pre-combustion air includes delivering the pre-combustion air to a plurality of internal flow channels in thermal communication with the plurality of combustion channels.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0013] A preferred embodiment of the invention will now be described by reference to the following diagrammatic figures in which:

[0014] FIG. 1 shows an overall (partly exploded) perspective view of a heater according to preferred embodiment of the invention;

[0015] FIG. 2 shows a side elevation of burner assembly of the heater of FIG. 1;

[0016] FIG. 3 shows a side cross section of the radiant tubes and the reflector assembly of the heater of FIG. 1;

[0017] FIGS. 4 shows a perspective view of the heat exchanger assembly of the heater of FIG. 1;

[0018] FIG. 5 shows a perspective view of FIG. 4 in exploded form;

[0019] FIG. 6 shows the heat exchanger block of the heat exchanger at assembly of FIG. 4; and

[0020] FIG. 7 shows a second embodiment of the invention with an over-shield.

DETAILED DESCRIPTION OF THE INVENTION

[0021] A preferred embodiment of the invention will now be described by reference to FIGS. 1-6.

[0022] FIG. 1 shows a radiant tube heater 10 comprising; a fuel burner assembly 12; a combustion air fan 14; a radiant tube assembly 16; a reflector/insulator unit 18; and an air pre-heater heat exchanger 20. In use, fuel (typically natural gas) is combusted with preheated air (slightly compressed by passing through fan 14) in burner assembly 12. Hot combustion gases from the burner 12 pass into and through the U-shaped radiant tube assembly 16 before entering heat exchanger 20 where residual sensible heat in the hot combustion products is used to preheat combustion air fed to burner assembly 12 (via fan 14); typically to a temperature of between 100 and 120 C. Above and around the sides of the radiant tube assembly 16 there is located a reflector unit. The purpose of the reflector unit is to reflect radiant heat energy downwardly (that is away from the reflector) such that in use the maximum amount of radiant energy is directed in a downward direction towards the floor of the space being heated.

[0023] FIG. 2 shows a side elevation (cross section) of the burner assembly 12 and also the entry portion of the radiant tube assembly 16. Gaseous fuel (G) enters a control valve 22 where the fuel flow-rate is regulated and passes from the exit of valve 22 into a straight nozzle feed pipe 24 and thence to burner nozzle 26. Burner nozzle 26 comprises at least one axial outlet orifice 28 and a plurality of radially directing orifices 30. The burner nozzle 26 ejects fuel into a pre-mixer 32 where the fuel is premixed with combustion air (A). The axial and radial orifices 28 and 30 help promote turbulence in the pre-mixer and generally promote good mixing of air and fuel prior to combustion. This advantageously encourages a long flame and results in a more consistent flame quality. Combustion air enters the pre-mixer 32 through one or more orifices 34. Air feed to the burner is drawn through combustion air pre-heater 20 (as a result of suction fan 14) where it is preheated prior to entering plenum chamber 36 located between control valve 22 and burner nozzle 26 and surrounding feed pipe 24. Thus, gaseous fuel flowing through pipe 24 is preheated owing to the higher temperature of the pre-heated air flowing through plenum chamber 36. Primary air orifices 34 are located in a wall that otherwise separates the plenum chamber 36 and the pre-mixer 32. Pre-mixer 32 comprises a cylindrical tube 38 and is preferably formed by extruding aluminium or an alloy thereof. Pre-mixer 32 is located within the radiant tube assembly 16 such that an annular channel 42 is formed along which pre-heated air from plenum chamber 36 may flow via one or more secondary air orifices 44. This simplifies the design of the plenum chamber 36. The downstream end of the pre-mixer tube 38 terminates at a burner head 46 that may comprise an array of circular or rectangular orifices. Burner head 46 extends radially outwardly beyond pre-mixer 32 so that an annular portion, containing a ring of circumferentially spaced apertures 50, partly seals the downstream end of annular channel 42. Burner head 46 ensures that the base of flame (F) is retained on the exit surface of burner head 46. Pre-heated secondary air enters the flame F by flowing along annular channel 42 and through apertures 50. This advantageously, assists mixing of secondary air with the products of combustion the secondary air enters flame F. Ignition means 48 (for example spark ignition) is provided to allow initial lighting of the burner.

[0024] FIG. 3 shows further details of the reflector unit 18, located above the tubes 52 of the radiant tube assembly 16. The reflector unit is located some way above the radiant heater tubes and extends part away around the outer side of each tube, the order to maximise the extent of downward reflection of radiant heat energy. The invention provides insulation means 54, located at least in part proximal to reflector unit 18. This insulation means 54 may comprise a layer of refractory material or the like or alternatively may be provided by other insulating material such as a substantially enclosed air pocket. The latter may be provided by placing an insulating panel 56 above and close to reflector unit 18. This is most effective if the layer of enclosed air (air pocket) is relatively thin.

[0025] FIGS. 4-6 shows details of a heat exchanger unit 20. Referring to FIG. 5 the combustion air pre-heater exchanger 20 comprises a heat exchanger block 60 which is shown in more detail in FIG. 6. Heat exchanger block 60 is formed from an array of heat exchanger ducts 62 arranged side-by-side and providing an internal flow channel 64 through which combustion air flows during preheating. The array of heat exchanger ducts 62 are held in place by end plates members 66. In use, hot combustion products pass (preferably in a direction orthogonal to preheat air flow) through the channels 68 located between individual exchanger ducts 62. Assembly member 70 provides a space for the preheated air to turn after passing through a first array of ducts (62a) before flowing in an opposite direction through a second array of ducts (62b). Assembly member 70 is sealed to the lower panel 72 (see FIG. 5) of the heat exchanger unit housing by means of a gasket 74. A separation assembly 76 similar to assembly member 70 but having an additional central member 78 in combination with gasket 80 provides a seal with the upper portion 84 (see FIG. 5) of the heat exchanger unit and ensures that air entering the exchanger through inlet flange 86 must flow through the first array of tubes 62a and cannot bypass the exchanger.

[0026] The heat exchanger block is located within housing 90 which takes the form of a box having a hot combustion products inlet duct 92, a cooled combustion products outlet duct 94, a combustion air inlet duct 86, and a preheated air outlet duct 88.

[0027] FIG. 5 shows the position of combustion air inlet duct 86 and preheated air outlet duct 88 relative to the heat exchanger block 60. In this example, the heat exchanger block 60 comprises (see FIG. 6) 10 ducts 62 that in use function as two separate blocks (62a and 62b) of 5 ducts. Thus, when assembled heat air pre-heater exchanger unit 20 directs combustion air through inlet duct 86 which then passes through internal flow channels of the first 5 ducts 62a. The partly preheated air then makes a U-turn and passes (in the opposite direction) through the remaining 5 ducts 62b and thence to preheated air outlet duct 88 and thence through a duct 94 to the inlet of air fan 14 (see FIG. 1). Further, in use combustion products pass horizontally through spaces of 68 (located between individual exchanger ducts 62) thereby providing the energy required to preheat the combustion air. In consequence, during passage of combustion products in said horizontal direction sensible heat is lost resulting in further cooling of the combustion products. Thus, heat exchanger block 60 in combination with the heat exchanger housing 90 provide a cross flow heat exchanger in which combustion air is partly preheated in a first portion of the exchanger block 62a, then makes a U-turn and is further preheated as he passes in an opposite direction through a second portion of the exchanger block 62b.

[0028] Naturally, the exchanger block 60 can comprise a wide range of individual exchanger ducts 62 and is not limited to a 5 plus 5 duct arrangement. Indeed, it is possible to have exchanger blocks 60 were the first portion of the exchanger block has more or less ducts and the second portion of the exchanger block. Preferably, the first portion will have either a slightly more ducts or an equal number of duets than the second portion.

[0029] FIG. 7 shows a further embodiment of the invention similar to the embodiment described above in most respects apart from the reflector 118, which in this embodiment is not insulated. Also, located between the reflector and the radiant tube assembly 140 there are over-shields 100. Over-shields 100 are preferably located slightly above each tube of a U-shaped radiant tube assembly 140. The over-shields reduce the amount of radiant energy that is incident upon the reflector 118 located above. This results in an improved (useful) radiant energy efficiency as energy losses associated with heating the reflector are reduced (this energy ultimately being dissipated largely as convective heat loss).