Patent Application
20140076307
This application claims the priority, under 35 U.S.C. §119, of European Patent Application EP 12 184 904.6, filed Sep. 18, 2012; the prior application is herewith incorporated by reference in its entirety.
The present invention relates to an infrared tube heater including a beam tube and a burner device having a burner and a fan. The fan is configured to supply air to the burner and the burner is configured to emit a flame into the beam tube.
In the commercial/industrial sector, infrared tube heaters are frequently used, in particular, for heating production, storage and sports halls or facilities. Infrared tube heaters generate heat by burning a preferably gaseous or liquid fuel. For that purpose, infrared tube heaters include burners with beam tubes. The burning is therefore invisible, hence the name infrared tube heater or dark radiator. The hot gases which are produced heat the surface of the beam tubes which emit the heat predominantly in the form of radiation, in particular in the infrared range. The fuel being used is, for example, natural and liquid gas with ambient air added in.
In terms of construction, infrared tube heaters are themselves formed substantially of the burner, the beam tube (with and without a reflector) and the exhaust gas system as main components. The flame is formed within the beam tubes which are attached subsequently. The beam tubes are connected linearly or in a U-shaped manner generally continuously downstream of the burner and are intended to radiate the heat generated as uniformly as possible over the entire length of the tube. The burner technology used is restricted in the case of infrared tube heaters exclusively to what are referred to as free-flame burners which produce a long diffusion flame in the beam tube and are preferably operated in one or two stages or within narrow limits with a sliding modulation of the burner power.
The burner and the beam tube have to be coordinated with each other in the construction of the infrared tube heaters. Ideally, the flame extends over the entire length of the beam tube so that, ultimately, the beam tube can also be identically heated overall. In particular, in the case of comparatively long beam tubes or beam tubes twisted in a meandering manner, that requirement, of course, cannot be met, and therefore at least one flame which is as long as possible or a flame which fills the beam tube as fully as possible is intended to be achieved.
However, the formation of the flame or the length of the flame has a direct effect on pollutants, in particular nitrogen oxides, released by the combustion of the fuel. The following relationship can thus be produced, at least approximately.
Short flames generally have a high burning temperature, which may result in high emissions due to the temperature dependency of the formation of nitrogen oxide. By contrast, too cold a burning results in high carbon monoxide emissions. In particular, completely premixing Venturi burners, as are frequently used in gas boilers and thermal springs, are therefore not suitable for use on infrared tube heaters because of the short flame formation since, due to the structural shape, in particular of the beam tube, there is no possibility in that case of reducing the flame temperature, for example by using recirculation of exhaust gases or by construction as a surface burner.
It is accordingly an object of the invention to provide an improved infrared tube heater, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, in particular to provide an infrared tube heater in which a flame is as long as possible or a beam tube is charged with a flame over as great a length as possible, with as little an emission of nitrogen oxides as possible being produced.
With the foregoing and other objects in view there is provided, in accordance with the invention, an infrared tube heater, comprising a beam tube and a burner device including a burner and a fan. The fan is configured to supply air to the burner. The burner has a mixer and at least one secondary air duct, the burner is configured to supply a portion of the air supplied by the fan to the mixer, the burner is configured to supply another portion of the air supplied by the fan to the at least one secondary air duct, and the burner is configured to emit a flame into the beam tube. The mixer is configured to mix the air with a fuel for burning a fuel/air mixture in the flame and the at least one secondary air duct is configured to supply the portion of the air supplied to the at least one secondary air duct to the flame without fuel.
A comparatively long flame with little emission of nitrogen oxides can be achieved, in comparison to a burner without a secondary air duct, due to the fact that the burner is equipped with a mixer and with at least one secondary air duct, the burner is constructed in such a way that a portion of the air supplied by the fan is supplied to the mixer and another portion of the air is supplied to the at least one secondary air duct, the mixer is constructed for mixing the air with a fuel, the fuel/air mixture is burned in the flame, and the secondary air duct is constructed to supply the portion of the air supplied to the secondary air duct to the flame without fuel.
Further advantageous refinements of the present invention emerge, in particular, from the dependent claims. The features of the dependent claims can, in principle, be combined with one another.
In an advantageous refinement of the invention, provision can be made for the outlets of the secondary air ducts to be disposed around the outlet of the mixer. In this way, the flame can be encased to a certain extent by the secondary air. The radial configuration of the secondary air ducts in this case ensures a uniform distribution of the secondary air around the flame. This measure substantially contributes to achieving a comparatively long flame with little emission of nitrogen oxides.
In a further advantageous refinement of the invention, provision can be made for the outlet of the mixer to be provided with a flame tube, wherein the outlets of the secondary air ducts are disposed around the flame tube. Ultimately, the same effect as above is achieved by this measure. However, the reference point for the configuration of the secondary air outlets is directed in this case at the flame tube as the reference point.
In a further advantageous refinement of the invention, provision can be made for the outlets to be constructed in such a manner that the flow rate of the fuel/air mixture at the outlet or the outlets is lower than the flow rate of the secondary air at the outlet or the outlets of the secondary air duct or of the secondary air ducts. The effect which can be achieved by using this measure is that the secondary air can be entered a good distance into the flame tube. This measure contributes substantially to achieving a comparatively long flame with little emission of nitrogen oxide.
In a further advantageous refinement of the invention, provision can be made for the outlet of the at least one secondary air duct to have a smaller cross section than the outlet of the fuel/air mixture. The respective configuration of the cross section of the corresponding outlets constitutes a measure in order to obtain the above-desired outlet rates of the secondary air or of the fuel/air mixture. The outlet rates can be set in a particularly simple manner by the corresponding selection of the relevant cross sections.
In a further advantageous refinement of the invention, provision can be made for the mixer to be configured as a Venturi mixer. A “Venturi” mixer is particularly readily suitable for setting the substoichiometric burning of the fuel/air mixture initially prevailing after the mixer outlet or directly at the flame tube.
In a further advantageous refinement of the invention, provision can be made for the mixing chamber to be provided with a cavity having an inlet for air and fuel and having an outlet for the fuel/air mixture, wherein the cross section of the cavity increases from its inlet to its outlet, and/or for the inlet of the mixing chamber to have an annular gap which is formed by the inlet nozzle and through which the fuel is introduced, and/or for the inlet nozzle to have a tubular element for introducing the air into the mixing chamber, with that element being surrounded by the annular gap. Such a configuration of the mixing chamber is particularly advantageously suitable for providing a fuel/air mixture which is intended to be burnt initially in substoichiometric burning.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an infrared tube heater, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawings in detail and first, particularly, to
The beam tube S is preferably configured in the shape of a hollow cylinder. As viewed over the length, the beam tube S is preferably laid rectilinearly or in a meandering manner.
The exhaust gas system A can be constructed as a simple chimney which is fitted on that side of the beam tube S which faces away from the burner device or the burner B.
The reflector R can be configured, for example, as a correspondingly tilted, hood-shaped sheet which is fitted along the beam tube S and, in an installation position of the infrared tube heater, substantially reflects infrared radiation in the direction of a hall floor.
The burner device substantially includes a burner B and a fan G.
As is seen in
The burner B substantially includes a housing 13, a mixing unit 1 with a mixing chamber 3, an inlet nozzle 2, an annular gap 5 for supplying fuel, a flashback guard 4, a flame tube 8 and at least one secondary air duct 7.
The burner housing 13 is preferably configured in a cylindrical manner and accommodates the above-mentioned components of the burner B. Furthermore, the burner housing 13 is provided with a connecting flange 14 for connecting the fan G and with a connecting flange 18 for connection to the beam tube S.
Further alternative structural forms of the infrared tube heater according to the invention that cannot be enumerated herein are also conceivable. For example, provision can be made for the burner housing 13 and fan housing 10 to be configured as a single part and therefore, for example, the flanges can be dispensed with. The beam tube S can also have a multi-part configuration, or the fan G, with its suction side on the end side of the beam tube S, can be fitted on the side of the exhaust gas system A.
Further details of the present invention emerge in particular from a description of the function of the infrared tube heater according to the invention.
The fan G conveys air out of its outlet 11 into the burner B, in particular into a burner air inlet 15. In this respect, a direction of flow of air from an input side of the burner toward a side on which a flame emerges is produced. For the sake of simplicity, the direction of flow of the air and of a subsequent air/fuel mixture is indicated schematically by an arrow 19.
As seen in the direction of flow of the air or of the air/gas mixture, the burner B is constructed as follows: inlet nozzle 2, mixing unit 1 with mixing chamber 3, flashback guard 4 and flame tube 8.
The inlet nozzle 2 and the mixing unit 1 with the mixing chamber 3 substantially form a mixer for mixing air and fuel.
In principle, the mixing unit 1 has a cylindrical outer construction, for example in the form of a round cylinder or a cylinder with a rectangular or square cross section.
The mixing chamber 3 is preferably configured as a funnel-shaped cavity with a mixing chamber inlet 16 and a mixing chamber outlet 17. The cross section of the cavity increases from the inlet to the outlet, i.e. in the direction of flow. The cavity could also take on other shapes.
The inlet nozzle 2 is configured approximately as a plate 23 with a central opening 20, as is seen in particular in
The annular gap 5 for supplying fuel is provided between the tubular element 21 and the mixing unit 1. In order to form a chamber between the mixing unit 1 and the inlet nozzle 2, in particular the plate 23 of the inlet nozzle 2, the above-mentioned elements can be fitted at a small distance from one another. A likewise annular seal 6, through which the inlet nozzle 2 can be spaced apart from the mixing unit 1, is provided between the mixing unit 1 and the inlet nozzle 2, in particular the plate 23 of the inlet nozzle 2. Finally, this forms a chamber through which the annular gap 5 can be supplied with fuel. Fuel can be introduced into the chamber through a connection Br seen in
The combination of the mixing chamber 3 and the annular gap 5 can function according to the Venturi principle, i.e. the air flowing past the annular gap 5 generates a negative pressure, through the use of which, in turn, the fuel is sucked out of the annular gap 5. However, it is alternatively also conceivable for the fuel to be blown out of the annular gap 5 by using positive pressure, and therefore the Venturi effect is not used or is not required.
The flashback guard 4 is fitted on the outlet side 17 of the mixing chamber 3. The flashback guard 4 is substantially configured as a circular or square plate which covers the outlet 17 of the mixing chamber 3. The mixing chamber 3 can also have a number of outlets. The flashback guard 4 has a suitable perforation which can be penetrated by the fuel/air mixture produced in the mixing chamber 3, but with it being ensured that the flame produced in the direction of flow downstream of the flashback guard 4 does not ignite the fuel/air mixture in the mixing chamber 3. The flashback guard 4 can be configured, for example, as a perforated ceramic plate or as a metal mesh.
Furthermore, the flame tube 8, which is preferably configured as a cylindrical tube with a round cross section, can be fitted further in the direction of flow. The walls of the flame tube 8 can be provided with openings.
Provision is made for the burner, in particular the mixing unit 1, to be provided with at least one, preferably with a plurality of, secondary air ducts 7. It is assumed below by way of example that there is a plurality of secondary air ducts 7.
The secondary air ducts 7 can be configured, for example, as secondary air bores. The secondary air ducts 7 can run parallel to the direction of flow or longitudinal direction of the mixing chamber 3. The secondary air ducts have outlets 24. The secondary air ducts 7 or outlets 24 can be disposed, preferably at the same distance, in the circumferential direction of the mixing unit 1, as is seen particularly in
Furthermore, some of the air supplied by the secondary air ducts 7 flows along the inner wall of the beam tube S. Due to the secondary air being guided annularly at the outer regions of the beam tube, a flame bearing against the tube wall can likewise be avoided. Furthermore, tube cooling can be obtained and a premature mixing with the substoichiometric fuel/air mixture can be prevented.
Through the use of the at least one secondary air duct 7, the burning of the fuel/air mixture, i.e. the flame of the burner, is divided into substantially two main regions. There is firstly a substoichiometric premixing of fuel and air. The substoichiometric premixing takes place in the mixing chamber, which subsequently leads to a flame burning substoichiometrically in the first region. The air ratio downstream of the mixing chamber is preferably 0.5 to 0.9. In this respect, a premixing chamber can also be mentioned for the mixing chamber 3, since only some of the air supplied by the fan G is mixed in this case with fuel. To a certain extent, further air is “admixed” with the actual flame by using the secondary air ducts. The substoichiometric burning is substantially caused by the fact that a quantity of air actually required for stoichiometric burning (lambda=1) is partially conducted away through the secondary air ducts and is only supplied again later on.
Secondly, the secondary air ducts or the supplied secondary air result in the formation of a long diffusion flame because of delayed and specific supplying of the secondary air. Through the use of the configuration of the secondary air ducts, for example, in the form of bores, the secondary air can be introduced into the burner tube at relatively high speeds, and therefore relatively high throwing ranges can be achieved. The position and configuration of the secondary air ducts is therefore important for the function of the burner. The radial configuration of the secondary air ducts ensures a uniform distribution in this case of the secondary air around the flame.
The higher speed of the secondary air at the outlet of the secondary air duct in relation to the outlet for the fuel/air mixture at the outlet of the mixing chamber can be realized, for example, by using a corresponding configuration of the cross sections. It can thus be provided, for example, that the cross section of the outlet of the at least one secondary air duct is smaller than the cross section of the at least one outlet of the mixing chamber.
As a result, with the at least one secondary air duct, the nitrogen oxide emissions of the burner and therefore of the infrared tube heater can be reduced in comparison to an infrared tube heater or burner without secondary air ducts.
The at least one secondary air duct also makes it possible to provide a burner with lower nitrogen emissions, which burner can operate in a sliding modulating manner. The sliding modulating manner of operation can be achieved, inter alia, by what is referred to as an air/fuel coupling (gas/air composite); in this case, the pressure generated by the burner fan can be used for activating the supply of gas. The gas pressure in this case operates proportionally to the fan pressure. Through the use of control of the rotational speed of the fan, the pressure which is built up can therefore be changed and hence the air and supply of gas adapted to the required output. The use of the secondary air ducts also functions in this manner of operation, since the premixing continues to take place substoichiometrically and the secondary air can be conveyed a long way into the beam tube. A further possibility constitutes the use of electronically controllable gas valves for adapting the gas pressure and therefore the burner output.
Furthermore, through the use of the at least one secondary air duct, what are referred to as “hot spots,” i.e. regions which are untypically hot for the infrared tube heater and which are locally limited and burn generally red to yellow, can be avoided on and in the region of the beam tube in the vicinity of the burner. The specific supplying of the secondary air over the outer region of the beam tube effectively cools the latter and prevents the possible resting of the flame against the inner wall of the tube. The resting of the flame against the latter leads, in particular in the case of burners of higher power, to burning tube points which rapidly become worn because of the high thermal loading. Furthermore, the flame temperature is reduced by the burning, which initially proceeds substoichiometrically, and therefore, through the reduction in the flame radiation in this region and stretching of the burning zone, the thermal loading is more uniform over the radiation tube.
Furthermore, the burner permits the production of an ignitable fuel/air mixture under virtually all operating and loading states due to partial premixing. The premixing takes place in the mixing chamber. The secondary air ducts in this case do not have any effect on the gas/air composition in the direct outlet region downstream of the mixing chamber.
The secondary air is introduced at increased speed a long way into the radiation tube through the secondary air ducts, which are ideally constructed as a bore or nozzle, and therefore the region of further mixing with the gas/air mixture can be delayed by using flame diffusion. Due to this measure, complete burn-up can be achieved by using diffusion through a graduated supply of the secondary air during the further course of the flame.
The mixing unit 1 and the inlet nozzle 2 can be configured in a solid monolithic construction in order to reduce sound emissions from the burner and from the subsequent beam tube. The complete mixer can be manufactured from two main parts, the inlet nozzle and the mixing unit. These are fixedly connected to each other and form a solid unit filling the full cross section of the burner. Of course, the suppression of the sound emissions originates firstly from the laminar flame. However, it can be assumed that a reduction is achieved by using the construction and the damping material properties.
As already indicated above, the fan G can also be disposed downstream of the mixing unit 1 in the direction of flow. Accordingly, the air would be sucked into the air inlet 15 of the burner B.
An embodiment of the exhaust gas system as what is referred to as a common exhaust gas system is also possible. What is referred to as a common exhaust gas system denotes the parallel exhaust gas convergence of two or more infrared tube heaters to form an exhaust gas collecting line. The collecting line normally contains a central exhaust gas fan for generating a negative pressure at the burners, and also for removing the exhaust gases. A burner fan is generally not used in exhaust gas collecting systems.
The burner of the infrared tube heater according to the invention also permits prevention of flame failure by using partial premixing. The premixing produces an ignitable mixture, and should the gas/air quantity be greatly reduced by using a low power setting, the flame is withdrawn at maximum to the flashback guard. Due to the low flow rate in the flame tube, the flame is not extinguished.
The burner of the infrared tube heater according to the invention also makes it possible to prevent lifting-off of the flame by using partial premixing. At high power settings, an ignitable gas/air mixture is likewise produced by the premixing. The mixture burns shortly downstream of the flame tube. In the case of systems without premixing, because of insufficient mixing, the flame may lift off at high powers and associated high flow rates and ignite only during the further course of the beam tube. In this case, the burning flame is no longer detected by a flame monitoring device integrated in the burner and the burner is automatically switched off by an electronic control system.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12 184 904.6 | Sep 2012 | EP | regional |
